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Patented Oct. 22, 1946
Corhart Refractories Company, Louisville, Ky.,
a corporation of-Delaware
5N0 Drawing. Application ‘January ‘29, ‘1942,
Serial N0. 428,795
‘7 ‘Claims. ‘('01. 106-57)
2 .
For use as a basic refractory, magnesia has
been widely used for several years, and more re
cently its orthosilicate, forsterite, has also been
any combination of available _materials which
will yield the desired chemical composition in the
, ?nal :meltwill give equivalent results. ‘There ap
favorably received. As made by the traditional
pears ‘to be no significant advantage in using
burning process, such refractories are necessarily 5 purer: materials; except that the ‘iron oxide coh
porous which permits in?ltration of slafgs or
tent ‘must be kept reasonable “to avoid porous
vapors ‘with consequent increased rate of corro
castings. A certain amount of iron oxide is re
sion in use. Furthermore “magnesia ‘refractories ‘ duced and removed by the carbon of the elec
made by burning are notoriously‘weak ‘in spalling
trodes and only with olivenes too high in FeO
has porosity been troublesome. Even these cast
To eliminate this porosity and to ‘produce a
ings, however, were free from cracks and suitable
stronger bond it has been proposed to electrically
‘for some purposes. Any lime, titania, iron oxide
melt and cast to shape, mixtures of magnesia and
'or other minor impurities are 'found in the non‘
silica in such proportions as to yield a mixed
crystalline matrix since in practice, "crystalliza
periclase and forsterite refractory, the silica per 15 tion of my refractories is never complete.
mitting the magnesia to be melted at a practical
Since the extent of ‘crystallization depends
temperature and the excess magnesia yielding a
upon the rate-of cooling, the size of the casting,
more basic refractory. '
the ‘extent of annealing, the chemical composi
When'such melts are made, 'however, the po
tion and other ‘variable factors, ‘in the following
rosity is found to persist, ranging from large 20 disclosure of tiny new refractories, I have elected
blebs and blow holes at the highest magnesia per
to indicate ‘the basicity of the compositions in
centages (highest melting points and greatest
terms of the amounts of major "crystal phases, as
volatilization) to fairly well distributed porosity
calculated ‘from ‘the ‘chemical ‘composition, ‘which
would be present under equilibrium conditions,
that is, after in?nitely slow cooling. In this way
at the periclas'e-forsterite eutectic which porosity
is nevertheless ‘of such volume that it is capable 25
of preventing and eliminating normal pipe for
an idea of the relative basicity is obtained even
mation which should occur when the liquid crys
though this is obscured in practice ‘by the ‘fact
tallizes to a more e?icient packing of the mole-‘
that ‘substantial amounts ‘of glassy matrix may
cules. It is further observed that castings high
be present particularly if the silica is high.
in magnesia are quite brittle while those high in 30» ‘In the ‘binary ‘system, Zl‘Oz is known ‘to take
forsterit‘e exhibit a characteristic splitting in‘ the
Met) into ‘solid solution up to 25% by weight at
plane of the major axis.
the ‘freezing point, ‘but the ‘solubility ‘decreases
In the ?eld of less basic refractories it has been
rapidly with-temperature. ‘ Since the solution of
proposed to further add alumina to the magnesia
MGO converts "the birefringent ZrOgcrystal to an
and silica in forming a melted and cast refrac 35 isometric '(cubic) crystalof lower refractive in
tory. The alumina forms magnesia spinel which
cl'ék,‘ petro'graphic examination Will reveal Wheth
is compatible with periclase and forsterite, but
of‘ ‘solid solution is present. I have found some
, for best results the 'spinel must exceed 50% and
solid solution when Zl‘Ozis added to ‘forsteri‘te but
when spinel is further added, the solid solution
the silica must be vrestricted to 11% (26% for
sterite as a. maximum) which results in a consid
erably less basic refractory than desirable for
many purposes.
-I have‘ discovered that certain compositions of
is apparently suppressed; Finally when periclase
is further added, solid solution returns. Since the
equilibrium ‘conditions for this solid ‘solution are
not accurately ‘known, for‘the purpose of indicat
ing the basicity of my compositions, I have ig
are non-porous, non-brittle ‘and uncracked if 4 01 nored the solution and tabulated qZrOz ‘alone.
zirconia is‘ included with the basic phases of peri
In its broadest aspects the new system is qua
‘clase, forsterite and magnesia spinel. In the
ternary ‘but the quaternary system will be best
new system in contrast to the earlier system, 11%
understood after a discussion of‘the component
binary and tertiary systems. Thebinary systems
silica appears to‘be aminimum limitrather than
a, maximum: limit. A gradation in basicity re-‘ 50 containing the new-phase, zirconia, are zirconia
sults according to which phases are used with
pericla'se, madam-magnesia spinel and zirconia
the neutral ZrOz. ‘
fo‘i'stei‘ite. Ih supporter the ‘necessity or ‘iflcl'u'd
vMy new refractories can be melted in an elec
ing some ll% silica, I have found that the silica
melted and cast refractories can be made which
tric furnace and cast into preformed molds, for
to techniques
Fulcher. given
I have employed zirkite, zircon, magnesite, talc,
bauxite, kyanite and olivene although obviously
free systems zirconia-periclase and zirconia
55 magnesia spinel yield castings which ‘are porous
and subjectv to cracking during cooling. From
the practical standpoint these two binary systems
are less desirable ‘anyway because of the expense
What I claim is:
sterite in a non-crystalline matrix, the forster- V
1. A heat cast refractory consisting essentially
ite amounting to 21%.
of zirconia, magnesia, alumina and silica and
5. A heat cast refractory containing substan
in which the Zirconia is not less than 15% and
tial amounts of crystalline zirconia and forsterite
the silica is not less than 11% and the mols of
in a non-crystalline matrix and in which the zir
magnesia are substantially equal to the mols of
conia is not less than 15%, the silica is not less
alumina plus twice the mols of silica.
than 11% and. the magnesia is not less than 15%
2. A heat cast refractory consisting essentially
by weight by chemical analysis.
of zirconia, magnesia, alumina and silica and in
6. A heat cast refractory having as two of its
which the zirconia is not less than 15%, the alu 10 three major crystalline constituents zirconia and
mina is not less than 11%, the silica is not less
forsterite in a non-crystalline matrix and in
than 11% and the mols 0f magnesia are greater
than the mols of alumina plus twice the mols
of silica.
3. A heat cast refractory containing a substan
tial amount of crystalline Zirconia and over 21%
forsterite in a non-crystalline matrix and in
spinel and a sOlid solution of periclase, and zir
which the zirconia is not less than 15% and the
which the zirconia is not less than 15%, the sil
ica is not less than 11% and the MgO is not less
than 15% by weight by chemical analysis.
'7'. A heat cast refractory having as its major
conia, and containing by chemical analysis silica
between 11 and 24%, alumina between 10' to 40%,
20 zirconia between 15 to 59%, and magnesia be
4. A heat cast refractory having as two of its
tween 10 tO 53%.
major crystalline constituents zirconia and for
silica not less than 11% by weight by chemical
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