Powder Metallurgy

The traditional methods of shaping metals by casting or by hot or cold working are difficult and sometimes impossible to apply to many metals. Such refractory metals include tungsten (m.p. 3380°C), molybdenum(2622°C) and tantalum (2996°C) whose melting points are too high to enable them to be melted by conventional means. In these cases an alter­native procedure has emerged based on the fact that metals in powdered form may be caused to adhere together without being melted by employ­ment of high pressure. The technique known as powder metallurgy con­sists in subjecting the powdered metal contained in a mould or die of the shape desired to a high pressure followed by sintering at a suitable tem­perature. The method provides either finished metal components or com­pact blocks of metal for subsequent mechanical working. Having been applied first to the refractory metals the method has been extended to many of the more tractable metals.

The technique originated more than a century ago. The prepara­tion of compact platinum from the then infusible metal by W.H. Wollas-ton in 1830 represents one of the earliear applications of powder metal­lurgy.

Production of powder of the requisite properties is an important stage in the procedure of powder metallurgy. Powders of metals and alloys may be produced by mechanical methods such as grinding, machining and milling; other metal powders can be obtained by reduction of the metal oxide by hydrogen or carbon. Copper, iron, cobalt, molybdenum and tungsten can all be so prepared in powder form from their oxides. Electrolysis is also used, and aluminium, tin, and lead are transformed into powder form by atomization, molten metal being poured through an orifice into a chamber and sprayed with a high pressure jet of inert gas, the instantaneous chilling converting the metal into a finely divided dust.

At the present day powder metallurgy is mainly used in making large numbers of identical components usually of relatively small size, such as permanent magnets, coins, medals, small gear wheels and brushes for motors and dynamos. A novel extension of its application is in the manufacture of the oilless bearing which can be impregnated with oil and made self-lubricating. Such bearings are designed to retain with­in their structure a sufficient amount of oil to last for several years.

Metallurgy in Canada

Look through the text and find answers to the following questions:

1. Is Canada rich in mineral resources?

2. When did people start searching for gold in Canada?

3. Was their search for gold a success?

4. What branch of metallurgy is of vital importance for Canada?

5. Will it be possible to avoid atmospheric pollution by developing a hydro-metallurgical method for the commercial production of copper?

Canada is richly endowed with mineral wealth: it ranks among the world's largest producers of minerals. A great deal of Canada's history is closely entwined with mineral exploration and development, beginning with Frobisher's search for illusory gold in the 16th century. Coal in Nova Scotia and iron ore in Quebec were discovered and later mined in the 17th and 18th centuries. The Geological Survey of Canada founded in 1842, encouraged the collection of information about Canada's minerals. In the next decade came the first gold rush - to Barkerville in the Cariboo district of British Columbia. Silver, zinc and lead were subsequently found in the Kootenay district, as well as the riches in copper and nickel.

The most famous event in Canadian mining history undoubtedly was the Klondike gold rush of 1896, but more significant have been the dis­coveries in the 20th century of cobalt, silver, uranium, asbestos and potash among other minerals, as well as more copper, nickel and iron ore.

The production of steel is vital to the development of all sectors of the Canadian economy, including energy. There are three separate projects that are attempting to circumvent the need for the blast furnace and dependence on coking coal. One steel company has developed the rotary kiln process for the direct reduction of iron ore. Another is operating a pilot plant at Niagara Falls, Ont., on a rotary kiln process, also for direct reduction of iron ore. The Metals Reduction and Energy Centre of the Department of Energy, Mines and Resources (EMR) has successfully demonstrated a process called the Shaft Electric Reduction Furnace (SERF), which utilizes the waste gases from an electric reduction furnace to preheat and pre-reduce iron ore.

Two mineral processing companies have co-operated on a multi-million dollar, multi-year project to develop a hydro-metallurgical method for the commercial production of copper. This technique would avoid atmospher­ic pollution which typifies copper smelters, and be environmentally acceptable. Moreover, the process would recover sulphur, rather than hav­ing it emitted to the environment. The successful commercialization of this process would give Canada a strong position in copper production in an era when environmental concerns are forcing restrictions on the tradition­al smelters.