Posts Tagged ‘South Africa’
Palladium – The Other White Precious Metal
Palladium, not to be confused with platinum, is one of a group of white precious metals that can be used for a variety of commercial applications (i.e. computers, mobile phones, dentistry, medical equipment, fuel cells) as well as in the manufacturing of beautiful pieces of fine jewelry. Most palladium today, however, is used in the manufacture of automobile catalytic converters.
Palladium, named after the asteroid Pallas, was first discovered in 1803 by William Hyde Wollaston. Palladium is a rare metal with the largest deposits found in South Africa, Montana, Canada, and Russia.
The first recorded use of palladium in jewelry was in 1939 as an alternative to platinum or white gold. This precious metal provides the contemporary look of a white metal. Unlike white gold, palladium is naturally bright white and its color will never fade. Palladium has a low melting point but becomes very strong when cooled, making it a good alternative to softer white metals. It can be hammered into very thin leaves just like gold, and can, in fact, be used in the production of white gold.
Palladium offers many of the desirable traits of platinum at a terrific price, considered a fashionable, affordable choice for custom jewelry. The metal is 40% lighter, harder and less expensive than platinum and provides a hypoallergenic metal suitable for those with nickel sensitivities.
Until recently, the use of palladium in jewelry has been limited due to the difficulty of casting this metal. Recent advances, however, have produced a new alloy of palladium that is perfectly suited for jewelry manufacturing, offering consumers an ideal substitution for platinum at a reasonable cost. The most common combination of the metal is 95% palladium and 5% ruthenium, known as 950 Palladium.
Palladium settings are preferred over gold for extra large diamonds and gemstones, since the metal is more durable than gold and less likely to incur damage during every-day wear. Many customers who opt to wear their fine jewelry selections daily prefer the lighter feel of palladium. Larger earrings and necklaces made of palladium can be worn comfortably all day.
If you have found that you are allergic to other types of metals, you may find that palladium is just what you have been looking for. It is a hypoallergenic metal, meaning it won’t leave you itching or with a rash where it touches your skin. Since many pierced earring wearers are especially sensitive to some metals, finding studs, hoops and posts that are made of palladium can truly make wearing earrings fun again.
The Chinese have historically been the biggest buyers and producers of palladium jewelry. However, the advances in palladium casting techniques and recent escalation in gold and platinum prices are driving an increasing demand for palladium fine jewelry around the world. The demand is expected to continue to increase as many consumers discover the beauty, durability, and lightness of this lustrous white precious metal. As a result, there is an increasing availability of palladium jewelry in jewelry stores around the world, especially wedding bands and engagement sets, in jewelry stores around the world.
Posted in Metal Casting | 
Tags: Amy Carrington, asteroid pallas, Canada, gold palladium, Jewelry, Metal, Montana, Palladium, Pallas, Precious, Russia, South Africa, White, William Hyde, william hyde wollaston | 
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The Zinc-aluminium Die Casting Alloys
The zinc-aluminium die casting alloys
New high performing zinc-aluminium ZA casting alloys (zA-8, ZA-12, ZA-27) give superior mechanical properties which designers can apply utilizing die casting technology. In general the ZA alloys are stronger, harder and offer more creep resistance than standard zinc alloys and can be used where bearing properties are important.
Aluminium alloys with 0.5-0.9% Fe content have largely replaced 1350 EC alloy for making electrical circuits because the latter continuously suffered from gradual loosening at terminals, which led to overheating. This problem has been totally removed in new conductor alloys without sacrifice of conductivity.
To get economic benefit of weight advantage of aluminium wire should be capable of attaching securely to standard fixtures without special handling techniques. But EC wire on binding screw terminals tightened to a standard torque may become loose, when the wire heats due to being overloaded. The wire gets expanded more than the Cu-alloy fixture and creeps to relax the added stress.
On getting cool it contracts to a smaller dimension, whereby the area of contact is reduced and it permits oxide to form at interface. On a subsequent current overflow, the overheating increases which leads to further loosening of wire. EC wire annealed for adequate bend ability gets sub structurally loosened at 200°C and ultimately fails due to repetitions of these cycles.
The new alloys (800 series) of 0.5-0.9% Fe have much better microstructural stability and creep resistance and, therefore, they are not prone to these failures.
While annealed to the same ductility or bend ability, the high Fe alloys are double strong. This capability has been established by practical field use of many years in USA, Europe and South Africa after these alloys were introduced in 1968.
Better and latest alloys which not only provide high integrity to terminations but are suitable for magnet wire after normal hot annealing have been made after adding a third alloy to improve its performance examples are 0.5% Fe with 0.5% Co and 0.5% Fe with 0.2-0.4% Si.
Processing and microstructure:
In continuous casting a bar of 50cm2 is made at 16 m/min on a 2.5m diameter copper wheel. The quick solidification results in a 20 μm dendrite arm spacing and eutectic red cpacing of about 0.2 μm with a supersaturation of about 0.1% Fe. These very fine particles play a significant role in giving stability to substructure while being incapable of nucleating crystallization.
The presence of sub grains has been known in hot worked aluminiums but without quantitative determinations of the dimensions or the effects on properties. As the temperature rises from 200-450°C, the cold yield strength of the hot worked product decreases greatly from the strengthening made by 97.5% cold rolling.
As has been seen in many hot worked metals, the yield strength is inversely proportional to sub grain diameter. Because the temperature is less and strain rate is high in a given pass than those in the previous one, substructure “inherited” from i.e., carried forward from, the latter is altered by dislocations to the existing walls to raise their density and by formation of new walls to subdivide the sub grains lessening their size.
Posted in Small Business |
Tags: aluminium alloys, die, Europe, South Africa, Steve Manik, sub, USA, wire, za alloys, zinc alloys |
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