US2438511A - Copper, chromium, arsenic compound for wood preserving - Google Patents

Description

Patented Mar. 30, 1948 COPPER, CHROMIUM,

ABSENIG COMPOUND.

FOR WOOD PRESERVING William McMahon, Summit, at. 1., asslgnor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application December 31,1941,

Serial No. 425.125

This invention relates to preservative compositions for cellulosic material. such as wood; and the present application constitutes a continuation in part of my prior application, Serial No. 323,698, filed March 13, 1940 on Wood preservation, now abandoned.

The principal object of the invention is the provision of such a preservative composition that when applied to the cellulosic material it will not only preserve the material but will also result in a treated material of high insulation resistance.

Another object of the invention is to provide a water-borne preservative which when applied to cellulosic material, such as wood, forms no watersoluble salts.

A further object is to fix effectively and simultaneously in one operation compounds of copper, chromium and arsenic in wood or other material containing cellulose and lignin while avoiding the formation in the material of any permanently water-soluble salt.

In the preferred embodiment of the invention the wood preservative composition consists of an aqueous solution comprising chromic acid, arsenic acid and a compound of another metal such as copper, where the said copper compound consists of one or more of the following: copper hydroxide, copper carbonate, copper oxide, copper chromate, copper dichromate or copper arsenate. Copper dichromate is soluble in water while the other copper compounds mentioned are soluble in an aqueous solution of arsenic acid and chromic acid. Stated in a somewhat different manner, the preferred composition comprises a Water-soluble compound of chromium, a compound of another metal such as copper, and if desired, a water-soluble compound of arsenic, where the compounds selected are of such a nature that when the wood is impregnated with an aqueous solution of these compounds in the proper proportions the reaction of certain substances in the wood with the impregnating solution results in the formation of newcompounds, all of which are water-insoluble.

The feature of having all of the reaction products water-insoluble is of particular importance in the impregnation of telephone poles Or other timber having galvanized iron or other metallic members aiiixed thereto. If the reaction between the wood and the impregnating solution Claims. (01. 167-385) 2 is-such as to form a new salt which is water-soluble, the insulation resistance 01' the pole would be decreased by the presence of such a compound; and if the new water-soluble compound is a salt. such as chloride or sulphate, the presence of such a salt would tend to accelerate corrosion of the pole line hardware.

For example, when an aqueous solution of chromium trioxide, copper hydroxide and arsenic pentoxide is injected into the wood the reaction of these compounds with the wood produces the following new compounds: chromium hydroxide, chromium arsenate, chromium chromate. copper arsenate, and copper chromate. All of these new compounds are insoluble in water and hence none of the new compounds is of such a nature as to increase the conductivity of the pole when subsequently exposed to moisture or running water; and, further, none of these new compounds tends to accelerate the corrosion of any metallic article ailixed to the pole.

It has previously been proposed to employ certain chromium salts for the fixation of copper and arsenic in the wood to afford protection against wood-eating insects and wood-destroying fungi, where the fixation is believed to be due to the reduction of the chromate ions by certain substances in the wood. The present invention in that respect is similar to'these earlier proposals but provides an improvement thereon particularly for those uses of the treated timber which require the attachment of metal fixtures to the timber, such as the hardware usually employed on telephone poles. Since the wood treated with the solution of this invention has a markedly higher electrical resistance than would be the case if the reaction of the ingredients on the wood produced a. water-soluble by-product, it follows that the treated wood of this invention can also be advantageously used for poles for power transmission lines and the like.

In the above description of the preferred compositions, certain compounds of copper have been listed but, if desired, the corresponding compounds of nickel, zinc, cobalt or barium may wholly or partially replace the copper compounds. A further permissive variation is to omit the arsenic compound entirely where the fungidestroying property 0! arsenic is not needed. It may also be noted that when the arsenic is added aeaaau in the form of a metallic arsenate, the arsenic pentoxide may be absent or present in a correspondingly reduced amount; while when the maior portion of the chromium is added in the form of a metallic chromate or dichromate it will still be advisable to add some chromium trioxide or its equivalent to produce chromic acid in the aqueous solution.

The following data include several examples of the preferred compositions of this invention and indicate in parts by weight the amount of each compound which is advantageous to employ. approximate upper and lower limits being given for each compound. In general, it may be stated that in the preferred wood preservative compositions of this invention each of the elements, chromium. arsenic and copper or other substituted metal. is present insufflcient amount to exert a substantial toxic action on wood-destroying organisms.

Example I Permissible Pren [erred Porto Arsenic pentoxide mam. 2E0) 5 to 15 parts.-- 5 a t dmtasaw ma ".".-Z -12 .3; 3:: 800 to am a more parts.

where the copper hydroxide may be replaced wholly or in part by the chemically equivalent weight of one or more of the hydroxides of zinc, nickel,.cobalt orbarium. For example, if the copper hydroxide of Example I is wholly replaced by zinc hydroxide (Zn(OH) the permissible variation would be 6 to 9 parts with 6 parts preferred; if replaced by nickel hydroxide (Ni(OH) 2) the permissible variation would be 5.5 to 8.5 parts with 5.5 parts preferred; if replaced by cobalt hydroxide (Co(OH)r) the permissible variation would be 5.5 to 8.5 parts with 5.5 parts preferred; or if replaced by barium hydroxide (Ba(OH) 2.8H2O) the permissible variation would be 19 to 29 parts with 19 parts preferred.

-11. desired, the copper hydroxide of Example I may be replaced by the chemically equivalent weight of any one of the other permissible copper compounds, as indicated by the subsequent examples:

Example I! Preierrcd Parts Arsenic pentoxide (AssOaZHsO) Chromium trioxide (CrOs) gil copper carbonate [2CuC0;.Ou(0H);1.

'IOWtar by cobalt carbonate (C0003) the permissible I variation would be 7 to 11 parts with 8 parts preferred; or if replaced by barium car onate d (BaCOs) the permissible variation would be 12 to 19 parts with 18.5 parts preferred.

Example III Permissible Pre- Variation ierred A ul 1 t as (A 0 211,0 e

rse c no e s chromiu r r trioxide (dr6r)..--- l5 Oupric oxide (OuO) 5 Water permissible variation would be 4.5 to 7 parts with i 4.5 parts preferred; or if replaced by barium oxide (BaO) the permissible variation would be 9.5 to 14.5 parts with 9.5 parts preferred.

where the copper chromate may be replaced wholly or in part by the chemically equivalent weight of one or more of the corresponding chromates of zinc, nickel, cobalt or barium. For example, if the copper chromate of Example IV is wholly replaced by zinc chromate (ZnCrOa'IHaO) the permissible variation would be 18.5 to 28 parts with 18.5 parts preferred; if replaced by nickel chromate (NiCrOr) the permissible variation would be 10.5 to 16 parts with 10.5 parts preferred; if replaced by cobalt chromate (CoCrOi) the permissible variation would be 10.5 to 16 parts with 10.5 parts preferred; or if replaced by barium chromate (BaCrOu) the permissible variation would be 15 to 23 parts with 15 parts preferred. It also is to be noted that when the chromate of zinc, nickel, cobalt or barium is substituted for the basic copper chromate of Example IV, there is a slight change in the permissible variation of the chromium trioxide over the amounts given in Example -IV, namely that the permissible amounts of chromium trioxide would become 5 to 15 parts, with 10 parts preferred.

Example V Permissible Variation Parts Arsenic ntoxide (As O .28 0

cunnin trioxide 2036.).--)

Copper dichromate CuCnOMEhO) rowan where the copper dichromate may be replaced wholly or in part by the chemically equivalent weight of one or more of the dichromates of zinc,

Perierred nickel, cobalt or barium. For example, it the copper dichromate of Example V is wholly replaced by zinc dichromate (ZnCrzOr) the permissible variation would be 17 to 25.5 parts with 17 parts preferred: if replaced by nickel dichromate (2N1C12O1.3H2O) the permissible variation would be 18 to 27.5 parts with 18 parts preferred; it replaced by cobalt dichromate (CoCrzOaHaO) the permissible variation would be 17.5 to 26.5 parts with 17.5 parts preferred; or it replaced by barium dichromate (BaCi'zOv) the permissible variation would be 21 to 32 parts with 21 parts preferred.

where the copper arsenate may be replaced wholly or in part by the chemically equivalent weight of one or more of the arsenates of zinc, nickel, cobalt or barium. For example, if the copper arsenate of Example V1 is wholly replaced by zinc arsenate (Zn3(AsO4)2.8I-I2O) the permissible variation would be 12.5 to 19 parts with 12.5 parts preferred; it replaced by nickel arsenate (Ni3(ASO4) 2.8H2O) the permissible variation would be 12 to 18 parts with 12 parts preferred; if replaced by cobalt arsenate (Ca(ASO4)a.8I-I2O) the permissible variation would be 12 to 18 parts with 12 parts preferred; or if replaced by barium arsenate (Ba3(AsO4)z.3H2O) the permissible variation would be 15 to 23 parts with 15 parts preferred.

In the event that it is desired to fix only a compound of copper but not of arsenic .in the wood the arsenic compound in the above examples may be omitted entirely, so that Example I, for instance, would become:

Example VII Permissible variation Chromium trioxide (Cr 03) 10 to 20 parts Copper hydroxide [Cu(OH)2] 5 to parts Water 300 to 3000 or more parts where the chromium trioxide and the copper hydroxide are preferably used in the ratio of 2 to 1 and where the copper hydroxide may be replaced wholly or in part by the chemically equivalent weight of one or more of the corresponding hydroxides of zinc, nickel, cobalt or barium.

The following remarks, as specifically applied to Composition I, are offered in explanation of the listing of preferred limits for the various ingredients employed in the wood preservative of this invention. As shown in Example I, the preferred limits for arsenic pentoxide are about 5 to parts. Below about 5 parts the arsenic pentoxide is not present in suflicient amount to secure the desired efiectiveness in wood preservation; while when substantially more than 15 parts are employed the arsenic is not so permanently fixed in the wood, as is the case when the amount employed is within the desired limits, and there 15 Water 6 would be an undesired'leaching oi the arsenic from the wood. With respect to copper hydroxide the same observations apply as for the arsenic compound. A minimum of about 6 parts of copper hydroxide is needed to secure the desired effectiveness in wood preservation; and when substantially more than 9 parts of copper hydroxide are employed the copper is not so permanently fixed in the wood as is the case when the amount employed is within the stated limits. The chromium compound is needed to cause the fixation of the copper and arsenic in the wood. The lower limit of about 10 parts of chromium trioxide is needed to maintain the arsenic and copper compounds in solution and precipitation will occur if a substantially smaller amount of chromium trioxide is employed. For the maximum amounts of the arsenic and copper compounds given in Example I, any amount of chromium trioxide beyond about 20 parts is unnecessary and superfluous in obtaining the desired fixation of the copper and arsenic compounds in the wood.

A composition of 5 parts arsenic pentoxide, 17 parts chromium trioxide and 6 parts copper hydroxide dissolved in 1000 parts of water has a pH value of 1.02.

The amount of water employed with the above compositions depends to some extent upon the type of treatment employed in impregnating the wood. In the full cell treatment, where the wood is first subjected to a partial vacuum and is then immersed in the solution under pressure for some time, the amount of water for the above examples should be in the neighborhood of 1000 to 2000 parts. In the so-called empty cell treatment, where the wood is first placed under greater than atmospheric pressure to drive air into the wood, and is then immersed in the solution under still greater pressure for a certain period of time, after which the wood is removed from the solution and placed under a partial vacuum, the solution employed should have a higher degree of concentration employing water in the neighborhood of 500 to 1000 parts.

It should be noted that the preservative composition of this invention can be safely used in iron or steel tanks or other wood-treating equipment without any objectionable corrosive action.

Several fungicides for treating wood telephone poles including the solutions of the present invention have been studied to determine their relative corrosiveness towards galvanized iron pole hardwarewith which they might come in contact. This was done by measuring the potential of iron immersed in the respective solution with a tenth normal calomel reference electrode by means of a continuously recording potentiometer where the readings were taken over a period of fifty minutes. In the following tabulation, solutions A and B are representative of this invention, while solutions C and D represent certain prior proposals.

Solution A consisted of:

Parts Copper hydroxide [Cu(OI-I)i] 10 Chromium trioxide (CrOa) 17 Water 1000 Solution B consisted of: I

Parts Arsenic pentoxide (AszOs.2I-Iz0) 5 Copper hydroxide [Cu(OH)2] 6 Chromium trioxide (CrOa) 1'7 aisas r:

Solution C was an aqueous solution. of certain compounds of arsenic, copper and chromium j where the compounds'were such, when used as 1 a wood preservative, as to produce a water-solusulphate would be formed as a by-product in the reaction of the solution on the wood but diflered from solution by the omissionof arsenic and the addition of a small amount of an organic acid.

its potential after fifty minutes exposure to the solution were as follows:

Potential Initial Solution Potential fi zg g in-Volts Minute,

.4. --o.12s -0.o3 B. -o.a1 -o.a1s o. -o.scs -o.41o D -o.es -o.eo

From these data it is apparent that solutions A and B passivate the iron more strongly than solutions C and D since the potential values for vsolutions A and B are more electropositive than solution is the one giving the wood the higher,

insulation resistance. In thesetests of the insulation resistance, air-seasoned poles were treated with the various solutions and then'were exposed in the open air for about eleven months before the following measurements were taken, where the insulation resistance given is in megohms per foot of test section length:

B 1. 7449 0 0.2053 D. 0.2603 Standard creosote treatment 0.6582

The preservative of this invention may be injected into the wood in a. variety of ways as by placing the wood under a partial vacuum and then immersing the wood in the solution under a pressure greater than atmospheric'pressure; by the empty cell treatment previously described; or by dipping the wood in open-vessels containing the preservative solution; or by brush or spray painting the wood with the solution.

After the preferred ingredients, arsenic pentoxide, chromium trioxide, and a copper compound such as copper hydroxide, are dissolved in water,

1 the resulting solution may be considered as one containing arsenic acid, .chromic acid and the copper compound; and hence, in the following claims any reference to chromic. acid or arsenic acid is also intended. to include the, oxide of chromium orarsenic.

copper are dissolved in water, the solution consists substantially exclusively of ions \of copper, ions of hydrogen, chromate ions, dichromate ions, and arsenate ions. It may also be noted that the copper, nickel, zinc, cobalt or barium compound employed in the solution of the present invention is preferably one in which the metal is divalent.

WhatIclaimis:

1. A preservative for wood consisting of ingradients which. when dissolved in water, are capable of reacting with certain substances in said material to form compounds which are all water-insoluble, said ingredients comprising chromium trioxide and a substantial amount of a copper compound the component of which, other than copper, is selected from the group consisting of hydroxide, carbonate, chromate, dichromate and arsenate, said chromium trioxide being present in a substantial amount at least suilicient to maintain the metal compound in solution when the ingredients are added to water.

2. A wood preservative consisting of ingredients which, when dissolved in water, are capable of reacting with certain substances in the wood to form salts which are all water-insoluble, said ingredients comprising arsenic pentoxide, chromium trioxide and a copper compound in wood preserving amounts, the component of the copper compound other than copper being selected from the group consisting of hydroxide, carbonate, chromate, dichromate andarsenate.

3. A wood preservative comprising an aqueous solution of arsenic acid, chromic acid and a copper compound which is insoluble in water but is soluble in a water solution of arsenic acid and chromic acid, the component of said copper compound other than copper being selected from the group consisting of hydroxide, carbonate, chromate, dichromate and arsenate, said-arsenic acid,

chromic acid andcopper compound being present in suihcient amounts to exert a substantial toxic action on-wood-destroyin organisms.

4. A wood preservative consisting of an aqueous solution of chromium trioxide, copper hydroxide and arsenic pentoxide, where the ingredients are present inthe following amounts by Weight: approximately 10 to 20 parts of chromium trioxide, approximately 6 to 9. parts of copper hydroxide and approximately'5 to 15 parts of arsenic pentoxide.

5. A wood'preservative consisting of an aqua weight: about 10 to-20 parts of chromium trioxide, about '1 to 11 parts of copper carbonate and about 5 to 15 parts of arsenic pentoxide.

6. A wood preservative comprising by weight about 5 to 15 parts arsenic pentoxide, 10 to 20 parts chromium trioxide, and 6 to 9 parts copper hydroxide, where the amount of chromium trioxide employed is about twice the combined amount of arsenic pentoxide and copper hydroxide.

'7. A wood preservative comprising by weight about 5 to 15 parts arsenic pentoxide, 10 to 20 parts chromium trioxide and 7 to 11 parts copper carbonate, where the amount of chromium 7 further expl'anationflof v the language employcdin some oftheappende'd. claims it may be noted that .When'arsenic pentox-' 'ide, chromium trioxide, and the oxide, hydroxide,

carbonate, chromate, dichromate or arsenate of.

trioxide employed is about twice the combined amount or copper carbonate and arsenic pentoxide.

8. An acidic impregnating solution for preserving wood which comprises a copper compound dissolved in an aqueous solution oi. arsenic acid and chromic acid, the component of the copper compound other than copper being selected from the group consisting of hydroxide, carbonate, chromate, dichromate and arsenate characterized in that when the wood is impregnated with the said solution, all of the compounds formed by the reaction of the solution with the wood are insoluble in water.

9. An acidic impregnating solution for preserving wood which comprises a metal compound dissolved in an aqueous solution oi! arsenic acid and chromic acid, characterized in that said metal compound comprises copper hydroxide and "further characterized in that when the wood is impregnated with said solution all of the compounds formed by the reaction of the solution with the wood are insoluble in water.

10. An acidic impregnating solution for preserving wood which comprises a metal compound dissolved in an aqueous solution of arsenic acid and chromic acid, characterized in that said metal compound comprises copper carbonate and further characterized in that when the wood is impregnated with said solution all of the com--- 5 pounds formed by the reaction or the solution with the wood are insoluble in water.

WILLIAM MoMAHON.

REFERENCES CITED The following references are oi! record in the file of this patent: UNITED STATES PATENTS