CEMENT-FREE SPINEL-BASED REFRACTORY MATERIALS
and A. Belyanin
Translated from Novye Ogneupory, No. 6, pp. 95 – 98, June, 2005.
Channel induction furnaces can operate at temperatures as high as 2000 °C, which requires the use of
high-temperature refractory materials resistant to corrosion. CaO, a conventional component of the corun
dum-containing refractory castables, produces a degrading effect on high-temperature properties; for this rea
son, low- and ultralow cement materials fail to meet the needed requirements. Therefore a cement-free refrac
tory of the DALCAST series in the Al
– MgO binary system based on an Al
fully hydratable binder has
been developed. Physical properties (strength and hardening behavior) of a standard low-cement castable and
a newly developed product based on the results of their practical use in channel induction furnaces are com
pared and discussed.
At present, the channel-type induction furnaces (CIF)
have found wide application in the production of high-alloy
gray cast iron. In these furnaces, infiltration of molten metal
and slag into the refractory material causes chemical corro-
sion and thus accelerate the wear of the furnace lining. Slag
is capable of building up a crust on the lining, which results
in the narrowing of the passage area of the inductor mouth.
Furthermore, with the furnace operating at about 1900°C, the
working lining is capable of caking, and the solid caked layer
thus formed makes the maintenance and repair work more
costly and laborious.
To improve performance of the CIF working lining, a
new cement-free refractory of the series DALCAST (NCC)
using a hydratable alumina bond (Alphabond 300Ô) has
been developed. The hydratable alumina enter into a reaction
with water to form alumina hydrates which, when sintered at
temperatures above 1000°C, convert to a-alumina with a
strong ceramic bonding . In the earlier related work 
concerned with the creep behavior, the high-alumina
refractories with a hydratable bond revealed a low strain rate.
Furthermore, replacing calcium aluminate by hydratable alu
mina has led to an improved thermal stability and increased
strength in the hot state; also, refractories high in alumina ex
hibited an increased resistance to corrosion [1, 3]. Using a
quartz filler in the material gives NCC refractories an added
advantage since, along with the formation of strong
mullite-based ceramic bonds, no low-melting phases in the
– SiO system could be found [2,4–6].
(DEVELOPMENT OF A CEMENT-FREE CASTABLE)
An NCC cement-free refractory and a low-cements re-
fractory have been developed: their fractional and chemical
compositions are given below:
coarse-grain fraction (tabular alumina, high-alumina spinel) 73
fine-grain fraction (fired alumina, reactive alumina,
high-alumina spinel) 21
bond (hydrated alumina for NCC, fired alumina for LCC) <5
Mass fraction, %: NCC LCC
MgO 5.8 5.4
CaO <0.2 1.4
The two refractories show a similar particle size distribu
tion. They mainly differ in CaO content. Specimens for test
ing were sampled in conformance with DIN ENV 1402 re
quirements. The mixing was carried out with 4% water
added; the mixing time was 5 min. To gain insight into the
hardening of refractories, the ultrasonic pulse velocity was
measured as a function of time and temperature. Relevant
data for the temperature range of 5 to 25°C are given in
Fig. 1. Zero point on the X-axis corresponds to the termina
tion of mixing.
The ultrasonic velocity in the LCC refractory within the
initial period of time was constant, and the period length
Refractories and Industrial Ceramics Vol. 46, No. 4, 2005
1083-4877/05/4604-0256 © 2005 Springer Science+Business Media, Inc.
Eisenberger Klebsandwerke (EKW) GmbH, Germany.
Gruppa Magnezit Joint-Stock Co., Russia.