A comparison of two- and three-dimensional size distributions in a cellular material

This investigation concerns the comparison of two- and three-dimensional data obtained on a cellular material. By quantitative micrography techniques and spatial measurements, the cellular structure corresponds most closely with the shape of pentagonal dodecahedra, twelve-faced cells having five edges per face. The cell volumes have a normal distribution.The areal distributions of planar sections for various shapes of polyhedra were taken from existing literature. The measured volume distributions from this study were then applied by numerical computer calculations to create a transformation which carried the distribution of volumes (three-dimensional) to the expected distribution of planar areas (two-dimensional). The results of the expected and measured areal data agreed well for assumed complex polyhedral symmetry such as pentagonal dodecahedra, and unsatisfactorily for spherical symmetry. These results demonstrate that the pentagonal dodecahedron is a measurable prototype of cell in grain shapes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32704/1/0000071.pd

Microstructure and Properties of Al₂O₃-Al(Si) and Al₂O₃-Al(Si)-Si Composites Formed by in Situ Reaction of Al with Aluminosilicate Ceramics

Al2O3-Al(Si) and Al2O3-Al(Si)-Si composites have been formed byin situ reaction of molten Al with aluminosilicate ceramics. This reactive metal penetration (RMP) process is driven by a strongly negative Gibbs energy for reaction. In the Al/mullite system, Al reduces mullite to produce α-Al2O3 and elemental Si. With excess Al (i.e., x \u3e 0), a composite of α-Al2O3, Al(Si) alloy, and Si can be formed. Ceramic-metal composites containing up to 30 vol pct Al(Si) were prepared by reacting molten Al with dense, aluminosilicate ceramic preforms or by reactively hot pressing Al and mullite powder mixtures. Both reactive metal-forming techniques produce ceramic composite bodies consisting of a fine-grained alumina skeleton with an interpenetrating Al(Si) metal phase. The rigid alumina ceramic skeletal structure dominates composite physical properties such as the Young’s modulus, hardness, and the coefficient of thermal expansion, while the interpenetrating ductile Al(Si) metal phase contributes to composite fracture toughness. Microstructural analysis of composite fracture surfaces shows evidence of ductile metal failure of Al(Si) ligaments. Al2O3-Al(Si) and Al2O3-Al(Si)-Si composites produced byin situ reaction of aluminum with mullite have improved mechanical properties and increased stiffness relative to dense mullite, and composite fracture toughness increases with increasing Al(Si) content

Effect of the Addition of Potassium or Lithium on the Columbite Precursor Microstructure

Pechini method has been used to synthesize MN powders with stoichiometric control. By this method, K and Li-doped MN in the range from 0.1 to 5.0 mol% of dopants have been obtained at relatively lower temperatures than it is possible with the conventional mixture of oxides. The results from BET analysis indicated that the doped powders have lower surface area and the attrition milling promotes an increase in surface area values for all powders. Rietveld method was used to calculate the mean crystallite size and the microstrain in the crystal. With additions of up to 5.0 mol% of K or 2.0 mol% of Li, it is possible to obtain MN as a solid solution. Both dopants change the cell parameters of the columbite phase crystal, reduce the microstrain, and increase the main crystallite size. The analysis of results from SEM indicates that powders prepared with addition of dopants are more agglomerate than pure PMN powder