CN117645301B - High-purity submicron-order Mg 2 Si preparation method and continuous vacuum rotary kiln - Google Patents
High-purity submicron-order Mg 2 Si preparation method and continuous vacuum rotary kiln Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 16
- 229910019018 Mg 2 Si Inorganic materials 0.000 title claims description 12
- 239000011777 magnesium Substances 0.000 claims abstract description 52
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims abstract description 46
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 43
- 238000001816 cooling Methods 0.000 claims abstract description 39
- 239000011863 silicon-based powder Substances 0.000 claims abstract description 37
- 239000002245 particle Substances 0.000 claims abstract description 23
- 238000010438 heat treatment Methods 0.000 claims abstract description 18
- 238000007789 sealing Methods 0.000 claims abstract description 15
- 238000004321 preservation Methods 0.000 claims abstract description 13
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- 239000000463 material Substances 0.000 claims description 71
- 238000007599 discharging Methods 0.000 claims description 22
- 239000000203 mixture Substances 0.000 claims description 13
- 238000002156 mixing Methods 0.000 claims description 6
- YTHCQFKNFVSQBC-UHFFFAOYSA-N magnesium silicide Chemical compound [Mg]=[Si]=[Mg] YTHCQFKNFVSQBC-UHFFFAOYSA-N 0.000 abstract description 38
- 229910021338 magnesium silicide Inorganic materials 0.000 abstract description 38
- 238000006243 chemical reaction Methods 0.000 abstract description 26
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- 230000035484 reaction time Effects 0.000 abstract 1
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- 238000000034 method Methods 0.000 description 29
- 239000000047 product Substances 0.000 description 26
- 230000000052 comparative effect Effects 0.000 description 22
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- 239000011553 magnetic fluid Substances 0.000 description 17
- 229910052749 magnesium Inorganic materials 0.000 description 15
- 230000008569 process Effects 0.000 description 13
- 239000002994 raw material Substances 0.000 description 13
- 229910052786 argon Inorganic materials 0.000 description 11
- 238000005275 alloying Methods 0.000 description 8
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 7
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- 229910052751 metal Inorganic materials 0.000 description 5
- 239000002184 metal Substances 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
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- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
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- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910000861 Mg alloy Inorganic materials 0.000 description 1
- 229910017639 MgSi Inorganic materials 0.000 description 1
- 229910001361 White metal Inorganic materials 0.000 description 1
- HMDDXIMCDZRSNE-UHFFFAOYSA-N [C].[Si] Chemical compound [C].[Si] HMDDXIMCDZRSNE-UHFFFAOYSA-N 0.000 description 1
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- 150000002681 magnesium compounds Chemical class 0.000 description 1
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Abstract
The invention provides a high-purity submicron Mg 2 The preparation method of Si is that silicon powder and magnesium powder are mixed and then react in a continuous vacuum rotary kiln, and the silicon powder and the magnesium powder react at a lower temperature to directly generate submicron high-purity magnesium silicide by controlling the conditions of reaction temperature, reaction time, rotating speed, vacuum degree, filling quantity and the like, so that secondary crushing treatment is not needed, and the preparation method is safe and efficient; and the prepared Mg 2 The Si has high purity and small particle size, and the average particle size of primary particles can reach 200-800nm. The invention simultaneously provides a continuous vacuum rotary kiln, which is provided with a three-stage vacuum system, a dynamic and static sealing system, a multistage vacuum sealing material inlet and outlet bin, a heating zone, a heat preservation zone, a cooling zone and a cooling zone, so that when the vacuum degree is 0.001-10Pa, the furnace body has a vacuum rotary sintering function, and Mg is eliminated 2 Si spraying, overburning and impurity problems. The invention realizes high-purity submicron Mg 2 The continuous production of Si greatly improves the production efficiency, reduces the energy consumption and has great market value.
Description
Technical Field
The invention relates to the technical field of magnesium silicide preparation, in particular to a high-purity submicron-level Mg 2 Si preparation method and continuous vacuum rotary kiln.
Background
Magnesium silicide (Mg) 2 Si) is an alloy compound, is an important industrial raw material, and is mainly used for producing silane, absorbing oxygen and releasing hydrogen as a medicinal carrier or used as a raw material of a silicon-carbon negative electrode material and the like. The synthetic method of magnesium silicide is to mix silicon powder and magnesium powder, heat to about 500-650 deg.C under protective atmosphere or vacuum to carry on alloying reaction, produce magnesium silicide, its ideal reaction formula is: 2Mg+Si→Mg 2 Si Δg= -75.6 kJ/mol. Because the alloying reaction is exothermic, the temperature in the production process is very easy to be uncontrollable, and the purity and the yield of the generated magnesium silicide can be directly influenced by the temperature in the reaction process. In another aspect the reactants for silicon and magnesium further comprise: mg of 9 Si 5 、MgSi、Mg 3 Si 2 And the like, the compounds with low magnesium content have poor stability and are easy to react with water oxygen in the air to generate silicon dioxide and magnesium oxide, so that the final product is impure. ImpureMg 2 Si in turn affects the performance and safety of the preparation of silane or elemental silicon materials.
In the prior art, mg 2 The synthesis methods generally used for Si include batch production methods and continuous synthesis methods. The batch production method mainly utilizes a fixed bed batch reactor, but because of the limitation of the reactor, the batch production method requires procedures of charging, heating, heat preservation, cooling, material taking and the like, so that the batch production method has low efficiency, high energy consumption and high danger. Chinese patent CN102574818A discloses a method for preparing magnesium silicide powder, which comprises ball milling magnesium powder and silicon powder under stirring, and heat treating at 450-600 ℃ under argon condition to obtain magnesium silicide. However, the temperature is not easy to control during the preparation, the problems of overhigh temperature, high risk and the like exist, and the prepared magnesium silicide has large particles and needs to be subjected to subsequent ball milling and crushing and other treatments.
The continuous synthesis process is easier to control than the intermittent synthesis process in temperature, good in product quality, high in yield, and greatly improved in safety, and can realize large-scale continuous production of magnesium silicide. Thus, the continuous synthesis method becomes an important production method of magnesium silicide. Chinese patent CN2011101190283 discloses a method and apparatus for producing magnesium silicide, which uses a tank reactor to realize continuous production of magnesium silicide by adding magnesium powder into silicon powder, and alleviate the problem of magnesium silicide agglomeration during reaction due to local overheating caused by exothermic material reaction. However, the magnesium vapor leaks, and raw materials and clinker in the reaction tank are mixed, which easily results in low reaction efficiency. Thus, how to safely and efficiently prepare high-purity Mg 2 Si, realize Mg 2 The large-scale continuous production of Si is still the current research focus and production difficulty.
Disclosure of Invention
In view of the above problems, the present invention provides a high-purity submicron-order Mg 2 Si preparation method and continuous vacuum rotary kiln, lower reaction temperature can be controlled in the production process, and high-purity Mg can be continuously and efficiently prepared 2 Si; the higher vacuum degree is controlled in the reaction process, hydrogen, argon and the like are not needed, and the method is safe and reliable; and the prepared Mg 2 The grain size of Si is small,the powder does not agglomerate, does not need to be subjected to secondary crushing treatment, and greatly improves the production safety.
In one aspect, the invention provides a high purity submicron grade Mg 2 The preparation method of Si comprises the following specific steps:
step S1: mixing magnesium powder and silicon powder in a mixer according to the mass ratio, and transferring the mixture to a vacuum sealing feeding bin of a continuous vacuum rotary kiln after uniform mixing;
step S2: controlling the maximum filling amount of the mixture in the furnace, conveying the mixture of magnesium powder and silicon powder into a furnace body of a continuous vacuum rotary kiln through spiral feeding, and discharging the material through a heating zone, a heat preservation zone, a cooling zone and a cooling zone under the condition that the furnace body keeps rotating and vacuum, wherein the produced material is the product Mg after the material passes through a vacuum sealing discharging bin 2 Si；
The temperature of the heating area in the step S2 is 300-400 ℃, and the operation is carried out for 1-2h; the temperature of the heat preservation area is 520-580 ℃, and the operation is carried out for 1-4 hours; the temperature of the cooling area is 300-400 ℃, and the operation is carried out for 1-3 hours; the temperature of the cooling area is below 80 ℃ and the operation is carried out for 1-3h.
Preferably, in the step S1, the mass ratio of the magnesium powder to the silicon powder is 1.72-1.85:1. For example, the mass ratio of the silicon powder to the magnesium powder may be: 1.72:1, 1.75:1, 1.77:1, 1.8:1, 1.82:1, 1.85:1, but are not limited to the recited values, as other non-recited values within the range of values are equally applicable.
Preferably, the particle size of the magnesium powder is more than or equal to 60 meshes, and the purity is more than or equal to 98%.
Preferably, the grain diameter of the silicon powder is less than or equal to 10um, and the purity is more than or equal to 98 percent.
Preferably, the vacuum degree in the furnace of the continuous vacuum rotary kiln is 0.001-10Pa, and the rotating speed of the furnace body is 1-6 rpm/min.
Preferably, the maximum filling amount of the mixture in the furnace of the continuous vacuum rotary kiln is less than or equal to 15 percent.
The magnesium silicide produced has high activity, and is very easy to burn when the particle size is too small. In the prior art, therefore, coarse metal silicon powder is generally used as a raw material, and is reacted with magnesium powder under argon to generate magnesium silicide with large particle size, and then the magnesium silicide is subjected to treatments such as crushing, sieving and the like. However, when the coarse metal silicon powder is used as a raw material, the activity is low compared with the fine silicon powder, the reaction rate is slower, and higher reaction temperature and high energy consumption are required when the coarse metal silicon powder reacts with magnesium powder. The invention uses the silicon powder with the grain diameter less than or equal to 10um, and the silicon powder with the finer grain diameter has higher activity and low reaction temperature. The vacuum condition of the invention is especially matched, the alloying reaction can be carried out at a lower temperature, the problems of overhigh temperature and the like in the alloying reaction can be effectively avoided, and the generated magnesium silicide is submicron and does not need to be crushed and other treatments.
Under the high vacuum condition, the saturated vapor pressure of the magnesium powder is low, the reaction activation energy is low, the magnesium powder can effectively react with silicon powder at a lower temperature, and the problems of magnesium silicide thermal decomposition, non-stoichiometric ratio generation and the like caused by overhigh temperature (Mg is often generated when the temperature is higher) are effectively avoided 3 Si 2 An iso-low magnesium compound). The silicon powder used is small in particle size, so that submicron magnesium silicide is directly generated, and subsequent treatments such as crushing and the like are avoided; however, superfine magnesium silicide is easy to explode in air, so that the cooling section is specially arranged in the invention, the quenching of the prepared magnesium silicide is avoided, and the stability of the magnesium silicide is greatly improved.
The inventor finds that under the condition of the invention, if the rotating speed of the continuous rotary kiln body is too high during the reaction, powder is seriously adhered, so that part of silicon powder and magnesium powder can not react, thereby generating clamped raw materials and affecting the product quality. However, if the rotation speed is too slow, mg is added due to the rise of temperature 2 Si is decomposed to generate impurities, mg 2 The purity of Si is reduced, and the yield is reduced; and heat accumulation is easily caused to cause caking of the product, so that the speed of the rotary furnace needs to be controlled within a reasonable range.
If the filling amount is too large, the raw materials are easily clamped, and the product quality is affected. The raw materials are easy to accumulate, heat generated during the reaction of silicon powder and magnesium powder cannot be released, so that the temperature in the furnace body is increased, the higher the temperature is, the faster the decomposition speed of magnesium silicide is, and the more magnesium vapor overflows; and as the temperature is further increased, the pyrolysis products are further decomposed into silicon and magnesium. Thereby influencing the product composition and leading the finally prepared magnesium silicide to have more impurities; and the low-melting point eutectic is easy to form, and the molten material is combined with other solid matters, so that the quality of a product is affected, the prepared magnesium silicide is agglomerated and the particle size is enlarged, and the subsequent treatment difficulty and the subsequent danger are increased.
The invention prepares the high-purity submicron-order Mg according to the preparation method 2 Si, the high purity submicron order Mg 2 The primary particle size of Si is less than or equal to 800nm, the purity is more preferably greater than or equal to 98%, and if silicon powder and magnesium powder with higher purity are selected, the purity of the generated magnesium silicide is higher.
In another aspect, the invention provides a continuous vacuum rotary kiln for carrying out the above high purity submicron Mg 2 The preparation method of Si, the vacuum rotary kiln comprises the following steps: the spiral feeder and discharger are three-stage vacuum system comprising mechanical pump, roots pump and diffusion pump, dynamic and static sealing system comprising magnetic fluid and mechanical sealing structure system, furnace rotating system comprising motor speed reducing disc, furnace, etc., temperature controlling system comprising heating wire, furnace heat insulating layer and temperature controlling instrument, vacuum feeding bin, vacuum discharging bin, automatic control system and relevant parts.
Preferably, the three-stage vacuum system and the dynamic and static sealing system can keep the set vacuum degree of the continuous rotary kiln in the high-temperature rotation process, and can also keep the set vacuum degree of the material inlet and outlet bins, and the vacuum pressure rise rate is less than or equal to 1 Pa/h.
Preferably, the dynamic and static sealing system is provided with a cooling system, and the temperature of the dynamic and static sealing position is controlled to be 10-35 ℃.
Preferably, the vacuum feeding bin and the discharging bin are at least three-level, and are provided with an inclined stirrer and a vibration motor.
Preferably, the temperature control system can divide the temperature in the furnace into four sections of a heating zone, a heat preservation zone, a cooling zone and a cooling zone, wherein the temperature control range of the heating zone, the heat preservation zone and the cooling zone is 100-1400 ℃, the temperature control range of the cooling zone is 0-100 ℃, and the temperature difference between the inside and outside of each zone is not more than 30 ℃.
Preferably, the continuous vacuum rotary kiln body is of an auger type fin structure, and a transverse lifting plate is arranged in the middle of the fin.
Preferably, the continuous vacuum rotary kiln is provided with a metal telescopic pipe and a moving trolley to buffer the problem of expansion of the high-temperature furnace pipe in the length direction.
Because of the hazards of magnesium powder and magnesium silicide powder, safety is a priority for its use and synthesis. The common magnesium silicide synthesis is intermittent synthesis under the protection of argon, and the argon is safer, but the consumption of the argon is larger, the oxygen content is still higher, the reactivity of magnesium powder and silicon powder is low, the temperature needs to be increased, and otherwise, the production danger is increased. There is also a batch vacuum furnace, i.e., a static synthesis reaction, but the reaction of silicon and magnesium is an alloy intercalation process, the volume of the resultant is 2-4 times that of the raw material, and a large amount of heat is released, so that a furnace spraying phenomenon often occurs under static vacuum, resulting in impure final products. The continuous vacuum rotary kiln disclosed by the invention has the characteristics of safety and low-temperature high-efficiency production, the danger of an oxidant to the process is controlled by controlling the vacuum degree in a material inlet and outlet bin and a furnace, meanwhile, the material is effectively turned over, so that the material is not sintered, hardened and sprayed, and silicon powder and magnesium powder sequentially pass through a heating section, a heat preservation section, a cooling section and a cooling section to obtain the high-safety submicron-level magnesium silicide powder in one step.
The beneficial effects are that:
(1) According to the invention, magnesium powder and silicon powder with specific particle sizes are used, and the preparation device is matched, so that the silicon powder and the magnesium powder are subjected to one-step continuous reaction at a lower temperature to directly generate submicron-level high-purity magnesium silicide by simultaneously controlling vacuum conditions, temperature, running time, rotating speed and other conditions, the production risk is greatly reduced, and the production efficiency is greatly improved.
(2) The invention directly generates submicron high-purity magnesium silicide, which can be obtained without crushing oversized magnesium silicide for multiple times in other modes, and the product keeps high purity and small grain diameter.
(3) The continuous vacuum rotary kiln realizes the continuous feeding and discharging, vacuum, high-temperature multi-temperature zone heating, rotation and other functions as a whole, and the continuous alloying reaction of the booster magnesium powder and the silicon powder is eliminated through the internal structural design and expansion. The process and the device cooperate to ensure that the produced magnesium silicide has high purity and is not easy to sinter, and the phenomena of expansion and non-uniformity brought by furnace spraying during the synthesis of the magnesium silicide are eliminated.
(4) The invention does not need to use a large amount of expensive high-purity argon or hydrogen-argon mixed gas as the shielding gas, so that the production cost is low and the production is safer and more reliable.
(5) The continuous vacuum rotary kiln can also be used in other fields requiring vacuum heat treatment, such as continuous vacuum annealing, vacuum brazing and the like.
Drawings
FIG. 1 is a diagram showing the overall construction of a continuous vacuum rotary kiln according to embodiment 1 of the present invention;
FIG. 2 is a detailed view of the construction of the conical feed port 101, vacuum valve 102 and upper feed bin 103 in a continuous rotary kiln;
FIG. 3 is a detailed view of the structure of the screw feeder 107 in the continuous rotary kiln;
FIG. 4 is a detailed view of the structure of the expansion joint 108 and the magnetic fluid dynamic and static seal 109 in the continuous rotary kiln;
FIG. 5 shows Mg according to example 1 of the present invention 2 A physical photograph of the Si material;
FIG. 6 is a Mg of example 1 of the present invention 2 SEM images of Si material;
FIG. 7 is a diagram showing the Mg content in example 1 of the present invention 2 Laser particle size spectrum of Si material;
FIG. 8 is a Mg of example 1 of the present invention 2 XRD pattern of Si material;
FIG. 9 is a diagram showing the Mg content of example 1 of the present invention 2 XRD refinement of Si material;
FIG. 10 is a Mg of example 4 of the present invention 2 XRD refinement of Si material;
FIG. 11 shows Mg according to example 2 of the present invention 2 Laser particle size spectrum of Si material;
FIG. 12 is an SEM image of the product of comparative example 2 of the present invention;
FIG. 13 is a laser particle size spectrum of the product of comparative example 2 of the present invention;
FIG. 14 is an XRD refinement of the product of comparative example 3 of the present invention;
description of the drawings: 101-conical feed inlets, 102-vacuum valves, 103-upper feed bins, 104-middle feed bins, 105-lower feed bins, 106-inclined stirring motors, 107-screw feeders, 108-expansion joints, 109-magnetic fluid dynamic and static seals, 110-cooling sleeves, 111-transmission devices and motors, 112-air cooling devices, 113-furnace tubes, 114-furnace bodies, 115-tail end magnetic fluid sealing devices, 116-fixed brackets, 117-furnace tail covers, 118-blanking holes, 119-upper discharge bins, 120-middle discharge bins, 121-lower discharge bins, 122-screw dischargers and 123-furnace body brackets; 201-a vacuum valve electric control part, 202-a material level gauge and 203-a vacuum interface; 301-blanking pipe, 302-spiral pusher, 303-motor, 304-outer pipe and 305-magnetic fluid structure seal; 401-static end part, 402-dynamic end part, 403-movable trolley, 404-slide rail, 405-roller.
Detailed Description
The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the accompanying drawings, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention. Those skilled in the art may choose what is not specifically described in the embodiments of the present invention, and the present invention is further explained below with reference to specific embodiments.
Examples
Example 1
As shown in FIG. 1, is a high purity submicron-order Mg 2 The preparation method of Si and the continuous vacuum rotary kiln comprise a conical feed inlet 101, the diameter of which is 1.5m and the taper of which is 45 degrees; the vacuum valve 102, one of the feeding inlet 101, the upper feeding bin 103, the middle feeding bin 104, the lower feeding bin 105 and the screw feeder 107, one of the blanking inlet 118, the upper discharging bin 119, the middle discharging bin 120, the lower discharging bin 121 and the screw discharger 122, respectively, is resistant to vacuum of more than 0.001 Pa; the upper feeding bin 103 is provided with a double-cone straight cylinder with the diameter of 1.5m, the height of the straight cylinder of 0.8m and the taper of 45 degrees; the feeding bins 104 and 103 are the same; lower feed bins 105, identical to 103; inclined stirring motor 106, upper feeding bin 103, middle feeding bin 104. The cone of the lower feeding bin 105, the upper discharging bin 119 and the middle discharging bin 120 are respectively provided with a spiral stirring paddle; a screw feeder 107 positioned below the lower feeding bin 105, wherein a motor drives a screw stirring paddle to convey materials, the total length is 2m, the diameter is 0.2m, and the materials penetrate into the furnace for 0.3m; the expansion joint 108 is connected with the furnace body frame and the static and dynamic sealing end through a flange; magnetic fluid dynamic and static seal 109, which is positioned between expansion joint 108 and cooling sleeve 110 and resists dynamic vacuum of more than 0.001 Pa; the cooling sleeve 110 is positioned at the outer end of the dynamic end of the magnetic fluid dynamic and static seal 109 and is mainly used for cooling and protecting the magnetic fluid end; the transmission device and the motor 111 are positioned between the magnetic fluid dynamic and static seal 109 and the air cooling device 112, and the motor drives the speed reducer to drive the furnace body to rotate; the air cooling device 112 is used for mainly cooling the furnace body when cooling; furnace tube 113 is 16m long and 0.8m in diameter, and is internally provided with a screw conveyor type transverse lifting plate structure; the furnace body 114 sequentially comprises a heating element, a heat insulation material, a shell and a main heat source from inside to outside; tail end magnetic fluid seal 115, 109; the fixed bracket 116 is used for fixing the static end of the tail end magnetic fluid sealing device 115, so that the high-temperature expansion of the whole furnace tube expands towards the feeding direction; a tail hood 117, a material blanking area; a blanking port 118, a square conical structure, for collecting materials for temporary storage; an upper discharge bin 119, a middle discharge bin 120, which are all identical to the upper feed bin 103; a lower discharging bin 121, an upper conical lower straight cylinder structure, is a second temporary storage chamber for discharging materials; a screw discharger 122 of an inclined structure for discharging accumulated materials; the furnace body support 123 is used for supporting the whole furnace body; the temperature control device is used for controlling the furnace body to be provided with a heating area, a heat preservation area and a cooling area, and the temperature can be regulated and controlled to be 100-1400 ℃; and the mechanical pump, the Roots pump and the diffusion pump three-stage vacuum pump device are respectively connected with the furnace body and the material inlet and outlet bin, and the vacuum degree is regulated.
Fig. 2 is a detailed view of the conical feed inlet 101, the vacuum valve 102 and the upper feed bin 103, the electric control part 201 of the vacuum valve is positioned on the right side of the vacuum valve 102 and connected with a control cabinet, the material level gauge 202 is positioned above the cone of the upper feed bin 103, the depth of materials in the bin is monitored, the vacuum interface 203 is positioned beside the material level gauge 202 and connected with a vacuum system, and vacuum is pumped into the bin. The inclined stirring motor 106 mainly stirs materials in the warehouse to avoid accumulation of materials. Fig. 3 is a detailed view of the structure of the screw feeder 107, wherein a blanking pipe 301 is communicated with the lower feeding bin 105, and the material is pushed by a screw pusher 302 to move forward into the furnace after falling. The motor 303 and the feeder outer tube 304 are sealed by adopting a magnetic fluid 305 structure, so that the aim of sealing and feeding under 0.001Pa vacuum is fulfilled. Fig. 4 is a detailed view of the expansion joint 108 and the magnetic fluid dynamic and static seal 109, wherein the expansion joint 108 is a corrugated pipe with the diameter of 0.3m and the length of 0.6m, two ends of the corrugated pipe are fixed, the magnetic fluid dynamic and static seal 109 is divided into a static end part 401 and a movable end part 402, the rotary seal is realized, the magnetic fluid static end is fixed on a movable trolley 403, and sliding rails 404 and rollers 405 are arranged on two sides of the magnetic fluid static end, so that the expansion of a furnace pipe at a high temperature is mainly eliminated.
In the specific embodiment, 54kg of magnesium powder (200 meshes, 99% purity) and 30kg of silicon powder (D50.ltoreq.3μm,99% purity) are weighed and mixed uniformly in a V-shaped mixer, and the mixture is conveyed to a conical feed inlet 101 of a continuous vacuum rotary kiln through airflow and directly enters an upper feed bin 119. Closing the vacuum valve 102, opening the vacuum to reduce the vacuum in the bin to 1Pa, opening the lower vacuum valve to allow the material in the upper feed bin 119 to enter the middle feed bin 120, closing the vacuum valve, opening the vacuum to reduce the vacuum in the bin to 0.1Pa, opening the lower vacuum valve to allow the material in the middle feed bin 120 to enter the lower feed bin 121, closing the vacuum valve, opening the vacuum to reduce the vacuum in the bin to 0.001Pa, and opening the lower vacuum valve to allow the material to enter the screw feeder 107. The material was fed into furnace tube 113 under screw drive, and the rotational speed of the screw feeder was controlled to maximize the charge of material in the furnace by about 10%. At this time, the furnace tube 113 was operated at a speed of 2 rpm/min under the start of the transmission and motor. The heating system of the furnace body 114 is started, four temperature sections are arranged, materials are enabled to run for 1.5h (the temperature is 350 ℃) in a heating zone in the furnace tube, the temperature is kept for 2.5h (the temperature is 550 ℃), the temperature is lowered for 2h (the temperature is 350 ℃), the temperature is lowered for 2h (the temperature is below 50 ℃), and the vacuum degree in the furnace is controlled to be less than or equal to 0.1 and Pa through a vacuum system. The expansion of the furnace tube during high temperature heating is eliminated by expansion joint 108. And opening the cooling sleeve 110 to cool the magnetic fluid dynamic and static sealing system 109 at the two ends. After the material is subjected to 8h of turnover sintering, the material enters an upper discharging bin 119 from a blanking port 118, and a material level gauge is closed after responseAn upper vacuum valve is opened, a lower vacuum valve is opened, materials enter a middle discharging bin 120, after the middle discharging bin is temporarily stored for a period of time, the upper vacuum valve is closed, the lower vacuum valve is opened, the materials enter a lower discharging bin 121, after discharging is finished, the lower vacuum valve is immediately closed, a vacuum device is opened, the vacuum in the bin is reduced to 0.001Pa, the materials are conveyed to a packaging area through a screw discharger 122, and Mg with D50 less than or equal to 500 and nm is obtained after vacuum packaging 2 Si material.
Example 2
The present embodiment uses the same apparatus and procedure as in embodiment 1.
In this embodiment, 55kg of magnesium powder (100 mesh, 98.5% purity) and 30kg of silicon powder (D50.ltoreq.8μm,99% purity) were weighed and mixed uniformly in a V-type mixer, and after mixing, the mixture was conveyed to the conical feed inlet 101 of the continuous vacuum rotary kiln by air flow, and then entered into the furnace tube 113 in accordance with the procedure of example 1. The rotational speed of the screw feeder was controlled to maximize the charge of material in the furnace by about 8%. The furnace tube was run at a rate of 4 rpm/min. The materials are operated for 1.2h (temperature 380 ℃) in a temperature rising area in a furnace tube, 3h (temperature 530 ℃) in a heat preservation area, 2.5h (temperature 370 ℃) in a cooling area, 3h (temperature below 50 ℃) in a cooling area, and the vacuum degree in the furnace is controlled to be less than or equal to 0.01 and Pa through a vacuum system. After the material is subjected to overturning sintering for 10.7 hours, blanking and conveying the material to a packaging area through a spiral discharger 122, and vacuum packaging to obtain Mg with D50 less than or equal to 700 nm 2 Si material.
Example 3
The present embodiment uses the same apparatus and procedure as in embodiment 1.
In this embodiment, 51.6 kg magnesium powder (300 mesh, 99.9% purity) and 30kg silicon powder (D50.ltoreq.2μm,99.9% purity) were weighed and mixed uniformly in a V-blender, and the mixture was conveyed to the conical feed inlet 101 of the continuous vacuum rotary kiln by air flow and then entered into the furnace tube 113 in accordance with the procedure of example 1. The rotational speed of the screw feeder was controlled to maximize the charge of material in the furnace by about 5%. The furnace tube was run at a rate of 1 rpm/min. The materials are operated for 1h (temperature 300 ℃) in a heating zone in a furnace tube, 1h (temperature 520 ℃) in a heat preservation zone, 1h (temperature 300 ℃) in a cooling zone, 1h (temperature below 50 ℃) in a cooling zone, and a vacuum system is adoptedThe vacuum degree in the furnace is controlled to be less than or equal to 0.001 and Pa. After 4 hours of turnover sintering, the material is conveyed to a packaging area through a spiral discharger 122 after blanking, and then Mg with D50 less than or equal to 300 nm can be obtained through vacuum packaging 2 Si material.
Example 4
The present embodiment uses the same apparatus and procedure as in embodiment 1.
In this embodiment, 55.5kg of magnesium powder (60 mesh, 98% purity) and 30kg of silicon powder (D50.ltoreq.10μm,98% purity) were weighed and mixed uniformly in a V-type mixer, and after mixing, conveyed to a conical feed inlet 101 of a continuous vacuum rotary kiln by air flow, and entered into a furnace tube 113 in accordance with the procedure of example 1. The rotational speed of the screw feeder was controlled to maximize the charge of material in the furnace by about 15%. The furnace tube was run at a rate of 6 rpm/min. The materials are operated for 2h (the temperature is 400 ℃) in a temperature rising area in the furnace tube, the temperature is kept for 4h (the temperature is 580 ℃), the temperature is lowered for 3h (the temperature is 400 ℃), the temperature is lowered for 3h (the temperature is below 80 ℃), and the vacuum degree in the furnace is controlled to be less than or equal to 10Pa through a vacuum system. After 12 hours of turnover sintering, the material is conveyed to a packaging area through a spiral discharger 122 after blanking, and Mg with D50 less than or equal to 800nm can be obtained after vacuum packaging 2 Si material.
Comparative example 1
The present example uses the same equipment and procedure as example 1, except that 60kg of magnesium powder was used as example 1.
Comparative example 2
The apparatus and process used in this example are the same as those in example 1, except that the silicon powder used had a particle diameter D50 of 20 μm or less.
Comparative example 3
The equipment and the process of the embodiment are the same as those of embodiment 1, and the difference from embodiment 1 is that the temperature of the heat preservation area is 650 ℃, the running time is 1h, and the vacuum degree of the furnace body is 1000 Pa.
Comparative example 4
The present example uses the same equipment and procedure as in example 1, except that the temperature of the incubation zone was set at 500 ℃.
Comparative example 5
The equipment and the process used in the embodiment are the same as those in embodiment 1, and the difference between the equipment and the process is that a cooling area is not arranged, namely the temperature running time of the material in the cooling area is 0, and the temperature is consistent with the temperature of the cooling area.
Comparative example 6
The apparatus and process used in this example are the same as those in example 1, except that the rotation speed of the continuously revolving vacuum furnace is 0.5 rpm/min.
Comparative example 7
In the embodiment, the equipment and the process used in the embodiment are the same as those in embodiment 1, and the difference from embodiment 1 is that the vacuum system is not started, argon is used in the whole process, namely, argon is used for flushing a feeding and discharging bin, and argon is used as working gas of the rotary kiln, so that the effect of isolating air is achieved; the soak temperature was set at 650 ℃ (otherwise non-reactive).
Comparative example 8
In the specific embodiment, 5.4kg of magnesium powder (200 meshes, 99% purity) and 3.0kg of silicon powder (D50 is less than or equal to 3 mu m,99% purity) are weighed and mixed uniformly in a V-shaped mixer, the mixture is placed in a corundum sagger, placed in a static high-vacuum furnace, continuously vacuumized to 0.1Pa, a heating program of the vacuum furnace is set to be 350 ℃/1.5h,550 ℃/2.5h and 350 ℃/2h, and the temperature is reduced to below 50 ℃ along with the furnace, and the product material is obtained after the furnace is opened.
Performance testing
1. Visual inspection: ideal Mg 2 Si is a blue material, white metal magnesium exists if no reaction exists, and yellow silicon and metal magnesium particles exist if excessive reaction exists.
2、Mg 2 Si purity test: the material was tested using an X-ray diffractometer (XRD) and the spectra were refined, wherein magnesium was not quantitatively analyzed by XRD due to extremely uneven dispersion, and only visual inspection was possible.
3. Microcosmic morphology testing: observed by Scanning Electron Microscopy (SEM).
4. Particle size testing: tested by a laser particle size analyzer.
The products of examples 1-4 and comparative examples 1-8 were subjected to the above performance tests, the test results of which are shown in Table 1 below.
TABLE 1
The visual inspection, purity and particle size test results of the example and comparative products are shown in table 1. As shown in FIG. 5, which is a photograph of the product of example 1, it can be seen that the high purity magnesium silicide is a dark blue material, and has no impurities such as white, yellow, etc. FIG. 6 is an SEM image of example 1, which shows that the synthesized magnesium silicide is relatively loose, has a primary particle size of about 100-400nm, and shows that the synthesized magnesium silicide has a D10 of 208 nm, a D50 of 411nm, and a D90 of 879nm, and exhibits typical submicron-level powder characteristics, as determined by laser particle size analysis (laser particle size diagram, see FIG. 7). The XRD pattern of example 1 is shown in FIG. 8, and it can be seen that high purity Mg is present on XRD 2 Si peak, no other impurity peak. Due to Mg 2 The purity of Si is more difficult to determine in other ways, so it is analyzed by XRD refinement, the refinement results fit as shown in FIG. 9, the results are shown in Table 1, the product of example 1 is composed of Mg 2 Two phases of Si and MgO, wherein Mg 2 Si is as high as 99.21%, mgO depends on the raw material and oxygen in the system, and cannot be completely eliminated.
In examples 2-4, mg with purity of 98% or more was obtained by changing the parameters within the scope of the claims 2 Si is relatively pure because of no overburning and no raw materials due to proper temperature. As shown in FIG. 10, the XRD pattern for example 4, mg 2 Si content is up to 98.4%. The results of the laser particle sizer of example 2 are shown in FIG. 11, with D50 of 651nm. The grain size and purity are affected by the grain size, vacuum degree and temperature of the silicon powder as raw material.
When the amount of magnesium (comparative example 1) was increased, although the purity was as high as 98.27%, the remaining magnesium accumulated in the material due to the excessive amount of magnesium and was unevenly dispersed, resulting in a certain error in the result, and the true purity was lower than 98.27%. And because alloying occurs faster, some Mg is produced 3 Si 2 . When silicon powder of large particle size (comparative example 2) is used, the product is blue, but due to magnesium entering the central travel of the silicon particlesLengthening, the existence of limiting steps, insufficient alloying reaction and incapacity of timely discharging central heat, and Mg is generated 3 Si 2 . SEM (fig. 12) and laser particle size analysis (fig. 13) of the product of comparative example 2 also showed that the product was relatively coarse, a micron-sized material, which would affect the application of the subsequent material. When the holding temperature was increased and the run time and vacuum were reduced (comparative example 3), the XRD refinement of the product was as shown in FIG. 14, and it was found that Mg 2 Si has begun to decompose, producing 16.18% of yellow elemental Si with an increase in MgO. When the temperature of the holding zone is lowered (comparative example 4), the alloying reaction rate becomes lower, less blue color exists in the product, and magnesium and silicon which are not reacted exist, and the particle size analysis also shows that the particle size of the raw materials is high. If no cooling zone is provided (comparative example 5), mg is caused 3 Si 2 As a result, the low-magnesium alloy is unstable and accumulates to some extent, and may ignite due to friction and static electricity, so that the presence of the cooling zone can eliminate Mg 3 Si 2 . While if the rotary kiln speed was lowered continuously (comparative example 6), it was found that Mg was generated again 2 Si is decomposed because the material accumulation cannot dissipate heat, the lower the rotation speed is, the higher the Si simple substance content is, and meanwhile, the D50 of the sintered material is increased. If the conventional rotary kiln is used for preparing Mg 2 Si (comparative example 7), the product was found to be pale blue and had a purity of only 95.70% after temperature elevation, yielding more MgO, si and Mg 3 Si 2 And D50 of the sintered product increased to 2.814 μm. If the direct vacuum batch furnace is adopted without rotary sintering (comparative example 8), the furnace spraying phenomenon is unavoidable, namely, the material is sprayed to the whole hearth, the vacuum pump is always operated, the vacuum system is seriously polluted, and the proportion of the material is not uniform after the material is sprayed, so that the purity of the product is not high, and even Mg is generated 2 Decomposition of Si.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (2)
1. High-purity submicron-order Mg 2 The preparation method of Si is characterized by comprising the following specific steps:
step S1: mixing magnesium powder and silicon powder in a mixer according to a mass ratio of 1.72-1.85:1, and transferring the mixture to a vacuum sealing feeding bin of a continuous vacuum rotary kiln after uniform mixing;
step S2: controlling the maximum filling amount of the mixture in the furnace, conveying the mixture of magnesium powder and silicon powder into a furnace body of a continuous vacuum rotary kiln through spiral feeding, and under the condition that the furnace body keeps rotating and vacuum, discharging the material through a heating area, a heat preservation area, a cooling area and a vacuum sealing discharging bin, wherein the produced material is high-purity submicron-level Mg 2 Si; the particle diameter of the primary particles is less than or equal to 800nm, and the purity is more than or equal to 98%;
the grain diameter D50 of the silicon powder in the step S1 is less than or equal to 10 mu m, and the purity is more than or equal to 98%;
the temperature of the heating area in the step S2 is 300-400 ℃, and the operation is carried out for 1-2h; the temperature of the heat preservation area is 520-580 ℃, and the operation is carried out for 1-4 hours; the temperature of the cooling area is 300-400 ℃, and the operation is carried out for 1-3 hours; the temperature of the cooling area is below 80 ℃ and the cooling area is operated for 1 to 3 hours;
the vacuum degree in the furnace of the continuous vacuum rotary kiln in the step S2 is 0.001-10Pa, and the rotating speed of the furnace tube is 1-6 rpm; the maximum filling amount of the mixture in the furnace of the continuous vacuum rotary kiln is less than or equal to 15 percent.
2. A high purity submicron Mg according to claim 1 2 The preparation method of Si is characterized in that the particle size of the magnesium powder is more than or equal to 60 meshes, and the purity is more than or equal to 98 percent.
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