CN104016351A - Efficient boron-removing slag former and preparation method thereof and method for removing boron and slagging - Google Patents

Efficient boron-removing slag former and preparation method thereof and method for removing boron and slagging Download PDF

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CN104016351A
CN104016351A CN201310718123.4A CN201310718123A CN104016351A CN 104016351 A CN104016351 A CN 104016351A CN 201310718123 A CN201310718123 A CN 201310718123A CN 104016351 A CN104016351 A CN 104016351A
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silicon
boron
slag former
solution
sodium carbonate
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CN104016351B (en
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谢兴源
杨凤炳
李伟生
龚炳生
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Fujian Shanghang Xingheng silicon products Co.,Ltd.
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FUJIAN XING ZHAOYANG SILICON MATERIALS Co Ltd
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Abstract

The invention relates to the technical field of polysilicon purification, and particularly relates to an efficient boron-removing slag former and a preparation method thereof, and a method for removing boron and slagging. The boron-removing slag former comprises the following components: 40-60wt% of nanosilicon dioxide and 40-60wt% of sodium carbonate, preferably, 40-50wt% of nanosilicon dioxide and 50-60wt% of sodium carbonate, wherein the grain diameter of the nanosilicon dioxide is 50-130nm, preferably 60-120nm. By using common silicon dioxide, the proportion of a component B of a slag system is 4; by using the nanosilicon dioxide, the proportion of the component B is increased to 7-10. The nanosilicon dioxide is large in surface activity, high in boron-removing distribution coefficient, and significant in effect; the dosage of the slag former can be effectively reduced, the slagging time is shortened, and the cost is greatly reduced.

Description

A kind of efficient except boron slag former, its preparation method and the method except boron slag making
Technical field
The present invention relates to a kind of polycrystalline silicon purifying technical field, particularly relate to a kind of efficient the boron slag former that removes, its preparation method and the method except boron slag making.
Background technology
At current energy worsening shortages, under the day by day serious background of environmental pollution, solar energy power generating is due to features such as technology maturation, resource are never exhausted, environmental pressure is little, becomes 21 century to be hopeful one of clean energy of large-scale application most, enjoys countries in the world to pay close attention to unique advantage.Polysilicon is described as " blood of modern industry, the foundation stone of microelectronics information industry ", is basic raw material and the strategic material of development electronics and photovoltaic industry.
Polycrystalline silicon purifying mainly contains chemical method and metallurgy method at present.Chemical method mainly contains improved Siemens, silane thermal decomposition process and fluidized bed process, utilize chemical method to purify and can obtain polysilicon more than purity 9N, but chemical method investment is large, energy consumption is high and seriously polluted.Metallurgy method is produced polysilicon and is referred to taking metallurgical grade industrial silicon as raw material, in the situation that not changing silicon materials physical property, silicon to be purified, the purity of Pure Silicon Metal is not less than 99.9999%, boron content is not higher than 0.3ppm, to be suitable as the requirement of solar cell material.This method most important feature is that production cost is low, and the pollution causing to environment is little, simple to operate, easily scale operation.
In polysilicon, impurity is divided into metallic impurity and nonmetallic impurity.Metallic impurity are because segregation coefficient is much smaller than 1, and available directional solidification method is removed.And nonmetallic impurity B, the P segregation coefficient in silicon is 0.8,0.35, far above metallic element, particularly B, close to 1, cannot remove by directional freeze, also cannot be as P because saturation steam forces down, and vacuum available melting is removed.At present except the main method of boron has slag making, air blowing, pickling, vacuum, electron beam, plasma body etc.Slagging boron removal is the at present main boron mode of removing, and effect is remarkable and cost is low, is suitable for industrialization and produces.
US Patent No. 5788945 discloses a kind of by the method for continuous adding slag former in silicon liquid, and slag former composition is 60%CaO and 40%SiO 2, boron drops to 1ppmw from 40ppmw.This continuously with the method for slag former, owing to wrapping up in slag, silicon is more, cause silicon loss large, and in slagging process, the consumption of slag former is relatively too high, causes cost to increase, and silicon also can produce certain metallic pollution simultaneously.
Patent CN1926062A discloses a kind of method of removing boron from silicon, and this patent is by add slag former Na in Pure Silicon Metal 2cO 3and SiO 2, form slag, the boron content in silicon can be reduced to 0.3ppmwt left and right by 12ppmwt, but this technique repeats 3 slag making, the quantity of slag is large, and cost is high, and silicon loss is higher, is not suitable for scale operation in industry.
Application 201310337757.5 discloses a kind of slag former and the using method in polycrystalline silicon medium melting is purified thereof.This slag former, by weight percentage, is mixed by following raw material: Na 2siO 350%~79%, SiO 220%~40% and TiO 21%~15%.In polycrystalline silicon medium melting is purified, add slag former of the present invention, the partition ratio LB numerical value by boron in slag agent and silicon liquid has effectively improved 1~2 from 2~4, improves except effect of boron, and the boron content of silicon material is reduced to below 0.3ppmw.
Application " 201310337930.1 " discloses a kind of slag former and the using method in polycrystalline silicon medium melting is purified thereof.Slag former, is: Na by weight percentage 2siO 330%~60%, SiO 220%~50%, TiO 21%~15% and Al 2o 31%~5%.In polycrystalline silicon medium melting is purified, add slag former of the present invention, the partition ratio LB numerical value by boron in slag agent and silicon liquid has effectively improved 1~2 from 2~4, improves except effect of boron, and the boron content of silicon material is reduced to below 0.20ppmw.
Application " 201310337756.0 " discloses a kind of slag former and the using method in polycrystalline silicon medium melting is purified thereof.This slag former, by weight percentage, is mixed by following raw material: Na 2siO 330%~70%, SiO 220%~60%, TiO 21%~15% and FeO1~5%.In polycrystalline silicon medium melting is purified, add slag former of the present invention, the partition ratio LB numerical value by boron in slag agent and silicon liquid has effectively improved 1~2 from 2~4, improves except effect of boron, and the boron content of silicon material is reduced to below 0.27ppmw.
When relating to a kind of polycrystalline silicon medium melting, application 201310244836.1 is convenient to slag former and using method thereof that white residue separates.Slag former is mixed by following raw material: SiO 250%~80%, CaO10%~35% and CaCl 25%~15%.Using method is: (1) joins silicon material in plumbago crucible, adopts medium-frequency induction furnace to be heated to silicon material and is all fused into silicon liquid; (2) slag former is joined in mixer and mixed according to raw material composition; (3) slag former after mixing joins in silicon liquid, and medium melting is carried out in insulation; (4), after medium melting finishes, the old slag producing is all poured out; (5) repeating step (3)~(4) 2~4 times, silicon liquid, through cooled and solidified, is measured its boron content through ICP-MS.The present invention can improve slag silicon separating effect, and while reducing the separation of slag silicon, the viscosity of slag, improves the rate of recovery, reduces costs.
At present, tradition is except the silicon-dioxide in boron slag former is mainly from high purity quartz ore deposit, and high purity quartz ore resources is limited, and streaking removes effect of boron unstable.
Summary of the invention
Primary goal of the invention of the present invention be to propose a kind of for polysilicon except boron slag former.
The second goal of the invention of the present invention has been to propose this preparation method except boron slag former.
The 3rd goal of the invention of the present invention has been to propose to use this to remove boron slag former and carry out the method for slagging boron removal.
In order to realize object of the present invention, the technical scheme of employing is:
For polysilicon except a boron slag former, described consisting of except boron slag former: nano silicon 40~60wt%, sodium carbonate 40~60wt%; Preferred: nano silicon 40~50wt%, sodium carbonate 50~60wt%; Wherein the particle diameter of nano silicon is 50~130nm; Preferably 60~120nm.
The particle diameter that wherein particle diameter of sodium carbonate is described sodium carbonate is 20~45 μ m; Preferably 25~40 μ m.Described sodium carbonate adopts and grinds preparation.
The invention still further relates to a kind of preparation method except boron slag former for polysilicon, comprise the following steps:
(1) combusting rice hull is produced to rice hull ash, temperature of combustion is 550~600 DEG C, and be 5~6h combustion time;
(2) rice hull ash and NaOH solution are mixed, heated and stirred, has reacted rear filtration, obtains water glass solution;
(3) water glass solution, hydrochloric acid, oxalic acid are added in reactor and heated, Heating temperature is 50~60 DEG C, and the reaction times is 50min, and in reaction process, the pH value of solution is 8~8.5, and the pH value of reaction end is 7~8;
(4) hydrochloric acid is splashed into the solution of step (3) gained, regulating pH value is 4~4.5;
(5) add Witco 1298 Soft Acid and sodium polyacrylate to carry out ageing, Aging Temperature is 90~100 DEG C, and digestion time 1h separates out white slip;
(6) by the white slurry filtration of separating out, use deionized water wash 1~5 time, use washing with alcohol 1~3 time, heating volatilization ethanol, dry, pulverize, and makes nano silicon;
(7) above-mentioned prepared nano silicon and sodium carbonate are mixed with and are obtained except boron slag former.
The first optimal technical scheme of the present invention is: in step (2), the concentration of NaOH solution is 0.6mol/L, and the ratio of described rice hull ash and NaOH solution is 1kg:15L~18L; Heating temperature is 105~110 DEG C, and the described reaction times is 4.5~5h.
The second optimal technical scheme of the present invention is: in step (3), concentration of hydrochloric acid is that 1mol/L, concentration of oxalic acid are 0.1mol/L.
The 3rd optimal technical scheme of the present invention is: in step (5), and 4~6wt% that the weight of Witco 1298 Soft Acid is solution; The weight of sodium polyacrylate is 4~6wt% of solution.
A kind of method except boron slag former that the invention still further relates to polysilicon, comprises the following steps:
(1) metallic silicon power is dropped into heat fused in plumbago crucible, after melting, add the boron slag former that removes claimed in claim 1, be then incubated slag making;
(2) after slag making is complete, silicon liquid is injected to holding furnace and solidify, after silicon ingot is cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
Wherein, adopt intermediate frequency induction heating device by metallic silicon power heat fused, described silicon particle size is 60~200 orders, and the temperature of silicon liquid is 1500~1700 DEG C;
The mass ratio of metallic silicon power and slag former is 1:0.2~1:1, preferably 1:0.3~1:1, more preferably 1:0.4~1:1;
The slag making time is 15~20 minutes.
Below technical scheme of the present invention is made further explanation.
The present invention adopts high-temp combustion rice hull ash can make organic compound combustion complete, in precipitin reaction process, add oxalic acid to make more stable dispersion of water glass solution, acidization is conducive to the Impurity removal in silicon-dioxide, in ageing process, two kinds of tensio-active agents adds the formation that has hindered chemical bond between particle, thereby play the effect of discrete particles, be conducive to the formation of nanoparticle, therefore, the high and narrow particle size distribution of nano silicon purity prepared by present method.In addition, lower for slagging boron removal partition ratio in slagging process, cause slag former consumption high, cause cost high, the slag making time is long, and more owing to wrapping up in silicon in slag, cause silicon to lose a large difficult problem, the present invention adopts self-control nano silicon, utilize nano silicon to mix slag former with sodium carbonate preparation, concise by intermediate frequency furnace slag making, can effectively boron from industrial silicon content be reduced to below 0.3ppm, the present invention has not only solved rice husk and has prepared the difficult problem that nano silicon purity is not high, and it is low to have solved slagging boron removal partition ratio, slag former consumption is high, cost is high, the difficult problem that the slag making time is long.Use general silica, the B partition ratio of slag system is 4, uses nano silicon, and B partition ratio is increased to 7~10.
The present invention compared with prior art has the following advantages:
Present method can be prepared high-purity nano silicon-dioxide, has enriched the scope of selecting material of slag former;
Present method slag former adopts nano silicon and sodium carbonate to be mixed with, because nano-silica surface exists the hydroxyl of undersaturated residual bond and different bond styles, stable silica structure has been departed from because of anoxic in surface, therefore have very strong activity, compared with general silica, surfactivity is larger, can absorb more boron impurities, removes boron partition ratio high, effect is remarkable, can effectively reduce the consumption of slag former, shorten the slag making time, greatly reduce cost.
The particle diameter of sodium carbonate of the prior art is 180 μ m left and right, because the particle diameter difference of nano level silicon-dioxide and sodium carbonate is excessive, in the time preparing slag former, there is the phenomenon that is difficult to mix, thereby affect the proportioning of two kinds of compositions in slag former, thereby affect the effect of slagging boron removal; And contriver found through experiments, sodium carbonate is processed into the particle that particle diameter is less, can discharge more uniformly positively charged ion, thereby increase speed of response and reaction efficiency, thereby shorten the slag making time.
The specific embodiment of the present invention only limits to further explain and explanation the present invention, not to Composition of contents restriction of the present invention.
Embodiment
Embodiment 1 prepares nano silicon
1. combusting rice hull is produced to rice hull ash, temperature of combustion is 550 DEG C, and be 5h combustion time;
2. rice hull ash and 0.6mol/LNaOH solution are added in the reactor of band stirring, and heated and stirred, Heating temperature is 105 DEG C, reaction times is 5h, after question response is complete, reaction mass is filtered, obtain water glass solution, the ratio of described rice hull ash and NaOH solution is 1kg:15L;
3. above-mentioned water glass solution, 1mol/L hydrochloric acid, 0.1mol/L oxalic acid are added in reactor and heated simultaneously with the feed rate of metering, Heating temperature is 60 DEG C, and timing sampling is measured the pH value of material, reaction times is 50min, the pH value of guaranteeing solution in reaction process is 8~8.5, and the pH value of reaction end is 7~8;
4. 1mol/L hydrochloric acid being splashed in the solution of step 3 gained and carry out acidifying, is 4~4.5 o'clock until the pH value of solution, stops splashing into hydrochloric acid;
5. in the solution after above-mentioned acidifying, add solution 4wt% ten DAADBSA and solution 6wt% sodium polyacrylate to carry out ageing, Aging Temperature is 90~100 DEG C, and digestion time 1h separates out white slip;
6. after ageing has been reacted, by the white slurry filtration of separating out, and with deionized water wash 5 times;
7. by AG washing with alcohol 2 times for step 6 gained filtrate, and heating volatilization ethanol, then the filtrate after volatilization is placed to the oven drying of 150 DEG C, filtrate is pulverized through simple after to be dried, make nano silicon.The particle diameter of nano silicon is 50~130nm.
Embodiment 2
1. combusting rice hull is produced to rice hull ash, temperature of combustion is 600 DEG C, and be 6h combustion time;
2. rice hull ash and 0.6mol/LNaOH solution are added in the reactor of band stirring, and heated and stirred, Heating temperature is 110 DEG C, reaction times is 4.5h, after question response is complete, reaction mass is filtered, obtain water glass solution, the ratio of described rice hull ash and NaOH solution is 1kg:18L;
3. above-mentioned water glass solution, 1mol/L hydrochloric acid, 0.1mol/L oxalic acid are added in reactor and heated simultaneously with the feed rate of metering, Heating temperature is 50 DEG C, and timing sampling is measured the pH value of material, reaction times is 50min, the pH value of guaranteeing solution in reaction process is 8~8.5, and the pH value of reaction end is 7~8;
4. 1mol/L hydrochloric acid being splashed in the solution of step 3 gained and carry out acidifying, is 4~4.5 o'clock until the pH value of solution, stops splashing into hydrochloric acid;
5. in the solution after above-mentioned acidifying, add 6wt% ten DAADBSA of solution and the 4wt% sodium polyacrylate of solution to carry out ageing, Aging Temperature is 90~100 DEG C, and digestion time 1h separates out white slip;
6. after ageing has been reacted, by the white slurry filtration of separating out, and with deionized water wash 5 times;
7. by AG washing with alcohol 1 time for step 6 gained filtrate, and heating volatilization ethanol, then the filtrate after volatilization is placed to the oven drying of 150 DEG C, filtrate is pulverized through simple after to be dried, make nano silicon.The particle diameter of nano silicon is 60~120nm.
Embodiment 3: prepare sodium carbonate
By abrasive dust equipment, it is 325~700 orders that sodium carbonate is worn into particle diameter, i.e. the powder of 20~45 microns.
Embodiment 4: prepare sodium carbonate
By abrasive dust equipment, it is 375~500 orders that sodium carbonate is worn into particle diameter, i.e. the powder of 25~40 microns.
Embodiment 5: slagging boron removal:
1. get sodium carbonate prepared by nano silicon prepared by embodiment 1 and embodiment 3 and be mixed with except boron slag former, described except in boron slag former, nano silicon is 40%, and sodium carbonate is 60%;
2. take 100kg metallic silicon power and drop into heat fused in plumbago crucible, after melting, add that step 1 prepares except boron slag former 20kg, insulation slag making; Described silicon particle size is 60~200 orders, and Heating temperature is 1500 DEG C; The slag making time is 15 minutes;
3. after slag making is complete, silicon liquid is injected to holding furnace and solidify, after silicon ingot is cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
Embodiment 6: slagging boron removal
1. get sodium carbonate prepared by nano silicon prepared by embodiment 1 and embodiment 3 and be mixed with except boron slag former, described except in boron slag former, nano silicon is 40%, and sodium carbonate is 60%;
2. take 100kg metallic silicon power and drop into heat fused in plumbago crucible, after melting, add that step 1 prepares except boron slag former 60kg, insulation slag making; Described silicon particle size is 60~200 orders, and Heating temperature is 1600 DEG C, and the slag making time is 18 minutes;
3. after slag making is complete, silicon liquid is injected to holding furnace and solidify, after silicon ingot is cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
Embodiment 7: slagging boron removal
1. get sodium carbonate prepared by nano silicon prepared by embodiment 2 and embodiment 4 and be mixed with except boron slag former, described except in boron slag former, silicon-dioxide is 40%, and sodium carbonate is 60%;
2. take 100kg metallic silicon power and drop into heat fused in plumbago crucible, after melting, add that step 1 prepares except boron slag former 80kg, insulation slag making; Described silicon particle size is 60~200 orders, and Heating temperature is 1600 DEG C; The slag making time is 20 minutes;
3. after slag making is complete, silicon liquid is injected to holding furnace and solidify, after silicon ingot is cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
Embodiment 8: slagging boron removal
1. get sodium carbonate prepared by nano silicon prepared by embodiment 2 and embodiment 4 and be mixed with except boron slag former, described except in boron slag former, nano silicon is 50%, and sodium carbonate is 50%;
2. take 100kg metallic silicon power and drop into heat fused in plumbago crucible, after melting, add that step 1 prepares except boron slag former 100kg, insulation slag making; Described silicon particle size is 60~200 orders, and Heating temperature is 1700 DEG C; The slag making time is 20 minutes;
3. after slag making is complete, silicon liquid is injected to holding furnace and solidify, after silicon ingot is cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
Boron assay:
The content of silica flour raw material B in above-described embodiment is denoted as to X, the content of the B of the refining low boron Pure Silicon Metal after purification be denoted as Y, get silicon ingot central part, measure by ICP~MS, measuring result is as table 1.
Table 1:
? X/ppmw Y/ppmw Test set
Embodiment 5 3.0 0.87 ICP~MS
Embodiment 6 3.0 0.42 ICP~MS
Embodiment 7 3.0 0.25 ICP~MS
Embodiment 8 3.0 0.18 ICP~MS
Comparative example 1~4:
Get nano silicon prepared by the embodiment of the present invention 1 and embodiment 2 and commercially available common sodium carbonate (particle diameter be 175~185 μ m), replace the sodium carbonate in the present invention, carry out slagging boron removal by the method for embodiment 5~8 respectively, the Pure Silicon Metal that is 3.0ppm to boron-containing quantity is processed (X), the content of the B of the refining low boron Pure Silicon Metal after purification be denoted as Y, get silicon ingot central part, measure by ICP~MS, measuring result is as table 2.
Table 2:
? X/ppmw Y/ppmw Test set
Comparative example 1 3.0 1.09 ICP~MS
Comparative example 2 3.0 0.65 ICP~MS
Comparative example 3 3.0 0.48 ICP~MS
Comparative example 4 3.0 0.32 ICP~MS
From this comparative example, adopt the sodium carbonate of particle diameter of the present invention can increase speed of response and reaction efficiency, and adopt commercially available common sodium carbonate except effect of boron poor.
Comparative example 5~8:
Get commercially available general silica (particle diameter be 75~200 μ m) and commercially available common sodium carbonate (particle diameter be 175~185 μ m), carry out slagging boron removal according to the method for embodiment 5~8, the Pure Silicon Metal that is 3.0ppm to boron-containing quantity is processed (X), the content of the B of the refining low boron Pure Silicon Metal after purification be denoted as Y, get silicon ingot central part, measure by ICP~MS, measuring result is as table 3.
Table 3:
? X/ppmw Y/ppmw Test set
Comparative example 5 3.0 1.66 ICP~MS
Comparative example 6 3.0 0.87 ICP~MS
Comparative example 7 3.0 0.56 ICP~MS
Comparative example 8 3.0 0.39 ICP~MS
Comparative example 9~12
Get the sodium carbonate that nano silicon that embodiment 1 prepares and embodiment 3 prepare, prepare slagging boron removal agent according to the ratio of table 4, the ratio that is 1:1 with slag former weight ratio by metallic silicon power is mixed, the Pure Silicon Metal that is 3.0ppm to boron-containing quantity is processed (X), the content of the B of the refining low boron Pure Silicon Metal after purification be denoted as Y, get silicon ingot central part, measure by ICP~MS, measuring result is as table 5.
Table 4:
? Nano silicon (wt%) Sodium carbonate (wt%)
Comparative example 9 10 90
Comparative example 10 20 80
Comparative example 11 30 70
Comparative example 12 70 30
Comparative example 13 80 20
Comparative example 14 90 10
Table 5:
? X/ppmw Y/ppmw Test set
Comparative example 9 3.0 1.12 ICP~MS
Comparative example 10 3.0 0.45 ICP~MS
Comparative example 11 3.0 0.29 ICP~MS
Comparative example 12 3.0 0.35 ICP~MS
Comparative example 13 3.0 0.78 ICP~MS
Comparative example 14 3.0 1.39 ICP~MS
Known according to above-mentioned simultaneous test, it removes effect of boron the best to adopt ratio of the present invention.And nano silicon is too much or very few, remove effect of boron all poor.

Claims (10)

  1. For polysilicon except a boron slag former, it is characterized in that described consisting of except boron slag former: nano silicon 40~60wt%, sodium carbonate 40~60wt%; Preferred: nano silicon 40~50wt%, sodium carbonate 50~60wt%; Wherein the particle diameter of nano silicon is 50~130nm; Preferably 60~120nm.
  2. According to claim 1 for polysilicon except boron slag former, it is characterized in that, the particle diameter of described sodium carbonate is 20~45 μ m, preferably 25~40 μ m.
  3. 3. the preparation method except boron slag former for polysilicon claimed in claim 1, is characterized in that, comprises the following steps:
    (1) combusting rice hull is produced to rice hull ash, temperature of combustion is 550~600 DEG C, and be 5~6h combustion time;
    (2) rice hull ash and NaOH solution are mixed, heated and stirred, has reacted rear filtration, obtains water glass solution;
    (3) water glass solution, hydrochloric acid, oxalic acid are added in reactor and heated, Heating temperature is 50~60 DEG C, and the reaction times is 50min, and in reaction process, the pH value of solution is 8~8.5, and the pH value of reaction end is 7~8;
    (4) hydrochloric acid is splashed into the solution of step (3) gained, regulating pH value is 4~4.5;
    (5) add Witco 1298 Soft Acid and sodium polyacrylate to carry out ageing, Aging Temperature is 90~100 DEG C, and digestion time 1h separates out white slip;
    (6) by the white slurry filtration of separating out, use deionized water wash 1~5 time, use washing with alcohol 1~3 time, heating volatilization ethanol, dry, pulverize, and makes nano silicon;
    (7) above-mentioned prepared nano silicon and sodium carbonate are mixed with and are obtained except boron slag former.
  4. 4. preparation method according to claim 3, is characterized in that, in step (2), the concentration of described NaOH solution is 0.6mol/L, and the ratio of described rice hull ash and NaOH solution is 1kg:15L~18L; Heating temperature is 105~110 DEG C, and the described reaction times is 4.5~5h.
  5. 5. preparation method according to claim 3, is characterized in that, in step (3), described concentration of hydrochloric acid is that 1mol/L, concentration of oxalic acid are 0.1mol/L.
  6. 6. preparation method according to claim 3, is characterized in that, in step (5), and 4~6wt% that the weight of Witco 1298 Soft Acid is solution; The weight of sodium polyacrylate is 4~6wt% of solution.
  7. 7. the method except boron slag former of polysilicon, is characterized in that, comprises the following steps:
    (1) metallic silicon power is dropped into heat fused in plumbago crucible, after melting, add described in claim 1 or 2 except boron slag former, be then incubated slag making;
    (2) after slag making is complete, silicon liquid is injected to holding furnace and solidify, after silicon ingot is cooling, remove silicon ingot surface clinker, obtain the refining low boron Pure Silicon Metal after purifying.
  8. 8. method according to claim 7, is characterized in that, in step (1), adopts intermediate frequency induction heating device by metallic silicon power heat fused, and described silicon particle size is 60~200 orders, and the temperature of silicon liquid is 1500~1700 DEG C.
  9. 9. method according to claim 7, is characterized in that, in step (1), the mass ratio of described metallic silicon power and slag former is 1:0.2~1:1, preferably 1:0.3~1:1, more preferably 1:0.4~1:1.
  10. 10. method according to claim 7, is characterized in that, in step (1), the slag making time is 15~20 minutes.
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