The use of platinum and its alloys, such as 10% rhodium/platinum, is well established in the glass industry. However, their applications often mean high temperature operation of these materials. At high temperatures these materials are weak and subject to creep. They are also subject to contamination failure.
Johnson Matthey has developed a form of platinum, Zirconia Grain Stabilized (ZGS), that is resistant to grain growth, the effect of contamination and deformation at high temperatures. An exclusive development by Johnson Matthey, ZGS platinum materials offer significantly improved performance over conventional platinum and its alloys.
ZGS materials have fine, evenly dispersed, particles of zirconia present throughout their matrix. These particles then slow down the processes of degradation dramatically. They achieve this by pinning
dislocation networks formed during thermo-mechanical processing, so inhibiting the movement of these dislocations to the grain boundaries. With ZGS materials microstructural degradation is effectively restricted, giving extended operating lives when compared to conventional platinum group metals and alloys.
Another benefit of ZGS materials is that of improved resistance to intergranular contamination.
This is achieved through retention of the high aspect-ratio grain structure, which provides a long and tortuous route for intergranular contaminants to travel.
WHY ZGS?
• It resists contamination failure for extended periods.
• Extended plant service by virtue of superior stress rupture properties.
• It is an alternative to high rhodium content alloys that can discolour glass.
• ZGS offers an opportunity to reduce component weight while maintaining material integrity.
• ZGS materials are produced in 16 Kg batches which are totally consistent in properties.
• Products are available in ZGS platinum, ZGS 10% rhodium/platinum and
ZGS 5% gold/platinum.
SUCCESSFUL ZGS PLATINUM MATERIAL APPLICATIONS INCLUDE:-
• ZGS rhodium/platinum baseplates for bushings, used in the production of continuous glass fibre, resist creep induced sagging and eliminate the need for extra platinum supports.
• Glass carrying apparatus, designed with thinner wall sections in ZGS platinum, in optical glass production where rhodium containing alloys lead to discolouration of the glass.
• Batch melting of crystal glass in large ZGS platinum crucibles has extended operating lives and increased resistance to attack from contaminants.
• Lightweight ZGS thermocouple pockets fabricated with walls thinner than the conventional
standard.
• ZGS 5% gold/platinum is the alloy of choice for crucibles and casting dishes for XRF analysis using borate fluxes.