JPH04108672A - Method for calcining ceramic tube - Google Patents

Abstract

PURPOSE:To eliminate defective articles due to cracking with a simple and economical process by discharging the decomposed gas into a kiln from the contact surface between the open end of a crucible and base, and then heating the ceramic tube to the calcining temp. CONSTITUTION:The ceramic tube is calcined in a kiln in conformity to a heat curve shown in the figure. Namely, the tube is slowly heated at the rate of 70 deg.C/hr to point A (600 deg.C) which is the degreasing temp. and degreased. After the decomposed gas in a crucible 1 is discharged, the tube is heated in the kiln at the rate of 150 deg.C/hr to point D (1620 deg.C) which is the calcining temp., kept at that temp. for 30min and calcined. The sintered tube is then cooled to ordinary temp. at the rate of 100-500 deg.C/hr, and the product is taken out. Consequently, a series of the processes from the degreasing stage to calcining stage are carried out in the same kiln with only the temp. controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for firing ceramic tubes that can also be subjected to degreasing treatment.

(Prior art) When an organic binder is used as a forming aid and the formed ceramic tube molded body is fired in a protected atmosphere and manufactured, a degreasing step is usually required before the main firing. Ceramic tubes have been manufactured by firing in a firing furnace. For example, a bottomed cylindrical β-alumina tube with one end closed and the other open is used for solid electrolyte tubes for sodium ion conduction in sodium-sulfur batteries and thermoelectric conversion devices, solid electrolyte tubes for SOx sensors, etc. As a firing method, a method of firing in an alkaline atmosphere in a ceramic protective tube called a crucible is known. In this case, in order to prevent a decrease in the bulk density of the β-alumina tube after firing, it was necessary to perform a degreasing process in the previous process to decompose and burn the organic binder in the β-alumina tube formed body. .

However, when this degreasing treatment is performed inside the crucible, the binder decomposition gas generated creates a reducing atmosphere inside the crucible, making the binder insufficiently decomposed and causing a decrease in the density of β-alumina during the main firing. Degreasing cannot be carried out in-house, and is carried out in a separate kiln that does not use a crucible, which complicates the processing process and increases equipment costs, making it uneconomical. There is also the problem that cracks occur in the β-alumina tube due to rapid cooling during subsequent kiln removal and handling during kiln removal, resulting in defective products.

(Problem B to be Solved by the Invention) The present invention solves the above-mentioned conventional problems, and allows degreasing treatment to be performed in conjunction with firing treatment without using a separate kiln, thereby simplifying the treatment process. This method was completed with the aim of providing a method for firing ceramic tubes that is simple and economical and does not produce defective products due to cracks, unlike conventional methods.

(Means for Solving the Problems) The present invention, which has been made to solve the above problems, provides a ceramic tube firing method in which a ceramic tube molded body is fired inverted in a crucible that covers a base in a firing furnace. When the crucible is filled with gas decomposed at the degreasing temperature of the organic binder used for molding, it is further rapidly heated and then rapidly cooled to make the internal pressure of the crucible sufficiently higher than the internal pressure of the firing furnace to reduce the pressure at both times. The method is characterized in that the decomposed gas is released into the firing furnace from the contact surface between the open end of the crucible and the heel by a pressure difference, and then heated to the main firing temperature to fire the ceramic tube molded body. .

(Example) Next, the present invention will be described in detail with reference to the illustrated embodiments.

In the figure, (1) is a crucible that covers a base (2) set in a firing furnace (not shown) to form a firing space inside, and the crucible (1) and base (2) are made of MgO, spinel, This is a ceramic product made of alumina, etc., and the base (2) has β-
A common substrate base (5) made of the same material as the β-alumina tube molded body (4) used for holding the alumina tube flat body (4) upside down is mounted.

With this structure, if the firing process is performed in the firing furnace according to the heat curve shown by the solid line in Figure 2, the degreasing temperature A will be reached at a rate of 70°C/hr.
Degreasing treatment is carried out at the stage where the temperature is slowly heated to a temperature of 600°C, and the moisture and organic binder components in the β-alumina tube molded body (4) are decomposed and burned by this heating, and the decomposed gas becomes crucible. (1) will be filled with the inside. Once the degreasing process has been completed in this way, next, the temperature at point B (1000°C
), and then immediately rapidly cooled down to point 0 (600°C) at a rate of 400°C/hr, the internal pressure of the crucible (1), that is, the binder filled inside, will be reduced during the rapid heating stage. The pressure of the cracked gas and the internal pressure of the calcining furnace are sufficiently increased. However, in the subsequent rapid cooling stage, the internal pressure of the calcining furnace immediately decreases as the ambient temperature decreases, but the internal pressure of the crucible (1) remains unchanged. Since the temperature drop inside the crucible () is much smaller than the drop in the ambient temperature of the firing furnace, there is almost no drop in internal pressure, and as a result, the difference between the internal pressure of the firing furnace and the internal pressure of the crucible (1) A large pressure difference is generated, and the cracked gas in the crucible (1), which is under high pressure, is naturally released from the contact surface between the open end of the crucible (1) and the base into the firing furnace, which is under low pressure. Almost no decomposed gas exists in the crucible (1). Note that the decomposition gas of the binder filling the inside of the β-alumina tube molded body (4) in the crucible (1) is also caused by the β-alumina tube because the β-alumina tube molded body (4) is porous due to calcination. After passing through the molded body (4), the β-alumina tube molded body (
4) is discharged to the outside and further discharged into the firing furnace. In this case, a notch is provided at the open end of the β-alumina pipe molded body (4) to improve gas flow, or a gas vent hole is provided in the common substrate base (5) to form a β-alumina pipe molded body (4). It is preferable that the gas inside the β-alumina tube molded body (4) be in communication with the gas outside the β-alumina tube molded body (4). In this way, the Crucible (
1) Once the decomposition gas has been released, the temperature inside the firing furnace is raised to the main firing temperature at a rate of 150°C/hr to point D (1620″C) and held for 30 minutes. By performing the main firing of the β-alumina tube molded body (4), the β-alumina tube molded body (4) and the common base plate (5) are fired.
) contraction due to sintering occurs rapidly at 1200°C to 1400°C, and at the same time, the evaporation of NazO and MgO becomes active, and the binder is maintained in an alkaline atmosphere by vapors such as Na2O instead of decomposed gas. Sintering will be performed in this state. After the sintering process is carried out in this way, the
The product can be taken out after being cooled to room temperature at a rate of r, and a series of steps from the degreasing process to the main firing process can be performed in the same firing furnace by temperature control alone. In addition, in FIG. 2, the broken line shows the case where the rapid heating and rapid cooling were performed at a rate of 300°C/hr, the - dotted line shows the case where the rapid cooling was performed at a rate of 200°C/hr, and other shows the heat curve under the same conditions. The bulk density of the β-alumina tube thus obtained was measured by the Archimedes method (the solvent was ethyl alcohol), and the results are shown in the table below.

According to the above table, the bulk density of the β-alumina tube obtained by the method of the present invention is higher than that of β-alumina obtained by the conventional method in which the degreasing process is performed in a separate furnace and then transferred to the firing furnace for main firing. Average density of the tube 3.25 g/Cm' (n = 50
It was confirmed that it is equivalent to the book). In addition, there were no cracks in the β-alumina tubes obtained by the method of the present invention (all of them were good products). The average bulk density of the β-alumina tube when sintered while remaining in the
m' (n=10 pieces), and the quality was poorer than that obtained by the method of the present invention, confirming that the method of the present invention is superior.

The technology of the present invention can be applied to a single kiln, a continuous furnace, etc., and can also be applied to an electric furnace, an oil-fired combustion furnace, a gas-fired combustion furnace, a hybrid furnace thereof, etc.

(Effect of the invention) As is clear from the above explanation, in the present invention,
In the past, products were degreased in a separate furnace and then transferred to a firing furnace for final firing, but now the series of processes from degreasing to final firing are set in the same firing furnace, with only the firing temperature controlled. Since it can be carried out in the same crucible, processing is simple and economical, there is no extra transport process, and the bulk density is the same as that of products obtained by conventional methods, and cracks do not occur. This has the excellent effect of reliably preventing the occurrence of defective products.

Therefore, the present invention greatly contributes to the development of industry as a ceramic tube firing method that eliminates the problems associated with conventional ceramic tube firing.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the state during the degreasing process in an embodiment of the method of the present invention, and FIG. 2 is a graph showing the heat curve during the baking process. (1): Crucible, (2) Bibase, (4): β-
Alumina tube molded body, (5): Co-base base.

Claims (1)

[Claims] In a ceramic tube firing method in which an inverted ceramic tube molded body is fired in a crucible that covers the base in a firing furnace, when the crucible is filled with gas decomposed at the degreasing temperature of the organic binder, which is a forming aid, Furthermore, after rapid heating, the crucible is rapidly cooled to make the internal pressure of the crucible sufficiently higher than the internal pressure of the firing furnace, and the decomposition gas is released into the firing furnace from the contact surface between the open end of the crucible and the base due to the pressure difference between the two internal pressures, A method for firing a ceramic tube, comprising: thereafter heating the ceramic tube molded body to a main firing temperature to fire the ceramic tube molded body.