共查询到20条相似文献,搜索用时 15 毫秒
1.
P. K. Jena E. A. Brocchi M. L. Dos Reis 《Metallurgical and Materials Transactions B》1999,30(3):375-381
Studies on the kinetics of carbothermic chlorination of zirconium dioxide in gaseous chlorine were carried out with petroleum
coke fines in powder form. The amounts of ZrO2 chlorinated were found to be directly proportional to the time of chlorination in the temperature range studied (973 to 1273
K). The activation energy values for chlorination of ZrO2, in mixture with petroleum coke, was found to be 18.3 kJ/mole. The influence of particle size of petroleum coke on the chlorination
of ZrO2 (−38 + 25 μm) was studied, and it was found that the rate of chlorination increased up to the size range of −75 to +53 μm, and the size finer than this produced negligible increase. The amount of petroleum coke in the mixture above 17.41 pct
in excess of the stoichiometry resulted in very little increase in the rate. The effect of the partial pressure of chlorine
(pCl2) on the rate of chlorination was found to obey the following relationship, derived from the Langmuir adsorption isotherm:
where v is the amount of ZrO2 (g/min) reacted, k is the rate constant, and K is the equilibrium constant for adsorption of two chlorine atoms (obtained from the dissociation of a molecule of Cl2 at the carbon surface) on the surface of ZrO2. By plotting 1/v vs 1/pCl2, a straight-line relationship with an intercept in x-axis is obtained, further supporting the preceding equation. The dissociation of the adsorbed complex, Cl … ZrO2 … Cl to ZrCl2 and O2 is suggested to be the rate-controlling step. Subsequently, the less stable ZrCl2 combines with Cl2 to form ZrCl4 and the oxygen combines with C to form CO and CO2. 相似文献
2.
Kinetics of the chlorination of Nb2O5 powder by CCl4 vapor in mixture with N2 in a static bed in the temperature range of 698 to 853 K were carried out at different partial pressures of CCl4 (p
CCl
4), varying from 0.10 to 0.75 atm. The fraction of Nb2O5 chlorinated R at p
CCl
4 of 0.6 atm in the temperature range of 698 to 773 K was found to be proportional to time t, and the activation energy E is calculated to be 112 kJ/mole. Results on the effect of p
CCl
4 (0.4, 0.6, and 0.75 atm) at 723 K suggest that the rate v (R/min) is proportional to p
CCl
4
1.5. However, at p
CCl
4 of 0.2 atm, R is not linear with t, rather, R
1/2 is linear with t. Based on these results, two mechanisms, one at low p
CCl
4 (0.2 atm) and another at higher p
CCl
4 values, in the temperature range of 698 to 773 K have been suggested. Similar studies in the higher temperature range (793
to 853 K), where p
CCl
4 used to decompose to elemental chlorine and carbon, were also carried out. At all temperatures and p
CCl
4 values, R is found to be directly proportional to t. At two higher p
CCl
4 (0.4 and 0.6 atm), v is proportional to p
CCl
4
1.5, whereas at two lower p
CCl
4 (0.1 and 0.2 atm) it is proportional to p
CCl
4
1.5. The E values obtained in the temperature range of 793 to 853 K at p
CCl
4 of 0.6 and 0.2 atm are found to be 57 and 115 kJ/mole, respectively. In this higher temperature range, two different reaction
mechanisms have been proposed. 相似文献
3.
P. K. Jena E. A. Brocchi M. P. A. C. Lima 《Metallurgical and Materials Transactions B》2001,32(5):801-810
Studies on the kinetics of chlorination of tantalum pentoxide powder by carbon tetrachloride vapor in dilution with nitrogen
have been carried out by weight-loss measurements in two temperature ranges, i.e., 698 to 773 K and 793 to 853 K. The effect of time, temperature, and partial pressure of CCl4
on the kinetics of chlorination of the powder Ta2O5, (−105+74 μm) has been investigated. In both the temperature ranges, the chlorination results have been found to fit the following relationship
during the “initial periods:”
where α is the fraction of the oxide reacted in time t and k
1 is the rate constant. In the low- and high-temperature ranges, the activation-energy (E) values have been calculated and were found to be 145 and 71 kJ/mole, respectively. The k
1 value was found to be proportional to P
CCl4
1.5
in the lower-temperature range, while in the higher-temperature range, it was found to be proportional to P
CCl4
0.9
.
In the “latter periods” of the chlorination of Ta2O5, the following relationship was found to be applicable in both the temperature ranges:
where k
2 is the rate constant and c is another constant. However, in the latter periods of the chlorination, the activation energy in the lower-temperature range
was calculated to be 31 kJ/mole, while that in the higher-temperature range was found to be 142 kJ/mole. Further, in the lower-temperature
range, k
2 was found to be nearly independent of
, while in the higher-temperature range, it was found to be proportional to P
CCl4
0.9
, as observed in the initial periods.
Based on these kinetics results, two different mechanisms for the chlorination of Ta2O5 by CCl4 vapor have been suggested for the two temperature ranges studied.
It was possible to chlorinate >92 pct of Ta2O5 (−105+74 μm) at 833 K in 210 minutes, by using CCl4 at a partial pressure of 0.6 atm. 相似文献
4.
Low-temperature chlorination of vanadium pentoxide by carbon tetrachloride vapor in dilution with nitrogen has been carried
out. The effect of time, particle size, partial pressure of CCl4 vapor (0.1 to 0.6 atm), and temperature (553 to 788 K) on the extent of chlorination of V2O5 has been investigated. The extent of chlorination of the oxide is found to increase with a decrease in its particle size.
In all cases, the reaction followed a topochemical reaction model, obeying the following relationship:
where α is the fraction of V2O5 chlorinated in time t and k is the rate constant. The rate constant has been found to be directly proportional to the partial pressure of CCl4 (PCCl4). The activation energy values between 553 and 643 K and that between 683 and 788 K have been calculated and found to be
38.9 and 11.5 kJ/mole, respectively. Based on the kinetics results, mechanisms of reaction in the two temperature ranges have
been suggested. It has been possible to chlorinate V2O5 at 753 K to about 87 pct in 30 minutes, using a very low partial pressure of CCl4 of 0.15 atm. 相似文献
5.
Kinetics of chlorination of V2O5 with Cl2-air, C12-N2, and C12-CO-N2 gas mixtures have been studied by nonisothermal and isothermal thermogravimetric measurements. In the temperature range of
500 °C to 570 °C, the chlorination of V2O5 with C12-N2 gas mixture is characterized by an apparent activation energy of about 235 kJ/mole. This could be attributed to chemical
reaction. Between 570°C and 650 °C, the apparent activation energy is equal to 77 kJ/mole, indicating that the overall reaction
rate is controlled by chemical reaction and pore diffusion. The reaction order with respect to chlorine is 0.78. The apparent
activation energy of the carbochlorination of V2O5 by C12-CO-N2 gas mixture is about 100 kJ/mole in the temperature range of 400 °C to 620 °C. In this case, the chemical reaction is the
limiting step. At temperatures higher than 620 °C, an anomaly is observed in the Arrhenius plot, probably due to thermal decomposition
of COC12 formedin situ and/or transformation of the vanadium oxide physical state. The maximum reaction rate is obtained by using a C12-CO-N2 gas mixture having a C12/CO volume ratio equal to about 1.
Formerly Graduate Student, Mineral Processing and Environmental Engineering Team.
Formerly Graduate Student, Mineral Processing and Engineering Team, Institut National Polytechnique de Lorraine, Vandoeuvre,
France. 相似文献
6.
The kinetics of chlorination of MgO particles with HCl gas in the temperature range from 450 °C to 650 °C were measured and
analyzed in terms of the shrinking core model. The MgO particles were produced by the thermal decomposition of MgOHCl manufactured
in-house and were found to have a d50 of 510 nanometers. Over 90 pct of the MgO was converted to MgCl2 within 30 minutes at 650 °C. Analysis of the data indicated that the chlorination process was initially controlled by the
kinetics of the chemical reaction between MgO and HCl, but as the thickness of the MgCl2 product layer increased as the chlorination progressed, the rate of chlorination became controlled by the diffusion of HCl
through the MgCl2 ash layer surrounding a MgO core in the particles. A mathematical model that predicted the shrinkage of the MgO core with
time was found to be in good agreement with the measurements over the range of temperatures studied. The ash layer thickness
for the onset of the diffusion control regime was found to increase linearly with temperature. The apparent rate constant
for chlorination in the initial reaction-controlled regime was well described by the Arrhenius equation: k (m/s)=0.0787 exp (−7596/T). 相似文献
7.
Kinetics of chlorination and carbochlorination of pure Nb2O5 and Ta2O5 were studied by thermogravimetric analysis between 385 °C and 1000 °C using Cl2-N2 and Cl2-CO-N2 gas mixtures. Standard free energy changes of the reactions and phase stability diagrams of Nb-O-Cl and Ta-O-Cl systems were
calculated. The chlorination reaction order, for both oxides, with respect to Cl2 in the Cl2-N2 gas mixture was 0.82. The apparent activation energies (E
a
) for Nb2O5 chlorination were 208 and 86 kJ/mole for temperatures lower and higher than 850 °C, respectively. The experimental data could
be described by a shrinking sphere model between 700 °C and 1000 °C. The chlorination mechanism, between 700 °C and 850 °C,
was likely controlled by the chemical reaction. For T > 850 °C, the overall Nb2O5 chlorination rate was affected by the allotropic transformation of the Nb2O5
T form to M form. Between 925 °C and 1000 °C, E
a
for Ta2O5 chlorination was 246 kJ/mole. In this case, the most appropriate model was also that of shrinking sphere suggesting that
the chlorination of Ta2O5 was controlled by the chemical reaction. For both oxides, the carbochlorination reaction order with respect to Cl2+CO partial pressure, in the gas mixture, was about 2. The mathematical analysis of carbochlorination data indicates that
Nb2O5 and Ta2O5 reactions could be described by shrinking sphere or cylinder, respectively. Below 600 °C, the E
a
values of Nb2O5 and Ta2O5 carbochlorination were 74 and 110 kJ/mole, respectively. Chemical reaction was probably the rate controlling step in both
cases. An anomaly characterized by a decrease of the reaction rates occurs in the Arrhenius plots between 600 °C and 800 °C.
This anomaly could be attributed to the thermal decomposition of COCl2 formed in situ during the carbochlorination. 相似文献
8.
Evandro B. Augusto Herenilton P. Oliveira 《Metallurgical and Materials Transactions B》2001,32(5):785-791
Among the rare earth minerals, fluorides, phosphates, and oxides have received attention from the rare earth industry. Traditional
methods of decomposition of these minerals, usually alkaline or acid processes, involve several operations. Another possibility
to obtain lanthanide chlorides or oxychlorides is reacting the mineral with chlorinating agents, such as gaseous chlorine,
hydrogen chloride, thionyl chloride, and carbon tetrachloride, reducing the operation costs and making the process less complicated.
In this context, we investigated the decomposition of xenotime using carbon tetrachloride at temperatures from 873 to 1173
K and kinetic and mechanistic studies have been performed. Powder X-ray diffraction, scanning electronic microscopy, energy
dispersive X-ray spectrometry, ultra-violet/visible spectroscopy, and thermal analysis techniques were used in this study.
The results showed that the reaction follows the shrinking-unreacted-core model with formation of a product layer (lanthanide
oxychloride), confirmed by powder X-ray diffraction. Moreover, microstructural changes of xenotime grains during the chlorination
reaction were verified. 相似文献
9.
《Canadian Metallurgical Quarterly》2013,52(4):291-295
AbstractWhen Cu2S is chlorinated with Cl2 gas, CuS, CuCl and CuCl2 are observed at various stages of the reaction. It is proposed that CuCl2 and CuS are the first products, which then react to produee CuCl and elemental sulphur. The elemental sulphur is then chlorinated to S2Cl2, which acts as a liquid bridge for the transport of dissolved sulphur away from the reaction interface. CuCl2 forms only when all of the sulphide has been eliminated, and the partial pressure of chlorine in the CuCl2 layer can exceed that for the stability of CuCl. The activation energy proposed for the diffusion of sulphuralong the gradient in a pore filled with S2Cl2 is 8.6 ± 0.5 kcal. Résumé Quand Cu2S est chloruré par Cl2 gaz, on observe CuS, CuCl et CuCl2 à divers stades de la réaction. L’hypothèse proposée est que le CuCl2 et le CuS sont les premiers produits formés qui réagiront ensuite pour produire CuCl et S. Le soufre élémentaire est ensuite chloruré en S2Cl2, et agit alors comme un pont liquide pour éloigner le S dissout de l’interface de réaction. CuCl2 se forme quand tout le sulfure a été éliminé, et la pression partielle de Cl2 dans la couche de CuCl2 peut excéder celle correspondant àCuCl stable. L’énergie d’activation proposée par la diffusion du soufre dans S2Cl2est 8.6 ± 0.5 kcal. 相似文献
10.
L. J. Schwartz M. Kolodney R. A. Graff 《Metallurgical and Materials Transactions B》1971,2(5):1429-1432
The rate of growth of Ta5Si3 in the Ta?TaSi2 system has been measured with good accuracy in the temperature range of 1150° to 1370°C (2100° to 2500°F) using couples consisting of dense wafers of the components. The isothermal growth is shown to be parabolic and the temperature dependence of the growth constant is given byk=5 exp (?77,000/RT) It has been shown that tantalum diffusion is negligible by comparison with silicon diffusion. The Ta5Si3 was found to exist in both tetragonal and hexagonal forms. A more limited investigation of silicon loss from TaSi2 to W, Mo, Nb, Zr, Ti, and Re indicates that none of these is superior to tantalum in limiting the degradation of the tantalum disilicide. In most instances a layer of composition M5Si3 forms on the metal side of the couple. 相似文献
11.
The reaction of alloys with HCI gas is generally more complicated than that of pure metals, and is, typically, a dealloying
process. In this work the rates of a model dealloying process, Co(Co-Pt) + 2HC1 → CoCl2(g) + H2 were measured in the temperature range 973 to 1273 K. The only reaction product for the HC1/H2 gas mixtures used in the experiments was gaseous CoCl2. Weight loss during the reaction was continuously monitored with a recording balance. Experimental variables included gas
composition, gas flow rate, and temperature for Co-10 at. pct Pt and for pure Co samples. The rate of the reaction was constant
with time and very nearly as high for the alloy as for the pure metal, in spite of the fact that Pt was inert for the conditions.
A surface instability occurred for the alloy yielding an open porous structure of ever increasing surface area. Transport
of CoCl2(g) in the gas boundary layer was important for determining the rate of the chlorination reaction for both the alloy and pure
metal.
Formerly Research Associate, Department of Materials Science and Engineering, The Pennsylvania State University, University
Park, PA 16802. 相似文献
12.
13.
Extraction of tantalum and niobium from tin slags by chlorination and carbochlorination 总被引:3,自引:0,他引:3
Chlorination and carbochlorination of tantalum and niobium low-grade concentrate (LGC) and high-grade concentrate (HGC), obtained
by leaching of tin slag, were studied using Cl2 + N2 and Cl2 + CO + N2 gas mixtures. Thermogravimetric analysis and conventional boat experiments were performed between 200 °C and 1000 °C. Chemical
analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to characterize the samples and reaction
products. Chlorination of LGC led to the recovery of about 95 pct of tantalum and niobium compounds at 1000 °C. However, the
tantalum and niobium chlorinated compounds were contaminated by chlorides of Fe, Mn, etc. For HGC, chlorination at 1000 °C allowed the extraction of about 84 and 65 pct of the niobium and tantalum compounds, respectively.
The recovered condensates were composed of pure tantalum and niobium chlorinated compounds. The apparent activation energies
E
a for the chlorination of LGC and HGC, between 850 °C and 1000 °C, were 166 and 293 kJ/mole, respectively. At temperatures
lower than 650 °C, the apparent activation energies for the LGC and HGC carbochlorination were 116 and 103 kJ/mole, respectively.
Total extraction of the tantalum and niobium compounds was achieved by the carbochlorination of the LGC at 1000 °C. The generated
tantalum and niobium chlorinated compounds were contaminated by the chlorides of Fe, Mn, Al, and Ca. The carbochlorination
of the HGC at 500 °C allowed complete extraction and recovery of pure tantalum and niobium compounds. These results confirm
the importance of obtaining an HGC from tin slag before its subsequent chlorination. The carbochlorination of such a concentrate
could be an efficient process for the recovery of relatively pure tantalum and niobium chlorinated compounds at low temperatures. 相似文献
14.
Z. A. Foroulis 《Metallurgical and Materials Transactions A》1982,13(1):153-159
This report deals with the kinetics and mechanism of the reaction of iron-chromium and iron-chromium-molybdenum alloys (containing
1.25 pct Cr-0.5 pct Mo, 5 pct Cr-0.5 pct Mo, and 12 pct Cr) with low partial pressure chlorine gas in the temperature range
270 to 550 °C. The rate of reaction generally decreases with exposure time and, in the case of alloys containing five pct
Cr and higher chromium content, the kinetics follows a parabolic rate law. The reaction kinetics is influenced by surface
films containing FeCl2 and CrCl3 which have very low vapor pressure in the temperature range studied. The effect of molybdenum on the reaction is negligible.
In the case of alloys containing five pct Cr-0.5 pct Mo and 12 pct Cr, the reaction product film consists essentially of CrCl3 (outer layer) and much smaller concentration of FeCl2 (inner layer). For these alloys, the observed parabolic kinetics is attributed to kinetic control of the overall reaction
by solid-state diffusion through the reaction product surface film. In the case of the 1.25 pct Cr-0.5 pct Mo alloy, the film
consists essentially of a mixture of FeCl2 and CrCl3. In this case, an outer CrCl3 film layer is not formed and the overall kinetics is influenced by the rate of formation of volatile FeCl3 speciesvia the reaction 2 FeCl2 + Cl2 (FeCl3)2. 相似文献
15.
研究了微波加热条件下(500~800 ℃),AlCl3氯化钒渣中有价金属Fe、Mn、V和Cr变温动力学。通过X射线衍射和扫描电镜能谱表征了氯化产物随时间的物相演变和形貌变化,考察了AlCl3/钒渣的质量比和熔盐配比对氯化提取率的影响。结果表明,AlCl3/钒渣的质量比为1.5、(NaCl-KCl)/AlCl3熔盐质量比为1.66∶1时Fe、Mn、V和Cr的提取率最佳,分别为91.66%、92.96%、82.67%、75.82%和63.14%,微波加热30 min,5种元素的提取率达到或者超过常规加热方式6 h的氯化提取效果。通过热力学和动力学分析,橄榄石相优先于尖晶石相发生氯化反应。而且V和Cr的氯化反应速度小于Fe和Mn。Fe和Mn氯化过程为扩散控制,其非等温扩散活化能为17.02和17.10 kJ·mol?1, V和Cr在氯化过程中的限制性环节为界面化学反应,其表观活化能分别为40.00和50.92 kJ·mol?1;微波与熔盐耦合强化氯化反应的机理可以描述为扩散作用增强和局部化学反应增强。 相似文献
16.
The kinetics of the homogeneous gas phase reaction between niobium oxychloride and phosgene was studied between 380° and 450°C
in a constant volume reactor. The reaction was found to be essentially irreversible with the only detected reaction products
being niobium pentachloride and carbon dioxide. The data obtained were fit by an elementary second-order rate equation. Values
of the Arrhenius frequency factor and activation energy were found to be 1.33 × 106 liter per g mol sec and 21.9 kcal per g mol with standard deviations of 0.05 × 106 and 1.4, respectively. 相似文献
17.
铜渣中含有30 %~40 %的Fe, 对铜渣中的Fe进行回收, 有利于缓解中国依赖进口铁矿石的压力.基于热力学分析氯化除铜的可行性, 在823 K、873 K、923 K、973 K温度下, 通过热重分析研究CuO-FeCl2体系的氯化过程动力学, 并考察反应温度和Ar气流量对反应的影响: CuO-FeCl2体系的氯化率随温度的升高而增大, 当Ar流量为50 mL/min时, 氯化率达到最大值为62.46 %.通过推导氯化反应动力学公式, 确定CuO-FeCl2体系的氯化反应为0级反应, 并且在873 K时由氯化过程动力学区过渡到扩散区, 动力学区的反应速率取决于CuCl2的挥发速率, 扩散区的反应速率取决于FeCl2向CuO表面扩散的速率. 相似文献
18.
Kinetics of chlorination of MoO3 with Cl2-air, Cl2-N2, and Cl2-CO-N2 gas mixtures have been studied by nonisothermal and isothermal thermogravimetric measurements, between ambient temperature
and 900 °C. Between 500 °C and 700 °C, the chlorination reaction of MoO3 with Cl2-N2 gas mixture has an apparent activation energy of about 165 kJ/mole, reflecting that a chemical reaction is the rate-controlling
step. The reaction order with respect to Cl2 partial pressure is about 0.75. The apparent activation energy for carbochlorination with Cl2-CO-N2 gas mixture is about 83 kJ/mole, between 400 °C and 650 °C. The carbochlorination of MoO3 was controlled by the chemical reaction, probably affected by the pore diffusion regime. The maximum reaction rate is obtained
by using a Cl2-CO-N2 gas mixture, having a Cl2/CO volume ratio equal to about 1. The total apparent reaction order with respect to Cl2 + CO in Cl2-CO-N2 gas mixture is about 1.5 for a Cl2/CO ratio equal to 1.
Laboratoire Environnement et Minéralurgie, associated with the Centre National de la Recherche Scientifique, Mineral Processing
and Environmental Engineering team. 相似文献
19.
JG Williams 《Canadian Metallurgical Quarterly》1997,73(865):697-700
The clinical features of acute chlorine gas inhalation, and its management are reviewed. Current medical views on the chronic effects of an acute overwhelming exposure on lung function (reactive airways dysfunction syndrome), and the more controversial field of lung disease secondary to repeated inhalations of lower concentrations of chlorine gas are discussed. 相似文献
20.
Reduction of titania using methane-containing gas was investigated in a laboratory fixed-bed reactor in the temperature range
1373 to 1773 K. The reduction product is titanium oxycarbide, which is a solid solution of TiC and TiO. At 1373 K, the formation
rate of TiC is very slow. The rate and extent of reaction increase with increasing temperature to 1723 K. A further increase
in temperature to 1773 K does not affect the reaction rate and extent. An increase in methane concentration to 8 vol pct favors
the reduction process. A further increase in methane concentration above 8 vol pct causes excessive carbon deposition, which
has a negative effect on the reaction rate. Hydrogen partial pressure should be maintained above 35 vol pct to depress the
cracking of methane. Addition of water vapor to the reducing gas strongly retards the reduction reaction, even at low concentrations
of 1 to 2 vol pct. Carbon monoxide also depresses the reduction process, but its effect is significant only at higher concentrations,
above 10 vol pct. 相似文献