Palladium alloys

In dentistry, palladium alloys are widely used as alternatives to base metal alloys in the manufacture of crowns and bridges as weU as the replacement of lost or damaged teeth (see Dental materials). Such alloys contain over 80% palladium, and hence offer significant cost benefits over alloys containing a high proportion of gold. 

Palladium and Palladium Alloys. Palladium is not used in the pure state in dentistry. However, it is a usehil component of many gold casting alloys, as shown in Tables 6 and 7. 

In addition to the metals Hsted above, many alloys ate commercially electroplated brass, bronze, many gold alloys, lead—tin, nickel—iron, nickel—cobalt, nickel—phosphoms, tin—nickel, tin—zinc, ziac-nickel, ziac-cobalt, and ziac-iron. Electroplated alloys ia lesser use iaclude lead—iadium, nickel—manganese, nickel-tuagstea, palladium alloys, silver alloys, and zinc—manganese. Whereas tertiary and many other alloys can feasibly be electroplated, these have not found commercial appHcations. 

Palladium and Palladium Alloys. Palladium is used in telephone equipment and in electronics appHcations as a substitute for gold in specific areas. Palladium is plated from ammoniacal and acid baths available along with chelated variations as proprietary processes. One typical alkaline bath uses 8 g/L diammine-dinitropalladium, 100 g/L ammonium nitrate, and 10 g/L sodium nitrite. The pH is adjusted to 9—10 using ammonium hydroxide, and the bath is operated at 100 A/m at 50° C. If ammonium sulfamate, 100 g/L, is used in some baths to replace the nitrate and sodium nitrite salts, the bath is mn at lower temperature, 25—35°C, and a pH of 7.5—8.5. A palladium—nickel alloy, 75% Pd, is plated from a bath having 6 g/L palladium from the same salt, 3 g/L nickel from nickel sulfamate concentrate, and 90 g/L ammonium hydroxide. The bath is operated at 20—40°C with 50-100 A/m/... 

Bessing, C., Bergman, M. and Thoren, A. Potentiodynamic Polarization Analysis of Low-gold and Silver-Palladium Alloys in Three Different media. Dental Materials, 3, 153-159 (1987)... 

Metzger, P. R., Vrijhoef, M. M. A. and Greener, E. H. Corrosion Resistance of Three High-Palladium Alloys , Dental Materials, 1, 177-179 (1985)... 

Silver-copper-palladium alloys with liquidus temperatures of 800-1 000°C have very low vapour pressures combined with good wetting and flow characteristics and are widely employed in vacuum work. They exhibit a lower tendency to stress corrosion than silver-copper, and do not form brittle alloys with other metals. 

The addition of beryllium and silicon to nickel-palladium alloys gives very good high-temperature brazes, especially for alloys containing aluminium and titanium. 

The oxidation kinetics of both gold and palladium alloys as a function of temperature and pressure have been reported by Opara et al and the behaviour of palladium and palladium oxide when heated in gaseous hydrochloride acid at 20-1000° by Ivashentsev and Ryumin . 

In this part of the review palladium alloys refers to those containing more than 40% Pd, i.e. such alloys which are able to form a (3-hydride phase. 

Gold-palladium alloys, see Palladium-gold alloys... 

Savadogo O, Lee K, Oishi K, Mitsushimas S, Kamiya N, Ota K-I. 2004. New palladium alloys catalyst for the oxygen reduction reaction in an acid medium. Electrochem Commun 6 105 109. 

Shao MH, Huang T, Liu P, Zhang J, Sasaki K, Vukmirovic MB, Adzic RR. 2006a. Palladium monolayer and palladium alloy electrocatalysts for oxygen reduction. Langmuir 22 10409-10415. 

Palladium electrocatalysts, 183 Palladium-alloy electrocatalysts, 298-300 Pareto-optimal plot, 85 Platinum-alloy electrocatalysts, 6, 70-71, 284-288, 317-337 Platinum-bismuth, 86-87, 224 Platinum chromium, 361 362 Platinum-cobalt, 71, 257-260, 319, 321-330, 334-335 Platinum-iron, 319, 321, 334-335 Platinum-molybdenum, 253, 319-320... 

The stereochemistry of electrochemical reduction of acetylenes is highly dependent upon the experimental conditions under which the electrolysis is carried out. Campbell and Young found many years ago that reduction of acetylenes in alcoholic sulfuric acid at a spongy nickel cathode produces cis-olefins in good yields 126>. It is very likely that this reduction involves a mechanism akin to catalytic hydrogenation, since the reduction does not take place at all at cathode substances, such as mercury, which are known to be poor hydrogenation catalysts. The reduction also probably involves the adsorbed acetylene as an intermediate, since olefins are not reduced at all under these conditions and since hydrogen evolution does not occur at the cathode until reduction of the acetylene is complete. Acetylenes may also be reduced to cis olefins in acidic media at a silver-palladium alloy cathode, 27>. 

Palladium-based dense metallic membranes have been known to be completely selective for hydrogen permeation and are used in commercially available small-scale hydrogen purification units (e.g., Johnson Matthey, 2007 REB Research, 2007 Power + Energy, 2007 ATI Wah Chang, 2007). These hydrogen purification units typically use palladium-alloy... 

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