Calorimetric study of liquid gadolinium-based alloys

The enthalpies of mixing of liquid Gd-Si (1770±5 K) and Al-Gd (1760±5 K) alloys have been measured by high-temperature isoperibolic calorimetry. The calorimetric study of the gadolinium-based liquid alloys demonstrates the great negative enthalpies of mixing, which is associated with the contribution of GdSi and GdAl₂ intermetallides into the liquid-state thermodynamics. The comparison of obtained results with literature data has been performed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Calorimetric investigation of the Cu-Sn-Bi lead-free solder system

The thermodynamic properties play a crucial role in the development of new solder materials. In this work a calorimetric investigation of the ternary Cu-Sn-Bi system was carried out by using a Calvet-type calorimeter in order to obtain the molar limiting partial enthalpy of Cu in liquid Sn-Bi alloys with different compositions. The molar limiting partial enthalpy of Cu at 820 K was determined in the Sn-75 at% Bi, Sn-43 at% Bi and Sn-26 at% Bi liquid bath showing an endothermic behaviour. The results are compared with the literature data available for Cu in the pure liquid Bi and Sn and then discussed.     

Calorimetric investigations of the MBr−NdBr3 melts (M=Li,Na, K,Cs)

Present work is a part of thermodynamic research program on the MX?LnX₃ system (M=alkali metal,X=Cl, Br andLn=lanthanide). Molar enthalpies of mixing in the LiBr?NdBr₃, NaBr?NdBr₃ and KBr?NdBr₃ liquid binary systems have been determined at temperature 1063 K by direct calorimetry in the whole range of composition. Investigated systems are generally characterized by negative enthalpies of mixing with minimum atX _NdBr3≈0.3–0.4. These enthalpies decrease with decrease of ionic radii of alkali metals. Molar enthalpies of solid-solid and solid-liquid phase transitions of K₃NdBr₆ and Cs₃NdBr₆ have been also determined by differential scanning calorimetry (DSC). K₃NdBr₆ is formed at 689 K from KBr and K₂NdBr₅ with enthalpy of 44.0 kJ·mol^?1 whereas Cs₃NdBr₆ is stable at ambient temperature and undergoes phase transition in the solid state at 731 K with enthalpy of 8.8 kJ·mol^?1. Enthalpies of melting have been also determined.     

铁-镍-钒三元系固态合金的量热研究——双子、差示、高温量热计

本文介绍一种自制双子、差示、高温量热计, 此仪器用于测量固态合金的生成焓和相变焓。最高工作温度可达1200 ℃。通过测定已知焓值的纯铁的相变焓, 证明量热计可靠。用这台量热计测量了8种不同成份的Fe-Ni-V固态合金的生成焓, 其中包含σ相和γ相。为该体系的热力学研究提供了必要的热化学数据。     

Calorimetric Analysis of Vesicular Systems

A number of studies of micellar aggregation in aqueous solutions of ethylene oxide-propylene oxide block copolymers — using high sensitivity differential scanning calorimetry (HSDSC) — are reviewed. The review attempts to show how the calorimetric output can be analysed, using a model fitting procedure, to obtain estimates for various thermodynamic parameters, which characterise the micellization event, as observed by HSDSC. These important parameters include: T _1/2 the temperature at which half the surfactant has been incorporated into micelles; H _cal — the calorimetric enthalpy for the process which is measured by integration of the calorimetric output; H _vH — the van't Hoff enthalpy — which characterises the functional dependence of the equilibrium composition of the system upon temperature and which is derived from the application of the van't Hoff isochore to the data analysis procedure; C _p — the heat capacity change between the initial and final states;and n the aggregation number.Using this data it is possible to examine how extent of aggregation functionally varies with temperature. Subsequent interpolation of these thermal aggregation plots permits an examination of how the extent of aggregation is affected by changes in solution composition under isothermal conditions. A large body of data is presented which shows how co-solvents, co-solutes and pH affect the aggregation process in aqueous solution.This revised version was published online in November 2005 with corrections to the Cover Date.     

Solution-reaction Calorimetric Study of Coordination Compounds of Rare Earth Perchlorates with Alanine and Imidazole

Introduction Since Anghileri firstly reported that complex of LaCl3 with glycine had the antitumor function in 1975,1 coordination compounds of rare earth with amino acid have attracted increasing attention.2-4 People have found that some compounds of rare earth with amino acids possess disinfection, elimination of inflammation, de-crease of the level of blood sugar and anti-cruor func-tions. Imidazole is a wreath compound, and presents unique biological activities. Ternary coordination com-…     

Calorimetric investigation of thermodynamic properties and ions rotation of some perbromates

Low temperature heat capacity of ammonium, rubidium and cesium perbromates has been studied by method of adiabatic calorimetry. Anomaly of the heat capacity of cesium perbromate has been found, which corresponds to a structural phase transition. The separation of heat capacity into components has been carried out by the additive scheme. The torsion oscillation of BrO ₄ ^– anions in solid perbromates at low temperatures has been found. Ammonium ions retardedly rotate aroundC ₂ axes in the crystal lattice of NH₄BrO₄.

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Zusammenfassung Mittels adiabatischer Kalorimetrie wurde die Tieftemperatur-Wärmekapazität von Ammonium-, Rubidium- und Zäsiumperbromat untersucht. Man fand eine Anomalie für die Wärmekapazität von Zäsiumperbromat, in deren Hintergrund eine Phasenumwandlung steht. Anhand eines Additivschema wurde die Wärmekapazität in Komponenten gespalten. In festen Perbromaten fand bei man bei tiefen Temperaturen eine Torsionsschwingung der BrO ₄ ^– -Anionen. Die Ammoniumionen zeigen eine verlangsamte Rotation um die C₂-Achsen im Kristallgitter von NH₄BrO₄.

     

烟酸的低温热容和标准摩尔生成焓

利用精密自动绝热热量计测量了分析纯烟酸在78～400 K温区的低温热容. 用最小二乘法将实验摩尔热容对温度进行拟合, 得到了热容随温度变化的多项式方程. 用此方程进行数值积分, 得到在此温区每隔5 K的舒平热容值和相对于298.15 K时的热力学函数值. 利用精密静止氧弹燃烧热量计测定了烟酸在298.15 K时的恒体积燃烧能为 Δ_cU＝ －(24528.3±16.1) J•g^－1. 依据物质燃烧焓定义计算出烟酸的标准摩尔燃烧焓为: Δ_cH_m^o＝－(3019.05±1.98) kJ•mol^－1. 最后, 依据Hess定律计算出烟酸的标准摩尔生成焓为: Δ_fH_m^o＝－(56.76±2.13) kJ•mol^－1.     

Advanced Calorimetric Techniques in Polymer Engineering

Summary: In polymer synthesis, reaction calorimetry (RC) is an appropriate technique for on-line process monitoring, since polymerization reactions are highly exothermic. Measurements are noninvasive, rapid, and straightforward. Nowadays RC is the technique recognized as the most powerful way to study such process in near-to-the- industrial conditions. Our approach was focused on temperature oscillation calorimetry (TOC). Two different reaction calorimeters were used, i.e. a isoperibolic calorimeter and a Calvet type high sensitivity differential calorimeter, respectively. A special attention was paid to the interpretation of the measured signals in order to obtain reliable calorimetric data. The evolution of heat transfer coefficient UA was followed by performing appropriate Joule effect calibrations, before and after the reaction. A convolution differential method of the measured heat flow by the generated one was used for determining the time constants and deconvoluting the measured heat flow.     

Calorimetric Studies on the pH Dependence in Hairpin Formation within the Human Enkephalin Enhancer Region

Two complementary 23 base-pair oligomers with sequences analogous to the 3, 5-cyclic adenosine monophosphate (cAMP) inducible enhancer region of the human enkaphalin gene were shown previously⁽⁶⁾ to undergo reversible conformational transformation from duplex to two individual hairpin structures, with two GT and two AC base mismatches, respectively. The present study uses differential scanning calorimetry (DSC) to determine H values for both the dissociation of the duplex formed by the complementary stands and the melting of each hairpin structure. Melting of the hairpins was studied at several different pH values and both the H and cooperative unit (CU) parameters for the hairpin with the AC base mismatches was found to be pH dependent. Increased values for H of melting and cooperative unit size at lower pH values supports the possibility of protonation of adenosine bases and formation of stable AC base pairs in this latter hairpin.     

对氨基苯甲酸热力学性质的量热和热分析研究

在80～400 K温区,用高精度全自动绝热量热仪测定了对氨基苯甲酸摩尔热容,得到摩尔热容随温度的变化的关系式为：     

Calorimetric study of thermal decomposition of lithium hexafluorophosphate

Enthalpy of formation of lithium hexafluorophosphate was calculated based on the differential scanning calorimetry study of heat capacity and thermal decomposition. It was found that thermal decomposition of LiPF₆ proceeds at normal pressure in the temperature range 450-550 K. Enthalpy of LiPF₆ decomposition is Δ_d H(LiPF₆, c, 298.15 K)= 84.27±1.34 kJ mole^-1. Enthalpy of formation of lithium hexafluorophosphate from elements in standard state is Δ_f H ⁰(LiPF₆,c, 298.15 K) = -2296±3 kJ mol^-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calorimetric determination of activated carbons in aqueous solutions

The interactions among five samples of activated carbons, obtained from different lignocellulosic materials with different degrees of activation of approximately 20% and aqueous solutions of phenol and 4-nitro phenol are studied by means of the determination of immersion enthalpies. It is established that the obtained activated carbons are of a basic character and show values for the pH at the point of zero charge, pH_PZC, that range from 7.4 to 9.7 and, in all cases, higher total basicity contents than the values obtained for total acidity. The immersion heat of the activated carbons in CCl₄ and water is determined obtaining values which are higher for CCl₄ immersion and vary from 31.4 to 48.6 J g⁻¹. The hydrophobic factor, hf, it is calculated from the relation between of the immersion heat of the activated carbons in CCl₄ and the immersion heat in water, the obtained values were 2.98 and 6.75, which are greater than 1 due to the greater values obtained in CCl₄ when compared to the values obtained in water. Immersion enthalpies in phenol solution range from 7.6 to 13.9 J g⁻¹ and for the case of 4-nitro phenol such enthalpies range from 12.7 to 20.5 J g⁻¹; all the 5 samples studied showed a higher value for the heat of immersion in aqueous solutions of 4-nitro phenol.     

Diagnosis of Phase Shift in a Temperature-Modulated Calorimetric Method

In a temperature-modulated calorimetric method using the same apparatus as a standard differential scanning calorimeter, we have to pay attention to the thermophysical parameters of the apparatus, which cause phase shift in ac temperatures, such as heat capacity of base plate, heat capacity of a pan, thermal conductance between a heater and base plate, and thermal conductance between a pan and base plate. We performed the analysis of the thermal system of the apparatus with these parameters. Beside the theoretical consideration, we carried out heat capacity measurement in a wide range of modulation periods. We found that the experimental results were well-expressed in terms of these thermophysical parameters. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calorimetric studies of special cements

The kinetics and even the mechanism of cement reaction with water can be successfully investigated by use of microcalorimetry. In this study this method was applied to follow the hydration of the new family of portland cements containing C₁₂A₇ ^* and C₁₁A₇·CaF₂ addition as well as special cement with C₃A replacement by calcium sulphoaluminate. It has been found that C₁₁A₇·CaF₂ acted as hydration retarder. The heat evolution curves for C₁₂A₇ containing samples without CaF₂ are very similar to those for the reference portland cement samples. XRD and SEM studies confirm the results described above, relating to the retardation of alite hydration. The process is positively modified by the addition of anhydrite. In the presence of calcium sulphoaluminate (4CaO·3Al₂O₃·SO₃) the hydration at early stage occurs with the rapid formation of large amount of the ettringite phase. The calcium fluoride acts as a set retarder. The full compatibility of calorimetry with SEM and XRD results should be underlined. In cement chemistry the following notation is used:C=CaO,A=Al₂O₃,S=SiO₂,H=H₂O etc. for the main oxide constituents of portland cement clinker and hydrates.     

氯化烷基咪唑系列离子液体标准摩尔燃烧焓和生成焓

用精密氧弹热量计测定了4种离子液体: 氯化1-甲基-3-乙基咪唑(C2MIC), 氯化1-甲基-3-丁基咪唑(C4MIC), 氯化1-甲基-3-戊基咪唑(C5MIC)和氯化1-甲基-3-己基咪唑(C6MIC)的燃烧热, 计算了它们的标准摩尔燃烧焓 和标准摩尔生成焓 , 结合文献中的标准摩尔溶解焓, 估算了烷基咪唑阳离子在水溶液中的标准摩尔生成焓, 以及亚甲基对标准摩尔燃烧焓和标准摩尔生成焓的贡献.     

Enthalpy of Phase Transitions and Heat Capacity of Stoichiometric Compounds in LaBr3-MBr Systems (M=K,Rb, Cs)

Molar enthalpies of solid-solid and solid-liquid phase transitions of the LaBr₃, K₂LaBr₅, Rb₂LaBr₅, Rb₃LaBr₆ and Cs₃LaBr₆ compounds were determined by differential scanning calorimetry. K₂LaBr₅ and Rb₂LaBr₅ exist at ambient temperature and melt congruently at 875 and 864 K, respectively, with corresponding enthalpies of 81.5 and 77.2 kJ mol^-1. Rb₃LaBr₆ and Cs₃LaBr₆ are the only 3:1 compounds existing in the investigated systems. The first one forms from RbBr and Rb₂LaBr₅ at 700 K with an enthalpy of 44.0 kJ mol^-1 and melts congruently at 940 K with an enthalpy of 46.7 kJ mol^-1. The second one exists at room temperature, undergoes a solid-solid phase transition at 725 K with an enthalpy of 9.0 kJ mol^-1 and melts congruently at 1013 K with an enthalpy of 57.6 kJ mol^-1. Two other compounds existing in the CsBr-based systems (Cs₂LaBr₅ and CsLa₂Br₇) decompose peritectically at 765 and 828 K, respectively. The heat capacities of the above compounds in the solid as well as in the liquid phase were determined by differential scanning calorimetry. A special method - 'step method' developed by SETARAM was applied in these measurements. The heat capacity experimental data were fitted by a polynomial temperature dependence. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low-temperature heat capacities and standard molar enthalpy of formation of aspirin

Molar heat capacities (C _p,m) of aspirin were precisely measured with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 383 K. No phase transition was observed in this temperature region. The polynomial function of C _p,m vs. T was established in the light of the low-temperature heat capacity measurements and least square fitting method. The corresponding function is as follows: for 78 K≤T≤383 K, C _p,m/J mol^-1 K^-1=19.086X ⁴+15.951X ³-5.2548X ²+90.192X+176.65, [X=(T-230.50/152.5)]. The thermodynamic functions on the base of the reference temperature of 298.15 K, {ΔH _T -ΔH _298.15} and {S _T-S _298.15}, were derived. Combustion energy of aspirin (Δ_c U _m) was determined by static bomb combustion calorimeter. Enthalpy of combustion (Δ_c H ^o _m) and enthalpy of formation (Δ_f H ^o _m) were derived through Δ_c U _m as - (3945.26±2.63) kJ mol^-1 and - (736.41±1.30) kJ mol^-1, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Standard Enthalpy of Formation of Monoclinic Ammonium Paratungstate

Monoclinicammoniumparatlingstate,(NH.),,H,W,,O.,4H,O(s),isanessentialintermediatecompoundintheextractionoftungstenfromitsoresl.Theknowledgeofthepropertiesofammoniumparatungstateisdesirableforcontrollingitscrystallizationanditsthermaldecomposition.However,thestudyonthethermodynamicpropertieshasnotbeenreported.Inthepresentwork,theenthalpyofreactionforthethermaldecompositionofammoniumparatungstatewasmeasured,anditsstandardenthalpyofformationat298.15Kisobtained.Thesampleofmonoclinicanunoniumpa…     

溶解量热法测三氧化钼标准生成焓

用溶解量热法,以KIO_4和KOH组成的弱碱性溶液为量热溶剂,设计3个不同的热化学循环,用RD-1型热导式自动量热计测定了MoO_3的标准生成焓,并推荐其值为ΔH_(t(moO_3))~0(298.15K)=-765.0±6.8kJ·mol~(-1)。