The influence of sulfur on interfacial reaction kinetics in the decarburization of liquid iron by carbon dioxide

The kinetics of decarburization of continuously carbon-saturated liquid iron by CO₂ have been studied between 1280 and 1600?C at sulfur concentrations between 0.01 and 1 wt pct. The results are consistent with a surface blockage mechanism by chemisorbed sulfur which shows an essentially ideal adsorption isotherm. The adsorption coefficient of sulfur, in (wt pct)^-1, is given by the equation logK = 3600/T + 0.57 for carbon-saturated alloys. A small residual rate at apparent surface saturation is observed. This leaves about 1.4 pct of the active surface sites available for reaction, essentially independent of temperature. Studies with varying carbon concentration suggest that to a first approximation, and above about 3 wt pct C, the adsorption equilibrium for sulfur depends only on the thermodynamic activity of sulfur.     

The influence of sulfur on interfacial reaction kinetics in the decarburization of liquid iron by carbon dioxide

The kinetics of decarburization of continuously carbon-saturated liquid iron by CO₂ have been studied between 1280 and 1600‡C at sulfur concentrations between 0.01 and 1 wt pct. The results are consistent with a surface blockage mechanism by chemisorbed sulfur which shows an essentially ideal adsorption isotherm. The adsorption coefficient of sulfur, in (wt pct)^-1, is given by the equation logK = 3600/T + 0.57 for carbon-saturated alloys. A small residual rate at apparent surface saturation is observed. This leaves about 1.4 pct of the active surface sites available for reaction, essentially independent of temperature. Studies with varying carbon concentration suggest that to a first approximation, and above about 3 wt pct C, the adsorption equilibrium for sulfur depends only on the thermodynamic activity of sulfur. DR. SAIN was formerly a Graduate Student.     

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.     

Carbochlorination kinetics of titanium dioxide with carbon and carbon monoxide as reductant

Kinetic study of the chlorination of titanium dioxide (rutile and anatase) was carried out in a fixedbed reactor at temperature ranging from 800 °C to 1000 °C and normal pressure. In our experiment, titanium dioxide powder and gaseous chlorine with carbon or carbon monoxide as reductant were used. The products of the reaction are all in gaseous phase under the temperatures and pressure studied. With CO as reductant, reaction is of noncatalytic gas-solid nature and experimental data fit the shrinking core model. When using C as reductant, solid-solid reaction is involved. Reactivity is highly enhanced by solid carbon and it is concluded that an activated C-TiO₂-Cl complex contributes to the enhanced reactivity. A reaction model based on phase boundary control applies to the experimental data. Thermodynamic analysis supports the experimental observation.     

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.     

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.     

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.     

On the kinetics of oxidation of liquid copper and copper-sulfur alloys by carbon dioxide

The rates of transfer of oxygen between CO₂-CO gas mixtures and liquid copper and copper-sulfur alloys have been studied by a steady-state electrochemical technique. For sulfur-free stagnant copper, and under the conditions of the experiments, the rates are shown to be controlled by the diffusion of oxygen in the metal. The resulting diffusivities are in close accord with the bulk of the previous determinations. At high sulfur concentrations, the rate is found to be controlled by an interfacial reaction which is first order with respect to the pressure of CO₂ and inversely proportional to the sulfur concentration. The rate constant, in mole (at. pct)cm⁻² s⁻¹ atm⁻¹, is approximately 8 × 10⁻⁹ at 1146°C. Formerly a Graduate Student.     

Extraction kinetics of neodymium from chloride medium using HEH/EHP saponified with magnesium bicarbonate solution

Magnesium bicarbonate solution is considered as an environmentally friendly extractant saponification agent for the solvent extraction of rare earth elements due to its advantage of minimum water pollution.In order to reveal the extraction regularity, optimize production-process and guide the use of this new extraction system, the extraction of Nd(Ⅲ) in chloride medium with HEH/EHP saponified by magnesium bicarbonate solution was investigated with the self-designed constant interfacial area cell. Besides, the effects of stirring rate, temperature, specific interfacial area and concentration of Mg-HEH/EHP on the extraction rate of Nd(Ⅲ) were systematically investigated. Results show that, the rate of extraction is governed by both diffusion and chemical reaction, and the extraction reaction takes place at the interface. The apparent activation energy of the extraction reaction is 16.88 kJ/mol. The corresponding rate equation is deduced. The mechanisms and rate-determining step are speculated based on interfacial reaction models, which is consistent with the experimental results.     

Structural effects in the reaction between carbon dioxide and coke doped with various potassium bearing catalytic precursors

The rate of reaction between carbon dioxide and coke with and without the additions of KCN, KOCN, and K₂CO₃ was studied using thermogravimetry. Since both potassium and carbon are lost during the reaction, the concentration of potassium in the coke samples was determined as a function of the extent of the reaction by atomic absorption spectrometry. The changes in the specific surface area due to the reaction were studied by the nitrogen adsorption technique. The changes in the pore structure of coke were investigated by mercury porosimetry and scanning electron microscopy. The distribution of potassium in the coke structure was examined as a function of the reaction time by the energy dispersion X-ray technique. Furthermore, since sulfur is known to influence the rate of the C-CO₂ reaction, the sulfur content of the coke samples with or without the addition of catalytic precursors was monitored as a function of the extent of reaction. The influences of the structural parameters and the concentration of potassium on the rate of the coke-CO₂ reaction were determined. The rate data were analyzed on the basis of a structural model to examine the contributions of the chemical reaction and the pore diffusion on the overall rate of the coke-CO₂ reaction. M. ALAM, formerly Graduate Student, now     

The influence of CSF calcium and magnesium on the ventilatory response to carbon dioxide during hyperoxia

Respiratory responses to inhaled carbon dioxide were measured in anaesthetized cats during perfusion of the ventriculocisternal system with artificial cerebrospinal fluid. A study was performed to evaluate the effect of changes in the magnesium and/or calcium concentration of the CSF on the CO2 response curve which was described as VE = S (PCSF, CO2 -- B). A decrease of S was observed when the magnesium concentration of the perfusion fluid was increased; the B-value remaining the same. The reverse was true down to magnesium concentrations of 0.6 mmol-1-1. Below this concentration S remained the same or decreased; the B-value was lowered. When both the calcium and magnesium concentrations of the CSF were changed, the relation between S and these concentrations could be described as to be proportional to CCAa-CMgb. The effect of changes in the calcium concentration was much more pronounced than comparable changes of the magnesium concentration as reflected by the magnitude of the exponents a and b which were found to be -2.80 (S.D. 0.11) and -0.60 (S.D. 0.03) respectively.     

The influence of carbon dioxide and body position on near-infrared spectroscopic assessment of cerebral hemoglobin oxygen saturation

Near-infrared spectroscopy may allow continuous and noninvasive monitoring of regional brain hemoglobin oxygen saturation by measuring the differential absorption of infrared light by oxyhemoglobin and deoxyhemoglobin. We have previously examined the correlation between the spectroscopic signal generated by a prototype cerebral oximeter (Invos 3100; Somanetics, Troy, MI), and global brain hemoglobin oxygen saturation calculated from arterial and jugular venous bulb oxygen saturations. Because the technology does not distinguish between arterial and venous hemoglobin saturation, changes in the proportion of cerebral arterial and venous blood volume, which may result from changes in blood flow or venous distending pressure, may confound measurements. In eight conscious volunteers breathing hypoxic oxygen mixtures, we examined the influence of supine, 20 degrees Trendelenburg, and 20 degrees reverse Trendelenburg positions on the correlation of the spectroscopic measurement of cerebral oxygen saturation in the field assessed by the probe (CSfO2) and the calculated brain hemoglobin oxygen saturation (CScombO2), estimated as 0.25 x arterial saturation plus 0.75 x jugular venous bulb oxygen saturation. We found that changes in position did not influence the association between CSfO2 and CScombO2 (r2 = 0.69-0.885) during hypoxic challenge. In a second set of eight volunteers, we studied the influence of hypercapnia and hypocapnia and body position on the association between CSfO2 and CScombO2, and found that they were less well correlated (r2 = 0.366-0.976) in individual patients. Because changes in body position and Paco2 confound the relationship between CSfO2 and CScombO2, changes in CSfO2 can best be assessed if position and Paco2 are constant.     

二氧化碳相变致裂技术研究进展与展望

二氧化碳相变致裂作为一种环境友好的绿色破岩技术,具有破岩效率高、振动小、无污染等优点,近年来已成为岩石破碎与开挖领域的热门研究课题,相关研究发展迅速。大量学者运用理论分析、实验研究和数值模拟等手段对二氧化碳相变致裂技术进行了广泛探究,并取得了一些有益进展。通过对现有相关研究成果的调研分析,阐述了二氧化碳相变致裂技术的破岩机理,回顾了二氧化碳相变致裂荷载特征及其测试手段,归纳了致裂荷载表征方法,概括了致裂荷载与致裂效果的主要影响因素,分析了二氧化碳相变致裂的有害效应,总结了二氧化碳相变致裂技术在多领域的应用,并探讨了二氧化碳相变致裂当前存在的问题与未来挑战,以期为二氧化碳相变致裂技术的理论研究和工程应用推广提供参考。      

Clusters in carbon martensite: Thermodynamics and kinetics

An original method of evaluation of the cluster population in carbon martensite has been developed. Using this method, it is shown that Kurdjumov’s model of carbon redistribution within the different octahedral site sublattices can quantitatively account for both observed normal and abnormal tetragonality in carbon martensite. It is also shown that the existence of the internal strains in martensite constitutes a necessary and sufficient condition for the energetic preference of tetrahedral over the cubic lattice. The presence of the residual tetragonal distortion in the quasi-cubic phase of k-martensite is associated with the presence of the mixed clusters formed of the atoms belonging to O _c sublattice as well as to remaining ones. By using a computer simulation of the dynamical behavior of carbon martensite approaching the thermodynamical equilibrium, it was found that the ultimate state of this system is strongly beyond the thermal equilibrium. Even after long-term aging, the free energy is far beyond the minimum value allowed for this system. The reason for such a behavior and the possible aging processes proceeding in this system are discussed at the molecular level. All of the ordering parameters are affected by the aging process. The evolution proceeds in the distinctly different time intervals for different parameters. At first, the long-range ordering parameter that determines the tetragonality of martensite evolves and reaches the stable value. In the next stage, the formation and then disintegration of two-particle clusters occurs. Disintegration of two-particle clusters coincides with the stage when three-particle cluster formation occurs at a high rate. Threeparticle clusters also disintegrate when some time elapses. The same pattern repeats regarding four-, five-, six-, seven-, and eight-particle clusters. To simplify the calculations, the nine-particle clusters are assumed to be the largest possible and are identified with an existence of superstructure. The formation of 100 pct of nine-particle clusters with no contribution of free atoms in an alloy ceases all aging processes. The evolution of these processes is illustrated graphically in the time range from 16 seconds to 1500 years, as estimated on the basis of experimental data.     

二氧化碳活化制备烟杆基颗粒活性炭的研究

进行了以烟杆废弃物为原料、木焦油为主的复合黏结剂、二氧化碳为活化剂制备颗粒活性炭的研究。系统地研究了活化温度、活化时间、二氧化碳流量等因素对烟杆基颗粒活性炭活化效果的影响，得到了该试验条件下最佳工艺条件：活化温度为900℃，活化时间为100min，二氧化碳流量为0．5L／min。该工艺条件下制备的颗粒活性炭碘吸附值为901．36mg／g，亚甲基蓝吸附值为80ml/g，活性炭得率为38.53％。同时，测定了该活性炭氮吸附，通过BET计算了活性炭的比表面积，并通过密度函数理论（DFT）表征了活性炭的孔结构。结果表明：制备的活性炭为微孔型，BET比表面积为947.81m^2／g，总孔容为0．48ml／g。     

Carbon dioxide stimulates peroxynitrite-mediated nitration of tyrosine residues and inhibits oxidation of methionine residues of glutamine synthetase: both modifications mimic effects of adenylylation

The activity of glutamine synthetase (EC 6.3.1.2) from Escherichia coli is regulated by the cyclic adenylylation and deadenylylation of Tyr-397 in each of the enzyme's 12 identical subunits. The nitration of Tyr-397 or of the nearby Tyr-326 by peroxynitrite can convert the unadenylylated enzyme to a form exhibiting regulatory characteristics similar to the form obtained by adenylylation. The adenylylated conformation can also be elicited by the oxidation of surface-exposed methionine residues to methionine sulfoxide. However, the nitration of tyrosine residues and the oxidation of methionine residues are oppositely directed by the presence and absence of CO2. At physiological concentrations of CO2, pH 7.4, nitration occurs but oxidation of methionine residues is inhibited. Conversely, in the absence of CO2 methionine oxidation is stimulated and nitration of tyrosine is prevented. It was further established that adenylylation of Tyr-397 precludes its nitration by peroxynitrite. Furthermore, nitration of Tyr-326 together with either nitration or adenylylation of Tyr-397 leads to inactivation of the enzyme. These results demonstrate that CO2 can alter the course of peroxynitrite-dependent reactions and serve notice that (i) the reactions have physiological significance only if they are shown to occur at physiological concentrations of CO2 and physiological pH; and (ii) the peroxynitrite-dependent nitration of tyrosine residues or the oxidation of methionine residues of metabolically regulated proteins can seriously compromise their biological function.     

Intraoperative end-tidal carbon dioxide values and derived calculations correlated with outcome: prognosis and capnography

OBJECTIVE: To determine how much information concerning resuscitation and outcome is provided by the end-tidal CO2 and derived variables obtained during surgery. DESIGN: Retrospective chart review. SETTING: Emergency hospital operating room. PATIENTS: One hundred critically ill or injured patients requiring major surgery and having a mortality rate of 41%. INTERVENTIONS: Standard intraoperative monitoring, including continuous capnography, plus arterial blood gas analyses every 1 to 1.5 hrs during surgery. MEASUREMENTS AND MAIN RESULTS: There was only a fair correlation between the PaCO2 and end-tidal CO2 (r2 = .14). The mortality rates in these patients were highest in those patients who had the lowest end-tidal CO2 values, the highest arterial to end-tidal CO2 differences, and the highest estimated alveolar deadspace fraction. A persistent end-tidal CO2 of < or = 28 torr (< or = 3.8 kPa) was associated with a mortality rate of 55% (vs. 17% in those patients with a higher end-tidal CO2). The mortality rate was also increased in patients with a persistent arterial to end-tidal CO2 difference of > or = 8 torr (> or = 1.1 kPa) (58% vs. 23%). CONCLUSIONS: End-tidal CO2 and derived values should be monitored closely in critically ill or injured patients. Efforts should be made--by increasing cardiac output and core temperature and by adjusting ventilation as needed--to maintain the end-tidal CO2 at > or = 29 torr (> or = 3.9 kPa) and the arterial to end-tidal CO2 difference at < or = 7 torr (< or = 1.0 kPa).     

The influence of carbon deposition on the reduction kinetics of commercial grade hematite pellets with CO,H2, and N2

Experimental measurements are reported on the rate at which commercial grade, low silica hematite pellets react with a gas mixture consisting of CO, H₂, and N₂ over the temperature range 500 °C to 1200 °C. Systems of this type are of considerable practical interest, both regarding the operation of direct reduction processes and ironmaking in the blast furnace. The results of the work may be summarized as follows: No carbon deposition was found when operating the system above 900 °C and in the absence of CO gas. When operating the system below 900 °C carbon deposition occurred, which in effect prevented the normal conversion from reaching completion. The maximum rate of carbon deposition was found to occur between 500 °C and 600 °C. In general hydrogen (in the presence of CO) tended to promote carbon deposition, while the presence of nitrogen appeared to retard the deposition process. When the reaction process was being carried out below 900 °C with CO + H₂ gas mixtures, the reduction process occurred simultaneously with carbon deposition. At lower temperatures, say around 500° to 600 °C, the deposition process dominated, while at the higher temperatures, and particularly at a high hydrogen content of the reactant gas, the reduction process was dominant. The structural examination of the partially reacted specimens has shown that the carbon deposited was found primarily in the form of elemental carbon rather than cementite. Furthermore, X-ray analysis of the free pellet surface has indicated that iron was present in the carbon deposit phase. The practical industrial implications of these findings are discussed in the paper.