The kinetics of thermal decomposition of a series of uranyl nitrate complexes with N-alkylcaprolactams (alkyl=C2H5, C4H9, C6H13, C8H17, C10H21 or C12H25) was studied by means of non-isothermal gravimetry under a nitrogen atmosphere. From the TG-DTG curves, the kinetic parameters
relating to the loss of two molecules of coordinated ligand were obtained by employing two groups of methods: (I) a group
of conventional methods involving the Coast-Redfern, Freeman-Carroll, Horowitz-Metzger, Dharwadkar-Karkhanavala and Doyle
(modified by Zsakó) equations; (II) a new method were suggested by J. Máleket al.. The results obtained using two types of methods were compared, and it emerged that the results of method II were much more
meaningful and reasonable in this work. Additionally, the effects of the molecular structure of the ligands on the kinetic
data and models were studied and are discussed.
Authors:J. Zeng, Z. Cao, D. Yang, L. Sun, and L. Zhang
One of the greatest challenges in the application of organic phase change materials (PCMs) is to increase their thermal conductivity
while maintaining high phase change enthalpy. 1-Tetradecanol/Ag nanowires composite PCM containing 62.73 wt% (about 11.8 vol%)
of Ag nanowires showed remarkably high thermal conductivity (1.46 W m−1 K−1) and reasonably high phase change enthalpy (76.5 J g−1). This behavior was attributed to the high aspect ratio of Ag nanowires, few thermal conduct interfaces, and high interface
thermal conductivity of Ag nanowires in the composite PCM. These results indicated that Ag nanowires might be strong candidates
for thermal conductivity enhancement of organic PCMs.
Barium benzoate was synthesized in a hydrothermal reaction. The complex was characterized by elemental analysis, IR spectroscopy and X-ray powder diffraction. It was monoclinic and had a layered structure. The mechanism of thermal decomposition of the barium benzoate was studied by using TG, DTA, IR and gas chromatography-mass spectrometry. In a nitrogen atmosphere, the barium benzoate decomposed to form BaCO3 and organic compounds: mainly benzophenone, triphenylmethane, etc.
The paper describes a new transient hot wire instrument which employs 25.4 μm diameter tantalum wire with an insulating tantalum
pentoxide coating. This hot-wire cell with a thin insulating layer is suitable for measurement of the thermal conductivity
and the thermal diffusivity of electrically conducting and polar liquids. This instrument has been used for experimental measurement
of the thermal conductivity and the thermal diffusivity of poly(acrylic acid) solution (50 mass%) in the temperature range
of 299 to 368 K at atmospheric pressure. The thermal conductivity data is estimated to be accurate within ±4%. Thermal diffusivity
measurements have a much higher uncertainty (±30%) and need further refinement.
Polyaniline/α-Al2O3 (PANI/α-Al2O3) composites were synthesized by in situ polymerization through ammonium persulfate ((NH4)2S2O8, APS) oxidized aniline using HCl as dopant. XRD and FTIR were used to characterize the PANI/α-Al2O3 composites. The thermal stabilities and glass transition temperature (Tg) of PANI/α-Al2O3 composites were tested using thermogravimetric (TG) method and modulated differential scanning calorimetry (MDSC) technique.
The results of TG showed that the thermal stability of PANI/α-Al2O3 composite increased and then decreased with the increase in α-Al2O3 content. The derivative thermogravimetry (DTG) curves showed one step degradation of PANI when the α-Al2O3 content was lower than 52.5 mass%, and exhibited two steps degradation when the α-Al2O3 content was higher than 63.6 mass%. The MDSC curves showed that the Tg of PANI/α-Al2O3 composites increased and then decreased with the augment of α-Al2O3 for the interaction between PANI chains and the surface of α-Al2O3.
Authors:F. Tian, L. Sun, J. Venart, R. Prasad, and S. Mojumdar
Various techniques and methodologies of thermal conductivity measurement have been based on the determination of the rate
of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy
of the rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables
contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude
of transient thermal diffusivity along these directions. The transient hot-wire technique is broadly used for absolute measurements
of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous
measurement of both thermal conductivity and thermal diffusivity together with the determination of the specific heat. However,
these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. Recently
developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. A
thermal conductivity cell for measurement of the thermal properties of electrically conducting fluids has been developed and
Authors:S. Mojumdar, M. Sain, R. Prasad, L. Sun, and J. Venart
There are many thermoanalytical techniques but only several of them such as thermogravimetric analysis (TG), high resolution
thermogravimetric analysis (Hi-Res™ TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA), calorimetry,
differential scanning calorimetry (DSC), modulated differential scanning calorimetry (MDSC), evolved gas analysis (EGA), transient
thermal analysis (TTA) and thermal conductivity (k) have selected to be discussed in this paper. Simultaneous thermal analysis (STA) is ideal for investigating issues such
as the glass transition of modified glasses, binder burnout, dehydration of ceramic materials or decomposition behaviour of
inorganic building materials, also with gas analysis. Selected applications of various thermoanalytical techniques from medicine
to construction have also been discussed in this paper.
Authors:Y. Shi, L. Sun, F. Tian, J. Venart, and R. Prasad
The transient hot-wire technique is widely used for absolute measurements of the thermal conductivity of fluids. Refinement
of this method has resulted in a capability for accurate and simultaneous measurement of both thermal conductivity and thermal
diffusivity together with a determination of the specific heat. However, these measurements, especially those for the thermal
diffusivity, may be significantly influenced by fluid radiation.
The present work investigates the effect of fluid radiation on the measurements of the thermal conductivity of propane. Recently
developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. Measurements
at 372 K with a hot-wire instrument demonstrate the presence of radiation effects in both the liquid and vapor phase. The
influence is much more pronounced in liquid propane at 15.5 MPa than in the vapor phase at 881.5 kPa. The technique employed
to obtain radiation-free thermal conductivity measurements is described.
The transient hot-wire technique is widely used for absolute measurements
of the thermal conductivity and thermal diffusivity of fluids. It is well
established that fluid radiation effects significantly influence these measurements,
especially those for the thermal diffusivity. Corrections for radiation effects
are based on the models developed and deviations of the measured data from
the ideal line source model. In this paper, the effect of fluid radiation
on the measurements of the thermal conductivity of n-pentane
is presented. For comparison, the influence of thermal radiation effect on
measurement of transparent fluids, such as argon is also shown. The difference
between the influence of natural convection and thermal radiation is also
Molar heat capacities
of acetaminophen were precisely measured with a small sample precision automated
adiabatic calorimeter over the temperature range from 80 to 330 K. A solid-solid
transition at 149.96 K was found from the Cp,m-T curve. The polynomial functions of Cp,.m(J
K-1 mol-1) vs. T were established
on the heat capacity measurements by means of the least square fitting method.
processes of acetaminophen have been studied by thermogravimetry. And the
thermal decomposition kinetics parameters, such as activation energy E, pre-exponential factor A
and reaction order n, were calculated by
TG-DTG techniques with the Freeman-Carroll method, Kissinger method
and Ozawa method. Accordingly the thermal decomposition kinetics equation
of acetaminophen is expressed as: dα/dt=2.67107e-89630/RT(1-α)0.23.
The process of fusion has been investigated through
DSC. The melting point, molar enthalpy and entropy of fusion are to be (441.890.04)
K, 26.490.44 kJ mol-1 and 59.801.01
J K-1 mol-1,