Silicon-based solid waste resource utilization method

Abstract

The invention relates to the technical field of industrial solid waste resource utilization, in particular to a silicon-based solid waste resource utilization method. The method for resource utilization of the silicon-based solid waste comprises the following steps: grinding the silicon-based solid waste to obtain a first mixture with D50 of 40-80 microns; carrying out water washing treatment and alcohol washing treatment on the first mixture to obtain a second mixture; roasting the second mixture to obtain a third mixture; carrying out acid pickling treatment and suction filtration treatment on the third mixture to obtain silicon powder; wherein the content of silicon in the silicon-based solid waste is 70-96 wt%; acid liquor used in the pickling treatment comprises at least one of sulfuric acid or hydrochloric acid and hydrofluoric acid; the temperature of the suction filtration treatment is 60-80 DEG C. According to the method, the high-purity silicon powder (the purity is greater than or equal to 99wt%) can be obtained, Si3N4 with the nitridation rate close to 100% can be prepared based on the silicon powder, and the Si3N4 powder contains high-alpha-phase Si3N4, so that enough alpha phase is converted into beta phase during sintering, and a ceramic body has good physical properties. According to the method, the added value of the product can be improved, efficient recovery of resources is realized, the production cost is reduced, and cyclic utilization of the resources is realized.

Description

Technical Field

[0001] The invention relates to the technical field of industrial solid waste resource utilization, and in particular to a method for resource utilization of silicon-based solid waste. Background Art

[0002] Under the background of rapid economic development, especially the development of electronics, photovoltaics, new energy and other industries, the amount of silicon-based solid waste has shown a rapid growth trend. Silicon-based solid waste refers to the waste generated in the production, processing and utilization of silicon materials, including silicon mud, silicon slag, silicon powder, etc., which also brings huge challenges to environmental protection and resource utilization. The rapid development of electronics, photovoltaics, new energy and other industries is also an important energy choice for achieving the "dual carbon" goal. Diamond wire cutting technology is required in the production process of silicon materials, which inevitably produces a large amount of silicon-based solid waste. The annual output of silicon waste generated by diamond wire cutting reaches 600,000 tons, which not only wastes raw materials, but also causes serious pollution to the atmosphere and water resources. In the industrial silicon industry chain, downstream industries have higher requirements for silicon purity except for photovoltaics and silicon semiconductor industries. Other industries such as non-ferrous metals do not have strict requirements for silicon purity as photovoltaics and semiconductors, and they also have great demand. Using silicon-based solid waste to purify and prepare high-purity silicon powder can not only produce midstream products and provide them as raw materials for downstream products, but also use the purified silicon powder to prepare silicon nitride (Si 3 N 4 ) powder, thus increasing the added value of products. Therefore, the development of purification technology for silicon-based solid waste and its application can efficiently recycle these resources, reduce dependence on raw materials, and achieve the recycling of resources.

[0003] At present, research on the treatment and resource utilization of silicon-based solid waste has also made certain progress, such as slag refining, vacuum refining, directional solidification, etc. However, these methods have problems such as low efficiency, high energy consumption, and difficulty in removing impurities from silicon raw materials with high impurity content. At the same time, the purification of silicon powder in the existing technology in this field is mainly focused on the purification of waste silicon powder and metallurgical grade silicon, and lacks further application of purified silicon powder. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present invention provides a method for resource utilization of silicon-based solid waste, which can obtain high-purity silicon powder (purity ≧99wt%), and based on the silicon powder, Si with a nitridation rate close to 100% can be prepared. 3 N 4 , and Si 3 N 4 The powder contains high α-phase Si 3 N 4, so that enough α phase is transformed into β phase during sintering, so that the ceramic body obtains good physical properties. This method can increase the added value of the product, realize efficient resource recovery, reduce production costs, and realize the recycling of resources.

[0005] To this end, the present invention provides a method for resource utilization of silicon-based solid waste, comprising:

[0006] Silicon-based solid waste is ground to obtain D 50 A first mixture of 40-80 μm;

[0007] The first mixture is subjected to water washing and alcohol washing to obtain a second mixture;

[0008] calcining the second mixture to obtain a third mixture;

[0009] The third mixture is subjected to acid washing and suction filtration to obtain silicon powder;

[0010] Wherein, the silicon content in the silicon-based solid waste is 70-96wt%;

[0011] The acid solution used in the pickling treatment includes at least one of sulfuric acid or hydrochloric acid and hydrofluoric acid;

[0012] The temperature of the suction filtration treatment is 60-80°C.

[0013] The present invention can purify silicon-based solid waste with different silicon contents to obtain silicon powder with a purity of ≥99%. When the silicon content of the silicon-based solid waste is 87-96wt%, the purity of the silicon powder can reach ≥99.9%. The obtained micron-level high-purity silicon powder can meet the silicon requirements of the silicon-carbon negative electrode used in lithium batteries. In addition, it can also be used for Si 3 N 4 Preparation of Si containing high α phase 3 N 4 , so that enough α phase is transformed into β phase during sintering, so that the ceramic body obtains good physical properties and improves the added value of the product.

[0014] According to an embodiment of the present invention, in the water washing treatment, the solid-liquid mass ratio of the first mixture to water is 1:(5-10).

[0015] According to an embodiment of the present invention, in the alcohol washing treatment, the solid-liquid mass ratio of the first mixture to the alcohol compound is 1:(5-10).

[0016] According to an embodiment of the present invention, the temperature of the calcination treatment is 400-800°C.

[0017] According to an embodiment of the present invention, the calcination treatment time is 0.5-2h.

[0018] According to an embodiment of the present invention, the calcination treatment is performed in an inert atmosphere, and the flow rate of the inert atmosphere is 0.2-0.8 L / min.

[0019] According to an embodiment of the present invention, the pickling treatment is carried out at 50-80°C.

[0020] According to an embodiment of the present invention, the pickling treatment time is 3-6 hours.

[0021] According to an embodiment of the present invention, the solid-liquid mass ratio of the third mixture to the acid solution is 1:(15-25).

[0022] According to an embodiment of the present invention, the content of sulfuric acid or hydrochloric acid in the acid solution is 9-12 wt %.

[0023] According to an embodiment of the present invention, the content of hydrofluoric acid in the acid solution is 1-3 wt %.

[0024] According to an embodiment of the present invention, when the silicon content in the silicon-based solid waste is 87-96 wt %, the hydrofluoric acid content in the acid solution is 1 wt %.

[0025] According to an embodiment of the present invention, when the silicon content in the silicon-based solid waste is 82-86 wt %, the hydrofluoric acid content in the acid solution is 2 wt %.

[0026] According to an embodiment of the present invention, when the silicon content in the silicon-based solid waste is 70-81 wt%, the hydrofluoric acid content in the acid solution is 3 wt%.

[0027] According to an embodiment of the present invention, the purity of the silicon powder is ≧99%.

[0028] According to an embodiment of the present invention, the method further comprises:

[0029] Grinding the silicon powder until D50 is 500-600 nm;

[0030] The ground silicon powder is nitrided to obtain silicon nitride.

[0031] According to an embodiment of the present invention, the temperature of the nitridation treatment is 1350-1600°C.

[0032] According to an embodiment of the present invention, the nitriding treatment time is 6-10 hours.

[0033] According to an embodiment of the present invention, the nitridation treatment is performed in a nitrogen atmosphere, and the flow rate of the nitrogen is 0.8-1.5 L / min.

[0034] According to an embodiment of the present invention, the nitriding rate of the nitriding treatment is 98-100%.

[0035] According to an embodiment of the present invention, the content of α phase in the silicon nitride is 89-93wt%.

[0036] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0038] Figure 1 The XRD diagram of the high-purity silicon powder obtained in step (4) of Example 1 of the present invention is shown;

[0039] Figure 2 The XRD pattern of the silicon nitride powder obtained in step (6) of Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0040] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0041] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Further, in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0042] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0043] In order to make the present invention more easily understood, certain technical and scientific terms are specifically defined below. Unless otherwise clearly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by those skilled in the art to which the present invention belongs.

[0044] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention but not excluding other contents.

[0045] As used herein, the terms "optionally", "optional" or "optionally" generally mean that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0046] According to an embodiment of the present invention, the present invention provides a method for resource utilization of silicon-based solid waste, comprising:

[0047] (1) Grinding silicon-based solid waste to obtain D 50 The first mixture is 40-80 μm.

[0048] According to a specific embodiment of the present invention, the grinding method is not particularly limited, including but not limited to ball milling.

[0049] Specifically, the ball milling can be carried out in a ball mill. The ball mill speed and ball milling time are not particularly limited, and those skilled in the art can select them according to the circumstances. As some specific examples, the ball mill speed is 200-300 r / min, and the ball milling time is 2-4 h.

[0050] According to a specific embodiment of the present invention, the silicon content in the silicon-based solid waste is 70-96wt%. As some specific examples, the silicon-based solid waste may also include other element impurities, such as Fe, Cl, Cu, Ti, Ca, Al, etc., which do not affect the subsequent resource utilization method.

[0051] (2) The first mixture is subjected to water washing treatment and alcohol washing treatment to obtain a second mixture.

[0052] The first mixture is subjected to water washing treatment and alcohol washing treatment to remove some impurities in the first mixture.

[0053] According to a specific embodiment of the present invention, the solid-liquid mass ratio of the first mixture to water in the water washing treatment is 1:(5-10). As some specific examples, the solid-liquid mass ratio of the first mixture to water in the water washing treatment may be 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.

[0054] According to a specific embodiment of the present invention, the solid-liquid mass ratio of the first mixture to the alcohol compound in the alcohol washing treatment is 1:(5-10). As some specific examples, the solid-liquid mass ratio of the first mixture to the alcohol compound in the water washing treatment may be 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.

[0055] Specifically, the type of the alcohol compound is not particularly limited, and those skilled in the art may select it according to circumstances. As some specific examples, the alcohol compound includes but is not limited to ethanol.

[0056] According to a specific embodiment of the present invention, this step further comprises: washing the first mixture with water, washing with alcohol, and drying to obtain the second mixture.

[0057] (3) The second mixture is calcined to obtain a third mixture.

[0058] The calcination process can remove organic matter on the surface of the second mixture.

[0059] According to a specific embodiment of the present invention, the temperature and time of the calcination treatment are not particularly limited, and those skilled in the art may select them according to the circumstances. As some specific examples, the temperature of the calcination treatment may be 400-800°C, such as 400°C, 500°C, 600°C, 700°C, 800°C, etc. The heating rate is also not particularly limited, and may be 10°C / min. The time of the calcination treatment may be 0.5-2h, such as 0.5h, 1h, 1.5h, 2h, etc.

[0060] According to a specific embodiment of the present invention, the calcination process is performed in an inert atmosphere. The type of the inert atmosphere is not particularly limited. As some specific examples, the inert atmosphere includes but is not limited to nitrogen.

[0061] Specifically, the flow rate of the inert atmosphere is 0.2-0.8 L / min. As some specific examples, the flow rate of the inert atmosphere may be 0.2 L / min, 0.3 L / min, 0.4 L / min, 0.5 L / min, 0.6 L / min, 0.7 L / min, 0.8 L / min, etc.

[0062] (4) subjecting the third mixture to an acid-washing treatment and a suction filtration treatment to obtain silicon powder;

[0063] The acid solution used in the pickling treatment includes at least one of sulfuric acid or hydrochloric acid and hydrofluoric acid;

[0064] The temperature of the suction filtration treatment is 60-80°C.

[0065] According to a specific embodiment of the present invention, the solid-liquid mass ratio of the third mixture to the acid solution is 1:(15-25). As some specific examples, the solid-liquid mass ratio of the third mixture to the acid solution may be 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23, 1:24, 1:25, etc.

[0066] According to a specific embodiment of the present invention, the content of sulfuric acid or hydrochloric acid in the acid solution is 9-12wt%, and as some specific examples, the content of sulfuric acid or hydrochloric acid in the acid solution is 9wt%, 10wt%, 11wt%, 12wt%, etc. The content of hydrofluoric acid in the acid solution is 1-3wt%, and as some specific examples, the content of hydrofluoric acid in the acid solution is 1wt%, 2wt%, 3wt%, etc.

[0067] Specifically, when the silicon content in the silicon-based solid waste is 87-96 wt %, the content of hydrofluoric acid in the acid solution is 1 wt %, thereby having a better pickling effect.

[0068] Specifically, when the silicon content in the silicon-based solid waste is 82-86 wt%, the content of hydrofluoric acid in the acid solution is 2 wt%, thereby having a better pickling effect.

[0069] Specifically, when the silicon content in the silicon-based solid waste is 70-81 wt%, the content of hydrofluoric acid in the acid solution is 3 wt%, thereby having a better pickling effect.

[0070] According to a specific embodiment of the present invention, the temperature and time of the pickling treatment are not particularly limited, and those skilled in the art may select them according to the circumstances. As some specific examples, the pickling treatment is carried out at 50-80°C, and the time of the pickling treatment is 3-6h.

[0071] According to a specific embodiment of the present invention, this step further comprises: subjecting the third mixture to acid washing, washing and suction filtration to obtain silicon powder.

[0072] Specifically, the washing treatment may be a water washing treatment or an ammonia washing treatment. The temperature of the water washing treatment is preferably 60-80° C., and the concentration of the ammonia water may be 1-3 wt %.

[0073] According to a specific embodiment of the present invention, the purity of the silicon powder is ≧99%.

[0074] According to a specific embodiment of the present invention, the method further comprises: grinding the silicon powder to D 50 The silicon powder after grinding is nitrided to obtain silicon nitride. The purified micron-level high-purity silicon powder is used to prepare Si with a nitridation rate of nearly 100%. 3 N 4 , and Si 3 N 4 The powder contains high α-phase Si 3 N 4, so that enough α phase is transformed into β phase during sintering, so that the ceramic body obtains good physical properties and improves the added value of the product.

[0075] Specifically, the grinding method is also not particularly limited, including but not limited to ball milling in a ball mill, the speed of the ball mill can be 300-500 r / min, and the ball milling time can be 4-8 h.

[0076] Specifically, the nitridation treatment is not particularly limited, and can be performed in a nitrogen atmosphere. The flow rate of the nitrogen can be 0.8-1.5 L / min, and the purity of the nitrogen can be ≧99.999%.

[0077] Specifically, the temperature and time of the nitriding treatment are not particularly limited, and those skilled in the art may select them according to the circumstances. As some specific examples, the temperature of the nitriding treatment may be 1350-1600° C., and the time of the nitriding treatment may be 6-10 hours.

[0078] Specifically, the nitridation rate of the nitridation treatment is 98-100%, and the α-phase content in the silicon nitride is 89-93wt%. The "nitridation rate" should be understood as the proportion of nitrogen atoms from silicon-based solid waste that are converted into silicon nitride.

[0079] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0080] Example 1

[0081] (1) 30 g of silicon-based solid waste was ball-milled, wherein the silicon content in the silicon-based solid waste was 92.738 wt %, the ball mill speed was 200-300 r / min, and the ball milling time was 2-4 h to obtain D 50 The silicon powder with a diameter of 48.92 μm was sampled and analyzed for impurity content;

[0082] (2) washing the silicon powder obtained in step (1) with water and alcohol at room temperature, wherein the solid-liquid ratio of silicon powder to water (ethanol) is 1:5, and then filtering and drying;

[0083] (3) 20 g of the silicon powder obtained in step (2) was calcined under nitrogen atmosphere protection, with a nitrogen flow rate of 0.2 L / min, a heating rate of 10°C / min, a calcination temperature of 600°C, and a calcination time of 2 h to remove organic matter on the surface of the waste silicon powder;

[0084] (4) 15 g of the silicon powder obtained in step (3) was added to a mixed acid solution for heating and stirring. The content of hydrochloric acid in the mixed acid solution was 10 wt %, the content of hydrofluoric acid was 1 wt %, the solid-liquid ratio was 1:20, the heating temperature was 60° C., and the mixture was kept warm and stirred for 4 h. After the reaction was completed, high-purity silicon powder was obtained by washing with hot water at 70° C., filtering, and drying. After sampling, X-ray fluorescence spectroscopy (XRF) analysis and X-ray diffraction (XRD) analysis were performed. The results are shown in Tables 1 and Figure 1 ;

[0085] (5) 10 g of the high-purity silicon powder obtained in step (4) was ball-milled at a ball-to-material ratio of 30:1, a ball mill speed of 400 r / min, and a ball milling time of 8 h to obtain D 50 High-purity silicon powder with a diameter of 585.36nm;

[0086] (6) Take 10 g of the high-purity silicon powder obtained in step (5) and nitride it under nitrogen to obtain Si 3 N 4 The nitriding temperature was 1400°C, the nitriding time was 8 hours, the purity of the nitrogen used was ≧99.999%, and the flow rate of the nitrogen was 0.8 L / min. Si 3 N 4 The nitriding rate is 100%, the α phase content is 92.84%, and the Si 3 N 4 The XRD pattern of Figure 2 .

[0087] Table 1

[0088]

[0089]

[0090] Among them, "-" means non-existence.

[0091] Example 2

[0092] The difference between this embodiment and embodiment 1 is that the silicon content in the silicon-based solid waste is 84.496wt%, the content of hydrofluoric acid in the mixed acid solution is 2wt%, and other parameters remain unchanged. The element content in the silicon powder obtained in step (4) is shown in Table 2. 3 N 4 The nitriding rate is 100% and the α phase content is 92.68%.

[0093] Table 2

[0094]

[0095] Among them, "-" means non-existence.

[0096] Example 3

[0097] The difference between this embodiment and embodiment 1 is that the silicon content in the silicon-based solid waste is 70.723wt%, the content of hydrofluoric acid in the mixed acid solution is 3wt%, and other parameters remain unchanged. The element content in the silicon powder obtained in step (4) is shown in Table 3. 3 N 4 The nitriding rate is 100% and the α phase content is 91.53%.

[0098] Table 3

[0099]

[0100] Among them, "-" means non-existence.

[0101] Comparative Example 1

[0102] The difference between this comparative example and Example 1 is that only 10 wt% hydrochloric acid is used in step (4), and the element contents in the silicon powder obtained in this step are shown in Table 6. This shows that using a single acid solution in the pickling treatment cannot effectively improve the purity of silicon powder.

[0103] Table 6

[0104]

[0105] Comparative Example 2

[0106] The difference between this comparative example and Example 1 is that cold water filtration is used in step (4). The element contents in the silicon powder obtained in this step are shown in Table 7. This shows that the purity of the silicon powder cannot be effectively improved without the filtration treatment defined in the present invention.

[0107] Table 7

[0108]

[0109]

[0110] Comparative Example 3

[0111] The difference between this comparative example and Example 1 is that the ball milling treatment in step (5) is not performed. 3 N 4 It is not completely nitrided, and the α phase content is 78.29%. This shows that ball milling of high-purity silicon powder can effectively improve the subsequent nitridation rate and the α phase content in silicon nitride.

[0112] Comparative Example 4

[0113] The difference between this comparative example and Example 1 is that the ball milling treatment in step (1) is not performed. The element contents in the silicon powder obtained in step (4) are shown in Table 8. This indicates that failure to perform ball milling treatment on silicon-based solid waste will affect the purity of subsequent silicon powder.

[0114] Table 8

[0115]

[0116] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0117] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for resource utilization of silicon-based solid waste, characterized in that: include: Silicon-based solid waste is ground to obtain D 50 A first mixture of 40-80 μm; The first mixture is subjected to water washing and alcohol washing to obtain a second mixture; calcining the second mixture to obtain a third mixture; The third mixture is subjected to acid washing and suction filtration to obtain silicon powder; Wherein, the silicon content in the silicon-based solid waste is 70-96wt%; The acid solution used in the pickling treatment includes at least one of sulfuric acid or hydrochloric acid and hydrofluoric acid; The temperature of the suction filtration treatment is 60-80°C.

2. The method according to claim 1, characterized in that The solid-liquid mass ratio of the first mixture to water in the water washing treatment is 1:(5-10); Optionally, in the alcohol washing treatment, the solid-liquid mass ratio of the first mixture to the alcohol compound is 1:(5-10).

3. The method according to claim 1, characterized in that The temperature of the calcination treatment is 400-800°C; Optionally, the calcination treatment time is 0.5-2h; Optionally, the calcination treatment is performed in an inert atmosphere, and the flow rate of the inert atmosphere is 0.2-0.8 L / min.

4. The method according to claim 1, characterized in that: The pickling treatment is carried out at 50-80°C; Optionally, the pickling treatment time is 3-6 hours.

5. The method according to claim 1, characterized in that The solid-liquid mass ratio of the third mixture to the acid solution is 1:(15-25); Optionally, the content of sulfuric acid or hydrochloric acid in the acid solution is 9-12wt%; Optionally, the content of hydrofluoric acid in the acid solution is 1-3wt%; Optionally, when the silicon content in the silicon-based solid waste is 87-96 wt %, the content of hydrofluoric acid in the acid solution is 1 wt %; Optionally, when the silicon content in the silicon-based solid waste is 82-86 wt %, the content of hydrofluoric acid in the acid solution is 2 wt %; Optionally, when the silicon content in the silicon-based solid waste is 70-81 wt%, the content of hydrofluoric acid in the acid solution is 3 wt%.

6. The method according to claim 1, characterized in that The purity of the silicon powder is ≧99%.

7. The method according to claim 1, characterized in that The method further comprises: The silicon powder is ground to D 50 500-600nm; The ground silicon powder is nitrided to obtain silicon nitride.

8. The method according to claim 7, characterized in that The temperature of the nitriding treatment is 1350-1600°C; Optionally, the nitriding treatment time is 6-10 hours.

9. The method according to claim 7, characterized in that: The nitridation treatment is carried out in a nitrogen atmosphere, and the flow rate of the nitrogen is 0.8-1.5 L / min.

10. The method according to claim 7, characterized in that The nitriding rate of the nitriding treatment is 98-100%; Optionally, the α-phase content in the silicon nitride is 89-93 wt %.

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