Review: Fabrication of engineering ceramics by injection moulding. I. Materials selection

Thermodynamic analysis of the high-temperature stability of silicon nitride and silicon carbide

The isothermal oxidation behavior of commercial hot-pressed Si3N4 was evaluated for temperatures from 1300° to 1500°C Multiphase scales were formed, consisting mainly of α-cristobalite and enstatite A large increase in reaction rate above 1450°C is believed to be caused by melting in the scale and the consequent increase in the rate of oxygen transport No oxygen pressure dependence was observed at 1400°C over the oxygen pressure range 10-9 atm to 600 torr However, a small decrease in the kinetics was observed when measurements were made in reduced total pressures of oxygen as compared to O2/N2mixtures at a constant total pressure

Oxidation of Si3N4 in the Range 1300° to 1500°C

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. An electrically-insulating material 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 article 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 and 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.

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

The strength of 1500 sintered alumina and reaction-bonded silicon nitride flexure specimens was measured by seven laboratories in four countries. Consistent results were obtained only with a well-defined standard test method. Older procedures were less consistent or gave erroneous results. A simple statistical procedure allowed a quick estimate of consistency, and outlier samples could be appraised for the likelihood of their occurrence.

Advanced Structural Ceramics: A Round Robin

: The demonstration of uncooled brittle materials in structural applications at 2500 F is the objective of the 'Brittle Materials Design, High Temperature Gas Turbine' program. Ford Motor Company, the contractor, will utilize a small vehicular gas turbine while Westinghouse, the subcontractor, will use a large stationary gas turbine. A significant achievement in the vehicular turbine project was the successful engine test, 175 hours at 1930 F, of a silicon nitride stator. Durability testing on a nose cone was extended to 246 hours, equalling the previously demonstrated durability of 245 hours on 1st and 2nd stage rotor tip shrouds. A 'Refel' silicon carbide combustor previously demonstrated 171 hours durability, crack-free, including 20 hours at 2500F. Two additional combustors of the same material were tested for 10 hours each. Eight hours of testing the stationary ceramic flowpath at 2500 F were accumulated; non-catastrophic cracks occurred in the nosecone and stator after surviving three hours crack-free. Two stator vanes survived 1000 cycles to 2500-2600 F plus 3720 cycles to 2900 F in the thermal shock rig. A concentrated effort on turbine rotor fabrication development was initiated. Improvements in the rotor fabrication processes have been made. Reduction of the MgO content increased the hot strength of the hot-pressed silicon nitride rotor hub material. Over 500 rotor blade rings were fabricated using the injection molding process and some high density rotor blade rings were also fabricated by slip-casting.

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Brittle Materials Design, High Temperature Gas Turbine

A thin outer metallic housing surrounds and is spaced from a one-piece cylindrical ceramic liner that insulates, supports and houses high temperature and rotating parts of the engine, the end faces of the liner constitute rubbing seal surfaces against which are directly mounted ceramic core rotating regenerators, the liner and housing having aligned holes through which is mounted the inline hot gas flow path components.

One-piece ceramic support housing for a gas turbine with a rotary regenerator

Design with Structural Ceramics

Four-wheel driven gas turbine vehicle with clutch-controlled drive to front axle

A porous ceramic regenerator core its in the shape of a 12-sided regular polygon is surrounded by a metal ring gear having gear teeth on its exterior surface. Locating members transmit driving torque from the ring gear to the core while permitting the core to move radially and axially relative to the ring gear. Narrow slots can be cut into the outer edge of the ceramic core to relieve thermally induced stresses.

Arthur F Mclean

Papers

Brittle Materials Design, High Temperature Gas Turbine

One-piece ceramic support housing for a gas turbine with a rotary regenerator

Design with Structural Ceramics

Four-wheel driven gas turbine vehicle with clutch-controlled drive to front axle

Gas turbine heat exchanging system using flexible locating members for torque transmission