United Kingdom Atomic Energy Authority

Peter Kennedy

Kenneth Parkinson

Bernard North

John O Ware

A method of producing spheroids comprising a coherent mixture of carbon and silicon carbide powders for subsequent siliconizing and if desired grinding to improve their sphericity, involves the steps of preparing a slip consisting essentially of a suspension of silicon carbide and carbon powders in a liquid, and introducing drops of the slip into a medium in which the drops form individual solid casts. The said liquid may be water to which a dispersant (which may be a deflocculent) has been added. Sodium alginate may advantageously be added to the slip. The said medium may be an aqueous solution of an electrolyte such as a calcium salt. An organic liquid phase, immiscible with the electrolyte, may be provided on the surface thereof. Examples of organic liquid are petroleum ether, kerosene, and cyclohexanol.

Reacting-bonded silicon carbide spheroids and process of making

The production of a reaction-bonded silicon carbide artefact by siliconizing a green body comprising a coherent mixture of carbon and silicon carbide particles includes the step of forming a layer of carbon of open cellular structure on the green body by carbonization of a sleeve or tube on the green body by carbonization of a sleeve or tube of carbonaceous material in contact with the body. This material may be impregnated with particulate silicon suspended in water or a paste. The material may be a quilted or woven fabric of fibrous material or it may be in the form of paper. The material is in a flexible strip or sheet form to enable it to be wrapped around the green body or a former about which the green body is to be formed.

Production of reaction-bonded silicon carbide bodies

A silicon carbide-silicon matrix composite incorporates unreacted coarse carbon particles (e.g. graphite particles) dispersed throughout the composite. The coarse particles are incorporated in a coherent mixture of carbon and silicon carbide powders which, after compaction, is infiltrated with molten silicon to form a matrix of reaction bonded silicon carbide in a substantially continuous free silicon carbide phase. By using coarse carbon particles of density of at least 0.963 g/ml, the molten silicon reacts only with the surfaces of those particles which may as a result remain unreacted and dispersed throughout the composite.

Reaction bonded silicon carbide artefacts

Reaction-bonded silicon carbide artefacts are produced by siliconizing a green body formed from a coherent mixture of silicon carbide and carbon powders. The surface of the green body is coated with a paste comprising silicon powder suspended in a carbonizable viscous medium which, on heating of the coating, is converted to an open cellular carbon structure and then, on siliconizing the green body, to a silicon carbide skeleton through which molten silicon is drawn.

A reaction-sintered silicon carbide body having portions differing from each other in free silicon content and such a body with a surface layer rendered more readily abradable than the remainder of the body by the removal of free silicon from the surface layer. It has a particular application in the provision of shrouds for gas turbines, which can be produced by slip-casting in two stages.

Silicon carbide bodies and their production

A reaction bonded silicon carbide body in which there is included in the free silicon phase of the body to modify the electrical resistivity of the body, at least one of the Group III elements boron and indium or at least one of the Group V elements antimony and tantalum. The element may be added in compound form and may be included in the green body prior to reaction bonding or in the silicon with which it is reaction bonded.

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Preston, United Kingdom

Peter Kennedy