Preparation of Na<sub>1-<i>x</i></sub>Ti<sub>2+<i>x</i></sub>Al<sub>5-<i>x</i></sub>O<sub>12</sub> Whiskers by Calcining with Excess Na<sub>2</sub>O
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Na1-xTi2+xAl5-xO12 (NTAO) whiskers were effectively grown by the solid reactions in the presence of excess Na2O. The excess Na2O was evaluated by a y value in an experimental formula Na1-x+yTi2+xAl5-xO12+y/2. The best condition of whisker growth was obtained by heating for 3-5h with y=0.2-0.4 under the steady state of x=0.2 at 1350°C. The whiskers were 30-100μm in length and 5-10μm in diameter. The excess Na2O played very important roles to promote following reactions through two stages. The first stage is the formation of freudenbergite by a reaction between rutile and Na-β''-alumina which was made with α-alumina and Na2O. The second stage is the formation and growth of NTAO whiskers by a reaction between freudenbergite and Na-β''-alumina in the existence of Na2O liquid phase.Keywords:
Rutile
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The morphological mechanisms of tin whisker growth on the surface of oxidized CeSn3 and ErSn3 precipitates were investigated during the aging.The results indicate that most tin whiskers have constant cross section and regular shape.However,few irregular tin whiskers with special morphologies are also observed,including the spiral whiskers,whiskers with a non-constant cross section,branch-type whiskers and joining-type whiskers.Since the produced lattice expansion of the rare earth precipitates oxidization provides driving force for the tin whisker growth,and the oxidization is extremely uneven.Therefore,the changes of stress around the tin whisker root will primary cause that results in the growth of irregular tin whiskers.
Monocrystalline whisker
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Incubation period
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Monocrystalline whisker
Vapor–liquid–solid method
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Supersaturation
Monocrystalline whisker
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Stress relaxation
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The first compound whisker grown by squeeze technique (In2Bi) is reported. Rotating crystal x-ray analysis and melting-point measurements confirmed that the whiskers were In2Bi. The whisker axis coincided with the 〈001〉 direction for all four whiskers. A scanning electron microscope photograph indicates that the whiskers have diameters of a few μ and a morphology similar to tin whiskers.
Monocrystalline whisker
Morphology
Crystal (programming language)
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Morphology
Monocrystalline whisker
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It has been found that Se whiskers grow on Mg and its alloys with Al and Zn immersed in an aqueous solution of selenious acid (H2SeO3), and the effects of the concentration of the solution and of the alloying elements on the whisker growth were studied under a metallurgical microscope and by X-ray analysis. Some whiskers appeared first on Mg or its alloys immersed in the solution for 20∼30 minutes, and after 1∼5 hours the number of the whiskers increased remarkably. Then, the whisker growth retarded and stopped after 24 hours. The time required for the growth of each whisker was 30∼120 seconds. In 2% solution whiskers hardly grew, and in 4% solution the number of the whiskers increased remarkably, but in more concentrated solutions the number of the whiskers remained almost the same. With increasing content of Zn and Al up to 8%, the number of the whiskers and their sizes became larger, while the whiskers hardly grew on Mg-40%Al alloy. The maximum length of the whiskers was 2 cm. The whiskers had round pipe-like section and their diameter was 0.1∼0.01 mm. The crystal structure of the whiskers is hexagonal and each whisker is not a single crystal but a polycrystal.
Monocrystalline whisker
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The material of articles were reviewed and analyzed the results of previous studies of whisker crystals on non-traditional growing methods, namely, one of them – the "pull" of metal whiskers from solutions. Analysis of published data shows that the problem in modern conditions given enough attention to that, no doubt, talking about the relevance of the research topic and, therefore, these issues need to be addressed. The results of this analysis show that if prepared solution at a certain temperature is rapidly cooled to a lower temperature, there appear corresponding metal whiskers. The whiskers begin to appear again after the completion of the main stage of crystallization and if it begins to lower the temperature, the amount of the crystal needles will gradually increase. Reaching a certain "threshold overflow" volume growth of whisker crystals becomes an avalanche, and then almost stopped, at the final stage it is appeared whisker curled in a spiral around the axis of growth. The growth of whiskers of metal salts by rapid cooling of saturated solutions occurs at dislocations occurring on the particles of impurities. It is only stopped after the complete drying following solutions. The spectrum of use of whisker crystals in modern industry is expanded, so keeping and use of research will improve the implementation of environmental requirements for the protection of human health and environment.
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