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clay for ceramics


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  • 1.  Ball Clay The wide use of ball clay is mainly due to its contribution of workability, plasticity and strength to the bodies in drying.
  • 2. BALL CLAY is a variety of Kaolinite, like china-clay. It differs from china-clay in having high plasticity and less refractoriness. In chemical composition, ball and china clays do not differ greatly except that the former contains a larger proportion of silica. It has derived its name from the practice of removing it in the form of ball-like lumps from the clay pits in the UK.
  • 3. The main utility of ball clay is its plasticity and it is mixed with non-plastic or less plastic clays to make them ecquire the requisite plasticity. The high plasticity of ball clay is attributed to the fact that it is fine-grained and contains a small amount of montmorillonite.
  • 4. invarious types of ceramicscomposition: Vitreous sanitary-ware 10 to 40 % Hotel china-ware 6 to 15 % Floor and wall tiles 12 to 35 % Spark plug porcelain 10 to 35 % Semi-vitreous white ware 20 to 45 % Saggar bodies 10 to 25 % Glass melting-pot bodies 15 to 20 %
  • 5. China Clay China clay occurs in the deposits in the form of china clay rock, a mixture of up to 15 per cent china clay and up to 10 per cent mica, and the remainder being quartz.
  • 6. China clayOne of the purest of the clays, composed chiefly of the mineral kaolinite usually formed when granite is changed by hydrothermal metamorphism. Usage of the terms china clay and kaolin is not well defined; sometimes they are used synonymously for a group of similar clays, and sometimes kaolin refers to those obtained in the United States and china clay to those that are imported.
  • 7. China clays have long been used in the ceramic industry, especially in fine porcelains, because they can be easily molded, have a fine texture, and are white when fired.Early 20th CenturyChina clay in ceramic manufacture, porcelain; bone china; earthenware; white tile body; graniteware; white stoneware; glazes.
  • 8. Mid 20th centuryCeramics (excluding refractories), bone china; hard porcelain (including tiles, tableware, sanitary and electrical porcelain); fine earthenware; earthenware (lower grade); earthenware (sanitary); porous wall tiles; electrical porcelain (England); semi-vitreous china (American); semi-vitreous porcelain (American); hotel china (American); household china (American); belleek (American); glazes (mill additions and frit additions); porcelain enamels
  • 9. Fire Clay A good fireclay should have 24-26% plasticity and shrinkage after firing should be within 6-8% maximum. It should also not contain more than 25% Fe2O3.The Present Scenario Because of the abundant supply of fireclay and its comparative cheapness, the refractory bricks made out of it are the most common and extensively used in all places of heat generation
  • 10. A group of refractory clays which can stand temperatures above Pyrometric Cone Equivalent (PCE) 19 are called fireclay. The clay which fuses below PCE 19 is not included under refractory. Fireclay is essentially of kaolinite group and has a composition similar to that of china-clay.
  • 11. In nature it is usually found to contain 24-32 per cent Al2O3, 50-60% SiO2 and LOI between 9 to 12%. Impurities like oxides of calcium, iron, titanium and magnesium and alkalies are invariably present, making it white, grey and black in colour.
  • 12. Kaolinite Aluminum Silicate Hydroxide Al2Si2O5(OH)4 Kaolinite shares the same chemistry as the minerals halloysite, dickite and nacrite.
  • 13. The History Says Kaolinite is also known as china clay and kaolin, named after Gaoling ("High Hill") in Jingde Town, Jiangxi, China. It was Discovered in the year 1867 in Kao-Ling, China.The Present Scenario Kaolinite is important to the production of ceramics and porcelain, and to produce glossy paper for magazines.
  • 14. Kaolinite is a common phyllosilicate mineral. It is named for its type locality, Kao-Ling, Jianxi, China. It forms Kaolinite Group, members of which even belong to larger general group, Clays. Kaolinites structure is composed of silicate sheets (Si2O5) bonded to gibbsite layers, aluminum oxide/hydroxide layers, Al2(OH)4.
  • 15. Feldspar KAlSi3O8 - Orthoclase KAlSi3O8 - Microcline NaAlSi3O8 - CaAl2Si2O8 - Plagioclase In the manufacture of high-class, colourless glass, feldspar should have a maximum of 0.1% Fe2O3 though upto 0.3% is permissible.
  • 16. Feldspar is generally used for three purposes In making the body composition of several types of procelain, china and earthenware and also in the preparation of glazes and enamel. As an important ingredient in the glass sand batch. As a bonding agent in the manufacture of bonded abrasives like wheels and discs of garnet, corundum, emery etc.The glass and ceramic industries are the major consumers of feldspar and account for 95% of the total consumption.
  • 17. In ceramic bodies, the main vitrifying (fluxing) agent is feldspar. The majority of white ware bodies contain good proportions of feldspar. It acts as a flux. In the ceramic industry, the flux is defined as that portion of the body which develops glass phase. This is provided mostly by feldspar. The amount of flux in a ceramic body should be only in such a proportion as to develop the desired amount of vitrification. If excess of flux is added, the fired body becomes very glassy and consequently, brittle.