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Transformacje strukturalne w kryształach wywołane reakcjami fotochemicznymi

Turowska-Tyrk I., Bąkowicz J.

Wiadomości Chemiczne

2014

[Z] 68, 5-6

381--402

Structural changes induced in crystals by photochemical reactions were presented. The changes concern: a) the distances between neighbouring reactant molecules and their mutual orientation in the case of intermolecular reactions, b) the distances and angles between fragments of a molecule for intramolecular reactions, c) the position of molecules in crystals, d) geometry of hydrogen bonds, e) cell constants, and f) the content of product molecules in crystals. For most intramolecular reactions, the distances between reactive atoms are constant for a long time in phototransformation and decrease rapidly at its end (Figs. 3 and 5). In the case of intermolecular reactions, the distances between reactive atoms of reactant molecules decrease linearly along with the phototransformation of crystals (Fig. 7). Additionally, unreacted molecules become, to a certain degree, similar to product molecules in terms of their shape (Figs, 4 and 8). Reactant and product molecules do not assume a fixed place in crystals. Product molecules change their orientation towards that of which is observed in a pure product crystal and reactant molecules gradually move away from the position they took in pure reactant crystals. All this has an influence on the geometry of hydrogen bonds existing in crystals (Fig. 9). The above-mentioned structural transformations find their expression in values of cell constants (Fig. 10). The factors influencing the photoreactivity of molecules in crystals were also described. Knowledge of crystal and molecular structures of partly reacted crystals, determined thanks to X-ray structure analysis which is a branch of crystallography, reveals the behaviour of molecules in crystals in which photochemical reactions proceed and helps to understand a pathway of these reactions.

The influence of thermal treatment on structure and properties of plasma sprayed oxide and carbide coatings.

Nitkiewicz Z., Iwaszko J.

Inżynieria Materiałowa

1998

R. XIX, nr 4

1077-1080

This paper presents the results of the investigations of oxide (Cr2O3, Al2O3, ZrO2) and carbide (Cr3C2, W2C) coatings as applied onto the steel substrate by the plasma spraying method and subsequently remelted. Diverse methods of remelting were used in the experiments - the single and repeated treatments with the continuous microplasma arc, the impulsive remelting technique and TIG method. The coatings were examined both prior to, and after the thermal treatment with the use of light an scanning microscopy, X-ray structural analysis, and the measurements of surface roughness. A reduction of surface roughness, an increase in intensities of diffraction lines and a densification of ceramic and bond layers as a result of reduction of porosity and voids, were observed.