A Versatile Metal —- Titanium


Titanium was discovered in the form of titanium oxide from black magnetic iron placer by the British mineral fan W. Gregor in 1789. In 1795, German chemist M. Klaproth found that this is an oxide with new element in the study of rutile; two years later, he confirmed that the oxide is what W. Gregor had found, and named the new element of it as titanium. Titanium has excellent heat resistance with melting point up to 1,725°C. At room temperature, titanium can coexist with a variety of acid and alkali solution. Even aqua regia —- the acid with strong corrosive is unable to corrode it.

Titanium is hard to react with sea water. Once titanium is sunk to the sea; it is not rusty and still shiny excluding many small undersea animals and plants five years later. Now, people begin to produce submarines with titanium —- titanium submarines. Because titanium is too strong to withstand high pressure, such submarines can sail at a depth of 4,500 meters in the deep sea. With its corrosion resistance, titanium is often used in the chemical industry. In the past, chemical reactor parts with hot nitric acid are usually made by the stainless steel. As stainless steel is also corroded by the strong corrosive —- hot nitric acid, all such parts must be replaced every six months. Now, although the cost of the parts manufactured with titanium is more expensive than that of stainless steel, it can be used continuously years so that it is much more worthwhile.

The biggest drawback of titanium is difficult to extract, because titanium is easy to compound with oxygen, carbon, nitrogen compounds and many other elements at a high temperature. Therefore, regardless of in the process of the smelting or foundry, it must be careful to prevent these elements from reacting with titanium. In the smelting of titanium, air and water are strictly prohibited close to it, and even common metallurgical alumina crucible also prohibited, because titanium would wrest oxygen from alumina oxide. Now, the titanium’s extraction can be achieved by the reaction of magnesium and titanium tetrachloride in an inert gas —- helium or argon. In steelmaking, nitrogen is easily dissolved in the molten steel; when steel ingots cooling, there are bubbles in the steel ingots, affecting the quality of steel. Therefore, steelmakers put metal titanium into the molten steel so as to make it compound with the nitrogen; then it will obtain a slag —- titanium nitride which floats on the molten steel surface; finally the ingot is more pure.

When a supersonic aircraft is flying, its wing temperature can reach 500°C. Even the wings made by a relatively heat-resistant aluminum alloy may not withstand such high temperature. And there must be a light, tough and high-resistant material instead of aluminum alloys, while aluminum alloy titanium B just meets these requirements. Titanium can withstand the test of minus 140°C. At such low temperatures, it still has good toughness rather than fragileness. Titanium and zirconium have strong absorption capacity of air so that they can absorb air resulting in a vacuum. For example, a vacuum pump made of titanium can absorb air to one out of ten thousand.

Titanium dioxide, a white powder, is the best white pigment. Previously, the main purpose to mine titanium ore is to obtain titanium dioxide. Titanium dioxide has strong adhesion; chemical change is not easy; and it is always white. Titanium dioxide without toxicity is especially valuable. With high melting point, it is used to make fire-resistant glass, glaze, enamel, clay and other heat-resistant labwares.

Metal powder such as titanium powder and titanium alloy powder is an important raw material of laser rapid prototyping technology. This technology melts deposition layer by layer through laser (“Growing Manufacturing”), with “near net shape” of high-performance large-scale overall structure done directly by CAD models. Compared with traditional manufacturing techniques, laser rapid prototyping technology has significant technical advantages. Laser rapid prototyping technology is a high-tech developed in the 1980s, which makes use of technologies such as laser, CAX, automatic control and new material to directly model and rapidly manufacture a product model. Laser rapid prototyping technology has changed the traditional “remove” molding process to adopt “stacked” molding process, which has great significance in the processing areas. Currently, laser rapid prototyping technology is mainly used in the aerospace, automotive, toy manufacturer and other industries.