TECHNOLOGY water scrubbed and treated b y a wet Cottrell before it is converted into liquid sulfur dioxide b y Canadian Industries ( 1 9 5 4 ) Ltd. T h e production of liquid sulfur dioxide involves drying the cleaned gas with sulfuric acid, then compressing and cooling the gas to condense the sulfur dioxide. Using gas from this furnace and other smelter units, Canadian Industries (1954) Ltd. says that last year it produced approximately 70,000 tons of liquid sulfur dioxide for use b y the Canadian sulfite
pulp industry as well as about 65,000 tons of 100% sulfuric acid. International says the low-cost oxygen which makes the process economically possible is produced by a tonnage oxygen unit known as Oxyton, which was built for International by Canadian Liquid Air. This unit is said to produce 3 2 5 tons of 95% pure oxygen every 2 4 hours, corresponding to 2 2 / s billion cubic feet of oxygen per year, or three times the production of all the cylinder oxygen plants in Canada.
Titanium Goes to Prison Westinghouse purifies titanium a n d other hard-toget metals by imprisoning them inside self-made cages \Srr ESTINGHOUSE Electric has come up
* ^ -with a n e w refining process to purify titanium and other hard-to-get metals. The process, called cage zone refining, allows a bar of metal to act as its own crucible while melting thus preventing contamination b y any containing vessel. T h e n e w technique is applied to metals which are so active at high temperatures that they react with any sort of a crucible. Ordinary zone refining is melting a bar progressively from o n e end to the other. At Westinghouse, it is a standard process for purifying certain metals. T o prepare germanium metal having impurities of about o n e part in 10 billion, the process is used routinely at Westinghouse. The process capitalizes on the fact that most impurities in metals have a preference for either the liquid or solid state of the metal. With titanium, iron is a common impurity and it has a preference for liquid titanium over the solid metal. When a bar of impure titanium is melted progressively from e n d to end, the iron concentrates in t h e liquid titanium and remains there as the solid metal freezes out behind it. Therefore, the iron is swept to one end o f the bar as the molten zone moves along. Each time the process is repeated, more iron is carried to the e n d of the bar. This end then is cut off and discarded, leaving the rest of the titanium bar more pure. The heating is done electromagnetically by passing the bar through a coil which carries high-frequency alternating current. At titanium's melting point, over 3000° F., it reacts chemically with the air and with metal, graphite, o r ceramic containers. The n e w Westinghouse cage zone processing is claimed to eliminate such sources of contamination during its refining. 1968
Westinghouse makes its n e w technique work by standing a square bar of impure titanium on end on a metal platform. The platform is slowly raised lifting the bar lengthwise through the heating coil. A high-frequency current at 10,000 cycles per second flows in the coil and induces large eddy currents inside the bar. These eddy currents, flow against the electrical resistance of the metal, causing t h e bar to melt from the inside. T h e four corners of the bar are less affected b y the induced currents and rapidly lose what heat they possess to the surrounding atmosphere. Therefore, the corners do not melt, but act as a cage within which the molten titanium is imprisoned. According
to Westinghouse, tlie molten zone moves along inside its cage a s the metal bar progresses througL· the heating coil. After t h e impurities are concentrated at t h e end of the bar, this end and the impure corners are c u t away. In one variation of t h e new Westinghouse process a roundl bar i s machined so that several ridges or fins run lengthwise along its surface, rnuco like those on the fluted columns of certain buildings. These unmelted. ridges then form the cage and since trxey can be placed at will, says WestingoOuse, they permit longer bars of larger diameter to be purified. Westinghoiose scientists foresee the techniques being applied to bars as much as three inches in diameter and of any desired length. Cage zone refining, was developed by P. H. Brace, consulting metallurgist; A. W . Cochardt of tJae metallurgy department, and George Comenetz, advisory engineer to the metallurgical consulting staff of the Westinghouse Labs. Commenting o n t h e significance of the n e w development, Clarence Zener, associate director of Westinghouse research labs and manager of die metallurgy department, says, "the metallurgy of many important metals such as titanium is still i n i t s infancy. Much basic research on these pure metals is needed before w e c a n begin to realize their potential applications. W e hope this n e w refining method -will enable us t o speed such research b y providing increased quantities of those metals which are especially difficult to prepare in a highly purified state."
In an inert atmosphere of argon oi helium gas inside the bell jar, the titanium bar rises vertically through the heating coil and melts progressively from top to bottom. Impurities, such as iron, dissolve in the molten metal and are swept to the bottom of the bar. George Comenetz, advisory engineer at Westinghouse here checks the temperature of molten zone of titanium with an optical pyrometer CHEMICAL
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