UA114253C2 - PLATINUM ALLOY FOR CATALYTIC NETWORKS - Google Patents

Abstract

The invention relates to the field of the metallurgy of noble metals, and more particularly to platinum alloys for the manufacture of catalyst gauzes that can be used in the chemical industry. The claimed alloy contains the following components (in wt%): 15.5-16.5 palladium; 2.7-3.3 rhodium; 0.005-3.3 tantalum; the remainder platinum. The aim of the invention is to develop a composition for a platinum alloy for catalyst gauzes which provides the formation of a homogeneous fine-grained structure during the production of cast billets and semi-finished products, has stable mechanical properties and enables the long-term use of catalyst bundles manufactured from said alloy, while maintaining a high level of catalytic activity.

Description

The invention relates to the field of metallurgy of precious metals, in particular, platinum alloys intended for the production of catalyst meshes used in the chemical industry.

The use of catalytic mesh bags at chemical industry enterprises in ammonia oxidation processes (during the production of nitric acid and its derivatives) is widely practiced at enterprises of various countries around the world. The catalytic function is performed, as a rule, by grids made of platinum alloys. Harsh operating conditions (high temperature and pressure) lead to gradual erosion and destruction of the mesh.

The need to ensure high catalytic activity of the mesh and preserve its mechanical characteristics for the longest possible period of operation imposes increased and specific requirements for the quality of platinum alloys used for the manufacture of catalyst meshes.

Platinum-based alloys containing rhodium and palladium are most widely used in the production of catalyst meshes.

Yes, a known platinum alloy for catalyst grids with the following composition, 95 wt: - platinum 92.2-92.8; - palladium 3.8-4.2; - rhodium 3.3-3.7.

IGOST 13498-79. "Platinum and platinum alloys. Brands". USSR State Committee on Standards. Moscow. Standards publishing house. - 1980...5 s|.

This alloy has high catalytic activity, is sufficiently technological for mesh production, provides suitable survivability of catalytic packages during their operation and is an analogue of the claimed alloy.

The disadvantage of the analog alloy is its excessively high cost, caused by the high content of expensive platinum (from 92.2 95 to 92.8 95).

The closest in composition to the claimed alloy is the well-known platinum alloy for catalyst grids, which contains 95 wt: - platinum - 80.3-81.7; - palladium - 14.5-15.5; - rhodium- 3.1-3.9; - ruthenium - 0.2-0.8.

International standard GOST 13498-79. "Platinum and platinum alloys. Brands".

USSR State Committee on Standards. Moscow. Standards publishing house. - 1980...September 5

This alloy has a platinum content reduced to 81 95 with a relatively high concentration of palladium, at the same time it is characterized by high catalytic activity, provides suitable survivability

From the catalytic packages during their operation and is considered the prototype of the claimed alloy.

The defects of the prototype alloy include the insufficient stability of the mechanical properties of the alloy and the semi-finished products made from it in terms of their length and cross-section, which is caused by the formation of zones with a heterogeneous structure during the crystallization of the cast blanks. The presence of grains with increased sizes in the structure of the cast alloy-prototype is undesirable, as it leads to technological difficulties in the manufacture of thin wire and mesh fabric.

The task to be solved by the proposed technical solution is the development of the composition of a new platinum alloy for catalyst meshes, which ensures the formation of a homogeneous fine-grained structure during the production of cast blanks and semi-finished products, which is characterized by stable mechanical properties, which ensures the long-term operation of catalytic packages made from it with preservation of high catalytic activity.

The technical result is achieved by the fact that the platinum alloy for catalyst grids, containing palladium and rhodium, additionally contains tantalum under the condition of the following ratio of components, 9Uo by mass: - palladium - 15.5-16.5; - rhodium - 2.7-3.3; - tantalum - 0.005-3.3; - the rest is platinum.

Common to the prototype alloy and the claimed platinum alloy is the presence of platinum, palladium and rhodium in the alloy.

The inclusion of tantalum admixture, which is an effective modifier, in the composition of the claimed alloy ensures the formation of a fine-grained homogeneous structure during the crystallization of the melt, which makes it possible to obtain cast blanks and semi-finished products with stable mechanical properties both in terms of their length and cross-section. Thus, the introduction of tantalum to the platinum alloy increases the technological properties of the alloy in the case of its use for the production of thin wire and mesh fabric, reduces the wear of the dies and the number of wire breaks, and facilitates the operation of the equipment during the production of catalyst meshes. It is important to note that the introduction of tantalum impurities into the alloy is accompanied by a corresponding decrease in the amount of expensive platinum, that is, it reduces the cost of the package, without deterioration, as experimental testing showed, of the catalytic activity of the grid.

Reducing the content of tantalum in a platinum alloy below 0.005 95 is undesirable, as it leads to a weakening of the modifying effect of tantalum on the alloy.

Exceeding the upper limit of the tantalum content (3.395) in the platinum alloy is impractical, as it does not lead to an improvement in the technological characteristics of the alloy during its further use in the production of catalyst meshes, but may negatively affect the catalytic activity of the mesh package.

The ratio of components in the claimed alloy is proposed on the basis of experimental studies, which involve the preparation of various alloys, the manufacture of thin wire and catalyst meshes from them, and the use of the latter in catalytic packages in ammonia oxidation devices.

The content of rhodium in the claimed alloy, in the range from 2.7 9o to 3.3 95, ensures the preservation of the necessary mechanical characteristics in the alloy, the meshes made of it, and is optimal.

The ratio of platinum and palladium in the claimed alloy is also optimal, chosen experimentally, based on the need to maintain high catalytic activity of the grid, ensure a long period of its operation and reduce the concentration of expensive platinum as much as possible.

Example

Platinum alloy for catalyst grids was produced by direct fusion of pure components. Smelting was carried out in an induction furnace U!1B-63-10-0.01

From the RELTEK company in a crucible made of zirconium dioxide, stabilized by Sao.

The composition of the charge: - chopped ingots and shavings of refined platinum grade PlA-0 (with a purity of 99.98 95) - 5792.0

D; - pieces of tantalum (with a purity of 99.7% of the main component), weighing -1.1g; - chopped ingots, powder and shavings of refined palladium - 1150.0 g; - rhodium powder (with a purity of at least 99.95 95 of the main component) - 214.1 g.

Rhodium powder was mixed with palladium powder and shavings and platinum shavings. The mass of palladium or platinum shavings (powder) should not be less than the mass of rhodium powder. All components of the charge were loaded into the melting crucible of the induction furnace, pieces of tantalum were placed at the bottom of the crucible. The total mass of the charge that was loaded was selected according to the capacity of the melting crucible and it was - (72002100) g. The estimated composition of the charge, 95 mass: Ra- 16.10; Ap-3.00; Ta-0.015; The rest.

The charge was melted in an argon atmosphere. The melt was subjected to isothermal aging for 10 minutes, the melting of the melt was carried out at a temperature of 1780 "C (according to the optical pyrometer), in an argon atmosphere, in a copper mold preheated to 200 "C.

The ingot was cooled in the pouring chamber for 30 minutes, after which the furnace lid was opened, the ingot was unloaded and its further cooling was carried out by immersion in running water.

The weight of the obtained alloy was 7150.2 g. After mechanical cleaning of the surface, the obtained ingot was tested, the sample was subjected to chemical analysis.

Chemical analysis of the sample showed that the obtained platinum alloy contains 16.05 95 palladium, 2.95 95 rhodium, 0.010 95 tantalum, the rest - platinum.

The obtained alloy was forged into darts with a cross-section of 15715 (mm), length (260-290) mm, and was successfully used for the production of a catalyst mesh.

Claims (1)

FORMULA OF THE INVENTION A platinum alloy for catalyst grids containing palladium and rhodium, which is distinguished by the fact that it additionally contains tantalum, with the following ratio of components, wt. 90: for palladium 15.5-16.5 rhodium 2.7-3.3 tantalum 0.005-3.3 platinum the rest.