SYNTHESIS OF THERMAL STABILITY AND WEAR RESISTANCE OF GLASS CERAMICS V. Yu. Goikhman, E. S. Orlova, L. To Konik, and N. S. Naumenko
The intensive development creating new materials capable media, and abrasive wear. The be accessible and economical. glass ceramics obtained on the
UDC 666.263.2:539.4
of technology has confronted researchers with the problem of of operating under conditions of high temperatures, corrosive important requirements placed on such materials are that they These requirements are satisfied most fully by glasses and basis of diverse mineral wastes.
The treatment of solid fuel in different branches of industry involves a considerable quantity of mineral wastes. For a long time it had been assumed that the mineral components of solid fuel are a troublesome ballast during treatment. The by-product, wastes, are stockpiled as tailings and waste heaps, taking up large tracts of land. The contents of the tailings and waste heaps at coal mines and coal dressing plants pose considerable difficulties since they pollute the environment. Each year coal dressing plants in the Ukraine send 5 million tons of flotation railings to waste heaps. At present the Donbass has about i000 waste heaps on more than 800 hectares of land. The expenditures for maintaining them increase with each year. With regard to uses of coal-dressing wastes, promising work has been done on developing new glass ceramics and vitreous materials with a prescribed ensemble of properties, based on coal-dressing wastes, for technical and construction purposes. At the Avtosetklo Scientific-Research Institute we have examined the possibilities of using wastes from dressing plants for obtaining glasses and glass ceramics. We have studied wastes from the coal dressing plants of the Donetsk Coal Dressing Industrial Amalgamation, especially the Chumakovka and Gorlovka central coal dressing plants (CCDP's), with a view to synthesizing glasses to obtain a glass ceramic. The chemical composition of the batches of coal-dressing wastes are given in Table I. The coal-dressing wastes have a stable chemical composition, AI203 in addition to SiO 2, KaO, and CaO.
containing Fe203, FeO, and
On the basis of the coal-dressing wastes we synthesized glasses with a pyroxene composition in the CaO--MgO--SiO a system. Pyroxenes are distinguished by a high crystallizability and ensure enhanced physicochemical properties of the crystalline material. The tendency of pyroxenes to extensive isomorphism enables diverse cations to be incorporated easily into the lattice. Because of this, abundant raw materials and industrial wastes can be used to synthesize pyroxene glass-ceramic materials.
TABLE i Mass
content
%
i CCDP
~
~ ~ ~ D,
~
,.4'
0
0
0
~ r
"~ o
,'~
,,.-,~ ,,~ ~
Chumakovka
57,62 2 6 , I 4 58, 10 26,09
6,14 6,03
0,27 0,01 0,10 1,73 i,61 1,07 3,00 0 , 3 1 0,74 0,06 1,04 1,37 ~25 3,12
0,78 0,58
--
1,14 1,39
C~or l o v k a
57,78
25,74
7,00
--
0,8I 0,04 1,55 1,41 0,70 3,36
0,71
0,31
]
57.77
26.43
5,7)3
0,87
0,34
r 0~9
i
Avtosetklo Scientific-Research 12-13, May, 1990.
- 0.~4 0.06
Institute.
0361-7610/90/0506-016551.250
9
1.87 |,60 0,80
3,54
Translated from Steklo i Keramika,
1991 Plenum Publishing Corporation
No. 5, pp.
165
TABLE 2
Indicator Mass loss BY abrasion, kg/m~ Microhardness. MPa Thermal stabilityw ~ Density, I0= kg/m Acid resistance in 96% H2SO~ % Alkali resistance in 35% NaOH, %
Material* based on coal-dressing wastes composi- composition 1 tion 2 0,308
0,295
6776 550
6920--7005 550--600
2,93
2,98
99, 15
99,78
83.08
83,68
*The phase composition of the material with composition 1 is represented by compounds from the crystal-chemical group of the diopside Ca(Mg, Fe)Si20 s as well as the spinels (Mg, Fe)Fe20 ~ while that of the material with composition 2 is represented by compounds from the crystal-chemical group of the pyroxene (Mg, Fe 2+, Ti, AI, Cr)2~ AI)2"O 6. Glass obtained on the basis of coal-dressing wastes possessed satisfactory melting, working, and crystallization properties. The wastes made up 60-70% of the mixture for the synthesized glasses. Sodium sulfate and soda as well as some additives used in glassmaking (chalk, dolomite, and sand) were introduced to provide the Na20. As the crystallization catalysts we introduced wastes containing iron and chromium that form during the concentration of iron and chromium ores. The glasses were melted at 1450-1480~ crystallization occurred at a maximum temperature of 900~ The resulting glasses were homogeneous and suitable for industrial production. They have a tendency to bulk crystallization in the temperature range 800-950~ The introduction of iron ore into the mixture ensures that a fine-grained pyroxene structure forms after appropriate heat treatment. Such a material possesses a high wear resistance and enhanced strength properties on a par with those of well known slag glass-ceramics.. The synthesized glass-ceramic material belongs to the CaO--MgO--SiO 2 system in which Mg ions can be substituted isomorphically by AI, Fe, and other ions. The main crystal phase of the material obtained is represented by a compound of the crystal-chemic~l group of the diopside CaAI2"Si=O 8. The presence of this phase is the determining factor in the formation of wear-resistant materials. We can assume that the spinels Mg(AI, Fe)20 ~, wollastonite BCaSiO 3, or anorthite CaAl2Si20s are also present in addition to the main phase. When wastes containing chromium were introduced into the mixture, the crystal phase of the resulting glass-ceramic material could be identified with augite Ca(Mg, Fe)Si206. Chromium, which was introduced at a rate of 0.3-2.8%, acts as a crystallization stimulator. Chromium (at a Cr20 ~ content of 3-5%), in combination with an increased content of 9 aluminum and iron, not only acts as a crystallization stimulator but is also incorporated as a structural element into the augite formed. The formation of augite ensures that the material has a high degree of crystallization and enhanced thermal stability (350-600~ Glass ceramics based on coal-dressing wastes with additions of chromium-containingwastes are characterized by a fine-grained structure, consisting of crystals which have a size of 0.51.0 um and are uniformly distributed between crystals of a layer of residual glass. This structure of the material determines its physicomechanical properties (transverse bending strength 85-109 MPa, compressive strength 600-700 MPa).
166
The high thermal stability makes it possible to use the resulting material to make ~roducts for gas-duct linings, heat-exchange surfaces, and other compounds operating under conditions of the simultaneous action of high temperatures and abrasive and corrosive media. The mixture used in the production of a and some additives used in glassmaking (sand, production of glass ceramics on the basis of making technology. Accordingly, glassmaking ucts from such materials.
glass ceramic chalk, soda, coal-dressing equipment can
contains 50% coal-dressing wastes etc.). The technology for the wastes does not differ from glassbe used in the manufacture of prod-
The physicochemical and mechanical properties of the glass ceramics obtained on the basis of coal-dressing wastes are given in Table 2. Synthesized glass ceramic can be used to protect or replace metal in the coal, cement, chemical, electric power, and other industries. The economic gain from the production of glass ceramic based on coal-dressing wastes is 2.2 million rubles and about 70,000 tons of metal per year is saved at an annual output of 20,400 tons of the glass ceramic.
167
