Nonequilibrium crystallization in eutectic melts of the system CaO-Al2O3-SiO2

by Erofeeva N. T., Rumyantsev P. F., Sakharov L. G.

Izvestia Academia Of Science USSR
Inorganic Materials
1987, v.23, N 9, p. 2026-2028. ( offprint rus.)

Processes of non-equilibrium crystallization in silicate systems determine the properties of materials obtained in the course of various technological processes, such as stone casting, the production of glass-crystalline materials and cement. Non-equilibrium crystallization in silicate melts has been the subject of study in a number of papers [1-7].

It is of interest to study the effect of small additions of oxides on the course non-equilibrium crystallization in melts of complex composition, in which simultaneous growth of crystalline phases take place, which is important for the purposeful regulation of the phase composition and microstructure of products in these technologies. In the present work, the dependence of the growth rate of crystals on temperature in melts of two triple eutectic of the CaO (C) -Al2O3 (A) -SiO2 (S) system: eutectic 1 (Ca2AlSiO7 + CaAl2SiO8 + CaSiO3) + additive 0.1 Ox. eutectic. 2 - (Ca2Al2SiO7 + CaAl2Si2O8 + Al2O3) + additive 0.1 Ox, where Ox = FeO1.5, CuO, LiO0.5.

X-ray phase analysis and bending strength measurements were performed on crystallized at 1100 C of the glass powders (holding time 10 min and 1 hour.) of content eutectic 1 and 2 with additions of named above oxides and without them. X-ray phase analysis showed that in the eutectic samples 1. there are three main phases: anorthite (CAS2), gehlenite (C2AS) and wollastonite (CS); in the samples of eutectic 2 - two main phases: anorthite and gehlenite.

In addition to the main phases, the grossularite Ca3Al2Si3O12 (C3AS3) [8] in small samples is crystallized in the samples of the eutectic 1. and the metastable compound Ca3Al6SiO14 (C3A3S) in the eutectic samples. 2. The amount of crystalline phase increases insignificantly with increasing holding time.

The results of measuring the flexural strength are shown in Table. 1. Additions of oxides to eutectic 1 increase the strength of the samples by almost 2 times, the greatest effect of increasing the strength is manifested when Fe2O3 is introduced, the addition of oxides to the eutectic. 2 strength is reduced. The increase in the time of high-temperature exposure from 10 min to 1 h leads in most cases to a decrease in strength, which is probably associated with a decrease up to the disappearance of the glass phase.

Table 1. Bending strength in crystallized at 1100 C glass powders at a holding time of 10 minutes and 1 hour
Content σ, MPa Content σ, MPa
10 min 1 h 10 min 1 h
Eutectic 1 48 22 Eutectic 2 54 -
Eutectic 1+Fe2O3 113 22 Eutectic 2+Fe2O3 29 40
Eutectic 1+CuO 101 22 Eutectic 2+CuO 43 13
Eutectic 1+Li2O 86 22 Eutectic 2+Li2O 34 16

Using a high-temperature microscope [9], based on data on the morphology of growing crystals, it was possible to obtain temperature dependences of the linear growth rate of crystalline phases independently of each other crystallizing in the melts studied. These dependencies are shown in the figure, they have speed peaks growth in the region (6.5-7.8) 104 / T, K-1; additions of oxides modify the course curves: there may be a shift in the maximums (or) narrowing (expansion) of the temperature range in which the crystal growth process takes place.

The temperature dependencies of the linear growth rate of crystals in melt of two triple eutectics of the CaO-Al2O3-SiO2 system (a - d - eutectic 1, e - h - eutectic 2 with additions of Fe203 (b, f), CuO (c, g), Li20 (d, h), races The present crystalline phase: 1-CAS2, 2-C2AS, 3-C2AS3, 4-CS, b- eutectic, 6 - C3A3S

The experimental data are approximated by a semi-empirical equation

 v = k (ΔT/T)c×exp (-E/ RT)                         (1)

where k, c, E are empirical coefficients.

A Table. 2 presents the results of mathematical processing of experimental results by the method of least squares on a computer BESM6. The value of c, determined by the mechanism of the transition of structural elements from the melt into the crystal, varies within a wide range from 0.7 up to 4.6, which indicates the influence of small additions of oxides of Fe203, CuO, Li20 on the mechanism of non-equilibrium crystallization.

Thus, the change in the composition of the melt, including 1r, as a result of small additions of oxides Fe203, Cu0, Li20, has a significant effect: influence on crystallization of eutectic melts and on strength properties of crystallized glass powders, which is probably mainly due to a significant modification of the structure of the melt ahead of crystallization fronts.

Table 2. Values of empirical coefficients
Content Crystalline phase To, K c ln K, μ/s E, KJ/mol
Eutectic 1 CAS2 1540±10 3.0±1.5 63±25 660±250
  C2AS 1540±10 4.60.7 6910 700100
  C3AS3 1470±10 2.00.6 4015 430±150
Eutectic 1 + Fe2O3 C2AS 1590±10 0.8±0.1 173 21030
  C3AS3 1540±10 1.80.4 307 33070
Eutectic 1 +CuO CS 1490±10 3.8±1.5 7310 740±100
  C2AS 1510±10 2.20.7 76±25 850±250
  CAS2 1600±10 2.6±0.5 63±25 48070
Eutectic 1 + Li2O CAS2 1540±10 3.0±1.5 43±25 290±50
  CAS2 1600±10 1.80.3 48±5 230±40
Eutectic 2 Eutectic 1650±10 3.5±0.5 454 49060
  C2AS 1640±10 2.6±0.3 444 48040
  C3A3S 1640±10 2.3±0.3 63±25 47040
Eutectic 2 + Fe2O3 Eutectic 1650±10 1.50.8 279 27090
  C2AS 1640±10 1.80.4 406 43060
  C3A3S 1520±10 4.02 10030 1000100
Eutectic 2 + CuO Eutectic 1510±10 3.01 90±25 970±250
  CAS2 1690±10 1.60.4 5010 600100
  C2AS 1640±10 1.20.4 406 46060
Eutectic 2 + Li2O CAS2 1660±10 2.50.5 506 54060
  C2AS 1560±10 1.00.2 255 26030


The temperature dependences of crystal growth rates were studied: in melts of two triple eutectics of the CaO-Al2O3-Si02 system, with small additions of iron, copper, and lithium oxides, and the effect of these additives on the strength properties of glass-crystalline materials obtained from the melt of these eutectics by powder sintering. glass.


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Institute of Silicates Chemistry

Academy of Sciences of the USSR

 Received by the Editor Feb. 25, 1986

May. 18, 2018; 08:51 EST


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