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TekniskTidskrift
KEMI
REDAKTÖR: FRITHIOF H. STENHAGEN
HÄFTE 1 UTGIVEN AV SVENSKA TEKNOLOGFÖRENINGEN -J-| JAN. 1941
INNEHALL: Reactions in the solid state between calcium oxide and dehydrated kaolin, mica, feldspar,
sillimanite or mullite, by J. Arvid Hedvall. — Metallernas namn. ■— Litteratur. — Föreningsmeddelanden.
Reactions in the solid state between calcium oxide
and dehydrated kaolin, mica, feldspar, sillimanite
or mu il,te.
By J. ARVID HEDVALL.1
Experiments carried out by: L. Andersson, K. O. Hagman, Th. Hansson, G. Lindedal, T. Lindquist and Y. Lindquist.
Summary.
An examination has been made of the reactivity
between 400 and 1100°C of a number of kaolin
minerals puré or containing feldspar and mica, of
sillimanite, and of mullite when mixed with CaO in the
solid state. It has been shown, that for preparations
free from water preheating at high temperatures or
for prolonged periods generally decreases the
reactivity at löw reaction temperatures (below 800—900°C).
The influence is not so marked at higher reaction
temperatures, where the reactions are möre complex and
where the lattice particles possess an increased
mova-bility. It has been found, that in these reactions as in
industrial processes the different kaolin minerals show
a very dissimilar behaviour. This cannot be explained
as effected by the mineral impurities. It is evident, that
the formation of meta-kaolin, its decomposition, the
subsequent transitions of A1203 and Si02 and their
recombination are all processes, which are profoundly
influenced by preparation methods, especially thermal
treatment. All kaolin preparations, even if rather
impure, will after preheating at 1000 °C for short
periods (about 1 hour or less) show a maximum of
CaO-consumption at reaction temperatures of about
500°C. This must be due to the imperfect lattices
of the free oxides A1203 and Si02, which are thus
highly reactive so that. basic compounds are
inter-mediately especially easily formed, which shows that
topochemical factors may influence reactions not only
quantitatively but even qualitatively. This
interpretation is supported by results obtained ön heating
CaO with sillimanite or mullite. A maximum ön the
yield curves is obtained when using sillimanite
preparations preheated at temperatures where the
sillimanite decomposes to give an unstable transition phase,
but is not obtained with the stable mullite phase.
Acknowledgment.
This investigation has been made possible through
a grant from the Skånska Cement Aktiebolaget.
i Author’s manuscript received Sept. 16th, 1940.
Thanks are also due to Professor Otto Krause of
Breslau, the Neuroder Kohlen- und Tonwerke, and
the Rörstrands Porslinsfabrik, Göteborg, who have
placed kaolin materials at our disposal.
Survey of earlier investigations.
Some twenty years ago reactions between solids
were still regarded with great distrust — especially
by those chemists, who were only interested in
equilibria and did not make allowance for the
con-siderable speed, with which reactions with solids
often occur even at comparatively löw temperatures.
To the applied chemistry, however, it came natural
to perceive the importance of investigations of the
reactivity of solids. Of course the fact that some of
the results first obtained concerned the reactivity of
oxides such as CoO, ZnO, A1203, MgO, CaO and SiOj1,
and therefore did interest workers in different
branches of ceramics and the technology of glass and
cement, was one of the reasons. It must however be
emphasized that the investigators, dealing whith this
branch of chemistry, conceived that reactions in solid
state were of great importance also indirectly, because
in powder mixtures they produce changes which
influence the compositions of melts and consequently
also the reactions between solid and liquid phases
at higher temperatures. The work of Dyckerhoff2
ön the reactions between Si02 or A1203 and CaC03
in the manufacture of Portland cement and the
following quotation from Lea and Desch in their
excellent work: Chemistry of Cement and Concrete
(London 1935, p. 100) may be referred to in this
connection: "The burning of cement consists of a
series of reactions taking place between finely divided
solids, and it is only in the final stages of burning
i J. A. Hedvall: Z. anorg. u. allg. Chem. 86 (1914), 201,
296 ; 92 (19X5), 301, 369, 381; 93 (1915), 313; 96 (1916), 64,
71 ; 98 (1916), 57.
- w. Dyckerhoff : Dissert. Frankfurt a/M 1925.
11 jan. 1941
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