CN113233916B

CN113233916B - A kind of preparation device and method of porous alumina microfiber based on microfluidic chip

Info

Publication number: CN113233916B
Application number: CN202110553650.9A
Authority: CN
Inventors: 满佳; 周晨晨; 李建勇; 于海博; 满录明; 夏荷; 祁斌; 李剑峰
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2021-05-20
Filing date: 2021-05-20
Publication date: 2022-03-11
Anticipated expiration: 2041-05-20
Also published as: CN113233916A

Abstract

The invention relates to a preparation device and method for porous alumina microfibers based on microfluidic chips. The specific steps are: mixing the base phase mixed solution and the solidified phase mixed solution through a micro-reaction device, heating to generate a polymerization reaction to obtain a microfiber green body; the microfiber green body is cleaned, aged, dried, and sintered to obtain a porous alumina microfiber. fiber. The base phase mixed liquid is composed of alumina nano-dispersion liquid, prepolymer and porogen, and the porogen is soluble starch; the solidified phase is composed of initiator, catalyst and water. The porogen is selected from soluble starch, which helps to obtain alumina microfibers with a porous structure. Porous alumina fibers have high porosity and round cross-sections, and can be used in aerospace, purification and separation, biological scaffolds, sound absorption and shock absorption.

Description

Preparation device and method of porous alumina microfiber based on microfluidic chip

Technical Field

The invention belongs to the technical field of preparation of porous ceramic microfibers, and particularly relates to a preparation device and a preparation method of porous alumina microfibers based on a microfluidic chip.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

The porous ceramic microfiber has the excellent properties of light weight, large specific surface area, good permeability, low thermal expansion, high temperature resistance, corrosion resistance, wear resistance and the like, and can be applied to the fields of aerospace, purification and separation, biological supports, sound absorption and shock absorption and the like. The porous ceramic microfiber prepared at the present stage mainly comprises methods such as electrostatic spinning, 3D printing and microfluid. In the prior art, the method for preparing micron-sized porous SiO by adopting an electrostatic spinning technology is reported₂-TiO₂The method for preparing the ceramic fiber comprises the steps of using mixed inorganic alkoxide of tetrabutyl titanate (TBT) and tetraethyl orthosilicate (TEOS) as a precursor of an electrostatic spinning solution, utilizing the rapid hydrolysis and polycondensation characteristics of the mixed inorganic alkoxide to form a three-dimensional network with amphiphilic polyvinylpyrrolidone (PVP), forming multi-scale pores in the fiber after phase separation, and preparing the micron-sized porous SiO after sintering₂-TiO₂Ceramic fibers. However, the microfiber size prepared by the electrospinning method is mainly in the micro-nano level, and depends on high-voltage equipment, and the ceramic precursor material suitable for the method is limited. The 3D printing technology can also be used for preparing the porous ceramic microfiber, and the prior document records that the porous ceramic microfiber is obtained by drying, curing and sintering after printing ceramic slurry mixed with ceramic powder, a polymer microsphere pore-forming agent and aluminum phosphate sol by an ink direct writing 3D printer, but the porous ceramic microfiber prepared by the method has poor surface quality and difficult size control, and a green body lacks flexibility and low operability. In addition, the existing literature reports a method for preparing hundred-micron porous silica ceramic fibers based on a microfluid technology, wherein a silica precursor fiber liquid column wrapped with air bubbles is generated through a water-in-oil air-encapsulated nested glass capillary structure, then a polymerization reaction of a prepolymer in a transparent precursor is initiated through downstream ultraviolet light to generate a silica microfiber green compact, and the silica microfiber is obtained after sintering. The ceramic microfiber green compact prepared by the micro-fluid technology is mainly formed by photocuring, the photocuring has high requirements on the transparency of a precursor, and the high-concentration nanoparticle dispersion can be realized and the high-transparency material of the precursor can be maintained at presentOften limited, porous ceramic microfiber preparation for opaque precursors such as alumina, zirconia, and the like, is yet to be explored further.

Disclosure of Invention

In view of the problems in the prior art, the present invention is directed to an apparatus and method for preparing porous alumina microfibers based on a microfluidic chip.

In order to solve the technical problems, the technical scheme of the invention is as follows:

a preparation method of porous alumina microfiber based on a microfluidic chip comprises the following specific steps:

mixing the base phase mixed solution and the curing phase mixed solution through a micro-reaction device, and heating to perform polymerization reaction to obtain a microfiber green compact;

and cleaning, aging, drying and sintering the microfiber green compact to obtain the porous alumina microfiber.

The base phase mixed solution consists of alumina nano dispersion liquid, prepolymer and pore-forming agent, wherein the pore-forming agent is soluble starch;

the curing phase consists of an initiator, a catalyst and water.

The present invention relates to the preparation of a porous alumina microfiber having several tens to several hundreds of micrometers-sized pores distributed from the inside to the surface. In the preparation process, the base phase and the curing phase solution are mixed and subjected to polymerization reaction under the heating condition to obtain a microfiber green compact; the microfiber green compact is sintered after being washed, aged and dried, organic matters such as polyacrylamide and starch are gradually removed in the sintering process, and the alumina nano particles are mutually bonded to form a porous ceramic structure.

The pore-forming agent in the invention is soluble starch, and can be selectively added into a base phase or a solidified phase. If a porogen is added to the cure phase, two problems arise:

first, the viscosity of the solidified phase is greatly increased, and the matrix phase also has a certain viscosity due to the high content of alumina nanoparticles dispersed therein. The reynolds number of the two-phase viscous liquid is low in the process of flowing in the micro-pipeline, the flowing mode is mainly carried out in a laminar flow mode, the convection mixing effect between the two is weak, and the diffusion mixing effect is weakened due to the high viscosity of the two phases, so that the two phases cannot be well mixed finally.

Secondly, considering the solidification effect and the strength of the fiber after solidification, the solidification phase is less than the base phase in the system proportion, namely the flow of the solidification phase flowing into the channel is less than that of the base phase, in order to promote the channel filling performance of the solidification phase, a thin needle is used as an inlet, and if the viscosity of the solidification phase is high, the needle inlet can be directly blocked.

In summary, the present invention adds soluble starch to the base phase, which increases the viscosity of the base phase to some extent, but the viscosity of the solidified phase is lower, so that the above two problems can be solved well.

In some embodiments of the invention, the starch is distributed in colloidal microfibers that, upon sintering, form pores of a size of tens to hundreds of microns.

In some embodiments of the invention, the alumina nanodispersion is comprised of alumina powder, water, dispersant; the further dispersant is ammonium citrate; further, in the alumina nano dispersion liquid, the volume ratio of alumina powder to water is 1-1.2: 1; further, the average particle size of the alumina powder is 0.8 to 1.2 μm, and further, ammonium citrate is 0.6 to 1.2% by mass of the alumina powder.

In some embodiments of the present invention, the alumina powder is present in the base phase mixture in an amount of 55 to 60wt.% and the prepolymer is present in the base phase mixture in an amount of 6 to 8 wt.%.

In some embodiments of the invention, the soluble starch is present in an amount of 2-10 wt.% of the alumina nanodispersion; still further 4-8 wt.%. The soluble starch has good adaptability with the base phase solution, and pores or pores can be formed within the range. When the content of the soluble starch is more than 10wt.%, the flowability of the base phase in the microchannel becomes poor, the time for stable preparation is reduced, and the surface of the resulting microfiber is deformed and has poor morphology.

In some embodiments of the present invention, the prepolymer is composed of the following raw materials in parts by weight: 85-86 parts of acrylamide and 14-15 parts of N, N' -methylene bisacrylamide.

In some embodiments of the invention, the initiator is present in the cured phase in an amount of 9 to 10wt.%, the catalyst is present in an amount of 2 to 3wt.%, and the remainder is water.

In some embodiments of the invention, the initiator is ammonium persulfate.

In some embodiments of the invention, the catalyst is tetramethylethylenediamine.

In some embodiments of the invention, the flow rate ratio of the base phase fluid and the solidified phase fluid is 3-7: 1, the total flow rate is 10-14 μ L/min.

In some embodiments of the invention, the temperature of the heating zone is from 45 ℃ to 70 ℃, preferably from 50 ℃ to 65 ℃. Too high or too low a temperature in the heating zone does not result in porous ceramic colloidal microfibers: if the temperature is low, curing cannot be initiated; if the temperature is too high, the oxygen barrier layer on the wall surface of the channel cannot ensure a thickness that allows the microfibers to flow smoothly.

In some embodiments of the present invention, the micro-reaction device comprises a micro-pipe, the micro-pipe is divided into a filling zone, a mixing zone and a heating zone which are adjacent, the filling zone is provided with an inlet pipe and a metal feeding pipe, the mixing zone is provided with a metal stirring micro-rod, and the heating zone is provided with a heating copper ring.

Furthermore, two metal stirring micro-rods are arranged, namely a transverse metal stirring micro-rod and a longitudinal metal stirring micro-rod which are vertically arranged at intervals, so that disturbance in the flowing process of the base phase fluid and the solidified phase fluid in the micro-channel is increased, and the two phases of liquid are uniformly mixed.

Further, the base phase inlet is located at one end of the microchannel, the curing phase inlet is arranged along a direction perpendicular to the base phase inlet, and the curing phase inlet is arranged on the side wall of the microchannel.

In some embodiments of the present invention, the base phase is first introduced into the microchannel, and after the base phase is introduced, the solidification phase is injected into the center of the channel, so that the solidification phase is uniformly diffused into the base phase.

In one embodiment, a copper ring is arranged on the side wall of the heating zone, and the copper ring is used for heating so as to enable the copper ring to generate a curing reaction.

In one embodiment, the diameter of the microchannel is 0.6 to 0.65mm and the diameter of the metal stir micro-rod is 0.2 to 0.25 mm. In one embodiment, the microchannel is made of Polydimethylsiloxane (PDMS), and is formed by inserting a metal filament into a circular cross-section channel to form a mold, and then casting liquid PDMS and heating and curing the mold. The microchannel is made of polydimethylsiloxane with air permeability, oxygen is diffused on the inner wall of the microchannel to form an oxygen inhibition layer in the process of forming the microfiber green compact, and the inhibition layer serves as a lubricating film in the process of pushing the microfiber to the downstream, so that the resistance is reduced, and the blockage is prevented.

In one embodiment, the heating zone has a length of 4.5 to 6 mm.

The base phase inlet is connected with a base phase inlet pipe, the curing phase inlet is connected with a curing phase inlet pipe, and in one embodiment, the inner diameter of the base phase inlet pipe is 0.4-0.45mm, and the outer diameter of the base phase inlet pipe is 0.7-0.78 mm; the inner diameter of the solidification phase inlet pipe is 0.1-0.15mm, and the outer diameter is 0.2-0.35 mm. In one embodiment, the base phase inlet tube is made of teflon. The material of the solidified phase inlet tube is a metal material, generally a thin needle.

In some embodiments of the invention, the cleaning solution of the green microfiber blank is an aqueous solution of initiator, and the amount of initiator in the cleaning solution is 2 to 4wt.%, further 3 wt.%.

In some embodiments of the invention, the aging solution is a mixed solution of an initiator and a catalyst, the initiator is present in the aging solution in an amount of 8 to 10wt.%, and the catalyst is present in an amount of 1 to 2 wt.%.

In some embodiments of the invention, the aging time is 1h or more and the temperature is 65 ℃ or more; preferably 1-2h, 65-75 ℃.

In some embodiments of the invention, the drying is drying at ambient temperature for 10-14 hours. During drying, the microfibers shrink in diameter.

In some embodiments of the invention, the process of sintering is: 110-.

Common pore-forming agents are divided into organic pore-forming agents and inorganic pore-forming agents, wherein starch, pine wood powder, polyvinyl alcohol, polyethylene glycol and the like belong to the organic pore-forming agents; ammonium carbonate, ammonium chloride and other high temperature decomposable salts and various carbon powders belong to inorganic pore forming agents. The type and content of the pore-foaming agent added in the invention have great influence on the porosity and morphology of the obtained porous microfiber.

The pore-forming principle of carbon powder, polyvinyl alcohol, polyethylene glycol and starch is as follows: the pore-forming agent is removed by sintering when reaching a certain temperature in the air, and holes or pores and gaps formed by stacking of the ceramic particles are left, the holes or pores are continuously reduced and removed along with the migration of the ceramic particles along with further sintering, and the moving distance and speed between the ceramic particles are limited under the condition of a certain sintering temperature, so that a large number of holes or pores are preserved.

The urea pore-forming principle is as follows: the urea is decomposed to generate gas in the sintering process, so that a plurality of pores appear in the green body

Experiments show that the pore-foaming agents except the starch have poor adaptability to the micro-fibers prepared by the method, and a porous structure cannot be formed after sintering. The starch pore-forming agent can form holes more easily, starch, a base phase and a curing phase can be well fused together, the fluidity is good, the prepared microfiber green compact is smooth in appearance, and the pore distribution of corresponding porous ceramic fibers is uniform.

One or more technical schemes of the invention have the following beneficial effects:

(1) the invention adopts the innovative formula of the traditional gel injection molding and the preparation and production mode of on-line mixing and instant thermosetting molding based on microfluid to realize the preparation of the porous alumina ceramic microfiber, and the device, the formula and the production method can be popularized to the preparation of the porous microfiber of various ceramic materials such as zirconia, silicon nitride and the like.

(2) The invention is based on a microfluid chip with cross-flow configuration, and the micro-reactor of the porous alumina microfiber green body is prepared by using materials such as a Teflon tube, a metal micro-tube and a copper sheet, and the micro-reactor is easy to manufacture and low in price. In addition, a micro-injection pump and a small heater are used as power and energy sources, so that the consumption is low, and the preparation cost is low.

(3) The invention separates the initiator and the catalyst from the traditional gel-casting ceramic slurry system, the initiator and the catalyst are mixed with water to form a solidified phase, the solidified phase is mixed with a base phase consisting of other components of the slurry system on line, and the mixture is thermally solidified and instantly formed to obtain the alumina microfiber green compact.

(4) According to the invention, porous alumina microfiber is prepared by adding pore-forming agent soluble starch into a precursor of a microfiber green body, and porous ceramic microfiber with different porosities is prepared by adjusting the content of a pore-forming agent. In addition, the diameter and the surface appearance of the porous alumina microfiber can be conveniently adjusted by controlling the flow rate of the base phase and the curing phase and the temperature of a heating zone.

(5) The micro-fluid chip micro-channel used by the invention adopts the polydimethylsiloxane material with air permeability, and in the forming process of the microfiber green body, oxygen is diffused on the inner wall of the micro-channel to form an oxygen inhibition layer, and the inhibition layer serves as a lubricating film in the process of advancing the microfiber downstream, so that the resistance is reduced, and the blockage is prevented.

(6) The prepared alumina microfiber green compact has the characteristics of large size span, uniformity, controllability, round section, good flexibility in the presence of water and high operability, and the sintered porous alumina microfiber has a guiding effect on the application of ceramic microfiber in the fields of aerospace, purification and separation, biological support, sound absorption and shock absorption and the like.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the invention and not to limit the invention.

FIG. 1 is a schematic structural diagram of an apparatus for preparing a green body of porous alumina microfiber according to example 1 of the present invention.

FIG. 2 is a flow chart of porous alumina fiber prepared in example 4 of the present invention.

FIG. 3 is a scanning electron microscope photomicrograph of the side and cross-sectional morphology of porous alumina microfibers obtained after cleaning, aging, drying and sintering of the green alumina microfiber prepared in example 4 of the present invention.

FIG. 4 is a scanning electron microscope photomicrograph of the side and cross-sectional morphology of the porous alumina microfiber of example 7.

FIG. 5 is a scanning electron microscope photomicrograph of the side and cross-sectional morphology of the porous alumina microfiber of example 8.

FIG. 6 is a scanning electron microscope photomicrograph of the side and cross-sectional morphology of the porous alumina microfiber of example 9.

FIG. 7 is a scanning electron micrograph of the side and cross-sectional morphology of the porous alumina microfiber of example 10.

FIG. 8 is a scanning electron micrograph of the side and cross-sectional morphology of the porous alumina microfiber of example 11.

FIG. 9 is a scanning electron microscope photomicrograph of the side and cross-sectional morphology of the porous alumina microfiber of example 12.

FIG. 10 is a SEM photograph of the bulk structure of example 13.

FIG. 11 is a scanning electron micrograph of the side and cross-sectional morphology of the porous alumina microfiber of example 14.

FIG. 12 is a scanning electron micrograph of the side and cross-sectional morphology of the porous alumina microfiber of example 15.

FIG. 13 is a scanning electron micrograph of the side and cross-sectional morphology of the porous alumina microfiber of example 16.

FIG. 14 is a scanning electron micrograph of the side and cross-sectional morphology of the porous alumina microfiber of example 17.

Wherein the symbols represent: 1-inlet pipe, 2-micro pipeline, 3-metal feeding pipe, 4-first metal stirring micro rod, 5-second metal stirring micro rod and 6-heating copper ring.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The invention will be further illustrated by the following examples

Example 1

The preparation device of the porous alumina microfiber based on the microfluidic chip comprises an inlet pipe 1, a microchannel 2, a metal feeding pipe 3, a first metal stirring micro-rod 4, a second metal stirring micro-rod 5 and a heating copper ring 6. The inlet tube 1 is the internal diameter and is 0.41mm, and the external diameter is 0.71mm, 2 internal diameters of microtube are 0.6mm, 3 internal diameters of metal feed pipe are 0.13mm, and the external diameter is 0.31mm, 5 diameters of first metal stirring micro-rod 4, second metal stirring micro-rod are 0.20mm, 6 thickness of heating copper ring are 0.20mm, and length along the flow direction is 5mm, 2 non-copper ring contact regions of microtube are arranged in the air, and heating copper ring 6 is connected with the heater.

Example 2

The preparation of the precursor of the porous alumina microfiber based on the microfluidic chip comprises the preparation of an alumina nano dispersion liquid, a base phase mixed liquid and a curing phase mixed liquid.

(1) Preparing an alumina nano dispersion liquid: 39g of alumina powder, 0.39g of ammonium citrate and 10g of deionized water are weighed, mixed and ball-milled for 24 hours in a planetary ball mill at 450 revolutions per minute to obtain alumina dispersion liquid with the volume ratio of the alumina powder of 50 percent.

(2) Preparing a base phase mixed solution: weighing 1g of acrylamide, 0.165g N, N' -methylenebisacrylamide, 0.55g of soluble starch and 5mL of the alumina nanodispersion described in step 1 of this example, wherein the soluble starch content was 6 wt.% of the mass of the alumina nanodispersion, and mixing by vortexing for 5 minutes.

(3) Preparing a curing phase mixed solution: weighing 1g of ammonium persulfate and 9g of deionized water, and carrying out vortex oscillation for 2 minutes to obtain 10wt.% of ammonium persulfate aqueous solution, and weighing 20 mu L of tetramethylethylenediamine and 20 mu L of deionized water, and carrying out vortex oscillation for 30s to obtain 50 vol.% of tetramethylethylenediamine aqueous solution; 500 mu L of 10wt.% ammonium persulfate aqueous solution and 20 mu L of 50 vol.% tetramethylethylenediamine aqueous solution are weighed and mixed, and vortex oscillation is carried out for 2 minutes to obtain a solidification phase mixed solution.

Example 3

The alumina nano dispersion obtained in step (1) of example 2 was used in an amount of 50 vol.%. The solidification phase mixture obtained in step 3 of example 2 was used.

Preparing a base phase mixed solution: 1g of acrylamide, 0.165g N, N' -methylenebisacrylamide, 1.165g of soluble starch and 5mL of the alumina nanodispersion described in step (1) of this example were weighed and mixed, and vortexed for 5 minutes.

Example 4

As shown in fig. 2, a method for preparing porous alumina microfiber based on microfluidic chip comprises the following steps:

the preparation of the green porous ceramic microfiber was carried out using the apparatus described in example 1 and the mixed base phase and curing phase solution described in example 2, specifically:

(1) connecting the prepared base phase with a Teflon tube through an injector and leading the base phase into an inlet tube 1 so as to enter a micro-pipeline 2; after the micro-pipe 2 is filled with the base phase fluid, the solidified phase fluid is introduced into the metal feeding pipe 3 through the Teflon pipe connected with the injector. The flow rates of the base phase fluid and the solidified phase fluid in the micro-pipeline are respectively set to be 10 mu L/min and 2 mu L/min, the temperature of the heating copper ring is set to be 60 ℃, and the test is carried out.

(2) The green microfiber prepared at the end of the microreactor in step 1 of this example was received in a 10wt.% aqueous ammonium persulfate solution, and the uncured slurry liquid on the surface of the green microfiber was washed with a 10wt.% aqueous ammonium persulfate solution, and after washing, the green microfiber was placed in an aqueous solution containing 3wt.% ammonium persulfate and 2wt.% tetramethylethylenediamine, and aged at 65 ℃ for 1 hour.

(3) After aging, the green microfiber was removed and placed on a teflon film for drying for 12 hours, during which time the diameter of the green microfiber was reduced.

(4) After drying, placing the porous microfiber green body in a sintering furnace, heating to 600 ℃ from room temperature at 1 ℃/min, and then heating to 1550 ℃ at 5 ℃/min; wherein the temperature is respectively kept at 114 ℃,235 ℃,374 ℃,495 ℃ and 600 ℃ for 1 hour, and at 1550 ℃ for 2 hours, and then the porous alumina ceramic microfiber is obtained by furnace cooling, and the morphology of the porous alumina ceramic microfiber is shown in figure 3.

Example 5

The difference from example 4 is that the preparation of a green porous ceramic microfiber was carried out using the apparatus described in example 1 and the mixed base and curing phase solution described in example 3.

Example 6

The difference from example 4 was that the temperature of the copper ring heated in step (1) was set to 55 ℃.

Comparative example 1

The difference from example 4 was that the temperature of the copper ring heated in step (1) was set to 35 ℃.

Comparative example 2

The difference from example 4 was that the temperature of the heated copper ring in step (1) was set to 75 ℃.

Comparative example 3

The difference from example 4 is that the base phase and the solidified phase used in step (1) introduced into the inlet pipe and the metal feed pipe are both mixed by mixing the base phase and the solidified phase, i.e. the microfibres are prepared by conventional gelcasting.

Example 7

The difference from example 2 is that the soluble starch content is 2wt.% of the mass of the alumina nanodispersion. The remaining operation steps were the same as in example 4, to obtain porous alumina ceramic microfibers. The results are shown in FIG. 4.

Example 8

The difference from example 2 is that the soluble starch content is 4wt.% of the mass of the alumina nanodispersion. The remaining operation steps were the same as in example 4, to obtain porous alumina ceramic microfibers. The results are shown in FIG. 5.

Example 9

The difference from example 2 is that the soluble starch content is 10wt.% of the mass of the alumina nanodispersion. The remaining operation steps were the same as in example 4, to obtain porous alumina ceramic microfibers. The results are shown in FIG. 6.

Example 10

The difference from the example 2 is that the pore-forming agent is carbon powder, and the content of the carbon powder is 2 wt% of the mass of the alumina nano dispersion liquid. The remaining operation steps were the same as in example 4, to obtain porous alumina ceramic microfibers. The results are shown in FIG. 7.

Example 11

The difference from the example 2 is that the pore-forming agent is carbon powder, and the content of the carbon powder is 8 wt% of the mass of the alumina nano dispersion liquid. The remaining operation steps were the same as in example 4, to obtain porous alumina ceramic microfibers. The results are shown in FIG. 8.

Example 12

The difference from example 2 is that the porogen is polyvinyl alcohol, and the content of polyvinyl alcohol is 2wt.% of the mass of the alumina nano dispersion. The remaining operation steps were the same as in example 4, to obtain porous alumina ceramic microfibers. The results are shown in FIG. 9.

Example 13

The difference from example 2 is that the porogen is polyvinyl alcohol, and the content of polyvinyl alcohol is 8wt.% of the mass of the alumina nano dispersion. The same procedure as in example 4 did not yield fibers, and the results of directly heating the cured precursor to obtain a bulk structure are shown in FIG. 10.

Example 14

The difference from the example 2 is that the pore-forming agent is polyethylene glycol, and the content of the polyethylene glycol is 2 wt% of the mass of the alumina nano dispersion liquid. The remaining operation steps were the same as in example 4, to obtain porous alumina ceramic microfibers. The results are shown in FIG. 11.

Example 15

The difference from the example 2 is that the pore-forming agent is polyethylene glycol, and the content of the polyethylene glycol is 8 wt% of the mass of the alumina nano dispersion liquid. The remaining operation steps were the same as in example 4, to obtain porous alumina ceramic microfibers. The results are shown in FIG. 12.

Example 16

The difference from example 2 is that the porogen is urea, and the content of urea is 2wt.% of the mass of the alumina nano-dispersion. The remaining operation steps were the same as in example 4, to obtain porous alumina ceramic microfibers. The results are shown in FIG. 13.

Example 17

The difference from example 2 is that the porogen is urea, and the content of urea is 8wt.% of the mass of the alumina nano-dispersion. The remaining operation steps were the same as in example 4, to obtain porous alumina ceramic microfibers. The results are shown in FIG. 14.

Performance testing

FIG. 3 is a scanning electron microscope photograph of the microfiber side and section of the porous alumina ceramic prepared in example 4, respectively, from which it can be seen that: the side and the cross section of the alumina ceramic microfiber are distributed with micro-open pores with the diameter of 20-60 μm, and the cross section of the microfiber is round.

Comparative example 1 no ceramic microfiber green body was obtained because the base phase and the cured phase were not heat-initiated to cure in the heating zone due to too low a temperature.

Comparative example 2 due to the excessive temperature, the oxygen barrier layer on the channel wall surface could not ensure the thickness of smooth flowing of the microfibers during the curing and forming process of the base phase and the curing phase in the heating zone, so that the microfibers were clogged in the microchannels.

In comparative example 3, under the normal temperature condition that the copper ring is not heated, the precursor liquid column in the channel can be solidified within 10s to block the channel, and the precursor in the injector can be solidified within 10s correspondingly. Even if the concentration of the curing phase component is diluted, it is difficult to increase the ratio of the base phase and the curing phase so that the porous microfiber green body can be stably produced in the microchannel for a long time with a small injection power.

As can be seen by comparing fig. 3 to 6, different amounts of porogen have a greater effect on the porosity and morphology of the microfibers, with the increasing of the starch content, the microfibers gradually increasing in porosity, with less porosity at 2wt.%, and the pore distribution being non-uniform. At 10wt.%, there are more pores, but the precursor is more viscous due to the more starch added, the preparation process is easily blocked, and the obtained microfibers have irregular morphology and poor size uniformity. The soluble starch is adapted to the solution system, and the better morphology and the concentration range of pores of the microfibers can be maintained to be 4-8%.

From fig. 7 to 8, it can be seen that the effect of carbon powder as a pore-forming agent is: increasing the content to 8 wt% also did not produce samples with significant porosity, and continued increase in content resulted in significant impairment of the flow properties of the fluid in the channels and a reduction in the quality of the microfibers produced. The reason is that the material shrinkage rate is high in the sintering process, the grain boundary migration rate of crystal grains is high, and pores left by burnt carbon powder are greatly shrunk and even eliminated.

From fig. 9 to 10, it can be seen that the polyvinyl alcohol has the following effects as a porogen: when the addition amount is 2wt.%, pores cannot be formed, when the addition amount is 8wt.%, the viscosity is too high, the microfibers cannot be prepared through the channels, and the prepared block structure can observe larger pores, the pore size of the pores is equivalent to the diameter size of the channels, and the preparation method is not suitable for preparing the porous microfibers.

From fig. 11 and 14, it can be seen that the effect of polyethylene glycol and urea as pore-forming agent is: even if different amounts are added, the microfibers with micron-sized porous structures cannot be prepared, and in addition, the addition of the two porogens causes the prepared microfibers to have poor size uniformity.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. a preparation method based on the porous alumina microfiber of microfluidic chip, is characterized in that: Concrete steps are:

Mixing the base phase mixed solution and the solidified phase mixed solution through a micro-reaction device, heating to generate a polymerization reaction to obtain a microfiber green body;

The microfiber green body is cleaned, aged, dried and sintered to obtain porous alumina microfibers;

The base phase mixed liquid is composed of alumina nano-dispersion liquid, prepolymer and pore-forming agent, and the pore-forming agent is soluble starch; the content of soluble starch is 4-8 wt.% of the alumina nano-dispersion liquid;

The solidified phase consists of initiator, catalyst and water.

2 . The method for preparing porous alumina microfibers based on a microfluidic chip according to claim 1 , wherein pores of tens to hundreds of microns are distributed from the inside to the surface of the porous alumina microfibers. 3 .

3. The method for preparing porous alumina microfibers based on a microfluidic chip as claimed in claim 1, wherein the alumina nano-dispersion is composed of alumina powder, water and a dispersant; the dispersant is ammonium citrate; In the alumina nano-dispersion, the volume ratio of alumina powder and water is 1-1.2:1; the average particle size of the alumina powder is 0.8-1.2µm, and the mass of ammonium citrate accounts for 0.6-1.2% of the alumina powder.

4. The method for preparing porous alumina microfibers based on a microfluidic chip as claimed in claim 1, wherein the content of the alumina powder in the base phase mixed solution is 55-60 wt. The polymer content is 6-8 wt.%.

5. The method for preparing porous alumina microfibers based on a microfluidic chip as claimed in claim 1, wherein the prepolymer is composed of the following raw materials in parts by weight: 85-86 parts of acrylamide, N,N' - 14-15 parts of methylenebisacrylamide;

Or, the content of the initiator in the solidified phase is 9-10wt.%, the content of the catalyst is 2-3wt.%, and the remainder is water;

Or, the initiator is ammonium persulfate;

Alternatively, the catalyst is tetramethylethylenediamine.

6. The method for preparing porous alumina microfibers based on a microfluidic chip as claimed in claim 5, wherein the flow rate ratio of the base phase fluid and the solidified phase fluid is 3-7:1, and the total flow rate is 10-14µL /min;

Alternatively, the temperature of the heating zone is 45°C-70°C.

7 . The method for preparing porous alumina microfibers based on a microfluidic chip according to claim 6 , wherein the temperature of the heating zone is 50-65° C. 8 .

8. The method for preparing porous alumina microfibers based on a microfluidic chip as claimed in claim 1, wherein the microreaction device comprises a micropipe, and the micropipe is divided into adjacent mixing areas and heating areas, and in the mixing area A metal stirring micro-rod is set, and the base-phase inlet and the solid-phase inlet are respectively set in the mixing area of the micro-pipe;

There are two metal stirring micro-rods, which are the horizontal metal stirring micro-rods and the vertical metal stirring micro-rods arranged at a vertical interval from each other;

The base phase inlet is located at one end of the microchannel, the solidified phase inlet is arranged along the direction perpendicular to the base phase inlet, and the solidified phase inlet is arranged on the sidewall of the microchannel;

The base phase first enters the microchannel, and when the base phase enters the microchannel, the solidified phase begins to be injected.

9. The preparation method of porous alumina microfibers based on microfluidic chips as claimed in claim 1, wherein the cleaning solution of the microfiber green body is an aqueous solution of an initiator, and the content of the initiator in the cleaning solution is 2- 4wt.%;

Or, the aging solution is a mixed solution of an initiator and a catalyst, and the content of the initiator in the aging solution is 8-10wt.%, and the content of the catalyst is 1-2wt.%;

Or, the aging time is greater than or equal to 1h, and the temperature is greater than or equal to 65°C;

Or, dry at room temperature for 10-14 hours.

10 . The method for preparing porous alumina microfibers based on a microfluidic chip according to claim 9 , wherein the content of the initiator in the cleaning solution is 3 wt.%. 11 .

11 . The method for preparing porous alumina microfibers based on a microfluidic chip according to claim 9 , wherein the aging time is 1-2 hours, and the temperature is 65-75° C. 12 .

12. The method for preparing porous alumina microfibers based on a microfluidic chip according to claim 1, wherein the sintering process is: 110-115°C, 230-240°C, 370-380°C, 490-500°C ℃, 590-600 ℃ for 1-1.5 hours, 1545-1555 ℃ for 2-2.5 hours, the heating rate before 600 ℃ is 0.5-1 ℃/min, and then the heating rate is 5-8 ℃/min.