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Titanium Processing Technology

Edit: Baoji Jinshan Titanium Industry Co.,Ltd    Date: Feb 14, 2017
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Titanium Processing Technology

 

Titanium has a unique performance: low density, high specific strength, high temperature strength, superior corrosion resistance. Titanium as a structural metal, in the crust in the fourth place, second only to iron, aluminum, magnesium, nickel, copper, chromium, lead, tin and zinc more than the sum. However, the current titanium production system is very complex, and the high cost. Titanium is expensive because the current refining process from ore to metal is a multi-step, high temperature batch process. This article will first talk about the current titanium technology, and then discuss the four most promising ways to reduce the cost of titanium. These methods include Kroll, Hunter, Cambridge and Armstrong.

1. The current titanium extraction method

Titanium production is now from rutile (TiO2) began. Rutile is treated with chlorinated carbon in a fluidized bed reactor at 1000 ° C (1830 ° F) to produce TiCl4.

TiO2 + 2Cl2 + C → TiCl4 + CO2

Titanium production can also start with other low-cost materials, such as ilmenite or slag, but they contain more iron and other impurities. The liquid TiCl4 was purified and about 90% TiCl4 was oxidized to TiO2 for the pigment industry.

TiCl4 is a starting point for all commercial processes. The two main reasons for starting from TiCl4 are the high purity of TiCl4, and the separation of titanium from oxygen.

2. Kroll method

The current use of the Crow method and DuPont developed in 1948 compared to the method did not change much, it mainly includes the following steps. Heat the dry, clean stainless steel steamer and stir the argon. The magnesium used for the reduction of TiCl4 was introduced into the steamer. The steamer is heated to 800 ° C to 900 ° C (1470 ° C to 1650 ° F) and then the TiCl 4 is fed slowly into the evaporator. The reaction of magnesium to reduce TiCl4 is as follows:

TiCl4 + 2Mg → Ti + 2MgCl2

As the reduction progresses, MgCl2 is periodically branched out. After a few days, depending on the size of the steamer, the reaction stops and the evaporator pressure rises. At this point, about 30% of the magnesium did not react. Forming a sponge-like porous material of titanium metal.

Now there are titanium metal (sponge titanium), unreacted magnesium and some MgCl2. These impurities can be removed by leaching or vacuum distillation. Vacuum distillation by removing the temperature of the steamer and in the vacuum removed unreacted magnesium and MgCl2, while the remaining titanium sponge. The reactor is then opened and the titanium is removed. The sponge titanium cut into 15px (0.25 ") block, adding alloying metal, there may be some titanium residue, and then smelting into ingots. To ensure uniformity and removal of slag, ingots to melt once or twice The

From the outset, it was criticized that the high cost of karofa method was inefficient. It is a batch of steps, many of which are labor intensive. However, after 50 years, although there are a variety of new processes, but no one can replace it. In fact, the Kroll law made little change. The main difference is that the size of the steamer becomes larger and magnesium reduction and vacuum distillation are carried out in the same reactor.

The Hunt law is very much like the Crow law, but magnesium is replaced by sodium. Even if the method is similar, but the cost of Hunt law is slightly higher, so the Hunter law is currently only used for small batch, special high purity powder production.

There is little research on the theory of the kolor method, so there are many people who want to learn. Some of the work recently done by Okabe et al. Shows that the Kroll and Hunt reactions can be interpreted as an electrochemical reaction. A better understanding of the Crow law helps people to improve it. Possible improvements may include reducing the amount of excess magnesium, or reducing the amount of titanium grade due to contamination on the wall, or better controlling the nitride slag. It is even possible to improve the Kroll law or the Hunt law so that they can be continuous.

If you want to revolutionize the Kroll law to significantly reduce its price seems unlikely, but by gradually doing some small changes can also reduce the cost of titanium.

Electrolysis

In 1953, Kroll predicted that after 15 years will use electrolysis to produce titanium. But why after 50 years still no commercial electrolytic titanium plant built?

It has been expected that electrolysis can have the same effect as the introduction of the Hall-Heroult method greatly reduces the production costs of aluminum. Before Hall-Heroult, aluminum was reduced with sodium, and the cost was 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 ° C (1800 ° F) higher than aluminum. Thus, so far, all electrolytic production of solid titanium has a dendritic structure and is lost due to procrastination. In the electrolytic bath, aluminum has only one steady-state valence, and titanium has two. This multiple valence state causes loss of electron efficiency. But the main problem is that the electrolysis method may not be cheaper than the Crow method, since both are beginning with TiCl4. Some economic analyzes show that the electrolysis method can be saved more than the Kerr method. But some of the company's production scale of the test did not prove this point.

Electrolysis has become one of the main areas of electrolysis. But never carried out industrial production. The reality is that everyone has spent hundreds of dollars to build experimental factories, and then gave up these projects.

Part of the reason is that a process development time is longer than the titanium market cycle, no one experimental plant in the market downturn can be spared. Another reason may be the titanium market growth is slow. In fact, commercial producers are also decreasing. In 1958, at least six companies in the United States produced sponge titanium, and only Timet. It has also been argued that the cost of electrolysis is never lower than the Crow law.

Titanium can be produced by electrolysis, the problem is economy. GTT's Marco Ginatta continues to use chlorination and has established a large experimental plant in Torino, Italy. Perhaps one day the industrial electrolysis plant can replace the Kroll manufacturing plant, but starting with the TiCl4 electrolysis method in order to greatly reduce the titanium price seems unlikely.

4. FFC Cambridge Law

The other is Cambridge University Derek Fray announced a more radical electrolytic reduction method, to bring people to the excitement. In this method, TiO2 was compressed into pellets and then dried at 950 ° C (1740 ° F) in a calcium chloride (CaCl2) bath using a graphite electrode as the anode. When the current is passed, oxygen is ionized and dissolved in the CaCl2 bath. As the monovalent oxygen in the solution, eliminating the problem of divalent titanium ions. This method produces titanium only oxygen 60ppm, the scale is kilograms.

The method begins with rutile, so theoretically the production cost of titanium should be greatly reduced. However, rutile is not pure TiO2. It is necessary to find a method that can be used instead of chlorination for purification. In addition, one of the reasons is that the chlorination method is to separate titanium from oxygen. Many of the previous production of low oxygen content titanium work failed.

To make the process can be carried out smoothly, not only requires the success of TiO2 electrolysis, but also to find less expensive pure titanium supply. There is still a long way to go from small-scale production to ton-scale industrialization. Because the method has the potential to greatly reduce the cost of titanium, it is worth to study.

5. Titanium powder

Armstrong Law (developed by Chicago International Titanium Powder Company) is considered an improvement on the Hunt law. Titanium powder is produced by a continuous process rather than a batch process. Armstrong is produced by the reduction of sodium with titanium tetrachloride to produce titanium. In this method, TiCl4 is injected into the molten sodium. The flow of sodium exceeds the stoichiometric requirements for sodium reduction of TiCl4. The excess sodium cools the reaction product and takes them to the separation stage to remove excess sodium and salt. The reaction product is a continuous powder stream. Modification of this process can also be used to produce vanadium / aluminum titanium alloy.

International Titanium Powder has used this method to produce a large amount of titanium. An analysis by the Department of Energy at the Albany Research Center showed that the oxygen content was as low as 0.2%, in line with the Gr2 titanium standard. Some titanium powders have been melted into buttons for tensile test samples and also meet Gr2 titanium strength and ductility standards.

The advantage of Armstrong is that it is a relatively simple method of producing titanium powder. Has been able to reduce the oxygen content to less than 0.2%, enough for some titanium applications. Some of the new, demanding plants can further reduce the oxygen content.

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 5 kg (11 lb) of titanium, while also building a pilot scale plant that produces about 120 kg (265 lb) of titanium per test.

International Titanium Powder's approach is close to commercialization. However, there are still some issues that need to be addressed. What is the oxygen content of the product? How much will the cost of titanium be produced by Armstrong? Because it also starts with TiCl4, the cost of raw materials and the Hunter method is the same. But the international titanium powder company's method has more advantages than the Hunt law:

· International Titanium Powder's production method is continuous and running at low temperatures, resulting in a significant reduction in capital and labor costs.

The product does not require additional purification, while Hunter produces sponge titanium.

Powder is suitable for a variety of applications such as powder metallurgy, sputter molding and other rapid machining methods.

Direct production of small diameter, high purity powder, no waste.

Salt is the only byproduct, can be broken into sodium and chlorine, can be reused.

There are many well-developed processes that convert powder into plates, rods or more complex profiles such as gears. However, there is little direct production of titanium parts from powder. Or powder is doped, the price down to an acceptable range (the production of low parts); or high purity, expensive powder, the production of high-strength parts, the price is high.

The cost of high-quality parts made from International Titanium Powder's high-purity powder is only a small percentage of the current processing cost of machining or powder forming. The powder can be used as several selection materials for near-net forming techniques such as laser deposition and metal injection molding.


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