Sun Lixian

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.

Investigation of thermodynamic properties of Co2O3 powder

The isobaric molar heat capacities of powder of Co2O3 were determined by an adiabatic calorimeter in the temperature range from 78 to 350 K. No phase transition takes place in this temperature range. The relationship of C-p,C-m with thermodynamic temperature T was established as C-p,C-m = -5 x 10(-6)T(3) + 0.0026T(2) + 0.0325T + 4.2592 (J K-1 mol(-1)), fitting coefficient R-2 = 0.9996. According to this relationship and the relationships between thermodynamic functions, the thermodynamic functions of powder of C2O3 were derived with 298.15 K as reference temperature. Thermal decomposition of Co2O3 powder was studied through thermogravimetry (TG). The possible mechanism of the thermal decomposition reaction was suggested according to the TG result

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 Capacity and Thermal Analysis of Caffeine, Theophylline and Aminophylline

Caffeine, theophylline, and aminophylline are important methyl-substituted xanthines and are widely used in clinics. in this work, the thermodynamic characteristics of the three drugs were studied by adiabatic calorimetry, thermogravimetric analysis (tg) and differential scanning calorimetry (dsc). the low temperature molar heat capacities of caffeine (in the. crystal form), theophylline and aminophylline were measured by heating the system from 80 to 370 k using an adiabatic calorimeter. the results indicate that the molar heat capacity of aminophylline is the largest while that of theophylline is the smallest. the experimental molar heat capacities of the three drugs were fitted to a polynomial of c-p,c- m vs the reduced temperature (t) by means of the least fitting square method from 80 to 370 k. their molar heat capacities at 298.15 k were calculated to be 226.49 j . k-1 . mol(-1) (for caffeine), 218.13 j . k-1 . mol(-1) (for theophylline), and 554.78 j . k-1 . mol(-1) (for aminophylline) using the polynomial c-p,c- m-t. thermodynamic parameters (such as enthalpies and entropies relative to 298.15 k) were calculated for these drugs based on the polynomial c-p,c- m-t. the results of thermal analysis show that the order of thermal stability for these drugs is aminophylline

Thermodynamic investigation of the azeotrope of water and ethanol

The molar heat capacities of the azeotrope in the binary system of water and ethanol were measured by an adiabatic calorimeter in the temperature range from 78 K to 320 K. The functions of the heat capacity with respect to the thermodynamic temperature were established. The glass transition occurred at 98. 496 K. The phase transitions took place in the temperature ranges from 123.08 K to 156.96 K and 269.03 K to 273.20 K corresponding to the solid-solid phase transition of ethanol, solid-liquid phase transition of ethanol, and solid-liquid phase transition of water, respectively. The thermodynamic functions and the excess thermodynamic functions of the azeotrope relative to 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity with respect to the temperature.

The Standard Molar Enthalpy of Formation of Room Temperature Ionic Liquid EMIES

using rbc-ii type oxygen-bomb combustion calorimeter, the molar combustion enthalpies of room temperature ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate (emies), and 1-methylimidazole were determined at t = (298.15 +/- 0.01) k. for emies delta(c)h(m)(circle minus) =(-2671 +/- 2) kj (.) mol(-1) and for 1-methylimidazole (-286.3 +/- 0.5) kj (.) mol(-1), respectively. the standard formation enthalpies delta(f)h(m)(circle minus) were calculated to be (-3060 +/- 3) kj (.) mol(-1) for emies and (-2145 +/- 4) kj (.) mol(-1) for 1-methylimidazole. the reaction:

Thermodynamic Investigation of the High Efficient Working Fluid Used for a Heat Pipe

The heat capacities of the high efficient working fluid used for a heat pipe( C-p) were measured by a low temperature adiabatic calorimeter over the range from 78 to 320 K. No thermal anomaly was observed in the range from 78 to 245 K and 274 to 320 K. The functions of C-p vs T were established based on the measured heat capacity data by least-square fitting method to be C-p/(J . K-1 . g(-1)) = 0. 5369 T + 0. 07279 in the range of 78. 41 similar to 245. 19 K. The freezing point, freezing enthalpy and freezing entropy of it were determined to be 271. 21 K, 353. 6 J . g(-1) and 1. 304 J . K-1 . g(-1), respectively. The heat capacities of it are near a constant to be C-p/ (J . K-1 . g(-1)) = 3. 403 +/- 0. 020 in the range 274 K less than or equal to T less than or equal to 320 K. According to the relationship of thermodynamic functions, the thermodynamic function values of the working fluid were calculated in the temperature range of 280 similar to 320 K with 5 K intervals.

Low Temperature Heat Capacities and Thermodynamic Functions of Potassium Dichromate

The molar heat capacities ( C-p,C-m) of crystalline potassium dichromate (K2Cr2O7) were measured with a precision automated adiabatic calorimeter over the temperature range from 100 K to 390 K. No phase transition or other thermal anomaly was observed in this temperature region. However, it was found that the relationship of C-p,C-m with respect to temperature T is different in different temperature regions. The polynomial functions of C-p,C-m vs. T were established in different temperature regions based on the heat capacity measurements by means of the least-fitting square method. These functions are as following: for 100 K less than or equal to T less than or equal to 275 K, C-p,C-m = 0. 005 T-2 - 1.0320 T + 125. 22 (J . K-1 . mol (-1)); for 275 K less than or equal to T less than or equal to 350 K, C-p.m = 209. 37 J . K-1 . mol - 1; for 350 K less than or equal to T less than or equal to 390 K, C-p,C-m = 0. 0266T(2) - 18. 823T + 3542. 3 J . K-1 . mol (-1). According to the relationship of C-p,C-m vs. T and thermodynamic equations, the values of thermodynamic function of potassium dichromate were calculated in the temperature range of 298. 15 similar to 400. 15 K with 5 K intervals.