Metals

Gold

What is gold

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Because gold is an element, a piece of pure gold contains nothing but gold atoms.

(Elements & Compounds)
Gold is a dense inert bright yellow element that is the most malleable and ductile metal, occurring in rocks and alluvial deposits: used as a monetary standard and in jewellery, dentistry, and plating.

The radioisotope gold-198 (radiogold), with a half-life of 2.69 days, is used in radiotherapy.

Symbol: Au; atomic no: 79; atomic wt: 196.96654; valency: 1 or 3; relative density: 19.3;

melting pt: 1064.43°C;

boiling pt: 2857°C.

Because pure gold is very soft and easily marred, it is often alloyed with other metals to make jewelry, coins and other precious objects.

18k Gold is 750 parts fine gold with 250 parts alloy . see our Alloy page

Adding alloy allows it to be coloured such as Red, Pink, White and Green. and allows it to be harden

Silver

The chemical symbol for silver is Ag, from the Latin argentum, which means white and shining

screen-shot-02-12-17-at-09-38-pmSilver was one of the earliest metals known to humans, and it has been considered a precious metal since ancient times.
it is usually found in ores with less rare metals, such as copper, lead, and zinc, silver was apparently discovered in nugget form, called native silver, about 4000 B.C. Silver is the whitest metallic element. It is rare, strong, corrosion resistant,

it does react with sulfur, which is always present in the air, even in trace amounts. The reaction causes
silver to tarnish, therefore, it must be polished periodically to retain its luster

Pure silver, which would be too soft to be durable, is mixed with 5-20% copper in an alloy known as sterling silver.

The Manufacturing
Process
Silver was first obtained in sixteenth-century Mexico by a method called the patio process. It involved mixing silver ore, salt, copper sulphide, and water. The resultant silver chloride was then picked up by adding mercury. This inefficient method was superseded by the von Patera process. In this process, ore was heated with rock salt, producing silver chloride, which was leached out with sodium hyposulfite. Today, there are several processes used to extract silver from ores.
A method called the cyanide, or heap leach, process has gained acceptance within the mining industry because it is a low-cost way of processing lower-grade silver ores. However, the ores used in this method must have certain characteristics: the silver particles must be small; the silver must react with cyanide solutions; the silver ores must be relatively free of other mineral contaminants and/or foreign substances that might interfere with the cyanidation process; and the silver must be free from sulfide minerals. The idea for cyanidation actually dates back to the eighteenth century, when Spanish miners percolated acid solutions through large heaps of copper oxide ore. The process developed into its present form during the late nineteenth century. The cyanide process is described here.
Preparing the ore
1 Silver ore is crushed into pieces, usually with 1-1.5 in (2.5-3.75 cm) diameters, to make the material porous. Approximately 3-5 lb (1.4-2.3 kg) of lime per ton of silver ore is added to create an alkaline environment.

The ore must be completely oxidized so the precious metal is not confined in sulfide minerals. Where fines or clays exist, the ore is agglomerated to create a uniform leach pile. This process consists of crushing the ore, adding cement, mixing, adding water or a cyanide solution, and curing in dry air for 24-48 hours.
2 Broken or crushed ore is stacked on impermeable pads to eliminate the loss of the silver cyanide solution. Pad material may be asphalt, plastic, rubber sheeting, and/or clays. These pads are sloped in two directions to facilitate drainage and the collection of the solutions.
Adding the cyanide solution and curing
3 A solution of water and sodium cyanide is added to the ore. Solutions are delivered to the heaps by sprinkler systems or methods of ponding, including ditches, injection, or seepage from capillaries.
Recovering the silver
4 Silver is recovered from heap leach solutions in one of several ways. Most common is Merrill-Crowe precipitation, which uses fine zinc dust to precipitate the precious metal from the solution. The silver precipitate is then filtered off, melted, and made into bullion bars.
5 Other methods of recovery are activated carbon absorption, where solutions are pumped through tanks or towers containing activated carbon, and the addition of a sodium sulfide solution, which forms a silver precipitate. In another method, the solution is passed through charged resin materials which attract the silver. The recovery method is generally decided based on economic factors.
Silver is rarely found alone, but mostly in ores which also contain lead, copper, gold, and other metals which may be commercially valuable. Silver emerges as a byproduct of processing these metals. To recover silver from zinc-bearing ores, the Parkes process is used. In this method, the ore is heated until it becomes molten. As the mixture of metals is allowed to cool, a crust of zinc and silver forms on the surface. The crust is removed, and the metals undergo a distillation process to remove the zinc from the silver.
To extract silver from copper-containing ores, an electrolytic refining process is used. The ore is placed in an electrolytic cell, which contains a positive electrode, or anode, and a negative electrode, or cathode, in an electrolyte solution. When electricity is passed through the solution, silver, with other metals, accumulates as a slime at the anode while copper is deposited on the cathode. The slimes are collected, then roasted, leached, and smelted to remove impurities. The metals are formed into blocks which are used as anodes in another round of electrolysis. As electricity is sent through a solution of silver nitrate, pure silver is deposited onto the cathode.

Read more: http://www.madehow.com/Volume-3/Silver.html#ixzz4YVdTfmqq

Platinum

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Platinum is a heavy, grayish-white, highly malleable and ductile metallic element, resistant to most chemicals, practically unoxidizable except in the presence of bases, and fusible only at extremely high temperatures: used for making chemical and scientific apparatus, as a catalyst in the oxidation of ammonia to nitric acid, and in jewellery. Symbol: Pt; atomic weight: 195.09; atomic number: 78; specific gravity: 21.5 at 20°C.

It has a light, metallic gray with very slight bluish tinge when compared with silver.

Called the “King of Metals”, platinum is a very heavy (nearly twice the weight of gold), silver-white metal that is very ductile. Although it is a soft metal, platinum is not easily scratched and is very strong and durable. In fact, as the strongest precious metal used in jewelry, platinum also has a high melting point and good resistance to corrosion and chemical attack. Small amounts of iridium and ruthenium are commonly added to it, to give it a harder, stronger alloy that retains the advantages of pure platinum. The platinum family actually comprises six metals: platinum, palladium, iridium, osmium, rhodium and ruthenium. The six metals are generally found together in nature, with platinum and palladium being the most abundant, and the other four being more rare.

Palladium

Palladium, a precious metal, belongs to the same chemical family as the much better-known metals platinum and rhodium. screen-shot-02-12-17-at-09-56-pmFound alongside platinum, palladium is similar in color to platinum–white-silver in appearance. It is lighter than platinum, but durable enough for jewelry applications.

Palladium has much in common with its sister metal, platinum. In jewelry alloys, it is 95 percent pure, similar to platinum. Its true, white-silver appearance rarely tarnishes and needs no plating to retain its color.
It is the areas where palladium diverges from platinum that makes this metal attractive to jewelers and consumers alike. A much lighter metal than platinum, jewelers can cast palladium in much more intricate fashions. Its lighter weight also means it is less expensive. In other words, it retains platinum’s appearance, while resolving the two issues that made platinum out of reach for many consumers–weight and price

Two factors, however, contributed to the disappearance of palladium on the jewelry market during the last half of the 20th century. These were the difficulty to create a palladium alloy for mass-market jewelry, and the increasing popularity of gold jewelry.



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