Effects of varying oxygen partial pressure on molten silicon-ceramic substrate interactions

The silicon sessile drop contact angle was measured on hot pressed silicon nitride, silicon nitride coated on hot pressed silicon nitride, silicon carbon coated on graphite, and on Sialon to determine the degree to which silicon wets these substances. The post-sessile drop experiment samples were sectioned and photomicrographs were taken of the silicon-substrate interface to observe the degree of surface dissolution and degradation. Of these materials, silicon did not form a true sessile drop on the SiC on graphite due to infiltration of the silicon through the SiC coating, nor on the Sialon due to the formation of a more-or-less rigid coating on the liquid silicon. The most wetting was obtained on the coated Si3N4 with a value of 42 deg. The oxygen concentrations in a silicon ribbon furnace and in a sessile drop furnace were measured using the protable thoria-yttria solid solution electrolyte oxygen sensor. Oxygen partial pressures of 10 to the minus 7 power atm and 10 to the minus 8 power atm were obtained at the two facilities. These measurements are believed to represent nonequilibrium conditions

Dense Chromium Sesquioxide

A sintered, fine grained, polycrystalline, essentially fully dense, essentially single phase Cr2O3 body is prepared by sintering Chromium Sesquioxide (Cr2O3) at essentially the equilibrium oxygen partial pressure (PO2) for the formation of CrO 3 from its elements at the sintering temperature. To achieve optimum theoretical density a second metal oxide dopant such as MgO, capable of controlling the grain size, is added. In addition, Cr2O3 bodies are rendered more stable, and thus have a longer life, by maintaining over the body an atmosphere which is essentially equilibrium Po, for the formation of Cr2O3, from its elements at that temperature

Electron Emitter Tips and Method

Boron is deposited on the (110) plane facet at the center of a tungsten electron emitter tip by chemical vapor deposition of boron triiodide. The emission current density is greatest in the center of the emitting area (FIG. 2)

A preliminary study of the effect of heat treatment on the strength and microstructure of a glass-ceramic material

The strength and microstructure of a glass-ceramic material of the composition 53 percent SiO₂, 19 percent Al₂O₃, 15 percent MgO, and 13 percent Li₂O were studied. Cylindrical specimens of glass were formed and heat-treated to six different temperature levels for various time periods. The method of strength testing used was a diametral compression loading technique. It was found that the strength of this material increased initially with heat-treatment but then decreased. The strength characteristics of the completely crystallized glass ceramic material were found to be dependent on the initial nucleation period. Some factors which influenced anomalous crystal growth are described. The relationship of stress and nucleation in this study is discussed. Mechanisms of nucleation and crystallization were observed by transmitted and reflected light microscopy. The phases at various time periods were determined by X-ray diffraction, and the changes in softening characteristics were recorded by means of thermal dilatometer tests --Abstract, page ii

Control of Oxygen and Carbon Related Crystal Defects in Silicon Processing

In the production of silicon articles at an elevated temperature, a stream comprising a controlled mixture of an oxygen-containing first gas and a second gas is admitted to the processing chamber. The first gas is one which partially dissociates under the conditions in the chamber to form both oxygen and the second gas. The second gas is one which is not harmful to silicon at the conditions in the chamber. Substantially equilibrium conditions are established in the chamber so that the dissociation of the first gas to oxygen occurs reversibly. The partial pressure of oxygen (PO2) is sensed in the chamber during processing of the article. In response to the PO2 level, the ratio of the rates of flow of the oxygen-containing gas and the second gas is adjusted so as to maintain the PO2 at a level less than about 10-6 atmosphere, and usually no greater than about 10-10 atmosphere, at which the density of oxygen-related defects in the processed silicon article is acceptably low. Oxygen-related defects in the silicon are thereby reduced. If graphite structures are present in the hot zone of the processing chamber, they are preferably coated with an impervious coating which will stand the high temperature and will prevent the gas stream from coming into contact with the hot graphite. Carbon-related defects in the silicon are thereby also reduced

Structural Ceramic Incorporating Boron Carbide Whiskers for the Strengthening Thereof

Ceramic composites, and in particular structural ceramic composites, have enhanced strength, toughness and abrasion resistance due to the presence of up to about 40 volume percent of relatively large boron carbide whiskers. Although whiskers of various sizes were studied, those of particular interest are whiskers having an average diameter greater than about 3 micrometers, and particularly about 5 to about 8 micrometers, with an average aspect ratio of about 50. Due to the larger size, which had been predicted to be detrimental, there is less respiratory health risk when using these whiskers in the manufacturing of thse improved ceramic composites. Since boron carbide whiskers have many properties superior to silicon carbide whiskers, the most common strengthening agent, the findings should lead to several improved ceramic composites

Formation and Densification of Cadmium Manganese Ferrite

Formation of Ni-ferrite, Mn-ferrite, NiZn-ferrite, Zn-ferrite and Mg-ferrite have been investigated using X-ray diffraction analysis. Jander\u27s diffusion equation described the data from these investigations over a portion of the temperature ranges studied. However, the reaction mechanisms and sequences involved in the formation of mixed ferrites have not been well defined in the literature. The purposes of this investigation were: ( 1) To further the understanding of the formation of CdMnferrite by studying first the kinetics of the formation of Cd-ferrite and Cd-manganite, which provides a basis for understanding the details of the mixed CdMn-ferrite reaction and to obtain the optimum temperature-time cycle for calcination and sintering, along with the reaction sequence and densification behavior for polycrystalline CdMn-ferrite. (2) To determine the magnetic properties of CdMn-ferrite as a function of composition, bulk density and grain size

Magnetic Properties of Cadmium Manganese Ferrite

The room-temperature saturation magnetization of CdxMn1-xFe2O4 decreased with increasing cadmium concentration. When 0 \u3c x \u3c 0.5, the decrease in saturation magnetization was due to the increase in the amount of non-mgnetic distorted cubic Cd(Mn, Fe) 2O4