MX2007000357A

MX2007000357A - A method for producing iron oxide nano particles.

Info

Publication number: MX2007000357A
Application number: MX2007000357A
Authority: MX
Inventors: Aharon Eval; Asher Vitner
Original assignee: Joma Chemical As
Priority date: 2004-06-27
Filing date: 2005-06-27
Publication date: 2008-03-13
Also published as: BRPI0511319A; EA200700135A1; WO2006001018A2; JP2008504202A; NO20070512L; EP1814825A2; WO2006001018A3; AU2005257059A1; KR20070044817A; CA2572190A1; WO2006001018B1

Abstract

The invention provides a method for the formation of small-size iron oxide particles comprising the steps of preparing a starting aqueous solution comprising at least one of ferric ions and complexes thereof, at a concentration of at least 0.1% w/w iron and a pH greater than about 1.5; maintaining said solution at a temperature lower than 55 degree C for a retention time in which hydrolysis takes place, the extent of said hydrolysis being sufficient to decrease the pH by at least 0.2 units, wherein said time does not exceed 14 days, to form a system containing a modified solution; and adjusting the conditions in said system by at least one of the steps of heating the modified solution to elevate the temperature thereof by at least 10 degree C; elevating the pH of the modified solution by at least 0.3 units; and diluting the modified solution by at least 20%; whereby there are formed particles, wherein the majority of the particles formed are between about 2nm and about 500nm in size.

Description

METHOD TO PRODUCE IRON OXIDE NANOPARTICLES DESCRIPTIVE MEMORY The present invention describes a method for producing iron oxide nanoparticles and more particularly, a method for producing iron oxide particles of desired particle size, particle size distribution and dominant shape in an industrially and economically useful manner. In the present invention, the term iron oxide means that it includes iron oxides of the formula FexOy (for example, Fe2O3 as a hematite and magnetite), iron hydroxides of the formula Fep (OH) qOr (for example, FeOOH, as a goetite and Akageneite) several forms of hydration of these and compositions where these are the main components, where x, y, p, q, r are integers. Recently iron oxide powders are widely used in the industry for various applications: magnetic data storage materials, catalysts, organic pigments and precursors for the synthesis of ferrite. To produce materials with advanced properties (such as nano-crystallinity, reduced particle size distribution, preparation of metastable phases, etc.) chemical techniques that include hydrothermal metallurgical synthesis, are widely used. In the case of hydrothermal metallurgical synthesis of ultra fine iron oxide powders, iron hydroxide, formed in neutral or alkaline solutions, is more frequently used as a precursor. The preparation of iron oxide (III) from homogenous acid solutions at elevated temperatures has been perceived less studied. Iron oxides come in a variety of size, color, density, porosity, surface area and shape. These parameters have a great impact on their uses and performances. The properties of the final product depend on procedures developed for the precipitation and maturation of the products. Iron oxide nanoparticles exhibit color variation from amapllo to brownish yellow (limonite and geotite), light red to deep red (hematite), orange (lepidocrotite) and coffee (akaganeite). The color of each iron oxide depends on the particle size, particle size distribution and dominant shape. For example, hematite particles have different colors that vary from light red to deep red. Hematite particles that have a large particle size tend to exhibit a deeper hue. For example, granular hematite particles having an average particle diameter of not more than 200 nm (nanometers), for example 50-200 nm, which exhibits a light red color, while those having an average particle diameter of 400-600 nm exhibit a deep red color. Numerous patents address the issues of producing iron oxide particles of defined size, size distribution and dominant shape. For example, in USP 6391450 (2002) a method for producing needle-shaped goetite particles and needle-shaped hematite particles, containing selected amounts of cobalt and aluminum having a uniform particle size, a diameter, is described. of smaller major axis, and a suitable aspect ratio and are very excellent in the sintering that prevents performance, and for alloy particles based on magnetic iron in the form of a needle that are obtained from particles of hematite in the form of a needle . The patent of E.U.A. 5652192 relating the catalyst materials and production methods thereof, herein described and claimed a method and apparatus for making nano-sized particles, such as iron oxide, titanium oxide, nickel oxide, zirconium oxide, aluminum and silica oxide by the continuous fluid of a solution through a hot container, and which forms particles inside the hot container by pressurizing and heating said fluid solution to initiate chemical reactions, followed by tempering said fluid solution and stopping the growth of the solid particles. Said patents prevent the production rates of ten grams of particles per hour to about several kilograms of particles per hour, but do not show or provide an industrial process capable of producing at least several ten kilograms of particles per hour. Numerous studies deal with the heat transformation of iron oxide particles of high hydration level to iron oxide particles of low hydration level. The result of this transformation is the production of high porosity particles with a dominant crystal shape and similar size to the mother particles. The present invention deals with the production of iron oxide particles that can be used as is, but also of higher qualities that concern their behavior in the transformation reaction. An object of the present invention is to provide a process that is economically and industrially feasible to produce iron oxide particles of desired particle size, size distribution and dominant shape. The particles produced in this way are easy to transform by heating in another type of iron oxide particles of low hydration level in this way particles with high porosity and of type, morphology, crystal size, size distribution of crystal and dominant shape required. To accomplish this purpose, a method is provided here for producing iron oxide particles in aqueous solution, which comprises maintaining an aqueous solution of ferrous salt at a temperature below 55 ° C, for a sufficient time to reduce the pH of the solution in at least 0.2 pH units due to hydrolysis. The resulting solution is then subjected to a change in the temperature and / or concentration of Fe (III) (dilution) and or the addition of a reagent in this way increases the pH of the solution. The preferred modification of said parameters is at a high speed. In a second aspect of the present invention, starting material for the production of other iron oxide particles is provided here by the heat transformation of the obtained particles. More specifically according to the present invention, a method for transforming iron oxide particles of small size is now provided, comprising the steps of: a) preparing a starting aqueous solution comprising ferric ions or their complexes, in a concentration of at least 0.1% w / w iron and a pH higher than about 1.5. b) maintaining said solution at a temperature below 55 ° C for a retention time in which the hydrolysis takes place, the extension of the hydrolysis which is sufficient to lower the pH by at least 0.2 units, wherein said time does not exceed 14 days, to form a system containing a modified solution and c) adjust the conditions of the system in at least one of the stages of: i) heating the modified solution to raise its temperature by at least 10 ° C, ii) pH elevation of the modified solution by at least 0.3 units; and iii) diluting the modified solution by at least 20% whereby particles are formed, where most of the particles formed are between about 2 nm and about 500 nm in size. In preferred embodiments of the present invention said solution is maintained under modified conditions for at least 0.5 minutes. Preferably said modification of conditions is carried out over a period of up to 1 hour. In preferred embodiments of the present invention, said process produces at least 50 kilograms of particles per hour. Preferably said modification of conditions is carried out at a pressure of up to 100 atmospheres. In preferred embodiments of the present invention said method is further characterized in that most of the particles formed have a degree of crystallinity of less than 50%. Preferably said method is further characterized in that the size ratio between the smallest particle and the largest of 50% of the particles formed is less than about 10. In especially preferred embodiments said method is further characterized in that the size ratio Between the smallest particle and the largest particle of 50% of the particles formed is less than about 5. Preferably said method is further characterized in that most of the particles formed are of a different configuration from the elongated one. In preferred embodiments of the present invention said method is further characterized in that the majority of the particles formed have a configuration wherein the ratio between one dimension and any other dimension is less than about 3.

In other preferred embodiments of the present invention most of the particular ones formed are of an elongated configuration. Preferably most of the particles formed have a surface area of at least 30 m2 / g. Preferably most of the particles formed have a surface area of at least 100 m2 / g. In especially preferred embodiments of the present invention said method further comprises the step of: (iv) dehydrating the particles formed at a dehydration temperature on a scale of about 60 ° C and about 800 ° C to form dehydrated particles. In said preferred embodiments, said method further comprises preferably the step of removing the water in said particle suspension after facilitating and before, simultaneously with or after said dehydration. In preferred embodiments said dehydration is preferably conducted under super-atmospheric pressure. In said preferred embodiments the temperature of the particle suspension is preferably elevated to said dehydration temperature over a period of up to 2 hours. In such especially preferred embodiments, most dehydrated particles are preferably of a different configuration from the elongated one.

In such especially preferred embodiments, most dehydrated particles preferably have a surface area of at least 30 m2 / g. Preferably said particles are selected from the group consisting of hematite and magnetite goethite. Especially preferred are particles having the FeOOH formula. Also preferred are particles having the formula Fe203-3H20. In preferred embodiments of the present invention said preparation of an aqueous solution involves oxidation. Preferably the pH of the aqueous solution is between about 1.0 and about 5 during at least a fraction of the facilitation stage. Especially preferred is a method wherein the pH of the aqueous solution is between about 1.5 and about 4 during at least a fraction of said facilitation step. More preferred is a method wherein the pH of the aqueous solution is between about 1.7 and about 2.5 during at least a fraction of the facilitation stage. In preferred embodiments of the present invention the preparation of an aqueous solution involves the oxidation of ferrous ions. Preferably the oxidation uses an oxidant selected from a group consisting of oxygen, hydrogen peroxide, nitric acid and nitrate.

Preferably said oxidation is conducted in a solution comprising sulfuric acid and nitric acid. In preferred embodiments said oxidation is conducted at a pH of less than about 5. Preferably the oxidation is chemically or biologically catalyzed. In preferred embodiments of the present invention the preparation of an aqueous solution involves the dissolution of an iron compound. In preferred embodiments, the iron compound is preferably selected from the group consisting of iron salts, iron oxides, iron dioxides, iron ores and combinations thereof. Preferably the iron compound is selected from the group consisting of iron oxides, iron hydroxides, minerals containing the same and mixtures thereof and the compound is dissolved in an acid solution comprising an acid selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, its acid salts and combinations thereof. In preferred embodiments of the present invention the aqueous solution prepared comprises an anion selected from the group consisting of sulfate, chloride, nitrate, phosphate and mixtures thereof. In preferred embodiments of the present invention the modification comprises at least two heating steps.

In said preferred modification step at least one heating step is preferably conducted by contacting a preventative stream selected from the group consisting of hot aqueous solutions, hot gases and steam. In preferred embodiments, the method preferably additionally comprises particles formed by grinding. In preferred embodiments, the method preferably further comprises particles formed by screening. In preferred embodiments, the method preferably further comprises particles formed by hydrogenation. The present invention is also directed to iron oxide particles each time they are formed according to the methods defined above and products of their conversion. The present invention is further directed to a preparation comprising the particles. In preferred embodiments of the preparation the particles are preferably dispersed in a liquid, supported in a solid compound or agglomerated to longer particles. In another aspect of the present invention, there is provided here a process for the production of a preparation as defined above comprising the steps selected from the group consisting of the dispersion of said particles, the addition of a support, heat treatment, mixing, evaporation of water and its combinations.

In especially preferred embodiments of the present invention the particles and preparations are used in the manufacture of a paint. In other preferred embodiments of the present invention the particles and preparations are used in the manufacture of a catalyst. In another preferred embodiment of the present invention, there is now provided a method for the formulation of small iron oxide particles, comprising the steps of: a) preparing a starting aqueous solution comprising at least one of the Ferric ions and their complexes, in a concentration of at least 0.1% w / w iron, whose solution has a pH of at least 1.2; b) the preparation of an aqueous solution for modification of a temperature higher than 80 ° C; c) contacting the starting solution with the modification solution in a continuous manner in a mixing chamber to form a modified system, d) removing the modified solution from the mixing chamber in a manner of expense type piston, and the method is characterized in that: (i) the residence time in a mixing chamber is less than about 1 minute, (ii) here are formed particles or their aggregates, wherein most of the particles formed are between about 2 nm and about 500 nm in size; and (ii) the particles formed comprise FeOOH, Fe203, Fe (OH) 3, Fe3O or their combination. In particularly preferred embodiments of the present invention the modified solution remains in a mixing chamber for at least 5 seconds and in a more preferred embodiment the modified solution remains in the mixing chamber for at least 1 second. In preferred embodiments of the present invention, mixing in the mixing chamber is carried out using the flow velocity of the incoming solution or by using a mechanical manner of mixing or other manner of mixing. In preferred embodiments of the present invention the modified solution leaves the mixing chamber in a piston-type manner of expenditure. In a more preferred embodiment the piston-type expense continues for more than OJ seconds and in a more preferred mode the piston-type expense continues for more than 5 seconds. In preferred embodiments of the present invention, the solution emerging from the piston-type expense enters a container. In a more preferred embodiment of the present invention the solution in the container is mixed. The present invention is now deciphered in detail later. First, the process for producing iron oxide particles according to the present invention is described. The aqueous starting iron salt solution used in the present invention is preferably an aqueous solution of iron salt comprising ferric ions or their complexes in a concentration of at least OJ% w / w iron and a higher pH of about 1.5. According to a preferred embodiment, the w / w concentration of iron in the starting solution is at least 1%, more preferably at least 5%, more preferably at least 10%. There is no upper limit for the concentration of the starting solution. Still, according to a preferred embodiment, the concentration is below the saturation level. A high viscosity is not desired according to another preferred embodiment. According to a preferred embodiment, the pH of the starting solution is at least 1.7, preferably at least 1.9. According to a particularly preferred embodiment, the pH of the starting solution prepared is acidic or neutral, for example, as determined by the OH / Fe ratio in the solution.

According to a preferred embodiment, the ratio is smaller than 3, more preferably smaller than 2.5. According to a preferred embodiment, the temperature of the prepared start solution is lower than 55 ° C. Any source of iron is suitable for the preparation of the starting solution of the present invention which includes various pieces of iron such as cut iron pieces or the like, the iron that contains mineral, fractions of said minerals, products of its processing, salts of iron or iron that contains solutions such as aqueous solution that leaves the iron that contains minerals. According to a preferred embodiment, step (b) is conducted shortly after both the desired concentration and pH are performed. According to another preferred embodiment, the solution used in step b) is prepared within a short time and does not contain ferric ions or their complexes, which are prepared at different times and then mixed together. For a similar reason, the extended preparation time is not desired. According to a preferred embodiment, the preparation time is shorter than 20 hours, preferably shorter than 10 hours, more preferably shorter than 2 hours. In cases where there is an older solution (for example, a recycled solution) and you want to mix it with a fresh solution to form the starting solution, the oldest solution is first treated with acid, as described later. The freshly prepared ferric salt solution may contain any anion, including chloride, sulfate, nitrate phosphate, carboxylate, organic acid anions, and various mixtures thereof, etc. According to a preferred embodiment, the freshly prepared solution comprises ferric sulfate. According to another preferred embodiment, the salt is an organic acid. A freshly prepared salt solution for use in the process of the present invention can be a solution that is produced (under natural conditions, such as solutions coming out of mines with iron containing minerals) or a solution that is prepared by artificial methods that they include chemical or biological oxidations. Said solution could be prepared by several methods or their combinations, which include the dissolution of ferric salts, the dissolution of ferrous salts, the dissolution of double salts, the dissolution of minerals containing iron oxide in an acid solution, the dissolution of pieces of iron in oxidized solutions, such as solutions of ferric salt, nitric acid, the leaching of iron-containing minerals, such as pyrite and chalcopyrite, etc. The preparation of the aqueous solution is conducted in a simple step, according to a preferred embodiment. According to an alternative embodiment, the preparation comprises two or more stages. According to one embodiment, a concentrated ferric salt solution is prepared, for example, by dissolving a salt in water or in an aqueous solution. While momentarily and / or locally, during the dissolution, the required pH and concentration of the starting solution are enriched, usually the pH of the concentrated solution formed after at least partial homogenization is lower than that desired for the solution of start. According to a preferred embodiment, said momentary enrichment of the desired conditions is not considered the preparation of the starting solution. The pH of the concentrated solution is then brought to the desired level by any suitable means, such as the removal of an acid, the addition and / or increase of the concentration of a basic compound, or a combination of these. The formation of the starting solution in this case is considered the adjustment of the pH to the selected scale, according to the preferred modality, and the pH of the starting solution is one obtained later in at least partial homogenization, according to to another preferred embodiment. According to yet another preferred embodiment, a concentrated solution is prepared and the pH is adjusted to a level that is a little less than desired. The start solution is then prepared by diluting the solution, which increases the pH to the desired level. Here again, the pH of the starting solution is one obtained after at least partial homogenization, according to a preferred embodiment. The same is true for other multi-stage preparation methods of the startup solution, as for example, in the case of the formation of a solution of a ferrous salt and the oxidation of it to form a solution of a ferric salt. In some cases of the present invention, the iron source for the solution may be a piece of iron or the like and / or iron (II) and an oxidation step must be performed in order to obtain the ferrous solution. Said oxidation can use any known oxidant, such as air, oxygen, hydrogen peroxide, nitric acid and nitrate and their combinations. Oxidation could be done at any temperature and pressure. Usually, the elevated temperature and the high pressure accelerate the oxidation reaction. A biological catalyst, a chemical catalyst or a combination could be used. Complete oxidation is not required and the particles of the invention could be formed from a solution containing both ferric and ferrous ions.

According to a preferred embodiment, the startup solution is freshly prepared. According to another preferred embodiment, the solution does not comprise ions and / or complexes prepared at different times, as in the case of mixing a recycled solution with a freshly prepared one. A lower pH of 1.5, high concentration (for example, close to 10% of iron) and low temperatures (for example, lower than 40 ° C), a solution maintains its freshness for a long time, and could serve as a mother solution , according to a preferred embodiment. In other conditions, the solution is not considered fresh after a few hours or a few days, according to another preferred embodiment. According to a preferred embodiment, the freshness of the solution is recovered by treatment with acid. Said less fresh solution is acidified at a lower pH of 2.0, preferably at a lower pH of 1.5 and is preferably mixed, stirred or shaken for at least 5 min, before increasing the pH back to 1.7 antepores to reform a fresh solution. Said fresh reformed solution is mixed with another fresh solution according to a preferred embodiment. In the next process step, the ferrous solution is preferably held at a temperature below 55 ° C for a retention time not exceeding 10 days. During the retention time, hydrolysis takes place. Preferably, the retention time is sufficient for the pH to decrease by at least 0.2 units due to said hydrolysis. According to another preferred embodiment, the retention time is the time needed to produce at least 1 H + millimolar (protons) in solution.

According to yet another preferred embodiment, the retention time is the time required to form in the solution 0.0001 mol of proton atoms per mole of Fe (lll) in the solution, more preferably 0.001 mole of proton ions per mole of Fe (lll) in the solution. In cases where a base or a base compound is added to the solution during the retention time, the retention time is the time that it could have been needed to form these amounts of protons without addition of base. According to a preferred embodiment, the retention time decreases with the pH increase of a prepared solution. Thus, for example, at a pH lower than 2.5, the retention time is preferably from 1 hour to a few days. At a pH between 2.5 and 5.0 the retention time is preferably less than 1 day. In cases of pH variation during the retention time, the latter is affected by the maximum enriched pH. Usually, the retention time decreases with the increase in the temperature of the solution. The third stage needed in order to perform the above manner of precipitation, is the modification of the conditions of the solution to perform at least one of an increase in pH and / or temperature and or dilution of the solution. The modification of the conditions is preferably done in a short time and the modified conditions are maintained for a short time. The duration in the modified conditions is less than 24 hours, according to an exemplary embodiment, preferably less than 4 hours, more preferably less than 1 hour, more preferably less than 10 minutes. In other preferred embodiments of the present invention, modification of the conditions is conducted within 1 hour, preferably within 10 minutes, more preferably 1 minute. The increase in pH in step (c) can be carried out by any known method, such as the removal of an acid or the addition of or increase in the concentration of a base compound. The removal of the acid can be conducted by known methods, such as extraction or distillation. Any basic compound can be added. According to a preferred embodiment, a basic compound is a compound that is more basic than ferric sulfate, as measured by the comparison of the pH of its equimolar solutions. In this waysaid basic compound is preferably at least one of an inorganic or organic base or precursor of a base, for example, an oxide, hydroxide, carbonate, bicarbonate, ammonia, urea, etc. According to another preferred embodiment, the basic compound is ferrous salt tai as ferrous sulfate. According to a preferred embodiment, the sulfate is formed in situ by the introduction of metallic iron. Said methods of increasing the pH are also suitable for use in step (a) of the preparation of the starting solution. According to a preferred embodiment, the basic pH is avoided by more than one method, so that the pH that increases in step (c) is conducted so that during more than the duration of this step, the pH It is acidic, or slightly acidic.

According to another preferred embodiment, the solution is diluted in step (c). According to a preferred embodiment, the dilution is at least 20%, more preferably at least 100%, more preferably at least 200%. According to another preferred embodiment, the temperature of the solution is increased. According to a preferred embodiment, the temperature is increased by at least 10 ° C, more preferably by at least 30 ° C more preferably by at least 50 ° C. The increased temperature can be affected by any method, such as contact with a hot surface, with hot liquid, with hot vapors, infra-red irradiation, microwaves or a combination of these. According to another preferred embodiment two of the three of the modifications are conducted sequentially or simultaneously. In this way, according to a preferred embodiment, the basic compound is added to the ferric salt solution after the retention time, in an aqueous solution, which also dilutes the ferric salt. According to another preferred embodiment, the ferric salt solution is contacted with a dilution solution comprising water and / or an aqueous solution, which is of a temperature higher than that of the solution of the ferric salt solution. at least 50 ° C according to a first preferred embodiment, preferably at least 100 ° C. According to an alternative embodiment, the temperature of the dilution solution is between about 100 ° C and 250 ° C, between 100 ° C and 180 ° C according to a preferred embodiment and between 150 ° C and 25 ° C, according to another preferred embodiment. According to another preferred embodiment, the dilution solution comprises a reagent that interacts with ferric ions, their complexes and / or particles containing these. According to yet another preferred embodiment, the ferric salt solution after the retention time is combined in step (c) with a second aqueous solution comprising a solute which is more basic than the ferric salt, the second solution of which is at a temperature higher than that of the ferric salt solution. According to a preferred embodiment, the ferric salt solution and said second solution is mixed, for example, mechanically, in a suitable equipment that provides for the strongest mixing to rapidly realize a homogeneous system. In cases where the temperature of at least one of these solutions is above the boiling point, the mixing equipment is preferably selected so as to resist super-atmospheric pressure. According to a preferred embodiment, mixing is conducted by contacting the ferrous salt solution flowing with the second flowing aqueous solution, for example in a piston-type manner of expenditure. Preferably, the mixed stream is maintained at the temperature formed or at another temperature obtained by cooling or heating for a short duration, less than 1 day according to an exemplary embodiment, preferably between 1 and 60 minutes, more preferably between 3 and 15 minutes. The degree of heating, the raising of the pH and the dilution, when conducted as a simple means for modification or in combination, affects the chemical nature of the particles formed. For example, usually, the higher the temperature, the lower the degree of hydration of the particle components. The crystalline form and the shape are also affected. In this way, the conditions selected for example 1, leave spherical particles. According to a preferred embodiment, the final product oxide is formed in step (c) of the process. According to another preferred embodiment, the product of step (c) is processed and further processed to the desired final product. In this way the ferric hydroxide in the particles is transformed, according to a preferred embodiment, to goethite or hematite. Said additional processing comprises heating, according to a preferred embodiment. Preferably the heating is at a temperature in the range of about 60 ° C to 800 ° C. According to a preferred modality, the heating is a solution comprising the particles formed as obtained in step (c), or after some treatment, for example, partial removal of water. According to another preferred embodiment, the particles formed are first separated from the solution. The separated particles could be treated as or after further treatment, for example, washing and / or drying. The heating in the solution is preferably done at a super-atmospheric pressure and in a suitable equipment for said pressure. According to a preferred embodiment, an external pressure is applied. The heating nature is also a control factor, so that the results of gradual heating are in some cases different from rapid heating. According to a preferred embodiment, step (c) and additional heating are conducted sequentially, preferably in the same vessel. The dominant crystal shape of the transformed particles is generally dominant in the particles of origin from which they are produced, according to a preferred embodiment. For example, rod-like goethite particles can be transformed into elongated hematite particles, or in another embodiment of the present invention, amorphous particles with low particle size ratio can be transformed into goethite of low particle size ratio. In another embodiment of the present invention, the agglomerates with dominant rod-like shape or agglomerates of spherical dominant shape can be transformed into particles of goatite or hematite with a rod-like dominant shape or agglomerates with a spherical dominant shape, respectively. As will be analyzed, the present invention provides conditions for the production of precipitates that are easy to transform as well as that provide a transformation product with superior properties. According to a preferred embodiment, at least one dispersant is present in at least one of the steps of the method. As used herein, the term "dispersant" means and includes dispersants, surfactants, polymers and Theological agents. In this manner, a dispersant is introduced into a solution in which a ferric salt is dissolved or is to be dissolved, or is added to a precursor of the solution, such as a metallic mineral, according to a preferred embodiment. According to another preferred embodiment, a dispersant is added to the solution during or after the retention time. According to an alternative embodiment, a dispersant is added to the solution before the adjustment step or after said step. According to yet another preferred embodiment, a dispersant is added before a transformation step, during said step or after it. According to another preferred embodiment, the method further comprises a step of modifying the concentration and / or the nature of the dispersant during the process and / or other dispersant is added. According to a preferred embodiment, suitable dispersants are compounds that have the ability to adsorb onto the surface of nanoparticles, and / or nuclei. Suitable dispersants include cationic polymers, anionic polymers, nonionic polymers, polyionic surfactants and mixtures thereof. In the present specification the term "dispersant" describes molecules capable of stabilizing dispersions of formed particles, and / or modifying mechanisms of nanoparticle formation, and / or modifying the structure, properties and size of any of the species formed. during the process of nanoparticle formation. According to a preferred embodiment, the dispersant is selected from the group consisting of polyadyl dimethyl ammonium chloride, sodium carboxymethyl cellulose, polyacrylic acid salts, polyethylene glycol, and commercial dispersants such as Solsperse grade, Efka grades, Disperbyk or Byk grades., Daxad degrees and Tamol grades (factory names). According to a preferred embodiment, the method further comprises an ultrasound step that treats the solution during or after at least one of the process steps. According to a preferred embodiment, the method further comprises a microwave stage that treats the solution during or after at least one of the process steps. According to another preferred embodiment, the additional processing comprises the reduction of iron oxide in the formed particles of Fe (III) or Fe (II) or to the metal iron. The reduction is partial according to a preferred modality and the termination of approximations according to another. Any reducing agent could be used, for example, hydrogen. According to a preferred embodiment, the reduction is conducted as a separate step, according to an alternative embodiment, the reduction is conducted as part of a process of converting the particles into a final product, such as a catalyst. According to a preferred embodiment, the additional processing comprises particles that partially fuse to larger particles. According to another preferred embodiment, the aggregates of the particles are mechanically treated for grinding. The product of the present invention is formed in step (c) or after further processing, preferably small particles of iron oxide. The particle size is on the scale between 2 nm and 500 nm, according to a preferred embodiment. According to another preferred embodiment, the particle size distribution of the product is reduced so that the size ratio between the smallest particle and the largest of 50% of the particles formed is less than about 10, more preferably less than 5, more preferably less than 3. The separated particles are formed according to a preferred embodiment. According to another embodiment, the particles formed are at least partially agglomerated. According to a preferred embodiment, the majority of the particles formed have a degree of crystallinity of less than 50% as determined by X-ray analysis. According to a preferred embodiment, the shape of the particles formed in the stage ( c) or after further processing, is elongated such as in needles, bars or rafts. According to another preferred embodiment, the particles are spherical or nearly spherical, so that most of the particles formed have a configuration in which the relationship between one dimension and any other dimension is less than about 3. According to a modality preferred, most of the particles formed have a surface area of at least 30 m2 / g, more preferably at least 100 m2 / g. The high surface area particles of the present invention are suitable for use in the preparation of the catalyst. The process of the present invention is capable of the formation of highly pure iron oxide from a precursor of relatively low purity, such as an iron ore, for example, pyrite or chalcopyrite. According to a preferred embodiment, the purity with respect to other metals is at least 95%, more preferably at least 99%. According to another preferred embodiment, the iron oxide particles are mixed with atoms or atoms of other transition metals. According to a preferred embodiment, the particles are obtained in a form selected from the group consisting of particles dispersed in a liquid, particles supported on a solid compound, particles agglomerated to larger particles, partially fused particles, coated particles, or their combinations . The particles, their preparation and / or products of their conversion are suitable for use in many industrial applications, such as in the production of pigments, catalysts, coatings, thermal coatings etc. The particles are used in these and other applications as such, according to a preferred embodiment, additionally processed, according to another, or formed as part of the preparation material for said application, according to still another preferred embodiment. Many of the procedures described in the literature are of the nature and size of the laboratory, for example, starting with the highly pure precursor, which works with highly diluted solution and / or at low volumes and / or speeds. The method of the present invention is highly suitable for economically attractive industrial scale production. According to a preferred embodiment, the method is operated at a speed of at least 50 kg / hour, more preferably at least 500 kg / hour, more preferably at least 5 tons / hour. According to a preferred embodiment, the pH of the solution falls during the process due to the hydrolysis of the ferric salt and thereby an acid is formed, for example, sulfuric acid. Said acid is reused according to a preferred embodiment, for example, for the formation of ferric salt solution, for example, in the dissolution of an iron-containing mineral. According to another preferred embodiment, the acid formed is partially or totally neutralized during the process, which forms with which an acid salt. According to a preferred embodiment, the salt is for industrial use, for example in the case where the neutralization is done with ammonia to form ammonium salts suitable for use as fertilizers. According to an alternative method, at least partially dehydrated iron oxide particles are formed. The method comprises the steps of preparing an aqueous starting solution comprising ferrous atoms or their complexes, in a concentration of at least 0.1% w / w iron, the solution having a pH of at least 1.2.; the preparation of an aqueous solution of modification of a temperature higher than 80 ° C; which contains the starting solution with the modification solution to form a modified system and which retains the modified system at a temperature greater than 80 ° C for at least 0.5 minutes. Most of the particles formed are between about 2 nm and about 500 nm in size and comprise FeOOH, Fe2O3, Fe3O or their combination. The preparation of the starting solution can use methods similar to those described above. According to a preferred embodiment, the concentration of iron in said starting solution is greater than 2%. According to a preferred embodiment, the pH of the starting solution is at least 1.5, more preferred of at least 1.7. According to an alternative modality, the molar ratio of OH / Fe in the starting solution is at least 0.05. According to a preferred embodiment, the temperature of the modification solution is on the scale between 100 ° C and 300 ° C. At least one of the starting solution and the modification solution comprises according to a preferred embodiment a reagent which is capable of interacting with ferric ions, their complexes or with particles containing them. According to a preferred embodiment said reagent are dispersants or basic compounds. Where used, the basic compound is preferably ammonia, ammonium carbonate, ammonium bicarbonate or urea. According to a preferred embodiment, the basic pH is avoided in the modified solution. Preferably, the molar ratio of OH / Fe in the solution of said modified system is less than 3, more preferably between 0.5 and 2. The temperature of the modified solution is determined by the temperatures of the starting solution and the modification solution. hot, for its heat capacity and its relative amounts. According to preferred embodiments, the temperature of the modified solution is maintained with minimal changes, for example without changes greater than 20 ° C. According to a preferred embodiment, the modified system is retained at this temperature for a duration of between 1 and 30 minutes, more preferably between 3 and 15 minutes. According to another preferred embodiment, the startup solution is maintained for a preliminary retention time before said contact with the modification solution. Preferably, during the preliminary retention time the solution is maintained at a temperature lower than 55 ° C and pH greater than 1.5. The duration of the preliminary retention time is sufficient for the pH to decrease by at least 0.2 units, but it does not exceed 14 days, according to a preferred embodiment. According to a preferred embodiment, the particles formed in the process are subjected to selected steps of a group consisting of the dispersion of said particles, the addition of a support, heat treatment, mixing, evaporation of water, spray drying, spraying thermal and its combination. According to preferred embodiments of the present invention, an aqueous starting solution comprising at least one ferric ion and its complexes, in a concentration of at least 0.1% w / w iron, whose solution has a pH of at least 1.2 is prepared. An aqueous solution of modification of a temperature higher than 80 ° C and the starting solution are contacted in a continuous manner in a mixing chamber to form a modified system. The mixing chamber is constructed in a manner to ensure rapid and efficient mixing of the solutions. The modified solution is removed from the mixing chamber in a piston-type expenditure manner. During the piston-type expense the precipitation is completed or in another preferred embodiment the solution is not exhausted during the piston-type expenditure time and the continuous precipitation in another container. Mixing in the mixing chamber is preferably carried out using the flow rate of the entering solution or by using mechanical mixing means or other mixing modes. In a preferred embodiment, the temperature in the mixing chamber and during the piston type expense are similar. In another preferred embodiment the temperature of the solution during the piston-type expense is higher in the mixing chamber and in yet another preferred embodiment the temperature of the solution during the piston-type expense is lower than in the mixing chamber. In a preferred embodiment of the present invention, the residence time in a mixing chamber is less than about 5 minutes and more preferred is a residence time of less than 1 minute. In still a more preferred embodiment, the residence time in a mixing chamber is less than about 5 seconds and in an especially preferred embodiment the residence time is less than 1 second. In preferred embodiments of the present invention the solution leaving the piston expense enters a container. In a more preferred embodiment of the present invention the solution in the container is mixed. While the invention will now be described in connection with certain preferred embodiments in the following examples while the aspects thereof may be more fully understood and appreciated, they are not intended to limit the invention of these particular embodiments. Otherwise, it is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention as defined by the appended claims. Thus, the following examples including the preferred embodiments that serve to illustrate the practice of this invention, it is understood that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and they present in the cause of providing that they are believed to be more useful and the easily understandable description of the formulation procedures as well as the principles and conceptual aspects of the invention.

EXAMPLE 1 Prepare 100 g of fresh solution of Fe2 (S0) 3 0.25 M (about 2.8% iron) by dissolving Fe2 (SO) 3 crystals in water and adjust the pH to 2.3 with ammonia. The solution is maintained at 25 ° C for one hour. The pH is enriched to 1.9. The conditions of the solution are adjusted by addition, while mechanically stirring vigorously at 600 rpm, of 900 g of water at 80 ° C, which is diluted, the solution is heated and the pH is increased. After 10 min, the mixing stops. The particles are observed. After they are regulated for 1 hour, the clear liquid phase is removed. The precipitate is washed 3 times with water and then centrifuged. The material obtained is in the form of ultra-fine mono-dispersed Fe (OH) 3 powder. The SEM photographs indicate that the particle size is uniform and is close to 45 nm with the average dimension ratio of about 1.5. The particles have a spherical shape.

EXAMPLE 2 100 g of fresh 0.25 M Fe2 (S0) 3 solution are prepared and retained at 25 ° C as in example 1. The solution is added while stirring vigorously at 600 rpm to 900 g of water at 122 ° C in a Pressure vessel in a pressure formed of about 2 atmospheres.

After 30 min, mixing stops and the particles are observed. The particle suspension is allowed to cool to room temperature and a precipitate is observed. The precipitate is separated and washed 3 times with water and then centrifuged. The material obtained is in the form of ultra-fine mono-dispersed FeOOH powder. The particles are spherical and have an average dimension ratio of about 1.5.

EXAMPLE 3 The procedure in Example 1 is repeated with a difference. The 900 gr of hot water contains 0.1% dispersant - poly (diallyldimethylammonium chloride) (PDAC) with a molecular weight scale of 200,000 to 300,000. After 10 minutes, mixing stops. A suspension of particles is observed. The particles do not settle during their stay for one hour. The particles are separated by centrifugation and washed as in example 1. The particles formed are similar to those of example 1.

EXAMPLE 4 Prepare 1000 g of fresh solution of Fe2 (S0) 3 0.2 M (about 2.8% iron) by dissolving Fe2 (SO4) 3 crystals in water. Ammonia is added to 100 g samples of the solution to enrich the molar ratio of NH3 / Fe of 1. The solution is maintained at 25 ° C for several retention times (Tret). After the retention time, each of the solutions formed is mixed with 900 g of water, which contains - in some cases - 0.25% dispersant (PDAC) at various temperatures and is maintained in a Parr unit (high pressure vessel) with mechanical stirring at 600 rpm. After 5 minutes, the agitation stops. The particles are observed and separated from the solution by centrifugation. The precipitate is washed 3 times with water and then centrifuged. The material obtained by water content is analyzed by thermo-gravimetric analysis (TGA) and by SEM photographs. The results are presented in table 1.

TABLE 1 Deviation (50%) * = the particle size scale of 50% of the particles around the average size (nm). * The particles in the samples that do not contain dispersants condense into aggregates while those with dispersants are freely bound to one another.

EXAMPLE 5 1000 g of fresh 25% Fe2 (SO) 3 solution is prepared by dissolving Fe2 (SO4) 3 crystals in water. Ammonia is added to 100 g samples of the solution to enrich several molar ratios of NH3 / Fe. The solutions are maintained at 25 ° C during several retention times (Tret). After the retention time, each of the solutions is added, to 900 g of water at 85 ° C, containing 0.1% dispersant (PDAC), while stirring vigorously. After 10 min, the agitation stops. The particles are observed. The solution is removed and centrifuged. The precipitate is washed three times with water and then centrifuged. The material obtained is analyzed through SEM photographs. The results are presented in table 2.

TABLE 2 COMPARATIVE EXAMPLE A Three different 25% Fe2 (SO) 3 solutions are prepared by mixing several 25% Fe2 (S04) 3 solutions of various NH3 / Fe ratios and various incubation times.

Add 15 g of each of the three solutions, to 135 g of water at 90 ° C, while stirring vigorously. After 5 minutes, mixing stops. The particles are observed in all three cases. The solutions are removed by centrifugation. The precipitates are washed 3 times with water and centrifuged. The materials obtained through SEM photographs are analyzed. In all cases, the particles are distorted in large distribution bars.

EXAMPLE 6 1000 gr of fresh 0.21 M Fe2 (SO4) solution is prepared by dissolving Fe2 (S04) 3 crystals in water. Several amounts of ammonia are added to 25 g samples of the solution as described in Table 3. The solutions are maintained at 25 ° C for several retention times (Tret). 225 g portions of water are pumped through a heat exchanger that is placed in an oil bath at 150 ° C or 190 ° C, in a 0.25 ml mixing chamber. 25 g of each Fe2 (SO) 3 solution are pumped simultaneously after retention in the same mixing chamber, where it is mixed with the pre-heated water to form modified solutions. Each of the modified solutions is then flowed through a heated 50 ml tube (placed in the same oil bath) in the Parr unit (high pressure vessel) in which the temperature is maintained as in the bath of oil and the mixing chamber. After an additional 5 min, mixing stops and the Parr solution is removed and cooled. The solution is centrifuged and the clear liquid phase is removed. The precipitate is washed 3 times with water and centrifuged. The material obtained is analyzed by the water content (TG) and by SEM photographs. The results are presented in table 3.

TABLE 3 Deviation (50%) * = particle size scale of 50% particles around average size (nm).

EXAMPLE 7 Prepare 100 g of fresh solution of Fe2 (S04) 3 0.25 M (about 2.8% of iron) by dissolving crystals of Fe2 (SO) 3 in water. The weak anion exchanger (Reillex 425tm) is added to increase the pH to 2.5. The solution is maintained at 25 ° C for 1 hour. The enriched pH is 2.0. The conditions in the solution are adjusted by adding, while mechanically stirring vigorously at 600 rpm to 900 g of water at 80 ° C, which is diluted, the solution is heated and the pH is increased. After 10 min, the mixing stops. The particles are observed. After regulating for 1 hour, the clear liquid phase is removed. The precipitate is washed 3 times with water and then centrifuged. The material obtained is in the form of ultra-fine mono-dispersed Fe (OH) 3 powder. The SEM photographs indicate that the particles are spherical with uniform particle size of about 40 nm. It will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and that the present invention can be specified in other specific forms without departing from the essential attributes thereof, and is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive, the reference made to the appended claims, different from the foregoing description, and all the changes that come within the meaning and scale of equivalence of the claims therefore intends to be understood here.

Claims

NOVELTY OF THE INVENTION CLAIMS 1. - A method for the formation of iron oxide particles of small size, comprising the steps of: a) the preparation of a fresh starting aqueous solution comprising at least one of the ferric ions and their complexes, in a concentration of at least 0.1% w / w of iron and at a pH higher than about 1.5 and the maintenance of said freshly prepared solution at a temperature lower than 55 ° C during a retention time in which the hydrolysis takes place, the extension of said hydrolysis which is sufficient to lower the pH in at least 0.2 units, where said time does not exceed 14 days, to form a system containing a modified solution; and b) adjusting the conditions of the system in at least one of the steps of: i) heating the modified solution to raise its temperature by at least 10 ° C, ii) raising the pH of the modified solution by at least 0.3 units; and iii) dilution of the modified solution by at least 20%; with which particles are formed, where most of the particles formed are between about 2 nm and about 500 nm in size. 2. The method according to claim 1, further characterized in that the solution is maintained under said adjusted conditions for at least 0.5 minutes. 3. - The method according to claim 1, further characterized in that the adjustment of conditions is carried out for less than 1 hour. 4. The method according to claim 1, further characterized in that most of the particles formed have a degree of crystallinity of less than 50%. 5. The method according to claim 1, further characterized in that at least 50% of the particles formed are characterized by a size ratio between the smallest and largest particles of less than 10: 1. 6. The method according to claim 1, further characterized in that at least 50% of the particles formed is characterized by a size ratio between the smallest and largest particles of less than 5: 1. 7. The method according to claim 1, further characterized in that most of the particles formed are of a different configuration from the elongated. 8. The method according to claim 1, further characterized in that the majority of the particles formed have a surface area of at least 30 m2 / g. 9. The method according to claim 1, further characterized in that it comprises the step of: c) dehydrating the particles formed at a dehydration temperature on a scale between 60 ° C and 800 ° C to form dehydrated particles. 10. The method according to claim 9, further characterized in that the dehydration is conducted under super-atmospheric pressure. 11. The method according to claim 9, further characterized in that the dehydration step and the adjustment step are conducted simultaneously. 12. The method according to claim 11, further characterized in that the adjustment involves heating up to dehydration temperature. 13. The method according to claim 9, further characterized in that the majority of the dehydrated particles are of a different configuration than the elongated one. 14. The method according to claim 9, further characterized in that the majority of dehydrated particles have a surface area of at least 30 m2 / g. 15. The method according to claim 12, further characterized in that the particles are selected from the group consisting of goethite, hetatite and magnetite. 16. The method according to claim 1, further characterized in that the oxide has the formula FeOOH. 17. The method according to claim 1, further characterized in that the oxide has the formula Fe (OH) 3. 18. - The method according to claim 1, further characterized in that the preparation of an aqueous solution involves at least one oxidation of iron metal, the oxidation of ferrous ions, the oxidation of sulfur ions, the dissolution of an iron compound and the acidification of an iron salt solution. 19. The method according to claim 18, further characterized in that the oxidation uses an oxidant selected from a group consisting of oxygen, hydrogen peroxide, nitric acid, nitrate and combinations thereof. 20. The method according to claim 18, further characterized in that the oxidation is chemically or biologically catalyzed. 21. The method according to claim 18, further characterized in that the iron compound is selected from the group consisting of iron oxides, iron hydroxides, minerals containing the same and their mixtures and wherein the compound is dissolved in an acid solution comprising an acid selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, an organic acid, its acid salts and combinations thereof. 22. The method according to claim 1, further characterized in that the aqueous solution prepared comprises an anion selected from the group consisting of sulfate, chloride, nitrate, phosphate and organic acid and mixtures thereof. 23. - The method according to claim 1, further characterized in that most of the anions in the prepared aqueous start solution are sulfate anions. 24. The method according to claim 1, further characterized in that the concentration of iron in the prepared solution is greater than 5%. 25. The method according to claim 1, further characterized in that the pH of the solution is less than 6 during at least 80% of the duration of the process. 26. The method according to claim 1, further characterized in that the pH of the solution in step (a) is maintained between 2 and 3 during at least a portion of the maintenance time of step (a). 27. The method according to claim 1, further characterized in that the pH of the aqueous solution is between 1.5 and 4 during at least a portion of the time during which the conditions of the system are adjusted according to the step (b) ). 28.- The method according to claim 1, further characterized in that it comprises the step of removing at least part of the water in the particle suspension after adjustment of the stage (b) 29. The method according to claim 1, further characterized in that it comprises at least two of the heating steps. 30. The method according to claim 1, further characterized in that it comprises at least one of the grinding of the particles formed and the screening of the particles formed. 31. The method according to claim 1, further characterized in that it comprises at least partially the reduction of ferric ions in the particles formed. 32. The method according to claim 1, further characterized in that at least one dispersant is present in at least one stage of a group consisting of preparation, maintenance, facilitation, dehydration and grinding. 33. The method according to claim 32, further characterized in that at least one dispersant is selected from a group consisting of cationic polymers, nonionic polymer anionic polymers, surfactants, and mixtures thereof. 34.- The method according to claim 32, further characterized in that it comprises the step of modifying the quantity of at least one dispersant. 35. The method according to claim 1, further characterized in that the solution is treated by at least one ultrasound and microwave. 36.- Iron oxide particles formed each time according to the method of claim 1 and the products of their conversion. 37.- The iron oxide particles according to claim 36, characterized further because the purity with respect to other metals is at least 95%. 38. The iron oxide particles according to claim 36, further characterized in that they are in a shape selected from the group consisting of a spherical shape, a bar shape and a raft shape. 39. The iron oxide particles according to claim 36, further characterized in that they are mixed with atoms of other compounds. 40.- A preparation comprising the iron oxide particles prepared according to the method of claim 1. 41.- The preparation according to claim 40, further characterized in that the particles are dispersed in a liquid, they are supported in a solid compound, they agglomerate to larger particles, they are partially fused, they are coated or their combination. 42.- A method for the production of a preparation according to claim 40, comprising the steps selected from the group consisting of the dispersion of the particles, the addition of a support, heat treatment, mixing, evaporation of water, spray drying, thermal spraying and their combinations. 43.- A pigment comprising at least one of the iron oxide particles prepared according to the method of claim 1, or the preparation of claim 40. 44.- A catalyst comprising at least one of the particles of iron oxide prepared according to the method of claim 1, or the preparation of claim 40. 45. A coating comprising at least one of the iron oxide particles prepared according to the method of claim 1, or the preparation of claim 40. 46.- The industrial production of iron oxide particles prepared according to the method of claim 1, wherein the particles are formed at a rate of at least 50 kg / hour. 47.- A method for the formation of a pigment, comprising the steps of claim 1. 48.- A method for the formation of a catalyst, comprising the steps of claim 1. 49.- A method for training of iron oxide particles of small size, comprising the steps of: a) the preparation of a fresh start aqueous solution comprising at least one of the ferric ions and their complexes, at a concentration of at least 0.1% p / p of iron, whose solution has a pH of at least 1.2; b) the preparation of the modification of an aqueous solution of a temperature greater than 80 ° C; c) contacting the starting solution with the modification solution in a continuous manner in a mixing chamber to form a modified system; d) the removal of the modified system from the mixing chamber in a piston-type manner of expenditure; and whose method is characterized by: ¡. the residence time in a mixing chamber is less than about 1 minute, ii. here are formed particles or their aggregates, where most of the particles formed are between about 2 nm and about 500 nm in size; and iii the particles formed comprise FeOOH, Fe2O3, Fe (OH) 3, Fe3O4 or their combination. 50.- The method according to claim 49, further characterized in that the concentration of iron in the starting solution is greater than 2%. 51. The method according to claim 49, further characterized in that at least one of the fresh start solution and the modification solution comprises a reagent selected from a group of dispersants and basic compounds. 52. The method according to claim 51, further characterized in that the basic compound is selected from a group consisting of ammonia, ammonium carbonate, ammonium bicarbonate and urea. 53. The method according to claim 51, further characterized in that the molar ratio of OH / Fe in the solution of the modified system is less than 3. 54. The method according to claim 51, further characterized in that the ratio molar OH / Fe in the solution of the modified system is between 0.5 and 2. 55. The method according to claim 49, further characterized in that the temperature of the modification solution is in the range of between 100 ° C and 300 ° C. 56.- The method according to claim 49, further characterized in that the modified system is retained at a pressure of less than 100 atmospheres. 57. The method according to claim 56, further characterized in that the retention of the modified system is for a duration of between 1 and 30 minutes. 58. The method according to claim 56, further characterized in that during retention the temperature is maintained within less than 20 ° C of the temperature of the modified system. 59. The method according to claim 49, further characterized in that it comprises a step of retention of the aqueous solution prepared freshly before contacting at a temperature of less than 55 ° C and a pH greater than 1.5 for a period of time. sufficient preliminary retention time for the pH to decrease by at least 0.2 units, where the preliminary retention time does not exceed 14 days. 60.- The method according to claim 49, further characterized in that the residence time in the mixing chamber is less than 5 seconds. 61. - The method according to claim 49, further characterized in that the residence time in the mixing chamber is less than 0.5 seconds. 62. The method according to claim 49, further characterized in that the modified system removed remains at least 0.5 minutes. 63. Iron oxide particles formed in accordance with the method of claim 49 and the products of their conversion. 64. The iron oxide particles according to claim 63, further characterized in that the purity with respect to other metals is at least 95%. The iron oxide particles according to claim 63, further characterized in that they are in a form selected from the group consisting of a spherical shape, a bar shape and a balsa form. 66. The iron oxide particles according to claim 63, further characterized in that they are mixed with atoms of other compounds. 67.- A preparation comprising iron oxide particles prepared according to the method of claim 49. The preparation according to claim 67, further characterized in that the particles are dispersed in a liquid, are supported in a solid compound, they agglomerate to larger particles, they are partially fused, they are coated or their combination. 69. The method according to claim 49, further characterized in that at least 50% of the particles formed are characterized by a size ratio between the smallest particles and the largest ones of less than 10: 1. The method according to claim 49, further characterized in that at least 50% of the particles formed are characterized by a size ratio between the smallest particles and the largest ones of less than 5: 1. 71. The method according to claim 49, further characterized in that the majority of the particles formed have a surface area of at least 30 m2 / g.