TECHNOLOGICAL FIELD

This invention generally relates to organic-material-doped metals, uses thereof and processes for their preparation.

BACKGROUND

Corrosion of metallic structures has a significant impact on the world economy, as reflected in infrastructure, transportation, utilities, production facilities and home applications. Typically the cost of corrosion amounts to 3-5% of the gross national product (GNP) of the industrialized nations, which translates into a staggering half a trillion Euros each year. The repeated emphasis in the voluminous literature on corrosion protection is that new ideas are needed, because the current approaches are reaching their limits, and the damage and cost to society are still very high. The new materials methodology which enables, for the first time, to produce alloys between metals and organic components, seems promising from that point of view, as earlier studies have shown that such organic doping or alloying affects a whole range of metal properties, ranging from physical properties such as conductivity, to chemical properties such as catalysis, and to biological properties, such as biocidal activity.

The preparation of metallic materials was based on a variety of metal-cation reduction methods in the presence of the organic component to be entrapped. Reduction methods have included the use of water soluble reducing agents, reducing metals, reducing solvents, and electrochemical reduction - all of which were applied on ions of coin metals and noble metals.

US patent application no. 2010/0297724 [1] to inventors of the present application concerns a composition of matter comprising a hydrophobic organic substance entrapped in metal, produced by reducing the metal of the metal salt in the presence of dissolved hydrophobic moiety, entrapping the hydrophobic moiety in the metal. This technology is readily applicable to easily reduced metals such as silver, gold, copper and platinum. International patent application no. WO 2011/135563 [2] concerns a similar concept of easily reduced metals (such as silver), entrapping therapeutically active agents, such as biocides and releasing the active agents over prolonged periods of time.

Utilization of the procedures employed by the above -referenced technologies, for metals that are high on the electrochemical series, that is, of small positive reduction potentials or negative reduction potentials (such as iron), is not possible as extreme and harsh reducing conditions are required; conditions which would cause damage the organic moieties to be entrapped.

Thus, there exists the need for a technology which would permit entrapment of organic materials in metals that are high on the electrochemical series, i.e., of small positive reduction potentials or negative reduction potentials.

REFERENCES

[1] US 2010/0297724

[2] WO 2011/135563

SUMMARY OF THE INVENTION

The presently known composites of a metal entrapping (doped with) organic materials do not include composites of metals characterized by small positive or negative reduction potentials, i.e., corrodible, non-noble metals. This is mainly due to the fact that existing processes for the production of such composites are inadequate for obtaining non-corroding metal composites.

An object of the invention is to provide novel composites comprising each a corrodible metal doped with an organic material, the organic material endowing the corrodible metal with corrosive -resistance properties.

Another objective of the present invention is to provide novel composites comprising a metal at the zero oxidation state and an organic material, wherein said composite being substantively free of the metal in a positive oxidation state.

Thus, in a first aspect of the invention there is provided a corrodible metal doped (entrapped, embedded) with at least one organic material, said composite being resistant to corrosion. The metal doped with said organic material may be in the form of a composite material, which may or may not comprise additional components. In some embodiments, the composite comprises a corrodible metal and at least one organic material, and in other embodiments, the composite consists a corrodible metal and at least one organic material; in either of the two cases, said composite exhibits resistant to corrosion.

Without wishing to be bound by theory, and as further elaborated below, the at least one organic material endows the corrodible metal with the resistance to corrosion. While the observed resistance is dependent on the organic material present, the amount of the organic material, relative to the amount of the corrodible metal is small.

In some embodiments, the metal is in the form of a metallic matrix and the organic material dopes the metal in the matrix.

The "composite" of the present invention, comprising a corrodible metal is a material composition having one or more component domains, comprising a metal and an organic material capable of decreasing or preventing corrosion of said metal. The composite material is characterized by having the organic material entrapped (embedded) in the metal (e.g., being typically in the form of a metallic matrix), which would have been susceptible to corrosion if not for the presence of said organic material. In some embodiments, the metal is in the form of a metallic matrix having a continuous phase domain, namely demonstrating material continuity.

The composite of the invention may be formed in any solid state form. In some embodiments, the composite is in one or more of the following forms: granules, powders, sub-micron particles, clusters, or thin films. The different forms of the composite of the invention may be in any size or shape. In some embodiments, the composite is in the form of particles.

In some embodiments, the particle diameter (one dimension of the particles) is in the nanometric scale. In some embodiments, the particles diameter is less than 100 nm. In other embodiments, the particle diameter is less than 10 nm. In further embodiments, the particles diameter is between 5 to 100 nm.

In some embodiments, the particles are formed in clusters; the clusters size may be in the range of a micrometer or in the nanometer scale. In some embodiments, the cluster size is less than 1,000 nm. In other embodiments, the cluster size ranges from 200 to 500 nm.

As stated, the composite of the invention constitutes an organic material which is entrapped (embedded) within a metallic "matrix" comprising at least one metal. The matrix may be formed as a continuous form of aggregates or particles of a metallic material, which may be in a crystalline phase. The aggregates or particles may be associated to each other via physical and/or chemical bonds, such as electrostatic and/or Van der Waals forces, forming a porous matrix characterized by pores and inner voids.

Typically, the matrix may additionally be characterized by a plurality of inner pores (inner voids, holes), which may be randomly distributed within the matrix. The pores may be nanometric in size, namely having a mean diameter smaller than 1,000 nm. In some embodiments, the mean pore diameter is between about 10 nm and 500 nm. In further embodiments, the mean pore diameter is between about 10 nm and 100 nm. In other embodiments, the mean pore diameter is between about 20 nm and 50 nm.

There may be several parameters affecting or determining the pores size, such as the size of the entrapped material; the quantity of entrapped material within a pore; molecular weight of the entrapped material; conditions of production, e.g., temperature may affect the density and arrangement of the matrix particles/aggregate within the composite; and others.

The organic material is said to be entrapped in the metal, if the organic material is surrounded by metallic particles and immobilized to the metal by forces other than covalent bonding; for example, the force holding the two components together may be selected from multiple physical and chemical adsorptive interactions such as electrostatic and Van-der- Waals, π-π and/or σ-π interactions, charge-transfer interactions and hydrophobic or hydrophilic interactions. In other words, the organic material does not coat the bulk of the metallic matrix, but is rather incorporated therein.

Since the corrosion resistance is a property of the material down to its smallest nanometric level, the corrosion resistance property remains unchanged upon mechanical damages or upon impact. Whenever an inner portion or region of the material becomes exposed to air, below the impact scratch or break, the exposed material remains corrosion resistant. This unique characteristic of a composite according to the invention, allows for corrosion resistance properties, which are not known in articles or composites simply coated with an anticorrosive film or coat. Because the presence of surface defects known in coating technologies, such as pitting corrosion defects generated on a surface of a corrodible metal, are avoided or greatly minimized (or diminished) in composites according to the invention, the improvement in the fatigue properties is substantially maintained, with a clear improvement in the corrosion resistance.

At least some of the metal entrapping the organic material may be in a metallic form, i.e., in zero oxidation state. In some embodiments, substantially all (e.g., between 95-100% of) the metal within the matrix is in zero oxidation state. In other embodiments, a large portion of the metal (e.g., between 50-95%) within the matrix is in zero oxidation state.

In some embodiments, 100% of the metal in the matrix having a zero oxidation state. In other embodiments, more than 90% of the metal within the matrix having a zero oxidation state. In additional embodiments, more than 80% of the metal within the matrix having a zero oxidation state. In further embodiments, more than 70% of the metal within the matrix having a zero oxidation state. In still additional embodiments, more than 60% of the metal within the matrix having a zero oxidation state. In other embodiments, more than 50% of the metal within the matrix having a zero oxidation state. In additional embodiments, more than 30% of the metal within the matrix having a zero oxidation state.

It should be clarified that where the composite comprises in addition to the metal forming the matrix at least one additional metal component, not part of the metal- forming matrix, the at least one additional metal component may be in any form selected from a metal having a zero oxidation state, metal salt, metal alloy, metal oxide, and others.

Despite the presence of the organic material in the metal or matrix thereof, the matrix or the metal entrapping the organic material retains its metallic characteristics, e.g., appearance, for example, its metallic luster, color; electronic characteristics, thermal conductivity; and malleability. In some embodiments, the metallic characteristics are maintained after subjecting the composite to pressure, forming from the powder full bodies of a variety of articles.

In some embodiments, the matrix of the invention comprises two or more metals (together forming the matrix). The two or more metals may be in the form of a mixture of said metals or metallic alloys, said alloy may be in the form of a partial (two or more phases that may be homogeneous and/or heterogeneous in distribution) or a complete blend of one or more elements in the metallic matrix (exhibiting a single solid phase microstructure).

As used herein, the term "corrodible, non-noble metal" refers to a metal that readily (easily) corrodes, i.e., has a tendency to corrode, or has low resistance to oxidation, even at mild environment conditions, such as, at room temperature. As may be understood, the corrodible metal is one which would have undergone corrosion (oxidation) if not for the at least one organic material present in a composite according to the invention.

The electrochemical series give indication to corrosive metals, as it lists chemical species according to their tendency to be reduced/oxidized. Therefore, in some embodiments, the corrodible metal is a metal that is high on the electrochemical series, namely that is of a small positive reduction potential or a negative reduction potential. In some embodiments, the corrodible metal is selected from metals having a positive reduction potential. In some embodiments, said positive reduction potential is smaller than 0.15V. In some embodiments, the corrodible metal is selected from metals having a reduction potential smaller than 0.1V. In some embodiments, the corrodible metal is selected from metals having a reduction potential smaller than 0.05V.

In other embodiments, the corrodible metal is selected from metals having a negative reduction potential. In some embodiments, the corrodible metal is selected from metals having a reduction potential smaller than -0.1V. In some embodiments, the corrodible metal is selected from metals having a reduction potential smaller than -0.15V. In some embodiments, the corrodible metal is selected from metals having a reduction potential smaller than -0.2V. In some embodiments, the corrodible metal is selected from metals having a reduction potential smaller than -0.4V. In some embodiments, the corrodible metal is selected from metals having a reduction potential smaller than -0.5V. In some embodiments, the corrodible metal is selected from metals having a reduction potential smaller than -0.7V.

In some embodiments, the corrodible metal is selected from Fe, Al, Ga, Ge, Ni, Cr, Mn, Ti, Zn and Pd, or any combination thereof. In further embodiments, the metal is selected from Fe, Al, Ga, Ge, Ni, Cr, Mn, Ti and Zn or any combination thereof. In additional embodiments, the metal is selected from Fe, Al, Ga, Ge, Ni, Cr and Mn, or any combination thereof. In further embodiments, the metal is selected from Fe, Al, Ni and Cr.

In some embodiments, the metal is selected from Fe, Al and Cr. In additional embodiments, the metal is Fe.

The "organic material" entrapped within a matrix comprising the at least one corrodible metal, refers to any compound that endows the corrodible metal with corrosive -resistance properties, namely which is capable of decreasing or preventing corrosion of said corrodible metal. The organic material may be a small, medium or large organic molecule; it may be a mixture of two or more different organic molecules, a complex, a conjugate, a bundle or any other form of compounds or combinations thereof.

In some embodiments, the organic molecule is selected amongst reducing agents or molecules that affect the redox potential of the corrodible metal. In some other embodiments, the organic material is selected from hydrophobic organic molecules.

In some embodiments, the organic material is selected from organic acids, such as oxalic acid and formic acid; phenolic oxidation inhibitors, such as 2,6-di-tert-butyl paracresol (BHT); hydrides such as Hantzsch ester and polysilanes of the general formula (Si(RiR ₂ )-0-)n, wherein each of Ri and R ₂ are selected independently from H, Ci-Cealkyl and Ce-Cioaryls; and n is an integer between 1 and 100, or between 1-50, or between 1-30, or between 1-10.

In some embodiments, the organic material is selected amongst conducting polymers which may short-circuit metal defects of different electric potentials. In some embodiments, the conductive polymer is polyaniline (PANI).

In some embodiments, the organic material is selected from dyes, such as Congo red (CR), Safranin-0 (SaO), thionine (Th) and sudan III (S-III).

In some embodiments, the organic material is l-butyl-3-methylmidiazolium nitrate.

In some embodiments, the organic material is selected amongst hydrophobic organic molecules, which may enhance the hydrophobicity of the corrodible metal. Non-limiting examples of hydrophobic organic molecules include poly- (dimethylsiloxane) (PDMS), poly(acrylonitrile) (PAN), polyethylene, polypropylene, polycarbosilanes and fluorinated polyalkenes.

In some embodiments, the organic material is selected from polysterene (PS), polystyrene sulfonic acid (PSSA), poly (vinyl alcohol) (PVA) and poly(vinylbenzyl trimethyl ammonium hydroxide).

Typically, the amount of the entrapped organic moiety in the corrodible metal is less than 20% w/w. In some embodiments, the amount is less than 10%. In other embodiments, the amount is between 0.05% to 20% w/w. In some other embodiments, the amount is between 0.1% to 15% w/w.

In some embodiments, the composite of the invention comprises iron and PANI.

In some embodiments, the composite of the invention comprises iron and polydimethylsiloxane (PDMS). In some embodiments, the iron is metallic iron.

In some embodiments, the composite of the invention comprises at least one organic material selected from PANI and PDMS.

In some embodiments, the composite comprises iron, e.g., metallic iron as the corrodible metal.

As stated herein, the composite of the invention exhibits resistance to corrosion. The resistance to corrosion reflects on the property of a composite according to the invention to resist to corrosion attack in a particular environment at defined operating conditions, pressure, temperature, presence of oxidizing materials and others. Without wishing to be bound by theory, this resistance stems from the presence of the organic material in the metallic matrix. In some embodiments, the corrosion resistance is reflected in any one of the following:

1. Increased resistance to corrosion as compared to the bare metal;

2. Slow reaction kinetics, e.g., oxidation reactions in the presence of humidity, oxygen, oxidizing materials etc;

3. Better fatigue properties;

4. Increased, partial or complete resistance to cervice corrosion;

5. Increased, partial or complete resistance to microbial corrosion;

6. Increased, partial or complete resistance to high-temperature corrosion;

7. Increased, partial or complete resistance to catastrophic (metal dusting) corrosion; 8. Increased, partial or complete resistance to atmospheric corrosion;

9. Increased, partial or complete resistance to erosion corrosion;

10. Increased, partial or complete resistance to stress-related corrosion.

In another aspect of the invention, there is provided a composite of at least one metal and at least one organic material, the composite being substantially free of the metal in a non-zero oxidation state.

The composite of this aspect of the invention (namely that which is substantially free of metal in a non-zero oxidation state) is a material composition having one or more component domains, comprising said metal and an organic material. The composite material is characterized by having the organic material entrapped (embedded) in the metal, typically in the form of a metallic matrix in a zero oxidation state. In some embodiments, the metallic matrix is in the form of a continuous phase domain, namely demonstrating material continuity.

The composite of the invention may be formed in any solid state form. In some embodiments, the composite is in one or more of the following forms: granules, powders, sub-micron particles, clusters, or thin films. The different forms of the composite of the invention may be in any size or shape. In some embodiments, the composite is in the form of particles.

In some embodiments, the particle diameter (one dimension of the particles) is in the nanometric scale. In some embodiments, the particles diameter is less than 100 nm. In other embodiments, the particle diameter is less than 10 nm. In further embodiments, the particles diameter is between 5 to 100 nm.

In some embodiments, the particles are formed in clusters; the clusters size may be in the range of a micrometer or nanometer scale. In some embodiments, the cluster size is less than 1,000 nm. In other embodiments, the cluster size ranges from 200 to 500 nm.

As stated, the composite of the invention constitutes an organic material which is entrapped (embedded) within the metallic "matrix" comprising at least one metal at a zero oxidation state. The matrix may be formed as a continuous form of aggregates or particles of a metallic material, which may be in a crystalline phase. The aggregates or particles may be associated to each other via physical and/or chemical bonds, such as electrostatic and/or Van der Waals forces, forming a porous matrix characterized by pores and inner voids.

Typically, the zero oxidation state metallic matrix may additionally be characterized by a plurality of inner pores (inner voids, holes), which may be randomly distributed within the matrix. The pores may be nanometric in size, namely having a mean diameter smaller than 1 ,000 nm. In some embodiments, the mean pore diameter is between about 10 nm and 500 nm. In further embodiments, the mean pore diameter is between about 10 nm and 100 nm. In other embodiments, the mean pore diameter is between about 20 nm and 50 nm.

There may be several parameters affecting or determining the pores size, such as the size of the entrapped material, the quantity of entrapped material within a pore, molecular weight of the entrapped material, conditions of production e.g., temperature may affect the density and arrangement of the matrix particles/aggregate within the composite.

In some embodiments, an organic material is said to be entrapped in the metal if the organic material is surrounded by metallic particles and immobilized to the metal by forces other than covalent bonding; for example, the force holding the two components together may be selected from multiple physical and chemical adsorptive interactions such as electrostatic and Van-der-Waals, π-π and/or σ-π interactions, charge-transfer interactions and hydrophobic or hydrophilic interactions.

As stated, substantially all of the metal within the matrix is in zero oxidation state. In other embodiments, the composite of this aspect of the invention is substantially free of a metal in a non-zero oxidation state.

The expression "substantially free of metal in a non-zero oxidation state" refers to a composite in which the metal cation content is less than 5%, less than 4%, less than 3%, less than 2%, less than 1%, or less than 0.5% of the metal content in the composite of the invention. Similarly, the expression "substantially metal at a zero oxidation state" refers to the composite in which the metal is all or nearly all in zero oxidation state, e.g., between 95% and 100% of the metal content in the matrix is in a zero oxidation state; or between 96 and 100%; or between 97 and 100% or between 98 and 100%; or between 99 and 100% or between 99.5 and 100%. Wherein substantially all the metal within the matrix is in zero oxidation state, the metal may be selected from any metal of the Periodic Table. In such embodiments, the metal is selected from Sc, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Y, Zr, Nb, Tc, Ru, Mo, Rh, W, Au, Pt, Pd, Ag, Mn, Co, Cd, Hf, Ta, Re, Os, Ir, Hg, Al, Ga, In, Sn, Tl, Pb, Bi, Ge, Sn or any combination thereof.

In some embodiments, the metal is Sc, and/or Ti, and/or V, and/or Cr, and/or Mn, and/or Fe, and/or Ni, and/or Cu, and/or Zn, and/or Y, and/or Zr, and/or Nb, and/or Tc, and/or Ru, and/or Mo, and/or Rh, and/or W, and/or Au, and/or Pt, and/or Pd, and/or Ag, and/or Mn, and/or Co, and/or Cd, and/or Hf, and/or Ta, and/or Re, and/or Os, and/or Ir, and/or Hg, and/or Al, and/or Ga, and/or In, and/or Sn, and/or Tl, and/or Pb, and/or Bi, and/or Ge, and/or Sn.

In some embodiments, the metal is selected from Fe, Al, Ga, Ge, Ni, Cr, Mn, Ti, Zn and Pd, or any combination thereof. In further embodiments, the metal is selected from Fe, Al, Ga, Ge, Ni, Cr, Mn, Ti and Zn or any combination thereof. In additional embodiments, the metal is selected from Fe, Al, Ga, Ge, Ni, Cr and Mn, or any combination thereof. In further embodiments, the metal is selected from Fe, Al, Ni and Cr. In still additional embodiments, the metal is Fe.

In some embodiments, the matrix of the invention comprises two or more metals. The two or more metals may be in the form of a mixture of said metals or metallic alloys, said alloy may be in the form of a partial (two or more phases that may be homogeneous and/or heterogeneous in distribution) or a complete blend of one or more elements in the metallic matrix (exhibiting a single solid phase microstructure).

Wherein substantially all the metal within the matrix is in zero oxidation state, the organic material entrapped within a matrix comprising at least one metal, may be any organic material which endows the metal with added characteristics or for which the metallic matrix acts as a carrier. The organic material may be small, medium or large organic molecule, it may be a mixture, a complex, a conjugate, a bundle or any other form of compounds or combinations thereof.

In some embodiments, the organic molecule is selected from reducing agents or molecules that affect the redox potential of the corrodible metal. In some other embodiments, the organic material may be selected from hydrophobic organic molecules. In some embodiments, the organic material is selected from organic acids, such as oxalic acid and formic acid; phenolic oxidation inhibitors, such as 2,6-di-tert-butyl paracresol (BHT); hydrides such as Hantzsch ester and polysilanes.

In other embodiments, the organic material is selected from conducting polymers which may short-circuit metal defects of different electric potentials. In some other embodiments, the conductive polymer is polyaniline (PANI).

In some embodiments, the organic material is selected from dyes, such as congo red (CR), Safranin-0 (SaO), yhionine (Th) and sudan III (S-III).

In some embodiments, the organic material is l-butyl-3-methylmidiazolium nitrate.

In some embodiments, the organic material is selected from hydrophobic organic molecules, which may enhance the hydrophobicity of the corrosivable metal. Non-limiting examples of hydrophobic organic molecules include poly(dimethylsiloxane) (PDMS), poly(acrylonitrile) (PAN), polyethylene, polypropylene, polycarbosilanes and fluorinated polyalkenes.

In some embodiments, the organic material is selected from polysterene (PS), polystyrene sulfonic acid (PSSA), poly (vinyl alcohol) (PVA) and poly(vinylbenzyltrimethylamonium hydroxide) .

Typically, the ratio of the entrapped organic material in the metal is less than 20% w/w. In some embodiments, the ratio is less than 10%. In other embodiments, the ratio is between 0.05% to 20% w/w. In some other embodiments, the ratio is between 0.1% to 15% w/w.

In some embodiments, the composite of the invention comprises iron and PANI. In some embodiments, the composite of the invention comprises iron and polydimethylsiloxane (PDMS). In some embodiments, the iron is metallic iron.

In another aspect of the invention, there is provided a process for the manufacture (or production) of a metallic composite, the process comprising:

-forming a mixture of a metal source and at least one organic material, e.g., in at least one solvent, in which both said metal source and at least one organic material are soluble;

-treating said mixture of the metal source and said at least one organic material under conditions selected from: (1) conditions permitting decomposition of the metal source; or

(2) condition permitting disproportionation of the metal source;

to thereby obtain a composite of a metal, e.g., at the zero oxidation state; and at least one organic material.

As may be understood from the disclosure herein, under the conditions of manufacture, the integrity of the at least one organic material is not affected.

In some embodiments, the mixture formed is a solution in said at least one solvent; the solvent being aqueous or non-aqueous (organic). In some embodiments, the solvent is a non-aqueous solvent. In some embodiments, the non-aqueous solvent may be selected from methanol, propanol, acetone, acetonitrile, chloroform, dimethyl sulfoxide, ethyl acetate, hexane, tetrahydrofuran, toluene and xylene. In some embodiments, the non-aqueous solvent is xylene. In some embodiments, the at least one solvent is a mixture of two or more different solvents.

In some embodiments, the process for manufacturing a composite of the invention (whether that which comprises a corrodible metal or a metal at a zero oxidation state) comprises:

-providing at least one metal source, said metal source being selected from:

(i) a metallic complex, wherein the metal in the complex is at the zero oxidation state; and

(ii) a metallic salt, e.g., capable of disproportionation upon heating; -mixing the metal source with at least one organic material to be entrapped in a metallic mixture;

-treating the mixture under conditions selected from thermolysis, photolysis, ultrasonic treatment and microwave treatment, e.g., thermolysis conditions.

In some embodiments, the process comprises:

-providing at least one metal complex, wherein the metal in the complex is at the zero oxidation state;

-mixing the metal complex with at least one organic material to be entrapped in a metallic mixture, under conditions such as those disclosed above, e.g., thermolysis conditions. In such embodiments, the metal in said metallic matrix is substantially at zero oxidation state; the composite being free of the metal in non-zero oxidation state.

In some further embodiments, the process comprises:

-providing at least one metal salt, e.g., capable of disproportionation upon heating;

-mixing the metal salt with at least one organic material to be entrapped in a metallic mixture to be formed under conditions descried above, e.g., thermolysis conditions.

In some embodiments, conditions for obtaining a composite according to the invention include thermal treatment under an elevated temperature. Typically, the conditions involve thermal treatment at a temperature of between 30°C and 500°C .In some embodiments, the temperature is in the range of 40°C and 300°C. In other embodiments, the temperature is in the range of 50°C and 150°C.

In some other embodiments, the temperature is above 100°C or above 150°C.

The different reaction steps of the invention may be carried out under stirring and for a period which may range from minutes to several hours.

As stated above, the metal source may be one of:

(i) a metal complex wherein the metal is in a zero oxidation state; or

(ii) a metal salt which provides the zero oxidation state metal by disproportionation of the cation with its ligands.

The metal source may be of any of the metals disclosed hereinabove. In some embodiments, the metal source is a source of a corrodible metal, such as Fe, Al, Ga, Ge, Ni, Cr, Mn, Ti, Zn and Pd. In some embodiments, said metal is selected from Fe, Al, Ga, Ge, Ni, Cr, Mn, Ti and Zn. In other embodiments, the metal is selected from Fe, Al, Ga, Ge, Ni, Cr and Mn. In further embodiments, the metal is selected from Fe, Al, Ni and Cr, or from Fe, Al and Cr. In other embodiments, the metal is Fe.

The term "metal complex" encompasses compounds having at least one metal species at any form or oxidation state, bonded to non-metallic species (ligands), typically through coordinative bond. In some embodiments, the non-metallic species is organic. In other embodiments, the metal species is bonded to the carbon atom(s) in the non-metal species. In further embodiments, the organic species may be selected from one or more of the following ligands carbonyl, phenyl, alkyl, keton, alkoxide, etc, and any combination thereof. In some embodiments, the metal complex is selected from triirondodecacarbonyl, diironnonacarbonyl, bis(acetylcyclopentadienyl)iron, bis(methylcyclopentadienyl)iron, bis(l ,5-cyclooctadiene)nickel(0), tetrakis(triphenyl phosphite)nickel(O), bis(triphenylphosphine)nickel(0)dicarbonyl, chromium(O) hexacarbonyl, bis(benzene)chromium(0), tricarbonyl(cycloheptatriene) chromium(O), tricarbonyl(naphthalene)chromium(0), tricarbonyl(N-methylaniline) chromium(O) and manganese(0)carbonyl.

In other embodiments, the metal source is selected from iron pentacarbonyl (Fe(CO)s), Fe(C ₅ H ₅ ) ₂ , Fe ₂ (CO)4(C ₅ H ₅ )2, Ni(CO) ₄ , NiCl ₂ (PPh ₃ ) ₂ , Ni(cod) ₂ Co ₂ (CO) ₈ , Mn ₂ (CO)io, Cr(CO) ₆ , Cr(CO) ₄ (PPh ₃ ) ₂ and Cr(C ₆ H ₆ ) ₂ .

In some embodiments, the metal source is selected from Fe(CO)s, Fe(CsH5) ₂ and Fe ₂ (CO) ₄ (C ₅ H ₅ ) ₂ .

In some embodiments, the metal complex is iron pentacarbonyl (Fe(CO)s).

In some embodiments, where the composite comprises a metallic matrix of two metals, the process involves the thermolysis of two or more metal sources; e.g., may be a metal complex and the other a metal salt, or both may be metal complexes or metal salts.

The ratio of the metal source, e.g., metal complex, to the organic material in a reaction mixture may a ratio determined by the final intended use of the composite. In some embodiments, the ratio of the metal source to the organic material is in the range of 1000:1 to 1 : 1. In some embodiments, the ratio is in the range of 100: 1 to 1 : 1. In other embodiments, the ratio is in the range of 10:1 to 1 :1.

Wherein the metal source is a metal salt, the process comprises reducing a cation of the metal in the presence of the organic material. In some embodiments, the reduction process is arrested after at least 50% of the material is entrapped. Optionally, the reduction is carried out under such conditions that leave most of the salt reduced. In some embodiments, only 10% or less of the salt is reduced. In other embodiments, 1% or less of the salt is reduced.

In another aspect of the invention, there is provided a composite manufactured according to a process of the invention. The composites of the invention may be processed to provide different composite form, which may range up to several centimeters in diameter. None-limiting examples of such processing comprises compressing, annealing, sintering, or any combination thereof.

In some embodiments, where the composite is in the form of particles, the particles are pressed and may be accompanied with heating to form disks. The pressed disks may be in various sizes, e.g., having thickness of several millimeters.

The composite of the invention may used in a variety of industrial applications, as the composites exhibit high resistance to corrosion. Therefore, in another aspect, the invention provides a composite for use in the manufacture of products (articles, devices, parts, elements) for industrial use. The composite of the invention may be used in an industry where metallic elements are employed. In some embodiments, the industry may be the iron industry, for the production of e.g., construction or infrastructure elements, transportation, e.g., car parts, aerospace parts and plains, utilities, production facilities and home applications.

In a further aspect, the invention provides an article comprising a composite of the invention. The article may be a structural member that includes a metal member produced with a composite of the invention or a composite manufactured according to a process of the invention. The structural member not only has excellent fatigue properties, but also exhibits improved corrosion resistance as compared with the metal.

In some embodiments, the composite may be used in medicine, e.g., implants, dentistry devices etc.

Thus, as disclosed herein, the present invention provides means for the inhibition of corrosion of various metals. The inhibition is achieved by doping the metal with redox-altering molecules; with reducing agents; with agents that affect the oxidation of the metal; or with agents that short-circuit metal defects of different electric potential. A great variety of organic materials, such as small organic molecules or polymers, may be used to enhance the metal stability to oxidative corrosion. Modified- metal powders for high-pressure articles production ("greens"), and modified-metal powders used for thin film protective coatings, are material products of this methodology. While the iron may be the industrially most important corrodible metal, oxidation inhibition has also been observed in other metals as well. As demonstrated herein, the temperature of onset of oxidation of Co, due to doping with citric acid, and other reducing agents, was elevated by ~110°C (!) as compared to pure Co, and the weight increase due to oxidation dropped from -15% to only a few percent.

A remarkable observation detailed below is that iron doped with polydimethylsiloxane (PDMS), was not corroded in simulated sea water for two weeks; iron without this dopant disintegrated to brownish rust pieces.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Figs. 1A-D present SEM images of the pristine Fe matrix (Fig. 1A); PANI@Fe (Fig. IB); PAN@Fe (Fig. 1C); and PDMS@Fe (Fig. ID).

Fig. 2 presents XRD patterns of the powders PAN@Fe, Fe, PANI@Fe, PDMS@Fe, all produced at 100°C. The bottom pattern is the pattern for PANI@Fe produced at a lower temperature of 60°C.

Figs. 3A-C present conducting tip AFM images of a PDMS@Fe disk showing the surface morphology (Fig. 3A) and the conduction areas (Fig. 3B). A higher magnification of the marked part in Fig. 3B is shown in Fig. 3C, revealing non-uniform conduction regions.

Figs. 4A-B present curves of weight changes during thermogravimetric analysis (Fig. 4A) and its first derivative (Fig. 4B) for Fe powders: pristine Fe produced in the entrapment condition, PANI@Fe, PAN@Fe, and PDMS@Fe.

Figs. 5A-B are photos of Fe and PANI@Fe disks after 2 h of immersion in 1M NaCl. The photos demonstrate corrosion inhibition.

Figs. 6A-D are microscope images of 10mm diameter disks after 72 hours of immersion in 1M NaCl: Fe matrix (Fig. 6A); PAN@Fe (Fig. 6B); PANI@Fe (Fig. 6C); and PDMS@Fe (Fig. 6D). Figs. 7A-D present XRD patterns taken of the disk surfaces after immersion in 1M NaCl for 3 weeks: Fe matrix (Fig. 7A); PAN@Fe (Fig. 7B); PANI@Fe (Fig. 7C); and PDMS@Fe (Fig. 7D).

Figs. 8A-D are SEM images of inner sections of the disks of: Fe made under the entrapment conditions (Fig. 8A), PANI@Fe (Fig. 8B), PAN@Fe (Fig. 8C) and PDMS@Fe (Fig. 8D).

Fig. 9 presents curve of weight gain of disks during immersion in 1M NaCl.

Figs. 10A-B present XPS spectra for the Fe 2p electrons of the disks of Fe (Fig. 10A) and PDMS@Fe (Fig. 10B) after 3 weeks of immersion.

DETAILED DESCRIPTION OF EMBODIMENTS

Iron, the prime candidate for corrosion studies posed a challenge, because Fe ⁺³ is not easily reduced, and harsh reducing conditions would most probably affect the dopant as well. Thus, for doping of metals such as iron, a new approach has been developed. The approach involve thermolysis of metal complexes such as Fe(CO)s, in which Fe is at oxidation state of zero. In particular, it was found that this thermolysis was succesful for entrapment of various polymers, such as polyaniline (PANI), poly(dimethylsiloxane) (PDMS) and poly(acrylonitrile) (PAN), within a metal, e.g., iron. Following a thorough characterization of the new materials, it was observed that the polymers affect the oxidation and corrosion rate of the metal, with PDMS@Fe being by far the best alloy from that point of view.

The present invention is thus based on the realization that it is possible to entrap organic materials in metals, by employing a process that provides the metal zero oxidation state. This was achieved by either having the desired metal in a zero oxidation state in the complex, or by having the desired metal in a complex which provides the metal at zero oxidation state by a thermal disproportionation reaction of the cation with it ligands, in the presence of the organic material to be entrapped.

This approach is applicable to iron, aluminum, titanium, gallium, germanium, zinc, nickel, chromium, cobalt, manganese, and also to metal-cations of highly positive reduction potentials such as palladium, platinum and rohdium. 1. Results

Characterization of the polymer@Fe composite:

Iron penta-carbonyl decomposes easily through a range of intermediate iron carbonyls, forming magnetic iron clusters. When this thermolysis is carried out at 100°C, in solution in the presence of a dissolved polymer, a composite powdered material, polymer@iron, forms.

TGA indicates that under the experimental conditions described below, the composites contain 1.5% of PANI, 2% of PAN and 7% by weight of PDMS. The microscopic morphology of these materials is shown in Fig. 1A. It can be seen that pure Fe aggregates from small particles -20 nm in size, to form large spherical clusters of 200-500 nm in size. In the composites, the added polymer reduces these dimensions significantly. For example, in the case of PDMS@Fe (Fig. ID) the aggregates are as small as 20-30 nm and they are formed by even smaller particles with a diameter lower than 5 nm. This effect is attributed to the surfactant-like interaction between the polymer and the metallic nanocrystal, an effect which has been observed in other metal- entrapment studies.

That the elementary particles are very small is evident from the XRD patterns of the powders (Fig. 2) as well. It can be seen that all of the powders are almost amorphous with a small peak around 44.7°, which corresponds to iron in the BCC structure. As a reference the reaction conditions were changed to 60°C in order to create larger particles to confirm that the material is iron in its BCC structure (Fig. 2, lower graph). Using Scherer's equation, the particle size of the lower trace was found to be 8 nm, and obviously the particle sizes of the other composites are much smaller (not larger than 2 nm). This observation reveals that even the small aggregates seen in the SEM pictures are not the elementary particles, but that they are formed from smaller building blocks.

The PDMS@Fe composite powders were pressed to form disks which were examined by conductive atomic force microscopy (AFM). Figs. 3 A and 3B show, respectively, the morphology and the conductivity of a typical point on the surface. It can be seen that while the surface is quite flat, the conductivity map indicates that it is formed of aggregates of iron that encapsulate the polymer within. Fig. 3C shows a large magnification of the marked part of Fig. 3B and it reveals that the aggregates themselves are not uniform in nature and that there are conductive and non-conductive parts within the aggregates, with iron particles as small as 5 nm that entrap polymer between them. This observation reveals for the first time polymer entrapment within metals on scales smaller than 100 nm, and it implies that the obtained composite is a genuine blend between the metal and the polymer.

Air-oxidation of the polymers @ iron:

Exposure of iron to air at elevated temperature (more than 200°C) usually increases the mass due oxygenation into iron oxides. TGA of pure iron in air indeed shows this significant weight increase (Fig. 4A, as indicated in the graph). A similar, although smaller, weight increase was seen for PANI@Fe and PAN@Fe (Fig. 4A, as indicated in the graph). This smaller weight increase is mainly due to the oxidative decomposition of the polymer, but probably also to some extent by the mild oxidative protection seen in the derivatives Fig. 4B; Both polymers shift the oxidation peak to higher temperature by several tens of degrees. However, a completely different behavior is seen in the case of PDMS@Fe: no weight increase was observed at all; and furthermore, the degradation of the organic part of PDMS was clearly seen from 400°C and on.

Corrosion inhibition of the doped iron:

The composite disks were immersed in 1M NaCl solution and the corrosion development was determined. Expectedly, the NaCl solution accelerates iron corrosion by cathodic oxygen reduction and anodic metal dissolution followed by the formation iron oxide. After 2 h of immersion extensive bubbling was observed in the Fe disk while no bubbles were observed in the doped disks (Fig. 5). The appearance of bubbles instantly upon immersion of the Fe disc indicated the availability of a large number of active sites on the iron surface which are shielded in the doped disked. This was a direct indication of the onset of corrosion on the surface of the Fe disk and of its inhibition in the PANI@Fe disk. The same results were obtained with the other composites. A closer look under a microscope at the surface of the disks after 72 h of immersion in the salt solution reveals that while Fe was corroded extensively (Fig. 6A), PAN@Fe and PANI@Fe were corroded mildly (Figs. 6B and 6C, respectively), and PDMS@Fe (Fig. 6D) was hardly corroded at all: the original polishing marks on the surface could still be clearly seen. This behavior was observed even after 3 weeks of immersion.

After immersion for 3 weeks in the salt solution the surfaces of the disks were analyzed by XRD to detect the formation of oxide layers. Figs. 7A-C show that the surfaces of Fe, PANI@Fe and PAN@Fe are composed of the Fe ₃ 0 ₄ oxide (Figs. 7A-C). In contrast, PDMS@Fe retained its amorphous structure as in the powder form (Fig. 2).

Next, the disks which were immersed for 3 weeks were sectioned and examined by SEM: The formation of porosity was clearly evident (Fig. 8). In the case of pure Fe, the porous structure was very pronounced (Fig. 8A), whereas for PAN@Fe (Fig. 8B) and PANI@Fe (Fig. 8C) a lower degree of porosity was apparent. Clearly, in the case of PDMS@Fe, almost no porosity was observed and the material was rather dense (Fig. 8D).

Perhaps the most striking evidence for the corrosion resistance of PDMS@Fe comes from weight-increase monitoring of the immersed disks, due to oxide formation (Fig. 9). It is clearly seen that the addition of PANI (and to some extent of PAN) inhibited the corrosion process (Fig. 9), and that, remarkably, the PDMS@Fe disk did not change its weight during all the immersion measurement and hardly any iron oxide particles could be seen in the solution. Some iron oxide brownish particles were released into the solution (except for the PDMS case); however, the resulting positive weight gain suggests that the oxidation process was much faster than the degradation related weight loss).

The observed phenomenon of corrosion inhibition is not completely understood. For PDMS being a very hydrophobic polymer, its presence in the composite adds protection in the aqueous solution.

2. Experimental details

Chemicals: Polyaniline (PANI, emeraldine base, w ~ 100 000), Fe(CO) ₅ (99.999% trace metals basis) and polydimethylsiloxane (PDMS, bis(3-aminopropyl) terminated, Mw ~ 27000) was from Aldrich. Polyacrylonitrile (PAN, Mw « 150 000) and was from Scientific Polymer Products, NY. Linear low density polyethylene was supplied by Carmel olefins. Entrapment ofPDMS within iron: To a hot stirred solution of 50 mL of xylene, 0.1 g of PDMS was added. The flask was connected to a Schlenk line and pumped for 15 min following by a flow of Ar for another 15 min. This procedure was repeated twice. Using a condenser the mixture was boiled to 100 °C and 3.5 ml of Fe(CO)s were added dropwise while stirring. The combined solution was heated and stirred for another 2 h. The precipitate was filtered and washed with two portions of 10 mL of cyclohexane and dried under vacuum for a few hours. Entrapment of PAN and PANI was carried out in a similar way.

Preparation of doped iron disc: For corrosion measurements thin discs of polymer@Fe were prepared by pressing 0.3 g of polymer@Fe granules and 0.03g linear low density polyethylene using a Carver hydraulic press, model 2518, at 140 °C with a pressure of 4.4 MPa for 15 min. Discs of approximately 0.3 mm thickness were obtained.

Instrumentation: XRD measurement were carried out with Philips automated powder diffractometer (with PW1830 generator, PW1710 control unit, PW1820 vertical goniometer, 40 KV, 35 mA, Cu KR (1.5405 A)). SEM was carried on a Sirion (FEI) HR-SEM instrument (operating voltage is indicated for each picture). Thermogravimetric thermal analysis (TGA) was performed on a Mettler TC10A/TC15 TA controller from 25 to 800°C at a heating rate of 10°C/min in flowing dry air or N ₂ . For a more exact analysis of the TGA graphs, the derivative weight loss was calculated usingthe supplied software. The XPS (X-ray photoelectron spectroscopy) measurements were performed on a Kratos Axis Ultra X-ray photoelectron spectrometer. Spectra were acquired with a monochromated Al KR (1486.7 eV) X-ray source with a 0° takeoff angle. The pressure in the test chamber was maintained at 1.5*10 ^~9 Torr during the acquisitionprocess. High-resolution XPS scans were collected for C Is, O Is, Si 2p and Fe 2p peaks with pass energy of 20 eV and a step size of 0.1 eV. Data analysis and processing were performed with Vision processing data reduction software (Kratos Analytical Ltd.) and CasaXPS (Casa Software Ltd.). Conductive tip atomic force microscopy images were taken by Scaning Probe Microscopy - Nanoscope Dimension 3100 using the supplied TUNA program.