CN115321494A - Alkali treatment and purification process for cubic boron nitride - Google Patents
Alkali treatment and purification process for cubic boron nitride Download PDFInfo
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- 239000003513 alkali Substances 0.000 title claims abstract description 177
- 229910052582 BN Inorganic materials 0.000 title claims abstract description 139
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 title claims abstract description 137
- 238000000746 purification Methods 0.000 title claims abstract description 27
- 239000000463 material Substances 0.000 claims abstract description 101
- 238000009835 boiling Methods 0.000 claims abstract description 66
- 238000000034 method Methods 0.000 claims abstract description 61
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- 230000008569 process Effects 0.000 claims abstract description 43
- 238000006243 chemical reaction Methods 0.000 claims abstract description 18
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 68
- 239000000203 mixture Substances 0.000 claims description 26
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 24
- 238000000926 separation method Methods 0.000 claims description 16
- 238000010438 heat treatment Methods 0.000 claims description 14
- 238000001816 cooling Methods 0.000 claims description 13
- 239000002253 acid Substances 0.000 claims description 12
- 238000002791 soaking Methods 0.000 claims description 12
- 238000000498 ball milling Methods 0.000 claims description 11
- 239000003054 catalyst Substances 0.000 claims description 11
- 238000004140 cleaning Methods 0.000 claims description 11
- 239000011259 mixed solution Substances 0.000 claims description 10
- 238000007873 sieving Methods 0.000 claims description 10
- 238000004506 ultrasonic cleaning Methods 0.000 claims description 10
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 8
- 229910052799 carbon Inorganic materials 0.000 claims description 8
- 239000002994 raw material Substances 0.000 claims description 7
- 229910052751 metal Inorganic materials 0.000 claims description 6
- 239000002184 metal Substances 0.000 claims description 6
- 238000002156 mixing Methods 0.000 claims description 6
- 238000005406 washing Methods 0.000 claims description 6
- 238000002419 base digestion Methods 0.000 claims description 4
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- 239000012467 final product Substances 0.000 claims description 4
- PXXKQOPKNFECSZ-UHFFFAOYSA-N platinum rhodium Chemical compound [Rh].[Pt] PXXKQOPKNFECSZ-UHFFFAOYSA-N 0.000 claims description 4
- 229910052903 pyrophyllite Inorganic materials 0.000 claims description 4
- 239000011265 semifinished product Substances 0.000 claims description 4
- 239000007788 liquid Substances 0.000 claims description 3
- 238000009210 therapy by ultrasound Methods 0.000 claims description 2
- 239000000047 product Substances 0.000 abstract description 73
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- 239000013078 crystal Substances 0.000 description 19
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 18
- 230000000052 comparative effect Effects 0.000 description 16
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- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 3
- 238000009825 accumulation Methods 0.000 description 3
- 238000005520 cutting process Methods 0.000 description 3
- 239000008367 deionised water Substances 0.000 description 3
- 229910021641 deionized water Inorganic materials 0.000 description 3
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- 238000001704 evaporation Methods 0.000 description 3
- 230000008020 evaporation Effects 0.000 description 3
- 238000007711 solidification Methods 0.000 description 3
- 229910001220 stainless steel Inorganic materials 0.000 description 3
- 239000010935 stainless steel Substances 0.000 description 3
- -1 bright surface Substances 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 238000004898 kneading Methods 0.000 description 2
- 238000006386 neutralization reaction Methods 0.000 description 2
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- 235000011837 pasties Nutrition 0.000 description 2
- 239000002585 base Substances 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B21/00—Nitrogen; Compounds thereof
- C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
- C01B21/064—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with boron
- C01B21/0648—After-treatment, e.g. grinding, purification
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
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Abstract
The invention belongs to the technical field of superhard material purification, and particularly relates to a cubic boron nitride alkali treatment purification process. The process can realize the purification of the cubic boron nitride product through the working procedures of pretreatment, alkali treatment, post-treatment and the like, and the impurity content in the purified product is not more than 0.4wt%, so that the process meets the acceptance standard. The process can control key temperature control points in the alkali boiling process, reduce the product reverse conversion probability and reduce loss, thereby improving the labor efficiency and the product quality and being beneficial to industrial production. The process method ensures the full reaction of the hexagonal boron nitride and the alkali substances by determining the proper alkali dosage and monitoring the slope of the temperature curve, avoids the occurrence of impurities of the hexagonal boron nitride in the product, lays a foundation for the product quality and greatly reduces the rework probability.
Description
Technical Field
The invention belongs to the technical field of superhard material purification, and particularly relates to a cubic boron nitride alkali treatment purification process.
Background
Cubic Boron Nitride (CBN) is an artificially synthesized superhard material, has high hardness and good wear resistance, and is widely applied to the machining industry. Cubic boron nitride is synthesized from hexagonal boron nitride and a catalyst at high temperature and high pressure, and can replace artificial diamond in some fields. One of the most important characteristics of cubic boron nitride is that when mixed with alkali, the cubic boron nitride is reversely converted when reaching a certain temperature, i.e. part of cubic boron nitride is converted into hexagonal boron nitride, so that the prepared cubic boron nitride product needs to be purified.
The alkali treatment in the purification process of cubic boron nitride products is a core step, and is characterized by that the cubic boron nitride material (product containing hexagonal boron nitride impurity) and industrial alkali (NaOH, etc.) and water are uniformly stirred according to a certain proportion to obtain a mixture, then the mixture is placed in an alkali pot (the capacity of each alkali pot is about 24kg, and the size of the alkali pot is phi 300 x 300), and heated on an electric furnace, the heated alkali liquor is up to above 350 deg.C, and the high-temperature alkali liquor and hexagonal boron nitride are reacted to remove hexagonal boron nitride impurity so as to implement the purification of cubic boron nitride product.
Wherein, the alkali treatment process technology of the cubic boron nitride product has 7 key points, which specifically comprise the following steps: 1. ratio of base to material; 2. how to lower the melting point; 3. the amount of water used; 4. a temperature point at which cubic boron nitride starts to undergo reverse transformation after the hexagonal boron nitride completely reacts with the alkali; 5. the state of the alkali mixture when the alkali is dissolved after cooling; 6. alkali dissolving process; 7. and (5) cleaning the materials. The key points are process steps capable of influencing the purification effect of the cubic boron nitride product, so that precise regulation and control are required.
However, the alkali treatment process of the existing cubic boron nitride product is basically manual operation, and key control points are completely empirical and lack reliability. In order to reduce the risk of the alkali treatment process, improve the efficiency and realize the automation of the operation, a new alkali treatment and purification process of cubic boron nitride is needed to be provided so as to overcome the defects in the prior operation.
Disclosure of Invention
In view of the technical problems, the invention aims to provide a cubic boron nitride alkali treatment purification process, which can realize the purification of a cubic boron nitride product through the working procedures of pretreatment, alkali dissolving treatment, post-treatment and the like and meets the acceptance standard of the national standard (GB/T6408-2018 superhard abrasive cubic boron nitride).
The process can control key temperature control points in the alkali boiling process, reduce the product reverse conversion probability and reduce loss, thereby improving the labor efficiency and the product quality and being beneficial to industrial production.
In order to achieve the technical purpose, the invention adopts the following technical scheme:
a cubic boron nitride alkali treatment purification process comprises the following steps:
(I) pretreatment
(1) Primary separation: adding water into a cubic boron nitride synthetic rod block (the synthetic rod block is a cubic boron nitride semi-finished product synthesized by using hexagonal boron nitride and catalyst raw materials, and contains incompletely converted hexagonal boron nitride and impurities such as auxiliary materials of carbon paper, metal catalyst, pyrophyllite and the like), stirring and mixing uniformly to obtain a mixture, and then vibrating on a shaking table; after separation by a shaking table, ball milling is carried out for 0.5-1.5 h by using a ball mill, hexagonal boron nitride adhered to the cubic boron nitride is knocked off, some leftover materials formed by continuous crystals of the cubic boron nitride are removed, and free hexagonal boron nitride is smashed to obtain a mixed material containing the cubic boron nitride, the hexagonal boron nitride and impurities;
(2) Acid soaking: adding industrial hydrochloric acid into the mixture after the primary separation to soak for 20-30 min;
(3) Ultrasonic impurity removal: adding water into the mixture after acid soaking, and treating for 2-5 min by using ultrasonic waves to realize the separation of cubic boron nitride and impurities to obtain a cubic boron nitride material;
(II) alkali digestion treatment
(4) Mixing the pretreated cubic boron nitride material with mixed alkali and water to obtain a mixed solution, and heating and boiling the mixed solution by using a thermocouple; when the alkali is boiled, water is continuously evaporated along with the continuous rise of the temperature, when the temperature rises to be in a molten state, the hexagonal boron nitride and the alkali start to react, when the hexagonal boron nitride finishes the reaction, the cubic boron nitride starts to carry out reverse conversion, and at the moment, the heating is stopped, so that the alkali boiling is finished;
(III) cooling and alkali-dissolving treatment
(5) Cooling the mixture after the alkali boiling treatment, when the temperature is reduced to 140-180 ℃, separating alkali from the material and keeping the mixture in a semi-solidification state, adding water to dissolve the alkali, adding water to change the alkali into semi-solid paste, pouring out the alkali, and finally obtaining the material after the alkali boiling purification;
(IV) post-treatment
(6) Primary cleaning: cleaning the material after alkali boiling and purification by using clear water;
(7) Ultrasonic cleaning: adding deionized water into the cleaned material, and ultrasonically cleaning for 2-5 min;
(8) Sieving: and drying and sieving the cleaned materials to obtain the final product.
Preferably, in the step (1), the type of the ball mill used for ball milling is QHQM-100, and the ball milling rotating speed is 40-60 r/min.
Preferably, in the step (2), the addition amount of the industrial hydrochloric acid is as follows: adding 1800-2000 ml hydrochloric acid with mass fraction of 37% into every 5 million ct of mixed materials.
Preferably, in the step (3), the model of the ultrasonic instrument selected for ultrasonic treatment is JRC-2500, the ultrasonic power is 2-3 kw, and the ultrasonic impurity removal treatment is performed for 2-3 times.
Preferably, in the step (4), the ratio (mass ratio) of the cubic boron nitride material to the mixed alkali is 1 (0.2-0.6).
Preferably, in the step (4), the amount of water is: every 3 million (6 kg) of water is 1000-1200 ml of water, namely the solid-to-liquid ratio of the material to the water is 6g: (1-1.2) mL; during the alkali boiling process, a proper amount of water is added to accelerate the melting speed of the alkali liquor, so that the materials and the alkali are fully mixed.
Preferably, in the step (4), the thermocouple is a WRP-130 type platinum rhodium thermocouple, the working temperature range is 0-1600 ℃, and a stainless steel sleeve is arranged outside the thermocouple.
Preferably, in the step (4), the temperature recorder is FX1004 and has the specification of-4-3-L, and is provided with an alarm for monitoring the trend of the temperature curve through the temperature recorder; the water is boiled in the early stage of alkali boiling, the temperature slowly rises in the water evaporation process, and the slope of the curve of the temperature changing along with the time is relatively stable; when the water is completely evaporated, the temperature is continuously increased, the alkali is in a molten state, the hexagonal boron nitride and the alkali start to react, and the slope of the curve of the temperature along with the change of time is slowly increased; when the reaction of the hexagonal boron nitride is finished, the cubic boron nitride starts to perform reverse conversion, the temperature suddenly increases in an accelerated manner, the slope of the curve of the temperature along with the change of time is multiplied, the temperature is set as the alarm temperature of an alarm, the cubic boron nitride starts to react with alkali at the temperature, the heating is immediately stopped, and the alkali boiling process is finished;
through experiments, the following results are obtained:
if the slope of the curve of the temperature changing along with the time is stable (the alarm temperature is not reached), stopping heating, and performing microscopic examination on the obtained product to obtain a product with obvious hexagonal boron nitride impurities, wherein the product needs to be reworked, and the material loss is about 2 percent compared with the weight after alkali boiling before alkali boiling;
when the slope of the curve of the temperature change along with the time is multiplied greatly (namely, the slope of the temperature change curve rises suddenly and reaches the alarm temperature), the heating is stopped immediately, the impurity content of the obtained product is not more than 0.4wt% when the product is subjected to microscopic examination (the product meets the acceptance standard of national standard (GB/T6408-2018 superhard abrasive cubic boron nitride), namely, impurities are not easy to find), the material loss is about 3% when the weight of the product is compared with that after alkali boiling, the material shape and edge angle are clear, and the surface of a few crystal forms is corroded;
when the slope of the curve of the temperature changing along with the time is multiplied, continuously boiling alkali for a plurality of minutes (the slope exceeds the alarm temperature at the moment), stopping heating (taking the continuous alkali boiling for 10 minutes as an example), wherein the weight loss of the material before the alkali boiling is about 10 percent compared with that after the alkali boiling (the material is subjected to reverse conversion, and cubic boron nitride participates in the reaction), although impurities cannot be seen, the surface of the material is completely corroded, and the crystal form is round; although the time for boiling alkali can be properly prolonged to obtain materials with different crystal forms after the alarm occurs, the appearance, the physical and chemical properties, the bulk density and the like of the materials are changed, and the materials cannot be used as raw materials of cutting tools.
Preferably, in the step (4), the mixture ratio of the mixed alkali is as follows: KOH =3 (2-2.5) (mass ratio); the melting point of NaOH or KOH is above 318 ℃, the melting point is not easy to reach by using single alkali, the energy consumption is increased, and after the NaOH and the KOH are mixed in proportion, the melting point is reduced to about 300 ℃, so that the melting point during melting is reduced, and the energy is saved.
Preferably, in the step (5), a mode of adding water for multiple times is adopted to avoid splashing of the alkali liquor, the water is added for 3 to 5 times, the water adding interval is 2 to 3min, and the water adding amount is 1200 to 1600ml.
Preferably, in the step (6), the washing is performed for 2 to 3 times by using clean water.
Preferably, in the step (7), the ultrasonic cleaning is performed for 2 to 3 times.
Preferably, in the step (7), the ultrasonic power is 2-3 kw.
The process can realize the purification of the cubic boron nitride product through the working procedures of pretreatment, alkali treatment, post-treatment and the like, and the purified product can realize that the impurity content does not exceed 0.4wt% and meets the acceptance standard of national standard (GB/T6408-2018 superhard abrasive cubic boron nitride).
Compared with the prior art, the invention has the beneficial effects that:
1. the alkali treatment method of the invention obviously improves the efficiency and reduces the labor intensity; the process method avoids waste and environmental pollution caused by excessive alkali amount by determining the dosage ratio of the materials to the alkali.
2. The alkali treatment purification process can accurately control the key point of the reverse conversion of the cubic boron nitride, provide accurate information for operators and avoid the misuse of an empirical method by people.
3. The process method ensures the full reaction of the hexagonal boron nitride and the alkali substances by determining the proper alkali dosage and monitoring the slope of the temperature curve, avoids the occurrence of impurities of the hexagonal boron nitride in the product, lays a foundation for the product quality and greatly reduces the rework probability.
4. The process method provided by the invention has the advantages that alkali liquid splashing is reduced, the safety factor is obviously improved, and the potential safety hazard is reduced by monitoring the temperature during alkali dissolution.
Drawings
FIG. 1 is a microscopic image of the product of comparative example 1;
FIG. 2 is a microscopic view of the product of example 1;
FIG. 3 is a microscopic image of the product in comparative example 2;
FIG. 4 is a microscopic view of the product of comparative example 3;
FIG. 5 is a microscopic view of the product of example 2;
FIG. 6 is a microscopic image of the product in comparative example 4.
Detailed Description
The following will clearly and completely describe the technical solutions in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
The alkali treatment and purification process of cubic boron nitride includes the following steps:
(I) pretreatment
(1) Separating by a shaking table: placing a synthetic rod block (the synthetic rod block is a cubic boron nitride semi-finished product synthesized by using hexagonal boron nitride and a catalyst raw material, and contains incompletely converted hexagonal boron nitride and impurities such as auxiliary materials of carbon paper, a metal catalyst, pyrophyllite and the like) in a stirring tank, adding water, fully stirring to obtain a mixture, and then vibrating the mixture on a shaking table to perform primary separation of the hexagonal boron nitride and the cubic boron nitride;
(2) Ball-milling separation: after the separation by the shaking table, free hexagonal boron nitride still adheres to the cubic boron nitride, and meanwhile, some cubic boron nitrides adhere to each other to form a connected crystal, so that each single crystal needs to be separated;
the method comprises the following specific steps: using a ball mill (model: QHQM-100) to ball-mill for 30min (ball-milling rotating speed of 45 r/min) to remove hexagonal boron nitride adhered on the cubic boron nitride, removing leftover materials formed by continuous crystals of some cubic boron nitride, and simultaneously crushing free hexagonal boron nitride to obtain a mixed material containing the cubic boron nitride, the hexagonal boron nitride and impurities;
(3) Acid soaking
Adding industrial hydrochloric acid (the addition amount of the hydrochloric acid is that 2000ml of hydrochloric acid with the mass fraction of 37 percent is added into every 5 ten thousand ct of the mixture) into the mixture after ball milling, soaking for half an hour, and kneading once; as the hexagonal boron nitride is alkaline, the acid soaking plays a role in neutralization, the hexagonal boron nitride becomes loose and light, carbon paper in impurities after acid soaking also becomes fluffy, and the acid can also react with unreacted catalyst (metal) in the mixed material, so that part of impurities in the mixed material are removed, and the table separation is facilitated;
(4) Ultrasonic impurity removal
Adding water (about 3500 ml) into the kneaded mixture, treating for 3min by using ultrasonic waves (ultrasonic instrument model: JRC-2500), wherein the ultrasonic power is 2.5kw, part of lighter hexagonal boron nitride and carbon paper impurities can float out of the surface, the cubic boron nitride can sink when being heavier, and then, pouring water and shaking are carried out to realize the separation of the cubic boron nitride and the impurities, so as to obtain a cubic boron nitride material, and the step is carried out for 2-3 times;
(II) alkali digestion treatment
(5) Mixing the pretreated cubic boron nitride material with mixed alkali and water, placing the mixture in an alkali pot to obtain a mixed solution, then inserting a temperature conducting head of a thermocouple into the mixed solution, heating, and boiling alkali, wherein a WRP-130 type platinum-rhodium thermocouple is adopted in the embodiment, the working temperature range is 0-1600 ℃, and a stainless steel sleeve is arranged outside the thermocouple;
the alkali dosage and the water dosage in the alkali boiling process are as follows:
in the embodiment, the pretreated cubic boron nitride material is a CBN 220-grade product (the grade product is amber single crystal, has regular crystal form, high crystal transparency, high strength, strong wear resistance, wide application range and strong service life, and belongs to the class of CBN 200-grade), and after pretreatment, the material with the weight of 3 million ct (wherein the content of impurities is more than 3 wt%) is taken for alkali boiling treatment; in this example, the addition amount of the alkali-boiling mixed alkali is 1.8kg (including 1.08kg of NaOH and 0.72kg of KOH, and the ratio of the NaOH to the KOH is 3:2), that is, the mass ratio of the material to the mixed alkali is = 0.3, and 1200ml of water is added in the alkali-boiling process; when boiling alkali, inserting the thermal head of the thermocouple into the mixed solution, and heating;
according to different product strengths (low-strength, medium-strength and high-strength products according to the strength), the proportion of the materials to the alkali can be finely adjusted, so that waste and environmental pollution caused by excessive alkali are avoided; waste such as rework caused by insufficient alkali quantity and incomplete treatment is avoided;
during the alkali boiling process, proper amount of water is added to accelerate the melting speed of the alkali liquor, so that the materials and the alkali are fully mixed;
the method for judging the alkali boiling completion time comprises the following steps:
the thermocouple is connected with a temperature recorder (model: FX1004 specification: 4-3-L) through an electric signal, the temperature recorder can receive a temperature signal of the thermocouple and record a change curve of temperature along with time, and an alarm is arranged on the temperature recorder; in the measuring process, a temperature recorder is used for obtaining a curve of temperature changing along with time, the slope of the temperature changing curve is calculated, and whether the alkali boiling is stopped or not is judged according to the change of the slope;
the thermocouple and the temperature recorder can be connected in a common mode in the prior art, which is not the invention point of the invention, so that the description is omitted;
in the process, the trend of a temperature curve needs to be monitored; the water is boiled in the early stage of alkali boiling, the temperature slowly rises in the water evaporation process, and the slope of the curve of the temperature changing along with the time is relatively stable; when the water is completely evaporated, the temperature is continuously increased, the alkali is in a molten state, the hexagonal boron nitride and the alkali start to react, and the slope of the curve of the temperature along with the change of time is slowly increased; when the reaction of the hexagonal boron nitride is finished, the cubic boron nitride starts to perform reverse conversion, the temperature suddenly increases in an accelerated manner, the slope of the curve of the temperature along with the change of time is multiplied, the temperature is set as the alarm temperature of an alarm, the cubic boron nitride starts to react with alkali at the temperature, the heating is immediately stopped, and the alkali boiling process is finished;
the final determination criteria for alkali cooking were: taking the slope of the temperature change curve which rises suddenly as a standard for judging the completion of alkali boiling, and setting the temperature at the moment as the alarm temperature of an alarm;
specifically, in this embodiment, the slope of the temperature change curve is recorded, when the alkali is boiled for 90min, the slope of the temperature change curve rises suddenly, it is determined that the alkali is boiled at this time, and the thermocouple is turned off;
(III) cooling and alkali-dissolving treatment
(6) Placing an alkali cooking pot after alkali cooking treatment on an iron frame with an angle of less than 30 degrees, cooling for 30min, measuring the temperature of a mixture in the alkali cooking pot after alkali cooking, measuring and displaying the temperature to be 160 ℃, separating alkali from materials and keeping the alkali in a semi-solidification state, starting adding water to carry out alkali dissolution, adding water for 2min at intervals, adding 3 times in total, adding 1500ml of water in total, adding water to obtain alkali which becomes pasty, pouring out the alkali, and finally obtaining a material after alkali cooking purification;
(IV) post-treatment
(7) Primary cleaning: cleaning the material after alkali boiling and purification by using clear water, washing the material from the bottom of the material upwards during cleaning to roll the material completely, then pouring water, and repeating the operation for three times;
(8) Ultrasonic cleaning
Adding deionized water into the cleaned material, performing ultrasonic cleaning for 3min at an ultrasonic power of 2.5kw, slightly rotating the container, pouring out trace impurities, performing ultrasonic cleaning twice, and then washing once with warm water;
(9) Sieving
Drying the cleaned material, and then sieving the dried material by using a No. 40 sieve to obtain a final product; the purpose of sieving is to pass the agglomerated materials out (prevent the materials from having continuous crystals); on the other hand, the hexagonal boron nitride is prevented from being stuck on the material wall during alkali boiling.
The indexes of the purified CBN220 product are tested, the material loss is 3.2 percent and the impurity content is not more than 0.4 weight percent before alkali boiling compared with the weight after alkali boiling, the acceptance standard (GB/T6408-2018 ultra-hard abrasive cubic boron nitride) is met (impurities are not easy to find), the surface of an extremely individual material is slightly corroded, the integral edge angle is clear, the product is sharp in use (the product granularity is 80/100, and the bulk density is 1.810), and the obtained product result is shown in figure 2.
Comparative example 1
Comparative example 1 differs from example 1 in that the thermocouple was turned off when the soda was boiled for 80 min; then, the treatment was carried out by the same method as the cooling, alkali treatment and post-treatment in the step (iii) and the step (iv) in example 1;
the indexes of the purified CBN220 product are tested, the material loss is 1.7 percent before alkali boiling compared with the weight after alkali boiling, the proportion of visible impurities is more than 1wt percent, the product does not meet the acceptance standard that the content of the impurities in the national standard (GB/T6408-2018 superhard abrasive cubic boron nitride) is less than 0.4wt percent, rework is needed, and the obtained product result is shown in figure 1.
Comparative example 2
The difference between the comparative example 2 and the example 1 is that when boiling alkali for 90min, the slope of the temperature change curve rises suddenly, then boiling alkali for 10min is continued, and then the thermocouple is closed; then, the treatment was carried out by the same method as the cooling, alkali treatment and post-treatment in the step (iii) and the step (iv) in example 1;
the indexes of the purified CBN220 product are checked, the material loss is 11.6 percent compared with the weight of the purified CBN220 product after alkali boiling, the surface of the material is totally corroded, the crystal grains are round and smooth, no impurities are seen, although the content of the impurities reaches the standard, the purified CBN220 product is not sharp and cannot be used as a raw material of a cutting tool, but the product is relatively wear-resistant (the product granularity is 80/100, the bulk density is 1.869, the obtained product result is shown in figure 3), and the product can only be used as a wear-resistant material.
Note: in example 1, comparative example 1 and comparative example 2, the packing criteria for the CBN220 product with particle size of 80/100 was:
in the national standard (GB/T6408-2018 superhard abrasive cubic boron nitride), the accumulation is not less than 1.79;
in the enterprise standard (Q/ZNJT 01-2018 cubic boron nitride technical condition), the accumulation is 1.810-1.870.
Example 2
The alkali treatment and purification process of cubic boron nitride includes the following steps:
(I) pretreatment
(1) Separating by a shaking table: placing a synthetic rod block (the synthetic rod block is a cubic boron nitride semi-finished product synthesized by using hexagonal boron nitride and a catalyst raw material, and contains incompletely converted hexagonal boron nitride and impurities such as auxiliary materials of carbon paper, a metal catalyst, pyrophyllite and the like) in a stirring tank, adding water, fully stirring to obtain a mixture, and then vibrating the mixture on a shaking table to perform primary separation of the hexagonal boron nitride and the cubic boron nitride;
(2) Ball milling separation: after the separation by the shaking table, free hexagonal boron nitride still adheres to the cubic boron nitride, and meanwhile, some cubic boron nitrides adhere to each other to form a connected crystal, so that each single crystal needs to be separated;
the method comprises the following specific steps: using a ball mill (model: QHQM-100) to ball-mill for 1.2h (ball-milling rotation speed of 45 r/min) to remove hexagonal boron nitride adhered on the cubic boron nitride, removing some leftover materials formed by continuous crystals of the cubic boron nitride, and simultaneously crushing free hexagonal boron nitride to obtain a mixed material containing the cubic boron nitride, the hexagonal boron nitride and impurities;
(3) Acid soaking
Adding industrial hydrochloric acid (the addition amount of the hydrochloric acid is that 2000ml of hydrochloric acid with the mass fraction of 37 percent is added into every 5 ten thousand ct of the mixture) into the mixture after ball milling, soaking for half an hour, and kneading once; as the hexagonal boron nitride is alkaline, the acid soaking plays a role in neutralization, the hexagonal boron nitride becomes loose and light, carbon paper in impurities after acid soaking also becomes fluffy, and the acid can also react with unreacted catalyst (metal) in the mixed material, so that part of impurities in the mixed material are removed, and the table separation is facilitated;
(4) Ultrasonic impurity removal
Adding water (about 3500 ml) into the kneaded mixture, treating for 3min by using ultrasonic waves (ultrasonic instrument model: JRC-2500), wherein the ultrasonic power is 2.5kw, part of lighter hexagonal boron nitride and carbon paper impurities can float out of the surface, the cubic boron nitride can sink when being heavier, and then, pouring water and shaking are carried out to realize the separation of the cubic boron nitride and the impurities, so as to obtain a cubic boron nitride material, and the step is carried out for 2-3 times;
(II) alkali digestion treatment
(5) Mixing the pretreated cubic boron nitride material with mixed alkali and water, placing the mixture in an alkali pot to obtain a mixed solution, then inserting a temperature conducting head of a thermocouple into the mixed solution, heating, and boiling alkali, wherein a WRP-130 type platinum-rhodium thermocouple is adopted in the embodiment, the working temperature range is 0-1600 ℃, and a stainless steel sleeve is arranged outside the thermocouple;
the alkali dosage and the water dosage in the alkali boiling process are as follows:
in the embodiment, the pretreated cubic boron nitride material is a product of a CBN121 grade (black single crystal, bright surface, medium strength, high thermal stability, and good sharpness and grindability) (the product of the grade is a black single crystal, bright surface, medium strength, high thermal stability, good sharpness and grindability, and belongs to the big class of CBN100 grade), and after pretreatment, the material with the weight of 3 kilo-tons (the impurity content is more than 3 wt%) is taken for alkali boiling treatment; in this example, the addition amount of the alkali-boiling mixed alkali is 3kg (wherein, the ratio of the NaOH 1.8kg to the KOH 1.2kg is 3:2), that is, the mass ratio of the material to the mixed alkali is = 0.5, and 1400ml of water is added in the alkali-boiling process; when boiling alkali, inserting the thermal head of the thermocouple into the mixed solution, and heating;
according to different product strengths (low-strength, medium-strength and high-strength products according to the strength), the proportion of the materials to the alkali can be finely adjusted, so that waste and environmental pollution caused by excessive alkali are avoided; waste such as rework caused by insufficient alkali and incomplete treatment is avoided;
during the alkali boiling process, a proper amount of water is added to accelerate the melting speed of the alkali liquor, so that the materials and the alkali are fully mixed;
the method for judging the alkali boiling completion time comprises the following steps:
the thermocouple is connected with a temperature recorder (model: FX1004 specification: 4-3-L) through an electric signal, the temperature recorder can receive a temperature signal of the thermocouple and record a change curve of temperature along with time, and an alarm is arranged on the temperature recorder; in the measuring process, a temperature recorder is used for obtaining a curve of temperature changing along with time, the slope of the temperature changing curve is calculated, and whether the alkali boiling is stopped or not is judged according to the change of the slope;
the thermocouple and the temperature recorder can be connected in a common mode in the prior art, which is not the invention point of the invention, so that the description is omitted;
in the process, the trend of a temperature curve needs to be monitored; the water is boiled in the early stage of alkali boiling, the temperature slowly rises in the water evaporation process, and the slope of the curve of the temperature changing along with the time is relatively stable; when the water is completely evaporated, the temperature is continuously increased, the alkali is in a molten state, the hexagonal boron nitride and the alkali start to react, and the slope of the curve of the temperature along with the change of time is slowly increased; when the reaction of the hexagonal boron nitride is finished, the cubic boron nitride starts to perform reverse conversion, the temperature suddenly increases in an accelerated manner, the slope of the curve of the temperature along with the change of time is multiplied, the temperature is set as the alarm temperature of an alarm, the cubic boron nitride starts to react with alkali at the temperature, the heating is immediately stopped, and the alkali boiling process is finished;
the final determination criteria for soda boiling were: taking the slope of the temperature change curve which rises suddenly as a standard for judging the completion of alkali boiling, and setting the temperature at the moment as the alarm temperature of an alarm;
specifically, in this embodiment, the slope of the temperature change curve is recorded, when the alkali is boiled for 1.1h, the slope of the temperature change curve rises suddenly, it is determined that the alkali is boiled at this time, and the thermocouple is turned off;
(III) cooling and alkali-dissolving treatment
(6) Placing an alkali cooking pot after alkali cooking treatment on an iron frame with an angle of less than 30 degrees, cooling for 40min, measuring the temperature of a mixture in the alkali cooking pot after alkali cooking, measuring and displaying the temperature to be 155 ℃, separating alkali from materials and keeping the alkali in a semi-solidification state, starting adding water to dissolve alkali, adding water for 3min at intervals, adding water for 5 times totally, adding water for 1500ml totally, adding water to enable the alkali to become pasty, pouring out the alkali, and finally obtaining the material after alkali cooking purification;
(IV) post-treatment
(7) Primary cleaning: cleaning the material after alkali boiling and purification by using clear water, washing the material from the bottom of the material upwards during cleaning to roll the material completely, then pouring water, and repeating the operation for three times;
(8) Ultrasonic cleaning
Adding deionized water into the cleaned material, ultrasonic cleaning for 3min with ultrasonic power of 2.5kw, slightly rotating the container, pouring out trace impurities, ultrasonic cleaning twice, and then washing with warm water once;
(9) Sieving
Drying the cleaned materials, and then sieving the materials by a No. 40 sieve to obtain a final product; the purpose of sieving is to pass the agglomerated materials out (prevent the materials from having continuous crystals); on the other hand, the hexagonal boron nitride is prevented from being stuck on the material wall during alkali boiling.
The indexes of the purified CBN121 product are tested, the material loss is 3.6 percent before alkali boiling and the weight after alkali boiling are compared, the impurity content is not more than 0.4wt percent, the product meets the acceptance standard (impurities are not easy to find) of the national standard (GB/T6408-2018 super-hard abrasive cubic boron nitride), the surface of an extremely individual material is slightly corroded, the integral edge angle is clear, the product is sharp in use (the product granularity is 80/100, the bulk density is 1.742), and the obtained product result is shown in figure 5.
Comparative example 3
Comparative example 3 differs from example 2 in that the thermocouple was turned off when the soda was boiled for 90 min; then, the treatment is carried out according to the same method of the cooling, the alkali dissolving treatment and the post-treatment in the step (III) in the embodiment 2;
the indexes of the purified CBN121 product are tested, the material loss is 1.2 percent before alkali boiling and the weight after alkali boiling are compared, the proportion of visible impurities is more than 1wt percent, the product does not meet the acceptance standard that the content of the impurities in the national standard (GB/T6408-2018 superhard abrasive cubic boron nitride) is less than 0.4 percent, rework is needed, and the obtained product result is shown in figure 4.
Comparative example 4
The difference between the comparative example 4 and the example 2 is that when alkali is boiled for 1.1h, the slope of the temperature change curve rises suddenly, then the alkali is boiled for 15min, and then the thermocouple is closed; then, the treatment was carried out by the same method as the cooling, alkali treatment and post-treatment in the step (iii) and the step (iv) in example 2;
the indexes of the purified CBN121 product are tested, the material loss is 13% compared with the weight of the purified CBN121 product after alkali boiling, the surface of the material is totally corroded, the crystal grains are round and smooth, no impurities are seen, although the content of the impurities reaches the standard, the purified CBN121 product is not sharp and cannot be used as a raw material of a cutting tool, but the product is wear-resistant (the product granularity is 80/100, the stacking density is 1.798, the obtained product result is shown in figure 6), and the product can only be used as a wear-resistant material.
Note: in example 2, comparative example 3 and comparative example 4, the stacking criteria for the CBN121 product with a particle size of 80/100 are:
in the national standard (GB/T6408-2018 superhard abrasive cubic boron nitride), the accumulation is not less than 1.71;
in the enterprise standard (Q/ZNJT 01-2018 cubic boron nitride technical condition), the pile-up is 1.740-1.80.
The process method can purify cubic boron nitride products with different brands, and accords with the acceptance standard of national standard (GB/T6408-2018 superhard abrasive cubic boron nitride), and meanwhile, the process can control key temperature control points in the alkali boiling process, reduce the product reverse conversion probability and reduce loss, thereby improving the labor efficiency and the product quality and being beneficial to industrial production.
While specific embodiments of the present invention have been described above, it should be understood that the present invention is not limited to the specific embodiments described above. Various changes or modifications may be made by those skilled in the art within the scope of the claims without departing from the spirit of the invention.
Claims (9)
1. The alkali treatment and purification process of cubic boron nitride is characterized by comprising the following steps of:
(I) pretreatment
(1) Primary separation: adding water into the cubic boron nitride synthetic rod block, uniformly mixing, vibrating, and then ball-milling for 0.5-1.5 h to obtain a mixed material containing cubic boron nitride, hexagonal boron nitride and impurities; the synthetic rod block is a cubic boron nitride semi-finished product synthesized by using hexagonal boron nitride and catalyst raw materials, and contains incompletely converted hexagonal boron nitride, and auxiliary materials of carbon paper, metal catalyst and pyrophyllite impurities;
(2) Acid soaking: adding hydrochloric acid into the mixture after the primary separation to soak for 20-30 min;
(3) Ultrasonic impurity removal: adding water into the mixture after acid soaking, and treating for 2-5 min by using ultrasonic waves to obtain a cubic boron nitride material;
(II) alkali digestion treatment
(4) Mixing the cubic boron nitride material subjected to pretreatment with mixed alkali and water to obtain mixed solution, and heating and boiling the mixed solution by using a thermocouple; when the temperature is increased to the state that the alkali is molten during alkali boiling, the hexagonal boron nitride and the alkali start to react, when the hexagonal boron nitride finishes the reaction, the cubic boron nitride starts to perform reverse conversion, the heating is stopped, and the alkali boiling is finished;
(III) cooling and alkali-dissolving treatment
(5) Cooling the mixture after the alkali boiling treatment, adding water to dissolve alkali when the temperature is reduced to 140-180 ℃, pouring out the alkali, and finally obtaining the material after the alkali boiling purification;
(IV) post-treatment
(6) Primary cleaning: washing the material after alkali boiling and purification with water;
(7) Ultrasonic cleaning: adding water into the cleaned material, and carrying out ultrasonic cleaning for 2-5 min;
(8) Sieving: and drying and sieving the cleaned materials to obtain the final product.
2. The process of claim 1, wherein in step (1), the ball mill used for ball milling is QHQM-100.
3. The process of claim 1, wherein in step (2), the amount of hydrochloric acid added is: adding 1800-2000 ml hydrochloric acid with mass fraction of 37% into every 5 million ct of mixed materials.
4. The process of claim 1, wherein in step (3), the ultrasonic treatment is carried out using an ultrasonic instrument having a model number of JRC-2500 and an ultrasonic power of 2-3 kw.
5. The process as claimed in claim 1, wherein in the step (4), the mass ratio of the cubic boron nitride material to the mixed alkali is 1 (0.2-0.6).
6. The process of claim 1, wherein in step (4), the amount of water used is: the solid-liquid ratio of the material to water is 6g: (1-1.2) mL.
7. The process of claim 1, wherein in step (4), the thermocouple is a platinum rhodium thermocouple of the WRP-130 type; the temperature recorder is FX1004 with the specification of-4-3-L.
8. The process according to claim 1, wherein in the step (4), the mass ratio of the mixed alkali is as follows: KOH =3 (2-2.5).
9. The process according to claim 1, wherein in step (7), the ultrasonic power is 2 to 3kw.
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