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TekniskTidskrift
Reacted CaO in per cent by weight ofentire CaO-quantity
900 mo mo
Reaction temp.°C
not perfectly puré.
Without going into
de-tails it is quite sure
that this slow process
includes the formation
of intermediate phases
of transition of status
nascens type which are
always characterized by
imperfect lattices and
high activity. This will
always be the case if
the sillimanite has only
been preheated at
temperatures a little above
1000°, this
tempera-ture however being
considerably dependent
ön the kind of
sillimanite preparation used
and of course also ön
the heating period.
Preparations of sillimanite
preheated in this way
Fig.
temperatures where it begins to decompose, because
of the interest of this for problems dealt with here.
In the introduction of this paper it has been shown
that sillimanite is not stable at higher temperatures,
but that mullite is formed:
3 [Al,Og • SiOJ 3 A1203 • 2 Si02 + Si02.
Previous work makes probable that the transformation
into mullite and cristobalite begins at about 1 000°
at least when using a sillimanite mineral which is
Tab. 0.
I Mixtures Thermal
treat-ment of
sillimanite before reaction (preheating) Reaction temperatures (°C) heating times and reacted CaO in per cents by weight of entire OaO-quantity
1000
lh. 5 h.
CaO + sillimanite molar CaO 2 ratio A1203 • Si02 1 800° 5 h. 29,3 37,3
molar CaO _ 3 ratio AhOs-SiOa 1 800 ° 5 h. 26,4 34,5
Tab. 5. Reaction temperatures (°C) and reacted CaO in per cents by weight of entire CaO-quantity.
Mixtures Thermal
treat-ment of
sillimanite before reaction (preheating) 400 500 600 700 800 900 1000 1100
CaO + sillimanite CaO 2 molar ratio _ = Als Os • SlOa 1 600° 1 h. 3,6 3,9 5,3 6,1 7,6 17,7 34,7 59,3
5 „ 3,3 3,6 4,8 5,7 8,9 17,5 36,1 59,8
800° 1 „ 3,6 4,4 4,5 5,7 7,9 18,3 35,9 57,4
» 5 ,, 2,8 3,3 3,4 4,2 5,0 15,6 29,3 47,4
1 000° 1 „ 4,6 17,2 6,3 7,4 7,6 15,8 29,0 45,1
»> 5 ,, 3,6 9,1 4,1 4,9 7,0 15,7 29.4 46,0
CaO 3 molar ratio .. „—= T AUO» • SlOa 1 600° 1 h. 3,7 3,6 4,4 4,5 7,1 15,6 27,4 46,1
„ 5 „ 2,2 3,1 3,7 4,2 6,5 11,1 26,2 46,5
800° 1 „ 4,1 5,2 3,9 4,6 6,0 16,0 28,1 47,1
„ 5 „ 3,8 4,7 4,5 4,3 5,7 13,6 26,4 48,2
1000° 1 „ 3,3 9,8 7,3 6,7 7,7 17,1 30,7 46,8
5 „ 3,4 6,8 4,8 5,3 7,6 14,3 27,8 44,9
Tab. 7.
Mixtures Thermal treatment of mullite before reaction Reaction temperatures (°C) and reacted CaO in per cents by weight of entire CaO quantity
(preheating) 400 500 600 700 800 900 1000 1100
CaO + mullite Dried atll0°lli 5,9 6,5 6,4 8,4 8,2 18,4 38,1 72,6
CaO molar ratio —s-hw = 3 AlaOa • 2 S1O2 7 T 700° 5 h 3,4 • 4,2 5,1 5,0 6,3 21,6 35,2 57,1
26
11 okt. 1941
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