Kroll trial
The Kroll process is a process invented by William Justin Kroll and patented in 1940 for the extraction of technically pure titanium .
Ilmenite (FeTiO 3 ) is an important raw material for titanium production. In order to produce rutile (TiO 2 ) from the ilmenite , it is reduced in an electric arc with carbon . The liquid iron collects on the bottom and is tapped from time to time.
In industry, however, one often starts directly from natural rutile or synthetic rutile (obtained by HCl leaching from ilmenite). In the past, titanium slag (see below) was also important.
TiO 2 ( titanium (IV) oxide ) is converted into titanium tetrachloride ( titanium (IV) chloride ) in the chloride process at temperatures of 750–1000 ° C with chlorine and coke (reducing chlorination).
The titanium chloride is obtained by fractional distillation and mostly u. a. vanadium removal separated from the impurities present in the ore. The starting material for the Kroll process is pure titanium tetrachloride, which is already available in very large quantities for the production of white pigments. The pure TiCl 4 is reduced to metallic titanium with magnesium at temperatures of approx. 800–900 ° C under a protective gas atmosphere ( helium , argon ) .
The magnesium chloride (MgCl 2 ) is tapped batchwise in the major amount. Due to the principle of the smallest constraint , more and more titanium is reproduced. The trapped residues of magnesium chloride as well as the residues of unreacted magnesium , which is introduced in excess, are either dissolved out of the titanium sponge with hydrochloric acid or, better, since a higher purity is achieved, removed by vacuum distillation .
The Kroll process provides what is known as the titanium sponge, a hard, porous mass that, after vacuum distillation, has to be laboriously worked out of the process plant using turning or other machining methods. In the past, this was even done with a jackhammer . The same applies to the Hunter method.
Further processing into a first technically usable product (ingot): This titanium sponge must then be pressed into meter-long melting electrodes (diameter typically 500 to 1200 mm, depending on the furnace), any alloy components (such as Al, V) are welded on outside as strips. In most cases, it is necessary to remelt it three times in a vacuum arc furnace in order to obtain technically usable, homogeneous titanium ingots (cast bars). Due to the high reactivity of hot and liquid titanium, only water-cooled copper can be used as the wall material.
According to the older Hunter method, TiCl 4 is reacted with Na instead of Mg. Both the NaCl and MgCl 2 formed are thermodynamically more stable; the reactions are practically complete and also very exothermic.
Technical titanium (Grade 2) contains up to 0.3% iron as well as up to approx. 0.25% oxygen.
This production, which is still particularly complex and consumes metallic magnesium, also causes the high price.
The production of purer Ti (in small quantities) takes place - as with many other metals - using the Van-Arkel-de-Boer process .
Individual evidence
- ↑ Patent US2205854 : Method for manufacturing titanium and alloys thereof. Published June 25, 1940 , inventor: Wilhelm Kroll.
- ^ CE Mortimer: Chemistry - The basic knowledge of chemistry . 7th edition, Thieme Verlag, Stuttgart 2001, ISBN 3-13-484307-2 , p. 391.
- ^ CE Mortimer: Chemistry - The basic knowledge of chemistry . 7th edition, Thieme Verlag, Stuttgart 2001, ISBN 3-13-484307-2 , p. 478.
- ^ ASM Aerospace Specification Metals, Inc.