Ignition and chemical mechanisms of volume combustion synthesis of titanium diboride

Reaction ignition and chemical mechanisms in volume combustion synthesis of TiB₂ via TiO₂–B₂O₃–Mg precursors were studied using in-situ differential thermal analysis, X-ray diffraction, scanning electron microscopy and thermochemical modeling. Mg–TiO₂ samples ignited at 607 °C through a sudden single step solid-solid reaction while Mg–B₂O₃ samples ignited at 810 °C after melting of magnesium. X-ray diffraction analysis revealed that reduction of TiO₂ occurs in multiple steps and forms intermediate compounds. Results showed that heat released from the first reaction between TiO₂ and Mg ignites the reactions between Mg, Ti and B₂O₃ resulting in the formation of TiB₂. Samples with larger TiO₂ particle size or a higher sample surface to volume ratio showed a two-step reaction behavior and the released heat in the first solid state reaction was insufficient for the propagation of the reaction throughout the sample. In addition, Mg₃B₂O₆ undesired by-product was formed as a result of this two-step reaction.     

Design of Phosphonated Imidazolium-Based Ionic Liquids Grafted on γ-Alumina: Potential Model for Hybrid Membranes

Imidazolium bromide-based ionic liquids bearing phosphonyl groups on the cationic part were synthesized and grafted on γ-alumina (γ-Al₂O₃) powders. These powders were prepared as companion samples of conventional mesoporous γ-alumina membranes, in order to favor a possible transfer of the results to supported membrane materials, which could be used for CO₂ separation applications. Effective grafting was demonstrated using energy dispersive X-ray spectrometry (EDX), N₂ adsorption measurements, fourier transform infrared spectroscopy (FTIR), and special attention was paid to ³¹P and ¹³C solid state nuclear magnetic resonance spectroscopy (NMR).     

喀斯特地基中土洞对地基变形的影响

喀斯特地区的建筑物建成后 ,地基中由于地下水或地表水的作用 ,往往还会发育土洞。根据弹塑性理论 ,可求出土洞周围土体的应力状态 ,继而推求出地基中任一点的变形沉降。结合工程实例针对各种土层中发育的土洞对地基变形的影响进行了探讨 ,得出了一些有借鉴意义的结论供同行参考。     

工程机械企业发展战略的影响因素分析

运用分解法提出了企业的更新概念 ,阐述了目前我国工程机械企业运营模式存在的问题 ,分析了国家对工程机械企业的宏观政策 ,进而提出企业制订经营发展战略的步骤及要点。     

The Interface Position and Centre Concentration during Freezing of Carrot Juice in Cylindrical Containers

Finite difference modelling, incorporating a variable space network approximation, was used to study the freezing of carrot juice in cylindrical containers. Ambient temperatures ranged from −6·5 to −14·2°C. The problem was formulated as a moving boundary to find the position of the hypothetical solid–liquid interface and the concentration at the centre. Experimental results obtained for the freezing of carrot juice were satisfactorily represented by the variable space network approximation technique, except for failure at the central positions. This failure was believed to be due to some simplifying assumptions such as constant thermophysical properties and a sharp interface, as well as possible experimental errors.     

加强管理是企业增效的关键

面对我国加入WTO的机遇和挑战,文章提出了我国企业增效是应加强企业的自身管理,同时分析了我国企业现有管理的不足之处,并提出了相应改进措施,对企业解困增效有一定的借鉴意义。     

梅山矿区煤中微量元素分布规律和赋存状态分析

对梅山矿区煤灰的化学成分、微量元素分布及煤灰的岩石学特征等进行了详细研究,并讨论了微量元素与三态硫、挥发分的相关性.研究结果表明,梅山矿区煤为中低磷煤,煤中U元素的含量低于地壳中的平均含量,煤中Ge和Ga的含量略高于地壳中的平均含量.煤中微量元素的赋存状态对煤炭的加工利用和燃烧工艺起着重要作用,并能为其成因提供相关地质...     

一类多体系统的非完整运动规划最优控制

研究一类带有非完整约束的多体系统运动规划问题。由于非完整约束的存在,运动规划和控制问题比一般的多体系统要困难得多。讨论了非完整系统的特性及可控性条件,利用无限维优化和控制理论,结合非完整控制系统特性,以系统耗散能量为性能指标,给出一类非完整运动规划的最优数值方法。最后将该方法用于自由漂浮空间双臂机器人,仿真结果实现了该类非完整系统的运动规划。