Nanostructured ␤-SiC, with crystallite size in the range of 5-20 nm in agglomerates of 50 -150 nm, was formed by reactive high-energy ball milling and consolidated to a relative density of 98% by sintering at 1700°C without the use of additives. X-ray line broadening analysis gave a crystallite size of 25 nm, while transmission electron microscopy observations showed the crystallite size to be in the range of 30 -50 nm. Evidence demonstrating the role of a disorder-order transformation in the densification process is provided by changes in the diffraction peak patterns and in the integral width with temperature. R. Riedel-contributing editorManuscript No. 10245.

is one of the most versatile ceramics, utilized in an amazing range of structural and optical applications. In fact, chromium-doped single crystal Al 2 O 3 was the basis for the fi rst laser. Today, most photoluminescent (PL) materials rely on rare earth (RE) rather than transition-metal dopants because RE doping produces greater effi ciencies and lower lasing thresholds. RE-doped alumina could provide an extremely versatile PL ceramic, opening the door for a host of new applications and devices. However, producing a transparent RE:Al 2 O 3 suitable for PL applications is a major challenge due to the very low equilibrium solubility of RE ( ∼ 10 −3 %) in Al 2 O 3 in addition to alumina's optical anisotropy. A method is presented here to successfully incorporate Tb 3+ ions up to a concentration of 0.5 at% into a dense alumina matrix, achieving a transparent light-emitting ceramic. Sub-micrometer alumina and nanometric RE oxide powders are simultaneously densifi ed and reacted using current-activated, pressure-assisted densifi cation (CAPAD), often called spark plasma sintering (SPS). These doped ceramics have a high transmission ( ∼ 75% at 800 nm) and display PL peaks centered at 485 nm and 543 nm, characteristic of Tb 3+ emission. Additionally, the luminescent lifetimes are long and compare favorably with lifetimes of other laser ceramics. The high transparencies and PL properties of these ceramics have exciting prospects for high energy laser technology.

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Boron carbide (B4C) was synthesized from the elements at temperatures ranging from 1300° to 2100°C using the spark plasma synthesis method. Significant densification commenced at about 1500°C and was accompanied by a corresponding decrease in the defect structure of this carbide. Changes in the X‐ray diffraction patterns were in agreement with predictions of simulation studies based on the presence of twins. Transmission electron microscopy observations were consistent with the experimental observations and the modeling predictions.

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The influence of the pulsed DC current and the electric field on the growth of TiC and ZrC layers using Spark Plasma Sintering was investigated at temperature ranging from 1373 to 1823 K. From the results of XRD and EDS analyses, the product layer formed between Ti and C was only TiC, and the layer between Zr and C was only ZrC. In all systems, the thickness and the growth rate constant of the product layers were enhanced in the system with the current compared to that in the system with the negligible current. The activation energy for the TiC layer growth was calculated to be 269 ± 3 kJ/mol in the system with the current, which is smaller than the activation energy of 273 ± 2 kJ/mol in the system with the negligible current. In the Zr-C system, these values were 205 ± 7 kJ/mol and 224 ± 1 kJ/mol, respectively. The increase in the growth of the TiC and ZrC layers was unaffected by the current direction and suggested that the increased point defect mobility by passing the current was a dominant cause of the enhanced growth.