Titanium processing technology
Titanium has unique characteristics of low density, high specific strength, high temperature strength, strong corrosion resistance.
As a kind of titanium metal structure, the content in the crust in the fourth row, second only to iron, aluminum, magnesium, nickel, more than the sum of copper, chromium, lead, tin and zinc.
However, the current system of titanium production is very complex, and the cost is high. Titanium is expensive because the metal from ore to refining process is a multi-step batch process, high temperature.
This paper will first describe the current titanium technology, then discuss the four most promising method to reduce the cost of titanium. These methods include Kroll, Hunter, and Cambridge Armstrong method.
1 the current titanium extraction method
The production of titanium metal are from Jin Hongshi (TiO2) began. Rutile and petroleum coke together, at
1000 DEG C (1830 degrees Fahrenheit) temperature, in a fluidized bed reactor by chlorination treatment, to
production of TiCl4.
TiO2 + 2Cl2 + C, TiCl4 + CO2
Production of titanium can also be started from other low cost materials, such as titanium iron ore or slag,
but they contain more iron and other impurities. The liquid TiCl4 was purified, and about 90% of the
oxidation of TiCl4 to TiO2, used in pigment industry.
TiCl4 is a starting point of all business processes. From the two main reasons for TiCl4 start is TiCl4 with
high purity, the titanium and oxygen separation.
2 Kroll method
Kroll and the DuPont Co in 1948 developed compared to the currently used does not change much, it mainly
includes the following steps. Dry and clean stainless steel vacuum evaporator, and argon. Then for reduction
of TiCl4 magnesium into the steamer. The steam is heated to 800 DEG to 900 DEG C (1470 degrees Fahrenheit
to 1650 degrees Fahrenheit), and then TiCl4 slowly into the steamer. Magnesium reduction reaction of TiCl4:
TiCl4 + 2Mg, Ti + 2MgCl2
With the reduction of MgCl2 periodic points out. A few days later, the steamer stop depends on the size,
reaction, steam pressure rise.
At this time, yet about 30% of magnesium reaction. The formation of a similar spongy titanium metal porous material.
Now in the steamer titanium (Hai Miantai), the unreacted magnesium and some MgCl2. These impurities can be
removed by leaching or vacuum distillation. Vacuum distillation by increasing the evaporator temperature and under vacuum to remove unreacted mg and MgCl2, and the rest of the titanium sponge.
Then open the reactor, removal of the titanium. The titanium sponge cut into 0.6cm (0.25 ") block, adding alloying metal, there may be some titanium scrap, then melted into ingots. In order to ensure the uniformity and removal of slag and ingot remelting to one or more than two times.
From the beginning, some people criticized Kroll's method of high cost and low efficiency. It is a batch of steps, many of which have high labor intensity. However, in 50 years despite produced a variety of new technology, but no one can replace it. In fact, Kroll made a little change. The main difference is that the size of the evaporator, for magnesium reduction and vacuum distillation in the same reactor.
Huntfa and Kroll were very similar, but was replaced with sodium magnesium. Even if the method is similar, but the Hunter method cost slightly higher, therefore, the Hunter method is only used in small batch, special high purity powder production.
There are few theoretical researches on Kroll's law, so there are many things that people want to learn. Recent work by Okabe et al. Showed that Kroll and Hunter reactions can be interpreted as an electrical chemical reaction. A better understanding of Kroll's law will help people to improve their.
Improvements may be made that may include reducing the amount of excess magnesium, or reducing the number of titanium grades due to contamination of the walls, or better control of nitride. It is even possible to improve the Kroll method or the Hunter method, so that they can continuously.
If you want to make a revolutionary improvement to the Kroll law, it seems unlikely to reduce its price significantly, but can also reduce the cost of titanium by gradually doing some small changes.
3 electrolysis method
In 1953, Kroll predicted that 15 years later, the electrolysis process will be used to produce titanium. But why after more than 50 years, there is still no commercial electrolytic titanium plant built it?
People have been counting on electrolysis to bring about the same effect as the introduction of the Hall-Heroult method, which greatly reduces the cost of production of aluminum. Before Hall-Heroult, aluminum sodium reduction, cost is more expensive than gold. However, due to the large difference between titanium and aluminum, it is more difficult to produce titanium by electrolysis.
On the one hand, the melting point of titanium is 1000 degrees (1800 degrees Fahrenheit), higher than that of aluminum. Therefore, so far, all the electrolytic method of production of solid titanium has branched, and due to delay and was lost to electrolyte loss.
In the electrolytic bath in aluminum, only a steady state and has two valence, titanium. This multi valence state caused by electron efficiency loss.
But the main problem is that electrolysis may not be cheaper than the Kroll method, since both are starting at TiCl4.
Some economic analysis shows that Kroll should be saved than electrolytic method. But some companies are not able to prove this.
The electrolytic method has become a main research field of power extraction. But has never been
industrialized production. The reality is that we have spent hundreds of thousands of dollars to build the factory, then abandoned the project.
Part of the reason is due to a process of development time is longer than the titanium market cycle, not a
pilot plant in the market downturn can be spared. Another possible reason is that titanium market growth is
relatively slow. In fact, commercial producers are also reduced. In 1958, the United States at least 6
companies producing titanium sponge, but currently only a Timet. It is also argued that, electrolysis is
never more than the Kroll method with low cost.
Titanium can be produced by electrolysis, the problem is the economy. GTT Marco Ginatta continued use of
chlorination, and has a Torino in Italy built a large experimental production factory. Maybe one day to
replace Kroll industrial electrolysis plant production plant, but at the beginning of the TiCl4 electrolysis method to greatly reduce the price of titanium seems unlikely.
4 Cambridge FFC
The other one is the University of Cambridge Derek Fray announced a more radical reduction method, bring up.
In this method, TiO2 was pressed into a pellet, and then in a bath of 950 DEG C (17.4 degrees Fahrenheit)
and calcium chloride (CaCl2) as cathode and graphite electrode as the anode. When current is applied, the
oxygen is ionized and dissolved in CaCl2 bath. Because the price of oxygen in solution, eliminating two
valent titanium ion problem. This method of production of titanium containing only oxygen 60ppm, size kg.
The method begins by Jin Hongshi, so the theory should greatly reduce the production cost of titanium.
However, Jin Hongshi is not a pure TiO2. Must find a substitute for chloride purification method.
In addition, one of the reasons is to be separated from the chlorination of titanium oxide. Many of the
old production work on titanium oxygen content have failed.
In order to make the process can be carried out smoothly, not only requires TiO2 electrolysis to succeed,
but also to find a less expensive pure TiO2 source. From the scale of production to the process of
industrialization ton is still a long way to go. Because this method has greatly reduced the cost of
titanium potential, worthy of study.
5 titanium powder
Armstrong method (developed by the international titanium powder in Chicago) is considered to be an
improvement in Hunter law. Titanium powder is produced in a continuous process, rather than batch method.
Armstrong method is the production of titanium by reduction of sodium and four titanium chloride.
In this method, TiCl4 steam injection in molten sodium. Sodium flow exceeds the stoichiometric reduction of sodium TiCl4 requirements. The excess sodium cooling the reaction product, and bring them to the stage of separation, removal of excess salt and sodium. The reaction product is a continuous flow of powder.
This process is used to produce aluminum vanadium / titanium alloy.
International titanium powder has produced large amounts of titanium using this method. The analysis made by the Department of energy research center in Albany showed that the oxygen content has been as low as 0.2%, with Gr2 titanium standard. Some titanium powder has been melted into buttons with tensile test samples, also meet the strength and ductility of Gr2 titanium.
The advantages of Armstrong's method is that it is a relatively simple method for producing titanium powder. It is now possible to put the oxygen content is reduced to less than 0.2%, enough for some applications in titanium. The content of new and strict requirements for some factories can lower oxygen.
At present, the international titanium powder company is building engineering facilities to carry out more tests. The system will allow each test to produce about 5kg (11lb) of titanium, but also in the construction of pilot scale factories, each test can produce about 120kg (265lb) of titanium.
International titanium powder company's approach is close to commercialization. However, there are still
some issues that need to be raised. What will be the oxygen content of the product? By the method of the cost of production of titanium Armstrong will be? Because it also starts with TiCl4, the cost of raw materials is the same as that of the Hunter method. But the international titanium powder company has more advantages than the Hunter method:
International titanium powder production process is continuous, and operating at low temperature, and thus greatly reduce the cost of capital and labor.
Products do not require additional purification, and the production of sponge titanium Hunter method is required.
Powder is suitable for all kinds of applications, such as powder metallurgy, sputtering and other fast processing methods.
Direct production of small diameter, high purity powder, no waste.
Salt is the only by-product that can be broken into sodium and chlorine, which can be used again.
There are a number of development and improvement processes that can be converted into plates, rods, or more complex shapes such as gears. However, at present, very little from the powder directly to the production of titanium parts. Or powder for doping, the price down to an acceptable range (low production parts); or high purity, expensive powder, the production of high strength parts, the price is very high.
The cost of high quality parts produced by the international titanium powder company is only a small percentage of the cost of the current machining or powder molding process. The powder can be used as a selection of near net forming technology such as laser deposition and metal injection molding.