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Patented Sept. 24, 1946
, . „ Corhart Refractories Company,
Louisville, Ky.,
~ arcorporatîon of Delaware
Application August 1, 1944, Serial No. 547,565v
6 Claims.
(o1. 10s-59.)
of as much as V50% FeO.A120a to the good
FeQCrzOa inthe syt'em disclosed in my U. S. Pat
ent 2,271,365 promotes swelling of this also. It is
very surprising therefore that my tests show
f, that mixtures of al1 three spinels, FeO.Cr2Os,
MgO.Cr2O3 and FeO.Al2O3 give a remarkably
stable> refractory with a minimum of reaction
This invention relates. to a novel heat cast
chromite refractory, which is particularly suit
able for use at high temperatures in contact With
slags high in iron oxide. lBy heat cast is meant
the complete melting as for example with the
techiniques disclosed in U.; S. Patent #1,615,750
to Fulcher, and shaping .into the desired form
by casting into molds and solidifying. ’
The extensive use of electric furnaces for melt
ing alloy steels~ has created new refractory prob
with‘the slag." ' The inclusion of the FeO.Al2O3
decreases the Cr2O3 necessary and therefore low
10> ers cost. A solid solution of course results when
a melt containing oxides in spinel proportions isl
lems since the slags which arepreferred may
cooled and the spinels do not have individual
be quite diñerent from thel traditional high al
existences inthe crystal phase. Nor is it essen
kaline earth slags of the blast ‘furnace and the
tial that the bivalentand trivalent oxides be
open hearth. The slag in an electric furnace
present in exactly equal molar quantities since
melting chrome steel commercially for examplel
an’excess of as much as 20% of one or the
analysed roughly 72% FeO, 16% A1202, 4% Cr203,
other can apparently bev absorbed by the solid l
6% -Si02- and only 2% CaO and MgO, and such
»solution In other words it is suflicient that the
a slag has been used for test purposes on the
moles of trivalent oxidev (A1202 and CrzOa) lie
novel refractories disclosed below. In such a fur
between 80 and 120% of the moles of bivalent
nace, attack on the refractories is partly chem 20 oxide (FeG and MgO). Since both FeO and
ical corrosion» and partly mechanical erosion.
CrzOa are easily reduced during melting in the
I have found that a heat cast refractory is par
presence of carbon electrodes and since MgO
ticularly advantageous where erosion Yis a factor
volatilizes to som-e extent, the permissibility ofV
since the crystals in forming on solidiñcation ap
some variation is a distinct advantage. Since
parently interlock and at anyrate give a strongly 25 excess FeO is harmful to resistance and since
coherent body even whenj- reheated above the
Cr2O3 is the most expensive ingredient, I prefer
softening ltemperature of the amorphous matrix
to calculate spinel proportions for the batch with
associated with such refractories.` This matrixl
the result that the product will err on the side
replaces both the porosity and the ?luxing bond > of‘ higher A1203 and MgO- rather than higher
of theburnt refractory and since it is in sub
stantial equilibrium' with the crystals it is not
FeO or CrzOs.
To minimize the reduction to
metallic iron I prefer -to add the iron oxide as
appreciably corrosive on these crystals as` the
Fe2Oa or'lï‘eaOiv While commercial chrome green
temperature is increased and onthe’other Ahand u may ¿be used for Cr203 and a good grade of com
by its substitution ~>for porosity> prevents ready , mercial magnesite for the MgO, the alumina be
access of slags which` are corrosive into the body-V
ing the chemically pure vgrade used'vfor metal
ofthe refractory. ,_
In my U. S. Patent 2,271,363 I have disclosed
a heat cast refractory consisting of FeO.Cr2Os,
to be made from pure materials since this was
developed for use against commercial glasses
Where the presence of SiO2 or MgO and A1203
together is harmful. V„l have found that pure
FeQCrzOs> is excellent in chemical resistance to
high FeO slags also but the high Cr2O3 content
(68%) and the cost of pure materials is a draw
back to general commercial use. Also expen
sive and even higher in Cr2O3 content (79%) is
pure MgO.Cr2O3 as disclosed in my U. S. Patent
2,271,362 but this refractory also has limitations>
in its tendency to swell and disrupt undermoxi
dizing conditions. Even the Vcombination of as`
much as 50% FeO.Cr2Os with MgO.Cr2O3 in the
system `disclosed in my U. S. Patent 2,271,364 did
not entirely prevent this swelling in contact With
the high FeO slag. On the otherV hand addition
production _by electrolysis.
Specimen batches
which I have heat cast and tested against the
high FeO slag are illustrated in Table I below.
The analyses are calculated into approximate
spinel proportions as shown in Table II and test
results,-- with the high F‘eO- slag are indicated.
Batch composition, in per cent by weight
A120: ,
Calculated proportions in mol percent
Slag tests were made by mixing 25% byxvolume
slag with the powdered refractory and vfiring for
71/2 hours at 1500° C.
The shrinkage and de-`
crease in apparent porosity was taken as an indi-v
cation of the extent of interaction, while oxida- y
refractory. With complete melting it is also pos
sible to adjust the composition to minimize non
spinel crystallization. In Table IlI are listed
batches with chrome ore as an ingredient which
have all given good tests against the high FeO,
tion was indicated by swelling. >With pure mate
low alkaline earth slag. ,„
rials it was found that equally good results were 20
obtained with melt H which has 17% less Cr203
than melt A and subsequent service tests with
brick of this composition have given outstand
C2203 FeO MgO A1203 m . . O »
ing performance where commercial burnt refrac
tories failed rapidly.
I have also discovered that unlike the results
in tests against commercial bottle glass, a certain
amount of Si02 can be tolerated without ruining
the resistance to slag despite high FeO content.
Good results were obtained when as much as 8%
SiOz was added to ferrous chromite.
The possibility of including SiO2 as well as
MgO and A1203 permits the substitution of chrome
ore for at least part of the chrome green with a
distinct saving in costs. Tests with chrome ore
included in the batch have shown however that
the S102 should still be kept as low as possible.
For this reason as well as to permit maximum
These batches were made by using the maxi
mum amount of the above chrome ore, adding to
it necessary amounts of chrome green, alumina,
magnesite or Fe304 (and in one case kyam'te) to
give the indicated analysis. At the lower Cr203
substitution of the chromev ore for chrome green ~
it is desirable to use a high grade, chemical typev 40. level the resistance to slag clearly decreased as
MgO replaced FeO contrary to the usual teach
of chrome ore. One which I have found suitable
ings for burnt chrome refractorles for use against
high alkaline earth slags. This effect is so pro
nounced in fact that substantially equivalent re
analysed 52.55% Cr2O3, 14.56% (total Fe as) FeO,
15.72% MgO, 11.72% A1203, 1.57% CaO, and 3.31%
As it occurs in nature, the primary component 45 sults were obtained on the test for melt VJ with
20% Cr203 and melt O with 38.6% C1203, the
of chrome ore is usually considered to be
former being high in FeO and the latter in MgO.
With FeO maintained high however, resistance
increased as Cr203 increased. Even the 1% -of
Si02 in melt Q in comparison with melt H showed
but considerable of the FeO is replaced with MgO
and considerable of the Cr203 is replaced by 50 a measurable effect on resistance and in general
A1203 while of even greater» importance to its
characteristics as a refractory, a gangue is also l
present in which the following magnesium sil
icates have been identified in various ores:
Si02 should be kept below 5% to gain the full
advantage of such batches.
Fig. 1 is the conventional representation by an
equilateral tetrahedron of all compositions on a
55 weight per cent basis which exist in the four-
component system CrzOs-MgO-FeO-AlgOs. The
six binary systems, i. e., FeO-CrzOa, MgO-Cr20s,
For use in burnt refractories an attempt to sta
bilize and distribute this gangue is often made by
heating the ore to recrystallization temperatures
MgO-AlzOa, are represented' by compositions
60 along the edges of the tetrahedron. The four
ternary systems, i. e., FeO-MgO-CrzOs, CrzOs
MgO-AlzOs, Al2O2-FeO-Cr2O3 and FeO-MgO
A1203, are represented by compositions on the
before compounding. Complete recrystallization 65 triangular faces of the tetrahedron. All composi
tions of four oxides are represented by points
through fusion has been tried-»but it was found
Within the tetrahedron. Four of the binary sys
that the secondary component was generally
tems are between a bivalent oxide and a trivalent
poorer from the refractory standpoint than when
the same ore was recrystallized at a temperature
below the fusion point. "
When the refractory compositions are com-._
pletely melted and cast to shape however these
oxide and these form spinels l(FeO.Cr2O3,
MgO.Cr2O3, FeO.Al2O3 and Mg0.Al2Os) at the
70 points indicated on the edges of the tetrahedron.
A11 four ternary systems have solid solutions be
tween two spinels (FeO.Cr20a-MgO.Cr2O3,
considerations are unimportant because the re
MgO.Cr203-MgO.Al2O3, MgO.A12O3-FeO.Al2Oa and
fractory is held together by interlocking crystalsv
thev compositions of which
rather than by the fluxing matrix as in the burnt 75 Fe0.Al2O3-FeO.'Cr2O3),
are represented by points on theV straight lines
FeO.Fe203 and.-ll'llîgo?xllezO3` as >components 'with
the? other .fóur' spirielsï" ln burnt refractories this
lî‘e203` is preservedfand. in fact 'some additional
Fe203 may. be formed during burning by oxida
tionzof :part'oïf the'lì‘eO.y In manufacture» of the
which connect' the two spinel's on the: triangular
faces of the tetrahedron'; All compositions of four
oxides in whichv the moles oflbivalent oxide 4are
equal ‘to theinoles of trivalent oxide fall on the
shaded ’plane of Fig. 1 which passes‘thrïougn the
four spinel compositions. All compositions which
heat cast refractory »in thek .presence of carbon
electrodes however, conditions are reducing and
the .oxide> must be in equilibrium with metallic
iron being formed, so'that k1ï‘e20'3 originally pres
entjis substantially all converted to FeO, keeping
the system'. quaternary.V Since FeO‘Jï‘ezOa is not
Ihave found resistant to- high FeO, low alkaline
earth'slag are on, or yclose to, this plane in conr
. Because only three points' are required‘toiix a 10
plane but four spinels are located on this plane
n very refractory. this 'is another advantage of the
it follows that compositions on the plane can be
vheat cast refractory over a burnt refractory.
expressed in more than one way in terms of the
While the burnt refractory art teaches that
Fe0.Cr203 is unstable at elevated temperatures
and that it is advantageous to add MgO to con
vert to Mg0.Cr203 and FeO, I have not found heat
cast refractories high in FeO.Cr203 especially sus
lation however and for that reason I express my
ceptible to oxidation. I attribute this to the lack
compositions in terms of individual spinels. All
of porosity which confines any oxidation attack
compositions in the shaded plane of Fig. 1 are
to the surface alone.
shown on a magnified scale as a spinel tetra
In Table V below I give the mol values of the
hedron in Fig. 2. According to my discoveries it
four major constituents of melts'G to T inclusive
is advantageous to select for a high FeO, low
of the above Tables I and III:
alkaline earth slag, a spinel composition with ap»
preciable percentages of Fe0.Cr203 and FeO.A1203
spinels present.> Actually, since a solid solution
occurs between these spinel oxides, description in
terms of individual spinels is artificial anyway.
Such description has advantages in batch calcu
as well as MgO.Cr2O3 and Mg0.Al203. f A single
Mzllzmols in 100 grams of batch
composition of FeO, MgO, Cr203> and A1203 can
in general be represented by a line in the spinel
tetrahedron with its ends in two different faces
of the tetrahedron; that is, as long as the moles
of bivalent oxide equal the moles of trivalent oxide
the Quaternary composition can be represented
by points in two ternary spinel planes or «by those
Quaternary spinel compositions along a line con
necting in the tetrahedron the two ternary com
Thus in Table IV are given the two calculated
‘terminal ternary Ispinel compositions for such
composition lines for the batches in Table III.
The calculations ignore the» S102 and CaO im
purities and therefore add up to 100% for visualizing their location in Fig. 2. With the normal
amount of annealing given a heat cast refractory,
In the following claims I meanby “principally”
over 90% of the total composition of the re
the composition does not crystallize completely
and the Si02 remains as an amorphous matrix
What I claim is:
1. A heat cast refractory composed principally
of Cr203, FeO, A1203 and MgO in which the moles
of Cr2013 plus Al203 lie between 80% and 120%
of the moles of FeO plus MgO and in which the
FeO is not less than 8%, the MgO not less than
containing any impurities and residual amounts
of spinel forming oxides.
1.5%, the C`r203 not less than 11% and the A1203
not over 50% by weight by chemical analysis and
in which the ratio of the mols of MgCl to the'mols
of FeO lies between 0.1 and 4.
2. A heat cast refractory composed principally
of Cr203, FeO, A1203 and MgO in which the moles
of Cr203 plus A1203 lie between 80% and 120%
of the moles of FeO plus MgO and in which the '
FeO lies between 8% and 38%, the MgO lies be
60 tween 1.5% and 21%, the Cr203 lies between y11%
and 80% and the A1203 lies >between 5% and 50%
by weight by chemical analysis and in which the
ratio of the mols of MgO to the mols of FeO lies
' between 0.1 and 4.
It is characteristic of these novel compositions
that appreciable percentages are in the propor
tions of Fe0.Cr2O3 and F‘e0.Al203 and that all
four spinel forming oxides are present. ì
In natural chrome ores, varying amounts of
the iron oxide are present as Fe203 and such ores
should be considered in a sexenary system with .
3. A heat cast refractory composed principally
of Cr203, FeO, A1203 and MgO substantially in
the proportions of their spinels in which the pro
portion of Fe0.Cr203 liesbetween 40% and 60%,
the proportion of Mg0.Cr203 lies between 20%
and 40% and the pro-portion of Fe0.Al20_3 lies
between 20% and 40% by weight and in which
`theiron oxide is in excess of 20%` by weight.
4. A heat cast refractory composed principally
of Cr203, FeO, A1203, MgO and S102 in which the
>moles of C1203 plus A1203 lie between 80% and
120% of the moles of FeOplus MgO vand in which
the FeO is not less than 8%, the MgO is not less
than 1.5%, the'CrzOs is not less than 11%, the
A1203 is not over-50% and the SîOz is not over 8%
'by weight by chemical analysis and in which the
ratio of the mols of MgO to the mols of FeO lies
between 0.1 and 4.
5. A heat cast refractory composed principally
of 8-38% Feo, 1.5-21% Mgo, 11-80% Crzoa,
5-50% A1203 and 0-8% SiOz by weight and in
which the moles of 01'203 plus A1203 lie between
80% and 120% of the moles of FeO plus MgO and
in which the ratio of the mols of Mg0 to the mols
of FeO lies between 0.1 and 4.
6. A heat cast refractory composed principally
of 1-5% S102 and of CrzOa, FeO, A1203 and MgO
substantially the proportions of their spinels and
in which the proportion of Fe0.Cr203 lies be
tween 40% and 60 %, the proportion of Mg0.Cr20a
lies between 20% and 40% and the proportion of
FeO.Al2O3 lies between 20% and 40% by Weight
and in which the iron oxide is in excess of 20%
by weight.
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