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4
Teknisk Tidskrift
Preheating temperature Preheating time Designation: Pho, VA, VL, VG, Musc, Orth .(Instances)
600° 1 hour 5 hours VGeoo/i h. VL600/5 h.
800° 1 hour 5 hours Pho800/1 h.
900° 1 hour 5 hours VA900/5 h.
1 000° 1 hour 5 hours M11SC8OO/5 h.
1 200° 1 hour Orth/1 h.
These preparations proved not to be practically
dehydrated until after heating at 600° for 5 hours.
Small quantities of Ii,O, the amount of which, if
necessary, was taken into account when calculating
the ratio CaO:meta-kaolin, are still lef t in the
preparations YA, VG and VL when heated below 800°. These
are due to the mica contained in these kaolins. The
percentage of meta-kaolin (A1203. 2 Si02) varies
be-tween about 77 (VA), 80 (VL), 81 (VG) and 98
(pholerite). Consequently, only the pholerite
prepara-tion can be regarded as almost puré meta-kaolin
The impurities of the other preparations consist
practically only of feldspar (about 10—11 p. c.) and
dehydrated mica (about 5—9 p. c.). The reactions
of these substances have been shown (cf below) to be
of no great importance, having only a small influence
ön the results obtained with kaolin mixtures.
The preheating treatment of sillimanite appears in
the following table.
Preheating
temperature
Preheating time
600° 1 hour
5 hours Slll600/5 h-
800 ° 1 hour Sillsoo/l h.
5 hours and so ön
1 000° 1 hour
5 hours
Designation: Sill
(Instances)
In the same way the treatment of midlite in order
to produce preparations of different activity can be
seen in the following.
Preheating
temperature
Preheating time
Designation: Mu
(Instances)
110° 1 hour Muioo/1 h.
7000 5 hours Mu700/5 h.
As basic oxide CaO was used. CaO was produced
through thermal decomposition of CaC03 (pro analysi)
at 950°.
All of the preparations now described were kept in
small portions and sealed from the atmosphere, before
being mixed with the other component for heating
at different reaction temperatures.
Preparing, heating and analyzing the reaction
mixtures.
In order to keep the preparations unattacked by
moisture and carbonic acid during the mixing
pro-cedure we have used special types of mixing tubes
and weighing bottles, the construction of which
appears from fig. 2.
The mixing tube (A and B) is taken from the
desic-cator, the cap (B) is put ön and the whole vessel is
weighed. The weighing bottle (fig. 2 C and D),
like-wise kept in a desiccator, is weighed and a suitable
quantity of the oxide (CaO or BaO) brought into A
(fig. 2 C and A), whereupon the bottle is weighed
again. In the same way the calculated quantity of
the silicate preparation is added to the oxide in A,
whereupon B is put ön and A -f- B shaken and rotated
under exactly the same conditions for all mixtures.
c
J
3
Fig. 2.
The quantity of the silicate added to the oxide is
calculated in accordance with the proportions oxide:
dehydrated silicate (meta-kaolin, sillimanite, mullite)
used in the different experiments.
For each experiment small portions of this
per-fectly homogenous mixture are taken out, the weights
of which are determined by weighing the mixing tube,
which contains a quantity of the mixture sufficient
for an entire series of reaction experiments.
The heating has been carried out in a horizontal
electric furnace with great heat capacity and large
range of constant temperature. The furnace is kept
at the reaction temperature in question and two small
platinum vessels, containing portions of the reaction
mixture (about 0,3 g), are heated parallelly in the
heating tube of quarz glass in a current of air, free
from H20 and C02, kept at constant slow speed. The
reaction time has been 60 minutes throughout, except
in some experiments where other data are given. After
the reaction the vessels were moved to the cold part
of the tube outside the furnace for cooling and then
preserved in the desiccator before the analysis as
mentioned above.
No other analyses were made than the
determina-tion of the amount of non-reacted CaO, which was
carried out by means of the glycolate-method by
Schläpfer and Bukowski25. This method gives
quite exact values, when all directions given by the
authors are carefully followed.
The results obtained with the different preparations
appear in the t a b 1 e s showing the amount of
re-acted CaO in per cent by weight of entire
CaO-quan-tity and refer to heated mixtures of CaO and de-
% CaO _ 2
meta-kaolin 1
hydrated kaolin with the molar ratio
(tables 1 and 3) oi (tables 2 and 3). In the mixtures
of CaO with mica, feldspar (table 4), sillimanite
25 P. Schläpper a. R. Bukowski, Swiss. Fed. Test. Mat.
Lab., Zürich, Rep. 63, 1933 ; Schweizer Arch. angew. Wiss.
Techn. 2 (1936), 283—96 ; Röck Products 40 nr 8 (1937),
72—74.
6
11 jan. 1941
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