Effect of immobile impurities on two-dimensional nucleation

We study the dependence of the critical size of the nucleus on the density of impurity by carrying out a Monte Carlo simulation. We assume that the impurities are fixed on a crystal surface, and neglect restoration of bonds between an impurity atom and an adsorbed atom. We initially prepare one cluster in the system and investigate the change of the cluster size. When the cluster size is the critical value, the frequency of increasing the cluster size is equal to that of decreasing the size. With increasing the impurity density, the critical nucleus becomes large. When the impurity density is sufficiently high, regardless of the initial cluster size, the cluster vanishes after a long time interval, namely, the critical cluster size is diverged. © 2011 American Physical Society

HIGH TEMPERATURE COMPOSITES WITH REINFORCING OXIDE FIBERS AND PLATES AND NiAl AND AL2O3 MATRICES

Fibrous and layered composites with intermetallic NiAl and oxide Al2O3 matrices reinforced with composite fibers or plates obtained by internal crystallization method were obtained by diffusion welding in vacuum. LaAl11O18–Al2O3 fibers and plates provide acceptable strength and fracture toughness of composites in the temperature range of 20–1400 °C.Методом диффузионной сварки в вакууме получены волокнистые и слоистые композиты с интерметаллидной NiAl и оксидной Al2O3 матрицами, армированные композитными волокнами или пластинами, полученными методом внутренней кристаллизации. LaAl11O18–Al2O3 волокна и пластины обеспечивают приемлемую прочность и трещиностойкость композитов в диапазоне температур 20–1400 °C.Работа выполнена при финансовой поддержке Российского фонда фундаментальных исследований (проект № 17-03-01136 а)

COMPOSITE OXIDE FIBERS FOR REINFORCING BRITTLE MATRICES

By the method of internal crystallization fibers based on the systems of oxides Al2O3–CaO, Al2O3–BaO, and Al2O3–La2O3 were obtained. The fibers are tested for strength.The strength of the fibers is ensured by sapphire, and the fracture toughness is ensured by calcium hexaaluminates, or barium, or lanthanum, which are part of their structures.Методом внутренней кристаллизации получены волокна на основе систем оксидов Al2O3–CaO, Al2O3–BaO, Al2O3–La2O3. Волокна испытаны на прочность. Прочность волокон обеспечивается сапфиром, а трещиностойкость — гексаалюминатами кальция, или бария, или лантана, входящими в состав их структур.Работа выполнена при финансовой поддержке Российского фонда фундаментальных исследований (проект № 17-03-01136 а)

Impurity phases in beryllium oxide ceramic

An x-ray spectrographic method with an electron probe and a scanning electron microscope are used to study industrial ceramic specimen surface composition, distinguished by presence of a different color for both the main part, and impurity phases. BeO-ceramic specimens, having a visually differing color, are conditionally separated into three types. In reflected electron microphotographs impurities are distinguished qualitatively with respect to electrical conductivity. Iron impurity is invariably present within the composition of electrically conducting phases and inclusions. Apart from iron, all impurity phases contain carbon, aluminum, silicon, and calcium, and within individual phases there are admixtures of manganese, magnesium, chromium, potassium, sodium, zinc, phosphorus, and chlorine, which may be introduced into BeO-ceramic during production and sintering in repeatedly used industrial furnaces from linings and residual atmosphere. © 2013 Springer Science+Business Media New York

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研究報

LAYERED-FIBROUS COMPOSITE BASED ON NIOBIUM REINFORCED BY SAPPHIRE FIBERS

A structure was developed and specimens of composite materials with a niobium.based layered matrix, unidirectionally reinforced with single.crystal sapphire fibers, were obtained by the solid.phase method of diffusion welding. X.ray microanalysis and mechanical tests of the obtained materials were carried out.Разработана структура, и твердофазным методом диффузионной сварки получены образцы композитных материалов со слоистой матрицей на основе ниобия, однонаправленно армированные монокристаллическими волокнами сапфира. Проведены рентгеноструктурный микроанализ и механические испытанияполученных материалов