Note: Descriptions are shown in the official language in which they were submitted.
1~8982
This invention relates to a method of making clayware
and in particular to the use of a novel flux for making clay-
ware.
Clayware such as porcelain, bone china, earthenware,
the so-called ironstones, aluminous ceramics, hotel wares and
ceramic tiles, is produced by firing a composition containing
clay and flux.
Fluxes conventionally used in making clayware, such
as exemplified above, are feldspars, nepheline syenite and
Cornish stone. U.S. Patent 3,704,146 describes fluxes for
"white~ware" ceramic compositions comprising clay, flint and
a flux, the fluxes being ground vitreou~ frits which may
contain up to about 45% by weight of boric oxide. U.S. Patent
4,219,360 describes use of B2O3 containing frits in manufac-
turing bone china. However, a frit i9 expensive to produce
because of the energy consumption, the need for refractory
furnace linings and because of the need to grind the product.
Furthermore, the frits have been found not to be suitable for
some clayware compositions due to slight leaching of boric
oxide from the frit during manufacture of ceramic articles,
for example, in preparing casting slips. U.S. Patents
3,303,036 and 3,532,522 also describe use of inorganic borates
in manufacturing ceramic ware.
Zeolites have been proposed as components of ceramic
compositions especially in the production of lightweight cera-
mics~ See, for example, Japanese Patent Nos. 69 23,815,
69 23,816 and 69 23,817 of Y. Ookawa all published October 9,
1969 (Chem. Abs. 79, 15378, 15352 and 15350 respectively),
Onoda Cement Co., Ltd. published June 11, 1973, (Chem. Abs. 79,
96,191). Howe~er, none of the zeolites are known to contain
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boron and the zeolites are used to confer refractory pro-
perties on the ceramics and are not used as fluxes.
The present invention provides a method of making
a clayware by firing a composition containing clay and a
boron-containin~ flux, wherein the flux i8 a synthetic alkali
metal and/or alkaline earth metal aluminosilicate having the
crystal structure of a zeolite and containing boron entrapped
within that structure. For convenience, the flux to be used
in accordance with the invention will be referred to as a
"boronated zeolite".
The boron component of the boronated zeolite is
less soluble than that of the ground vitreous frits. Thus,
when entrapped in a zeolitic structure, boron in its oxide
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~ 19L8982
1 form may be incorporated into clayware compositions in a
2 water insoluble form and can contribute its valuable fluxing
3 properties without detriment to the clayware products or to
4 their methods of manufacture. It may have been predicted
that the sodium oxide content of a sodium aluminosilicate
6 zeolite, such as sodalite hydrate, would contribute to the
7 fluxing properties of the material but it has been found that
8 this effect is not significant. However, it has clearly been
9 demonstrated that when boron is incorporated in the structure,
the resultant material becomes an unexpectedly powerful flux.
11 This is possibly because temperatures attained in clayware
12 manufacture are not sufficiently high to melt a zeolite and
13 activate its sodium oxide content as a flux; but when boric
14 oxide is also present that melting point is decreased allowing
sodium oxide and boric oxide to flux with synergistic effect.
16
17 Although the material used as flux according to
18 the present invention is termed "boronated zeolite" it should
~9 be appreciated that the presence of boron in the boronated
zeolite so reduces the water absorption capacity of the
21 material that it could be considered feldspathoidal rather
22 than zeolitic. -
23
24 A boron-containing zeolite has previously been
disclosed (J. Chem. Soc. (A) 1970, pp. 1516-23) and the use
26 of boron to accelerate zeolite formation without leaving
27 boron in the zeolite structure has also been disclosed
28 (German OS 24 50 708). The present invention resides in
29 the use of the boronated zeolite as one component, a flux,
of a composition for making clayware.
31
32 A preferred example of clayware in which the
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1 boronated zeolite can be used as flux is earthenware when a
2 composition containing ball clay, china clay, flint and the
3 boronated zeolite is fired. Other types of clayware in
4 which the boronated zeolite is valuable as a flux are
porcelain, bone china, ironstones and hotel wares as well
6 as ceramic tiles. Thus, for example, bone china can be
7 prepared by firing, usually at a temperature below about
8 1200C., preferably about 1180C.j a composition comprising -
9 calcined bone, china clay and the boronated zeolite.
10 ~ .
11 The boronated zeolite can be synthesised in the
12 form of fine crystals, for example having a particle size
13 below 5 microns, which are of a size very suitable for use
14 in the production of clayware. There is thus no need to
15 resort to grinding as with the vitreous frits previously .
16 used as boron-containing fluxes. In addition, it has been
17 found that bone china made according to this invention with
18 a boronated zeolite flux has a translucency at least equal
19 to that of bone china made with a conventional flux and that
this translucency can be achieved at a lower firing temperature
21 and in a shorter firing time.
22
23 The boronated zeolite flux used according to the
24 present invention can be made by any of the conventional
processes for hydrothermal crystallisation of zeolites, for
26 example sodalite hydrate, from a source of silica, a source
27 of alumina and a source of alkali metal or alkaline earth
28 metal (such as sodium,-calcium, potassium, magnesium,
29 lithium, but preferably a source of sodium), but with a
source of boron such as boric acid or a sodium borate in
31 the synthesis mixture: The resultant zeolite has a B2O3
32 content of about 2 to 10 per cent by weight, preferably
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1 about 3 to 7.5 per cent B2O3.
3 Two examples of the production of a boronated zeolite
4 are as follows:
S . '
6 Example 1
8 1712 g. sodium hydroxide and 751 g. borax decahydrate
9 were dissolved in 4000 g. distilled water in a stainless steel
beaker. 1085 g. china clay having a particle size below 1
11 micron were added and the mixture was stirred for 24 hours
12 at 85C. (From observation, it appeared that 24 hours for
13 crystallisation was more than needed; crystallisation appeared
14 to be complete after about 6 hours.) After filtering, washing
well with distilled water, and drying overnight at 130C., .
16 1175 g. of product were obtained. Its X-ray diffraction
17 powder pattern was substantially identical to that of the
18 mineral nosean confirming the skeletal structure of the
19 cage around the boron atom. Chemical analysis showed that
the product contained 20.5% Na2O, 5.0~ B2O3, 31.4~ A12O3 and
21 39.8~ ~iO2, the balance being water ~all percentages being by
22 weight). The particle size was mostly less than 5 microns.
2~ 10 g. of product were stlrred with 100 g. distilled water for
24 6 hours at 25C but no more than one fiftieth of the B2O3 was
25 leached out.
26
27 Example 2
28
29 A boronated zeolite having the same properties as
that produced by the method of Example 1 was made using sodium
31 aluminate and sodium silicate as the source of alumina and
32 l ¦ sil a, instead of china clay
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1 The following Examples illustrate the present inven-
2 tion.
4 Example 3
'
6 The boronated zeolite made by Example 1 was mixed
7 with china clay and calcined bone to form a body mix for
8 making bone china of the following composition:
9 Calcined bone 55 parts by weight
China clay 25 parts by weight
11 ¦ Boronated zeolite 20 parts by weight
12 ¦ ' This mix was made into a casting slip with 50 parts
13 of water using Dispex N40 (a polyacrylate) as deflocculant.
14 Discs 4.4 cm. in diameter x 0.3 cm. were cast and, after
drying, were fired using a heating rate of 150C/hour to a
16 ~inal temperature of 1180C. After holding at this temperature
17 for 2 hours, the discs were allowed to cool slowly. The
18 apparent porosity wa's found to be 2.1% and the translucency
19 was found to be 40% more than that of a standard bone china
fired at 1250C. Translucency is expressed as the amount of '
21 light transmitted compared with standard bone china fired at
22 1250C.
23 '
24 Example 4
26 To illustrate the advantages of the boronated
27 zeolites as fluxes for clayware, comparative trials were
28 carried out between body mixes containing the boronated
29 zeolite of Example 1 and body mixes containing respectively
as fluxes sodalite and "Zeolite A".
31 .
32 The procedure was as follows:
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1 Body mixes were prepared to the following composition:
2 Calcined bone 55 parts by weight
3 China clay 25 parts by weight
4 Flux 20 parts by weight
200 g. of the body mix were blunged with 100 ml. of
6 water to form a slip. Dispex N40 was used as deflocculant.
8 Discs 4.4 cm. diameter x 0.3 cm. were cast, dried
9 and fired to various temperatures at a heating rate of 150C/hr.
The discs were held for 2 hours at each temperature and then
11 allowed to cool. After cooling, translucency and apparent
2 porosity measurements were carried out.
14 The results were as shown in Table 1.
18
19
22
23
24
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1 These results indicate that neither "Zeolite A" nor
2 sodalite is a suitable flux material.
4 The boronated zeolite shows good fluxing properties
at the firing temperature of 1180C. Discs fired at the
6 higher temperatures of 1220 and 1255C. were found to be
7 badly bloated and distorted indicating overfiring.
9 Discs containing "Zeolite Al' or sodalite were not
adequately fired even at 1255C. as indicated by high apparent
11 porosity and low translucency.
12 I
13 Examples 5-7
14
Trials were carried out comparing earthenware body
16 mixes containing a boronated zeolite with a standard earthenware
17 body mix.
18
19 Body mixes were prepared to the following compositions
in which parts are by weight:
21
A* B C D* E*
22 Ball clay 25 25 25 25 25
23 China clay 25 25 25 25 25
Flint 35 35 35 35 35
24 Cornish stone 15
Zeolite - 3 S 5 5
26 ~hese mixes were made up as castins slips as follows:
A* B C D* E*
27 Ball clay 50 50 50 50 50
28 China clay 50 50 50 50 50
Flint 70 70 70 ~70 70
29 Cornish stone 30 - - - -
Zeolite - 6 10 10 10
31 Water 95 90 80 80 80
32 Dispex N40 0.8 0.8 0.8 0.8 0.8
*Comparative
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1 Discs 4.4 cm. diameter x 0.3 cm. were cast from
2 each slip, dried and fired according to the following Examples.
3 (Zeolite in B and C = boronated zeolite: in D = sodalite
4 hydrate: in E = Zeolite A)
6 Example 5
8 Discs were fired at different temperatures as shown
9 in Table 2 in a gradient kiln at a heating rate of 300C. per
hour and then allowed to cool. Apparent porosity and bulk
11 density measurements were carried out after cooling. The
12 results obtained are shown in Table 2.
13 ,
14 TABLE 2
_
16
17 (a) Apparent Porosity %
_
18 Temp (C.) A* B C D* E*
19 1205 12.0 10.0 2.5 9.2 13.6
1155 18.9 15.3 12.4 15.6 20.1
21 1095 26.8 22.9 19.0 22 7 26.7
22
23 (b) Bulk density g/cm3
24 Temp (C.) A* B C D^ E*
1205 2.20 2.22 2.29 2.24 2.16
26 llS5 2.07 2.14 2.19 2.14 2.05
27 1095 1.88 1.99- 2.06 1.99 1.89
28 *Comparative
29 Example 6
31 Example 5 was repeated but the discs were given a one
32 hour soak at the highest temperature. As before, apparent ?
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1 porosity and bulk density measurements were carried out after
2 cooling. The results obtained are shown in Table 3.
4 TABLE 3
S
S Rpparent porosity % Bulk density g/cm
7 Temp (C.) A* B C A* B C
9 1265 6.64.5 0.052.272.27 2.32
1240 9.07.6 0.062.242.26 2.31
1195 13.411.6 6.12.18 2.21 2.28
11 .
12
13 Example 7
14
Discs were fired at different temperatures in a gradi,ent
16 kiln at a heating rate of 50C. per hour with a two hour soak at
17 the highest temperature. Apparent porosity and bulk density ,
18 measurements were carried out. The results are shown in Table 4.
19
TABLE 4
22 ~ Apparent porosity ~ Bulk density g/cm
23 Temp (C.) A* B C A~ B C
1155 17.7 17.3 11.5 2.09 2.11 2.20
L140 18.7 18.0 12.6 2.07 2.09 2.18
26 1105 23.7 21.3 17.3 1.97 2.03 2.10
27 1080 27.8 24.7 20.8 1.87 1.95 2.03
28 *Comparative
29
The results obtained in Tables 2 to 4 clearly demon-
31 strate improvements achieved using a boronated zeolite as a flux
32 in fired earthenware products compared with the known flux Cornish
stone. -11-
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1 Various changes and modifications of the invention .
2 can be made and, to the extent that such variations incorporate
3 the spirit of this invention, they are intended to be included
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