Aging Behavior of A356.2 with Yb Modified

The effect of aging treatment on the aging hardening of 0% Yb and 0.4% Yb modified A356.2 alloy was investigated by hardness measurements and optical microscope. In this work, A356.2 was first subjected to 535°C for 5h and then subjected to 150°C, 180°C for 2h-12h hours. Results show that during aging process, there was a hardness peak along the increasing of aging temperature and time. With increasing aging progress, the morphology of Si phases became shorter and spherical. After optimum time, Si phases was coarse and the dendritic grain was broken. The peak-aged of unmodified alloys was 150°C for 10h and 180°C for 6h，and corresponding hardness values were 62.35HB and 77.10HB, respectively. With Yb addition, the hardness reached 87.58HB and 98.28HB on peak aging of 150°C/8h and 180°C/ 6h, respectively. The greatest degree of hardness was increased by 40.46% and 27.47%, combined with no Yb addition. XRD shows the interplanar crystal spacing of A356.2 with 0.4% Yb addition, which was larger than fresh A356.2 alloy. When adding 0.4%Yb under 180°C for 6h aging progress, the ultimate tensile strength was 284 MPa 12.7% increasing compared with former work.

Can agitation determine the polymorphs of calcium carbonate during the decomposition of calcium bicarbonate?

Free of external disturbance, Ca2+ ions stack in the (0001) faces in the mode of (a), corresponding to thermodynamically least stable vaterite phase. To maximally reduce coulomb repulsion under external agitation, one Ca2+ ion moves up and the other moves down for one third of interplanar crystal spacing (b), corresponding to the stable calcite phase.

Studied on Preparation Montmorillonite Modified by CTAMB and Adsorption Performance on Nitrobenzene

Na-montmorillonite was modified by CTAMB through the intercalation. The effects of amount, temperature, time on microstructure were characterized by X-ray diffraction; Fourier transforms infrared spectrometer, and N2adsorption isotherms. At same time, the adsorption performance on the nitrobenzene was compared by UV-visible absorption spectra. The results show that: CTAMB can effectively increase the crystal spacing of sodium montmorillonite. The reaction time and reaction temperature has little effect on the reaction process. The modified montmorillonite by CTAMB can adsorption nitrobenzene, and its adsorption properties relate with the crystal spacing. At the same time pore volume of modified montmorillonite can be increased, it is beneficial to the adsorption of nitrobenzene. Compare with OTAC, the pore radius of montmorillonite modified by CTAMB is smaller.

The shape of reflections on X-ray, single-crystal photographs (With Plates X and XI)

In the early days of X-ray crystallography the study of the atomic and molecular structure of crystals was of primary importance. It was more necessary to know the arrangement of the atoms in, say, rocksalt, quartz, diamond, or graphite, than to know the exact distances apart of the atoms, or the small deviations from the mean atomic structure which may result from heat movements, eccentricity of growth, mechanical distortion, and other factors.Now, however, the range of problems is widening, and X-ray methods are being used as a research tool by many workers whose main interest is in other branches of science. It is necessary, therefore, to point out that the familiar Bragg law, nλ = 2d sin θ, which relates order of spectrum n, wave-length λ, crystal spacing d, and diffraction angle θ in an ideal crystal, though still of course applicable, must be applied with some caution to crystals which are not ideal in either structure or texture, and which may be of irregular or eccentric shape.