Method of encapsulating particulate material

Abstract

A method of encapsulating particulate materials that enables the particulate materials to be used in end use applications where they currently are not useful. The method uses specific sol gel technology to encapsulate solid particles. In addition, the method can be used to multiple coat a coated particle.

Claims

1. A method of encapsulating particulate materials the method consisting of: a. providing acidified water at least sufficient for hydrolyzing a predetermined amount of alkoxysilane; b. thereafter dispersing at least one type of particulate material in the acidified water; c. thereafter slowly adding a predetermined amount of alkoxysilane having the general formula:
R.sub.xSi(OR).sub.4-x wherein R is selected from the group consisting essentially of alkyl groups, substituted alkyl groups, aryl groups, substituted aryl groups, vinyl, allyl, and hydrogen, wherein the substituents are selected from the group consisting of fluorine, amino, hydroxy, and combinations thereof, and wherein R is selected from hydrogen and alkyl groups of 1 to 4 carbon atoms; d. thereafter allowing sufficient time for the alkoxysilane to hydrolyze and build a predetermined particle size.

2. The method as claimed in claim 1 wherein, in addition, there is a step e. in which the product of d. is neutralized with base.

3. The method as claimed in claim 1 wherein, in addition, the water is removed from the dispersion and any solids in the dispersion are dried.

4. The method as claimed in claim 2 wherein, in addition, the dry solids are ground to a fine powder.

5. An encapsulated particulate material prepared by the method of claim 1.

Description

EXAMPLES

(1) Various metal salt solid particles were encapsulated by the method of this invention in the following manner by first determining their Ksp. (TABLE I)

(2) TABLE-US-00001 TABLE I Metal Salt Ksp Potassium chloride (KCl) total solubility Copper Chloride (CuCl.sub.2) 70.6 gm/100 ml Lithium Chloride (LiCl) 76.9 gm/100 ml Barium Chloride (BaCl.sub.2) 31 gm/100 ml Zinc Chloride (ZnCl.sub.2) 81 gm/100 ml

(3) It is necessary to determine the solubility constant (Ksp) of each of the metallic particles, as a stoichiometric amount of water is required to properly form the sol gel and the water is also necessary to dissociate the metallic salt in the mixture. Further, it is unknown what effect the free chloride from the dissociation of the metallic salt will have on the sol gel formation.

Example 1

(4) Potassium chloride was dissolve in acidified water. Thereafter, methyltrimethoxysilane was slowly added to allow for the hydrolysis of the alkoxy silane. The methyltrimethoxysilane was added in two equal portions to allow the sol gel to build to the appropriate particle size. After the reaction, the sol gel was neutralized to cause the precipitation of the matrix. The sample was oven dried at 45 C. overnight to remove the water followed by grinding the resulting metallic salt sol gel to a powder about the size of table salt.

Example 2

(5) To a 200 ml beaker, 35 grams of distilled water was added. To this water, 8 grams of lithium chloride was added with agitation. The temperature of the distilled water was measured at 23 C. During dissociation of the lithium chloride the temperature rose to 60 degrees, an exotherm of 37 degrees centigrade. After cooling back to 23 degrees, 2.3 grams of Dow Corning 6070 silane (methyltrimethoxysilaneDow Corning Corporation, Midland, Mich.) was added drop wise and allowed to mix and hydrolyze. After continuous mixing for 60 minutes, 2.3 grams of Dow Corning 6070 silane was added drop wise and allowed to mix for 120 minutes. The resulting reaction product was filtered through filter paper to collect the encapsulated metal salt. This was dried for 16 hours at 45 C. resulting in a white crystalline powder. This powder was placed in a porcelain crucible and ground to a fine white powder about the size of table salt.

(6) Thereafter, each of the sol gel versions of the salts set forth in TABLE I were produced by virtually the same procedure. The results can be found in TABLE II.

(7) TABLE-US-00002 TABLE II SAMPLE # 1 2 3 4 5 Solubility WATER 35 35 35 35 35 POTASSIUM 8 INFINITE COPPER 8 70.6/100 ML Lithium 8 76.9/100 ml Barium 8 31/100 ml Zinc 8 81/100 ml MTM.sup.1 2.3 2.3 2.3 2.3 2.3 MTM.sup.2 2.3 2.3 2.3 2.3 2.3 NaOH 1.2 1.2 0 1.2 0 Product 3 gms 3 gms 3 gms Water 15 gms 15 gms 15 gms Dry weight 0.46 g 0.61 g 0.26 g .sup.1first addition of methyltrimethoxysilane .sup.2second addition of methyltrimethoxysilane

(8) TABLE-US-00003 TABLE III Table III shows additdonal reactions. 1 2 3 4 5 WATER 175 175 175 175 175 K 40 CU 40 LI 40 BA 40 ZN 40 RXN.sup.1 ENDO EXO EXO ENDO EXO MTM 11.5 11.5 11.5 11.5 11.5 MTM 11.5 11.5 11.5 11.5 11.5 NaOH 6 6 6 6 6 Solution OPAQUE BLUE/ OPAQUE OPAQUE OPAQUE Color GREEN Exotherm 40 60 17 Temperature C.

(9) Table IV has additional reaction data demonstrating a reduction in the amount of water required for the sol-gel formation.

(10) TABLE-US-00004 TABLE IV 1 2 3 WATER 35 35 35 Cu 28 Li 30.4 Ba 11.7 MTM 8.7 8.7 8.7 MTM 8.7 8.7 8.7 EXO TEMP. C. 60 40 17 SOLN pH 2 6

(11) Table V has additional data showing the double coating technique. The encapsulated material from experiment 1 of table V was used herein. The water and lithium chloride was allowed to equilibrate and a sample of the final product was added to this mixture. The product from experiment 1 of table IV was not soluble in the water solution. However, upon the addition of the first quantity of methyltrimethoxysilane, the material was able to go into solution. The second addition of methyl trimethoxysilane completed the final encapsulation product.

(12) TABLE-US-00005 TABLE V 1 WATER 17.5 Li 15.7 MTM 4.35 MTM 4.35 SAMPLE 1 FROM TABLE V 5.0 EXO TEMP C. 67 SOLUTION pH 4