United States Patent (19)
`Nakayama et al.
`
`11)
`(45)
`
`4,385,086
`May 24, 1983
`
`
`
`-
`
`73 Assignee:
`
`(54) METHOD FOR PREVENTING LEACHING
`OF CONTAMINANTS FROM SOLD
`SURFACES
`75) Inventors: Muneo Nakayama, Tokyo; Hisashi
`Nakane, Kawasaki; Akira Yokota,
`Yamato; Shingo Asaumi, Fujisawa,
`all of Japan
`Tokyo Ohka Kogyo Kabushiki
`Kaisha, Kawasaki, Japan
`(21) Appl. No.: 100,930
`(22 Filed:
`Dec. 6, 1979
`30)
`Foreign Application Priority Data
`Dec. 7, 1978 JP
`Japan ................................ 53-151841
`Aug. 13, 1979 JP
`Japan ................................ 54-102994
`51) int. Cl. ............................................... B05D3/02
`52 U.S. C. ...................................... 427/387; 427/82;
`427/95; 427/397.7
`58 Field of Search ................... 427/95, 82,226, 387,
`427/397.7; 65/60 D; 428/428
`References Cited
`U.S. PATENT DOCUMENTS
`3,556,841 1/1971 Iwasa et al. ........................... 427/95
`3,925,583 12/1975 Rau et al........
`... 428/428
`3,927,697 12/1975 Baumler et al.
`... 428/428
`4,041,190 8/1977 Dubois et al...
`... 427/95
`4,107,388 8/1978 Gambaretto ....................... 65/60 D
`
`(56)
`
`- - - - - 427/226
`
`- - - - - - - - - -
`
`- - - - - - 427/95
`
`4,277,525 7/1981 Nakayama et al. ................. 427/387
`FOREIGN PATENT DOCUMENTS
`661372 4/1963 Canada ................................ 427/387
`71 14847 5/1972 Netherlands .......
`885118 12/1961 United Kingdom
`Primary Examiner-John D. Smith
`Attorney, Agent, or Firm-Brisebois & Kruger
`57
`ABSTRACT
`An efficient method is proposed for preventing leaching
`of contaminants from the surface of a solid, such as
`sodium ions from the surface of soda glass or nickel,
`chromium or iron from the surface of stainless steel in
`order to minimize detrimental contamination of highly
`pure substances in contact with the solid surface.
`The effect is basically obtained by providing a coating
`film of oxidized silicon on to the solid surface and the
`coating film is formed by applying a coating solution
`containing a hydroxysilane compound to the surface
`followed by baking of the coating layer at a temperature
`not lower than 150° C., the coating solution being pre
`pared by the equilibration reaction of an alkoxysilane
`with a carboxylic acid and an alcohol, of an acyloxysi
`lane with an alcohol, or of an alkoxysilane with water in
`an alcohol where the molar ratios of the individual
`reactants are in the specified ranges.
`8 Claims, No Drawings
`
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`

`METHOD FOR PREVENTING LEACHING OF
`CONTAMINANTS FROMSOLID SURFACES
`
`4,385,086
`2
`surfaces thereof by use of a coating solution as specified
`below.
`The method of the present invention for preventing
`leaching of contaminants from the surface of a solid
`comprises
`(a) providing a coating layer on the surface of the solid
`with a coating solution containing a hydroxysilane
`compound represented by the general formula
`
`5
`
`O
`
`15
`
`RSi(OH)4-
`(I)
`where R is a group selected from the class consisting of
`hydrocarbon groups, alkoxy groups and acyloxy groups
`and n is a number of 0, 1, 2 or 3, and
`(b) heating the thus coated solid at a temperature not
`lower than 150 C.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`As is understood from the above description, the
`hydroxysilane compound as the main ingredient of the
`coating solution used in the inventive method has at
`least one silanolic hydroxy group and represented by
`the above general formula (I). In the general formula
`(I), the groups denoted by R are each a group selected
`from the class consisting of hydrocarbon groups, alkoxy
`groups and acyloxy groups. When two or more of the
`groups R are present in a molecule, they may not be
`identical with each other.
`The hydrocarbon group suitable as the group R is
`exemplified by alkyl groups such as methyl, ethyl, pro
`pyl and butyl groups, aryl groups such as phenyl group
`and alkenyl groups such as vinyl and allyl groups.
`The alkoxy group suitable as R is exemplified by
`methoxy, ethoxy, propoxy, butoxy and pentoxy groups,
`of which the most preferred are methoxy and ethoxy
`groups. The acyloxy group suitable as R is exemplified
`by acetoxy and propionyloxy groups, of which acetoxy
`group is preferred.
`In the preferred embodiments of the invention, the
`groups expressed by R are selected from the class con
`sisting of alkoxy groups, e.g. methoxy and ethoxy
`groups, and acyloxy groups, e.g. acetoxy group so that
`the hydroxysilane compound can be represented by the
`general formula
`
`BACKGROUND OF THE INVENTION
`The present invention relates to a method for pre
`venting leaching of contaminants from the surface of a
`solid or, in particular, to a method for preventing con
`tamination of a material in contact with a solid such as
`a glass, ceramic, metal and the like by the ingredients
`leached out of the surface of the solid.
`In various kinds of fine technologies such as the man
`ufacture and processing of semiconductors or semicon
`ductor devices, preparation and storage of medicines
`and microanalytical procedures, it is of utmost impor
`tance to avoid contamination of the materials or chemi
`cals under handling by trace amounts of impurities,
`especially, such as alkali metals originating in the solid
`surface with which the material or the chemical in ques
`20
`tion is in contact. For example, contamination with an
`alkali metal element is unavoidable when the material or
`chemical is contained in a vessel or handled with a tool
`made of a glass because containers for photoresist mate
`rials, glass bottles for reagents and medicines, ampules,
`beakers and flasks made of glass cannot be free from the
`25
`problem of exudation or leaching out of the ingredients
`of the glass such as alkali metals so that the chemicals
`contained in such vessels are always subject to contami
`nation with an alkali metal. In the manufacuture of
`semiconductors, in particular, contamination with a
`30
`trace amount of alkali metal ions may sometimes be
`very detrimental for the performance of the semicon
`ductor produced under the contamination.
`Most of the glass vessels or tools used for handling
`chemicals are made of a glass belonging to the class of
`35
`so-called soda glass and are rather disadvantageous
`from the standpoint of contamination by the ingredients
`leached out of the surface even when they are used after
`the most careful cleaning treatment by dipping in a
`chromic acid mixture or in a strong alkali solution for
`40
`several days to have the surfaces freed from the contam
`inants.
`When the contamination from the vessels or tools
`must be minimized to an extremely low extent, several
`kinds of materials with little leaching out of the ingredi
`ents, such as borosilicate glass, high-silicate glass and
`fused quartz glass, are employed or, alternatively, a
`protective film of a fluorocarbon polymer is provided
`on the surface of the vessel or tool. These vessels or
`tools are, however, very expensive and they are not
`always suitable for industrial uses. Accordingly, it has
`long been desired to develop a simple and effective
`means with less expensive materials by which the leach
`ing out of contaminants can be prevented regardless of
`the materials of the substrate solid surfaces.
`55
`SUMMARY OF THE INVENTION
`Thus, it is an object of the present invention to pro
`vide a novel method for preventing leaching of contam
`inants from the surface of a solid to cause contamination
`60
`of the materials in contact with the solid surface.
`The present invention has been established on the
`basis of the discovery as a result of the extensive investi
`gation undertaken by the inventors to solve the above
`described problem, according to which the exudation
`65
`or leaching of the contaminants from the surface of any
`conventional vessels or tools can be effectively pre
`vented by providing an oxidized film of silicon on the
`
`45
`
`50
`
`(II)
`
`O
`(RO)(RCO)SiOH)4-a-b,
`where, preferably, R is a methyl or ethyl group; R2 is a
`methyl group and a and b are each zero or a positive
`integer with the proviso that a--b is not exceeding 3.
`The procedure for the preparation of the coating
`solution used in the inventive method is now described
`below.
`First, for example, 1 mole of an alkoxysilane is ad
`mixed with 2 to 5 moles of a carboxylic acid and 2 to 10
`moles of an alcohol together with a small amount of a
`reaction promotor. It is necessary that the amount of
`the alcohol is at least equimolar to the carboxylic acid.
`The reaction takes place even at room temperature with
`temperature elevation by the heat evolved in the exo
`thermic reaction and an ester of the carboxylic acid and
`a hydroxysilane compound are formed, the latter being
`the hydrolysis product of the alkoxysilane compound
`with the water produced in the esterification reaction. It
`is usual that the starting alkoxysilane disappears within
`
`Eton Ex. 1123
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`
`

`

`O
`
`15
`
`4,385,086
`3
`4.
`These reaction promotors are used in an amount of
`2 to 5 hours from the start of the reaction and the
`amount of the carboxylic acid gradually decreases
`0.001 to 20% be weight based on the amount of the
`alkoxysilane or acyloxysilane according to the desired
`reaching 20% or smaller of the initial amount after 2 to
`reaction velocity.
`5 days at room temperature. When the content of the
`carboxylic acid has decreased to the extent as above, the
`The proceeding of the reaction in the reaction mix
`reaction mixture is suitable as a coating solution since a
`ture formulated as described above can readily to traced
`by means of gas chromatography, infrared absorption
`reaction mixture containing an excessive amount of the
`carboxylic acid cannot spread evenly over the surface
`spectroscopy and other suitable methods and the forma
`tion of hydroxy-containing silane compounds can be
`of various substrate materials. Thus the resultant hy
`droxysilane is a mixture of several types of the com
`detected. When an equilibrium of the esterification re
`pounds represented by the general formula (II) above.
`action or the transesterification reaction has been estab
`The second method for the preparation of the coating
`lished in the reaction mixture, the reaction mixture can
`solution is the reaction of an acyloxysilane compound,
`be used as a stable coating solution with which various
`which is obtained by the reaction of a carboxylic acid
`kinds of substrate surfaces are provided with a smooth
`and a halogenosilane, with an alcohol to produce a
`and uniformly spreading film of the oxidation product
`hydroxysilane, in which some of the acyloxy groups in
`of silicon with subsequent heating.
`the starting acyloxysilane have been replaced with the
`It is of course optional that the reaction mixture is
`alkoxy groups, and an ester of the carboxylic acid. In
`diluted with a suitable organic solvent to have a viscos
`ity or consistency suitable for application to the sub
`this case, at least 4 moles of an alcohol is employed per
`mole of the acyloxysilane which in turn is prepared by
`strate surfaces and, if necessary, the solution is filtered
`20
`with a filter having micropores of a diameter of 1 p.m or
`the reaction of one mole of a halogenated silane with 4
`to 6 moles of the carboxylic acid.
`smaller.
`It was noted in carrying out the reaction of an acylox
`The diluent solvent as mentioned above is not limita
`ysilane with an alcohol that the carboxylic acid was first
`tive in so far as it can dissolve all of the constituents in
`liberated from the acyloxysilane by the ester exchange
`the reaction mixture and spread uniformly over the
`with the alcohol followed by gradual decrease of the
`surface of the solid substrate to which the solution is
`content of the carboxylic acid by the esterification reac
`applied depending on the kind of the material of the
`solid and is exemplified by alcohols, ketones, polyvalent
`tion with the remaining portion of the alcohol. When
`the content of the carboxylic acid has decreased to 20%
`alcohols and esters thereof and 3-diketones as well as
`30
`mixtures thereof. Alcohols are exemplified by methyl
`or less of the theoretical amount calculated on the as
`sumption that 4 moles of the carboxylic acid are liber
`alcohol, ethyl alcohol, propyl alcohol, butyl alcohol,
`amyl alcohol and the like, esters are exemplified by
`ated from mole of the acyloxysilane, the reaction is
`methyl acetate, ethyl acetate, propyl acetate, butyl ace
`complete and the reaction mixture is suitable for use as
`the desired coating solution. The reaction is complete
`tate and the like, ketones are exemplified by acetone,
`methyl ethyl ketone, methyl isobutyl ketone, cyclohex
`within about 48 hours at room temperature but may be
`accelerated by heating.
`anone and the like, and polyvalent alcohols and esters
`thereof are exemplified by ethyleneglycol, ethylenegly
`In the third method for the preparation of the coating
`col monomethyl ether, ethyleneglycol monoethyl ether,
`solution, an alkoxysilane, water and a monovalent alco
`ethyleneglycol diethyl ether, ethyleneglycol monoiso
`hol, e.g. methyl alcohol, ethyl alcohol, propyl alcohol,
`propyl ether, ethyleneglycol monobutyl ether, ethyl
`butyl alcohol and amyl alcohol, are blended together
`eneglycol dibutyl ether, propyleneglycol, glycerine and
`with a small amount of a reaction promotor. The mixing
`the like. The concentration of the coating solution upon
`ratios of the water and the alcohol to the alkoxysilane
`dilution with the organic solvent is usually in the range
`are 2 to 5 moles of water and 3 to 30 moles of the alco
`hol per mole of the alkoxysilane.
`from 1 to 20% by weight calculated as SiO2.
`The alkoxysilane compound used in the first and the
`The material of the objective solid articles to be
`third methods is exemplified by orthomethylsilicate,
`coated with the thus prepared coating solution includes
`methylitriethoxysilane, orthoethylsilicate, ethyltrie
`glass, ceramics, mica, metals, e.g. stainless steel, plastics
`thoxysilane, orthopropylsilicate, orthobutylsilicate, tet
`and the like and the shapes of the articles are not limita
`raphenoxysilane, vinyltrimethoxysilane, vinyltriethox
`tive including plates, rods, tubes, balls, bottles and any
`ysilane and the like.
`other irregular forms.
`The coating procedure with the coating solution is
`The reaction promotors used in the above reactions
`are exemplified by several inorganic and organic acids
`conventional according to the shapes of the objective
`articles including dipping method, spraying method,
`such as hydrochloric acid, sulfuric acid, nitric acid,
`carbonic acid, hydrogen bromide, perchloric acid,
`pouring method, brushing and the like. The solid article
`coated with the coating solution is then subjected to
`phosphoric acid, boric acid, oxalic acid, citric acid,
`salicylic acid, picric acid, maleic acid, chloroacetic acid
`air-drying to remove the solvent or solvents by evapo
`ration to leave a coating film of a hydroxy-containing
`and benzenesulfonic acid as well as salts and oxides of
`silane compound which is further converted to a film of
`several metallic elements such as gold chloride, zinc
`chloride, aluminum chloride, iron chloride, copper
`oxidized silicon by the silanol condensation between the
`hydroxy groups when kept standing in atmospheric air
`chloride, nickel chloride, chromium chloride, arsenic
`chloride, antimony chloride, tin chloride, gallium chlo
`or further baked at 150° C. or higher.
`The baking temperature is preferably as high as possi
`ride, indium chloride, platinum chloride, titanium tetra
`chloride, copper sulfate, zinc sulfate, lead nitrate, zinc
`ble in so far as the material of the solid substrate can
`nitrate, aluminum nitrate, iron nitrate, copper nitrate,
`withstand in order to enhance the hardness of the baked
`film of the oxidized silicon. The length of the baking
`nickel nitrate, indium nitrate, boron oxide, phosphorus
`65
`treatment is also as long as possible but it is usually in
`pentoxide, arsenic trioxide and the like. Preferred reac
`the range from 10 to 60 minutes from the standpoint of
`tion promotors are hydrochloric acid, nitric acid, sulfu
`working efficiency. It is sometimes advisable to admix
`ric acid, phosphoric acid, boric acid and carbonic acid.
`
`45
`
`25
`
`35
`
`50
`
`55
`
`Eton Ex. 1123
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`
`

`

`4,385,086
`5
`upside down for a while. After spontaneous evapora
`the coating solution with a vitrification promotor such
`as phosphorus pentoxide and boron oxide in an amount
`tion of the solvent for about 30 minutes, the bottle was
`gradually heated up to a temperature of 500 C. where
`smaller than 10% by weight of the SiO2 content in the
`it was kept for 30 minutes followed by gradual cooling
`solution so as that the baking temperature may be de
`creased. The addition of these vitrifying agents is rec- 5 to room temperature. The resultant thin film of silicon
`ommendable only when the presence of such an ingredi-
`dioxide formed on the inner walls of the glass bottle had
`ent is not undesirable.
`a thickness of about 0.2 p.m.
`In practicing the above described method of the in-
`Several of the physical and chemical properties of the
`vention, the surface of the solid substrate, e.g. inner
`above obtained coating film were as follows as deter
`walls of a vessel, is provided with a continuous coating 10 mined with a glass plate with the same coating solution
`film having a thickness of 0.1 to 1.0 pm and having no
`simulating the above described coating procedure.
`pin-holes composed of high purity oxidized silicon
`readily and economically so that the exudation or leach
`ing out of contaminants from the solid surface can be Ent
`5X 10-7/°C.
`effectively prevented giving advantages in various in- 15 Thermal expansion coefficient
`1 x 1015 ohm/O
`dustrial applications.
`Sheet resistance
`100 A?second (1 molar HF,
`In the following, the method of the present invention
`Velocity of etching
`25° C)
`is further illustrated in detail by way of examples.
`Comparisons were made for the leaching velocity of
`EXAMPLE 1.
`the ingredients in the glass bottle from the surface be
`Into a mixture composed of 152 g of orthomethylsili-
`tween the bottles coated with silicon dioxide as de
`cate, 240 g of glacial acetic acid and 240 g of methyl
`scribed above and uncoated bottles. Thus, each of the
`alcohol kept at room temperature was added 10 g of
`bottles, having been subjected to the cleaning treatment
`finely pulverized oxalic acid with agitation. The reac-
`tion took place exothermically and the temperature of 25 by dipping in a 5% hydrochloric acid solution for 2
`the reaction mixture increased to about 40° C. as the
`hours, followed by rinsing with deionized water and
`reaction proceeded. The gas chromatographic and in-
`drying, was filled with methyl alcohol, acetone or butyl
`frared absorption spectral analyses indicated the forma-
`acetate and kept at 25-27 C. for weeks. Small portions
`tion of large amounts of methyl acetate and hydroxy-
`of the solvent were taken periodically and analyzed for
`containing silane compounds.
`30 the concentration of the sodium ions leached out of the
`After standing at room temperature for 3 days, the
`glass surface along with the measurement of the electric
`reaction mixture was analyzed for the solid content
`conductivity at 25 C. The results are summarized in
`which was found to be 12.5% by weight as measured by
`Table 1 below.
`TABLE 1.
`After
`After
`After
`3 weeks 6 weeks 9 weeks
`0.07
`0.08
`0.09
`0.02
`0.02
`0.02
`0.7
`0.8
`0.9
`0.6
`0.6
`0.6
`0.04
`0.05
`0.07
`0.03
`0.03
`0.03
`0.6
`0.6
`0.7
`0.6
`0.6
`0.6
`0.06
`0.07
`0.09
`0.04
`0.04
`0.04
`0.4
`0.4
`0.5
`0.4
`0.4
`0.4
`
`Initial
`0.02
`
`0.6
`
`0.03
`
`0.6
`
`0.04
`
`0.4
`
`After
`After
`2 weeks 15 weeks
`0.10
`0.4
`0.02
`0.03
`1.0
`2.
`0.6
`0.7
`0.09
`0.20
`0.03
`0.03
`0.9
`1.3
`0.6
`0.6
`0.14
`0.2O
`0.04
`0.04
`0.7
`1.2
`0.4
`0.4
`
`20
`
`Solvent
`Methyl
`alcohol
`
`Glass bottle
`Concentration of Uncoated
`Na ions, p.p.m.
`Coated
`Electric conduc-
`Uncoated
`tivity, umho/cm Coated
`Acetone Concentration of Uncoated
`Naions, p.p.m.
`Coated
`Electric conduc-
`Uncoated
`tivity, unho/cm Coated
`Concentration of Uncoated
`Naions, p.p.m.
`Coated
`Electric conduc-
`Uncoated
`tivity, umho/cm Coated
`
`Butyl
`acetate
`
`a
`
`heating at 140 C, for 3 hours. The reaction mixture was
`diluted by adding isopropyl alcohol to give a solid con
`tent of 5.9% weight followed by filtration with a filter
`having micropores of 0.45 um diameter to give a coat
`ing solution.
`The impurity levels of several metallic elements in
`the coating solution were determined by atomic absorp-
`tion spectrophotometry to give the results below.
`
`50
`
`EXAMPLE 2
`Tetraacetoxysilane was prepared by the reaction of
`125 g of silicon tetrachloride and 400 g of acetic acid as
`blended and stirred at room temperature. When the
`55 evolution of hydrogen chloride gas had ceased with
`precipitation of white crystalline tetraacetoxysilane, the
`unreacted acetic acid was removed by stripping under a
`reduced pressure and the residue was dissolved in 300 g
`of ethyl alcohol. The reaction between the tetraacetox
`60 ysilane and ethyl alcohol was carried out by heating the
`above reaction mixture at 60° C. with agitation for 10
`hours. The formation of large amounts of ethyl acetate
`and hydroxy-containing silane compounds was detected
`in the resultant reaction mixture which had a solid con
`tent of 5.9% by weight upon dilution by adding 120g of
`ethyl alcohol.
`The reaction mixture was further diluted by adding
`n-butyl alcohol to a solid content of 3.0% and the solu
`
`Impurity
`element
`Concentration,
`p.p.m.
`
`Na K Ca Mg Zn Al Fe Cu
`0.01 005 0.1
`01 01 0 1 0.1
`0.
`
`About 50 ml of the thus prepared coating solution
`was introduced into a narrow-necked glass bottle of
`1,000 ml capacity and whole surface of the inner wall of 65
`the bottle was wetted with the solution by tumbling the
`bottle followed by discharging of the solution and drip
`ping of the excessive solution by keeping the bottle
`
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`4,385,086
`7
`8
`tion was filtered with a filter having micropores of 0.45
`1. A method of preventing leaching of a contaminant
`from the surface of a solid which comprises
`un diameter to give a coating solution.
`(a) providing a coating layer on the surface of the
`A container of 20 liter capacity made of 18-8 stainless
`solid with a coating solution containing a hydrox
`steel was coated with the above prepared coating solu
`ysilane compound represented by the general for
`tion on the inner walls by spraying followed by heating
`mula
`treatment at 400 C. for 60 minutes.
`The thus coated container was filled with a 5% hy
`drochloric acid and kept standing at room temperature
`for 10 days and the hydrochloric acid was analyzed for
`the concentration of metallic elements to give a result
`that no noticeable amounts of nickel, chromium and
`iron were dissolved out of the container.
`
`5
`
`O
`
`15
`
`EXAMPLE 3
`Into a mixture composed of 209 g of orthoethylsili
`cate, 54 g of water and 572 g of ethyl alcohol was added
`0.5 g of 35% hydrochloric acid with agitation. The
`reaction took place and proceeded with evolution of
`heat. The analysis undertaken with the reaction mixture 20
`after standing a room temperature for 3 days indicated
`formation of large amounts of hydroxy-containing si
`lane compounds.
`The reaction mixture containing 9.0% by weight of
`25
`solid as measured by heating at 140 C. for 3 hours was
`diluted by adding acetone to a solid content of 8.0% by
`weight followed by filtration with a filter having micro
`pores of 0.45 pum diameter to give a coating solution.
`A glass plate having dimensions of 80 mm x 120
`mm x 0.7 mm was dipped in the thus prepared coating
`solution and then pulled up at a velocity of 30 cm per
`minute to be coated with the solution and the coated
`glass plate was subjected to drying at 100° C. for 15
`minutes and then baking at 500 C. for 60 minutes to
`form a coating film of oxidized silicon having a thick
`ness of 0.15 um.
`Leaching test of sodium ions was undertaken with the
`thus coated glass plate and a similar glass plate before
`coating by dipping them separately for 10 minutes in
`900 ml of diluted hydrochloric acid of 10% concentra
`tion at 60° C. in a beaker of fused quartz glass after
`washing with 5% hydrochloric acid for 5 minutes.
`The concentration of sodium ions in the hydrochloric
`45
`acid after leaching was determined by atomic absorp
`tion spectrophotometry taking the starting hydrochlo
`ric acid as the reference to give a result that the concen
`tration or rather the increment of the concentration of
`50
`sodium ions in the acid in which the coated glass plate
`was dipped was 0.01 p.p.m. while the value for the
`uncoated glass plate was 0.34 p.p.m.
`What is claimed is:
`
`30
`
`35
`
`55
`
`60
`
`65
`
`where R is a group selected from the class consisting of
`hydrocarbon groups, alkoxy groups and acyloxy groups
`and n is a number of 0, 1, 2 or 3, and
`(b) heating the thus coated solid under oxidizing con
`ditions at a temperature not lower than 150° C. to
`form on the surface a coating film of oxidized sili
`con which prevents leaching, and wherein the
`hydroxysilane compound is a reaction product of
`an acyloxysilane with an alcohol.
`2. The method as claimed in claim 1 wherein the
`acyloxysilane is an acetoxysilane.
`3. The method as claimed in claim 1 wherein the
`amount of the alcohol is at least 4 moles per mole of the
`acyloxysilane.
`4. The method as claimed in claim 1 wherein the
`heating in the step (b) is carried out for at least 10 min
`tes.
`5. The method as claimed in claim 1 wherein the
`coating film of the oxidized silicon has a thickness of at
`least 0.1 um.
`6. A method according to claim 1 wherein said step
`(b) of heating comprises heating the coated solid in air.
`7. A method of preventing leaching of a contaminant
`from the surface of a solid which comprises
`(a) providing a coating layer on the surface of the
`solid with a coating solution containing a hydrox
`ysilane compound represented by the general for
`mula
`
`where R is a group selected from the class consisting of
`hydrocarbon groups, alkoxy groups and acyloxy groups
`and n is a number of 0, 1, 2 or 3, and
`(b) heating the thus coated solid under oxidizing con
`ditions at a temperature not lower than 150 C. to
`form on the surface a coating film of oxidized sili
`con which prevents leaching, and wherein the
`hydroxysilane compound is a reaction product of a
`tetraalkoxysilane with water in an alcohol.
`8. The method as claimed in claim 7 wherein the
`amounts of water and the alcohol are in the ranges from
`2 to 5 moles and from 3 to 30 moles per mole of the
`tetraalkoxysilane, respectively.
`
`x:
`
`:
`
`:
`
`K
`
`Eton Ex. 1123
`5 of 5
`
`