还原气氛下Si-B2O3-TiO2系反应的热力学分析

通过热力学计算,探讨Si-B2O3-TiO2系在还原性气氛下TiB2,Ti(C,N)的可能性、生成途径以及产物在此体系中的相对稳定性。结果表明：Si-B2O3-TiO2系在还原性气氛下TiB2的生成有2种可能性,生成物中TiB2要比TiN和TiC稳定。在1843K左右,TiC和TiN可以形成固溶体Ti(C,N)。     

TiO2 碳热还原氮化反应的热力学分析

通过热力学计算和分析,绘制了Ti-C-N-O系中氮化物、碳化物与氧化物稳定存在区域图(即优势区相图);讨论了碳热还原氮化法合成TiN和TiC粉末过程中的主要影响因素及最佳条件.     

埋炭条件下Si-MgO体系的高温相组成

为了探究Si-Mg O体系在埋炭热处理过程中的反应及高温相组成,通过热力学计算对Si-Mg O系材料的高温凝聚相组成进行了预测,表明在1 550℃埋炭热处理条件下,Si-Mg O体系中的凝聚相应为Mg_2Si O4和Si_2N_2O。实际试验表明,将粒度均0.074 mm的电熔镁砂粉与硅粉按7 3的质量比混合后制备的Si-Mg O系材料,在1 550℃保温2 h埋炭热处理后,由于体系中反应没有进行完全,还存在少量Si_3N_4。同时,原料中的杂质Ca O和Al_2O_3也参与反应,生成了固溶少量铝的透辉石相。其在高温时虽然能够形成液相而促进烧结,但是不利于材料的高温强度。因此,在实际生产中应控制原料中Ca O和Al_2O_3的含量,以达到最佳的使用效果。     

碳热还原镁橄榄石合成MgO-SiC复合粉体的热力学研究

本文对碳热还原镁橄榄石合成MgO-SiC复合粉体进行了热力学研究,结合实验,分析了反应的中间过程,对合成粉体具有重要的指导意义.热力学分析表明:当T=1923 K时,所形成的产物,从容易到困难排序依次为:MgO+SiC,MgO+Si,MgO+SiO,Mg+SiC,Mg+Si,Mg+SiO,Mg+SiO2;增大惰性气体流速,降低CO的分压,可以降低镁橄榄石解构温度.在不同氩气流量下的实验证明,增大氩气流量,促进了镁橄榄石的碳热还原反应,有益于MgO-SiC复合粉体的合成.以镁橄榄石与炭黑物质的量比为1∶5配料,混合均匀后,在氩气保护下,在气体流量分别为100 mL/min,300 mL/min,500 mL/min时,1650℃保温3h合成粉体.用X射线衍射仪(XRD)测试合成的物相,用扫描电子显微镜(SEM)观察各物相形貌.实验结果表明,合成的产物MgO为八面体,SiC为条形.过程分析表明,碳还原镁橄榄石生成MgO和SiO,是合成复合粉体的重要中间过程.     

碳还原硫酸锶反应的热力学分析

研究了碳还原法制备碳酸锶过程中碳还原反应的机理.通过热重分析初步确定了主反应发生的温度范围在800～1 100 ℃,选用Gibbs-Helmholtz方程、Van′t Hoff方程和Kirchhoff方程对反应过程中的热力学函数随温度的变化情况进行了探讨,从而判断该反应过程的反应机理.对影响反应的反应时间、反应温度、反应物粒度这3个因素进行了考察.结果表明,反应温度越高,反应物粒度越小,反应速度越快,反应时间越短;但反应温度过高、反应时间过长均不利于反应的进行.适宜的反应条件为:反应温度为1 050 ℃,反应时间为45 min,反应物粒度为130 μm.在此条件下,水溶性锶产率达到92.87%.     

碳热法合居AIN的热力学及动力学

本文对碳热法合成ＡＩＮ粉末的反应过程进行了实验研究并理论计算了反应过程的Ｃｉｂｂｓ自由能的变化，用零级反应模型的Ｊａｎｄｅｒ方程回归分析了氮化速率。     

气氛对煤矸石中矿物质高温碳热还原反应的影响

利用煤矸石制备复合耐火材料是实现煤矸石高值利用的有效途径之一.以山西平朔煤矸石为研究对象,利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)分别研究了1200~1500 ℃氩气(Ar)和氮气(N2)气氛下煤矸石中矿物质的碳热还原反应情况,并通过变换两种气体通入次序,研究了气氛通入次序对矿物质碳热还原反应的影响.结果显示,只通入Ar时,高温样品中的莫来石在1300 ℃时开始发生碳热反应生成碳硅石(SiC);只通入N2时,莫来石在1300 ℃时发生碳热还原氮化反应生成β-Sialon相(Si5AlON7)和刚玉相(Al2O3);当先通入Ar并停留1 h后通入N2停留2 h时,样品中生成的碳硅石在通入N2后转化为β-Sialon相,而且中间体碳硅石的生成能够明显促进莫来石向β-Sialon相的转化.当煤矸石中碳含量较低时,热处理过程中难以同时生成SiC相和Sialon相.高温下煤矸石样品中β-Sialon相的生成使样品表面的棒状颗粒增多.     

还原气氛下铝热还原法合成TiN-Al2O3复合材料

以金属铝粉和钛白粉为原料,在匣钵中埋炭保护气氛下采用铝热还原氮化法制备了TiN-Al2O3复合材料。采用XRD、SEM和TEM等分析手段,研究了铝热还原氮化法制备TiN-Al2O3复合材料在不同热处理条件下(分别为1300℃3h、1400℃3h和1500℃3h)的物相组成、晶格常数、显微结构。研究结果表明:在埋炭气氛下采用铝热还原氮化法可以制备TiN-Al2O3复合材料;处理温度明显影响着铝热反应的程度及产物的形貌,随着处理温度的上升,处理后的产物中TiN含量逐渐增加,晶粒逐渐长大,晶格常数逐渐接近理论值。热力学计算发现,埋炭条件下,在较低的处理温度下,铝除参与铝热还原反应外,还与炭粉床中氧发生反应,导致参与铝热反应的金属铝不足,造成产物中有剩余的金红石存在。     

碳热还原法合成ALON粉体的研究

本文以γ-Al_2O_3和活性碳为原料,采用碳热还原法合成高纯超细γ-ALON粉.并以γ-Al_2O_3和碳粉的配比、合成温度、保温时间以及除碳等方面分别探讨了碳热还原法合成γ-ALON粉的适宜工艺条件;通过对合成粉料的XRD、SEM分析,表明该方法合成的ALON粉晶形发育完善、粒度均匀、纯度高.     

Thermodynamic Analysis for Carbothermal Reduction and Nitridation of TiO2

The diagrams of stability relations(namely,Predominance area phase diagram,PAPD)of nitride,carbide and oxides in Ti-C-N-O system were plotted by thermodynamic calculation.The optimum conditions and main influence factors for the synthesis of titanium nitride and titanium carbide by carbothermal reduction in nitrogen atmosphere were discussed.     

水热法一步合成核壳型TiO2/Al2O3纳米粉体的热力学分析

水热法一步合成核壳结构的工艺路线具有简化生产工艺、大大缩短生产时间的特点.所以研究制备具有核壳结构的前驱体热力学条件有重要的指导意义.热力学分析表明,在纳米Ti(OH)4表面包覆Al(OH)3的过程中,存在核包覆和膜包覆的竞争;而在其它条件不变的情况下,包覆物的过饱和度对包覆形态起到了决定性的影响.在较低的过饱和度下,可形成膜包覆;如果过饱和度过高,则形成核包覆.     

Thermodynamic and kinetic analyses of vacuum synthesis of AlN by the alumina carbothermal reduction nitridation method

Ultrafine single-phase aluminium nitride (AlN) particles were successfully synthesized by the vacuum carbothermal reduction nitridation (VCRN) method at shorter times and lower temperatures. The mechanism of the process was investigated. By analyzing the X-ray diffraction (XRD) patterns and thermodynamic calculations, the main reaction path was determined to be Al₂O₃→Al₂CO→Al₄C₃→Al₅C₃N→AlN. By investigating the kinetics mechanism, the process was a gas–solid reaction model, which was controlled by the crystalline chemical reaction from 0.5  to 1.5 h, combination control from 1.5 to 2 h, and gas diffusion control from 2 to 2.5 h. Moreover, the apparent activation energy (E_a) was calculated from the nitridation ratio, the value obtained, 237.71 kJ mol^–1, is 31% of the energy reported for the conventional synthesis method. These results show that ultrafine AlN could be effectively synthesized at 1823–1873 K and 300 Pa N₂ pressure for 2.5 h.     

碳热法合成AIN的热力学及动力学

本文对碳热法合成AIN粉末的反应过程进行了实验研究并理论计算了反应过程的Gibbs自由能的变化,用零级反应模型和Jander方程回归分析了氮化速率。     

Microstructure evolution and characteristic of Ti(C,N)-based cermets prepared by in situ carbothermal reduction in TiO2

Ti(C,N)-based cermets were prepared by in situ carbothermal reduction in TiO₂ and subsequent liquid phase sintering under vacuum. The prepared cermets were examined using XRD, SEM, TEM, and EDX. During solid-state sintering, fine TiC particles were formed through the carbothermal reduction in TiO₂. A great number of (Ti,W,Mo)C complete solid solutions containing more W and Mo subsequently formed through the counter diffusion of the fine TiC and carbides. The majority of the coarse TiN particles in the raw powders remained undissolved. During liquid phase sintering, Ti-based carbonitride complex solid solutions with less W or Mo precipitated on the coarse TiN particles and fine (Ti,W,Mo)C particles, resulting in black core/gray rim structures and white core/gray rim structures, respectively. Moreover, small amounts of Ti-based carbonitride complex solid solutions precipitated directly from the liquid binder phase in some areas enriched in W and Mo during the cooling stage after sintering, resulting in coreless grains. Ultimately, after being sintered at 1400°C for 1 hour, the present cermets were characterized with white core/gray rim grains, black core/gray rim grains and a few gray grains. In addition, the interfaces between the black core/gray rim grains and binder phase were atomically smooth, exhibiting a orientation relationship with a perfect coherency state.     

氧化羰基化法合成碳酸二苯酯过程热力学分析

采用Benson基团贡献法,对氧化羰基化法合成碳酸二苯酯(DPC)的反应焓变、反应熵变、吉布斯自由能变及平衡常数进行热力学估算.结果表明:此反应为一放热反应,较低的反应温度对其有利;热力学平衡常数比较大,此反应有向正方向自发进行的趋势.     

Properties of supercritical N2, O2, CO2, and NH3 mixtures from the virial equation of state

We report virial coefficients up to sixth order in density for N₂ , O₂ , NH₃ , and CO₂ , covering temperatures from 50 to 1,000 K. The reported values include coefficients and their first three temperature derivatives, for the pure species as well as all of those needed to evaluate full composition dependence of mixtures formed from any or all of these compounds. The values are obtained by calculation of appropriate cluster integrals using Mayer sampling Monte Carlo, with intermolecular interactions described by the Transferable Potential for Phase Equilibria (TraPPE) force field. All coefficients are fit as a function of temperature, yielding a thermodynamic model with analytic dependence on temperature, density, and composition. The coefficients and properties computed from them are compared to experimental data where available.