DECLINE OF IRON

Greymouth Evening Star, 16 February 1937, Page 3

DECLINE OF IRON

TREMENDOUS ANNUAL WASTE.

The use of metals is one of the characteristics of civilisation, says a writer in the Melbourne “Age.” It has increased tremendously in the last century, and is accelerating. In the hundred years from the Napoleonic wars until the outbreak of the World War the white population of the world increased threefold. In the same time the output of tin increased twentysix times, of copper sixty-three times, of iron over one hundred, times. The ores of these metals are not inexhaustible, and it is the duty of the chemist to minimise corrosion in every possible way, so that we may lose as little, of these precious elements by the process of oxidisation or other forms of attack.

Sir William Hadfield has estimated that 29,000,000 tons of steel are rusted away annually, and irrevocably lost to industry, and already the ironmasters are viewing with anxiety the prospective exhaustion of the supply of high-grade ores, containing more than 50 per cent, of the metal. The utilisation of lower-grade ores is becoming imperative, and it is fortunate, that these are magnetic, for a process of magnetic concentration of the ironbearing particles seems to offer considerable hope that they may be made available to the smelter.

Having once secured your iron, what steps can be taken to ensure its freedom from rusting? A coat of paint is the first solution, and corrosion-re-sisting paints have been greatly improved in recent years. But the painting of large structures is a big and continuous job; the Sydney Harbour Bridge, for example, is being painted all the time, ami when after six years the painters have completed their task of covering every foot of metal in the huge span, they have straight away to return to the beginning and start again. OFFERS POSSIBILITIES,. A recent process devised by Dr. Blom, a Swiss chemist, offers possi- ' bilities. He prepares a special paint [containing oxide of lead with which I is mixed very finely-divided particles of the metal itself. These specks of lead gradually penetrate the surface of the iron, and confer upon it an immunity to rust which appears to be permanent. It. is in the production of alloys, however, that most progress has been made, and here the chemist seems to have made a real advance. Chromium has been the element which has come to the assistance of the metallurgist in his search for a rustless steel. In the proportion of 12 to 11 per cent, together with a quarter to two-fifths pet cent, of carbon, it gives us the stain less steel so widely used in cutlery Special heat treatment yields an al loy of iron and chromium containing in solution carbides of the two metak and very bard and resistant to abras ion as well as to corrosive influences Rustless iron, containing not more than one part of carbon in a thousam is softer than stainless steel, and cat ■ be worked cold. The rapidly increas . ing use of chromium ores has beer offset by the discovery of extensivt ’ deposits in Rhodesia. Nickel is another metal which al

toys with iron to form corrosion-re-sisting metals, whilst in combination with copper it is extensively used under the name of Monel in all forms of industrial plant. Other metals, particularly vanadium, are used in special steels, but with the object of hardening them, or rendering them heatresistant, rather than with the view of preventing rusting. In 1926 it was. estimated that onehalf of the copper, one-third of the lead, and two-thirds of the tin used in America were reclaimed from the junk pile, whilst 35 per cent, of the charge in the open-hearth furnaces consisted of scrap steel. The chemist' plays a large part in these economies, but must still seek further methods of reclamation. Zinc used for galvanising, and in the form of pigments is all lost, as is the lead in lead paints. A really satisfactory process for recovering the thin coating of tin from the tin can has yet to be worked out. x If we are rapidly exhausting the available supplies of the older metals, we are more than compensating for this by the production of the newer ones. Aluminium as an industrial metal is barely fifty years old, yet it has already taken its place as one of the most important. Charles Martin Hall discovered in 1886 the method of electrolysing a solution of aluminium oxide in molten cryolite, itself an aluminium mineral, the process which is the basis of the production of the metal to-day. In 1888 he produced 501 b of metal a day. at a cost of 2 dollars a lb.; by 1911 his production had reached 40,000,0001 b a year at 22 cents a lb.

ALUMINIUM EXPENSIVE

Aluminium is still too expensive. The raw material is still the mineial known as bauxite, the supply of which j is limited. But. 8 per cent oi the crust of the earth is aluminium ami | there is no doubt whatever that in time the chemist will solve the problem of producing it cheaply from ordinary clay and then iron may be displaced from its position as the most important metal. We can already heat-process aluminium so that it has the ductility and strength of mid steel, and we are on the very threshold of its introduction as a constructional material. Duraluminium has been used in aeroplanes and airships; magnaliiim. an alloy with magnesium, is as light as aluminium and nearly as strong as steel. Vanalium, its alloy with vanadium. is tough and resistant. and seems to offer unbounded possibilr, ties. Aller aluminium and iron, niagne..' ium is the most plentilul constituent of I he earth's crust. Long known only as the basis of (lie photographer’s flashlight, magnesium metal is now competing even with aluminium in many applications where strength and lightness are essential. One particular aeroplane engine has seventeen different parts made of magnesium castings, and it has also proved successful for propellers. The great advantage of these newer metals is that they are virtually non-corrosive under ordinary conditions. Perhaps it would be better to say that they are self-protective, for exposure to the air instantly produces a very thin, but hard and resistant coating of oxide, which protects the metal beneath from

further attack. If bronze was the metal of a bygone age and iron is the metal of today. aluminium and magnesium are certainly the metals of to-morrow. Their applications are growing daily, and the predominance is only a matter of time.