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Teknisk Tidskrift
when heating mixtures of lime and kaolin together
was anorthite formed so rapidly that a direct
formation may be considered probable.
lf mixtures of free oxides were heated, the
formation of anorthite was always found to be a secondary
or ternary reaction, simple aluminates, silicates and
gehlenite being primarily formed. With short reaction
times, such as one hour or less (as in our
experiments), Jander22 found that the basic compounds
12 CaO • 7 A1203 (because of the complexity of this
formula, which is introduced by Büssem and Eitel,
it seems possible that this phase may be regarcled
as a solid solution of CaO in 5Ca0-3Al203; in
the following we shall however use the formula
12 CaÖ • 7 A1,03) and 2 CaO • SiO, were formed very
rapidly as primary products, which, if the heating was
continued, reacted with free oxides to other
inter-mediate or end products, the composition of which
depends ön the proportions of the mixture.
In the same investigations Jander also carried out
some experiments with mixtures containing CaO and
sillimanite (A1,03 • Si02) and it was shown that
gehlenite was formed with considerable speed when
heating such mixtures at temperatures above about
1050°:
A1203 • SiO, + 2 CaO — 2 CaO • A1,03 • SiO;2,
the yield being möre than 50 % after about 7 hours
at 1 050°—1 100°.
At last it must be once möre emphasized that the
reaction yield and all other reaction data in systems
like these are highly dependent ön impurities or other
individual differences between the substances used as
well as ön the thermal and mechanical treatment of
the mixtures, and also that reactions undoubtedly may
occur with considerable intensity at much lower
temperatures than those quoted above, which refer to
investigations in which the principal aim was the
obtaining of large yields. This is especially the case
if one or möre of the reacting substances exist as
transition phases with topochemically distorted
lat-tices (Hedvall23) as in the case of mixtures
containing heated kaolin preparations.
Plan of om’ experiments.
It has been necessary to survey the results of some
research work made ön powder systems containing
oxides of the kind mentioned above, or their
compounds, in order to make clear that there are still
many questions to which we have to find an answer
because of their importance for those branches of
applied chemistry which are concerned with the
chemical reactions between CaO, A1203, SiO, and the
CaO- or Al-silicates. It should also be considered
that mixtures consisting of substances of this kind
possess individual properties, due to impurities or
other locally changing factors, which often make it
impossible to apply results obtained with one mixture
to another, at least in details.
One of those questions especially demanding a
systematical examination is to what extent the
re-activity of meta-kaolin and Al-silicates with basic
oxides depends ön their thermal treatment before the
reaction.
The following silicates were used for this purpose:
kaolin, sillimanite and mullite. Because of the désiré
to obtain useful results for the cement, refractory and
ceramic industries only the following clays or kaolin
minerals and no synthetic preparations were used.
Consequently none of them corresponds perfectly to
the formula A1203 • 2 Si02 • 2 H20, the pholerite
however coming very close to it.
Analyses of reaction substances.
Pholerite from Neurode. Theoretical composition
of puré kaolin
(AI0O3 • 2 Si02 • 2 H20).
Si02 ............ 45,7 % 46,50 %
A1203 ........... 38,0 % 39,55 %
Ho O ............ 14,15 % 13,95 %
Vä::::::::::::
MgO ............ 0,4 %
K20 ............ 0,3 %
Na20 ........... 0,2 0/0
99,40 %
"Kaolin VA" (white) from St. Austell Cornwall
(Rörstrand Potteries, Sweden).
Analysis: Compound analysis:
Si02 ............ 47,9 % Kaolin .......... 77,5 %
AI0O3 ........... 36,7 «/o Feldspar ........ 11,4 %
Pe203 ........... 0,7 % Mica............ 9,3 %
CaO ............ 0,7 % Org.
MgO ............ 0,2 % substance + C02 0,9
Ko O ............ 0,9 % Residue ......... 1,6 %
........... °>8 % 100,7 %
Loss of weight in
red-heat....... 12,4 %
100,1 o/0
"Kaolin V G" (yellow) from St. Austell Cornwall
(Rörstrand Potteries, Sweden).
Analysis: Compound analysis:
SiOo ........... 46,24 % Kaolin .......... 81,5 %
AI2O3 .......... 36,88 0/0 Feldspar ........ 10,4 %
Fe203 ......... 2,18 % Mica ........... 5,1 %
Ti02 ........... 0,24 % Org.
CaO ........... 0,33 % substance+C02 1,4 %
MgO .......... 0,18 % Residue ......... 2,9 %
........... I’16 % 101,3 %
Na20 .......... 0,46 %
Loss of weight in
red-heat...... 12,40 %
100,07 %
"Kaolin VL" (white) from St. Austell C ormoall
(Rörstrand Potteries, Sweden).
Analysis: Compound analysis:
Si02 ............ 47,0 % Kaolin .......... 80,6 %
AI0O3 ........... 37,7 % Feldspar ........ 10,1 %
Fe203 ........... 1,0 % Mica............ 7,9 %
CaO ............ 0,6 % Org.
MgO ............ 0,1 % substance-|-C02 0,7 %
K20 ............ 1,1 o/o Residue ......... 1,7 %
Na*0 ........... °’2 % 101,o %
Loss of weight in
red-heat ....... 12,4 %
100,1 %
22 W. Jander a. J. Petri, loc. cit. 751—752 ; w. Büssem a.
w. Eitel, Z. Kristallogr. u. Mineral 95 (1936), 175.
23 J. A. Hedvall: Reaktionsfähigkeit fester Stoffe, 68, 139,
141, 192, 211; J. A. Hedvall a. K. Ohlson: Z. anorg. u. allg-.
Chem. 2/,S (1940), 238.
4
11 jan. 1941
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