CA2365541A1 - Process for the production of elemental boron by solid reaction - Google Patents
Process for the production of elemental boron by solid reaction Download PDFInfo
- Publication number
- CA2365541A1 CA2365541A1 CA 2365541 CA2365541A CA2365541A1 CA 2365541 A1 CA2365541 A1 CA 2365541A1 CA 2365541 CA2365541 CA 2365541 CA 2365541 A CA2365541 A CA 2365541A CA 2365541 A1 CA2365541 A1 CA 2365541A1
- Authority
- CA
- Canada
- Prior art keywords
- process according
- boron
- reducing agent
- operated
- elemental boron
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B35/00—Boron; Compounds thereof
- C01B35/02—Boron; Borides
- C01B35/023—Boron
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Manufacture Of Metal Powder And Suspensions Thereof (AREA)
Abstract
The invention relates to a process for the production of elemental boron. The process of the invention comprises subjecting a mixture of a reducible boron compound and a reducing agent to mechanical activation, whereby the boron compound is reduced to elemental boron by the reducing agent. Such a process enables one to produce elemental boron at low cost.
Description
PROCESS FOR THE PRODUCTION OF ELEMENTAL BORON BY SOLID
STATE REACTION
The present invention relates to a process for the production of elemental boron by solid state reaction.
Boron, the fifth element in the periodic table, is a hard and brittle element which is classified among nonmetals such as carbon, arsenic, germanium, etc... Non-metals differ markedly from metals in electronic structure, physical and chemical properties such as electronegativity, thermal and electrical conductivity.
Boron was discovered as an element by the English chemist Davy and by the French chemists Gay-Lussac and Thenard in 1808. It took almost 100 years before this element was obtained in 80% purity. Now, boron may be prepared from its compounds by different methods such as chemical reduction, nonaqueous electric reduction or thermal decomposition.
Reduction with hydrogen at high temperatures, especially hot filament reaction with boron halides, is the conventional method for obtaining high purity boron (>99% pure). Boron can also be prepared by electrolysis of melts containing borates or fluoroborates. Another way to obtain elemental boron is direct decomposition of boron from compounds such as halides and hydrides, to high purity boron at high temperatures (800-1100 °C). All these methods need high temperature operations and are costly and difficult to scale-up.
The most common method for producing large amounts of elemental boron is the exothermic reduction of boron trioxide with magnesium:
B203 + 3Mg ->3Mg0 + 2B
In this method, B203 and Mg powders are mixed and heated. The exothermic reaction occurs and causes an increase in temperature in excess of 800°C.
The resulting material is a mixture of boron and Mg0 which is removed by acid washing. Boron obtained by this method is amorphous and impure (usually <90%).
In order to obtain crystalline or pure boron, further processes are required.
Boron can be purified by zone refining or other thermal techniques.
Crystalline boron is obtained by dissolving amorphous boron in liquid aluminum and cooling it down slowly. During cooling, crystalline boron is precipitated in the Al matrix. The matrix is removed by chemical reactions and the crystalline boron is recovered. Amorphous boron can be converted to ~3-rhombohedral above 1000 °C. As amorphous boron is highly reactive and spontaneously flammable at high temperatures, handling or processing of it at high temperatures requires special and costly precautions.
Ball milling, specially high energy ball milling, is an alternative technique to induce solid-state reactions. US Patent No. 5,328,501 teaches that certain metal oxides can be reduced by milling the oxide and a reducing agent. For example, metal oxides such as CuO, CdO, Fe203, V205, ZnO, can be reduced to elemental Cu, Cd, Fe, V, Zn, ... by high energy ball milling. However, the reduction of nonmetal compounds to nonmetal elements by this technique is not evident. For example, milling of Si02 in the presence of active metals results in the formation of intermetalic compounds such as silicates instead of elemental silicon.
It is therefore an object of the present invention to overcome the above drawbacks and to pmvide a process for the production of elemental boron by solid state reaction.
According to the invention, there is thus provided a process for the production of elemental boron, comprising subjecting a mixture of a reducible boron compound and a reducing agent to mechanical activation, whereby the boron compound is reduced to elemental boron by the reducing agent.
Examples of suitable boron compounds include boron trioxide (82O3), orthoboric acid (CH3B03), methaboric acid (HB02), sodium borate (NaBO3~4H20) and anhydrous sodium tetraborate (NaZB40~). Boron trioxide is preferred.
Examples of suitable reducing agents include aluminum, magnesium, calcium, titanium and sodium. Magnesium and calcium are preferred.
Mechanical activation is advantageously performed by mechanical milling in a ball mill, attrition mill, shaker mill, rod mill or any other suitable milling device. High energy ball milling using a SPEX (trademark) vibratory ball mill operated 8-25 Hz is preferred. It is also possible to use a rotary ball mill operated at 300-1500 rpm or a rotary attritor operated at 50-300 rpm. A ball-to-powder ratio of 1:1 to 20:1 is generally used. The mechanical impact on the powder mixture results in a solid-state chemical reaction between the boron compound and the reducing agent.
STATE REACTION
The present invention relates to a process for the production of elemental boron by solid state reaction.
Boron, the fifth element in the periodic table, is a hard and brittle element which is classified among nonmetals such as carbon, arsenic, germanium, etc... Non-metals differ markedly from metals in electronic structure, physical and chemical properties such as electronegativity, thermal and electrical conductivity.
Boron was discovered as an element by the English chemist Davy and by the French chemists Gay-Lussac and Thenard in 1808. It took almost 100 years before this element was obtained in 80% purity. Now, boron may be prepared from its compounds by different methods such as chemical reduction, nonaqueous electric reduction or thermal decomposition.
Reduction with hydrogen at high temperatures, especially hot filament reaction with boron halides, is the conventional method for obtaining high purity boron (>99% pure). Boron can also be prepared by electrolysis of melts containing borates or fluoroborates. Another way to obtain elemental boron is direct decomposition of boron from compounds such as halides and hydrides, to high purity boron at high temperatures (800-1100 °C). All these methods need high temperature operations and are costly and difficult to scale-up.
The most common method for producing large amounts of elemental boron is the exothermic reduction of boron trioxide with magnesium:
B203 + 3Mg ->3Mg0 + 2B
In this method, B203 and Mg powders are mixed and heated. The exothermic reaction occurs and causes an increase in temperature in excess of 800°C.
The resulting material is a mixture of boron and Mg0 which is removed by acid washing. Boron obtained by this method is amorphous and impure (usually <90%).
In order to obtain crystalline or pure boron, further processes are required.
Boron can be purified by zone refining or other thermal techniques.
Crystalline boron is obtained by dissolving amorphous boron in liquid aluminum and cooling it down slowly. During cooling, crystalline boron is precipitated in the Al matrix. The matrix is removed by chemical reactions and the crystalline boron is recovered. Amorphous boron can be converted to ~3-rhombohedral above 1000 °C. As amorphous boron is highly reactive and spontaneously flammable at high temperatures, handling or processing of it at high temperatures requires special and costly precautions.
Ball milling, specially high energy ball milling, is an alternative technique to induce solid-state reactions. US Patent No. 5,328,501 teaches that certain metal oxides can be reduced by milling the oxide and a reducing agent. For example, metal oxides such as CuO, CdO, Fe203, V205, ZnO, can be reduced to elemental Cu, Cd, Fe, V, Zn, ... by high energy ball milling. However, the reduction of nonmetal compounds to nonmetal elements by this technique is not evident. For example, milling of Si02 in the presence of active metals results in the formation of intermetalic compounds such as silicates instead of elemental silicon.
It is therefore an object of the present invention to overcome the above drawbacks and to pmvide a process for the production of elemental boron by solid state reaction.
According to the invention, there is thus provided a process for the production of elemental boron, comprising subjecting a mixture of a reducible boron compound and a reducing agent to mechanical activation, whereby the boron compound is reduced to elemental boron by the reducing agent.
Examples of suitable boron compounds include boron trioxide (82O3), orthoboric acid (CH3B03), methaboric acid (HB02), sodium borate (NaBO3~4H20) and anhydrous sodium tetraborate (NaZB40~). Boron trioxide is preferred.
Examples of suitable reducing agents include aluminum, magnesium, calcium, titanium and sodium. Magnesium and calcium are preferred.
Mechanical activation is advantageously performed by mechanical milling in a ball mill, attrition mill, shaker mill, rod mill or any other suitable milling device. High energy ball milling using a SPEX (trademark) vibratory ball mill operated 8-25 Hz is preferred. It is also possible to use a rotary ball mill operated at 300-1500 rpm or a rotary attritor operated at 50-300 rpm. A ball-to-powder ratio of 1:1 to 20:1 is generally used. The mechanical impact on the powder mixture results in a solid-state chemical reaction between the boron compound and the reducing agent.
The mechanical activation is preferably carried out in an inert gas atmosphere such as argon, to prevent oxidation of the elemental boron as well as undesirable oxidation of the reducing agent.
Since the product obtained comprises a powder mixture of elemental boron and an undesired compound, usually an oxide of the reducing agent, pure boron can be obtained by removing the undesired compound by leaching or other purification techniques. Preferred leaching media include:
HCI when the reducing agents is Mg; the leaching temperature may range from 10 to 100°C, 60°C being preferred.
KOH when the reducing agent is Al; the leaching temperature may range from 10 to 100°C, 90°C being preferred.
H2S04, HCl when the reducing agent is Ca; the leaching temperature may range from 10 to 100°C, 60°C being preferred.
A preferred leaching method consists in adding the leaching medium into the milling crucible at the Iast stage when the reduction reaction is completed.
This method is more effective than adding the aforesaid powder mixture into an acid solution bath because agglomerates are broken during milling and the leaching medium is in contact with fresh surfaces so that the rate of dissolution increases.
However, such a method requires a special acid resistant coating on the inner surface of the crucible.
Crystalline boron can be directly obtained by the process according to the invention. Short milling times (< 20 h) and low ball-to-powder ratios (1:1 to 10:1) results in the formation of an ultrafine boron powder with crystalline structure (rhombohedral). Due to mechanical impacts during milling, the crystalline structure of boron is stressed and is slightly deformed. In order to obtain a stress-free crystalline structure, a heat treatment (> 500°) of the powder is required. On the other hand, longer milling times (>20h) results in the formation of amorphous boron.
The following non-limiting examples illustrate the invention.
3.6 g pure Mg powder (99.8%) were mixed with 3.4 g pure B2O3 powder (99.9%) and milled in a hardened steel crucible with operated at a frequency at a speed of about 17 Hz. The operation was performed under a controller argon atmosphere to prevent oxidation. After 3 hours of milling the reaction was completed.
Since the product obtained comprises a powder mixture of elemental boron and an undesired compound, usually an oxide of the reducing agent, pure boron can be obtained by removing the undesired compound by leaching or other purification techniques. Preferred leaching media include:
HCI when the reducing agents is Mg; the leaching temperature may range from 10 to 100°C, 60°C being preferred.
KOH when the reducing agent is Al; the leaching temperature may range from 10 to 100°C, 90°C being preferred.
H2S04, HCl when the reducing agent is Ca; the leaching temperature may range from 10 to 100°C, 60°C being preferred.
A preferred leaching method consists in adding the leaching medium into the milling crucible at the Iast stage when the reduction reaction is completed.
This method is more effective than adding the aforesaid powder mixture into an acid solution bath because agglomerates are broken during milling and the leaching medium is in contact with fresh surfaces so that the rate of dissolution increases.
However, such a method requires a special acid resistant coating on the inner surface of the crucible.
Crystalline boron can be directly obtained by the process according to the invention. Short milling times (< 20 h) and low ball-to-powder ratios (1:1 to 10:1) results in the formation of an ultrafine boron powder with crystalline structure (rhombohedral). Due to mechanical impacts during milling, the crystalline structure of boron is stressed and is slightly deformed. In order to obtain a stress-free crystalline structure, a heat treatment (> 500°) of the powder is required. On the other hand, longer milling times (>20h) results in the formation of amorphous boron.
The following non-limiting examples illustrate the invention.
3.6 g pure Mg powder (99.8%) were mixed with 3.4 g pure B2O3 powder (99.9%) and milled in a hardened steel crucible with operated at a frequency at a speed of about 17 Hz. The operation was performed under a controller argon atmosphere to prevent oxidation. After 3 hours of milling the reaction was completed.
The resulting powder was then leached in a 2M HCl solution bath for 2 hours in order to remove undesirable magnesium oxide. The solution was then filtered, washed with water and dried at 90°C for 1h. The resulting black powder was crystalline boron with 85% purity, or better.
4.43 g pure Ca powder (99%) were mixed with 2.5 g pure B2O3 powder (99.9%) and milled in a hardened steel crucible with a ball-to-powder ratio of 5:1 using a SPEX 8000 vibratory ball operated at a frequency of about 17 Hz.
All the operating conditions were the same as in Example 1, except that the leaching solution used was HZS04 (2M).
3.06 g pure A1 powder (99.8%) were mixed with 3.94 g pure B203 powder (99.9%) and milled in a hardened steel crucible with a ball-to-powder ratio of 5:1 using a SPEX 8000 vibratory ball mill operated at a frequency of about 17 Hz. All the operating conditions were the same as in Example 1, except that the leaching solution used was KOH (3M) and a leaching time of 15h was chosen. During leaching, the temperature of the solution was maintained at 90°C.
72 g pure Mg powder (99.8%) were mixed with 68 g pure B203 powder (99.9%) and milled in a hardened steel crucible with a ball-to-powder ratio of 10:1 using ZOZ (trade-mark) rotary ball mill operated at a speed of about 1000 rpm.
The operation was performed under a controlled argon atmosphere to prevent oxidation. After 2 hours of milling, the reaction was completed. The resulting powder was then leached in a 2M HCl solution for 3 hours in order to remove undesirable magnesium oxide. The solution was then filtered, washed with water and dried at 90°C for 1h. The resulting black powder was crystalline boron with 85%
purity, or better.
The same operation as in Example 4 was performed using a UNION
PROCESS (trade-mark) rotary ball mill with a milling time of 10h.
3.6 g pure Mg powder (99.8%) were mixed with 3.4 g pure B2O3 powder (99.9%) and milled in a hardened steel crucible with a ball-to-powder ratio of -S-5:1 using a SPEX 8000 vibratory ball mill operated at a frequency of about 17 Hz.
The operation was performed under a controlled argon atmosphere to prevent oxidation. After 3 hours of milling, the reaction was completed. 1 g of the resulting powder was charged in a Si3N4 ceramic crucible together with 20 ml HCl solution (4M) and milled for 10 minutes. The solution was then filtered, washed with water and dried at 90°C for 1h. The resulting black powder was crystalline boron with 85%
purity, or better.
3.6 g pure Mg powder (99.8%) were mixed with 3.4 g pure B2O3 powder (99.9%) and milled in a hardened steel crucible with a ball-to-powder ratio of 10:1 using a SPEX 8000 vibratory ball mill operated at a frequency of about 17 Hz.
The operation was performed under a controlled argon atmosphere to prevent oxidation. After 20 h of milling, the reaction was completed. The resulting powder was then leached in a 2M HCl solution bath for 2 hours in order to remove undesirable magnesium oxide. The solution was then filtered, washed with water and dried at 90°C for 1h. The resulting black powder was amorphous boron.
4.43 g pure Ca powder (99%) were mixed with 2.5 g pure B2O3 powder (99.9%) and milled in a hardened steel crucible with a ball-to-powder ratio of 5:1 using a SPEX 8000 vibratory ball operated at a frequency of about 17 Hz.
All the operating conditions were the same as in Example 1, except that the leaching solution used was HZS04 (2M).
3.06 g pure A1 powder (99.8%) were mixed with 3.94 g pure B203 powder (99.9%) and milled in a hardened steel crucible with a ball-to-powder ratio of 5:1 using a SPEX 8000 vibratory ball mill operated at a frequency of about 17 Hz. All the operating conditions were the same as in Example 1, except that the leaching solution used was KOH (3M) and a leaching time of 15h was chosen. During leaching, the temperature of the solution was maintained at 90°C.
72 g pure Mg powder (99.8%) were mixed with 68 g pure B203 powder (99.9%) and milled in a hardened steel crucible with a ball-to-powder ratio of 10:1 using ZOZ (trade-mark) rotary ball mill operated at a speed of about 1000 rpm.
The operation was performed under a controlled argon atmosphere to prevent oxidation. After 2 hours of milling, the reaction was completed. The resulting powder was then leached in a 2M HCl solution for 3 hours in order to remove undesirable magnesium oxide. The solution was then filtered, washed with water and dried at 90°C for 1h. The resulting black powder was crystalline boron with 85%
purity, or better.
The same operation as in Example 4 was performed using a UNION
PROCESS (trade-mark) rotary ball mill with a milling time of 10h.
3.6 g pure Mg powder (99.8%) were mixed with 3.4 g pure B2O3 powder (99.9%) and milled in a hardened steel crucible with a ball-to-powder ratio of -S-5:1 using a SPEX 8000 vibratory ball mill operated at a frequency of about 17 Hz.
The operation was performed under a controlled argon atmosphere to prevent oxidation. After 3 hours of milling, the reaction was completed. 1 g of the resulting powder was charged in a Si3N4 ceramic crucible together with 20 ml HCl solution (4M) and milled for 10 minutes. The solution was then filtered, washed with water and dried at 90°C for 1h. The resulting black powder was crystalline boron with 85%
purity, or better.
3.6 g pure Mg powder (99.8%) were mixed with 3.4 g pure B2O3 powder (99.9%) and milled in a hardened steel crucible with a ball-to-powder ratio of 10:1 using a SPEX 8000 vibratory ball mill operated at a frequency of about 17 Hz.
The operation was performed under a controlled argon atmosphere to prevent oxidation. After 20 h of milling, the reaction was completed. The resulting powder was then leached in a 2M HCl solution bath for 2 hours in order to remove undesirable magnesium oxide. The solution was then filtered, washed with water and dried at 90°C for 1h. The resulting black powder was amorphous boron.
Claims (18)
1. A process for the production of elemental boron, comprising subjecting a mixture of a reducible boron compound and a reducing agent to mechanical activation, whereby the boron compound is reduced to elemental boron by the reducing agent.
2. A process according to claim 1, wherein the boron compounds is selected from the group consisting of boron trioxide, orthoboric acid, methaboric acid, sodium borate and anhydrous sodium tetraborate.
3. A process according to claim 2, wherein the boron compound is boron trioxide.
4. A process according to claim 1, 2 or 3, wherein the reducing agent is selected from the group consisting of aluminum, magnesium, calcium, titanium and sodium.
5. A process according to claim 4, wherein the reducing agent is magnesium or calcium.
6. A process according to claim 4, wherein the elemental boron produced is in admixture with an undesired compound, and wherein the undesired compound is removed by leaching.
7. A process according to claim 6, wherein the reducing agent is magnesium and wherein the mixture of elemental boron and undesired compound is leached in hydrochloric acid at a temperature of 10 to 100°C.
8. A process according to claim 6, wherein the reducing agent is aluminum and wherein the mixture of elemental boron and undesired compound is leached in potassium hydroxide at a temperature of 10 to 100°C.
9. A process according to claim 6, wherein the reducing agent is calcium and wherein the mixture of elemental boron and undesired compound is leached in sulfuric acid and hydrochloric acid at a temperature of 10 to 100°C.
10. A process according to any one of claims 1 to 5, wherein the mechanical activation is performed by mechanical milling in a ball mill, attrition mill, shaker mill or rod mill.
11. A process according to claim 10, wherein the mechanical activation is performed by high energy ball milling using a vibratory ball mill operated 8-25 Hz.
12. A process according to claim 11, wherein the vibratory ball mill is operated at about 17 Hz.
13. A process according to claim 10, wherein the mechanical activation is performed in a rotary ball mill operated at 300-1500 rpm.
14. A process according to claim 13, wherein the rotary ball mill is operated at about 1000 rpm.
15. A process according to claim 10, wherein the mechanical activation is performed in a rotary attritor operated at 50-300 rpm.
16. A process according to claim 15, wherein the rotary attritor is operated at 250 rpm.
17. A process according to any one of claims 10 to 16, wherein the mechanical activation is carried out in an inert gas atmosphere.
18. A process according to any one of claims 10 to 17, wherein the mechanical activation is carried out for a period of time of less than 20 hours at a ball-to-powder ratio ranging from 1:1 to 10:1, whereby elemental boron having a stressed crystalline structure is obtained, and wherein the elemental boron having a stressed crystalline structure is subjected to a heat treatment at a temperature higher than 500°C to convert the stressed crystalline structure to a stress-free crystalline structure.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2365541 CA2365541A1 (en) | 2001-12-19 | 2001-12-19 | Process for the production of elemental boron by solid reaction |
| AU2002350330A AU2002350330A1 (en) | 2001-12-19 | 2002-12-19 | Process for the production of elemental boron by solid state reaction |
| PCT/CA2002/001939 WO2003051773A1 (en) | 2001-12-19 | 2002-12-19 | Process for the production of elemental boron by solid state reaction |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2365541 CA2365541A1 (en) | 2001-12-19 | 2001-12-19 | Process for the production of elemental boron by solid reaction |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2365541A1 true CA2365541A1 (en) | 2003-06-19 |
Family
ID=4170888
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2365541 Abandoned CA2365541A1 (en) | 2001-12-19 | 2001-12-19 | Process for the production of elemental boron by solid reaction |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU2002350330A1 (en) |
| CA (1) | CA2365541A1 (en) |
| WO (1) | WO2003051773A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1887092B1 (en) | 2004-10-08 | 2010-12-15 | Rohm And Haas Company | Preparation of boron and sodium from sodium tetrataborate by reduction |
| DE102008045858B4 (en) | 2008-09-05 | 2017-08-10 | H.C. Starck Gmbh | reduction process |
| CN102211777A (en) * | 2011-03-05 | 2011-10-12 | 兰州理工大学 | Method for preparing pure boron |
| CN102583420B (en) * | 2012-02-24 | 2013-03-13 | 深圳市新星轻合金材料股份有限公司 | Circulating preparation method for producing simple substance boron and synchronously producing sodium cryolite based on sodium fluoborate as intermediate raw material |
| CN102557096B (en) * | 2012-02-24 | 2013-01-09 | 深圳市新星轻合金材料股份有限公司 | Circulating preparation method for producing simple substance boron by using potassium fluoborate as intermediate material and synchronously producing elpasolite |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2893842A (en) * | 1954-10-27 | 1959-07-07 | United States Borax Chem | Production of elemental boron |
| US2866688A (en) * | 1955-08-22 | 1958-12-30 | American Potash And Chemical C | Process for producing amorphous boron of high purity |
| US2897056A (en) * | 1956-10-18 | 1959-07-28 | United States Borax Chem | Production of elemental boron by magnesium reduction |
| EP0449890B1 (en) * | 1988-12-22 | 1996-02-21 | The University Of Western Australia | Process for the production of metals, alloys and ceramic materials |
| RU1770276C (en) * | 1989-01-31 | 1992-10-23 | Институт структурной макрокинетики АН СССР | Method of boron production |
-
2001
- 2001-12-19 CA CA 2365541 patent/CA2365541A1/en not_active Abandoned
-
2002
- 2002-12-19 AU AU2002350330A patent/AU2002350330A1/en not_active Abandoned
- 2002-12-19 WO PCT/CA2002/001939 patent/WO2003051773A1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| WO2003051773A1 (en) | 2003-06-26 |
| AU2002350330A1 (en) | 2003-06-30 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4241037A (en) | Process for purifying silicon | |
| JP4766837B2 (en) | Method for removing boron from silicon | |
| US7455822B2 (en) | Method for production of silicon | |
| EP2089318A1 (en) | Purification method | |
| PL154684B1 (en) | A method of fundamentally pure aluminium oxide production | |
| JP2021525833A (en) | A method for producing fine metal powder from a metal compound | |
| CA2365541A1 (en) | Process for the production of elemental boron by solid reaction | |
| JPH0645456B2 (en) | Rare earth element boride manufacturing method | |
| US4732751A (en) | High purity lithium oxide process | |
| US2974013A (en) | Boron nitride production | |
| US3148131A (en) | Process for the purification of silicon | |
| JPS58115016A (en) | Preparation of fine powdery silicon carbide | |
| JP7191410B1 (en) | Nano-silicon manufacturing method | |
| JP6565232B2 (en) | Silver recovery method | |
| US2998302A (en) | Preparation of titanium diboride | |
| JPH05170411A (en) | Production of ultra-fine pulverized titanium nitride | |
| JPH0575694B2 (en) | ||
| US3026178A (en) | Preparation of boric oxide and boric acid | |
| RU2052528C1 (en) | Scandium obtaining method | |
| JPS6332725B2 (en) | ||
| RU1770276C (en) | Method of boron production | |
| CN117185330A (en) | Temperature-control sedimentation chloride molten salt purification preparation method | |
| RU2049056C1 (en) | Method for production of powder of high-purity silicon | |
| JP2698424B2 (en) | Liquefaction method of iridium | |
| JPS638043B2 (en) |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |