Platinum Metals Rev., 1986, 30, (3), 130
Platinum Technology Transfer
Johnson Matthey Continues Long Tradition
For almost 150 years Johnson Matthey has promoted fabricated platinum products at industrial exhibitions in many parts of the world. Earlier this year this long established tradition continued when senior technical staff from Johnson Matthey Metals Limited took part in “Technology ‘86” an international exhibition specialising in the application of modern technology in industry, which was held in Moscow during March.
In addition to exhibiting products manufactured from platinum metals, technical papers were presented by A. E. Heywood, R. A. Benedek and J. Stokes. These were concerned, respectively, with the development and application of high strength zirconia grain stabilised platinum alloys, the recovery of platinum from ammonia oxidation plants and the deposition of platinum from fused salt electrolytes, and glass fibre bushings.
Zirconia grain stabilised platinum, platinum-rhodium and gold-platinum alloys manufactured by a proprietary process possess outstanding high temperature strengths due to uniformly distributed, extremely fine particles of zirconia. These prevent grain growth and other deleterious changes in the micro-structure. In addition the elongate grains produced during the thermomechanical operations impart an improved resistance to contamination, while the presence of zirconia does not adversely affect the corrosion resistance or the mechanical working properties of the alloys, which can still be formed by the usual techniques. Grain stabilisation with zirconia enables the rhodium content of alloys to be reduced, or even eliminated for applications in the optical glass industry where the possibility of rhodium contamination must be avoided. Thus substantial cost savings can result from the use of these ZGS materials.
For the producer of continuous glass fibre the zirconia grain stabilised alloys offer significant advantages. Working in partnership with glass plant designers, Johnson Matthey Metals has developed an advantageous method of fabricating bushing base plates. These may contain up to 2000 jets, with bore diameters as small as 1.1 millimetres, giving fibre diameters as fine as 6 micrometres. This proprietary process is used by Johnson Matthey companies throughout the world and it has also been licensed to a number of other organisations, the most recent being a glass fibre production plant in Polotsk, U.S.S.R. To date in excess of 30,000 base plates have been made by this process.
A thorough understanding of the needs of the nitric acid manufacturer has enabled Johnson Matthey Metals to develop an improved system for recovering platinum metals lost from catalyst gauzes during the ammonia oxidation reaction. The gold-free Plus-Pac™ recovery system enables customers to achieve a combination of metal recovery and costs which best suits their particular needs. Depending upon the type of plant, recoveries of 70 to 85 per cent may be achieved, a marked improvement on the 50 to 60 per cent recovery which is typically obtained with the early gold-palladium catchment systems. Plus-Pac™ is generally supplied in the form of hinged quadrants, so reducing both transport and installation difficulties.
The Electroplating of Platinum
Platinum deposited from aqueous electrolytes is generally brittle, it may be poorly bonded to the substrate and highly stressed. As a consequence coatings can suffer from spalling and delamination, so deposits are usually restricted to thicknesses of 12 micrometres or less. In contrast the deposition of platinum from fused salt electrolytes enables thick, ductile coatings to be produced on a variety of metals and alloys including nickel, niobium, palladium, stainless steel and tantalum. These coatings are of high purity, adherent and notably free from porosity. Where necessary they may be up to 150 micrometres thick, and the surface finish can either be matt or drawn bright. Fused salt platinum plated molybdenum and tungsten wires are used in the manufacture of halogen lamps and electronic valves, where a combination of high temperature refractoriness and oxidation resistance is required. The remarkable throwing powers of the fused salt electrolyte also enables complex shaped superalloy turbine blades to be coated to a high degree of uniformity. In addition the fluxing action of the electrolyte overcomes the adhesion problems frequently associated with plated titanium, so enabling soundly bonded platinum titanium composites to be produced for use as cathodic protection electrodes.
Since platinum first began to excite the interest of the world’s scientists, gifts and loans of metal and the ready exchange of experimental results have facilitated the determination of its properties, and the identification of applications. A continuation of this co-operation will ensure that the valuable properties of platinum and its allied metals are further employed to satisfy the growing needs of the high technology industries.