WO2019196183A1 - 一种ma-m2t尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器及其制备方法 - Google Patents

一种ma-m2t尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器及其制备方法 Download PDF

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WO2019196183A1
WO2019196183A1 PCT/CN2018/089574 CN2018089574W WO2019196183A1 WO 2019196183 A1 WO2019196183 A1 WO 2019196183A1 CN 2018089574 W CN2018089574 W CN 2018089574W WO 2019196183 A1 WO2019196183 A1 WO 2019196183A1
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magnesium oxide
ceramic
solid solution
sintering
magnesium
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PCT/CN2018/089574
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English (en)
French (fr)
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丁之光
刘子利
刘希琴
叶兵
丁文江
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凤阳爱尔思轻合金精密成型有限公司
上海交通大学
南京航空航天大学
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Priority to US16/753,572 priority Critical patent/US11529577B2/en
Publication of WO2019196183A1 publication Critical patent/WO2019196183A1/zh

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    • C04B35/04—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 magnesium oxide, calcium oxide or oxide mixtures derived from dolomite based on magnesium oxide
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Definitions

  • the invention relates to a magnesium oxide based foam ceramic filter and a preparation method thereof, in particular to a MA-M 2 T spinel solid solution reinforced magnesium oxide based foam ceramic filter and a preparation method thereof, belonging to the field of metal materials and metallurgy.
  • the filter prepared by the invention is particularly suitable for the filtration and purification of magnesium and its alloy melt, and can also be used for the filtration and purification of aluminum and its alloy melt.
  • Magnesium is chemically active. It is easily reacted with oxygen, nitrogen and water vapor during casting and processing. The resulting product remains in magnesium, affecting the internal quality of the product and deteriorating the performance of the product. According to the type and nature of inclusions in magnesium alloys, inclusions are generally divided into two categories: metal inclusions and non-metallic inclusions: (1) Metal inclusions: Magnesium alloys are inevitably introduced during the production and processing of raw magnesium. Some metal elements or metal compounds are intercalated, and they remain in the form of particles or clusters on the matrix or grain boundary of the magnesium alloy, mainly including metal elemental ⁇ -Fe particles and manganese-iron metal compounds such as (Fe, Mn) 3 .
  • Non-metallic inclusions in magnesium alloys are mainly magnesium oxynitrides such as MgO, Mg 3 N 2 , etc.;
  • a refining agent mainly composed of chloride KCl, NaCl, MgCl 2 , etc.
  • the flux cannot be completely removed during the refining process, and a small amount of flux remains in the magnesium melt, causing inclusion of the magnesium metal flux.
  • the suspended oxidized inclusions are pushed toward the grain boundaries by the crystallization front during crystallization, and the inclusions generally remain in the form of a film, a particle, or a cluster at the grain boundary of the magnesium alloy.
  • Statistics show that MgO accounts for more than 80% of all inclusions in magnesium alloys, and its distribution is film-like, granular and cluster-like.
  • the inclusions generated during the magnesium alloy casting process not only seriously deteriorate the mechanical properties and corrosion resistance of the alloy, but also reduce the surface quality of its machining and anodizing.
  • the content of the film-like and particulate oxide inside the alloy needs to be controlled to 100 cm 2 /kg and 100 mm 3 /kg or less to meet the normal use requirements. Therefore, the purification process for removing inclusions in the magnesium melt during the casting process to improve the purity of the melt becomes the key to the production of the magnesium alloy.
  • the melt purification process can be divided into two categories: flux purification and non-flux purification.
  • the flux purification process is a purification process commonly used in the production of magnesium alloys due to high impurity removal efficiency, low cost, and convenient operation.
  • the flux purification also has the disadvantages of increased metal loss, flux inclusion, and inability to degas, especially in the melting of rare earths.
  • the flux also consumes a large amount of rare earth elements in the alloy.
  • the non-flux purification process can not only make up for the deficiency of the flux purification process, but also has excellent purification effect.
  • the special three-dimensional porous ceramic foam ceramic filter can pass the filter cake effect due to its high porosity (70%-90%), strong adsorption capacity and chemical corrosion resistance.
  • the adsorption effect and the rectification effect have a good filtering effect on the inclusion particles in the alloy melt.
  • the foam ceramic filtration method not only filters out fine inclusion particles as small as 10 ⁇ m to 20 ⁇ m in the alloy melt, but also filters out liquid flux inclusions which are difficult to filter out by a general filter medium.
  • US Patent Document US3962081A (Ceramic foam filter), US4024212A (Ceramic foam and method of preparation), Chinese patent document CN103787691A (a method for preparing alumina foam ceramics) and the like all disclose some aluminum alloy, steel melt filtration inclusions
  • the reaction dissolves rapidly, thereby blocking its filtration pores or eroding into the melt of magnesium and its alloys as a harmful component. Therefore, these prior art foam filters are not suitable for the melt of magnesium and magnesium alloys. filter.
  • MgO is a cubic crystal NaCl structure with a lattice constant of 0.411 nm. It is an ion-bond compound with a melting point of 2852 ° C, which is much higher than the commonly used Al 2 O 3 (2054 ° C) and SiO 2 (1650 ⁇ 50 ° C). Therefore, magnesium oxide products have good chemical stability, high electrical resistivity and strong corrosion resistance to metals, slag and alkaline solutions. Compared with commonly used ceramic materials, MgO has good high-temperature chemical stability with magnesium and its alloy melts, does not react with molten slag composed of molten chloride and fluorate, and has a wetted angle with the flux. It is small and easy to adsorb the flux inclusions in the magnesium melt. Therefore, the MgO foam ceramic is an ideal material for the smelting purification of magnesium alloy liquid.
  • the research shows that the heat loss per unit product will be reduced by more than 10% for each reduction of the firing temperature in the sintering ceramics.
  • the addition of sintering aid is an important technical means to reduce the sintering temperature of MgO foam ceramics.
  • V 2 O 5 powder is added, MgO forms a liquid phase of approximately Mg 3 V 2 O 8 with V 2 O 5 at 1190 ° C, promotes sintering, and can significantly reduce the sintering temperature of MgO foam ceramic, but V 2 O 5 has a detrimental effect on the respiratory system and skin during use, and has strict restrictions on operation.
  • cobalt oxide is also a good low-temperature sintering aid, but it is also limited as a highly toxic substance and a rare resource.
  • Fluoride is a strong solvent and mineralizer commonly used in ceramic industry sintering.
  • Fluoride can enter the human body through the respiratory tract, digestive tract and skin. It has toxic effects on the central nervous system and myocardium. Low concentrations of fluorine pollution can cause brittle calcification of teeth and bones. Fluoride is specified in the Ceramic Industry Pollutant Discharge Standard (GB25464-2010). The emission standard must be less than 5.0mg/m 3 . Fluoride as a low-temperature sintering aid for magnesia ceramics will inevitably increase the emission of gaseous fluoride and increase the burden of environmental protection.
  • the fluoride ion in the solid solution fluoride remaining in ceramics is In the form of replacing oxygen ions, the chemical stability of the intergranular bond is lowered, and it is difficult to resist the long-term corrosion of the flux inclusion in the magnesium melt.
  • the foam ceramic filter disclosed in Chinese Patent Publication No. CN101138691A water glass, silica sol and ethyl silicate are used as the binder, and the presence of the SiO 2 component between the sintered foam ceramic particles makes it easy to be combined with magnesium and The alloy melt is reacted according to the formula (4), which also reduces the chemical stability of the foamed ceramic.
  • Chinese patent document CN100536986C magnesia foam ceramic filter
  • CN103553686A a magnesium aluminum spinel foam ceramic filter and its preparation method
  • boron trioxide and borax as the low temperature of magnesium oxide ceramics
  • the sintering aid forms a liquid phase when the boron trioxide is higher than 450 ° C.
  • the reaction with magnesium oxide forms magnesium borate in the form of a liquid phase to lower the sintering temperature.
  • boron trioxide is easily reacted with magnesium and aluminum, and is unstable in the melt of magnesium and aluminum alloy.
  • gallium oxide is a homologous oxide of boron trioxide, which forms a spinel-type MgGa 2 O 4 with magnesium oxide at a lower temperature to reduce the sintering temperature, but has a small amount of gallium resources (gallium is a strategy). Reserve metals), the higher price of gallium oxide limits its use in ordinary ceramics.
  • An object of the present invention is to provide a MA-M 2 T spinel solid solution reinforced magnesium oxide based ceramic foam filter which is excellent in chemical stability and thermal shock resistance, which can be sintered at a low temperature, and a preparation method thereof.
  • a MA-M 2 T spinel solid solution reinforced magnesium oxide based ceramic foam filter is obtained by coating a magnesium oxide based ceramic slurry containing a nano titanium oxide sintering aid on a polyurethane foam carrier by drying and sintering.
  • a method for preparing a MA-M 2 T spinel solid solution reinforced magnesium oxide based ceramic filter comprises the following steps:
  • Forming nano alumina sol was added ⁇ -Al 2 O 3 coating film on the surface of TiO 2 powder light burned magnesium oxide particles and highly dispersed uniformly, ⁇ -Al Al 2 O 3 sol in contact with the sintering process
  • the MgO particles react in situ to form a magnesium-aluminum spinel (MgAl 2 O 4 , MA) phase, and the MA and M 2 T are completely miscible at above 1350 ° C.
  • the foam ceramic filter prepared by the invention has only one side. Magnesia MgO and MA-M 2 T spinel solid solution phase.
  • the rheological agent is a mixture of polyacrylic acid and cellulose ether, wherein polyacrylic acid accounts for 20% by mass of the rheology agent, and the cellulose ether is used in industrial hydroxyethyl cellulose or hydroxypropyl methyl cellulose.
  • Cellulose ether and polyacrylic acid are not only good dispersing agents for nano-titanium oxide powder, but also prevent agglomeration of the slurry, and can also act as a binder when preparing the green body.
  • the slurry can be relatively firm after impregnation. Adhered to the polyurethane foam template, the green body has great strength, and it is easy to escape during the sintering process without polluting the product, thus ensuring the quality of the ceramic foam filter.
  • the magnesium oxide ceramic powder containing the nano titanium oxide sintering aid is a mixture of magnesium oxide powder and nano titanium oxide powder.
  • Nano-titanium dioxide is added to the ceramic component, and Ti 4+ , which is a variable-valence oxide, diffuses into the crystal of the periclase, increases crystal defects such as vacancies inside the crystal, activates the crystal lattice, and forms Ti 4+ ions to replace the Mg 2+ ion.
  • the solid solution promotes direct intercrystalline bonding.
  • the lattice constant of Al 2 O 3 is similar to that of MgO, and it can be dissolved into the MgO lattice during sintering to cause lattice distortion of MgO crystal; the diffusion rate of Al 3+ is small, and Al 2 O 3 is in the magnesia MgO.
  • the solubility is very small (the solubility of Al 2 O 3 in periclase MgO at 1700 ° C is only 3%), the sintering process is mainly to form a new compound MA phase by reaction sintering, and a limited solid solution is formed between MA phase and MgO, thereby promoting The combination of sintering and particle phase.
  • Nano-powder refers to ultrafine powder with particle size ⁇ 100nm, which has the characteristics of large specific surface area, high surface energy and high activity. Therefore, nano-powder is easily combined with other atoms, so its melting point and sintering temperature are lower than that of micropowder. many.
  • the sintering aid added in the form of nano titanium oxide and nano aluminum sol can fill the gap between the raw material micropowder particles, optimize the ceramic particle gradation and mixing uniformity, and at the same time, the nano powder has its own surface and interface effects.
  • the magnesium oxide powder is an fused magnesium oxide powder having a high hydration resistance, and has a particle diameter of 250 mesh to 500 mesh (medium diameter d 50 is 25 ⁇ m to 58 ⁇ m).
  • the particulate fused magnesia is surrounded by a continuous nano-aluminum sol film and is in intimate contact with highly dispersed nano-titanium oxide particles.
  • MgO magnesium-aluminum spinel MA and magnesium-titanium spinel M during sintering.
  • MA and M 2 T are completely mutually soluble at 1350 ° C or higher, and the cristobalite MgO grains are directly welded together during sintering, and the intergranular secondary spinel is desolvated and precipitated during cooling (intercrystalline spinel)
  • M 2 T and MA can compensate the stress on the critical surface of each phase, so that the stress relaxation of the material during firing cooling, and the pinning action of the spinel solid solution phase inhibit the rapid growth of the magnesium oxide particles, thereby Refines the structure of the foam ceramic and increases the density of the ceramic.
  • the nanometer titanium oxide powder accounts for 1% to 2% of the mass of the ceramic powder, and the nanometer titanium oxide powder has a particle diameter of 30 to 60 nm.
  • the nano aluminum sol has a solid content of 20% to 25%.
  • the preparation method of the ceramic slurry is as follows: adding the fused magnesium oxide powder to the ball mill tank according to the ratio, preparing the nano aluminum sol, the rheological agent and the deionized water into a solution, adding the nano titanium oxide powder, and ultrasonically treating After 30min ⁇ 60min, the nanometer titanium oxide powder is fully dispersed in the solution and then added to the ball mill tank. Then, the corundum ball is added according to the ratio of the ball to the ratio of 2:1, and the ball is ground for 2 to 4 hours at 60-120 rpm for uniform mixing. Vacuum evacuation was carried out for 10 min to 15 min under a vacuum of 0.02 MPa to 0.05 MPa.
  • the polyurethane foam stencil has a specification of 10 PPI to 20 PPI (Pores per inch , the average number of holes per unit length), and is immersed in a 15% to 20% NaOH aqueous solution at 40 ° C to 50 ° C for 40 min before use. After 60 minutes, it was washed with water and naturally dried, and then immersed in an aqueous solution of 2% to 4% of a dodecylbenzenesulfonic acid wetting agent, and taken out and dried to obtain. After the surface is roughened by NaOH etching and treated by an aqueous solution of a dodecylbenzenesulfonate wetting agent, the ceramic slurry is easily uniformly applied to the polyurethane foam template.
  • the dried green body is placed in a sintering furnace, heated to a temperature of 1400 ° C to 1600 ° C for high-temperature sintering, and cooled to room temperature with a furnace to obtain a magnesium oxide-based ceramic foam filter.
  • the sintering process is heated to 550 ° C at a heating rate of 30 ° C / h to decompose and vaporize the organic matter (polyurethane foam, rheological agent, etc.) in the foam ceramic filter blank, and then at a heating rate of 200 ° C / h Heating to a temperature of 1100 ° C, in the low-temperature sintering stage, the lower heating rate can prevent the polyurethane foam and the rheological agent from decomposing too fast, resulting in collapse or deformation damage of the green body. Finally, it is heated to a temperature of 1400 ° C to 1600 ° C at a heating rate of 50 ° C / h and kept at this temperature for 2 to 3 h.
  • the lower heating rate can ensure the uniform temperature in the sintered body, while avoiding the uniform formation rate of the spinel and avoiding the deformation stress and cracking of the sintered body due to excessively rapid phase transformation stress. .
  • the preparation method of the magnesium oxide-based ceramic foam filter provided by the invention has the advantages of simple process, low cost, high efficiency, suitable for large-scale production, etc., and the prepared magnesium oxide-based ceramic foam filter does not contain any chemical stability.
  • the nano-aluminum sol acts as a binder, and the highly uniformly dispersed nano-alumina sol and nano-titanium oxide react with magnesium oxide particles to form MA-M 2 T which is chemically stable to the melt of magnesium and its alloys.
  • the spinel solid solution and the magnesium oxide particles are welded together. Therefore, the ceramic foam filter has good strength, chemical stability and thermal shock resistance, and is particularly suitable for filtering and purifying inclusions in the melt of magnesium and its alloys. It can be used for melt filtration and purification of aluminum and its alloys. Compared with the prior art solutions, the technical effects of the present invention:
  • the MA-M 2 T spinel solid solution reinforced magnesium oxide foam ceramic filter of the present invention has excellent chemical stability.
  • TiO 2 has substantially no solid solution in MgO.
  • the nano titanium oxide added in the solution of the present invention promotes sintering of MgO and reacts with MgO to form magnesium titanium spinel (Mg 2 TiO 4 with high chemical stability).
  • M 2 T) phase Although the raw material aluminum sol component contains ⁇ -Al 2 O 3 which reacts with the magnesium liquid, the added nano aluminum sol forms ⁇ -Al 2 O on the surface of the lightly burned magnesium oxide particles and the highly uniformly dispersed nano TiO 2 powder.
  • the foam ceramic filter prepared by the present invention has only the periclase MgO and MA-M 2 T spinel solid solution phases.
  • reaction formula (1) In the reaction system of the magnesium melt and the alumina-added MgO-Al 2 O 3 sintered ceramic, in addition to the reaction formula (1), the following reaction may exist:
  • the Gibbs free energy ⁇ G 5 of the formula (5) of the reactive magnesium melt and the alumina-forming magnesium aluminate spinel is the smallest at different temperatures, indicating that the reaction takes precedence at the usual melting temperature of the magnesium alloy.
  • the reaction formula (7) of magnesium liquid and magnesium aluminum spinel is thermodynamically achievable, but the reaction is essentially a reaction between the magnesium solution and the decomposition product of magnesium aluminate spinel, but it is known from Table 1. At the melting temperature of magnesium alloy, the reaction of magnesium aluminate spinel into alumina and magnesia is difficult to carry out (reaction of reaction formula (6)), and the residual alumina in the sintered ceramic is also preferred to magnesium.
  • Magnesium-aluminum spinel is formed according to reaction formula (5); on the other hand, the MgO side of the MgO-Al 2 O 3 phase diagram is a eutectic phase diagram of the periclase solid solution and the MA spinel solid solution, which is generated in situ by reaction. There is almost no O 2- diffusion in the MA process. Only Mg 2+ and Al 3+ diffuse through the fixed oxygen lattice. The rate of formation is determined by the slower diffusion of Al 3+ , and the MA phase is mainly in Al 2 O 3 .
  • the side is formed by the internal growth method, resulting in the formation of a finite solid solution between the MA phase and the MgO, while the MgO content in the outer layer of the MA in contact with the MgO particles is much higher than the average value, and the MgO does not react with the magnesium melt, therefore,
  • the magnesium-aluminum spinel phase in which the magnesia particles are fused together in the sintered ceramic structure is in the magnesium melt Enough stable.
  • the MA-M 2 T spinel solid solution reinforced magnesium oxide foam ceramic filter of the present invention does not contain any component which reduces its chemical stability, and the added nano aluminum sol is not only lightly burned with magnesium oxide particles but also highly uniformly dispersed.
  • the surface of the nano-TiO 2 powder forms a ⁇ -Al 2 O 3 coating film and acts as a binder. In the sintering process, Al 2 O 3 and TiO 2 together with MgO are synthesized in situ to the magnesium and its alloy melt.
  • the chemically stable MA-M 2 T spinel solid solution phase avoids the damage of the chemical stability of the foam ceramics by the addition of silica sol, ethyl silicate and other binders to the existing products;
  • the sodium salt (such as sodium carboxymethyl cellulose is not used in the rheological agent) avoids the inhibition of ceramic sintering by Na + with a large residual ionic radius.
  • the melting temperatures of aluminum and its alloys are the same as those of magnesium and its alloys, MgO and MA spinel phases and aluminum and
  • the alloy melt does not undergo the reverse reaction of the reaction formulas (1) and (5); it is the same as that used for the melt of magnesium and its alloy, avoiding the addition of a binder such as silica sol or ethyl silicate to the foam ceramic in aluminum and Chemical stability damage in the alloy melt (even if the material contains 1% SiO 2 , the melt of aluminum and its alloy will react with SiO 2 in the ceramic to form Al+SiO 2 ⁇ Al 2 O 3 +Si at high temperature. Therefore, the prepared MA-M 2 T spinel solid solution reinforced magnesium oxide foam ceramic filter can also be used for the smelting purification of aluminum and its alloys.
  • the MA-M 2 T spinel solid solution reinforced magnesium oxide foam ceramic filter of the present invention has good low temperature sintering properties.
  • nano titanium dioxide is added to the ceramic component, and Ti 4+ , which is a variable oxide, diffuses into the crystal of the periclase, increases crystal defects such as vacancies inside the crystal, activates the crystal lattice, and forms Ti 4+ .
  • the ion replaces the solid solution of Mg 2+ ions to promote direct intergranular bonding.
  • the lattice constant of Al 2 O 3 is similar to that of MgO, and it can be dissolved into the MgO lattice during sintering to cause lattice distortion of MgO crystal; the diffusion rate of Al 3+ is small, and Al 2 O 3 is in the magnesia MgO.
  • the solubility is very small (the solubility of Al 2 O 3 in periclase MgO at 1700 ° C is only 3%), the sintering process is mainly to form a new compound MA phase by reaction sintering, and a limited solid solution is formed between MA phase and MgO, thereby promoting The combination of sintering and particle phase.
  • Nano-powder refers to ultrafine powder with particle size ⁇ 100nm, which has the characteristics of large specific surface area, high surface energy and high activity. Therefore, nano-powder is easily combined with other atoms, so its melting point and sintering temperature are lower than that of micropowder. many.
  • the sintering aid added in the form of nano titanium oxide and nano aluminum sol can fill the gap between the raw material micropowder particles, optimize the ceramic particle gradation and mixing uniformity, and at the same time, the nano powder has its own surface and interface effects.
  • the sufficient contact of the highly reactive nano- ⁇ -Al 2 O 3 with the MgO particles in the nano-titanium oxide and the aluminum sol rapidly increases the reaction rate, lowers the sintering temperature, improves the density and mechanical properties of the ceramic, and the reduction of the sintering temperature is favorable. Reduce energy consumption and production costs of ceramic foam filters.
  • the test shows that when the sintering temperature is lower than 1400 °C, the sintering structure of the magnesium oxide particles is not enough to cause the strength to be low, and the MA-M 2 T spinel solid solution reinforced magnesium oxide foam ceramic filter has a sintering temperature of 1400. °C ⁇ 1600 °C.
  • the MA-M 2 T spinel solid solution reinforced magnesium oxide foam ceramic filter of the present invention has good thermal shock resistance.
  • the use of fused magnesium oxide has strong resistance to hydration.
  • the formation of MA by reaction of magnesium oxide and aluminum oxide causes volume expansion (linear expansion ratio of 2.3%, volume expansion ratio of 6.9%) to increase the sintering burden.
  • ⁇ -Al 2 O 3 alumina is a porous substance with an oxygen ion approximately close to the vertical aspect, and Al 3+ is irregularly distributed in the octahedral and tetrahedral voids surrounded by oxygen ions.
  • the stable transition crystal structure is the same as that of the magnesium aluminate spinel MA crystal.
  • the granular fused magnesia is surrounded by a continuous nano-aluminum sol film and is in close contact with the highly dispersed nano-titanium oxide particles, and reacts with MgO in situ to form a magnesium-aluminum spinel during sintering.
  • Stone MA and magnesium-titanium spinel M 2 T phase, MA and M 2 T are completely mutually soluble at 1350 ° C or higher, and the cristobalite MgO grains are directly welded together during sintering, and decomposed and precipitated twice during cooling.
  • Spinel (intercrystalline spinel) M 2 T and MA can compensate the stress on the critical surface of each phase, causing the stress relaxation of the material during firing and cooling, and the pinning of the spinel solid solution phase is inhibited.
  • the rapid growth of the magnesium oxide particles refines the structure of the foamed ceramic and increases the density of the ceramic; compared with MgO and Al 2 O 3 , the spinel phase has a small thermal expansion coefficient and a low thermal conductivity, and thus is prepared.
  • the MA-M 2 T spinel solid solution reinforced magnesium oxide foam ceramic filter has high mechanical properties, high temperature impact resistance and thermal shock resistance.
  • the polyurethane foam is a surface-inert hydrophobic material, which has poor wettability with the ceramic slurry, thereby affecting the hanging performance of the polyurethane foam template.
  • the surface is roughened by NaOH etching, and then After the aqueous solution of the dodecylbenzenesulfonate wetting agent is treated, the ceramic slurry is easily uniformly applied to the polyurethane foam template; and the cellulose ether and polyacrylic acid as the rheological agent are not only the nano titanium oxide powder.
  • a good dispersant can prevent the agglomeration of the slurry, and can also act as a binder when preparing the green body.
  • the slurry can be relatively firmly attached to the polyurethane foam template, so that the green body has a large The strength, while being easily escaping during the sintering process without contaminating the product, thus guarantees the quality of the ceramic foam filter.
  • FIG. 1 is a flow chart showing the preparation process of a MA-M 2 T spinel solid solution reinforced magnesium oxide based ceramic foam filter. detailed description
  • MA-M 2 T spinel solid solution reinforced magnesium oxide foam ceramic filter which is coated with a light-burning magnesium oxide-based ceramic slurry containing a nano-cerium oxide sintering aid on a polyurethane foam carrier, dried and sintered.
  • the specific preparation process is shown in Figure 1.
  • nanometer titanium oxide According to the ratio of nanometer titanium oxide to 1% of the mass of ceramic powder, nanometer titanium oxide with a particle diameter of 30 nm and fused powder of magnesium oxide having a particle size of 250 mesh (medium diameter d 50 of 58 ⁇ m) were used to prepare ceramic powder.
  • the rheological agent was mixed according to the ratio of the polyacrylic acid and the hydroxyethyl cellulose in a mass ratio of 1:4.
  • the nano-alumina sol with a solid content of 20% is 15% (the pH is near-neutral commercial nano-aluminum sol, the same below), the rheological agent is 0.8%, and the rest is made of ceramic powder.
  • the fused magnesium oxide powder is added into the ball mill tank according to the ratio, and the nano aluminum sol, the rheological agent and the appropriate amount of deionized water (determined according to the solid content of the ceramic slurry, the same amount, the same below) are prepared into a solution.
  • the nanometer titanium oxide powder was added, and the nanometer titanium oxide powder was sufficiently dispersed in the solution after ultrasonic treatment for 30 minutes, and then added to the ball mill tank, and then the corundum ball was added in a ratio of 2:1 of the ball to the ball ratio, and the ball was ground at 60 rpm for 4 hours. After uniformity, vacuum evacuation was carried out for 15 min under a vacuum of 0.02 MPa to obtain a ceramic slurry having a solid content of 60%.
  • 10PPI polyurethane foam stencil was selected, immersed in a 15% NaOH aqueous solution at 40 ° C for 60 min, washed with water and dried naturally, then immersed in an aqueous solution of 2% dodecylbenzenesulfonic acid wetting agent, and taken out dry. .
  • the polyurethane foam stencil is then immersed in a ceramic slurry, and the polyurethane foam stencil is pressed by a roll press to remove excess immersion slurry to form a green body, and then the green body is dried by heating to 80 ° C.
  • the dried green body is placed in a sintering furnace and heated to 550 ° C at a heating rate of 30 ° C / h to decompose and vaporize the organic foam such as polyurethane foam and rheological agent in the ceramic foam filter, and then at 200 ° C /
  • the heating rate of h was heated to a temperature of 1100 ° C, and finally heated to a temperature of 1600 ° C at a heating rate of 50 ° C / h and held at this temperature for 2.5 h, and cooled to room temperature with a furnace to obtain a magnesium oxide based ceramic foam filter.
  • nanometer titanium oxide According to the ratio of nanometer titanium oxide to 2% of the mass of ceramic powder, nanometer titanium oxide with a particle diameter of 60 nm and fused powder of magnesium oxide having a particle size of 500 mesh (medium diameter d 50 of 25 ⁇ m) were used to prepare ceramic powder.
  • the rheological agent was mixed according to the ratio of polyacrylic acid and hydroxypropylmethylcellulose in a ratio of 1:4.
  • the nano-alumina sol with a solid content of 25% is 20%
  • the rheological agent is 1.5%
  • the rest is made of ceramic powder.
  • the fused magnesia powder was added to the ball mill tank according to the ratio.
  • the nano-alumina sol, the rheological agent and the appropriate amount of deionized water were prepared into a solution, and then the nano-titanium oxide powder was added, and the nano-titanium oxide powder was ultrasonicated for 45 minutes.
  • 20PPI polyurethane foam stencil was used, soaked in a 20% NaOH aqueous solution at 50 °C for 40 min, washed with water and dried naturally, then immersed in an aqueous solution of 4% dodecylbenzenesulfonic acid wetting agent, and taken out dry. .
  • the polyurethane foam stencil is then immersed in the ceramic slurry, and the polyurethane foam stencil is pressed by a roll press to remove the excess immersion slurry to form a green body, and then the green body is dried by heating to 120 ° C.
  • the dried green body is placed in a sintering furnace and heated to 550 ° C at a heating rate of 30 ° C / h to decompose and vaporize the organic foam such as polyurethane foam and rheological agent in the ceramic foam filter, and then at 200 ° C /
  • the heating rate of h was heated to a temperature of 1100 ° C, and finally heated to a temperature of 1400 ° C at a heating rate of 50 ° C / h and held at this temperature for 3 h, and cooled to room temperature with a furnace to obtain a magnesium oxide based ceramic foam filter.
  • nanometer titanium oxide According to the ratio of nanometer titanium oxide to 1.5% of the mass of ceramic powder, nanometer titanium oxide with a particle diameter of 50 nm and fused magnesium oxide powder with a particle size of 325 mesh (medium diameter d 50 of 45 ⁇ m) were used to prepare ceramic powder.
  • the rheological agent was mixed according to the ratio of the polyacrylic acid and the hydroxyethyl cellulose in a mass ratio of 1:4.
  • the nano-alumina sol with a solid content of 22% was 25%
  • the rheological agent was 1.0%
  • the rest was made of ceramic powder.
  • the fused magnesia powder was added to the ball mill tank according to the ratio.
  • the nano-alumina sol, the rheological agent and the appropriate amount of deionized water were prepared into a solution, and then the nano-titanium oxide powder was added, and the nano-titanium oxide powder was ultrasonicated for 60 minutes.
  • 15PPI polyurethane foam stencil was selected, immersed in a 15% NaOH aqueous solution at 45 ° C for 50 min, washed with water and dried naturally, then immersed in an aqueous solution of 3% dodecylbenzenesulfonic acid wetting agent, and taken out dry. .
  • the polyurethane foam stencil is then immersed in a ceramic slurry, and the polyurethane foam stencil is pressed by a roll press to remove excess immersion slurry to form a green body, and then the green body is dried by heating to 100 ° C.
  • the dried green body is placed in a sintering furnace and heated to 550 ° C at a heating rate of 30 ° C / h to decompose and vaporize the organic foam such as polyurethane foam and rheological agent in the ceramic foam filter, and then at 200 ° C /
  • the heating rate of h was heated to a temperature of 1100 ° C, and finally heated to a temperature of 1500 ° C at a heating rate of 50 ° C / h and held at this temperature for 2 h, and cooled to room temperature with a furnace to obtain a magnesium oxide based ceramic foam filter.
  • nanometer titanium oxide with a particle diameter of 60 nm and fused powder of magnesium oxide having a particle size of 300 mesh (medium diameter d 50 of 48 ⁇ m) were used to prepare ceramic powder.
  • the rheological agent was prepared by mixing the polyacrylic acid: hydroxypropylmethylcellulose: hydroxyethylcellulose in a mass ratio of 2:4:4.
  • 20% of the nano-alumina sol with a solid content of 20%, a rheological agent of 1.0%, and the rest were made of ceramic powder.
  • the fused magnesia powder was added to the ball mill tank according to the ratio.
  • the nano-alumina sol, the rheological agent and the appropriate amount of deionized water were prepared into a solution, and then the nano-titanium oxide powder was added, and the nano-titanium oxide powder was ultrasonicated for 45 minutes.
  • 15PPI polyurethane foam stencil was selected, immersed in a 15% NaOH aqueous solution at 45 ° C for 50 min, washed with water and dried naturally, then immersed in an aqueous solution of 4% dodecylbenzenesulfonic acid wetting agent, and taken out dry. .
  • the polyurethane foam stencil is then immersed in a ceramic slurry, and the polyurethane foam stencil is pressed by a roll press to remove excess immersion slurry to form a green body, and then the green body is dried by heating to 100 ° C.
  • the dried green body is placed in a sintering furnace and heated to 550 ° C at a heating rate of 30 ° C / h to decompose and vaporize the organic foam such as polyurethane foam and rheological agent in the ceramic foam filter, and then at 200 ° C /
  • the heating rate of h was heated to a temperature of 1100 ° C, and finally heated to a temperature of 1550 ° C at a heating rate of 50 ° C / h and held at this temperature for 2 h, and cooled to room temperature with a furnace to obtain a magnesium oxide based ceramic foam filter.

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Abstract

一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器及其制备方法，该制备方法包括步骤：(1)按照质量百分比将15％～25％纳米铝溶胶，0.8％～1.5％流变剂，其余为含纳米氧化钛烧结助剂的氧化镁陶瓷粉料进行配料，添加去离子水经球磨混合均匀，然后经真空排气制成固含量为60％～70％的陶瓷浆料；(2)将聚氨酯泡沫塑料模版浸入到该陶瓷浆料中，通过辊压机挤压聚氨酯泡沫塑料模版去除多余的浸挂浆料后制成素坯，然后将素坯加热到80℃～120℃进行烘干；(3)将干燥的素坯放入烧结炉内，升温至1400℃～1600℃温度下进行高温烧结，随炉冷却至室温得到氧化镁基泡沫陶瓷过滤器。

Description

一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器及其制备方法 技术领域
本发明涉及一种氧化镁基泡沫陶瓷过滤器及其制备方法，具体是一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器及其制备方法，属于金属材料与冶金领域。本发明所制备的过滤器特别适用于镁及其合金熔体的过滤净化，亦可以用于铝及其合金熔体的过滤净化。
背景技术
镁的化学性质活泼，在铸造及加工过程中，极易与氧、氮及水蒸气发生化学反应，生成的产物残留在镁中，影响制品的内部质量，恶化制品性能。根据镁合金中夹杂物的种类和性质，一般将夹杂物分为金属夹杂和非金属夹杂两大类：(1)金属夹杂物：镁合金在原镁生产和后期加工过程中，会不可避免的引入一些金属单质或者金属化合物夹杂，它们以粒子状、簇状等形态残留在镁合金的基体或者晶界上，主要包括金属单质α-Fe粒子、锰-铁的金属化合物如(Fe,Mn) 3Si，(Fe,Mn) 5Si 3等；(2)非金属夹杂物：镁合金中的非金属夹杂物主要以镁的氮氧化合物为主，如MgO，Mg 3N 2等；镁合金在熔炼过程中添加以氯化物(KCl、NaCl、MgCl 2等)为主的精炼剂，精炼过程中熔剂不能完全去除，会有少量的熔剂残留在镁熔体中，造成镁金属熔剂夹杂。悬浮的氧化夹杂在结晶时由结晶前沿被推向晶界，夹杂物一般以薄膜状、粒子状、簇状的形态残留在镁合金晶界处。有统计资料表明，MgO占镁合金的所有夹杂物的80％以上，分布形态为薄膜状、粒子状及簇状。镁合金熔铸过程中产生的夹杂物不仅严重恶化合金的力学性能和耐蚀性能，而且降低了其机加工和阳极氧化处理的表面质量。对于压铸镁合金而言，其合金内部的薄膜状和粒子状氧化物的含量需要控制在100cm 2/kg和100mm 3/kg以下才能满足正常的使用要求。因此，在熔铸过程中去除镁熔体中的夹杂物以提高熔体的纯净度的净化工艺成为镁合金生产的关键。
熔体净化工艺可分为熔剂净化与非熔剂净化两大类。熔剂净化工艺因 除杂效率高、成本低、操作方便而成为镁合金生产中普遍采用的净化工艺，但是熔剂净化也存在着金属损耗增加、熔剂夹杂、不能除气等不足，尤其是在熔炼稀土镁合金时，熔剂还会大量消耗合金中的稀土元素。非熔剂净化工艺不但能弥补熔剂净化工艺的不足而且具有优异的净化效果，成为目前应用发展的重要熔体净化工艺并相继开发了过滤净化、旋转喷吹净化、电磁净化、超声波处理等多种非熔剂净化技术。相比简单的金属网熔体过滤，具有特殊的三维多孔陶瓷结构泡沫陶瓷过滤器，因其孔隙率高(70％～90％)、吸附能力强、耐化学腐蚀等特点，能够通过滤饼效应、吸附效应及整流效应对合金熔体中的夹杂物颗粒具有很好的过滤效果。泡沫陶瓷过滤法不但可以滤掉合金熔体中小至10μm～20μm的微细夹杂物颗粒,而且能过滤掉一般过滤介质难以滤除的液态熔剂夹杂。
美国专利文献US3962081A(Ceramic foam filter)，US4024212A(Ceramic foam and method of preparation)，中国专利文献CN103787691A(一种氧化铝泡沫陶瓷的制备方法)等都公开了一些用于铝合金、钢铁熔体过滤夹杂物的Al 2O 3，ZrO 2，SiC、SiO 2基泡沫陶瓷的方法，然而，MgO的标准生成自由焓很低，活性很高的镁熔体非常容易与泡沫陶瓷基体材料发生(1)～(4)式反应而迅速溶解，从而堵塞其过滤孔隙或熔蚀进入镁及其合金熔体内成为有害成分，因此，这些现有材质的泡沫过滤器并不适合于镁和镁合金熔体的过滤。
3Mg (l)+Al 2O 3(s)＝3MgO (s)+2Al (l)  (1)
2Mg(l)+ZrO 2(s)＝2MgO(s)+Zr(s)  (2)
6Mg(l)+4Al(l)+3SiC(s)＝3Mg 2Si(s)+Al 4C 3(s)  (3)
4Mg(l)+SiO 2(s)＝2MgO(s)+Mg 2Si(s)  (4)
MgO为立方晶系NaCl型结构，晶格常数为0.411nm，属于离子键化合物，其熔点为2852℃，远高于常用的Al 2O 3(2054℃)和SiO 2(1650±50℃)，因此，氧化镁制品具有良好的化学稳定性、高的电阻率以及对金属、熔渣和碱性溶液有较强的抗侵蚀能力等特性。与常用的陶瓷材料相比，MgO与镁及其合金熔体具有很好的高温化学稳定性，与熔融的氯盐和氟酸盐组成的熔剂夹渣不 发生反应，并且与熔剂夹杂润湿角较小而容易吸附镁熔体中的熔剂夹杂，因此，MgO材质泡沫陶瓷是镁合金液熔炼净化的理想材料。
在低于氧化物组成的熔点温度之下进行烧成是制备陶瓷材料所必须的、最关键的步骤，而在高温下所发生的烧结、晶粒长大等过程决定着陶瓷材料的显微组织和性能。中国专利文献CN1011306B(纯氧化镁泡沫陶瓷过滤器及其制取工艺)、CN101138691A(铸造用镁质泡沫陶瓷过滤器的制备方法)等以纯氧化镁为原料制备泡沫陶瓷，因MgO具有很高的熔点和热膨胀系数(13.5×10 -6/℃)高，因此，导致其烧结困难(烧结温度不低于其熔点的0.8倍)和抗热震性较差，限制了MgO泡沫陶瓷的应用与发展。
研究表明：在烧结陶瓷过程中烧成温度每降低100℃，单位产品热耗会降低10％以上，通过添加烧结助剂是降低MgO泡沫陶瓷烧结温度的重要技术手段。添加V 2O 5粉体时，MgO在1190℃时会与V 2O 5形成近似组成为Mg 3V 2O 8的液相，促进烧结，能够显著降低MgO泡沫陶瓷的烧结温度，但是V 2O 5在使用过程中对呼吸***和皮肤有损害作用，对操作有严格的限制。与V 2O 5相同，氧化钴也是良好的低温烧结助剂，但作为高毒物质和稀有资源也限制了应用。氟化物是陶瓷工业烧结中常用的强助溶剂和矿化剂，中国专利文献CN100536986C(氧化镁质泡沫陶瓷过滤器)、CN1473947A(镁和镁合金熔体净化用泡沫陶瓷)、CN101785944B(用于镁和镁熔体过滤用氧化镁泡沫陶瓷过滤器的制备方法)中添加萤石(熔点1423℃)及氟化镁(熔点1248℃)，在烧结过程中氟化物的固溶不仅增大了基体氧化镁的晶格畸变，而且本身易形成低熔点液相，从而降低氧化镁陶瓷的烧结温度；然而，在烧结过程中氟化物中的F与Si、Al、Fe、Ca结合，大部分(在瓷砖生产中约占70％)以气态形式挥发不仅本身侵蚀坯体而损害烧结陶瓷的质量，更为严重的是排放到大气中会造成氟化物污染，氟化物可经呼吸道、消化道及皮肤进入人体，对中枢神经***、心肌有毒性作用，低浓度氟污染会导致牙齿和骨骼脆钙化，《陶瓷工业污染物排放标准》(GB25464-2010)中规定氟化物的排放标准必须低于5.0mg/m 3，以氟化物作为氧化镁陶瓷的低温烧结助剂必然增加气态氟化物的排放并加重环保投 入负担；另外，陶瓷中残留的固溶氟化物中氟离子是以取代氧离子的形式存在，造成晶粒间结合的化学稳定性降低，难以抵抗镁熔体中熔剂夹杂的长时间侵蚀。中国专利文献CN101138691A等公开的泡沫陶瓷过滤器的制备浆料中采用水玻璃、硅溶胶及硅酸乙酯作为粘接剂，烧结的泡沫陶瓷颗粒间SiO 2成分的存在，使其易与镁及其合金熔体按(4)式反应，同样降低了泡沫陶瓷的化学稳定性。中国专利文献CN100536986C(氧化镁质泡沫陶瓷过滤器)、CN103553686A(一种镁铝尖晶石质泡沫陶瓷过滤器及其制备方法)等专利文献中，三氧化二硼及硼砂作为氧化镁陶瓷的低温烧结助剂，三氧化二硼高于450℃时即形成液相，在烧结温度超过1350℃时，与氧化镁反应生成硼酸镁以液相形式存在而降低了烧结温度。然而，三氧化二硼易与镁、铝反应，在镁、铝合金熔体中并不稳定；同时，由于三氧化二硼溶于水和乙醇等溶剂，在空气中可强烈地吸水生成硼酸，在泡沫陶瓷的制备过程中添加的三氧化二硼溶于水形成硼酸水溶液，易与氧化镁反应形成硼酸镁沉淀而降低其作用。氧化镓是三氧化二硼的同族氧化物，在较低的温度下与氧化镁形成尖晶石型的MgGa 2O 4而起到降低烧结温度的作用，但镓资源量很少(镓是战略储备金属)，氧化镓较高的价格限制了其在普通陶瓷中的应用。
发明内容
本发明的目的是提供一种能在低温下实现烧结的、化学稳定性和抗热震性优异的MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器及其制备方法。
为了达到上述技术目的，本发明的技术方案是：
一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器，其是将含纳米氧化钛烧结助剂的氧化镁基陶瓷浆料涂覆在聚氨酯泡沫载体上经干燥、烧结得到。
一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器的制备方法，包括以下步骤：
(1)按照质量百分比将15％～25％纳米铝溶胶，0.8％～1.5％流变剂， 其余为含纳米氧化钛烧结助剂的氧化镁陶瓷粉料进行配料，添加去离子水经球磨混合均匀，然后经真空排气制成固含量为60％～70％的陶瓷浆料。加入的纳米铝溶胶在轻烧氧化镁颗粒及高度均匀分散的纳米TiO 2粉体表面形成γ-Al 2O 3包覆膜，在烧结过程中铝溶胶中的γ-Al 2O 3与其接触的MgO颗粒原位反应生成镁铝尖晶石(MgAl 2O 4，MA)相，MA与M 2T在1350℃以上完全互溶，根据XRD分析结果表明，本发明所制备的泡沫陶瓷过滤器只有方镁石MgO和MA-M 2T尖晶石固溶体相。
所述流变剂为聚丙烯酸和纤维素醚的混合物，其中聚丙烯酸占流变剂质量的20％，所述纤维素醚为工业用羟乙基纤维素、羟丙基甲基纤维素中的一种或其混合物。纤维素醚和聚丙烯酸不但是纳米氧化钛粉体的良好分散剂，能够防止浆料产生团聚现象，而且在制备素坯时还能起到粘接剂的作用，浸渍后浆料能比较地牢固附着在聚氨酯泡沫模板上，使素坯具有很大的强度，同时在烧结过程中极易逸出而不污染制品，因而保证了泡沫陶瓷过滤器的质量。
所述含纳米氧化钛烧结助剂的氧化镁陶瓷粉料为氧化镁粉体和纳米氧化钛粉体的混合物。在陶瓷组分中加入纳米二氧化钛，作为变价氧化物的Ti 4+扩散进入方镁石晶体内，增加了晶体内部的空位等晶体缺陷，活化了晶格，形成Ti 4+离子置换Mg 2+离子的固溶体而促进晶间直接结合。Al 2O 3的晶格常数与MgO相近，在烧结过程中能够固溶到MgO晶格而导致MgO晶体发生晶格畸变；Al 3+的扩散速度小，Al 2O 3在方镁石MgO中的溶解度很小(Al 2O 3在方镁石MgO中1700℃时的溶解度仅3％)，烧结过程主要为反应烧结生成新的化合物MA相，同时MA相与MgO间形成有限固溶体，从而促进了烧结和颗粒相间的结合。纳米粉体是指颗粒尺寸<100nm的超微细粉末，具有比表面积大、表面能高、高活性等特点，因此，纳米粉体很容易与其他原子结合，故其熔点和烧结温度比微粉低得多。以纳米氧化钛和纳米铝溶胶的形式加入的烧结助剂，能够填充原料微粉颗粒间的空隙，优化了陶瓷颗粒级配和混合均匀性，同时，纳米粉体因其自身的表面和界面效应，纳米氧化钛和铝溶胶中高反应活性的纳米γ-Al 2O 3与MgO颗粒的充分接触使反应速度迅速提高，降低了烧结温度，提高陶瓷的致 密度和力学性能，而烧结温度的降低有利于降低能耗和泡沫陶瓷过滤器的生产成本。所述氧化镁粉体为抗水化能力强的电熔氧化镁粉体，其粒径为250目～500目(中径d 50为25μm～58μm)。颗粒状的电熔氧化镁被连续的纳米铝溶胶膜包围并和高度分散的纳米氧化钛颗粒密切接触，在烧结过程中与MgO原位反应生成镁铝尖晶石MA和镁钛尖晶石M 2T相，MA与M 2T在1350℃以上完全互溶，烧结过程中将方晶石MgO晶粒直接熔接在一起，在冷却时脱溶析出晶间二次尖晶石(晶间尖晶石)M 2T及MA，可补偿各相临界面上的应力，使材料在烧成冷却时产生的应力松弛，同时尖晶石固溶体相的钉扎作用抑制了氧化镁颗粒的快速长大，从而细化了泡沫陶瓷的组织并提高了陶瓷的致密度。
所述纳米氧化钛粉体占陶瓷粉料质量的1％～2％，纳米氧化钛粉体的粒径为30～60nm。
作为优选，所述纳米铝溶胶的固含量为20％～25％。
所述陶瓷浆料的制备方法为：按照配比将电熔氧化镁粉料加入球磨罐中，将纳米铝溶胶、流变剂及去离子水制备成溶液后加入纳米氧化钛粉体，超声处理30min～60min使纳米氧化钛粉体在溶液中充分分散后加入到球磨罐内，再按照球料比2:1的比例加入刚玉球，以60～120rpm转速球磨2h～4h使其混合均匀，然后在0.02MPa～0.05MPa的负压下进行真空排气10min～15min。
(2)将聚氨酯泡沫塑料模版浸入到上述的陶瓷浆料中，通过辊压机挤压聚氨酯泡沫塑料模版去除多余的浸挂浆料后制成素坯，然后将素坯在加热到80℃～120℃进行烘干。
所述聚氨酯泡沫塑料模版的规格为10PPI～20PPI(Pores per inch ,单位英寸长度上的平均孔数)，使用前在40℃～50℃的15％～20％NaOH水溶液中浸泡表面刻蚀40min～60min后用清水洗涤自然晾干，然后浸入到2％～4％十二烷基苯磺酸润湿剂的水溶液中，取出干燥后得到。通过NaOH刻蚀使其表面粗糙化，再通过十二烷基苯磺酸盐润湿剂的水溶液处理后，陶瓷浆料易于均匀涂挂到聚氨酯泡沫模板上。
(3)将干燥的素坯放入烧结炉内，升温至1400℃～1600℃温度下进行 高温烧结，随炉冷却至室温得到氧化镁基泡沫陶瓷过滤器。
所述烧结工艺是以30℃/h的升温速度加热至550℃使泡沫陶瓷过滤器素坯内的有机物(聚氨酯泡沫及流变剂等)分解气化排出，然后以200℃/h的升温速度加热至1100℃温度，在低温烧结阶段，较低的升温速度可以防止聚氨酯泡沫及流变剂分解速度过快导致素坯塌陷或变形损坏。最后以50℃/h的升温速度加热至1400℃～1600℃温度并在该温度下保温2～3h。在高温烧结阶段，烧结温度超过1100℃后，较低的升温速度可以保证烧结体内的温度一致，同时避免生成尖晶石的生成速度均匀并且避免过快产生的相变应力造成烧结体变形和开裂。
本发明所提供的氧化镁基泡沫陶瓷过滤器的制备方法具有工艺简单、成本低、效率高、适合规模化生产等优点，所制备的氧化镁基泡沫陶瓷过滤器不含任何降低其化学稳定性的组分，纳米铝溶胶能够起到粘结剂的作用，高度均匀分散的纳米铝溶胶和纳米氧化钛与氧化镁颗粒反应生成对镁及其合金熔体具有化学稳定性的MA-M 2T尖晶石固溶体并将氧化镁颗粒熔接在一起，因此，泡沫陶瓷过滤器具有良好的强度、化学稳定性和抗热震性，特别适用于过滤净化镁及其合金熔体中的夹杂物，亦可用于铝及其合金熔体过滤净化。与现有的技术方案相比，本发明的技术效果：
一、本发明的MA-M 2T尖晶石固溶体增强氧化镁泡沫陶瓷过滤器具有优异的化学稳定性。TiO 2在MgO中基本无固溶作用，本发明方案中所添加的纳米氧化钛会促进MgO的烧结，并与MgO反应生成具有较高化学稳定性的镁钛尖晶石(Mg 2TiO 4，M 2T)相。虽然原料铝溶胶组分中含有会与镁液反应的γ-Al 2O 3，但加入的纳米铝溶胶在轻烧氧化镁颗粒及高度均匀分散的纳米TiO 2粉体表面形成γ-Al 2O 3包覆膜，在烧结过程中铝溶胶中的γ-Al 2O 3与其接触的MgO颗粒原位反应生成镁铝尖晶石(MgAl 2O 4，MA)相，MA与M 2T在1350℃以上完全互溶，根据XRD分析结果表明，本发明所制备的泡沫陶瓷过滤器只有方镁石MgO和MA-M 2T尖晶石固溶体相。
在镁熔体与添加氧化铝的MgO-Al 2O 3烧结陶瓷的反应体系中，除存在 反应式(1)外，还可能存在如下反应：
3Mg (l)+4Al 2O 3(s)＝3MgAl 2O 4(s)+2Al (l)  (5)
氧化铝与氧化镁生成镁铝尖晶石MgAl 2O 4的反应为：
MgO (s)+Al 2O 3(s)＝MgAl 2O 4(s)  (6)
镁熔体与镁铝尖晶石MgAl 2O 4发生的反应为：
3Mg (l)+MgAl 2O 4(s)＝2Al (l)+4MgO (s)  (7)
根据《纯物质热化学数据手册》(伊赫桑·巴伦主编，程乃良等译，北京：科学出版社，2003年)，在900～1200K时镁熔体与镁铝尖晶石反应体系的物质Gibbs自由能数据和反应(1)、5)、(6)和(7)的Gibbs自由能变化ΔG 1、ΔG 5、ΔG 6、ΔG 7的计算结果如表1所示。
表1 在900～1200K镁熔体与镁铝尖晶石反应体系中各个反应的吉布斯自由能变化ΔG计算结果
Figure PCTCN2018089574-appb-000001
反应式镁熔体与氧化铝生成镁铝尖晶石的(5)式的Gibbs自由能ΔG 5在不同温度下均最小，说明在镁合金的常用熔炼温度下该反应会优先发生。镁液与镁铝尖晶石的反应式(7)尽管从热力学上是可以进行的，但该反应本质上为镁液与镁铝尖晶石的分解产物氧化铝间反应，但由表1可知，在镁合金的熔炼温度下，镁铝尖晶石分解为氧化铝和氧化镁的反应难以进行(反应式(6)的逆反应)，同时烧结的陶瓷中残留的氧化铝也会与镁液优先按反应式(5)生成镁铝尖晶石；另一方面，MgO-Al 2O 3相图中MgO一侧为方镁石固溶体和MA尖晶石固溶体共晶相图，在原位反应生成MA过程中几乎没有O 2-扩散，只有Mg 2+和Al 3+通过固定的氧晶格相互扩散，其生成速度由扩散较慢的Al 3+所决定，MA 相主要在Al 2O 3一侧通过内延生长方式生成，导致在MA相与MgO间形成有限固溶体，同时与MgO颗粒接触的MA外层中MgO含量远高于其平均值，而MgO并不与镁熔体反应，因此，烧结陶瓷组织中将氧化镁颗粒熔接在一起的镁铝尖晶石相在镁熔体中是能够稳定存在。
本发明的MA-M 2T尖晶石固溶体增强氧化镁泡沫陶瓷过滤器中不含任何降低其化学稳定性的组分，加入的纳米铝溶胶不仅会在轻烧氧化镁颗粒及高度均匀分散的纳米TiO 2粉体表面形成γ-Al 2O 3包覆膜而起到粘结剂的作用，在烧结过程中Al 2O 3与TiO 2一起和MgO原位合成对镁及其合金熔体具有化学稳定性的MA-M 2T尖晶石固溶体相，避免了现有产品加入硅溶胶、硅酸乙酯等粘结剂对泡沫陶瓷化学稳定性的损害；同时，陶瓷组分中亦不含钠盐(如流变剂中不采用羧甲基纤维素钠)，避免了残留的离子半径较大的Na +对陶瓷烧结的阻碍。
因反应式(1)、(5)在镁合金的常用熔炼温度下能够自发进行，而铝及其合金的熔炼温度与镁及其合金熔炼温度相同，MgO和MA尖晶石相与铝及其合金熔体不会发生反应式(1)、(5)的逆反应；与用于镁及其合金熔体相同，避免了加入硅溶胶、硅酸乙酯等粘结剂对泡沫陶瓷在铝及其合金熔体中化学稳定性的损害(即使材质中含有1％的SiO 2，铝及其合金熔体在高温下也会和陶瓷中SiO 2发生Al+SiO 2→Al 2O 3+Si的反应)；因此，所制备的MA-M 2T尖晶石固溶体增强氧化镁泡沫陶瓷过滤器亦可以用于铝及其合金的熔炼净化。
二、本发明的MA-M 2T尖晶石固溶体增强氧化镁泡沫陶瓷过滤器具有良好的低温烧结性能。本发明的技术方案中在陶瓷组分中加入纳米二氧化钛，作为变价氧化物的Ti 4+扩散进入方镁石晶体内，增加了晶体内部的空位等晶体缺陷，活化了晶格，形成Ti 4+离子置换Mg 2+离子的固溶体而促进晶间直接结合。Al 2O 3的晶格常数与MgO相近，在烧结过程中能够固溶到MgO晶格而导致MgO晶体发生晶格畸变；Al 3+的扩散速度小，Al 2O 3在方镁石MgO中的溶解度很小(Al 2O 3在方镁石MgO中1700℃时的溶解度仅3％)，烧结过程主要为反应烧结生成新的化合物MA相，同时MA相与MgO间形成有限固溶体，从而促进了 烧结和颗粒相间的结合。纳米粉体是指颗粒尺寸<100nm的超微细粉末，具有比表面积大、表面能高、高活性等特点，因此，纳米粉体很容易与其他原子结合，故其熔点和烧结温度比微粉低得多。以纳米氧化钛和纳米铝溶胶的形式加入的烧结助剂，能够填充原料微粉颗粒间的空隙，优化了陶瓷颗粒级配和混合均匀性，同时，纳米粉体因其自身的表面和界面效应，纳米氧化钛和铝溶胶中高反应活性的纳米γ-Al 2O 3与MgO颗粒的充分接触使反应速度迅速提高，降低了烧结温度，提高陶瓷的致密度和力学性能，而烧结温度的降低有利于降低能耗和泡沫陶瓷过滤器的生产成本。试验表明，烧结温度低于1400℃时氧化镁颗粒间烧结组织结合不够充分致使其强度偏低，组织结合良好的MA-M 2T尖晶石固溶体增强氧化镁泡沫陶瓷过滤器的烧结温度为1400℃～1600℃。
三、本发明的MA-M 2T尖晶石固溶体增强氧化镁泡沫陶瓷过滤器具有良好的抗热震性。选用电熔氧化镁，其抗水化能力强。因氧化镁和氧化铝反应烧结形成MA会发生体积膨胀(线膨胀率为2.3％，体积膨胀率为6.9％)而增加了烧结负担。γ-Al 2O 3氧化铝是一种多孔性物质，具有氧离子近似为立方面心紧密堆积、Al 3+不规则地分布在由氧离子围成的八面体和四面体空隙之中的介稳性过渡晶体结构，与镁铝尖晶石MA晶体结构相同。采用γ-Al 2O 3取代α-Al 2O 3将改变MgO-MA物料的烧结特性，形成MA时体积收缩2.7％，从而提高了烧结的致密性。在本发明所提供的方案中，颗粒状的电熔氧化镁被连续的纳米铝溶胶膜包围并和高度分散的纳米氧化钛颗粒密切接触，在烧结过程中与MgO原位反应生成镁铝尖晶石MA和镁钛尖晶石M 2T相，MA与M 2T在1350℃以上完全互溶，烧结过程中将方晶石MgO晶粒直接熔接在一起，在冷却时脱溶析出晶间二次尖晶石(晶间尖晶石)M 2T及MA，可补偿各相临界面上的应力，使材料在烧成冷却时产生的应力松弛，同时尖晶石固溶体相的钉扎作用抑制了氧化镁颗粒的快速长大，从而细化了泡沫陶瓷的组织并提高了陶瓷的致密度；与MgO和Al 2O 3相比，尖晶石相热膨胀系数小、导热系数低，因此，所制备的MA-M 2T尖晶石固溶体增强氧化镁泡沫陶瓷过滤器具有较高的力学性能，耐高温冲击和抗热震性。
此外，聚氨酯泡沫塑料为表面惰性的疏水性材料，与陶瓷浆料的润湿性较差，从而影响聚氨酯泡沫模板的挂浆性能，本发明制备方法中通过NaOH刻蚀使其表面粗糙化，再通过十二烷基苯磺酸盐润湿剂的水溶液处理后，陶瓷浆料易于均匀涂挂到聚氨酯泡沫模板上；同时作为流变剂的纤维素醚和聚丙烯酸不但是纳米氧化钛粉体的良好分散剂，能够防止浆料产生团聚现象，而且在制备素坯时还能起到粘接剂的作用，浸渍后浆料能比较地牢固附着在聚氨酯泡沫模板上，使素坯具有很大的强度，同时在烧结过程中极易逸出而不污染制品，因而保证了泡沫陶瓷过滤器的质量。
附图说明
图1为MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器的制备工艺流程图。具体实施方式
下面结合附图和具体实施方式对本发明作进一步详细的说明。
MA-M 2T尖晶石固溶体增强氧化镁泡沫陶瓷过滤器，其将含纳米氧化镧烧结助剂的轻烧氧化镁基陶瓷浆料涂覆在聚氨酯泡沫载体上，经干燥、烧结得到。具体的制备工艺如图1所示。
实施例1
按照纳米氧化钛占陶瓷粉料质量的1％的配比，称量粒径为30nm的纳米氧化钛和粒径为250目(中径d 50为58μm)的电熔氧化镁粉体配制陶瓷粉料；按照聚丙烯酸和羟乙基纤维素的质量比为1:4的比例混合配制流变剂。
按照质量百分比将固含量为20％的纳米铝溶胶15％(选择PH值近中性的商业化纳米铝溶胶，下同)，流变剂0.8％，其余为陶瓷粉料进行配料。首先按照配比将电熔氧化镁粉料加入球磨罐中，将纳米铝溶胶、流变剂及适量的去离子水(根据陶瓷浆料的固含量确定其加入量，下同)制备成溶液后加入纳米氧化钛粉体，超声处理30min使纳米氧化钛粉体在溶液中充分分散后加入到球磨罐内，再按照球料比2:1的比例加入刚玉球，以60rpm转速球磨4h使其混合均匀，然后在0.02MPa的负压下进行真空排气15min得到固含量为60％的陶瓷浆料。
选用10PPI聚氨酯泡沫塑料模版，在40℃的15％NaOH水溶液中浸泡表面刻蚀60min后用清水洗涤自然晾干，然后浸入到2％十二烷基苯磺酸润湿剂的水溶液中，取出干燥。然后将聚氨酯泡沫塑料模版浸入到陶瓷浆料中，通过辊压机挤压聚氨酯泡沫塑料模版去除多余的浸挂浆料后制成素坯，然后将素坯在加热到80℃进行烘干。
将干燥的素坯放入烧结炉内，以30℃/h的升温速度加热至550℃使泡沫陶瓷过滤器素坯内的聚氨酯泡沫及流变剂等有机物分解气化排出，然后以200℃/h的升温速度加热至1100℃温度，最后以50℃/h的升温速度加热至1600℃温度并在该温度下保温2.5h，随炉冷却至室温得到氧化镁基泡沫陶瓷过滤器。
实施例2
按照纳米氧化钛占陶瓷粉料质量的2％的配比，称量粒径为60nm的纳米氧化钛和粒径为500目(中径d 50为25μm)的电熔氧化镁粉体配制陶瓷粉料；按照聚丙烯酸和羟丙基甲基纤维素的质量比为1:4的比例混合配制流变剂。
按照质量百分比将固含量为25％的纳米铝溶胶20％，流变剂1.5％，其余为陶瓷粉料进行配料。首先按照配比将电熔氧化镁粉料加入球磨罐中，将纳米铝溶胶、流变剂及适量的去离子水制备成溶液后加入纳米氧化钛粉体，超声处理45min使纳米氧化钛粉体在溶液中充分分散后加入到球磨罐内，再按照球料比2:1的比例加入刚玉球，以120rpm转速球磨2h使其混合均匀，然后在0.05MPa的负压下进行真空排气10min得到固含量为65％的陶瓷浆料。
选用20PPI聚氨酯泡沫塑料模版，在50℃的20％NaOH水溶液中浸泡表面刻蚀40min后用清水洗涤自然晾干，然后浸入到4％十二烷基苯磺酸润湿剂的水溶液中，取出干燥。然后将聚氨酯泡沫塑料模版浸入到陶瓷浆料中，通过辊压机挤压聚氨酯泡沫塑料模版去除多余的浸挂浆料后制成素坯，然后将素坯在加热到120℃进行烘干。
将干燥的素坯放入烧结炉内，以30℃/h的升温速度加热至550℃使泡沫陶瓷过滤器素坯内的聚氨酯泡沫及流变剂等有机物分解气化排出，然后以200℃/h的升温速度加热至1100℃温度，最后以50℃/h的升温速度加热至1400℃ 温度并在该温度下保温3h，随炉冷却至室温得到氧化镁基泡沫陶瓷过滤器。
实施例3
按照纳米氧化钛占陶瓷粉料质量的1.5％的配比，称量粒径为50nm的纳米氧化钛和粒径为325目(中径d 50为45μm)的电熔氧化镁粉体配制陶瓷粉料；按照聚丙烯酸和羟乙基纤维素的质量比为1:4的比例混合配制流变剂。
按照质量百分比将固含量为22％的纳米铝溶胶25％，流变剂1.0％，其余为陶瓷粉料进行配料。首先按照配比将电熔氧化镁粉料加入球磨罐中，将纳米铝溶胶、流变剂及适量的去离子水制备成溶液后加入纳米氧化钛粉体，超声处理60min使纳米氧化钛粉体在溶液中充分分散后加入到球磨罐内，再按照球料比2:1的比例加入刚玉球，以90rpm转速球磨3h使其混合均匀，然后在0.03MPa的负压下进行真空排气12min得到固含量为70％的陶瓷浆料。
选用15PPI聚氨酯泡沫塑料模版，在45℃的18％NaOH水溶液中浸泡表面刻蚀50min后用清水洗涤自然晾干，然后浸入到3％十二烷基苯磺酸润湿剂的水溶液中，取出干燥。然后将聚氨酯泡沫塑料模版浸入到陶瓷浆料中，通过辊压机挤压聚氨酯泡沫塑料模版去除多余的浸挂浆料后制成素坯，然后将素坯在加热到100℃进行烘干。
将干燥的素坯放入烧结炉内，以30℃/h的升温速度加热至550℃使泡沫陶瓷过滤器素坯内的聚氨酯泡沫及流变剂等有机物分解气化排出，然后以200℃/h的升温速度加热至1100℃温度，最后以50℃/h的升温速度加热至1500℃温度并在该温度下保温2h，随炉冷却至室温得到氧化镁基泡沫陶瓷过滤器。
实施例4
按照纳米氧化钛占陶瓷粉料质量的2％的配比，称量粒径为60nm的纳米氧化钛和粒径为300目(中径d 50为48μm)的电熔氧化镁粉体配制陶瓷粉料；按照聚丙烯酸：羟丙基甲基纤维素：羟乙基纤维素的质量比为2:4:4的比例混合配制流变剂。
按照质量百分比将固含量为20％的纳米铝溶胶20％，流变剂1.0％，其余为陶瓷粉料进行配料。首先按照配比将电熔氧化镁粉料加入球磨罐中，将 纳米铝溶胶、流变剂及适量的去离子水制备成溶液后加入纳米氧化钛粉体，超声处理45min使纳米氧化钛粉体在溶液中充分分散后加入到球磨罐内，再按照球料比2:1的比例加入刚玉球，以100rpm转速球磨3h使其混合均匀，然后在0.02MPa的负压下进行真空排气15min得到固含量为65％的陶瓷浆料。
选用15PPI聚氨酯泡沫塑料模版，在45℃的15％NaOH水溶液中浸泡表面刻蚀50min后用清水洗涤自然晾干，然后浸入到4％十二烷基苯磺酸润湿剂的水溶液中，取出干燥。然后将聚氨酯泡沫塑料模版浸入到陶瓷浆料中，通过辊压机挤压聚氨酯泡沫塑料模版去除多余的浸挂浆料后制成素坯，然后将素坯在加热到100℃进行烘干。
将干燥的素坯放入烧结炉内，以30℃/h的升温速度加热至550℃使泡沫陶瓷过滤器素坯内的聚氨酯泡沫及流变剂等有机物分解气化排出，然后以200℃/h的升温速度加热至1100℃温度，最后以50℃/h的升温速度加热至1550℃温度并在该温度下保温2h，随炉冷却至室温得到氧化镁基泡沫陶瓷过滤器。
上述实施例中，实验表明所制备的泡沫陶瓷具有优异的抗热震性和强度，在900℃空气中冷却50次均未见开裂；75mm×75mm×25mm，10PPI的泡沫陶瓷过滤器的常温强度不低于2MPa。
上述实施例不以任何方式限制本发明，凡是采用等同替换或等效变换的方式获得的技术方案均落在本发明的保护范围内。

Claims (9)

  1. 一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器，其特征在于将含纳米氧化钛烧结助剂的氧化镁基陶瓷浆料涂覆在聚氨酯泡沫载体上经干燥、烧结得到。
  2. 一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器的制备方法，其特征在于包括以下步骤：
    (1)按照质量百分比将15％～25％纳米铝溶胶，0.8％～1.5％流变剂，其余为含纳米氧化钛烧结助剂的氧化镁陶瓷粉料进行配料，添加去离子水经球磨混合均匀，然后经真空排气制成固含量为60％～70％的陶瓷浆料；所述流变剂为聚丙烯酸和纤维素醚的混合物，其中聚丙烯酸占流变剂质量的20％，所述纤维素醚为工业用羟乙基纤维素、羟丙基甲基纤维素中的一种或其混合物；所述含纳米氧化钛烧结助剂的氧化镁陶瓷粉料为氧化镁粉体和纳米氧化钛粉体的混合物；
    (2)将聚氨酯泡沫塑料模版浸入到上述的陶瓷浆料中，通过辊压机挤压聚氨酯泡沫塑料模版去除多余的浸挂浆料后制成素坯，然后将素坯在加热到80℃～120℃进行烘干；
    (3)将干燥的素坯放入烧结炉内，升温至1400℃～1600℃温度下进行高温烧结，随炉冷却至室温得到氧化镁基泡沫陶瓷过滤器。
  3. 根据权利要求2所述的一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器的制备方法，其特征在于：所述纳米铝溶胶的固含量为20％～25％。
  4. 根据权利要求2所述的一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器的制备方法，其特征在于：所述纳米氧化钛粉体占陶瓷粉料质量的1％～2％。
  5. 根据权利要求2所述的一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器的制备方法，其特征在于：所述氧化镁粉体为电熔氧化镁粉体，其粒径为250目～500目。
  6. 根据权利要求2所述的一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器的制备方法，其特征在于：所述纳米氧化钛粉体的粒径为30～60nm。
  7. 根据权利要求2所述的一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器的制备方法，其特征在于所述陶瓷浆料的制备方法为：按照配比将电熔氧化镁粉料加入球磨罐中，将纳米铝溶胶、流变剂及去离子水制备成溶液后加入纳米氧化钛粉体，超声处理30min～60min使纳米氧化钛粉体在溶液中充分分散后加入到球磨罐内，再按照球料比2:1的比例加入刚玉球，以60～120rpm转速球磨2h～4h使其混合均匀，然后在0.02MPa～0.05MPa的负压下进行真空排气10min～15min。
  8. 根据权利要求2所述的一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器的制备方法，其特征在于：所述聚氨酯泡沫塑料模版的规格为10PPI～20PPI，使用前在40℃～50℃的15％～20％NaOH水溶液中浸泡表面刻蚀40min～60min后用清水洗涤自然晾干，然后浸入到2％～4％十二烷基苯磺酸润湿剂的水溶液中，取出干燥后得到。
  9. 根据权利要求2所述的一种MA-M 2T尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器的制备方法，其特征在于在所述步骤(3)中，所述烧结工艺为：以30℃/h的升温速度加热至550℃使泡沫陶瓷过滤器素坯内的有机物分解气化排出，然后以200℃/h的升温速度加热至1100℃温度，最后以50℃/h的升温速度加热至1400℃～1600℃温度并在该温度下保温2～3h。
PCT/CN2018/089574 2018-04-08 2018-06-01 一种ma-m2t尖晶石固溶体增强氧化镁基泡沫陶瓷过滤器及其制备方法 WO2019196183A1 (zh)

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