Ytterbium oxide (Yb 2 O 3 ) was used as a sintering aid toobtain Si 3 N 4 with excellent high-temperature properties, it is necessary to minimize the amount of grain boundary phases or enhance the mechanical properties of silicon nitride (Si 3 N 4 ) to crystallize them by some treatment. ceramics. The amount of Yb 2 O 3 had significant effects onTo achieve toughening of Si 3 N 4 by a crack bridging or crack microstructural evolution and the composition of secondary deflection process, formation of large elongated grains is necesphases at the grain boundary. When the Yb 2 O 3 added was sary. However, the existence of the elongated grains does not less than 8 wt%, small homogeneous grains were formed. guarantee these processes. These toughening processes occur At the grain boundary, crystalline Yb 2 Si 2 O 7 was formed only when cracks propagate along the grain interfaces. For the along with a glassy phase. As the amounts of Yb 2 O 3 were intergranular fracture mode, debonding at the interface between increased to higher than 8 wt%, large elongated grains the grains and grain boundary phase should occur. The interwere developed in the fine matrix. In those cases, the grain facial strength can be controlled by modifying the chemistry of boundary crystalline phase was changed from Yb 2 Si 2 O 7 to the grain boundary phase. For example, promotion of interfacial Yb 4 Si 2 O 7 N 2 . Mechanical properties were influenced by debonding was observed by increasing the ratio of yttria to these changes in microstructure and grain boundary phase.alumina or by decreasing the nitrogen content in Si-Al-O-N The fracture toughness increased with the Yb 2 O 3 content up glasses at the grain boundaries. Therefore, both the microstructo 8 wt% and decreased slightly thereafter. The increase in ture and the interfacial debonding energy are critical for fracture toughness was apparently due to the formation of increasing the fracture toughness of Si 3 N 4 . 5-7 In addition, there the large elongated grains. When more than 8 wt% of Yb 2 O 3 is one more aspect to be considered, i.e., the high-temperature was added, interfacial debonding energy between the elonproperties. The grain boundary conditions that give excellent gated grains and grain boundary phase became too large,properties at low temperatures are not necessarily suitable for resulting in a decrease in the fracture toughness. The roomhigh-temperature applications. To obtain conditions suitable for temperature flexural strength was not significantly affected high-temperature applications, crystallization of the amorphous by the Yb 2 O 3 content or the microstructure, other than in phase at the grain boundary by heat treatment after sintering the case of 2 wt% addition. The high-temperature strength has been employed. 1,3 in nitrogen, however, increased steadily with Yb 2 O 3 content.Rare-earth oxides have been used as sintering aids to enhance The highest strength, 870 MPa at 1400؇C, was observed the densification and grain growth by in situ phase transformawhen 16 wt% of Yb 2 O 3...

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O 3 as a sintering aid were investigated. The specimens were exposed to air at temperatures between 1200°and 1500°C for up to 200 h. Parabolic weight gains with respect to exposure time were observed for both specimens. The oxidation products formed on the surface also were similar, i.e., a mixture of crystalline Yb 2 Si 2 O 7 and SiO 2 (cristobalite). However, strength retention after oxidation was much higher for the nanocomposite Si 3 N 4 -SiC compared to the monolithic Si 3 N 4 . The SiC particles of the nanocomposite at the grain boundary were effective in suppressing the migration of Yb 3+ ions from the bulk grain-boundary region to the surface during the oxidation process. As a result, depletion of yttribium ions, which led to the formation of a damaged zone beneath the oxide layer, was prevented.

Arrays of graphite nanocones were fabricated by oxygen-plasma etching of highly oriented pyrolytic graphite (HOPG). As it turned out gold nanoparticles, which were deposited by immersing HOPG samples pretreated with 3-(2-aminoethylamino) propyltrimethoxysilane into colloidal gold solutions, were very efficient for the self-aligned formation of graphite nanocones; the density of nanocones were found comparable with that of gold nanoparticles deposited on HOPG surfaces. We were able to control the shapes and sizes of nanocones by manipulating the plasma-etching parameters such as plasma power and etching time. In particular, nanopillars were formed using high plasma-etching power together with relatively short etching time. Graphite nanocones showed a potential to be good electron-emitters. The emission from the graphite nanocone arrays was turned on at 2.3 V/μm, and the emission current from the area of 6 mm diameter reached the level of 100 μA.

The high complexity and the short lifetime of 3D graphics acceleration hardware increase the necessity of an environment for hardware development. For easy modification and fast testing of architecture, a high-level language based environment is desirable. Therefore, in this paper we propose a Graphics Architecture Testing Environment (GATE) that is based on Microsoft Visual C++. GATE models overall graphics hardware architecture through a modular approach, supports OpenGL, and offers easy modification and rapid testing of architecture. It also gathers computational statistics. A layered approach and Hardware Description Macro (HDM) support hardware modeling and architecture modification. Pre-defined types and operations provide statistical information. Several case studies of 3D graphics architecture on GATE show the capability of our environment.