Summary of the invention
The invention provides that a kind of preparation technology is simple, production cost is low, environmentally friendly and be easy to the preparation method of polycrystalline silicon of industrialization.
A kind of preparation method of polycrystalline silicon, described preparation method comprise the steps: reaction raw materials is inserted in the reaction vessel, and described reaction raw materials comprises silicofluoride and as the metal of reductive agent; Insert electrode in described reaction vessel, described electrode comprises positive pole and negative pole, applies voltage between described positive pole and the negative pole; Heating and stir described reaction raw materials under the shielding gas atmosphere; After continuing described reaction raw materials to the first temperature of heating, the insulation scheduled time, cooling obtains reduzate; Described reduzate is used pure water, acid elution and drying treatment successively, obtain described polysilicon.
Preferably, the voltage range that is applied between described positive pole and the negative pole is 2-12V.
Preferably, described just very silicon chip or graphite, described negative pole are silicon chip.
Preferably, the purity grade of described silicofluoride is at least analytical pure, and described silicofluoride is selected from potassium silicofluoride or Sodium Silicofluoride.
Preferably, the purity grade of described metal is at least chemical pure, and described metal is selected from potassium or sodium.
Preferably, the weight ratio scope of described silicofluoride and metal is 2.8:1 to 4:1.
Preferably, described first temperature range is 140-200 ℃.
Preferably, the purity grade of described acid is that electronics is pure, is selected from hydrochloric acid, hydrofluoric acid, at least a in the sulfuric acid.
Preferably, described drying treatment is vacuum-drying or lyophilize.
Preferably, described shielding gas is selected from nitrogen or argon gas.
Preparation method of polycrystalline silicon provided by the invention, in the process of preparation polysilicon, in reaction system, provide electric energy, thereby reduced the temperature of reacting required, make reaction conditions gentleer, optimized the processing condition of preparation silicon, and obtained to have high-purity polycrystalline by further purification process, this method has industrial prospect.
Embodiment
A kind of preparation method of polycrystalline silicon comprises the steps: reaction raw materials is inserted in the reaction vessel, and reaction raw materials comprises silicofluoride and as the metal of reductive agent; Insert electrode in reaction vessel, electrode comprises positive pole and negative pole, applies voltage between positive pole and negative pole; Heating and stirring reaction raw material under the shielding gas atmosphere; After continuing reacting by heating raw material to the first temperature, the insulation scheduled time, cooling obtains reduzate; Reduzate is used pure water, acid elution and drying treatment successively, obtain polysilicon.
Silicofluoride as one of reaction raw materials needs before inserting reaction vessel through drying treatment, mainly be to remove the water that may exist in the silicofluoride, when containing less water in the silicofluoride, can react with metal, thereby produce unnecessary by product, the temperature range of dry silicofluoride is 100-140 ℃, and time of drying, scope was 1-12 hour, and drying process can be to finish in vacuum drying oven.The purity grade of silicofluoride is at least analytical pure, to avoid introducing other impurity in reaction system.Silicofluoride is the silicofluoride of IA family metallic element, and silicofluoride can be selected from solid Sodium Silicofluoride or anhydrous potassium silicofluoride.
Metal as reductive agent is used for the reduction silicofluoride, and metal is IA family metallic element, is selected from sodium Metal 99.5 or potassium metal.Same, the purity grade of metal is at least chemical pure.Preferably, the metallic element in the silicofluoride is same with the metallographic phase as reductive agent.Metallic element in silicofluoride is with as the metallographic phase of reductive agent simultaneously, reduction reaction carry out more thoroughly and by product few, be conducive to the purification of polysilicon.In addition, when metal is potassium, with the Sodium Silicofluoride reaction constantly, the relative metal of temperature that reduction reaction takes place is sodium, low, therefore low to the requirement of conversion unit when silicofluoride is Sodium Silicofluoride, but sodium Metal 99.5 is compared potassium and had cost advantage.
The scope of the weight ratio of silicofluoride and metal is 2.8:1 to 4:1.Silicofluoride is excessive a little with respect to metal, so that the intact silicofluoride of the unreacted in the water dissolving and reducing product in the follow-up purification process, reach the purpose of purified silicon, and when silicofluoride is too much, the required water amount is also many in the purification process, therefore, preferred, the part by weight of the metal of silicofluoride and reductive agent is 3:1.In embodiment, silicofluoride contains the solid Sodium Silicofluoride, and metal contains sodium Metal 99.5, and the reaction principle that specifically prepares silicon is: 4Na+Na
2SiF
6=Si+6NaF.
Silicofluoride with insert reaction vessel in the lump as the metal of reductive agent after, in reaction vessel, insert electrode, electrode comprises positive pole and negative pole, the voltage range that is applied between positive pole and the negative pole is 2-12V.Positive pole can be silicon chip or graphite flake, and negative pole can be silicon chip.Specifically be applied to the voltage difference between positive pole and the negative pole, the temperature that reduction reaction takes place is different, and in an embodiment, reaction raw materials is Sodium Silicofluoride and sodium Metal 99.5, the voltage that is applied between positive pole and the negative pole is 3.4V, and reduction reaction can take place under 170 ℃; In another embodiment, the voltage that is applied between positive pole and the negative pole is 3.7V, and reduction reaction can take place under 160 ℃.
Preparation method of polycrystalline silicon provided by the invention, added volts DS at reaction raw materials, namely in reaction system, provide energy, added electric work, according to the Gibbs free energy law, burst into reversible work to system, opened up a kind of new reaction path, reduction reaction activation energy reaction activity when not switching on is low during energising, reduced reaction and carried out required temperature fully, it is milder that reduction reaction is carried out, and optimized the processing condition of preparation polysilicon, requirement to conversion unit simultaneously reduces, and makes that the application of this preparation method in industrialization is more feasible.
The present invention reaches the purpose that electric energy is provided to reaction system by insert electrode in reaction vessel, thereby optimizes the condition that reduction reaction takes place, and any improvement based on this purpose of those skilled in the art all belongs within the scope of protection of present invention.
In the reduction reaction process, for silicofluoride is fully contacted with metal as reductive agent, reduction reaction is carried out more fully, need stir reaction raw materials, in embodiment, add stirring-head in reaction vessel, the specific form of stirring-head is not limit, and can be mechanical stirring head or magnetic agitation head.
Silicofluoride needs carry out under the shielding gas atmosphere with as the metal generation reduction reaction of reductive agent the time, to avoid air reaction is impacted, and produces unnecessary by product, and shielding gas does not react with reducing metal.Shielding gas is selected from a kind of in nitrogen, the argon gas.In concrete embodiment, shielding gas is nitrogen.
Under the shielding gas atmosphere; reaction raw materials is heated; after air drains in the question response container; stir and lasting reacting by heating raw material to the first temperature; when reductive agent was sodium Metal 99.5 and Sodium Silicofluoride reaction, the scope of first temperature was 140-200 ℃; after temperature reaches first temperature; the insulation scheduled time, purpose is to make reduction reaction continue to take place for some time, and scheduled time scope is 0.5-4 hour; in embodiment; when reductive agent was sodium Metal 99.5 and Sodium Silicofluoride reaction, voltage was 3V; remain in 165 ℃ of oil baths, reduction reaction can be carried out fully.Preparation method provided by the invention owing to provide electric work to the reduction reaction system, therefore makes reduction reaction can take place smoothly under lower temperature, thereby makes required polysilicon, has optimized the technology of preparation polysilicon.
The weight ratio scope of the metal of silicofluoride and reductive agent is 2.8:1 to 4:1, silicofluoride is excessive a little, therefore reduzate not only contains silicon, fluoride salt, also has the intact reaction raw materials silicofluoride of unreacted simultaneously, therefore, in order to obtain highly purified silicon, need further do purification processes to reduzate.
The present invention obtains to have high-purity polycrystalline by optimizing preparation process and wash environment, and the pollution of avoiding koniology and reaction vessel etc. to bring uses dissolved in purified water salt mode to come purified silicon, and silicon is water insoluble when normal temperature.
Reduzate is used pure water, acid elution successively, filter the back oven dry, obtain having high-purity polycrystalline.In purification process, the purity grade of acid is that electronics is pure, is selected from hydrofluoric acid, hydrochloric acid, at least a in the sulfuric acid.The concrete selection as iron, calcium, magnesium, aluminium etc., but can not cause the elemental silicon oxidation, thereby obtain high-purity silicon according to being that acid can be removed by the impurity of sodium reduction under the normal temperature.Acid can be single acid, also can be the mixing of several acid, and mixing acid has stronger acidity with respect to single acid, and is better to the solvability of impurity.In embodiment, adopt pure water, acid elution reduzate respectively 3-5 time, and suction filtration, last, the silicon that purification processes is crossed carries out drying treatment.
Because silicon at middle high temperature surface oxidation takes place easily, so temperature is unsuitable too high during drying treatment silicon.Concrete, can be with the silicon of purifying 20 ~ 50 ℃ of following vacuum drying treatment, when dry vacuum tightness at least less than 0.5 pascal, or employing lyophilize, drying temperature is less than 25 ℃, with the minimizing silicon surface oxidation.
The technology of existing purified silicon mainly is the purity that improves silicon by high melt, and temperature is generally up to thousands of degree, and is in vacuum oven, and the purification condition is very harsh.In preparation method of the present invention, mainly be by improving experimental situation, optimize preparation process, adopt clean reaction raw materials, washing reagent, the pollution of avoiding koniology and reaction vessel etc. to bring, so not only obtained highly purified silicon, but also avoided the high melt process of power consumption, processing condition harshness, the preparation method of polycrystalline silicon industrial applications prospect that makes the present invention disclose is more objective.
In the embodiment specific to preparation silicon, reaction raw materials Sodium Silicofluoride and sodium Metal 99.5 are weighed, insert to send out and answer in the container, add top electrode and stirring-head in reaction vessel, electrode comprises positive pole and negative pole, just very silicon chip, negative pole is silicon chip, feed nitrogen in the container to get rid of air wherein to sending out to answer, the reacting by heating raw material is treated to begin after air drains to start and is stirred, continue subsequently that reacting by heating is former expects 160 ℃, be incubated 2 hours and carry out reduction reaction, obtain reduzate, cooling.Because reduzate not only contains silicon, therefore need carry out purification processes to reduzate, concrete purification step is: adopt pure water washing reduzate 3 times, vacuum filtration, the product that obtains behind the suction filtration is washed 3 times by pure other hydrochloric acid of level of electronics, the silicon after the washing was obtained polysilicon in 12 hours 50 ℃ of following vacuum-dryings.
The present invention is further described below by embodiment.
Embodiment 1
According to weight ratio 3: 1 weighing reaction raw materials Sodium Silicofluoride and sodium Metal 99.5, reaction raw materials is inserted in three mouthfuls of clean vials, feed N
2Get rid of the air in the bottle, in bottle, add electrode and stirring-head, electrode comprises positive pole and negative pole, anodal and negative pole is all silicon chip, and the volts DS that is attached between positive pole and the negative pole is 3.7V, and reacting by heating raw material to 100 ℃ also starts stirring, continue 160 ℃ of reacting by heating raw material to the first temperature subsequently, be incubated 2 hours, stop to stir, be cooled to room temperature.Change the reduzate of gained over to clean beaker that pure water is housed, washing and vacuum filtration with pure water washing 3 times, are used electronics pure hydrochloric acid further washing and vacuum filtration, at last 60 ℃ of following vacuum-dryings 12 hours with the product behind the suction filtration again.
Fig. 1 is the X ray diffracting spectrum of the polysilicon that makes of embodiment 1.Finally analyze the purity of demonstration silicon 99.9999% by ICP-Mass.
Embodiment 2
In embodiment 2, the electrode auxiliary voltage is 3.4V, and the first corresponding temperature is 170 ℃, and all the other preparation methods are with embodiment 1.
Embodiment 3
In embodiment 3, the electrode auxiliary voltage is 3V, and the first corresponding temperature is 165 ℃, and all the other preparation methods are with embodiment 1.
Embodiment 4
In embodiment 4, the electrode auxiliary voltage is 2V, and the first corresponding temperature is 200 ℃, and all the other preparation methods are with embodiment 1.
Embodiment 5
In embodiment 5, the electrode auxiliary voltage is 12V, and the first corresponding temperature is 140 ℃, and all the other preparation methods are with embodiment 1.
Changed the auxiliary voltage of electrode among the embodiment 2-5, correspondence changes first temperature simultaneously, and reduction reaction all can take place, and the silicon that finally makes has the purity up to 69.
Embodiment 6
In embodiment 6, reaction raw materials Sodium Silicofluoride and sodium Metal 99.5 amount of substance ratio are 0.3, and Sodium Silicofluoride is excessive a little, and all the other prepare the method for polysilicon with embodiment 1.
Comparative Examples 1
In Comparative Examples 1, the amount of substance ratio of reaction raw materials Sodium Silicofluoride and sodium Metal 99.5 is 0.25, and the amount of silicofluoride and sodium Metal 99.5 is just in time according to reaction metering ratio.All the other prepare the method for polysilicon with embodiment 1.
Comparative Examples 2
In Comparative Examples 2, the amount of substance ratio of reaction raw materials Sodium Silicofluoride and sodium Metal 99.5 is slightly less than 0.25, and sodium Metal 99.5 is excessive a little, and all the other prepare the method for polysilicon with embodiment 1.
Fig. 2 is the X ray diffracting spectrum of the silicon that makes in embodiment 6, the Comparative Examples 1 and 2.R represents the amount of substance ratio of raw material Sodium Silicofluoride and sodium Metal 99.5, and to represent that R obtained silicon greater than 0.25 o'clock purer for the result among the figure, and R is less than 0.25, and the expression sodium Metal 99.5 is excessive, causes the reaction subsequent step to be difficult to purify, and when R was 0.3, impurity peaks was minimum.
Although technical scheme of the present invention has been done detailed elaboration and for example above; for a person skilled in the art; on the basis that does not break away from essence of the present invention, above-described embodiment is modified and/or flexible or adopt similar replacement scheme, also in protection scope of the present invention.