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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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studies by Voldan (1955 - -1976).
Further development in the field of fused rock exploitation has been
aimed at correcting the composition of natural raw materials by additions
to the charge, and at the introduction of nucleating agents; the results
are glass-ceramics called petrositals having a finer grain resulting from
controlled crystallization, and properties superior to those of normal
petrurgical materials.
The initial raw materials are igneous rocks (basalt, diabase, granite,
phonolite, nepheline syenite, etc.) with correcting additions of sand,
clay, limestone, dolomite and other natural raw materials. Fluorides
(CaF2, Na2SiF6) are usually used as nucleating agents. A Czechoslovak
material of this type, called Petrokryston, is produced by melting
phonolite or granite (50% and 80% respectively) with limestone or
dolomite additions and fluoride nucleating agents. The content of iron
oxides is comparatively low(l to 1.5%). The powdered mixture of raw
materials can be melted
* Pyroxenes are abundant natural metasilicates with chain-arranged
Si04 tetrahedra. The most frequently arising monoclinic pyroxenes contain
chains jointed laterally by cations Mg2 + , Ca , Fe2+ and others. Their
structure is analogous to that of diopside CaMgSi206 which constitutes
the basis of a wide series of pyroxene solid solutions.

239
and processed by classical glass-forming techniques. The ware is
subjected to controlled crystallization; nucleation is induced by
separation of the fluoride phase on which plagioclase crystallizes with a
possible small amount of pyroxene.The original blue--green colour of the
translucent product is turned grey-brown or grey by crystallization,
while becoming less translucent (Voldan, 1976).
Another type of Petrokryston made from natural basalts and similar
basic rocks usually contains, as its main crystalline phase, fine-grained
pyroxene which renders the product extremely resistant to abrasion and
acid attack.
Petrositals based on pyroxenes of the diopside series can be derived
from the system CaO -MgO -Si02; further components present are A1203,
Fe203, MnO, Na20 and others.
The phase diagram of the system CaO-MgO-Si02 is shown in Fig. 148. The
following primary phases separate in the system during crystaltization:
cristobalite and tridymite (Si02),
20 30 AO 50 60 70
80 90 M9O
-------wi\ %
FIG. 348. Phase diagram of the system CaO-MgO-Si02 (from Muan and Osborn,
1965).
240
pseudowollastonite and wollastonite (CaO . Si02), rankinite (3 CaO . 2
SiOz), forsteiile (2 MgO . . Si02). protoenstatite (MgO . Si02), diopside
(CaO . MgO . 2 SiOz), akermanite (2 CaO . . MgO . 2 Si02), merwinite (3
CaO . MgO , 2 Si02) and monticellite (CaO . MgO . Si02) and finally CaO
and MgO (periclase). Many of these compounds enter into solid solutions
mutually and with other minerals. Figure 149 shows a partial diagram of
the system CaO- MgO- A1203 - - Si02 at a constant content of 5% A1203, in
which there arises an additional region of melilite (solid solution of
akermanite and gehlenite 2 CaO . A1203 . Si02) and of pyroxene - a solid
solution based for the most part on diopside and enstatite. The region of
pyroxene stability is maintained up to 15 - 20% A1203.
SI 0 2 / A90 \
0 I n
FIG. 149. Phase diagram of the system CaO -MgO -A1203 -SiO^ with 5% A1203
(from Muan and Osborn, 1965). (Mer. = merwinite).
The pyroxene solid solution is a desirable phase of petrositals; its
structure can be entered by various mono-, di- and trivalent cations.
With this type it is therefore possible to attain the so-called
monomineral crystallization, i.e. formation of a single crystalline
phase.
1
241
Petrositals based on basalt containing crystallized magnetite, augite
and plagioclase have been developed in the USS R. Materials based on a
mixture of basalt and feldspar have been suggested in Poland, while
petrositals from the system NaaO - A1203 - SiO ^ (nepheline-based) have
been developed in the USA. The composition range of petrositals is very
wide, and provides various possibilities for combining natural, waste and
synthetic raw materials.
- 7" I C )
F=~-.... i p=j -stage
^ J_g_Q_Q pr"1 stage
melting crystallization annealing
forming
FIG. 150. Slagsital manufacture (after Pavlushkin, 1970).
Siagsitals. The term has been derived from that used for these
materials in the USSR, where both theoretical principles and industrial
manufacturing processes have been evaluated. These principles permit
effective utilization of waste metallurgical slags, in particular blast-
furnace slags. The first products were obtained in the USSR in 1959 and
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