Leah Gal-Or

Electrochemical ZrO2 and Al2O3 coatings on SiC substrates

SiC was electrochemically coated with ZrO2 and with Al2O3 from 0.1 m aqueous solutions of metal-nitrate-hydrates with ethanol added. Amorphous zirconia and alumina coatings were formed with current densities from 10 to 70 mA cm−2, and deposition durations of 1–60 min. The as-deposited coatings contained microcracks caused by drying shrinkage. Sintering of zirconia at 900 °C for 1 h and of alumina at 1200 °C for 2 h in air was accompanied by crystallization to a mixture of tetragonal and monoclinic phases in the former and to α-alumina in the latter. The absence of intermediate phases between the coatings and the substrates and the good adherence of the sintered coatings indicate the high-temperature stability of these coatings.

Electrochemical Al2O3–ZrO2 composite coatings on non-oxide ceramic substrates

Aqueous solutions of xAl(NO3)3+(1−x)ZrO(NO3)2 were used for electrodeposition of ceramic Al2O3–ZrO2 composite on TiC, TiB2 and SiC sunstrates. The weight of the deposit was studied versus the duration of deposition, the current density and the temperature of the bath for Al-rich (x=0.9), Zr-rich (x=0.4) and eutectic (x=0.75) electrolyte compositions. Optimal current densities and durations of deposition were determined to obtain maxima weights of deposits. Amorphous deposits with thicknesses up to 10 μm were formed. The microstructure and microchemical composition of the as-deposited and sintered deposits were characterized. Increase in the temperature of the bath inhibited microcracking due to shrinkage during drying. Coated TiC substrates exhibited enhanced oxidation resistance in air at 1100°C.

Characterization of zirconium, lanthanum and lead oxide deposits prepared by cathodic electrosynthesis

Cathodic electrosynthesis of zirconium, lanthanum and lead oxides was performed from aqueous solutions of ZrOCl2 · 8H2O, La(NO3)3 · 6H2O and Pb(NO3)2, respectively. The deposits were characterized by X-ray diffraction, thermogravimetric and differential thermal analyses. Crystallite sizes of zirconia were derived at different temperatures from X-ray broadening data. The influence of hydrogen peroxide on the electrosynthesis process, crystallization and phase evolution of deposits has been studied. A possible mechanism of electrosynthesis and the role of hydrogen peroxide are discussed.

Electrolytic PZT films

A novel method of cathodic deposition of complex oxide compounds has been demonstrated on the deposition of ferroelectric PZT films. In the proposed approach, PZT film formation on graphite and carbon fibre mat substrates was achieved via a peroxoprecursor. It was established that the atomic ratio of lead, zirconium and titanium in the deposit closely corresponded to that in the starting solutions. Formation of a perovskite PZT phase was observed at 500°C. By variation of current density and deposition time the amount of the deposited material could be controlled. It was established that films obtained from solutions with hydrogen peroxide as an additive showed less tendency to crack.

Electrochemical Al2O3–Cr2O3 alloy coatings on non-oxide ceramic substrates

Aqueous solutions of xAl(NO3)3 + (1−x)Cr(NO3)3 were used for electrodeposition of ceramic Al2O3–Cr2O3 alloy coatings on TiC, TiB2 and SiC substrates. Cell voltage and deposit weight were studied as function of deposition duration, current density and electrolyte composition. It was shown that the electrochemical parameters permit simple control of the deposition process. Optimal current densities and deposition durations were determined to obtain maximal deposit weights for different solutions and substrates. Deposits with thicknesses up to 10 μm were formed. The green deposits revealed a crystalline nature for compositions of x < 0.3, and an amorphous nature for x ≥ 0.3, independent of the substrate material. Voltage–electrolyte composition dependencies exhibited an ubiquitous minimum at x ≈ 0.3 to 0.4 independent of substrate type and deposition duration. These minima were attributed to the change in the electrical resistance of the deposit with composition and degree of crystallinity.

A copper-based intrauterine device with gold or platinum core: In vitro and in vivo studies

The use of copper intrauterine contraceptive devices is currently limited to 2-3 years, mainly due to wire fragmentation, which was observed as early as after 8 months of use. In the resulting search for a long-lasting device, two new systems of duplex wire, with gold and platinum cores electrolytically coated with copper, were devised and studied. Initially, duplex wires and controls were exposed to physiological solution. Copper dissolution rate, and corrosion morphology were studied by weight-loss measurements and optical metallography. Similar systems were then surgically implanted in rat uteri for varying periods up to 26 weeks. Electron microanalysis of corrosion products in addition to weight-loss measurements and metallography was performed. The results showed that a uniform and ductile copper coating is obtainable by electroplating on gold and platinum wires. The rate of copper dissolution is similar to that of solid copper wire. No dissolution of gold and platinum in the controls or coated wires was detected by weight loss, metallography or atomic absorption measurements. Microanalysis of the deposits and corrosion products on the wires in the uterine environment showed the presence of compounds containing sulphur, chlorine, calcium and copper. The results of this study suggest that supplementing IUDs with copper-coated gold or platinum wires may result in significant prolongation of the life-span of the device by preventing uncontrolled loss of copper caused by wire fragmentation.

Grain-refined recrystallized 14-carat gold alloy

Prevention of excessive grain growth during annealing treatments is important for jewellery applications of gold alloys. The beneficial effects of small amounts of a number of metals of high melting points and low solubilities in gold to dental gold alloys are well known. Some of these elements, and others, have been added singly or in combinations, to a 14-carat gold jewellery alloy and their effects on grain size, on recrystallization, and on the formation of ‘orange peel’ during subsequent cold working have been studied. Possible mechanisms by which grain refining during solidification and annealing is brought about by small additions of certain elements are discussed in the light of the data obtained.

Symposium on Jewellery Manufacturing Technology, Santa Fe, USA

The second Santa Fe Symposium on Jewellery Manufacturing took place on 21-24 September 1988. It was organized by Dave Schneller of Vimar Corp., Boulder Co., and E. Bell of Rio Grande, Albuquerque, New Mexico. The main objectives of the Symposium, as stated by the organizers, were to provide a forum for the presentation to jewellery manufacturers of the results of research performed in academic and industrial institutions to promote scientific approaches to problem solving in this industry, and to encourage the exchange of experience and know-how among attendees.The lectures presented at the Symposium represent three aspects of jewellery manufacturing: raw materials, processes and safety. The aspect of raw materials was dealt with in four papers presented by Dr. Ch. Raub and D. Ott from the Precious Metals Institute (F.E.M.) in Germany, and by researchers from Leach & Garner Co. in the U.S. Dr. Raub discussed the historical development of jewellery alloys beginning with those used by ancient goldsmiths, through the recipes of a 12th century monk and up to modern alloys. His talk was based on papers published in Gold Bulletin from 1968 to 1987. J. Deroner and R. Carrano from Leach & Garner Co. presented their work on the effect of common additives (Si, B, Co and Ir) on the properties of two 14 carat castings alloys. The properties studied were form filling, strength, hardness, grain refining, surface roughness and porosity. D. P. Agarwal and G. Raykhtsaum also from Leach & Garner, discussed the enhancement and measurement of colour in jewellery alloys. They presented the basic principles of quantitative colour measurement, the effects of various alloying additives on colour, the limits of the range of colours which could be achieved in 14 carat alloys, and showed how colour could be used as a measurable criterion in studies of tarnishing, heat treatment and phase composition. D. Ott presented a most detailed discussion of the properties of investment and of their testing. He discussed the effect of water content on setting time, strength, permeability and surface roughness of the investment. He also described methods used for measuring properties of the slurry (such as viscosity) as well as properties of the mould (such as strength and gas permeability). A variety of jewellery manufacturing processes were discussed at the Symposium. Casting, the dominant process in jewellery production, was the subject of several lectures. D. Ott surveyed in detail the casting methods used, their principles, relative advantages and the effect of process variables on product quality. L. Diamond (private consultant) presented an original approach for determining the solidification time for various jewellery items. He applied the Chervanov equation and suggested that the area of an item could be determined by measuring the amount of nickel plated out on it as compared to the amount plated out under the same conditions on a known surface area. J. Nielsen from Polytechnic University New York, who has pioneered research on the casting of gold alloys for many years, discussed the application of controlled solidification in casting of jewellery. E. Bell of Rio Grande Co. presented his ideas on how to produce a temperature gradient in the casting flask for directional solidification. He also reported results on experiments on the heating and cooling characteristics of investment molds. Sheet and wire production was discussed by W. Kilgore from James Avery Craftsman Inc. in a lecture entitled The Fabrication and Quality Assurance of 14 Carat Gold and Sterling Silver Sheet and Wire for Jewellery Products. Kilgore emphasized the origins of defects likely to arise in the various production steps, and the related process control parameters. The finishing of jewellery received considerable attention in papers dealing with electroplating, electropolishing, chemical polishing (bombing) and mass media finishing. Ch. Raub surveyed the early development of jewellery plating in the 19th century, the importance of substrate surface quality, pretreatment, intermediate layers, and of electrolyte variables. He emphasized the need for specifications in jewellery plating, similar to those for precious metal plating in the field of electronics. The electropolishing of gold alloys was discussed by L. Gal-Or from the Center of Noble Metals in Israel. Applications in jewellery finishing, and advantages and disadvantages as compared with mechanical polishing were presented. Also, the mechanism, composition of solutions, and process variables were discussed. D. Schneller from Vimar Corp. presented two lectures on chemical polishing (bombing) at room temperature. This process, widely practiced in the U.S., is based on a violent reaction between KCN and H202. In his first lecture, Schneller discussed the safety hazards of this process and the methods to counteract them. In his second lecture he analyzed the process variables such as CI\I and H2O concentrations, pH and mixing procedures, and recommended rinsing stages. Mass media finishing was discussed in detail by S. Nigro from Rio Grande Co. He surveyed media types, shapes and sizes, explained the functions of compounds and considerations to be taken into account when selectiing equipment. He dwelt at length on the interrelationships between those variables. Recovery of gold from cyanide solutions such as spent plating and bombing baths was discussed by L. Gal-Or. Mechanisms and kinetics of electrochemical and chemical deposition by dissolution of aluminium were presented. E. Salomon from Armbrust Chain Co. lectured on An Economic Approach to Waste Minimization and Environmental Risk Reduction in Electroplating for the Jewellery Industry. He discussed ways to minimize waste based on efficient use of water, described waste disposal methods and reported studies on waste generation in 10 jewellery plants in Rhode Island. Safety in jewellery manufacturing was one of the main subjects of the Symposium, J. Bellows from the California Department of Health Services presented A Survey of Hazards in the Jewellery Industry. He enumerated the hazards in the various stages of jewellery production, which he considers a most hazardous industry. His talk was based on a survey conducted in 15 companies in the Los Angeles area during which air sampling, and interviews with workers and employers were performed, D. Schneller discussed cases of cyanide poisoning, available antidotes and safety measures to be taken. P. Pryor from the U.S. Public Health Service presented a talk on Silica Hazards and Safety Procedures in the Handling of Investment. He explained the conditions that lead to silicosis, and means for protection against it. He also presented the results of a study he had performed on the concentration of Si02 in the air at different stages of investment handling. An interesting lecture on Technology Transfer was presented by A. Tasker from the World Gold Council. He discussed the application of CAD-CAM in dentistry and its potential application to jewellery manufacturing. The lecture also included data on the properties and development of the l%Ti-99%Au alloy and an analysis of black dermographism (inclusion of metallic particles in the skin) as related to jewellery wear. Proceedings of this Symposium will be published in the near future; tapes of the lectures are available as well as last years proceedings from: Santa Fe Symposium, 6801 Washington N.E., Albuquerque, NM 87109.