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35:
Schematic diagram of the CVT process. Point A is the reaction between the starting materials and the transport agent to form volatile intermediates. These intermediates then are free to move around the inside of the tube via diffusion or convection (point B), and when they reach point C some of the
103:. The technique requires that the two ends of the tube (which contains the sample to be crystallized) be maintained at different temperatures. So-called two-zone tube furnaces are employed for this purpose. The method derives from the
147:, then the solid of interest is transported from the cooler end (which can be quite hot) of the reactor to a hot end, where the equilibrium constant is less favorable and the crystals grow. The reaction of
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Michael
Binnewies, Robert Glaum, Marcus Schmidt, Peer Schmidt "Chemical Vapor Transport Reactions – A Historical Review" Zeitschrift für anorganische und allgemeine Chemie 2013, Volume 639, pages 219–229.
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derivative reverts to the parent solid and the transport agent is released at the end opposite to which it originated (see next section). The transport agent is thus
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Alternatively, when the reaction of the solid and the transport agent is endothermic, the solid is transported from a hot zone to a cooler one. For example:
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are reportedly observed at the mouths of volcanoes because of chemical transport reactions whereby volcanic hydrogen chloride volatilizes iron(III) oxides.
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into volatile derivatives. The volatile derivative migrates throughout a sealed reactor, typically a sealed and evacuated glass tube heated in a
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The sample of iron(III) oxide is maintained at 1000 °C, and the product is grown at 750 °C. HCl is the transport agent. Crystals of
383:
P. Kleinert, D. Schmidt (1966). "Beiträge zum chemischen
Transport oxidischer Metallverbindungen. I. Der Transport von α-Fe
356:
van Arkel, A. E.; de Boer, J. H. (1925). "Darstellung von reinem
Titanium-, Zirkonium-, Hafnium- und Thoriummetall".
251:. The tungsten is evaporated from the tungsten filament and converted with traces of oxygen and iodine into the WO
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259:, at the high temperatures near the filament the compound decomposes back to tungsten, oxygen and iodine.
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which was used for the purification of titanium and vanadium and uses iodine as the transport agent.
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Using 10 milligrams of iodine for 4 grams of the solid, the process requires several days.
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of the reaction between the solid and the transporting agent. When the reaction is
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J. H. Dettingmeijer, B. Meinders (1968). "Zum system W/O/J. I: das
Gleichgewicht WO
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and which gives conformal coatings. The technique, which was popularized by
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Cases of the exothermic and endothermic reactions of the transporting agent
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Schäfer, H. "Chemical
Transport Reactions" Academic Press, New York, 1963.
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Günther Rienäcker, Josef
Goubeau (1973). "Professor Harald Schäfer".
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Process for purification and crystallization of non-volatile solids
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migrates from the cooler end (700 °C) to the hotter end (900 °C):
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95:. Because the tube is under a temperature gradient, the
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Transport reactions are classified according to the
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23:Gold crystals grown by chemical transport using
36:gaseous species react to form solid products.
48:describes a process for purification and
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155:is an exothermic process, thus the MoO
243:A similar reaction like that of MoO
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391:über dimeres Eisen(III)-chlorid".
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151:with the transporting agent
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46:chemical transport reaction
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105:Van Arkel de Boer process
65:chemical vapor deposition
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407:10.1002/zaac.19663480305
370:10.1002/zaac.19251480133
334:10.1002/zaac.19733950202
130:as the transport agent.
27:as the transport agent.
307:10.1002/zaac.201300048
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477:Solid-state chemistry
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227:> 0 (endothermic)
472:Inorganic chemistry
283:< 0 (exothermic)
183:< 0 (exothermic)
149:molybdenum dioxide
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89:chemical compounds
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114:Crystals of
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466:Categories
288:References
145:exothermic
73:→ Si + 2 H
120:Van Arkel
101:catalytic
69:(e.g. SiH
61:volcanoes
42:chemistry
428:, g = WO
233:hematite
116:titanium
97:volatile
85:elements
54:volatile
25:chlorine
424:, f + J
124:de Boer
52:of non-
171:⇌ MoO
153:iodine
57:solids
436:,g".
279:, ΔH
271:⇌ WO
223:O ΔH
219:+ 3 H
204:+ 6
267:+ I
167:+ I
87:and
44:, a
448:doi
444:357
403:doi
399:348
366:doi
362:148
330:doi
326:395
303:doi
281:rxn
225:rxn
208:⇌
206:HCl
181:rxn
163:MoO
40:In
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442:.
397:.
324:.
263:WO
214:Cl
210:Fe
195:Fe
179:ΔH
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432:J
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387:O
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275:I
273:2
269:2
265:2
257:2
255:I
253:2
245:2
221:2
216:6
212:2
201:3
199:O
197:2
177:2
175:I
173:2
169:2
165:2
157:2
128:2
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75:2
71:4
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