阅读说明：本技术 一种基于水煤气变换反应与碳热还原反应获得核壳结构纳米线的制备方法 (Preparation method for obtaining core-shell structure nanowire based on water gas shift reaction and carbothermic reduction reaction ) 是由 康鹏超 赵旗旗 孙兆群 王平平 辛玲 姜龙涛 武高辉 于 2021-11-15 设计创作，主要内容包括：一种基于水煤气变换反应与碳热还原反应获得核壳结构纳米线的制备方法,本发明涉及核壳结构纳米线的制备方法领域。本发明要解决目前核壳结构纳米线制备工艺复杂、原材料和反应条件苛刻,产物纯度较低,氧化层厚度不可控的技术问题。方法：在高温高湿箱中对硅粉进行湿度氧化处理；在气氛烧结炉中与石墨合成核壳结构SiC纳米线。本发明所制备的核壳结构纳米线,具有氧化层厚度可控、界面处为原子尺度的紧密结合等优点。本发明用于制备核壳结构SiC纳米线。(The invention discloses a preparation method for obtaining a core-shell structure nanowire based on a water gas shift reaction and a carbothermic reduction reaction, and relates to the field of preparation methods of core-shell structure nanowires. The invention aims to solve the technical problems of complex preparation process, harsh raw materials and reaction conditions, low product purity and uncontrollable oxide layer thickness of the existing core-shell structure nanowire. The method comprises the following steps: carrying out humidity oxidation treatment on the silicon powder in a high-temperature high-humidity box; and synthesizing the SiC nano wire with the core-shell structure with graphite in an atmosphere sintering furnace. The core-shell structure nanowire prepared by the invention has the advantages of controllable thickness of an oxide layer, close combination of atomic scales at an interface and the like. The method is used for preparing the SiC nanowire with the core-shell structure.)

1. A preparation method for obtaining core-shell structure nanowires based on water gas shift reaction and carbothermic reduction reaction is characterized by comprising the following steps:

firstly, silicon powder pretreatment:

putting the silicon powder into a high-temperature high-humidity box, controlling the temperature of the high-temperature high-humidity box to be 80-150 ℃ and the humidity to be 20% -98% R.H, carrying out heat preservation treatment, and then cooling the furnace to obtain silicon powder with oxidized humidity;

secondly, synthesizing the SiC nanowire:

putting the silicon powder treated in the step one into a graphite crucible, adding a graphite cover, putting into an atmosphere sintering furnace, vacuumizing, and controlling the vacuum degree to be 0.1-1.0 Pa; then argon is filled into the atmosphere sintering furnace; then controlling the heating rate to be 5-20 ℃/min, heating to 500-900 ℃ and preserving heat for 0.5-1.0 h, then controlling the heating rate to be 5-20 ℃/min, heating to 1000-1350 ℃ and preserving heat for 0.5-6.0 h; and then cooling the furnace body to 300-600 ℃, cooling the furnace body to room temperature along with the furnace, and opening the furnace to obtain the core-shell structure nanowire, thereby completing the preparation.

2. The preparation method of core-shell structure nanowires based on water gas shift reaction and carbothermic reduction reaction according to claim 1, wherein the heat preservation treatment time in step one is 2-48 h.

3. The preparation method of core-shell structure nanowire based on water gas shift reaction and carbothermic reduction reaction as claimed in claim 1, wherein the first step is to control the temperature of the high temperature and high humidity chamber to 150 ℃ and the humidity to 20% R.H for heat preservation treatment for 4 h.

4. The preparation method of core-shell structure nanowire based on water gas shift reaction and carbothermic reduction reaction according to claim 1, wherein the average diameter of the silicon powder in step one is 30nm to 5 μm.

5. The method for preparing the core-shell structure nanowire based on the water gas shift reaction and the carbothermic reduction reaction according to claim 1, wherein the graphite crucible in the second step is made of one or more of electrode graphite, high-purity graphite, carburized graphite and oxidation-resistant graphite.

6. The method for preparing the core-shell structure nanowire based on the water gas shift reaction and the carbothermic reduction reaction according to claim 1, wherein the graphite cover in the second step is made of one or more of electrode graphite, high-purity graphite, carburized graphite and oxidation-resistant graphite.

7. The method for preparing the core-shell structure nanowire based on the water gas shift reaction and the carbothermic reduction reaction according to claim 1, wherein argon is introduced in the second step to control the initial pressure of the gas in the atmosphere sintering furnace to be-0.2 to 0.5 MPa.

8. The preparation method of the core-shell structure nanowire based on the water gas shift reaction and the carbothermic reduction reaction according to claim 1, wherein the cooling rate of the furnace body is controlled to be 1-10 ℃/min in the second step.

9. The method for preparing the core-shell structure nanowire based on the water gas shift reaction and the carbothermic reduction reaction according to claim 1, wherein the initial pressure of the gas in the atmosphere sintering furnace is controlled to be 0.5MPa in the second step; then controlling the heating rate to be 20 ℃/min, heating to 900 ℃, keeping the temperature for 1.0h, then controlling the heating rate to be 10 ℃/min, heating to 1150 ℃, keeping the temperature for 6.0 h; then the furnace body is cooled to 600 ℃ at the cooling rate of 5 ℃/min.

10. The method for preparing the core-shell structure nanowire based on the water gas shift reaction and the carbothermic reduction reaction according to claim 1, wherein the initial pressure of the gas in the atmosphere sintering furnace is controlled to-0.2 MPa in the second step; then controlling the heating rate to be 5 ℃/min, heating to 900 ℃, keeping the temperature for 1.0h, then controlling the heating rate to be 5 ℃/min, heating to 1350 ℃, keeping the temperature for 6.0 h; then the furnace body is cooled to 300 ℃ at the cooling rate of 1 ℃/min.

Technical Field

The invention relates to the field of preparation methods of core-shell structure nanowires.

Background

The silicon carbide nanowire material has the advantages of high length-diameter ratio, high current emission density, lower threshold emission electric field, high strength, high rigidity, high thermal conductivity, low thermal expansion coefficient and the like, and has wide application prospect in the aspects of photoelectric devices such as field emission displays, microwave power amplification tubes, x-ray source tubes and the like, light-weight high-strength high-rigidity composite material members, hydrogen storage, photocatalysts, sensors and the like. However, the nano material has a very large specific surface area, so that the surface inevitably generates defects, and the surface defects seriously inhibit the field emission property of the silicon carbide and greatly reduce the field emission efficiency. Research shows that a layer of SiO is coated on the surface of the SiC nanowire₂Formation of SiC/SiO by oxidation layer₂The core-shell structure can greatly reduce the surface defects of the nano material, so that the nano wire has more excellent field emission, more efficient photoelectrocatalysis, and special photoluminescence and other characteristics.

At present, the preparation method of the core-shell structure nanowire is various, and mainly comprises a laser ablation method, an arc discharge method, a chemical vapor deposition method, a sol-gel method, a carbothermic method and the like. Although the method can prepare the core-shell structure nanowire, the following defects exist: 1) the preparation process is complex, the requirements on raw materials and reaction conditions are strict, the equipment is complex, the cost is high, the operation is not easy, and the cost is high; 2) most prepared products contain catalyst impurities (such as Ni, Fe and the like) or are not uniform in appearance (such as cross, net, chain bead-like and the like), and the performance of the nano-wire is seriously influenced; 3) the thickness of the oxide layer is not controllable in the preparation process, and the core-shell structure nanowire with oxide layers with different thicknesses needs to be prepared through post-treatment (such as acid, alkali washing or oxidation) so as to further increase the preparation period and cost.

Disclosure of Invention

The invention provides a preparation method for obtaining core-shell structure nanowires based on water gas shift reaction and carbothermic reduction reaction, aiming at solving the technical problems of complex preparation process, harsh raw materials and reaction conditions, low product purity and uncontrollable oxide layer thickness of the existing core-shell structure nanowires.

A preparation method for obtaining core-shell structure nanowires based on water gas shift reaction and carbothermic reduction reaction comprises the following steps:

firstly, silicon powder pretreatment:

putting the silicon powder into a high-temperature high-humidity box, controlling the temperature of the high-temperature high-humidity box to be 80-150 ℃ and the humidity to be 20% -98% R.H, carrying out heat preservation treatment, and then cooling the furnace to obtain silicon powder with oxidized humidity;

synthesis of Si/SiC nanowires

Putting the silicon powder treated in the step one into a graphite crucible, adding a graphite cover, putting into an atmosphere sintering furnace, vacuumizing, and controlling the vacuum degree to be 0.1-1.0 Pa; then argon is filled into the atmosphere sintering furnace; then controlling the heating rate to be 5-20 ℃/min, heating to 500-900 ℃ and preserving heat for 0.5-1.0 h, then controlling the heating rate to be 5-20 ℃/min, heating to 1000-1350 ℃ and preserving heat for 0.5-6.0 h; and then cooling the furnace body to 300-600 ℃, cooling the furnace body to room temperature along with the furnace, and opening the furnace to obtain the core-shell structure nanowire, thereby completing the preparation.

Wherein the graphite crucible and the graphite cover serve as a carbon source.

The invention has the beneficial effects that:

according to the invention, the silicon source is subjected to high-temperature and high-humidity treatment, so that amorphous SiO is generated on the surface of the silicon powder₂An oxidation layer which reacts with Si to generate SiO gas in the synthesis process of the nanowire, and on the other hand, water in the silicon powder reacts with graphite to generate a large amount of H in the water gas shift reaction in the synthesis process of the nanowire₂With CO, SiO and CO providing the growth molecule, H, for nanowire growth₂SiO with nanowire surface₂The reaction is carried out, and the atmosphere concentration in the growth process of the nanowire is controlled by adjusting the humidity of the silicon powder, so that the aims of controlling the growth of the nanowire and the thickness of an oxide layer are fulfilled.

1. The invention has the advantages of simple preparation process, energy saving, environmental protection, easy control, low cost and the like.

2. The nano-wire prepared by the invention does not contain catalyst, silicon or carbon and other impurities, does not need acid washing or alkali washing, and has the advantages of uniform appearance and purity higher than 90%.

3. The core-shell structure nanowire prepared by the invention has the advantages of controllable thickness of an oxide layer, close combination of atomic scales at an interface and the like.

4. The core-shell structure nanowire prepared by the invention has wide application prospect in the fields of aviation, reinforced composite materials, medicine, semiconductors and the like.

The method is used for preparing the SiC nanowire with the core-shell structure.

Drawings

FIG. 1 is an XRD pattern of a core-shell structure nanowire prepared in the first example;

FIG. 2 is a TEM image of the core-shell structure nanowire prepared in the first example; (ii) a

FIG. 3 is an XRD pattern of the core-shell structure nanowire prepared in example two;

FIG. 4 is a TEM image of the core-shell structure nanowire prepared in example two;

FIG. 5 is an XRD pattern of the core-shell structure nanowire prepared in example three;

FIG. 6 is a TEM image of the core-shell structure nanowire prepared in example III.

Detailed Description

The technical solution of the present invention is not limited to the specific embodiments listed below, and includes any combination of the specific embodiments.

The first embodiment is as follows: the preparation method for obtaining the core-shell structure nanowire based on the water gas shift reaction and the carbothermic reduction reaction comprises the following steps:

firstly, silicon powder pretreatment:

putting the silicon powder into a high-temperature high-humidity box, controlling the temperature of the high-temperature high-humidity box to be 80-150 ℃ and the humidity to be 20% -98% R.H, carrying out heat preservation treatment, and then cooling the furnace to obtain silicon powder with oxidized humidity;

secondly, synthesizing the SiC nanowire:

putting the silicon powder treated in the step one into a graphite crucible, adding a graphite cover, putting into an atmosphere sintering furnace, vacuumizing, and controlling the vacuum degree to be 0.1-1.0 Pa; then argon is filled into the atmosphere sintering furnace; then controlling the heating rate to be 5-20 ℃/min, heating to 500-900 ℃ and preserving heat for 0.5-1.0 h, then controlling the heating rate to be 5-20 ℃/min, heating to 1000-1350 ℃ and preserving heat for 0.5-6.0 h; and then cooling the furnace body to 300-600 ℃, cooling the furnace body to room temperature along with the furnace, and opening the furnace to obtain the core-shell structure nanowire, thereby completing the preparation.

The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: and step one, the heat preservation treatment time is 2-48 h. The rest is the same as the first embodiment.

The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: step one, controlling the temperature of the high-temperature high-humidity box to be 150 ℃ and the humidity to be 20% R.H, and carrying out heat preservation treatment for 4 h. The other is the same as in the first or second embodiment.

The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: in the first step, the average diameter of the silicon powder is 30 nm-5 μm. The others are the same as in one of the first to third embodiments.

The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: and the graphite crucible in the second step is made of one or any combination of several of electrode graphite, high-purity graphite, carburized graphite and antioxidant graphite. The other is the same as one of the first to fourth embodiments.

The sixth specific implementation mode: the difference between this embodiment and one of the first to fifth embodiments is: and the graphite cover in the second step is made of one or any combination of several of electrode graphite, high-purity graphite, carburized graphite and antioxidant graphite. The other is the same as one of the first to fifth embodiments.

The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: and step two, argon is filled to control the initial pressure of the gas in the atmosphere sintering furnace to be-0.2-0.5 MPa. The other is the same as one of the first to sixth embodiments.

The specific implementation mode is eight: the present embodiment differs from one of the first to seventh embodiments in that: and step two, controlling the cooling rate of the furnace body to be 1-10 ℃/min. The other is the same as one of the first to seventh embodiments.

The specific implementation method nine: the present embodiment differs from the first to eighth embodiments in that: step two, controlling the initial pressure of the gas in the atmosphere sintering furnace to be 0.5 MPa; then controlling the heating rate to be 20 ℃/min, heating to 900 ℃, keeping the temperature for 1.0h, then controlling the heating rate to be 10 ℃/min, heating to 1150 ℃, keeping the temperature for 6.0 h; then the furnace body is cooled to 600 ℃ at the cooling rate of 5 ℃/min. The rest is the same as the first to eighth embodiments.

The detailed implementation mode is ten: the present embodiment differs from one of the first to ninth embodiments in that: step two, controlling the initial pressure of the gas in the atmosphere sintering furnace to be-0.2 MPa; then controlling the heating rate to be 5 ℃/min, heating to 900 ℃, keeping the temperature for 1.0h, then controlling the heating rate to be 5 ℃/min, heating to 1350 ℃, keeping the temperature for 6.0 h; then the furnace body is cooled to 300 ℃ at the cooling rate of 1 ℃/min. The other is the same as one of the first to ninth embodiments.

The following examples were used to demonstrate the beneficial effects of the present invention:

the first embodiment is as follows:

the preparation method for obtaining the core-shell structure nanowire based on the water gas shift reaction and the carbothermic reduction reaction comprises the following steps:

firstly, silicon powder pretreatment:

putting silicon powder with the diameter of 4 mu m into a high-temperature high-humidity box, controlling the temperature of the high-temperature high-humidity box to be 150 ℃ and the humidity to be 20% R.H, carrying out heat preservation treatment for 4h, and then cooling the furnace to obtain silicon powder with oxidized humidity;

synthesis of Si/SiC nanowires

Putting the silicon powder treated in the step one into a graphite crucible, adding a graphite cover, putting into an atmosphere sintering furnace, vacuumizing, and controlling the vacuum degree to be 1.0 Pa; then argon is filled into the atmosphere sintering furnace, and the initial pressure of the gas in the atmosphere sintering furnace is controlled to be 0.5 MPa; then controlling the heating rate to be 20 ℃/min, heating to 900 ℃, keeping the temperature for 1.0h, then controlling the heating rate to be 10 ℃/min, heating to 1150 ℃, keeping the temperature for 6.0 h; then the furnace body is cooled to 600 ℃ at the cooling rate of 5 ℃/min, then the furnace body is cooled to room temperature, and the core-shell structure nanowire is obtained after the furnace is opened, thus completing the preparation.

And step two, the material of the stone mill cover is electrode graphite.

The XRD pattern of the core-shell structure nanowire prepared in this example is shown in FIG. 1, wherein diamond-solid represents SiC,represents SiO₂It can be seen that only SiC and SiO are present in XRD test of the obtained product₂The characteristic peak of (1) does not contain other impurities, which indicates that the purity of the nanowire is not less than 95%, wherein SiC and SiO₂The mass fractions are respectively 49.16% and 50.84%;

the TEM image of the core-shell structure nanowire prepared in this example is shown in FIG. 2, and it can be seen from the TEM image that the nanowire has a smooth surface and a core-shell structure, the core is SiC, and the outer layer is SiO₂，SiO₂Tightly coating SiC to form a dense coating layer, the diameter of the nanowire is about 90nm, the diameter of the core is about 30nm, and SiO is arranged outside₂The layer thickness is about 30 nm.

Example two:

the preparation method for obtaining the core-shell structure nanowire based on the water gas shift reaction and the carbothermic reduction reaction comprises the following steps:

firstly, silicon powder pretreatment:

putting silicon powder with the diameter of 2 mu m into a high-temperature high-humidity box, controlling the temperature of the high-temperature high-humidity box to be 120 ℃ and the humidity to be 50% R.H, carrying out heat preservation treatment for 4h, and then cooling the furnace to obtain silicon powder with oxidized humidity;

synthesis of Si/SiC nanowires

Putting the silicon powder treated in the step one into a graphite crucible, adding a graphite cover, putting into an atmosphere sintering furnace, vacuumizing, and controlling the vacuum degree to be 0.5 Pa; then argon is filled into the atmosphere sintering furnace, and the initial pressure of the gas in the atmosphere sintering furnace is controlled to be 0.1 MPa; then controlling the heating rate to be 20 ℃/min, heating to 600 ℃, keeping the temperature for 1.0h, and then controlling the heating rate to be 20 ℃/min, heating to 1200 ℃, keeping the temperature for 4.0 h; then the furnace body is cooled to 600 ℃ at the cooling rate of 5 ℃/min, then the furnace body is cooled to room temperature, and the core-shell structure nanowire is obtained after the furnace is opened, thus completing the preparation.

And step two, the material of the stone mill cover is electrode graphite.

The XRD pattern of the core-shell structure nanowire prepared in this example is shown in FIG. 3, wherein diamond-solid represents SiC,represents SiO₂It can be seen that only SiC and SiO are present in XRD test of the obtained product₂The characteristic peak of (1) does not contain other impurities, which indicates that the purity of the nanowire is higher than 90%, wherein SiC and SiO₂The mass fractions are 84.54% and 15.46% respectively;

the TEM image of the core-shell structure nanowire prepared in this example is shown in FIG. 4, and it can be seen from the TEM image that the nanowire has a smooth surface and a core-shell structure, the core is SiC, and the outer layer is SiO₂，SiO₂Tightly coating SiC to form a compact coating layer, wherein the diameter of the nanowire is 50nm, the diameter of the SiC nanowire at the core part is 38nm, and the SiO at the outer layer₂The layer thickness was 6 nm.

Example three:

the preparation method for obtaining the core-shell structure nanowire based on the water gas shift reaction and the carbothermic reduction reaction comprises the following steps:

firstly, silicon powder pretreatment:

putting silicon powder with the diameter of 30nm into a high-temperature high-humidity box, controlling the temperature of the high-temperature high-humidity box to be 80 ℃ and the humidity to be 98% R.H, carrying out heat preservation treatment for 2h, and then cooling the furnace to obtain silicon powder with oxidized humidity;

synthesis of Si/SiC nanowires

Putting the silicon powder treated in the step one into a graphite crucible, adding a graphite cover, putting into an atmosphere sintering furnace, vacuumizing, and controlling the vacuum degree to be 0.1 Pa; then argon is filled into the atmosphere sintering furnace, and the initial pressure of the gas in the atmosphere sintering furnace is controlled to be-0.2 MPa; then controlling the heating rate to be 5 ℃/min, heating to 900 ℃, keeping the temperature for 1.0h, then controlling the heating rate to be 5 ℃/min, heating to 1350 ℃, keeping the temperature for 6.0 h; then the furnace body is cooled to 300 ℃ at the cooling rate of 1 ℃/min, and then the furnace body is cooled to room temperature, and the core-shell structure nanowire is obtained after the furnace is opened, thus completing the preparation.

And step two, the material of the stone mill cover is electrode graphite.

The XRD pattern of the core-shell structure nanowire prepared in the embodiment is shown in FIG. 5, SiC is represented by diamond-solid, and it can be seen from the XRD pattern that only the characteristic peak of SiC is observed in the obtained product, and no other impurities are contained;

the TEM image of the core-shell structure nanowire prepared in this example is shown in fig. 6, and it can be seen from the image that the surface of the nanowire is smooth and clean, and the diameter of the nanowire is about 30 nm.