Microstructure and properties of the new Pt-Rh based alloys for high temperature applications Zbigniew M. Rdzawski and Jerzy P. Stobrawa The Non-Ferrous Metals Institute ul. Sowińskiego Gliwice

Introduction Working environment of platinum and rhodium alloys Results of alloys examination after taking them out of service Results of examination of microstructure and properties of the modified PtRh10-based alloys Conclusions PLAN OF THE PRESENTATION

INTRODUCTION Platinum and its alloys are used for manufacture of: catalyst gauzes for ammonia oxidation and for processes of hydrogen cyanide production tools for liquid glass defibering crucibles for glass melting wires for thermoelements laboratory equipment chemical compounds for various applications

WORKING ENVIRONMENT OF PLATINUM AND RHODIUM ALLOYS 40 x Nitric industry Glass industry Input: 6,7% NH 3 + air temp. of mixture ca. 200 o C Output: 12% NO, 71% N 2, 11% H 2 O, 6% O 2 temp. of mixture 900 o C, pressure 5 bar alloys: PtRh5, PtRh8, PtRh10 Liquid glass, temp o C PtRh10, PtRh20 ODS (Oxide Dispersion Strenghtened) ZGS (Zirconia Grain Stabilised) DPH (Dispersion Particle Hardened)

RESULTS OF ALLOYS EXAMINATION AFTER TAKING THEM OUT OF SERVICE Tools for liquid glass defibering 300 x3000 x 100 x 3000 x

100 x 1000 x Images of surface of PtRh10 catalyst gauze after taking it out of industrial service SEM

Reactor borderReactor centre 1000 x Surface of catalyst gauge wire from PtRh8 alloy after taking it out of industrial service SEM

1100 x Ew Platinum arrangement Rhodium arrangement Image of catalytically etched surfaces of PtRh8 alloy gauze wire and electron images of platinum and rhodium arrangement

100 x 3000 x 1000 x Image of PtRh10 alloy knitted gauze of excessive brittleness SEM

EW line of analysis 2300 x Platinum, rhodium and oxygen arrangement along the line of analysis on the lenghtwise section of PtRh10 gauze wire

40 x Image of surface of PtRh alloys gauzes wires after taking them out of industrial service (5974 hours) SEM PtRh10 PtRh5 40 x LpPt [%] Rh [%] O 2 [%] 1 89,6710, ,2716, ,5074,01 18,49 4 4,5576,79 18,66 EW 2000 x Image of the third (knitted) PtRh5 gauze Observation in direction opposite to the flow of gasses

Results of examination of mechanical properties of the PtRh10, PtRh10B and PtRh10Y alloys

PtRh10PtRh10BPtRh10Y Exemplary microstructure images of platinum alloys in the initial state and after annealing at the temperature of C for 1, 10 and 100 hours. Optical microscope, chemically etched specimen. Magnification 120x.

Results of grain size examination

Microstructure of PtRh10B and PtRh10Y alloys with marked points of analysis of the boron and yttrium contents

200 nm Microstructure (TEM) and grain size distribution in the PtRh10 alloy (average equivalent diameter = 46,43  m)

200 nm Microstructure (TEM) and grain size distribution in the PtRh10 alloy (average equivalent diameter = 0,52  m)

200 nm Microstructure (TEM) and grain size distribution in the PtRh10 alloy (average equivalent diameter = 0,61  m)

Microstructure of PtRh10Y alloy. HRTEM.

Microstructure of PtRh10Y alloy. HRTEM. Different place.

CONCLUSIONS  Addition of boron into PtRh10 alloy in the amount of ca. 5 ppm inhibits excessive growth of grains in high temperature.  Has a positive influence on stability and homogeneity of microstructure as well as on improvement of mechanical properties.  Gives possibilities for increase of service live of the catalysts gauzes.  There is a possibility of elevating the temperature of gauzes operation, which may increase efficiency and selectivity of ammonia oxidation and limit N 2 O emission to the atmosphere.  Addition of yttrium into PtRh10 alloy in the amount of 0,2% significantly inhibits excessive growth of grains in high temperature.  Has a positive influence on stability and homogeneity of microstructure as well as on improvement of mechanical properties in high temperatures.  Application of that alloy in production of tools for liquid glass defibering should significantly increase their service life.  Production costs of the modified alloys are comparable with production costs of classical PtRh10 alloy.

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