CN114213142B - A kind of preparation method of extruded 3D printing silicon aluminum oxide ceramic aerogel - Google Patents

Abstract

The invention discloses a preparation method of extruded 3D printing silicon-alumina oxide ceramic aerogel, which aims to realize the additive manufacturing of aluminum oxide ceramic aerogel and satisfy the requirements of low density and low heat of silicon-alumina oxide ceramic aerogel. Under the requirements of electrical conductivity and high temperature resistance, silicon-alumina-oxide ceramic inks can achieve controlled thermal curing by means of temperature induction, and obtain 3D-printed silicon-alumina-oxide ceramic aerogels with high structural integrity and high shape fidelity. The technical solution is: preparing a thermally curable silicon-alumina oxide ceramic ink, 3D printing a silicon-alumina oxide ceramic ink, temperature-controlled thermal curing, supercritical drying, and high-temperature heat treatment to obtain a 3D-printed silicon-alumina oxide ceramic aerogel. The invention can realize the controllable thermal curing of the silicon-alumina oxide ceramic ink, and obtain 3D printing silicon-alumina oxide ceramics with low density, low thermal conductivity, high temperature resistance, high structural integrity and high shape fidelity, and aerogel The hollow porous structure can be maintained after calcination at 1100℃.

Description

A kind of preparation method of extruded 3D printing silicon aluminum oxide ceramic aerogel

technical field

The invention relates to the technical field of additive manufacturing of ceramic aerogels, in particular to a preparation method of extruded 3D printed silicon-alumina oxide ceramic aerogels.

Background technique

Ceramic aerogels have high porosity, large surface area, low density, low thermal conductivity, and excellent thermal oxidation resistance, and are widely used in thermal/acoustic/electrical insulation, catalyst supports, filters, and energy storage materials. However, ceramic aerogels have inherent brittleness problems, and it is difficult to impart complex structures and shapes to ceramic aerogels by traditional subtractive manufacturing processes such as turning, milling, planing, and grinding. Compared with the subtractive manufacturing process, additive manufacturing (also known as three-dimensional printing, 3D printing) provides new ideas and new solutions for the custom molding and complex structural design of ceramic aerogels.

3D printing is a new technology that relies on accumulating materials layer by layer to realize the transformation of 3D models into solid objects. It is known as the main promoter of the fourth industrial revolution. So far, three main 3D printing techniques have been applied to make ceramic aerogels, which include extrusion 3D printing, inkjet 3D printing, and photocuring 3D printing. Among these printing strategies, the biggest advantage of extrusion 3D printing is the good compatibility of its inks. A wide variety of materials, including zero-dimensional nanoparticles, one-dimensional nanowires or nanofibers, and two-dimensional nanosheets, can be integrated into ink formulations to achieve tunable printing rheology and impart functionalities to 3D printed aerogel designs. Benefiting from the low complexity of extrusion 3D printing equipment and negligible limitations of printing conditions, existing graphene, graphene oxide, carbon nanotubes, silver nanowires, boron carbide, cellulose, resorcinol-formaldehyde and carbon All aerogels can achieve additive manufacturing, which provides a precedent demonstration and theoretical support for 3D printing ceramic aerogels.

Silica aerogel is one of the types of ceramic aerogel, and its additive manufacturing technology is a hot research direction at present. [ACS Applied Materials&Interfaces, 2018, 10(26): 22718-22730] reported a preparation method for extrusion 3D printing of silk protein-containing silica aerogels. The 3D printed aerogels exhibited low density (0.11-0.20 g cm ^-3 ) and low thermal conductivity (0.033 to 0.039 W·m ^-1 ·K ^-1 ). However, silica aerogel prepared by this extrusion 3D printing method is essentially an organic-inorganic hybrid material, and a large amount of organic matter is easily decomposed when the temperature exceeds 300 °C, which cannot meet the requirements of high-temperature applications; [Applied Materials Today, 2021, 24: 101083] reported a preparation method of photocuring 3D printing silica aerogel, which can realize the construction of aerogel on the sub-micron scale and endow the aerogel with fine and complex structure, and finally obtained 3D printing silica aerogel. The aerogel has low density (0.16 g·cm ^-3 ) and high specific surface area (580 m ² ·g ^-1 ), and its performance is comparable to that of traditional silica aerogel. However, the significant disadvantage of this photocuring 3D printing method for preparing silica aerogel lies in its harsh molding conditions, which usually rely on photosensitive resin to maintain the material shape, and achieve ceramic transformation through heat treatment at about 700 °C. In addition to the above methods, [Nature, 2020, 584(7821): 387-392] reported a preparation method of extruded 3D printed silica aerogel, in which ammonia vapor induced the generation of silica sol in ink The polycondensation reaction, macroscopically manifested as the spontaneous curing of the ink in an ammonia vapor atmosphere, and after supercritical drying, the 3D printed silica aerogel showed high structural integrity and high shape fidelity. However, this method aims to obtain pure 3D printed silica aerogels. According to the literature [Advances in Colloid and Interface Science 282(2020):102189], the temperature resistance of pure silica aerogels is theoretically difficult to exceed 600 °C, which limits its high temperature applications.

At present, although some progress has been made in the additive manufacturing technology of silicon oxide aerogels, the existing 3D printing methods of silicon oxide aerogels have design defects and are difficult to be generally applied to additive manufacturing of ceramic aerogels, especially for 3D printing silicon oxide aerogels. For oxide ceramic aerogel, no relevant literature has been found to report its 3D printing process and method. Compared with silicon oxide aerogel, silicon aluminum oxide ceramic aerogel has higher high temperature resistance, and the operating temperature is higher than the limit temperature of silicon oxide aerogel (600℃), which is more conducive to meet the needs of high temperature heat insulation design . To this end, the realization of additive manufacturing of silicon-alumina oxide ceramic aerogels has practical significance for high-temperature applications of porous ceramic materials.

In summary, silicon-alumina oxide ceramic aerogel has excellent high temperature resistance and is an ideal material for high-temperature heat insulation. The existing 3D printing method of silicon oxide aerogel is difficult to apply to silicon-alumina oxide ceramic aerogel At the same time, the method of preparing silicon aluminum oxide ceramic aerogel by extrusion 3D printing technology has not been reported yet. For this reason, it is still a major technical problem to develop a preparation method for extruded 3D printed silicon-alumina oxide ceramic aerogel under the requirement of low density, low thermal conductivity and high temperature resistance of ceramic aerogel. The key to realizing the preparation and application of 3D printed oxide ceramic aerogels in the industrial and civil fields in the future.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a preparation method of extruded 3D printing silicon-alumina oxide ceramic aerogel, which can meet the performance requirements of low density, low thermal conductivity and high temperature resistance of silicon-alumina oxide ceramic aerogel. The silicon-alumina oxide ceramic ink can achieve controlled thermal curing by means of temperature induction, thereby obtaining 3D printed silicon-alumina oxide ceramic aerogels with high structural integrity and high shape fidelity.

To achieve the above object, the technical scheme adopted by the present invention is as follows:

The present invention is an extruded 3D printing silicon-alumina oxide ceramic aerogel. After supercritical drying, the main components of the initial state 3D-printing silicon-alumina oxide aerogel are composed of amorphous silicon oxide and crystalline boehmite. Among them, silicon oxide accounts for 60-100% of the mass fraction of the initial 3D printed silicon-alumina oxide aerogel, and boehmite accounts for 0-40% of the mass fraction of the initial 3D-printed silicon-alumina oxide aerogel; after heat treatment , the boehmite inside the initial state 3D printed silicon-alumina oxide aerogel was transformed into the corresponding γ-phase alumina to obtain the 3D-printed silicon-alumina oxide ceramic aerogel.

The preparation method of the extrusion 3D printing silicon-alumina oxide ceramic aerogel mainly comprises the following steps: preparing a thermally curable silicon-alumina oxide ceramic ink, extruding the 3D-printing silicon-alumina oxide ceramic ink, temperature-controlled heat Curing, supercritical drying and high temperature heat treatment.

Specific steps are as follows:

The first step is to prepare a thermally curable silicon-alumina-oxide ceramic ink by:

1.1 Mix nano-silica powder, water-based silica sol, water-based aluminum sol, polyvinyl alcohol, urea and water, and stir to prepare the initial mixed slurry. Among them, nano-silica powder acts as an ink thickener to adjust the rheological properties of the ink; polyvinyl alcohol acts as an ink cross-linking agent to assist the nano-silica powder to adjust the rheological properties of the ink; urea acts as a temperature-induced catalyst to decompose and release alkaline ammonia, It can promote the polycondensation reaction of water-based silica sol and water-based alumina sol, which is the key to the thermal curing of silica-alumina oxide ceramic ink. In this ink composition, nano-silica powder, water-based silica sol, water-based alumina sol, polyvinyl alcohol, urea and water respectively account for the mass fraction of silica-alumina oxide ceramic ink in the range of 10, 15-55, 0-50, 0- 5, 1 to 5, 1 to 40.

The nano-silica powder refers to gas-phase silica powder with a specific surface area of 50-1000 m ² ·g ^-1 ;

The water-based silica sol refers to an aqueous dispersion of nano-silica particles with a solid content of about 40 wt%;

The water-based alumina sol refers to a boehmite aqueous dispersion with a solid content of about 20wt%;

1.2 Put the initial mixed slurry in a centrifugal defoaming mixer and stir for 1-30 minutes to obtain a silicon-alumina oxide ceramic ink that is free of bubbles, heat-curable and self-supporting. In the preparation process, the revolution speed of the mixer is controlled at 400-1000rpm, and the rotation speed is controlled at 100-800rpm;

The second step is to extrude the 3D printed silicon aluminum oxide ceramic ink to obtain a 3D printed part. The method is as follows:

The silicon aluminum oxide ceramic ink is encapsulated in the 3D printer silo, and the structure and shape of the silicon aluminum oxide ceramic aerogel is designed based on the three-dimensional modeling software. According to the surface accuracy requirements, the 3D printer nozzle with the corresponding outlet diameter is selected. The printing path is planned according to the numerical control programming language (G code), and the nozzle of the 3D printer is controlled to print on a two-dimensional plane at a certain printing speed. After printing a layer of ink, the nozzle of the printer is automatically lifted up according to the programmed path, and the next layer is carried out. print until a 3D print is obtained;

The diameter of the outlet of the nozzle of the 3D printer is 0.1 to 3.0 mm;

The certain printing speed means that the movement speed in the x-axis and y-axis directions of the 3D printer is controlled within 0.2 to 40 mm/s;

The third step, temperature-controlled heat curing, the method is:

The 3D printed parts prepared in the second step are placed in a closed container, and the 3D printed parts are heated in a constant temperature water bath to decompose the urea contained in the 3D printed parts and release alkaline ammonia. Under the catalysis of alkaline ammonia , the polycondensation reaction occurs between the nano-silica particles and the boehmite particles in the 3D printing part, and the 3D printing part gel solidifies, and then the thermal curing 3D printing part is obtained;

The constant temperature range means that the external heating temperature is controlled at 60-90°C;

The fourth step, supercritical drying, to obtain the initial state 3D printing silicon aluminum oxide aerogel, the method is:

The thermally cured 3D printed parts prepared in the third step are soaked in anhydrous ethanol (concentration ≥99.5%) at a certain temperature, and the solvent is replaced 3 to 8 times to remove impurities, and the replacement time is 6 to 36 hours each time. The thermally cured 3D printed parts containing ethanol were then dried in a _CO2 supercritical drying fluid to obtain the initial 3D printed silicon-alumina oxide aerogel;

The certain temperature refers to a temperature range of 25 to 80 °C;

The CO ₂ supercritical drying conditions refer to a temperature of 35 to 70° C. and a pressure of 8 to 15 MPa.

The fifth step, high temperature heat treatment, to obtain 3D printing silicon aluminum oxide ceramic aerogel, the method is:

The initial state 3D printed silicon-alumina oxide aerogel prepared in the fourth step was heat-treated in a muffle furnace controlled by a certain program at a constant temperature for 2 hours, and then cooled naturally to obtain a 3D-printed silicon-alumina oxide ceramic aerogel. The purpose of high temperature heat treatment is to realize the transformation of boehmite in the initial state 3D printed silica-alumina oxide aerogel to γ-phase alumina, and to remove a small amount of organic polyvinyl alcohol, drying residual ethanol and a small amount of adsorbed water during the heat treatment process to obtain 3D printed silicon-alumina-oxide ceramic aerogels with porous ceramming structures.

The certain program control means that the heating rate of the muffle furnace is controlled at 1-10°C/min;

The constant temperature refers to the steady-state heat treatment temperature reached by the muffle furnace after the temperature rise under program control, and the selection range of the constant temperature is controlled at 600-1100°C.

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

(1) The urea in the first step of the present invention acts as a temperature-inducing catalyst for the thermally curable silicon-alumina oxide ceramic ink. When the temperature is close to or higher than 60°C, the urea will decompose itself and release basic ammonia. Under the catalytic action of the ink, a polycondensation reaction occurs between the silica sol particles and the boehmite particles in the ink, so that the silica-alumina oxide ceramic ink can be thermally cured and formed. Controlled thermal curing to obtain 3D printed silicon-alumina-oxide ceramic aerogels with high structural integrity and high shape fidelity. In the first step, urea is evenly mixed in the silicon-alumina oxide ceramic ink. When the external temperature meets the urea decomposition conditions, theoretically, no matter what volume of 3D printed parts can achieve complete thermal curing, the silicon-alumina oxide ceramic gas can achieve complete thermal curing. Additive manufacturing of gels is not limited by size requirements. In addition, urea has the property that it does not decompose at room temperature, and according to this property, it is possible to store ink in a room temperature environment.

(2) In the first step of the present invention, adding nano-silica powder and polyvinyl alcohol to the silicon aluminum oxide ceramic ink can adjust the rheological properties of the ink, because the two tend to form stable and reversible hydrogen in the ink. key cross-linked network. Under the action of external force, the silicon-alumina oxide ceramic ink exhibits a shear-thinning flow behavior, which ensures that the ink can be smoothly extruded from the nozzle; after the external force is removed, the ink exhibits solid characteristics and can be self-supporting after printing. Avoid structural damage caused by gravity collapse.

(3) The 3D printed silicon-alumina-oxide ceramic aerogel prepared by the present invention has relatively low density and thermal conductivity. In the third step, the thermally cured 3D printed parts can be converted into low-density 3D-printed silicon-alumina-oxide ceramic aerogels by supercritical CO ₂ drying, with a density distribution ranging from 0.14 to 0.62 g·cm ^-3 ; low density means 3D printing The silicon-alumina oxide ceramic aerogel has abundant pore structure inside, which makes the 3D printed silicon-alumina oxide ceramic aerogel exhibit low thermal conductivity, and the thermal conductivity ranges from 0.029 to 0.104W·m ^-1 ·K ^-1 , The low density and low thermal conductivity further demonstrate that the method of the present invention can be used for additive manufacturing of silicon-alumina-oxide ceramic aerogels.

(4) Using the method of the present invention, a 3D printed silicon-alumina-oxide ceramic aerogel with robust structure and high temperature resistance can be obtained. In the fifth step, heat treatment of the initial state 3D printed silicon-alumina oxide aerogel can realize partial sintering of silicon oxide in the aerogel and the transformation of boehmite to γ-phase alumina, which makes the 3D printing of silicon-alumina oxide ceramic aerogel possible. It exhibits structural robustness. Fumed silica has good sintering resistance and can effectively avoid the collapse of the internal pore structure of the aerogel during heat treatment, which is why the aerogel can maintain a high specific surface area after heat treatment. The specific surface area distribution of 3D printed silicon-alumina oxide ceramic aerogels ranges from 172 to 308 m ² ·g ^-1 , and the high temperature specific surface area retention rate is 55 to 99%. The relatively high specific surface area and specific surface area retention rate mean that the The 3D printed silicon-alumina oxide ceramic aerogel of the invention has excellent high temperature resistance performance. Experiments have shown that the 3D-printed silicon-alumina oxide ceramic aerogel of the invention can still maintain a hollow porous structure after being calcined at 1100 °C, and no structural damage occurs. Damaged shape.

(5) 3D printing silicon-alumina-oxide ceramic aerogels with different surface precisions can be obtained by using the method of the present invention. 3D printed silicon-alumina oxide ceramic aerogel is used as a thermal insulation component, and the components are precisely and tightly assembled to achieve high-efficiency thermal insulation. In the second step of 3D printing the silicon-alumina oxide ceramic ink, the nozzle diameter of different printers directly affects the surface accuracy of the 3D printed part. glue. In the present invention, different printer nozzles within the range of 0.1-3 mm are selected for printing, and 3D printing silicon-alumina oxide ceramic aerogels with different surface precisions can be obtained.

(6) The 3D printing silicon-alumina oxide ceramic aerogel of the present invention has abundant raw material sources, low price, simple 3D printing method and strong practicability, and urea as a temperature-induced catalyst has the advantages of non-toxicity and harmlessness. The printing method is expected to realize the mass production of silicon aluminum oxide ceramic aerogel, which has certain practical significance for industrial application.

Description of drawings

Fig. 1 is a flow chart of the preparation method of the 3D printing silicon-alumina-oxide ceramic aerogel of the present invention.

FIG. 2 is the initial state 3D printed silicon-alumina oxide aerogel prepared in the fourth step of Example 1 of the present invention. The additive manufacturing of the initial 3D printed silicon-alumina oxide aerogel uses a 1.2mm diameter nozzle to deposit ink, and the ink is overlapped to form a layer-by-layer scaffold structure.

FIG. 3 is the 3D printed silicon-alumina-oxide ceramic aerogel prepared in the fifth step of Example 1 of the present invention. The 3D printed silicon-alumina-oxide ceramic aerogel can still maintain the hollow and porous scaffold structure after heat treatment at 1100 °C for 2 h.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and embodiments. In the examples, the density, thermal conductivity, specific surface area and high temperature specific surface area retention rate of the 3D printed silicon-alumina oxide ceramic aerogels concerned by the present invention are mainly studied. Among them, in the examples, the density of the 3D printed silicon-alumina oxide ceramic aerogel was obtained by calculating the volume and mass, the thermal conductivity was tested by a thermal conductivity constant instrument (Hotdisk), and the specific surface area was calculated by BET theory using nitrogen adsorption equipment ( The nitrogen adsorption-desorption isotherm collected by Quantachrome) was obtained, and the high-temperature specific surface area retention rate was obtained by calculating the ratio of the specific surface area of the same formula sample to the specific surface area of the initial 3D printed silicon-alumina oxide aerogel at different heat treatment temperatures.

In the process of preparing 3D printed silicon aluminum oxide ceramic aerogel, the amount of water-based silica sol and water-based aluminum sol in the first step and the heat treatment temperature in the fifth step have an effect on the density and thermal conductivity of 3D printed silicon aluminum oxide ceramic aerogel. The density, thermal conductivity, specific surface area and high temperature specific surface area retention rate of the 3D printed silicon-alumina oxide ceramic aerogels concerned in the present invention have little effect. The following discusses the relationship between the three key parameters of the amount of water-based silica sol, the amount of water-based aluminum sol, and the heat treatment temperature on the density, thermal conductivity, specific surface area and high-temperature specific surface area retention rate of 3D printed silica-alumina oxide ceramic aerogels. , and further illustrate the present invention through examples, the protection scope of the present invention should not be construed as being limited to these examples.

As shown in Figure 1, preparation example 1 comprises the following steps:

The first step is to prepare a thermally curable silicon-alumina-oxide ceramic ink by:

1.1 Mix fumed silica powder with a specific surface area of 400m ² ·g ^-1 , 40wt% aqueous silica sol, 20wt% aqueous alumina sol, polyvinyl alcohol, urea and water, and stir to prepare a primary mixed slurry. In the ink composition, the mass fraction of fumed silica powder, water-based silica sol, water-based alumina sol, polyvinyl alcohol, urea and water accounted for 10, 30, 36, 1, 3, and 20 of the silicon-alumina oxide ceramic ink, respectively.

1.2 The initial mixed slurry was placed in a centrifugal defoaming mixer and stirred for 3 minutes to obtain a silicon-alumina oxide ceramic ink without bubbles, heat-curable, and self-supporting. In the preparation process, the revolution speed of the mixer is controlled at 800rpm, and the rotation speed is controlled at 400rpm;

The second step is to extrude the 3D printed silicon aluminum oxide ceramic ink to obtain a 3D printed part. The method is as follows:

The thermally curable silicon-alumina oxide ceramic ink is encapsulated in the 3D printer silo, and the structure and shape of the silicon-alumina oxide ceramic aerogel is designed based on the three-dimensional modeling software. The nozzle with a diameter of 1.2mm is selected and planned according to the G code language. control the 3D printer nozzle to print on a two-dimensional plane at a speed of 15mm/s. After printing a layer of ink, the printer nozzle automatically lifts up according to the programmed path, and performs the next layer of printing until the 3D printing is obtained. printout;

The third step, temperature-controlled heat curing, the method is:

Place the 3D printed part prepared in the second step in an airtight container, heat the 3D printed part in a water bath with a constant temperature of 60°C, and after 6 to 8 hours, the 3D printed part is completely gelled and solidified to obtain a thermally cured 3D printed part;

The fourth step, supercritical drying, to obtain the initial state 3D printing silicon aluminum oxide aerogel, the method is:

The heat-cured 3D printed parts prepared in the third step were immersed in anhydrous ethanol (concentration ≥99.5%) at 50°C for solvent replacement, and the replacement was performed 5 times to remove impurities, and each replacement time was 24 hours. The thermally cured 3D printed parts with impurities removed were then dried in a _CO2 supercritical drying fluid at 55 °C and 13 MPa to obtain the initial 3D printed silicon-alumina oxide aerogel. Figure 2 shows the initial 3D printed silicon-alumina oxide aerogel with a complex scaffold structure, which is a hollow porous structure formed by the accumulation of ink tows, showing good structural integrity and shape fidelity. Feasibility of printing technology to obtain complex structural shapes of silicon aluminum oxide aerogels.

The fifth step, high temperature heat treatment, to obtain 3D printing silicon aluminum oxide ceramic aerogel, the method is:

The initial state 3D printed silicon-alumina oxide aerogel prepared in the fourth step was heated to 1100°C at a rate of 10°C/min in a muffle furnace, and heat-treated at a constant 1100°C for 2 hours, followed by natural cooling in the furnace to obtain 3D Printing silica-alumina-oxide ceramic aerogels. The density of the 3D printed silicon-alumina oxide ceramic aerogel is 0.35g·cm ^-3 , the thermal conductivity is 0.083W·m ^-1 ·K ^-1 , and the specific surface area is 183m ² ·g ^-1 . Figure 3 shows the 3D printed SiAlO ceramic aerogel obtained by heat treatment at 1100°C for 2 h in the initial state of the 3D printed SiAlO aerogel with complex scaffold structure in Figure 2. After heat treatment, the aerogel can still maintain The good hollow porous structure without structural and shape damage proves that the 3D printed silicon-alumina-oxide ceramic aerogel has good high temperature resistance properties.

In the first step of the present invention, the density, thermal conductivity, specific surface area and high temperature of the 3D printed silicon-alumina oxide ceramic aerogel concerned by the present invention are adjusted by adjusting the dosage of polyvinyl alcohol, urea and water within the required range. The specific surface area retention rate has no effect; the amount of polyvinyl alcohol and water only affects the self-supporting formability of the 3D printed part, the amount of urea only affects the curing rate of the silicon-alumina oxide ceramic ink, and the stirring time of the centrifugal defoaming mixer , the speed has no effect on the density, thermal conductivity, specific surface area and high temperature specific surface area retention rate of the 3D printing silicon aluminum oxide ceramic aerogel concerned by the present invention, and the stirring time and speed only affect the debubbling of the silicon aluminum oxide ceramic ink. In addition, nano-silica powders with different specific surface areas have little effect on the density and thermal conductivity of the 3D printed silicon-alumina oxide ceramic aerogel concerned by the present invention, but have little effect on the specific surface area and high-temperature specific surface area retention rate, and can basically neglect. In the second step, the size of the nozzle diameter of the 3D printer only affects the surface accuracy of the 3D printed silicon aluminum oxide ceramic aerogel, and the movement speed of the 3D printer nozzle only affects the speed of the 3D printing process. The density, thermal conductivity, specific surface area and high temperature specific surface area retention rate of 3D printed silicon aluminum oxide ceramic aerogel have no effect. In the fourth step, the solvent replacement and drying conditions have no effect on the density, thermal conductivity, specific surface area and high temperature specific surface area retention rate of the 3D printed silicon-alumina-oxide ceramic aerogel concerned in the present invention. In the fifth step, the muffle furnace heating rate, solvent replacement and drying conditions have no effect on the density, thermal conductivity, specific surface area and high temperature specific surface area retention rate of the 3D printed silicon-alumina oxide ceramic aerogel concerned in the present invention. Therefore, the above conditions have no effect on the density, thermal conductivity, specific surface area and high temperature specific surface area retention rate of 3D printed silicon aluminum oxide ceramics. As long as the selection is within the range described in the content of the invention, 3D printing with good performance can be obtained. Printing silica-alumina-oxide ceramic aerogels. The main factors that affect the density, thermal conductivity, specific surface area and high temperature specific surface area retention rate of 3D printed silicon-alumina oxide ceramic aerogel are the amount of water-based silica sol and water-based aluminum sol in the first step of the present invention and the fifth step of the present invention. High temperature heat treatment temperature in the step.

The process parameters adopted in Examples 2 to 27 are shown in Table 1. Observing the data in Table 1, the density range of 3D printed silicon-alumina oxide ceramic aerogel is 0.14～0.62g·cm ^-3 , the thermal conductivity range is 0.029～0.104W·m ^-1 ·K ^-1 , the specific surface area range is It is 172-308 m ² ·g ^-1 , and the specific surface area retention rate at high temperature ranges from 55 to 99%, which indicates that the 3D printed silicon-alumina oxide aerogel is not completely sintered in a high-temperature environment, and the porous structure of the aerogel can still be maintained. . The density of 3D printed silicon-alumina oxide ceramic aerogel increases with the increase of the amount of water-based silica sol and water-based aluminum sol, which also leads to a similar variation in thermal conductivity; as the heat treatment temperature increases, 3D-printed silicon-alumina The specific surface area and high-temperature specific surface area retention rate of oxide ceramic aerogels showed a trend of decreasing slowly at first and then decreasing rapidly.

According to the results of the embodiments of the present invention, the 3D printed silicon-alumina oxide ceramic aerogel prepared by the present invention is relatively single, non-toxic and harmless, has low density and low thermal conductivity, and can realize complex structural design and high-precision shape. . In addition, the temperature-controlled thermal curing scheme can realize the large-scale additive manufacturing of silicon-alumina oxide ceramic aerogels, which is of great significance for the industrial production of silicon-alumina oxide ceramic aerogel materials.

The above-mentioned embodiments are only the preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any changes made by adopting the design principles of the present invention and non-creative work on this basis shall belong to the protection of the present invention. within the range.

Table 1 Preparation process parameters and related properties of 3D printed silicon-alumina-oxide ceramic aerogels

Claims (12)

1. A preparation method of an extruded 3D printed silicon-aluminum oxide ceramic aerogel is characterized by comprising the following steps:

firstly, preparing the heat-curable silicon-aluminum oxide ceramic ink, which comprises the following steps:

1.1 mixing nano silicon oxide powder, aqueous silica sol, aqueous aluminum sol, polyvinyl alcohol, urea and water, and uniformly stirring to prepare a primary mixed slurry; wherein, the nano silicon oxide powder is used as an ink thickener to adjust the rheological property of the ink; the polyvinyl alcohol is used as an ink cross-linking agent to assist the nano silicon oxide powder to adjust the rheological property of the ink; urea is used as a temperature induction catalyst, is decomposed to release alkaline ammonia, promotes the water-based silica sol and the water-based aluminum sol to perform polycondensation reaction, and realizes the thermal curing of the silicon-aluminum oxide ceramic ink; in the ink composition, the mass fractions of nano silicon oxide powder, aqueous silica sol, aqueous aluminum sol, polyvinyl alcohol, urea and water in the silicon-aluminum oxide ceramic ink are respectively 10, 15-55, 0-50, 1-5 and 1-40; the mass fraction of the aqueous aluminum sol is not 0;

1.2, placing the primarily mixed slurry in a centrifugal defoaming stirrer to be stirred to obtain the silicon-aluminum oxide ceramic ink which is bubble-free, can be thermally cured and can be molded in a self-supporting way;

and secondly, extruding the silicon-aluminum oxide ceramic ink for 3D printing to obtain a 3D printed piece, wherein the method comprises the following steps:

packaging silicon-aluminum oxide ceramic ink in a 3D printer bin, designing the structural shape of silicon-aluminum oxide ceramic aerogel by means of three-dimensional modeling software, selecting a 3D printer nozzle with a corresponding discharge port diameter according to the surface precision requirement, planning a printing path according to a numerical control programming language (namely G code), controlling the 3D printer nozzle to print on a two-dimensional plane, and after printing one layer of ink, automatically lifting the printer nozzle upwards according to the programming path, and printing the next layer until a 3D printed part is obtained;

thirdly, controlling temperature and performing thermocuring, wherein the method comprises the following steps:

placing the 3D printing piece prepared in the second step into a closed container, heating the 3D printing piece in a water bath kettle with constant temperature to decompose urea contained in the 3D printing piece and release alkaline ammonia, carrying out polycondensation reaction between nano silica particles and boehmite particles in the 3D printing piece under the catalysis of the alkaline ammonia, and carrying out gel curing on the 3D printing piece to obtain a thermocured 3D printing piece;

and fourthly, supercritical drying to obtain the initial 3D printed silicon-aluminum oxide aerogel, wherein the method comprises the following steps:

soaking the thermocuring 3D printing piece prepared in the third step in absolute ethyl alcohol, and removing impurities by solvent replacement; the thermally cured 3D print containing ethanol was then printed in CO ₂ Drying in supercritical drying fluid to obtain initial 3D printed silicon-aluminum oxide aerogel;

fifthly, carrying out high-temperature heat treatment to obtain the 3D printed silicon-aluminum oxide ceramic aerogel, wherein the method comprises the following steps:

carrying out heat treatment on the initial 3D printed silicon-aluminum oxide aerogel prepared in the fourth step in a muffle furnace controlled by a program at a constant temperature for 2 hours, and naturally cooling to obtain a 3D printed silicon-aluminum oxide ceramic aerogel; converting boehmite in the initial 3D-printed silicon-aluminum oxide aerogel into gamma-phase alumina, and removing a small amount of organic polyvinyl alcohol, dry residual ethanol and a small amount of adsorbed water in the heat treatment process to obtain the 3D-printed silicon-aluminum oxide ceramic aerogel with the porous ceramic structure; the constant temperature refers to a steady-state heat treatment temperature reached by the muffle furnace after temperature rise through program control, and the selection range of the constant temperature is controlled to be 600-1100 ℃.

2. The preparation method of the extruded 3D printed silicon-aluminum oxide ceramic aerogel according to claim 1, wherein the nano silicon oxide powder in the step 1.1 has a specific surface area of 50-1000 m ² ·g ^-1 The gas-phase silicon oxide powder of (2); the water-based silica sol is nano silica colloidal particle water dispersion with the solid content of 40 wt%; the aqueous alumina sol refers to a boehmite aqueous dispersion with a solid content of 20 wt%.

3. The preparation method of the extruded 3D printed silicon-aluminum oxide ceramic aerogel according to claim 1, wherein 1.2 the step of placing the initial mixed slurry in a centrifugal defoaming mixer for stirring is carried out for 1-30 minutes.

4. The preparation method of the extruded 3D printed silicon-aluminum oxide ceramic aerogel as claimed in claim 1, wherein in the 1.2 steps, the revolution speed of the stirrer is controlled to be 400-1000 rpm, and the rotation speed is controlled to be 100-800 rpm.

5. The preparation method of the extruded 3D printed silicon-aluminum oxide ceramic aerogel according to claim 1, wherein the diameter of a discharge hole of a nozzle of the 3D printer in the second step is 0.1-3.0 mm.

6. The preparation method of the extruded 3D printed silicon-aluminum oxide ceramic aerogel according to claim 1, wherein the printing speed of the nozzle of the 3D printer in the second step is controlled to be 0.2-40 mm/s when the nozzle of the 3D printer prints on a two-dimensional plane, namely the movement speed of the direct-writing printer in the x-axis and y-axis directions.

7. The preparation method of the extruded 3D printed silicon-aluminum oxide ceramic aerogel according to claim 1, wherein the constant temperature range in the third step is that the external heating temperature is controlled to be 60-90 ℃.

8. The preparation method of the extruded 3D printed silicon-aluminum oxide ceramic aerogel according to claim 1, wherein the concentration of the absolute ethyl alcohol in the fourth step is greater than or equal to 99.5%, and the temperature range of the absolute ethyl alcohol is 25-80 ℃.

9. The preparation method of the extruded 3D printed silicon-aluminum oxide ceramic aerogel according to claim 1, wherein the solvent replacement in the fourth step is performed 3-8 times, and each replacement time is 6-36 hours.

10. The method for preparing the extruded 3D printed silica alumina ceramic aerogel according to claim 1, wherein the fourth step is CO ₂ The supercritical drying conditions are 35-70 ℃ and 8-15 MPa.

11. The method of making an extruded 3D printed silica alumina ceramic aerogel according to claim 1, wherein the fourth step is comprised of amorphous silica and crystalline boehmite; wherein the mass fraction of the silicon oxide in the initial 3D-printed silicon-aluminum oxide aerogel is 60-100%, and the mass fraction of the boehmite in the initial 3D-printed silicon-aluminum oxide aerogel is 0-40%; the mass fraction range of the silicon oxide in the initial 3D-printed silicon-aluminum oxide aerogel is not 100%, and the mass fraction range of the boehmite in the initial 3D-printed silicon-aluminum oxide aerogel is not 0.

12. The preparation method of the extruded 3D printed silicon-aluminum oxide ceramic aerogel according to claim 1, wherein the fifth step of program control means that the temperature rise rate of a muffle furnace is controlled to be 1-10 ℃/min.

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