Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/1204—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
  • C23C18/1208—Oxides, e.g. ceramics
  • C23C18/1216—Metal oxides
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/68—Temporary coatings or embedding materials applied before or during heat treatment
  • C21D1/70—Temporary coatings or embedding materials applied before or during heat treatment while heating or quenching
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/1229—Composition of the substrate
  • C23C18/1241—Metallic substrates
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C24/00—Coating starting from inorganic powder
  • C23C24/08—Coating starting from inorganic powder by application of heat or pressure and heat
  • C23C24/082—Coating starting from inorganic powder by application of heat or pressure and heat without intermediate formation of a liquid in the layer
  • C23C24/085—Coating with metallic material, i.e. metals or metal alloys, optionally comprising hard particles, e.g. oxides, carbides or nitrides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process

Definitions

• the invention contemplates tho P 1 7/70 SR, 71 M, 1 9 A, 127 53 17 22 33 uct so protected and a composition of matter compris- 31; 106/74, 84, 290, 1, 14; 148/62 ing chromium metal powder dispersed in an alkalistabilized silica sol particularly adapted to be used in 5 References Cited forming the green chromium oxide-silica film on met- UNITED STATES PATENTS 2,978,361 4/1961 Seidl et a1.
• the present invention is concerned with the protection of metal surfaces from interaction with the atmosphere surrounding them, especially at temperatures of hot working.
• Another object of the present invention is to provide protected metal bodies specifically adapted to be exposed to oxidizing atmospheres at high temperatures. i.e., temperatures in excess of about 1000F. (about 500C.), and to be worked in said atmospheres at said high temperatures which protected metal bodies and the products of'working said protected metal bodies are only minimally deteriorated, if at all, by oxidation, decarburization and the like at said temperatures.
• a further object of the present invention is to provide novel compositions of matter useful in the process of protecting the surface of metals from interaction with surrounding atmospheres.
• the present invention contemplates a process for protecting metal from the deleterious effects of interaction with atmospheres surrounding said metal which comprises forming on the surface of said metal a continuous film of chromium oxide which is green at room temperature (i.e., a green chromium oxide) and silica, said film directly overlying the underlying metal and said green chromium oxide coacting with the silica and any copresent alkali metal oxide to provide a film impervious to gas at temperatures of about 500C. to about 1300C.
• chromium oxide which is green at room temperature (i.e., a green chromium oxide) and silica
• the invention contemplates the product so protected and a composi tion of matter comprising chromium metal powder dispersed in an alkali-stabilized silica sol particularly adapted to be used in forming the green chromium oxide-silica film on metals.
• ferrous-base metals includes iron-base alloys containing at least about 50% iron, up to 30% chromium and up to 30% of other alloying ingredients normally employed to provide steels of commerce.
• the process of the present invention is particularly useful in inhibiting or minimizing the scaling of ferrous-base alloys such as mild steel, 9% nickel steel and austenitic, ferritic and duplex structured stainless steels.
• the present process is also useful for inhibiting decarburization of tool steels and iron-base powder compacts containing free graphite.
• ferrous-base alloys mentioned hereinbefore represent the greater bulk of metal production which can be facilitated by means of the present invention
• the invention is also applicable to the protection of surfaces of other metals or alloys which are normally heat treated and worked in air and melt (i.e., have soliduses) at temperatures in excess of about l000C. and which contain from 0% to about 40% chromium.
• the process of the present invention can be employed to prevent the formation of decarburized skins or carbon-depolarized nickel anode material and to inhibit oxidation of copper-base alloys, titaniumbase alloys, nickel-base alloys and cobalt-base alloys.
• the value of the coating of the present invention with chromium-containing, nickelbase, and cobalt-base alloys is not so much to prevent metal loss by sealing but rather to minimize the formation of thin, tightly adherent, difficultly removable oxide layers which often penetrate preferentially in grain boundary regions.
• PROCESS Metal to be protected in accordance with the present invention having a clean metallic surface, i.e., a surface devoid of any substantial amount of non-metallic substances such as oxides, grease, etc., is coated with metallic chromium and an aqueous alkali-stabilized silica sol both components being applied either simultaneously or the chromium coating being applied first, the total thickness being at least one micron.
• the coated surface is then dried in such a manner as to provide a continuous dry film on the metal surface and to avoid blistering and thereafter fired in an atmosphere at least oxidizing to chromium to produce a composite, continuous, green chromium oxide-silica film directly overlying the underlying metal surface.
• the chromium metal-silica film on the original billet can be as thick as desired but usually it need be no thicker than about 25 to about 60 or possibly 100 microns.
• electrodeposits of chromium followed by a silica coating derived from a silica sol as described hereinafter satisfactory results have been achieved with coatings as thin as about 10 microns.
• film will persist on the metal surface during hot working and will provide some lubricating effect.
• the film on the product of hot working will be considerably thinner than the original film, perhaps by an order of magnitude or greater. Further, after hot working, it will often be found that chromium is diffused into the surface of the underlying metal.
• the amount of chromium which is required to be coated on the clean metal surface differs substantially with the method of application and with the nature of the base metal.
• chromium is electroplated on the surface or deposited by chromizing techniques, a layer of about 2 X 10' inch (about 5 X cm.) (0.5 micron) on ferrous-base metal is all that is necessary.
• This thickness of chromium represents a dosage of about 3.6 grams of chromium per square meter of metal surface.
• chromium metal when substantially equiaxed, advantageously have mean particle diameters in the range of about 0.001 micron to about 25 microns. With chromium particles of about 3 microns average dimension, it has been found that good results are obtained on steel to be hot worked with dosages of about to grams per square meter (g/m of metal surface area.
• Chromium layers can be produced on any metal surface by thermal decomposition of chromium carbonyl and other thermally decomposable metallo-organic chromium compounds, such thermal decomposition processes being disclosed, for example, in U.S. Pat. No. 2,793,140 to Ostrofsky et al. and in U.S. Pat. No. 2,898,235 to Bulloff.
• the silica of the protective green chromium oxidesilica film used in the present invention is advantageously derived from alkali-stabilized, aqueous silica sols marketed by El. duPont de Nemours and Company, Inc. (du Pont) under the trademark Ludox and other designations and made in accordance with the teachings of any one or more of the Bechtold et al U.S. Pat. No. 2,574,902, the Rule U.S. Pat. No. 2,577,485, the Alexander U.S. Pat. No. 2,750,345, the Bird U.S. Pat. No. 2,244,325, the Voorhees U.S. Pat. No. 2,457,971 and the ller U.S. Pat. No.
• silica sols are also operative provided that they contain an effective amount of alkali metal, e.g., sodium, potassium, lithium ion associated with the negative charge sites on the silica sol particles.
• alkali metal e.g., sodium, potassium, lithium ion associated with the negative charge sites on the silica sol particles.
• the mole ratio of silica to alkali metal in such sols is about 4:1 to about 400:1
• Operative silica sols also can be modified to contain oxidic aluminum in place of part of the oxidic silicon on the surface of the silica sol particle.
• Such an alumina-modified silica sol is sold by du Pont under the trade designation Ludox AM.
• silica films containing alkali metal ion can be obtained by alkali hydrolysis of ethyl silicate, by partial neutralization and dialysis of 1:1 sodium silicate (water-glass) solutions and other means well known to those skilled in the art.
• Dosage rates for the silica portion of the coating advantageously are of the order of 5 to 60 g/m with associated ion from the group of sodium, potassium and lithium ion, measured as the oxide, advantageously being present in an amount of 0.5 to 2.5 parts for every 10 parts by weight of silica.
• the chromium, silica and alkali metal ion are in weight ratios within the ranges of 6 to I parts by weight of chromium to 0.4 to 2 parts by weight of silica to 0.02 to 0.2 parts by weight of alkali metal oxide.
• the surface bearing the chromium, the silica and the alkali metal is exposed to an atmosphere containing oxygen or an oxygen donor which atmosphere is at least oxidizing to chromium.
• the surface should be held at about 1500F. (about 800C.), to about I700F. (about 930C.) until the continuous green chromium oxide-silica film is established.
• Merely heating the object to be protected in furnace air up to a 1700F. (about 930C.) (or higher) furnace temperature will ordinarily be a satisfactory method of establishing the protective coating of the present invention.
• the film formed at 800C. or higher protects the underlying metal from reaction with the atmosphere at high temperatures. It is to be understood, however, that in order for this film to be effective, it must directly overlie metal. Accordingly, it is necessary that the initially applied ingredients, i.e., chromium metal and silica form or be included in a film which will prevent oxidation of underlying metal prior to formation of the film of the present invention.
• the amount of alkali metal ion present in the compositions useful in the practice of the present invention is limited to the aforestated maximum amounts in relation to the silica in order to avoid formation of fully liquid silica-alkali metal oxide phases at the elevated temperatures at which protection is required, e.g., up to about 2350F. (1290C.). Based upon tests made at 2300F.
• Slurry compositions containing chromium metal particles dispersed in an alkali-stabilized aqueous silica sol and usable in accordance with the present invention for coating on metal to be protected can contain about 5 to about 10 parts by weight of chromium, about 0.4 to about 2 parts by weight of sol form silica, about 0.02 to about 0.3 parts by weight of alkali metal ion (measured as Me O) the ratio of silica to Me O being at least about about 4, all components being dispersed or dissolved in about 4 to about 20 parts by weight of water.
• Total solids weight of the coating per unit area of surface being protected is an important determinant ofthe protection providable by means of the slurry compositions of the present invention.
• Table I sets forth in terms of temperature, degrees of protection and solids dosage per unit area, typical results of protection obtainable with the slurry compositions of the present invention used on carbon steel which, after coating, was held at the indicated temperature for 1 hours.
• Table I The data set forth in Table I is pertinent to slurries made up with chromium powder of about 2 to about 3 microns average dimension and carefully fractionated to exclude particles outside this size range.
• chromium powder of about 2 to about 3 microns average dimension and carefully fractionated to exclude particles outside this size range.
• watersoluble polar liquids such as alcohols, glycols, etc.
• substitution merely adds to cost and hazard without producing any particular advantages.
• Water-soluble or water-dispersible resins and other polymeric substances can sometimes be included with advantage in the chromium-containing slurry compositions of the present invention in order to increase viscosity, enhance the film forming of the silica sols and for other purposes.
• Acrylic Co-polymer Emulsions Acrylic Emulsions -e.g., Neo-cryl A. 234.U or Rhoplex D -e.g., RWU-20l or Rhoplex 360A TABLE II (ontinued RESINOUS POLYMERIC MATERIALS COMPATIBLE IN THE SLURRY COMPOSITIONS OF THE INVENTION e.g., Carbowax 4000 Ammonia Cut Ammonia Cut Dexlrins Gelatins Alginates Gum Arabic Gum Tragacanth Carob Gum Mucilage Starch Corn Syrups Xanthan Gum Shellac Ammonia cut Polyvinylpyrrolidone -e.g,, Neo-Rex' 5-71 or RWL 110 e.g,, Durez 17211 or Durex 19788 Na Carboxymethyl Cellulose Alkyl Hydroxyalkyl Celluloses Polyacryllic Acid Ammonia Cut Trademark of Polyvinyl Chemicals. Inc. "Trademark of Morton Chemical Co
• the chromium-containing slurry compositions of the present invention as well as the silica sols used with electroplated or chromized chromium layers advantageously contain either anionic or nonionic surfactants.
• Anionic surfactants such as sodium alkyl aryl sulfonate and sodium lauryl sulfate in amounts of 0.1% to 0.3% by weight based upon total silica plus alkali metal ion plus water are generally useful in the practice of the present invention.
• Nonionic surfactants such as ethylene oxide condensates, octylphenoxydiethoxyethanol, alkylphenoxypoly(ethyleneoxy)ethanol, polyethylene glycol tertiary-dodecylthioether and trimethylnonanol can also be used especially in conjunction with alkali-stabilized silica sols having a SiO /Me O ratio below about 120.
• chromium-containing slurry compositions along with silica and the alkali metal ion, small amounts of other ingredients such as alumina, magnesia, lime, clay (e.g., bentonite), and like materials which can alter somewhat the character of the green chromium oxide-silica film on the protected metal surface.
• alumina e.g., magnesia
• lime e.g., bentonite
• clay e.g., bentonite
• inclusion of aluminum in an amount of up to about 60% (by weight of the chromium metal present) in the slurry compositions of the present invention promotes pop-off of the film upon cooling after the steel has been heat treated.
• Table III sets forth (in percent by weight of chromium metal) amounts of these other ingredients which can be used in the slurry compositions of the present invention and which, in contrast to the organic additives set forth hereinbefore, do not burn off but rather become part of the fully oxidized film.
• EXAMPLE 1 A clean piece of SAE 1020 carbon steel (1 inch X 1 inch X 6 inches) (2.5 X 2.5 X 15.25 cm.) was coated over part of its surface by first, electroplating part of the surface with 0.00002 inch (about 0.00005 cm.) thickness of chromium from a standard chromic acidsulfate bath, coating the plated portion of the surface with alkali-stabilized silica sol, allowing the sol to dry to a layer less than 1000 angstroms thick and heating the thus partially coated metal. The heating was in air up to 2000F. (about 1090C.) at which temperature the metal was held for 1% hours. The metal piece was then hot rolled to /a-inch (0.32 cm.) thickness.
• the non-treated portion had heavy loose scale as expected; whereas a very thin, tenacious green chromium oxidesilica coating was observed on the treated portion of the specimen.
• Metallographic examination revealed no decarburization under the protective layer and no sealing appeared on the protected surface.
• the alkali stabilized silica sol used in treating part of the surface of the metal piece had a SiO /Me O weight ratio of 50.
• EXAMPLE ll Specimens of Type 430 ferritic stainless steel and a duplex structured stainless steel were coated as was the coated portion of the steel piece in Example 1. Similar specimens were given only the chromium plating treatment. Under oxidation in air at 1800F. (about 980C.) the specimens which were only chromium plated received no significant protection. Both of the specimens treated in accordance with the present invention had good oxidation resistance for 6 hours at 1800F.
• a 30 pound ingot of M tool steel (0.85% C, 4% Cr, 6.4% W, 5% Mo, balance essentially Fe) was cast and forged to a 2 /2 inch (6.35 cm.) bar.
• a piece of this bar was coated as described in Example I and heated to 2075F. (about 1140C.) in air for 30 minutes. The coating protected the surface from oxidation and give virtually complete resistance to decarburization.
• EXAMPLE IV A 9% nickel Steel (0.1% C, 9.0% Ni, 0.4% Mn, 0.3% Si, 0.015% P, 0.015% S, balance essentially Fe) in the form of a l-inch (about 2.5 cm.) diameter bar was partially coated with the green chromium oxide-silica film as described in Example I. The specimen was then soaked in air at 2100F. (about 1150C.) for 10 minutes and then air cooled. A loose scale formed on the uncoated portion of the specimen and, after it flaked off, a tenacious nickel-rich oxide layer remained together with underlying grain boundary oxidation. In contrast, where the specimen had been coated, only slight oxidation resulted. The thin, protective green chromium oxide-silica film remained intact with no underlying nickel-rich scale or grain boundary penetra tion.
• EXAMPLE V An Armco iron specimen of very low carbon content was coated with the green chromium oxide-silica film as described in Example 1 and thereafter pack carburized at 1700F. (about 930C.) for 2 hours along with an uncoated specimen. After the treatment, both specimens were sectioned and examined metallographically. The uncoated specimen was carburized deeply; whereas, the coated specimen was not carburized at all.
• Example V the coating used on the protected specimen in Example V was originally heated in air to a temperature of about 1700F. (about 930C.) Without this original heating in air, no green chromium oxide-silica film is formed and substantially no protection of the metal surface is obtained.
• EXAMPLE Vl A clean sample of SAE 1020 steel was coated at a dosage of about 0.1 gram/in (155 g/m with the dried residue of an aqueous slurry containing about 3.5 parts by weight of round grain chromium powder, the particles of which were about 3 microns in diameter. about 2.75 parts by weight of an aqueous lithium-stabilized 5 silica sol sold by E. 1. du Pont de Nemours and Company, Inc. as polysilicate 48 and containing about 20% by weight of SiO and about 2.1% by weight Li O with the balance being water and a volume of water equal to the volume of the silica sol.
• the coated sample was 1() then heated in air to about 1700F. (about 930C.) to form a continuous green chromium oxide-silica film on the steel surface.
• the steel was then capable of resisting high temperature oxidation both prior to and during hot working in the same manner as the coated portion of the steel sample described in Example 1.
• Example VI a slurry similar to theone used in Example VI was made up with green Cr O rather than with chromium metal.
• This slurry was applied to a steelsurface in the manner identical to that described in Example V1 to provide an equivalent (chromium metal) dosage and then heated in air to 1700F. (about 930C.)
• the coating thus formed gave substantially no protection against scaling at hot working temperatures. i.e.. temperatures well above 2000F.
• Use of the dried silica sol alone gives marginal protection only and only up to about 1500F. (about 815C.)
• EXAMPLE Vll A portion of a specimen of a 9% nickel steel similar to that steel described in Example [V was coated on a machine ground surface with a slurry containing about 8 parts by weight of 3 micron chromium powder, about 5.85 parts of the lithium-stabilized silica sol described in Example V1 and about 5 parts by weight of water. The dried coating weighed approximately 0.094 g/in (146 g/m The thus coated specimen was heated in air to 2100F. (about 1150C.), soaked 4 hours at this temperature and hot rolled from 1 3/16 inches (about 3.0 cm.) to t-inch (about 0.65 cm.) in 8 passes.
• the portion of the specimen having the green chromium-silica coating was completely protected whereas the non-coated portion of the specimen scaled heavily.
• Metallographic examination indicated a diffusion of chromium into the steel surface for a distance of about 25 microinches (about 0.62 micron).
• the surface of the rolled product still contained the green chromium oxide-silica coating on that portion corresponding to the originally coated portion of the specimen.
• This green coating can be removed by pickling, for example, in 15% by weight sulfuric acid, dried at C., or by sandblasting or by other methods well known to those skilled in the art.
• EXAMPLE XVlll Other tests carried out on powder masses containing in percent by weight 1% manganese, 4% nickel, 1% molybdenum, 0.5% carbon (as graphite) with the balance being essentially iron and compacted and sintered as described in Example XVll show that coating the compacts with chromium slurried in water or chromium slurried in alkali-stabilized silica sol will prevent oxidation of alloying elements during sintering in commercially available endothermic atmospheres, e.g., cracked ammonia of high dew point.
• Table V which table also contains the results of a room temperature ultimate tensile test conducted upon the sintered and reheated compacts.
• the uncoated sample had invention adherent to cooled, hot worked steels and a substantial metal loss whereas the coated sample had other metals are also highly useful as bases for organic no loss.
• the uncoated sample had a difficultly removand inorganic protective coatings such as paints, lacable oxide layer whereas the coated sample was easily quers, bonded polymeric films, etc. cleanable.
• Microprobe analysis results of metal near The coatings of the present invention are distinctly the surface is set forth in Table VII, in which Table eledifferent, both in comp n n in effectiveness, mental content is in weight percent with oxygen being from silica coatings of the prior art such as disclosed in l l d b diff n e the Cupery et al. US. Pat. No. 3,133,829.
• Samples of TABLE VII Type 304L stainless steel were treated as follows: Sample l was left uncoated as a control; Sample 11 was coated with a film derived from an alkali stabilized sil- Sample Dlszlilr paecgrom (g; 5;; 3 ,2 ica sol; and Sample III was coated with a composition (micron) of the present invention including chromium metal dispersed in an alkali-stabilized silica sol (coating weight 8223323 ,2 12 23;? Q2 f 240 g/m All the samples were heated at 2200F. Coated 6 31.9 67.1 2.
• Example XXlll when applied on a carbon steel surface at a dosage rate of 180 g/m limited weight loss from solid steel due to 2 hours exposure to oxidizing atmosphere at 1260C.
• Unprotected carbon steel subject to such exposure can be expected to exhibit metal weight losses due to scale formation of about 2000 to 3000 g/m
• the thus formulated vehicle is capable of efficiently carrying chromium particles onto a metal surface and retaining them there in a uniform continuous layer.
• melting point comprising a thin continuous layer overlying said metal of chromic oxide formed in situ by oxidation of metallic chromium in the presence of the dried residue of colloidally dispersed alkali stabilized sol form silica, said alkali stabilized silica sol having a mole ratio of silica to alkali metal oxide of about 4 to l to 400 to 1, said layer being directly bonded to said underlying metal, and said layer comprising an essentially impervious barrier to gases at said high temperatures.
• a protective coating as in claim 1 wherein the underlying metal is selected from the group of iron,
• balt-base, titanium-base and copper-base alloys are balt-base, titanium-base and copper-base alloys.
• a protective coating as in claim 1 wherein the underlying metal is an iron-base alloy.
• a protective coating as in claim 1 which also contains in situ oxidation products of at least one member of the group of aluminum and nickel.
• a protective coating as in claim 1 wherein the alkali metal oxide is selected from the'group of sodium oxide, potassium oxide and lithium oxide.
• a protective coating as in claim 2 wherein the green chromic oxide is the product of in situ oxidation of substantially equiaxed chromium powder having an average particle size of about 0.001 to about 25 microns.
• a process for protecting the surface of metal melting above about 1000C. from the deleterious effects of reaction with gases in contact therewith comprising oxidizing metallic chromium on the surface of said metal at a temperature of at least about 800C. while said metallic chromium is in intimate association with a mixture of silica and alkali metal oxide with the mole ratio of silica to alkali metal oxide being about 4 to 1 to about 400 to l to provide an essentially continuous, gas impermeable film comprising said silica, said alkali metal oxide and the product of the oxidation of said metallic chromium directly bonded to said metal surface.
• metal is selected from the group of iron, nickel, cobalt, copper and iron-base, titanium-base, nickel-base, cobalt-base and copper-base alloys.
• metal surface to be protected is the surface of an iron-base alloy and the unalloyed chromium is a chromium plate.
• alkali metal oxide is selected from the group consisting of sodium oxide, lithium oxide and potassium oxide.
• the slurry is an aqueous slurry and contains about 5 to about 10 parts by weight of substantially equiaxed chromium particles having an average particle size of about 0.001 to about 25 microns, about 0.4 to about 2 parts by weight of so] form silica and about 0.02 to about 0.3 parts by weight of alkali metal ion measured as Me O associated with said sol form silica.
• a process as in claim 16 wherein the surface to be protected is coated with at least about 50 g/m of chromium particles.
• a process as in claim 16 wherein the surface to be protected is coated with chromium particles in an amount of about 50 to about 500 g/m of metal surface.
• a slurry composition comprising particulate chromium dispersed in a liquid vehicle containing a film-forming alkali-metal stabilized silica sol, said chromium being in the form of substantially equiaxed particles having an average particle dimension of about 0.001 to about 25 microns and said silica sol having a mole ratio of silica to alkali metal oxide within the range of about 4 to l to about 400 to l.
• a slurry composition as in claim 23 which contains about to about parts by weight of chromium to each about 0.4 to about 2 parts by weight of silica.
• a protective coating impervious to gas at high temperatures of about 500C. to about l300C. on metal having a melting point above about lO0OC. and subject to be exposed to said high temperatures below said melting point comprising a thin continuous layer overlying said metal of chromic oxide formed in situ by oxidation at a temperature of at least about 800C. of metallic chromium in the presence of the dried residue of colloidally dispersed alkali stabilized silica sol, said silica sol being characterized by having at least I mole of alkali metal ion associated with every 400 moles of silica, said layer being directly bonded to said underlying metal and said layer comprising an essentially im pervious barrier to gases at said high temperature 29.
• a protective coating as in claim 28 which contains any one or more of the in situ oxidation products of nickel or aluminum, alumina, magnesia, lime, clay and rare earth metal oxide.

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Citations (6)

• 1972
  • 1972-11-20 US US307862A patent/US3861938A/en not_active Expired - Lifetime
• 1973
  • 1973-01-30 CA CA162,441A patent/CA1002860A/en not_active Expired
  • 1973-03-06 GB GB1070273A patent/GB1421271A/en not_active Expired
  • 1973-03-07 AU AU52993/73A patent/AU5299373A/en not_active Expired
  • 1973-03-12 IT IT48727/73A patent/IT979800B/it active
  • 1973-03-12 CH CH358973A patent/CH567107A5/xx not_active IP Right Cessation
  • 1973-03-12 LU LU67203A patent/LU67203A1/xx unknown
  • 1973-03-12 ES ES412553A patent/ES412553A1/es not_active Expired
  • 1973-03-12 FR FR7308745A patent/FR2175933B1/fr not_active Expired
  • 1973-03-13 JP JP48029349A patent/JPS48102748A/ja active Pending
  • 1973-03-13 NL NL7303490A patent/NL7303490A/xx unknown
  • 1973-03-13 AT AT222673A patent/AT327634B/de not_active IP Right Cessation

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