February 12, 2011

Titanium story 1 - What is “Titanium”? – “チタン”とは何?

What is titanium that we usually work with? I have been studying about titanium as a material for bikes. I think I will post some of what I have learned and am learning when I have a chance.

I post some about the production of metallic titanium (titanium sponge) as the first story because it is a significant matter to have more understanding titanium alloy like 3Al-2.5V (alpha alloy), 6Al-4V (alpha + beta alloy), and so on. If you are interested in it, keep reading. (It is not a difficult story, but it would rather be interesting.)

The starting ore for production of titanium is either rutile (TiO2) or ilmenite (FeTiO3). There are five distinct stages to extract metallic titanium.

1. Chlorination of the ore to produce TiCL4.
2. Distillation of the TiCl4 to purify it.
3. Reduction of the TiCl4 to produce metallic titanium.
4. Purification of the metallic titanium (sponge) to remove by-products of the reduction process.
5. Crushing and sizing of the metallic titanium to create a suitable product for subsequent melting of CP (pure) titanium and titanium alloys.

The chlorination occurs in fluidized bed containing TiO2, carbon (coke), and impurities. Cl2 contacts the TiO2 (impure) and TiCl4. The basic chlorination reactions are as follows:

TiO2 + 2Cl2 +C   to   TiCl4 +CO2
TiO2 +2Cl2 + 2C   to   TiCl4 + 2CO

(The second step in the production route is the distillation process because the starting grade of TiCl4 needs further purification.)

The next stage is the reduction of the TiCl4. The purified TiCl4 reacts metallic Mg* with inert gas and heated to 800-850 degrees C. The reaction is below.

TiCl4 +2Mg   to   Ti + 2MgCl2

This actually occurs in two steps:

TiCl4 + Mg   to   TiCl2 +MgCl2
TiCl2 + Mg   to   Ti + MgCl2

*Today, using Mg as the reducing agent is a main way because of the economic reason.

Process 1, 2, 3 above were done and the next step is the extraction of metallic titanium by removal of the MgCl2 (process 4.). In this process, one of the methods uses argon (inert gas method) to transport the MgCl2 vapor from a vessel to another vessel. There is another way that is VDP (vacuum distillation process. I will skip the explanation because it will be long.). In both processes, the Mg and Cl2 are recovered and recycled.

The last stage (process 5) is crushing and sizing of the titanium sponge. The sponge mass is crashed into granules of metallic titanium and sizing. The sponge granules are further sheared to reduce their size. These operations are conducted in air but require care.
These are the processes for production of titanium.

I keep writing about the production cost. The cost can be separated into five components. Those are labor (10%), equipment maintenance (15%), utilities (4%), Mg (19%), and TiCl4 (52%). The cost for TiCl4 is too much. This matter must be addressed. In fact, other processes for producing metallic titanium have been under investigation for years to reduce the production cost. (fx. Electrolytic production, Electro-Deoxidation Process.)



1. 原石を塩素化しTiCl4を生産する。
2. TiCl4を蒸留することによりそれを浄化する。
3. メタリックチタンを生産するためにTiCl4を削減する。
4. 削減プロセスにおける副産物を取り除くためのメタリックチタンの浄化
5. CPチタン(純チタン)やチタン合金のこの後のプロセス(溶融、融解)のためのクラッシングとサイズイング。



ここまでで上記のプロセス1.2.3.が修了し、次にプロセス4のMgCl2の移動によってメタリックチタンの浄化、抽出をする。このプロセスにおいては、不活性ガスを使用することによりMgCl2ガスを移動させる方法と、VDP(Vacuum Distillation Process)(説明省略)という方法がある。両方のプロセスではそのMgとCl2はリサイクルされる。



さらに生産コストについて少し。生産コストは5つに分けられる。それらは、労費(10%)、メインテナンス費(15%)、ユーティリティー費(4%)、Mg費(19%)、そしてTiCl4(52%)である。TiCl4にかかるコストの割合が高く問題となっているが、近年そのコスト削減のため他の生産プロセス(electrolytic production, Electro-Deoxidation process)が試みられている。

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