稀土元素异硫氰酸盐低水合物的制备,性质及标准生成焓的测定

制备了11种低水合物RE(NCS)_3·mH_2O(RE=La,Ce,Pr,Nd时,m=4.5;RE=Sm,Eu,Gd,Dy,HO,Yb,Y时,m=3)。测得了它们的熔点,并对其X射线物相分析进行了研究。采用量热法,测定了除Y以外的10种低水合物的标准生成焓,求得了它们的晶格能,以及从高水合物至相应的低水合物的标准脱水焓。还对Tb,Er,Tm,Lu 4种RE(NCS)_3·mH_2O(m=3)的相应数据进行了估算。     

Enthalpies of solution and crystallization of ammonium aluminum sulphate dodecahydrate in water at 25°C

Enthalpies of crystallization of NH₄Al(SO₄)₂·12H₂O from aqueous solutions at 25°C, measured using a calorimetric method and determined from previously published data on the concentration dependence of the enthalpy of solution, are reported. The results are compared with the values obtained from the temperature dependence of solubility and from vapor pressure data by using the Williamson equation. The integral and partial molar enthalpies of solution in concentrated and diluted solutions are given.     

Thermochemistry of Aqueous Solutions of Alkylated Nucleic Acid Bases. X. Enthalpies of Hydration of Cytosine and some Methylated, Hydroxy and Methoxy Derivatives of Cytosine

Enthalpies of solution in water, vapor pressures, and enthalpies of sublimation were determined for cytosine and a number of crystalline derivatives of cytosine: 1-methylcytosine, 1-methyl-N ⁴-hydroxycytosine, 1,5-methyl-N ⁴-methoxycytosine, 1,N ⁴,N ⁴-trimethylcytosine, 1,5,N ⁴-trimethylcytosine, 1,5-dimethyl-N ⁴-methoxycytosine, and l,N ⁴-dimethyl-5-ethylcytosine. Enthalpies of hydration were calculated. The latter were analyzed on the basis of the group additivity method. The relation between enthalpy of hydration and polarity of compounds is discussed.     

Thermodynamic properties of alkali halides. II. Enthalpies of dilution and heat capacities in water at 25°C

The enthalpies of dilution and volumetric specific heats of most alkali halides were measured in water at 25°C with flow microcalorimeters in the concentration range 0.01 to 1m. Apparent molal relative enthalpies _L, derived from the enthalpies of dilution, can be represented by a parametric equation in molality. Combining _L with osmotic data, excess entropies can be calculated. Excess free energies, enthalpies, and entropies are compared at 0.5m, and the observed trends are consistent with a model of structural interactions in aqueous alkali halide solutions. The apparent molal heat capacities _C were fitted with the equation _C= _C ^° +A_C(d₀m)^1/2+B _C m. The _C ^° are, in general, additive to better than 1 J-K^–1-mole^–1 and reflect mostly the structural part of ion-solvent interactions. Taking _C ^° (H⁺)=0, conventional ionic _C ^° are obtained. The parameterB _C for different pairs of ions follows approximately the same trends as the corresponding parameterB _V for apparent molal volumes and seems to reflect structural interactions between the ions.     

Enthalpies of solvation of alkylated uracils in water,nonaqueous and mixed solvents

The enthalpies of solution of uracil and its alkylated derivatives in water, methanol, N,N-dimethylformamide (DMF) and water+DMF mixtures were measured at 25°C. The enthalpies of solvation were determined. The enthalpies of cavity formation, corresponding to the enthalpies of solvent-solvent interactions were calculated and the enthalpies of solute-solvent interactions were obtained. The presence of the alkyl groups was found to have different effects on the enthalpy of interaction depending on the position and size of the substitution. The effect of alkylation at the nonpolar side of the uracil ring was found to arise mostly from the enhancement of the van der Waals interactions. The alkyl substitutions at the polar side resulted also in the removal of the solvent molecules interacting specifically with the polar groups of uracil. The enthalpy of those specific interactions was determined and found to be stronger in methanol and DMF than in water. Enthalpies of solvation in the binary water+DMF solvent were found to depend in a nonlinear way on the solvent composition. The nonlinearities in the water-rich region were found to arise from the decay of the hydrophobic hydration of the solutes with the increasing DMF content. The substitution of two methyl groups caused the uracil molecule to bahave as a predominantly hydrophobic solute. The nonlinearities in the DMF-rich region were found only for those solutes which can form hydrogen bonds with DMF.     

Enthalpies of Dilution of Aqueous Solutions of LiCl, KCl, and CsCl at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of LiCl, KCl, and CsCl at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and 350°C and 17.6 MPa. The concentration range of the chloride solutions was 0.5 to 0.02m. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for ion association of the chloride salts were estimated from the heat data. For all systems, the enthalpy and entropy changes were positive and had accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.     

Enthalpies of Dilution of Aqueous Solutions of NaOH, KOH, and CsOH at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of KOH and CsOH at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and for aqueous solutions of NaOH, KOH, and CsOH at 350°C and 17.6 MPa. Previously collected dilution enthalpies for aqueous solutions of NaOH at 300°C and 9.3 MPa and at 325°C and 12.4 MPa were included when fitting the Pitzer parameters. The concentration range of the hydroxide solutions was 0.5–0.02 molal. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for alkali metal ion association with hydroxide ion were estimated from the heat data. For all systems, the enthalpy changes and entropy changes were positive and had accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.     

Hydration of the organized molecular assembly of ionic surfactants as studied by vapor pressure and x-ray diffraction

Equilibrium vapor pressure of water was measured for ionic surfactant-water binary systems as a function of water content over the temperature range 5–11°C. The measurement of x-ray powder diffraction has also been performed to characterize the microscopic structures of these two-component systems. Examined surfactants were the homologs of sodium alkyl sulfate and alkyltrimethylammonium bromide. It was found that dodecyl and decyl sulfate formed solid di-and trihydrate respectively, while octyl sulfate and the cationic surfactants formed lyotropic liquid crystal instead. The x-ray long spacing of the liquid crystals scarcely varied with water content.Enthalpy of vaporization was calculated for both solid hydrates and lyotropic liquid crystals.     

Determination of Standard Enthalpies of Formation of the Tellurites of the Rare Earths Y,La, Ce and Pr by DSC Method

The standard enthalpies of tellurites of Y, La, Ce and Pr were determined by differential scanning calorimetric (DSC) method. The completeness of the chemical reactions between the metal oxides and tellurous oxide were checked by DSC and X-ray powder diffraction methods. The calculated standard enthalpies are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Di-hydroxybenzenes: Catechol, resorcinol, and hydroquinone: Enthalpies of phase transitions revisited

Molar enthalpies of sublimation of 1,2-di-hydroxybenzene, 1,3-di-hydroxybenzene, and 1,4-di-hydroxybenzene were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. The molar enthalpies of fusion of 1,2- and 1,4-isomers were measured by differential scanning calorimetry (DSC). A large number of the primary experimental results on the temperature dependences of vapor pressure and phase transitions have been collected from the literature and have been treated in a uniform manner in order to derive sublimation, vaporization and fusion enthalpies of di-hydroxybenzenes at the reference temperature 298.15 K. The data sets on phase transitions were checked for internal consistency. This collection together with the new experimental results reported here has helped to resolve contradictions in the available thermochemical data and to recommend consistent and reliable sublimation, vaporization and fusion enthalpies for all three isomers under study.     

Crystal structure of a high‐pressure phase of magnesium chloride hexahydrate determined by in‐situ X‐ray and neutron diffraction methods

A high‐pressure phase of magnesium chloride hexahydrate (MgCl₂·6H₂O‐II) and its deuterated counterpart (MgCl₂·6D₂O‐II) have been identified for the first time by in‐situ single‐crystal X‐ray and powder neutron diffraction. The crystal structure was analyzed by the Rietveld method for the neutron diffraction pattern based on the initial structure determined by single‐crystal X‐ray diffraction. This high‐pressure phase has a similar framework to that in the known ambient‐pressure phase, but exhibits some structural changes with symmetry reduction caused by a subtle modification in the hydrogen‐bond network around the Mg(H₂O)₆ octahedra. These structural features reflect the strain in the high‐pressure phases of MgCl₂ hydrates.     

离子液体1-丙基-3-甲基咪唑醋酸盐[C_3mim][OAc]蒸气压和蒸发焓的测定及极性预测

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水蒸气蒸馏-离子色谱法测定稀土氧化物中微量和痕量氟和氯

为准确测定高纯稀土氧化物中氟离子和氯离子的含量,建立了水蒸气蒸馏对样品进行前处理,离子色谱法同时测定氟离子和氯离子的分析方法。方法通过硫酸预蒸馏降低空白值。稀土氧化物经硫酸分解,其中的氟和氯随水蒸气逸出与样品分离,经水吸收,用阴离子分离柱分离,以氢氧化钾溶液梯度淋洗,抑制型电导检测器检测。通过保留时间对氟和氯进行定性分析,以标准曲线法对氟和氯进行定量分析,氟和氯的线性相关性为0.9998和0.9997,测定下限均为0.0006%。通过选择样品前处理方式、硫酸用量、样品量、蒸馏时间、吸收液等,确定实验的最佳条件。通过加标回收实验和方法比对实验评估验证方法的准确性,实验表明氟和氯的加标回收率分别在88.20%～99.68%和95.50%～103.46%之间,与现有标准方法GB/T 12690-2003测定结果相比较相对偏差小于5%。通过精密度实验验证方法的稳定性,方法的相对标准偏差氟和氯（n = 11）分别为1.66%～4.12%和1.74%～7.58%。结果表明所建立的分析方法检出限低、精密度良好、准确度高。本方法适用于对高纯稀土氧化物中微量和痕量氟离子和氯离子的快速测定,为高纯稀土氧化物中杂质氟和氯的质量与评价提供技术支撑。     

1-丁基-3-甲基咪唑四氟硼酸盐的热稳定性、平衡蒸汽压和标准蒸发焓

利用非等温、等温热重分析(TG)法,研究了高纯氮气气氛下1-丁基-3-甲基咪唑四氟硼酸盐([bmim][BF4])离子液体的热稳定性、平衡蒸汽压和标准蒸发焓.非等温热重(TG)曲线表明[bmim][BF4]的初始分解温度(Tonset)和最大分解速率对应的温度(Tm)分别为697和734K.然而长期等温TGA研究表明,[bmim][BF4]的最高可使用温度约为513K.另外,利用基于TG的蒸发技术研究了[bmim][BF4]的平衡蒸汽压(pe)与温度的关系并计算了标准蒸发焓.在503-543K温度范围内,离子液体[bmim][BF4]的pe和温度的关系是:lgpe=(16±1)+(-6.85±0.25)×103/T.[bmim][BF4]的标准蒸发焓为(131±5)kJ·mol-1.     

高氯酸镁吸收重量法测定铁矿石中结晶水的含量

建立了铁矿石中结晶水含量的测定方法.利用铁矿石中结晶水高温分解的特性,采用高纯氩气为载气,试样在1 000℃管式炉中加热,结晶水随载气逸出,由装有无水高氯酸镁的吸收管吸收后称量,计算出铁矿石中结晶水的含量.测定结果的相对标准偏差(RSD)小于3％(n=6),加标回收率在95％～ 104％之间.     

Vapor Pressure and Heat of Sublimation of Crystal Polymorphs

In order to determine the applicability of vapor pressure studies on polymorphic modifications, pairs of enantiotropically related modifications of caffeine, theophylline and carbamazepine were investigated. The studies were performed over a wide temperature range (71 to 191°C) and accordingly over a wide vapor pressure range (0.02 to 400 Pa) using an automatic instrument constructed on the basis of the gas saturation principle. This instrument enables an analytical determination of the main component and the impurities present by the chromatographic separation of the substances transported in the gas flow. Therefore, the real partial pressure of the main component can be measured. Due to the high precision of the applied method it was possible to determine partial pressure curves and the thermodynamic transition temperature — the point at which the vapor pressure of two crystal polymorphs is equal. The thermodynamic transition temperatures of caffeine and theophylline were determined to be 136 and 232°C, respectively. These values are in agreement with experimental or calculated values derived from DSC investigations but are more reliable. Vapor pressure measurements of carbamazepine are only meaningful in the low temperature range due to its decomposition at high temperatures. The thermodynamics, advantages and limits of vapor pressure determinations of polymorphic modifications are discussed.This revised version was published online in November 2005 with corrections to the Cover Date.     

1-烷基-4-氨基-1,2,4-三唑硝酸盐含能离子液体的蒸气压及其摩尔汽化焓的理论研究

合成了1-烷基-4-氨基-1,2,4-三唑硝酸盐含能离子液体([RATZ]NO₃),并通过核磁和红外进行了结构表征;采用Gaussian09/B3LYP/6-311+G(d,p)密度泛函理论,计算了[RATZ]NO₃的离子间相互作用能及摩尔体积;在298 K-323 K温度范围内,测定了不同配比[RATZ]NO₃-EtOH混合溶液的饱和蒸气压,其中乙醇摩尔分数分别为0.984、0.996、0.999以及1.000。系统研究了[RATZ]NO₃-EtOH混合溶液的饱和蒸气压、[RATZ]NO₃的蒸气压及摩尔汽化焓与温度、离子间相互作用能以及结构之间的关系。结果表明：[RATZ]NO₃-EtOH混合溶液的饱和蒸气压随着温度的升高、离子间作用能的减小以及阳离子体积的增大而增大,其沸点比纯溶剂高,且在298 K-323 K温度范围内[RATZ]NO₃的平衡蒸气压均低于250 mPa,因此说明含能离子液体具有不挥发性,蒸气压极低,并通过理论计算得到的离子间相互作用能及体积,解释了[RATZ]NO₃的摩尔汽化焓随烷基链增长而降低的原因。     

Single Crystal of Lanthanum Hydroxide La(OH)3: Controlled Synthesis by High Pressure Flux Method and Its Growth Mechanism

High pressure synthesis of solid material tends to increase the density,coordination number,symmetry of material and shorten bond length.The solid synthesized at a high pressure and decompressed to ambient pressure often exhibits a metastable "stretched" state,within the high pressure stability field.The crystal grown at a high pressure is of great importance with the development of high pressure technology.Crystal growth is an important factor in the material synthesis.And many methods including gas,solid and solution methods have been used to obtain various single crystals[1].Especially,flux method is an important method for crystal growth,where the components of the desired substance dissolved in a solvent(flux) grow in the process of deposit.Its advantage is that the crystal growth displays natural facets and the disadvantage is that the crystals are relatively small.Up to date,some solid materials have been successfully synthesized by high pressure flux method[2-7].     

MZn2HPO4PO4 (M=Na+, K+)的合成、表征和标准摩尔生成焓

采用低温固相法和水热法制备MZn2HPO4PO4 (M=Na+, K+) 并用XRD, FT-IR, TG and SEM对其进行表征,用等温量热计测定热化学性质。按照Hess’s定律,设计一新的热化学循环。结果表明,所合成的物质是等结构三斜晶系的目标产物,具有片层结构,分解温度分别为： 415 ℃和430 ℃。从测定的溶解焓和其他的标准热化学数据,计算出MZn2HPO4PO4 (M=Na+, K+) 的标准摩尔生成焓分别为：ΔfHm [NaZn2HPO4PO4, s]=-3042.38±0.31 kJ·mol-1; ΔfHm [KZn2HPO4PO4,s]=-3093.46 ±0.27 kJ·mol-1。     

Adsorption of Gases, Vapors and Liquids by Microporous Adsorbents

Adsorption of Xe, Kr, Ar, N₂, O₂, H₂ CH₄, CO₂, He, and freons by PAU-10 and ACC microporous carbon adsorbents as well as by A and X zeolites was investigated over a wide range of pressures (0.1 Pa – 20 MPa) and temperatures (77, 120–600 K). The amount of gases, vapors and liquids adsorbed by microporous adsorbents increases steadily with increasing pressure and does not change dramatically if phase transitions occur in the adsorptive. Isosteres of adsorption constructed as a curve of ln P against f(1/T)_a retain a linear form over a wide range of pressures and temperatures. The slope of isosteres does not vary on going through the critical temperature of the gaseous phase. At high pressures, due to non-ideality of the gaseous phase and non-inert behavior of the adsorbent the differential molar heat of adsorption is dependent on temperature. At high fillings of micropores the differential molar isosteric heat capacities of adsorption systems show maxima that indicate the occurrence of structural rearrangements in the adsorbate.