The chlorination kinetics of zirconium dioxide in the presence of carbon and carbon monoxide

Chlorination of zirconium dioxide, an important step in the commercial production of reactor grade zirconium metal, has been studied using carbon and carbon monoxide as reductants. Zirconium tetrachloride was produced when the oxide was reacted with chlorine alone above 1000°C; by introducing carbon the reaction temperatures could be lowered 200°C, and when carbon monoxide was used the reaction temperatures necessary for similar rates were even lower. With carbon monoxide the chlorination of zirconium dioxide is described by two regions differentiated by temperature and the dependence of reaction rate upon chlorine and carbon monoxide pressures.     

On the kinetics of the chlorination of titanium dioxide in the presence of solid carbon

Metallurgical and Materials Transactions B - The influence of solid carbon on the chlorination of TiO2 with Cl2 and CO-CO2-Cl2 gas mixtures was investigated gravimetrically using rutile and...     

硝酸银电位滴定法测定高纯二氧化锗中氯

我国行业分析标准采用硫氰酸汞分光光度法测定二氧化锗中氯含量,由于硫氰酸汞是一种剧毒试剂,影响工作人员身体健康和污染环境,为此,建立了一种无毒的测定高纯二氧化锗中氯的电位滴定法。实验结果表明:在pH 2～4的乙醇-水的介质中,以硝酸银标准溶液作为滴定剂,二级微商法确定滴定终点,滴定曲线突跃明显,终点准确,基体锗、大量的Na⁺、NO₃^-和二氧化锗中微量金属元素不影响氯的测定。方法用于高纯二氧化锗样品中氯的测定,测定结果与行业标准方法(硫氰酸汞分光光度法)相一致,相对标准偏差在0.89%～1.6%之间。     

硫酸亚铁-二氧化氯法处理高质量浓度含氰废水

试验研究了硫酸亚铁-二氧化氯处理含氰废水的方法,在高质量浓度含氰废水中,先加八硫酸亚铁处理后,过滤,再加入二氧化氯进行二次废水处理。该方法节省了反应单元,过滤时氰的质量浓度已达到排放标准,改善了操作环境,提高了铁蓝的质量。     

The extraction of hafnium (IV) by some organophosphorus reagents in the presence of two mineral acids

Extraction of hafnium (IV) was studied from solutions of mixtures of perchloric and nitric acids and of perchloric and hydrochloric acids of constant total acidity 2, 4, 6 and 8 M and c_Hf ? 4 × 10^?4mol l^?1. The organic phase consisted of solutions of various acidic or neutral organophosphorus reagents including di-n-butylphosphoric acid, di-n-amylphosphoric acid, di-n-octylphosphoric acid, n-decylphenylphosphonic acid, tri-n-butylphosphine oxide, tri-n-octylphosphine acid (TOPO), tri-n-phenylphosphine oxide, and tri-n-butylphosphate (TBP); or of 2-thenoyltrifluoroacetone, 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone, or N-benzoyl-N-phenylhydroxylamine in benzene, chloroform, or n-octane. Pronounced synergic extraction of hafnium occurs only with organophosphorus reagents from aqueous phases whose acidity is not lower than 3 M (HClO₄ + HNO₃) or 5 M (HClO₄ + HCl). The synergic effect was not affected markedly by variation of the initial concentration of hafnium in the range 1 × 10^?8 ?4 × 10^?4 mol l^?1, but it decreased with increasing initial concentration of the organophosphorus reagent and decreasing concentration of the H⁺ ions. No synergism was observed for the extraction of hafnium from mixtures of perchloric and sulphuric acids. It is suggested that the hafnium passes into the organic phase in the form of mixed complexes, the salting-out effect of perchloric acid playing an appreciable part.     

Heat and mass transfer limitations in gasification of carbon by carbon dioxide

Rates of gasification of carbon by carbon dioxide were measured in the laboratory using a thermogravimetry apparatus. The experiments were conducted at various temperatures and sample bed depths using powders of graphite and coconut char as sources of carbon, under flowing gas of CO₂. Various CO–CO₂ mixtures were also employed for the study of coconut char. The measured rate data were subjected to a heat and mass transfer analysis to find out the values of isothermal and non-isothermal effectiveness factors. These values were utilized to predict the intrinsic chemical reactivities of graphite and coconut char samples, free from heat and mass-transfer limitations. Extrapolation of experimental data to hypothetical zero bed depth showed good agreements with the above at various temperatures, thus providing valuable cross-checks. The activation energies were found to be 260 and 250 kJ/mol for graphite and coconut char, respectively, under CO₂. Carbon monoxide was found to decrease the rate of gasification but not as drastically as some literature reports predict.     

Kinetics of oxidation of carbon in liquid iron-carbon-silicon-manganese-sulfur alloys by carbon dioxide in nitrogen

The oxidation of carbon with the simultaneous oxidation of silicon, manganese, and iron of liquid alloys by carbon dioxide in nitrogen and the absorption of oxygen by the alloys from the gas were studied using 1-g liquid iron droplets levitated in a stream of the gas at 1575 °C to 1715 °C. Oxidation of carbon was favored over oxidation of silicon and manganese when cast iron (3.35 pct C, 2.0 pct Si, 0.36 pct Mn, and 0.05 pct S) reacted with CO₂/N₂ gas at 1635 °C. An increase in the flow rate of CO₂/N₂ gas increased the decarburization rate of cast iron. The rate of carbon oxidation by this gas mixture was found to be independent of temperature and alloying element concentrations (in the range of silicon = 0 to 2.0 pct manganese = 0 to 0.36 pct and sulfur = 0 to 0.5 pct) within the temperature range of the present study. Based on the results of a kinetic analysis, diffusion of CO₂ in the boundary layer of the gas phase was found to be the rate-limiting step for the reactions during the earlier period of the reaction when the contents of carbon, silicon, and manganese are higher. However, the limiting step changed to diffusion of the elements in the metal phase during the middle period of the reaction and then to the diffusion of CO in the gas phase during the later period of the reaction when the content of the elements in the metal were relatively low. For the simultaneous oxidation reactions of several elements in the metal, however, the diffusion of CO₂ in the gas phase is the primary limiting step of the reaction rate for the oxidation of carbon during the later period of reaction. Formerly Visiting Assistant Research Scientist, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109     

Electrotransport of carbon,nitrogen, and oxygen in hafnium metal

The electrotransport velocities of carbon, nitrogen, and oxygen in alpha and beta hafnium were determined for the temperature range of 1650 to 2130°C. Diffusion coefficients and effective valences were also obtained for each solute. These data were used to predict the degree of purification achievable in a hafnium rod after electrotransport at 2000°C for different times. A comparison was made between the predicted and experimentally observed results. Formerly Graduate Assistant, Department of Metallurgy, Iowa State University     

Interfacial reaction kinetics in the decarburization of liquid iron by carbon dioxide

The kinetics of decarburization of liquid iron have been studied between 1160 and 1600°C under conditions where mass transport of reactants is not rate determining. Studies with continuously carbon-saturated iron and of iron with varying carbon concentration have been used to show that the slow step at high concentrations of carbon is independent of carbon concentration and is first order with respect to the pressure of CO₂. For high purity iron, the forward rate constant, in mole cm² s^-1 atm^-1, is given by the equation ln k_f = -11,700/T-0.48. It is concluded that the data are consistent with the chemisorption process as the rate limiting step. A marked sensitivity of the rate to trace amounts of sulfur has been found and it is shown that this is consistent with ideal adsorption of sulfur and is in fair accord with the existing measurements of the depression of the surface tension of iron-carbon alloys by sulfur. D. R. Sain was formerly a Graduate Student.     

Decomposition of monocrotophos in aqueous solution by UV irradiation in the presence of titanium dioxide

The decomposition of monocrotophos in aqueous solution by UV/TiO2 reduction process was studied under various pH values, TiO2 dosages, light intensities, dissolved oxygen levels and other operating conditions. The presence of dissolved oxygen inhibits the recombination of electrons and holes, and enhance the decomposition of monocrotophos by UV/TiO2 process, but excessive dissolved oxygen posed no further effect on the decomposition of monocrotophos. The decomposition rates of monocrotophos were significantly higher for acidic solutions than those for alkaline solutions. Increasing the light intensity would drastically increase the decomposition rate of monocrotophos, but was ultimately influenced by the amount of TiO2 present in solutions. The quasi-global kinetics based on a simplified consecutive reaction scheme was developed to describe the temporal behavior of monocrotophos decomposition in aqueous solution by UV/TiO2 process.     

An experimental investigation of the gasification of graphite by carbon dioxide

The gasification of graphite by carbon dioxide was studied under atmospheric pressure in a fixed bed reactor in the temperature range of 1173–1773?K, CO₂ partial pressures 2–10?kPa and gas flow rate 0·5–2·0?L?min^?1. Iron presented in a small amount in graphite ash had a catalytic effect on the gasification reaction at 1373?K; this effect was weaker at 1473?K due to the melting of iron saturated with carbon. The gasification rate increased with increasing CO₂ partial pressure and total gas flow rate.     

Reduction of iron oxides by wet gas in the presence of carbon

The equilibrium parameters in the reduction of iron oxides by wet gas (CO + CO₂ + H₂ + H₂O) in the presence of carbon are calculated. Graphical representation of the results is discussed, and a diagram is plotted consisting of a set of three-phase equilibrium surfaces and four-phase equilibrium curves, whose point of intersection determines the parameters of invariant five-phase equilibrium. The composition of the wet gas in equilibrium with the following mixtures is established: Fe₃O₄-C, Fe₃O₄-FeO-C, FeO-C, FeO-Fe(C)-C, Fe(C)-C, and Fe₃O₄-Fe(C)-C. A method of graphical determination of the possible wet gas compositions in equilibrium with these mixtures is proposed.     

Effectiveness of chlorine dioxide in disinfection on two soft denture liners

OBJECTIVE: The purpose of this study was to evaluate a hydroxylapatite-based material and calcium sulfate when each was used under a resin-modified glass ionomer cement to repair furcation perforations. STUDY DESIGN: Perforations of pulp chamber floors were made in 72 teeth of 9 dogs. Perforations were divided into 3 equal-sized groups and repaired with resin-modified glass ionomer either alone or over an artificial floor. The artificial floor was either a hydroxylapatite-based material or calcium sulfate. Three dogs were killed at each of 3 intervals (1, 3, and 6 months). The tissue response to the tested materials was evaluated clinically, radiographically, and histologically. RESULTS: The hydroxylapatite-based material showed the highest radiographic success; this was followed by calcium sulfate and glass ionomer. From histologic evaluation, the average success rate was found to be 67% for calcium sulfate, 62% for the hydroxylapatite-based material, and 59% for glass ionomer. However, there was no statistical significant difference with the resin-modified glass ionomer when it was used alone and when it was used over a barrier. There was also no significant difference between the hydroxylapatite-based material and the calcium sulfate when they were used as artificial floors. CONCLUSION: The use of an artificial floor may not be necessary when flowable resin-modified glass ionomer cements are used.     

Glucose and carbon dioxide metabolism by Succinivibrio dextrinosolvens

Growth rates and culture conditions affect the molar yields of catabolic end products and cells of Succinivibrio dextrinosolvens growing on glucose. When growth in chemostats occurred, a trend toward decreased succinate and acetate formation, increased lactate formation, and a higher yield of cells correlated with an increase in the growth rate. End product and cellular yields on defined medium indicate a high maintenance requirement for S. dextrinosolvens and are consistent with energy conservation steps during the formation of acetate and succinate. Simultaneous carbon dioxide consumption and production were determined from batch studies with NaH14CO3, and the amounts were used to calculate a fermentation balance. These data also indicated that CO2 consumption lags behind CO2 production early in the growth phase, becoming equivalent to it toward stationary phase. Significantly more CO2 was fixed by S. dextrinosolvens when the organism was cultured in chemostats sparged with CO2. Formate is in part derived from free CO2 in the medium, as shown by 13C nuclear magnetic resonance studies, and may be sensitive to CO2 availability. Nuclear magnetic resonance data are consistent with the carboxylation of a C3 intermediate of the Embden-Meyerhof-Parnas pathway of glycolysis to a C4 compound to eventually form succinate.     

Adsorption of carbon dioxide by coconut activated carbon modified with Cu/Ce

A series of the coconut activated carbons (CAC) based absorbents modified with Cu and Ce (Cu/CAC, Cu/Ce/CAC) were prepared by impregnation technology for carbon dioxide capture. The adsocrption equilibriums of CO₂ on Cu/CAC and Cu/Ce/CAC were measured. The results showed that the adsorption capacity of CO₂ onto the activated carbon modified with Cu/Ce increased with the decreasing temperature in the same pressure. The adsorption capacity of CO₂ on Cu/CAC was higher than that of the blank CAC, and compared with the Cu/CAC, the adsorption capacity of CO₂ of Cu/Ce/CAC with the mass ratio of Cu/Ce=30 was improved at 298 and 303 K. In addition, the adsorption equilibrium data for CO₂ at various temperatures was fitted to Langmuir, Freundlich and D-R isotherm models. It was found that the D-R equation was the best model for fitting the adsorption data on Cu/Ce/CAC at different temperatures.     

Kinetics of chlorination of tantalum pentoxide in mixture with sucrose carbon by chlorine gas

The mechanism and kinetics of β-Ta₂O₅ chlorination, mixed with sucrose carbon, have been studied by a thermogravimetric technique. The investigated temperature range was 500 °C to 850 °C. The reactants and reaction residues were analyzed by scanning electronic microscopy (SEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller method for surface area (BET). The effect of various experimental parameters was studied, such as carbon percentage, temperature, chlorine partial pressure, and flow, use of the multiple sample method, and carbon previous oxidation. The carbon percentage and previous treatment have an effect on the system reactivity. The temperature has a marked effect on the reaction rate. In the 500 °C to 600 °C temperature interval, the apparent activation energy is 144 kJ/mol of oxide, while at higher temperatures, the activation energy decreases. With high chorine partial pressures, the order of reaction is near zero. The kinetic contractile plate model, X=kt, considering carbon oxidation as the controlling stage, is the one with the best fit to the experimental data. A probable mechanism for the carbochlorination of β-Ta₂O₅ is proposed: (1) activation of chlorine on the carbon surface, (2) chlorination of Ta₂O₅, (3) oxidation of carbon, and (4) recrystallization of β-Ta₂O₅.     

Adsorption of carbon dioxide by coconut activated carbon modified with Cu/Ce

A series of the coconut activated carbons(CAC) based absorbents modified with Cu and Ce(Cu/CAC,Cu/Ce/CAC) were prepared by impregnation technology for carbon dioxide capture.The adsocrption equilibriums of CO2 on Cu/CAC and Cu/Ce/CAC were measured.The results showed that the adsorption capacity of CO2 onto the activated carbon modified with Cu/Ce increased with the decreasing temperature in the same pressure.The adsorption capacity of CO2 on Cu/CAC was higher than that of the blank CAC,and compared with the Cu/CAC,the adsorption capacity of CO2 of Cu/Ce/CAC with the mass ratio of Cu/Ce=30 was improved at 298 and 303 K.In addition,the adsorption equilibrium data for CO2 at various temperatures was fitted to Langmuir,Freundlich and D-R isotherm models.It was found that the D-R equation was the best model for fitting the adsorption data on Cu/Ce/CAC at different temperatures.