US3798313A - Production of bismuth oxychloride crystals of enhanced luster and covering power - Google Patents

Abstract

BISMUTH OXYCHLORIDE CRYSTALS OF ENHANCED LUSTER AND COVERING POWER ARE PROVIDED BY FORCING THE CRYSTAL TO GROW SMALL AND THIN. THIS ACCOMPLISHED BY HYDROLYZING BISMUTH SALT DISSOLVED IN WATER USING HYDROCHLORIC ACID WITH THE BISMUTH SALT BEING FIRST CAUSED TO FORM CRYSTAL NUCLEI USING A RELATIVELY STABLE AQUEOUS SOLUTION THEREOF IN WHICH THE BI/HCL WEIGHT RATIO IS FROM 0.2:1 TO 0.8:1, AND THEN COMPLETING CRYSTAL GROWTH USING A RELATIVELY UNSTABLE SOLUTION HAING A BI/HCL WEIGHT RATIO OF FROM 1:1 TO 2:1.

Description

United States Patent 3 798 313 PRODUCTION OF BISNIUTH OXYCHLORIDE CRYS- TALS 0F ENHANCED LUSTER AND COVERING POWER Paul W. Wetzold, Armonk, N.Y. Paispearl Products, inc 24 Acqueduct Lane, Hastings-on-Hudson, N.Y.

0706) No Drawing. Filed Nov. 11, 1971, Ser. No. 197,975 Int. Cl. C01b 11/00 US. Cl. 423-472 13 Claims ABSTRACT OF THE DISCLOSURE Bismuth oxychloride crystals of enhanced luster and covering power are provided by forcing the crystal to grow small and thin. This is accomplished by hydrolyzing bismuth salt dissolved in water using hydrochloric acid with the bismuth salt being first caused to form crystal nuclei using a relatively stable aqueous solution thereof in which the Bi/HCl weight ratio is from 0.2:1 to 0.8:1, and then completing crystal growth using a relatively unstable solution having a Bi/HCl weight ratio of from 1:1 to 2: l.

The present invention relates to bismuth oxychloride crystals of enhanced luster and covering power and the production of such crystals.

The production of bismuth oxychloride crystals for use in cosmetics to provide an iridescent appearance is known. However, the prior art crystals have included many large agglomerates and the ratio of average maximum diameter to thickness has not been greater than about 5:1. As a result, the luster and coverage provided by these crystals has been inadequate. The excessive thickness of the crystals is easily seen under a microscope at 600 magnifications using visible light directed downwardly upon the crystals and then reflected back by the crystals, producing interference patterns which are directly related to the thickness. Thus, and directing attention to the smaller and flatter crystals, these are seen to possess at least about four concentric interference rings, and are hence known as targettype crystals. The thicker the crystals, the fatter they are in the middle, and the more rings are visible. The larger gggliomerates reveal a complex pattern of interference an s.

In this invention, very few large agglomerates are present, and the crystals are characterized by being of reduced thickness in comparison with their average diameter. This reduced thickness is revealed particularly by the clarity of the crystals, by the fact that some of them show no interference rings whatever, and by the fact that others include very few interference rings, e.g., two or less. The thinner crystals produced by this invention possess a ratio of average maximum diameter to thickness of 8:1 or greater, frequently about 10:1.

These novel bismuth oxychloride crystals are provided, per this invention, by a process in which the bismuth oxychloride is produced by the hydrolyzation of bismuth salt dissolved in water using the action of hydrochloric acid as the hydrolyzing agent. In the process of this invention, a relatively stable aqueous solution of dissolved bismuth salt is slowly introduced into a volume of water containing hydrochloric acid which is maintained at an elevated temperature in the range of from about 60 C. to the boiling point of water at the pressure of the reaction. This relatively stable aqueous solution has a Bi/HCl weight ratio of from 0.221 to 0.8:1 and the volume of water contains hydrochloric acid in an amount less than about /2% by weight to prevent spontaneous hydrolyzation so that the added bismuth salt precipitates slowly to form nuclei for further controlled crystal growth. The

growth of the crystals is completed by adding to the suspension of crystals produced by the slow addition of the relatively stable solution, a relatively unstable aqueous solution of disolved bismuth salt having a Bi/HCl weight ratio of from 1:1 to 2:1 which causes crystal growth to concentrate on the previously produced nuclei with growth being thereby forced to take place predominantly in the plane of the crystal to minimize the thickness of the crystals which are formed.

In the preferred process, the dissolved salt is bismuth nitrate and the hydrochloric acid content of the volume of water is at least .0l% by weight. The relatively stable aqueous solution is formulated to contain a hydrochloric acid concentration in the range of 813% and this solution is added, in a plurality of stages, to the volume of Water maintained at a temperature in the range of 75-99 C. to permit operation at atmospheric pressure. In the first stage, the solution is added very slowly until a turbidity forms, indicating the generation of crystal nuclei. Thereafter, the solution can be added more rapidly. The relatively unstable solution is desirably formulated to include hydrochloric acid in a concentration in the range of I3 18% and it is preferably added at a rate which is at least as fast as the most rapid rate of addition of the relatively stable solution. Other preferred operating conditions will become more fully apparent from the description which follows.

Referring first to the bismuth salt which is hydrolyzed, the preferred salt is bismuth nitrate as noted hereinbefore. However, any bismuth salt which is soluble in water with the aid of a mineral acid may be utilized, other salts being illustrated by bismuth trichloride, bismuth oxide (which forms a salt in the mineral acid solution), bismuth carbonate, bismuth oxycarbonate, bismuth oxynitrate, and the like.

The reaction is carried out in a volume of water maintained at elevated temperature, it being convenient to term this volume of water a heel. The temperature of the water in which the reaction is carried out should be at least about 60 C. and is preferably higher in order that the hydrolyzation reaction may proceed smoothly and uniformly. Preferred temperatures are from 75-99 C., and most preferably from 90-95 C. As is obvious, the reaction is preferably conducted at atmospheric temperature, but the use of pressure is possible in which event the boiling point of the water at the pressure used is not exceeded.

The volume of water must contain a small amount of hydrochloric acid (less than about /2% by weight) in order that the intial addition of bismuth salt solution not induce uncontrolled precipitation. At least about .0l% is sufficient for this purpose, but normally about .02.l% is utilized.

The first objective is to produce in the heated volume of water a suspension of crystal nuclei to enable further controlled crystal growth. This is achieved in this invention by adding to the volume of water a relatively stable aqueous solution having a Bi/HCl weight ratio of from 0.221 to 0.811, preferably from 0.4:1 to 0.7:1. This relatively stable solution is introduced at a slow rate beneath the surface of the volume of water and vigorous agitation is utilized to insure immediate distribution of the added solution in the reaction liquor. Desirably, the relatively stable aqueous solution is added in a plurality of stages, the subsequent stage or stages being added more rapidly than the earliest stage. Stated differentaly, the rate of addition of the relatively stable solution can be increased as soon as the reaction liquor becomes turbid indicating the presence of the desired crystal nuclei therein. As will be apparent, the initially formed nuclei grow with the addition of further solution, thus minimizing further nucleation and leading to the production of ultimate crystals of relatively uniform size distribution.

After the crystal nuclei have been formed and grown to appropriate size, it is desired to complete the crystal growth emphasizing growth in the plane of the crystal while minimizing increase in the thickness of the crystal. This is accomplished by adding to the suspension of crystals produced by the addition of the relatively stable solution, a relatively unstable aqueous solution of dissolved bismuth salt.

The relatively unstable solution is formulated to contain a Bi/HCl weight ratio of from 1:1 to 2: 1, preferably from 1.5:1 to 1.91:1. If crystal growth is completed using a higher proportion of hydrochloric acid, then the crystals tend to agglomerate permanently to form large crystals which are undesirable and, moreover, the yield of product decreases undesirably. What appears to occur in the pres ence of excessive hydrochloric acid is the production of crystals which are cohesive with one an other causing agglomeration of the crystals in a manner which resists subsequent breakup or delamination.

In preferred practice, the relatively stable solution is formulated to include a hydrochloric acid concentration of 813% and the relatively unstable solution is formulated to contain a hydrochloric acid content of 13-18%. Also, and in order that the rate of hydrolyzation be controlled throughout the reaction, the temperature of the reaction medium is maintained constant from beginning to end. It is also desirable that the relatively unstable solution be added at a rate which is at least as fast as the most rapid rate of addition of the relatively stable solution.

The invention is illustrated in the example which follows.

EXAMPLE There is introduced into a Pfaudler glass lined reactor of 57 liter capacity equipped with an agitator, a steam jacket, and a feed line 54 liters of deionized water containing .035% of HCl (61.5 ml. of 32% HCl added to the water). This solution is then heated to 90 C.

There is then provided a relatively stable aqueous solution of bismuth nitrate containing 95 grams of and 205 ml. of 32% HCl diluted to 680 ml. with deionized water. This relatively stable aqueous solution is slowly metered into the volume of heated acidified Water in the reactor below the surface thereof and while the water is agitated. The starting rate of addition is 15 ml./ minute for 4 minutes after which a turbidity is observed. Then, the addition is continued at a rate of 30 ml./minute for 8 minutes and then at a rate of 63.3 ml./ minute until the solution is completely added.

A relatively unstable solution is made up to contain 1020 grams of Bi(NO -H O and 650 ml. of 32% HCl, diluted to 1608 ml. with deionized water. This relatively unstable solution is then added at the rate of 63.3 ml./ minute until all of it has been added.

The Bi/HCl ratio of the relatively stable solution is 0.54:1 and the same ratio of the unstable solution is 1.82:1. The HCl concentration of the relatively stable solution is 11:2% and the HCl concentration of the unstable solution is 15%.

The entire procedure is carried out at 90 C. and the reaction is ended as soon as all of the unstable solution has been added. The crystals settle immediately and the clear liquor is decanted and discarded. The crystals are transferred to a Biichener funnel and washed with deionized water to neutrality. The product is then dispersed in castor oil in conventional fashion. Under the microscope it can be seenthat the largest crystals in the field range in size from 14.4-21 microns (average 17.3) and the 20 smallest particles range from 4.77-11.6 microns (average 8.2). Of the largest particles, about 30% exhibited no interference rings and another 30% exhibited two rings or less. The yield is 97% of theoretical.

The invention is defined in the claims which follow.

I claim:

1. A process for producing small thin crystals of bismuth oxychloride by the hydrolyzation of bismuth salt dissolved in water by the action of hydrochloric acid thereon, comprising slowly introducing a relatively stable aqueous solution of dissolved bismuth salt into a volume of water containing hydrochloric acid maintained at an elevated temperature in the range of from about 60 C. to the boiling point of water at the pressure of reaction, said relatively stable aqueous solution having a Bi/HCl weight ratio of from 0.2:1 to 0.821 and said volume of water containing hydrochloric acid in an amount less than about /2% by weight to prevent spontaneous hydrolyzation whereby the added bismuth salt precipitates slowly to form nuclei for further controlled crystal growth, and completing the growth of said crystals by adding to the suspension of crystals produced by the slow addition of said relatively stable solution, a relatively unstable aqueous solution of dissolved bismuth salt, said relatively unstable solution having a Bi/HCl weight ratio of from 1:1 to 2:1 to cause crystal growth to concentrate on the previously produced nuclei with growth being predominantly in the plane of the crystal whereby the thickness of the crystal is minimized.

2. A process as recited in claim 1 in which the dissolved salt is bismuth nitrate.

3. A process as recited in claim 2 in which the hydrochloric acid content of said volume of Water is at least .01% by weight.

4. A process as recited in claim 1 in which said relatively stable aqueous solution is added in stages, with the subsequent stage being added at a faster rate than the earliest stage.

5. A process as recited in claim 1 in which said aqueous solutions are introduced to said volume of water beneath the surface thereof with vigorous agitation.

6. A process as recited in claim 1 in which the rate of addition of said relatively unstable aqueous solution is at least as fast as the most rapid rate of addition of said relatively stable solution.

7. A process as recited in claim 1 in which the temperature is maintained at a uniform level throughout the reaction.

8. A process as recited in claim 2 in which the concentration of hydrochloric acid in said relatively stable solution is in the range of 8-13%.

9. A process as recited in claim 2 in which the concentration of hydrochloric acid in said relatively unstable solution is in the range of 13-18%.

10. A process as recited in claim 2 in which the temperature is maintained in the range of 7599 C.

11. A process as recited in claim 2 in which the temperature is maintained in the range of -95" C.

12. A process as recited in claim 2 in which said relatively stable aqueous solution has a Bi/HCl weight ratio of from 0.4:1 to 0.7:1.

13. A process as recited in claim 12 in which said relatively unstable aqueous solution has a Bi/HCl weight ratio of from 1.5:1 to 1.9:1.

References Cited UNITED STATES PATENTS 3/1961 Suchow 423-472 X 12/ 1923 Darling 423-472 X U.S. Cl. X.R. 423617