Refractory compositions and method

A basic refractory composition includes a magnesium oxide source, aluminum phosphate and an insulating material selected from the group consisting of perlite, vermiculite, diatomaceous earth, and mixtures thereof in an amount of 5.60% based on the total weight of the composition. The composition provides excellent temperature resistance while retaining unexpected strength for a magnesium oxide based chemically bound refractory material having a substantial portion of insulating material.

FIELD OF THE INVENTION 
The present invention relates to chemically bonded refractory compositions 
and method and more particularly relates to chemically bonded refractory 
ramming mix compositions including an aluminum phosphate binder a portion 
of which forms in situ to provide a strong, chemically bonded, refractory 
composition. The refractory composition is particularly useful for linings 
in furnaces, hot metal ladies and other uses well known in the refractory 
art, particularly where high temperatures above 1500.degree.-2000.degree. 
F. are encountered. In accordance with one embodiment of the present 
invention, an insulating material, such as perlite, vermiculite or 
diatomaceous earth is included in the composition to provide greater heat 
insulating resistance to the refractory composition, while retaining 
unexpectedly good strength prior to ceramic bond formation. The refractory 
compositions of the present invention have unexpectedly long shelf lives 
and increased strength while in the plastic or wet state. 
In accordance with another embodiment of the present invention, a dry, 
basic refractory material based upon magnesium oxide forms an in situ 
magnesium aluminum phosphate bond upon addition of water. 
BACKGROUND OF THE INVENTION 
Refractory ramming mix compositions containing a relatively high percentage 
of alumina chemically bound by phosphoric acid or an aluminum phosphate 
are well known in the art, particularly as described in the following 
patents: Salizar U.S. Pat. No. 3,547,664; Noda, et al. U.S. Pat. Nos. 
3,958,582 and 3,891,009; Beeler U.S. Pat. No. 4,177,308; and Erskine U.S. 
Pat. No. 4,248,810. In some of these patents, an insulating material, such 
as perlite, is included to provide a light, temperature resistant 
refractory heat-insulating composition. The compositions generally are 
mixed to the consistency of a paste or mortar consistency so that the 
composition can be mixed, spread into a desired shape and sliced to form a 
slab of predetermined dimensions before the slices or slabs are rammed or 
pounded into place in a moist condition to physically and chemically form 
a monolithic refractory lining. The lining is then heated to drive off the 
moisture and heated at high temperature to form the final set or ceramic 
bond necessary in a refractory lining. 
As set forth in my prior U.S. Pat. No. 3,547,664, two of the biggest 
problems in prior art high alumina ramming mixes are cracking upon drying 
and a need for higher strength at temperatures in which a mix must rely 
upon a chemical bond before the ceramic bond is formed. In accordance with 
my prior patent, I found that including ceramic fibers in an amount of 
about 2-6% by weight of clay in the mix provides a stronger ramming mix 
which does not crack upon drying. 
Another problem with prior art high alumina ramming mixes, particularly 
prevalent in chemically bound ramming mixes, is the inability to provide a 
ramming mix which has a shelf life of more than about three weeks. After a 
chemically bound ramming mix is sliced to form a slab of predetermined 
dimensions, the ramming mix begins to dry as a result of ambient 
conditions and, particularly, where a chemical binder such as aluminum 
phosphate is being formed in situ such as described in my prior U.S. Pat. 
No. 3,547,664, where phosphoric acid reacts with alumina to form the 
aluminum phosphate binder. This in situ reaction between phosphoric acid 
and alumina is exothermic resulting in moisture being driven away from the 
ramming mix. The ramming mix must be moist when rammed or pounded into 
position as a lining and, therefore, ramming mixes of the prior art 
generally have had a shelf life of about three weeks or less. Liquid 
aluminum phosphate has been added as the chemical binder in some prior art 
refractory ramming mixes and, generally, since these refractory ramming 
mixes do not depend upon an in situ reaction for the formation of the 
aluminum phosphate binder, it has been found that the shelf life problem 
is not as severe. However, no prior art refractory ramming wires using a 
chemical binder will remain sufficiently wet for ramming or pounding into 
place significantly more than about three weeks. 
SUMMARY OF THE INVENTION 
In accordance with one embodiment of the present invention, suprisingly it 
has been found that refractory compositions based upon alumina or aluminum 
silicate chemically bound by aluminum phosphate have a shelf life of three 
months to more than one year where the composition includes both liquid 
aluminum phosphate and phosphoric acid to form a portion of the aluminum 
phosphate binder in situ. In accordance with another embodiment of the 
present invention, increased strength is achieved by including alumina, 
and an aluminum silicate bearing material, such as clay, in the refractory 
composition to form the in situ aluminum phosphate bond from the reaction 
of phosphoric acid and aluminum silicate. The aluminum phosphate should be 
provided in the composition in an amount of about 5% to about 70% by 
weight of the bone dry composition and the phosphoric acid should be 
included in an amount in the range of about 1% to about 10% based on the 
weight of the bone dry composition to provide the suprisingly new and 
unexpected shelf life to the refractory composition. It has been found 
that the phosphoric acid will partially react with the alumina or aluminum 
silicate of the refractory composition and partially provide wetting to 
the refractory ramming mix. The phosphoric acid wetting does not 
deleteriously effect the aluminum phosphate chemical binder. In fact, 
suprisingly, it has been found that greater strength is achieved in the 
refractory composition when both the aluminum phosphate and the phosphoric 
acid are included together than in prior art refractory composition 
utilizing the aluminum phosphate binder which is added either as aluminum 
phosphate or as phosphoric acid for reaction with alumina in situ. 
Accordingly, suprisingly longer shelf lives and suprisingly greater 
crushing strengths are achieved by including both aluminum phosphate and 
phosphoric acid, in the amounts specified, in the refactory ramming mix. 
In accordance with another embodiment of the present invention, the 
aluminum phosphate and phosphoric acid together are particularly useful in 
a refractory ramming mix composition containing a heat insulator such as 
perlite, vermiculite, diatomaceous earth, expanded clay, flourspar, or an 
additive which is intended to be burned out to leave a void space at the 
intended use of the refractory, such as wood flour, sawdust, burnable 
fibers and the like. Refractory ramming mixes containing at least 5% of 
such an insulating component inherently are weaker, but are unexpectedly 
strengthened in accordance with the present invention by including both 
aluminum phosphate and phosphoric acid chemical binders. 
Accordingly, an object of the present invention is to provide a refractory 
material based on alumina, aluminum silicate or mixtures thereof having a 
much longer shelf life than similar prior art refractory materials. 
Another object of the present invention is to provide a refractory material 
based upon alumina, aluminum silicate or mixtures thereof which retains 
its plasticity or workability for unexpectedly long periods of time before 
curing. 
Another object of the present invention is to provide a refractory ramming 
mix based upon alumina, aluminum silicate or mixtures thereof wherein part 
of the binder is included in the refractory mix as aluminum phosphate and 
a portion of the binder is added as phosphoric acid for reaction in situ 
as the ramming mix is cured to provide a stronger refractory material 
having a longer shelf life. 
Another object of the present invention is to provide a refractory, 
insulating material based upon alumina, aluminum silicate or mixtures 
thereof and including an insulating material selected from the group 
consisting of perlite, vermiculite, diatomaceous path, expanded clay and 
mixtures thereof. 
Another object of the present invention is to provide a refractory ramming 
mix based upon alumina, aluminum silicate or mixtures thereof including 
expanded clay and a material such as perlite, vermiculite, sawdust or 
other material which will burn out at the temperature encountered in the 
environment of use leaving voids in the refractory material for the 
purpose of insulation to provide a refractory capable of withstanding 
temperatures of 2500.degree.-3500.degree. F. while retaining unexpectedly 
superior strength characteristics. 
Another object of the present invention is to provide a dry method and 
refractory article based upon magnesium oxide or mixtures of magnesium 
oxide with chrome ores to provide a basic refractory material. 
Another object of the present invention is to provide a basic refractory 
material based upon magnesium oxide or mixtures of magnesium oxide with 
chrome materials which can be mixed with water at the job site to provide 
a plastic or pastey consistency so that the basic refractory material can 
be trowled or otherwise suitably applied in place to act as a lining for a 
furnace or other high temperature environment thereby forming a magnesium 
aluminum phosphate chemical bond in situ. 
DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the present invention, a refractory ramming mix having a 
plastic or pastey consistency chemically bonded by a combination of liquid 
aluminum phosphate and an in situ binder formed by the reaction of 
phosphoric acid and alumina or an aluminum silicate bearing material, such 
as bentonite clay, is capable of withstanding temperatures in the area of 
2,000.degree.-3,500.degree. F. The plastic, chemically bonded refractory 
ramming mix has a suprisingly unexpected shelf life in the range of 3 
months to more than one year and is stronger than prior art refractory 
ramming mixes which utilize either prereacted aluminum phosphate or the in 
situ reaction of phosphoric acid with alumina or aluminum silicate. 
In accordance with an important embodiment of the present invention, the 
plastic refractory composition includes an insulating material such as 
perlite, vermiculite, or diatomaceous earth to provide an insulating, 
refractory plastic composition containing both liquid aluminum phosphate 
and a in situ reaction product binder formed from the reaction of 
phosphoric acid with alumina or an aluminum silicate containing material 
such as clay. It has been found that both increased shelf life and 
increased strength are achieved in accordance with the present invention, 
even with the inclusion of a substantial percentage, for example 5-60%, of 
the insulating material. Higher temperature resistance can be achieved by 
using what is commonly known as bubble alumina--an alumina containing void 
spaces or air pockets therein, or mixing a burnable material, such as 
sawdust, with alumina or aluminum silicate so that when fired, the 
burnable material contained in the alumina or aluminum silicate will 
pyrolyze leaving void spaces to increase its insulating properties. 
In accordance with one embodiment of the present invention, the refractory 
composition includes liquid aluminum phosphate in an amount of 5-70%; a 
refractory material comprising alumina, aluminum silicate or mixtures 
thereof in an amount of 2-94%; and phosphoric acid in an amount of 1-10% 
by weight of the total composition. Surprisingly, it has been found that 
this refractory composition using both liquid aluminum phosphate and 
phosphoric acid has unusually long, unexpected shelf lives of 3 months to 
more than 1 year as a result of the chemical bonding being formed 
partially in situ as the reaction product of the free phosphoric acid with 
the alumina or aluminum silicate refractory material. The shelf life is 
not only unexpectedly increased, but the product is stronger than if the 
refractory material is chemically bonded by aluminum phosphate alone or by 
completely forming the bond in situ by reaction of phosphoric acid with 
alumina or alumina silicate. It would be expected that the partial in situ 
binding as a result of the reaction between phosphoric acid and alumina or 
aluminum silicate would cause a decrease in the shelf life of the 
refractory ramming mix since the reaction is exothermic and would 
inherently drive off some of the moisture from the ramming mix slab. 
However, unexpectedly, the ramming mix composition of this embodiment of 
the present invention has unexpectedly long shelf lives of three months to 
more than one year. In fact, one test sample remains in a rammable or 
poundable plastic consistency after being sliced to predetermined 
dimensions more than one year ago. 
It is theorized that the liquid aluminum phosphate and the lquid phosphoric 
acid combine to provide a unique and unexpected wetting action to the 
refractory compositions of the present invention enabling the refractory 
ramming composition to remain wet and suitable for ramming into position 
for unexpected periods of time. Liquid aluminum phosphate alone, or 
phosphoric acid alone for in situ reaction to provide aluminum phosphate, 
provide shelf lives of at most about 3 weeks. Additionally, the 
combination of both aluminum phosphate and phosphoric acid provide a 
stronger product apparently resulting from the in situ partial bond by the 
reaction of phosphoric acid with either alumina or aluminum silicate. In 
either case, the reaction produces an in situ aluminum phosphate bond. 
Phosphoric acid in an amount of at least one percent should be included in 
the refractory ramming mix in order to achieve the in situ bonding and the 
unexpected shelf life and strength in the refractory product while more 
than 10% phosphoric acid may create a supersaturated mix which is 
difficult or impossible to cure. 
In accordance with another important feature of the present invention, it 
is unnecessary to add any water to the refractory ramming mix. Water may 
be added in an amount of 1-20% of the total weight of the composition if 
it is necessary in order to achieve a proper consistency or workability so 
that a plastic or pasty commposition can be spread to a desired shape, but 
the liquid aluminum phosphate and the free phosphoric acid contained in 
the refractory composition of the present invention is generally 
sufficient to provide the proper consistency and workability, particularly 
where the aluminum phosphate is contained in the composition in an amount 
in the range of 20-70% by weight. 
Generally, some water in an amount for example 1% by weight of the total 
composition is introduced into the mix with the phosphoric acid but it is 
otherwise unnecessary to add water for the purpose of plasticity or 
workability in the composition. It has been found that the addition of 
water in the composition of the present invention will result in a 
somewhat weaker product due to voids contained in the refractory material 
upon release of the water from the ramming mix, although voids may add 
further insulating characteristics to the refractory composition. Other 
refractory granular materials or ceramic fibers may be added to the 
composition of the present invention for economic reasons or to improve 
the strength of the composition. 
The alumina utilized in accordance with the composition of the present 
invention is a granular processed alumina which is relatively pure 
Al.sub.2 O.sub.3. The alumina may be tabular to achieve a denser product 
or calcined alumina and may include bubble alumina having a higher 
insulating value. For higher temperature resistance the alumina may be 
less dense calcined alumina generally having a density on the order of 
80-100 lbs. per cubic foot, but since calcined alumina is not normally 
commercially available in coarser grain sizes, it is generally preferred 
to include a mixture of tabular alumina and calcined alumina, as disclosed 
in my prior U.S. Pat. No. 3,547,664. Generally, for the purpose of the 
present invention, higher temperature resistance can be achieved if at 
least a portion of the alumina has a particle size of -325 mesh. 
Clay is useful in accordance with the composition of the present invention 
to aid in providing the requisite plasticity and workability necessary for 
ramming and also may be used as a source of aluminum silicate for reaction 
with the phosphoric acid to provide the in situ aluminum phosphate binder. 
Any of the plastic clays or any other source of aluminum silicate may be 
used in accordance with the principles of the present invention. 
Generally, some clay should be present in order to provide a thickening of 
the refractory composition to a pasty or mortar-like consistency. Kaolin 
clay, ball clay, bentonite and the like serve as thickening agents in the 
initial sheeting out of the refractory commposition of the present 
invention to a desired shape and, during curing, the clay or other source 
of aluminum silicate will react with the free phosphoric acid in the mix 
to provide in situ bonding thereby achieving unexpectedly long shelf lives 
and strength in the compositions of the present inventions. 
To achieve the full advantage of the present invention, clay should be 
included in the refractory composition in an amount in the range of about 
1 to about 30% by weight of the total composition to provide thickening 
and an aluminum silicate source for reaction with the phosphoric acid. 
Other aluminum silicates may be used for reaction with phosphoric acid to 
provide the aluminum phosphate in situ binder. The phosphoric acid 
included in the composition of the present invention reacts not only with 
the alumina or aluminum silicate refractory material but also with the 
clay component, when present, giving a stronger bond to the product. 
After the refractory composition of the present invention is spread into a 
desired shape and sliced to predetermined dimensions, the clay or other 
source of aluminum silicate begins to react with the phosphoric acid. Once 
the refractory slabs or slices are rammed or pounded into place, the 
material is heated to a temperature of at least 450.degree. F. to complete 
the reaction between the aluminum silicate or clay and the phosphoric 
acid, to dry the refractory material and to irreversibly set the 
phosphoric acid-aluminum silicate reaction. Thereafter the material is 
fused at a temperature of about 4,000.degree. F. to create the ceramic 
bond.

It has been found that by including an insulating material in the 
refractory composition of the present invention, an exceptionally high 
temperature resistance can be imparted to the composition while providing 
a composition with excellent strength and shelf life. The following 
examples show exemplary refractory material compositions having 
temperature resistance at various, indicated levels. The percentages 
indicated in the examples are percent by weight of the total composition: 
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EXAMPLE 1 - 2000.degree. F. 
Liquid aluminum phosphate 5-70% 
Aluminum silicate 10-89% 
Phosphoric acid 1-10% 
Perlite, vermiculite or diatomaceous earth 
5-40% 
EXAMPLE 2 - 2500.degree. F. 
Liquid aluminum phosphate 5-70% 
Alumina 20-88% 
Phosphoric acid 1-10% 
Perlite, vermiculite or diatomaceous earth 
5-40% 
Fibers burnable below 2500.degree. F., for 
example, cotton or polyester fibers 
5-20% 
EXAMPLE 3 - 3000.degree. F. 
Liquid aluminum phosphate 5-70% 
Alumina 25-88% 
Phosphoric acid 1-10% 
Expanded clay, i.e. bentonite 
1-30% 
Perlite, vermiculite or diatomaceous earth 
5-40% 
EXAMPLE 4 - 3000.degree. F. 
Liquid aluminum phosphate 5-70% 
Bubble alumina and expanded clay 
i.e. bentonite, in weight proportions 
of 1:2 to 2:1 25-88% 
Phosphoric acid 1-10% 
Perlite, vermiculite or diatomaceous earth 
5-20% 
fibers burnable below 3000.degree. F. 
Kaolin, ball clay or mixtures 
1-30% 
EXAMPLE 5 - 3500.degree. F. 
Liquid aluminum phosphate 5-70% 
Bubble alumina 10-78% 
Finely ground alumina (-325 mesh) 
10-78% 
Phosphoric acid 1-10% 
Perlite, vermiculite or diatomaceous earth 
5-40% 
Bentonite 1-30% 
EXAMPLE 6 
Liquid aluminum phosphate 50% 
Alumina -100 Mesh 7% 
-325 Mesh 7% 
Phosphoric acid (80% H.sub.3 PO.sub.4) 
2% 
Expanded Kaolin Clay 15% 
Expanded perlite* 16% 
Bentonite 1% 
Ball clay 2% 
______________________________________ 
*-10 Mesh -20 Mesh -200 Mesh 
Perlite 8% 4% 4% 
EXAMPLE 7 
Liquid aluminum phosphate 35% 
Alumina -100 Mesh 5% 
-325 Mesh 10% 
Phosphoric acid (80% H.sub.3 PO.sub.4) 
5% 
Expanded Kaolin Clay 10% 
Expanded perlite* 10% 
Bentonite 15% 
Ball clay 10% 
______________________________________ 
*-10 Mesh -20 Mesh -200 Mesh 
Perlite 2% 6% 2% 
EXAMPLE 8 
Liquid aluminum phosphate 40% 
Alumina -100 Mesh 10% 
-325 Mesh 10% 
Phosphoric acid (80% H.sub.3 PO.sub.4) 
4% 
Expanded perlite* 20% 
Expanded ball clay 8% 
Clay - Bentonite 2% 
Ball clay 1% 
Ceramic fibers 5% 
______________________________________ 
*-10 Mesh -20 Mesh -200 Mesh 
Perlite 5% 5% 10% 
______________________________________ 
In accordance with another important embodiment of the present invention, a 
basic refractory composition is prepared based upon magnesium oxide, 
magnesite, dolomite, chromemagnesite, or mixtures thereof to form a basic 
refractory material chemically bound with aluminum phosphate which reacts 
with the magnesium oxide when wet to form magnesium aluminum phosphate. 
In accordance with an important feature of this embodiment of the present 
invention, it has been found that the refractory composition can be 
initially made in a dried form prior to the addition of the water so that 
shelf life is not a problem with the M.sub.g O based composition of the 
present invention. In accordance with this embodiment of the present 
invention, the aluminum phosphate is added to the composition in dried 
form. For example, phosphoric acid may be reacted with an aluminum 
silicate clay, for example bentonite, and the reacted clay dried at a 
temperature at about 300-600.degree. F. to remove substantially all 
moisture. Dried magnesite or other dried magnesium oxide containing 
material can be added to the composition together with any other fillers, 
insulating materials and the like and water can be added to the 
composition at the job site in an amount suitable for proper consistency 
and workability prior to troweling or otherwise suitably applying the 
composition as a liner, industrial furnace cover and the like. Suitable 
examples of basic refractory compositions of the present invention, based 
upon M.sub.g O, are as follows: 
______________________________________ 
EXAMPLE 9 
Dried aluminum phosphate 5-70% 
A dried source of magnesium oxide, 
for example magnesite, chrome magnesite, 
dolomite or mixtures thereof 
20-96% 
Clay 1-30% 
EXAMPLE 10 
Dried aluminum phosphate 5-70% 
Dried magnesium oxide source of Example 6 
20-93% 
Clay 1-30% 
Phosphoric acid (the phosphoric acid can be 
1-10% 
added at the time of water addition) 
EXAMPLE 11 
Dried aluminum phosphate 5-70% 
Dried magnesium oxide source of Example 6 
20-89% 
Clay 1-30% 
Perlite, vermiculite or diatomaceous earth 
5-40% 
EXAMPLE 12 
Dried aluminum phosphate 5-70% 
Dried magnesium oxide source of Example 6 
20-84% 
Expanded clay, i.e. bentonite 
1-30% 
Perlite, vermiculite or diatomaceous earth 
5-40% 
Fibers burnable below 2000.degree. F. 
5-20% 
______________________________________ 
Water is added to the basic M.sub.g O based refractory compositions of the 
present invention in an amount of 1-20% by weight of the dried composition 
to provide a plastic or workable basic refractory composition and the 
reaction between aluminum phosphate and the M.sub.g O to form a magnesium 
aluminum phosphate bond. Phosphoric acid can be added to the basic M.sub.g 
O based composition to provide greater strength, but generally shelf life 
increase is not of consequence in the M.sub.g O based refractory since it 
will be wetted at the job site and immediately disposed in place. Further, 
if phosphoric acid is added together with the aluminum phosphate during 
manufacture of the basic dry composition, the phosphoric acid and aluminum 
phosphate should be dry prior to the addition of magnesium oxide to 
prevent initiation of the reaction. 
It has been found that when a insulating material such as perlite, 
vermiculite or diatomaceous earth is included in the composition in an 
amount of at least 5% by weight of the total composition, the refractory 
composition should not be in direct contact with a liquid metal due to the 
lower density of the insulating, refractory compositions. However, 
temperatures up to about 3500.degree. F. do not deliteriously affect 
suitable refractory compositions of the present invention. 
The refractory compositions of the present invention are useful in 
essentially all of the uses well known in the refractory art, particularly 
when an insulating material is included for temperature environments over 
2000.degree. F. Examples of suitable applications for the refractory 
materials of the present invention include original furnace liners, 
soaking pit walls, reheat furnace walls and roof liners, induction furnace 
covers, as a back-up lining for the aforementioned applications to act as 
an insulating lining behind a prior art refractory lining; refractory 
linings for boilers, and linings for forging furnaces. Other uses will be 
apparent to those skilled in the refractory art.