Tan Zhi-Cheng

Microencapsulation of n-hexadecane as a phase change material in polyurea

For thermal energy storage application, polyurea microcapsules about 2.5 mum in diameter containing phase change material were prepared using interfacial polycondensation method. in the system droplets in microns are first formed by emulsifying an organic phase consisting of a core material ( n-hexadecane) and an oil-soluble reactive monomer, toluene-2, 4-diisocyanate (tdi), in an aqueous phase. by adding water-soluble reactive monomer, diamine, monomers tdi and diamine react with each other at the interface of micelles to become a shell. ethylenediamine (eda), 1, 6-hexane diamine (hda) and their mixture were employed as water-soluble reactive monomers. the effects of diamine type on chemical structure and thermal properties of the microcapsules were investigated by ft-ir and thermal analysis respectively. the infrared spectra indicate that polyurea microcapsules have been successfully synthesized; all the tg thermographs show microcapsules containing n-hexadecane can sustain high temperature about 300 degreesc without broken and the dsc measurements display that all samples possess a moderate heat of phase transition; thermal cyclic tests show that the encapsulated paraffin kept its energy storage capacity even after 50 cycles of operation. the results obtained from experiments show that the encapsulated n-hexadecane possesses a good potential as a thermal energy storage material.

An adiabatic calorimeter for heat capacity measurements in the temperature range 300–600 K and pressure range 0.1–15 MPa

Abstract An adiabatic high pressure calorimeter for heat capacity measurement was constructed. The shape of the calorimeter cell was nearly spherical to minimize the cell mass relative to the volume of the sample chamber. The cell was made of stainless steel which is resistant to corrosion by the reactive specimens and has sufficient mechanical strength to withstand the applied pressure. The pressure in the cell was controlled by joining the cell through a transmitting tube to a stabilized highly pressure system in which nitrogen gas was used as the pressure-transmitting medium. The adiabatic conditions were achieved by controlling the temperature of the adiabatic shields surrounding the cell and the tube, and evacuating the space of the thermostat housing the cell. The apparatus is capable of heat capacity measurement under constant pressure from 0.1 to 15 MPa and over the temperature range from 300 to 600 K. The results of heat capacity measurements of liquid water and crystalline α-Al 2 O 3 demonstrated that the colorimeter has an accuracy of 0.5% for both liquid and solid samples.

An automated adiabatic calorimeter for heat-capacity measurements between 20 and 90 K

Abstract An adiabatic calorimeter and cryostat assembly with an automatic shield temperature control system has been constructed and tested by measurements on α-Al 2 O 3 . The heat capacity of α-Al 2 O 3 has been measured and the results are compared with those of other investigators.

Low-temperature heat capacities and standard molar enthalpy of formation of 4-(2-aminoethyl)-phenol (C8H11NO)

This paper reports that low-temperature heat capacities of 4-(2-aminoethyl)-phenol (C8H11NO) are measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 400 K. A polynomial equation of heat capacities as a function of the temperature was fitted by the least square method. Based on the fitted polynomial, 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 interval of 5 K. The energy equivalent, epsilon(calor), of the oxygen-bomb combustion calorimeter has been determined from 0.68 g of NIST 39i benzoic acid to be epsilon(calor)=(14674.69 +/- 17.49)J.K-1. The constant-volume energy of combustion of the compound at T=298.15 K was measured by a precision oxygen-bomb combustion calorimeter to be Delta U-c=-(32374.25 +/- 12.93)J.g(-1). The standard molar enthalpy of combustion for the compound was calculated to be Delta H-c(m)circle minus = -(4445.47 +/- 1.77) kJ . mol(-1) according to the definition of enthalpy of combustion and other thermodynamic principles. Finally, the standard molar enthalpy of formation of the compound was derived to be Delta H-f(m)circle minus(C8H11 NO,s) = -(274.68 +/- 2.06) kJ . mol(-1), in accordance with Hess law.

Synthesis, Characterization and Thermochemistry of the Hydrated Barium Nicotinate

A new compound. barium nicotinate trihydrate, wits synthesized by the method of room temperature solid phase synthesis and ball grinder. FTIR, chemical and elemental analyses, and X-ray powder diffraction techniques were applied to characterize the structure and composition of the complex. Low-temperature heat capacities of the solid coordination compound were measured by it precision automated adiabatic calorimeter over the temperature range from 78 to 400 K. A phase transition process occurred in the temperature range of 312-332 K in the heat capacity curve, and the peak temperature, molar enthalpy and entropy of the solid-to-solid phase transition of the complex were determined to be its follows: T-trs=(327.097+/-1.082) K, Delta H-trs(m)=(16.793+/-0.084) kJ center dot mol(-1) and Delta S-trs(m) =(51.340+/- 0.164) J center dot K-1 center dot mol(-1). The experimental values of the molar heat capacities in the temperature regions of 7 8-311 K and 333-400 K were respectively fitted to two polynomial equations. The polynomial fitted values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature of 298.15 K were calculated and tabulated at an interval of 5 K. In accordance with Hess law, it thermochemical cycle was designed, the reaction enthalpy of the solid phase reaction was determined its Delta H-t(m)0 =-(84.12+/-0.38) kJ center dot mol(-1), and the standard molar enthalpy of formation of the complex was calculated as Delta H-f(m)0 [Ba(Nic)(2) center dot 3H(2)O(s)]=-(2115.13+/-1.90) kJ center dot mol(-1) by using an isoperibol solution-reaction calorimeter.

Low temperature heat capacity of (S)-ibuprofen

Molar heat capacities of ( s)-ibuprofen were precisely measured with a small sample precision automated adiabatic calorimeter over the temperature range from 80 to 370 k. experimental heat capacities were fitted into a polynomial equation of heat capacities ( c-p,c- m) with reduced temperature ( x), [ x = f(t)]. the polynomial equations for ( s)-ibuprofen were c-p,c- m(s) = - 39.483 x-4 - 66. 649 x-3 + 95. 196 x-2 + 210. 84 x + 172. 98 in solid state and c-p,c- m(l) = 7. 191x(3) + 4. 2774 x-2 + 56. 365 x + 498. 5 in liquid state. the thermodynamic functions relative to the reference temperature of 298. 15 k, h-t - h-298.15 and s-t - s-298.15, were derived for the( s)-ibuprofen. a fusion transition at t-m = (324. 15 +/- 0. 02) k was found from the c-p - t curve. the molar enthalpy and entropy of the fusion transition were determined to be (18. 05 +/- 0. 31) kj.mol(-1) and (55. 71 +/- 0. 95) j.mol(-1).k-1, respectively. the purity of the ( s)-ibuprofen was determined to be 99. 44% on the basis of the heat capacity measurement. finally, the heat capacities of ( s)-ibuprofen and racemic ibuprofen were compared.

Studies on Thermal Decomposition Mechanism and Kinetics of Aspirin

The mechanism of thermal decomposition of aspirin was studied by both thermogravimetry and Mayer bond orders calculated by Cerius2 software. The parameters of thermal decomposition kinetics for aspirin, such as activation energy (E), reaction order (n) and frequency factor (A) were obtained by thermogravimetry. The kinetic equation of thermal decomposition of aspirin is expressed as:

Thermodynamic Properties of [Ho 2 (Ala) 4 (H 2 O) 8 ]Cl 6 (Ala=alanine)

The crystalline complex of holmium chloride with alanine, [Ho2(Ala)4(H2O)8]Cl6, was synthesized. Heat capacities of [Ho2(Ala)4(H2O)8]Cl6, were measured by adiabatic calorimetry over the temperature range from 78 to 363 K. A solid-solid phase transition was found between 214 K and 255 K with the peak temperature of 235.09 K. The enthalpy and entropy of the transition were determined to be 3.017 kJ•mol^(-1) and 12. 83 J•K^(-1)•mol^(-1), respectively. The molar heat capacities were presented by a fitted polynomial as a function of reduced temperature. The thermodynamic functions relative to the reference temperature 298.15 K were calculated based on the heat capacity data. Thermal stability of the complex was studied by thermogravimetry (TG) and differential scanning calorimetry (DSC) over the temperature range from 40 to 800℃. From the DTG curves, two peaks were observed in the process of the thermal decompositions for the complex. The first mass-loss peak started from 80 t and ended at 179℃, and the second mass-loss peak started from 242℃ and ended at 479℃. A possible mechanism of the thermal decomposition was presented.

Low-temperature heat capacities and standard molar enthalpy of formation of pyridine-2,6-dicarboxylic acid

This paper reports that the low-temperature heat capacities of pyridine-2,6-dicarboxylic acid were measured by a precision automatic calorimeter over a temperature range from 78 K to 380 K. A polynomial equation of heat capacities as a function of temperature was fitted by the least-squares method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated and tabulated at intervals of 5 K. The constant-volume energy of combustion of the compound was determined by means of a precision rotating-bomb combustion calorimeter. The standard molar enthalpy of combustion of the compound was derived from the constant-volume energy of combustion. The standard molar enthalpy of formation of the compound was calculated from a combination of the datum of the standard molar enthalpy of combustion of the compound with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.

Estimation and Prediction of the Physicochemical Properties of Imidazolium-Based Ionic Liquids

The physicochemical properties of ionic liquids (ILs) at 298.15 K could be estimated and predicted in terms of empirical and semi-empirical equations as well as by interstice model theory. In this paper, the molecular volume, density, standard molar entropy, lattice energy, surface tension, parachor, molar enthalpy of vaporization, interstice volume, interstice fraction, and thermal expansion coefficient are discussed. These properties were first estimated by experimentally determining the density and surface tension for 1-ethyl-3-methylimidazolium ethylsulfate ([C2mim][EtSO4]), 1-butyl-3-methylimidazolium octylsulfate ([C4mim][OcSO4]), and 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ([C2mim][NTf2]). The molecular volume and parachor of the three homologues of the imidazolium-based ILs [C(subscript n)mim][EtSO4], [C(subscript n)mim][OcSO4], and [C(subscript n)mim][NTf2] (n=1-6) were predicted and their densities and surface tensions were obtained. Other properties were also calculated using the obtained density and surface tension values. The predicted density was compared to the experimental values for [C4mim] [NTf2] and [C2mim] [OcSO4], which shows that the deviation between experimental and predicted data are within experimental error. Finally, we compared the values for the molar enthalpy of vaporization estimated by Kabos empirical equation with those predicted by Verevkins simple rule for [C2mim] [EtSO4], [C4mim][OcSO4], [C2mim] [NTf2], [C4mim][NTf2], N-butyltrimethylammonium bis (trifluoromethylsulfonyl)imide [N4111][NTf2], N-methyltrioctylammonium bis (trifluoromethylsulfonyl)imide ([N8881][NTf2]), and N-octyl-3-methylpyridinium tetrafluoroborate ([m3opy][BF4]) and found that the values obtained by these two equations were in good agreement with each other. Therefore, we suggest that the molar enthalpy of vaporization of ILs can be predicted by Verevkins simple rule when experimental data for density and surface tension are not available.