Coarse ceramic products

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. 

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). 

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. 

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

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... 

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. 

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. 

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. 

Extrusion is a much used process in many branches of the ceramics industry. Coarse earthenware as well as fine ceramic and industrial ceramic products, ranging from bricks to high performance catalysts are made in this way. Figure 1 shows an example of an extruded industrial ceramic product. 

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). 

Generally, coarse-grained, naturally occurring minerals are the raw materials for mechanical methods. The particle size is brought down by different equipments to get the final size. When economy is needed and purity is not the primary concern, these methods are used. Traditional ceramic products are generally made from the powders obtained from these methods. 

The so-called dry mixing or dry blending method has been used for the modification of" particles in the powder technology (59). In this method, surface modification of coarse particles is carried out by mixing fine particles and coarse particles with an auto ceramic mortar or with a centrifugal rotating mixer. This procedure can be applicable for the production of variety of composite magnetic particles. 

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