阅读说明：本技术 一种基于硅棒线切割废料制备硅氧化物的方法 (Method for preparing silicon oxide based on silicon rod wire cutting waste ) 是由 刘德全 闻震利 贺德衍 王晓哲 韩昀钊 于 2021-09-27 设计创作，主要内容包括：本发明提供一种基于硅棒线切割废料制备硅氧化物的方法,涉及硅材料领域。本发明将硅棒线切割产生的硅废料通过热氧化(和归中反应)直接得到硅氧化物材料,不需要经过蒸发和冷凝过程,也无需经过粉碎破裂,工艺过程简单,成本低廉；通过控制反应条件,可以实现氧原子和硅原子比例在0.16∶1～2∶1范围内的调节；充分利用硅棒线切割产生的硅废料来制备硅氧化物,进一步将其应用到制备锂离子电池或石英坩埚中,能够促进硅废料的高价值利用。(The invention provides a method for preparing silicon oxide based on silicon rod wire cutting waste, and relates to the field of silicon materials. According to the invention, silicon waste generated by linear cutting of the silicon rod is directly subjected to thermal oxidation (and neutralization reaction) to obtain the silicon oxide material, evaporation and condensation processes are not required, crushing and cracking are not required, the process is simple, and the cost is low; by controlling the reaction conditions, the ratio of oxygen atoms to silicon atoms can be adjusted within the range of 0.16: 1-2: 1; silicon waste materials generated by wire cutting of the silicon rod are fully utilized to prepare silicon oxide, and the silicon oxide is further applied to preparation of a lithium ion battery or a quartz crucible, so that high-value utilization of the silicon waste materials can be promoted.)

1. A method for preparing silicon oxide based on silicon rod wire-electrode cutting waste, which is characterized by comprising the following steps (1) and (2) and optionally comprising the step (3):

(1) sequentially carrying out acid washing, water washing and drying on silicon waste generated by the linear cutting of the silicon rod;

(2) oxidizing the silicon powder obtained after drying in the step (1) in an oxidizing atmosphere, wherein the oxidizing atmosphere comprises at least one of oxygen, air and water vapor;

(3) and (3) carrying out a centering reaction on the silicon powder obtained by oxidation in the step (2) in an inert atmosphere.

2. The method for preparing silicon oxide based on silicon rod wire cutting waste according to claim 1, characterized in that in step (1):

acid washing is carried out by adopting at least one of the following inorganic acids: hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and hydrogen peroxide; the pickling time is 5-15.5 hours, and the pickling temperature is 20-50 ℃;

the drying includes high temperature oven drying and/or freeze drying.

3. The method for preparing silicon oxide based on silicon rod wire cutting waste according to claim 1, characterized in that in step (2):

the oxidation temperature is 800-1300 ℃, the heat preservation time is 1-50 hours, and the temperature rising speed is 1-10 ℃/min, wherein the heat preservation is one temperature continuous heat preservation, or at least two different temperatures are continuously kept, and the temperature rising or reducing speed is 1-10 ℃/min when the different temperatures are switched;

the oxidation atmosphere is one of oxygen, air and water vapor atmosphere or a mixed atmosphere of oxygen and water vapor, wherein the content of oxygen is 21-100%, the content of water vapor is 0-40%, and the oxidation is carried out in one oxidation atmosphere or is carried out continuously in at least two different oxidation atmospheres.

4. The method for preparing silicon oxide based on silicon rod wire cutting waste according to claim 1, characterized in that in step (3):

the inert atmosphere comprises a nitrogen atmosphere and/or an argon atmosphere;

the conditions of the centering reaction are as follows: the air pressure is 1-20 bar, the reaction temperature is 1000-1550 ℃, and the heat preservation time is 1-50 hours; the temperature rising speed is 2-10 ℃/min, wherein the heat preservation is one temperature continuous heat preservation, or at least two different temperatures are continuously preserved, and the temperature rising or reducing speed is 2-10 ℃/min when the different temperatures are switched.

5. The method for preparing silicon oxide based on silicon rod wire cutting waste according to claim 1, characterized in that the method comprises steps (1) to (3), wherein,

in the step (2), the oxidation temperature is 800-1300 ℃, the heat preservation time is 1-40 hours, and the heating rate is 1-10 ℃/minute, wherein the heat preservation is continuous heat preservation at one temperature, or continuous heat preservation at least two different temperatures, and the heating or cooling rate is 1-10 ℃/minute when the different temperatures are switched; the oxidizing atmosphere is air atmosphere, or oxidizing in air atmosphere and then oxidizing in atmosphere with 100% oxygen concentration;

in the step (3), the conditions of the centering reaction are as follows: the air pressure is 1-20 bar, the reaction temperature is 1000-1550 ℃, and the heat preservation time is 1-50 hours; the temperature rising speed is 2-10 ℃/min, wherein the heat preservation is one temperature continuous heat preservation, or at least two different temperatures are continuously preserved, and the temperature rising or reducing speed is 2-10 ℃/min when the different temperatures are switched.

6. The method for preparing silicon oxide based on silicon rod wire cutting waste according to claim 1, characterized in that the method comprises step (1) and step (2), excluding step (3), wherein,

in the step (2), the oxidation temperature is 1200 ℃, the heat preservation time is 45 hours, the temperature rise speed is 1 ℃/minute, the oxygen content is 60% and the water vapor content is 40% in the oxidation atmosphere.

7. The method for preparing silicon oxide based on silicon rod wire cutting waste according to claim 1,

the silicon waste generated by the silicon rod linear cutting is submicron silicon powder, and preferably, the silicon waste generated by the silicon rod linear cutting is submicron flaky silicon powder.

8. The method for preparing silicon oxide based on silicon rod wire cutting waste according to claim 1,

in the step (2), the oxidation is carried out in an electric furnace, wherein the electric furnace comprises a tubular furnace, a box furnace, a rotary furnace, a roller kiln or a pushed slab kiln;

in the step (3), the centering reaction is performed in an electric furnace, wherein the electric furnace comprises a tubular furnace, a box furnace, a rotary furnace, a roller kiln, a pusher kiln or a vacuum furnace.

9. The method for preparing silicon oxide based on silicon rod wire cutting waste according to claim 8,

the ratio of oxygen atoms to silicon atoms in the silicon oxide is 0.16: 1-2: 1.

10. Use of silicon oxide obtained by the method of any one of claims 1 to 9 for the preparation of lithium ion batteries or quartz crucibles.

Technical Field

The invention relates to the field of silicon materials, in particular to a method for preparing silicon oxide based on silicon rod wire cutting waste.

Background

With the development of solar cells, a large amount of submicron silicon waste is generated during the slicing of crystalline silicon. The waste generated by the traditional mortar cutting process is mixed with a large amount of silicon carbide abrasive in the submicron silicon waste, and is difficult to recycle. In recent years, the diamond wire cutting technology is popularized in the production of solar-grade silicon wafers, the content of silicon in silicon waste is greatly improved, and new opportunities are brought to the high-value application of the silicon waste.

The silicon material has a lithium storage capacity as high as 4200mAh/g, so that the silicon material becomes a hot spot for the research of the next generation of lithium ion battery cathode materials. Several studies have been conducted around the application of submicron silicon waste in the preparation of lithium ion batteries. For example, chinese patent document CN104112850A discloses that a material prepared by removing impurities from silicon waste by acid washing and annealing in an inert atmosphere and performing surface oxidation modification by a wet chemical method is used as a negative electrode material of a lithium ion battery; chinese patent document CN111799461A discloses the preparation of silicon alloy lithium ion battery material by alloying silicon scrap with other metals at high temperature; chinese patent document CN105336922A discloses that silicon waste is coated with a carbon material to prepare a silicon-carbon composite lithium ion battery negative electrode material; chinese patent document CN111082033A discloses shaping a silicon material by ball milling to prepare a battery-grade nano silicon material with high capacity and long cycle stability.

However, the silicon material expands greatly during charging and discharging, so that the battery cycle performance is poor, and the actual requirement is difficult to meet. Silica materials have attracted considerable attention due to their relatively high capacity (2100mAh/g), low volume expansion. For example, chinese patent document CN103123967A discloses a method for preparing a silica/carbon composite material; chinese patent document CN112310384A discloses a method for preparing silicon oxide lithium ion battery negative electrode material; chinese patent document CN106356508A discloses a method for preparing a silicon oxide composite electrode material. A method for preparing silicon oxide by wire-cutting silicon waste using a silicon rod has not been reported.

Disclosure of Invention

Therefore, the technical problem to be solved by the present invention is to provide a method for preparing silicon oxide based on silicon rod wire-cutting silicon waste, so as to promote high-value utilization of silicon waste.

In a first aspect, the present invention provides a method for preparing silicon oxide based on silicon rod wire-cutting waste, comprising the following steps (1) and (2), with or without step (3):

(1) sequentially carrying out acid washing, water washing and drying on silicon waste generated by the linear cutting of the silicon rod;

(2) oxidizing the silicon powder obtained after drying in the step (1) in an oxidizing atmosphere, wherein the oxidizing atmosphere comprises at least one of oxygen, air and water vapor;

(3) and (3) carrying out a centering reaction on the silicon powder obtained by oxidation in the step (2) in an inert atmosphere.

Further, in step (1):

acid washing is carried out by adopting at least one of the following inorganic acids: hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and hydrogen peroxide; the pickling time is 5-15.5 hours, and the pickling temperature is 20-50 ℃;

the drying includes high temperature oven drying and/or freeze drying.

Further, in step (2):

the oxidation temperature is 800-1300 ℃, the heat preservation time is 1-50 hours, and the temperature rising speed is 1-10 ℃/min, wherein the heat preservation is one temperature continuous heat preservation, or at least two different temperatures are continuously kept, and the temperature rising or reducing speed is 1-10 ℃/min when the different temperatures are switched;

the oxidation atmosphere is one of oxygen, air and water vapor atmosphere or a mixed atmosphere of oxygen and water vapor, wherein the content of oxygen is 21-100%, the content of water vapor is 0-40%, and the oxidation is carried out in one oxidation atmosphere or is carried out continuously in at least two different oxidation atmospheres.

Further, in step (3):

the inert atmosphere comprises a nitrogen atmosphere and/or an argon atmosphere;

the conditions of the centering reaction are as follows: the air pressure is 1-20 bar, the reaction temperature is 1000-1550 ℃, and the heat preservation time is 1-50 hours; the temperature rising speed is 2-10 ℃/min, wherein the heat preservation is one temperature continuous heat preservation, or at least two different temperatures are continuously preserved, and the temperature rising or reducing speed is 2-10 ℃/min when the different temperatures are switched.

Further, the method comprises steps (1) to (3) wherein,

in the step (2), the oxidation temperature is 800-1300 ℃, the heat preservation time is 1-40 hours, and the heating rate is 1-10 ℃/minute, wherein the heat preservation is continuous heat preservation at one temperature, or continuous heat preservation at least two different temperatures, and the heating or cooling rate is 1-10 ℃/minute when the different temperatures are switched; the oxidizing atmosphere is air atmosphere, or oxidizing in air atmosphere and then oxidizing in atmosphere with 100% oxygen concentration;

in the step (3), the conditions of the centering reaction are as follows: the air pressure is 1-20 bar, the reaction temperature is 1000-1550 ℃, and the heat preservation time is 1-50 hours; the temperature rising speed is 2-10 ℃/min, wherein the heat preservation is one temperature continuous heat preservation, or at least two different temperatures are continuously preserved, and the temperature rising or reducing speed is 2-10 ℃/min when the different temperatures are switched.

Further, the method comprises step (1) and step (2), excluding step (3), wherein,

in the step (2), the oxidation temperature is 1200 ℃, the heat preservation time is 45 hours, the temperature rise speed is 1 ℃/minute, the oxygen content is 60% and the water vapor content is 40% in the oxidation atmosphere.

Further, the silicon waste generated by the silicon rod wire cutting is submicron silicon powder, and preferably, the silicon waste generated by the silicon rod wire cutting is submicron sheet silicon powder.

Further, in the step (2), the oxidation is carried out in an electric furnace, wherein the electric furnace comprises a tubular furnace, a box furnace, a rotary furnace, a roller kiln or a pushed slab kiln;

in the step (3), the centering reaction is performed in an electric furnace, wherein the electric furnace comprises a tubular furnace, a box furnace, a rotary furnace, a roller kiln, a pusher kiln or a vacuum furnace.

Further, the ratio of oxygen atoms to silicon atoms in the silicon oxide is 0.16: 1-2: 1.

In a second aspect, the invention provides an application of the silicon oxide obtained by the method in the preparation of a lithium ion battery or a quartz crucible.

The technical scheme of the invention has the following advantages:

1. according to the invention, silicon waste generated by linear cutting of the silicon rod is directly subjected to thermal oxidation (and neutralization reaction) to obtain the silicon oxide material, evaporation and condensation processes are not required, crushing and cracking are not required, the process is simple, and the cost is low.

2. The invention can realize the adjustment of the ratio of oxygen atoms to silicon atoms within the range of 0.16: 1-2: 1 by controlling the reaction conditions.

3. According to the invention, silicon waste generated by linear cutting of the silicon rod is fully utilized to prepare silicon oxide, and the silicon oxide is further applied to preparation of a lithium ion battery or a quartz crucible, so that high-value utilization of the silicon waste can be promoted.

Detailed Description

The following examples are provided to further understand the present invention, not to limit the scope of the present invention, but to provide the best mode, not to limit the content and the protection scope of the present invention, and any product similar or similar to the present invention, which is obtained by combining the present invention with other prior art features, falls within the protection scope of the present invention.

The examples do not show the specific experimental steps or conditions, and can be performed according to the conventional experimental steps described in the literature in the field. The raw materials or equipment used are all conventional products which can be obtained commercially, including but not limited to the raw materials or equipment used in the examples of the present application.

The method for detecting the proportion of oxygen atoms to silicon atoms in the silicon oxide prepared in the examples was measured by thermogravimetric analysis.

Example 1

The embodiment provides a method for preparing silicon oxide based on silicon rod wire cutting waste, which comprises the following steps:

(1) taking 1g of submicron flaky silicon waste generated by linear cutting of a silicon rod, carrying out acid pickling on the submicron flaky silicon waste by using mixed acid liquid containing 5% of hydrofluoric acid and 10% of hydrochloric acid, wherein the acid pickling temperature is 50 ℃, the time is 10 hours, then repeatedly washing the submicron flaky silicon waste by using deionized water for 5 times, and carrying out vacuum drying;

(2) placing the silicon powder obtained after drying in the step (1) into a box furnace, calcining and oxidizing at 940 ℃ in air atmosphere, and keeping the temperature for 1 hour at the heating speed of 5 ℃ for gamma minutes;

(3) and (3) placing the silicon powder obtained by oxidation in the step (2) into a tubular furnace for centering reaction, calcining at 1200 ℃ under the atmosphere of argon and the air pressure of 20 bar, preserving heat for 50 hours, and increasing the temperature at the speed of 5 ℃/min to obtain the silicon oxide material.

It was found that the silicon oxide material obtained in example 1 had a ratio of 1: 1 of oxygen atoms to silicon atoms.

ICP-MS testing gave a silicon oxide material of example 1 having a nickel content of less than 180ppm and other metals content of less than 20 ppm.

Example 2

The embodiment provides a method for preparing silicon oxide based on silicon rod wire cutting waste, which comprises the following steps:

(1) taking 1g of submicron flaky silicon waste generated by linear cutting of a silicon rod, carrying out acid pickling with a mixed acid solution containing 5% hydrofluoric acid and 10% hydrochloric acid at 50 ℃ for 5h, then carrying out acid pickling with 10% nitric acid at 20 ℃ for 0.5h, then carrying out acid pickling with a mixed acid solution containing 5% hydrogen peroxide and 10% hydrochloric acid at 20 ℃ for 10h, finally repeatedly washing with deionized water for 6 times, and carrying out vacuum drying;

(2) and (2) placing the silicon powder obtained after drying in the step (1) into a tube furnace, calcining and oxidizing the silicon powder at 1200 ℃ in an atmosphere containing 40% of oxygen gas and 60%, and keeping the temperature for 45 hours at the heating rate of 1 ℃/min. A silicon oxide material is obtained.

It was found that the silicon oxide material obtained in example 2 had a ratio of oxygen atoms to silicon atoms of 2: 1.

ICP-MS testing gave a silicon oxide material of example 2 having a nickel content of less than 180ppm and other metals content of less than 20 ppm.

Example 3

The embodiment provides a method for preparing silicon oxide based on silicon rod wire cutting waste, which comprises the following steps:

(1) taking 1g of submicron flaky silicon waste generated by linear cutting of a silicon rod, carrying out acid pickling with a mixed acid solution containing 5% hydrofluoric acid and 10% hydrochloric acid at the temperature of 50 ℃ for 5 hours, carrying out acid pickling with a mixed acid solution containing 5% hydrogen peroxide and 10% hydrochloric acid at the temperature of 20 ℃ for 10 hours, repeatedly washing with deionized water for 5 times, and carrying out vacuum drying;

(2) placing the silicon powder obtained after drying in the step (1) into a tubular furnace, calcining and oxidizing at 800 ℃ in air atmosphere, and keeping the temperature for 1 hour at the heating speed of 5 ℃/min;

(3) and (3) placing the silicon powder obtained by oxidation in the step (2) into a tubular furnace for centering reaction, calcining at 1000 ℃ under the atmosphere of argon and the air pressure of 1 bar, preserving heat for 40 hours, and increasing the temperature at the speed of 5 ℃/min to obtain the silicon oxide material.

It was found that the ratio of oxygen atoms to silicon atoms in the silicon oxide material obtained in example 3 was 0.16: 1.

ICP-MS testing gave a silicon oxide material of example 3 having a nickel content of less than 180ppm and other metals content of less than 20 ppm.

Example 4

The embodiment provides a method for preparing silicon oxide based on silicon rod wire cutting waste, which comprises the following steps:

(1) taking 1g of submicron flaky silicon waste generated by linear cutting of a silicon rod, carrying out acid pickling on the submicron flaky silicon waste by using mixed acid liquid containing 5% of hydrofluoric acid and 10% of hydrochloric acid, wherein the acid pickling temperature is 50 ℃, the time is 5 hours, then repeatedly washing the submicron flaky silicon waste by using deionized water for 5 times, and carrying out vacuum drying;

(2) placing the silicon powder obtained after drying in the step (1) into a tubular furnace, calcining and oxidizing at 900 ℃ in air atmosphere, and keeping the temperature for 1 hour at the heating speed of 5 ℃/min;

(3) and (3) placing the silicon powder obtained by oxidation in the step (2) into a tubular furnace for centering reaction, calcining at 1200 ℃ under the atmosphere of argon and the air pressure of 2 bar, preserving heat for 1 hour, and increasing the temperature at the speed of 5 ℃/min to obtain the silicon oxide material.

It was found that the silicon oxide material obtained in example 4 had a ratio of oxygen atoms to silicon atoms of 0.67: 1.

ICP-MS testing gave a silicon oxide material of example 4 having a nickel content of less than 180ppm and other metals content of less than 20 ppm.

Example 5

The embodiment provides a method for preparing silicon oxide based on silicon rod wire cutting waste, which comprises the following steps:

(1) taking 1g of submicron flaky silicon waste generated by linear cutting of a silicon rod, carrying out acid pickling on the submicron flaky silicon waste by using mixed acid liquid containing 5% of hydrofluoric acid and 10% of hydrochloric acid, wherein the acid pickling temperature is 50 ℃, the time is 5 hours, then repeatedly washing the submicron flaky silicon waste by using deionized water for 5 times, and carrying out vacuum drying;

(2) placing the silicon powder obtained after drying in the step (1) in a tubular furnace, calcining and oxidizing at 1100 ℃ in air atmosphere, and keeping the temperature for 10 hours at the heating speed of 2 ℃/min;

(3) and (3) placing the silicon powder obtained by oxidation in the step (2) into a tubular furnace for centering reaction, calcining at 1000 ℃ under the nitrogen atmosphere and the air pressure of 1 bar, preserving heat for 50 hours, and increasing the temperature at a speed of 10 ℃/min to obtain the silicon oxide material.

It was found that the ratio of oxygen atoms to silicon atoms in the silicon oxide material obtained in example 5 was 1.8: 1.

ICP-MS testing gave a silicon oxide material of example 5 having a nickel content of less than 180ppm and other metals content of less than 20 ppm.

Example 6

The embodiment provides a method for preparing silicon oxide based on silicon rod wire cutting waste, which comprises the following steps:

(1) taking 1g of submicron flaky silicon waste generated by linear cutting of a silicon rod, carrying out acid pickling on the submicron flaky silicon waste by using mixed acid liquid containing 5% of hydrofluoric acid and 10% of hydrochloric acid, wherein the acid pickling temperature is 50 ℃, the time is 5 hours, then repeatedly washing the submicron flaky silicon waste by using deionized water for 5 times, and carrying out vacuum drying;

(2) placing the silicon powder obtained after drying in the step (1) in a tube furnace, calcining and oxidizing at 1100 ℃ in air atmosphere, preserving heat for 10 hours, heating to 1150 ℃, preserving heat for 10 hours, heating to 1300 ℃, preserving heat for 10 hours, wherein the heating speed is 2 ℃/min;

(3) and (3) placing the silicon powder obtained by oxidation in the step (2) into a tubular furnace for centering reaction, calcining at 1550 ℃ under the atmosphere of argon and the air pressure of 1 bar, preserving heat for 10 hours, and increasing the temperature at the speed of 2 ℃/min to obtain the silicon oxide material.

It was found that the silicon oxide material obtained in example 6 had a ratio of oxygen atoms to silicon atoms of 1.95: 1.

ICP-MS testing gave a silicon oxide material of example 6 having a nickel content of less than 180ppm and other metals content of less than 20 ppm.

Example 7

The embodiment provides a method for preparing silicon oxide based on silicon rod wire cutting waste, which comprises the following steps:

(1) taking 1g of submicron flaky silicon waste generated by linear cutting of a silicon rod, carrying out acid pickling with a mixed acid solution containing 5% hydrofluoric acid and 10% hydrochloric acid at 50 ℃ for 5h, then carrying out acid pickling with 10% nitric acid at 20 ℃ for 0.5h, then carrying out acid pickling with a mixed acid solution containing 5% hydrogen peroxide and 10% hydrochloric acid at 20 ℃ for 10h, finally repeatedly washing with deionized water for 6 times, and carrying out vacuum drying;

(2) and (2) placing the silicon powder obtained after drying in the step (1) into a tubular furnace, calcining and oxidizing at 1200 ℃ in an air atmosphere, and keeping the temperature for 10 hours at a heating rate of 10 ℃/min. And continuously oxidizing at 1200 ℃ in an atmosphere with the oxygen concentration of 100%, and keeping the temperature for 30 hours. A silicon oxide material is obtained.

(3) And (3) placing the silicon powder obtained by oxidation in the step (2) into a tubular furnace for centering reaction, calcining at 1450 ℃ under the atmosphere of argon and the air pressure of 2 bar, preserving heat for 10 hours, and raising the temperature at the speed of 5 ℃/min to obtain the silicon oxide material.

It was found that the ratio of oxygen atoms to silicon atoms in the silicon oxide material obtained in example 7 was 1.97: 1.

ICP-MS testing gave a silicon oxide material of example 7 having a nickel content of less than 180ppm and other metals content of less than 20 ppm.

Example 8

The embodiment provides a method for preparing silicon oxide based on silicon rod wire cutting waste, which comprises the following steps:

(1) taking 1g of submicron flaky silicon waste generated by linear cutting of a silicon rod, carrying out acid pickling with a mixed acid solution containing 5% hydrofluoric acid and 10% hydrochloric acid at 50 ℃ for 5h, then carrying out acid pickling with 10% nitric acid at 20 ℃ for 0.5h, then carrying out acid pickling with a mixed acid solution containing 5% hydrogen peroxide and 10% hydrochloric acid at 20 ℃ for 10h, finally repeatedly washing with deionized water for 6 times, and carrying out vacuum drying;

(2) and (2) placing the silicon powder obtained after drying in the step (1) into a tubular furnace, calcining and oxidizing at 1200 ℃ in an air atmosphere, and keeping the temperature for 10 hours at the heating rate of 1 ℃/min. And continuously oxidizing at 1200 ℃ in an atmosphere with the oxygen concentration of 100%, and keeping the temperature for 30 hours. A silicon oxide material is obtained.

(3) And (3) placing the silicon powder obtained by oxidation in the step (2) into a tubular furnace for centering reaction, calcining at 1550 ℃ under the atmosphere of argon at the air pressure of 20 bar, preserving heat for 20 hours, and raising the temperature at the speed of 5 ℃/min to obtain the silicon oxide material.

It was found that the ratio of oxygen atoms to silicon atoms in the silicon oxide material obtained in example 8 was 1.98: 1.

ICP-MS testing gave a silicon oxide material of example 8 having a nickel content of less than 180ppm and other metals content of less than 20 ppm.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.