CN108584997B - Preparation method of magnesium oxide powder for fireproof cable - Google Patents
Preparation method of magnesium oxide powder for fireproof cable Download PDFInfo
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- CN108584997B CN108584997B CN201810760504.1A CN201810760504A CN108584997B CN 108584997 B CN108584997 B CN 108584997B CN 201810760504 A CN201810760504 A CN 201810760504A CN 108584997 B CN108584997 B CN 108584997B
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/02—Magnesia
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K21/00—Fireproofing materials
- C09K21/02—Inorganic materials
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
- H01B3/10—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances metallic oxides
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/02—Disposition of insulation
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
- H01B7/18—Protection against damage caused by wear, mechanical force or pressure; Sheaths; Armouring
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
- H01B7/29—Protection against damage caused by extremes of temperature or by flame
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
- H01B7/29—Protection against damage caused by extremes of temperature or by flame
- H01B7/295—Protection against damage caused by extremes of temperature or by flame using material resistant to flame
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/32—Thermal properties
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/40—Electric properties
Abstract
The invention relates to a preparation method of magnesia powder for fireproof cables, which comprises the following steps of (A-1) smelting magnesite, and cooling and crushing the magnesite after smelting to obtain fused magnesia; (A-2) grinding the fused magnesia obtained in the step (A-1) to obtain magnesia powder; (A-3) adding an additive into the magnesium oxide powder obtained in the step (A-2), mixing and stirring, and then statically storing, wherein the additive comprises white carbon black and an organic modifier; (A-4) drying the magnesium oxide powder obtained in the step (A-3). The magnesium oxide for the fireproof cable, which is obtained by the invention, has the characteristics of high cable production efficiency, strong fire resistance and good insulating property.
Description
Technical Field
The invention relates to the field of magnesium oxide manufacturing, in particular to a preparation method of magnesium oxide powder for a fireproof cable.
Background
Magnesium oxide, as a high-quality refractory material, has the advantages of high strength, high melting point, stable properties, strong insulating property and the like, and is widely applied to various industrial fields such as steel, chemical engineering, buildings and the like.
The magnesium oxide cable is a cable using magnesium oxide as an insulating material, and generally comprises a copper conductor, a magnesium oxide crystal powder insulating material filled in the middle, and a copper sheath. Because it does not contain organic materials, it has the characteristics of nonflammability, no smoke, no toxicity and fire resistance. In particular, the magnesium oxide cable has excellent fireproof, explosion-proof and flame-retardant performances, can continuously run for a long time at the temperature of 250 ℃, and can run for a short time within 30 minutes at the limit state of 1000 ℃.
Magnesium oxide can be obtained from magnesite by smelting. The chemical composition of magnesite is MgCO3The magnesite crystal belongs to a trigonal carbonate mineral. The magnesium-containing solution, after acting on calcite, changes calcite into magnesite, which thus also belongs to the calcite family.
Shaft kilns, rotary kilns and electric arc furnaces are common magnesium oxide smelting equipment in the industry. Electric arc furnaces utilize high temperature melting of ores and metals produced by an electrode arc. When the gas discharge forms an electric arc, the energy is concentrated, and the temperature of the arc area is more than 3000 ℃. For smelting metal, the flexibility of the device is higher than that of other smelting devices, impurities such as sulfur, phosphorus and the like can be effectively removed, the furnace temperature is easy to control, the occupied area of the device is small, and the device is suitable for smelting high-quality magnesium oxide. In the prior art, magnesite and the like are used as raw materials, the magnesite is smelted through an electric arc furnace to obtain fused magnesite after being cooled to a molten state, the fused magnesite is crushed and ground, certain additives are added, appropriate modification treatment is carried out, and then screening and iron removal are carried out, so that magnesia powder can be obtained.
For the grinding and crushing of the fused magnesia, the Bamark sand making machine is a grinding and crushing device widely used in the industry. The working principle is as follows: the material falls into the impeller rotating at high speed from the upper part of the machine vertically, under the action of high-speed centrifugal force, the material and the other part of the material are shunted around the impeller in an umbrella shape to generate high-speed impact and crushing, after the materials impact each other, the materials are crushed between the impeller and the casing by the multiple times of mutual impact and friction of the materials formed by vortex flow, and are directly discharged from the lower part to form closed-loop multiple circulation, and the required granularity of the finished product is achieved by the control of screening equipment. The Bamark sand making machine is suitable for crushing and shaping soft or medium hard and extremely hard materials, is widely applied to various ores, cement, refractory materials, bauxite chamotte, carborundum, glass raw materials, machine-made building sand, stone materials and various metallurgical slags, and has higher yield and efficiency on high-hard, ultra-hard and abrasion-resistant materials such as silicon carbide, carborundum, sintered bauxite, magnesia and the like than other types of crushers.
In conclusion, the performance of the magnesium oxide product is affected by the steps and processes of ore raw material selection, smelting calcination, grinding and crushing and the like. In fire-resistant cable products, magnesia powder used as an insulating material is required to have both good fire resistance and insulation properties. Therefore, how to improve the refractory performance and the insulating performance of the magnesia powder through the raw material proportion and the process control becomes a research focus and a hot spot in the field.
Disclosure of Invention
The invention discloses a preparation method of magnesium oxide powder for a fireproof cable, aiming at improving the fire resistance and the insulation performance of the magnesium oxide powder.
The invention is realized by the following technical scheme:
a preparation method of magnesium oxide powder for fireproof cables comprises the following steps,
(A-1) smelting magnesite, and cooling and crushing the magnesite after smelting to obtain fused magnesia;
(A-2) grinding the fused magnesia obtained in the step (A-1) to obtain magnesia powder;
(A-3) adding an additive into the magnesium oxide powder obtained in the step (A-2), mixing and stirring, and then statically storing, wherein the additive comprises white carbon black and an organic modifier;
and (A-4) drying the magnesium oxide powder obtained in the step (A-3), and cooling after drying to obtain the magnesium oxide powder for the fireproof cable.
Further, in the magnesite ore in the step (a-1), the mass percentage of magnesium oxide is greater than or equal to 46.60%, the mass percentage of sodium hydroxide is greater than or equal to 51.00%, the mass percentage of ferric oxide is less than or equal to 0.16%, the mass percentage of silicon dioxide is less than or equal to 0.25%, and the mass percentage of calcium oxide is less than or equal to 0.28%.
Further, in the step (A-1), the magnesite is smelted under the temperature condition of 2600-.
Further, in the step (a-1), when the magnesite is smelted, graphite is added to the magnesite.
Further, in the step (a-1), when smelting magnesite, the graphite is added to the magnesite many times, the graphite with a mass percentage of 2% of the total amount of the magnesite is added to the magnesite each time, and the time interval for adding the graphite each time is 1.5 hours.
Further, the particle size of the magnesium oxide powder in the step (a-2) is in the range of 60 to 325 mesh, and the particle size distribution of the magnesium oxide powder in the step (a-2) is +60 mesh: 0 to 3 percent; +80 mesh: 26 to 40 percent; +100 mesh: 13 to 20 percent; +150 mesh: 18 to 22 percent; +200 mesh: 12 to 18 percent; +325 mesh: 11 to 16 percent; 325 mesh: 0 to 1.5 percent.
Further, in the step (a-3), the additive includes white carbon black whose mass percentage is 0.15% of the total amount of the magnesium oxide powder, and an organic modifier whose mass percentage is 0.90% of the total amount of the magnesium oxide powder, and the organic modifier includes a mixed solution of hydrogen-containing silicone oil and a gasoline solvent with a volume ratio of 7: 2.
Further, in the step (a-3), the additive further comprises: the magnesium oxide powder comprises calcined kaolin, zirconia powder and serpentine, wherein the total amount of the calcined kaolin, the zirconia powder and the serpentine is 2.5% of the total amount of the magnesium oxide powder.
Further, in the step (a-3), the additive further comprises: the magnesium alloy comprises, by mass, 0.20% of the total amount of the magnesium oxide powder, titanium dioxide 0.10% of the total amount of the magnesium oxide powder, rubidium oxide 0.10% of the total amount of the magnesium oxide powder, and lanthanum oxide 0.10% of the total amount of the magnesium oxide powder.
The magnesium oxide powder for the fireproof cable is prepared by the preparation method of the magnesium oxide powder for the fireproof cable.
Compared with the prior art, the invention has the advantages that:
the preparation method disclosed by the invention has the advantages of high production efficiency, high product flow rate and stable product performance.
By improving the proportion of the additive and the process, the magnesium oxide powder obtained by the method can still reach the fire-proof standard under the condition that the magnesium content is 95 percent.
The magnesia powder obtained by the method has excellent fire resistance and insulating property.
The magnesium oxide powder obtained by the method has the advantages of quick heat dissipation, good flame retardant property and high mechanical strength, and is particularly suitable for manufacturing fireproof cables.
Detailed Description
The embodiment of the invention provides a preparation method of magnesium oxide powder for a fireproof cable, which comprises the following steps,
(A-1) smelting magnesite, and cooling and crushing the magnesite after smelting to obtain fused magnesia;
(A-2) grinding the fused magnesia obtained in the step (A-1) to obtain magnesia powder;
(A-3) adding an additive into the magnesium oxide powder obtained in the step (A-2), mixing and stirring, and then statically storing, wherein the additive comprises white carbon black and an organic modifier;
and (A-4) drying the magnesium oxide powder obtained in the step (A-3), and cooling after drying to obtain the magnesium oxide powder for the fireproof cable.
The preparation method provided by the embodiment of the invention has high production efficiency, is suitable for large-scale product production, and can obtain stable product performance.
In some embodiments of the present invention, in the magnesite in step (a-1), the mass percentage of magnesium oxide is greater than or equal to 46.60%, the mass percentage of sodium hydroxide is greater than or equal to 51.00%, the mass percentage of ferric oxide is less than or equal to 0.16%, the mass percentage of silicon dioxide is less than or equal to 0.25%, and the mass percentage of calcium oxide is less than or equal to 0.28%.
The magnesite ore with the content ratio meeting the numerical value is used as a raw material, so that white impurity-free fused magnesia with the magnesium content of more than or equal to 95% can be obtained, and various performances of the product are ensured.
In some embodiments of the present invention, in step (a-1), the magnesite is smelted at 2600-.
The magnesite can be fully smelted by adopting the smelting conditions, so that the magnesium oxide with homogeneity and stable performance can be obtained. During smelting, an electric arc furnace with the power of more than 1000KW, the voltage of 110V +/-5V and the current of not less than 9000A is preferably adopted for smelting. In the step (A-1), the cooling time is 120 hours or more. In the step (a-1), the fused magnesia is pulverized into a lump of about 10 × 10 cm.
In some embodiments of the present invention, in the step (a-1), graphite is added to magnesite when the magnesite is smelted.
In some embodiments of the present invention, in the step (a-1), when smelting magnesite, the graphite is added to the magnesite several times, the graphite is added to the magnesite 2% by mass of the total amount of the magnesite each time, and the time interval for adding the graphite each time is 1.5 hours.
Graphite is an allotrope of elemental carbon, with each carbon atom being covalently bonded at its periphery to three other carbon atoms (a plurality of hexagons arranged in a honeycomb pattern) to form a covalent molecule. It has the characteristics of high temperature resistance and stable chemical property. Therefore, the magnesium oxide is modified by adding the graphite, which is beneficial to improving the high-temperature resistance of the magnesium oxide. In addition, in the smelting process, the specific proportion and time interval are adopted, and the graphite is repeatedly added into the magnesite raw material for many times, so that the magnesium oxide with better high-temperature resistance and more uniform and stable product can be obtained. Preferably, in the step (a-1), when smelting magnesite, lump graphite having a low iron content and a low sulfur content is added to the magnesite.
In some embodiments of the invention, in step (a-1), when smelting magnesite, silicon-carbon coated graphite is added to the magnesite.
The silicon-carbon coated graphite is prepared by the following steps:
(B-1) mixing and ball-milling silicon dioxide and glucose according to the mass ratio of 1: 2 to obtain silicon-carbon mixed powder;
(B-2) heating the silicon-carbon mixed powder obtained in the step (B-1) to 150 ℃ in nitrogen, preserving heat for 2 hours, and cooling to obtain a silicon-carbon composite material;
(B-3) mixing and ball-milling the silicon-carbon composite material obtained in the step (B-2) and graphite according to the mass ratio of 1: 10 to obtain silicon-carbon-graphite mixed powder;
and (B-4) heating the silicon-carbon-graphite mixed powder obtained in the step (B-3) to 600 ℃ in nitrogen, preserving heat for 2 hours, and cooling to obtain the silicon-carbon coated graphite.
The silicon-carbon coated graphite obtained in the steps (B-1) to (B-4) is prepared by uniformly dispersing silica particles in glucose serving as a carbon source, and performing high-temperature carbonization composite treatment on the silica particles and the graphite to bond and coat silicon-carbon elements on the surfaces of the graphite particles, so that the thermal stability of the graphite is further improved, and the high-temperature resistance of the magnesium oxide is improved.
In some embodiments of the present invention, in the step (a-1), when smelting magnesite, ceramic powder-coated graphite is added to the magnesite.
The ceramic powder coated graphite is prepared by the following steps:
(C-1) mixing and ball-milling the ceramic powder and graphite according to the mass ratio of 1: 10 to obtain ceramic-graphite mixed powder;
and (C-2) heating the ceramic graphite mixed powder obtained in the step (C-1) to 800 ℃, preserving heat for 4 hours, and cooling to obtain the graphite coated with the ceramic powder.
Specifically, the ceramic powder in the step (C-1) is prepared by the following steps:
(C-1-1) preparing a ceramic powder raw material according to the mass percentage of silicon oxide, aluminum oxide, zirconium oxide, zinc oxide, germanium oxide and tellurium oxide of 40: 20: 10;
(C-1-2) adding polysiloxane with the mass 2 times that of the ceramic powder raw material into the ceramic powder raw material obtained in the step (C-1-1), performing wet ball milling, uniformly mixing, washing with water, filtering, and drying;
(C-1-3) heating the ceramic powder raw material obtained in the step (C-1-2) to 1200 ℃, preserving heat for 2 hours, and cooling to obtain ceramic powder.
Although graphite can improve the high temperature resistance of magnesium oxide, graphite has good electrical conductivity. Thus, the addition of graphite inhibits the insulating properties of magnesium oxide to some extent. In order to improve the insulating properties of magnesium oxide while ensuring good electrical conductivity, in some embodiments of the invention, it is preferred to add ceramic powder coated graphite to the magnesite when smelting the magnesite in step (a-1). The insulating property of the ceramic is utilized to suppress the conductive ability of the graphite coated therein. In addition, the ceramic powder obtained through the steps (C-1-1) to (C-1-3) has the advantages of both insulating property and quick heat dissipation, so that the method is particularly suitable for preparing the magnesium oxide powder for the fireproof cable.
Without being bound to any theory, the inventors believe that the reason why the ceramic powder passing through the steps (C-1-1) to (C-1-3) has good heat dissipation is that: in the wet ball milling process in the step (C-1-2), polysiloxane organic matter is fully mixed with the ceramic powder and is sintered at high temperature in the step (C-1-3), the polysiloxane organic matter plays a role of a framework, porous sieve-shaped loose nano ceramic particles are obtained, and the ceramic powder has high heat conductivity and heat dissipation performance in the radial direction and the axial direction.
In some embodiments of the present invention, the magnesia powder of step (A-2) has a particle size in the range of 60 to 325 mesh.
In some embodiments of the present invention, the magnesia powder of step (A-2) has a particle size distribution of +60 mesh: 0 to 3 percent; +80 mesh: 26 to 40 percent; +100 mesh: 13 to 20 percent; +150 mesh: 18 to 22 percent; +200 mesh: 12 to 18 percent; +325 mesh: 11 to 16 percent; 325 mesh: 0 to 1.5 percent.
The magnesium oxide powder meeting the requirements of the granularity and the granularity distribution has round material particles and optimal flowability. Preferably, in the step (A-2), the fused magnesia obtained by the step (A-1) is ground using a Bamark mill. The Bamark sand making machine is adopted to grind and crush the fused magnesia, and the method has the advantage of less mechanical iron abrasion. Preferably, the flow rate of the grinding and crushing is 29 to 31S/100g, and the tap density is 2.17 to 2.2g/cm3。
In some embodiments of the invention, in step (a-3), the additive further comprises: the magnesium oxide powder comprises calcined kaolin, zirconia powder and serpentine, wherein the total amount of the calcined kaolin, the zirconia powder and the serpentine is 2.5% of the total amount of the magnesium oxide powder.
In some embodiments of the present invention, in the step (a-3), the additive includes white carbon black in an amount of 0.15% by mass of the total amount of the magnesium oxide powder, and an organic modifier in an amount of 0.90% by mass of the total amount of the magnesium oxide powder, and the organic modifier includes a mixed solution of hydrogen-containing silicone oil and a gasoline solvent in a volume ratio of 7: 2.
Preferably, in the step (a-3), the white carbon includes fumed silica.
Preferably, in the step (a-3), the mixing and stirring time is 20 minutes, and the static storage time is 24 hours or more.
Preferably, in the step (a-3), the white carbon black and the organic modifier are sequentially added to the magnesium oxide powder obtained in the step (a-2), the white carbon black is added, then the mixture is mixed and stirred, the organic modifier is added, and the mixture is stirred under vacuum. Stirring is preferably carried out using a vacuum stirrer.
Preferably, in the step (A-4), the temperature range of the drying is 400-500 ℃. Preferably, in the step (a-4), after the cooling process, the fireproof cable is screened, deironized and packaged by using a 60-mesh rotary vibrating screen.
White carbon black is a general term for white powdery X-ray amorphous silicic acid and silicate products, mainly referring to precipitated silica, fumed silica and ultrafine silica gel, and also including powdery synthetic aluminum silicate, calcium silicate, and the like. The white carbon black is porous material, and its composition can be SiO2·nH2O represents, wherein nH2O is present in the form of surface hydroxyl groups. It is soluble in caustic alkali and hydrofluoric acid, and insoluble in water, solvent and acid (except hydrofluoric acid). High-temperature resistance, non-combustion, tastelessness, odorless and good electrical insulation. Therefore, the white carbon black is adopted to modify the magnesium oxide, so that the insulating property of the magnesium oxide can be further improved. In addition, the hydrogen-containing silicone oil can be crosslinked at a proper temperature under the action of a metal catalyst to form waterproof on the surfaces of various substratesThe film improves the hydrophobic moisture resistance and the dispersibility of the magnesium oxide.
In some embodiments of the invention, in step (a-3), the additive further comprises: the magnesium alloy comprises, by mass, 0.20% of the total amount of the magnesium oxide powder, titanium dioxide 0.10% of the total amount of the magnesium oxide powder, rubidium oxide 0.10% of the total amount of the magnesium oxide powder, and lanthanum oxide 0.10% of the total amount of the magnesium oxide powder.
And (3) adding the rare earth magnesium alloy, the titanium dioxide, the rubidium oxide and the lanthanum oxide into the magnesium oxide powder obtained in the step (A-2) in a particle or powder form, and mixing and stirring uniformly. The addition of the rare earth magnesium alloy is beneficial to improving the high-temperature resistance of the magnesium oxide powder for the fireproof cable. The addition of the white powder, the rubidium oxide and the lanthanum oxide is beneficial to improving the optical performance and the aesthetic degree of the magnesium oxide powder for the fireproof cable.
In some embodiments of the invention, the rare earth magnesium alloy is prepared by:
(D-1) weighing samarium, europium, terbium, yttrium, gadolinium, manganese, antimony, aluminum and magnesium in sequence as powdery raw materials;
and (D-2) smelting the powdery raw material obtained in the step (D-1), cooling and crushing to obtain the rare earth magnesium alloy.
Preferably, in the step (D-1), the powdery raw materials are weighed according to the mass percentage of 0.15-0.25 percent of samarium, europium, terbium, yttrium, gadolinium, manganese, antimony, aluminum and magnesium, 0.15-0.25 percent of 0.35-0.45 percent of 1.00-2.00 percent of 2.00-3.00 percent of 90.35-93.85 percent of 2.00-3.00 percent of 5-0.25 percent of manganese.
Preferably, in the step (D-2), the powdery raw material obtained in the step (D-1) is melted at a temperature of 1200 ℃ for 3 hours, cooled and pulverized to obtain the rare earth magnesium alloy.
Preferably, in the step (D-2), the rare earth magnesium master alloy is stirred during the melting process.
The rare earth magnesium alloy obtained by adopting the raw material proportion and the process has excellent high-temperature resistance and good mechanical property. Therefore, the rare earth magnesium alloy obtained by the raw material proportion and the process is used as the additive in the step (A-3), which is beneficial to further improving the physical properties, especially the mechanical strength, of the magnesium oxide powder for the fireproof cable.
In some embodiments of the present invention, the preparation of the rare earth magnesium alloy further comprises the steps of:
(D-3) subjecting the rare earth magnesium alloy obtained by the step (D-2) to surface treatment with neodymium hydroxide.
Preferably, in the step (D-3), the rare earth magnesium alloy obtained by the step (D-2) is subjected to surface treatment, specifically by the following substeps.
(D-3-1) dissolving neodymium nitrate powder in water to prepare a neodymium nitrate surface treatment solution with the molar concentration of 1.40 mol/L;
(D-3-2) dropwise adding a magnesium hydroxide aqueous solution into the neodymium nitrate surface treatment liquid obtained in the step (D-3-1), and adjusting the pH value of the neodymium nitrate surface treatment liquid to 12 to obtain a neodymium-magnesium mixed liquid;
(D-3-3) adding hydrogen peroxide with the concentration percentage of 15% into the neodymium magnesium mixed solution obtained in the step (D-3-2) to obtain neodymium hydroxide, wherein the addition amount of the hydrogen peroxide is 20 times of the mass of the neodymium nitrate powder in the step (D-3-1);
(D-3-4) mixing the neodymium hydroxide obtained in the step (D-3-3) and the rare earth magnesium alloy obtained in the step (D-2), and putting the mixture into an ultrasonic precipitation crystallization device for precipitation crystallization to obtain a rare earth magnesium alloy subjected to surface treatment, wherein the addition amount of the mixed rare earth magnesium alloy is 80 times of the mass of the neodymium nitrate powder in the step (D-3-1);
(D-3-5) washing, filtering and drying the surface-treated rare earth magnesium alloy obtained by the step (D-3-4).
Preferably, in the step (D-3-1), the neodymium nitrate powder is dissolved in water at a temperature of 60 ℃ to improve the dispersibility of the neodymium nitrate powder.
Preferably, in step (D-3)In-4), the ultrasonic frequency of the ultrasonic precipitation crystallization equipment is 50kHz, and the ultrasonic action intensity is 3.5W/Dm2The operation time is 90 min.
The reason why the rare earth magnesium alloy obtained by the step (D-2) is surface-treated with neodymium hydroxide by the above step (D-3) is that: and under the ultrasonic action, the neodymium hydroxide generates precipitation crystallization on the surface of the rare earth magnesium alloy to form a compact protective film, so that the oxidation resistance and the flame retardant property of the magnesium oxide powder for the fireproof cable are further improved.
Embodiments of the present invention will be described below by way of specific examples. It is to be noted that the raw materials and processing and testing equipment used in the present invention are those commonly used in the art and commercially available.
Examples 1 to 13
The magnesium oxide powders for a flameproof cable described in examples 1 to 13 were prepared by the following steps (A-1) to (A-4) in this order.
In the preparation of the magnesium oxide powder for a flameproof cable described in examples 2 to 6 and examples 12 and 13, graphite was added during the smelting in the step (A-1). The amount and source of the graphite added are listed in table 1. The graphite is uniformly added for multiple times, the adding amount of each time is 2% of the total mass of the magnesite, the time interval of each adding is 1.5 hours, and the adding is stopped until the preset adding amount is reached.
In the preparation of the magnesium oxide powder for a flameproof cable described in examples 7 to 13, additives were added during the mixing and stirring and static storage described in the step (A-3). The types, sources and amounts of the additives are listed in table 1.
Wherein, the percentage values listed in table 1 are the percentage of the graphite additive amount to the total mass of the magnesite ore, or the percentage of the additive amount of each additive to the total mass of the magnesium oxide powder.
And (A-1) selecting high-quality magnesite, and smelting the magnesite by adopting an electric arc furnace (the voltage is 110V +/-5V, and the current is 9000A) with the power of more than 1000 KW. Wherein, the magnesite ore selection standard is as follows: the mass percent of the magnesium oxide is greater than or equal to 46.60%, the mass percent of the sodium hydroxide is greater than or equal to 51.00%, the mass percent of the ferric oxide is less than or equal to 0.16%, the mass percent of the silicon dioxide is less than or equal to 0.25%, and the mass percent of the calcium oxide is less than or equal to 0.28%. The smelting temperature is kept in the range of 2600-. In the preparation of the magnesium oxide powders for flameproof cables described in examples 2 to 6 and examples 12 and 13, graphite was optionally added during the smelting process according to Table 1. After the smelting is finished, cooling for more than 120 hours, and crushing the smelting product to a lump material of about 10 x 10cm to obtain the fused magnesite.
(A-2) grinding the fused magnesite obtained in the step (A-1) by using a Bamark sand making machine, wherein the flow rate is 29-31S/100g, and the tap density is 2.17-2.2g/cm3To obtain magnesium oxide powder with a particle size range of about 60-325 mesh.
And (A-3) mixing and stirring the magnesium oxide powder obtained in the step (A-2) for 20 minutes in vacuum by using a vacuum stirrer, and statically storing for not less than 24 hours after stirring. Wherein, in the preparation of the magnesium oxide powder for a fire-proof cable described in examples 7 to 13, an additive was selectively added to the magnesium oxide powder according to Table 1 before mixing and stirring.
And (A-4) drying the magnesium oxide powder obtained in the step (A-3) at the temperature of 400-500 ℃, and cooling after drying to obtain the magnesium oxide powder for the fireproof cable.
TABLE 1
Example 14
The silicon-carbon coated graphite described in example 14 was prepared by the following steps (B-1) to (B-4) in this order.
(B-1) mixing and ball-milling silicon dioxide and glucose according to the mass ratio of 1: 2 by adopting a planetary ball mill to obtain silicon-carbon mixed powder;
(B-2) heating the silicon-carbon mixed powder obtained in the step (B-1) to 150 ℃ in nitrogen by adopting a resistance furnace, preserving heat for 2 hours, and cooling to obtain a silicon-carbon composite material;
(B-3) mixing and ball-milling the silicon-carbon composite material obtained in the step (B-2) and graphite according to the mass ratio of 1: 10 by adopting a planetary ball mill to obtain silicon-carbon-graphite mixed powder;
and (B-4) heating the silicon-carbon-graphite mixed powder obtained in the step (B-3) to 600 ℃ in nitrogen by using a resistance furnace, preserving the heat for 2 hours, and cooling to obtain the silicon-carbon coated graphite.
Example 15
The following steps were used in sequence to prepare the ceramic powder coated graphite described in example 15.
(C-1-1) preparing a ceramic powder raw material according to the mass percentage of silicon oxide, aluminum oxide, zirconium oxide, zinc oxide, germanium oxide and tellurium oxide of 40: 20: 10;
(C-1-2) adding polysiloxane with the mass 2 times that of the ceramic powder raw material into the ceramic powder raw material obtained in the step (C-1-1), performing wet ball milling, uniformly mixing, washing for 2-3 times, performing vacuum filtration, and drying in a drying box;
and (C-1-3) heating the ceramic powder raw material obtained in the step (C-1-2) to 1200 ℃ by adopting a resistance furnace, preserving the heat for 2 hours, and cooling the ceramic powder raw material to the normal temperature along with the furnace to obtain the ceramic powder.
(C-1) mixing the ceramic powder obtained by the step (C-1-3) with commercially available graphite in the ratio of 1: 10, performing mixing ball milling to obtain ceramic graphite mixed powder;
and (C-2) heating the ceramic graphite mixed powder obtained in the step (C-1) to 800 ℃, preserving heat for 4 hours, and cooling to obtain the graphite coated with the ceramic powder.
Example 16
The following procedure was used in order to prepare graphite co-coated with the silicon carbon material and ceramic powder described in example 16.
(C-1-1) preparing a ceramic powder raw material according to the mass percentage of silicon oxide, aluminum oxide, zirconium oxide, zinc oxide, germanium oxide and tellurium oxide of 40: 20: 10;
(C-1-2) adding polysiloxane with the mass 2 times that of the ceramic powder raw material into the ceramic powder raw material obtained in the step (C-1-1), performing wet ball milling, uniformly mixing, washing for 2-3 times, performing vacuum filtration, and drying in a drying box;
and (C-1-3) heating the ceramic powder raw material obtained in the step (C-1-2) to 1200 ℃ by adopting a resistance furnace, preserving the heat for 2 hours, and cooling the ceramic powder raw material to the normal temperature along with the furnace to obtain the ceramic powder.
(C-1) mixing and ball-milling the ceramic powder obtained in the step (C-1-3) and the silicon-carbon coated graphite prepared in example 14 in a mass ratio of 1: 10 to obtain ceramic silicon-carbon-graphite mixed powder;
and (C-2) heating the ceramic silicon carbon graphite mixed powder obtained in the step (C-1) to 800 ℃, preserving heat for 4 hours, and cooling to obtain graphite coated by the silicon carbon material and the ceramic powder.
Example 17
The rare earth magnesium alloy described in example 17 was prepared by successively carrying out the following steps (D-1) to (D-2).
(D-1) weighing samarium, europium, terbium, yttrium, aluminum and magnesium in a ratio of 0.15 to 0.35 to 1.00 to 2.00 to 93.85 percent in sequence as powdery raw materials;
(D-2) smelting the powdery raw material obtained in the step (D-1) at the temperature of 1200 ℃ for 3 hours, slowly stirring, cooling and crushing to obtain the rare earth magnesium alloy.
Example 18
The rare earth magnesium alloy described in example 18 was prepared by successively carrying out the following steps (D-1) to (D-2).
(D-1) weighing samarium, europium, terbium, yttrium, aluminum and magnesium in a ratio of 0.25 to 0.45 to 2.00 to 3.00 to 90.35 mass percent in sequence as powdery raw materials;
(D-2) smelting the powdery raw material obtained in the step (D-1) at the temperature of 1200 ℃ for 3 hours, slowly stirring, cooling and crushing to obtain the rare earth magnesium alloy.
Example 19
The rare earth magnesium alloy described in example 19 was prepared by successively carrying out the following steps (D-1) to (D-3-5).
(D-1) weighing samarium, europium, terbium, yttrium, aluminum and magnesium in a ratio of 0.15 to 0.35 to 1.00 to 2.00 to 93.85 percent in sequence as powdery raw materials;
(D-2) smelting the powdery raw material obtained in the step (D-1) at the temperature of 1200 ℃ for 3 hours, slowly stirring, cooling and crushing to obtain a rare earth magnesium alloy;
(D-3-1) dissolving neodymium nitrate powder in water at the temperature of 60 ℃ to prepare a neodymium nitrate surface treatment solution with the molar concentration of 1.40 mol/L;
(D-3-2) dropwise adding a magnesium hydroxide aqueous solution into the neodymium nitrate surface treatment liquid obtained in the step (D-3-1), and adjusting the pH value of the neodymium nitrate surface treatment liquid to 12 to obtain a neodymium-magnesium mixed liquid;
(D-3-3) adding hydrogen peroxide with the concentration percentage of 15% into the neodymium magnesium mixed solution obtained in the step (D-3-2) to obtain neodymium hydroxide, wherein the addition amount of the hydrogen peroxide is 20 times of the mass of the neodymium nitrate powder in the step (D-3-1);
(D-3-4) mixing the neodymium hydroxide obtained in the step (D-3-3) with the rare earth magnesium alloy obtained in the step (D-2), placing the mixture in an ultrasonic precipitation crystallization device for precipitation crystallization to obtain the rare earth magnesium alloy subjected to surface treatment, wherein the ultrasonic frequency of the ultrasonic precipitation crystallization device is 50kHz, and the ultrasonic action intensity is 3.5W/Dm2The operation time is 90min, and the mixed addition amount of the rare earth magnesium alloy is 80 times of the mass of the neodymium nitrate powder in the step (D-3-1);
(D-3-5) washing, filtering and drying the surface-treated rare earth magnesium alloy obtained by the step (D-3-4).
Example 20
The rare earth magnesium alloy described in example 20 was prepared by successively carrying out the following steps (D-1) to (D-3-5).
(D-1) weighing samarium, europium, terbium, yttrium, aluminum and magnesium in a ratio of 0.25 to 0.45 to 2.00 to 3.00 to 90.35 mass percent in sequence as powdery raw materials;
(D-2) smelting the powdery raw material obtained in the step (D-1) at the temperature of 1200 ℃ for 3 hours, slowly stirring, cooling and crushing to obtain a rare earth magnesium alloy;
(D-3-1) dissolving neodymium nitrate powder in water at the temperature of 60 ℃ to prepare a neodymium nitrate surface treatment solution with the molar concentration of 1.40 mol/L;
(D-3-2) dropwise adding a magnesium hydroxide aqueous solution into the neodymium nitrate surface treatment liquid obtained in the step (D-3-1), and adjusting the pH value of the neodymium nitrate surface treatment liquid to 12 to obtain a neodymium-magnesium mixed liquid;
(D-3-3) adding hydrogen peroxide with the concentration percentage of 15% into the neodymium magnesium mixed solution obtained in the step (D-3-2) to obtain neodymium hydroxide, wherein the addition amount of the hydrogen peroxide is 20 times of the mass of the neodymium nitrate powder in the step (D-3-1);
(D-3-4) mixing the neodymium hydroxide obtained in the step (D-3-3) with the rare earth magnesium alloy obtained in the step (D-2), placing the mixture in an ultrasonic precipitation crystallization device for precipitation crystallization to obtain the rare earth magnesium alloy subjected to surface treatment, wherein the ultrasonic frequency of the ultrasonic precipitation crystallization device is 50kHz, and the ultrasonic action intensity is 3.5W/Dm2The operation time is 90min, and the mixed addition amount of the rare earth magnesium alloy is 80 times of the mass of the neodymium nitrate powder in the step (D-3-1);
(D-3-5) washing, filtering and drying the surface-treated rare earth magnesium alloy obtained by the step (D-3-4).
Performance testing
The pressure resistance of the magnesium oxide powder for a fireproof cable prepared in examples 1 to 13 was tested using a pressure resistance tester model cs2672s, a Changsheng instruments Co., Ltd. The insulating properties of the magnesium oxide powder for a fireproof cable prepared in examples 1 to 13 were measured using a SUPER MEGOHMMETER SM-8215 type insulation resistance tester manufactured by TOA & DKK, Japan. The heat conductivity of the magnesium oxide powder for the fireproof cables prepared in examples 1 to 13 was tested by using a DZDR-S transient planar heat source method heat conductivity meter. The magnesium oxide powder used in comparative example 1 was purchased from Shanghai Crystal pure science and technology Ltd, and had an MgO content of 98%.
TABLE 2
The above test results show that the pressure resistance of the magnesium oxide powder prepared in examples 2 to 6, to which graphite is added during the smelting process, is significantly improved compared to the magnesium oxide powder prepared in example 1, to which no additive or graphite is added, and in particular, the pressure resistance of the magnesium oxide powder prepared in examples 4 to 6, to which silicon-carbon-coated graphite, or ceramic powder-coated graphite, or silicon-carbon and ceramic powder-coated graphite is added during the smelting process, is further improved compared to the magnesium oxide powder to which commercially available graphite is added. Particularly, the insulating property and the heat conducting property of the graphite coated by the ceramic powder or the magnesia powder of the graphite coated by the silicon carbon and the ceramic powder are relatively excellent. In addition, the magnesium oxide powder prepared in examples 12 and 13, which is prepared by using the graphite prepared in example 16 of the present invention and adding the rare earth magnesium alloy prepared in example 20 of the present invention during the smelting process, has very excellent performance in the aspects of pressure resistance, insulation performance and heat conductivity, and the appearance detection and observation show that the magnesium oxide powder has better glossiness and aesthetic degree in appearance compared with the magnesium oxide powder in comparative example 1 due to the addition of rubidium oxide, lanthanum oxide and titanium dioxide.
It is obvious that the above embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, those skilled in the art should also include various changes, modifications, substitutions and improvements without creative efforts to the embodiments.
Claims (7)
1. A preparation method of magnesium oxide powder for fireproof cables is characterized by comprising the following steps,
(A-1) smelting magnesite, adding graphite into the magnesite when smelting the magnesite, wherein the graphite is graphite coated by a silicon-carbon material and ceramic powder together, and cooling and crushing after smelting to obtain fused magnesia;
(A-2) grinding the fused magnesia obtained in the step (A-1) to obtain magnesia powder;
(A-3) adding an additive into the magnesium oxide powder obtained in the step (A-2), mixing and stirring, and then statically storing, wherein the additive comprises white carbon black and an organic modifier, and the organic modifier comprises a mixed solution of hydrogen-containing silicone oil and a gasoline solvent in a volume ratio of 7: 2;
(A-4) drying the magnesium oxide powder obtained in the step (A-3), and cooling after drying to obtain magnesium oxide powder for the fireproof cable;
in the step (A-3), the additive also comprises rare earth magnesium alloy, titanium dioxide, rubidium oxide and lanthanum oxide; the rare earth magnesium alloy is prepared by the following steps:
(D-1) weighing samarium, europium, terbium, yttrium, gadolinium, manganese, antimony, aluminum and magnesium in sequence as powdery raw materials;
(D-2) smelting the powdery raw material obtained in the step (D-1), cooling and crushing to obtain a rare earth magnesium alloy;
(D-3-1) dissolving neodymium nitrate powder in water to prepare a neodymium nitrate surface treatment solution with the molar concentration of 1.40 mol/L;
(D-3-2) dropwise adding a magnesium hydroxide aqueous solution into the neodymium nitrate surface treatment liquid obtained in the step (D-3-1), and adjusting the pH value of the neodymium nitrate surface treatment liquid to 12 to obtain a neodymium-magnesium mixed liquid;
(D-3-3) adding hydrogen peroxide with the concentration percentage of 15% into the neodymium magnesium mixed solution obtained in the step (D-3-2) to obtain neodymium hydroxide, wherein the addition amount of the hydrogen peroxide is 20 times of the mass of the neodymium nitrate powder in the step (D-3-1);
(D-3-4) mixing the neodymium hydroxide obtained in the step (D-3-3) and the rare earth magnesium alloy obtained in the step (D-2), and putting the mixture into an ultrasonic precipitation crystallization device for precipitation crystallization to obtain a rare earth magnesium alloy subjected to surface treatment, wherein the addition amount of the mixed rare earth magnesium alloy is 80 times of the mass of the neodymium nitrate powder in the step (D-3-1);
(D-3-5) washing, filtering and drying the surface-treated rare earth magnesium alloy obtained by the step (D-3-4).
2. The method for preparing magnesium oxide powder for a fireproof cable according to claim 1, wherein in the magnesite in step (A-1), the mass percentage of magnesium oxide is greater than or equal to 46.60%, the mass percentage of sodium hydroxide is greater than or equal to 51.00%, the mass percentage of ferric oxide is less than or equal to 0.16%, the mass percentage of silicon dioxide is less than or equal to 0.25%, and the mass percentage of calcium oxide is less than or equal to 0.28%.
3. The method as claimed in claim 1, wherein in the step (A-1), the magnesite is smelted at 2600-.
4. The method for preparing magnesium oxide powder for a fire-proof cable according to claim 1, wherein in the step (a-1), when smelting magnesite, the graphite is added to the magnesite several times, the graphite is added to the magnesite 2% by mass each time, and the time interval between the graphite additions is 1.5 hours.
5. The method of claim 1, wherein the magnesium oxide powder of step (A-2) has a particle size ranging from 60 mesh to 325 mesh, and the particle size distribution of the magnesium oxide powder is +60 mesh: 0 to 3 percent; +80 mesh: 26 to 40 percent; +100 mesh: 13 to 20 percent; +150 mesh: 18 to 22 percent; +200 mesh: 12 to 18 percent; +325 mesh: 11 to 16 percent; 325 mesh: 0 to 1.5 percent.
6. The method for preparing magnesium oxide powder for a fire-proof cable according to any one of claims 1 to 5, wherein in the step (A-3), the additive further comprises: the magnesium oxide powder comprises calcined kaolin, zirconia powder and serpentine, wherein the total amount of the calcined kaolin, the zirconia powder and the serpentine is 2.5% of the total amount of the magnesium oxide powder.
7. A magnesium oxide powder for a fire-proof cable, which is prepared by the method for preparing the magnesium oxide powder for a fire-proof cable according to any one of claims 1 to 6.
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