A Low-temperature Automated Adiabatic Calorimeter Heat Capacities of High-purity Graphite and Polystyrene

A computerized adiabatic calorimeter for heat capacity measurements in the temperature range 80–400 K has been constructed. The sample cell of the calorimeter, which is about 50 cm³ in internal volume, is equipped with a platinum resistance thermometer and surrounded by an adiabatic shield and a guard shield. Two sets of 6-junction chromel-copel thermocouples are mounted between the cell and the shields to indicate the temperature differences between them. The adiabatic conditions of the cell are automatically controlled by two sets of temperature controller. The reliability of the calorimeter was verified through heat capacity measurements on the standard reference material α-Al₂O₃. The results agreed well with those of the National Bureau of Standards (NBS): within ±0.2% throughout the whole temperature region. The heat capacities of high-purity graphite and polystyrene were precisely measured in the interval 260–370 K by using the above-mentioned calorimeter. The results were tabulated and plotted and the thermal behavior of the two materials was discussed in detail. Polynomial expressions for calculation of the heat capacities of the two substances are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Molar heat capacity and thermodynamic properties of crystalline [Nd(Glu)(H<Subscript>2</Subscript>O)<Subscript>5</Subscript>(Im)<Subscript>3</Subscript>](ClO<Subscript>4</Subscript>)<Subscript>6</Subscript>·2H<Subscript>2</Subscript>O

A complex of neodymium perchloric acid coordinated with L-glutamic acid and imidazole, [Nd(Glu)(H₂O)₅(Im)₃](ClO₄)₆·2H₂O was synthesized and characterized by IR and elements analysis for the first time. The thermodynamic properties of the complex were studied with an automatic adiabatic calorimeter and differential scanning calorimetry (DSC). Glass transition and phase transition were discovered at 221.83 and 245.45 K, respectively. The glass transition was interpreted as a freezing-in phenomenon of the reorientational motion of ClO₄⁻ ions and the phase transition was attributed to the orientational order/disorder process of ClO₄⁻ ions. The heat capacities of the complex were measured with the automatic adiabatic calorimeter and the thermodynamic functions [H _T-H _298.15] and [S _T-S _298.15] were derived in the temperature range from 80 to 390 K with temperature interval of 5 K. Thermal decomposition behavior of the complex in nitrogen atmosphere was studied by thermogravimetric (TG) analysis and differential scanning calorimetry (DSC).     

A small sample-size automated adiabatic calorimeter from 70 to 580 K

An automatic adiabatic calorimeter for measuring heat capacities in the temperature range 70-580 K, equipped with a small sample cell of 7.4 cm³ in the internal volume has been developed. In order to obtain a good adiabatic condition of the calorimeter at high temperature, the calorimeter was surrounded in sequence by two adiabatic shields, three radiation shields and an auxiliary temperature-controlled sheath. The main body of the cell made of copper and the lid made of brass are silver-soldered and the cell is sealed with a copper screw cap. A sealing gasket made of Pb-Sn alloy is put between the cap and the lid to ensure a high vacuum sealing of the cell in the whole experimental temperature range. All the leads are insulated and fixed with W30-11 varnish, thus a good electric insulation is obtained at high temperature. All the experimental data, including those for energy and temperature are collected and automatically with a personal computer using a predetermined program. To verify the accuracy of the calorimeter, the heat capacities of α-Al₂O₃ of the calorimetric standard reference material is measured. The standard deviations of experimental heat capacity values from the smoothed values are within ± 0.28%, while the inaccuracy is within ±0.4% compared with those of the National Bureau of Standards over the entire working temperature range. Project supported by the National Natural Science Foundation of China (Grant No. 29573133).     

镥晶体的绝热量热法测试和热力学函数

文章合成了Lu(NO₃)₃(C₂H₅O₂N)_4.H₂O,用红外和元素分析对其进行了表征。用高精度全自动绝热量热仪,测定了该配合物80-382 K温区的热容, 利用实验热容数据, 根据热容与焓、熵的热力学关系, 求出了配合物85-350 K温区内每隔5 K相对于298.15K的标准热力学函数(HT - H298.15)m和(ST - S298.15)m.在80-350 K温度区间内,配合物的热容随温度升高而增大,没有相转移点和热力学吸收峰的出现,该配合物在此温度区间内是稳定存在的。     

Molar heat capacity and thermodynamic properties of crystalline Ho(Asp)Cl<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O

The molar heat capacity, C _p,m, of a complex of holmium chloride coordinated with L-aspartic acid, Ho(Asp)Cl₂·6H₂O, was measured from 80 to 397 K with an automated adiabatic calorimeter. The thermodynamic functions H _T-H _298.15 and S _T-S _298.15 were derived from 80 to 395 K with temperature interval of 5 K. The thermal stability of the complex was investigated by differential scanning calorimeter (DSC) and thermogravimetric (TG) technique, and the mechanism of thermal decomposing of the complex was determined based on the structure and the thermal analysis experiment.     

Ho(NO3)3(C2H5O2N)4·H2O的低温热容和热力学函数

合成了稀土(钬, Ho)-氨基酸(甘氨酸, C₂H₅O₂N)二元配合物Ho(NO₃)₃(C₂H₅O₂N)₄·H₂O, 并且通过化学分析、元素分析和红外(IR)光谱对配合物进行了表征. 用高精度全自动绝热量热仪, 测定了该配合物在80-390 K温度区间的定压摩尔热容(C_p,m). 利用实验测定的热容数据, 采用最小二乘法, 将热容曲线上热容峰以外的两段平滑区的摩尔热容对折合温度进行拟合, 建立了热容随折合温度变化的多项式方程. 根据热容与焓、熵的热力学关系,计算出了配合物在80-390 K温度区间内,每隔5 K,相对于298.15 K的摩尔热力学函数(H_T,m-H_298.15,m)和(S_T,m-S_298.15,m). 通过热容曲线分析, 计算出了350 K附近转变过程的焓变(Δ_trsH_m)和熵变(Δ_trsS_m). 用差示扫描量热法(DSC)测定了配合物的热稳定性.     

Heat capacity and thermodynamical properties of the crystal of [RE2(Glu)2(H2O)8](ClO4)4·H2O (RE = Nd, Eu, Dy)

Thermodynamical data of rare earth complexes with amino acid are important for engineering chemistry and fundamental chemistry. However, they have rarely been reported. In this work, a series of crystalline complexes of rare earth perchlorate coordinated with glutamic acid have been synthesized in water medium, and their thermodynamical data, including the heat capacity in low temperature range and the standard enthalpy of formation, were determined. These complexes were identified to be [RE₂(Glu)₂(H₂O)₈](ClO₄)₄·H₂O (RE = Nd, Eu, Dy) by using thermogravimetric analysis (TG), differential thermal analysis (DTA), and chemical and elementary analyses. Their purity has been determined. No melting points were observed for all the three complexes. The heat capacity of the complexes was measured by an adiabatic calorimeter from 79 to 370 K. Abnormal heat capacity values were detected for two of the complexes and the decomposition range of one complex was found. The temperature, enthalpy change and entropy change of the decomposition processes of the three complexes were calculated. The polynomial equations of heat capacity in the experimental temperature range have been obtained by least squares fitting. The standard enthalpy of formation was determined by an isoperibol reaction calorimeter at 298.15 K. Supported by the Research Fund of Beijing Institute of Petro-Chemical Technology (N06-06)     

An adiabatic low-temperature calorimeter for heat capacity measurement of small samples

A small sample adiabatic calorimeter for measuring heat capacities in the temperature range 60–350 K using the Nernst method has been constructed. The sample cell of the calorimeter is 6 cm³ in the internal volume, equipped with a miniature platinum thermometer and surrounded by two adiabatic shields. Two sets of 6-junction chromel-copel thermocouples were mounted between the cell and the shields to indicate the temperature differences between them. The adiabatic conditions of the cell were automatically controlled by two sets of temperature controller. A mechanical pump was used to pump out the vapour of liquid nitrogen in the cryostat to solidify N₂ (1), and 60 K or even lower temperature was obtained. The performance of this apparatus was evaluated by heat capacity measurements on α-alumina. The deviations of experimental results from a smoothed curve lie within ±0.2%, while the inaccuracy is within ±0.5% compared with the recommended reference data in the wole temperature range.     

Low-temperature heat capacity and standard enthalpy of formation of neodymium glycine perchlorate complex [Nd2(Gly)6(H2O)4](ClO4)6·5H2O

Rare-earth perchlorate complex coordinated with glycine [Nd₂(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O was synthesized and its structure was characterized by using thermogravimetric analysis (TG), differential thermal analysis (DTA), chemical analysis and elementary analysis. Its purity was 99.90%. Heat capacity measurement was carried out with a high-precision fully-automatic adiabatic calorimeter over the temperature range from 78 to 369 K. A solid-solid phase transformation peak was observed at 256.97 K, with the enthalpy and entropy of the phase transformation process are 4.438 kJ mol⁻¹ and 17.270 J K⁻¹ mol⁻¹, respectively. There is a big dehydrated peak appears at 330 K, its decomposition temperature, decomposition enthalpy and entropy are 320.606 K, 41.364 kJ mol⁻¹ and 129.018 J K⁻¹ mol⁻¹, respectively. The polynomial equations of heat capacity of this compound in different temperature ranges have been fitted. The standard enthalpy of formation was determined to be −8023.002 kJ mol⁻¹ with isoperibol reaction calorimeter at 298.15 K.     

硼砂水溶液的低温热容及热化学性质研究

利用精密绝热量热仪测定了0.03355mol·kg-1的硼砂水溶液在78～351K温区的热容,从实验热容测定结果得到了该水溶液的凝固点为272.905K。用最小二乘法将实验热容值对温度进行拟合,建立了该溶液的热容随温度变化的多项式方程。根据热力学函数关系式,用此多项式方程进行数值积分,获得了以298.15K为基准的该溶液在80～350K温区每隔5K的热力学函数值,并计算出摩尔熔化焓和熔化熵分别为4.536kJ·mol-1和16.22J·K-1·mol-1。根据溶液凝固点降低值,计算出了该溶液的活度为0.99763。     

配位化合物Zn(Met)3(NO3)2·H2O(s)(Met=L-α-蛋氨酸)的低温热容及标准摩尔生成焓

利用精密绝热热量仪测定了化合物配合物Zn(Met)₃(NO₃)₂·H₂O (s) (Met=L-α-蛋氨酸)在78-371 K温区的摩尔热容. 通过热容曲线解析, 得到了该配合物的起始脱水温度为T_D=325.10 K. 将该温区的摩尔热容实验值用最小二乘法拟合得到了摩尔热容(C_p)对约化温度(T)的多项式方程, 由此计算得到了配合物的舒平热容值和热力学函数值. 基于设计的热化学循环, 选择100 mL of 2 mol·L^-1 HCl为量热溶剂, 利用等温环境溶解-反应热量计, 得到了298.15 K配合物的标准摩尔生成焓为Δ_fH_m⁰[Zn(Met)₃(NO₃)₂·H₂O(s),s]=-(1472.65±0.76) J·mol^-1.     

Thermodynamic studies of (R)-BINOL-menthyl dicarbonates

The (R)-BINOL-menthyl dicarbonates, one of the most important compounds in catalytic asymmetric synthesis, was synthesized by a convenient method. The molar heat capacities C _p,m of the compound were measured over the temperature range from 80 to 378 K with a small sample automated adiabatic calorimeter. Thermodynamic functions [H _T–H _298.15] and [S _T–S _298.15] were derived in the above temperature range with a temperature interval of 5 K. The thermal stability of the substance was investigated by differential scanning calorimeter (DSC) and a thermogravimetric (TG) technique.     

Low-temperature Heat Capacities and Thermodynamic Properties of Hydrated Sodium Cupric Arsenate [NaCuAsO4·1.5H2O（s）]

Low-temperature heat capacities of the solid compound NaCuAsO4·1.5H2O(s)were measured using a precision automated adiabatic calorimeter over a temperature range of T=78 K to T=390 K.A dehydration process occurred in the temperature range of T=368-374 K.The peak temperature of the dehydration was observed to be TD=(371.828±0.146)K by means of the heat-capacity measurement.The molar enthalpy and entropy of the dehydration were ΔDHm=(18.571±0.142)kJ/mol and ΔDSm=(49.946±0.415)J/(K·mol),respectively.The experimental values of heat capacities for the solid(Ⅰ)and the solid-liquid mixture(Ⅱ)were respectively fitted to two polynomial equations by the least square method.The smoothed values of the molar heat capacities and the fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were tabulated at an interval of 5 K.     

Heat Capacities and Thermodynamic Properties of a H2O + Li2B4O7 Solution in the Temperature Range from 80 to 356 K

The molar heat capacities of an aqueous Li₂B₄O₇ solution were measured with a precision automated adiabatic calorimeter in the temperature range from 80 to 356 K at a concentration of 0.3492 mol⋅kg⁻¹. The occurrence of a phase transition was determined based on the changes in the curve of the heat capacity with temperature. A phase transition was observed at 271.72 K corresponding to the solid-liquid phase transition; the enthalpy and entropy of the phase transition were evaluated to be Δ H _m = 4.110 kJ⋅mol⁻¹ and Δ S _m = 15.13 J⋅K⁻¹⋅mol⁻¹, respectively. Using polynomial equations and thermodynamic relationship, the thermodynamic functions [H _T −H _298.15] and [S _T −S _298.15] of the aqueous Li₂B₄O₇ solution relative to 298.15 K were calculated in temperature range 80 to 355 K at intervals of 5 K. Values of the relative apparent molar heat capacities of the aqueous Li₂B₄O₇ solution, C _p,φ, were calculated at every 5 K in temperature range from 80 to 355 K from the experimental heat capacities of the solution and the heat capacities of pure water.     

Low-temperature heat capacities and thermodynamic properties of rare-earth triisothiocyanate hydrates (III) —Sm(NCS)3 · 6H2O, Gd(NCS)3 · 6H20, Yb(NCS)3 · 6H20 and Y(NCS)3 · 6H20

The heat capacities of four RE isothiocyanate hydrates, Sm(NCS)₃, · 6H₂0, Gd(NCS)₃ · 6H₂0, Yb(NCS)₃, · 6H₂O and Y(NCS)₃, · 6H₂0, have been measured from 13 to 300 K with a fully-automated adiabatic calorimeter. No obvious thermal anomaly was observed for the above-mentioned compounds in the experimental temperature ranges. The polynomial equations for calculating the heat capacities of the four compounds in the range of 13–300 K were obtained by the least-squares fitting based on the experimentalC _P, data. TheC _P, values below 13 K were estimated by using the Debye-Einstein heat capacity functions. The standard molar thermodynamic functions were calculated from 0 to 300 K. Gibbs energies of formation were also calculated. Project supported by the National Natural Science Foundation of China.     

A study on the thermodynamic properties of polyimide BTDA-ODA by adiabatic calorimetry and thermal analysis

Polyimide BTDA-ODA sample was prepared by polycondensation or step-growth polymerization method. Its low temperature heat capacities were measured by an adiabatic calorimeter in the temperature range between 80 and 400 K. No thermal anomaly was found in this temperature range. A DSC experiment was conducted in the temperature region from 373 to 673 K. There was not phase change or decomposition phenomena in this temperature range. However two glass transitions were found at 420.16 and 564.38 K. Corresponding heat capacity increments were 0.068 and 0.824 J g^–1 K^–1, respectively. To study the decomposition characteristics of BTDA-ODA, a TG experiment was carried out and it was found that this polyimide started to decompose at ca 673 K.This revised version was published online in November 2005 with corrections to the Cover Date.     

水合烟酸铜Cu(Nic)2•H2O(s)(Nic＝烟酸)的合成、表征及热力学性质

近几十年来,烟酸盐类化合物或配合物由于优越的吸收率高和无毒副作用等特点使其在化妆品、药品和食品等领域作为营养添加剂具有重要应用前景。然而,这类化合物的基础热力学数据极其缺乏,从而限制了这类化合物的理论研究和应用开发的深入开展。为此,本论文利用室温固相合成方法和球磨技术合成了一种新化合物Cu(Nic)2•H2O(s),利用化学分析、元素分析、FTIR和X-射线粉末衍射技术表征了它的结构和组成,利用精密自动绝热热量计准确地测量了它在78-400 K温区的摩尔热容。在热容曲线的T ＝ 326-346 K温区观察到一个明显的固-液相变过程。利用相变温区三次重复实验热容的测量结果确定了此相变过程的峰温、相变焓和相变熵分别为：Tfus＝(341.290 ±0.873) K, DfusHm＝(13.582±0.012) kJ×mol-1, DfusSm＝(39.797±0.067) J×K-1×mol-1。通过最小二乘法将相变前和相变后的热容实验值分别拟合成了热容对温度的两个多项式方程。通过热容多项式方程的数值积分,得到了这个化合物的舒平热容值和相对于298.15 K的各种热力学函数值,并且将每隔5 K的热力学函数值列成了表格。     

配合物Zn(Met)SO4•H2O(s)的低温热容和标准摩尔生成焓

利用精密自动绝热热量计直接测定了配合物Zn(Met)SO₄•H₂O(s) 在78～370 K温区的摩尔热容. 通过热容曲线的解析得到该配合物的起始脱水温度为T₀＝329.50 K. 将该温区的摩尔热容实验值用最小二乘法拟合得到摩尔热容 (C_p,m)对温度(T)的多项式方程, 并且在此基础上计算出了它的舒平热容值和各种热力学函数值. 依据Hess定律, 通过设计热化学循环, 选择体积为100 cm³、浓度为2 mol•L^－1的盐酸作为量热溶剂, 利用等温环境溶解-反应热量计, 测定和推算出该配合物的标准摩尔生成焓为Δ_fH_m⁰＝－(2069.30±0.74) kJ•mol^－1.     

Low Temperature Specific Heat and Thermal Stability of Fe–B Ultrafine Amorphous Alloy Particles

Fe–B ultrafine amorphous alloy particles (UFAAP) were prepared by chemical reduction of Fe³⁺ with NaBHO₄ and confirmed to be ultrafine amorphous particles by transmission electron microscopy and X-ray diffraction. The specific heat of the sample was measured by a high precision adiabatic calorimeter, and a differential scanning calorimeter was used for thermal stability analysis. A topological structure of Fe-B atoms is proposed to explain two crystallization peaks and a melting peak observed at T=600, 868 and 1645 K, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermodynamic investigation of room temperature ionic liquid

The molar heat capacities of the room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF₄) were measured by an adiabatic calorimeter in temperature range from 80 to 390 K. The dependence of the molar heat capacity on temperature is given as a function of the reduced temperature X by polynomial equations, C _P,m (J K^–1 mol^–1)= 195.55+47.230 X–3.1533 X ²+4.0733 X ³+3.9126 X ⁴ [X=(T–125.5)/45.5] for the solid phase (80~171 K), and C _P,m (J K^–1 mol^–1)= 378.62+43.929 X+16.456 X ²–4.6684 X ³–5.5876 X ⁴ [X=(T–285.5)/104.5] for the liquid phase (181~390 K), respectively. According to the polynomial equations and thermodynamic relationship, the values of thermodynamic function of the BMIBF₄ relative to 298.15 K were calculated in temperature range from 80 to 390 K with an interval of 5 K. The glass translation of BMIBF₄ was observed at 176.24 K. Using oxygen-bomb combustion calorimeter, the molar enthalpy of combustion of BMIBF₄ was determined to be Δ_c H _m ^o= – 5335±17 kJ mol^–1. The standard molar enthalpy of formation of BMIBF₄ was evaluated to be Δ_f H _m ^o= –1221.8±4.0 kJ mol^–1 at T=298.150±0.001 K.