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Platinum Metals Rev., 2013, 57, (3), 230

doi:10.1595/147106713x668901

Final Analysis: ZGS Platinum Materials for Improved Glass Manufacturing Equipment and Laboratory Ware

    • Dominic Morris* and Rob McGrath
    • Johnson Matthey Noble Metals,
    • Orchard Road, Royston, Hertfordshire SG8 5HE, UK

*Email: dominic.morris@matthey.com

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The use of platinum and its alloys is well established in the automotive, chemical, glass, electrical and dental industries. However, many of these applications require high-temperature operation of the alloys. At high temperatures conventional platinum group metals (pgms) are subject to grain growth and, therefore, are weak and subject to creep deformation. They can also be subject to contamination failure.

Johnson Matthey developed zirconia grain stabilised (ZGS) platinum that is resistant to grain growth and contamination and deformation at high temperatures (1). Applications include glass manufacturing equipment (2) as well as a range of laboratory apparatus (3).

ZGS platinum materials are produced by incorporating fine ZrO2 ceramic particles, dispersed uniformly throughout the platinum metal matrix, a process called dispersion strengthening. These particles slow down the process of degradation in the alloy by pinning dislocation networks formed during thermomechanical processing, so inhibiting the movement of these dislocations to the grain boundaries (Figure 1) (2). Microstructural degradation is effectively restricted, giving extended operating lives compared to conventional pgms and alloys.

Fig. 1.

Representation at 100 × magnification of: (a) Pure platinum sheet after heating for 500 h at 1400°C; and (b) ZGS platinum sheet after the same treatment, showing significant reduction in grain growth

Representation at 100 × magnification of: (a) Pure platinum sheet after heating for 500 h at 1400°C; and (b) ZGS platinum sheet after the same treatment, showing significant reduction in grain growth

 

The principle of grain stabilisation has been established in the base metal world for some time (4). The difficulty had always been in achieving production of grain stabilised material on a large scale and with a stable dispersion of particles of the correct composition and size to be effective that does not coarsen or dissolve at the operating temperature. Johnson Matthey developed a unique process to meet those requirements, and have been using it for over 20 years.

ZGS platinum offers significantly improved performance over conventional platinum materials for use at elevated temperatures as the following examples show.

How ZGS Alloys Behave at Working Temperature

Figure 2 illustrates graphically the improvement in high-temperature life achieved by grain stabilisation. The time to failure at 1400°C under a stress of approximately 10 MPa shows that ZGS Pt lasts up to ten times as long as the conventional Pt-Rh alloy and ZGS Pt-10% Rh lasts more than ten times as long as ZGS Pt. In terms of the rate of deformation before failure, the load to cause a deformation rate of 0.1% h1 is approximately twelve times higher for ZGS platinum compared to Pt-20% Rh, while at 1% h1 it is three times higher (1).

Fig. 2.

Stress rupture properties of ZGS platinum, ZGS platinum-10% rhodium and the commercially important conventional alloys. The curves refer to tests carried out at 1400°C in air on 1.5 mm thick sheet specimens

Stress rupture properties of ZGS platinum, ZGS platinum-10% rhodium and the commercially important conventional alloys. The curves refer to tests carried out at 1400°C in air on 1.5 mm thick sheet specimens

 

Other properties of the ZGS platinum alloys are summarised in Tables I and II (2). All data given is for sheet.

Table I

How ZGS Platinum and Platinum-Rhodium Alloy Behave at Room Temperature Compared to Conventional Platinum and Its Alloys

PropertyZGS PtZGS Pt-10% Rh100% PtPt-10% RhPt-20% Rh
Specific gravity, g cm−3 21.4 19.8 21.4 20.0 18.8
Electrical resistivity at 20°C, μΩ cm 11.12 21.2 10.6 19.2 20.8
Temperature coefficient of electrical resistivity per °C 0.0031 0.0016 0.0039 0.0017 0.0014
Ultimate tensile strength, annealed, kg mm−2 19 36 13 34 49
Vickers hardness, annealed sheet 60 135 40 90 115
Table II

Ultimate Tensile Strength (Annealed) at Elevated Temperatures of ZGS Platinum and Platinum-Rhodium Alloy Compared to Conventional Platinum and Its Alloys

Temperature, °CUltimate tensile strength, kg mm−2

ZGS PtZGS Pt-10% Rh100% PtPt-10% RhPt-20% Rh
1000 5.2 16.7 2.4 8.4 23.5
1100 4.6 14.3 1.7 6.2 16.5
1200 3.8 12.8 1.3 4.8 10.1
1300 3.6 9.4 0.8 3.9 7.0
1400 2.9 8.5 0.4 3.0 5.0
1500 2.4 7.2 2.4 3.9

ZGS Platinum Applications

ZGS platinum and platinum alloys find particular application in products where high temperature causes creep, distortion and ultimately failure of unsupported conventional platinum and its alloys. Their principle application is in the glass manufacturing industry where their improved properties allow less material to be used while simultaneously improving equipment lifetimes.

ZGS platinum-rhodium baseplates for bushings, used for the production of continuous filament glass fibre, resist creep-induced sagging and eliminate the need for extra structural platinum supports. ZGS platinum alloys can also be used for glass carrying apparatus designed with thinner wall sections and lower rhodium content; such apparatus can have 50% greater useful life and the reduced rhodium content reduces the potential for discoloration of the glass. Lightweight thermocouple sheaths can be fabricated with walls half the conventional thickness, saving on costs. ZGS platinum can make possible the elimination of molybdenum and ceramic cores for glass stirrers, improving service life and reducing potential inservice problems. ZGS platinum-5% gold is used for crucibles and casting dishes for XRF analysis using borate fluxes.

The recommended maximum operating temperatures for the ZGS platinum and ZGS platinum alloy materials are typically 50–100°C above those of the conventional alloys. Table III (3) shows the maximum temperatures recommended for all applications.

Table III

Recommended Maximum Operating Temperatures for ZGS Platinum Materials Compared to Conventional Platinum and Its Alloys

MaterialTemperature, °C
Pt 1400
ZGS Pt 1500
Pt-10% Rh 1550
ZGS Pt-10% Rh 1600
Pt-5% Au 1300
ZGS Pt-5% Au 1400

Conclusions

ZGS platinum resists contamination failure for extended periods and extends the life of crucibles and other equipment. ZGS platinum also offers an opportunity to reduce the component weight while maintaining material integrity. Standard products including crucibles and dishes are available in ZGS platinum, ZGS platinum-10% rhodium and ZGS platinum-5% gold. Other alloys are available upon request from Johnson Matthey Noble Metals.

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References

  1.  G. L. Selman, J. G. Day and A. A. Bourne, Platinum Metals Rev., 1974, 18, (2), 46 LINK https://www.technology.matthey.com/article/18/2/46-57/
  2.  Johnson Matthey Noble Metals, ZGS Platinum Materials: http://www.noble.matthey.com/pdfs-uploaded/10%20ZGS%20Platinum%20Materials.pdf (Accessed on 23rd May 2013)
  3.  “Platinum Labware”, Alfa Aesar, A Johnson Matthey Company, Royston, UK, July 2012: http://www.alfa.com/en/docs/PlatinumLabware/flipviewerxpress.html (Accessed on 23rd May 2013)
  4.  E. Orowan, Rep. Prog. Phys., 1949, 12, (1), 185 LINK http://dx.doi.org/10.1088/0034-4885/12/1/309

The Authors

Dominic Morris is a Product Specialist in Sales at Johnson Matthey Noble Metals in Royston, UK. He works with industrial products, which incoporate pgm manufactured products including wire, tube, laboratory equipment and complex fabrications used in high-temperature applications and environments.

Rob McGrath is a Principal Metallurgist at Johnson Matthey Noble Metals. His areas of interest include manufacturing techniques and industrial applications for pgm products, pgm alloy development and coatings technology.

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