GB2321453A

GB2321453A - Ceramic body containing zirconium silicate

Info

Publication number: GB2321453A
Application number: GB9701561A
Authority: GB
Inventors: Hugh Padley
Original assignee: BERKSHIRE CHINA CO Ltd
Current assignee: BERKSHIRE CHINA CO Ltd
Priority date: 1997-01-25
Filing date: 1997-01-25
Publication date: 1998-07-29
Also published as: GB9701561D0; WO1998032710A1; AU5673698A

Abstract

A ceramic body contains zirconium silicate and may also comprise a clay, especially a Special Standard Porcelain clay, a flux and silica, all these components having a low content of iron, manganese and titanium. Articles made from the body are glazed and fired.

Description

CERAMIC BODY This invention concerns a ceramic body, and also a method of making a ceramic article.

The appearance of bone china is generally considered to be aesthetically pleasing. However, significant costs are involved in producing bone china due to the cost of the bone, and also the fact that it is generally not possible to produce articles by a single firing and certainly a single fast firing. The aesthetic appearance of porcelain is often, and particularly in the U.K., not considered as pleasing, particularly as white porcelain tends to have a slight blue-grey tinge, as opposed to the slight red-yellow tinge of white bone china.

All percentages expressed in this specification are by weight, and individual elements are expressed by oxide weight.

According to the present invention there is provided a ceramic body, the body including zirconium silicate.

The body preferably comprises less than 20% zirconium silicate, and desirably 5-15% zirconium silicate. The zirconium silicate preferably has a low total iron, manganese and titanium content, and desirably less than 0.4% iron, less than 0.05% titanium, and/or less than 0.01% manganese. The zirconium silicate preferably has a small particle size, and the mean particle size is preferably in the ranee 1 to 5 microns. A suitable form of zirconium silicate

would be Zircosil (Cookson).

The body preferably comprises 30-50% clay. The clay preferably has a low combined iron, manganese and titanium content, and desirably less than 0.5% iron, less than 0.1% titanium, and/or less than 0.01% manganese.

The body preferably comprises 10-30% flux. The flux preferably has a low combined iron, manganese and titanium content, and desirably less than 0.1% iron, less than 0.1% titanium, and/or less than 0.01% manganese The body may also comprise a high temperature flux, such as talc.

The body preferably comprises 15-35% silica, which desirably has a low combined iron, manganese and titanium content, and desirably less than 0.05% iron, less than 0.1% titanium, and/or less than 0.01% manganese The body may contain a plasticiser, which may be bentonite.

The body may contain a colour stain, which may be a cobalt stain.

The invention also provides a method of making a ceramic article, the method comprising shaping a piece of clay with a body according to any of the preceding eight paragraphs, applying a glaze to the shaped clay, and subsequently firing the shaped clay.

The shaped clay is preferably only fired once, and desirably in a fast fire schedule. The peak firing temperature is preferably between 1150 and 1225"C.

The glaze is preferably unleaded, and desirably substantially transparent.

An embodiment of the present invention will now be described by way of example only.

A clay body according to the present invention was made with the following components: Weight % SSP China Clay 39.48 Norfloat Potash Feldspar (Cookson) 25 Talc 3 HPF2 Sand (Hepworth) 22 Zircosil 1 (Cookson) 10 Bentonite 0.5 Cobalt Stain 0.02 The SSP China Clay (Special Standard Porcelain) has a low iron content of 0.39%, and also a low manganese and titanium content. This clay is very white in colour. The talc acts as an auxiliary flux and reduces the maturing temperature of the body. The sand also has a low combined iron, manganese and titanium content. The zirconium silicate has a low combined iron, manganese and titanium content, with 0.25-0.40% iron, 0.02-0.05% titanium, and only a trace of manganese. The zirconium silicate also has a small mean particle size, within the range 1 to 5 microns. This latter feature provides for a high amount of reaction, as well as more scatter of particles, thereby increasing the colour properties provided by this white component. The bentonite acts as a plasticiser and can be either Vee Gumlor bentonite L. The cobalt stain provides a very slight blue tint to the body.

The clay is mixed with water by blunging to give subsequent workability.

This blunging could take place for example at high shear for around thirty minutes, or at low speed for around one to two and a half hours. Once sufficient workability has been obtained, the other ingredients are mixed in.

The mixture is then sieved and passed over magnets to remove magnetic material such as metallic iron. The material is then dewatered in a filter press.

The dewatered material is de-aired in a pug mill and it is important to ensure that the pugging is carried out efficiently to exclude all air. The material is extruded to form a pug which is cut to an appropriate size and placed into a mould to make for example a mug. A roller head is applied to shape the pug. A handle is made by slip casting and adhered to the shaped body with slip. The shaped item is then dried.

A lead-free transparent glaze was formed in a conventional manner from the following components: Weight % Zinc Oxide 4.16 Whiting 13.09 Quartz 30.40 Petalite 20.00 S P China Clay 4.48 Dolomite 4.16 Norfloat K 23.71 This glaze was applied to the shaped clay by dipping, followed by subsequent drying. The glazed article was fired in a single fast fire schedule.

In this schedule the article is brought up to a peak firing temperature of 1200"C in one hundred and twenty minutes, and held at this peak temperature for a further thirty minutes. Rapid cooling then took place over ninety minutes.

The mug formed by this method had a pleasing white appearance, generally similar to that provided by bone china. This method and body permitted only a single fast firing to be used. By using the zirconium silicate in combination with a low combined iron, manganese and titanium content, a good white body colour is obtained which can be clearly seen by virtue of the transparent glaze. Also the high refractory index of zirconium silicate helps in providing the strong white colour. This material also acts as a refractory component to prevent sagging of the product. The fired article has a coefficient of water absorption of no more than 0.5%. The body and method according to the present invention permit relatively thin walled articles to be made.

Various modifications may be made without departing from the scope of the invention. For example, a wide range of clays could be used as long as they have a low total iron, manganese and titanium content. White clays such as New Zealand china clay may be suitable if a required plasticity can be obtained.

The proportion of clay could be different to that in the above example. Also, a wide range of fluxes, whether natural or synthetic, could be used and again in different proportions.

In some instances a high temperature flux may not be necessary. Again a wide range of different silicas could be used, and in different proportions.

The zirconium silicate could be of a different type and again could be provided in different proportions. Different plasticisers could be used, and a plasticiser may not always be required.

A wide range of different glazes could be used, as long as appropriate transparency is achieved so as not to affect the colour of the underlying body.

Appropriate glazes can obviously be chosen to correspond to the specific bodies to have the required relative thermal expansions. A wide range of articles could be made using a body and method according to the present invention.

Different firing conditions can be used. For the above described body the peak firing temperature can range from 1150 to 1225"C with a corresponding Bullers ring range of 27-34 pips.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAJMS:-

1. A ceramic body, the body includes zirconium silicate.

2. A ceramic body according to claim 1, wherein the body comprises less than 20% zirconium silicate.

3. A ceramic body according to claim 2, wherein the body comprises 5-15% zirconium silicate.

4. A ceramic body according to any of the preceding claims, wherein the zirconium silicate has a low total iron, manganese and titanium content.

5. A ceramic body according to any of the preceding claims, wherein the zirconium silicate contains less than 0.4% iron.

6. A ceramic body according to any of the preceding claims, wherein the zirconium silicate contains less than 0-05% titanium.

7. A ceramic body according to any of the preceding claims, wherein the zirconium silicate contains less than 0.01% manganese.

8. A ceramic body according to any of the preceding claims, wherein the zirconium silicate has a small particle size.

9. A ceramic body according to claim 8, wherein the mean particle size of the zirconium silicate is in the range of 1 to 5 microns.

10. A ceramic body according to any of the preceding claims, wherein the zirconium silicate is in the form of Zircosil 1 (Cookson).

11. A ceramic body according to any of the preceding claims, wherein the body comprises 30-50% clay.

12. A ceramic body according to any of the preceding claims, wherein the body comprises clay which has a low combined iron, manganese and titanium content.

13. A ceramic body according to any of the preceding claims, wherein the body comprises clay which contains less than 0.5% iron.

14. A ceramic body according to any of the preceding claims, wherein the body comprises clay which contains less than 0.1% titanium.

15. A ceramic body according to any of the preceding claims, wherein the body comprises clay which contains less than 0.01% manganese.

16. A ceramic body according to any of the preceding claims, wherein the body comprises 10-30% flux.

17. A ceramic body according to any of the preceding claims, wherein the body comprises a flux which has a low combined iron, manganese and titanium content.

18. A ceramic body according to any of the preceding claims, wherein the body comprises a flux which has less than 0.1% iron.

19. A ceramic body according to any of the preceding claims, wherein the body comprises a flux which has less than 0.1% titanium.

20. A ceramic body according to any of the preceding claims, wherein the body comprises a flux which has less than 0.01% manganese.

21. A ceramic body according to any of the preceding claims, wherein the body comprises a high temperature flux.

22. A ceramic body according to Claim 21, wherein the high temperature flux comprises talc.

23. A ceramic body according to any of the preceding claims, wherein the body comprises 15-35% silica.

24. A ceramic body according to any of the preceding claims, wherein the body comprises silica which has a low combined iron, manganese and titanium content.

25. A ceramic body according to any of the preceding claims, wherein the body comprises silica with less than 0.05% iron.

26. A ceramic body according to any of the preceding claims, wherein the body comprises silica with less than 0.1% titanium.

27. A ceramic body according to any of the preceding claims, wherein the body comprises silica with less than 0.01% manganese.

28. A ceramic body according to any of the preceding claims, wherein the body contains a plasticiser.

29. A ceramic body according to Claim 28, wherein the plasticiser comprises bentonite.

30. A ceramic body according to any of the preceding claims, wherein the body contains a colour stain.

31. A ceramic body according to Claim 30, wherein the stain is a cobalt stain.

32. A method of making a ceramic article, the method comprises shaping a piece of clay with a body according to any of Claims 1 to 31, applying a glaze to the shaped clay, and subsequently firing the shaped clay.

33. A method according to Claim 32, wherein the shaped clay is only fired once.

34. A method according to Claims 32 or 33, wherein the shaped clay is fired in a fast fire schedule.

35. A method according to any of Claims 32 to 34, wherein the peak firing temperature is between 1150 and 12250C.

36. A method according to any of Claims 32 to 35, wherein the glaze is unleaded.

37. A method according to any of Claims 32 to 36, wherein the glaze is substantially transparent.

38. A ceramic body substantially as hereinbefore described.

39. A method of making a ceramic article, the method being substantially as hereinbefore described.

40. Any novel subject matter or combination including novel subject matter disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.