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Jewellery Manufacturing LATEST ADVANCES REPORTED AT THE FOURTEENTH ANNUAL SANTA FE SYMPOSIUM

The 14th Santa Fe Symposium on man- but has not seen commercial application. Its use ufacturing technology was held in Albuquerque, for the production of wedding rings in carat New Mexico, from 21 st to 24th May 2000 and this and was described by P. Raw (Consultant year attracted a record 188 delegates from 19 coun- to Engelhard-CLAL, U.K.). Based on a press and tries. Twenty-five presentations on the latest sinter technique using water atomised powders, the research results and advances in technology cov- process not only to better technical proper- ered all the precious and gems, with ties, such as smaller grain size and increased platinum jewellery receiving considerable attention ductility (facilitatinga hgher degree of ring sizing), - as it has over recent years - and illustrating the but it is also faster and has hgher productivity, and considerable interest in this fashionable jewellery hence it is more economic. This process is a major . breakthrough and is already attracting attention The Symposium opened with Mark Grimwade from other jewellery fabricators. (Consultant, U.K.) giving his now customary The elecaoplating of the platinum group met- ‘Introduction to & Jewellery Alloys’ als: platinum, palladium and rhodium, for lecture, which this year was widened to include a decorative and functional applications was detailed section on platinum jewellery alloys. This reviewed by E. Salomon (Consultant, Technic Inc., was followed by John Wright (Consultant, U.K.) U.S.A.), with many practical tips for the small elec- talking about ‘Mechanical Properties and troplater. Rhodium, of course, finds application on Jewellery’, which gave an insight into how such white jewellery to improve colour. properties impact on manufacturing processes and The rapid production of platinum jewellery in the design of jewellery from an per- the small workshop by high speed investment cast- spective. The advantages to fabricators of the ing (lost wax ) was described by Jurgen unique properties of platinum in jewellery manu- Maerz (Platinum Guild International). Using mag- facture were highlighted. nesia-based dental investments, which can be fired The unusual macwproperties of platinum quickly, it is possible to make a successful casting have been the subject of much investigation, see in less than 2 hours. This will prove to be a boon (1) for example. More recently, new work to opti- to the designer/smith making individual pieces to mise parameters for surface quality has order. Modem of jewellery was been undertaken by C. Volpe (Tiffany & Co.) and origmally developed from the dental tech- R Lanam (Engelhard-CLAL) and their initial nology in the 1950s. This work once again results on platinum-5 per cent ruthenium illustrates how technology has been successfully were presented at Santa Fe last year. The second transferred across into the jewellery sector. part of their results, presented at this Symposium, On the broader precious metal jewellery front, extended their earlier work to other platinum jew- a number of papers were presented on aspects of ellery alloys includmg a new age-hardenable 950 jewellery technology. R. Carter (Ransom & platinum alloy. Surface quality was evaluated by Randolph, U.S.A.) described the effect of water surface roughness measurements and by examina- quality and on investments for lost tion under a scanning , and wax casting of precious metals. The use of de- results showed polycrystaJline diamond tools to be ionised water to maintain a consistent quality was superior to cermet tools. The best surface texture recommended. New research into the thermal sta- was found on the age-hardenable alloy. bility of investments was also reported by G. M. as a process for producing Ingo (CNR, Italy). The stability of investments is precious metal jewellery has long been attractive, important to the lost wax casting of jewellery.

PhtinwnMetals Rev., 2000,44, (4), 156157 156 Instability is often a cause of a number of casting mance and aaining evaluation was discussed. defects including gas ; progress is being Other presentations looked at copyright and achieved in improving stability. patent law, quality assurance and at the metallurgy The influence of the metallurgy and and properties of other precious metals. of jewellery materials on the processes used in jew- The presentations at this Santa Fe Symposium elleiy manufacture was discussed by D. Ott (FEM, and previous Symposia are available from: The Germany). This topic was also picked up by H. Santa Fe Symposium, 7500 Bluewater Road NW, Freye (Techform, U.S.A.) in considering the NM 87121, U.S.A. Tel: +1 505 839 3249; Fax: +1 ceramics used in casting of high temperature 505 839 3248; E-mail: [email protected]. alloys includulg platinum. C. W. CORTl G. Normandeau described the metallurgical References training programmes used by his company, 1 R W. E. Rushforth, P/atinlrm Metah Rcu., 1978, 22, Imperial & Ltd., Canada. This (119 2 includes subject matter unique to platinum as The Author Chris Corti is editor of Gold Bulletin and Gold Technology. His main as gold and . All staff on the shop floor are interests are the manufacturing technology of gold jewellery and the trained and the impact of this on staff perfor- industrial applications for that metal. High Breakdown Voltage of Au/Pt/GaN Schottky Diodes In power electronics (power > 1 MW), merit (Vrn)'/RON,(hN = on-state resistance) were , +um arsenide and +um nimde (GaN) 4.2 to 4.8 MW crn-'. The reverse leakage currents are being developed as alternative materials to sili- and forward on-voltages were shghdy higher than con. Silicon carbide is already used in solid-state theoretical minimum values, but comparable with power electronic devices, such as diodes, thyristors reported Sic Schottky rectifiers. The GaN-devices and transistors. Wide bandgap GaN, with hlgh show promise for use in ultralugh-power switches. breakdown voltage, is also under extensive invesd- gation for power device uses, but little work has Damping in Ruthenium Alloys been reported on breakdown in GaN diode devices. An important physical property of an alloy is its Schottky diodes can switch faster than junction damping capacity in response to an imparted diodes and are often used to measure the quality of mechanical force. High damping in -rutheni- material. Now, a team of researchers, from the um alloys is closely linked to the amount of E National Central University, Taiwan, the martensite present. University of Florida, Sandia National Scientists at Yonsei University, Seoul, Korea, , Bell Laboratories, and a consultant, have investigated the damping capacity of iron- U.S.A., have examined breakdown using ruthenium alloys, containing 25 and 13 per cent Ru Au/Pt/GaN Schottky diode rectifiers (G. T. Dang, at room temperature, using samples processed to A. P. Zhang, M. M. Mshewa, F. Ren, J.-I. Chyi, C.- contain various amounts of E martensite (H.-C. M. Lee, C. C. Chuo, G. C. Chi, J. Han, S. N. G. Shin, J.-H. Jun and C.3. Choi, Sm. Muter., 2000,42, Chu, R G. Wilson, X A. Cao and S. J. Pearto&]. (lo), 981-986). VM.Sci. Technol. A, 2000,18, (4), 1135-1 143). Fe-13% Ru, which undergoes a y+a' marten- GaN was grown by MOCVD on sapphire via site transformation to give a' Mephase, showed NH, and trimethylgalhum precursors. The ohmic poor damping capacity. Fe-25% Ru undergoes a contacts were formed by Pt/Au liftoff. They were Y+E martensite transformation and has hlgh damp- annealed before Pt/Au deposition. Optimised high- ing capacity, dependent on the strain amplitude. density etchmg conditions were developed For Fe-25% Ru, damping capacity increases with for GaN, to give minimal degradation in reverse increasing E martensite content at < 3 xIO" strain current leakage in pi-ti mesa diodes. Reverse amplitude. At strain amplitude > 4 x104 it reached breakdown voltages (V,) of up to 550 V on verti- a peak for a volume fraction of - 42 per cent of & cally depleting structures and > 2000 V on lateral martensite. Stackmg fault boundaries inside the E devices were obtained. Values for the figure-of- martensite plates act as damping sources.

Pkatinum Metah Rex, 2000,44, (4) 157