Thermodynamic Properties of Wolfram Oxytetrachloride
(Part I. of the "Fundamental Study on the Chlorine Metallugy of Wolfram")
（Received 12 September 1967） KotaroUCHIMURA KoemonFUNAKI Synopsis Advartages of the chlorine metalligy of wolfram were discussed comparing with the metallurgical process being now used． In this paper， the sublimation and evaporation pressure of WOCI4， which is one of the chlorinating products of the mixture of WO3 and C， were measured． From the measurements， thermodynamic functions of the sublimation， evaporation and fusion were obtained． 1． Introduction At present， for the production of metallic wolfram powder， hydrogen reduction of pure wolframtrioxide which is produced from the minerals by treating with alkalic methodi 6） or acidic method6−9）according to the kinds of minerals， is used． On the other hand， metallic wolfram powder is also obtainable by the hydrogen reduction of chlorination products of wolfram minerals which were purified by distillation or by other methods．9，10）This method is specially suitable for the preparation of’；high purified and highly dispersed wolfram powder． On the chlorine metallurgy of wolfram， few studies have ever been published， and the chlorination reaction of wolfram Ihinerals， properl ies of chlorination products and other fundamental studies on the chlorine metallurgy of wolfram are almost left unknown． It is already known that the chlori・ nation products of the mixture of WO3 and carbon are volatile WOC14 and WO2Cl212−16）． Generally， in the chlorine metallurgy， the formation of oxychlorides are undesirable， be− cause there is the risk of inclusion of oxygen in the final metals． But in the case of wolfram， as will be expected from the fact ＊This work had been carried out at Institute of Technology． Published Kagaku 30，35（1962）in Japanese． that pure the Tokyo in DenkiL ＊＊Institute of the Inorganic Synthesis， Yamanashi University． ＊＊＊Tokyo Institute of Technology．
wolfram can be obtained by the hydrogen
reduction of WO3， pure wolfram powder can also be obtained by the hydrogen reduction of the oxychlorides of wolfram as will be shoWn in the later section． Therefore in this study， the process of chlorine metallurgy of wolfram using wolfram oxychlorides as intermediate products， was studied． The studies on the oxychlorides of wolfram are very few and are all old ones， and the quantitative studies are almost not performed． In this section， the thermodynamic properties of red WOCl4， which is one of the chlorination products of wolfram trioxide， are reported． 2．Preparation of the sample and tlle measuring method 2．1 1）アopara彦ion（’f the samPle The rnixture of WO3 and carbon in the molar ratio of 1：3 was chlorinated at the temperature of about 600°C， where the WO3 was the purity for chemical analysis and the carbon was made from the puri丘ed cane sugar． The chlorinated product was consisted of red t’ WOCI4 and yellow WO2Cl2， From this reaction product， the part rich in red WOCI4 was taken， and was put into the part A of Fig．1． The systeln was evacuated from F and the part A was warmed by oil bath gently， then red WOCI4 sublimed to the wall of the part B and ， yellow WO2Cl2 remained in part A． Then the part a was sealed and the same operation was repeated several tirnes， the丘nal re丘ned WOCI4 was collected in D and this was used for vapor 一 156一Thermodynamic Properties of Wolfram Oxytetrachloride F Fig．1 Purifing apparatus of WOCI4． B A ） E D b 一 Fig．2 Bourdongauge used for the vapor pressure measurement of WOCI4． pressure measurement and for chemical analysis． 2．2 ノレfeasuring method Sublimation pressure and evaporation pressure of WOCI4 were measured and the therrnody・ namic functions were deduced from the meas− urement of sublimation and evapolation pres・
sure， the Bourdon gaugeas was shown in
Fig．2was used． The sensitivity of the ap− paratus is the oder of about O．1mmHg． In the part A of the Fig．2， the ampule filled with purified WOC14 which was broken at one end was inserted， and after the system was evacuated to the oder of 10−3mmHg， part A was warmed gently and WOC14 was sublimed to part B and further to part C． After adequate amount of WOC14 was collected in part C，「E 800 700 600 500 400 300 200 100 盲 亘 ぎ 一 2｝Presen・A・・h・・s Measured Value Reinder Calculated Value Van Liempt 170 180 190 200 210 220 Fig．3 Vapor pressure of WOCI4． 2．00 230℃ ／・rese・1・A・・h・rs ●一● Measured Valve． Reinder O＿＠Calculated Value Van Liempt 2．08 2．12 2．16 1／T×103 Fig．4 Vapor pressure of WOCl4．and D were sealed． Around the Bourdon
gauge， the electric furnace was set and thesublimation and evaporation pressure were
measured． The temperature was measured by L calibrated thermometer．一157一
Dec．1967 Reports of the Faculty of Engineering， Yamanashi University No．18 3．The results of the experiments The results of the experiments were shown in Figs．3and 4． 工n Fig．3， the relation be’ tween 1）（mmHg）anp t℃and in Fig．4， the relation between log P（mmHg）and 1／T°K were shown． As can be seen from these figures， the curves consist of two parts． Lower temperature part corresponds to the sublimation of WOCl4（S） and the higher temperature part corresponds to the evaporation of WOCI4（L）． From Fig．4， the following experimental formulas for subli− mation and evaporation were obtained： for sublimation， 4．40 1・gP…（mmHg）＝一・“” s×103＋11・76±0・02 and for evaporation， 3．33 ×103十9．54±0．02．log Pevap（mmHg）＝一一 T
4．Thermodynamic pmperties of WOC14
From the above measurments， thermody− namic functions for the sublimation and evapo− ration and other properties of WOCI4 were obtained． ．For the sublimation， WOCI4（S）：ゴWOCI4（G） 4F°sub＝−4．57τlog Ps・b（atm） ＝20．14×103−40．13Tcal／mo1 （170−210°C） 4Hsub＝20．14×103±0．05×103 cal／mol （170−210°C） ∠fSsub＝40．43±0．1 e．u． （170−210°C）． For the evaporation， WOCI4（L）＝ゴWOC14（G） AF°evap＝15．16×103−30．32 T cal／mol （210−230°C） 4He。，、p＝15．16×103±0．05×103 cal／mol （210−230°C） aSevap＝・30．32±0．1 e．u． （210−230°C）． AF° evap，an
the relation ∠IF°evap＝0． For the fusion， WOCI4（S）＝こWOCL4（L） from the relation 4F°fusi。n＝AF°sub−AF°evap， 4F°fusl。n＝4．98×103−10．11 T cal／mol AHfusi。n＝4．98×103±0．05×103 Cal／mOl 4S，。，i。n＝10．11±0．1e．u． Furthermore， from the relation 4F°sub＝ melting pOint of 209°C was obtained， dthe boiling point 227℃was obtained from 5． Consideration of the results On the measurements of sublimation and evaporation pressures， W． Reinders and J．A．M． Van Liempt17）had、already reported． They published the following experimental formulas， 400 10g Psuし（atm）＝一 ×103−十一7．98 Tand
l・9・P…P（・tm）一一3・警4×1・・＋7．3， and experimental values． The values calculated from the above formula and the experimental data are both plotted in Fig．3and 4． From these figures， experimental data and the cal− culated values do not agree and the experi− mental values shows considerable dispersions．Thermodynamic values given by various
authors are listed in Table 1． Comparing the above data， it can be seen that on the melting point， all、 the measurements coincide well comparatively， but on the boiling point， Reinder and Van Liempt gives a con− siderably higher value． On the heat of sublimation and evaporation， there seems no measurements except Reinder and． Van Liempt and present authors， but there exist considerable differences between them， specially on the heat of fusion． From the fact Table l Thermodynamic Properties of WOCl4 authors melting pt．（°C） boiling pt．（°C） heat of fusion へぱ heat of evap． heat of sub． Uchimura， Funaki 209 227 4980cal／mo1 15160 2．0140 Reinders， Van Liempt 209 232 1440．cal／moI 16840 18280 other authors 206．718），208∼21019）22），21120），2042i） 227．51s）， 22021） i ＿ i 11・5kcal／m・121） 一 158一Thermodynamic Properties of Wolfra些一CxytetrachlgridC． that Reinder and Van Liempt’s experimental formula and their experimental data showed considerable uncoincidence， and boiling Points seemed too high， it can be said that the ac・ curacy bf their experiment is not so high， and our experiment is considered to be more re− liable． 6． Conclusions From the chlorinating products of the mixture of pure WO3 and carbon， pure WOCI4 was isolated and its sublimation and evaporation
