US3645895A - Sodium chlorate compositions of reduced fire hazard containing an alkali metal silicate fire retardant - Google Patents

Abstract

AN ALKALI METAL SILICATE ALONE OR IN COMBINATION WITH ONE OR MORE ALKALI METAL OR AMMONIUM-CHROMATE, HYDROXIDE, CARBONATE, SULFATE, BORATE AND PHOSPHATE WHEN ADDED TO SOLUTIONS OF AN ALKALI METAL OR AMMONIUM CHLORATE IN MINOR AMOUNTS WILL ACT AS FLAME RETARDANTS FOR COMBUSTIBLE ORGANIC MATERIAL UPON WHICH THE CHLORATE HAS BEEN DEPOSITED. THE FUNCTION OF THESE FLAME RETARDANTS WHEN ADDED TO CHLORATE CONTAINING SOLUTIONS DOES NOT DETACT FROM THE FUNCTION OF THE CHLORATE SOLUTION IN ELECTROCHEMICAL MACHINING, MILLING AND GRINDING OPERATIONS OR IN AGRICULTURAL APPLICATIONS.

Description

United States Patent Olfice 3,645,895 Patented Feb. 29, 1972 3,645,895 SODIUM CHLORATE COMPOSITIONS OF RE- DUCED FIRE HAZARD CONTAINING AN ALKALI METAL SILICATE FIRE RETARDANT John A. Peterson, Niagara Falls, N.Y., and Albert H. Ross, Niagara Falls, Ontario, Canada, assignors to Hooker Chemical Corporation, Niagara Falls, N.Y. No Drawing. Filed Jan. 15, 1968, Ser. No. 697,637 Int. Cl. C09k 3/28; A01n 5/00; B23p 1/16 US. Cl. 252-8.1 14 Claims ABSTRACT OF THE DISCLOSURE An alkali metal silicate alone or in combination with one or more alkali metal or ammonium-chromate, hydroxide, carbonate, sulfate, borate and phosphate when added to solutions of an alkali metal or ammonium chlorate in minor amounts will act as flame retardants for combustible organic material upon which the chlorate has been deposited. The function of these flame retardants when added to chlorate containing solutions does not detract from the function of the chlorate solution in electrochemical machining, milling and grinding operations or in agricultural applications.

This invention relates to compositions of matter containing an alkali metal or ammonium chlorate (preferably sodium chlorate), an alkali metal silicate and optionally other inorganic compounds. These compositions find utility in the field of agricultural chemistry as soil sterilizers, defoliants, and weed killers. These compositions also have utility as electrolytes for use in electrochemical machining and grinding operations. The compositions are especially useful because of their flame retardant properties.

Alkali metal and ammonium chlorates, especially sodium chlorate, are ideal electrolytes for use in electrochemical machining operations. The major problem attending their use resides in their tendency to rapidly oxidize combustible materials. The advantages and problems residing in the use of chlorates as the electrolyte in electrochemical machining operations are summarized in the article appearing in Metal Progress, March 1967, pp. 81-84. For example, when some of the chlorate containing electrolyte comes into contact with the clothing of the operator, or any combustible material near an electrochemical machining operation, the tendency to initiate fire is great after the wetted material has dried.

By electrochemical machining operations it is intended to include those operations by which a workpiece is machined, milled, or ground so that the metal is removed by an electrochemical process to produce shaped or curved structures. These operations also include the production of smooth flat surfaces and the formation of holes in a workpiece. The workpiece to be shaped functions as the anode in electrically conducting relationship with the cathode die through a suitable electrolyte. Metal is dissolved from the workpiece anode. Some electrolytes used in electrochemical machining are described in US. 2,798,846 to Comstock, issued July 9, 1957 as NaNO Na CRO KNO K CrO the amines of sodium nitrate, sodium and potassium dichromate, sodium and potassium chlorate and sodium and potassium chlorite. Essentially, the selection of the electrolyte is based upon its conducting properties, its tendency to attack the electrodes, its performance in electrochemical machining operations and its cost. Comstock mentions the rusting of a workpiece and its prevention through the use of a rust inhibiting agent as the electrolyte.

Sodium chlorate is an excellent electrolyte for electrochemical machining operations. Sodium chlorate solutions used as the electrolyte in electrochemical machining are typically aqueous solutions containing about 350 g./1 .NaClO Solutions containing from about 300 to 400 grams per liter NaClO are typical examples of efficient electrolytic solutions. The used electrolyte solutions, usually of pH above about 6 to 7, contain precipitated hydroxides of the metal removed from the workpiece. For example, where the workpiece contains iron, nickel or chromium, the corresponding iron, nickel or chromium hydroxides are formed.

In the electrochemical machining of chromium containing alloys, some soluble sodium chromate is introduced into the sodium chlorate electrolyte. The introduction of small amounts of sodium chromate into the electrolyte actually increases the fire hazard attending the action of chlorate on combustible organic material. Hence, any flame retardant additive will have to function in the presence of at least low concentrations of dissolved CrO; ions. It is also important that any additive must not change the characteristics of sodium chlorate in its operation as an electrolyte. However, it is most desirable that an additive both act as a flame retardant and improve the properties of sodium chlorate as an electrolyte.

In the field of agricultural chemistry, alkali metal chlorates have been used as defoliauts (especially for cotton), Weed killers, soil sterilizers, insecticides and as seed disinfectants. One of the major drawbacks to the use of chlorates as agricultural chemicals resides in the problem of its flammability when dried in contact with organic matter such as the workers clothing. The discovery of additives such as an alkali metal silicate alone or in conjunction with a co-additive for the chlorate solutions used in agricultural applications obviates this objection to the use of chlorates and broadens the field for uses of chlorates at concentrations heretofore considered too dangerous for handling by the layman.

It is the object of this invention to develop compositions of matter containing a major proportion alkali metal chlorate in combination with one or more additives, the latter functioning as flame retarding agents when said compositions are deposited in a dry state upon combustible organic materials.

It is an additional object of this invention to provide compositions of matter containing a major proportion of alkali metal chlorate with minor proportions of one or more additives which will function as a flame retardant and as the electrolyte in electrochemical machining operations with the same degree of effectiveness as sodium chlorate alone.

DETAILED DESCRIPTION OF THE INVENTION It has been discovered that an alkali metal silicate, when dissolved in a solution with an alkali metal or ammonium chlorate, will act as a flame retardant when the solution is dried on a combustible material. The ratio of Si0 to chlorate may vary from 1:4 to about 1:40 on a dry weight basis. The preferred ratio of Na SiO to NaClO is between 1:4 and 1:10 on a dry weight basis. In an electrolytic solution, this ratio represents, for a solution containing between about 300 to 400 grams per liter NaClO from about 7-75 grams of SiO (as a soluble silicate) per liter and preferably between about 15 to 50 grams Si0 per liter.

The preferred silicate additive for chlorate containing solutions employed as electrochemical machining or grinding electrolytes is sodium metasilicate (Na SiO which may be added either as the anhydrous salt or as a hydrate such as the nona-hydrate (Na SiO .9H O).

Other silicates such as the disilicate (Na Si O and tetrasilicate (Na Si O commonly referred to as water glass may be employed as the fire retardant additive for various chlorate containing compositions. However, as an electrolyte in electrochemical machining and grinding operations sodium metasilicate is preferred to silicates of lower Na/Si ratios such as water glass because the tendency of the latter silicates is to deposit hydrous SiO from solution in the presence of chlorate.

Co-additives which may be advantageously employed in conjunction with the silicate additive are alkali metal or ammonium chromates, carbonates hydroxides, phosphates, sulfates, and borates. These co-additives are effectively present in an amount between 10 and 80 grams per liter of solution in the use of chlorate-silicate solutions as the electrolyte for electrochemical machining and grinding operations. On a dry weight basis, the ratio of silicate, expressed as SiO and independently the coadditive to chlorate may be 1:440, while a more preferred ratio is about l025 parts of sodium metasilicate to from about 4l0 parts of sodium metaborate for every 100 parts of sodium chlorate and the most preferred ratio is 2:1:16 sodium metasilicate to sodium metaborate to sodium chlorate. Exemplary mixtures containing sodium chromate as the co-additive are those containing on a dry weight basis a mixture of about l0-25 parts of sodium metasilicate and from about 10 to parts of sodium chromate for every 100 parts of sodium chlorate. The most preferred mixture containing sodium chromate as the co-additive is 12118 sodium metasilicate to sodium chromate to sodium chlorate.

The most preferred aqueous solutions of electrolyte for electrochemical machining operations are those containing from 300 to 400 grams sodium chlorate per liter and from to 100 grams sodium metasilicate per liter; or 30 to 100 grams sodium metasilicate per liter in combination with from about 12-40 grams per liter sodium metaborate; or from about 30-100 grams per liter sodium metasilicate in combination with about 30-80 grams per liter sodium chromate.

Since an aqueous solution containing between about 300 to 400 grams per liter of sodium chlorate and up to about 100 grams per liter of sodium metasilicate is alkaline in pH, it is desirable to include an appropriate amount of NaOH whenever an acidic co-additive such as borax (Na B O sodium pentaborate (Na B O or Na HPO is used. If NaOH is not employed in conjunction with acidic co-additives, the pH drop of the electrolyte solution causes hydrolysis of the silicate and precipitation of hydrous SiO- The alkali metal silicate additives alone are very effective flame retardant additives for chlorate induced combustion of organic materials in many applications. However, a further factor which must be considered in evaluating the flammability of chlorate electrochemical machining or grinding electrolyte which has been dried on cloth, is the presence of trace amounts of chromate ion in the chlorate containing solution. Trace amounts of chromate, usually equivalent to 0.05 to 2 grams of hexavalent chromium per liter appear in the electrolyte used in the processing of chromium containing metals as the probable result of complete oxidation of the chromium to CrO during the machining or grinding operation. These trace amounts of chromate serve to accelerate the combustion of organic material which has been wetted by the chlorate containing solution and dried. This acceleration is very pronounced when a cloth wetted with the chlorate containing solution is quite dry (e.g. under normal room conditions at 20 percent relative humidity). The accelerating effect of chromate on chlorate induced combustion is less pronounced when the organic material contains more moisture, as under normal room conditions at percent relative humidity, but it remains a very important factor to be considered relative to the effectiveness of a flame retardant additive. The effect of trace chromate on chlorate induced combustion is clearly illustrated in Example 1 of this specification.

An additional problem in the determination of flame retardant properties of additives for chlorates resides in the fact that the combustion rate of a cloth impregnated with sodium chlorate and a prospective flame retardant is often dependent upon the size of the ignition source. A large flame may cause rapid burning while a small ignition source such as a match or the coal of a cigarette may cause slow combustion. A flame retardant additive which is effective with respect to common accidental ignition sources which may attend the personal habit of an operator of an electrochemical machining apparatus, such as a match flame or cigarette coal, may be considered adequate for the protection of that person. However, the degree of effectiveness for the same additive may be less in flame retardancy towards a large ignition source.

The alkali metal silicates are extremely effective flame retardants for chlorate induced combustion. In the presence of trace amounts of chromate ions, the effectiveness of an alkali metal silicate as a flame retardant is somewhat diminished although it is still adequate to provide the degree of protection needed for the machine operator. However, the introduction of a co-additive in conjunction with the silicate, will produce a silicate based additive which is more effective than silicate alone under the conditions of low humidity, the presence of trace chromate and a large ignition source. The silicate based additives are superior to most other additive systems tested.

In essence, in any application of solutions containing chlorate ions, conventional formulations applicable to the art may be supplemented with the silicate fire retardant of this invention with or without the addition or complementary fire retardant additives.

For example, in the field of electrochemical machining, it may be desirable to add minor amounts of other electrolytes to the sodium chlorate solution containing the fire retardant additives of this invention. Such supporting electrolytes may be NaCl, NaBr, NaF, NaNO etc.

It is to be understood that whenever chromate is referred to in the specification as a co-additive, it is intended to include Na CrO or sodium dichromate or chromic acid in the presence of suflicient NaOH to produce chromate in situ via the reaction:

Chromic acid or Na Cr O +xNaOH+Na CrO The following Examples I-XVI represents specific embodiments of this invention. They represent applicable additive concentration levels which will produce the desired result. The minimum operable concentration of the flame retardant additives is desirable because excessive concentrations may cause inferior performance of the chlorate solution as electrolyte in an electrochemical machining or grinding operation.

To determine the effect of an alkali metal silicate with and without other additives as a flame retardant for organic materials impregnated with alkali metal or ammonium chlorate, the following experiments were conducted.

EXAMPLES I-XVI The burning tests employed in the determination of the effectiveness of a given flame retardant additive were conducted as follows:

Strips of cotton twill 6 feet by 1.5 inch were soaked in the test solution, wrung out and dried under controlled condition of humidity. The cloth strips were then hung vertically and ignited at the bottom with a 4 inch gas flame (large ignition source) or a 0.5 inch gas flame (small source). The time required to burn (or char) a 52 inch section of cloth was determined. In its original state, without treatment, this standard cloth burns in 35 seconds. Hence, any additive which will prevent more rapid burning produced by the alkali metal or ammonium chlorate is an effective fire retardant. In each test, the cloth strip was loaded with about one gram of solution per gram of cloth. Each solution contained 400 grams sodium chloto the electrochemical reaction which may be considered rate per liter. This concentration approximates the usual oxidation of the iron in the workpiece to the ferrous or concentration of chlorate used for electrochemical machinferric state. A suspension of hydrous metal oxides was ing (3 pounds per gallon=359 grams per liter). formed in the recirculating electrolyte and slowly settled TABLE 1.BURNING TIMES FOR COTTON TWILL STRIPS IMPREGNATED WITH NaClOa+ADDITIVES [Burning time=sec./52-inch section, 1% inches wide] Drying of strip, Burning time for strip, sec., when solution contained gins. Cr/liter Solution composition, gins/liter percent rel. Ignition (present as NraCrOr) of:

humidity, flame Ex. NaClOs Add1tive(s) 25 0. size N Cr 0.05 Cr 0.1 Cr 0.5 Cr 1.0 Cr 2.0 Cr Other Cr III }No additive 1 2 9 0 9 3 None Water only 400 77.9 NazCrOi 400 12 NaOH 288 has NazSiO: (=25 SiOs) 400 77 NazSiOs (37.5 S102) :88 }50.8 NazSiOa plus 26.3 nsnoz 400 Cr=50 sec.

400 }so.s NnzSiOa plus 46.7 NazCrOr 15 CF38 m It is apparent from this data that the burning time of in the electrolyte reservoir to form a brownish sludge. the original cloth (Example 3) is drastically reduced by For an 0.05 inch deep cut, the grinder drew 1500 emperes chlorate and further reduced by chlorate in the presence at 11 volts and the 3 inch long cut was completed in 80 of trace amounts of chromate (Examples 1 and 2). seconds. For a depth of cut of 0.10 inch, 1900 amperes "Experiments presented in Examples 4-6 demonstrate were drawn at 10 volts and a 3 inch cut required 140 secthe eifects of low humidity and large ignition flame size onds for completion. The ground sulface was smooth and in decreasing the burning time of the chlorate impregnated there was no evidence of excessive overcutting. The humcloth in the presence of sodium chromate as a flame reing time of cloth impregnated with the used electrolyte tardant additive. The same effects are illustrated in Examwas approximately the same as that for the original soluples 7-9, as well as the effect of trace amounts of chrotion. mate, for the flame retardant sodium hydroxide. The presence of sodium metasilicate and sodium meta- Experiments resulting in the data presented in Examples horate had no deleterious effect on the performance of 10 and 12 illustrate the flame retardant effect of sodium sodium chlorate as an extremely efficient electrolyte in metasilicate in the presence of trace amounts of chromate the electrochemical grinding operation. Likewise the alkali and at a low humidity for a small ignition source. The metal based silicate flame retardant additives of this in addition 0f both sodium metasilicate and sodium metavention when employed in conjunction with chlorate as horate exemplified in Examples 13 and 14 demonstrates an electrochemical grinding or machining electrolyte prefllfi higher degree of flame l'etafdallcy attending the use sent no deleterious efiect in the actual grinding or machinof a co-additive with the silicate. ing operation while affording the advantage of flame re- EXampleS 15 and 16 demonstrate the flame Tetafdant tardancy to protect the operator and his clothing from properties of another silicate based additive of this invenid l damage f fi i d d b h 1 1 m Specifically Sodium metasilicate and Sodium The illustration of a specific electrolyte containing solumate. tion in conjunction with an electrochemical grinding oper- The alkali metal or ammonium chro Carbonate, ation is representative of the operation of all the disclosed hydroxide, P p Sulfate, horate co-additives 9 compositions in grinding and machining operations. alkali metal silicate based flame retardant additives of th1s Having disclosed the invention, it i be apparent to invention perform the Same function and may be used those skilled in the art that obvious modifications may be in substantially the same amounts as illustrated for chromade, For example, in any of the disclosed combinations mate and metaborate to achieve substantially the same f additives f c o the amount f silicate plus results. additive present may be increased without deleterious EXAMP XVII effects. The minimum amount of the flame retardant additive or additives is the critical factor to be considered in The So described in EXtIIIlP16S 13 and 14 in the most applications because of possible deleterious effects preceding table was cha ged t the TESBIIVOiT of an f that may impair the function of the chlorate as an electrochemical gn'llding machine The grinmflg wheel (1 F chemical machining electrolyte. Therefore, the examples in Width) was a conducuve'bonded mlxmre of alumma herein presented are intended to be illustrative of the inand coppler g i i 1 332 gi gg g g i g ventive concept rather than limitations upon the actual ode relative to e wor plece-a scope of the contribution 3 inch Wide bar of Stainless Steel) was fed mm the If higher or lower chlorate concentrations are desired wheel which was set to give a specified depth of cut. I During the cutting operation, the electrolyte solution was In electrochemlfial g g dln g operatlon, the pumped from the reservoir and injected betwaen the grind relative proportion of silicate and co-additive may be eming wheel and the workpiece. Used electrolyte drained P Y back to the reservoir. Several cuts were made across the W t IS claimed 1s: I

workpiece as slots 1 inch wide and 0.05 to 0.10 inch deep. 1. A composition of matter comprising a member se- The feed rate of the workpiece into the grinding wheel lected from the group consistlng of an alkali metal chlowas varied when necessary to maintain a light load on the rate, ammonium chlorate and mixtures thereof, and a grinding wheel drive motor. The power input to the drive flame retardant proportion of a member selected from the motor was kept at about 10 percent of the load theoretigroup consisting of an alkali metal sihcate and hydrates cally needed to cut the metal workpiece by abrasion alone. thereof, in which the silicate, expressed as S10 to chlo- Therefore, practically all of the metal removal was due rate weight ratio is between about 1:4 to 1:40'.

2. The composition of claim 1 in which sodium metasilicate and sodium chlorate appear in the weight ratio of about 1:4 to 1:10.

3. A composition of matter comprising a member selected from the group consisting of an alkali metal chlorate, ammonium chlorate and mixtures thereof; a flame retarding proportion of a member selected from the group consisting of an alkali metal silicate and hydrates thereof; and a flame retarding proportion of a co-additive selected from the group consisting of an alkali metal chromate, borate, carbonate, phosphate, sulfate, hydroxide, ammonium analogs thereof, hydrates thereof and mixtures thereof, in which the silicate, expressed as SiO co-additive and chlorate are in the weight ratio of 1:1:4-40.

4. The composition of claim 3 comprising about 10-25 parts of sodium metasilicate, and about 4-10 parts of sodium metaborate to each 100 parts of sodium chlorate.

5. The composition of claim 3 in which the weight ratio of sodium metasilicate to sodium metaborate to sodium chlorate is about 211216.

6. The composition of claim 3' comprising about 10-25 parts of sodium metasilicate and about 10-20 parts of sodium chromate to each 100 parts of sodium chlorate.

7. The composition of claim 3 in which the weight ratio of sodium metasilicate to sodium chromate to sodium chlorate is about 1:118.

8. [An aqueous solution of an electrolyte comprising from about 300 to about 400 grams per liter of a member selected from the group consisting of an alkali metal chlorate, ammonium chlorate and mixtures thereof; about 7 to about 75 grams per liter of an alkali metal silicate, expressed as SiO and from 10 to about 80 grams per liter of a co-additive selected from the group consisting of an alkali metal chromate, borate, carbonate, phosphate, sulfate, hydroxide, the ammonium analogs thereof and mixtures thereof.

9. The solution of claim 8 in which the chlorate is sodium chlorate, the silicate is sodium metasilicate and the co-additive is sodium metaborate.

10. The solution of claim 9 which contains from about 30-100 grams per liter of sodium metasilicate and from about 12-40 grams per liter of co-additive sodium metaborate.

11. The solution of claim 8 in which the chlorate is sodium chlorate, the silicate is sodium metasilicate and the co-additive is sodium chromate.

12. The solution of claim 11 which contains from about 30-100 grams per liter of sodium metasilicate and from about 30-80 grams per liter of co-additive sodium chromate.

13. The solution of claim 8 in which the chlorate is sodium chlorate, the silicate is sodium metasilicate appearing in from about 30 to 100 grams per liter and the amount of co-additive present is zero.

14. A method of retarding chlorate induced combustion of organic material which comprises incorporating into aqueous solutions containing the chlorate ion, a flame retardant proportion of an alkali metal silicate and a flame retardant amount of a co-additive selected from the group consisting of an alkali metal chromate, carbonate, borate, phosphate, sulfate, hydroxide, ammonium analogs thereof and mixtures thereof, in which the silicate, expressed as 'SiO co-additive and chlorate are in the weight ratio of 1:1:4-40.

References Cited UNITED STATES PATENTS 225,858 3/1880 OConnor 117-138 280,500 7/1883 Meyer 1l7-138 671,548 4/1901 Gordon 117138 1,271,506 7/1918 Ferguson 117138 1,534,289 4/ 1925 Teppet 71-128 2,704,243 3/ 1955 Seibert 7169 2,749,227 5/ 1956 Bales 71-69 2,886,425 5/1959 Seibert 71128 3,464,810 9/ 1969' Young 7l128 3,306,765 2/ 1967 Du Fresne et a1. 117-138 OTHER REFERENCES Thomas et al.: Effect of Alkali-Metal Compounds on Combustion, Industrial and Engineering Chemistry, June Hodgman et al.: Handbook of Chemistry and Physics, Chem. Rubber Pub. Co., Cleveland, 1959, pp. 652-661.

JOHN T. GOOLKASIAN, Primary Examiner D. I. FRITSCH, Assistant Examiner US. Cl. X.R.

John A. Peterson and Albert H. Ross Patent No. Dated February 29, 1972 Inventofls) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

in Column 3, 1 1' ne 12, 'carbonaces" should read ---carbonates,,---. 7

ad ---addition Of--- Column ne 33, "addition or" should re Column 6, line 26, "emperes" should read ---amperes---; l ine "sulface" should read ---surface---.

Signed and sealed this 18th day of July 1972.,

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 52 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORREC'NQN 3, +5, 95 Dated February 29, 1972 John A. Peterson and Albert H. Ross Patent No.

Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

F- Column 3', line 12, "carbonates should read ---carbonates,,--.

should read ---addition of---;

Column he 33, "addition or' Column 6, line 26, "emperes' should read ---amperes--- line 30, 'sulface" should read ---surface---.

Signed and sealed this 18th day of July 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK EDWARD M.FLETCHER,JR. Attesting Officer Commissioner of Patents