Van Arkel–de Boer process: Difference between revisions

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{{Short description|Process for the commercial production of pure titanium and zirconium}}

The '''Crystal bar process''' (or [[Iodide process]]) was discovered by [[Anton Eduard van Arkel]] and [[Jan Hedrik de Boer]] in 1925. This process was the first industrial process for the commercial production of pure ductile metallic [[zirconium]].

[[File:Titan-crystal bar.JPG|thumb|right|A 5.5" long high purity 99.995% titanium crystal bar weighing {{Nowrap|283 g}} made by this process during the [[Soviet era]] at the [[URALREDMET]] plant in [[Yekaterinburg]]]]

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The '''van Arkel–de Boer process''', also known as the '''iodide process''' or '''crystal-bar process''', was the first industrial process for the commercial production of pure ductile [[titanium]], [[zirconium]] and some other metals. It was developed by [[Anton Eduard van Arkel]] and [[Jan Hendrik de Boer]] in 1925 for [[Philips Nv]].<ref name=zaac25>{{cite journal | doi = 10.1002/zaac.19251480133 | title = Darstellung von reinem Titanium-, Zirkonium-, Hafnium- und Thoriummetall | first = A. E. | last = Van Arkel |author2=De Boer, J. H. | volume = 148 | issue = 1 | pages =345–350 | year = 1925 | journal = Zeitschrift für anorganische und allgemeine Chemie | language = German}}</ref><ref name=van24a>{{US patent|1582860}}</ref><ref name=van24b>{{US patent|1666800}}</ref><ref name=van25a>{{US patent|1718616}}</ref><ref name=van25b>{{US patent|1709781}}</ref> Now, it is used in the production of small quantities of ultrapure titanium and zirconium. It primarily involves the formation of the metal [[iodide]]s and their subsequent decomposition to yield pure metal, for example, at one of the [[Allegheny Technologies]]' Albany plants.<ref name=siddall79>{{US Patent|4487629}}</ref>

ItThis process was superseded commercially by the [[Kroll process]] (based on the [[Redox|reduction]] of [[titanium tetrachloride]] by metallic [[magnesium]]).

[[File:Van-Arkel-de-Boer-Apparat.png|thumb|left|upright|An apparatus used for the process. The main body is [[quartz glass]]. (1) to vacuum pump, (2) {{Nowrap|6 mm}} molybdenum electrode, (3) molybdenum net, (4) chamber for the raw metal, (5) tungsten wire]]

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==Process==

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As seen in the diagram, impure titanium, zirconium, [[hafnium]], [[vanadium]], [[thorium]] or [[protactinium]] is heated in an evacuated vessel with a [[halogen]] at 50–250&nbsp;°C. The patent specifically involved the intermediacy of [[titanium tetraiodide|TiI₄]] and [[zirconium tetraiodide|ZrI₄]], which were volatilized (leaving impurities as solid).

At atmospheric pressure [[Titanium tetraiodide|TiI₄]] melts at 150&nbsp;°C and boils at 377&nbsp;°C, while [[Zirconium(IV) iodide|ZrI₄]] melts at 499&nbsp;°C and boils at 600&nbsp;°C. The boiling points are lower at reduced pressure. The gaseous metal [[tetraiodide]] is decomposed on a white hot [[tungsten]] filament (1400&nbsp;°C). As more metal is deposited the filament conducts better and thus a greater electric current is required to maintain the temperature of the filament. The process can be performed in the span of several hours or several weeks, depending on the particular setup.

Generally, the crystal bar process can be performed using any number of metals using whichever halogen or combination of halogens is most appropriate for that sort of transport mechanism, based on the reactivities involved. The only metals it has been used to purify on an industrial scale are [[titanium]], [[zirconium]] and [[hafnium]], and in fact it is still in use today on a much smaller scale for special purity needs.{{citation needed|date=June 2021}}

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==References==

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{{DEFAULTSORT:Van Arkel-de Boer process}}

[[Category:Industrial processes]]

[[Category:Zirconium]]

[[Category:Dutch inventions]]

[[Category:Methods of crystal growth]]

[[Category:Titanium processes]]

[[Category:Metallurgical processes]]

[[Category:Materials science]]

[[Category:1925 introductions]]

[[Category:20th-century inventions]]

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