Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
1999-07-02
2001-03-13
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
Reexamination Certificate
active
06200381
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a settable composition and especially to an inorganic settable composition which can be mixed with fillers and additives to provide a range of set compositions.
BACKGROUND ART
Cements are well known, and inorganic cements, such as Portland Cement, are well known and used to form mortar, concrete, and the like.
A drawback with Portland Cement is its relatively high weight per unit of volume. Another disadvantage with Portland Cement is that it is not suitable to use with fillers which are organic in nature. That is, Portland Cement is more or less limited to use with mineral type fillers. Thus, Portland Cement will not readily bind with fillers containing soils and clays. This means that gravel and sand when used as fillers for Portland Cement must be thoroughly washed and free from salts, humus, clay and certain types of acid.
Another disadvantage with Portland Cement is that the mix water must be clean and free from contamination. Salt water, bore water, brackish water, and water containing a high percentage of other types of salts cannot be used as a mix water with Portland Cement.
Another known type of cement is a magnesium oxychloride cement (Sorel cement) which is a cement used in interior work such as floors in hospitals and public buildings. This cement is made by adding in proper proportions a strong solution of magnesium chloride to magnesia. This cement can be used with organic fillers such as wood flour, cork, and inorganic fillers, such as stones, to provide a set mass in a short period of time which can take a high polish. These oxychloride cements can also use other types of organic fillers such as wood shavings, sawdust and straw.
Disadvantages with magnesium oxychloride cements are their brittleness, porosity and low shelf life. Another disadvantage with this type of cement is that it is not easily handled and is not like Portland Cement which is a dry flowable powder which is relatively easy to handle and use. A further disadvantage is that magnesium oxychloride cements are unstable in water and lose strength on prolonged exposure to water.
Another type of cement is a magnesium oxysulphate cement which is weaker than a magnesium chloride cement, and is obtained by the reaction of magnesium oxide with an aqueous solution of magnesium sulfate. The cements are unstable in water.
OBJECT OF THE INVENTION
The present invention is directed to a settable composition which, in the dry form, can be in the form of a powder which can be handled more or less like Portland Cement powder and which can be mixed with various fillers and water to obtain a set or hardness.
The present invention is also directed to the use of certain types of additives to the composition which can allow a set to be obtained with contaminated water, and where fillers, such as organic fillers, can be used.
The present invention is also directed to various products of the composition and various uses of the composition.
In one form the invention resides in a settable composition, the composition comprising a calcium carbonate and a caustic magnesium oxide.
The term caustic magnesium oxide includes a magnesium composition which comprises magnesium carbonate and a decarbonated magnesium. The term also covers a magnesium carbonate which has been treated, for instance, by heating, to liberate carbon dioxide, thereby forming a composition which is partially calcined. The exact structure of the composition and of the caustic magnesium oxide is not known, but the term will be used to include the structure formed by heating magnesium carbonate to partially decarbonate it, especially at the temperature ranges described.
The composition of calcium carbonate and caustic magnesium oxide can be formed by treating dolomite. Dolomite is a calcium magnesium carbonate found in nature. A true dolomite comprises about 54% calcium carbonate and 43% magnesium carbonate. Natural dolomites contain impurities of various differing types which can include alumina, iron and silica.
The percentage of the calcium and magnesium carbonate can vary in dolomites. For instance, dolomite containing 65% calcium carbonate and 30% magnesium carbonate is called a low magnesium dolomite. Conversely, a dolomite containing 60% magnesium carbonate and 30% calcium carbonate is called a high magnesium dolomite.
It is found that heating dolomite will cause carbon dioxide to be liberated, and the rate of liberation or carbon dioxide can be controlled and varied to provide fully or partially calcined dolomites.
If the dolomite is heated at 1,500° C., all the carbonate is liberated as carbon dioxide and a mixture of calcium oxide and magnesium oxide is left. These oxides are well known as for use in refractory material, but the oxides are not suitable for a cementitious material.
If dolomite is heated at a lower temperature, not all of the carbonate decomposes to liberate carbon dioxide. Indeed, it is noted that the heating can be controlled such that the magnesium carbonate preferentially releases carbon dioxide over the calcium carbonate.
Thus, heating at a temperature range of typically between 500° C. to 800° C. will cause preferential decomposition of the magnesium carbonate.
By controlling the preferential decomposition, dolomite can be treated to form a settable composition by converting the dolomite into a composition comprising a calcium carbonate and a caustic magnesium oxide.
The preferential decomposition of dolomite can be enhanced by additives such as inorganic salts. A suitable salt is sodium chloride which can be added from 0.1%-15% prior to heating. The salt appears to preferentially decrease the decarbonisation temperature of MgCO
3
without substantially affecting the higher decarbonisation temperature of CaCO
3
. The salt can increase the differential temperature from 100° C. to 200° C.
Suitably, the caustic magnesium oxide has between 2%-50% of the carbon dioxide retained within the magnesium carbonate, and preferably between 23%-28%. While the molecular structure may be difficult to envisage, the structure may comprise a mix of calcium carbonate, magnesium oxide, and magnesium carbonate. The amount of carbon dioxide retained in the composition has an effect on various parameters such as hardness, and setting rare. Between 20%
14
30% retained carbon dioxide offers a suitable set rate for many applications. Increasing the amount of carbon dioxide decreases the set rate, and decreasing the amount of carbon dioxide increases the set rate.
The composition can also be prepared synthetically by mixing or blending calcium carbonate with preformed caustic magnesium oxide. In this variation, the caustic magnesium oxide can be prepared by subjecting magnesium carbonate to heat to partially drive off carbon dioxide until the desired level of calcination is obtained.
Test results have shown that when heating naturally occurring dolomite, or a synthetic blend of calcium carbonate with magnesium carbonate, within the temperature range of 500° C. to 800° C. to partially drive off carbon dioxide, and neither the dolomite nor the synthetic blend contain more than 14% calcium carbonate, less than 1.5% “free lime” (CaO) is produced. The free lime can only come from calcining the calcium carbonate, not the magnesium carbonate, so a concentration of 1.5% free lime indicates negligible effect of the calcining process on the calcium carbonate. That is, the calcining is truly preferential in that essentially only the magnesium carbonate is calcined. A concentration of over approximately 5% free lime is detrimental to the setting process and gives rise to a weaker and more chalky product with time.
In a further variation, a natural dolomite may be heated in the manner described above to provide a composition comprising calcium carbonate and caustic magnesium oxide, and if the natural dolomite is magnesium deficient (for instance, a low magnesium dolomite), additional caustic magnesium oxide can be added to the mixture.
For example, a low magnesium dolomite ore containing 65% calcium carbonate and 30%
Collard & Roe P.C.
Marcantoni Paul
Periclase Pty. Ltd.
LandOfFree
Settable composition and uses therefor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Settable composition and uses therefor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Settable composition and uses therefor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2547346