CN111925217A

CN111925217A - Method for drying wet gel blank of ceramic precursor and method for preparing ceramic body

Info

Publication number: CN111925217A
Application number: CN202010690014.6A
Authority: CN
Inventors: 杨现锋; 谢呵瀚; 郭金玉; 周哲; 刘鹏; 徐协文
Original assignee: Changsha University of Science and Technology
Current assignee: Changsha University of Science and Technology
Priority date: 2020-07-17
Filing date: 2020-07-17
Publication date: 2020-11-13
Anticipated expiration: 2040-07-17
Also published as: CN111925217B

Abstract

The invention provides a drying method of a wet gel blank of a ceramic precursor and a preparation method of a ceramic body, wherein the drying method of the wet gel blank of the ceramic precursor comprises the following steps: step 1, providing a wet gel blank of a ceramic precursor, step 2, drying liquid, sequentially placing the wet gel blank in polyethylene glycol with gradually increased molecular weight, standing for more than 4 hours respectively, taking out the wet gel blank, extracting the wet gel blank in an extraction liquid to remove the polyethylene glycol in the wet gel blank, step 3, drying the wet gel blank in air, and finally taking out the wet gel blank and drying the wet gel blank in the air to obtain a dry blank. According to the method for drying the wet gel blank of the ceramic precursor, on the basis of removing part of moisture to ensure that the blank has certain strength, the polyethylene glycol with higher molecular weight and higher osmotic pressure is used for further removing residual moisture, so that the problems of deformation and cracking caused by overlarge stress due to overlarge primary shrinkage in the further drying process are solved.

Description

Method for drying wet gel blank of ceramic precursor and method for preparing ceramic body

Technical Field

The invention relates to the technical field of material preparation, in particular to a drying method of a wet gel blank of a ceramic precursor and a preparation method of a ceramic body.

Background

The gel has the advantages of uniform components, stable dispersion and the like. In the field of ceramic materials, precursor gel of ceramic powder can be adopted, and the nano ceramic powder is prepared through steps of drying, calcining and the like. However, gels are not generally used to produce block products having specific shapes, mainly because the moisture content of the gels is high, and the drying process is often accompanied by large drying stress and drying shrinkage, resulting in difficulty in drying the block gels.

If the traditional hot air drying method is adopted, the blank body is large in shrinkage and stress due to the rapid loss of a large amount of moisture, and is difficult to keep undeformed and not cracked. And if a low-temperature high-humidity drying method is adopted, the efficiency is extremely low, and hundreds of hours are often needed.

On the other hand, a method of drying by a liquid medium has been proposed. However, the conventional liquid medium drying method has the problems of low efficiency, easy cracking of a blank, easy generation of cracks during sintering and the like.

Disclosure of Invention

Repeated researches by the inventor show that the traditional liquid phase medium drying is one-step drying, and if a low molecular weight liquid phase drying medium is adopted, the drying efficiency is low and the drying is not thorough; if a high molecular weight liquid phase drying medium is adopted, the blank is easy to crack due to higher osmotic pressure.

Furthermore, the present inventors have found that the liquid medium can reverse-permeate into the green body by drying the liquid medium, and this portion of the liquid medium generates gas during sintering, which if released abruptly, can easily cause cracking or the like of the final ceramic body.

In view of the above, the present invention provides a method for drying a wet gel blank of a ceramic precursor, which can effectively improve the drying efficiency, solve the cracking problem during drying of a gel-formed ceramic blank, and further, enable the dried blank to be directly sintered.

In addition, the invention also provides a preparation method of the ceramic body.

A method for drying a wet gel blank of a ceramic precursor according to an embodiment of the first aspect of the invention comprises the steps of:

step 1, providing a wet gel blank of a ceramic precursor,

and step 2, drying the liquid,

sequentially placing the wet gel blanks in polyethylene glycol with gradually increased molecular weight, standing for more than 4 hours respectively, taking out the wet gel blanks, extracting in an extraction liquid to remove the polyethylene glycol therein,

and step 3, drying the mixture in air,

and finally, taking out the blank and carrying out air drying in the air to obtain a dry blank.

According to the method for drying the wet gel blank of the ceramic precursor, provided by the embodiment of the invention, liquid drying is carried out step by step through polyethylene glycol with different molecular weights, namely, on the basis of removing part of water in the polyethylene glycol to ensure that the blank has certain specific strength, the polyethylene glycol with higher molecular weight and higher osmotic pressure is used for further removing the residual level, so that the advantages of drying a low-molecular-weight liquid-phase drying medium and a high-molecular-weight liquid-phase drying medium are combined, and the problems of deformation and cracking caused by overlarge stress due to overlarge primary shrinkage in further drying are avoided while the drying efficiency is ensured. In addition, the extraction liquid is adopted to extract and remove the polyethylene glycol reversely permeated into the green body, so that ceramic body cracks and the like caused by gas generation in the sintering process are effectively avoided.

Further, the temperature of the polyethylene glycol is 40-80 ℃. The temperature of the liquid medium, namely polyethylene glycol, is properly increased, which is beneficial to improving the drying speed. However, too high a temperature tends to cause a problem of concentration of drying stress. Preferably, the temperature of the polyethylene glycol is, for example, 60 ℃.

Further, the step 2 specifically includes:

placing the wet gel blank in polyethylene glycol 200(PEG200), polyethylene glycol 400(PEG400) or a mixed solution thereof, and standing for 4-72 hours;

thereafter, the wet gel base is taken out and placed in polyethylene glycol 600(PEG600), polyethylene glycol 800(PEG800), polyethylene glycol 1000(PEG1000), or a mixture thereof, and left to stand for 4 to 72 hours;

thereafter, the wet gel mass is removed and placed in polyethylene glycol (PEG) with a molecular weight greater than 1000 for a period of 4-72 hours.

That is, the liquid drying is performed in three steps, the average molecular weight of polyethylene glycol in the first step is gradually increased, the molecular weight of polyethylene glycol used in the last step is more than 1000, and the polyethylene glycol has a sufficiently high osmotic pressure, and the residual moisture is controlled to be small after the liquid phase drying in the 3 steps.

Preferably, the step 2 specifically includes:

placing the wet gel blank in polyethylene glycol 200, and standing for 4-12 hours;

then, taking out the wet gel blank, placing the wet gel blank in polyethylene glycol 600, and standing for 4-12 hours;

thereafter, the wet gel base was taken out and placed in polyethylene glycol 2000, and left to stand for 4 to 12 hours.

Through the three-step liquid drying, the problems of cracking of the blank and the like can be solved, and the moisture in the blank can be removed as quickly as possible, namely, the balance between the drying speed and the strength and integrity of the blank can be comprehensively considered.

Further, in the step 2, the extract is one or more of ethanol, ethyl acetate, butyl acetate, acetone, benzene and toluene. After being dried by a liquid medium, particularly after being dried by high molecular weight polyethylene glycol, the high molecular weight polyethylene glycol enters the internal grids of the green body, and if the high molecular weight polyethylene glycol is not removed, a large amount of gas is released due to oxidation in the subsequent sintering process, so that the ceramic body is likely to crack, collapse and the like. The above-mentioned extract is preferable in view of its ability to dissolve polyethylene glycol and its ease of volatile removal (that is, its low boiling point).

Preferably, in the step 2, the extraction time is 2 to 12 hours.

Further, the drying temperature of the air drying is 20-110 ℃, and the drying time is 3-24 hours. Therefore, the residual extract can be evaporated and volatilized to be removed, and simultaneously, the residual moisture can be further removed.

Further, in the step 1, the solid phase mass content of the gel-formed ceramic body is 10-40% in terms of oxide. According to the drying method of the present invention, it is possible to dry a wet gel body having a solid phase mass content as low as 25% which is difficult to obtain a complete body by a conventional drying method. The solid phase mass content is a value calculated by converting the solid content into an oxide.

Further, in the step 1, the gel-formed ceramic body is obtained by a gel injection molding method or a 3D printing method.

According to the preparation method of the ceramic body in the second aspect of the embodiment of the invention, the ceramic body is obtained by heating the ceramic body dried by the drying method in any one of the embodiments to the sintering temperature at the rate of 4-10 ℃/min under normal pressure and preserving the temperature for a predetermined time. By the drying method provided by the embodiment of the first aspect of the invention, drying stress and green body cracks are effectively avoided, cracking of the ceramic body caused by gas generated in the sintering process of the liquid phase drying medium is effectively avoided, so that direct sintering can be performed, the sintering rate can be as high as 10 ℃/min, and the production efficiency is effectively improved while the yield of the ceramic body is ensured.

Drawings

FIG. 1 is a photograph of a wet gel blank, a dry blank, obtained according to example 1, wherein (a) shows the wet gel blank and (b) shows the dry blank;

FIG. 2 is a photograph of a dried body obtained according to comparative example 1;

FIG. 3 is a graph showing the change of drying shrinkage with time according to example 1 and comparative example 2, in which (a) shows the graph of example 1 and (b) shows the graph of comparative example 2.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of the invention.

The method for drying a wet gel blank of a ceramic precursor according to an embodiment of the present invention will be first described specifically.

The method for drying the wet gel blank of the ceramic precursor comprises the following steps:

step 1, providing a wet gel blank of a ceramic precursor.

The wet gel blank of the ceramic precursor can be prepared by a gel injection molding method or by screw extrusion direct-writing 3D printing molding. Both methods result in a product containing a large amount of moisture.

The ceramic precursor may be, for example, pseudo-boehmite.

In addition, the solid phase mass content of the gel-formed ceramic body is 10-40% in terms of oxide. That is, the gel-formed ceramic body contains a large amount of moisture therein. Drying such gel-formed ceramic bodies by conventional methods tends to make it difficult to maintain the integrity of the body.

And step 2, drying the liquid,

and sequentially placing the wet gel blanks into polyethylene glycol with gradually increased molecular weight, respectively standing for more than 4 hours, taking out the wet gel blanks, and extracting in an extraction liquid to remove the polyethylene glycol in the wet gel blanks.

Specifically, the step 2 may specifically include:

placing the wet gel blank in polyethylene glycol 200, polyethylene glycol 400 or a mixed solution thereof, and standing for 4-72 hours;

then, taking out the wet gel blank, placing the wet gel blank into polyethylene glycol 600, polyethylene glycol 800, polyethylene glycol 1000 or a mixture thereof, and standing for 4-72 hours;

thereafter, the wet gel mass is removed and placed in polyethylene glycol having a molecular weight greater than 1000 for a period of 4-72 hours.

Preferably, the wet gel blank is placed in polyethylene glycol 200 and left for 4-12 hours;

Firstly, PEG200 is adopted to remove partial moisture, and a blank shrinks and has certain strength. Due to the low osmotic pressure of PEG200, no cracking or deformation occurs. Then, with PEG600, the osmotic pressure is increased to further remove moisture, since the green body already has a certain strength to withstand the drying stress without deformation or cracking. If only low molecular weight PEG such as PEG200 or PEG600 is used, further water removal is not possible after the drying equilibrium is reached due to the low osmotic pressure. Thus, by continuing to use PEG2000, and by eliminating residual moisture, the green body is strong enough to withstand high osmotic pressures without deformation cracking through the first two steps.

In addition, in the step 2, the extract is one or more of ethanol, ethyl acetate, butyl acetate, acetone, benzene and toluene. Preferably, in the step 2, the extraction time is 2 to 12 hours. Since in the previous three steps there was also a small amount of PEG that permeated into the wet gel matrix, the dried matrix was then placed in ethanol or ethyl acetate, which could displace this portion of PEG. And finally, placing the blank in a hot air oven, wherein the vapor pressure of the ethanol or the ethyl acetate is high, and the ethanol or the ethyl acetate can be quickly removed.

And step 3, drying the mixture in air,

finally, it is taken out and air-dried in air to obtain a dry blank.

Preferably, the drying temperature of the air drying is 20-110 ℃, and the drying time is 3-24 hours. Therefore, the residual extract can be evaporated and volatilized to be removed, and simultaneously, the residual moisture can be further removed. The present invention will be described in detail with reference to specific examples.

Example 1

A: wet gel blank of alumina ceramic precursor

The raw materials were weighed as follows: 350g of pseudo-boehmite, 700g of deionized water, 9g of nano alumina, 0.9g of magnesium oxide and 54g of 4mol/L nitric acid.

Mixing the raw materials, heating to 70 ℃, and stirring for 1 hour to prepare the pseudo-boehmite gel.

And 9g of hydroxyethyl cellulose is slowly added into the obtained pseudo-boehmite gel and mechanically stirred for 1 hour to prepare the pseudo-boehmite gel for printing.

The pseudo-boehmite gel for printing is printed and molded by a screw extrusion 3D printing method (using equipment: SYNO-SOURCE, Inc., Chuannan, a SOURCE of Chuangao, etc.) to obtain a wet gel blank.

B: drying of liquids

First, in 60 degrees C PEG200 immersion for 4 hours, then after taking out in 60 degrees C PEG600 immersion for 4 hours, finally in 60 degrees C PEG2000 immersion for 4 hours.

Thereafter, the mixture was extracted with ethanol at 60 ℃ for 6 hours

C: air drying

The resultant was dried with hot air in an oven at approximately 40 ℃ for 6 hours to obtain a dried body.

In addition, in order to compare the effect of the drying process on the green body, comparative example 1 and comparative example 2 were simultaneously prepared by the following method.

Comparative example 1

A: wet gel blank of ceramic precursor

The preparation method is as described in example 1 above.

B: drying of liquids

The wet gel base obtained above was immersed directly in PEG2000 for 12 hours.

C: air drying

The resultant mixture was dried with hot air in the same manner as in example 1 to obtain a dried body.

Comparative example 2

The same as in comparative example 1 except that PEG200 was used in liquid drying.

FIG. 1 shows photographs of wet gel and dry gel blanks prepared according to example 1 of the present invention. It can be seen from the figure that the drying process according to the invention results in dried bodies without significant cracking.

Fig. 2 is a photograph showing a dried green body obtained according to comparative example 1, and it can be seen that, when the liquid medium is dried in one step by directly using PEG2000 having a high osmotic pressure, the green body is easily cracked due to a large drying stress.

Fig. 3 shows the drying shrinkage curves according to example 1 and comparative example 2 over time, wherein (a) represents the curve of example 1 and (b) represents the curve of comparative example 2. As can be seen from the figure, according to the drying method of the embodiment of the present invention, the drying shrinkage of the green body reaches about 17% after the PEG200 is dried, the drying shrinkage further reaches about 23% after the PEG600 is further dried, and the drying shrinkage further increases to about 30% after the PEG2000 is dried, and after the PEG is extracted by ethanol, the drying shrinkage slightly falls back because the ethanol enters the green body, and finally, the drying shrinkage reaches about 45% or more after the PEG is dried by hot air. That is, the drying method of the present invention can be applied to a gel-formed green body having a drying shrinkage of 45% or more without causing cracking or the like of the green body.

In contrast, as shown in fig. 3, the green body of comparative example 2, after the drying shrinkage reached approximately 20%, the PEG200 could not further dehydrate it, and on this basis, hot air drying was performed, directly resulting in cracking and collapsing of the green body.

Example 2

A: wet gel blank of zirconia ceramic precursor

200g of ethanol and 800g of deionized water were mixed in a beaker to obtain a mixed solution, and the temperature was raised to 40 ℃.

550g of zirconium oxychloride octahydrate (ZrOCl)₂-8H₂O) is added to the mixed solution and stirred continuously until it is completely dissolved. Then 200g of hydrogen peroxide (H) was added₂O₂) And continuously stirred for 30 minutes. Then 1.5mol/L ammonia water is added dropwise to adjust the PH value to 5, and the transparent zirconium sol can be obtained.

10g of carboxymethyl cellulose is slowly added into the zirconium sol and rapidly stirred for 2 hours, then the mixture is slowly injected into a stainless steel mould with a specific shape, and the mixture is stood for 12 hours at the temperature of between 20 and 30 ℃ to obtain a wet gel blank.

B: drying of liquids

First, the wet gel blank was immersed in PEG200 at 60 ℃ for 4 hours, then taken out and immersed in PEG600 at 60 ℃ for 4 hours, and finally immersed in PEG2000 at 60 ℃ for 4 hours.

Thereafter, the mixture was extracted with ethyl acetate at 60 ℃ for 6 hours.

C: air drying

The obtained dried blank has no defects such as cracks and the like when observed by naked eyes.

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for drying a wet gel blank of a ceramic precursor, comprising the steps of:

step 1, providing a wet gel blank of a ceramic precursor,

and step 2, drying the liquid,

and step 3, drying the mixture in air,

2. The drying method according to claim 1, wherein the temperature of the polyethylene glycol in the step 2 is 40 to 80 ℃.

3. The drying method according to claim 2, wherein the step 2 specifically comprises:

4. The drying method according to claim 3, wherein the step 2 specifically comprises:

5. The drying method according to claim 1, wherein in the step 2, the extract is one or more of ethanol, ethyl acetate, butyl acetate, acetone, benzene and toluene.

6. The drying method according to claim 5, wherein the extraction time in the step 2 is 2 to 12 hours.

7. The drying method according to claim 1, wherein the air drying is carried out at a drying temperature of 20 to 110 ℃ for 3 to 24 hours.

8. The drying method according to claim 1, wherein in the step 1, the gel-formed ceramic body has a solid phase content of 10 to 40% by mass in terms of oxide.

9. The drying method according to claim 1, wherein in the step 1, the gel-formed ceramic body is obtained by a gel injection molding method or a 3D printing method.

10. A method for preparing a ceramic body, characterized in that a ceramic body dried by the drying method according to any one of claims 1 to 9 is heated to a sintering temperature at a rate of 4 to 10 ℃/min under normal pressure and is kept for a predetermined time to obtain the ceramic body.