United Kingdom Atomic Energy Authority

James L Woodhead

James A Cairns

Robert L Nelson

Alan Wilcockson

Keith Taylor Scott

John D Ramsay

Graham Raw

Roger W Davidge

The invention provides a process for the preparation of a dispersible cerium compound (i.e. a cerium compound which may be dispersed in a liquid to give a colloidal dispersion (i.e. a sol)). The process involves replacing a first species of ions associated with the cerium compound by a second species of ions (e.g. hydroxyl ions) and subsequently replacing the second species of ions of the cerium compound with a third species of ions (e.g. counter-ions). The replacing of the ions may be effected, for example, by ion-exchange. Cerium (IV) oxide hydrate is an example of a cerium compound which can be made dispersible in accordance with the invention.

Preparation of dispersible cerium compound

The present invention relates to compounds and more particularly to cerium compounds and cerium compounds in association with other elements. The invention provides a process for the preparation of a dispersible product containing a cerium compound which comprises heating a cerium (IV) oxide hydrate in the presence of a salt to cause deaggregation of aggregated crystallites in the cerium (IV) oxide hydrate and produce a dispersible product containing a cerium compound. The salt may be chosen such that a selected chemical element is present in the dispersible product.

Process for the preparation of a dispersable product containing a cerium

The present invention relates to materials and more particularly to particulate materials suitable for use as thermal spraying powders. There is disclosed a process for the preparation of a particulate material suitable for use as a thermal spraying powder which includes treating a mixture comprising an inorganic substance as a major component (as defined in the Specification) and a sol to gel the sol thereby to form an intermediate material comprising inorganic substance and gel and heating the intermediate material. One example of thermal spraying is plasma spraying.

Materials

Sintered materials are known comprising a ceramic matrix (e.g. of Al.sub.2 O.sub.3) and, distributed therein, a refractory material in a metastable, high temperature enantiotropic form of higher density than its room temperature enantiotropic form such as ZrO.sub.2 which has a metastable tetragonal form and a room temperature monoclinic form. The sintered materials have enhanced fracture and bending strength. The invention provides a method of making such materials from a mixture where the refractory material and optionally the ceramic material are in the form of a sol. The mixture is dried and subsequently sintered to give a product where the refractory material is distributed very uniformly and in its metastable form. Improved properties have been obtained by including a stabilizing agent (e.g. Y.sub.2 O.sub.3) in the final product.

Ceramic materials by sol-gel route

Carbonaceous deposition on the surface of steel cracker tubes in chemical plant for the thermal cracking of hydrocarbons is a serious problem. It is met, in the invention, by providing the surface with a refractory oxide coating by contacting the surface with a sol comprising an aqueous dispersion of substantially unaggregated primary particles, the sol being capable of conversion to a gel the bulk density of which being at least 40% of the theoretical density of the refractory oxide when measured at ambient temperature and the gel being convertible to the refractory material, converting the sol to the gel, and firing.

Method of coating steel substrates to reduce carbonaceous deposition

A catalyst suitable for use in the treatment of motor vehicle exhaust emissions is made by contacting a substrate, preferably of an aluminium bearing ferritic alloy, with a first sol of refractory material followed by drying and firing, and preferably then contacting with a second sol of refractory material, which additionally contains a salt convertible to catalytic material, followed by drying and firing. The sols are obtained from refractory material, e.g., alumina, made by a vapor phase condensation method.

Method of preparing a catalyst

The present invention relates to compounds and more particularly to cerium compounds. According to one aspect of the present invention there is provided a process for the preparation of a dispersible cerium compound which comprises heating a substantially dry cerium (IV) oxide hydrate in the presence of a deaggregating agent to cause deaggregation of aggregated crystallites in the cerium (IV) oxide hydrate and produce a dry dispersible cerium compound.

Cerium compounds

The invention is concerned with providing substrates with coatings obtainable from sols, for example to protect the substrate (such as in nuclear reactors or hydrocarbon cracking plant) or to provide a carrier for catalytically active material. Hitherto, coatings obtained from sols have had a high porosity and high surface area so that they have not been entirely satisfactory for the above applications. In the invention, dense, low-porosity coatings are provided by contacting the substrate with a sol of refractory material (e.g. CeO.sub.2 or SiO.sub.2) convertible to a gel of density at least 40% of the theoretical density of the refractory material, and converting the sol to the gel. Optionally, the gel may be converted to a ceramic coating by firing.

Method of producing dense refractory oxide coatings on metallic

The invention is concerned with the preparation of dispersions and particularly with the preparation of dispersions of cerium compounds. The invention provides for the preparation of an aqueous dispersion of ceria or hydrated ceria by a process which includes acid treatment of cerium IV hydroxide. Aqueous dispersions in accordance with the present invention find application in a number of technical fields (e.g. in the preparation of dense ceria coatings for use in catalysis and protective coatings, for example, for metals and alloys).

Process for preparing aqueous dispersion of ceria and resulting product

A colloidal dispersion is disclosed in which colloidal particles of an inorganic substance, and a compound of a Group IIA, or of a Group IIIA, or of a lanthanide (rare earth) element are dispersed throughout a liquid. The colloidal dispersion can be dried to form gels and the gels calcined to form porous ceramic materials.

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Didcot, United Kingdom

James L Woodhead