Mechanism and Kinetics of the Thermal Oxidation of Natural Sphalerite

The oxidation of natural sphalerite on heating in an oxidative medium is studied by thermogravimetry coupled with scanning calorimetry, mass spectrometry of released gases, and X-ray powder diffraction analysis. The mechanism of sphalerite oxidation when the particle surface is equally accessible and sulfur dioxide is removed from the reaction zone is the formation of ZnO, ZnFe₂O₄, and SO₂. The process is found to be one-stage, as determined by a nonisothermal kinetic method. The activation energies are from 293 to 317 kJ/mol depending on the model used. Natural sphalerite is oxidized in the kinetic regime, and the rate-determining steps are the formation and growth of new-phase nuclei.     

Reaction Mechanism and Kinetics of Enargite Oxidation at Roasting Temperatures

Roasting of enargite (Cu₃AsS₄) in the temperature range of 648?K to 898?K (375?°C to 625?°C) in atmospheres containing variable amounts of oxygen has been studied by thermogravimetric methods. From the experimental results of weight loss/gain data and X-ray diffraction (XRD) analysis of partially reacted samples, the reaction mechanism of the enargite oxidation was determined, which occurred in three sequential stages:

1. $4{\text{Cu}}_{ 3} {\text{AsS}}_{ 4} \left( {\text{s}} \right){\text{ + 13O}}_{ 2} \left( {\text{g}} \right){\text{ = As}}_{ 4} {\text{O}}_{ 6} \left( {\text{g}} \right){\text{ + 6Cu}}_{ 2} {\text{S}}\left( {\text{s}} \right){\text{ + 10SO}}_{ 2} \left( {\text{g}} \right) $
2. $ 6{\text{Cu}}_{ 2} {\text{S}}\left( {\text{s}} \right){\text{ + 9O}}_{ 2} \left( {\text{g}} \right){\text{ = 6Cu}}_{ 2} {\text{O}}\left( {\text{s}} \right){\text{ + 6SO}}_{ 2} \left( {\text{g}} \right) $
3. $ 6{\text{Cu}}_{ 2} {\text{O}}\left( {\text{s}} \right){\text{ + 3O}}_{ 2} \left( {\text{g}} \right){\text{ = 12CuO}}\left( {\text{s}} \right) $

The three reactions occurred sequentially, each with constant rate, and they were affected significantly by temperature and partial pressure of oxygen. The kinetics of the first stage were analyzed by using the model X?=?k ₁ t. The first stage reaction was on the order of 0.9 with respect to oxygen partial pressure and the activation energy was 44?kJ/mol for the temperature range of 648?K to 898?K (375?°C to 625?°C).     

Sodium Aluminate Concentration Effects on Microstructure and Corrosion Behavior of the Plasma Electrolytic Oxidation Coatings on Pure Titanium

Metallurgical and Materials Transactions A - Sodium aluminate (NaAlO2) concentration was varied in order to understand the influence of the chemical composition of electrolyte on the spark...     

Kinetics and Mechanism of High-Temperature Oxidation in Air of Au - Cu Alloy

We have used thermogravimetry to study the kinetics of high-temperature (up to 800 °C) oxidation of the alloy 58.3 mass% Au - 41.7 mass% Cu with isothermal heating of the specimens. Using petrographic analysis of the oxide layers, we determined the reaction products. We have shown that up to 200 °C, the indicated alloy is not oxidized at all. More rapid oxidation of the alloy is observed at temperatures above 400 °C. Up to 500 °C, an inner layer consisting of Cu₂O predominates in the two-layer scale on the alloy, while the outer CuO layer has a significantly smaller thickness. At 600 °C, the upper layer of scale contains Cu₂O while the lower layer contains Cu₂O and gold. At higher temperatures, all the way up to 800 °C, the scale is two-layer as before but its upper layer contains CuO while its lower layer contains Cu₂O and small gold rods distributed in that oxide. Thus we have established three oxidation regions characterized by different scale phase compositions and different mechanisms for the process, mainly due to transition from an ordered state of the alloy (intermetallic AuCu₃) to a completely disordered solid solution of gold in copper. We used the Arrhenius equation to calculate the apparent activation energy for oxidation: E₁ = 20.4 kJ/mole for the temperature range 400–500 °C and E₂ = 9.5 kJ/mole for 600–800 °C. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 85–91, July–August, 2005.     

Kinetics of the Oxidation of CaS

The kinetics of the oxidation of dense pellets of CaS by the reaction:

$$2CaS(s) + 3O_2 (g) \to 2CaO(s) + 2SO_2 (g)$$

was examined by continuous thermogravimetric analysis. The experiments covered a temperature range of 1673 to 1853 K, Ar-O₂-SO₂ mixtures varying from 1 to 40 pct O₂ and 0 to 20 pct SO₂, and gas velocities ranging from 20 to 57 cm/s at the reaction temperature. Analysis of the data shows that the initial rate of the reaction is controlled by the mass transfer of O₂ through the gaseous boundary layer of the pellet and is subsequently controlled by the diffusion of O₂ through the porous layer of the reaction products. To verify these results, the permeation rates of SO₂ through the reaction products were measured at room temperature and compared to values calculated from the thermogravimetric data.

     

钢液温度和硫含量对脱氮动力学了影响

在LECO436氧氮分析仪上研究了1600~2813℃温度范围内钢液脱氮动力学。结果表明:温度低时,脱氮受液相边界层传质及界面化学反应混合控制,温度高时,脱氮受液相边界层传质过程控制。在2250℃以下,温度对k₁'的影响服从Arrhenius公式。硫对脱氮的阻碍作用随着温度的升高而降低,在温度2250℃以上,硫的表面活性作用消失。     

添加剂Nb和烧结温度对ZrN粉末材料性能的影响

在ZrN粉末中添加Nb粉,经热压烧结得到Nb-ZrN粉末材料,研究添加剂Nb与烧结温度对Nb-ZrN材料烧结和力学性能的影响。结果表明:提高烧结温度有利于加快材料的致密化,Nb-ZrN1480粉末出现了1个致密化速率峰,其它粉末材料还生成了另外2个小的致密化速率峰,烧结Nb-ZrN1680粉末的相对密度达到98.6%。各粉末材料的X射线衍射谱图中都存在ZrO₂衍射峰,添加剂Nb在烧结阶段全部溶入ZrN内。添加Nb后,ZrN晶格常数减小,随烧结温度上升,ZrN晶格常数基本保持稳定。纯ZrN材料表现为沿晶断裂,添加Nb后,粉末材料发生穿晶断裂,气孔数明显降低。     

抗坏血酸对锂电铜箔抗氧化性能的影响

抗坏血酸(AA)作为一种包含多个羟基的有机配体,易与金属Cu离子螯合形成配位聚合物附着于铜箔表面。采用抗坏血酸为钝化剂,以浸渍法在电解铜箔表面构建了钝化膜,探究不同浓度钝化液对铜箔表面高温防氧化性能的影响,发现10 g/L抗坏血酸可显著提高锂电铜箔的耐蚀性。通过电化学及相关表征试验研究了表面膜的钝化性能,结果表明,钝化膜的自腐蚀电流密度逐渐降低,电压升高,且高频区的半径增大,具有良好的抗氧化性能。此外,钝化膜表面光滑致密,有效阻挡了腐蚀介质的侵蚀,仍能使铜箔保持良好的工艺性能。该钝化工艺操作简单且成本较低,具有良好的工业应用前景。     

铝型材阳极氧化及电泳涂装关键控制点的探讨

主要探讨阳极氧化和电泳涂装工艺上的关键控制点,通过对其的控制以获得更好的产品质量,进而降低生产成本。     

定电位电解法测定固定源氮氧化物的探讨

文章对定电位电解法和盐酸萘乙二胺分光光度法进行了对比实验,证实两种方法测试结果无显著性差异,探讨定电位电解法在固定源氮氧化物监测中的具体应用,对实际工作具有较好的参考价值。     

钛铁矿流态化氧化机理研究

对低品位钛铁矿进行预氧化、预还原等预处理后可满足硫酸法生产钛白粉工艺所需高品位钛铁矿的要求。本试验采用流态化预氧化方法处理风化程度低、含硫较高的钛铁矿。结果表明 :流态化氧化可大幅度地降低钛铁矿中硫含量 ;钛铁矿流态化氧化的适宜温度为 :80 0～ 90 0℃ ,且在此温度范围内 ,随温度的升高 ,钛铁矿的氧化速度增加 ,在 90 0℃时 ,5 0min钛铁矿基本能完成氧化     

电解涂硅机理及应用工艺

在大量试验的基础上,推断出电解涂硅在钢板表面呈空间网状结构,明确了影响涂硅是硅酸根离子浓度,得出电解涂硅的机理为特性吸附的结论,并分析了涂硅量对后续加工的影响,结果显示电解涂硅对后续加工无影响.在此基础上确定了合理的带钢涂硅量和工艺参数,冷轧黏结发生率大幅下降,实际应用效果良好.     

铟电解精炼中添加剂明胶的影响及其机制研究

研究了明胶对阴极极化、电流效率、电解液比电阻的影响，研究了在电解过程中明胶的电析消失现象，探讨了明胶的作用机理。研究表明：明胶能增大阴极过电位，能提高阴极电流效率，提高电解液的比电阻。明胶的电析消失速度随电流密度的增大而增大。明胶极有可能与In^3 形成络合物的形式参与电解过程。     

Investigation of Magnetite Oxidation Kinetics at the Particle Scale

Metallurgical and Materials Transactions B - The induration of magnetite pellets is a complex physico-chemical process that involves oxidation, sintering, and heat transfer. The thermal- and...     

加压氧化浸出工艺的机理研究

加压浸出法具有流程短、砷浸出率高、浸出时间短及无SO2等有毒物质产生的优点,是预处理含硫、砷金矿石或金精矿的有效手段.在酸性介质中,硫化物、铁化合物与砷化物发生高温氧化的主要反应包括3种形式:硫化物全部被氧化成硫或硫酸盐,反应过程中产生的Fe2+被氧化成Fe3+,砷被氧化成砷酸盐.随着易处理矿石资源日益减少,加压浸出法...     

热障涂层的氧化机理分析

热障涂层因其具有优良的抗高温氧化和抗热腐蚀性能而被广泛应用于航空航天、化工、冶金和能源等领域.描述了热障涂层体系中的氧化过程,并对热障涂层体系中热生长氧化层中的生长应力和热应力作了一个初步分析.     

The Redox Kinetics of the Oxidation for CO on EuFeO_3 Catalyst

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Kinetics of Oxidation Reaction for Magnetite Pellets

An experiment for the oxidation process of single magnetite pellet and theoretical analysis based on modified unreacted core shrinking (MUCS) model were carried out, and the controlling mechanisms of the initial and developing reactions were examined, respectively. From the study of the initial reaction, it was found that the chemical reaction of surface is the controlling step of the overall reaction when the temperature is up to about 750 K, while the mass transfer through the gaseous boundary layer dominates the reaction rate when the temperature is above 750 K. As the reaction developing within the pellet, the mass transfer through the produced layer becomes the controlling step. In addition, the effects of reaction conditions (such as oxygen concentration, temperature) on the fractional oxidation of magnetite pellet were determined.