COARSE CERAMICS

Some products of the coarse ceramic industry are bricks, hollow building bricks, paving bricks, roof tiles, drain pipes, vitrified clayware products and insulation materials. 

Vitrified clayware is sintered stoneware which is hardly porous and can withstand chemical and mechanical outside influences. For those reasons vitrified clayware is used for sewers, as a coating for vessels, reactor inlets, pipes, valves and pumps. Plastic clay with a relatively high content of aluminium and alkali metals and a low lime content is used as raw material 

For the synthesis of insulation materials organic substances are added to the clay mass. During the firing the combustion products from those substances are responsible for the formation of cavities in the material. 

In The Netherlands locally found clay is almost exclusively used as main raw material. The most important clay deposits for (paving) bricks are found along the river banks of Holland s main rivers. River clay from the polders is mostly fat to very fat and deficient in lime consequently it is used in the production of e g. roof tiles. We call a clay type fat when it contains a high percentage of minute particles. The Dutch coarse-ceramic clay is a sediment, appr. 45 % of whose particles have a diameter of 10 pm. The coarser sand and silt fractions 

After the Kastenbeschicker several other machines carry out the subsequent pretreatment.The type of raw material and factory procedures determine which machines are used. Some of these machines are clay rasp or Kollerwalze, differential rollers, Kollergang and pregrinder. Let us have a closer look at the Kollergang. 

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Vb Carbonates are used, for example, in masses for fine ceramics and in glazes. Well-known examples are calcite or calcspar CaC03 which is the main component of limestone, magnesite MgC03 and dolomite CaMg[C03]2. In coarse ceramics lime is added to clay to obtain yellow-firing bricks. 

Minerals of the feldspar group are for example used in fine and coarse ceramics. 

Natural clays are coloured due to pollutions of the clay minerals. After baking the colour is strongly affected by the Ca/Fe ratio. When the baking colour is not white, this is caused by metal ions with d-valence electrons (see glazings in the paragraph Fine ceramics and baking colour in the paragraph Coarse ceramics). 

The name fine ceramics is based on the grain size distribution of the hard components in the ceramic mass. This rather differs from the distribution as it is seen in the ceramic branch of industry which produces for instance bricks, the coarse ceramic industry. Another difference is that all fine ceramic products are provided with a protective and in some cases also decorative coating, a so-called glaze. In this section much attention will be paid to glazes because this technique is rather unique for fine ceramics and because it offers the possibility to explore the subject glass and some important physical and chemical properties of materials. 

The (simplified) theory of coloured compounds with metal ions from groups 3 up to and including 12 described above can be applied to solids and liquids. In this chapter, it serves to explain the colours of glazes and in chapter 11.2 Coarse Ceramics it explains the red colour of certain bricks. 

In the industrial world bricks are mostly made in an automated production process. After the raw materials have obtained the correct composition and plasticity, the forming process follows. In The Netherlands hand moulding, press moulding and extrusion moulding are applied in coarse ceramics. Occasionally the stamping press is still used, mainly in the manufacture of roof tiles. 

A stamping press is used in the manufacture of roof tiles. This is a machine which compresses a plastic clay mass between two moulds to obtain the desired shape. This compression technique is only rarely applied in coarse ceramics. 

The firing colour was discussed in the paragraph on coarse ceramics. Colours are measured quite often in the plastics industry, but I have not be able to find out if the method applied there is also applied in the ceramics industry. It is certain,however, that colours are measured visually in the brick industry, i.e. colour charts are used as reference... 

The procedures described above are used chiefly in fine ceramics. For plastic forming of coarse ceramics, it is common to use wet pan mixers or pug mills in which the wet mix is kneaded with rotating knives. Subsequent degassing in a vacuum chamber and extrusion are usual. 

Ceramic materials are divided according to various aspects, for example, according to chemical and phase composition, porosity (dense and porous ceramics) and structure (coarse and fine ceramics). The group of fine ceramics includes, for instance, porcelain and technical ceramics, whilst the coarse ceramic materials are represented by brickmaking products and by refractories for the construction of industrial furnaces. According to the purpose and fields of application, ceramics are also divided into building ceramics, technical ceramics, domestic ware, refractories, etc. 

Coarse ceramic products are tiles and hard bricks... 

The clay products used in the construction industry are so-called coarse ceramic products. They include bricks, roofing tiles, clinkers (hard bricks), drainpipes and protection covers for cables. The manufacture of such products hardly differs from that described in Section 5.5.3 for the general manufacture of ceramic products. 

Within both groups the bulk homogeneity is an important distinguishing characteristic, fine ceramic products have grains less than 0.2 mm in size, whereas coarse ceramics have larger pores and crystal sizes. 

Whereas finely ground raw materials are required for fine ceramic products, mixtures of raw materials with different particle sizes are utilized for coarse ceramic products. 

A survey of the fine ceramic clay-containing products will be given in this section, the coarse ceramic products having been for the most part dealt with in the sections concerned with construction materials (see Section 5.3.5) and refractory products (see Section 5.5.5.3). 

One of the advantages of lasers for activating gas phase reactions is the feasibility to control the dimension of the process zone by laser focus. In this way very small regions may be achieved where nucleation and particle growth happen. The same advantage is applicable to processes where the laser is used for evaporating coarse ceramic material in order to get nano-scale ceramic powders by re-condensation via homogeneous nucleation [232]. This technique has also been used to prepare SiC nanopowder with yields up to 100 g h [233]. However, with this approach, traces of free silicon were also detectable. 

Heavy clay industry silicate ceramic (clay ceramic) coarse ceramic bodies 1000 80 5-150 bricks, roofing tiles, ceiling bricks, wall and floor tiles... 

Figure 3.27 Position of nonrefractory coarse ceramics in the (muitinary) system (RO + R2O)-(Ai20j + Fe20j)-Si02. 1 Tiles and terracotta 2 bricks 3 stoneware pipe 4 range of coarse ceramics.

UP resins have a long and continuing use as stone adhesive for the reasons stated early in its use (Hanpel, 1968) - the commercial products can be readily modified to suit the needs of stone workers, and can be further adjusted in the field. UP resins are similarly used as strong adhesives for coarse ceramics where the viscosity prevents penetration into the porous substrate (Buys and Oakley, 1996). 

Lignin addition rates of 0.10-0.15% for fine grain and 0.20-2.0% for coarse ceramic materials will improve handling in prefiring stages of ceramic mannfactnring. (See BINDERS.)... 

Thick media cartridges can then be made by fixing a layer of plastic foam to a perforated core. A major alternative use is the formation of coarse ceramic foams, as discs, to be used as filters in the removal of contaminants from molten metal. 

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