Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Cement composites
Background Of The Invention
Sorel cement is a term used to refer to various
compositions having as basic ingredients a combination
of magnesia (MgO) and magnesium chloride (MgCl2) in an
aqueous solution. This basic Sorel formula system when
cured is a magnesium oxychloride hydrate.
Sorel cement was discovered almost 100 years ago. It
gets harder, and sets faster than Portland cement, but its
wide-spread use had been greatly limited because of its
inherent poor water resistance. The magnesium oxychloride
hydrate crystals that compose the Sorel cement have been
found to have a structure very much like gypsum in that the
physical properties of the cement depend on an intimate
infiltration of the crystals, one with another, but with
no real bond between the crystals. The Sorel cement
product is also somewhat soluble in water with the result
that exposure to water virtually eliminates the adhesion
between the crystals.
Various attempts have been made to overcome this
difficulty such as the addition of materials which have
the property of forming insoluble magnesium salts, such
as phosphates and aluminates. The results have been only
partially successful and in fact usually with the further
disadvantage that the hardening rate is greatly slowed.
Various fillers have been reported in the literature,
but mainly from the point of view of their compatibility
rather than that they impart any special properties to the
cement. Glass fibers have been tried with some success,
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but the bond between the glass fibres and the Sorel cement
is destroyed by exposure to water and thus the structural
advantages of the glass fibers are only temporary.
It is obvious from repeated statements in the litera-
ture that had it not been for the water sensitivity ofSorel cement products, their use would have been much more
general and wide spread. It is exactly because of this
drawback of these cement products that there remains a
large potential for these materials if the water sensi-
tivity problem could be solved. The superior hardeningrate, greater strength and excellent fire retardant
properties of Sorel cement could then be taken advantage
of in a host of building materials where its use is
presently not considered.
Summary Of The Invention
According to one aspect of the invention there is
provided a Sorel cement formula composition comprising
magnesium chloride, magnesium oxide, water and nucleating
amount of a premix formula comprising the reaction product
of waterl a relatively small amount of magnesium oxide and
possibly an amount of magnesium chloride.
In accordance with another aspect of the invention
there is provided a process of manufacture of Sorel cement
products which comprises admixing magnesium chloride,
magnesium oxide, water and a nucleating amount of a premix
formula comprising the reaction product of water, magnes-
ium chloride and a relatively small amount of magnesium
oxide to yield a Sorel cement formula and thereafter
curing said formula.
Other aspects of this invention are claimed in our
Canadian patent application 329,028 filed on June 4, 1979,
of which the present application is a division.
The present invention thus relates to water/moisture
resistant magnesium oxychloride hydrate (Sorel cement)
formulae compositions and processes for producing the
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same. The invention further comprises the addition of
various substances, reinforcing materials or fillers such
as glass fibers to the compositions of this invention.
Detailed Description of The Invention
Applicant has discovered that the aforediscussed dis-
advantage of present day Sorel cement formulae, and
especially as relates to the very poor stability in and
sensitivity to water of the resulting cement products,
can be largely overcome either by addition of a certain
material to the standard Sorel cement formula or develop-
ing a formula and processes which will result in greater
stability and strength.
To this end, and as concerns the former case, applicant
has discovered that when an ethyl silicate is added to a
standard Sorel cement formula there~results a material
whose water resistance and strength properties are con-
siderably improved. Although the exact order of addition
of the reactants, the relative amount of reactants and the
condition under which the reaction is to take place are
not critical, it has been found advantageous to first mix
and dissolve the MgC12.6H2O in the water, after which
the MgO is dispersed. Subsequent to this the ethyl
silicate is dispersed therein, preferably under conditions
of high agitation. Although, as noted, the amount of
ethyl silicate is not critical and the same need only be
added in a water stabilizing amount, it has been found
advantageous to add from about .5-2% by weight of ethyl
silicate based upon the total weight of the Sorel cement
formula. The resulting formula may then be cured under
normal and well known conditions such as at room
temperature and over an extended period of time.
The other mode of achieving substantially improved
water stability and strength involves improving the
solution of the MgO in the MgC12 in accord with the
nucleation theory of this aspect of the invention as the
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same explained in more detail below. The improved results
are obtained by first preparing a premix formula which is
comprised of water, a relatively large amount of MgC12.6H2O
and a relatively small amount of MgO. The premix formula
is thereafter added to a standard Sorel cement formula
and acts, in effect, as a seeding solution. Particularly
improved results are obtained when the premix formula is
added to a Sorel cement formula which contains ethyl sili-
cate in accord with the first aspect of this invention.
More particularly, it is preferred that the premix
formula be prepared under such conditions that MgC12
concentration in solution is maximized, this will in turn
increase the solubility of MgO and the resulting formation
of magnesium oxychloride hydrate. To this end, it is
preferred that a near saturated solution of MgCl2 and
water, preferably deionized water, be prepared at or near
the boiling point (about 120C). This will insure that
there results a concentrated solution of MgC12 and
increased solubility of MgO so that when a small amount
of the MgO is added to the solution, preferably under
conditions of vigorous stirring, the same will quickly
and almost completely react with the MgC12 to form the
magnesium oxychloride hydrate. As can be seen from the
foregoing, the relative amounts of the MgC12, MgO and
water reactants in the premix formula, as well as the
reactive conditions, are not critical, it being only
required that substantially all of the MgO react to form
the magnesium oxychloride hydrate.
The order in which the ingredients of the Sorel cement
formula of this aspect of the invention are admixed,
including the premix formula constituent thereof, as well
as the relative amounts of each such ingredient and the
conditions under which admixture is to take place, are not
critical. The same applies also in the case wherein the
Sorel cement formula contains ethyl silicate in accord
with the first aspect of this invention. It is however,
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preferred to first dissolve all of the MgC12.6H20 in
all of the water that is to be used, preferably at room
temperature and to thereafter add the premix formula. As
noted, the amount of premix formula that is added is not
critical, it only being required that the premix formula
be added in an amount sufficient to effectuate nucleation.
It has been found, however, that the premix formula may
advantageously be added in an amount of from about 1-5%
-by weight based on the total weight of the Sorel cement
formula. After the premix formula is added, the entire
amount of MgO that is to be used is added. In the case
where ethyl silicate is to be employed, the same is finally
added. The resulting Sorel cement formula may then be
cured under normal and well known conditions such as at
room temperature and over an extended period of time.
It should be observed that the Sorel cement formulae
of the present invention may contain other ingredients
besides MgC12.6H20, MgO and H20 as these other
ingredients are customary and well known in the art.
; 2~ These include ferrous chloride, feltspar, a release agent,
etc.
Moreover, particular strength, both wet and dry
strength as these properties are discussed below, may
be imparted to the Sorel cement formulae of the present
invention by incorporating therein reinforcing or filler
materials, and particularly glass fibers. It has been
found that the Sorel cement formulae of the present
invention, contrary to the other conventional Sorel cement
formulae, tend to bond exceptionally well to the rein-
forcing material which is admixed therewith and to remainwell bonded under all conditions. The relative amount of
the reinforcing material, i.e., glass fibers, in the Sorel
cement formulae of this invention is not critical and will
be easily determined by one skilled in the art, it being
3~ only required that the same be added in a strength
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increasing amount -- from about 1-10~ by weight being more
than adequate to yield the desired strength characteristics
-- and in such a manner as to ensure that the glass fibers
are uniformly and well distributed and dispersed within
the Sorel cement formulae.
The method under which the Sorel cement formulae of the
present invention are cured is, as noted, not critical and
techniques and conditions cenYentional in the art may be
employed. It has been found, however, that yet added
water stability and resulting increase in strength can be
realized when curing takes place under relatively saturated
atmospheric conditions.
While applicant does not wish to be bound by any
specific theory, it is believed that Sorel cement consists
essentially of a combination of magnesium oxide (MgO),
magnesium chloride (MgC12~ and water (H2O) in which
the reactions that take place when these three components
are mixed are, in the most simple terms, as follows:
1) Solution of magnesium oxide;
2) Hydration of magnesium oxychloride; and finally
3) Precipitation of magnesium oxychloride hydrate.
The material thus formed has been found to have an inter-
meshed crystal structure whose properties depend on its
density and the bond between the crystals.
It is assumed that it is the hydration reaction that
is exothermic and which produces the magnesium oxychloride
hydrate crystals of the Sorel cement. But this hydration
can occur only after sufficient MgO has dissolved to form
an aqueous ion mix that is supersaturated with respect to
the oxychloride hydrate. Once hydration becomes dominant,
the free water is removed and the dissolution of MgO stops.
If, at this time, insufficient MgO has dissolved to react
with all the MgC12 present, then the end product will
consist of an intimate mixture of crystals of magnesium
oxide, magnesium chloride hydrate and magnesium oxychloride
hydrate. This material would be weak because the residual
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MgO cannot contribute to the new crystal entanglement, and
hence to the strength and stability of the cement, and it
would be very sensitive to water exposure since the mag-
nesium chloride is soluble and is easily leached out,
eliminating the necessary intimate contact between the
magnesium oxychloride hydrate crystals which is responsible
for the stability and strength of the end-product cement
material.
If this physical picture is correct, it would suggest
the possi~ility of a greatly improved Sorel cement formula
provided that these reactions could be controlled and
residual MgC12 eliminated - that is, if the solution of
the MgO can be completed before the hydration reaction
starts. The foregoing would appear to depend on the phen-
omenon of nucleation. This phenomenon may be visualizedand understood by considering the two essential features
of the cement production process. To start with, only MgO
powder is dispersed in a solution of MgC12 in water.
The MgO starts to dissolve adding its ions to the aqueous
solution. As more and more MgO dissolves the solution
becomes supersaturated with respect to the magnesium
oxychloride hydrate end product. Eventually nucleation
takes place and the magnesium oxychloride hydrate precipit-
; ates out forming the Sorel cement. As free water is
removed from the system, i.e., by formation of the hydrate,
the solution of MgO is slowed and finally stopped. There-
fore, the chemical make up of the resulting cement will
vary depending on the vagaries of nucleation.
More particularly, if, for example, nucleation takes
place early at only a few places, then supersaturation
would be minimal and growth of the cement would be from
thése nucleation points, resulting in a series of widely
separated zones rich in unreacted salt. If this nuclea-
tion took place on the surfaces of the MgO particles, as
;~ 35 seems most likely, then the solution of MgO would thereby
~ also be greatly inhibited. If on the other hand,
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nucleation would be prevented at the MgO surface, and
therefore did not take place until a much higher concentra-
tion of ions was present, and sufficient MgO was dissolved
to react with all of the MgC12 present, then nucleation
could take place spontaneously from many more sites pro-
ducing a more heavily enteined crystal growth with little
or no soluble salt left over. It is thus theorized by
the present inventor that the poor water resistance of
Sorel cement as so far known has been the result of too
early and premature nucleation, such that if nucleation of
the hydration reaction could be substantially inhibited,
the very serious drawbacks of present Sorel cement formulae
could be overcome.
It is in this vein that the premix formula aspects of
the present invention is directed. That is, the premix
seeding mixture is believed to cause precipitation of the
magnesium oxychloride hydrate upon the premix nuclei, as
opposed to nucleation at the MgO surface, and to thus
promote the solution of MgO into the MgC12 solution for
yet further hydrate formation and subsequent precipitation.
As shown in the following Examples, the improved water
resistance of the Sorel cement products obtained from
the formulae of the present invention is evidenced by a
decrease in weight loss and an increase in hardness or
strength of the resulting product. The decrease in weight
loss when exposed to water indicates that the constituents
of the formulae are not leached out and the cement products
remain stable. Improved strength of the resulting Sorel
cement product after exposure to water, as compared to
products prepared from conventional Sorel cement formulae
and similarly exposed to water, is especially indicative
of the improvements of the present invention. The ratio
of wet strength -- after immersion of the cement product
in water -- to dry strength is also indicative. All of
these measurements provide quantitative proof of
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substantially improved Sorel cement products as compared
to products obtained with conventional Sorel cement
formulae. Visual observation of the resulting cement
products, including the structural integrity thereof, also
established the improvements flowing from the present
invention.
The following examples are offered only for purposes
of illustrating the invention and are in no way intended
to limit the scope of protection to which the applicant is
otherwise entitled.
EXAMPLE 1
Effect of Ethyl Silicate addition to Sorel cement
The following materials were mixed in the order and in the
amounts listed below:
Formula Control
Deionized water71 71
MgC12 6H2 107 107
MgO 221 221
; Ethyl SilicateX 5
I 20 Silbond 50 was used which is a trademarked product
'I manufactured by Stauffer Chemical Company.
Twenty separate test samples were made with each
' formula of this Example. 50 gram samples were poured into
polyethylene cups and allowed to harden for a period of 24
hours. They were then submerged in distilled water for
a period of eight days and thereafter dried for an add-
itional period of 24 hours in a 70C air circulating oven.
All samples without ethyl silicate disintegrated into
small grains. All samples containing ethyl silicate
retained substantially all of their original physical
characteristics and appearance.
When similar production sheets of Sorel cement were
made using 5% chopped glass fiber in both the ethyl
silicate - containing formula and in the control formula,
the ratio of wet strength (24 hours of water submersion
after seven days air cure) to dry strength increased from
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30% to 85% in those samples that contained the ethyl
silicate.
EXAMPLE 2
Effect of Nucleation Premix
The following materials were mixed in the order and in the
amounts listed below:
Formula Lab.Scale Grams Plant Scale Kg.
Tap Water 60.6 27.420
g 2- 2 108.8 49.220
Feltspar (Potassium
Aluminosilicate) 73.0 33.000
Premix formula (Seed)13.1 5.940
MgO 221.0 100.000
Ethyl SilicateX 4.9 2.200
H2O2 (release agent)2.2 1.000
403.6 218.78
x Silbond 50 was used which is a trademarked product
manufactured by Stauffer Chemical Company.
Premix Formula
Deionized water 35 1.250
g 2 2 125 4.500
MgO 5 0.180
165 5.930
The above premix formula or seed was prepared by
mixing the MgC12.6~2O and the water and heating the
resulting solution to a temperature of about 110 to
120C. While maintaining this temperature the MgO was
added under conditions of constant stirring, and the
mixture maintained under this condition for a period of
about 10 minutes. The premix formula was thereafter added
to the main Sorel cement formula in the amounts as
indicated above.
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Production sheets containing 5% glass fiber were made
with both a premix-containing formula and a control
formula without the premix having been added thereto but
otherwise the formula was the same in all respects.
After 7 days air cure:
The production sheets were formed by mixing the
chopped glass fibers into both the premix-containing
formula of Example 2 and the control formula without the
premix and thereafter the resulting mixtures were sprayed
into forms. After hardening for a period of 24 hours,
the sheets were removed from the forms and stored at room
temperature for a period of seven days. The boards were
then cut up into small samples and the dry bending strength
measured according to well known and generally practiced
techniques. The wet bending strength was similarly
measured after subsequent submersion of the samples in
water for a period of 24 hours.
Bending Strength Kp/cm2
Example 2 Control
Dry 586 380
Wet 391 282
The cement mixture of Example 2 and including the
control but not containing any glass fibers, was also cast
into polyethylene cups (75 gms) and cured, i.e., hardened
in air, for a period of 24 hours. The cured cements were
then soaked in distilled water for a period of 24 hours
and dried over a period of 24 hours at 70C in an air
circulating oven under relative humidity conditions of 50%
and 100%. The weight changes, based on the original wet
30 weight, were as follows:
~ of Initial Wet Weight
Example 2 Control
cured at 100~ RH +0.3 - 9.8
cured at 50~ RH -1.7 - 11.3
