US 2406172 A
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Patented Aug. 20, 1946 PLATINUM OR ALLIED METALS, (SR THEIR ALLOYS, AND ARTICLES MADE THERE- FROM Colin James Smithells, Rugby, England, assignor, by mesne assignments, to Baker and Co. Inc.,
Newark, N. J.
No Drawing. Application Mai-ch 9, i943, Serial 1109122478552. In Great Britain February '7', g
6 Claims. (Cl. i 22) This invention relates to platinum, or any of the following allied metals in the platinum group, namely, rhodium, iridium, ruthenium, and palladium, and to alloys in which any of these metals forms the principal ingredient. The invention also relates to articles made from such metals or alloys and required to be able to withstand high temperatures and corrosive actions, such as sparking plug electrodes, thermocouples, electric furnace heating elements, and wire gauzes foruse as catalyst gauzes in chemical operations. to minimise the normal tendency of the initially fine-grained structure of such metals or their alloys to change into a coarse-grained structure when subjected to high temperatures with consequent deterioration of their mechanical properties.
The invention consists of a material, or an article made therefrom, in the form of a compacted and sintered agglomerate of platinum or any of the allied metals above specified or an alloy thereof, and refractory oxide, the constituents being initially in a finely divided condition.
For the production of materials consisting essentially of platinum, I may use commercially pure platinum, but preferably I use an alloy containing for example, about rhodium, or about 4% tungsten, or up to 30% iridium, or up to 30% ruthenium, the balance being platinum. The required finely divided condition is obtained by any known and suitable process such as precipitation, or decomposition and reduction in hydrogen, and the metal in this condition is intimately mixed with any suitable and finely divided oxide, such as alumina, thoria,
zirconia, lime, or oxides of the rare earths or alkaline earths, which are not easily reducible at the sintering temperature. Alternatively the refractory oxide, or compound adapted to produce it subsequently, is mixed with a compound of the metal (or compounds of the metals) before the reduction or decomposition. Thequantity of oxide required is usually from about 0.1% to 1% of the weight of the metal, and preferably about 0.25%. The best amount for any particular purpose is readily ascertainable by experiment. If too little is used there will be insuflicient control of grain growth; if too much is used the resulting metal will be difficult to shape by swaging, rolling or drawing. The mixture is then compacted by pressure, sintered, and subsequently swaged, rolled, drawn, or otherwise The object of the invention is rhodium, and thorium oxide.
treated to bring it to the form of a wire, or sheet 55 "is added an aqueous solution of rhodium ammonium chloride containing 10 grams of rhodium,
and an aqueous solution of thorium nitrate containing 0.5 gram of thorium oxide (ThOz). The resultant paste is evaporated to dryness with constant stirring to ensure a uniform distribution of the constituents. The dried mass is then heated in a current of hydrogen at about 850 C. to decompose the rhodium and the thorium salts,.leaving an intimate mixture of platinum, The product is sieved, packed into a steel mould and compressed under a pressure of about tons per square inch in order to form a coherent mass. The compressed material is then heated at about 1400-1550 C. in hydrogen for about one hour, the effect of this heating being to alloy the rhodium with the platinum, and to sinter the mass into a dense body, sufiiciently strong to enable it to be swaged, rolled, drawn, or otherwise treated to bring it to the form of a wire, sheet or any other desired condition.
In another example, I employ 96 grams of platinum dissolved in aqua regia, a solution of ammonium tungstate containing 4 grams of tungsten, and another or the same solution containing thorium nitrate having 0.2% grams of thorium oxide. The tungsten and thorium solutions are added to the platinum solution, and after neutralising with ammonia, the mixture is evaporated to dryness. The resulting powder is heated at about 800 C. in air and then heated to about 1000 C. in hydrogen. The product consisting of finely divided platinum, tungsten and thorium oxide is formed into a bar by pressing in a steel mould at about 50 tons per square inch. The bar is then sintered in hydrogen for about two hoursat about 1450 C. and finally swaged, rolled or drawn to the required form and dimensions.
Materials made in accordance with the invention are characterised by having a higher tensile strength and greater hardness than corresponding materials made in the usual way, and by a crystalline structure which is satisfactorily stable at high temperatures.
In the foregoing I have described the application of my invention to platinum or platinum alloys. But the invention is applicable in essentially the same way to the other allied metals already mentioned, namely, rhodium, iridium, ruthenium, and palladium.
The platinum, and platinum alloys produced in accordance with my invention are especially useful for use as sparking plug electrodes. They are also useful for thermo-couples, furnace heating elements, catalyst gauzes, and other articles required to resist high temperatures (of the order of 1000" C. or more), or corrosive actions under which metals produced in ordinary ways are liable to coarsening of the grain structure or other deterioration resulting in weakening such mechanical properties as strength or hardness.
As regards materials produced from any of the other allied metals mentioned or alloys in which these metals form the principal ingredients I am unable on the basis of my present experience to specify any purpose for which they are especially useful, but such metals or their alloys, also possess the same property as the platinum materials above described, in that their grain size is satisfactorily stable at high temperatures, and.
therefore they may be applicable to a variety of uses in which this property serves a useful purpose.
In the foregoing I have given examples which enable anyone skilled in the art to produce materials in accordance with the invention, but I wish it to be understood that my invention is not limited to those examples, as the relative proportions of the ingredients, the nature of the metals to be alloyed with the principal metal, the nature of the oxides used, the temperatures employed for heating the substances, and the mode of bringing the ingredients to the finely divided condition may be varied, provided always that the end product consists of the desired comacted, sintered a l merat As regards the pressures to which the ingredients are subjected,
these may vary over a wide range, as for example from 5-50 tons per square inch, the most appropriate pressure being dependent on the metal or alloy and the fineness of the powder, in all cases it being advantageous to make the compressed mass as dense as possible.
Having thus described my invention what I claim as new and desire to secure by Letters Patent is:
l. A material in the form of a compacted and sintered agglomerate of a metal chosen from the group consisting of platinum, rhodium, iridium, ruthenium, palladium and alloys of these metals, and a refractory oxide, the constituents being initially in a finely divided condition.
2. A material in the form of a compacted and sintered agglomerate of platinum alloyed with a metal chosen from the group consisting of rhodium, tungsten, iridium nd ruthenium, in the approximate proportions specified, and a refractory oxide, both being initially in a finely divided condition, and the proportion of oxide being from about 0.1% to 1.0% of the weight of the metal. v
3. A material as claimed in claim 2, in which the oxide consists of thorium oxide.
4. A material as claimed in claim 2, which contains platinum alloyed with about 10% of rhodium, and about 0.5% of thorium oxide.
5. A material as claimed in claim 2, which contains platinum alloyed with about 4% of tungsten, and about 0.2% of thorium oxide.
6. Sparking plug electrodes, thermo-couples, electric furnace heating elements, catalyst gauzes, or like articles required to resist high temperatures or corrosive chemical actions, and
. made from a compacted and sintered agglomerate as claimed in claim 1 and containing platinum as the principal ingredient.
- COLIN JAMES SMI'I'HELLS.