Microstructure and properties of the new Microstructure and properties of the new Pt-Rh based alloys for high temperature Pt-Rh based alloys for high temperature

applicationsapplications

Zbigniew M. Rdzawski and Jerzy P. Stobrawa

The Non-Ferrous Metals Institute

ul. Sowińskiego 5

44-100 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 PRESENTATIONPLAN OF THE PRESENTATION

INTRODUCTIONINTRODUCTION

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 WORKING ENVIRONMENT OF PLATINUM AND RHODIUM ALLOYSALLOYS

40 x 40 x

Nitric industry Glass industry

Input: 6,7% NH3 + air

temp. of mixture ca. 200oC

Output: 12% NO, 71% N2, 11% H2O, 6% O2

temp. of mixture 900oC, pressure 5 bar

alloys: PtRh5, PtRh8, PtRh10

Liquid glass, temp. 1250oC

PtRh10, PtRh20ODS (Oxide Dispersion Strenghtened) ZGS (Zirconia Grain Stabilised)DPH (Dispersion Particle Hardened)

RESULTS OF ALLOYS EXAMINATION AFTER TAKING THEM OUT OF RESULTS OF ALLOYS EXAMINATION AFTER TAKING THEM OUT OF

SERVICESERVICETools for liquid glass defibering

300 x

3000 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 border Reactor centre

1000 x1000 x

Surface of catalyst gauge wire from PtRh8 alloy after taking it out of industrial service

SEM

1100 x

EwPlatinum 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

Pt

Rh O2

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

PtRh10

PtRh5

40 x

40 x

Lp Pt [%] Rh [%] O2 [%]

1 89,67 10,33 -

2 83,27 16,73 -

3 7,50 74,01 18,49

4 4,55 76,79 18,66

EW

1

42

3

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

AlloysNo Processing stage Property

PtRh10 PtRh10B PtRh10YRm [MPa] 665,1 671,0 734,0R0,2 [MPa] 588,6 608,0 683,71

Initial state, after cold-workingwith 80 % reduction (roomtemperature tests) A [%] 5,7 3,1 3,1

Rm [MPa] 314,1 408,7 461,0R0,2 [MPa] 123,4 181,1 -2

After annealing 9500C/10 h(room temperature examination )

A [%] 40,0 38,6 26,6

Rm [MPa] 224,0 261,0 410,03

After annealing 9500C/100 h(room temperature examination) A [%] 10,7 15,5 17,6

Rm [MPa] 300,0 - 445,04

After annealing 11500C/2 h(room temperature examination) A [%] 40,0 - 37,0

Rm [MPa] 273,7 - 376,5R0,2 [MPa] 113,0 - 206,85

After annealing 12500C/10 h(room temperature examination) A [%] 22,6 - 26,6

Rm [MPa] 162,0 - 311,76 Examination at 6000CA [%] 40,0 - 40,0

PtRh10 PtRh10B PtRh10Y

Exemplary microstructure images of platinum alloys in the initial state and after annealing at the temperature of 9500C for 1, 10 and 100 hours. Optical microscope, chemically etched specimen. Magnification 120x.

After annealing at 9500C for 1 hour

After annealing at 9500C for 10 hours

After annealing at 9500C for 100 hours

Results of grain size examination

Average diameter of flat grain [mm]Annealing time [hours]Material

1 10 100Annealing temperature - 9500C

PtRh10PtRh10BPtRh10Y

0,035 – 0,0450,035 – 0,045

~ 0,010

0,060 – 0,0700,045 – 0,050

~ 0,015

0,070 – 0,0900,060 – 0,070

~ 0,025Annealing temperature - 12500C

PtRh10PtRh10BPtRh10Y

0,090 – 0,1200,090 – 0,1200,060 – 0,070

0,150 – 0,2000,150 – 0,2000,120 – 0,150

~ 0,800~ 0,200

0,150 – 0,200

PtRh10B PtRh10Y

200 m 10 m

Analyze pointElement1 2 3 4 5 6 7 8 9 10 11

Boron [%] 0,030 0,000 0,000 0,000 0,040 0,060 0,070 0,040 0,050 0,080 0,000Ytrium [%] 0,174 0,155 0,238 0,061 0,005 0,198 0,228 0,203 0,208 0,262 0,257

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

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

10 20 30 40 50 60 70 80 90 100

Equivalent diameter [m]

Rel

ative

freq

uenc

y [%

]

200 nm

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

0

5

10

15

20

25

0 200 400 600 800 1000 1200 1400

Equivalent diameter [nm]

Rel

ativ

e fr

eque

ncy

[%]

200 nm

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

0

2

4

6

8

10

12

14

16

18

20

0 200 400 600 800 1000 1200 1400 1600

Equivalent diameter [nm]

Rel

ativ

e fr

eque

ncy

[%]

200 nm

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

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 N2O 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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