JP2007112670A - Firing vessel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a firing vessel having excellent reaction resistance and thermal shock resistance and capable of high speed firing or being made large-sized in a degree of 300 mm square. <P>SOLUTION: The firing vessel comprises a raw material having ≤3 mm maximum particle diameter and composed essentially of magnesia and magnesia spinel, wherein the total quantity of MgO is 60-90 wt.% and the quantity of Al<SB>2</SB>O<SB>3</SB>contained in powder having about ≤50 μm particle diameter is ≤2.0 wt.%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a firing container, and more particularly to a firing container suitable for heat treatment and firing of ceramics containing a large amount of alkali and electronic ceramics containing heavy metals.

  Magnesia has been used as a baking container for glass because of its excellent corrosion resistance against alkalis such as Na, K and Li and heavy metals such as Pb and Bi.

On the other hand, firing containers of electronic ceramics typified by alumina-mullite have many materials containing SiO ₂ and when used in products containing a large amount of alkalis and heavy metals, the vitrification characteristics are remarkably affected by these components. There is a problem that the durability deteriorates rapidly, and magnesia has been used.

  However, since magnesia has a large thermal expansion, it is generally inferior in thermal shock resistance. For this reason, it is difficult to use in applications where thermal stress is likely to occur, such as high-speed firing or large-sized products, and only setters and sheaths of about 200 mm □ or less can be used.

Incidentally, a MgO · _Al 2 _{O 3} containing as a main component, the firing vessel to the ZrO ₂ and secondary component is proposed (Patent Document 1).
JP-A-8-208324

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a firing container that has excellent reaction resistance and thermal shock resistance, and can realize high-speed firing and an increase in size of about 300 mm □.

In order to achieve the above-described object, the firing container according to the present invention is a firing container having a maximum particle size of 3 mm or less and composed mainly of magnesia and magnesia spinel, and the total amount of MgO is 60 to 90 wt%, and The amount of Al ₂ O ₃ contained in the powder having a particle size of 50 μm or less is 2.0 wt% or less.

Preferably, 3 to 10 wt% of zirconia is added in an external ratio.
Further, 3 to 10 wt% of zirconia-mullite is preferably added in an external ratio.

  According to the firing container of the present invention, it is possible to provide a firing container that is excellent in reaction resistance and thermal shock resistance and can realize high-speed firing and an increase in size of about 300 mm □.

  Hereinafter, an embodiment of a firing container according to the present invention will be described.

The firing container according to the present invention is a firing container having a maximum particle size of 3 mm or less, the main components of which are magnesia and magnesia spinel, and the total amount of MgO is 60 to 90 wt% and contained in powder having a particle size of 50 μm or less. The amount of Al ₂ O ₃ is 2.0 wt% or less.

  Preferably, 3 to 10 wt% of zirconia is added to the above raw material as an outer portion, or 3 to 10 wt% of zirconia-mullite is added as an outer portion.

The firing container according to the present invention can improve thermal shock resistance while maintaining the original corrosion resistance of magnesia by combining magnesia and spinel. Magnesia spinel is a compound having a spinel structure (AB ₂ X ₄ type), which has good corrosion resistance against alkalis and heavy metals, and its thermal expansion is one of magnesia compared with the coefficient of thermal expansion (%) at 1000 ° C. .45 is 0.94, which is advantageous for thermal shock resistance. Thermal shock resistance is improved by combining magnesia and spinel with magnesia. The results of studying the optimum composite ratio will be described below.

  When the proportion of magnesia is small, the reaction resistance is lowered, and when it is used in a product containing a large amount of alkali or heavy metal, the lifetime is reduced by the reaction, so MgO is preferably 60% or more. If the combined amount of magnesia and spinel is small, the effect of improving the thermal shock resistance decreases, so MgO is preferably 90% or less.

The maximum particle diameter of the raw material used as the aggregate is preferably 3 mm or less. When the maximum particle size is larger than this, density unevenness occurs when a product having a thickness of 10 mm or less is formed. The fine powder part of 50 μm or less involved in sintering is preferably composed of MgO centers. When the amount of magnesia spinel in the fine powder part increases, the thermal shock resistance tends to decrease. Moreover, the reactivity is also easily influenced by the raw material species constituting the fine powder, and is preferably composed of MgO having excellent corrosion resistance. For this reason, it is necessary to suppress the ratio of Al ₂ O ₃ contained in the fine powder part of 50 μm or less to 2 wt% or less.

  Addition of zirconia or zirconia-mullite is effective for further improving the thermal shock resistance of materials made mainly of magnesia and magnesia spinel. Any of the raw materials is a raw material excellent in corrosion resistance, has a thermal expansion coefficient different from that of magnesia, and the thermal shock resistance can be improved by adding an appropriate amount.

  When the amount added is 3 wt% or less, the effect is small, and when 10 wt% or more is added, the thermal shock resistance is lowered, and therefore 3 to 10 wt% is preferable.

  According to the firing container of the present invention, heat treatment and firing of ceramics containing a large amount of alkali, such as a positive electrode material for lithium batteries and dielectric materials, varistors containing heavy metals such as Pb and Bi, and electronic ceramics such as capacitors. In addition, since it has excellent reaction resistance and heat shock resistance at the same time, a firing container capable of high-speed firing and upsizing of about 300 mm □ is realized.

[Example 1]
As shown in Table 1, a sheath having a ratio of MgO and Al ₂ O ₃ of 300 mm □ and a height of 100 mm was produced. The magnesia raw material used had a particle size of 3 mm or less and a purity of 99% or more. The magnesia spinel material used had a purity of 99% or more and a particle size of 3 mm or less and 0.25 mm or more, and the amount of Al ₂ O _{3 of} 0.5 mm or less was suppressed to 0.1%. Molding was performed by press molding with the addition of methylcellulose. Firing was performed at 1700 ° C.

(Reaction resistance evaluation)
On a test piece (130 × 130 × 9 t) cut out from the obtained sheath, 500 g of Na ₂ SO ₄ was loaded, and maintained in the atmosphere at 1250 ° C. for 4 hours for 3 cycles. Measure the dimensions of the specimen before and after heating and calculate the residual expansion rate. Compared to the treatment, the test piece was expanded by 0.18%.

(Evaluation of thermal shock resistance)
The thermal shock resistance of the sheath obtained using an electric furnace was evaluated. Assuming that the sheath is used for heat treatment of powder, it is evaluated whether the sheath is cracked under a rapid cooling condition in which the sheath is filled with alumina particles, heated to 600 ° C in a pusher type electric furnace and then taken out of the furnace. did. When the sheath did not break, the heating temperature was raised by 50 ° C. and the above operation was repeated. When the sheath did not break, the heating temperature was further raised by 50 ° C. and the evaluation was continued. Eventually, the sheath was cracked during rapid cooling after heating to 850 ° C. This temperature was defined as the thermal shock temperature ΔT and compared with other test specimens.

[Examples 2-5, Comparative Examples 2-6]
Saya having the same shape was produced in the same process as in Example 1 at the ratio of MgO, Al ₂ O ₃ , SiO ₂ , and ZrO ₂ shown in Table 1. The obtained sheath was subjected to the same reaction resistance evaluation and thermal shock resistance evaluation as in Example 1.

(Examples 2 and 3)
In this example, zirconia was added. The zirconia was CaO partially stabilized zirconia having a particle size of 150 μm or less. Addition of zirconia increases the thermal shock resistance temperature ΔT. The residual expansion rate is slightly increased, and the reaction resistance tends to decrease slightly.

(Examples 4 and 5)
In this example, zirconia-mullite was added, and particles having a particle size of 200 μm or less were added at 5 wt% and 10 wt%, respectively. Addition of zirconia increases the thermal shock resistance temperature ΔT. In Example 4 in which 5 wt% was added, the best thermal shock resistance was shown among those evaluated at ΔT = 1000 ° C. The residual expansion rate is somewhat large, the reaction resistance tends to be slightly reduced, and the tendency to decrease is large compared to the addition of zirconia.

(Comparative Example 1)
A sheath of the same shape as in Example 1 was made of alumina-mullite. Although the thermal shock resistance is high, the residual expansion due to the reaction is large, and the reaction resistance is inferior to the magnesia-spinel quality of each of the examples.

(Comparative Example 2)
This is an example of magnesia without addition of magnesia-spinel, which has excellent reaction resistance but thermal shock resistance.

(Comparative Example 3)
This is an example of magnesia-spinel with a MgO ratio of 60 wt% or less, and the reaction resistance is insufficient.

(Comparative Example 4)
This is an example in which the proportion of magnesia-spinel 50 μm or less Al ₂ O ₃ is 5.0 wt% or more, and the amount of MgO is 60 wt% or more, but the residual expansion rate is large and the reaction resistance is insufficient. ΔT is as low as 700 ° C. and the thermal shock resistance is insufficient.

(Comparative Example 5)
Although this is an example of magnesia-spinel and zirconia added in an amount of 10.0 wt% or more, the thermal shock resistance is insufficient.

(Comparative Example 6)
Although it is an example in which the amount of zirconia and mullite added is 15.0 wt% or more in magnesia-spinel, the thermal shock resistance is insufficient.

Claims (3)

A firing container having a maximum particle size of 3 mm or less and a main component of magnesia and magnesia spinel, wherein the total amount of MgO is 60 to 90 wt% and the amount of Al ₂ O ₃ contained in the powder having a particle size of 50 μm or less is 2 A baking container characterized by being not more than 0 wt%. The calcination container according to claim 1, wherein 3 to 10 wt% of zirconia is added in an external ratio. The firing container according to claim 1, wherein 3 to 10 wt% of zirconia-mullite is added in an outer ratio.