Search Results

You are looking at 1 - 10 of 14 items for :

  • Author or Editor: M. Gabal x
  • Chemistry and Chemical Engineering x
  • Refine by Access: All Content x
Clear All Modify Search

The influences of inactive, flowing atmospheres (noble gases, nitrogen, carbon dioxide, synthetic air) and vacuum (10−2 and 10−5 torr) on the thermal decompositions of inorganic and organic substances are discussed on the basis of literature and experimental data.

Restricted access

The temperature dependence of the thermal properties (specific heat,C p, thermal diffusivity,a, and thermal conductivity,K) of endellite clay has been investigated over the temperature rangeR·T⩽T≲/280 °C using the plane temperature wave technique. The experimental results showed that in the initial stage of temperature rise botha andK diminish exponentially with increasing temperature up to ∼100 °C. Above 100 °C, the thermal parameters are found to reach stable values, namely,C p=0.22±0.008 cal g−1 deg−1,a=(5.0±0.18)−10−4 cm2 sec− 1 andK=(2.2±0.16) · 10−4 cal cm−1 sec−1 deg−1. The explanation of the results was supported by using DTA and TG analysis.

Restricted access

Abstract  

The macrocyclic complexes of Co(II) and Ni(II) having chloride or thiocyanate ions in the axial position have been synthesized and characterized. These complexes are synthesised by the template condensation of o-phenylenediamine or 2,3-butanedionedihydrazone with the appropriate aldehydes in NH4OH solution in the presence of the metal ions, Co(II) and Ni(II). The complexes were characterized by spectroscopic methods (IR, UV-Vis and ESR) and magnetic measurements as well as thermal analysis (TG and DTA). The results obtained are commensurate with the proposed formulae. Spectral studies indicate that these complexes have an octahedral structure. From conductivity measurements the complexes are non-electrolytes. The kinetic of the thermal decomposition of the complexes was studied and the thermodynamic parameters are reported.

Restricted access

Abstract  

The thermal decomposition behavior of hard coal fly ash (HCA2), obtained from the combustion of an Australian hard coal in thermoelectric power plants, in different atmospheres (air, N2 and N2-H2 mixture), was studied using thermogravimetry (TG), infrared-evolved gas analysis (IR-EGA), differential scanning calorimetry (DSC) and thermodilatometry (DIL) techniques. It was found that changing of the applied atmosphere affects the carbon content of the ash which results in different thermal decomposition behaviors. In air, the carbon content was oxidized to carbon dioxide before the decomposition of carbonate. In N2 or in N2-H2 atmospheres, the carbon content acts as a spacer causing a fewer points of contact between calcium carbonate particles, thus increasing the interface area which results in a decrease of the carbonate decomposition temperature. Following the carbonate decomposition, the iron oxide content of the ash undergoes a reductive decomposition reaction with the unburned carbon. This oxidation-reduction reaction was found to be fast and go to completion in presence of the N2-H2 mixture than in the pure nitrogen atmosphere due to the reducing effect of the hydrogen. The kinetics of the carbonate decomposition step, in air and N2-H2 mixture was performed under non-isothermal conditions using different integral methods of analysis. The dynamic TG curves obeyed the Avrami-Erofeev equation (A2) in air, and phase boundary controlled reaction equation (R2) in N2-H2 mixture. The change in the reaction mechanism and the difference in the calculated values of activation parameters with the change of the atmosphere were discussed in view of effect of the atmosphere on the carbon content of the ash.

Restricted access

Abstract  

The thermophysical properties (thermal diffusivitya, specific heatC p and thermal conductivity λ), of Bi1.5Sb0.5Te3 were measured in the temperature range 300–700 K. The results showed that the contribution of the charge carriers to the thermal conduction is negligibly small in comparison with the contribution of phonons at high temperatures. On the other hand, the heat conduction due to the simultaneous thermal diffusion of electrons and holes is important as well as the lattice thermal conduction. The explanation of the results was supported by using electrical conductivity measurements and X-ray diffraction.

Restricted access

The thermal decomposition of the ferric and nickel acetate salts has been followed. It was found that the heating rate affects the decomposition steps. For a heating rate of 1 K min−1 the product is either Fe2O3 or NiO. For a higher heating rate the suboxides are obtained and reoxidized again on further heating. The decomposition of the mixed salt is an overlap of the DTA for the separate salts but the decomposition reactions are shifted to lower temperatures.

Restricted access

Summary  

Proton-ligand dissociation constant of 2-mercapto-5-(2-hydroxynaphthylideamino)-1,3,4-thiadiazole (MHT) and the stepwise stability constants of its metal complexes were determined potentiometrically in 40 mass/mass% ethanol-water mixture containing 0.1 M KCl. The stabilities of the complexes follow the order: Cu2+>Ni2+>Co2+>Mn2+. The dissociation constant (pKH) of MHT and the stability constants (logK) of its metal complexes were determined at different temperatures and the corresponding thermodynamic parameters were calculated and discussed. The proton dissociation process is non-spontaneous, endothermic and entropically unfavoured. The formation of the metal complexes was found to be spontaneous, endothermic and entropically favoured.

Restricted access

Abstract  

The thermal behaviour of kaolinites intercalated with formamide, dimethyl sulphoxide and hydrazine has been studied by simultaneous TG-DTG-DTA-EGA and TG-MS techniques. The complexes can be decomposed completely without dehydroxylating the mineral. It was found that the amount of intercalated guest molecules per inner surface OH-group is close to unity for the formamide and dimethyl sulphoxide intercalates. For the intercalation of hydrazine it was found that hydrazine is locked in the expanded mineral as hydrazine hydrate and its amount is somewhat higher than that obtained for the other two reagents. The thermal evolution patterns of the guest molecules revealed that all the three reagents are bonded at least in two different ways in the interlayer space.

Restricted access

Solid-state reactions in the CaCO3-SiO2 system with different mass ratios (CaCO3:SiO2=from 1∶0.2 to 1∶10) were studied by means of thermogravimetry, quantitative DTA and high-temperature X-ray diffraction up to 1500 °C.

Restricted access