Synthetic silicate pellet composition and methods of making...

Details Synthetic silicate pellet composition and methods of making... Synthetic silicate pellet composition and methods of making...

2000-11-01

2002-07-16

Group, Karl (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S029000

Reexamination Certificate

active

06420289

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to glass-making, and, more particularly, to a method of making a synthetic calcium/magnesium silicate pellet having varied properties, such synthetic silicate pellets themselves, and to the using of such synthetic silicate pellets in glass-making systems.
BACKGROUND
In general, glass-making involves the combination of precursive materials for melting and reacting together to form a desired glass composition. The volume and use of glass is such that natural resources are traditionally favored with a cost-optimal amount of beneficiation of such materials for glass-production purposes.
Some of the historical glass-making schemes involved the combining of sand (as a silica source), lime (as a calcium source) and soda ash (as a sodium source) along with other materials and processing to form the ubiquitous glass products. Such processes traditionally suffered from, and continue to suffer from, production limitations. Among the more critical limitations are batch-free time (the time required to completely dissolve the combined materials) and the fining time (the time to remove gases from the melt which form undesired bubbles in the melt and resulting glass). Other limitations involve the handling problems associated with the precursive materials, such as crumbling, dusting, clumping, sintering deficiencies and the like.
Progress has been made in the glass-making processes by the use of specially processed or beneficiated materials intended for use as glass precursive materials. In particular, a class of synthetic silicates have been developed encompassing various forms of synthetic calcium silicates, magnesium silicates and/or calcium magnesium silicates. Exemplary of such materials are SYNSIL™ synthetic silicates. While such synthetic silicates can provide beneficial results, there continues to be a need for enhanced precursive materials for the glass-making technologies.
SUMMARY
An object of the present invention is to provide a synthetic silicate as a precursive glass-making material in a composition and form which reduces handling problems in the glass-making process.
Another object of the present invention is to provide a synthetic silicate as a precursive glass-making material in a composition and form which enhances the melting process in the glass-making process.
These and other objectives are achieved by providing a synthetic silicate composition comprised of a calcium/magnesium silicate material of controlled formulation, an alumina silicate binder, a catalyst and silica fines. The binder and catalyst are alternatively present or both may be present, providing respectively preferred advantages of enhanced compression strengths and enhanced melting characteristics.
DETAILED DESCRIPTION OF INVENTION
An embodiment of the present invention is a novel composition comprising (i) a silicate material having an empirical formula of Ca
x
Mg
y
Si
z
O
(x+y+2z)
, wherein the values of x, y, and z are such that at least one of x and y are not zero and the values are such that the novel composition is suitable as a glass precursor material; (ii) an alumina silicate binder in an amount effective to impart a compression strength sufficient to enable a pellet formed from the novel composition to be handled at ambient temperature and sintered without substantial structured damage to said pellet; and (iii) silica fines in an amount such that the composition is suitable as a glass precursor material. This composition has use as precursive material in the glass-making process. Other additives or elements of composition may be added with regard to the particular specific glass being produced. The manufacturer of such glass will make the adjustments to the variables of the elements of the composition so as to be suitable for his intended end glass product.
One embodiment of the present composition invention is a silicate material having an empirical formula of Ca
x
Mg
y
Si
z
O
(x+y+2z)
. The values chosen for such empirical formula are such that the composition is suitable as glass precursor material as discussed above. Either x or y may be zero, but both x and y are not zero. Accordingly, the silicate material may be of a nature as to be a wollastonite-type (Ca
x
Si
1
O
3
) material or a diopside-type (Ca
x
Mg
y
Si
2
O
6
) material or an enstatite-type (Mg
y
Si
1
O
3
) material and the like. What is meant by “type” material is exemplified as follows: a wollastonite-type material may in fact be natural or synthetic wollastonite (Ca
1
Si
1
O
3
) or a compound whose elemental proportions approximates such formula. Similarly, a diopside-type material may be a natural or synthetic diopside (Ca
1
Mg
1
Si
2
O
6
) or a compound with similar elemental proportions. For instance, the proportions of calcium to magnesium need not necessarily be one to one. In a preferred embodiment of the present invention a preferred ratio of calcium to magnesium is about one-half to about ten, more preferably about one to about two. A particularly more preferred range is a proportion of calcium to magnesium between the values of about 1.4 to about 1.7. Similarly, an enstatite-type material may be a synthetic or natural enstatite (Mg
1
Si
1
O
3
) or a compound with similar elemental proportions. For instance, an enstatite-type material may not strictly have a one to one proportion between the magnesium and silica in the compound. Accordingly the present invention involves compounds with a general empirical formula of Ca
x
Mg
y
Si
z
O
(x+y+2z)
, whose relative proportions may duplicate the natural wollastonite, diopside, or enstatite material or be approximations. In all instances for the present invention, however, at least a significant amount of calcium or magnesium should be present in the silicate material. Other non-listed elements may be present in non-effective amounts in the compounds as trace or contaminant materials as long as such does not significantly alter the benefits of the present inventive compositions in the intended glass formation products. Throughout the specification it will also be appreciated by those in the art that the empirical values for the oxygen content may not strictly be x+y+2z, but will be sufficiently approximate to such so that the composition is able to perform as though mathematically balanced and chemically equivalent.
The alumina silicate binder can be any alumina silicate binder whose use permits the forming of a pellet with sufficient compression strength so as to be handled at ambient temperatures in the manufacturing process and then sintered in a kiln, furnace or other heating apparatus. Throughout this specification the “pellet” form can be of any structure or shape such as an amorphous glob, a sphere, a bead, a brickette, a cube, a wafer, a flake or a cylinder shape and the like. For instance, when sintered in a rotary kiln, the preferred formation is a cylindrical or spherical pellet whose size and aspect ratio is suitable for the intended glass manufacturing process using such pellet. A sufficient amount of the alumina silicate binder is used to substantially reduce the breakage of the pellet and the formation of powder or fines in the heating apparatus, such as those which might appear in a rotary kiln causing wall build up and kiln rings. Such formations affect the thermal profile in a heating apparatus, such as a kiln, and results subsequently in insufficient burning or sintering of the material. Accordingly, there should be a sufficient amount of binder so as to substantially reduce or prevent insufficient sintering of the pellet for the ultimate intended use. Prior to use in the glass-making process the pellet may be beneficiated or sized for achieving ease or enhancement in use. Accordingly, the pellet may be further treated to size the pellet down into smaller pellets. Such treatment may be by crushing, rolling hammer or other similar processing known in the art for size reduction, such as that used for glass sand or other solid materials. Preferred pellet sizes for som

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