Chemistry: analytical and immunological testing – Silicon containing
Reexamination Certificate
1998-03-18
2001-05-22
Soderquist, Arlen (Department: 1743)
Chemistry: analytical and immunological testing
Silicon containing
C501S141000
Reexamination Certificate
active
06235533
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method for selecting a clay deposit, particularly useful for selecting clay deposits that can be purified into a polymer-grade clay for use in nanocomposites. More particularly, the present invention is directed to a method of determining the composition of a clay deposit including the type and amount of crystalline impurities, such as quartz and feldspar, as well as amorphous impurities, such as amorphous silica, to determine if the clay impurities can be separated such that the purified clay includes 5% by weight or less impurities, preferably 3% by weight or less, more preferably 2% by weight or less of impurities.
BACKGROUND OF THE INVENTION AND PRIOR ART
It is well known that layered materials, such as phyllosilicates, can be separated or exfoliated into their individual clay platelets, as disclosed in this assignee's U.S. Pat. Nos. 5,552,469; 5,578,672; and 5,698,624. The exfoliated platelets are useful as fillers for polymeric materials to achieve increases in strength, temperature resistance, gas impermeability, and other properties. While the technology has existed for many years for exfoliating clay platelets and combining such clay platelets with polymeric materials, this technology has not been commercialized, for one reason, among others, that while the addition of exfoliated clay platelets to the polymeric materials has substantially enhanced one or more properties of the polymer, the addition of clay impurities together with the exfoliated platelets has caused a marginal improvement, or has actually caused a decrease in properties that the platelets are designed to increase. Thus far, it has been impossible to sufficiently purify a layered material, such as a phyllosilicate, particularly a smectite clay, such that exfoliated platelets obtained from the purified clay are sufficiently free from clay impurities to significantly enhance the desired properties of the polymer.
Prior attempts to purify a layered material, such as a smectite clay, have included the step of analyzing the clay, such as by x-ray fluorescence, to deterine an elemental analysis of the clay, and then analyzing the clay, such as by an x-ray diffraction (XRD) analysis, in order to identify existing crystalline impurities. These impurities, such as feldspar, quartz and the like can be separated from the smectite clay deposit using well-known physical separation techniques, such as one or more hydrocyclones or a centrifuge. It has been found that identification of crystalline impurities by a technique such as x-ray diffraction is insufficient since it has been found that clay deposits, particularly smectite clay deposits, such as sodium montmorillonite and/or calcium montmorillonite, may include a substantial proportion of amorphous impurities, such as amorphous silica, which cannot be identified by x-ray diffraction. Also, it has been found that using existing technology, it is commercially and/or economically extremely difficult to separate any impurity, e.g., amorphous silica or crystalline impurities, if the impurity is present in the clay deposit in a particle size of five microns or less, particularly less than about one micron.
Thus, there exists a need in the art for a method of identifying clay compositions that include crystalline and amorphous impurities, particularly amorphous silica, within the clay compositions. In accordance with the present invention, it has been found that by using a combination of a means to identify the crystalline components of a clay deposit, such as x-ray diffraction and x-ray fluorescence, together with a means for determining amorphous impurities, which requires a knowledge of crystalline chemistry and mineralogy or clay structure, the components of the clay composition can be determined, including the amount and type of amorphous impurities, particularly amorphous silica impurities, such that the composition of a clay deposit can be determined, accurately, prior to purification of the clay.
SUMMARY OF THE INVENTION
In brief, the present invention is directed to a method of identifying montmorillonite clay-containing compositions and non-montmorillonite clay impurities that are purifiable such that the purified montmorillonite clay has impurities in an amount of less than about 5% by weight, preferably less than about 2% by weight, more preferably less than about 1% by weight. Impurities, in accordance with a preferred embodiment of the present invention, are hereby defined as any material that is not a smectite clay.
Accordingly, one aspect of the present invention is to provide a method of determining an identity and amount of non-smectite clay impurities, both crystalline and amorphous, contained in a clay sample that contains predominantly smectite clay, particularly montmorillonite clay.
Another aspect of the present invention is to provide a method of analyzing a predominantly montmorillonite clay sample to determine a source of Si detected in the sample and, more particularly, to what degree the Si detected is from the montmorillonite clay, or from a non-montmorillonite impurity.
Another aspect of the present invention is to provide a method of analyzing a predominantly montmorillonite clay sample to determine a source of SiO
2
detected in the sample and, more particularly, to what degree the SiO
2
detected is from the montmorillonite clay, or from a non-montmorillonite impurity.
Another aspect of the present invention is to provide an iterative method of analyzing a predominantly montmorillonite clay sample that includes the steps of analyzing the sample for number of Si
+4
cations per montmorillonite formula unit, first assuming that all of the Si
+4
cations are derived from SiO
2
contained in the montmorillonite clay contained in the sample; calculating the Si
+4
per montmorillonite formula unit, and if the number of Si
+4
cations per formula unit is greater than 4.0, based on the assumption that all Si
+4
is montmorillonite-derived, reducing the number of Si
+4
cations per montmorillonite formula unit to a number between 3.8 and 4.0—the quantity of the reduction of the Si
+4
cations being proportional to the Si
+4
cations contained in non-montmorillonite impurities contained in the sample.
Still another aspect of the present invention is to calculate the number of Si
+4
cations contained in non-montmorillonite impurities, as above, and analyzing the clay for Si
+4
-containing crystalline impurities, such as by x-ray diffraction—the difference being proportional to the amount of amorphous impurities containing Si
+4
.
Another aspect of the present invention is to provide an iterative method of analyzing a predominantly montmorillonite clay sample for composition, including impurities, that includes the steps of analyzing the sample for number of Si
+4
cations per montmorillonite formula unit, first assuming that all of the Si
+4
cations are derived from SiO
2
contained in the montmorillonite clay contained in the sample; calculating the weight percent of SiO
2
in the sample, and number of Si
+4
cations per montmorillonite formula unit, and if the number of Si
+4
cations per formula unit is greater than 4.0, based on the assumption that all SiO
2
is montmorillonite-derived, reducing the weight percent of montmorillonite-derived SiO
2
—the quantity of the reduction of the montmorillonite-derived SiO
2
weight percent being proportional to the weight percent of SiO
2
contained in non-montmorillonite impurities contained in the sample.
Still another aspect of the present invention is to provide a method of determining the composition of a clay sample that includes the step of calculating the weight percent of SiO
2
contained in non-montmorillonite impurities, as above, and analyzing the clay for SiO
2
-containing crystalline impurities, such as by x-ray diffraction, and calculating a reduced weight percent of montmorillonite-contained SiO
2
that provides 3.8 to 4.0 Si
+4
cations in
Beall Gary W.
Clarey Mark
Edwards James
Eisenhour Don D.
Tsipursky Semeon J.
Amcol International Corporation
Cross Latoya J.
Marshall O'Toole Gerstein Murray & Borun
Soderquist Arlen
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