Crystallization of glass in fireclay refractories; part III: Detailed study on the mullite crystal size in the ‘synthetic’ glass

Poor-grade fireclay products contain substantial amount of glass. A glass of similar composition was synthesized, nucleated and heat-treated for crystallization of mullite. The size and size-distribution of mullite crystals, the rate of change of size and the aspect ratio of the crystals were investigated in relation to the nucleating agents and temperature.     

ASPECTS OF YEAST FLOCCULATION. SIZE DISTRIBUTION AND ZETA-POTENTIAL

The technique of laser diffraction particle sizing has been used to directly measure the size distribution of the components of wort during fermentation. The work has been carried out for three yeasts, a bottom cropping ale yeast, a top cropping ale yeast and a lager yeast. Samples for sizing have been taken from the bottom and middle of the fermentation vessel at various times during the course of fermentation, with the results being reported as number distributions. It Is found that yeast sedimented to the bottom of the fermentation vessel is present either as single cells or as small cell aggregates with a characteristic dimension of about three times that of the single cells. This shows that flocculation is not necessary for sedimentation and that the basic units in stable aggregates are relatively small. The relative proportion of the sedimented cells in aggregated form increases as fermentation proceeds. The time dependence of the size distribution of materials remaining dispersed during fermentation is more complex. There is generally a bimodal distribution of single cells and small aggregates with variable amounts of sub-micron trub which in some cases increases in importance as fermentation becomes more vigorous. The electrokinetic properties of the yeast cells and trub have been studied with the results reported as zeta-potentials. It is found that toward the end of fermentation, and especially in the case of ales, there will be attractive electrostatic interactions between the yeast cells and the trub which would make a contribution in facilitating flocculation.     

粒度分布对Cu包覆SiC颗粒相分布均匀性的影响

利用歧化反应原理,在SiC颗粒表面包覆金属Cu.通过俄歇电子能谱(AES),分析粒度分布对Cu包覆SiC颗粒相分布均匀性的影响.SiC颗粒的粒度分布范围过宽,Cu倾向于包覆在大颗粒表面而无法分散到细小颗粒表面.减小粒度分布范围,纳米SiC颗粒同样能被Cu均匀包覆.应当控制纳米SiC颗粒在一个较小的分布范围,以保证理想的Cu包覆效果和两相分散均匀性.