Compositions: ceramic – Ceramic compositions – Refractory
Patent
1997-05-02
1998-06-09
Green, Anthony
Compositions: ceramic
Ceramic compositions
Refractory
501130, 501131, 501141, 501153, 501154, C04B 3300
Patent
active
057633452
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a synthetic clay for ceramics and a process for production thereof.
BACKGROUND ART
Pottery is generally defined as any ware produced from silicate and alumina, as the main constituent, and feldspar, sericite, talc, etc, as the accessory constituent, which contain alkali metals and alkaline earth metals, by mixing, forming, glazing, and sintering at a prescribed temperature (1250.degree.-1450.degree. C.). Porcelain clay used for pottery is composed of silicastone, feldspar, and clay, the first containing silicate, the second containing alkali metals, alumina, and silicate, and the third containing alumina and silicate, respectively as their main constituents. It plays an important role in forming. In other words, silicastone, feldspar, and clay are the three major elements constituting pottery. Clay should ideally have a high degree of plasticity and be free of impurities. Plasticity makes clay formable and permits clay to be easily formed by machine into complicated shape with high precision. Unfortunately, naturally-occurring clay of high quality is being exhausted rapidly in recent years.
Natural clay, on the other hand, has some drawbacks. It has an average grain size of 0.5-2.0 .mu.m after purification. This grain size is not necessarily satisfactory for clay's formability (such as mobility and ductility) and green strength. In addition, natural clay contains iron-containing minerals and titanium-containing minerals and organic matters. Upon firing, these minerals develop an undesirable color which impairs the whiteness of fired ware. It is practically impossible to remove these impurities by elutriation and chemical treatment without deteriorating the characteristic properties of clay. Any treatment makes the resulting clay unstable. In the case where treatment involves a coagulant, the resulting clay needs a large amount of peptizer at the time of its use. Another disadvantage of natural clay for ceramics is that it is subject to shrinkage which varies in directions. This is because clay mineral is composed of crystalline particles of definite shape (platy or columnar), and such crystalline particles orient in the direction of pressure under shearing stress. The directionally variable shrinkage reduces the dimensional accuracy of the product.
The present invention was completed to address the above-mentioned problems involved in natural clay. It is an object of the present invention to provide a synthetic clay for ceramics which is characterized by small grain size (below 0.4 .mu.m which is the minimum grain size of natural clay), good water retentivity, ability to form a large amount of water film, low content of iron and titanium, freedom from particle orientation, good dimensional accuracy, and improved sinterability due to high activity. It is another object of the present invention to provide a process for producing a synthetic clay for ceramics in a simple, easy manner without requiring any harmful additive.
DISCLOSURE OF THE INVENTION
The gist of the present invention resides in a synthetic clay for ceramics which comprises 30-65 wt % of fine amorphous silica, 30-65 wt % of alumina trihydrate, and 2-20 wt % of any one or more species of sepiolite, palygorskite, and bentonite.
The amorphous silica should preferably be fumed silica. The alumina trihydrate should preferably be aluminum hydroxide. Of the three materials as the third component, sepiolite is most desirable. The third component is intended to impart viscosity to the synthetic clay.
According to the present invention, the synthetic clay is produced by a process which comprises preparing slurries from respective raw materials by wet milling and then mixing them together such that the resulting product contains, excluding water, 30-65 wt % of amorphous silica, 30-65 wt % of alumina trihydrate, and 2-20 wt % of any one or more species of sepiolite, palygorskite, and bentonite. The thus obtained slurry may undergo partial dehydration to give a water-containing clay. The water-contain
REFERENCES:
patent: 4111868 (1978-09-01), Ficken
patent: 5026744 (1991-06-01), Callandar
patent: 5304706 (1994-04-01), Hooykaas
JAPIO Abstract No. JP402157116A which is an abstract of Japanese Patent Specification No. 2-157116 (Jun. 1990).
Kikuhata Akira
Ohshima Iemitsu
Cosmo Clay & Ceramics Co., Ltd.
Green Anthony
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