US2137058A

US2137058A - Method of producing crystalline boric oxide

Info

Publication number: US2137058A
Application number: US156829A
Authority: US
Inventors: Mcculloch Leon
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1937-07-31
Filing date: 1937-07-31
Publication date: 1938-11-15
Anticipated expiration: 1955-11-15

Description

Patented Nov. 15, 1938 UNITED STATES PATENT OFFICE METHOD OF PRODUCING CRYSTALLINE BORIC OXIDE Leon McCulloch, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application July 31, 1937,, Serial No. 156,829

5 Claims.

having a moderate purity which can be purchased in the open market.

These technical grades of the boric acid are to be preferred for the formation of the first seed crystals since it has been found through experiments that the growing of the crystals may be accomplished at a faster rate with the moderately pure boric acid than where chemically pure boric acid is employed.

In order to induce an initial crystallization, the crystals of which may be employed for the purpose of seeding other liquids, as described hereinafter, a quantity of the moderately pure boric acid may be placed in a suitable container, not shown, which is open to the atmosphere through a small vent and then subjected to a substantially constant temperature above the melting point of boric acid to fuse it until it becomes a viscous liquid. The heating of the boric acid in'the container may be by any suitable means, although it is preferred that the heating be accomplished in an electric furnace provided with an automatic temperature control for controlling the heating temperature.

The heating may be continued until all of the excess steam escapes to the atmosphere and an examination of the viscous liquid reveals that the fused boric acid retains water in solution in an amount ranging from 8% to 14% by weight. It has been found necessary to have water in solution in the fused boric acid within the ranges given in order that crystallization of the liquid may be obtained. This is the percentage of water that remains in boric acid when fused at atmospheric pressure within the temperature range employed. If higher temperatures were employed, it would be necessary also to go to pressures higher than atmospheric pressure.

With the content of the water in solution ranging from 8% to 14% by Weight and preferably from 10% to 12% by weight at atmospheric pressure, the viscous liquid may be further subjected to the substantially constant temperature. When subjected to the substantially constant temperature for a period of time of from 1 to 30 days, it has been found that minute crystalline bodies begin to develop and form about the walls of the container. An examination of the minute crystalline bodies developed in the viscous liquid reveals that they are of rounded or spheroidal shape of about .3 millimeter in diameter. Continued application of the substantially constant temperature to the viscous liquid causes the initial minute crystalline bodies to multiply with the liberation of water vapor until the whole of the liquid in the container becomes solidified. If the viscous liquid is examined when only 1% remains uncrystallized,

it will be found that the 1% of the liquid still has a content of water in solution in the boric acid ranging from 8% to 14% by weight indieating that this content is necessary in order that the crystallization may be completed. As an example of the speed at which the viscous liquid crystallizes, a liter of the boric acid of moderate purity completely crystallized in a period of 7 days when heat treated as described hereinbefore whereas a liter of boric acid of chemical purity required twice as long a time.

In heating the viscous liquid to induce the initial crystallization and cause the liquid to completely crystallize, it is necessary that the temperature of the heating be below the temperature at which the crystals will dissolve and also to maintain the content of waterin solu tion with the fused boric acid within the ranges given hereinbefore. A particularly effective heating range has been found to be between 220 C. and 250 'C.

In order to produce the crystalline boric oxide in quantity, the crystals formed by the initial crystallization described hereinbefore may be employed as seeds for initiating the crystallization of other viscous liquids of fused boric acid. The initial crystals from the viscous liquid in the container before the liquid has become completely crystallized, or the solidified initial crys talline mass may be powdered and a portion thereof may be employed as seeds to induce crystallization of other viscous liquids of boric acid.

In producing the crystalline boric oxide in quantities, a quantity of boric acid may be fused in a similar manner to that described in producing the initial crystallization. After being fused under atmospheric pressure at a temperature above the melting point of boric acid and brought to a temperature of between 225 C. and

o/ll

250 C., the seeds obtained from the initial crystallization may be introduced into the viscous liquid.

The crystalline boric oxide seeds added to the viscous liquid may be in any desired amount, although it is found that crystalline boric oxide seeds of the order of .l% to 1% by weight of the liquid to be crystallized are sufficient to cause a rapid crystallization of the viscous liquid. If a larger quantity of the initial crystals or seeds of boric oxide is added to the viscous liquid the crystallization action will be carried to completion in a shorter period of time.

An examination of the viscous liquid during 5 the crystallization transformation reveals that at first a cloudiness is formed in the clear fused boric acid which increases with the escape of steam as bubbles therefrom, until the liquid becomes more and more pasty and finally solid. The crystals obtained are of microscopic size, the resulting crystalline mass being an anhydrous, white, opaque, non-glasslike, stony solid and strong product which is somewhat resilient under blows from a hammer.

Since the crystalline boric oxide is free of water and, therefore, non-volatile, it is particularly useful in certain branches of industrial chemistry and in particular glass making. Other uses of the crystalline boric oxide produced by this invention are as reagents in analytical chemistry or as fluxes for use in welding as in metallurgy. A crystalline boric oxide produced by this invention may also be employed in the production of elemental boron and boron alloys by reduction with magnesium or other active metals. A further use of the crystalline boric oxide of this invention is as a desiccating agent, since it can take up about 77% of its weight of water in going back to boric acid.

Although this invention has been described with reference to a particular method, it is, of course, not to be limited thereto except insofar as is necessitated by the prior art and the scope of the appended claims.

I claim as my invention;

1. The method of producing crystalline boric oxide which comprises, fusing boric acid and subjecting it to a temperature above its melting point to form a viscous liquid, continuing the heating to drive off moisture from the liquid until the content of water in solution in the liquid is sufficient to cause crystallization of the viscous liquid, continuing the heating of the liquid containing the water in solution to cause crystalline v) bodies of boric oxide to be formed with a liberation of water vapor, the heating temperature being maintained at a value below the temperature at which the crystals dissolve until a desired amount of the crystalline boric oxide is developed, the content of the water in solution in the uncrystallized portion of the liquid maintaining a substantially contant ratio asthe crystals are formed.

2. The method of producing crystalline boric oxide which comprises, fusing boric acid and subjecting it to a temperature above its melting point to form a viscous liquid, continuing the heating to drive off moisture from the liquid until the content of the water in solution at atmospheric pressure is between about 8% and 14%, and continuing the heating of the liquid containing the water in solution to cause crystalline bodies of boric oxide to be formed with a liberation of water vapor, the heating temperature being maintained at a substantially constant value below the temperature at which the crys: tals dissolve until the desired amount of the crystalline boric oxide is developed.

3. The method of producing crystalline boric oxide which comprises, fusing boric acid and subjecting it to a temperature above its melting point to form a viscous liquid, seeding the viscous liquid with a minor portion of crystalline boric oxide, and continuing the heating of the seeded viscous liquid to cause the crystallization of the liquid to proceed with a liberation of water vapor therefrom, the heating of the seeded viscous liquid being at a temperature above the melting point of the boric acid and below the temperature at which the seed of crystalline boric oxide dissolves.

4. The method of making crystalline boric oxide which comprises, fusing boric acid and sub- 1 jecting it to a temperature above its melting point to form a viscous liquid, seeding the viscous liquid with a small but effective amount up to 1% by weight of crystalline boric oxide, and

continuing the heating of the seeded viscous liq- :n"

above its melting point to .form a viscous liquid,

continuing the heating to drive 01f moisture from the liquid until the content of the water in solution at atmospheric pressure is between about 8% and 14%, continuing the heating of the viscous liquid containing the water in solution to cause crystalline bodies of boric oxide to be formed, removing a portion of the crystalline bodies from the container and introducing them into a second container having a viscous liquid of fused boric acid therein, the viscous liquid in the second container being heated at a temperature of betweenthe melting point of boric acid and the temperature at which the crystalline boric oxide dissolves, and continuing the heating of the liquid in the second container to cause the crystallization of the viscous liquid to proceed with the evolution of water vapor therefrom.

LEON MCCULLOCH.