DE102012206004A1 - Metal oxide-containing powder, useful e.g. in silicone rubber and as component of polymer composition, comprises iron as mixed oxide, lanthanum/cerium, and additional metal component consisting of cobalt, manganese, nickel and lanthanide - Google Patents

Abstract

Metal oxide-containing powder comprises 30-85 atm.% of iron (Fe) as a mixed oxide, lanthanum (La) or cerium (Ce), and at least one 3-15 atm.% of additional metal component consisting of cobalt (Co), manganese (Mn), nickel (Ni) and lanthanide. An independent claim is included for preparing the powder containing metal oxide, comprising preparing aerosol by atomizing a solution, reacting the solution in a reaction chamber using an oxyhydrogen flame, and cooling the reaction mixture and then separating the solid from the solution as a salt of Fe, La, Co, Mn, Ni, lanthanide, aluminum (Al), silicon (Si), gallium (Ga) and/or tin (Sn).

Description

The invention relates to a metal mixed oxide containing powder, process for its preparation and use.

In the WO 2010/063557 discloses iron-silicon oxide particles which can be used for inductive heating of materials in a magnetic or electromagnetic alternating field. The particles have a core-shell structure, with the iron oxide phases hematite, magnetite and maghemite as the core, an amorphous shell of silicon dioxide and one or more shell-core compounds of the elements silicon, iron and oxygen. It is further disclosed that the iron-silicon oxide particles may contain up to 2% by weight of manganese, cobalt, chromium, europium, yttrium, samarium, nickel or gadolinium as doping component. The iron-silicon oxide particles are prepared by reacting a halosilicon compound, ferric chloride and dopants with an excess of oxygen or an oxygen-containing gas, and subsequently admixing reducing gases with the reaction mixture.

It has been shown that in the WO 2010/063557 disclosed iron-silicon oxide particles for inductive heating in a magnetic or electromagnetic alternating field are in principle suitable and thus acceptable heating rates can be achieved. Nevertheless, it seemed desirable to further improve the achievable heating rates.

The technical task of the present invention therefore consisted in the provision of further improved particles with regard to the achievable heating rate. Another object was to provide a process for producing these particles.

The invention relates to a powder containing metal mixed oxide containing as mixed oxide component Fe, La or Ce and at least one further metal component from the group consisting of Co, Mn, Ni and a lanthanide, which 30-85 atom% Fe and 3-15 atom% of the other metal components, each based on the metal content of the powder. A lanthanoid in the context of the invention means an element of the group consisting of Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Particularly preferred is an embodiment in which the lanthanoid Dy is.

The metal fractions can be determined by wet chemical analysis by digestion or by X-ray fluorescence analysis. The particles forming the powder can be present as isolated and / or aggregated individual particles. The majority of the particles is usually present as largely spherical individual particles with a mean diameter of 0.1-1 .mu.m. The BET surface area of the particles is preferably 5-25 m ² / g.

In order to achieve rapid heat-up times, not all metal components must be present within a single particle. In addition to metal mixed oxide, the powder according to the invention may also contain purely metallic constituents, such as iron, iron-manganese compounds or iron-cobalt compounds, which do not adversely affect the heating-up time. The detection of these purely metallic compounds can be carried out, for example, by means of X-ray diffractometry. On the basis of the corresponding reflexes, a proportion of up to 20 wt .-%, preferably 0-10 wt .-%, each based on the powder, are determined.

As a further metal component, the metal mixed oxide containing powder Al, Si, Ge or Sn, with a proportion of 3-15 atom%, each based on the metal content of the powder. Silicon should be referred to as metal within the scope of the invention.

In a particular embodiment, silicon in the form of amorphous silica surrounds the particles of the powder according to the invention. Amorphous is understood to mean a material in which no diffraction signals can be detected by the usual methods of X-ray diffractometry. The outer shell is a tight shell. By dense is meant that upon contact of the particles with hydrochloric acid under certain reaction conditions less than 50 ppm of iron are detectable. At room temperature, 0.33 g of the particles are brought into contact with 20 ml of 1 N hydrochloric acid solution for 15 minutes. Part of the solution is subsequently analyzed for iron by means of suitable analysis techniques, for example ICP (inductively coupled plasma spectroscopy). The thickness of the outer shell is preferably 1-40 nm, more preferably 5-20 nm.

The particles thus coated with silicon dioxide have very rapid heating times and, in addition, are often more chemically resistant than uncoated particles due to the shell. Furthermore, the reagglomeration of the magnetic cores is significantly reduced in use.

A further particular embodiment of the invention is directed to a powder which has a mass fraction of oxygen, based on the powder, of 50-98%, preferably 70-95%, of the mass fraction of the oxides Me ₂ O ₃ with Me = Fe , La, Co, Ni, Mn and lanthanide calculated composition.

It holds that O _q [%] = O _experimental / O _{stoichiometric} · 100,
with O _experimental = experimentally determined oxygen content and
O _{stoichiometric} = calculated, stoichiometric oxygen content.

These thus represent low-oxygen powders, which have a compared to a powder which has a mass fraction of more than 98%, a further improved heating time. For powders with less than 50% oxygen content, the heating time is negatively affected.

The heating time is understood to be the time required to heat a sample of the powder according to the invention from room temperature, that is to say from 20 to 25 ° C., to a specific temperature in an alternating magnetic field. The sample can be the powder according to the invention in the form of a compact or the powder can be part of a polymer mixture, for example a silicone rubber. The alternating magnetic field can be a medium-frequency or high-frequency magnetic field. The middle frequency is to be understood as a range of 0.5 kHz-500 kHz, preferably 10-100 kHz, and high-frequency refers to a range of 501 kHz-30 MHz, preferably 600-1000 kHz.

Preferably, a compact of the powder according to the invention in the high-frequency magnetic alternating field has a heating time to a temperature of 200 ° C of less than 2 s, particularly preferably 0.3-1.5 s on. If the powder according to the invention is incorporated in silicone rubber, then in the high-frequency magnetic alternating field the heating time to a temperature of 100 ° C. is preferably less than 5 s, particularly preferably 1-4 s. In the determination of the heating time in silicone rubber is based on a concentration of powder according to the invention of 4.76 wt .-%, based on the sum of silicone rubber and powder. The shortest heating times are achieved with metal mixed oxide containing powders containing 70-90 atom% Fe and 3-10 atom% each of La, Si and Mn.

The surface of the particles of the powder according to the invention has hydroxyl groups. These can react with organosilanes or organo-siloxanes. Depending on the ratio of the number of OH groups to the amount used and the type of organosilane or organopolysiloxane, surface-modified particles result. The proportion of carbon is preferably 0.5-15 wt .-%, particularly preferably 1-10 wt .-%, based on the non-surface-modified particles. Low proportions of carbon may also result from the preparation of the powder according to the invention, if carbonaceous starting materials were used. In this case, the carbon is distributed over the entire particle and is usually at most 0.1 wt .-%.

Another object of the invention is a process for preparing the metal mixed oxide containing powder in which one brings an aerosol, which is produced by atomizing a solution in a reaction space in a hydrogen / oxygen flame to the reaction, the reaction mixture is cooled and then the solid wherein the solution contains a salt of Fe and La and at least one of the group consisting of Co, Mn, Ni and lanthanide and optionally at least one selected from the group consisting of Al, Si, Ga and Sn and wherein the amounts of the salts so are chosen such that the solution 30-85 atomic% Fe and 3-15 atomic% La and 3-15 atomic% of the metal components Co, Mn and Ni and lanthanide and optionally 3-15 atom% of the metal component Al, Si Contains Ge and Sn. The average residence time of the reaction mixture in the reaction space is preferably 10 ms-1 s, more preferably 300-600 ms.

Powder according to the invention is obtained only when all the metal compounds are present dissolved in a solution. The metal compounds can be both organic and inorganic in nature. Organic refers, for example, to alkoxides or carboxylates of the metals. By inorganic is meant, for example, chlorides or nitrates. Iron, cobalt, manganese and nickel compounds are usually used in the oxidation state +2, lanthanum and lanthanide compounds usually in the oxidation state +3. Due to better availability, nitrates are used in particular. The solvent is tailored to the metal compounds. Suitable are water, alcohols, carboxylic acid and any mixtures thereof, as long as a solution results in the presence of the metal compounds. The concentration of the solution is preferably 3-20 wt .-%, more preferably 5-15 wt .-%, each based on the metal content of the solution. The viscosity of the solution may, if desired, be varied by varying the temperature. In general, the temperature of the solution during atomization is 10 to 50 ° C, preferably 20 to 35 ° C. The aerosol is obtained by spraying the solution. In this case, a multi-substance nozzle is preferably used. As the sputtering gas, an inert gas or air or mixtures thereof may be used. The average droplet diameter is preferably less than 100 μm.

The molar ratio of the oxygen fed to the flame to the amount of oxygen stoichiometrically required to convert the hydrogen and the solution to the corresponding mixed oxides, defined as lambda, can be chosen to be greater than one. As a general rule, £ 1 lambda £ 2. For the calculation of lambda, the oxides of Me = Fe, La, Co, Ni, Mn, lanthanide, and Al are Me ₂ O ₃ and Me = Si, Ge, and Sn are MeO ₂ based on.

It has been found that powders with a particularly short heating time are obtained when oxygen is used in a stoichiometric amount. Preferably, the process may be carried out such that 0.6 lb. lambda <1. Particularly preferred is 0.7 pounds lambda <0.9. In these settings, in addition to the mixed oxides probably metallic phases are formed.

Essentially two methods are suitable for coating the particles of the powder according to the invention with amorphous silicon dioxide. In the first method, a reaction step is added to the preparation of the powder according to the invention, in which the solid as obtained after cooling and separation in an aqueous phase, preferably water, in the presence of at least one aqueous-phase-soluble, basic-reacting Compounds with one or more silicon compounds of the general formula X _n Si (OR) _4-n , where X = halogen or H, R = H or a linear or branched alkyl radical having 1-8 C atoms and n = 0 - 4 with R is not H for n = 4. Particularly preferred is Si (OC ₂ H ₅ ) ₄ . As the base, for example, NH ₃ , NH ₄ OH, NaOH, KOH, R ₄ NOH (tetraalkylammonium hydroxides), (NH ₄ ) ₂ CO ₃ , NH ₄ HCO ₃ , Na ₂ CO ₃ , NaHCO ₃ , amines of the general formula R ₃ N , R ₂ NH, RNH ₂ , with R = alkyl, cycloalkyl or aryl, are used. The proportion of base is preferably 1-5 wt .-%, based on the total reaction medium. The temperature in this process is not critical as long as the reaction medium is liquid. Preference is given to a reaction temperature of 15-30 ° C. The reaction product can be separated by filtration and optionally washed and dried.

In the second method for coating with amorphous silica is introduced after the aerosol, but before the cooling of the reaction mixture in the reaction space, one or more silicon compounds of the general formula X _n Si (OR) _4-n , gaseous or liquid. The best results are obtained when the temperature during the introduction of the silicon compound in a temperature range of 600-850 ° C takes place. The meaning of the general formula is the same as in the first-mentioned method of encapsulation. Preferably, Si (OC ₂ H ₅ ) _{4 is} used. The average residence time of the reaction mixture from the addition of the silicon compound is preferably 0.1-10 s, more preferably 1.5-3.0 s. Under these conditions, a complete, dense envelope of amorphous silica is ensured. This second method has the advantage that the formation and the coating of the particles take place in a single reaction step.

Of course, silicon can also be part of a powder according to the invention which has no shell.

It is also possible to silylate the surface of the particles of the powder by reacting the powder with an organosilane or organopolysiloxane. The reaction takes place between the silylating agent and the Hydroxxgruppen located on the surface of the particles.

As organosilane at least one of the general formula OH, OR, OCOR or O (CH _{2) x} OR may preferably SiX _z Y _4-z (I) are used, with X = hydrocarbon radical having 1 to 18 carbon atoms, Y = chlorine, , R = hydrocarbon radical having 1 to 8 C atoms, z = 1 or 2 and x = 1, 2 or 3, wherein the elements of the groups X, Y or R may each be the same. Examples of suitable organosilanes are dimethyldiacetoxysilane, dimethyldichlorosilane, dimethyldiethoxysilane, dimethyldimethoxysilane, divinyltetramethyldisilazane, hexamethyldisilazane, methyltriacetoxysilane, methyl trichlorosilane, methyltriethoxysilane, methyltrimethoxysilane, octadecylmethyldichlorosilane, octadecyltrichlorosilane, octyltrichlorosilane, octamethylcyclotetrasilazane, octylmethyldichlorosilane, octyltriethoxysilane, octyltrimethoxysilane, trimethylacetoxysilane, trimethylchlorosilane, trimethylethoxysilane, trimethylmethoxysilane, trimethylsilanol, vinyldimethylchlorosilane , Vinyldimethylethoxysilane, vinyldimethylmethoxysilane, vinylmethyldichlorosilane, vinylmethyldiethoxysilane, vinylmethyldimethoxysilane, Vinyltrichlorosilane, vinyltriethoxysilane and vinyltrimethoxysilane. As organosiloxanes of the formula it is possible to use linear or cyclic dimethylpolysiloxanes having an average number of dimethylsiloxy units of 5-100, with trimethylsiloxy or dimethylhydroxysiloxy end groups.

Another object of the invention is a powder containing metal mixed oxide whose mass fraction of oxygen, based on the powder, is further reduced, namely to 20-40%, which is obtainable by thermally treating the metal mixed oxide-containing powder in a reducing atmosphere. The mass fraction of oxygen is calculated as described above and refers to the oxides Me ₂ O ₃ with Me = La, Fe, Co, Ni, Mn and lanthanide and optionally the oxides Al ₂ O ₃ , and Me ₂ O ₃ with Me = Si , Ge or Sn. the thermal treatment is preferably carried out at temperatures of 500-1200 ° C over a period of 2-48 hours. As a reducing atmosphere is forming gas, carbon monoxide, hydrogen, ammonia or mixtures of these gases. The powder thus obtained has a higher saturation magnetization than the powder used. The saturation magnetization is more than 100 Am ² / kg, preferably 100-200 Am ² / kg.

Another object of the invention is a silicone rubber containing the mixed metal oxide powder according to the invention. The silicone rubber may be an HTV silicone rubber known to the person skilled in the art, an LSR silicone rubber or an RTV 1-K silicone sealant. It is preferably an HTV silicone rubber.

Another object of the invention is the use of the metal mixed oxide containing powders as a component of rubber mixtures, as a component of polymer formulations, as a component of adhesive compositions, as a component of obtainable by welding in electromagnetic alternating field plastic composite moldings and for the preparation of dispersions.

Examples

Analytical procedures

The metal concentrations are determined by ICP-OES. The samples were measured with the ICPOES Optima, PerkinElmer. The uncertainty of results is relative to the metals with the exception of Si 0.5-2% relative and for Si 2-5% relative.

The oxygen content is determined by means of the element analyzer TCH600, LECO. The result uncertainty is 0.8-1.0%.

The BET surface area was determined after DIN 66131 ,

The pellets used to determine the heating time (t _{200 ° C} ) are obtained by weighing 200-400 mg of powder into a mold and adding, at a pressure of 1.5 t, to a tablet of dimensions Ø × h = 13 mm × 1 mm pressed. The tablets were measured on a plate coil with a diameter of 80 mm, at a frequency of 40 kHz. The coupled power was 1.9 kW. An induction unit type EW5W from IFF GmbH is used. The surface temperature of the tablet is detected and the time required to heat the tablet from room temperature to 200 ° C is stopped.

To determine the heat-up time (t _{100 ° C)} of the powder, a silicone composition is prepared according to the following formulation: 33 g ELASTOSIL ^® E50, 13 g of silicone oil type M1000, respectively Momentive Performance Materials, 4 g of Aerosil ^® 150, Evonik Industries, and 2.5 g the powder of the invention. The content of powder corresponds to a concentration of 4.76 wt .-%, based on the silicone composition. Measure the silicone mass, which is applied by means of 1 mm doctor blade to a glass substrate, on a disk coil with a diameter of 80 mm, at a frequency of 650 kHz. The coupled power is 2.5 kW. An induction unit of the type GTMC 25 KW, Fives Celes, is used. The surface temperature of the tablet is detected and the time required to heat the silicone mass from room temperature to 100 ° C is stopped.

The maximum specific magnetization M _s was determined by means of an Alternating-Gradient Magnetometer (AGM) of the type Micromag 2900 from Princeton.

Preparation of Solutions A-M: The solvent is water. The information given in Table 1 to wt .-% refer to the proportion of metals, so for example Fe or La, in the solution. The viscosities of the solutions is 0.9-1.05 mPas / 25 ° C.

Implementation of the solutions in an oxygen / hydrogen flame

Example 1:

2000 g / h of the solution A are sprayed with 3.0 Nm ³ / h of nitrogen by means of a two-fluid nozzle. The resulting aerosol, which has a mean droplet diameter of <100 microns, is burned in a reaction chamber in a flame. The flame results from the ignition of 4.6 Nm ³ / h of hydrogen and 10.6 Nm ³ / h of air. The lambda value is 0.91. Subsequently, the hot gases and the solid product are cooled in a cooling section and the solid product is deposited on filters.

Examples 2 to 13 are carried out analogously to Example 1. The reaction parameters of all examples are listed in Table 2 and the properties of the products in Table 3.

Examples 12 and 13 are comparative examples.

Compared to the products of Comparative Examples 12 and 13, the powders according to the invention have significantly shorter heating times of the compacts, as well as significantly shorter heating times as a constituent of silicone rubber. In addition, the saturation magnetization of the powders according to the invention is significantly higher.

Example 14: Preparation of a Coated with SiO ₂ Powder

2000 g / h of the solution A are sprayed with 3.0 Nm ³ / h of nitrogen by means of a two-fluid nozzle. The resulting aerosol, which has a mean droplet diameter of <100 microns, is burned in a reaction chamber in a flame. The flame results from the ignition of 4.6 Nm ³ / h of hydrogen and 10.6 Nm ³ / h of air. In the stream of about 750 ° C hot reaction mixture 0.16 kg / h of vapor tetraethoxysilane be given. Subsequently, the reaction mixture is cooled and the resulting solid is deposited on a filter of the gaseous substances.

The shell can be occupied by TEM images. The thickness of the shell is 3-6 nm. The chemical composition of the shell is determined by means of TEM-EDX (Transmission Electron Microscopy [TEM] in conjunction with an energy-dispersive analysis of characteristic X-rays [EDX]) as SiO ₂ .

Example 15: Treatment under reducing conditions

500 g of the powder from Example 1 are treated at 650 ° C. over a period of 4 in a Formiergasatmosphäre (80:20 vol .-% H ₂ / N ₂ ). The BET surface area of the resulting powder is 19 m ² / g. It has an oxygen content of 15.2% by mass. Its magnetization M _s is 145.3 Am ² / kg.

Example 16: Preparation of a surface-modified powder

100 parts by weight of the powder from Example 1 are placed in a mixer and sprayed with intensive mixing first with 0.5 parts by weight of water and then with 5 parts by weight of octyltrimethoxysilane. After the spraying is finished, it is annealed at 120 ° C for 2 hours. The resulting powder has a carbon content of 1.1% by weight and a magnetization M _s of 130.2 Am ² / kg.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2010/063557 [0002, 0003]

Cited non-patent literature

• DIN 66131 [0031]

Claims (16)

A mixed metal oxide-containing powder containing as mixed oxide component Fe, La or Ce and at least one further metal component selected from the group consisting of Co, Mn, Ni and a lanthanide, characterized in that it contains 30-85 atom% Fe and 3-15 atom each -% of the other metal components, each based on the metal content of the powder contains. Metal mixed oxide-containing powder according to claim 1, characterized in that the majority of the particles are present as largely spherical individual particles having an average diameter of 0.1-1 microns. Metal mixed oxide-containing powder according to claims 1 or 2, characterized in that it contains as further metal component Al, Si, Ge or Sn, with a proportion of 3-15 atomic%, each based on the metal content of the powder. Metal mixed oxide-containing powder according to claims 1-3, characterized in that the particles of the powder are coated with SiO ₂ . A metal mixed oxide containing powder according to claims 1-4, characterized in that it has a mass fraction of oxygen, based on the powder, which is 50-98% of the mass fraction of the oxides Me ₂ O ₃ with Me = Fe, La, Co, Ni, Mn and Lanthanoid calculated calculated composition. A mixed metal oxide-containing powder according to claims 1-5, characterized in that it contains 50-90 atom% Fe and 5-10 atom% each of La, Si and Mn. Mixed metal oxide-containing powder according to claims 1-6, characterized in that its carbon content is 0.5-15 wt .-%. A process for the preparation of the metal mixed oxide containing powder according to claims 1-7, characterized in that one brings an aerosol, which is produced by sputtering a solution in a reaction space in a hydrogen / oxygen flame to the reaction, the reaction mixture is cooled and then the solid is separated, the solution containing a salt of Fe and La and at least one of the group consisting of Co, Mn, Ni and lanthanide and optionally at least one selected from the group consisting of Al, Si, Ga and Sn and wherein the amounts of Salts are selected so that the solution 30-85 atomic% Fe and 3-15 atomic% La and 3-15 atomic% of the metal components Co, Mn and Ni and lanthanide and optionally 3-15 atom% of the metal component Al Contains Si, Ge and Sn. A method according to claim 8, characterized in that 1 lambda £ 2, wherein lambda defined as the molar ratio of the oxygen supplied to the flame to the amount of oxygen which is stoichiometrically required for the reaction of the hydrogen and the solution into the corresponding mixed oxides, where the oxides of Me = Fe, La, Co, Ni, Mn, lanthanide and Al are calculated as Me ₂ O ₃ and of Me = Si, Ge and Sn as MeO ₂ . A method according to claim 8, characterized in that 0.6 lambda λ <1 applies. Process according to claims 8-10, characterized in that a reaction step is added, in which the particles of the solid are coated with silica by reacting the solid in a liquid phase with one or more silicon compounds of the general formula X _n Si (OR) _4-n , where X = halogen or H, R = H or a linear or branched alkyl radical having 1-8 C atoms and n = 0-4 with R is not H for n = 4. Process according to claims 8-10, characterized in that one adds a reaction step in which the particles of the solid are coated with silicon dioxide by one or more after the introduction of the aerosol into the reaction space but before the cooling of the reaction mixture into the reaction space Silicon compounds of the general formula X _n Si (OR) _4-n , gaseous or liquid introduces, wherein X = halogen or H, R = H or a linear or branched alkyl radical having 1-8 C atoms and n = 0 - 4 with R is not H for n = 4. Process according to claims 8-12, characterized in that a reaction step is added in which the surface of the particles of the powder is silylated by reacting the powder with an organosilane or organopolysiloxane. Mixed metal oxide containing powder with a mass fraction of oxygen, based on the powder, the 20-40% of the mass fraction of the oxides Me ₂ O ₃ with Me = La, Fe, Co, Ni, Mn and lanthanide and optionally the oxides Al ₂ O ₃ and Me ₂ O ₃ with Me = Si, Ge or Sn calculated composition obtainable by thermally treating the metal mixed oxide containing powder according to claims 1-6 in a reducing atmosphere. Silicone rubber containing the metal mixed oxide containing powder according to claims 1-7. Use of the metal mixed oxide-containing powder according to claims 1-7 and 14 as a constituent of rubber mixtures, as a constituent of polymer formulations, as a constituent of adhesive compositions, as a constituent of plastic composite moldings obtainable by welding in electromagnetic alternating field and for the preparation of dispersions.