A review of the processing, composition, and temperature-dependent mechanical and thermal properties of dielectric technical ceramics

Abstract

The current review uses the material requirements of a new space propulsion device, the Variable Specific Impulse Magnetoplasma Rocket (VASIMR ® ) as a basis for presenting the temperature dependent properties of a range of dielectric ceramics, but data presented could be used in the engineering design of any ceramic component with complementary material requirements. A material is required for the gas containment tube (GCT) of VASIMR ® to allow it to operate at higher power levels. The GCT's operating conditions place severe constraints on the choice of material. A dielectric is required with a high thermal conductivity, low dielectric loss factor, and high thermal shock resistance. There is a lack of a representative set of temperature-dependent material property data for materials considered for this application and these are required for accurate thermo-structural modelling. This modelling would facilitate the selection of an optimum material for this component. The goal of this paper is to determine the best material property data values for use in the materials selection and design of such components. A review of both experimentally and theoretically-determined temperature-dependent & room temperature properties of several materials has been undertaken. Data extracted are presented by property. Properties reviewed are density, Young's, bulk and shear moduli, Poisson's ratio, tensile, flexural and compressive strength, thermal conductivity, specific heat capacity, thermal expansion coefficient and the factors affecting maximum service temperature. Materials reviewed are alumina, aluminium nitride, beryllia, fused quartz, sialon and silicon nitride.

Regression analysis of temperature-dependent mechanical and thermal properties of dielectric technical ceramics

“…The dataset analysed contains experimental observations from numerous different experiments [1], and differing numbers of observations are reported from each experiment. A procedure is required to ensure that experiments reporting observations at closely spaced temperature intervals do not unduly influence the calculation of the regression coefficients over those experiments reporting observations at fewer temperatures.…”

“…Density measurements come from both X-ray diffraction measurements and direct density estimates [1]. These two measurements are used together for some but not all materials to estimate density.…”

“…Where lattice parameter data are also available, global regression analysis can be performed on these and macoscopic CTE data in order to yield the best overall data set. Data for mean and instantaneous CTE, definitions of which may be found in [1], must be clearly distinguished. In this work 0 • C is taken as the reference temperature for the mean CTE.…”

“…The data of Munro [10] is for the mean CTE, so this has been converted to instantaneous CTE values. For aluminium nitride and for beryllia the data presented by Slack & Bartram [17], not included in the preceeding work by the current authors [1], are considered the most reliable are used as the recommended curve. The regression coefficients in Table 4 for aluminium nitride and beryllia are for a curve fit of these data.…”

“…authors for material specifications of alumina, aluminium nitride, beryllia, fused quartz, sialon and silicon nitride [1]. The material specifications have been chosen to best reflect advanced commercially available material grades.…”