Enthalpies of formation of TM–X compounds (X=Al,Ga, Si,Ge, Sn). Comparison of ab-initio values and experimental data

Nowadays first-principles calculations have achieved considerable reliability for the prediction of the properties of materials. These calculations are based on the density functional theory. In the present work, we have obtained a large number of enthalpies of formation of binary intermetallic compounds of transition metals with the elements Al, Ga, Si, Ge or Sn. The ab-initio values have been calculated with VASP in the generalized gradient approximation. We have compared the calculated enthalpies of formation of compounds to the values obtained with calorimetric methods. An excellent agreement is observed in the cases of aluminum and silicon based compounds. We also observe that in the case of highly negative values of enthalpies of formation of early transition metal alloys the experimental values are often more negative than the calculated values but it is not the case in Pt based compounds. In the cases of the Pt, Mo, Ru, Rh compounds with Al, Ga, Si, Ge or Sn, a very nice agreement between calculated and experimental values is observed.     

Structural stability of intermetallic phases in the Ga-Ti system

The total energies of intermetallic compounds in the Ga-Ti system are calculated employing electronic density functional theory (DFT) using pseudopotentials constructed by the projector augmented waves (PAW) method in the generalized gradient (GGA) approximation for the exchange and correlation energy. The calculations are performed for the experimentally observed compounds at their ideal stoichiometry as well as for structures which are stable in systems of early transition metals or rare earth elements with p elements of columns IIIB, IVB, and VB. The calculated formation enthalpy of the hexagonal B8₂-GaTi₂ compound is in excellent agreement with the value obtained by direct reaction calorimetry. The composition dependence of the enthalpies of formation is slightly asymmetric, the values of the enthalpies of formation being slightly more negative in the Ga-rich side. For the stable intermetallic compounds, the calculated zero-temperature lattice parameters agree well with those obtained experimentally at ambient temperature. Furthermore, for stable phases with unit-cell-internal degree(s) of freedom, the results of ab initio calculations show good agreement when compared with data obtained by structural analysis of X-ray diffraction.     

Enthalpies of formation of Cd–Pr intermetallic compounds and thermodynamic assessment of the Cd–Pr system

In the present study standard enthalpies of formation were measured by reaction and solution calorimetry at stoichiometric compositions of Cd₂Pr, Cd₃Pr, Cd₅₈Pr₁₃ and Cd₆Pr. The corresponding values were determined to be −46.0, −38.8, −35.2 and −24.7 kJ/mol(at), respectively. These data together with thermodynamic data and phase diagram information from literature served as input data for a CALPHAD-type optimization of the Cd–Pr phase diagram. The complete composition range could be described precisely with the present models, both with respect to phase equilibria as well as to thermodynamic input data. The thermodynamic parameters of all intermetallic compounds were modelled following Neumann–Kopp rule. Temperature dependent contributions to the individual Gibbs energies were used for all compounds. Extended solid solubilities are well described for the low- and high-temperature modifications of Pr and also for the intermetallic compound CdPr. A quite good agreement with all viable data available from literature was found and is presented.     

Phase equilibria and thermodynamic investigation of the In–Li system

Phase equilibria and thermodynamic properties of the In–Li system were analyzed by combining the first-principles approach and Computer Coupling of Phase Diagrams and Thermochemistry (CALPHAD) methodology. The enthalpies of formation for all the stable compounds were calculated by first-principles calculations based on the density functional theory (DFT). Phase diagram of the In–Li system was calculated for the first time, and a set of self-consistent thermodynamic parameters was finally obtained by CALPHAD approach coupling experimental measurements and first-principles calculations. An associate model of (In, In₂Li₃, Li) was used to describe the liquid phase, and InLi and InLi₂ were treated by sub-lattice models. Other intermediate phases were considered to be stoichiometric compounds. The calculated phase diagram, voltage curve and thermodynamic properties can reproduce the available experimental data reasonably.     

First-principles calculations of binary Al compounds: Enthalpies of formation and elastic properties

Systematic first-principles calculations of energy vs. volume (E-V) and single crystal elastic stiffness constants (c_ij’s) have been performed for 50 Al binary compounds in the Al-X (X = Co, Cu, Hf, Mg, Mn, Ni, Sr, V, Ti, Y, and Zr) systems. The E-V equations of state are fitted by a four-parameter Birch-Murnaghan equation, and the c_ij’s are determined by an efficient strain-stress method. The calculated lattice parameters, enthalpies of formation, and c_ij’s of these binary compounds are compared with the available experimental data in the literature. In addition, elastic properties of polycrystalline aggregates including bulk modulus (B), shear modulus (G), Young’s modulus (E), B/G (bulk/shear) ratio, and anisotropy ratio are calculated and compared with the experimental and theoretical results available in the literature. The systematic predictions of elastic properties and enthalpies of formation for Al-X compounds provide an insight into the understanding and design of Al-based alloys.     

Thermodynamic assessment of the Molybdenum–Rhenium system

A thermodynamic optimization of the Mo–Re system by the Calphad method is proposed, taking into account new experimental data obtained in this work. According to recent crystal chemistry work, the χ and σ Frank–Kasper phases were modeled using two independent sublattices of variable occupation. This was made possible by including experimental site fractions in the different sublattices as input data for the parameter optimization. A consistent set of parameters is proposed. Good agreement is found between calculated and selected experimental values for different kinds of data: phase diagram, thermodynamic and crystallographic data.     

Miniaturized ceramic differential scanning calorimeter with integrated oven and crucible in LTCC technology

A miniaturized ceramic differential scanning calorimeter (MC-DSC) with integrated oven and crucible is presented. Despite its small size of only 11 mm × 39 mm × 1.5 mm, all functions of a conventional DSC apparatus are integrated in this novel device - including the oven. The MC-DSC is fully manufactured in thick-film and green glass ceramic tape-based low temperature co-fired ceramics (LTCC) technology. Therefore, production costs are considered to be low. Initial results using indium as a sample material show a good dynamic performance of the MC-DSC. Full width at half maximum of the melting peak is 2.4 °C (sample mass approx. 11 mg, heating rate approx. 50 °C/min). Repeatability of the indium melting point is within ±0.02 °C. The melting peak area increases linearly with the sample mass up to at least 26 mg. Simulations of a strongly simplified finite element model of the MC-DSC are in a good agreement with measurement results allowing a model-based prediction of its basic characteristics.     

Structural stability of intermetallic phases in the Sn–Ti system

The total energies of intermetallic compounds in the Sn–Ti system are calculated employing electronic density-functional theory (DFT) using pseudopotentials constructed by the projector augmented waves (PAW) method in the generalized gradient (GGA) approximation for the exchange and correlation energy. The calculations are performed for the experimentally observed compounds at their ideal stoichiometry as well as for structures which are stable in systems of early transition metals or rare earth elements with p-elements of columns IIIB, IVB, and VB. The calculated formation enthalpy of the hexagonal Sn₅Ti₆ compound is slightly less exothermic than the value obtained by direct reaction calorimetry. For the stable intermetallic compounds, the calculated zero-temperature lattice parameters agree well with those obtained experimentally at ambient temperature. More, for stable phases with unit cell-internal degree(s) of freedom, the results of ab initio calculations show good agreement when compared with data obtained by structural analysis of X-ray diffraction. The composition dependence of the enthalpies of formation is slightly asymmetric. The electronic densities of state of the D8₈- Sn₃Ti₅ compound have been computed; the curve shows the hybridization of Sn 5p states with Ti 3d states. The stability of the intermetallic compounds in the Ti–Sn system is due to this hybridization.     

混合煤气流量测量的计算过程和实现方法

煤气是重要的能源介质,在钢铁企业中被广泛作为燃料使用。煤气在工艺上有大量的流量检测点,实现煤气流量的准确测量既是重点又是难点。介绍了混合煤气流量测量过程中的参数计算、公式变换、状态转换和温度压力补偿,以及采用不同设备的实现方法和实际应用中的量程调整原理,实现了煤气流量准确测量。这对所有气体能源介质的流量测量都具有普遍的适用性和指导意义。     

微机控制滴定量热仪的数据采集及计算机程序

本文提出一种微机控制滴定量热仪的数据采集方法及相应的计算机程序。它较已有的各种滴定量热数据采集方法具有简单、快速和准确的特点。它不仅对快反应适用,而且还可用于受动力学因素控制的慢反应。所用量热仪为美国 TRONAC 公司生产的MODEL1250微机控制滴定量热仪。采集得到的滴定量热数据不仅可以立即给出溶液中反应的热量随滴定剂体积的变化关系,进行定量分析,还可用来确定反应的△H 值。在某些情况下,还可对数据进行进一步处理(另文发表)而得到反应的 AH、lgβ、△G、△S 和其它有关信息。     

碳,氢,氧,氮物系的焓值与燃烧温度

根据函数关系设计出一种表格,任何只含C,H,O,N 4种元素的可燃物质在标准大气压下与氧,空气或者任意比例的氧,氮混合物或化合物按化学计量比进行绝热燃烧时达到的温度都可精确地查得.本表还可用于非绝热燃烧过程的计算.     

燃油热水锅炉水循环动态数学模型及仿真

该文介绍“锅炉仿真培训系统”中采暖燃油热水锅炉水循环动态数学模型及仿真策略,提出了补水泵、循环泵和压力节点的基本方程,给出了模型参数估算方法和模型求解策略,举例说明了热水锅炉采暖外网持水量估算方法,最后介绍了该模型的特点和实际应用情况。