GB2139642A

GB2139642A - Ceramic stains

Info

Publication number: GB2139642A
Application number: GB08410313A
Authority: GB
Inventors: John Kenneth Olby
Original assignee: HMR Group Ltd
Current assignee: HMR Group Ltd
Priority date: 1983-05-10
Filing date: 1984-04-19
Publication date: 1984-11-14
Also published as: GB8410313D0; GB2139642B

Abstract

A grey ceramic stain which consists of zircon containing vanadium sulphide or tin sulphide as a colourant.

Description

SPECIFICATION Improvements in ceramic stains This invention provides a grey stain which is suitable for use in ceramic glazes and consists of zircon containing vanadium sulphide or tin sulphide as a colourant.

The stains according to the invention may be made using a chemically reactive zirconia and silica, the desirable physical state of which varies according to the method of preparation of the stain. Suitabie sources of zirconia are hydrous zirconia or milled chemical zirconia. Silica may be used in the form of milled quartz sand or of precipitated silica.

The sulphide chromophore may be generated during the firing of the stain by the reaction of a source of vanadium pentoxide or tin oxide, a source of sulphur and a reducing agent, e.g.

carbon. Suitable materials are ammonium sulphate or sulphur as the source of sulphur, sugar as the source of carbon, ammonium metavanadate or vanadium pentoxide as the source of vanadium pentoxide and stannic oxide as the source of tin oxide. The stains may thus be produced by firing a mixture of reactive zirconia, preferably hydrated, silica, a source of vanadium pentoxide or of tin oxide, a source of sulphur, a reducing agent and a conventional mineraliser for example lithium fluoride or sodium fluoride, which assists in the reaction of the zirconia and silica to form zircon. The sulphides incorporated in the zircon are probably V2S3 and Sn S, though this is not certain.

The most intense stains are prepared by coprecipitation of the zirconia and the source of vanadium pentoxide or of tin oxide. Stannous sulphate is a convenient source of soluble tin for the coprecipitation but vanadium only has sufficient solubility in a reduced state. Reduction and solubilisation of vanadium pentoxide may be effected with a hydrazinium salt or a hydroxylammonium salt.

Free sulphide in the fired stains must be removed to prevent blistering in glaze. This may be effected either by a second oxidising fire of the stain in an open crucible or by milling the stain and then leaching it with hot dilute nitric acid. In cases where complete removal of the free sulphide is more difficult, a mixture of concentrated nitric and sulphuric acid may be used.

The invention will now be further explained by reference to the following Examples: 1. 76 ml zirconium acetate solution of density 1.30 containing approximately 22% by weight ZrO2 was hydrolysed with a mixture of 1 5 ml 0.880 ammonia and 30 ml water.

The product was washed, filtered and sucked dry, then mixed with the following ingredients: 11.49 ground quartz sand 1.79 lithium fluoride 2.7g sodium fluoride 6.19 ammonium sulphate 6.19 sugar 3.69 ammonium metavanadate.

The mixture was fired for 1 hour at 830"C in a covered crucible. The product was milled, extracted with hot dilute nitric acid, washed and dried. The product was a grey glazestable stain.

2. 76 ml zirconium acetate solution of density 1.30 containing approximately 22% by weight ZrO2 was hydrolysed with a mixture of 1 5 ml 0.880 ammonia and 30 ml water.

The product was washed, filtered and sucked dry, then mixed with the following ingredients: 11.49 ground quartz sand 1 .7g lithium fluoride 2.7g sodium fluoride 2.7g sodium fluoride 4.1g ammonium sulphate 5.39 sugar 4.59 stannic oxide The mixture was fired for 1 hour at 830"C in a covered crucible. The product was milled, extracted with hot dilute nitric acid, washed and dried. The product was a grey glazestable stain.

3. 100 ml zirconium acetate solution containing 22 by weight ZrO2 6g vanadium pentoxide 6g hydrazinium sulphate were mixed and made up to 300 ml with water. The mix was heated until it became blue and all suspended matter had dissolved.

The product was added dropwise to a mechanically stirred solution of 40 ml 0.880 ammonia in 1000 ml water. The resulting coprecipitate was washed, filtered and dried at 130"C. It was then milled, suspended in 35 ml sodium silicate solution (density 1.50) made up to 200 ml with water. 25% v/v sulphuric acid was added to the liquor until it gelled. The product was washed, filtered and dried and used to make up the following mix: 24.09 dried coprecipitate 1.5g sulphur 2.2g sugar 0.5g lithium fluoride These components were mixed and fired + hour at 1050"C in a covered crucible. The product was milled, extracted with a mixture of concentrated nitric and sulphuric acids and washed to give a strong grey glaze-stable stain.

10.79 stannous sulphate was dissolved in 200 ml water and 100 ml zirconium acetate solution was added. The product was added dropwise to a mechanically stirred solution of 32 ml 0.880 ammonia in 1000 ml water.

The resulting coprecipitate was washed, filtered and dried at 130"C. The product was milled, suspended in 35 ml sodium silicate solution (density 1.50) made up to 200 ml with water. 25 v/v sulphuric acid was added to the liquor until it gelled. The product was washed, filtered and dried and used to make up the following mix: 41.09 dried coprecipitate 1.39 sulphur 2.49 sugar 0.4g lithium fluoride These components were mixed and fired Q hour at 1050"C in a covered crucible. The product was milled, leached with nitric acid, and washed to give a grey glaze-stable stain.

Claims

1. A grey ceramic stain which consists of zircon containing vanadium sulphide or tin sulphide as a colourant.

2. A method preparing a stain as claimed in claim 1, which comprises firing a mixture of reactive zirconia, silica, a source of vanadium pentoxide or of tin oxide, a source of sulphur, a reducing agent and a mineraliser and removing free sulphide from the fired stain.

3. A method as claimed in claim 1, which comprises the preliminary step of coprecipitating the zirconia and the source of vanadium pentoxide or of tin oxide.

4. A method as claimed in claim 2 or claim 3, in which free sulphide is removed by an oxidising fire.

5. A method as claimed in claim 2 or claim 3, in which free sulphide is removed by milling the fired stain and then leaching it with hot dilute nitric acid.

6. A method as claimed in claim 2 or claim 3, in which free sulphide is removed by milling the fired stain and then leaching it with a mixture of concentrated nitric and sulphuric acids.

7. A stain as claimed in claim 1, when prepared as described in any of the foregoing Examples.