CN110282995A - A kind of porous silicon carbide wood ceramic preparation based on cellulose aerogels template - Google Patents

Abstract

The invention provides a method for preparing porous silicon carbide wood ceramics based on a cellulose airgel template, using Balsa wood cellulose aerogel that removes part of hemicellulose and lignin as a template, impregnated by ceramic precursors- Preparation of porous silicon carbide wood ceramics by pyrolysis process. This method destroys part of the wood cell wall structure, opens the cell corners, penetrates part of the pit membrane, and creates more pore structures inside the template, thereby improving the absorption effect of the template on the ceramic precursor solution and improving the efficiency of the existing process. The low porosity and poor connectivity of porous silicon carbide wood ceramics lay the foundation for the functional application of porous silicon carbide wood ceramics.

Description

A preparation method of porous silicon carbide wood ceramics based on cellulose airgel template

technical field

The invention relates to a method for preparing porous silicon carbide wood ceramics based on a cellulose airgel template, and belongs to the technical field of biomass material preparation.

Background technique

Silicon carbide wood ceramics is the introduction of plant-sourced biomass materials into the preparation process of pure silicon carbide ceramics, combining the excellent physical and chemical properties of silicon carbide ceramics itself with high strength, corrosion resistance, thermal shock resistance, etc., as well as the renewable and wide sources of biomass materials. A new type of biomass-based silicon carbide composite material was obtained. Porous silicon carbide wood ceramics has broad application prospects in the fields of electrode materials, dust removal and filtration, heat insulation media, etc., but the current method of preparing porous silicon carbide wood ceramics is mainly based on solid wood The organic precursor polycarbosilane (PCS) is cracked at high temperature to obtain porous silicon carbide wood ceramics. This method of preparing porous silicon carbide wood ceramics by using solid wood directly as a bionic template faces problems such as large variability in wood microstructure and anisotropy. The finished product is simple in shape, small in size, low in porosity, and poor in pore structure connectivity, which is not conducive to further development and utilization. Therefore, it is necessary to improve the preparation method of silicon carbide wood ceramics.

The main components of wood are cellulose, hemicellulose and lignin. Cellulose endows wood with tensile strength and constitutes the basic skeleton structure of wood. Hemicellulose and lignin are filled in the cellulose skeleton as matrix substances, and the fibrils composed of cellulose are bonded together. If some hemicellulose and lignin in wood are removed by chemical means, cellulose aerogels with a three-dimensional porous structure can be obtained. Because the chemical treatment removes part of the hemicellulose and lignin of the wood, the wood cell wall structure is destroyed, the cell corners are opened, and part of the pit membrane is penetrated, so this cellulose airgel is light in weight, high in porosity, and pore connectivity. Well, while being somewhat absorbent. Based on these characteristics of cellulose aerogels, based on the impregnation-cracking process of ceramic precursors, cellulose aerogels are used as bionic templates for porous silicon carbide wood ceramics, and PCS solution is impregnated in negative pressure, which can be sintered into porous Silicon carbide wood ceramic. Compared with the existing method of using solid wood as a template, the use of cellulose airgel as a template first improves the permeability of the template, making it easier for the precursor solution to be fully impregnated; secondly, the porosity of the cellulose airgel template And the pore connectivity is higher, so it can effectively improve the problem of low porosity and poor connectivity of porous silicon carbide wood ceramics, and lay the foundation for the functional application of porous silicon carbide wood ceramics.

Contents of the invention

The object of the present invention aims at the deficiencies of the prior art, and provides a method for preparing porous silicon carbide wood ceramics using cellulose aerogel as a template. The preparation method is simple, easy to control, and low in energy consumption. Balsa wood cellulose airgel, which is chemically treated to remove part of hemicellulose and lignin, is used as a bionic template for porous silicon carbide wood ceramics, which helps to improve porous carbonization. The problem of low porosity and poor connectivity of pore structure of silicon wood ceramics can improve the quality and performance of porous silicon carbide wood ceramics. The technical solution adopted in the present invention is: a method for preparing porous silicon carbide wood ceramics based on cellulose airgel template, and its specific steps are as follows:

(1) Dissolve an appropriate amount of NaOH and Na ₂ SO ₃ in deionized water to prepare a mixed solution for later use. The concentration of NaOH and Na ₂ SO ₃ in the mixed solution is 2.5 mol/L and 0.4 mol/L, respectively.

(2) Process balsa wood (Latin name Ochroma lagopus) into a cube of a certain size, wrap it in medical degreasing gauze, and immerse it in the above mixed solution for cooking for a period of time.

(3) Take out the cooked wood block together with the gauze, wash it with deionized water, and place it in 30 wt% H ₂ O ₂ aqueous solution to continue cooking for a period of time.

(4) Take out the treated wood block together with the gauze, boil it in deionized water for 3 hours to remove the residual H ₂ O ₂ , then freeze-dry it for 24 hours, remove the wrapped gauze, and obtain the cellulose aerogel.

(5) Take an appropriate amount of polycarbosilane solid powder, dissolve it with xylene as a solvent, and configure it into a 40wt% ceramic slurry. Cut the bulk cellulose airgel into appropriate size, put it into the ceramic slurry for vacuum impregnation for 12 hours, take it out, heat it properly to remove the xylene solvent, and obtain the porous silicon carbide wood ceramic pre-sintered body.

(6) Put the pre-sintered porous silicon carbide wood ceramics into a graphite crucible, place it in a high-temperature sintering furnace for sintering, and cool down in the furnace to obtain porous silicon carbide wood ceramics.

Preferably, in the step (1), the volume of the mixed solution configured should be 20-30 times the volume of the balsa wood to be treated.

Preferably, in the described step (2), the side length of the balsa wood cube block should be controlled at 10-20mm, and the cooking time with the mixed solution is 20-24h.

Preferably, in the step (3), the cooking time with H ₂ O ₂ aqueous solution is 8-10 hours.

Preferably, in the step (5), the polycarbosilane used should be a powder of more than 100 meshes to promote dissolution, and the slurry configuration process should use magnetic stirring to mix and pay attention to sealing the container to prevent xylene volatilization and block air condensation The glue should be cut into sheets with a thickness not exceeding 3mm, and the vacuum degree of vacuum impregnation should be 0.08MPa.

Preferably, in the step (6), the sintering temperature is 1400-1500°C, the whole process is protected by argon, the heating rate is 5-15°C/min, the heating is stopped after 1 hour of heat preservation, and the sample is cooled with the furnace.

Compared with the prior art, the present invention has the following advantages and effects:

1. Using cellulose aerogel as the biomimetic template of porous silicon carbide wood ceramics, the precursor impregnation-cracking process was used to prepare porous silicon carbide wood ceramics. The permeability of the bulk solution is greatly improved, the required impregnation time is shorter, and the impregnation is more complete, so the amorphous carbon content in the ceramic product that has a negative impact on the mechanical strength is less.

2. Compared with solid wood, there are a large number of visible and invisible pore structures in cellulose airgel templates. These pore structures can be replicated by the precursor impregnation-cracking process. The porosity and pore connectivity of the obtained porous wood ceramic products It has been greatly improved, effectively improving the problems of low porosity and poor connectivity of porous silicon carbide wood ceramics under the existing technology, and laying a foundation for the functional application of porous silicon carbide wood ceramics.

3. The preparation method has simple flow, simple process, easy control, low energy consumption, good development prospects and the value of further research.

Detailed ways

Below in conjunction with specific implementation example, the present invention is described in detail:

Example 1

(1) Take 40g NaOH and 20.16g Na ₂ SO ₃ and carefully dissolve them in 400ml deionized water to prepare a mixed solution for later use.

(2) Process 20cm ³ bal fir into cubes of 20mm square, wrap them in medical degreasing gauze, immerse in the above mixed solution and cook for 20h.

(3) Take out the cooked wood block together with the gauze, wash it with deionized water, and place it in 30wt% H ₂ O ₂ aqueous solution to continue cooking for 8 hours. Take an appropriate amount of poplar wood powder and impregnate the ceramic slurry of the same quality, mix well and let it stand for 24 hours.

(4) Take out the treated wood block together with the gauze, boil it in deionized water for 3 hours to remove the residual H ₂ O ₂ , then freeze-dry it for 24 hours, remove the wrapped gauze, and obtain the cellulose aerogel.

(6) Grinding 30 g of polycarbosilane solid into 100-mesh powder, dissolving it in xylene as a solvent, and preparing a 40 wt % ceramic slurry. Cut the massive cellulose airgel into 2 mm thick square pieces, put them into the ceramic slurry and immerse them in a vacuum of 0.08 MPa for 12 hours, take them out, and heat them appropriately to remove the xylene solvent to obtain a pre-sintered porous silicon carbide wood ceramics.

(6) Put the porous silicon carbide wood ceramic pre-sintered body flat into a graphite crucible, place it in a sintering furnace and sinter it under the protection of argon gas at 1400 °C, the heating rate is 5 °C/min, and keep it for 1 hour. The sample is cooled with the furnace to obtain porous carbonization Silicon wood ceramics.

Example 2

(1) Take 80g NaOH and 40.32g Na ₂ SO ₃ and carefully dissolve them in 800ml deionized water to prepare a mixed solution for later use.

(2) Process 40cm ³ Bal fir into cubes of 15mm square, immerse in the above mixed solution and cook for 24h.

(3) Take out the cooked wood block together with the gauze, wash it with deionized water, and place it in 30 wt% H ₂ O ₂ aqueous solution to continue cooking for 10 h. Take an appropriate amount of poplar wood powder and impregnate the ceramic slurry of the same quality, mix well and let it stand for 24 hours.

(4) Take out the treated wood block together with the gauze, boil it in deionized water for 3 hours to remove the residual H ₂ O ₂ , then freeze-dry it for 24 hours, remove the wrapped gauze, and obtain the cellulose aerogel.

(6) Grind 60 g of polycarbosilane solid into 100-mesh powder, dissolve it in xylene as a solvent, and configure it into a 40 wt % ceramic slurry. Cut the massive cellulose airgel into 3 mm thick square pieces, put them into the ceramic slurry and immerse them in a vacuum of 0.08 MPa for 12 hours, take them out, and heat them properly to remove the xylene solvent to obtain a porous silicon carbide wood ceramic pre-sintered body.

(6) Put the porous silicon carbide wood ceramic pre-sintered body flat into a graphite crucible, place it in a sintering furnace and sinter it under the protection of argon gas at 1500°C, heat up at a rate of 10°C/min, keep it for 1h, and the sample is cooled with the furnace to obtain porous carbonization Silicon wood ceramics.

Claims (6)

1. a kind of porous silicon carbide wood ceramic preparation based on cellulose aerogels template, which is characterized in that including as follows Several steps:

(1) appropriate NaOH and Na is weighed₂SO₃Be dissolved in deionized water configure mixed solution it is spare, in mixed solution NaOH with Na₂SO₃Substance withdrawl syndrome be respectively 2.5mol/L and 0.4mol/L；

(2) Ba Ersha wooden (latin name Ochroma lagopus) is processed as the cube of certain size, is wrapped in medical degreasing In gauze, boiling is immersed in above-mentioned mixed solution for a period of time；

(3) wooden unit after boiling is taken out together with gauze, after being washed with deionized water, is placed in the H of 30wt%₂O₂Aqueous solution Middle continuation boiling is for a period of time；

(4) by treated, wooden unit takes out together with gauze, is placed in boiling 3h in deionized water, removes remaining H₂O₂, later Freeze-drying for 24 hours, removes the gauze of package, obtains cellulose aerogels；

(5) appropriate Polycarbosilane solid powder is taken, is dissolved using dimethylbenzene as solvent, is configured to the ceramic slurry of 40wt%, it will Bulk fibers element aeroge is cut into suitable dimension, is put into ceramic slurry and takes out after vacuum impregnation 12h, and appropriate heating removes two Toluene solvant obtains the ceramic pre-sintered body of porous silicon carbide wood；

(6) the ceramic pre-sintered body of porous silicon carbide wood is put into graphite crucible, atmosphere sintering in high temperature sintering furnace is placed in, with furnace It is cooling to obtain porous silicon carbide wood ceramics.

2. a kind of porous silicon carbide wood ceramic preparation based on cellulose aerogels template according to claim 1, It is characterized in that, the mixed liquor volume of configuration should be 20-30 times of Ba Ersha wood volume to be processed in the step (1).

3. a kind of porous silicon carbide wood ceramic preparation based on cellulose aerogels template according to claim 1, It is characterized in that, the side length of Ba Ersha cube wooden unit should be controlled in 10-20mm in the step (2), steamed with mixed solution The time boiled is 20-24h.

4. a kind of preparation method of the wooden ceramic body of silicon carbide according to claim 1, which is characterized in that the step (3) in, H is used₂O₂The time of aqueous solution boiling is 8-10h.

5. a kind of porous silicon carbide wood ceramic preparation based on cellulose aerogels template according to claim 1, It is characterized in that, Polycarbosilane used should be the powder of 100 mesh or more to promote to dissolve, and slurry configured in the step (5) Journey, which should use magnetic agitation to mix and pay attention to sealing in container, prevents dimethylbenzene from volatilizing, and Monolithic aerogel should be cut into thickness and not surpass The sheet of 3mm is crossed, vacuum-impregnated vacuum degree should be 0.08MPa.

6. a kind of porous silicon carbide wood ceramic preparation based on cellulose aerogels template according to claim 1, It is characterized in that, sintering temperature is 1400-1500 DEG C in the step (6), overall process leads to argon gas protection, heating rate 5-15 DEG C/min, stop heating, sample furnace cooling after keeping the temperature 1h.