CN101567242A - Method for preparing magnetic nano composite particles of FeCr alloy dispersed in ceramic crystal grain - Google Patents

Abstract

The invention belongs to the field of inorganic magnetic nanocomposite materials, and is a method for preparing magnetic nanocomposite particles of FeCr alloy dispersed in ceramic crystal grains, which is characterized in that it comprises the following steps: 1) raw material selection: Al in aluminum salt, Si in silicon source, iron The amount of Fe in the salt and Cr in the chromium salt conforms to the chemical formula (Al _6－x－y Fe _x Cr _y )Si ₂ O ₁₃ , where 0<x+y≤1, and x≥y, y>0, choose the aluminum salt , silicon source, iron salt and chromium salt raw materials for later use; 2) adopt one of the following two methods: a) sol-gel method for gelation; b) co-precipitation method for gelation; 3) pre-baking: dry gel Roasting at 400-600°C for 1-5h under flowing air to obtain amorphous oxide powder; 4) Calcination: Calcining amorphous oxide powder in air at 1000-1500°C for 1-5h; 5) High-temperature reduction: reducing gas at 1200- Reduction at 1400°C for 1 to 10 hours; magnetic nanocomposite particles are obtained. The invention has the characteristics of superparamagnetic physical properties and high stability.

Description

Preparation method of magnetic nanocomposite particles of FeCr alloy dispersed in ceramic grains

technical field

The invention belongs to the field of inorganic magnetic nano-composite materials, and specifically relates to a preparation method of an inorganic magnetic nano-composite particle formed by monodispersing high-stability FeCr alloy magnetic nano-particles inside mullite ceramic crystal grains with mullite ceramics as a matrix .

Background technique

Due to the potential application in magnetic recording, catalysis, magnetic fluid, magnetic resonance imaging and magnetic targeting drug carriers, the preparation and properties of Fe, Co, Ni and other magnetic metal single substance nanoparticles have attracted extensive attention in recent years. However, compared with simple metal nanoparticles, people can easily adjust the magnetic properties of alloy nanoparticles by adjusting the alloy composition, so the preparation and performance research of magnetic alloy nanoparticles has attracted more and more attention. The preparation and properties of FeCo, CoNi, FeNi and other magnetic alloy nanoparticles formed by mutual solid solution of Fe, Co, Ni and other metals have been extensively studied. Commonly used preparation methods include: reverse micelles (I.Ban, M.Drofenik, D.Makovec, J.Magn.Magn.Mater.307, 250 (2006).), chemical vapor condensation (Z.H.Wang, C.J. Choi, J.C.Kim, B.K.Kim, Z.D.Zhang, Mater.Lett.57, 3560(2003).), electrochemical deposition method (S.Banerjee, S.Roy,.J.W.Chen, D.Chakravorty, J.Magn.Magn .Mater.219, 45(2000).), mechanical alloying method (Y.D.Kim, J.Y.Chung, J.Kim, H.Jeon, Mater.Sci.Eng.A291, 17(2000).), liquid phase chemical reduction Synthetic method (C.W.Kim, Y.H.Kim, H.G.Cha, H.W.Kwon, Y.S.Kang, J.Phys.Chem.B, 110, 24418 (2006).) and high temperature chemical reduction method (G.Ennas, A.Falqui, S. Marras, C. Sangregorio, G. Marongiu, Chem. Mater. 16, 5659 (2004).) et al. Metal elemental Cr has antiferromagnetism, and the magnetic properties of the FeCr alloy formed by it and ferromagnetic metal Fe are greatly affected by the alloy composition. Fe-rich alloys exhibit ferromagnetism while Cr-rich alloys exhibit antiferromagnetism; in addition, The solid solution of Cr helps to improve the oxidation resistance of FeCr alloy particles, so Fe-rich FeCr alloy nanoparticles are expected to become an important class of magnetic materials, but there are few studies on the preparation and properties of such materials.

It is well known that the magnetic properties of materials are directly related to the size of the magnetic particles and their interactions. When the particle size is reduced below the critical scale, the ferromagnetic material will transform from a magnetic multi-domain structure to a magnetic single-domain structure and then produce superparamagnetic phenomena. Generally, the surface atoms in metal nanoparticles account for a large proportion and have high surface energy, so they are easily lost due to oxidation or agglomeration. In order to make metal nanoparticles exist stably and avoid oxidation and agglomeration, they must be dispersed into the matrix of organic or inorganic materials, thus forming magnetic nanocomposite particles dispersed by metal nanoparticles. The magnetic properties of the nanocomposite particles not only depend on the intrinsic properties of individual magnetic nanoparticles but also greatly depend on the binding state between the nanoparticles and the matrix. At present, the matrix materials used to disperse magnetic metal and alloy nanoparticles are usually organic solvents such as polyols, amorphous SiO ₂ , Al ₂ O ₃ aerogels, and the like. For example, Chinese Invention Patent Publication No. CN1919507A reports a method of simultaneously adding polymer dispersant polyvinylpyrrolidone (PVP K-30) and ethanol to disperse nano-metal Fe particles. Chinese invention patent number ZL200410041128.9 reported a method for obtaining amorphous _SiO2- coated metal Fe nanoparticles by wet chemical methods such as sol-gel combined with high-temperature chemical reduction. However, polymers and amorphous SiO ₂ and other coating materials have poor thermal stability and other properties. For example, metal Fe nanoparticles coated on the surface of polymers can only exist stably at room temperature, and metal Fe nanoparticles coated with amorphous SiO ₂ Particles oxidize when the ambient temperature is higher than 150°C.

Ceramics have many characteristics such as high temperature resistance, high hardness, oxidation resistance, wear resistance, and corrosion resistance. If magnetic alloy nanoparticles can be dispersed in the ceramic matrix, it is expected to greatly improve the high temperature resistance, oxidation resistance, and wear resistance of magnetic nanoparticles. , Anti-corrosion and other properties. Generally speaking, alloy nanoparticles can be dispersed in the ceramic matrix by reducing the mixture of metal oxide precursors at high temperature, or a ceramic/alloy-core/shell structure in which alloy particles are coated with ceramic particles can be formed (for example, Chinese Invention Patent No. ZL200510094459.3 ). However, the alloy nanoparticles prepared by this method are located between or on the surface of ceramic grains, and the nanoparticles are easy to agglomerate and oxidized. At the same time, the size of the nanoparticles is easily affected by the metal oxide precursor, and the particle size distribution and monodispersity are relatively low. It is difficult to control, and the generated alloy nanoparticles often reach tens to hundreds of nanometers, which leads to the loss of its special magnetic properties.

Contents of the invention

The purpose of the present invention is to provide a method for preparing magnetic nanocomposite particles of FeCr alloy dispersed in ceramic crystal grains. The nanocomposite particles prepared by the method have the characteristics of superparamagnetic physical properties and high stability.

In order to achieve the above object, the technical scheme of the present invention is: the preparation method of the magnetic nano-composite particles of FeCr alloy dispersed in the ceramic crystal grain, it is characterized in that it comprises the steps:

1) Selection of raw materials: the amount of Al in aluminum salt, Si in silicon source, Fe in iron salt and Cr in chromium salt conforms to the chemical formula (Al _6-xy Fe _x Cr _y )Si ₂ O ₁₃ , where 0<x+y ≤1, and x≥y, y>0, select aluminum salt, silicon source, iron salt and chromium salt as raw materials;

2), using one of the following two methods (precursor preparation):

a) Sol-gel gelation: Dissolve aluminum salts, iron salts and chromium salts in distilled water or absolute ethanol to form a solution with a sum of metal ion molar concentrations of 1 to 2 mol/L, and heat it in a water bath to 60 to 90 After stirring for 1-6 hours at ℃; add HNO ₃ with a molar concentration of 1-2 mol/L dropwise to the solution, adjust the pH value of the solution to 2.5-3.5 and continue stirring for 1-3 hours; add silicon source drop by drop with a molar concentration of 13 ~15mol/L NH ₃ ·H ₂ O to adjust the pH value of the solution to 4.5~5.5, continue to stir for 3~5 hours, then move to a constant temperature water bath at 60~90°C for aging until xerogel is formed;

b) co-precipitation method to form a gel: the aluminum salt, iron salt and chromium salt are pre-prepared into solutions with a molar concentration of 1-2 mol/L with distilled water or absolute ethanol as a dispersant, and the above three solutions (aluminum salt solution , iron salt solution and chromium salt solution) after mixing, add silicon source drop by drop and mix for 1-6 hours to obtain a mixed solution; add NH ₃ · H ₂ O, adjust the pH value of the solution to 6.5-7.5 and stir for 2-6 hours to obtain a slurry; pour the obtained slurry into a rotary evaporator for drying at 60-90°C to obtain a xerogel;

3) Pre-calcination: the xerogel is roasted at 400-600°C for 1-5 hours under flowing air to remove organic volatiles in the xerogel to obtain amorphous oxide powder;

4) Calcination: The amorphous oxide powder is calcined in the air at 1000-1500°C for 1-5 hours to obtain a mullite solid solution ceramic powder in which Fe ³⁺ and Cr ³⁺ ions are completely dissolved;

5) High-temperature reduction: Fe ³⁺ and Cr ³⁺ ions are completely solid-dissolved mullite solid solution ceramic powder with reducing gas at 1200-1400°C for 1-10 hours; magnetic nanocomposite particles of FeCr alloy dispersed in ceramic grains are obtained .

Commonly used aluminum salts are aluminum nitrate, aluminum isopropoxide or aluminum chloride; silicon source is tetraethyl orthosilicate; iron salt is ferric nitrate, ferric sulfate or ferric chloride; chromium salt is chromium nitrate or chromium chloride.

The reducing gas is H ₂ or a mixed gas containing H ₂ , such as: H ₂ , H ₂ -Ar or H ₂ -N ₂ .

The principle of the present invention is: using wet chemical method combined with heat treatment, Fe ³⁺ and Cr ³⁺ ions replace part of Al ³⁺ ions through solid solution reaction to evenly occupy the lattice points of the substitutional mullite solid solution ceramic crystal . Under the action of high temperature and reducing atmosphere, Fe ³⁺ and Cr ³⁺ are easier to be reduced to simple substances than Al ³⁺ and Si ⁴⁺ , and then they are solid-soluted with each other to form FeCr alloys. At the same time, highly stable Al ³⁺ and Si ⁴⁺ ions are It is maintained in the form of mullite oxide ceramic grains. Since the generated FeCr alloy is formed inside the mullite grains, its growth and agglomeration are greatly restricted, so it can maintain the nanoscale, uniform dispersion, and controllable particle size distribution. At the same time, the unreduced mullite ceramic grains with high stability serve as a matrix material to stabilize the FeCr alloy nanoparticles. FeCr alloy nanoparticles are wrapped in the interior of mullite ceramic grains, and the material transport on which the growth of nanoparticles depends is difficult because of the hindrance of ceramic grains. The particle size of FeCr alloy nanoparticles obtained in this way is generally several to Between tens of nanometers, it exhibits superparamagnetic physical properties and high stability.

The product prepared by the present invention is characterized by structure and performance by the following means: the phase composition of the material is determined by the RU-200B target X-ray diffractometer of Japan Rigaku Company; the morphology and size of FeCr alloy nanoparticles are determined by the Japanese Hitachi Company Direct observation with H-8000 transmission electron microscope; the magnetic properties of the material were measured by the MPMS superconducting quantum magnetometer of Quantum Design Company in the United States; the high temperature stability of the material was measured by the TG-DTA 2020SAF thermogravimetric-differential thermal analyzer of Bruker Axs Company in Japan evaluate.

The beneficial effects of the present invention are: the FeCr alloy magnetic nanoparticles are monodispersely distributed inside the mullite ceramic grains, the particle size is uniform, and the average particle size is less than 15nm, and its magnetic properties are affected by the composition of Fe and Cr in the solid solution. Paramagnetic properties and strong oxidation resistance; because the FeCr alloy magnetic nanoparticles are distributed inside the mullite ceramic grains, the thermal stability is greatly improved, and the oxidation temperature in the air is above 1000 ° C, and the thermal stability is strong. Since the mullite ceramic grains are used as a stable matrix, alloy nanoparticles grow inside the ceramic grains, which not only hinders the material transport that causes the growth of alloy particles through the ceramic grains, but also ensures the nanostructure and monodispersity of the alloy particles. And uniformity, and make full use of the high temperature resistance, corrosion resistance, oxidation resistance and other characteristics of ceramic grains to greatly improve the stability of alloy nanoparticles.

Description of drawings

Fig. 1 is in the preparation process in the embodiment 1 of the present invention, the mullite solid solution ceramic powder (abbreviation solid solution) of precursor, Fe ³⁺ and Cr ³⁺ ion complete solid solution and its XRD of the sample obtained after reduction at different temperatures Spectrum, there are 5 spectral lines. It shows that the single-phase mullite solid solution is formed by heat treatment of the amorphous precursor, and the cubic FeCr alloy phase is obtained in the mullite matrix when the reduction temperature of the solid solution exceeds 1200 °C. Precursor: a) spectral line; solid solution obtained by heat treatment at 1200°C: b) spectral line; sample reduced at 1200°C: c) spectral line; sample reduced at 1300°C: d) spectral line; Sample: e) Spectral line.

Figure 2a is a TEM photo of the product obtained after reduction at a temperature of 1200°C during the preparation process of Example 1 of the present invention;

Figure 2b is a TEM photo of the product obtained after reduction at a temperature of 1300°C during the preparation process of Example 1 of the present invention;

Figure 2c is a TEM photo of the product obtained after reduction at a temperature of 1400°C during the preparation process of Example 1 of the present invention;

Figure 2a, Figure 2b, and Figure 2c illustrate that FeCr alloy nanoparticles are monodispersely distributed within the mullite ceramic grains. The particle size of the nanoparticles is uniform and small, and the average particle size is less than 15nm. Elevation has increased.

Figure 3a is the 10K and 300K hysteresis loop diagrams of the products obtained after reduction at 1200°C during the preparation process of Example 1 of the present invention;

Fig. 3b is a 10-300K field cooling-zero field cooling curve of the product obtained after reduction at a temperature of 1200°C during the preparation process of Example 1 of the present invention.

Fig. 4a is a thermogravimetric curve of oxidation weight gain of the product obtained after reduction at 1200°C in the air during the preparation process of Example 1 of the present invention;

Fig. 4b is a curve diagram of the oxidation temperature of the sample after reduction at different temperatures during the preparation process of Example 1 of the present invention;

The results in Figure 4a and Figure 4b show that the oxidation temperature increases with the increase of the reduction temperature of the sample.

Figure 5 shows the magnetic properties of FeCr alloy nanoparticles obtained by reducing mullite solid solutions with different compositions at 1200°C during the preparation process of Example 2 of the present invention: curve a) coercive force at 300K; curve b) coercive force at 10K force. The results show that the nanocomposite particles obtained by reducing mullite solid solutions with different compositions are all superparamagnetic, and their low-temperature magnetic properties are affected by the composition of Fe and Cr in the solid solution.

Detailed ways

The following examples are intended to further illustrate the process characteristics of the present invention rather than limit the present invention, wherein Examples 1-6 adopt the sol-gel method to form gels, and Examples 7-11 utilize the co-precipitation method to form gels. All reagents used in the examples were of analytical grade. Note: in the embodiment of the present invention, the amount of aluminum salt, silicon source, iron salt, and chromium salt raw material is only accurate to the last two digits of the decimal point, and the present invention can be realized in the experiment; ordinary technicians in the technical field can follow the content of the invention Some technical solutions are more accurate.

Example 1:

According to the chemical formula Al _5.4 Fe _0.36 Cr _0.24 Si ₂ O ₁₃ , 0.54mol Al(NO ₃ ) ₃ ·9H ₂ O, 0.036mol Fe(NO ₃ ) ₃ ·9H ₂ O and 0.024mol Cr(NO ₃ ) ₃ ·9H Dissolve ₂ O in 400ml of absolute ethanol to form a solution with a sum of molar concentrations of metal ions of 1.5mol/L, heat in a water bath to 60°C and stir vigorously with a magnetic force; after stirring the solution for 6 hours, add HNO ₃ with a molar concentration of 1.5mol/L dropwise Solution, adjust the pH value of the solution to 3 and continue to stir for 3 hours; add 0.2mol tetraethyl orthosilicate (TEOS) dropwise to the solution, and add NH ₃ ·H ₂ O with a molar concentration of 15mol/L dropwise to adjust the pH of the solution value to 5, continue to stir for 5 hours, and then move the sol to a constant temperature water bath at 80°C for aging until a xerogel (or precursor) is formed. The xerogel was calcined at 500 °C for 5 h in flowing air to obtain amorphous oxide powder (ie precursor powder); the obtained precursor powder was calcined at 1200 °C in air for 4 h to form Fe ³⁺ and Cr ³⁺ ions completely solidified Dissolved mullite solid solution ceramic powder (referred to as solid solution); Fe ³⁺ and Cr ³⁺ ions completely dissolved mullite solid solution ceramic powder with H ₂ gas at 1200-1400°C (such as 1200°C, 1300°C, 1400°C) for 1 hour, and the obtained product is magnetic nanocomposite particles of FeCr alloy dispersed in ceramic grains (or inorganic magnetic nanocomposite particles formed by nanometer FeCr alloy particles dispersed in mullite ceramic grains).

During the preparation process, the precursor, solid solution and the XRD spectrum of the sample obtained after reduction at different temperatures are shown in Figure 1, indicating that the single-phase mullite solid solution is formed by heat treatment of the amorphous precursor. When the reduction temperature of the solid solution exceeds 1200 At ℃, a single cubic FeCr phase is formed in the mullite matrix. The TEM photos of FeCr alloy nanoparticles in the product obtained after reduction at different temperatures are shown in Figure 2a, Figure 2b, and Figure 2c. The particle size of the nano-alloy particles distributed inside the mullite ceramic grains increases with the increase of the reduction temperature. , the average particle size is 5-15nm. The hysteresis loop of the 1200°C reduction product measured at 300K and 10K (as shown in Figure 3a) shows that the coercive force (220Oe) of the product at 10K is significantly higher than that at 300K (47Oe); field cooling at 10-300K -The zero-field cooling curve (as shown in Figure 3b) shows that the FeCr alloy nanoparticles in the product exhibit superparamagnetism, and the blocking temperature is 30K. Figure 4a is the thermogravimetric curve of the oxidation weight gain of the product obtained after reduction at 1200°C in the air during the preparation process of Example 1 of the present invention; Figure 4b is the relationship between the oxidation temperature and the reduction preparation temperature of the product obtained by reduction at different temperatures; The products obtained at different reduction temperatures have different thermal stability in air, and the oxidation temperature increases slightly with the increase of reduction temperature, but they are all higher than 1000°C.

Under the same process, use aluminum isopropoxide and aluminum chloride to obtain similar results as above.

Example 2:

According to the chemical formula Al _5.4 (Fe _1-x Cr _x ) _0.6 Si ₂ O ₁₃ , (x=0.1~0.5), Al(NO ₃ ) ₃ 9H ₂ O, Fe(NO ₃ ) ₃ 9H ₂ O, Cr (NO ₃ ) ₃ 9 _H 2O and tetraethyl orthosilicate (TEOS) are used as raw materials for proportioning, and according to the process of Example 1, a mullite solid solution ceramic powder that forms a complete solid solution of Fe ³⁺ and Cr ³⁺ ions is obtained ; The mullite solid solution ceramic powder with complete solid solution of Fe ³⁺ and Cr ³⁺ ions was reduced with H ₂ gas at 1200°C for 1 h, and the obtained products were magnetic nanocomposite particles of FeCr alloy dispersed in ceramic grains with different compositions. It shows that the nanocomposite particles obtained by reducing mullite solid solutions with different compositions are all superparamagnetic, and their low-temperature magnetic properties are affected by the composition of Fe and Cr in the solid solution.

Example 3:

According to the chemical formula Al _5.9 Fe _0.09 Cr _0.01 Si ₂ O ₁₃ , 0.59mol Al(NO ₃ ) ₃ ·9H ₂ O, 0.009mol Fe(NO ₃ ) ₃ ·9H ₂ O and 0.001mol CrCl ₃ ·9H ₂ O were dissolved in In 600ml of absolute ethanol, a solution with a sum of molar concentrations of metal ions of 1 mol/L was formed, heated in a water bath to 90°C and stirred strongly by magnetic force; after the solution was stirred for 1 hour, a solution of HNO ₃ with a molar concentration of 1 mol/L was added dropwise to adjust the pH value of the solution After reaching 3.5, continue stirring for 3 hours; add 0.2 mol tetraethyl orthosilicate (TEOS) dropwise to the solution, and add NH ₃ ·H ₂ O with a molar concentration of 13 mol/L dropwise to adjust the pH value of the solution to 5.5, and continue stirring After 5 hours, the sol was moved to a constant temperature water bath at 60° C. for aging until a xerogel (or precursor) was formed. The xerogel was calcined at 400 °C for 5 h in flowing air to obtain amorphous oxide powder (ie precursor powder); the obtained precursor powder was calcined at 1000 °C in air for 5 h to form Fe ³⁺ and Cr ³⁺ ions completely solidified Dissolved mullite solid solution ceramic powder; Fe ³⁺ and Cr ³⁺ ions completely dissolved mullite solid solution ceramic powder with H ₂ -Ar gas (the mass ratio of H ₂ and Ar is arbitrary, H ₂ >0) After reduction at 1200°C for 10 hours, the obtained product is magnetic nanocomposite particles of FeCr alloy dispersed in ceramic grains. Among them, the average particle diameter of FeCr alloy nanoparticles dispersed in the mullite ceramic grains is 7nm, and the oxidation temperature in air is 1057°C.

Example 4:

According to the chemical formula Al ₅ Fe _0.5 Cr _0.5 Si ₂ O ₁₃ , dissolve 0.5mol Al(NO ₃ ) ₃ 9H ₂ O, 0.05mol FeCl ₃ 6H ₂ O and 0.05mol CrCl ₃ 9H ₂ O in 300ml absolute ethanol Form a solution with the sum of the molar concentrations of metal ions being 2mol/L, heat it in a water bath to 60°C and stir it strongly with a magnetic force; after stirring the solution for 6 hours, add _HNO3 solution with a molar concentration of 2mol/L dropwise, adjust the pH value of the solution to 2.5 and continue stirring 1h; add 0.2mol tetraethyl orthosilicate (TEOS) dropwise to the solution, and add NH ₃ ·H ₂ O with a molar concentration of 15mol/L dropwise to adjust the pH value of the solution to 4.5, continue to stir for 3 hours, and then remove the sol Aging in a constant temperature water bath at 90°C until a xerogel (or precursor) is formed. The xerogel was calcined at 600 °C for 1 h under flowing air to obtain amorphous oxide powder (ie precursor powder); the obtained precursor powder was calcined at 1500 °C in air for 5 h to form Fe ³⁺ and Cr ³⁺ ions completely solidified Dissolved mullite solid solution ceramic powder; Fe ³⁺ and Cr ³⁺ ions completely dissolved mullite solid solution ceramic powder was reduced with H ₂ gas at 1200 ° C for 1 h, and the obtained product was the magnetic properties of FeCr alloy dispersed in ceramic grains. Nanocomposite particles (or inorganic magnetic nanocomposite particles formed by dispersing FeCr alloy nanoparticles inside mullite ceramic grains). Among them, the FeCr alloy nanoparticles dispersed in the mullite ceramic grains have an average particle size of 6nm, and the oxidation temperature in air is 1070°C.

Example 5:

According to the chemical formula Al ₅ Fe _0.5 Cr _0.5 Si ₂ O ₁₃ , 0.5mol AlCl ₃ ·9H ₂ O, 0.05mol Fe ₂ (SO ₄ ) ₃ ·9H ₂ O and 0.05mol Cr(NO ₃ ) ₃ ·9H ₂ O were dissolved in In 300ml of distilled water, a solution with a sum of molar concentrations of metal ions of 2 mol/L was formed, heated in a water bath to 90°C and stirred strongly by magnetic force; after the solution was stirred for 6 hours, a solution of HNO ₃ with a molar concentration of 1 mol/L was added dropwise to adjust the pH value of the solution to 3.5 Then continue to stir for 3 hours; add 0.2mol tetraethyl orthosilicate (TEOS) dropwise to the solution, and add NH ₃ ·H ₂ O with a molar concentration of 15mol/L dropwise to adjust the pH value of the solution to 5.5, and continue stirring for 5 hours The sol was aged in a constant temperature water bath at 90°C until a xerogel was formed. The xerogel was calcined at 400 °C for 5 h in flowing air to obtain amorphous oxide powder (ie precursor powder); the obtained precursor powder was calcined at 1000 °C in air for 1 h to form Fe ³⁺ and Cr ³⁺ ions completely solidified Dissolved mullite solid solution ceramic powder; Fe ³⁺ and Cr ³⁺ ions completely dissolved mullite solid solution ceramic powder with H ₂ -N ₂ gas (the mass of H ₂ and N ₂ is an arbitrary ratio, H ₂ > 0) Reducing at 1400° C. for 10 h, the obtained product is magnetic nanocomposite particles of FeCr alloy dispersed in ceramic grains. The average particle size of the FeCr alloy nanoparticles dispersed in the mullite ceramic grains is 14nm, and the oxidation temperature in air is 1255°C.

Embodiment 6:

According to the chemical formula Al _5.9 Fe _0.09 Cr _0.01 Si ₂ O ₁₃ , 0.59mol Al(NO ₃ ) ₃ ·9H ₂ O, 0.009mol Fe(NO ₃ ) ₃ ·9H ₂ O and 0.001mol CrCl ₃ ·9H ₂ O were dissolved in In 600ml of distilled water, a solution with a sum of molar concentrations of metal ions of 1 mol/L was formed, heated in a water bath to 60°C and strongly magnetically stirred; after the solution was stirred for 6 hours, a solution of HNO ₃ with a molar concentration of 2 mol/L was added dropwise to adjust the pH value of the solution to 2.5 Then continue stirring for 1 h; add 0.2 mol tetraethyl orthosilicate (TEOS) dropwise to the solution, and add NH ₃ ·H ₂ O with a molar concentration of 13 mol/L dropwise to adjust the pH value of the solution to 4.5, and continue stirring for 3 h The sol was aged in a constant temperature water bath at 90°C until a xerogel was formed. The xerogel was calcined at 600 °C for 5 h in flowing air to obtain amorphous oxide powder (ie precursor powder); the obtained precursor powder was calcined at 1500 °C in air for 1 h to form Fe ³⁺ and Cr ³⁺ ions completely solidified Dissolved mullite solid solution ceramic powder; Fe ³⁺ and Cr ³⁺ ions completely dissolved mullite solid solution ceramic powder with H ₂ -N ₂ gas (the mass of H ₂ and N ₂ is an arbitrary ratio, H ₂ > 0) Reducing at 1300° C. for 5 hours, the obtained product is magnetic nanocomposite particles of FeCr alloy dispersed in ceramic grains. The FeCr alloy nanoparticles dispersed in the mullite ceramic grains have an average particle size of 10nm and an oxidation temperature of 1175°C in air.

Embodiment 7:

According to the chemical formula Al _5.5 Fe _0.45 Cr _0.05 Si ₂ O ₁₃ , 550ml molar concentration of 1mol/L Al(NO ₃ ) ₃ ethanol solution, 45ml molar concentration of 1mol/L Fe(NO ₃ ) ₃ ethanol solution and 5ml molar The CrCl ₃ ethanol solution with a concentration of 1mol/L was mixed and 0.2mol tetraethyl orthosilicate (TEOS) was added dropwise to it, the solution was stirred and mixed in a constant temperature water bath at 75°C for 1h, and the molar concentration of 13mol/L was added dropwise. NH ₃ ·H ₂ O, adjust the pH value of the solution to 7.0 and continue to stir for 6 hours to obtain a slurry; the obtained slurry is poured into a rotary evaporator for drying at 80°C to obtain a xerogel; the xerogel is dried under flowing air at 500 Calcined at ℃ for 4 hours to obtain amorphous oxide powder (ie precursor powder); the obtained precursor powder was calcined at 1200℃ in air for 9 hours to form a mullite solid solution ceramic powder in which Fe ³⁺ and Cr ³⁺ ions were completely dissolved The mullite solid solution ceramic powder with complete solid solution of Fe ³⁺ and Cr ³⁺ ions is reduced with H ₂ gas at 1300°C for 1h, and the obtained product is magnetic nanocomposite particles of FeCr alloy dispersed in ceramic grains (or called FeCr alloy Inorganic magnetic nanocomposite particles formed by dispersing nanoparticles in mullite ceramic grains). Among them, the average particle diameter of FeCr alloy nanoparticles dispersed in the mullite ceramic grains is 9nm, and the oxidation temperature in air is 1147°C.

Under the same process, the use of aluminum isopropoxide or aluminum chloride obtained similar results to the above.

Embodiment 8:

According to chemical formula Al _5.9 Fe _0.05 Cr _0.05 Si ₂ O ₁₃ , 295ml molar concentration is 2mol/L Al(NO ₃ ) ₃ ethanol solution, 2.5ml molar concentration is 2mol/L FeCl ₃ ethanolic solution and 2.5ml molar concentration are 2mol/L Cr(NO ₃ ) ₃ ethanol solution was mixed and 0.2mol tetraethyl orthosilicate (TEOS) was added dropwise to it, the solution was stirred and mixed in a constant temperature water bath at 60°C for 6h, and the molar concentration was 15mol/L was added dropwise. L of NH ₃ ·H ₂ O, adjusted the pH value of the solution to 6.5 and continued to stir for 2 hours to obtain a slurry; the obtained slurry was poured into a rotary evaporator for drying at 80°C to obtain a xerogel; the xerogel was flowing Calcined at 600°C in air for 5h to obtain amorphous oxide powder (precursor powder); the obtained precursor powder was calcined at 1500°C in air for 1h to form mullite in which Fe ³⁺ and Cr ³⁺ ions were completely dissolved Solid solution ceramic powder; mullite solid solution ceramic powder with complete solid solution of Fe ³⁺ and Cr ³⁺ ions, using H ₂ -N ₂ gas (the mass ratio of H ₂ and N ₂ is arbitrary, H ₂ >0) at 1200°C After reduction for 10 hours, the obtained product is magnetic nanocomposite particles of FeCr alloy dispersed in ceramic crystal grains. Among them, the average particle size of FeCr alloy nanoparticles dispersed in the mullite ceramic grains is 9nm, and the oxidation temperature in air is 1115°C.

Embodiment 9:

According to the chemical formula Al _5.9 Fe _0.05 Cr _0.05 Si ₂ O ₁₃ , 590 ml of a molar concentration of 1 mol/L AlCl ₃ aqueous solution, 2.5 ml of a molar concentration of 2 mol/L Fe(NO ₃ ) ₃ aqueous solution and 2.5 ml of a molar concentration of 2 mol/L Mix L of CrCl ₃ aqueous solution and add 0.2 mol tetraethyl orthosilicate (TEOS) dropwise to it, stir and mix the solution in a constant temperature water bath at 80°C for 2 hours, and add NH ₃ ·H ₂ with a molar concentration of 15 mol/L dropwise O, adjust the pH value of the solution to 7.5 and continue to stir for 6 hours to obtain a slurry; the resulting slurry is poured into a rotary evaporator for drying at 80°C to obtain a xerogel; the xerogel is roasted at 400°C for 1 hour under flowing air , to obtain amorphous oxide powder (precursor powder); the obtained precursor powder was calcined in the air at 1000°C for 5 hours to form a mullite solid solution ceramic powder in which Fe ³⁺ and Cr ³⁺ ions were completely dissolved; Fe The mullite solid solution ceramic powder with ³⁺ and Cr ³⁺ ions in complete solid solution is reduced with H ₂ -Ar gas (the mass ratio of H ₂ and Ar is arbitrary, H ₂ >0) at 1400°C for 10 hours to obtain the product It is magnetic nanocomposite particles of FeCr alloy dispersed in ceramic grains. The FeCr alloy nanoparticles dispersed in the mullite ceramic grains have an average particle size of 15nm and an oxidation temperature of 1270°C in air.

Example 10:

According to the chemical formula Al ₅ Fe _0.5 Cr _0.5 Si ₂ O ₁₃ , 250ml molar concentration is 2mol/L Al(NO ₃ ) ₃ ethanol solution, 50ml molar concentration is 1mol/L Fe ₂ (SO ₄ ) ₃ ethanol solution and 25ml The CrCl ₃ ethanol solution with a molar concentration of 2mol/L was mixed and 0.2mol tetraethyl orthosilicate (TEOS) was added dropwise to it. The solution was stirred and mixed in a constant temperature water bath at 60°C for 1h, and the molar concentration was 13mol/L was added dropwise. NH ₃ ·H ₂ O, adjusted the pH value of the solution to 7.5 and continued to stir for 6 hours to obtain a slurry; the obtained slurry was poured into a rotary evaporator for drying at 80°C to obtain a xerogel; the xerogel was dried under flowing air Calcined at 600°C for 5 hours to obtain amorphous oxide powder (ie precursor powder); the obtained precursor powder was calcined at 1500°C in air for 5 hours to form a mullite solid solution ceramic in which Fe ³⁺ and Cr ³⁺ ions were completely dissolved Powder; solid solution ceramic powder is reduced with H ₂ gas at 1400°C for 1 hour, and the obtained product is magnetic nanocomposite particles of FeCr alloy dispersed in ceramic grains. The FeCr alloy nanoparticles dispersed in the mullite ceramic grains have an average particle size of 13nm and an oxidation temperature of 1235°C in air.

Example 11:

According to the chemical formula Al ₅ Fe _0.5 Cr _0.5 Si ₂ O ₁₃ , 250 ml of a molar concentration of 2 mol/L AlCl ₃ aqueous solution, 50 ml of a molar concentration of 1 mol/L FeCl ₃ aqueous solution and 50 ml of a molar concentration of 1 mol/L Cr(NO ₃ ) ₃ aqueous solutions were mixed and 0.2 mol tetraethyl orthosilicate (TEOS) was added dropwise thereto, the solution was stirred and mixed in a constant temperature water bath at 90°C for 6 hours, and NH ₃ ·H ₂ O with a molar concentration of 15 mol/L was added dropwise, Adjust the pH value of the solution to 6.5 and continue to stir for 2 hours; pour the obtained slurry into a rotary evaporator for drying at 80°C to obtain a xerogel; bake the xerogel at 400°C for 1h under flowing air to obtain an amorphous oxide powder ( That is, the precursor powder); the obtained precursor powder is calcined at 1000°C in the air for 5h to form a mullite solid solution ceramic powder with Fe ³⁺ and Cr ³⁺ ions completely dissolved; the precursor powder is calcined at 1000°C in the air 5h, forming and reducing with H ₂ -N ₂ gas at 1200°C for 1h, the obtained product is magnetic nanocomposite particles of FeCr alloy dispersed in ceramic crystal grains. The FeCr alloy nanoparticles dispersed in the mullite ceramic grains have an average particle size of 5nm and an oxidation temperature of 1045°C in air.

Each raw material enumerated in the present invention can realize the present invention, and the upper and lower limit value of each raw material, interval value can realize the present invention, the upper and lower limit value and interval value of process parameter (such as temperature, time etc.) of the present invention The present invention can be realized, and the embodiments are not listed one by one here.

Claims (6)

1. the preparation method of the magnetic Nano composite granules of disperse FeCr alloy in the ceramic crystalline grain is characterized in that it comprises the steps:

1), raw material is chosen: in the aluminium salt in Al, the silicon source in Si, the molysite in Fe and the chromic salts consumption of Cr meet chemical formula (Al _6-x-yFe _xCr _y) Si ₂O ₁₃, aluminium salt, silicon source, molysite and chromic salts raw material for standby are chosen in wherein 0＜x+y≤1, and x 〉=y, y＞0;

2), adopt one of following two kinds of methods:

A) sol-gel process becomes glue: aluminium salt, molysite and chromic salts are dissolved in distilled water or the absolute ethyl alcohol, and forming metal ion molar concentration sum is the solution of 1～2mol/L, and water-bath is stirred 1～6h after being heated to 60～90 ℃; Dripping molar concentration in the solution is the HNO of 1～2mol/L ₃, 1～3h is continued to stir in regulator solution pH value to 2.5～3.5 backs; Dropwise add the silicon source, dripping molar concentration is the NH of 13～15mol/L ₃H ₂O regulator solution pH value is 4.5～5.5, moves to ageing in 60～90 ℃ of waters bath with thermostatic control after continuing to stir 3～5h, until forming xerogel;

B) coprecipitation becomes glue: is that dispersant is mixed with the solution that molar concentration is 1～2mol/L in advance respectively with aluminium salt, molysite and chromic salts with distilled water or absolute ethyl alcohol, dropwise adds the silicon source after the mixing and mixes 1～6h, gets mixed solution; In 60～90 ℃ of waters bath with thermostatic control, be the NH of 13～15mol/L to the mixed solution and dripping molar concentration ₃H ₂O, regulator solution pH value to 6.5～7.5 backs are stirred 2～6h, are got slip; The gained slip carries out drying under 60～90 ℃, obtain xerogel;

3), preroast: xerogel is 400～600 ℃ of roasting 1～5h under moving air, obtain amorphous oxide powder;

4), calcining: amorphous oxide powder is 1000～1500 ℃ of calcining 1～5h in air, obtain Fe ³⁺And Cr ³⁺The mullite solid solution ceramic powder of the complete solid solution of ion;

5), high temperature reduction: Fe ³⁺And Cr ³⁺The mullite solid solution ceramic powder of the complete solid solution of ion uses reducing gas at 1200～1400 ℃ of reduction 1～10h; Obtain the magnetic Nano composite granules of disperse FeCr alloy in the ceramic crystalline grain.

2. according to the preparation method of the magnetic Nano composite granules of disperse FeCr alloy in the ceramic crystalline grain of claim 1, it is characterized in that: aluminium salt is aluminum nitrate, aluminium isopropoxide or aluminium chloride.

3. according to the preparation method of the magnetic Nano composite granules of disperse FeCr alloy in the ceramic crystalline grain of claim 1, it is characterized in that: the silicon source is a tetraethoxysilane.

4. according to the preparation method of the magnetic Nano composite granules of disperse FeCr alloy in the ceramic crystalline grain of claim 1, it is characterized in that: molysite is ferric nitrate, ferric sulfate or iron chloride.

5. according to the preparation method of the magnetic Nano composite granules of disperse FeCr alloy in the ceramic crystalline grain of claim 1, it is characterized in that: chromic salts is chromic nitrate or chromium chloride.

6. according to the preparation method of the magnetic Nano composite granules of disperse FeCr alloy in the ceramic crystalline grain of claim 1, it is characterized in that: reducing gas is H ₂Or contain H ₂Gaseous mixture.

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