NATIONAL STANDARD OF HEAT CAPACITY MEASUREMENT OF SOLIDS IN THE RANGE OF 4.2—90K——AN AUTOMATED ADIABATIC CALORIMETER FROM 25 TO 90K AND MOLAR HEAT CAPACITIES OF α-ALUMINA

The construction of an automated adiabatic calorimeter for heat capacity measurement ofsolids in the temperature range of 25- 90K is described in detail. The sample vessel of thecalorimeter has thin radial vanes which make no contact with its inner wall and are distrib-uted evenly, thus greatly improving the internal thermal equilibration of the vessel. Theprecision of temperature control for the adiabatic shields and electrical leads of the calori-metric system are heightened to a great extent by using the high precision ACD- 79 modeladiabatic controller specially developed by us for this purpose. Measurements of the heatcapacities of high purity α-Al_2O_3, one of the internationally-accepted standard referencematerials, agree with those of the National Bureau of Standards (NBS), USA within ±0.3%,demonstrating the reliability of this apparatus.     

Low-Temperature Heat Capacities and Thermodynamic Properties of Hydrated Nickel L-Threonate Ni（C4H7O5）2·2H2O（S）

Low-temperature heat capacities of the compound Ni（C4H7O5）2·2H2O（S） have been measured with an auto- mated adiabatic calorimeter. A thermal decomposition or dehydration occurred in 350--369 K. The temperature, the enthalpy and entropy of the dehydration were determined to be （368.141 ±0.095） K, （18.809±0.088） kJ·mol ^-1 and （51.093±0.239） J·K^-1·mol^-1 respertively. The experimental values of the molar heat capacities in the temperature regions of 78-350 and 368-390 K were fitted to two polynomial equations of heat capacities （Cp,m） with the reduced temperatures （X）, [X=f（T）], by a least squares method, respectively. The smoothed molar heat capacities and thermodynamic functions of the compound were calculated on the basis of the fitted polynomials. The smoothed values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were tabulated with an interval of 5 K.     

Low temperature heat capacities and thermodynamic properties of rare earth triisothiocyanate hydrates——Pr(NCS)_3· 7H_2O and Nd(NCS)_3· 7H_2O

Heat capacities of Pr(NCS)3·7H2O and Nd(NCS)3· 7H2O haw been measured from 13 to 300 K by using a fully automated adiabatic calorimeter. Schottky anomaly was observed for Pr(NCS)3·7H2O below 50 K. The polynomial equations for calculating the heat capacity values of the two compounds in the range of 13-300 K were obtained by the least-squares fitting based on the experimental Cp data. The Cp values below 13 K were estimated by using the Debye-Einstein and Schottky heat capacity functions. The standard molar thermodynamic functions were computed from 0 to 300 K. The standard entropies and Gibbs energies of formation of the two compounds were also calculated.     

Effect of initial nickel particle size on stability of nickel catalysts for aqueous phase reforming

The deactivation behavior by crystallite growth of nickel nanoparticles on various supports(carbon nanofibers, zirconia, Si C, α-Al_2O_3 and γ-Al_2O_3) was investigated in the aqueous phase reforming of ethylene glycol. Supported Ni catalysts of ~10 wt% were prepared by impregnation of carbon nanofibers(CNF),Zr O_2, SiC, γ-Al_2O_3 and α-Al_2O_3. The extent of the Ni nanoparticle growth on various support materials follows the order CNF ~ ZrO_2 SiC γ-Al_2O_3 α-Al_2O_3 which sequence, however, was determined by the initial Ni particle size. Based on the observed nickel leaching and the specific growth characteristics; the particle size distribution and the effect of loading on the growth rate, Ostwald ripening is suggested to be the main mechanism contributing to nickel particle growth. Remarkably, initially smaller Ni particles(~12 nm) supported on α-Al_2O_3 were found to outgrow Ni particles with initially larger size(~20 nm). It is put forward that the higher susceptibility with respect to oxidation of the smaller Ni nanoparticles and differences in initial particle size distribution are responsible for this behavior.     

LOW-TEMPERATURE HEAT CAPACITY AND THERMODYNAMIC FUNCTIONS OF 2-CHLORO-6-(TRICHLOROMETHYL)PYRIDINE

The heat capacity of 2- chloro- 6- (trichloromethyl)pyridine has heen measured with anadiabatic calorimeter in the range from 13 to 316K. There is no indication of any phasetransition or thermal anomaly in this temperature region for the present compound. Theresults have been compared with those reported in [1] in the overlapping temperaturerange. The experimental heat capacity data have been fitted to a smoothed curve by the aidof the effective frequency distribution method, and the heat capacities below 13K have beenobtained by extrapolating the fitting curve down to 0K. The standard molar thermodynamicfunctions between 0 and 400 K have been derived by combining the present heat capacitymeasurements with the previous ones. The values of C_p~o (T), S~o(T) - S~o(0), [H~o(T) -H~o(0)]/T, and - [G~o(T) - H~o(0)]/T at T = 298.15 K are 189.35, 244.60, 112 .45 and 132.15J·K~(-1)·mol~(-1), respectively.     

LOW-TEMPERATURE HEAT CAPACITIES AND THERMODYNAMIC PROPERTIES OF LANTHANUM AND CERIUM TRIISOTHIOCYANATE HYDRATESI (Ⅰ)——La(NCS)_3, 7H_2O AND Ce(NCS)_3. 7H_2O

The heat capacities of La(NCS)_3. 7H_2O and Ce(NCS)_3. 7H_2O have been measured from 13 to 300K with a fully-automated adiabatic calorimeter. The construction and procedures of the calorimetric system are described in detail. No obvious thermal anomaly was observed for both compounds in the experimental temperature range. The polynomial equations for calculating the heat capacity values of the two compounds in the range 13—300K were obtained by the least-squares fitting based on the experimental C_p data. The C_p values below 13K were estimated by using the Debye and Einstein heat Capacity functions. The standard molar thermodynamic functions were calculated from 0 to 300K. Gibbs energies of formation were also calculated.     

Low-temperature heat capacities and thermodynamic properties of rare-earth triisothiocyanate hydrates (Ⅲ)——Sm(NCS)_3·6H_2O,Gd(NCS)_3·6H_2O,Yb(NCS)_3·6H_2O and Y(NCS)_3·6H_2O

The heat capacities of four RE isothiocyanate hydrates,Sm( NCS)3 6H2O,Gd( NCS)3 6H2O,Yb(NCS)3 6H2O and Y( NCS)3 6H2O,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 tem-peiatnre ranges.The polynomial equations for calculating the heat capacities of the four compounds in the range of 13-300K were obtained by the least-squares fitting based on the experimental Cp data.The Cp values below 13 K were estimated by using the Debye-Einstem heat capacity functions.The standard molar thermodynamic functions were calculated from 0 to 300 K.Gibbs energies of formation were also calculated.     

A small sample-size automated adiabatic calorimeter from 70 to 580 K——Molar heat capacities of α-Al_2O_3

An automatic adiabatic calorimeter for measuring heat capacities in the temperature range 70—580 K, equipped with a small sample cell of 7.4 cm~3 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 processed automatically with a personal computer using a predetermined program. To verify the     

AN ADIABATIC CALORIMETER FOR HEAT- CAPACITY MEASUREMENTS FROM 80 TO 400K——HEAT CAPACITIES OF a-ALUMINA AND n-HEPTANE

An improved automatic adiabatic calorimeter for precision measurement of heat capacities of solid and liquid phases in the temperature range 80-400 K is described. Temperature control of the shield and electrical energy measurement are automated; data processing is performed by an electronic computer. The calorimeter proper has thin L-shaped vanes which make no contact with its inner wall and a device for helium filling, which greatly improves the internal thermal equilibration and effectively reduces the surface temperature gradient. Measurements of the heat capacities of a-alumina and n-heptane, two internationally accepted heat-capacity standards, show a precision of±0.1%, agree with those of the National Bureau of Standards (NBS) within ±0.2%, and demonstrate the reliability of the apparatus.     

Selective synthesis of carbon monoxide via formates in reverse water–gas shift reaction over alumina-supported gold catalyst

Thermal decomposition of formic acid on SiO_2, CeO_2 and γ-Al_2O_3 was studied as an elementary step of reverse water–gas shit reaction(RWGS) over supported Au catalysts. γ-Al_2O_3 showed the highest CO selectivity among the tested oxides in the decomposition of formic acid. Infrared spectroscopy showed the formation of four formate species on γ-Al_2O_3: three η~1-type and one μ~2-type species, and these formates decomposed to CO at 473 K or higher. Au-loaded γ-Al_2O_3 samples were prepared by a depositionprecipitation method and used as catalysts for RWGS. The supported Au catalyst gave CO with high selectivity over 99% from CO_2 and H_2, which is attributed to the formation of formates on Au and subsequent decomposition to CO on γ-Al_2O_3.     

EFFECT OF SUPPORT PORE STRUCTURE ON Pd-CATALYST ACTIVITY AND SELECTIVITY

The results from the tests in reaction temperature and space velocity suggest the reaction ofnitrite with CO is limited by pore diffusion resistance above 354 K.The effect of alumina and carbonsupports with different pore structure on the activity and selectivity of Pal-catalysts showed that thesupport with reasonable pore structure such as α-Al_2O_3 was favorable for the activity and selectivity ofthe catalyst.     

FRACTAL ANALYSIS OF CATALYST NiO/α-Al_2O_3

We found that the Freundlich formula H=kC~(ln)can be used todescribe the isothermal adsorption curve of support α-Al_2O_3 with fractalstructures in nickel nitrate solutions.where n is relative to the surface fractaldimension D of α-Al_2O_3.     

Crystal Structure and Thermodynamic Study of Ephedrine Hydrochloride C10H16NOCI（s）

The crystal structure of ephedrine hydrochloride was determined by means of X-ray crystallography.The crystal system of the compound is monoclinic,and the space group is P21.Unit cell parameters are a=0.7308(6) nm,b=0.6124(5) nm,and c=1.2618(11) nm;α=90°,β=102°,and γ=90°;Z=2.Low-temperature heat capacities of the title compound were measured with an improved precision automated adiabatic calorimeter over a temperature range from 77 K to 396 K.A polynomial equation of the heat capacities as a function of temperature in the temperature region was fitted by the least-squares.Based on the fitted polynomial equation,the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated and tabulated at the intervals of 5 K.     

THE PROCESS OF THE EMULSIFIER-FREE POLYMERIZATION IN THE PRESENCE OF BARIUM SULFATE POWDER

The process of emulsifier-free copolymerization of the Styrene-Butyl Acrylate-K_sS_sO_s-water in thepresence of Barium Sulfate(BS)powder was investigated under varied conditions within the range of BSpowder quantity,initiator concentration and reaction temperature.Experimental results showed thatthe rate of polymerization is proportional to 0.3-power of the BS quantity and 1.3-power of theinitiator concentration.There is a linear relationship of 2/3-power for the conversion and time.Aprocess for the polymerization is propose to explain the experimental results.     

Formation Process and Thermodynamic Poperties of Calcite

The fast mixing of aqueous solutions of calcium chloride and sodium carbonate resulted in crystalline forms of vaterite and calcite under vigorous stirring. Then, the vaterite was transformed to pure calcite within about 180 rain. The crystalline forms all grew with experimental time increase. Scanning electron microscopy （SEM）, Fourier transform infrared spectroscopy （FT-IR）, and X-ray diffraction spectroscopy （XRD） techniques were employed to characterize the as-prepared samples. The heat capacity of the stable as-synthesized calcite was determined by means of an adiabatic calorimeter from 80 to 390 K. The thermodynamic functions of the calcite were derived based on the relationships among the thermodynamic functions and the function of the measured heat capacity with respect to temperature.     

AN INVESTIGATION OF THE DISPERSION OF CuCl ON γ-Al_2O_3 SURFACE AND THE ADSORPTION OF ETHYLENE ON CuCl/γ-Al_2O_3 AND OTHER SUPPORTED TRANSITION METAL SALTS

In this work we investigate the dispersion of CuCl on γ-Al_2O_3 surface and the adsorptionof ethylene on CuCl/γ-Al_2O_3. X-ray diffraction experiments and u.v. diffuse reflectancespectra have shown that CuCl is highly dispersed on γ-Al_2O_3 surface, very likely as a mono-layer. The maximun amount of dispersion of CuCl on γ-Al_2O_3 surface determined by X-ray quantitative phase analysis is 0.095 g CuCl/100 M~2 on γ-Al_2O_3. The adsorption ofethylene on dispersed CuCl can be conveniently studied by the temperature programed de-sorption (TPD) method and shown to be achieved readily at ambient temperature and nor-mal pressure. The ability of adsorption for ethylene on CuCl/γ-Al_2O_3 is greater by threeorders of magnitude than that on undispersed CuCl particles of comparable size. The max-imum molecular ratio of ethylene adsorbed to dispersed CuCl is 0.19 C_2H_4/Cu~ . The cu-prous ions of dispersed CuCl can form surface complex with molecules such as C_2H_4 or C_3H_6so long as the stereochemical conditions are satisfied. These results may provide additionalscientific basis for separating unsaturated molecules from saturated ones by CuCl/γ-Al_2O_3.     

INFLUENCE OF SILVER-DOPING ON THE SUPERCONDUCTIVITY FOR YBa_2Cu_30_(7-y)

The effect of substituting silver for barium on the structure and superconducting properties of YBa_2Cu_3O_(7-y) has been studied. The structure of the silver-doping system (YBa_(2-x)Ag_xCu_3O_(7-y)) with x<0.3 is orthorhombic. For x>0.3, YBCO, Y_2BaCuO_5 phase and metallic silver ro-exist in the system. The superconducting transition temperature T (R=0) decrease with increasing silver content. However, the critic current density J_c is found to be enhanced from 56.6 A/cm~2 to 195 A/cm~2     

FOURIER TRANSFORM FAR INFRARED SPECTRA AND NORMAL COORDINATE ANALYSIS OF FIFTEEN RARE-EARTH OXALATE HYDRATES

The Fourier transform far infrared spectra of oxalate hydrates of whole rare-earth series except Pm and Sc are investigated in the range of 100-400 cm~(-1). The assignment of vibrational frequencies is made on the basis of normal coordinate analysis using our NORVIB program. The model used for the hghter elements of the lanthanide series (La to Eu) is based on the crystal structure of Nd_2(C_2O_4)_3. 10H_2O, in which each lanthanide ion is surrounded by nine O atoms, six from three oxalate ions and three from Water molecules.The model adopted for the heavier elements of the lanthanide series (Gd to Lu) and Ytterbium is based on the crystal structure of Yb_2(C_2O_4)_3· 6H_2O, in which each ion is surrounded by eight atoms, six from three oxalate ions and two from water molecules. The variation of the metal-ligand frequencies and force constants with the atomic numbers of lanthanides is plotted and discussed.     

Experimental study on high-pressure adsorption of hydrogen on activated carbon

A systematic measurement of H2 adsorption on activated carbon over a wide scope of conditions was completed for the first time using a novel cryostat developed by the present authors. The equilibrium temperatures covered 77-298 K with the space of about 20 K, and the equilibrium pressures increased from 0 to about 7MPa. A set of adsorption/desorption isotherms was obtained by a standard volumetric method. This set of experimental data was fitted to all the well-known models of type-I isotherms, and Dubinin-Astakhov (D-A) equation was found to be the best-fit one On the basis of D-A model one can predict adsorption with relative error of ±4%. A 3-dimensional adsorption surface was also constructed, and the isosteric heat of adsorption was analytically determined. Except in the low pressure area, the calculated values agreed well with the experimental ones. Finally, the troubles encountered in applying D-A equation to supercritical adsorption is discussed.     

Optimal paths for a light-driven engine with a linear phenomenological heat transfer law

An irreversible light-driven engine is described in this paper, in which the heat transfer between the working fluid and the environment obeys a linear phenomenological heat transfer law [ q ∝Δ(T -1)], with a working fluid composed of the bimolecular reacting system 2SO 3 F■S 2 O 6 F2. Piston trajectories maximizing work output and minimizing entropy generation are determined for such an engine with rate-dependent loss mechanisms of friction and heat leakage. The optimal control theory is applied to determi...