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The technology of glass and ceramics - Hlavac J.

Hlavac J. The technology of glass and ceramics - Oxford, 1983. - 429 p.
Download (direct link): tehnologyofglass1983.djvu
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Mashinostroenie, Moscow, 1970 (Павлушкин H.M., Основы технологии
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244
IV.
The Technology of Ceramics*
Ceramic materials are inorganic, non-metallic materials with a
heterogeneous structure composed of crystalline substances of various
compositions and arrangements, which may be permeated by a glassy phase.
They usually contain pores.
Ceramic production is based on the forming and heat treatment of
particulate systems that are strengthened and densified by firing. The
resulting hardened polycrystalline product may have a phase (mineral)
composition quite different from that of the initial mixture, as a
consequencc of high-temperature reactions. The crystalline phases in
ceramics are frequently minerals known in nature which exhibit strength,
chemical resistance and stability at elevated temperatures. However, the
crystalline phases in modern types of technical ceramics are often
artificial minerals exhibiting specific electrical, magnetic and other
properties.
Until recently, ceramic manufacture was mainly based on empirical
principles. Manufacturers utilized only certain types of raw' materials
(usually natural) and technologies developed on the basis of long-term
experience. Any change or deviation presented problems which were
difficult to solve because the principles of the ceramic systems and of
manufacturing processes were unknown. It was therefore impossible to
predict the consequences of various adjustments or measures. The
nesessary changes in technology, resulting for instance from the need to
replacc a raw material after depletion of its deposit, required extensive
trial-and-crror testing.
In order to improve this situation, studies have been made of the
individual isolated ceramic phases, and also of their formation and
distribution in the ceramic material. The method has proved satisfactory
for both classical and new types of ceramic materials, and still
represents a significant proportion of both physical and chemical
research in the field of ceramics. It has yielded many positive results,
in particular with respect to ceramics of simple phase and chemical
composition. From this point of view, it is also clear that development
of new ceramics for technical applications, with the strict requirements
for properties and tolerances involved, is based on the use of synthetic
raw materials, which allow for improved control of the respective
manufacturing processes.
* Ceramics, in the original sense of the word, were objects made of
clays and hardened by fire. Nowadays the sense of the term is wider and
not quite explicit. In the present book, it is used (as in most European
languages) to cover products related by the character of the material and
by the way of manufacture to the original sense of the term ceramics, not
including glass, cements, etc.

1
245
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 ccramic materials are represented by brick-making
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.
In the present treatise, use is made chiefly of classification from
the standpoint of chemical and phase composition.
1. MATERIAL PREPARATION
Traditional manufacture of ceramics is based on the use of fine natural
raw materials which are capable of producing easily worked plastic mass
(paste) with water. The formed bodies maintain their shape. The products
are strengthened and the shape fixed by firing at temperatures which were
attainable even in the primitive kilns. Kaolin and clays are the main
raw' materials which exhibit these required properties.
However, the more plastic the raw material from the point of view of
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