JPH08151231A - Production of porous or solid material and apparatus therefor - Google Patents

Abstract

PURPOSE: To prevent the cracking of a porous or solid material in drying and baking by a simple means. CONSTITUTION: In the drying of a porous material 8, a temperature controller 10 is operated with a CPU 16 in such a manner as to keep the variation of electrostatic capacity of the material at a prescribed level while monitoring the variation of electrostatic capacity with an electrostatic capacity measuring device 11. The heating rate of the drying apparatus is controlled by lowering the temperature in an electric furnace 7 when the decrease of the electrostatic capacity is too fast and the temperature is raised when the capacity decrease is too slow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing a porous body or a dense body.

[0002]

2. Description of the Related Art Generally, as a method for producing glass and ceramics via a porous body, for example, a sol-gel method using metal alkoxide, water glass, oxide particles such as SiO ₂ as a raw material is known. This is a method of producing a wet gel porous body, and drying and firing it to produce porous and dense glass or ceramics.

However, according to the conventional sol-gel method, cracks often occur when the porous body is dried.
For example, if the porous body is dried insufficiently and the process proceeds to a solvent removal step such as depressurization or heating, the porous body is cracked and the yield is very poor. Conventionally, in order to solve such a problem, as a method of monitoring the dry state of the gel porous body during the drying process, the weight loss of the porous body is measured to lower the drying temperature or to increase the pinhole opening ratio. The method of changing the values is disclosed in JP-A-62-100427 and JP-A-62-23062.
No. 9 publication. Further, a method for detecting the dry state by measuring the humidity in a dryer is disclosed in
It is disclosed in Japanese Patent Publication No. 61-168540.

Further, in the method of firing a porous body or a dense body, J. Non-Cryts is a method of firing in a complicated firing schedule depending on temperature and time in order to prevent cracks and the like.
t. Solids., 99 (1988) 160-167.

[0005]

[Problems to be Solved by the Invention] However, JP-A-62-100
As described in JP-A No. 427 and JP-A No. 62-230629, as a method for monitoring the dry state of the gel during the drying process,
With the method of measuring the weight loss and changing the opening ratio of the dryer, the gel has to be taken out from the dryer because it needs to be weighed each time, which is very time-consuming and difficult. Water often condensed inside the container and the gel absorbed moisture and cracked. On the other hand, it is possible to measure the weight in a dryer, but in order to keep the temperature distribution in the dryer constant, a fan is often rotated or gas is often flown. Therefore, it was difficult to directly weigh accurately.

Further, as in Japanese Patent Laid-Open No. 61-168540,
By measuring the humidity in the dryer, in the method of detecting the dry state, not only water in the wet gel porous body,
Since organic solvents such as alcohol and acetone are contained, and not only humidity is related to drying but also vapor pressure of organic solvent is related, so controlling humidity is not enough to prevent cracking. there were. For example, when the porous body contains a solvent such as IPA or glycols having a boiling point close to that of water or higher than that of water, the solvent remains in the porous body even when the humidity is constant, Since it often breaks during the subsequent temperature raising step, a method for simultaneously measuring the evaporation degree of water and a solvent other than water from the porous body was required.

Further, when glass or ceramics is manufactured by the conventional sol-gel method, a porous body is formed during the manufacturing process, but when the porous body is fired, particularly when it is made non-porous, gas is discharged from the porous body, At this time, stress was applied and cracks were often generated. For this, temperature and time,
It has been proposed that the firing is performed according to a complicated firing schedule depending on the atmosphere and the atmosphere as described above.
Even if the preparation conditions and composition of the precursor sol are changed even slightly, another complicated firing schedule must be determined in order to fire the porous body to a dense body without cracking. There was a need for mistakes, and a lot of man-hours were required.

The present invention has been made in view of the above conventional problems, and provides a method and an apparatus for manufacturing a porous body or a dense body capable of preventing cracks during drying and firing by simple means. The purpose is to

[0009]

In order to solve the above-mentioned problems, the invention according to claim 1 is such that, in the step of drying or firing the porous body, the electrostatic capacity of the porous body is measured while measuring the electrostatic capacitance of the porous body. The drying or firing is performed so that the capacitance becomes a predetermined value and / or the temporal change of the electrostatic capacitance becomes a predetermined value.

The invention according to claim 2 is characterized in that the porous body is produced by a sol-gel method.

According to a third aspect of the present invention, in a porous body or dense body manufacturing apparatus for drying or firing a porous body, measuring means for measuring the electrostatic capacitance of the porous body, and the measured electrostatic capacitance, and / or Or, comparing the measured capacitance value with a predetermined capacitance value, and / or comparing the measured capacitance value with a storage means for storing the capacitance temporal change. A comparison means for comparing a value with a value of a change in a predetermined capacitance with time, and a control device for controlling drying or baking so that the values compared by the comparison means become equal to each other .

That is, in the present invention, the dry state or the firing state of the porous body is monitored by measuring the electrostatic capacity, and by feeding back this, the temperature, humidity, vapor pressure of the organic solvent of the drying apparatus or the firing apparatus, The aperture ratio, pressure, air flow rate, atmosphere, etc. were changed to prevent cracks during temperature rise and cracks during firing.

[0013]

The operation in the case of utilizing the measurement of the electrostatic capacity during the drying will be described below. Object capacitance C (F)
When the object is considered to be a capacitor, the area of the capacitor is S (m ² ), and the distance between the electrodes of the capacitor is d
(M), where the relative permittivity of the capacitor is ε ₁ and the permittivity of vacuum is ε ₀ , it is expressed by Equation 1.

[0014]

[Equation 1]

Here, considering the electrostatic capacity of the porous body, for the sake of simplicity, the area S and the distance d between the electrodes do not change due to drying, and some of the pores are gathered as shown in FIG. Think of a model. This can be considered when the capacitors are connected in series, so that the capacitance C _t of the entire porous body is
When the electrostatic capacitance of the solid portion 1 is C _B and the electrostatic capacitance of the pore portion 2 is C _p, it is represented by the formula 2.

[0016]

[Equation 2]

Therefore, the electrostatic capacity C _tW of the porous body before drying in which the pore portion 2 is filled with the solvent is _equal to the solid portion 1
Where C _B is the electrostatic capacity and C _S is the electrostatic capacity of the pore portion 2 filled with the solvent, it can be expressed by Equation 3 according to the relationship of Equation 2.

[0018]

(Equation 3)

[0019] Here, the thickness of the solid portion 1 d _B, when the relative dielectric constant of the solid portion 1 was set to epsilon _B, the capacitance C _B of the solid portion 1 is indicated by the number 4.

[0020]

[Equation 4]

The capacitance C _S of the pore portion 2 filled with the solvent is the thickness of the pore portion 2 is d _S , the pore portion 2 is
When the relative permittivity of the solvent that is filled in is defined as ε _S , it is expressed by Equation 5.

[0022]

(Equation 5)

By substituting the _equations 4 and 5 into the _{equation 3,} the electrostatic capacity C _tW of the porous body before the drying in which the pore portion 2 is filled with the solvent is shown by the _equation 6.

[0024]

(Equation 6)

When the solvent is evaporated from the porous body and dried, the solvent is replaced with air. Therefore, when the relative permittivity of air is ε _a , the electrostatic capacity C _tD of the dried porous body is It becomes number 7.

[0026]

(Equation 7)

Generally, the relative dielectric constant of the solvent contained in the pores of the porous body is usually larger than that of air,
As shown in FIG. 3, the capacitance C _tW becomes smaller as the porous body dries, and becomes a constant value after the drying is completed. Here, as shown in FIG.
The capacitance of the porous body 3 can be measured by disposing it in between and measuring the current flowing when a voltage is applied from the power source 6.

The time change of the electrostatic capacity is fed back via the CPU or the like, and, for example, the temperature of the dryer or the like,
By changing the humidity, the vapor pressure of the organic solvent, the aperture ratio, the pressure, the air flow rate, etc., the drying rate can be adjusted to the dry state of the porous body (for example, the initial stage, the middle stage, the final stage). When the speed at which the capacitance decreases is faster than a predetermined speed, that is, when the drying is too fast, a command is sent to the temperature controller via the CPU or the like to lower the drying temperature. On the contrary, when the drying speed is slow, the opening of the damper is enlarged by the motor via the CPU, etc. The temperature controller may be operated to raise the drying temperature so that the capacity is reached. In this way, controlling the time change of the electrostatic capacity of the porous body controls the drying rate of the porous body, and the drying rate which has a great relation to the cracking of the porous body can be optimally controlled. Therefore, the porous body is not cracked and the yield is improved.

For example, when the porous body is dried by the temperature raising program as shown in FIG. 4, when the electrostatic capacity becomes constant, if the process goes to the next temperature raising step, the rapid evaporation of the solvent is eliminated, No cracks occur in the porous body. Therefore, the temperature raising program does not need to set the holding time and the like, and only needs to set the target temperature to be held, and even in the wet porous body prepared under various conditions, the drying conditions are automatically optimized. The porous body can be dried very easily without causing cracks.

The porous body may be dried until the electrostatic capacity becomes constant, but it is not always necessary to dry until the electrostatic capacity becomes constant, and the desired electrostatic capacity is obtained. At times, the process may be moved to the next temperature raising step, further drying and baking steps. Here, the capacitance being monitored is
Even if air flows into the dryer or the fan rotates, it does not change significantly and stable measurement can be performed. Therefore, by monitoring this change in capacitance, it is possible to know the dry state without contacting the porous body without moving the porous body. It won't crack. The desired capacitance value varies depending on the material and composition of the porous body, but is empirically determined by the size, length, surface area, porosity, etc. of the porous body. Such desired values are stored in memory means for storing the desired values in the comparing means. Further, the value stored in this memory means can be rewritten from the outside.

The above description utilizes the change in the electrostatic capacity for drying. However, if the change in the electrostatic capacity shows some change in the state, it is not limited to the case of drying, but for example, the sintering state. It can also be applied to monitors and surface condition monitors. For monitoring the surface condition, for example, the capacitance changes depending on the amount of hydroxyl groups on the surface of the porous glass, and thus the surface condition can be known.

Further, when the porous body is sintered, the pore portion 2 in the schematic diagram shown in FIG. 2 disappears and becomes denser, so that the capacitance gradually approaches the value of the solid portion 1 and completely. It will be a constant value when sintered. For example, when densifying the porous glass, the conditions must be set in consideration of the hydroxyl groups on the surface as described above, but for the sake of simplicity, the pore portion 2 is filled with only air. Then,
The change in the capacitance changes as shown in FIG.
Therefore, by utilizing this change, the present invention can be applied to a monitor of a sintered state when the porous body is sintered and densified. As the sintering proceeds, the pores of the porous body decrease, and the surface area decreases accordingly. Therefore, since the electrostatic capacity increases, if it is desired to obtain a desired surface area, the temperature increase may be stopped when the desired electrostatic capacity is reached. Further, by feeding back this capacitance through a CPU or the like, and changing firing conditions such as temperature of a firing furnace, atmosphere such as gas, pressure, etc., cracking and foaming at the time of temperature rise are prevented. be able to. That is, it is possible to easily prevent crystallization and foaming that occur due to excessive temperature rise.

Here, the electrode of the capacitance measuring device used in the sintering device may be a metal having high heat resistance, but Pt is particularly preferable from the viewpoint of heat resistance and corrosion resistance.

At this time, the porous body to be dried and fired may be prepared by any method, and the present invention can be applied to any material as long as it is a porous body. There is no limit. However, the present invention is particularly effective for the porous gel produced by the sol-gel method. This is because the mechanical strength of the porous gel in a wet state produced by the sol-gel method is very weak, and it is often difficult to withstand a slight impact, rapid evaporation of the solvent and the like. In the present invention, there is no impact due to the movement of the porous body and no moisture absorption by taking out from the dryer, and even a porous body having low mechanical strength can be dried without cracking. Further, since the drying rate can be controlled by monitoring the electrostatic capacity, there is no rapid evaporation of the solvent, and even a porous material having weak mechanical strength can be dried without cracking.

In an actual measuring device, the electrostatic capacitance measured by the device as shown in FIG. 1 is measured by combining the electrostatic capacitance between the porous body and the electrode and the electrostatic capacitance of the porous body. It will be. When the porous body shrinks with drying, especially when a bulky porous body is produced by the sol-gel method or the like, the vertical distance between the porous body and the electrode changes due to shrinkage,
The measurement error of the capacitance may increase. At this time, it is desirable to monitor the distance by a distance sensor using a laser beam or the like and drive a motor to keep the distance between the porous body and the electrode constant. Further, since shrinkage may occur in the radial direction (transverse direction) as well, it is desirable to set the value of capacitance or change rate that is suitable for the optimal drying rate, sintering rate, etc. in view of these.

It is also possible to measure the electrostatic capacity of the porous body as it is in the container by measuring the electrostatic capacity of the container in advance and subtracting this. The porous body may be in contact with either one of the electrodes, and the one of the electrodes may be, for example, a conductive part of a part of the drying device.

[0037]

【Example】

Example 1 7 ml of Si (OCH ₃ ) ₄ and 7 ml of S
i (OC ₂ H ₅ ) ₄ and 1/100 N-HCl aqueous solution 1
5 ml and 60 ml of 0.25 mol / l lead acetate aqueous solution,
10 ml of a 0.5 mol / l lead nitrate aqueous solution was added and hydrolyzed to prepare a sol, which was gelled in a cylindrical Teflon container having an inner diameter of 20 mm to prepare a wet gel. A part of this gel was immersed in an aqueous potassium nitrate solution having a concentration of 5 mol / l, and then immersed in acetone to precipitate fine crystals to obtain a wet gel having a concentration distribution. After this, drying was performed using the drying device shown in FIG.

In the drying apparatus shown in FIG. 6, a heater 9 is arranged around a porous body (wet gel) 8 housed in an electric furnace (dryer) 7 so as to surround it. The heater 9 is connected to the temperature controller 10. Further, one electrode 12 is provided in contact with the lower end surface of the porous body 8 in order to measure the electrostatic capacitance by the electrostatic capacitance measuring unit 11. Above the porous body 8, the electrode 1 is provided.
The other electrode 13 is provided so as to face 2. A distance sensor 14 is fixedly provided on the lower surface of the electrode 13 so that the distance between the electrode 13 and the porous body 8 can be monitored. A motor 15 is connected to the electrode 13 so that the electrode 13 can move toward and away from the porous body 8. The CPU 16 has an internal memory in which a predetermined rate of change data of capacitance is stored, and the capacitance measuring unit 11
It is possible to control the voltage applied to the heater 9 by the temperature controller 10 so that the rate of change of the measured value according to is a predetermined rate of change, and drive and control the electrode 13 by the motor 15 based on the detection result of the distance sensor 14. You can do it.

In the drying apparatus having such a structure, while monitoring the change in electrostatic capacity by the electrostatic capacity measuring unit 11,
The temperature controller 10 is operated via the CPU 16 so that the rate of change of the capacitance becomes a predetermined value. When the decrease of the capacitance is too fast, the temperature of the drying device is lowered, and when it is slow, the temperature of the drying device is lowered. To adjust the temperature rise rate of the dryer,
When dried to give a dry gel, no cracks occurred. At this time, since the porous body (wet gel) 8 shrinks due to drying, the distance sensor 14 using the laser light is used.
Was used to monitor the distance between the electrode 13 and the porous body 8, and the electrode 15 was moved by the motor 15 to keep the distance constant.

FIG. 7 shows a sintering apparatus, in which the electrode 13 is not provided with a distance sensor or a motor,
2 is not in contact with the porous body (dry gel) 8 and is He
The gas can be made to flow into the electric furnace 7. The CPU 16 has an internal memory in which a predetermined rate of change data of capacitance is stored, and is controlled by the temperature controller 10 so that the rate of change of the measured value by the capacitance measuring unit 11 becomes a predetermined rate of change. The voltage applied to the heater 9 can be controlled and the flow rate of He gas can be controlled.

Using the thus-configured sintering apparatus, the porous body (dry gel) 8 obtained as described above was sintered in the electric furnace 7 while monitoring the change in capacitance. At the time of firing, when the capacitance value becomes constant, the process proceeds to the next firing step, and He gas is flown when the capacitance value reaches 70% of the vitrification capacitance value. Then, the firing was terminated when the capacitance value when vitrified was reached. As a result, a glass rod having a refractive index distribution with a diameter of about 7 mm was obtained without cracking or change in shape of the porous body 8.

Comparative Example 1 A wet gel having a concentration distribution was obtained in the same manner as in Example 1. After that, when it was dried at a constant rate of temperature rise, cracking occurred in 40%. Further, when sintering was performed in an electric furnace according to a program whose firing schedule was controlled by time, cracking or foaming occurred in 30%.

Example 2 7 ml of Si (OCH ₃ ) ₄
And 7 ml of Si (OC ₂ H ₅ ) ₄ were hydrolyzed by adding a 1N-HCl aqueous solution to prepare a sol, which was gelled in a Teflon container to prepare a plate-like wet gel. This wet gel was dried using the drying device shown in FIG.

In the drying device shown in FIG. 8, the damper 1 is attached to the electric furnace 7.
7 is provided, and the opening ratio of the damper 17 can be adjusted by the motor 18. The CPU 16 has an internal memory in which a predetermined rate of change data of capacitance is stored, and is controlled by the temperature controller 10 so that the rate of change of the measured value by the capacitance measuring unit 11 becomes a predetermined rate of change. While controlling the voltage applied to the heater 9, the motor 18
The drive of can be controlled.

With the drying device having such a configuration, the motor 18 is driven via the CPU 16 while monitoring the change in electrostatic capacity. When the drying speed is slow, the opening of the damper 17 of the drying device is increased, and when it is fast, When drying was performed by reducing the opening of the damper 17 and adjusting the opening ratio of the damper 17 of the drying device, the porous body 8 was not cracked at all.

Example 3 51.1 g of Zr (OC ₄ H
₉ ) ₄ and 129.3 g of Si (OCH ₃ ) ₄ with 20
7.3 g ethanol and 72.0 g 1 / 100N
An aqueous HCl solution was added for hydrolysis, and gelation was performed in a glass container having an inner diameter of 20 mm to prepare a wet gel. The wet gel was aged at 40 ° C. and then washed with ethanol. Next, this gel was dried using the drying device shown in FIG.

The drying apparatus shown in FIG. 9 is constructed so that ethanol gas can flow into the electric furnace 7, and the CPU 16 has an internal memory in which a predetermined rate of change in capacitance data is stored. The capacitance measuring unit 11
It is possible to control the voltage applied to the heater 9 by the temperature controller 10 so that the rate of change of the measured value due to is a predetermined rate of change, and to control the drive of the motor 18.
In addition, the flow rate of ethanol gas can be controlled.

With the drying device having such a configuration, while monitoring the change in electrostatic capacity, when the drying speed is high, the valve is opened via the CPU 16 to allow ethanol vapor to flow into the drying device, and the ethanol vapor The pressure is increased to slow the drying speed, and when the drying speed is slow, the motor 18 is driven to open the damper 17 to lower the vapor pressure of ethanol and adjust the vapor pressure of ethanol in the drying device to dry. However, no cracks occurred in the porous body 8. Further, in order to obtain a desired surface area, the sintering apparatus of FIG. 7 was used to perform firing while monitoring the change in capacitance, and when the capacitance reached 50% of the value when densified, When firing was stopped, the reproducibility was 300 m ² with good reproducibility.
It was possible to produce a porous body having a surface area of / g.

[Comparative Example 2] A wet gel was prepared in the same manner as in Example 3 and dried, but no cracks occurred. In addition, when firing was performed using an ordinary electric furnace according to a time-controlled program, the surface area varied greatly, and a porous body could not be produced with good reproducibility.

[Example 4] Vycor porous glass was
It was immersed in a C _S NO ₃ aqueous solution at 100 ° C. for 3 hours to fill the pores with the C _S NO ₃ aqueous solution. Then 40v at 70 ° C
Immersing in H ₂ O containing ol% ethanol to gradually extract the C _S NO ₃ aqueous solution in the pores to the outside of the porous glass,
A convex concentration distribution was formed on Cs. Further, it is immersed in ethanol at 0 ° C. to precipitate fine crystals of CsNO ₃ ,
The concentration distribution of _S was fixed. The wet porous body was dried using the drying device shown in FIG.

The drying apparatus of FIG. 10 is connected to a vacuum pump 19 so that the inside of the electric furnace 7 can be depressurized. Further, the ethanol gas is configured to be able to flow into the electric furnace 7, and the CPU 16 has an internal memory in which a predetermined rate of change in capacitance data is stored. The voltage applied to the heater 9 can be controlled by the temperature controller 10 so that the rate of change of the measured value by the unit 11 becomes a predetermined rate of change, and the driving of the vacuum pump 19 can be controlled, and the flow rate of ethanol gas can be controlled. Can be controlled.

With the drying device having such a structure, C is used when the drying speed is fast while monitoring the change in electrostatic capacity.
The valve is opened via the PU 16 to allow ethanol vapor to flow into the drying device to increase the ethanol vapor pressure to slow the drying rate. When the drying rate is slow, the vacuum pump 19 is driven to drive the ethanol vapor pressure. Was lowered to adjust the vapor pressure of ethanol in the drying device and sufficiently dried, and no cracks were generated in the porous body 8. Further, this was fired up to 950 ° C. by the sintering machine shown in FIG. 7 to be vitrified. As a result, a glass body having a refractive index distribution with no cracking was obtained.

[0053]

As described above, according to the method and apparatus for producing a porous body or a dense body of the present invention, it is possible to easily produce a porous body or a dense body without cracks by a simple means with a good yield. Moreover, a porous material having a desired surface area can be produced with good reproducibility.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a manufacturing apparatus of the present invention.

FIG. 2 is a schematic view showing the structure of a porous body.

FIG. 3 is a graph showing a change in electrostatic capacity as the porous body dries.

FIG. 4 is a graph showing a drying program.

FIG. 5 is a graph showing a change in capacitance when the porous body is sintered.

FIG. 6 is a schematic configuration diagram showing a drying device used in Example 1.

FIG. 7 is a schematic configuration diagram showing a sintering apparatus used in Examples 1 and 4.

8 is a schematic configuration diagram showing a drying device used in Example 2. FIG.

FIG. 9 is a schematic configuration diagram showing a drying device used in Example 3.

FIG. 10 is a schematic configuration diagram showing a drying device used in Example 4.

[Explanation of symbols]

 3,8 Porous body 4,5,12,13 Electrode 7 Electric furnace 9 Heater 10 Temperature controller 11 Capacitance measuring unit 16 CPU 17 Damper 19 Vacuum pump

Claims (3)

[Claims] 1. In the step of drying or firing the porous body, while measuring the electrostatic capacitance of the porous body, the electrostatic capacitance has a predetermined value, and / or the temporal change of the electrostatic capacitance is predetermined. A method for producing a porous body or a dense body, which comprises performing drying or firing so as to obtain a value. 2. The method for producing a porous body or a dense body according to claim 1, wherein the porous body is produced by a sol-gel method. 3. An apparatus for producing a porous body or a dense body for drying or firing a porous body, a measuring means for measuring the electrostatic capacitance of the porous body, the measured capacitance, and / or the capacitance A storage means for storing a temporal change is used to compare the measured capacitance value with a predetermined capacitance value, and / or the temporal change value of the capacitance with a predetermined electrostatic capacitance value. A porous body or a dense body characterized by comprising a comparing means for comparing the value of the time-dependent change of the capacity, and a control device for controlling the drying or firing so that the values compared by the comparing means become equal. Body manufacturing equipment.