O. Hunter

Grain-size dependence of microcrack initiation in brittle materials

In this paper, the energy criterion is extended to predict the relationship between the temperature of microcrack initiation (TMB) caused by thermal stressing in brittle materials and the grain size. The relation can be extrapolated to room temperature to provide an estimate of the critical grain size. When the relation was compared to literature data, it was found that: (1) the predicted inverse square root relation of TMB to grain size is satisfied; (2) the room temperature intercept on the grain-size axis agrees well with the measured critical grain sizes. Also presented is a graphical method, based on the proposed relation, by which an engineering estimate of the critical grain size may be made from a minimal set of data.

Technique for preparing highly-sinterable oxide powders

Abstract A technique for preparing highly sinterable rare-earth, hafnium, and zirconium oxide powders has been developed. Acetone and toluene hydroxide gels to give a uniform and rapidly drying powder. After calcination and firing, these powders yield nearly theoretically dense specimenss. A characterization of these powders was performed and related to processing variables.

Microcracking in Large-grain Al2O3

Abstract The critical grain size for microcracking in Al2O3 was estimated to be 70 μm by a method, based on fracture mechanics, which predicts a linear relationship between the temperature TMB at which microcracking begins and the reciprocal square root of the grain size. TMB was interpreted as the temperature at which, on cooling, the relation between Youngs modulus and the temperature departed from the expected linear behavior.

Influence of precipitation procedure on sinterability of Y2O3 prepared from hydroxide precursor

Abstract The sinterability of Y 2 O 3 prepared from reverse strike hydroxide precursors was found to be highly dependent on final pH and precursor dewatering procedure, high pH precursors yielding poorly-sinterable oxides if oven dried, but quite sinterable oxides if dewatered either by acetone-toluene-acetone or controlled-humidity treatments. Direct strike hydroxide precursors yielded highly-sinterable Y 2 O 3 regardless of final pH or dewatering procedure.

Microcracking behavior of monoclinic GD2O3

Abstract Youngs modulus versus temperature measurements were made for ten Gd 2 O 3 specimens ranging in grain size from 15 to 40 μm. The Youngs modulus versus temperature curve for each specimen exhibited hysteresis and, upon cooling, the curves departed from the expected linear behavior at some temperature ( T MB ) above room temperature; thus, each specimen apparently microcracked. The T MB and grain size ( GS ) data fit the relation T MB = − C(GS) − 1 2 + T 0 relatively well. The critical grain size of monoclinic Gd 2 O 3 was estimated to be approximately 14 μm, in agreement with experimental determination.

Digitally controlled measurement of sonic elastic moduli and internal friction by phase analysis

An automated system is described for measuring internal friction and elastic moduli using sonic resonance techniques. This mirocomputer‐controlled device does phase angle analysis in addition to traditional decay and peak‐width internal friction measurement. The apparatus may be programmed to make measurements at any sequence of temperatures between room temperature and 1600 °C.

Grain-size dependence of microcrack initiation in two-phase brittle systems

This research was supported by the National Science Foundation under Grant No. DMR 8018672.

Teaching Quality Assurance Fundamentals to Ceramic Engineering Students

One of the most powerful tools available to the practicing ceramic engineer is the use of statistical methods in making decisions which he faces on a daily basis. In teaching students about this powerful tool and its various applications, a major effort must be made in convincing the students that he can, in fact, make sound decisions using statistical data. The objective of this paper is to summarize the necessary topics which must be taught to undergraduate ceramic engineering students in order for them to appreciate this tool and have some understanding not only of how statistical quality control works but also why it works.