Preparation Of AACHH Whisker By Homogeneous System And Its Preparation Conditions Research

AACHH whiskers were synthesized by a homogeneous method. Theurea was used as the precipitator; Sorbitol was used as template. Theaverage length of AACHH whiskers is between10to80μm; averagelength-diameter ratio of whiskers is10to20.To study the preparation conditions of AACHH whiskers, fourconditions which were different of relative concentration of CO₂, reactiontime, reaction temperature and template were studied. The study showed thatwhen the relative concentration of CO₂is low, there is another kind ofnon-whisker-like crystal NASCH without AACHH whiskers generated;When the relative concentration of CO₂is high, AACHH whiskers generatewhile using sorbitol as template after6hours in homogeneous system.AACHH whiskers belong to hexagonal crystal and their lattice parametersare a=1.3335nm、c=1.1941nm、Z=16、V=1.8388nm³。Therefore, thispaper argues that: When the concentration of CO₂reaches a certain range,AACHH whiskers can be synthesized in the homogeneous system.Homogeneous nucleation-convex budding-template step-linear grow upmechanism was putted forward. First in the steady state, amorphousspherical nuclear is formed by homogeneous nucleation. Then with the ureahydrolysis and ball nuclear surface dissolved the system reach tosupersaturation, the AACHH “crystal buds” are formed on the convexsurface of the ball of nuclear. Vicinal faces are formed on the interface ofnuclear by vicinal surface-step. Finally, primitives precipitate at the kink bythe proliferation—Whiskers grow along the C axis direction. The growthmechanism is different from the VSL and dislocation mechanism. It is aunique growth mechanism of homogeneous precipitation method forpreparing AACHH whisker.The study of heating mechanism shows: After calcinations, the peak of OH^-、NH₄⁺、CO₃^2-disappeared. It shows that: the water, ammonia, carbondioxide and other gases are produced when the whiskers were burned.Through the TG/DTA curves, AACHH reduced weight at200℃，the groupof OH^-、NH₄⁺、CO₃^2-were removed at255℃and the weight of AACHH nolonger changed at330℃. The loss of weight is57.9%.