RU2563113C1 - Platinum-based alloy for catalyst grating - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed titanium-based alloy for catalyst grating comprises the following components in wt %: rhodium - 4.5-10.5, iridium - 0.001-0.5, tantalum - 0.001-3.3, platinum making the rest. Homogeneous fine-grain structure is formed in production of cast blanks and semis to produce the alloy of stable mechanical properties.

EFFECT: longer service life of catalyst piles, sufficient catalytic activity.

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Description

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

The use of catalytic mesh bags at the chemical industry in the oxidation of ammonia (in the production of nitric acid and its derivatives) is widely practiced at enterprises around the world. The catalytic function in this case is performed, as a rule, by grids made of platinum alloys. Severe operating conditions (high temperature and pressure) lead to gradual erosion and destruction of the mesh web. The need to ensure high catalytic activity of the grid and preservation of its mechanical characteristics for the longest possible lifetimes impose increased and specific requirements on the quality of platinum alloys used for the manufacture of catalyst grids.

In the manufacture of catalytic systems, various platinum rhodium alloys are widely used. The content of rhodium in them can be different and varies, as a rule, from 5 to 10%.

The closest in composition and functional application to the claimed alloy is an alloy based on platinum for catalyst networks PlRd 92.5-7.5, containing, wt.%:

- platinum - 92.2-92.8;

- rhodium - 7.3-7.7

 [Interstate standard. GOST 13498-2010. “Platinum and alloys based on it. Stamps. " M., Standartinform. - 2011.5 p.].

This alloy has a high catalytic activity, provides acceptable survivability of the catalytic packages during their operation and is adopted as a prototype of the claimed alloy.

The disadvantage of the prototype alloy is the lack of stability of the mechanical properties of the semi-finished products made from it along their length and cross section, caused by the formation of inhomogeneous zones with a different grain structure, which forms during crystallization of cast billets, which causes process disruptions during wire drawing and mesh manufacturing. The presence of oversized grains along with small grains in the structure of the cast alloy prototype is undesirable, as it leads to technological difficulties in the manufacture of thin wire, and then the mesh fabric.

The task to which the proposed technical solution is directed is to develop the composition of a new alloy based on platinum for catalyst grids, which ensures the formation of a homogeneous fine-grained structure during crystallization of cast billets, obtaining semi-finished products with stable mechanical properties. The alloy should provide long-term operation of the catalyst networks made from it while maintaining high catalytic activity.

The technical result is achieved by the fact that the alloy based on platinum for catalyst networks containing rhodium additionally contains iridium and tantalum in the following ratio of components, wt.%:

- rhodium 4.5-10.5;

- iridium 0.001-0.5;

- tantalum 0.001-3.3;

- platinum - the rest.

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

The inclusion in the composition of the inventive alloy of the combined additives of iridium and tantalum, which are effective modifiers, ensures a high rate of nucleation of the new phase during crystallization of the melt and the formation of a fine-grained homogeneous structure, which allows to obtain cast billets and semi-finished products with stable mechanical properties, both along their length and cross section . Thus, the introduction of iridium and tantalum additives into the alloy increases the technological properties of the alloy when it is used for the manufacture of thin wire and mesh fabric.

A decrease in the concentration of both iridium and tantalum in a platinum alloy below 0.001% is unacceptable, since it leads to a noticeable weakening of the modifying effect on the alloy and reduces the stability of its properties.

Exceeding the upper limits of the declared content of both iridium (0.5%) and tantalum (3.3%) in a platinum alloy is also impractical, since it does not lead to further improvement of the technological characteristics of the alloy when used in a grid production, but can negatively affect on the catalytic activity of the catalyst network.

The ratio of the components in the inventive alloy is proposed on the basis of experimental studies, including the preparation of various alloys, the manufacture of thin wires and catalyst networks from them, the assessment of the survivability and catalytic activity of the latter, when they are included in various catalytic packages in ammonia oxidation apparatuses.

The content of rhodium in the inventive alloy in the range from 4.5% to 10.5% ensures the preservation of the necessary mechanical characteristics of the alloy and the nets made from it and is optimal.

The ratio of platinum and rhodium in the inventive alloy is also optimal, selected experimentally, based on the need to maintain high catalytic activity of the grids and ensure a long life.

Example

The preparation of a platinum alloy for catalyst networks was carried out by direct fusion of pure platinum, rhodium, tantalum, and PL-5 alloy, which was used as a ligature. Melting was carried out in an induction furnace UIPV-63-10-0.01 of the company "RELTEC" in a crucible made of zirconia stabilized with CaO.

The composition of the charge:

- chopped ingots and shavings of platinum of the refined grade PLA-0 (purity 99.98%) - 6630.0 g;

- shavings of the PLI-5 alloy - 20.0 g;

- tantalum (lump and shavings) - 11.0 g;

- rhodium powder (purity not less than 99.95% of the main component) - 540.1 g.

All components of the mixture were mixed and loaded into a melting crucible of an induction furnace. The total mass of the loaded charge was selected based on the capacity of the melting crucible and amounted to (7200 ± 100) g. The calculated composition of the charge,%: Rh - 7.50; Lr - 0.01; Ta - 0.15; Pt is the rest.

The mixture was melted in an argon atmosphere. The melt was subjected to isothermal exposure for 4 min, the melt was discharged at a temperature of 1800 ° C (according to the readings of an optical pyrometer), in an argon atmosphere, into a copper mold preheated to 200 ° C.

The ingot was cooled in the mold for 30 minutes, after which the furnace lid was opened, the ingot was unloaded, and its further cooling was carried out by lowering it into running water.

The mass of the obtained alloy was 7200.1 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 resulting alloy contains 7.49% rhodium, 0.011% iridium, 0.15% tantalum, the rest is platinum.

The resulting alloy was forged into bars with a cross section of 15 * 15 (mm), length (260-290) mm and was successfully used for the manufacture of a catalyst mesh.

Claims (1)

An alloy based on platinum for catalyst networks containing rhodium and iridium, characterized in that it additionally contains tantalum in the following ratio of components, wt.%:
rhodium 4.5-10.5; iridium 0.001-0.5; tantalum 0.001-3.3; platinum rest