THERMAL STABILITY OF NANOSTRUCTURED γ-Fe_2O_3 MAGNETIC POWDER

发现纳米γ－Ｆｅ２Ｏ３磁粉的ＤＴＡ曲线上出现了一个不能重现的放热峰Ｘ射线衍射分析证实此放热峰对应于从γ－Ｆｅ２Ｏ３向α－Ｆｅ２Ｏ３的结构相变，主要是结构相变和晶粒长大引起的。对比实验的结果表明，纳米γ－Ｆｅ２Ｏ３磁粉的结构相变明显高于普通的γ－Ｆｅ２Ｏ３磁粉。     

纳米晶体SnO2、ZnO的低温热容及热稳定性研究

测试纳米晶体SnO2、ZnO材料的热稳定性对于提高气体传感器的可行性是十分重要的。本文对纳米晶本SnO2、ZnO分别在80－370K和298－1773K温区进行了低温热容和热稳定性测量。利用热重分析仪（TGA）进行低温量热预处理，并且利用差式扫描－量热仪（DSC）对纳米晶体热稳定性进行了考察。     

Fe83Zr7B9Mn1非晶合金中α-Fe纳米晶化的HRTEM和结晶动力学研究

通过高分辨透射电子显微镜(HRTEM)和差示扫描量热法(DSC)研究了Fe83Zr7B9Mn1非晶合金中α-Fe纳米晶的结晶过程和非等温结晶动力学。通过HRTEM观察和X射线衍射分析,确定结晶析出相是α-Fe,在经过903K热处理之后,合金内部晶粒尺寸长大至20nm以上。对重叠放热峰进行了分峰拟合。利用Flynn-Wall-Ozawa方法确定了结晶过程的表观激活能Ea=260.3kJ/mol。进一步研究发现Fe83Zr7B9Mn1非晶合金中α-Fe纳米晶非等温结晶过程不适合用Johnson-Mehl-Avrami(JMA)模型描述,而可以利用esták-Berggren自催化模型进行描述。通过计算,α-Fe纳米晶结晶过程的指前因子以及转化函数分别为:lnA=30.6以及f(α)=α0.37(1-α)1.08。     

电镀纳米镍的结构及热稳定性

用透射电镜，Ｘ射线衍射分析，量热分析等技术研究了电镀纳米镍的微观结构及晶粒的热稳定性，结果表明：实验获得的纳米镀镍层中存在（２００）织构；镀层中的自由体积约为０．８％，随镀层厚度的增加，（２００）面的尺寸变化很大；晶粒开始长大的温度为３４５℃，晶界放热焓为３．２Ｊ·ｇ＾－１。     

Cu和Nb对非晶态Fe—Si—B合金等温晶化过程的影响

采用示差扫描量热卡计（ＤＳＣＩ）得到了非晶态Ｆｅ－Ｓｉ－Ｂ合金加入Ｃｕ和Ｎｂ后的等温晶化放热曲线，结合Ｘ射线衍射（ＸＲＤ）分析，明确了Ｃｕ和Ｎｂ在形成纳米α－Ｆｅ（Ｓｉ）晶体相时的作用。此外，非晶态Ｆｅ７６．５Ｓｉ１３．５Ｂ９Ｃｕ１Ｎｂ３等温化的α－Ｆｅ（Ｓｉ）放热峰呈明显的非对称形状。     

板钛矿基TiO2纳米晶的结构相变和热稳定性

研究含一定量锐钛矿和金红石的板钛矿基ＴｉＯ２纳米晶的热稳定性。发现其ＤＴＡ曲线上出现两个吸热峰。ＸＲＤ相似,晶粒度和相含量分析表明,出现于３０－１６０℃温区的Ａ峰对应于脱附过程;出现了７８０－８４５℃温区的Ｂ峰对应于样品结构从板钛矿经锐钛矿向着金红石的急剧一级相变;在Ｂ峰出现前,样品中存在板钛矿向锐钛矿的缓慢转变过程;相就促进了纳米晶粒的生长。     

锐钛矿型TiO2纳米粉的低温热容研究

采用溶胶－凝胶法制备了１６、２６nm锐钛矿型ＴiO2纳米晶超微粉末,测定了其纳米尺寸和记,在７８－３７０Ｋ温区测定了热容、拟合出热容随温度变经的多项式方程,并与锐态矿型粗晶ＴiO2热容文献值进行分析,从能量不同的角度分析了各曲线不同的原因。     

纳米CuFe_2O_4催化硫酸铜热分解及机理研究

通过硫酸铜的热分解行为研究了纳米铁酸铜的催化机理。采用共沉淀法制备不同物质的量比的纳米CuFe2O4催化剂,并测定了不同成分和用量的催化剂对硫酸铜热分解温度及热分解表观活化能的影响。通过X射线衍射和扫描电镜对铁酸铜晶体进行表征,用差热分析(TG-DSC)法测定硫酸铜的分解热变化量以衡量催化剂活性。结果表明:Cu2+、Fe3+物质的量比为1∶1,质量分数为20%的CuFe2O4对CuSO4的催化效果最佳,该条件下CuSO4的高温分解峰与低温分解峰重合,分解峰温度向低温方向移动了29.5℃,表观分解热吸热量降低了112.1 J/g。     

锐钛矿型TiO_2纳米粉的低温热容研究

采用溶胶－凝胶法制备了１６、２６ｎｍ锐钛矿型ＴｉＯ２纳米晶超微粉末,测定了其纳米尺寸和晶态．在７８～３７０Ｋ温区测定了热容,拟合出热容随温度变化的多项式方程,并与锐态矿型粗晶ＴｉＯ２热容文献值进行比较,从能量不同的角度分析了各曲线不同的原因．     

纳米氢氧化铜的均匀沉淀法制备及低温热容

使用氨水溶解硫酸铜，加入氢氧化钡沉淀分离硫酸根，所得铜氨清液加热蒸氨得氢氧化铜超细沉淀，沉淀分虽用氨水和无水乙醇洗涤，60℃干燥，放置干燥器中至恒重，XRD，TEM，ICP测定表明，其平均粒径尺寸为45nm，粒度分布范围窄，纯度高，用高粗密全自动量热仪的78－370K温区测定的热容，拟全出热容随温度变化的多项式方程，并对此氨浸新工艺－均匀沉淀法有关的热力学性质进行了讨论。     

Heat Capacity and Thermodynamic Properties of Poly(chlorotrifluoroethylene) from 2.5 to 620 K

Heat capacities and thermodynamic properties of a number of poly(chlorotrifluoToethylene) samples subjected to various thermal treatments, to achieve crystallinities ranging from approximately 10 to 90%, have been studied from 2.5 to 370 K by automated adiabatic calorimetiy and from 250 to 620 K by differential scanning calorimetry. Small heat capacity discontinuities in the temperature range from 320 to 350 K were observed in all samples with crystallinities greater than 40%. Spontaneous adiabatic temperature drifts associated with these anomalies were prasitive (exothermic) for quenched samples and negative (endothermic) for annealed samples. Therefore these anomalies were believed to be associated with a relaxation phenomenon similar to that of a glass transition. For highly quenched low crystallinity films, a much larger heat capacity discontinuity of greater than 15% was observed, amidst a crystallization exotherm. In addition to the above phenomena, annealing of the sample at any temperature between 240 to 400 K would produce a shift in the population distribution of crystallites from reorganization or melting and recrystallization. As a result, the apparent heat capacity became somewhat lowered at the annealing temperature and somewhat raised at about 20 K above the annealing temperature.     

Contributions to the heat capacity of alpha (HCP) titanium from 200–1000 K

The heat capacity at constant pressure C _p of alpha (HCP) titanium from 200 to 1000 K has been analyzed for contributions from lattice vibrations and electron excitations. Experimental data in the literature have been used to obtain the heat capacity at constant volume C _V by the dilation correction. From C _V has been subtracted an harmonic lattice contribution C _VH given by the Debye heat capacity using a single Debye temperature and an electronic contribution C _VE . The difference C _V –(C _VH +C _VE ) is positive, and from about 600 to 1000 K it is real in the sense that it is larger than the experimental uncertainty in C _V . This difference is attributed to an anharmonic lattice vibration contribution C _VA . Two models for C _VE have been used. One, which includes electron-phonon enhancement, leads to a C _VA of about 15% of C _V at 1000 K. The other takes into account the shift in the density of states with temperature and leads to a C _VA of about 5% of C _V      

Heat capacity measurement and EXAFS study of (U0.85Mg0.15)O2−x forx=0 and 0.11

Heat capacities and electrical conductivities of (U_0.85Mg_0.15)O_2−x (x=0 and 0.1) were measured simultaneously by means of a direct heating pulse calorimeter (DHPC) in the temperature range from 300 to 1500 K. Anomalous increases in the heat capacity curves of (U_0.85Mg_0.15)O₂−x) (x=0 and 0.1) were observed above about 800 and 1150 K, respectively. The values for the enthalpy of oxygen Frenkel defect formation were calculated from the excess heat capacity and were found to be similar to those for UO₂ doped with rare earth elements. On the other hand, no anomaly was seen in the electrical conductivity curve around the onset temperature of the anomalous increase in the heat capacity. It was, therefore, concluded that the excess heat capacity originates from the predominant contribution of the formation of Frenkel pair-like defects of oxygen. An extended X-ray absorption fine structure (EXAFS) experiment shows a different environment of oxygen around uranium and magnesium, and this should be a cause of the onset temperature difference. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5, 8, 1995, Tokyo, Japan.     

Heat capacity of fcc calcium

The lattice entropy derived from the measured heat capacity at intermediate and high temperatures is analyzed to yield a weakly temperature dependent entropy Debye temperature. An unusual temperature dependence of this quantity may be a sign of error in the heat capacity data. When this analysis is applied to heat capacity data recommended by Hultgren et al. (1973) for 20 nontransition metals, the result for fcc Ca stands out as anomalous. We have reconsidered heat capacity data of fcc Ca and find that measurements by Eastman et al. (1924), which were given little weight by Hultgren et al., are consistent with a normal behavior of the entropy Debye temperature up to 450 K.     

Thermodynamic Properties of Gases from Speed-of-Sound Measurements

A procedure for deriving thermodynamic properties of gases from speed of sound is presented. It is based on numerical integration of ordinary differential equations (ODEs) (rather than partial differential equations—PDEs) connecting speed of sound with other thermodynamic properties in the T-p domain. The procedure enables more powerful methods of higher-order approximation to ODEs to be used (e.g., Runge-Kutta) and requires only Dirichlet initial conditions. It was tested on gaseous argon in the temperature range from 250 to 450 K and in the pressure range from 0.2 to 12 MPa, and also on gaseous methane in the temperature range from 275 to 375 K and in the pressure range from 0.4 to 10 MPa. The density and isobaric heat capacity of argon were derived with absolute average deviations of 0.007% and 0.03%, respectively. The density and isobaric heat capacity of methane were derived with absolute average deviations of 0.006% and 0.09%, respectively.     

Experimental Determination of Isobaric Heat Capacities of R227 (CF<Subscript>3</Subscript>CHFCF<Subscript>3</Subscript>) from 223 to 283 K at Pressures up to 20 MPa.

A new experimental method for measuring isobaric heat capacity c_p down to 223 K at pressures up to 30 MPa was developed with the aim to study alternative refrigerants at sub-ambient temperatures and elevated pressures. The experiments are carried out in a batch mode, using a differential fluxmetric calorimeter Setaram BT-215, equipped with a customized high-pressure unit. The measurements are performed at constant pressure with a continuous scan of temperature. First, the method was tested at atmospheric pressure with methanol in the temperature range 223–283 K. The relative deviation from recommended isobaric heat capacity data in the literature is about 0.5%. Second, the measurements were performed at pressure up to 18.2 MPa with an alternative refrigerant R134a (1,1,1,2-tetrafluoroethane) of well-known heat capacity. Our results agree with representative literature values within 0.4%. New original results were obtained for refrigerant R227 (1,1,1,2,3,3,3-heptafluoropropane) in the temperature range from 223 to 283 K and at pressures of 1.1, 5, 10, 15, and 20 MPa. The consistency of our isobaric heat capacities with calorimetric values above 273 K and with pVT data reported in the literature is discussed.     

液体比热容实验系统的研制

基于流动型绝热量热法搭建了一套高温高压液体比热容实验系统,系统主要包括:流动型量热器、电加热控温系统以及内外绝热屏。该实验系统的温度范围为293~453 K,压力范围为0.1~20 MPa。为了检验实验系统的漏热损失,采用纯水在不同温度下进行标定;为了进一步检验实验系统的准确性,测量了甲苯和环己烷2种参考物质在不同温度和不同压力下的比定压热容,新实验系统的不确定性评定结果,比定压热容的扩展不确定度为1.41%（k=2）。     

The thermodynamics of the divalent metal fluorides. II. Heat capacity of the fast ion conductor BaSnF4 from 7 to 345 K

The heat capacity of the fast ion conductor BaSnF₄ was measured over the temperature range 7<T<345 K using adiabatic calorimetry. Our results show that a phase transition is not present. However, an anomalous rise in the molar heat capacity,C _p,m, occurs in the region 210<T<310 K; the entropy change of this rise amounts toS/R=0.112. This anomaly coincides with the temperature range where a break in the slope of the electrical conductivity has been observed, which results in a threefold decrease in the activation energy required in the temperature region above the break at 272 K. Standard molar thermodynamic functions are presented at selected temperatures from 5 to 345 K.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Aluminum. I. Measurement of the relative enthalpy from 273 to 929 K and derivation of thermodynamic functions for Al(s) from 0 K to Its melting point

The relative enthalpy of pure, polycrystalline aluminum (NBS Standard Reference Material 44f, for the freezing point of aluminum on IPTS-68) has been measured over the temperature range 273 to 929 K. The enthalpy measurements were made in a precision isothermal phase-change calorimeter and are believed to have an inaccuracy not exceeding 0.2%. Pt-10Rh alloy and quartz glass were used as the encapsulating materials. The enthalpy data for Al(s) and SiO₂(l) have been fitted by the method of least squares with cubic polynomial functions of temperature. Heat capacity data for Al(s), derived from these polynomials, have been smoothly merged using a spline technique to the most reliable low-temperature heat capacity data for Al(s) below 273 K. The merged data are compared with corresponding data from the literature as well as with published critical compilations of heat capacity data for Al(s). A new table of thermodynamic functions for Al(s) has been derived. A theoretical interpretation of the results apears in the following paper.     

Thermal Radiation Calorimeter for Measuring the Specific Heat Capacity of Liquid Samples

A new thermal radiation calorimeter for measuring the specific heat capacity of liquid samples continuously in the temperature range from 280 to 360 K is described. The heat input to the sample cell from the heater by thermal radiation is estimated using the effective emissivity, which is the apparatus constant. The heat capacity of a sample can be calculated from the temperatures of the sample and the heater, and the temperature change rate of the sample. The present sample cell was made of Pyrex glass; therefore most liquid samples do not react with the sample cell, and blackening of the surface of the sample cell is not necessary in the present temperature range. The specific heat capacities for ethanol, ethylene glycol, n-heptane, n-valeric acid, and water+ethanol mixtures were measured to confirm the reliability of the present calorimeter.