W热力学性质和弹性性质的第一性原理研究

使用第一性原理方法结合准谐近似理论研究了立方结构钨的热力学性质,包括平衡体积V、体弹模量B0、线膨胀系数α、熵S、振动自由能F、等压热容CP和等容热容CV随温度的变化关系。在计算体系的线膨胀系数、熵、振动自由能、等压热容和等容热容时考虑了热电子和热振动对自由能的贡献。计算结果表明：考虑热电子对自由能贡献后得到的线膨胀系数、熵、振动自由能和等压热容在0~2000 K范围内均与实验值符合较好。在得到平衡体积随温度变化的基础上,计算了钨立方结构的弹性性质,得到了弹性常数、体积模量、剪切模量和杨氏模量随温度的变化关系,所得结果与实验测量值符合较好     

Fe2TiAl结构和热力学性质的第一原理计算

采用基于密度泛函的第一原理平面波赝势方法,研究了Fe2TiAl的几何结构、电子结构和热力学性质,结果表明:Fe2TiAl相比TiAl,晶格常数有所增加,Fe加入会增加费米能级处的d电子数,增加面间可动性,从而改善合金塑性;Fe2TiAl在零温和零压下的晶格常数、体弹性模量及弹性常数与实验值符合较好。利用准谐德拜模型,得到了不同温度和不同压强下Fe2TiAl的热容、体弹性模量和德拜温度,发现德拜温度随压强增加而增加,热容随压强增加而减小,高压下温度对Fe2TiAl热膨胀系数的影响小于压强的影响,并成功获得了相对体积、体弹性模量、热膨胀系数与温度和压强之间的变化关系。     

新型Nb_3AlN三元陶瓷的材料设计（英文）

采用基于密度泛函理论的广义梯度近似下的平面波赝势方法,模拟了Nb3AlN基本性能,如能带结构和热力学性能。模拟结构表明,Nb3AlN与金属的性能相似,具有良好的导电性和导热性。热容随温度的增加和压强的减小而增加。Grüneisen参数γ随温度的增大而增大,并且随压强的增加Grüneisen参数γ呈非线性减小。德拜温度受温度和压强影响较大,随温度的增加而急剧减小,随压强增加而迅速增加。通过模拟吉布斯自由能和温度的关系表明,采用合适的工艺可以合成Nb3AlN。     

Materials Design of New Nb3AlN Ternary Ceramic

采用基于密度泛函理论的广义梯度近似下的平面波赝势方法,模拟了Nb3AlN基本性能,如能带结构和热力学性能。模拟结构表明,Nb3AlN与金属的性能相似,具有良好的导电性和导热性。热容随温度的增加和压强的减小而增加。Grüneisen参数γ随温度的增大而增大,并且随压强的增加Grüneisen参数γ呈非线性减小。德拜温度受温度和压强影响较大,随温度的增加而急剧减小,随压强增加而迅速增加。通过模拟吉布斯自由能和温度的关系表明,采用合适的工艺可以合成Nb3AlN。     

Co_6W_6C化合物的热力学研究

以高纯钨、钴、碳粉为原料,在真空条件下制备获得物相纯净的Co_6W_6C化合物,对Co_6W_6C进行系列实验测定并结合计算得出了其相关的热力学参数。结果表明:在原料粉中碳含量为0.98%~1.06%(质量分数)、真空反应温度为1000℃、保温时间为1 h的条件下,可制备获得物相纯净的Co_6W_6C。结合其等压热容及1173 K下氧化反应的反应焓测定结果,通过计算获得了Co_6W_6C的标准摩尔熵(S_m~Θ)、标准摩尔生成焓(Δ_fH_m~Θ)等热力学参数以及其等压热容(C_p)、焓(H)、熵(S)和吉布斯自由能(G)等基础热力学参量随温度变化的函数关系。     

金属元素Cu的热力学性质

采用SGTE纯单质数据库中Gibbs能的表达式,结合JANAF热力学实验数据,用最小二乘法对金属元素Cu的Gibbs能表达式进行重新评估。重新评估后的转变热容、转变焓和转变熵分别为-0.187 J/(mol.K)、13.138 kJ/mol和9.675 J/(mol.K),与实验数据符合很好。运用Debye-Grüneisen模型研究Cu从0 K到熔点的热力学性质,结果发现模型计算的低温热容值偏低,从而导致模型计算的转变熵和Gibbs能偏大。运用Debye-Grüneisen模型研究过冷液体的热力学性质,并通过保持熔点热容、焓和熵值的连续性,得到液相Cu的热容和Gibbs能等热力学性质,结果与实验值数据符合较好。     

Ni-Cu合金力学和热力学性质第一性原理研究

基于密度泛函理论,采用CASTEP和DMol3程序软件包研究了Ni_xCu_((1-x))(x=0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1)合金的力学性能和热力学性质。计算了合金的弹性常数、体模量(B)、剪切模量(G)、Young's模量(E)、Poisson比(v)、熵(S)、焓(H)、比热容(C)及吉布斯自由能(G)。结果表明:Ni-Cu固溶体都是延性相,Ni_(0.9)Cu_(0.1)抗变形能力、硬度最高,其次是Ni_(0.8)Cu_(0.2),然后是Ni_(0.1)Cu_(0.9)。而延展性和塑性Ni_(0.1)Cu_(0.9)最好,其次是Ni_(0.9)Cu_(0.1),说明Ni_(0.1)Cu_(0.9)、Ni_(0.9)Cu_(0.1)综合力学性能最好。随着温度的升高,Ni_xCu_((1-x))(x=0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1)合金体系的熵和焓都增大;比热容先增大,逐渐趋于一个定值。Gibbs自由能随着温度的升高而降低,表明温度升高,体系的热稳定性增强;且在同一温度下,随着Cu含量的升高,自由能依次减小,热稳定性增强。     

Mg_(1-x)Zn_x合金的弹性和热力学性质的第一性原理研究

基于密度泛函理论及密度泛函微扰理论为基础的第一性原理计算,采用虚晶近似的方法,研究了具有hcp结构且Zn含量在2%(原子分数)范围内的8种Mg_(1-x)Zn_x合金的晶格常数、弹性性质和热力学性质。通过优化结构计算Mg和Zn含量不同的Mg_(1-x)Zn_x合金弹性常数,对Young's模量、Poisson比、弹性各向异性等进行了详细分析,给出了Mg及Mg_(1-x)Zn_x合金的晶格振动Helmholtz自由能、内能、熵和定容热容等随温度变化情况。结果表明,随着Zn含量增加晶格常数a和c均相应减小,弹性常数、自由能和内能增大,熵及定容热容减小;另一方面,随温度升高,Zn含量对自由能和熵的影响程度增大,而对定容热容的影响程度先增大后减小。Mg_(1-x)Zn_x合金中Zn含量的增加有利于提高材料硬度和韧性,但也增大了材料的各向异性。     

退火工艺对FeSiB非晶薄带的模量和膨胀系数的影响

采用单辊法制备了宽4.5mm、厚25μm的Fe78Si9B13非晶薄带,并用Q800动态热机械分析仪(DMA)测试了非晶薄带的弹性模量、线形变和线膨胀系数,并分析了它们随着退火工艺及测试温度的变化关系。结果表明,退火可以提高非晶薄带的弹性模量、线形变和线膨胀系数;退火态与淬火态非晶薄带的弹性模量、线形变和线膨胀系数随测试温度的变化规律相同,即弹性模量都随测试温度的升高而减小;线形变都随测试温度的升高而增大;线膨胀系数在低温时都随测试温度的升高而增大,在高温时都随着测试温度的升高而减小。     

氢氧化钠溶液中丙炔醇对铝的缓蚀作用及吸附热力学研究

采用失重法研究了氢氧化钠溶液中丙炔醇在不同温度和浓度下对铝的缓蚀作用,发现丙炔醇在铝表面上的吸附是产生缓蚀作用的重要原因,且吸附规律服从Langmuir吸附等温式.用Sekine方法处理实验数据,获得了吸附过程相关的重要热力学参数.吸附过程是吸热过程,且熵值增大.随温度升高,吉布斯自由能减少,缓蚀率增大.     

韧性金属间化合物CeAg的第一性原理计算(英文)

采用第一性原理计算法研究具有B2(CsCl)结构的二元韧性金属间化合物CeAg的结构、力学性能、电子性质以及热力学性能。利用广义梯度近似计算得到的晶格常数为3.713,比自旋密度近似计算的结果更符合实验值。负的形成能表明具有B2结构的CeAg是热力学稳定相。Ce和Ag原子的d能带相互分离导致两者的键合杂化作用较弱,从而阻止具有方向性的共价键形成。计算得到了CeAg的3个独立弹性常数(C11,C12和C44),体模量、剪切模量、弹性模量、各向异性因子以及泊松比分别为57.6GPa、15.8GPa、43.4GPa、3.15和0.374。弹性常数符合所有力学稳定性准则。CeAg的Pugh判据值为3.65,当Pugh判据值大于1.75时,CeAg具有良好的韧性。此外,还计算和讨论了CeAg的体积、体模量、热容和热膨胀系数随温度或者压力的变化规律。     

VARIATIONAL CALCULATION OF THERMODYNAMIC PROPERTIES OF SUPERCOOLED LIQUID METALS

By means of Gibbs-Bogoliubov (GB) thermodynamic variational calculation,thethermodynamic properties of the supercooled liquid metals,such as the 3rd family elementsAl,Ga and Tl and transition metal Ti were calculated using the hard-sphere (HS) system asreference.The values of mean atomic volume,Helmholtz free energy,internal energy andentropy as well as specific heat at constant volume,isothermal bulk modulus,thermal expan-sion coefficient and specfic heat under constant pressure were evaluated.The glass transitiontemperature,T_g,is easily obtained from the C_p-T plot.The glass forming ability for metalcan be predicted from T_g/T_m,which is in agreement with the experimental results.     

过冷液态金属热力学性质的变分计算SCIEI

本文用Gibbs-Bogoliubov热力学变分计算方法,以硬球(HS)体系为参考体系,对第Ⅲ族中Al,Ga,Tl及过渡金属Ti进行了过冷液态热力学性质的计算,算出平均原子体积Ω,Helmholtz自由能F,内能E及熵S,并得到等容比热c_ν;等温体弹性模量B_T,热膨胀系数α_p和等压比热c_p.从c_p-T曲线得到非晶转变温度T_g。T_r(=Tg/Tm)的理论值表明了金属形成非晶的能力,和实验结果相符。     

高压高温下Re 2 N的弹性和热力学性能

采用基于密度泛函理论的第一性原理计算方法,系统研究高压高温下Re2N的晶体参数、力学性能和热力学性能。结果表明：在高压下Re2N具有明显的弹性各向异性,与弹性常数C12、C13、C44相比,C11和C33的变化随着压力的变化非常明显。此外,首次计算Re2N的体弹模量B、弹性模量E和剪切模量G沿不同晶轴的分布。弹性模量在一些主要晶轴方向上的大小分布趋势如下：[0001][1211][1010][1011]EEEE〉〉〉。计算结果还表明：在（0001）晶面,Re2N的抗剪切能力是最低的,从而极大地减小对大剪切变形的阻力。基于准简谐德拜模型,在0~50GPa压力和0~1600K温度下得到德拜温度、格林艾森参数、热传导以及热扩散系数的变化行为。     

金属Zr热力学性质的第一原理研究

应用基于密度泛函与密度泛函微扰理论的平面波赝势方法计算了一组不同晶格常数下hcp结构金属Zr的声子谱及相应的静态总能,由此得到不同晶格常数下的自由能,由准谐近似及自由能极小判据得到自由能与温度的关系,进而计算了金属Zr热膨胀系数、体弹性模量、定容及定压摩尔热容与温度的关系,计算结果在较宽的温度范围内与实验相符.对热膨胀系数,同时应用Debye-Grüneisen模型进行了计算,并与第一原理方法的结果进行了比较.对摩尔热容的计算考虑了电子的贡献,表明在高温区电子热容的贡献不能忽略.     

Thermodynamic properties and phase stability of nanocrystalline metals

The fundamental thermodynamic functions of enthalpy, entropy, and Gibbs free energy, as functions of the excess free volume at interfaces, temperature, and grain size, have been derived for single-phase metal nanocrystals. The model was applied to predict the thermal features of nano-grain boundaries and the characteristics of phase transformation in nanocrystalline metals, such as the transformation temperature and the critical grain size for phase transformation at a given temperature. The model predictions have been verified by experimental studies on the β-Co ←→α-Co phase transformation in nanocrystalline Co prepared by ball milling.     

Predictions of high-pressure structural, electronic and thermodynamic properties of α-Si3N4

The plane-wave pseudo-potential method within the framework of first-principles technique is used to investigate the fundamental structural properties of Si3N4 . The calculated ground-state parameters agree quite well with the experimental data. Our calculation reveals that α-Si3N4 can retain its stability to at least 45 GPa when compressed below 300 K. No phase transition can be seen in the pressure range of 0-45 GPa and the temperature range of 0-300 K. Actually, the α→β transition occurs at 1600 K and 7.98 GPa. Many thermodynamic properties, such as bulk modulus, heat capacity, thermal expansion, Gru¨neisen parameter and Debye temperature of α-Si3N4 were determined at various temperatures and pressures. Significant differences in these properties were observed at high temperature and high pressure. The calculated results are in good agreement with the available experimental data and previous theoretical values. Therefore, our results may provide useful information for theoretical and experimental investigations of the N-based hard materials like α-Si3N4.     

First-principle study on the physical properties of ultra-incompressible ReB2

The elastic and physical characteristics of ReB₂ crystal have been predicted through a method of density functional theory within the generalized gradient approximation (GGA). Five independent elastic constants are C₁₁=662 GPa, C₁₂=150 GPa, C₁₃=146 GPa, C₃₃=1090 GPa and C₄₄=263 GPa. The bulk modulus (B), shear modulus (G), Young's modulus (E), Poisson's ratio (γ) and the ratio of linear compressibility coefficient along the a- and c-axis crystal direction (Ka/Kc) are 356 GPa, 305 GPa, 711 GPa, 0.167 and 1.758, respectively. In addition, the dependence of bulk modulus (B) on temperature (T) and pressure (p) as well as the coefficient of thermal expansion (α_L) at various temperatures are evaluated and discussed. The coefficient of thermal expansion is consistent with the famous Gruneisen's law when the temperature is less than 1500K. Our results agree well with the other experimental results.     

Thermodynamic properties of 1-nutyl-3-methylimidazolium chloride (C<Subscript>4</Subscript>mim[Cl]) ionic liquid

Thermodynamic properties of 1-butyl-3-methylimidazolium chloride (C₄mim[Cl]) ionic liquid were determined using thermogravimetric (TG) differential thermal analysis (DTA). A new method called DTA mass-difference baseline, was used to measure the heat capacity and enthalpy change of phase transformation of ionic liquid from DTA curves. Based on this, the changes in standard enthalpy, entropy, and Gibbs energy were determined. The results show that standard enthalpy and entropy changes of C₄mim[Cl] increase nonlinearly with increasing temperature, while the standard Gibbs energy change decreases nonlinearly with increasing temperature within the temperature range studied (298–453 K). The standard enthalpy of melting and enthalpy of vaporization were determined to be 0.93 and 11.07 kJ/mol, respectively.