Engineering topics
Publications and source records attributed to Leiser, D. B..
Reaction-cured glasses resist thermal shock and maintain properties over range of -100 degrees Centrigrade to +1,480 degrees Centigrade. Stability makes these excellent materials for high-temperature glassware and tubing or as coatings for porous materials.
A correlation between the morphology, chemistry, and optical properties of space shuttle candidate reusable surface insulation coatings were made to determine the proper test environment for flight evaluation studies. The optical properties (solar absorption coefficient and total hemispherical emittance) for each coating were obtained as a function of exposure to radiant and convectively heated environments since these parameters define the surface temperature of the material during flight. Results are presented which show these optical properties differ in the two environments and can be related to the coating's surface and bulk chemistry.
A reusable silica surface insulation material is provided by bonding amorphous silica fibers with colloidal silica at an elevated temperature. The surface insulation is ordinarily manufactured in the form of blocks (i.e., tiles).
Silica and mullite fibers used to fabricate reusable surface insulation (RSI) for the space shuttle orbiter may devitrify/recrystallize within the temperature range anticipated upon reentry. This is shown to be dependent upon impurity level, temperature, and time at temperature. It is determined that the effects of the material improvement and optimization program are positive. The degree of crystallinity is shown to have a predominant effect upon the strength of fabricated RSI tile, and limits are determined. Models are developed to predict tensile strengths and shrinkage rates of silica tile based upon readily measurable parameters. Thermal cycling which simulates reentry results in an increase in the crystallinity and in the porosity of tile coatings.
Family of high-temperature, low-density refractory composite insulations made from aluminoborosilicate and silica fibers has insulating material with improved mechanical and thermal properties. Composition is useful for reusable heat-shield materials.
The effects of convective heating upon reusable surface insulation coatings were studied utilizing scanning electron microscopy, X-ray fluorescence, and X-ray diffraction. Samples of coated silica, mullite, and ceramic mullite fiber were cycled in an arc plasma stream up to 15 times for 15 minutes per cycle at surface temperatures simulating those on the space shuttle vehicle. The surfaces of ceramic mullite fiber and mullite coatings were roughened substantially by the convectively heated environment while the silica was significantly smoothed after testing. Scanning electron microscopy also showed surface cracking of varying degrees in all of the coatings. The surface chemistry of the coatings as examined by X-ray fluorescence revealed that significant changes in composition were occurring during cycling, particularly within the mullite coating.
Ceramic particle compaction as function of size, shape, loading rate and hardness for fused alumina, magnesia and mullite