The temperature-dependence of the extra lattice thermal resistivity of a doped sample due to the presence of electrons has been studied at low temperatures for the first time by analysing the extra lattice thermal resistivity due to electrons of five samples of phosphorus-doped Ge having different carrier concentrations in the range 1.2×1023–1.1×1024 m−3 in the temperature range 1–5 K. The variation of the extra lattice thermal resistivity of a doped sample due to electrons with the parameters η* (the reduced Fermi energy),m* (the density of states effective mass),ED (the deformation potential constant) andn (the carrier concentration) which are responsible for the electron-phonon scattering relaxation rate has also been analysed for the first time in the present study. A distinction has been made between non-peripheral and peripheral phonons in the present analysis. An analytical expression is reported for calculation of an approximate value of the extra lattice thermal resistivity of a doped sample due to the presence of electrons at low temperatures.
Authors:M. TunÇ, H. ErŞahan, S. Yapici, and S. Şolak
In the present study, the kinetic parameters of the thermal decomposition of ulexite were investigated by using TGA data. For the kinetic analysis, the Suzuki and Coats-Redfern methods were applied. It was determined that the process fits a first-order kinetic model, and the value of the activation energies and frequency factors decreased with decreasing particle size, which can be attributed to the increasing particle internal resistance to the escape of water as the grain size increases. The activation energy values were found to be 47.34–60.01 kJ mol−1 for region I and 0.225–1.796 kJ mol−1 for region II for the range of particle size fraction used. The frequency factors were calculated to be 9821.8−524.9 s−1 for region I and 3.05×10−44−2.807×10−5 for region II for the same conditions.
Authors:A. Béres, I. Pálinkó, Á. Fudala, I. Kiricsi, Y. Kiyozumi, F. Mizukami, and J. Nagy
Mg-Al L(ayered) D(ouble) H(ydroxide) was prepared and its thermal behaviour was characterized by thermoanalytical methods
(TG, DTG, DTA), 27Al M(agic) A(ngle) S(pinning) NMR spectroscopy, X-ray diffractometry (XRD) and S(canning) E(lectron) M(icroscopy). Heat treatment
destroyed the layered structure, which could only be partially reconstituted by rehydration. On calcination mixed oxide with
the predominance of basic sites were formed. Pillaring the LDH with Fe(CN)64- anions was also performed. The material was characterized by XRD and BET measurements. Heat stability of the pillared substance
was investigated, too. Pillaring proved to be successful, however, decreased heat resistance was found in the intercalated
material relative to the guest LDH.
The DSC characterisation of the morphology of the metastable a phase of stoichiometric nickel sulphide was carried out using
two calorimeters; a TA Instruments 2920 MDSC and a Perkin Elmer DSC-7, and two quenching histories. Based on these quenching
histories, significant differences were observed in the heat flow curves, including the observation of a second exothermic
peak which is tentatively assigned to be a metastable phase to metastable phase transformation. The kinetic constants for
the a to b recrystallisation were determined as a function of degree of conversion using a mechanism free isoconversional
model. Variations in the values of the kinetic constants were also ascribed to the quenching histories. Although the differences
in morphology observed were ascribed to the processing history, the shift in the position of the a to b recrystallisation
peak was partially attributed to the thermal resistances of the instruments used.
Authors:A. Książczak, A. Radomski, and T. Zielenkiewicz
Nitrocellulose porosity was investigated by thermoporometry, based on melting point depression of liquid in limited space.
Strange behaviour of water-saturated nitrocellulose was observed, which consisted of melting peak shifting of some of liquid.
Thermal resistance, connected with limited contact area of nitrocellulose walls and water, is supposed as the source of phenomenon.
Water is unable to completely penetrate into pores as nitrocellulose is a hydrophobic material, though prolonged stirring
or boiling of mixture improves saturation. Thus total pore volume cannot be estimated correctly. In spite of this pore radius
was calculated from obtained DSC curves. The results show good consistency for the same nitrocellulose materials, which proves
that thermoporometry is a useful method of nitrocellulose characterisation.
Authors:T. Zorba, E. Papadopoulou, A. Hatjiissaak, K. Paraskevopoulos, and K. Chrissafis
Urea-formaldehyde (UF) resins are the most used polycondensation resins today, in manufacturing particleboards. UF resins
possess some advantages such as fast curing, good performance in the panel, water solubility and low price. However, the main
chemical bonds of the UF resins macromolecules are hydrolysis sensitive. This causes low water and mositure resistance performance
and subsequent formaldehyde release from the UF-bonded panels. A multitude of pathways have been explored for the improvement
of UF resins’ behavior relating either to their synthesis procedure or application parameters during panel manufacture. In
this study, two UF resins (a conventional and an innovative one produced at very low pH and temperature conditions) were analyzed
for their specifications and characterized with TG-DTA technique in dynamic heating conditions and FTIR measurements both
in their pre-polymer and cured state.
This work is a study, by simultaneous thermogravimetry (TG) and differential thermal analysis (DTA), of the oxidation of a
water resistant aluminum nitride powder which has a special protective coating, and an uncoated AlN powder which has become
partially hydrated during its use. The activation energy for oxidation is estimated by the Kissinger and isoconversional methods.
In the former method, the temperatures of the oxidation peaks were obtained from DTA and DTG curves. The activation energies
for oxidation of the water resistant AlN, obtained by the Kissinger method, are 35710 kJ mol–1, 39212 kJ mol–1 using respectively DTG and DTA data. For the uncoated AlN, the values are 2437 and 2578 kJ mol–1, respectively. By the isoconversional method, the average values obtained for coated and uncoated samples are, respectively,
32310 and 2247 kJ mol–1. Therefore, the special coating, which protects the aluminum nitride from humidity action, also provides a higher resistance
Authors:A. Abderrahmane, L. Yi, G. Wen-Ying, S. Ping, and Q. Song-Sheng
In this paper, a promoter-probe plasmid pKK232-8 was used as a vector, which functioned in Escherichia coli TG1 host. The plasmid DNA fragments from Pseudomonas maltophilia AT18 chromosome DNA active as promoter inEscherichia coli TG1, the promoter function was studied by means of microcalorimetry, the promoter is about 800 bp DNA, it can promote the chloramphenicol
(Cm) gene in plasmid pKK232-8, the Cm resistance level is about 80 μg mL–1, the promoter activity is high. It implicates that there are probably many promoters in Pseudomonas maltophilia AT18 chromosome. All these information is readily obtained by an LKB 2277-204 heat conduction microcalorimeter. Microcalorimetry
is a quantitative, inexpensive, and versatile method for microbiological genetic research.
Authors:A Rozwadowska, A. Gronowski, and Z. Wojtczak
The processes of thermal destruction of copolymers of styrene with magnesium, calcium, strontium and barium acrylates have been investigated by TG and the temperature characteristics have been determined. Though the thermal stability of the metal acrylates exceeds markedly that of polystyrene, the introduction of low concentrations of the salts caused an observable deterioration of the thermal resistance of the copolymers. This was in agreement with the calculated values of the kinetic parameters of decomposition for the samples studied.
Principles and operation of the infrared gold image furnace are discussed and its advantages over conventional resistance
furnaces for studies of advanced materials listed. Using the gold image furnace in combination with a standard microscope
allows continuous monitoring of materials to very high temperatures. New approaches to measurement of heat capacity and thermal
diffusivity/conductivity are also described.