WO2001023320A1 - Procede de fabrication de grain abrasif - Google Patents

Procede de fabrication de grain abrasif Download PDF

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Publication number
WO2001023320A1
WO2001023320A1 PCT/US2000/002285 US0002285W WO0123320A1 WO 2001023320 A1 WO2001023320 A1 WO 2001023320A1 US 0002285 W US0002285 W US 0002285W WO 0123320 A1 WO0123320 A1 WO 0123320A1
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Prior art keywords
boehmite
abrasive grain
alpha alumina
dispersion
less
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PCT/US2000/002285
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English (en)
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Dwight D. Erickson
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3M Innovative Properties Company
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Priority to AU34761/00A priority Critical patent/AU3476100A/en
Publication of WO2001023320A1 publication Critical patent/WO2001023320A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
    • C04B35/111—Fine ceramics
    • C04B35/1115—Minute sintered entities, e.g. sintered abrasive grains or shaped particles such as platelets
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K3/00—Materials not provided for elsewhere
    • C09K3/14—Anti-slip materials; Abrasives
    • C09K3/1409—Abrasive particles per se

Definitions

  • This invention pertains to a method for making abrasive grain.
  • the abrasive grain can be incorporated into a variety of abrasive articles, including bonded abrasives, coated abrasives, nonwoven abrasives, and abrasive brushes.
  • sol gel abrasive grain are typically made by preparing a dispersion or sol comprising water, alumina monohydrate (boehmite), and optionally peptizing agent (e.g., an acid such as nitric acid), gelling the dispersion, drying the gelled dispersion, crushing the dried dispersion into particles, calcining the particles to remove volatiles, and sintering the calcined particles at a temperature below the melting point of alumina.
  • peptizing agent e.g., an acid such as nitric acid
  • the dispersion also includes one or more oxide modifiers (e.g., CeO 2 , Cr 2 O 3 , CoO, Dy 2 O 3 , Er 2 O 3 , Eu 2 O 3 , Fe 2 O 3 , Gd 2 O 3 , HfO 2 , La 2 O 3 , Li 2 O, MgO, MnO, Na 2 O, Nd 2 O 3 , NiO, Pr 2 O 3 , Sm 2 O 3 , SiO 2 , SnO 2 , TiO 2 , Y 2 O 3 , Yb 2 O 3 , ZnO, and ZrO 2 ,), nucleating agents (e.g., ⁇ -Al 2 O 3 , ⁇ -Cr 2 O 3 , and ⁇ -Fe 2 O 3 ) and/or precursors thereof.
  • oxide modifiers e.g., CeO 2 , Cr 2 O 3 , CoO, Dy 2 O 3 , Er 2 O 3 , Eu 2 O 3 , Fe 2 O 3 ,
  • Such additions are typically made to alter or otherwise modify the physical properties and/or microstructure of the sintered abrasive grain.
  • oxide modifiers, nucleating agents, and/or precursors thereof may be impregnated into the dried or calcined material (typically calcined particles). Further details regarding sol gel abrasive grain, including methods for making them, can be found, for example, in U.S. Pat. Nos.
  • Such aluminum oxide monohydrates are in the alpha form, and include relatively little, if any, hydrated phases other than monohydrates (although very small amounts of trihydrate impurities can be present in some commercial grade boehmite, which can be tolerated). They typically have a low solubility in water, and have a high surface area (typically at least about 180 m 2 /g). Boehmite typically includes at least about 2-6 percent by weight free water (depending on the humidity) on its surface.
  • the boehmite gel which is produced from the boehmite sol is typically a viscoelastic body having interconnected pores of submicrometric dimensions.
  • the gelled dispersion is known to contain a solid network that entraps a liquid phase (i.e. water with the optional acid in most cases).
  • the network consists of boehmite particles linked through hydrogen bonds of -OH groups on the surface of the particles.
  • the dried gel is usually calcined at a temperature range of 400°C to 800°C. At around 300°C, the formation of gamma-alumina from boehmite is initiated. Further, in the calcining step, the dried particles are densified by dehydroxylation (i.e. removal ofthe remaining free water and -OH groups), and by vaporizing volatiles.
  • the number of pores and their connectivity are substantially reduced.
  • the density of the material increases and the volume fraction of porosity decreases.
  • the temperature at which densification occurs is known as the densification temperature.
  • the density of a material is theoretically the highest if all pores are eliminated.
  • abrasive grain it is typically preferred to produce an such abrasive grain at a low sintering temperatures to reduce processing costs (e.g., energy costs), and to minimize detrimental crystal or grain growth of the alpha alumina which tends to increase as the sintering temperature increases. It is also typically preferred to have highly dense (e.g., greater than 90 percent, or even greater than 95 percent of theoretical density) abrasive grain. However, such densities are generally obtained by sintering at higher temperatures and/or for longer times, which leads undesirable grain growth. In addition, larger alpha alumina crystals may form if the boehmite particles are not properly dispersed (i.e., agglomerated particles) or a non-uniform sol is formed.
  • sintered alumina abrasive grain in particular sol gel-derived abrasive grain, have been used in a wide variety of abrasive products (e.g., bonded abrasives, coated abrasives, and abrasive brushes) and abrading applications, including both low and high pressure grinding applications.
  • abrasive products e.g., bonded abrasives, coated abrasives, and abrasive brushes
  • abrading applications including both low and high pressure grinding applications.
  • abrasive grain having dense, fine grained (e.g., a microstructure comprised of submicrometer alpha alumina) and high grinding performance characteristics (e.g., high substrate removal rates and long useful life) that are made using low cost raw materials and processes.
  • dense, fine grained e.g., a microstructure comprised of submicrometer alpha alumina
  • high grinding performance characteristics e.g., high substrate removal rates and long useful life
  • the present invention surprisingly provides a method for making alpha alumina-based ceramic abrasive grain, the method comprising: preparing a dispersion by combining components comprising liquid medium, peptizing agent (e.g., nitric acid), and boehmite, wherein the dispersion exhibits an alpha alumina transition transformation temperature, as determined by differential thermal analysis (DTA), of less than 1185°C (preferably, less than 1184°C, 1183°C, 1182°C, 1181°C, or even 1180°C) and wherein at least 25 % by weight (at least 35 % by weight, at least 50 % by weight, at least 75 % by weight, at least 90 % by weight, or even 100% by weight) of the boehmite, based on the total boehmite content of the dispersion, has a dispersability value in the range from 97.5 to 99% (preferably, up to 97.6, 97.7, 97.8, or even, 97.9%)
  • boehmites e.g., certain boehmites marketed by Alcoa Industrial Chemicals under the trade designation "HI-Q" boehmites
  • HI-Q boehmites which are lower in dispersability than the boehmites listed above, have been found to produce abrasive grain with excellent grinding performance and high density (i.e., greater than 95 percent of theoretical).
  • titania is known in the art as a densification aid and grain growth enhancer for alpha alumina. Titania is present as an impurity in some commercially available boehmites (including those marketed by Condea Chemie, GmbH under the trade designation “DISPERAL”, and by Condea Vista Company under the trade designations "DISPAL” and "CATAPAL”). For a given sintered density (e.g., 90 percent of theoretical), the presence of the titania in such boehmites allows the use of a lower sintering temperature and/or time than would be needed if such titania were not present. That is, the presence of the titania allows for a lower relative sintering temperature and/or time.
  • the boehmite contains, on a theoretical metal oxide basis, less than 600 ppm TiO 2 (less than 300 ppm TiO 2 , less than 150 ppm TiO 2 ), based on the theoretical Al 2 O 3 content of the boehmite.
  • certain embodiments of abrasive grain made according to the method of the present invention contain, on a theoretical metal oxide basis, less than 600 ppm TiO 2 (less than 300 ppm TiO 2 , less than 150 ppm TiO 2 ), based on the theoretical Al 2 O 3 content ofthe abrasive grain.
  • boehmite materials e.g., boehmites market by Alcoa Industrial Chemicals under the trade designation "HIQ”
  • HIQ Alcoa Industrial Chemicals
  • these "sharp" abrasive grains remove more metal than conventional abrasive grains (including sol-gel-derived alpha alumina-based abrasive grain made using boehmites market by Condea Chemie, GmbH under the trade designation "DISPERAL”, and by Condea Vista Company under the trade designations "DISPAL” and "CATAPAL”).
  • Abrasive grain precursor or “unsintered abrasive grain” refers to a dried alumina-based dispersion (i.e., “dried abrasive grain precursor”) or a calcined alumina-based dispersion (i.e., “calcined abrasive grain precursor”), typically in the form of particles, that has a density of less than 80% (typically less than 60%) of theoretical, and is capable of being sintered or impregnated with an impregnation composition and then sintered to provide alpha alumina-based ceramic abrasive grain.
  • Alpha alumina-based ceramic abrasive grain refers to a sintered abrasive grain that contains, on a theoretical oxide basis, at least 60% by weight Al 2 O 3 , wherein at least 50% by weight ofthe total amount of alumina is present as alpha alumina.
  • Dispersion or “sol” refers to a solid-in-liquid two-phase system wherein one phase comprises finely divided particles (in the colloidal size range) distributed throughout a liquid.
  • a “stable dispersion” or “stable sol” refer to a dispersion or sol from which the solids do not appear by visual inspection to begin to gel, separate, or settle upon standing undisturbed for about 2 hours.
  • “Impregnation composition” refers to a solution or dispersion of a liquid medium and a source of metal oxides that can be impregnated into abrasive grain precursor.
  • “Impregnated abrasive grain precursor” refers to a dried alumina-based dispersion (i.e., “impregnated dried abrasive grain precursor”) or a calcined alumina- based dispersion (i.e., "impregnated calcined abrasive grain precursor”) that has a density of less than 80% (typically less than 60%) of theoretical, and has been impregnated with an impregnation composition, and includes impregnated dried particles and impregnated calcined particles.
  • “Sintering” refers to a process of heating at a temperature below the melting temperature ofthe material being heated to provide densification and crystallite growth to provide a tough, hard, and chemically resistant ceramic material.
  • the alpha alumina-based ceramic abrasive grain according to the present invention is not made by a fusion process wherein heating is carried out at a temperature above the melting temperature ofthe material being heated.
  • Abrasive grain made according to the method of the present invention can be incorporated into abrasive products such as coated abrasives, bonded abrasives, non- woven abrasives, and abrasive brushes.
  • FIG. 1 is a fragmentary cross-sectional schematic view of a coated abrasive article including abrasive grain made according to the method of the present invention
  • FIG. 2 is a perspective view of a bonded abrasive article including abrasive grain made according to the method ofthe present invention
  • FIG. 3 is an enlarged schematic view of a nonwoven abrasive article including abrasive grain made according to the method ofthe present invention
  • FIGS. 4 and 6 are elevational plan views of an extruder useful in the methods according to the present invention, while FIG. 5 is an enlarged top plan of the extruder feed port;
  • FIG. 7 is a scanning electron photomicrograph of a fracture surface of an abrasive grain according to the present invention.
  • FIG. 8 is a back scattered electron photomicrograph of abrasive grain according to the present invention.
  • liquid medium e.g., water, preferably, deionized water
  • peptizing agent e.g., an acid such as nitric acid
  • boehmite is capable of converting to alpha alumina
  • the dispersion may be prepared, for example, by gradually adding a liquid component(s) to a component(s) that is non soluble in the liquid component(s), while the latter is mixing or tumbling.
  • a liquid containing water, nitric acid, and optionally metal salt may be gradually added to the boehmite, while the latter is being tumbled such that the liquid is more easily distributed throughout the boehmite.
  • the dispersion may be formed by combining boehmite, liquid medium and acid and then mixed to form essentially a homogeneous dispersion. Next, nucleating material metal oxide precursors may be added to this dispersion.
  • the alpha alumina transition transformation temperatures referred to herein with regard to the boehmite of dispersion are those as determined by the procedure set forth in the working examples below.
  • the boehmite(s) used to prepare the dispersion is selected and combined, optionally with other boehmite, to provide, with the other components of the dispersion (e.g., liquid medium and peptizing agent), dispersion that exhibits an alpha alumina transition transformation temperature, of less than 1185°C (preferably, less than 1184°C, 1183°C, 1182°C, 1181°C, or even 1180°C.
  • At least 25 by weight (at least 35 % by weight, at least 50 % by weight, at least 75 % by weight, at least 90 % by weight, or even 100% by weight) of the boehmite, based on the total boehmite content of the dispersion has a dispersability value in the range from 97.5 to 99% (preferably, up to 97.6, 97.7, 97.8, or even, 97.9%), wherein "dispersability value" as referred to herein is determined as set forth in the working examples below, and exhibits an alpha alumina transition transformation temperature, as determined by differential thermal analysis, of less than 1185°C.
  • Suitable boehmite for practicing the present invention includes that commercially available from Alcoa Industrial Chemicals under the trade designations "HIQ-30” and "HIQ-40".
  • the average particle size for these two boehmites is reported by the manufacturer to be 50 micrometers; the weight percent Al 2 O 3 is reported to be, by weight, 72%. Further the crystallite size for these two boehmites is reported to be, at the 020 peak, 33 angstroms and 42 angstroms, respectively; and at the 021 peak, 50 angstroms and 70 angstroms, respectively.
  • the liquid medium in which the boehmite is dispersed is typically water (preferably deionized water), although organic solvents, such as lower alcohols (typically C, ⁇ alcohols), hexane, or heptane, may also be useful as the liquid medium. In some instances, the liquid medium may be heated (e.g., 60-70°C).
  • the peptizing agent(s) is generally a soluble ionic compound(s) which is believed to cause the surface of a particle or colloid to be uniformly charged in a liquid medium (e.g., water).
  • Preferred peptizing agents are acids or acid compounds. Examples of typical acids include monoprotic acids and acid compounds, such as acetic, hydrochloric, formic, and nitric acid, with nitric acid being preferred.
  • the amount of acid used depends, for example, on the dispersability of the boehmite, the percent solids of the dispersion, the components of the dispersion, the amounts, or relative amounts of the components of the dispersion, the particle sizes of the components ofthe dispersion, and/or the particle size distribution ofthe components of the dispersion.
  • the dispersion typically contains at least, 0.1 to 20%, preferably 1% to 10% by weight acid and most preferably 3 to 9% by weight acid, based on the weight of boehmite in the dispersion.
  • the acid may be applied to the surface ofthe boehmite particles prior to being combined with the water.
  • the acid surface treatment may provide improved dispersability ofthe boehmite in the water.
  • the boehmite containing dispersions typically comprise greater than
  • dispersions comprise 35% by weight or more, 45% by weight or more, 50% by weight or more, 55% by weight or more, 60% by weight or more and 65% by weight or more by weight or more solids (or alternatively boehmite), based on the total weight ofthe dispersion.
  • the boehmite dispersion includes metal oxide (e.g., particles of metal oxide which may have been added as a particulate (preferably having a particle size (i.e., the longest dimension) of less than about 5 micrometers; more preferably, less than about 1 micrometer) and/or added as a metal oxide sol (including colloidal metal oxide sol)) and/or metal oxide precursor (e.g., a salt such as a metal nitrate, a metal acetate, a metal citrate, a metal formate, or a metal chloride that converts to a metal oxide upon decomposition by heating).
  • metal oxide e.g., particles of metal oxide which may have been added as a particulate (preferably having a particle size (i.e., the longest dimension) of less than about 5 micrometers; more preferably, less than about 1 micrometer
  • metal oxide sol including colloidal metal oxide sol
  • metal oxide precursor e.g., a salt such as a metal nitrate, a metal
  • the amount of such metal oxide and/or metal oxide precursor (that is in addition to the alumina provided by the boehmite) present in a dispersion or precursor (or metal oxide in the case of the abrasive grain) may vary depending, for example, on which metal oxide(s) is present and the properties desired for the sintered abrasive grain.
  • the metal oxides are typically present, on a theoretical metal oxide basis, up to about 25 percent by weight (preferably, in the range from about 0.1 to about 10 percent; more preferably, in the range from about 0.5 to about 10 percent by weight), based on the total metal oxide content of the abrasive grain; or if the abrasive grain is to be "unseeded" (i.e., prepared without the use of nucleating material), such metal oxides are preferably present in the range from about 1 to about 10 percent (more preferably, about 2 to about 10 percent) by weight; although the amount may vary depending, for example, on which metal oxide(s) is present.
  • Such other metal oxides include: praseodymium oxide, dysprosium oxide, samarium oxide, cobalt oxide, zinc oxide, neodymium oxide, yttrium oxide, ytterbium oxide, magnesium oxide, nickel oxide, manganese oxide, lanthanum oxide, gadolinium oxide, dysprosium oxide, europium oxide, hafnium oxide, and erbium oxide, as well as manganese oxide, chromium oxide, titanium oxide, and ferric oxide which may or may not function as nucleating agents.
  • Metal oxide precursors include metal nitrate salts, metal acetate salts, metal citrate salts, metal formate salts, and metal chloride salts.
  • nitrate salts include magnesium nitrate (Mg(NO ) -6H O), cobalt nitrate (Co(NO ) -6H O), nickel nitrate (Ni(NO ) -6 ⁇ 0), lithium nitrate (LiNO ), manganese nitrate (Mn(NO ) -4H 2 O), chromium nitrate (Cr(NO 3 ) 3 -9H2 ⁇ ), yttrium nitrate (Y(NO 3 ) 3 -6H 2 O), praseodymium nitrate (Pr(NO 3 ) 3 -6H 2 O), samarium nitrate (Sm(NO ) -6H O), neodymium nitrate (Nd(NO -6H O), lanthanum nitrate (La(
  • metal acetate salts include zirconyl acetate (ZrO(CH COO) ), magnesium acetate, cobalt acetate, nickel acetate, lithium acetate, manganese acetate, chromium acetate, yttrium acetate, praseodymium acetate, samarium acetate, ytterbium acetate, neodymium acetate, lanthanum acetate, gadolinium acetate, and dysprosium acetate.
  • citrate salts include magnesium citrate, cobalt citrate, lithium citrate, and manganese citrate.
  • formate salts include magnesium formate, cobalt formate, lithium formate, manganese formate, and nickel formate.
  • the colloidal metal oxides are discrete finely divided particles of amorphous or crystalline metal oxide typically having one or more of their dimensions within a range of about 3 nanometers to about 1 micrometer.
  • the average metal oxide (including in this context silica) particle size in the colloidal is preferably less than about 150 nanometers, more preferably less than about 100 nanometers, and most preferably less than about 50 nanometers. In some instances, the particles can be on the order of about 3-10 nanometers. In most instances, the colloidal comprises a distribution or range of metal oxide particle sizes.
  • the colloidal metal oxide sols are a stable (i.e., the metal oxide solids in the sol or dispersion do not appear by visual inspection to begin to gel, separate, or settle upon standing undisturbed for about 2 hours) suspension of colloidal particles (preferably in a liquid medium having a pH of less than 6.5).
  • Metal oxide sols for use in methods according to the present invention include sols of ceria, silica, yttria, titania, lanthana, neodymia, zirconia, and mixtures thereof.
  • Metal oxide (including silica) sols are available, for example, from Nalco of Naperville, IL; Nyacol Products, Inc. of Ashland, MA; Eka Nobel of Augusta, GA; Rhone-Ploulenc of Shelton, CT; Transelco of Perm Yan, NY; and Fujimi Corp. of Japan.
  • Silica sols include those available under the trade designations "NALCO 1115,” “NALCO 1130,” “NALCO 2326,” NALCO 1034A,” and “NALCOAG 1056” from Nalco Products, Inc. of Naperville, IL, wherein the latter two are examples of acidic silica sols; and "NYACOL 215" from Eka Nobel, Inc.
  • NALCO 1115 a trade designation for silica sols
  • NALCO 1130 NALCO 1130
  • NALCO 2326 NALCO 2326
  • NALCO 1034A NALCO 1256
  • a basic colloidal silica it is preferable to combine the basic colloidal silica with an acid source and convert it to an acidic colloidal silica dispersion (preferably having a pH of about 1-3) prior to combining it with either boehmite or a source of iron oxide.
  • the zirconia sol typically comprises finely divided particles of amorphous or crystalline zirconia having one or more dimensions preferably within a range of about 3 nanometers to about 250 nanometers.
  • Zirconia sols are available, for example, from Nyacol Products, Inc. under the trade designations "ZRl 00/20" and "ZRl 0/20".
  • Ceria sols are available, for example, from Rhone-Ploulenc of Shelton, CT; Transelco of Penn Yan, NY; and Fujimi Corp. of Japan.
  • ceria, silica, or zirconia sols see, for example, U.S. Pat. Nos. 5,429,647 (Larmie), 5,498,269 (Larmie), 5,551,963 (Larmie), 5,611,829 (Monroe et al.), and 5,645,619 (Erickson et al.).
  • the average metal oxide particle size in the colloidal metal oxide is preferably less than about 150 nanometers, more preferably less than about 100 nanometers, and most preferably less than about 50 nanometers. In some instances, the metal oxide particles can be on the order of about 3-10 nanometers. In most instances, the colloidal metal oxide comprises a distribution or range of metal oxide particle sizes.
  • the use of a metal oxide modifier may decrease the porosity of the sintered abrasive grain and thereby increase the density.
  • Certain metal oxides may react with the alumina to form a reaction product and/or form crystalline phases with the alpha alumina which may be beneficial during use of the abrasive grain in abrading applications.
  • the oxides of cobalt, nickel, zinc, and magnesium typically react with alumina to form a spinel, whereas zirconia and hafnia do not react with the alumina.
  • the reaction products of dysprosium oxide and gadolinium oxide with aluminum oxide are generally garnet.
  • reaction products of praseodymium oxide, ytterbium oxide, erbium oxide, and samarium oxide with aluminum oxide generally have a perovskite and/or garnet structure.
  • Yttria can also react with the alumina to form Y 3 Al 5 O 12 having a garnet crystal structure.
  • Certain rare earth oxides and divalent metal cations react with alumina to form a rare earth aluminate represented by the formula LnMAl ⁇ O 19 , wherein Ln is a trivalent metal ion such as La 3+ , Nd 3+ , Ce 3+ , Pr 3+ , Sm 3+ , Gd 3+ , Er 3* , or Eu 3+ , and M is a divalent metal cation such as Mg 2+ , Mn 2+ , Ni 2+ , Zn 2+ , or Co 2+ .
  • Such aluminates have a hexagonal crystal structure.
  • the boehmite dispersion contain nucleating material (i.e., material that enhances the transformation of transitional alumina(s) to alpha alumina via extrinsic nucleation).
  • the nucleating material can be a nucleating agent (i.e., material having the same or approximately the same crystalline structure as alpha alumina, or otherwise behaving as alpha alumina) itself (e.g., alpha alumina seeds, ⁇ -Fe 2 O 3 seeds, or ⁇ -Cr 2 O 3 seeds, Ti 2 O 3 (having a trigonal crystal structure), MnO 2 (having a rhombic crystal structure), Li 2 O (having a cubic crystal structure), titanates (e.g., magnesium titanate and nickel titanate) or precursor thereof.
  • a nucleating agent i.e., material having the same or approximately the same crystalline structure as alpha alumina, or otherwise behaving as alpha alumina
  • nucleating material if present, comprises, on a theoretical metal oxide basis (based on the total metal oxide content of the calcined precursor material before sintering (or the sintered abrasive grain)), in the range from about 0.1 to about 5 percent by weight.
  • a preferred nucleating material for practicing the present invention include is iron oxide or an iron oxide precursor.
  • Sources of iron oxide include hematite (i.e., ⁇ -Fe 2 O 3 ), as well as precursors thereof (i.e., goethite ( ⁇ -FeOOH), lepidocrocite ( ⁇ -FeOOH), magnetite (Fe 3 O 4 ), and maghemite ( ⁇ -Fe 2 O 3 )).
  • Suitable precursors of iron oxide include iron-containing material that, when heated, will convert to ⁇ -Fe 2 O 3 .
  • suitable nucleating materials may include ⁇ -Cr 2 O 3 precursors such as chromium nitrate (Cr(NO 3 ) 3 -9H 2 O) and chromium acetate; MnO 2 precursors such as manganese nitrate (Mn(NO 3 ) 2 » 4H 2 O), manganese acetate, and manganese formate; and Li 2 O precursors such as lithium nitrate (LiNO 3 ), lithium acetate, and lithium formate.
  • ⁇ -Cr 2 O 3 precursors such as chromium nitrate (Cr(NO 3 ) 3 -9H 2 O) and chromium acetate
  • MnO 2 precursors such as manganese nitrate (Mn(NO 3 ) 2 » 4H 2 O), manganese acetate, and manganese formate
  • Li 2 O precursors such as lithium nitrate (LiNO 3 ), lithium acetate, and lithium formate.
  • nucleating materials are also disclosed, for example, in U.S. Pat. Nos. 4,623,364 (Cottringer et al.), 4,744,802 (Schwabel), 4,964,883 (Morris et al.), 5,139,978 (Wood), and 5,219,806 (Wood).
  • a high solids dispersion is typically, and preferably, prepared by gradually adding a liquid component(s) to a component(s) that is non-soluble in the liquid component(s), while the latter is mixing or tumbling.
  • a liquid containing water, peptizing agent, and optional metal salt(s) may be gradually added to boehmite, while the latter is being mixed such that the liquid is more easily distributed throughout the boehmite.
  • Suitable mixers include pail mixers, sigma blade mixers, ball mill and high shear mixers.
  • Other suitable mixers may be available from Eirich Machines, Inc. of Gurnee, IL; Hosokawa-Bepex Corp. of Minneapolis, MN (including a mixer available under the trade designation "SCHUGI FLEX-O-MIX", Model FX-160); and Littleford-Day, Inc. of Florence, KY.
  • the dispersion may be heated to increase the dispersability of the alpha alumina monohydrate and/or to create a homogeneous dispersion.
  • the temperature may vary to convenience, for example the temperature may range from about 20°C to 80°C, usually between 25°C to 75°C.
  • the dispersion may be heated under a pressure ranging from 1.5 to 130 atmospheres of pressure.
  • the dispersion typically gels prior to, or during, drying. The addition of most modifiers may result in the dispersion gelling faster. Alternatively, ammonium acetate or other ionic species may be added to induce gelation of the dispersion.
  • the pH of the dispersion and concentration of ions in the gel generally determines how fast the dispersion gels. Typically, the pH ofthe dispersion is within a range of about 1.5 to about 5.
  • the dispersion may be extruded. It may be preferable to extrude a dispersion where at least 50 percent by weight of the alumina content is provided by particulate (e.g., boehmite), including in this context a gelled dispersion, or even partially deliquified dispersion.
  • the extruded dispersion referred to as extrudate, can be extruded into elongated precursor material (e.g., rods (including cylindrical rods and elliptical rods)). After firing, the rods may have an aspect ratio between 1.5 to 10, preferably between 2 to 6.
  • the extrudate may be in the form of a very thin sheet, see for example U.S. Pat. No.
  • extruders examples include ram extruders, single screw, twin screw, and segmented screw extruders. Suitable extruders are available, for example, from Loomis Products of Levitown, PA, Bonnot Co. of Uniontown, OH, and Hosokawa-Bepex of Minneapolis, MN, which offers, for example, an extruder under the trade designation "EXTRUD-O- MIX” (Model EM-6).
  • the dispersion is compacted, for example, prior to or during extrusion (wherein the extrusion step may inherently involve compaction of the dispersion).
  • the dispersion In compacting the dispersion, it is understood that the dispersion is subjected to a pressure or force such as experienced, for example, in a pellitizer or die press (including mechanical, hydraulic and pneumatic or presses) or an extruder (i.e., all or substantially all ofthe dispersion experiences the specified pressure).
  • a pressure or force such as experienced, for example, in a pellitizer or die press (including mechanical, hydraulic and pneumatic or presses) or an extruder (i.e., all or substantially all ofthe dispersion experiences the specified pressure).
  • a pressure or force such as experienced, for example, in a pellitizer or die press (including mechanical, hydraulic and pneumatic or presses) or an extruder (i.e., all or substantially all ofthe dispersion experiences the specified pressure).
  • compacting the dispersion reduces the amount of air or gases entrapped in the dispersion, which in turn generally produces a less porous microstructure, that is more desirable. Additionally the compaction
  • the elongated precursor material is a rod, it preferably has a diameter such that the sintered abrasive grain will have a diameter of, for example, about 150- 5000 micrometers, and preferably, an aspect ratio (i.e., length to width ratio) of at least 2.5:1, at least 4:1, or even at least 5:1.
  • the rod may have any cross sectional shape including a circle, an oval, a star shape, a tube and the like.
  • the rod abrasive grain may also be curved.
  • a preferred apparatus for compacting the dispersion (gelled or not) is illustrated in FIGS. 4-6.
  • Modified segmented screw extruder 40 has feed port 41 and auger 42 centrally placed within barrel 44.
  • Barrel 44 has grooves (not shown; generally known as "lands") running parallel down its length. Pins 48 extend centrally into barrel 44. Further, helical flight 46 extends the length of auger 42. Flight 46 is not continuous down the length of auger 42 but is segmented so that flight 46 on auger 42 does not come into contact with pins 48.
  • the dispersion (including in this context gelled dispersion) (not shown) is fed in feed port 41.
  • Packer screw 43 urges the dispersion against auger 42 so that the dispersion is compacted by auger 42 and extruded through die 49.
  • Die 49 can have a variety of apertures or holes therein (including a single hole or multiple holes).
  • the die apertures can be any of a variety of cross sectional shapes, including a circle or polygon shapes (e.g., a square, star, diamond, trapezoid, or triangle).
  • the die apertures can be any of a variety of sizes, but typically range from about 0.5 mm (0.02 inch) to 1.27 cm (0.5 inch), and more typically, from about 0.1 cm (0.04 inch) to about 0.8 cm (0.3 inch).
  • the extruded dispersion can be can be cut or sliced, for example, to provide discrete particles, and /or to provide particles having a more uniform length.
  • Examples of methods for cutting (or slicing) the dispersion include rotary knife, blade cutters and wire cutters.
  • the compacted dispersion can also be shredded and/or grated.
  • the drying step generally removes a significant portion of the liquid medium from the dispersion; however, there still may be a minor portion (e.g., about 10% or less by weight) of the liquid medium present in the dried dispersion.
  • Typical drying conditions include temperatures ranging from about room temperature to over about 200°C, typically between 50 to 150°C. The times may range from about 30 minutes to over days. To prevent salt migration, it may be desirable to dry the dispersion at low temperature.
  • the dried dispersion may be converted into precursor particles.
  • One typical means to generate these precursor particles is by a crushing technique.
  • Various crushing or comminuting techniques may be employed such as a roll crusher, jaw crusher, hammer mill, ball mill and the like.
  • Coarser particles may be recrushed to generate finer particles.
  • the dried dispersion be crushed to approximately the desired particle size distribution (e.g. desired grit size). It is generally easier to crush dried gel versus the sintered alpha alumina based abrasive grain. Thus it is preferred to generate the desired particle size distributions prior to sintering.
  • the dispersion may be converted into precursor particles prior to drying. This may occur for instance if the dispersion is processed into a desired grit shape and particle size distribution.
  • the dispersion may be extruded into rods that are subsequently cut to the desired lengths and then dried.
  • the dispersion may be molded into a triangular shape particle and then dried. Additional details concerning triangular shaped particles may be found in U.S. Pat. No. 5,201,916 (Berg et al.).
  • the dried dispersion is shaped into lumps with a high volatilizable content which then are explosively communited by feeding the lumps directly into a furnace held at a temperature above 350°C, usually a temperature between 600°C to 900°C.
  • the dried dispersion is calcined, prior to sintering, although a calcining step is not always required.
  • techniques for calcining the dried dispersion or ceramic precursor material, wherein essentially all the volatiles are removed, and the various components that were present in the dispersion are transformed into oxides are known in the art. Such techniques include using a rotary or static furnace to heat dried dispersion at temperatures ranging from about 400- 1000°C (typically from about 450-800°C) until the free water, and typically until at least about 90 wt-% of any bound volatiles are removed.
  • a metal oxide modifier source typically a metal oxide precursor
  • the metal oxide precursors are in the form metal salts.
  • ceramic precursor material i.e., dried alumina-based dispersion (or dried ceramic precursor material), or calcined alumina-based dispersion (or calcined ceramic precursor material)
  • a calcined ceramic precursor material typically has pores about 2-10 nanometers in diameter extending therein from an outer surface. The presence of such pores allows an impregnation composition comprising a mixture comprising liquid medium (typically water) and appropriate metal precursor to enter into ceramic precursor material. The metal salt material is dissolved in a liquid, and the resulting solution mixed with the porous ceramic precursor particle material. The impregnation process is thought to occur through capillary action.
  • the liquid used for the impregnating composition is preferably water (including deionized water), an organic solvent, and mixtures thereof. If impregnation of a metal salt is desired, the concentration of the metal salt in the liquid medium is typically in the range from about 5% to about 40% dissolved solids, on a theoretical metal oxide basis. Preferably, there is at least 50 ml of solution added to achieve impregnation of 100 grams of porous precursor particulate material, more preferably, at least about 60 ml of solution to 100 grams of precursor particulate material.
  • the resulting impregnated precursor particle is typically calcined to remove any volatiles prior to sintering.
  • the conditions for this calcining step are described above.
  • the precursor particle is sintered to provide a dense, ceramic alpha alumina based abrasive grain.
  • techniques for sintering the precursor material which include heating at a temperature effective to transform transitional alumina(s) into alpha alumina, to causing all of the metal oxide precursors to either react with the alumina or form metal oxide, and increasing the density of the ceramic material, are known in the art.
  • the precursor material may be sintered by heating (e.g., using electrical resistance, microwave, plasma, laser, or gas combustion, on batch basis or a continuous basis). Sintering temperatures are usually range from about 1200°C to about 1650°C, typically, from about 1200°C to about 1500°C.
  • the length of time which the precursor material is exposed to the sintering temperature depends, for example, on particle size, composition of the particles, and sintering temperature. Further, the sintering temperature and/or time needed to achieve a specified density decreases as the pore size of the calcined abrasive grain decreases. Typically, sintering times range from a few seconds to about 60 minutes (preferably, within about 3-30 minutes). Sintering is typically accomplished in an oxidizing atmosphere, although inert or reducing atmospheres may also be useful.
  • the longest dimension of the alpha alumina-based abrasive grain is typically at least about 1 micrometer.
  • the abrasive grain described herein can be readily made with a length of greater than about 50 micrometers, and larger abrasive grain (e.g., greater than about 1000 micrometers or even greater than about 5000 micrometers) can also be readily made.
  • the preferred abrasive grain has a length in the range from about 100 to about 5000 micrometers (typically in the range from about 100 to about 3000 micrometers), although other sizes are also useful, and may even be preferred for certain applications.
  • abrasive grain according to the present invention typically have an aspect ratio of at least 1.2:1 or even 1.5:1, sometimes, at least 2:1, and alternatively, at least 2.5:1.
  • Dried, calcined, and/or sintered materials provided during or by the method according to the present invention are typically screened and graded using techniques known in the art.
  • the dried particles are typically screened to a desired size prior to calcining.
  • Sintered abrasive grain are typically screened and graded prior to use in an abrasive application or incorporation into an abrasive article. Screening and grading of abrasive grain made according to the method of the present invention can be done, for example, using the well known techniques and standards for ANSI (American National Standard Institute), FEPA (Federation Europeenne des Fabricants de Products Abrasifs), or JIS (Japanese Industrial Standard) grade abrasive grain.
  • ANSI American National Standard Institute
  • FEPA Federation Europeenne des Fabricants de Products Abrasifs
  • JIS Japanese Industrial Standard
  • a first dispersion can be made as described above, dried, crushed, and screened, and then a second dispersion made by combining, for example, liquid medium (preferably, aqueous), boehmite, and deliquified material from the first dispersion, and optionally metal oxide and/or metal oxide precursor.
  • the first dispersion includes nucleating material.
  • the recycled material may provide, on a theoretical metal oxide basis, for example, at least 10 percent, at least 30 percent, at least 50 percent, or even up to (and including) 100 percent of the theoretical Al 2 O 3 content of the dispersion which is deliquified and converted (including calcining and sintering) to provide the sintered abrasive grain. It is also within the scope of the present invention to coat the abrasive grain with a surface coating such as described in U.S. Pat. Nos.
  • Abrasive grain or made by a method according to the present invention can be used in conventional abrasive products, such as coated abrasive products, bonded abrasive products (including vitrified and resinoid grinding wheels, cutoff wheels, and honing stones), nonwoven abrasive products, and abrasive brushes.
  • abrasive products i.e., abrasive articles
  • binder and abrasive grain at least a portion of which is abrasive grain made by a method according to the present invention, secured within the abrasive product by the binder. Methods of making such abrasive products are well known to those skilled in the art.
  • abrasive grain made by a method according to the present invention can be used in abrasive applications that utilize slurries of abrading compounds (e.g., polishing compounds).
  • Coated abrasive products generally include a backing, abrasive grain, and at least one binder to hold the abrasive grain onto the backing.
  • the backing can be any suitable material, including cloth, polymeric film, fibre, nonwoven webs, paper, combinations thereof, and treated versions thereof.
  • the binder can be any suitable binder, including an inorganic or organic binder.
  • the abrasive grain can be present in one layer or in two layers of the coated abrasive product. Methods of making coated abrasive products are described, for example, in U.S. Pat. Nos.
  • coated abrasive product 1 has a backing (substrate) 2 and abrasive layer 3.
  • Abrasive layer 3 includes abrasive grain 4 secured to a major surface of backing 2 by make coat 5 and size coat 6. In some instances, a supersize coat (not shown) is used.
  • Bonded abrasive products typically include a shaped mass of abrasive grain held together by an organic, metallic, or vitrified binder.
  • shaped mass can be, for example, in the form of a wheel, such as a grinding wheel or cutoff wheel. It can also be in the form, for example, of a honing stone or other conventional bonded abrasive shape. It is typically in the form of a grinding wheel.
  • grinding wheel 10 is depicted, which includes abrasive grain 11, at least a portion of which is abrasive grain made by a method according to the present invention, molded in a wheel and mounted on hub 12.
  • bonded abrasive products see, for example, U.S. Pat. Nos. 4,997,461 (Markhoff-Matheny et al.) and 4,898,597 (Hay et al.).
  • Nonwoven abrasive products typically include an open porous lofty polymer filament structure having abrasive grain distributed throughout the structure and adherently bonded therein by an organic binder.
  • filaments include polyester fibers, polyamide fibers, and polyaramid fibers.
  • FIG. 3 a schematic depiction, enlarged about lOOx, of a typical nonwoven abrasive product is provided.
  • Such a nonwoven abrasive product comprises fibrous mat 50 as a substrate, onto which abrasive grain 52, at least a portion of which is abrasive grain made by a method according to the present invention, are adhered by binder 54.
  • abrasive grain 52 at least a portion of which is abrasive grain made by a method according to the present invention, are adhered by binder 54.
  • Useful abrasive brushes include those having a plurality of bristles unitary with a backing (see, e.g., U.S. Pat. No. 5,679,067 (Johnson et al.)).
  • abrasive brushes are made by injection molding a mixture of polymer and abrasive grain.
  • Suitable organic binders for the abrasive products include thermosetting organic polymers.
  • suitable thermosetting organic polymers include phenolic resins, urea-formaldehyde resins, melamine-formaldehyde resins, urethane resins, acrylate resins, polyester resins, aminoplast resins having pendant ⁇ , ⁇ - unsaturated carbonyl groups, epoxy resins, and combinations thereof.
  • the binder and/or abrasive product can also include additives such as fibers, lubricants, wetting agents, thixotropic materials, surfactants, pigments, dyes, antistatic agents (e.g., carbon black, vanadium oxide, graphite, etc.), coupling agents (e.g., silanes, titanates, zircoaluminates, etc.), plasticizers, suspending agents, and the like.
  • additives such as fibers, lubricants, wetting agents, thixotropic materials, surfactants, pigments, dyes, antistatic agents (e.g., carbon black, vanadium oxide, graphite, etc.), coupling agents (e.g., silanes, titanates, zircoaluminates, etc.), plasticizers, suspending agents, and the like.
  • the amounts of these optional additives are selected to provide the desired properties.
  • the coupling agents can improve adhesion to the abrasive grain and/or filler.
  • the binder can also contain filler materials or grinding aids, typically in the form of a particulate material.
  • the particulate materials are inorganic materials.
  • particulate materials that act as fillers include metal carbonates, silica, silicates, metal sulfates, metal oxides, and the like.
  • particulate materials that act as grinding aids include: halide salts such as sodium chloride, potassium chloride, sodium cryolite, and potassium tetrafluoroborate; metals such as tin, lead, bismuth, cobalt, antimony, iron, and titanium; organic halides such as polyvinyl chloride and tetrachloronaphthalene; sulfur and sulfur compounds; graphite; and the like.
  • a grinding aid is a material that has a significant effect on the chemical and physical processes of abrading, which results in improved performance.
  • a grinding aid is typically used in the supersize coat applied over the surface of the abrasive grain, although it can also be added to the size coat.
  • a grinding aid is used in an amount of about 50-300 g/m 2 (preferably, about 80-160 g/m 2 ) of coated abrasive product.
  • the abrasive products can contain 100% abrasive grain made by a method according to the present invention, or they can contain a blend of such abrasive grain with conventional abrasive grain and/or diluent particles. However, at least about
  • abrasive grain in the abrasive products should be abrasive grain made by a method according to the present invention.
  • suitable conventional abrasive grain include fused aluminum oxide, silicon carbide, diamond, cubic boron nitride, garnet, fused alumina zirconia, and other sol-gel abrasive grain, and the like.
  • suitable diluent particles include marble, gypsum, flint, silica, iron oxide, aluminum silicate, glass, and diluent agglomerates.
  • Abrasive grain made by a method according to the present invention can also be combined in or with abrasive agglomerates.
  • HIQ-40 H-30 alpha-alumina monohydrate (boehmite) (obtained from Alcoa Industrial
  • HIQ-30 H-20 alpha-alumina monohydrate (boehmite) (obtained from Alcoa Industrial Chemicals under the trade designation "HIQ-20")
  • HIQ-10 H-X alpha-alumina monohydrate (boehmite) (obtained from Alcoa Industrial
  • HIQ alpha-alumina monohydrate
  • CATAPAL B C- D alpha-alumina monohydrate (boehmite); obtained from Condea Vista
  • CAPAL D AAMH-DIS alpha-alumina monohydrate (boehmite); obtained from Condea Vista Chemical Company under the trade designation “DISPAL 23N480” CS830 basic colloidal silica (30% solid); obtained from Nalco Products, Inc. of Augusta, GA, under the trade designation "NALCO 830"
  • ZRN zirconyl acetate solution (on a theoretical metal oxides basis, -22% ZrO 2 ; obtained from Magnesium Electron, Inc. of Flemington, NJ)
  • CS colloidal silica, 30% by weight solids obtained from Nyacol Products, Inc. of Ashland, MA under the trade designation "NYACOL 830"); average particle size 8-10 nm MEM a rare earth nitrate solution prepared by mixing a lanthanum, neodymium, and yttrium nitrate (having, on a theoretical metal oxide basis, 23% rare earth oxide (i.e., La 2 O 3 , Nd 2 O 3 , and Y 2 O 3 ); available from Molycorp of Lourviers, CO) with a sufficient amount of magnesium nitrate (Mg(NO 3 ) 2 -6H 2 O) solution (having, on a theoretical metal oxide basis, 11% MgO; available from Mallinckrodt Chemical of Paris, KY) and cobalt nitrate (Co(NO 3 ) 2 -6H 2 O) solution (having, on a theoretical metal oxide basis 19% CoO; available from Hall Chemical of Wickliffe, OH
  • DTA Differential Thermal Analysis
  • TGA Thermogravimetric Analysis
  • DTA Differential thermal analysis
  • TGA thermogravimetric analysis
  • a dispersion was also prepared in the same manner using AAMH-DIS except no nitric acid was added as this boehmite, as- received, includes nitric acid.
  • Sols were prepared mixing 444.3 grams of DWI, 5 grams of HNO 3 , and 66.7 grams ofthe respective boehmite powders using a conventional household blender (obtained under the trade designation "OSTERIZER” from Oster Products, Sunbeam Corp., Boca Raton, FL) at its lowest speed for one minute, except no acid was used to make the AAMH-DIS sol.
  • Each sol was centrifuged at 2400 rpm for 15 minutes (using a centrifuge obtained under the trade designation "IEC CENTRA-7 CENTRIFUGE” from Damon/IEC Division, Needham Heights, MA). The supernate for each sample was carefully removed and discarded. The remaining “sludge” was dried at 90°C for one hour. The dried "sludge” was then weighed.
  • the dispersability value reported in Table 1, above, is one minus the weight ratio ofthe dried sludge over the weight of the original powder used (i.e., 66.7 grams), times 100%.
  • Titania Content Of Various Boehmites The titania content of AAMH, H-10, H-20, H-30, H-40, C-A, C-B, C-D, and AAMH-DIS were determined by x-ray fluorescence using a wavelength dispersive x-ray fluorescence spectrometer obtained under the trade designation "SIEMENS SRS 200 DISPERSIVE X-RAY FLUORESCENCE SPECTROMETER" from Siemens AG, Kunststoff, Germany.
  • the titania contents of the boehmite materials are summarized below in Table 3.
  • Comparative Example A was prepared and tested as follows. A dispersion was made by mixing together 560 grams of AAMH, 28 grams of HNO 3 , 69 grams of IO1 at 7.8% solid, and 1,412 grams of DWT in a conventional 4 liter, food grade blender (Waring blender available from Waring Products Division, Dynamics Corp. of America, New Hartford, CT; Model 34BL22(CB6)). The DWT, HNO 3 , and IO1 were placed in the blender first and mixed. The AAMH was then added, and the contents mixed at low speed setting for 60 seconds.
  • a conventional 4 liter, food grade blender Waring blender available from Waring Products Division, Dynamics Corp. of America, New Hartford, CT; Model 34BL22(CB6).
  • the DWT, HNO 3 , and IO1 were placed in the blender first and mixed.
  • the AAMH was then added, and the contents mixed at low speed setting for 60 seconds.
  • the resulting dispersion was poured into a 22.86 cm x 30.48 cm) Pyrex glass tray and dried overnight at about 93 °C.
  • the resulting dried, friable solid, material was crushed with a pulverizer (type UA, available from Braun Corp., Los Angeles, CA) to provide precursor abrasive grain (particles).
  • the crushed material was screened to retain the particles that were in the -14+40 mesh (U.S.A. Standard Testing Sieves) size range.
  • the retained particles were fed into a calcining kiln to provide calcined abrasive grain precursor material.
  • the calcining kiln consisted of a 15 cm inner diameter, 1.2 meter in length, stainless steel tube having a 0.3 meter hot zone.
  • the tube was inclined at a 2.4 degree angle with respect to the horizontal.
  • the tube rotated at about 20 rpm, to provide a residence time in the tube of about 4-5 minutes.
  • the temperature ofthe hot zone was about 650°C.
  • the calcined abrasive grain precursor was fed into a rotary sintering kiln.
  • the sintering kiln consisted of an 8.9 cm inner diameter, 1.32 meter long silicon carbide tube inclined at 4.4 degrees with respect to the horizontal and had a 31 cm hot zone. The heat was applied externally via SiC electric heating elements.
  • the sintering kiln rotated at 2.8 rpm, to provide a residence time in the tube of about 10 minutes.
  • the sintering temperature was about 1300°C.
  • the density of the abrasive grain was determined with a helium gas pycnometer (obtained under the trade designation "MICROMERITICS ACCUPYC 1330" from Micromeritics Instruments Corp., Norcross, GA).
  • the density of the Comparative Example A abrasive grain was 3.88 g/cm 3 .
  • the bulk density of the abrasive grain was determined using an apparatus consisting of a glass funnel with an inside diameter of 9.5 cm at the top and an inside diameter at the stem of 1.4 cm. The entire height of the funnel was about 11.5 cm (including stem).
  • the funnel was placed on a ring-stand above a metal cup so that the base ofthe funnel stem was 7.62 cm (3 inches) above the top ofthe metal cup (lOcc aluminum sample cup obtained from Micromeritics Instrument Corporation, Norcross, GA as Part No. 133/25805/00).
  • the stem of the funnel was closed with a rubber ball attached to the outside of the funnel stem.
  • Abrasive grain was poured into the funnel.
  • the rubber ball was removed to allow the abrasive grain to empty into and eventually overflow the metal cup.
  • the abrasive grain was carefully leveled to the top of the cup, tapped to allow the abrasive grain to settle in the cup and then weighed.
  • the bulk density was determined by dividing the weight of the mineral and cup minus the weight of the cup by the volume ofthe cup (which was determined as described above to be 10.38 cc). The bulk density is reported an average of three independent measurements.
  • the bulk density of the Comparative A abrasive grain was 1.75 +/- 0.01 g/cm 3 .
  • the sintered alpha alumina-based ceramic abrasive grain was graded to retain the -25+30 and -30+35 mesh fractions (U.S.A. Standard Testing Sieves). These fractions were blended in a 1 : 1 ratio and incorporated into coated abrasive discs, which were tested for grinding performance.
  • the coated abrasive discs were made according to conventional procedures.
  • the abrasive grain were bonded to 17.8 cm diameter vulcanized fiber backings (having a 2.2 cm diameter center hole) using a conventional calcium carbonate-filled phenolic make resin (48% resole phenolic resin, 52% calcium carbonate, diluted to 81% solids with water) and a conventional cryolite-filled phenolic size resin (32% resole phenolic resin and 68% cryolite, diluted to 78% solids with water).
  • the wet make resin weight was 150 g/m 2 .
  • the abrasive grains were electrostatically coated.
  • the resulting construction was heated at 77°C for 15 minutes, and then at 93 °C for 90 minutes to partially cure the make resin.
  • the wet size weight was about 670 g/m 2 .
  • the size resin was precured for 1 hour at 77°C for one hour, followed by a final cure for 16 hours at 102°C.
  • the fibre discs were flexed prior to testing.
  • the coated abrasive discs were tested by attaching a disc to a 16.5 cm diameter, 1.57 mm thick hard, phenolic backup pad which was in turn mounted onto a 15.2 cm diameter steel flange. The mounted disc was rotated counterclockwise at 3550 rpm. The 1.8 mm peripheral edge of a 25 cm diameter disc of a 4130 steel (workpiece) was deployed 7 degrees from a position normal to the abrasive disc under a load of about 4 kg. The workpiece was weighed at the start of the test, and at 4 minute intervals, to determine the amount of steel removed (i.e., abraded). Two 4 minute intervals (for a total of 8 minutes of grinding) were conducted for each abrasive disc. The average (based on 4 discs) amount of metal removed during the 8 minute test was 211.3 grams.
  • Example 1 was prepared as described for Comparative Example A except the AAMH was replaced with H-40.
  • the density and bulk density of the Example 1 abrasive grain were determined as described for Comparative Example A to be 3.87 g/cm 3 and 1.66 +/- 0.01 g/cm 3 , respectively.
  • Comparative Example A The average (based on 4 discs) amount of metal removed during the 8 minute grinding performance test described in Comparative Example A was 236 grams.
  • Comparative Example B was prepared as described for Comparative Example A, except 22 grams of CS830 was added to the dispersion, and the sintering temperature was about 1450°C.
  • the density and bulk density of the Comparative Example B abrasive grain were determined as described for Comparative Example A to be 3.83 g/cm 3 and 1.75 +/- 0.01 g/cm 3 , respectively.
  • Example 2 was prepared as described for Comparative Example B except the AAMH was replaced with H-40.
  • the density and bulk density of the Example 2 abrasive grain were determined as described for Comparative Example A to be 3.86 g cm 3 and 1.69 +/- 0.01 g/cm 3 , respectively.
  • the average (based on 4 discs) amount of metal removed during the 8 minute grinding performance test described in Comparative Example A was 275 grams.
  • Comparative Example C was prepared and tested as follows. A dispersion was prepared by mixing 680 grams of AAMH, 36 grams of HNO 3 , and 1,284 grams of DWT together in the 4 liter, food grade blender (Model 34BL22(CB6)). The
  • DWT, HNO 3 , and IO1 were placed in the blender first, followed by the AAMH. The contents was then mixed at low speed setting for 60 seconds.
  • the resulting dispersion was poured into a glass tray ("PYREX”) and dried overnight at about 93 °C to provide dried, friable solid, material.
  • the dried material was crushed with a pulverizer (obtained under the trade designation "BRUAN"
  • Type UA Braun Corp.
  • the crushed material was screened to retain the particles that were in the -20+60 mesh (U.S.A.
  • Comparative example A except the tube was rotated at 7 rpm to provide a residence time in the tube of about 15 minutes.
  • Calcined material was impregnated by mixing 70 grams of MEM per
  • the (impregnated) calcined material was in the sintering kiln as described in Comparative Example A except the tune was rotated at 10.5 rpm, and the sintering to provide a residence time in the tube of about 4 minutes, the sintering temperature was about 1410°C.
  • the density and bulk density of the Comparative Example C abrasive grain was determined as described for Comparative Example A to be 3.94 g/cm 3 .
  • the sintered alpha alumina-based ceramic abrasive grain was graded to retain the -30+35 and -35+40 mesh fractions (U.S.A. Standard Testing Sieves). These fractions were blended in a 1:1 ratio and incorporated into coated abrasive discs, which were tested for grinding performance.
  • the coated abrasive discs were prepared as described in Comparative Example A except there were 2 minute intervals for a total test time of 10 minutes, and the workpieces were made of 304 stainless steel. The average (based on 4 discs) amount of metal removed during the 10 minute grinding performance test was 124.3 grams.
  • Example 3 was prepared as described for Comparative Example C, except the AAMH was replaced with H-X.
  • the density and bulk density of Example 3 abrasive grain was determined as described for Comparative Example A to be 3.93 g/cm 3 .
  • Example 3 grinding performance test was 157.8 grams.
  • Comparative Example D and Example 4 Comparative Example D was prepared and tested as follows.
  • a dispersion was prepared by mixing 680 grams of AAMH, 36 grams of HNO 3 , 51 grams of IO1 having 10% iron oxide (calculated on a theoretical metal oxide basis as Fe 2 O 3 ), 26 grams of CS1130, and 1,284 grams of DWT together in a the 4 liter, food grade blender (Model 34BL22(CB6)).
  • the DWT, HNO 3 , CS1130, and IO were placed in the blender first, followed by the AAMH. contents mixed at low speed setting for 60 seconds.
  • the resulting dispersion was poured into a glass tray ("PYREX”) and dried overnight at about 99°C to provide dried, friable solid, material.
  • the dried material was crushed with a pulverizer (type UA, Braun Corp.) to provide precursor abrasive grain (particles).
  • the crushed material was screened to retain the particles that were in the -20+50 mesh (U.S.A. Standard Testing Sieves) size range.
  • the screened material was calcined and sintered as described in Comparative example A.
  • the density of the Comparative Example D abrasive grain was determined as described for Comparative Example A to be 3.84 g/cm 3 .
  • the microhardnesses of the Comparative Example D abrasive grain was measured by mounting loose abrasive grain in mounting resin (obtained under the trade designation "EPOMET” from Buehler Ltd., Lake Bluff, IL). More specifically, abrasive grain were secured in a 2.5 cm (1 inch) diameter, 1.9 cm (0.75 inch) tall cylinder ofthe resin. The mounted sample was polished using a conventional grinder/polisher (obtained under the trade designation "EPOMET” from Buehler Ltd.) and conventional diamond slurries wdth the final polishing step using a 1 micrometer diamond slurry obtained under the trade designation "METADI” from Buehler Ltd. to obtain polished cross-sections ofthe samples.
  • EPOMET a conventional grinder/polisher
  • the hardness measurements were made using a conventional microhardness tester Obtained under the trade designation "Mitutoyo MVK-VL" from Mitutoyo Corp of Tokyo, Japan) fitted with a Vickers indenter using a 500-gram indent load.
  • the hardness measurements were made according to the guidelines stated in ASTM Test Method E384 Test Methods for Microhardness of Materials (1991), the disclosure of which is incorporated herein by reference.
  • the hardness values which are an average of five measurements, wherein each measurement was done on a separate abrasive grain.
  • the average microhardness of the Comparative Example D abrasive grain was 19.5 MPa.
  • the sintered alpha alumina-based ceramic abrasive grain was graded to retain the -35+40 and -40+45 mesh fractions (U.S.A. Standard Testing Sieves). These fractions were blended in a 1 : 1 ratio and incorporated into coated abrasive discs, which were tested for grinding performance.
  • the coated abrasive discs were prepared as described in Comparative Example A except the workpieces were made of 4130 steel. The average (based on 4 discs) amount of metal removed during the 10 minute grinding performance test was 220 grams.
  • Example 4 was prepared as described for Comparative Example D, except the AAMH was replaced with H-X.
  • the density of the Example 4 abrasive grain was determined as described for Comparative Example A to be 3.89 g/cm 3 . Further, the average microhardness of the Example 4 abrasive grain, as determined according to the Comparative Example D procedure, was 21.7 GPa.
  • the average (based on 4 discs) amount of metal removed during the 8 minute Example 4 grinding performance test was 250 grams.
  • H-40 powder Approximately 1200 grams of H-40 powder was ball-milled at 80 rpm in a polyurethane lined vessel (30 cm) 12 inches) x 23 cm (9 inches); Paul O. Abbe, Inc., Little Falls, NJ) containing about 8000 grams of 1.27 cm (0.5 inch) zirconia media (U.S. Stoneware, East furniture, OH) for 24 hours. After recovering the ball-milled powder, 1000 grams ofthe powder was mixed with an acid- water solution (prepared by mixing 60 grams of HNO 3 with 607.6 grams of DWT) by hand in a plastic wash-tub. The resulting powder material was allowed to stand over a weekend in sealed-plastic bags.
  • an acid- water solution prepared by mixing 60 grams of HNO 3 with 607.6 grams of DWT
  • the powdered material was then extruded through a single screw extruder containing a die with 36 2.54 mm (0.1 inch) openings.
  • the extrudate was dried through a tunnel oven at a rate of 1 m/min.
  • the tunnel oven had first zone, 2.43 meters in length, set at 71°C (160°F), and the second zone, 2.43 meters in length, set at 82°C (180°F).
  • the dried extrudate as collected in aluminum pans and allowed to stand for 2 hours in a forced air oven set at 80°C.
  • the resulting dried material was crushed into particles using a pulverizer
  • the retained particles were fed into a calcining kiln to provide calcined abrasive grain precursor material.
  • the calcining kiln consisted of a 15 cm inner diameter, 1.2 meter in length, stainless steel tube having a 0.3 meter hot zone. The tube was inclined at a 3.0 degree angle with respect to the horizontal.
  • the tube rotated at about 3.5 rpm, to provide a residence time in the tube of about 4-5 minutes.
  • the temperature ofthe hot zone was about 650°C.
  • the calcined particles were impregnated with MEM (solution), wherein the ratio of solution to particles was 60 ml of solution to 100 grams of particles.
  • the impregnated particles were dried using a blow gun. The dried, impregnated particles were then calcined again at 650°C as described above to provide abrasive grain precursor particles.
  • the calcined abrasive grain precursor particles were fed into a rotary sintering kiln.
  • the sintering kiln consisted of an 8.9 cm inner diameter, 1.32 meter long silicon carbide tube inclined at 4.4 degrees with respect to the horizontal and had a 31 cm hot zone. The heat was applied externally via SiC electric heating elements.
  • the sintering kiln rotated at 5.0 rpm, to provide a residence time in the tube of about 7 minutes.
  • the sintering temperature was about 1400°C.
  • Example 2 except the H-40 powder was not ball-milled. The average total cut (based on 4 discs) was 245 grams.
  • Example 6 was prepared as described for Example 5 except two identical alumina ball mills (17.78 cm in height and 15.24 cm in diameter), each with 1500 grams 0.635 cm (0.25 inch) alumina media, were used, and the samples were milled for 18 hours. Each mill contained 600 grams of H-40. The milled powder was combined into one sample.
  • An alumina ball mill measuring 17.78 cm height (without cover) and 15.24 cm in diameter (U.S. Stoneware), was filled with 1200 grams of H-30 powder and 3300 grams of 0.635 cm (0.25 inch) alumina media (U.S. Stoneware). The sample was milled at 80 rpm for 48 hours. The milled powder was recovered from the mill. The median particle size of the milled powder was measured using a laser scattering particle size analyzer (obtained under the trade designation "HORIBA LA-910" from Horiba Laboratory Products, Irvine, CA) and found to be 7.3 micrometers.
  • a sol was prepared by combining 338 grams of the milled powder, 31 grams of HNO 3 and 1550 grams of DWT together in a conventional 4 liter, food grade blender (Model 34BL22(CB6), Waring Products Division, Dynamics Corp. of America, New Hartford, CT). The contents of the blender were mixed at low speed for one minute.
  • the resulting sol was poured into a 23 cm (9 inch) x 30 cm (12 inch) glass pan (obtained under the trade designation "PYREX"). The sol was dried overnight in a forced air oven at 93°C (200°F).
  • the resulting friable material was crushed into particles using the pulverizer, screened, calcined, impregnated, re-calcined, and sintered as described in Example 5.
  • a solution was made by mixing together 650 grams of ZRN, 750 grams of CS, 1,250 grams of HNO 3 , 5,000 grams of IO2 having 4.7% iron oxide (calculated on a theoretical metal oxide basis as Fe 2 O 3 ), and 2,400 grams of DWT, 18,000 grams of H-30 were fed into a 19 liter (5 gallon) pail rotating at 55 rpm and inclined 28° longitudinally continuously and simultaneously as a stream ofthe solution was sprayed onto the H-30. Agglomerated balls about 3-5 mm in diameter were formed at about 60% solid. The agglomerated balls were fed into a catalyst extruder (available from Bonnot Co. of Uniontown, OH) and extruded through a die having thirty six 0.254 cm (0.1 inch) diameter openings.
  • a catalyst extruder available from Bonnot Co. of Uniontown, OH
  • the pressure inside the extruder was about 410-477 kg/cm 2 (1200-1400 psi).
  • the extruded material was placed on a conveyer belt which fed into a drying oven that was at about 93°C (200°F).
  • the dried material was crushed using pulverizer (having a 1.1 mm gap between the steel plates; obtained under the trade designation "BRAUN" Type UD from Braun Corp., Los Angeles, CA) to provide precursor abrasive grain (particles).
  • the crushed material was screened to retain the particles that were between about 0.25 to 1 mm in size. The retained particles were calcined as described in Comparative
  • Example A except the tube ofthe calcining kiln was inclined at a 3.0 degree angle with respect to the horizontal, and the tube rotated at about 3.5 rpm, to provide a residence time in the tube of about 4-5 minutes.
  • the calcined abrasive grain precursor was sintered as described in Comparative Example A, except the sintering kiln rotated at 2 rpm, to provide a residence time in the tube of about 17.5 minutes, and the sintering temperature was about 1400°C.
  • the composition ofthe sintered abrasive grain was, on a theoretical metal oxide basis, 93% Al 2 O 3 , 4% ZrO 2 , 1.5 SiO 2 , and 1.5% Fe 2 O 3 , based on the total metal oxide content of the sintered abrasive grain.
  • a fracture surface of an Example 8 abrasive grain was examined using a scanning electron microscope (SEM). The average size of the alpha alumina crystallites was observed to be less than one micrometer. Further, an Example 8 abrasive grain was mounted and polished with a conventional polisher (obtained from Buehler of Lake Bluff, IL under the trade designation "ECOMET 3 TYPE POLISHER- GRINDER"). The sample was polished for about 3 minutes with a diamond wheel, followed by three minutes of polishing with each of 45, 30, 15, 9, 3, and 1 micrometer diamond slurries. The polished sample was examined using SEM in the backscattered mode. The average size of the zirconia crystallites was observed to be less than 0.25 micrometer. In addition, the SEM analysis indicated that the microstructure was dense and uniform.
  • the alpha alumina ceramic abrasive grain which was graded into a 1 : 1 mix of -30+35 and -35+40 mesh fractions (U.S.A. Standard Testing Sieves), was incorporated into 439 cm x 335 cm (173" x 132") resin-treated YF weight cloth belts.
  • the coated abrasive belts were made according to conventional procedures.
  • the make coat was a conventional calcium carbonate-filled phenolic resin (48% resole phenolic resin, 52% calcium carbonate, diluted to 81% solids with water); the size coat a conventional cryolite-filled phenolic resin (32% resole phenolic resin, 2% iron oxide, 66% cryolite, diluted to 78% solids with water).
  • the wet make resin weight was about 185 g/m 2 .
  • the abrasive grain were electrostatically coated.
  • the make resin was precured for 90 minutes at 88°C.
  • the wet size weight was about 850 g/m 2 .
  • the size resin was precured for 90 minutes at 88°C, followed by a final cure of 10 hours at 100°C.
  • the cured belt material was then converted into 2.5 cm x 100 cm (1" x 40") belts.
  • the coated abrasive belts were flexed prior to testing.
  • Example 9 was prepared as described for Example 8 except the dispersion consisted of 18,000 grams of H-30, 4,750 grams of ZRN, 750 grams of CS2, 1,250 grams of HNO 3 , 5,000 grams of IO2 having 4.7% iron oxide (calculated on a theoretical metal oxide basis as Fe 2 O 3 ), and 1,250 grams of DWT.
  • Example 9 abrasive grain were examined using the SEM as described in
  • FIG. 7 is a photomicrograph of a fracture surface of the Example 9 abrasive grain showing the alpha alumina crystallites 61.
  • FIG. 8 is a photomicrograph a polished section of Example 9 abrasive grain in the back scattered mode showing zirconia crystallites 63.
  • the average size ofthe alpha alumina crystallites was observed to be less than 1 micrometer; the average size of the zirconia crystallites less than 0.25 micrometer.
  • the SEM analysis indicated that the microstructure was dense and uniform.
  • Example 10 was prepared as described for Example 8 except the dispersion consisted of 18,000 grams of H-30, 7,000 grams of ZRN, 750 grams of CS2, 1,250 grams of HNO 3 , 5,000 grams of IO2 having 4.7% iron oxide (calculated on a theoretical metal oxide basis as Fe 2 O 3 ).
  • Example 10 abrasive grain were examined using the SEM as described in Example 8. The average size of the alpha alumina crystallites was observed to be less than 1 micrometer; the average size of the zirconia crystallites less than 0.25 micrometer. In addition, the SEM analysis indicated that the microstructure was dense and uniform.
  • the Comparative Example F belt was prepared as described for Example 8, except the abrasive used was a sol-gel-derived alpha alumina ceramic abrasive grain available from the 3M Company under the trade designation "201 CUBITRON". This type of abrasive grain is designed to be used in high pressure grinding applications.
  • Example 8-10 and Comparative Example F coated abrasive belts were evaluated according to the following test procedure.
  • the 2.5cm x 100 cm (1" x 40") belts were placed around a metal wheel of a belt grinder (obtained under the trade designation "SPA2030ND” from Elb Grinders Corporation of Mountainside, NJ).
  • the metal wheel was rotating at a speed of 1,700 smm (surface meters per minute).
  • the 1018 mild steel workpieces (1.3 cm x 10.2 cm x 35.6 cm (0.5" x 4" x 14") dimension) were mounted on a bed oscillating at a speed of 6 mpm (meters per minute).
  • the belt was tested at a predetermined infeed rate for each pass.
  • the workpieces were water cooled after each pass.
  • the 152.4 micrometer (6 mils) infeed represents a relatively low grinding pressure application
  • the 177.8 micrometer (7 mils) infeed a relatively high grinding pressure application.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Ceramic Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Structural Engineering (AREA)
  • Polishing Bodies And Polishing Tools (AREA)

Abstract

L'invention concerne un procédé de fabrication d'un grain abrasif à base d'alpha-alumine. Ce grain abrasif peut être incorporé dans des produits abrasifs tels que les abrasifs appliqués, les abrasifs collés, les abrasifs non-tissés et les brosses abrasives.
PCT/US2000/002285 1999-09-28 2000-01-28 Procede de fabrication de grain abrasif WO2001023320A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU34761/00A AU3476100A (en) 1999-09-28 2000-01-28 Method for making abrasive grain

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US40778199A 1999-09-28 1999-09-28
US09/407,781 1999-09-28

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8628597B2 (en) 2009-06-25 2014-01-14 3M Innovative Properties Company Method of sorting abrasive particles, abrasive particle distributions, and abrasive articles including the same
US9079294B2 (en) 2010-11-18 2015-07-14 3M Innovative Properties Company Convolute abrasive wheel and method of making
CN113755099A (zh) * 2020-05-27 2021-12-07 万华化学集团电子材料有限公司 蓝宝石化学机械抛光液及其应用
EP3013525B1 (fr) 2013-06-28 2022-03-02 Saint-Gobain Ceramics & Plastics, Inc. Article abrasif comprenant des particules abrasives façonnées

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5641469A (en) * 1991-05-28 1997-06-24 Norton Company Production of alpha alumina
WO1999038817A1 (fr) * 1998-01-28 1999-08-05 Minnesota Mining And Manufacturing Company Procede permettant de fabriquer un grain abrasif par impregnation et articles abrasifs

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5641469A (en) * 1991-05-28 1997-06-24 Norton Company Production of alpha alumina
WO1999038817A1 (fr) * 1998-01-28 1999-08-05 Minnesota Mining And Manufacturing Company Procede permettant de fabriquer un grain abrasif par impregnation et articles abrasifs

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8628597B2 (en) 2009-06-25 2014-01-14 3M Innovative Properties Company Method of sorting abrasive particles, abrasive particle distributions, and abrasive articles including the same
US8961632B2 (en) 2009-06-25 2015-02-24 3M Innovative Properties Company Method of sorting abrasive particles, abrasive particle distributions, and abrasive articles including the same
US9079294B2 (en) 2010-11-18 2015-07-14 3M Innovative Properties Company Convolute abrasive wheel and method of making
EP3013525B1 (fr) 2013-06-28 2022-03-02 Saint-Gobain Ceramics & Plastics, Inc. Article abrasif comprenant des particules abrasives façonnées
CN113755099A (zh) * 2020-05-27 2021-12-07 万华化学集团电子材料有限公司 蓝宝石化学机械抛光液及其应用

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