Preparation and microstructure of machinable Al2O3/mica composite by ball milling and hot-press sintering

A machinable α-Al2O3/mica composite was prepared by hot-press sintering. In this experiment, a mica-contained glass ceramic in the MgO-Al2O3-SiO2-F glassy system was employed and the base glass powders were obtained by traditional melting-quenched method. Then, α-Al2O3 milling swarf was introduced by medium α-alumina milling ball to the glass powders. The test results indicate that the composites consist of mica crystal and mullite crystal, which are precipitated in the base glass. The α-Al2O3 shows an irregular polygon, which is inlayed in the base material. With the decrease of size of the base glass powders, the boundaries of composites among the sintered powders gradually vanish. The mica crystals in the composite also show an interlocking characteristic, which is a prerequisite of mica-contained glass ceramics with good machinability. Under different pressures, the tendency of preferred orientation is decreased with the reduction in grain size of glass powders, and the microstructure is proved to be consistent, significantly decreasing the composite’s hardness. Therefore, the machinability of the composite is improved.

History, Monumentality, and Interaction in the Appalachian Summit Middle Woodland

The Middle Woodland period in eastern North America witnessed a florescence of monumental architecture and material exchange linked to widespread networks of ritual interaction. Although these networks encompassed large geographic areas and persisted for several centuries, extant archaeological models have tended to characterize Middle Woodland interaction as an historically unitary process. Using new data from the Garden Creek site in North Carolina, I argue that these frameworks obscure important historical shifts in Middle Woodland interaction. Recent collections-based research, geophysical survey, targeted excavation, and14C dating (including Bayesian modeling) of this site reveal two coeval diachronic changes: a shift from geometric earthwork construction to platform mound construction; and a shift from the production of special artifacts {mica, crystal quartz) to the consumption of exotic artifacts in association with platform mound ceremonialism. These data hint at important changes in interregional relationships between the Appalachian Summit, the Hopewellian Midwest, and the greater Southeast during the Middle Woodland period, and provide a springboard for considering how processes of culture contact contributed to precolumbian cultural change.

The Influence of Technical Factor and Ingredient Design on Crystallization Behavior of MgO-SiO2-Al2O3-B2O3-KF Glass-Ceramics

In this paper, the the micro crystallization behavior of MgO-SiO2-Al2O3-B2O3-KF glass-ceramics which was prepared by sintering and water quenching method was discussed. The study indicated that the compacts shrinkage of MgO-SiO2-Al2O3-B2O3-KF glass-ceramics were related to its vitrification and its component crystallization degree; about the density of sintered compacts, the higher the crystallization degree, the higher the dense it owns. The conclusion reached above is significant in dimension control to the produce process. In the samples when the proportion of ingredient was closer to the atomic ratio of mica crystal, the higher the micro crystallization degree of the glass-ceramics will be. When sintering temperatuer is 1000oC,the MgO-SiO2-Al2O3-B2O3-KF glass-ceramics begain to present the crystallization; when it achieves to 1050°C, the crystallization degree is highest; continue to increase the sintering temperature, the micro crystallization will be melted again.