CA1149107A - Metallic powders - Google Patents
Metallic powdersInfo
- Publication number
- CA1149107A CA1149107A CA000352313A CA352313A CA1149107A CA 1149107 A CA1149107 A CA 1149107A CA 000352313 A CA000352313 A CA 000352313A CA 352313 A CA352313 A CA 352313A CA 1149107 A CA1149107 A CA 1149107A
- Authority
- CA
- Canada
- Prior art keywords
- particles
- core
- metallic powder
- silver
- peripheral layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
- A61K6/00—Preparations for dentistry
- A61K6/80—Preparations for artificial teeth, for filling teeth or for capping teeth
- A61K6/84—Preparations for artificial teeth, for filling teeth or for capping teeth comprising metals or alloys
- A61K6/847—Amalgams
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/17—Metallic particles coated with metal
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/18—Non-metallic particles coated with metal
Abstract
ABSTRACT OF THE DISCLOSURE
The invention provides a metallic powder containing particles comprising a core which contains a minor proportion of silver, and a peripheral layer of a silver-tin alloy surrounding the core. The use of a core containing a minor proportion of silver enables the particles overall to have a low silver content. It has been found that the metallic powders of the present invention can be used to form dental amalgams with properties comparable to amalgams produced with conventional alloys containing comparatively high amounts of silver.
The invention provides a metallic powder containing particles comprising a core which contains a minor proportion of silver, and a peripheral layer of a silver-tin alloy surrounding the core. The use of a core containing a minor proportion of silver enables the particles overall to have a low silver content. It has been found that the metallic powders of the present invention can be used to form dental amalgams with properties comparable to amalgams produced with conventional alloys containing comparatively high amounts of silver.
Description
~9~
The present invention relates to metallic p~wders~
Alloy powders which are used to produce dental amalgams upon admixture with m~rcury are typically composed of a particulate silver and tin alloy which may contain a proportion of copper or zinc. .~ach particle contains a relatively high proportion of silver ranging from at least 4~/0 by weight up to as high as 75% by weight. Further, the composition of each particle is essentially the same through-out its entire cross-section although thexe may be minor variations between the surface and the core of the particle.
Sil.ver is an expensive material and it would be desirable to produce metal particles which could effectively bond with mercury to form an amalgam whilst having a lower silver content than heretofore.
Surprisingly, it has now been found that alloy powders containing particles with a core containing a minor proportion of silver and a peripheral silver alloy layer can form dental amalgams with mercury having properties comparable to amalgams prepared from previously known alloy powders~
In accordance with the present invention there is provided a metallic powder containing particles comprising a core containing a minor proportion o~ silver and a peripheral layer of a silver-tin alloy surrounding the coreO The core may consist of a base metal such as copper or nic~el, or a metal alloy containing a major proportion of base metal or consisting of base metals such as a nickel-copper alloy.
Any base metal or alloy can be used for the core providing it lends itself to bonding to the peripheral layerO The core preferably contains less than 40/0 by weight silver~, more preferably less than 2~/o~ mos~ preferably less than 10%~ yet most preferably less than 5%, and may be entirely ~ree from silver. The cores of the particles of the present invention whe~er metallic or, as will ba described hereinafter, non-metallic, may be solid or hollow. For example, the core could be gasified during produ~i-on to render it hollow.
Tha peripheral layer contains silver and tin, pre-ferably in proportions ranging from 35% to 85%(more preferably , about 50 to 70%)by weight and 7.5% to 40/O (more preferably about 20 to 35%) by weight respectively. The peripheral layer may also contain copper preferably in amounts from to 40/0 (more preferably about 5 to 2~/o) by weight. The preferred proportions of silver, tin and copper recited above will result in a peripheral alloy layer which when alloyed with mercury will produce an amalgam suitable for dental purposes. The peripheral layer may also contain small amounts, such as 0-5%
typically 0 - 2% by weight, of other amalgamable metals such as zinc, indium, aluminium, gold, gallium and/or cadmium. The inclusion of such other metals may be necessary to achieve physical properties of a satisfactory degree such as compressive strength, static creep, and resid!.lal galnma 2 content of an amalgam derived from the alloy.
The paxticles of the meta~ powder of the present invention may have a size in the range rom 1 to 100 microns preferably in the range from 1 to 45 microns with the majority of particles lying within the size range from 5 to 40 microns.
The base metal core may have any configuration such as spherical or semi-spherical but it may be irregular and may have, for example, chip con~iguration.
The metallic powders of the present invention may be made by a variety of techniques all of which involve coating the base metal-core with layers of the metal components of the peripheral alloy layer.
~910~
Where the base metal core is copper th~ copp~r can be chemically precipita~ed from copper sulphate solution using pure zinc clnodes placed in the copper sulphate solution which is acidified by means of dilute sulphuric acid. The copper precipitates as a flake which is washed, dried and ball milled to obtain microscopic particl~s ~hich are then seived to obtain particles with a maxim~m size of, ~or example, up to 40 microns i.e. minus 400 mesh.
The resulting particles are in chip form and may be rendered spherical or semi~spherical b~r a technique to be des-cribed hereinafter. The copper sphere ~including semi-sphere where referred to hereinafter) is then coated with the c~mponents of ~heperipheral alloy layer to be produced.
The coating may be achieved by a variety of techniques such as rumbling, electroplating or electroless plating. These techniques will now be described in relation to a copper metal core but it should be understood that they are equally applicable to other cores.
In the rumbling method it has been found that contin-ual rumbling of different types of powder result in the p3wders physically bonding to each other~ In the presen~ case the following procedure may be used. m e copper spheres are washed in a solvent in which is dissolved a resin. The copper spheres are then dri0d leaving a thin layer of resin an3und each sphere. A predetermined weight of dried c~pper spheres are then added to a conventio i rumbler and predetermined weights of tin and silver flake of DLLnus 400 mesh size are added to the r~nbler. The silver and tin can be desposited sinultaneously or successively. R~bling is continued for a time sufficient of ensure that all the silver and tin has adhered to the copper spheres.
After the coated copper spheres are rem~v~d from the ru¢~31er they may then be washed in copper sulphate solution to ch~ically deposit a thin layer of copper around the ~ 9~
f sp~ere. The p~rticles are then dried and subjected to a heat txeatment to be described hexei~after so that the build up of silver and tin and optionally copper is alloyed together and bonded to the copper core to form the peripheral layer of the present invention~
The particles are then heated and chemically treaked by washing in hydrochloric acid to ensure that they are free of oxide. Finally, the particles may be heat treated in conventional manner to subject them to the traditional ageing process used for dental amalgam alloys.
In the electroplating method the coa~ing may be carried out in an electroplating barrel in which each compon-ent of the peripheral layer is plated sequentially onto the core. In the present case the following procedure may be used. The electroplating barrel typically contains a number of stainless steel electrodes which are electrically connected in such a manner as to produce the desired polarity. The copper spheres are placed in suspension in an electrolyte containing ions o~ the metal to be deposited. The barrel is rotated to agitate the materials contained therein and current supplied across the electrodes. This causes deposition of metal from the solution on to the copper spheres. The thick-ness o~ the deposited metal can be predetermined by trial and error and measured by miscroscopic measurement of individual particles and analysis of ths electrolyte. In this method, the components of the peripheral alloy layer are plated sequentially on to the core. The coated particles are then heat treated to alloy the coated layers ~nd subse~uently treated as described above for the rumbling method.
The e~ectroless plating method may be carried out ;
by the following procedure. Firstly, the copper spheres are acid etched by immersion in ~ulphuric acid. By using conventional electroless plating techni~les the tin component may be deposited on the copper spheres by rumbling the spheres in a container containing a tin supplying electroless plating solution. Once the desired thickness of tin is obtained ~determined by electrolyte analysis or particle measurement) the particles are remov~d from the electrolyte, washed and placed in a similar rumbling container containing the silver supplying electrole~s plating solution. The prccedure used ~or tin is repeated until the desired thickness of silver has been deposited.
Finally, a copper electroless pla~ing solution may be used to deposit the required amount of copper on the particles. The coated parti~les are then heat treated to alloy the coated layers and subsequently treated as for the rumbling method.
In each of the above ~ethods the order of deposition of the components which are to produce the peripheral alloyed layer is not critical. For example, the silver could be deposited first followed by the tin or the copper or the copper could be deposited first followed by the other compon-ents. The only important criterion is that the final product has a uniform peripheral alloy layer. Coating the copper last has the advantage that after the alloying procedure the absence of a copper colour could indicate com-plete alloying.
For dental purposes, the use of purP copper as the core material has the disaavantage that the copper will oxidise on exposure to air. When dental amalgam has been ~ ~9~7 placed in a cavity it is subject to polishing by the dental surgeon. Particles of the present invention which are subject to the dentists polishing instruments will he cut through and thus the copper core exposed. This is not a great problem but has the disadvantage that the copper oxidises quickly in the mouth.
Thus, for dental purposes, it is preferred to use other base metal cores which are not so readily oxidised. A
nickel-copper alloy or nickel metal could be used for the core~
1~ ~ickel in particular does ~ot oxidise readily in the mouth and thus the resulting amalgam would always be shiny. As mentioned above any metallic substance can be used for the metal core but for dental purposes it is preferred to use those which do not oxidise readily and w~ich are of high strength.
For dental purposes, the peripheral alloy layer of the particles should be at least 2 micron thick since it has been shown that approximately the outer 1~5 micron of an alloy particle is used in the mercury-alloy reaction when producing amalgam.
Preferably, the layers are at least three microns thick, more preferably at least 4 microns thick. A 4 micron thick layer containing 7~% by weight of silver, 25% by weight of tin and 5% by weight of copper would be formed from a 2.8 micron ~hick layex of silver, a 1.0 micron thick layer of tin and an O.Z ~icron thick layer of copperO
The base metal core may either be prepared by chemical double decomposition as described hereinabove for copper or it may be prepared by casting a round ingot of base 9~
netal an~ naXing fil mgs frcm the ingot in conventional ~nner.
The filings wDuld ke subject to further particle size reduction such as by kall milling or pin milling, and then converted into spherical or semi-spherical or chip configuration.
The present invention is equally as applicable to metal cores in the chip configuration as in the spherical configuration.
Providing the peripheral layer is uniform a chip metallic powder of the present invention will perfonm in the same way as a con-ventional fully alloyed dental ~malgam alloy.
The metallic powder of the present invention with a metallic core preferably contains from 2 to 40% by weight of si~ver more preferably from 5 to 25% by ~ight such as about 15% by weight.
Cbrrespondingly, tlle proportion of tin preferably ranges from 1 to 9% by weight. The overall percentage of copper depends on whe~her it is the core material. If it is then the powder pre-ferably contain~ 75% to 95% by weight of copper. If copper is not us~d as the core material but is used in the peripheral lay~r then it can be used in amounts as low as 0.01%.
- Where the core is non-metallic the metallic powder of the present invention preferably contains from about 10 to 90%
silver, frcm about 1 to 30% tin a~d, optionally, from 1 to 10% copper.
Apart from the cost saving achieved by redw tion in the am~und of silver required in the metallic powder of the present invention, it has also been found that the am~unt of gamma 2 phase produced in the resulting amalgams may be con-trolled. Gamma 2 phase is a known disadvantageous component of amalgams. Also, the actual strength of the amalgam may be increased because strong base metals can be used as the core material, whilst the uniform peripheral layer of alloy produces the required matrix to ensure strong attachment to - 8 ~
the particle.
The present invention also provides in another embodiment a ~etallic powder in which the core of the particles is non-metallicO In this embodiment, the core may be formed of an inorganic mineral such as glass. An advantage of using a non-metallic core is that it can be so coloured as to produce an amalgam having a toothlike colour, or at least a colour lighter than that produced by conventional amalgams, when the amalgam is cut and polished by dental instruments.
Further, a core formed of, for example, glass will not oxidise upon exposure to air and thus will not change colour.
A metallic powder in accordance with this embodi-ment of the present invention may be prepared by ~irst taking a glass powder o~ suitable strength characteristics and making the particles spherical by a method to be described hereinafter~
Alternatively, the particles may be left in the form of ~hips.
The glass particles are then subjected to treatment with hydrofluoric acid or o~her glass etching materials to etch the glass to give it a good surface for attachment of alloy components. The particles are then subject to treatment with chemicals conventionally used in electroplating prior to plating metals onto glass, such as palladium chloride solution.
Then the particles are treated to coat them with alloy components as is described above ~or essentially base metal cores and the same parameters apply. The coated paxt-icles are treated in the same manner as the base metal core particles to produce the alloy layer and subjected to the same post-treatments~
In this embodiment of the present invention, it is 9~37 .
preferred that the particles be fine since in this case less matrix area is exposed at the surface of the amalgam when the amalgam is cut and polished. The handling properties of the amalgams produced using powders of this embodiment of the pr~sent invention are more similar to conventional amalgams compared to conventional and anterior cements which are currently in use. rrhese cements contain glass as a filler and are bonded together using resins. They hav~ particularly difficult handling properties being, for example, extremely stic~y. In the present invention, the metals coated on the core are preferably alloyed by entraining the particles in a stream of an inert carrier gas under pressure, passing the stream of inert carrier gas containing the particles through a heating zone so as to melt the surface stratum and then cooling the particles.
This process is preferably carxied out in a closed container containing an atmosphere of an inert gas such as nitrogen or air. Also, the carrier gas is preferably inert and may be nitrogen or compressed air. r~he carrier gas may have a pressure of 40 to 100 psi but 45 to 55 psi is preferred.
The treated particles are preferably cooled by being immersed in a liquid coolant such as water.
rrhe heating zone can be in the form of a flame and the particles are passed through the reaucing section of the flame.
The heating zone may be created by a high frequency induction coil which ~reates a heat plasma.
Similarly, core particles such as the copper chips or g}ass particles described hereinabove can be made spherical or semi-spherical by being heat treated by the above method.
t ', ~he above described heat treating method is described in detail below, In accordance with the present invention there is fuxther provided a particle treatmen~ process wherein the particles have at least a surface stratum capable of being melted, which process comprises entraining the particles in a stream of an inert carrier gas under pressure, passing the stream of inert carrier gas containing the particles throuyh a heating zone so as to melt at least the surface stratum and lo then cooling the particles so as to solidify the melted portions of the particles.
The process of the present invention has a number of applications.
For example, metal alloy particles may be cut from an ingot of the alloy and such particles are of irregular, angular shape~ For some uses, such as alloys for producing dental amalgams, it is desirable to have spherical or semi-spherical particles~ The alloy particles cut from an ingot may be xendered spherical or semi-spherical by the process of the present invention as is described above.
Also, the process of the present invention can be used to spheridise non-metallic particles such as glass particles; as is also described above.
Further, where a particle contains a peripheral layer or layers of unalloyed metals the metals can be alloyed by the process of the present invention. Dental amalgam alloy particles conkaining a peripheral alloy layer axe described above.
The process of the present invention is preferably carried out in a closed container containing an atmosphere of . ~4 . . .
~9~L~7 inert gas~ The inert gas can be any gas which does not inter-act with the particles 50 as to alter their chemical comp~sit-ion under the conditions o the process. Preferably, the inert gas is nitrogen but for most purposes air can be used.
Similarly, the carrier gas in which the particles are entrained is also preferably inert and nitrogen is preferred but com-pressed air is usually satisfactory. ~he carrier gas in w~ich the particles are Pntrained may have a pressure in the range from 40 to 100 psi but a pressure in the range from 45 to 55 psi is preferred~
The heat treated particles are preferably cooled by being immersed in a liguid coolant. Preferably, the liquid coolant is water but any 1 quid which does not interact with~
the particles can be used.
The heating zone can be in the form of a flame.
The flame can be produced from a comhustible gas mixture at high pressure. The particles are preferably passed through the reducing section of the flame so as to avoid the psssibil-ity of the particles being oxidised although this is clearly not critical where the particles are of a non-oxidisable composition. The flame may be produced by combustion of any gas which produces a temp~rature sufficient to achieve the desired end result. Examples of suitable gases are oxy acetylene, hydrogen and liquid petroleum gas.
The particles are passed through the flame at a rate which is controlled by the carrier gas prassure. Too fast a speed will result in an insufficiently treated particle whilst too slow a speed will result in the particle being heated excessively. In another em~odiment of the process of the present invention, the heating zone is produced by means >
of a high frequency induction coil which creates a heat plasma. The entrained particles are passed through a tube ana whilst in the tube pass through a high frequency ~ield created by the coil which is connected to a conventional high frsquency generator.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-Figure 1 is a schematic illustration of the process of the present invention in accordance with a first embodiment; and Figure 2 is a schematic illustration of the process of the present invention in accordance with a second embodiment.
In Figure 1, there is shown a nozzle 10 in communication with a conduit 12. A combustible yas mixture is passed in the direction of the arrsw B through the conduit 12 and nozzle 10 at high pressure and combusted at the exit of the nozzle 10 to produce a flame 14. The flame comprises a reducing section 16.
A jet 18 is orientated towards the reducing section 16 of the ~lame 14 and terminates a short distance from the flame 14. Particles to be treated are entrained in a carrier gas ~nd passed through the jet 18 in the direction of the Arr~w A. The entrained particles leave the jet 1~ and pas~
through the reducing section 16 wherein they are heated such that at least a surface stratum i5 melted.
The particles are then passed into a liquid coolant 20 wherein they are cooled. The cooled particles sink to the bottom of the coolant for subsequent retrieval.
In Figure 2, there i5 shown a vertically orientated cylindrical tube 22 which may be of 3" diameter nd 48"
:
length. A jet 18 similar to that shown in Figure 1, i5 located adjac~nt the upper end of the tube 22 and is axially aligned therewith. The lower end of the tube 22 is immersed in a liquid coolant 20.
A high fre~uency induction coil 24 is wrapped around the cylinder 22. The coil 24 is connect~d to a high frequency generator ~not shown.) In use, the entrained particles pass through the tube 22 and the heating zone created by the coil 24. During passage through the heating zone the particles are heated such that at least a surface stratum is melted.
The particles then pass into the liquid coolant 20.
Vents 26 are provided in the tube 22 just about the liquid surface to allow excess gas to escape.
In each embodiment described above, the whole treatment is performed in a closed container (not shown) containing an inert gas.
In the embodiment described the treatment process ensures that each particle is separated from other particles during the heating step and during the time the particle is cooling after entering the coolant. This avoids the possib-ility of the particles adhering to one another whilst the - surfaces thereof are in melted condition.
The present invention will now be exemplified in the following example.
EXAMPLE: Copper powder was chemically made by depositing ; from copper sulphate and the resultant powder was dried, ball-milled and atomised during the process described above.
The resultant sp~erical powder was sieved through a 400 BSS sieve with the oversize being recycled. The portion which wa~ minu~ 400 c~nsi ~ed of the following particle size analysis:
~ 30 micron diameter 41%
- 30 ~ 20 micron diamet~r 3~/~
- 20 mi~ron diameter 2~/o This powder blend was acid etched and subjected to electroplating by silver, tin and copper in such a way as to build up an overall periphexal thicknass of approximately 2 microns per particle. The resultant electroplated alloy was then subjected to the atomising process described above using such conditions as to effectively alloy the peripheral elements and form a layer containing by weight silver 60D/o, tin 27% copper 13%.
The resultant powder particles were then collected and screened through a 400 BSS mesh sieve and were then heat treated and washed. This powder was then trituxated for 10 saconds with approximately 5~/O mercury. Tests were performed on the resultant amalgam according to specifications for dental amalgam alloysas dictated by A.D.A. The results obtained were as follows:
Tensile strength ~24 hours)8,050 psi Compressive strength (1 hour)35,353 psi Compressive strength (24 hours) 73,65~ psi Static creep (7 days) O~Q2%
Dimensional change ~0.05%
Corrosion resistance (Sodium sulphide test)Excellent Modifications and variations such as would be apparent to a skilled addressee are deemed within the scope of the present invention.
_ 15
The present invention relates to metallic p~wders~
Alloy powders which are used to produce dental amalgams upon admixture with m~rcury are typically composed of a particulate silver and tin alloy which may contain a proportion of copper or zinc. .~ach particle contains a relatively high proportion of silver ranging from at least 4~/0 by weight up to as high as 75% by weight. Further, the composition of each particle is essentially the same through-out its entire cross-section although thexe may be minor variations between the surface and the core of the particle.
Sil.ver is an expensive material and it would be desirable to produce metal particles which could effectively bond with mercury to form an amalgam whilst having a lower silver content than heretofore.
Surprisingly, it has now been found that alloy powders containing particles with a core containing a minor proportion of silver and a peripheral silver alloy layer can form dental amalgams with mercury having properties comparable to amalgams prepared from previously known alloy powders~
In accordance with the present invention there is provided a metallic powder containing particles comprising a core containing a minor proportion o~ silver and a peripheral layer of a silver-tin alloy surrounding the coreO The core may consist of a base metal such as copper or nic~el, or a metal alloy containing a major proportion of base metal or consisting of base metals such as a nickel-copper alloy.
Any base metal or alloy can be used for the core providing it lends itself to bonding to the peripheral layerO The core preferably contains less than 40/0 by weight silver~, more preferably less than 2~/o~ mos~ preferably less than 10%~ yet most preferably less than 5%, and may be entirely ~ree from silver. The cores of the particles of the present invention whe~er metallic or, as will ba described hereinafter, non-metallic, may be solid or hollow. For example, the core could be gasified during produ~i-on to render it hollow.
Tha peripheral layer contains silver and tin, pre-ferably in proportions ranging from 35% to 85%(more preferably , about 50 to 70%)by weight and 7.5% to 40/O (more preferably about 20 to 35%) by weight respectively. The peripheral layer may also contain copper preferably in amounts from to 40/0 (more preferably about 5 to 2~/o) by weight. The preferred proportions of silver, tin and copper recited above will result in a peripheral alloy layer which when alloyed with mercury will produce an amalgam suitable for dental purposes. The peripheral layer may also contain small amounts, such as 0-5%
typically 0 - 2% by weight, of other amalgamable metals such as zinc, indium, aluminium, gold, gallium and/or cadmium. The inclusion of such other metals may be necessary to achieve physical properties of a satisfactory degree such as compressive strength, static creep, and resid!.lal galnma 2 content of an amalgam derived from the alloy.
The paxticles of the meta~ powder of the present invention may have a size in the range rom 1 to 100 microns preferably in the range from 1 to 45 microns with the majority of particles lying within the size range from 5 to 40 microns.
The base metal core may have any configuration such as spherical or semi-spherical but it may be irregular and may have, for example, chip con~iguration.
The metallic powders of the present invention may be made by a variety of techniques all of which involve coating the base metal-core with layers of the metal components of the peripheral alloy layer.
~910~
Where the base metal core is copper th~ copp~r can be chemically precipita~ed from copper sulphate solution using pure zinc clnodes placed in the copper sulphate solution which is acidified by means of dilute sulphuric acid. The copper precipitates as a flake which is washed, dried and ball milled to obtain microscopic particl~s ~hich are then seived to obtain particles with a maxim~m size of, ~or example, up to 40 microns i.e. minus 400 mesh.
The resulting particles are in chip form and may be rendered spherical or semi~spherical b~r a technique to be des-cribed hereinafter. The copper sphere ~including semi-sphere where referred to hereinafter) is then coated with the c~mponents of ~heperipheral alloy layer to be produced.
The coating may be achieved by a variety of techniques such as rumbling, electroplating or electroless plating. These techniques will now be described in relation to a copper metal core but it should be understood that they are equally applicable to other cores.
In the rumbling method it has been found that contin-ual rumbling of different types of powder result in the p3wders physically bonding to each other~ In the presen~ case the following procedure may be used. m e copper spheres are washed in a solvent in which is dissolved a resin. The copper spheres are then dri0d leaving a thin layer of resin an3und each sphere. A predetermined weight of dried c~pper spheres are then added to a conventio i rumbler and predetermined weights of tin and silver flake of DLLnus 400 mesh size are added to the r~nbler. The silver and tin can be desposited sinultaneously or successively. R~bling is continued for a time sufficient of ensure that all the silver and tin has adhered to the copper spheres.
After the coated copper spheres are rem~v~d from the ru¢~31er they may then be washed in copper sulphate solution to ch~ically deposit a thin layer of copper around the ~ 9~
f sp~ere. The p~rticles are then dried and subjected to a heat txeatment to be described hexei~after so that the build up of silver and tin and optionally copper is alloyed together and bonded to the copper core to form the peripheral layer of the present invention~
The particles are then heated and chemically treaked by washing in hydrochloric acid to ensure that they are free of oxide. Finally, the particles may be heat treated in conventional manner to subject them to the traditional ageing process used for dental amalgam alloys.
In the electroplating method the coa~ing may be carried out in an electroplating barrel in which each compon-ent of the peripheral layer is plated sequentially onto the core. In the present case the following procedure may be used. The electroplating barrel typically contains a number of stainless steel electrodes which are electrically connected in such a manner as to produce the desired polarity. The copper spheres are placed in suspension in an electrolyte containing ions o~ the metal to be deposited. The barrel is rotated to agitate the materials contained therein and current supplied across the electrodes. This causes deposition of metal from the solution on to the copper spheres. The thick-ness o~ the deposited metal can be predetermined by trial and error and measured by miscroscopic measurement of individual particles and analysis of ths electrolyte. In this method, the components of the peripheral alloy layer are plated sequentially on to the core. The coated particles are then heat treated to alloy the coated layers ~nd subse~uently treated as described above for the rumbling method.
The e~ectroless plating method may be carried out ;
by the following procedure. Firstly, the copper spheres are acid etched by immersion in ~ulphuric acid. By using conventional electroless plating techni~les the tin component may be deposited on the copper spheres by rumbling the spheres in a container containing a tin supplying electroless plating solution. Once the desired thickness of tin is obtained ~determined by electrolyte analysis or particle measurement) the particles are remov~d from the electrolyte, washed and placed in a similar rumbling container containing the silver supplying electrole~s plating solution. The prccedure used ~or tin is repeated until the desired thickness of silver has been deposited.
Finally, a copper electroless pla~ing solution may be used to deposit the required amount of copper on the particles. The coated parti~les are then heat treated to alloy the coated layers and subsequently treated as for the rumbling method.
In each of the above ~ethods the order of deposition of the components which are to produce the peripheral alloyed layer is not critical. For example, the silver could be deposited first followed by the tin or the copper or the copper could be deposited first followed by the other compon-ents. The only important criterion is that the final product has a uniform peripheral alloy layer. Coating the copper last has the advantage that after the alloying procedure the absence of a copper colour could indicate com-plete alloying.
For dental purposes, the use of purP copper as the core material has the disaavantage that the copper will oxidise on exposure to air. When dental amalgam has been ~ ~9~7 placed in a cavity it is subject to polishing by the dental surgeon. Particles of the present invention which are subject to the dentists polishing instruments will he cut through and thus the copper core exposed. This is not a great problem but has the disadvantage that the copper oxidises quickly in the mouth.
Thus, for dental purposes, it is preferred to use other base metal cores which are not so readily oxidised. A
nickel-copper alloy or nickel metal could be used for the core~
1~ ~ickel in particular does ~ot oxidise readily in the mouth and thus the resulting amalgam would always be shiny. As mentioned above any metallic substance can be used for the metal core but for dental purposes it is preferred to use those which do not oxidise readily and w~ich are of high strength.
For dental purposes, the peripheral alloy layer of the particles should be at least 2 micron thick since it has been shown that approximately the outer 1~5 micron of an alloy particle is used in the mercury-alloy reaction when producing amalgam.
Preferably, the layers are at least three microns thick, more preferably at least 4 microns thick. A 4 micron thick layer containing 7~% by weight of silver, 25% by weight of tin and 5% by weight of copper would be formed from a 2.8 micron ~hick layex of silver, a 1.0 micron thick layer of tin and an O.Z ~icron thick layer of copperO
The base metal core may either be prepared by chemical double decomposition as described hereinabove for copper or it may be prepared by casting a round ingot of base 9~
netal an~ naXing fil mgs frcm the ingot in conventional ~nner.
The filings wDuld ke subject to further particle size reduction such as by kall milling or pin milling, and then converted into spherical or semi-spherical or chip configuration.
The present invention is equally as applicable to metal cores in the chip configuration as in the spherical configuration.
Providing the peripheral layer is uniform a chip metallic powder of the present invention will perfonm in the same way as a con-ventional fully alloyed dental ~malgam alloy.
The metallic powder of the present invention with a metallic core preferably contains from 2 to 40% by weight of si~ver more preferably from 5 to 25% by ~ight such as about 15% by weight.
Cbrrespondingly, tlle proportion of tin preferably ranges from 1 to 9% by weight. The overall percentage of copper depends on whe~her it is the core material. If it is then the powder pre-ferably contain~ 75% to 95% by weight of copper. If copper is not us~d as the core material but is used in the peripheral lay~r then it can be used in amounts as low as 0.01%.
- Where the core is non-metallic the metallic powder of the present invention preferably contains from about 10 to 90%
silver, frcm about 1 to 30% tin a~d, optionally, from 1 to 10% copper.
Apart from the cost saving achieved by redw tion in the am~und of silver required in the metallic powder of the present invention, it has also been found that the am~unt of gamma 2 phase produced in the resulting amalgams may be con-trolled. Gamma 2 phase is a known disadvantageous component of amalgams. Also, the actual strength of the amalgam may be increased because strong base metals can be used as the core material, whilst the uniform peripheral layer of alloy produces the required matrix to ensure strong attachment to - 8 ~
the particle.
The present invention also provides in another embodiment a ~etallic powder in which the core of the particles is non-metallicO In this embodiment, the core may be formed of an inorganic mineral such as glass. An advantage of using a non-metallic core is that it can be so coloured as to produce an amalgam having a toothlike colour, or at least a colour lighter than that produced by conventional amalgams, when the amalgam is cut and polished by dental instruments.
Further, a core formed of, for example, glass will not oxidise upon exposure to air and thus will not change colour.
A metallic powder in accordance with this embodi-ment of the present invention may be prepared by ~irst taking a glass powder o~ suitable strength characteristics and making the particles spherical by a method to be described hereinafter~
Alternatively, the particles may be left in the form of ~hips.
The glass particles are then subjected to treatment with hydrofluoric acid or o~her glass etching materials to etch the glass to give it a good surface for attachment of alloy components. The particles are then subject to treatment with chemicals conventionally used in electroplating prior to plating metals onto glass, such as palladium chloride solution.
Then the particles are treated to coat them with alloy components as is described above ~or essentially base metal cores and the same parameters apply. The coated paxt-icles are treated in the same manner as the base metal core particles to produce the alloy layer and subjected to the same post-treatments~
In this embodiment of the present invention, it is 9~37 .
preferred that the particles be fine since in this case less matrix area is exposed at the surface of the amalgam when the amalgam is cut and polished. The handling properties of the amalgams produced using powders of this embodiment of the pr~sent invention are more similar to conventional amalgams compared to conventional and anterior cements which are currently in use. rrhese cements contain glass as a filler and are bonded together using resins. They hav~ particularly difficult handling properties being, for example, extremely stic~y. In the present invention, the metals coated on the core are preferably alloyed by entraining the particles in a stream of an inert carrier gas under pressure, passing the stream of inert carrier gas containing the particles through a heating zone so as to melt the surface stratum and then cooling the particles.
This process is preferably carxied out in a closed container containing an atmosphere of an inert gas such as nitrogen or air. Also, the carrier gas is preferably inert and may be nitrogen or compressed air. r~he carrier gas may have a pressure of 40 to 100 psi but 45 to 55 psi is preferred.
The treated particles are preferably cooled by being immersed in a liquid coolant such as water.
rrhe heating zone can be in the form of a flame and the particles are passed through the reaucing section of the flame.
The heating zone may be created by a high frequency induction coil which ~reates a heat plasma.
Similarly, core particles such as the copper chips or g}ass particles described hereinabove can be made spherical or semi-spherical by being heat treated by the above method.
t ', ~he above described heat treating method is described in detail below, In accordance with the present invention there is fuxther provided a particle treatmen~ process wherein the particles have at least a surface stratum capable of being melted, which process comprises entraining the particles in a stream of an inert carrier gas under pressure, passing the stream of inert carrier gas containing the particles throuyh a heating zone so as to melt at least the surface stratum and lo then cooling the particles so as to solidify the melted portions of the particles.
The process of the present invention has a number of applications.
For example, metal alloy particles may be cut from an ingot of the alloy and such particles are of irregular, angular shape~ For some uses, such as alloys for producing dental amalgams, it is desirable to have spherical or semi-spherical particles~ The alloy particles cut from an ingot may be xendered spherical or semi-spherical by the process of the present invention as is described above.
Also, the process of the present invention can be used to spheridise non-metallic particles such as glass particles; as is also described above.
Further, where a particle contains a peripheral layer or layers of unalloyed metals the metals can be alloyed by the process of the present invention. Dental amalgam alloy particles conkaining a peripheral alloy layer axe described above.
The process of the present invention is preferably carried out in a closed container containing an atmosphere of . ~4 . . .
~9~L~7 inert gas~ The inert gas can be any gas which does not inter-act with the particles 50 as to alter their chemical comp~sit-ion under the conditions o the process. Preferably, the inert gas is nitrogen but for most purposes air can be used.
Similarly, the carrier gas in which the particles are entrained is also preferably inert and nitrogen is preferred but com-pressed air is usually satisfactory. ~he carrier gas in w~ich the particles are Pntrained may have a pressure in the range from 40 to 100 psi but a pressure in the range from 45 to 55 psi is preferred~
The heat treated particles are preferably cooled by being immersed in a liguid coolant. Preferably, the liquid coolant is water but any 1 quid which does not interact with~
the particles can be used.
The heating zone can be in the form of a flame.
The flame can be produced from a comhustible gas mixture at high pressure. The particles are preferably passed through the reducing section of the flame so as to avoid the psssibil-ity of the particles being oxidised although this is clearly not critical where the particles are of a non-oxidisable composition. The flame may be produced by combustion of any gas which produces a temp~rature sufficient to achieve the desired end result. Examples of suitable gases are oxy acetylene, hydrogen and liquid petroleum gas.
The particles are passed through the flame at a rate which is controlled by the carrier gas prassure. Too fast a speed will result in an insufficiently treated particle whilst too slow a speed will result in the particle being heated excessively. In another em~odiment of the process of the present invention, the heating zone is produced by means >
of a high frequency induction coil which creates a heat plasma. The entrained particles are passed through a tube ana whilst in the tube pass through a high frequency ~ield created by the coil which is connected to a conventional high frsquency generator.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-Figure 1 is a schematic illustration of the process of the present invention in accordance with a first embodiment; and Figure 2 is a schematic illustration of the process of the present invention in accordance with a second embodiment.
In Figure 1, there is shown a nozzle 10 in communication with a conduit 12. A combustible yas mixture is passed in the direction of the arrsw B through the conduit 12 and nozzle 10 at high pressure and combusted at the exit of the nozzle 10 to produce a flame 14. The flame comprises a reducing section 16.
A jet 18 is orientated towards the reducing section 16 of the ~lame 14 and terminates a short distance from the flame 14. Particles to be treated are entrained in a carrier gas ~nd passed through the jet 18 in the direction of the Arr~w A. The entrained particles leave the jet 1~ and pas~
through the reducing section 16 wherein they are heated such that at least a surface stratum i5 melted.
The particles are then passed into a liquid coolant 20 wherein they are cooled. The cooled particles sink to the bottom of the coolant for subsequent retrieval.
In Figure 2, there i5 shown a vertically orientated cylindrical tube 22 which may be of 3" diameter nd 48"
:
length. A jet 18 similar to that shown in Figure 1, i5 located adjac~nt the upper end of the tube 22 and is axially aligned therewith. The lower end of the tube 22 is immersed in a liquid coolant 20.
A high fre~uency induction coil 24 is wrapped around the cylinder 22. The coil 24 is connect~d to a high frequency generator ~not shown.) In use, the entrained particles pass through the tube 22 and the heating zone created by the coil 24. During passage through the heating zone the particles are heated such that at least a surface stratum is melted.
The particles then pass into the liquid coolant 20.
Vents 26 are provided in the tube 22 just about the liquid surface to allow excess gas to escape.
In each embodiment described above, the whole treatment is performed in a closed container (not shown) containing an inert gas.
In the embodiment described the treatment process ensures that each particle is separated from other particles during the heating step and during the time the particle is cooling after entering the coolant. This avoids the possib-ility of the particles adhering to one another whilst the - surfaces thereof are in melted condition.
The present invention will now be exemplified in the following example.
EXAMPLE: Copper powder was chemically made by depositing ; from copper sulphate and the resultant powder was dried, ball-milled and atomised during the process described above.
The resultant sp~erical powder was sieved through a 400 BSS sieve with the oversize being recycled. The portion which wa~ minu~ 400 c~nsi ~ed of the following particle size analysis:
~ 30 micron diameter 41%
- 30 ~ 20 micron diamet~r 3~/~
- 20 mi~ron diameter 2~/o This powder blend was acid etched and subjected to electroplating by silver, tin and copper in such a way as to build up an overall periphexal thicknass of approximately 2 microns per particle. The resultant electroplated alloy was then subjected to the atomising process described above using such conditions as to effectively alloy the peripheral elements and form a layer containing by weight silver 60D/o, tin 27% copper 13%.
The resultant powder particles were then collected and screened through a 400 BSS mesh sieve and were then heat treated and washed. This powder was then trituxated for 10 saconds with approximately 5~/O mercury. Tests were performed on the resultant amalgam according to specifications for dental amalgam alloysas dictated by A.D.A. The results obtained were as follows:
Tensile strength ~24 hours)8,050 psi Compressive strength (1 hour)35,353 psi Compressive strength (24 hours) 73,65~ psi Static creep (7 days) O~Q2%
Dimensional change ~0.05%
Corrosion resistance (Sodium sulphide test)Excellent Modifications and variations such as would be apparent to a skilled addressee are deemed within the scope of the present invention.
_ 15
Claims (42)
1. A metallic powder containing particles comprising a core which contains from 0 to about 40% by weight silver, and a discrete, peripheral layer of a silver-tin alloy surrounding the core; said peripheral layer containing a higher weight % of silver than said core.
2. A metallic powder as claimed in Claim 1, in which the core contains from 0 to less than about 20% by weight silver.
3. A metallic powder as claimed in Claim 1, in which the core contains from 0 to less than about 10% by weight silver.
4. A metallic powder as claimed in Claim 1, in which the core contains from 0 to less than about 5% by weight silver.
5. A metallic powder as claimed in Claim 1, in which the core is metallic and contains a major proportion of base metal.
6. A metallic powder as claimed in Claim 5, in which the core consists of base metal.
7. A metallic powder as claimed in Claim 5, in which the core is formed of a material selected from the group con-sisting of copper, nickel or copper-nickel alloy.
8. A metallic powder as claimed in Claim 1, in which the core is non-metallic.
9. A metallic powder as claimed in Claim 8, in which the core is formed of an inorganic material.
10. A metallic powder as claimed in Claim 8, in which the core is formed of glass.
11. A metallic powder as claimed in Claim 1, in which the peripheral layer additionally contains copper.
12. A metallic powder as claimed in Claim 1, in which the peripheral layer contains from about 35% to about 85% by weight silver, from about 7.5% to about 40% by weight tin and from 0 to about 40% by weight copper.
13. A metallic powder as claimed in Claim 12, in which the peripheral layer contains from about 50 to about 70% by weight silver, from about 20 to about 35% by weight tin and from about 5 to about 20% by weight copper.
14. A metallic powder as claimed in Claim 1, in which the particles have a size in the range from about 1 to about 100 microns.
15. A metallic powder as claimed in Claim 14, in which the particles have a size in the range from about to 1 to about 45 microns with the majority of particles lying within the size range from about 5 to about 40 microns.
16. A metallic powder as claimed in Claim 1, in which the peripheral layer is applied to the core by a rumbling technique comprising forming a resin coating around the core particles, contacting the coated core particles with particulate silver and tin and rumbling the particles for a time sufficient to bond the silver and tin to the coated core particles, and then heat treating the rumbled particles to alloy the components of the peripheral layer.
17. A metallic powder as claimed in Claim 16, in which the rumbled particles are subsequently contacted with a copper bearing solution to chemically deposit a layer of copper around the rumbled particles.
18. A metallic powder as claimed in Claim 1, in which the peripheral layer is applied to the core by an electro-plating technique comprising immersing the core particles sequentially in solutions containing metal ions corresponding to the metals of the peripheral layer and during each immersion applying an electrical potential to the solution to cause deposition of metal on the core particles, and then heat treating the particles to alloy the components of the peripheral layer.
19. A metallic powder as claimed in Claim 1, in which the peripheral layer is applied to the core by an electroless plating technique comprising immersing the core particles sequentially in electroless plating solutions containing metal ions corresponding to the metals of the peripheral layer to cause deposition of metal on the core particles, and then heat treating the particles to alloy the components of the peripheral layer.
20. A metallic powder as claimed in Claim 1, in which the peripheral layer is at least 1 micron thick.
21. A metallic powder as claimed in Claim 20, in which the peripheral layer is at least 2 microns thick.
22. A metallic powder as claimed in Claim 20, in which the peripheral layer is at least 4 microns thick,
23. A metallic powder as claimed in Claim 5, the particles of which contain in total from about 2 to about 40% by weight silver and from about 1 to about 9% by weight tin.
24. A metallic powder as claimed in Claim 5, the particles of which contain in total from about 5 to about 25% by weight silver and from about 1 to 9% tin.
25. A metallic powder as claimed in Claim 8, the particles of which contain in total from about 10 to about 90% by weight silver, and from about 1 to 30% by weight tin.
26. A metallic powder as claimed in Claim 8, the particles of which contain in total from about 10 to about 90% by weight silver, from about 1 to about 30% by weight tin and from about 1 to about 10% copper.
27. A metallic powder as claimed in Claim 1, in which the core particles are solid.
28. A metallic powder as claimed in Claim l, in which the core particles are hollow.
29. A metallic powder as claimed in Claim 1, in which the peripheral layer of a silver-tin alloy optionally contains small amounts of one or more other amalgamatable metals as alloying ingredients.
30. A metallic powder according to Claim 29, in which said other amalgamatable metals are present in an amount in the range of 0 to 5% by weight of the peripheral layer.
31. A metallic powder according to claim 29, in which said other amalgamatable metals are present in an amount in the range from 0 to 2% by weight of the peripheral layer.
32. A metallic powder as claimed in claim 1, in which the components of the peripheral layer are alloyed by entraining core particles having the metals of the peripheral layer bonded thereto, in a stream of an inert carrier gas under pressure, passing the stream of an inert carrier gas containing the particles through a heating zone so as to melt the metals of the peripheral layer and then cooling the particles.
33. A metallic powder as claimed in claim 1, in which the core contains from 0 to about 30% by weight silver.
34. An amalgamatable dental alloy powder comprising a metallic powder as claimed in claim 1, 2 or 3.
35. A particle treatment process wherein the particles comprise a core which contains from 0 to about 40% by weight silver, and silver and tin in a surface stratum surrounding the core, said surface stratum con-taining a higher weight % of silver than said core, which process comprises .
entraining the particles in a stream of an inert carrier gas under pressure, passing the stream of inert carrier gas containing the particles through a heating zone so as to melt the surface stratum and then cooling the particles so as to solidify the surface stratum to form a discrete layer of silver-tin alloy surrounding the core.
entraining the particles in a stream of an inert carrier gas under pressure, passing the stream of inert carrier gas containing the particles through a heating zone so as to melt the surface stratum and then cooling the particles so as to solidify the surface stratum to form a discrete layer of silver-tin alloy surrounding the core.
36. A process according to claim 35, wherein said stream of inert carrier gas is at a pressure in the range from about 40 to 100 p.s.i.
37. A process according to claim 36, wherein said stream of inert carrier gas is at a pressure in the range from about 45 to 55 p.s.i.
38. A process according to claim 35, wherein said heating zone is in the form of a flame produced by combustion of a gas at elevated pressure, said flame having a reducing cone and said particles being passed through said reducing cone.
39. A process according to claim 35, wherein the particles are passed through the heating zone in a closed container containing an atmosphere of an inert gas.
40. A process according to claim 39, wherein the inert gas is nitrogen.
41. A process according to claim 35, wherein the particles are cooled by being immersed in a body of liquid.
42 . A process according to claim 41, wherein the liquid is water.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AUPD882779 | 1979-05-17 | ||
| AUPD8826 | 1979-05-17 | ||
| AUPD882679 | 1979-05-17 | ||
| AUPD8827 | 1979-05-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1149107A true CA1149107A (en) | 1983-07-05 |
Family
ID=25642307
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000352313A Expired CA1149107A (en) | 1979-05-17 | 1980-05-16 | Metallic powders |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS55161003A (en) |
| CA (1) | CA1149107A (en) |
| DE (1) | DE3018874A1 (en) |
| FR (1) | FR2456582A1 (en) |
| GB (1) | GB2051132B (en) |
| IT (1) | IT1140843B (en) |
| NZ (1) | NZ193738A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57107501A (en) * | 1980-12-25 | 1982-07-05 | Sony Corp | Conduction material |
| US4528207A (en) * | 1982-06-04 | 1985-07-09 | The University Of Virginia Alumni Patents Foundation | Plated dental amalgam alloys |
| DE3240256C1 (en) * | 1982-10-30 | 1983-09-29 | Blendax-Werke R. Schneider Gmbh & Co, 6500 Mainz | Process for the production of silver-tin master alloys for dental amalgams |
| LU85322A1 (en) * | 1984-04-17 | 1985-11-27 | Metallurg Hoboken Overpelt A | PROCESS FOR PREPARING ZINC POWDER FOR ALKALINE BATTERIES |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2370242A (en) * | 1943-01-15 | 1945-02-27 | Mallory & Co Inc P R | Refractory metal composition |
| US3933961A (en) * | 1974-12-13 | 1976-01-20 | Pennwalt Corporation | Tabletting spherical dental amalgam alloy |
| CA1085239A (en) * | 1977-04-26 | 1980-09-09 | Vilnis Silins | Process for producing composite powder particles |
-
1980
- 1980-05-07 IT IT21844/80A patent/IT1140843B/en active
- 1980-05-16 FR FR8011000A patent/FR2456582A1/en active Granted
- 1980-05-16 JP JP6584080A patent/JPS55161003A/en active Pending
- 1980-05-16 DE DE19803018874 patent/DE3018874A1/en not_active Withdrawn
- 1980-05-16 CA CA000352313A patent/CA1149107A/en not_active Expired
- 1980-05-16 GB GB8016365A patent/GB2051132B/en not_active Expired
- 1980-05-16 NZ NZ193738A patent/NZ193738A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| JPS55161003A (en) | 1980-12-15 |
| FR2456582B1 (en) | 1984-12-07 |
| GB2051132B (en) | 1983-04-07 |
| DE3018874A1 (en) | 1980-11-27 |
| IT8021844A0 (en) | 1980-05-07 |
| NZ193738A (en) | 1983-02-15 |
| GB2051132A (en) | 1981-01-14 |
| FR2456582A1 (en) | 1980-12-12 |
| IT1140843B (en) | 1986-10-10 |
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