JP2016030715A - Composite heat insulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite heat insulator which maintains heat insulation property at high temperature and besides, has light weight and enables handleability thereof during work to be improved.SOLUTION: There is provided the composite heat insulator which is constituted of: a porous sintered body that is a spinel composed of a chemical formula XAlO, where X is one of Zn, Fe, Mg, Ni and Mn; and a fiber layer containing an aggregate of fiber composed of an inorganic material formed on at least one surface of the porous sintered body and which has a porosity of 70% or more. In the composite heat insulator, pore having a pore diameter of over 1000 μm accounts for 10 vol% or less of the whole pores, pore having a pore diameter of 0.01 to 0.8 μm accounts for 10 to 30 vol% of the pore having a pore diameter of 1000 μm or less and pore having a pore diameter of 0.8 to 10 μm accounts for 50 to 80 vol% of the pore having a pore diameter of 1000 μm or less, and a silica component in the fiber of the fiber layer is 55 wt.% or less.SELECTED DRAWING: None

Description

  The present invention relates to a composite heat insulating material including a spinel porous sintered body.

  As an example of a lightweight, high-strength heat insulating material, a composite material including a heat insulating material made of a porous material and a material containing fibers is known.

For example, Patent Document 1 discloses the following (A), (B) as a multilayer heat insulating material that can be used in a temperature range exceeding about 1500 ° C. and is excellent in mechanical properties and heat resistance manufactured by a simple method. ) And (C); (A) a heat-resistant layer containing 75 to 95% by weight of mullite fibers and 5 to 25% by weight of silica fibers, (B) an intermediate layer, (C) 15 to 35% by weight of mullite fibers and 65 of silica fibers. Invention of multi-layered heat insulating material consisting of three layers of a heat insulating layer containing ~ 85% by weight and having a three-dimensional network structure having a glassy boron compound that fixes the entanglement point of the fiber Have been described.

By the way, the ceramic porous body of magnesia spinel attracts attention as a material of the heat insulating material in which an increase in thermal conductivity is suppressed in a high temperature region of 1000 ° C. or higher and excellent in heat resistance.

Patent Document 2 or 3 discloses that a porous spinel ceramic body having a predetermined pore size distribution can suppress conduction heat transfer and radiation heat transfer, and thereby can be used as a heat insulating material having excellent heat resistance at a high temperature of 1000 ° C. or higher. Is described.

Japanese Patent Laid-Open No. 10-226582 JP 2012-229139 A JP 2013-209278 A

  In recent years, an increase in thermal conductivity is suppressed even in a high temperature region of 1000 ° C. or higher, and there is a tendency to require a lightweight and high-strength heat insulating material.

  When trying to apply the spinel-like ceramic porous body described in Patent Documents 2 and 3 to the invention described in Patent Document 1, while maintaining excellent heat insulation at high temperatures, The weight increased, handling was not easy, in other words, handling during construction was not sufficient. Moreover, when the weight increases, the volume specific heat increases, and there is a concern that the amount of heat required for the temperature rise of the heat insulating material increases.

  In view of the above technical problem, an object of the present invention is to provide a composite heat insulating material that is excellent in heat insulation at high temperatures, is lightweight, has a small volumetric specific heat, and is excellent in handling properties.

The composite heat insulating material according to the present invention is a spinel material having the chemical formula XAl ₂ O ₄ , wherein X in the chemical formula is any one of Zn, Fe, Mg, Ni and Mn, and the porous The porous sintered body has a porosity of 70% or more and a pore diameter of more than 1000 μm. The fibrous layer includes an aggregate of fibers made of an inorganic material formed on at least one surface of the porous sintered body. It is 10 vol% or less of the total pores in the porous fired body, and pores having a pore diameter of 0.01 μm or more and less than 0.8 μm are 10 vol% or more and 30 vol% or less of pores having a pore diameter of 1000 μm or less, and a pore diameter of 0.8 μm or more and less than 10 μm. The pores occupy 50 vol% or more and 80 vol% or less of the pores having a pore diameter of 1000 μm or less, and the silica component in the fiber in the fibrous layer is 55 wt% or less. .

By having such a configuration, it is possible to obtain a composite heat insulating material that is excellent in heat insulation at high temperatures, is light in weight, has a small volumetric specific heat, and is excellent in handling properties.

In the composite heat insulating material according to the present invention, the spinel material having the chemical formula XAl ₂ O ₄ is preferably MgAl ₂ O ₄ .

According to the present invention, it is possible to provide a composite heat insulating material that is excellent in heat insulation at high temperature, is lightweight, has a small volume specific heat, and is excellent in handling properties.

Hereinafter, the present invention will be described in detail. The composite heat insulating material according to the present invention is a spinel material having the chemical formula XAl ₂ O ₄ , wherein X in the chemical formula is any one of Zn, Fe, Mg, Ni and Mn, and the porous The porous sintered body has a porosity of 70% or more and a pore diameter of more than 1000 μm. The fibrous layer includes an aggregate of fibers made of an inorganic material formed on at least one surface of the porous sintered body. It is 10 vol% or less of the total pores in the porous fired body, and pores having a pore diameter of 0.01 μm or more and less than 0.8 μm are 10 vol% or more and 30 vol% or less of pores having a pore diameter of 1000 μm or less, and a pore diameter of 0.8 μm or more and less than 10 μm. The pores occupy 50 vol% or more and 80 vol% or less of the pores having a pore diameter of 1000 μm or less, and the silica component in the fibers in the fibrous layer is 55 wt% or less.

The present invention includes a porous sintered body in which a spinel material having the chemical formula XAl ₂ O ₄ and X in the chemical formula is any one of Zn, Fe, Mg, Ni, and Mn.

A spinel material having the chemical formula XAl ₂ O ₄ , preferably magnesia spinel where X is Mg, has a small variation in pore shape and size caused by grain growth at high temperature and bonding of grain boundaries, and has a low thermal conductivity. Since the effect of suppressing fluctuation can be maintained for a long time, it is suitable for use at high temperatures. The chemical composition and the spinel structure can be measured and identified by, for example, a powder X-ray diffraction method.

The porous sintered body has a porosity of 70% or more and a pore size of more than 1000 μm of 10 vol% or less of all pores in the porous fired body, and a pore size of 0.01 μm or more and less than 0.8 μm. Of the pores having a pore diameter of 1000 μm or less, 10 vol% or more and 30 vol% or less, and pores having a pore diameter of 0.8 μm or more and less than 10 μm account for 50 vol% or more and 80 vol% or less of the pores having a pore diameter of 1000 μm or less.

The porosity is calculated according to JIS R 2614 “Measurement method of specific gravity and true porosity of fireproof and heat insulating brick”. The pore volume ratio can be determined from the pore size distribution, and the pore size distribution can be measured by JIS R 1655 “Method for testing pore size distribution of molded ceramics by mercury porosimetry”.

If the porosity of the porous sintered body is less than 70%, the proportion of solids increases, so that conduction heat transfer increases and thermal conductivity may increase. In addition, since an intensity | strength will fall remarkably when a porosity is too high, 88% of the upper limit of a porosity is preferable.

If there are too many so-called giant pores having a pore diameter of more than 1000 μm in the porous sintered body, the temperature dependence of the thermal conductivity increases. Therefore, if the pores having a pore diameter of more than 1000 μm are made 10 vol% or less of the total pores, The effect can be suppressed to a level where there is no practical problem.

The pores having a pore diameter of 0.01 μm or more and less than 0.8 μm, so-called micropores, having a pore diameter of 1000 vol. As a result, the amount of phonon scattering in the film increases, and the effect of suppressing conduction heat transfer is obtained.

  When the micropores are less than 10 vol%, the number of grain boundaries per unit volume is small, and the effect of suppressing conduction heat transfer becomes insufficient. On the other hand, when the micropores exceed 30 vol%, it becomes difficult to obtain a porosity of 70% or more, and the thermal conductivity becomes high.

In the porous sintered body according to the present invention, pores having a pore diameter of 0.8 μm or more and less than 10 μm occupy 50 vol% or more and 80 vol% or less of pores having a pore diameter of 1000 μm or less. The micropores are within the scope of the present invention, and there is an appropriate amount of pores of 0.8 μm or more and 10 μm or less suitable for suppressing radiation heat transfer, so that the overall increase in thermal conductivity at high temperatures is achieved. Effectively suppressed.

The pore volume ratio for each pore diameter is determined in consideration of forming a fibrous layer on the surface. For this reason, the remarkable fall of the heat insulation at high temperature by the increase in radiation heat transfer by provision of a fibrous layer is suppressed, and it can be said that the original characteristic which the porous sintered compact of this invention has is maintained.

In this invention, the silica component in the said fiber in the said fiber layer is 55 wt% or less.

  The fibrous layer effectively complements the lack of toughness and light weight, which are the weak points of the porous sintered body in the present invention, without impairing the heat insulation properties at high temperatures.

  The porous sintered body of the present invention is excellent in heat insulation properties at high temperatures.For example, when it is plate-shaped, it is portable, stacked on the inner surface of the furnace body, etc., during construction including all other operations, There is a concern about the failure of breakage such as cracks, chips and breaks.

  As a countermeasure for these problems, there is a method of improving the strength of the porous sintered body itself. In this case, the increase in bulk density impairs the lightness, and there is a concern about the deterioration of workability during construction. In the present invention, workability at the time of construction is referred to as handling property for convenience.

  In addition, since the above method is intended to improve the strength as a so-called bulk body, for example, when a strong tensile stress is generated in the surface layer portion of the porous sintered body by bending due to its own weight in the plate-like material, a crack or the like is generated in the surface layer portion. And the porous sintered body, which is a brittle material, is easily damaged.

  Therefore, a method of forming a layer as reinforcement on the surface layer portion of the porous sintered body can be considered. This method can reduce the risk of breakage as described above while suppressing an increase in the overall bulk density unless the layer thickness is too thick. Moreover, since it also has a role of protecting the surface layer, it is also effective in preventing scratches and chipping.

However, the porous sintered body of the present invention has an effect of excellent heat insulation at high temperatures by having a pore volume ratio of its unique pore diameter, but simply forming a layer on its surface layer The heat insulation effect at high temperatures may be impaired.

  Therefore, in the present invention, in addition to optimizing the pore volume ratio of the porous sintered body, as a layer to be formed on the surface layer, by using a material containing fibers that are particularly resistant to tension, heat insulation at high temperatures, light weight, It is a composite heat insulating material that has both handleability and high toughness.

Here, being formed on at least one surface of the porous sintered body means that it is not an essential requirement that the entire surface of the porous sintered body is covered with the fibrous layer. Depending on the shape and method of use of the composite heat insulating material, it is difficult to cover the entire surface, but if the fiber layer is provided within the range where the effects of the present invention can be obtained, there is no particular limitation. .

If it is plate-shaped, the form that at least one main surface is covered with the fibrous layer may be sufficient. If it is a block body, only the surface to handle may be covered with the fibrous layer.

For the fiber made of an inorganic material, known inorganic materials applied to heat insulating materials and refractories can be widely used, and are not particularly limited. For example, alumina, mullite, zirconia and the like can be mentioned.

  Moreover, the form as a fiber is not specifically limited, You may select suitably according to a use purpose and a use. For example, a so-called short fiber dispersed in a matrix, a long fiber sheet or fabric, a composite of short fibers and long fibers, and the like can be mentioned.

The fibrous layer containing the aggregate of fibers made of inorganic material may contain other materials as timely constituent elements while making the fibers made of inorganic material an essential constituent element. For example, if the fiber alone cannot form a layer, an appropriate inorganic material is selected as the matrix. Further, a film for improving heat resistance and corrosion resistance may be further formed on the surface of the fibrous layer.

As described above, in the present invention, the form of the fibrous layer is not particularly limited, but the silica component in the fiber in the fibrous layer is 55 wt% or less. This is because if the silica component exceeds 55 wt%, the reaction between the spinel of the porous sintered body and the silica in the fiber becomes so large that the reaction cannot be ignored, and as a result, the risk of the fiber layer peeling off increases. It is.

  In addition, the silica component is contained in most fibers which consist of well-known inorganic materials and are applied to a heat insulating material or a refractory. For this reason, in the present invention, in order to avoid problems due to the excessive silica component, the ratio of silica contained in the fiber is limited.

  The thickness of the fibrous layer is not particularly limited, but for example, in the case of a plate-shaped composite heat insulating material, if the proportion of the fibrous layer is large with respect to the total thickness, the heat insulation at high temperature is Since it is damaged, it is designed in a timely manner in consideration of handling characteristics.

In addition, materials other than the porous sintered body and the fibrous layer can be further included as long as the effects of the present invention are not impaired. For example, fibers or the like may be added as a reinforcing material in the porous sintered body. The reinforcing material may be either the same material as the porous sintered body according to the present invention or a different material. In the above, a known pore former may be added.

In the composite heat insulating material according to the present invention, when the thermal conductivity is less than 0.4 W / (m · K) in the temperature range of 1000 ° C. or more and 1500 ° C. or less, the heat insulating property is reduced due to the provision of the fibrous layer. It can be said that the influence is minimized and it is more preferable.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not restrict | limited by the Example shown below.

(Examples 1-4, Comparative Examples 1-3)
11 mol of hydraulic alumina powder (BK-112; manufactured by Sumitomo Chemical Co., Ltd.) is mixed at a ratio of 9 mol of magnesium oxide powder (MGO11PB; manufactured by Kojundo Chemical Laboratory Co., Ltd.), and this is mixed with hydraulic alumina and magnesium oxide. A slurry was prepared by adding equal weight of pure water to the total weight of and uniformly dispersing pure water. And the pores as shown in Examples 1 to 4 and Comparative Examples 1 to 3 in the following Table 1 by changing the diameter and addition amount of the pore former and firing at 1500 ° C. for 3 hours. Each porous sintered body having the structure and was produced. Next, silica weight ratios as shown in Examples 1 to 4 and Comparative Examples 1 and 3 in Table 1 below, respectively, using alumina fibers of bulk fibers having an average diameter of 3 to 5 μm and an average length of 100 mm or less as the fibrous layer. The fiber layer is formed by mixing the alumina fiber having a thickness of 5 mm on one main surface of each of the porous sintered bodies, and then fixed at a firing temperature of 1500 ° C. and fired for 3 hours. A fired body of 25 mm × 50 mm × 200 mm was obtained. One main surface on which the fibrous layer is formed is an arbitrary surface of 50 mm × 200 mm surface, and Comparative Example 2 has no fibrous layer. As described above, evaluation samples of composite heat insulating materials as shown in Examples 1 to 4 and Comparative Examples 1 to 3 in Table 1 were prepared.

  About each porous sintered compact obtained in the above, the crystal phase was identified by X-ray diffraction (X-ray source: CuKα, voltage: 40 kV, current: 0.3 A, scanning speed: 0.06 ° / s). However, a magnesia spinel phase was observed.

For Examples 1 to 4 and Comparative Examples 1 to 3, the porosity, the pore volume ratio, and the thermal conductivity were measured or calculated, and the various evaluation results are summarized in Table 1 below. The porosity and the volume ratio of the pore are evaluated for the porous sintered body, the silica content is evaluated for the fibrous layer, and the thermal conductivity and handling properties are evaluated for the composite heat insulating material.

The pore volume was measured using a mercury porosimeter based on the method described above. The thermal conductivity was evaluated with reference to JIS A 1412-2. The evaluation of the handling property was judged by the shape holding condition when the portion of the fired body of 25 mm × 50 mm × 200 mm having a length of 200 mm was gripped and lifted horizontally by 50 mm from the end, and ◯ kept the shape. Things and x were broken.

  From the evaluation results shown in Table 1, it can be seen that the thermal conductivity at 1000 ° C. or higher is kept low in the implementation range according to the present invention. The handling property is also large compared to Comparative Example 2 which is a porous sintered body having no fibrous layer, and it can be seen that the toughness is improved.

On the other hand, Comparative Example 1 showed a tendency for the thermal conductivity to be high because the porosity was low and the silica component in the fiber was large compared to the implementation range of the present invention.

Moreover, as shown in Comparative Example 2, it can be said that the porous layer alone has poor handling and poor toughness.

Furthermore, as shown in Comparative Example 3, when fibers having a silica content of more than 55 wt% were used, peeling occurred between the porous layer and the fibrous layer. Therefore, measurement of thermal conductivity and handling property could not be performed.

The above examples are porous sintered body is a case of spinel composed of MgAl ₂ O _4, as described above, in the present invention _{ZnAl 2 O 4, FeAl 2 O} 4, NiAl 2 O 4, MnAl 2 O The same effect can be obtained with any of the spinel substances of No. ₄ . These are substantially the same as MgAl ₂ O ₄ described above except that, in order, a porous ceramic raw material by a combination of ZnO + Al ₂ O ₃ , Fe ₂ O ₃ + Al ₂ O ₃ , NiO + Al ₂ O ₃ , MnO + Al ₂ O ₃ is used. Can be manufactured.

None

Claims (2)

A porous sintered body having the chemical formula XAl ₂ O ₄ , wherein X in the chemical formula is any one of Zn, Fe, Mg, Ni and Mn, and at least one surface of the porous sintered body The porous sintered body has a porosity of 70% or more, and pores having a pore diameter of more than 1000 μm are all pores of the porous sintered body. The pores having a pore diameter of 0.01 μm or more and less than 0.8 μm are 10 vol% or more and 30 vol% or less, and the pores having a pore diameter of 0.8 μm or more and less than 10 μm are pores having a pore diameter of 1000 μm or less. The composite heat insulating material which occupies 50 vol% or more and 80 vol% or less, and the silica component in the fiber in the fibrous layer is 55 wt% or less. The composite heat insulating material according to claim 1, wherein the spinel material having the chemical formula XAl ₂ O ₄ is MgAl ₂ O ₄ .