Heat Treatment In Argon Research Articles

Effect of Atmosphere on Dielectric Properties of Plasma Polymerized Ethylene

The effect of atmosphere after polymerization on dielectric properties of plasma polymerized ethylene (PPE) is studied. ESCA and ESR measurements show that the PPE sample traps oxygen rapidly when it is exposed to air after polymerization. They also show that heat treatment in argon or in hydrogen can reduce the number of residual free radicals. The change in dielectric properties of tan δ and conduction current with atmosphere after polymerization can be explained if dielectric properties are closely related with residual free radicals and carbonyl groups formed in the sample.

X-ray and XPS studies of evaporated CuxS thin films

The structural changes in CuxS films have been monitored by x-ray diffraction and correlated to the chemical changes taking place on the CuxS surface, the latter monitored by XPS. The results show: evaporated CuxS films contained chalcocite, free copper phases, and probably a third phase (of sulfur); resistivity is related to the amounts of free Cu and S in the film; air heat treatments converted chalcocite to Cu deficient phases and resulted in the disappearance of the sulfide and predominance of CuSO4⋅nH2O and CuO; argon heat treatment tended to react Cu and S to form CuxS; Cd is detected on the surface of CuxS deposited onto CdS and is significantly increased in amount by heat treatments. These results can be related to chemical processes occurring on CuxS/CdS and CuxS/(Zn,Cd)S solar cells. For the CdS cell, oxides and sulfates of Cu and Cd are found on the CuxS surface and the sulfates are enhanced by the heat treatment in moist air. CuO and CuSO4 are formed in the absence of Cd, and dominate the CuxS surface.

A Comparison of Reducing and Oxidizing Heat Treatments of Hot-Pressed Silicon Nitride

The effects of postfabrication heat treatments in argon and air atmospheres at 1400°C on the microstructure of a hot-pressed silicon nitride are compared. Heating in argon leads to a disappearance of the intergranular glass phase (with the consequent formation of interconnected porosity) and a reduction in the content of silicon oxynitride, and results in a soft, easily abraded surface. On subsequent heating in air, an oxide scale, similar to that produced by oxidation, rich in impurity and additive cations, is formed on the surface. In addition, silicon oxynitride and silica are formed below the scale. On cooling, macroscopic cracking, attributed to the volume increase of SO2 on transformation to cristobalite, occurs. Material heated first in air and then in argon resembled that of material heated in argon alone.

The correlation of hydrogen diffusion with the relative concentrations of cubic and axial Fe3+ sites in KTaO3

Hydrogen in the form of OH− ions has been incorporated into Fe-doped KTaO3 single crystals by heat treatments in H2O vapor, air, and hydrogen gas. Heat treatments in argon and oxygen resulted in a removal of OH− from the crystal. The conditions resulting in the incorporation of OH− also produced a decrease in the intensity of an axial Fe3+ EPR signal relative to the cubic site iron spectrum while the removal of OH− was accompanied by a relative increase in the axial EPR signal. The removal of oxygen from Fe-doped KTaO3 by heat treatments in potassium metal vapor was also found to elminate the axial Fe3+ EPR spectrum. These results do not support the previously accepted oxygen vacancy model for the Fe3+ axial site configuration and are contrary to the results of similar investigations of Fe3+ in SrTiO3.

Tl− Centres in KCl Crystals

AbstractElectrolytic colouring at about 300 °C and 8000 V/cm, in KCl:T1+ single crystals with a 10−4 mol% concentration of T1+‐ions, gives rise to the appearance of two new absorption bands peaking at 4.35 and 3.35 eV. The modifications of the absorption spectra of the coloured crystals induced by different colouring conditions, by the recording temperature and by the heat treatments in argon, hydrogen, and water vapour atmospheres are investigated. All experimental data support the substitutional T1−‐ion model, proposed in this paper as the colour centre responsible for these two new bands.

Multi-stage activation of brown-coal chars with oxygen

Activation of xylitic brown-coal coke XBC 900 with water vapour and carbon dioxide, when modified by partial replacement of the basic activating agent with 10% oxygen at a lower temperature, results in products with an increased microporosity. Thus, oxygen as activating agent for xylitic coke develops, preferentially, micropores, and this property is more strongly pronounced for oxygen than for the carbon dioxide and water vapour. A drawback to the process of activation with oxygen, i.e. blockage of initially formed micropores by chemisorbed oxygen, can be eliminated by removal of the chemisorbed oxygen by heat treatment in argon (multi-stage oxygen activation). This increases the micropore volume of the xylitic brown-coal coke XBC 900 activated with oxygen to 70% total burnoff, from about 0.2 cm 3 g −1 to almost 0.5 cm 3 g −1. The increase of the total adsorptive volume (micropores and mesopores) of these samples is from 0.45 cm 3 g −1 to over 0.6 cm 3 g −1 and the surface area S BET in benzene increases from 650 m 2 g −1 to over 1200 m 2 g −1. These last values are close to the limiting conditions for 70% activation obtainable for this material. Temperature of carbonization of the brown-coal char has a strong effect on the possibility of pore development through further activation. Multi-stage oxygen activation of xylitic brown-coal semicoke XBC 500 produces a material with a smaller micropore volume and a lower surface area than that of xylitic brown-coal coke XBC 900 similarly activated.

Effects of heat treatment and plastic deformation on the photoelectronic properties of high-resistivity GaAs : Cr

The effects on the photoelectronic properties of high-resistivity GaAs : Cr crystals of heat treatment in argon at 580 °C are investigated, with and without plastic deformation. With reference to a nondeformed heat-treated sample, plastic deformation at 580 °C to a radius of 3.2 cm (Ga bending resulting in an etch-pit density of 2.3×107 cm−2) increases the electron density in the dark, but decreases the electron mobility in both dark and light, and decreases the electron lifetime over most of the temperature range. These effects probably result from the interaction of dislocations with crystalline defects and from consequences of sample inhomogeneity. Such GaAs : Cr crystals were much more brittle with respect to As bending, and comparable deformation could not be obtained before fracture.