WO1995016060A1 - Procede de preparation de materiaux et revetements ceramiques composites a haute temperature - Google Patents

Procede de preparation de materiaux et revetements ceramiques composites a haute temperature Download PDF

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Publication number
WO1995016060A1
WO1995016060A1 PCT/US1994/013707 US9413707W WO9516060A1 WO 1995016060 A1 WO1995016060 A1 WO 1995016060A1 US 9413707 W US9413707 W US 9413707W WO 9516060 A1 WO9516060 A1 WO 9516060A1
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Prior art keywords
metal
group
alcoholates
accordance
alcohol
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PCT/US1994/013707
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English (en)
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Igor Rozhkov
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White Eagle International Technologies, L.P.
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Priority to AU12970/95A priority Critical patent/AU1297095A/en
Publication of WO1995016060A1 publication Critical patent/WO1995016060A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B3/00—Electrolytic production of organic compounds
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
    • C04B41/4505—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements characterised by the method of application
    • C04B41/455—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements characterised by the method of application the coating or impregnating process including a chemical conversion or reaction
    • C04B41/4554—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements characterised by the method of application the coating or impregnating process including a chemical conversion or reaction the coating or impregnating material being an organic or organo-metallic precursor of an inorganic material
    • 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
    • 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

Definitions

  • This invention pertains to ceramics and, more particularly, to a process for preparing and using metal alcoholates to produce high strength composite ceramic materials and coatings.
  • Silicon ethylates have been prepared by electrochemical anode solution of an iron- silicide anode in an alcohol solution of or Zn Cl 2 using a carbon cathode. Electrolysis is carried out at a voltage of 70 volts and 2 amps current. Such conditions, however, only attain a relatively low yield of 60%. Electrochemical techniques have further been used to produce ethylates of iron, cobalt and nickel by electrochemical anode solution of a particular metal in an alcohol electrolyte solution with lithium perchlorate and lithium bromide. Such prior art electrolysis has been carried out at 50-60 volts at a current of 1.5 amps using a carbon cathode, but only attains a yield of 75%. This prior art process is also limited by the small amount of metals.
  • Another electrochemical technique includes synthesis by use of a cell with non-separated anode and cathode space, a stirrer and two electrodes including a carbon cathode and a metal anode.
  • This prior art electrochemical technique produces metal alcoholates with atomic numbers 14-82 by particular metal electrochemical anode solution using direct current in an electrolyte with C 1 -C alcohol and conductive ingredient of R 4 NX formula, where R- is hydrogen or alkyl, N is nitrogen, and X is a halogen.
  • Electrochemical solution of the anode takes place at a current of 0.5 to 2 amps and a voltage of 40-60 volts.
  • the electroconductive ingredient is NH 4 C1 and (CH 3 ) 4 NC1.
  • Electrosynthesis is held in the boiling electrolyte. Yield of products is 68-78%.
  • the disadvantage of this prior art method is that it can't be used to produce a number of metal alcoholates and the synthesis apparatus is complex. Furthermore, the yield is only 68-78%.
  • the above electrochemical methods suffer from high energy expenses and require sophisticated and expensive equipment. Furthermore, the above electrochemical methods and conventional industrial methods to produce composite ceramic materials and coatings are often difficult to use, cumbersome, inefficient, costly, and frequently result in non-uniform products and low yields. As a result, the quality, strength, and temperature resistance of the composite ceramics is rather poor.
  • An efficient alkoxy process is provided to prepare high-temperature, high-strength, composite ceramics.
  • the process is economical, reliable and effective.
  • the novel process achieves high yields of homogenous uniform composite ceramics.
  • the inventive technology has produced unexpected surprising results. Tests show that turbojet alloys protected with ceramic composite coatings created by means of the new technology withstand long time exposure in the presence of oxygen at 2000° C without perceptible corrosion. In the cases of steel tubes, alumina ceramic coating created with the use of the new technology provides long time protection in the air at the temperature up to 1100° C. Good protection for pistons in diesel engine has also been achieved with alumina-silica ceramics created by means of the new technology.
  • the inventive alkoxy process includes electrochemical preparation of metal alcoholates and organometallic compounds which are soluble in organic solvents, by electrolysis of a metal material in an alcohol in the presence of an electroconductive additive.
  • the electrolysis can be carried out by electrode dissolution by alternating current (AC) , direct current (DC) , or combinations thereof.
  • the metal material can be elemental metal, a metal compound, a metal alkoxide, or an organometallic precursor.
  • the alcohol is preferably ethanol, propanol, butanol, pentanol, or hexanol, and may be of primary , secondary, or tertiary structure, and chosen to ensure the correct range of volatility and reactivity in subsequent processing.
  • the organic solvent can. be: an enamel solvent, gasoline, petroleum ether, naphtha, benzene, toluene, acetone, hexane, or ethylcellosolve. In some circumstances it may be desirable to use other organic solvents.
  • Other electrolytes can also be used to enhance electrolysis, such as: acetonitrile, di ethyl-sulfoxide, dimethyl-formamide, benzene, and toluene.
  • the metal alcoholates can comprise alcoholates of one or more of the following metals: magnesium (Mg) , aluminum (Al) , gallium (Ga) , indium (In) , yttrium (Y) , lanthanum (La) , cerium (Ce) , titanium (Ti) , zirconium (Zr) , hafnium (Hf) , neodymium (Nd) , tantalum (Ta) , iron (Fe) , cobalt (Co) , nickel (Ni) , calcium (Ca) , selenium (Se) , praseodymiu (Pr) , , samarium (Sm) , silicon (Si) , tellurium (Te) , ytterbium (Yb) , tin (Sn) , scandium (Sc) , lead (pb) , vanadium (V) , terbium (Tb)
  • homogeneous monomolecular layers or regions of metal alcoholates and organometallic compounds are deposited on a substrate to produce the desired composite ceramics.
  • the electrochemically prepared metal alcoholates and organometallic compounds soluble in the organic solvents are applied and coated on the substrate, using a very dilute solution to insure formation of a uniform, homogenous monolayer of high surface activity.
  • the coated substrate is heated, preferably sintered, and the organic solvents are evaporated (vaporized) .
  • the substrate can comprise: metal, catalyst, ball bearings, a turbojet, combustion engine, chemical equipment, pipelines, aerospace components, pistons, cylinders, automobile parts, high temperature apparatus, tools, dental coatings and teeth, optical lenses, semiconductors, and superconductive materials.
  • the ceramic material provides a superior coating and excellent insulation, as well as superb petrochemical catalysts and oxidized ceramics for electronics.
  • the solvent evaporation and hydrolysis are enhanced by moist air or humid air, or by an inert gas saturated with or containing water vapor.
  • moist air is ambient air containing humidity at room temperature. Humidity is controlled by adding water vapor (steam) or by drying the air. Temperature and humidity control effect the desired rate of hydrolysis and solvent removal.
  • Moist air comprises oxygen, nitrogen and water vapor (moisture) . Air can also contain trace amounts of elements and compounds, such as argon, carbon dioxide, neon, helium, methane, krypton, nitrous oxide, hydrogen, etc. The alcoholates are hydrolyzed to oxides.
  • the process of the present invention provides high purity uniform ceramic composite coatings on metals and other substrates, such as optical glass or other inorganic materials.
  • the inventive process achieves: (a) exactly prescribed stoichio etry of the components in bulk coating; (b) good homogeneous ceramics; (c) high adhesion strength to the substrate surface; (d) substantial decrease of energy expenses; (e) faster sintering procedures; (f) lower sintering temperature; and (g) high quality ceramic film.
  • the inventive technology provides a process for preparation of high temperature composite ceramic materials and coatings.
  • the special process comprises an electrochemical step for preparation of starting alcoholates, preparation of raw composites, and application of coatings.
  • a direct one-step electrochemical method for preparation of high-purity metal alcoholates and organometallic compounds soluble in organic solvents is attained by electrode dissolution of metals in the corresponding alcohol.
  • This step is then followed by removal of the solvent from the metal alcoholate and organometallic compounds and subsequent hydrolysis.
  • the coatings can be produced from the raw composites by heating to about 400° C for an hour. In some circumstances, it may be desirable to heat at different temperatures and/or for different periods of time.
  • the inventive alkoxy technology for the preparation of composite ceramic materials includes a universal electrochemical method for preparation of starting alcoholates comprising a direct one-step electrochemical method for preparation of high-purity metal alcoholates and organometallic compounds soluble in organic solvents.
  • the alkoxy method comprises electrode dissolution of metals in the corresponding alcohol in the presence cf an electroconductive additive using either a direct or an alternating current.
  • the method is ecologically pure and free of toxic waste.
  • the main by-product is gaseous hydrogen which can be safely emitted into the atmosphere or used as a fuel. In case of combustion use, pure water is the only product. Desirably, no electrolyte is consumed during the electrolysis.
  • electrochemical preparation avoids the impurities inevitably present when salt exchange is used for electrolysis since corrosion of metals by salt impurities is a real problem.
  • the inventive alkoxy technology for the preparation of composite ceramic materials also includes preparation of raw composites.
  • a new approach to the preparation of raw composites has been developed in accordance with this invention. This is achieved by using metal alcoholates and organometallic compounds soluble in mixtures of organic solvents.
  • the processes of solvent removal and subsequent hydrolysis have been elaborated so as to allow preparation of raw composites highly homogeneous in composition.
  • the inventive alkoxy technology for the preparation of composite ceramic materials further includes production and application of coatings and their subsequent sintering.
  • the technology ensures good adhesion of the coatings to metals and a high protection against high-temperature oxidation.
  • the good adhesive strength of the ceramic/metal joints results from extremely fine and homogeneous distribution of alkoxides in the raw composite.
  • the alkoxides provide high surface activity, which promotes strong adsorption of monolayers which are sequentially added and stabilized by reaction.
  • the high chemical homogenous characteristics of the raw composite also enhances the quality of the coating, increases its working temperature and reduces the energy expenses on sintering.
  • the substrate surface is cleaned and treated, e.g.
  • the process of ceramic coating includes the steps of: (1) cleaning the substrate surface and fat removal; (2) preparing the alkoxide solution (dry air and dry solvents) ; (3) substrate coating, up to 10 layers, with the intermediate effect of water vapor under the temperature of 70° C after each coating (in some cases room air is sufficient) ; and (4) annealing in an inert (in some cases) atmosphere.
  • the temperature scale depends on the substrate.
  • Uniform fine-grain ceramics of great integrity can be made using alkoxides. Bonding, hydrolysis and volatility are important in selecting the alkoxides to be used. Control of reaction rates can also be important.
  • Equipment helpful for carrying out the process of the invention are: (a) a standard electrolyzer with (b) an anode made of Zr, Al, Hf, Ti, etc. and (c) a cathode made of Pt, Ni, etc., (d) a rotor evaporizer, and (e) a vacuum oven, preferably a high-temperature vacuum oven, for annealing or sintering, from 20 until 1500° C to 1700° C.
  • the alkoxy technology of the invention was used to produce a protective coating of zittrite (a solid solution of 10% yttrium oxide in zirconium oxide) .
  • the thickness of the coating was 45 mem.
  • the adhesion strength of the coating to thermostable alloys ranged from 125 to 175 kg/cm 2 .
  • the Knorr hardness of the coating was 720-950 kg/mm 2
  • the density of the coating was 4.5-5.7 g/cm 3 .
  • the complete conversion of the raw composite into a homogeneous cubic phase was achieved by heating to 400° C for one hour.
  • the coating withstood six 10 minute thermocycles 30° C to 2000° C to 30° C , and a 1.5 hours exposure in air at 2000° C without perceptible corrosion.
  • sintering of yttrium and zirconium oxides and zirconium oxides a similar phase transition occurred at 1100° C and took 6 to 8 hours.
  • the alkoxy method of the invention can be readily realized on an industrial scale as a continuous process.
  • a pilot plant for continuous production of tetrabutyloxytitanium from titanium powder has been developed.
  • the inventive method has also been used for preparation of yttrium (Y) , zirconium (Zr) , and hafnium (Hf) isopropylates.
  • the current efficiency for the inventive processes comes to 85-92% with yields to 96-98%.
  • the inventive alkoxy method has unexpectedly and surprisingly been found to be successful in preparation of the alcoholates of Mg, Al, Ga, In, Y, La, Ti, Zr, Hf, Nb, Ta, Fe, Co, Ni, Ca, Se, Pr, Ce, S , Si, Te, Yb, Sn, Pb, V, Nd, Gd and Tb.
  • all of the various alcoholates can be prepared using exactly the same equipment and technological techniques. This represents a substantial savings in equipment and energy resources.
  • Some of the many advantages of the electrochemical method and ceramic preparation process of the invention are: (a) technological simplicity; (b) ecological attractive; (c) no toxic by-products are formed; (d) safe; (e) the process is cyclic and allows complete regeneration of the electroconductive additive and solvent; (f) the process can be readily made continuous; and (g) standard electrolyzers and equipment can be used in the process.
  • all steps in creation of ceramic coating film should be carried out on the surface of the covered solid substrate. Any type of movement of any component of the composite should be excluded.
  • organometallic precursors are produced and used which can be easily transformed into ceramic under mild reaction conditions.
  • organometallic compounds are selected and used which are quite stable in organic solvents and can be easily placed on substrate surface without any decomposition.
  • the organic solvents should be volatile enough to be easily removed from the substrate surface.
  • any metal alkoxide will work. Several are listed below and others will work as well. Given freedom of choice of solvent, any stable alkoxide is suitable.
  • the universe of compounds is M(0R) n where the subscript n is chosen to satisfy the valence of the central metal moiety. It is desirable to use metal organic compounds which are stable in organic solvents to achieve precise control of reaction stoichiometry over the surface of the object.
  • M is a metal comprising Mg, Ca, Se, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Yb, Al, Ga, In, Ti, Zr, Hf, Si, Sn, Pb, V, Nb, Ta, Fe, Te, Co, Ni, or Sc;
  • O oxygen
  • R is a radical comprising C]_-C 6 primary, secondary and tertiary alkyl groups, or alkoxo-alcohols containing the OR group, or amino-alcohols containing the NR 2 group; n is an integer (whole number) .
  • the organic solvents should be volatile enough to be easily removed; e.g., by evaporation at low or moderate temperatures.
  • the objective is to concentrate uniformly the concentration of metal alkoxides on the surface of the object without disturbing the homogeneity of the solution.
  • the final objective of this step is to deposit a uniform residue of mixed or pure metal alkoxides on the surface of the substrate in a layer free of voids or inclusions.
  • solvents which may be utilized are isopropyl alcohol (isopropanol) , hexane, ethylcellosolve, enamel solvent, gasoline, petroleum ether, benzene, toluene, naphtha, acetone.
  • the alkoxide concentration in the solvent can be 5% to 10%.
  • volatile solvents While using one or another solvent, one should take into account not only time necessary for the treatment of the metal piece (substrate) but the porosity of the substrate or support. The more porous substrate there is, the more volatile solvent can be used. The solvent and the rate of evaporation of solvent can be determined based upon the complexity of the part being coated. If the time of solvent evaporation from a metal surface is increased, dispersion is also increased and the coating becomes harder and of higher quality. Control of the rate of the solvent removal should be exercised.
  • Fixation refers to the adsorption, e.g. chemisorption, of metal alkoxides on clean metal surfaces. Fixation is the adsorption process in which alkoxides are kept on the surface after removal of a solvent. Since homogeneous solutions of alkoxides in concentration of not more than 1.10 "1 M are used, a monomolecular film layer having phenomenal surface activity is obtained. This property helps in further successful growth of layers one after another. This results in an intermediate step of a uniform layer before the final preparation of the surface film prior to changing the chemical composition of the adsorbed molecular film.
  • the best reagent for metal alkoxide hydrolysis was found to be moist air at a moderate temperature of 20° C to 70° C at atmospheric pressure. Nearly equal rates of metal hydroxides formation and evaporation of produced alcohol are attained. The proximity of these rates avoids the distortion of geometrical arrangement of precursor atoms. The rate of reaction is controlled to ensure a uniform surface coating is achieved.
  • Hydrolysis is an important first step reaction. It is the control of the hydrolysis step which can be central to controlling the decomposition of the alkoxide to the oxide and alcohol. This hydrolysis is conveniently controlled by using the moisture in ordinary room air, "moist air". In some circumstances, it may be desirable to use other mild hydrolizing agents for the chemical conversion step.
  • organometallic precursors used is that crushing, even almost perfect crushing, of oxides and their mixtures gives after subsequent annealing undesirable bad coatings and products with a large amount of silvers.
  • Coatings, obtained according to the process of the invention have great surface activity. Homogeneous monomolecular layers of coatings are obtained.
  • Heating preferably comprises heating followed by annealing or sintering at mild conditions. It is preferred to heat at 400° C degrees during the synthesis of some ceramics. For example, a temperature of 400° C is a desirable condition for the mixture with crystal water, for example Zr0 2 /Y 2 0 3 formed on a metal surface, to transform from the amorphous to the crystal state, namely to the cubic modification of Zr0 2 alloyed with Y 2 0 3 (6-10%) . But in order to obtain a firmly attached ceramic coating on the surface, the product should be annealed at the temperature from 850° C until 1200° C to 1500° C degrees for 1 hour. Annealing conditions can be varied taking into account alloy properties (refractory alloys or stainless steel) .
  • an annealing temperature of 450° C-500° C is sufficient for duraluminium.
  • An annealing temperature of 850° C is sufficient for stainless steel. It may be helpful at this stage to define the term "metal alkoxide".
  • the binary metal alkoxides have the general formula M(0R) x . Metal alkoxides involve M-O-C bonds which are polarized due to the highly electronegative character of oxygen.
  • the degree of polarization in an alkoxide molecule depends upon the electronegativity of the central element (M) and the nature of these compounds varies from essentially covalent volatile monomers as in cases of electronegative elements like silicon, germanium, phosphorus and sulphur to more electrovalent polymeric solids in the cases of electropositive elements such as the alkali and alkaline earth metals as well as the lanthanons.
  • M central element
  • the covalent character of the M-0 bond increases with greater inductive effect of the alkyl group.
  • the tertiary butoxide should have the highest covalent character.
  • the decreasing order of molar conductivities of sodium methoxide, ethoxide, iso- propoxide and tert-butoxide in their parent alcohol appears to arise at least in part from the increasing +1 inductive effect of the alkyl group.
  • the polarity of the M-0 bond may also be partially offset in cases of electrophilic metals which undergo covalency expansion by intermolecular coordination through the oxygen atoms of the alkoxy groups. This type of molecular association appears to be sensitive to factors such as the ramification of the alkyl group.
  • the method required for the synthesis of alkoxy derivatives of an element generally depends on its electronegativity.
  • Highly electropositive elements with valencies up to three ions react directly with alcohols with the liberation of hydrogen and formation of metal alkoxides.
  • a catalyst may be required for successful synthesis of alkoxides.
  • Another general method of synthesis applicable to electronegative elements is the reaction of their covalent halides with the appropriate alcohol.
  • This method employing the anhydrous chloride as starting material does not appear to effect complete replacement of halide when the central metal atom is comparatively less electronegative.
  • the replacement of halide could be forced to completion by the use of bases such as pyridine, ammonia, etc.
  • reaction of metals with alcohols is best performed with strongly electropositive elements, such as alkali metals and alkaline earth metals.
  • strongly electropositive elements such as alkali metals and alkaline earth metals.
  • a catalyst iodine, mercuric chloride, mercuric iodide etc.
  • a similar role appears to be played by oxygen in the reactions of thallium with alcohol; thallus oxide or hydroxide formed on the surface of the metal appears to react with alcohol whereas the metal surface appears to be inert.
  • beryllium and magnesium may not react directly with alcohols, but may require a catalyst.
  • beryllium metal reacts with ethanol in the presence of a catalyst (e.g. iodide, mercuric chloride or beryllium dichloride) to form beryllium diethoxide.
  • a catalyst e.g. iodide, mercuric chloride or beryllium dichloride
  • Metal halides have been used quite extensively as starting materials for the synthesis of a large number of metal alkoxides. Metal chlorides can be dissolved in alcohol. Alkoxy derivatives of the elements tend to react with all hydroxy compounds resulting in the replacement of their alkoxy groups.
  • alcoholyses or alcohol interchange reactions can be represented by the following general equation:
  • Metal alkoxides react with a variety of primary secondary and tertiary alcohols as well as phenols to set up the following type of equilibrium:
  • a solvent like benzene which forms an azeotrope with the liberated alcohol facilitates fractionation of the liberated alcohol, but also makes it possible to carry out the reaction in any stoichiometric ratio of the reactants to get the desired mixed alkoxides.
  • the forward reaction is greatly facilitated by the instantaneous separation of the insoluble methoxide on mixing the alkoxide with excess of methanol.
  • the above alcoholysis reactions can be widely applied for the synthesis of a large number of metal alkoxides.
  • the physical properties of metal alkoxides are as follows.
  • the alkoxy derivatives of metals have at least one M-O-C system. Due to the strongly electronegative character of oxygen, alkoxides of metallic elements exhibit a strongly polar character. Metal-oxygen bonds in these derivatives may have around 65% ionic character for metals with electronegativity values of 1.5-1.3 (e.g. aluminum, titanium and zirconium) to about 80% ionic character for more electropositive metals with electronegativity values of the order of 1.2-0.9 (e.g., alkali metals, alkaline earths and lanthanons) . However, most of these alkoxides show a fair degree of volatility and solubility in common organic solvents; properties which can be considered as characteristic of covalent compounds.
  • metal methoxides are comparatively non- volatile and insoluble in common organic solvents.
  • the primary alkoxide derivatives of alkaline earth and other metals of group II are generally insoluble non-volatile compounds whereas their secondary and tertiary alkoxides tend to be comparatively more volatile and soluble in organic solvents.
  • Alkoxides of Group IV elements such as silicon and germanium alkoxides can be highly volatile.
  • Alkoxide derivatives of sulphur, selenium, tellurium, arsenic and antimony are highly volatile.
  • Alkoxide derivatives of divalent copper, chromium, nickel, cobalt and manganese are all insoluble non-volatile products.
  • Metal alkoxides are generally very reactive species which may be due to the presence of electronegative alkoxy groups making the metal atoms highly prone to nucleophilic attack. These metal alkoxides are, therefore, susceptible to hydrolysis by atmospheric moisture.
  • Metal alkoxides readily react with excess of hydrogen halides or acyl halides giving the metal halides. However, by using stoichiometric amounts of these halides, the metal halide alkoxides may be prepared.
  • metal alkoxides depend on their chemical reactivity coupled with their volatility and solubility in common organic solvents.
  • the chemical reactivity is manifest in the variety of catalytic applications of the alkoxides, ranging from redox catalysts for aluminum alkoxides, olefin polymerization catalysts for titanium and vanadium alkoxides to accelerators for protective coatings.
  • the alkoxides are valuable precursors to the metal oxides through hydrolysis.
  • the metal alkoxides offer considerable advantages as starting materials for the preparation of high purity oxides. This aspect has been stimulated by the rapid developments in the microelectronics field where the advantage of the ease of hydrolysis of the volatile metal alkoxides and the application of ceramics is especially appreciated.
  • Alkoxides are extremely useful reagents. They are powerful bases-stronger than hydroxide-and, by varying the alkyl group, their degree of basicity, their steric requirements, and their solubility properties can be varied. As nucleophiles, they can be used to introduce the alkoxy group into molecules.
  • M Ti, Mg, Sc, Al, Y, Ga, Zr, Hf, Nb, Ta, Fe,
  • n 2,3,4,5, is by means of electrochemical dissolution of a metal electrode or metal alloy electrode in an electrolyte containing alcohol and a conductive additive at the electrolyte boiling temperature.
  • the process can be carried out by means of alternating current using as conductive additive materials of the general formula KX, where:
  • K alkali metal cation, NH4+, or NR4+;
  • X Cl “ , Br “ , I “ , BF4 “ , PF6 “ , C104 “ , in the quantity of 2-20% by weight.
  • the electrolyte can contain CH 3 CN, DMSO, DMFA or benzene in the quantity of 1- 20% by weight.
  • M Ti, Mg, Al, Y, Zr, Nd, Ta, Ca, Se, Pr, Ce, Sm, Si, Te, Yb, Sn, Pb, Ga, In, Fe, Co,
  • n 2,3,4,5 is by means of alternating current electrochemical dissolution of the corresponding metal electrodes in an electrolyte containing alcohol and salt of general formula KX, where:
  • K alkali metal cations, NH4+ or NR4;
  • X C1-, Br-, I-, BF4-, PF6-, C104- in the quantity of 2-20 % by weight at the electrolyte boiling temperature.
  • Direct current electrolysis is carried out until the corresponding metal oxides precipitation stops.
  • Both the cathode and anode can be made of the same metal.
  • K Cation, chosen from alkali metal, ammonium or tetra-ammonium base
  • X Cl, Br, I, BF « , PF 6 , CIO,; in the amount of 2-20% weight at the electrolyte boiling temperature and carrying out the process under regular frequency AC.
  • Current can be 0.15-0.5 amps at a voltage of 130-220 volts.
  • It can be useful to add acetonitrile, dimethyl-sulfoxide, dimethyl-formamide or benzene in amount of 1-20% by weight to enhance the electrolyte.
  • Solvents such as acetonitrile, dimethyl-formamide, dimethyl- sulfoxide cause an increase in electrical conductivity when added.
  • Polar solvents have more dielectric constant then some alcohols, especially higher alcohols.
  • the process of the invention be based on the usage of direct and alternating current of industrial frequency or changeable frequency in connection with the nature of the metal and electrolyte.
  • electrolysis is carried out in the solution of corresponding alcohol plus neutral organic solvents with the aim to decrease the voltage and thereby decrease the overall energy expenses.
  • electrolysis is preferably performed in two stages, where the first-stage electrolysis is held under DC up to particular metal oxides precipitant formation and the second stage is held under AC. Running the process by this way, one can use commercial alcohols, which have up to 4% of water fraction. In the first DC stage water decomposes. Metal alcoholates synthesis takes place in the second AC stage.
  • the anode and cathode can be made of the same or different materials. Treatment of the reaction mixture is preferably carried out without distillation to decrease energy expenses.
  • the electrolytic processes can be carried out in dry or moist air.
  • Hydrolysis is the chemical decomposition or splitting of a compound by means of water, as in the following general equation:
  • R*X + H*OH R*H + X*OH
  • Water in the form of its hydrogen and hydroxyl ions, adds to the cleaved compound.
  • the addition of water is generally catalyzed by ions and without added ions may be a very slow process. Consequently, the addition of acid or base increases the concentration of hydrogen or hydroxyl ions with a corresponding increase in the rate of hydrolysis.
  • Certain enzymes also catalyze the hydrolysis of some organic compounds.
  • Alcoholates of metals are prepared by the inventive process.
  • metals including the Periodic Table Groups IA, IIA, all of the B groups, IIIA with the possible exception of boron, IVA with the possible exception of carbon and possibly silicon, VA with the exception of nitrogen and phosphorus, and VIA with the exception of oxygen and sulfur.
  • metals are solids with a metallic luster, conductive of electricity by electron flow, malleable, and of high physical strength. In compound form the metals have positive valences. Probably their most important characteristic is that when used as metals they are predominately in element form or alloyed with other metals. Metal occur most commonly as oxides or sulfides in ores that contain variable amounts of materials like lay, silica, granite, etc., from which the metallic compounds must be separated. Electrolysis offers the best means, and in some cases the only practical means, of producing many pure metals. Deposition from aqueous solution is used to prepare cadmium, copper, cobalt, gallium, indium, manganese, thallium and zinc.
  • metal As electrodeposited coatings, among them cadmium, copper, cobalt, chromium, palladium, platinum, rhodium, indium, tin tungsten, nickel and zinc.
  • the word "metal" has two somewhat different meanings. Chemically, a metal is a chemical element which tends to form positive ions in solution and whose oxides form hydroxides rather than acids with water. Physically, a metal is a phase containing free electrons which give it certain characteristic properties such as high electrical and thermal conductivity, metallic luster, and, often, plastic formability. These phases need not be pure substances; when they are not, they are called alloys.
  • organometallic compounds are produced.
  • An organometallic compounds is one which contains a metal (M) attached directly to carbon.
  • Organometallic compounds (RM) can be prepared of practically all the metals.
  • Simple organometallic compounds have only R groups attached to the metal, as Ri,M Iv .
  • Mixed organometallic compound have both R and X groups attached to the metal, as R 2 M ⁇ X.
  • the simple types may be further divided into symmetrical (as C 2 H 5 HgC 2 H 5 ) and unsymmetrical (as C 2 H 5 HgC 4 H 9 ) classes. Within these general groups there are many types of organometallic compounds.
  • Those having but one metal may contain one or more R groups and one or more X groups, depending on the valence number of metal and the stabilities of the organometallic compounds. Furthermore, two or more of the same or different metals may be present as in CH 2 (ZnI) 2 , (C 6 H 5 ) 3 SiSn(C 6 H 5 ) 3 , and (C 6 H 5 ) 3 GeLi.
  • Organometallic compounds may be classified in various ways, but one convenient system is by groups in the Periodic Table. , In any group or subgroup the higher the ionization potential of the metal, the less reactive will be its organometallic compounds. Organometallic compounds may be grouped by relative reactivities on the basis of two reactions: (a) addition to an olefinic linkage; and (b) addition to a carbonyl group. The highly reactive compounds add to both. The relatively unreactive compounds add to neither functional group.
  • Organometallic compounds derive from interaction of an RX compound with a metal, or its alloy, or amalgam. Generally, organometallic compounds can be made from all metals and metalloids. Reactive and moderately reactive organometallic compounds can undergo reactions with all functional groups. General reactions shown by RM compounds are oxidation, and cleavage by acids. General rules for the reactivities of RM compounds is that the organometallic compounds of the alkali metals form the most reactive group, and in this group the order of increasing reactivity is: Li, Na, K, Rb, Cs.
  • RM compounds vary over wide ranges. Some (like trimethylboron) are gases; many are liquids: but for the most part (particularly those having aryl groups) they are solids.
  • the less reactive organometallic compounds are unaffected by water; but the moderately and highly reactive RM compounds are decomposed vigorously by water. Water or other hydroxylated compounds should not be used as solvents for the reactive RM compounds. Some of the less reactive RM compounds can be dissolved in water if the R group in the RM compound has functional polar groups like -COOH, -OH, and -NH 2 which impart water-solubilizing characteristics to the molecule.
  • Alcohols from a chemical viewpoint, are those classes of organic compounds where one or more hydroxyl (OH) groups are present in a hydrocarbon molecule with no more than one (OH) group attached to a single carbon atom.
  • OH hydroxyl
  • Three principal types of nomenclature are used. Common or radical names with the word alcohol, are derived from natural sources, e.g., cetyl alcohol or from the hydrocarbon portion, e.g., ethyl alcohol from ethane. With simpler alcohols the common names are most often used. A common name simply consists of the name of the alkyl group followed by the word alcohol.
  • ethyl alcohol isopropyl alcohol, isobutyl alcohol, tert-butyl alcohol.
  • Substituted carbinol wherein this represents derivatives of methanol.
  • I.U.C. or Geneva name designates the name of the alcohol from the hydrocarbon having the longest straight chain and the alcohol function.
  • the final hydrocarbon "e” is replaced by "-ol” (or "-diol,” “- triol,” etc., according to the number of hydroxyl groups).
  • the parent structure with the longest continuous carbon chain that contains the OH groups is selected.
  • the parent structure is known as ethanol, propanol, butanol, etc.
  • each name is derived by replacing the terminal -e of the corresponding alkane name by -ol.
  • the position of the -OH group and other groups attached to the parent chain are identified. Examples of these names are as follows: (CH 3 ) 3 COH, tert-butyl alcohol, trimethylcarbinol, 2-methyl-2-propanol.
  • Alcohols are classified as primary, secondary, and tertiary, depending on the number of hydrogen atoms attached to the carbon atom with the hydroxyl group.
  • a primary alcohol contains two or more hydrogens, one hydrogen for a secondary alcohol, and no attached hydrogens for a tertiary alcohol. Typical examples are: Methyl alcohol CH 3 OH primary CH 3 OH
  • simple aliphatic alcohol such as ethyl alcohol (CH 3 CH 2 OH)
  • substituted aliphatic alcohol such as etholamine (NH 2 CH 2 CH 2 OH)
  • Alcohols in general are colorless liquids or solids. Alcohols occur widely in nature as volatile or essential oils, and as esters in volatile or essential oils, and as esters in volatile oils, fats and waxes. Normal primary alcohols from methanol to butanol are fluid liquids, those from C 5 to C n have an oily consistency, and those from C 12 and higher are solids at room temperature. All monohydroxy alcohols are soluble in organic solvents, and those with one to three carbon atoms are soluble in water. In general, water solubility decreases with increasing molecular weight or complexity of the formula. Conversely, boiling points rise with increases in the same factors. Additional hydroxyl groups increase water solubility and decrease solubility in ether and alcohol.
  • the reactions of alcohols are primarily those of the hydroxyl groups (unless other active groups are present) .
  • the hydroxyl group may be replaced by halogen or amino groups; the alcohol may be dehydrated; the hydrogen of the hydroxyl group can be replaced by a metal.
  • Methyl alcohol (methanol, wood alcohol, carbinol) is produced by destructive distillation of hard wood, or by catalytic synthesis from hydrogen and carbon monoxide.
  • Ethyl alcohol (ethanol, grain alcohol) is obtained by the fermentation of sugar solution and ashes of starch- containing materials, or synthetically from ethylene. Molasses is the most common raw material for the fermentation process. Most industrial ethanol is produced in petrochemical plants from the processing of ethane and ethylene.
  • Isopropyl alcohol is made by hydration of a propylene-sulfuric acid mixture, although smaller amounts are a by-product of fermentations.
  • Normal propyl alcohol comes from the Fischer-Tropsch process and is also a co-product of air oxidation of propane and butane mixtures.
  • Butyl alcohol (n-butanol) is produced by fermentation of starches and carbohydrates and also synthetically from ethanol or acetylene. Isobutyl alcohol is mostly synthesized from carbon monoxide and hydrogen at high pressure. Tertiary butyl alcohol is produced from the hydration of 1-butane.
  • Alcohols are compounds of the general formula ROH, where R is any alkyl or substituted alkyl group. The group may be open-chain or cyclic; it may contain a double bond, a halogen atom, an aromatic ring, or additional hydroxyl groups. As the functional group of alcohols, the hydroxyl group-OH determines the properties characteristic of the family. Variations in the structure of the R group bring about variations in these properties.
  • One reaction, oxidation which directly involves the hydrogen atoms attached to the carbon bearing the -OH group, takes an entirely different course for each class of alcohols.
  • an alcohol is a composite of an alkane and water. It contains a lipophilic, alkane-like group and a hydrophilic, water-like hydroxyl group. Of these two structural units, it is the -OH group which gives the alcohol its characteristic physical properties and the alkyl group which, depending upon its size and shape, modifies these properties.
  • the -OH group is highly polar and is capable of hydrogen bonding: hydrogen bonding to its fellow alcohol molecules to other neutral molecules and to anions. The physical properties of alcohols are shown in the table below.
  • alkoxides The acidity of alcohols is shown by their reaction with active metals to liberate hydrogen gas and form alkoxides. Since an alcohol is a weaker acid than water, an alkoxide is prepared by reaction of the alcohol with the active metal itself. Alkoxides are extremely useful reagents. They are powerful bases-stronger than hydroxide- and, by varying the alkyl group, their degree of basicity, their steric requirements, and their solubility properties can be varied. As nucleophiles, they can be used to introduce the alkoxy group into molecules.
  • an anion-exchange membrane is not desirable in the electrochemical process because it causes significant decrease of current density and consequently to increase of the electrolysis time and decrease of efficiency.
  • Membranes also limits the working temperature of the process. Preferably, the temperature should not be higher than 45° C.
  • the electrochemical process for many metals can be at least as high as 80° C.
  • no pump or magnetic stirrer is needed for circulation of electrolyte.
  • the circulation of electrolyte is provided with boiling electrolyte and/or with bubbles of hydrogen from the cathode. It becomes possible at much higher current density which can not be achieved with membranes.
  • Rapid thermal annealing is not preferred for preparation of high-temperature composite ceramic materials and coatings, because ceramic materials and coating need more time for sintering. Reorganization of atoms in hard phase into corresponding geometrical structure needs adequate sintering time.
  • hydrolysis instead of cracking, it is preferred to use hydrolysis at mild conditions, e.g. room temperature or 40° C. These conditions help control the process and organize the needed structure of the composite.
  • the hydrolysis procedure is carried out only after the replacement of metal alkoxide on the metal surface of the substrate. This is very important because such a procedure leads to the exact bulk stoichiometry of ceramics and to high adhesion strength.
  • Two of the many important aspects of the subject invention are: (1) the universal chemical method for obtaining of metal alcoholates; and (2) the process for preparation of high temperature composite ceramics on the basis of alcoholates.
  • the inventive procedure can be used to produce a polylayer coating in which every layer of the coating possesses the same chemical structure or a different chemical structure, when it is desired to do so. This is especially important for electronic and superconductive materials.
  • a broad range of metal alcoholates can be prepared using the same equipment.
  • Precursors-metal alkoxides can be easily produced in industrial scale and can be used for ceramic material and coatings as well as for other purposes.
  • High quality composites produced with the subject alkoxy technology can be advantageously used in: (a) turbojet and combustion engines; (b) high-temperature equipment and engineering; (c) chemical equipment and pipelines; (d) electronics and superconductive materials; and (e) catalysts for various chemical processes.
  • High quality composites produced with the subject alkoxy technology also has many other uses.
  • Impervious ceramic coatings made in accordance with this invention provide corrosion protection and hardness to any metal.
  • the oxide coating which is formed in air oxidation or by electrochemical means can be improved by the addition of alumina of the appropriate crystal phase. The prevention of corrosion or oxidation of all forms of structural metal is another important commercial application of the subject invention.

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Abstract

On utilise une technique de durcissement alcoxyque pour préparer des matériaux céramiques composites. Les composés de départ des matériaux céramiques composites comprennent des alcoolats métalliques. Les alcoolats de départ sont préparés par dissolution électrolytique de métaux dans un alcool correspondant en présence d'un additif électroconducteur. Cette préparation est sans danger pour l'environnement et ne contient pas d'autres sous-produits que l'hydrogène; elle permet une régénération totale de l'additif électroconducteur et du solvant, et peut être continue ou cyclique. Une large gamme d'alcoolats métalliques peuvent être préparés à l'aide de ces mêmes matériaux. Des matériaux composites bruts sont préparés à l'aide de ces alcoolats métalliques et de composés organométalliques solubles dans des solvants organiques, puis par élimination et hydrolyse du solvant. Le matériau composite obtenu peut être appliqué sur un substrat métallique ou autre substrat, et une fois fritté ou recuit à la température appropriée, permet d'obtenir une meilleure qualité et un revêtement céramique de haute résistance.
PCT/US1994/013707 1993-12-06 1994-12-02 Procede de preparation de materiaux et revetements ceramiques composites a haute temperature WO1995016060A1 (fr)

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WO1999011767A1 (fr) * 1997-08-28 1999-03-11 Meiji Seika Kaisha Ltd. Endoglucanase acc4
WO2006087114A2 (fr) * 2005-02-15 2006-08-24 Ks Kolbenschmidt Gmbh Couche protectrice contre la corrosion par gaz chauds dans la chambre de combustion d'un moteur thermique
CN100417748C (zh) * 2005-10-20 2008-09-10 株洲硬质合金集团有限公司 高纯钽醇盐的生产方法
CN102820445A (zh) * 2011-06-07 2012-12-12 通用汽车环球科技运作有限责任公司 施加非导电陶瓷到锂离子电池隔离器上的方法
WO2018115207A1 (fr) * 2016-12-22 2018-06-28 Electricite De France Procédé sol-gel de fabrication d'un revêtement anticorrosion sur substrat métallique
US10056590B2 (en) 2016-08-31 2018-08-21 GM Global Technology Operations LLC Methods of making separators for lithium ion batteries
US10680222B2 (en) 2017-12-19 2020-06-09 GM Global Technology Operations LLC Method of making thermally-stable composite separators for lithium batteries

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SU953008A1 (ru) * 1980-09-30 1982-08-23 Ордена Ленина институт элементоорганических соединений им.А.Н.Несмеянова Способ получени алкогол тов металлов
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US5132253A (en) * 1990-12-17 1992-07-21 Corning Incorporated Sol-gel method for making ceramic materials
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US3964983A (en) * 1972-10-05 1976-06-22 Studiengesellschaft Kohle M.B.H. Process for the electrochemical synthesis of organic metal compounds
US4250000A (en) * 1979-03-26 1981-02-10 Stauffer Chemical Company Electrochemical process for metal alkoxides
SU953008A1 (ru) * 1980-09-30 1982-08-23 Ордена Ленина институт элементоорганических соединений им.А.Н.Несмеянова Способ получени алкогол тов металлов
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999011767A1 (fr) * 1997-08-28 1999-03-11 Meiji Seika Kaisha Ltd. Endoglucanase acc4
WO2006087114A2 (fr) * 2005-02-15 2006-08-24 Ks Kolbenschmidt Gmbh Couche protectrice contre la corrosion par gaz chauds dans la chambre de combustion d'un moteur thermique
WO2006087114A3 (fr) * 2005-02-15 2008-09-12 Ks Kolbenschmidt Gmbh Couche protectrice contre la corrosion par gaz chauds dans la chambre de combustion d'un moteur thermique
CN100417748C (zh) * 2005-10-20 2008-09-10 株洲硬质合金集团有限公司 高纯钽醇盐的生产方法
CN102820445A (zh) * 2011-06-07 2012-12-12 通用汽车环球科技运作有限责任公司 施加非导电陶瓷到锂离子电池隔离器上的方法
US20120315384A1 (en) * 2011-06-07 2012-12-13 GM Global Technology Operations LLC Method of applying nonconductive ceramics on lithium-ion battery separators
US10056590B2 (en) 2016-08-31 2018-08-21 GM Global Technology Operations LLC Methods of making separators for lithium ion batteries
WO2018115207A1 (fr) * 2016-12-22 2018-06-28 Electricite De France Procédé sol-gel de fabrication d'un revêtement anticorrosion sur substrat métallique
FR3061210A1 (fr) * 2016-12-22 2018-06-29 Electricite De France Procede sol-gel de fabrication d'un revetement anticorrosion sur substrat metallique
CN110573656A (zh) * 2016-12-22 2019-12-13 法国电力公司 在金属基底上生成防腐蚀涂层的溶胶-凝胶方法
CN110573656B (zh) * 2016-12-22 2022-05-24 法国电力公司 在金属基底上生成防腐蚀涂层的溶胶-凝胶方法
US11519072B2 (en) 2016-12-22 2022-12-06 Electricite De France Sol-gel method for producing an anti-corrosion coating on a metal substrate
US10680222B2 (en) 2017-12-19 2020-06-09 GM Global Technology Operations LLC Method of making thermally-stable composite separators for lithium batteries

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