JP2014081072A - Heat insulation material and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat insulation material exhibiting a predetermined heat resistance property even at a high temperature, concretely at 1000°C.SOLUTION: In a heat insulation material, a pore volume with a pore diameter of 100 nm or less is 27 vol% or more, a heat transfer coefficient at 600°C is 0.1 W/mK or less, and a contraction coefficient after heating for three hours at 1000°C is 4% or less. The heat insulation material is obtained by calcining a row material of the heat insulation material containing an amorphous fireproof material of 30 mass% or more under a calcination condition in which the contraction coefficient after calcination is 7-40%.

Description

  The present invention relates to a heat insulating material having low thermal conductivity and excellent heat resistance, and a method for producing the same. In particular, heat insulation materials for steelmaking furnaces such as ladle, TPC, TD, heat insulation materials for rolling furnaces such as soaking furnaces, heating furnaces, heat insulation materials for heat treatment furnaces such as carburizing furnaces, metal sintering furnaces, induction processing furnaces, etc. , Insulation materials for non-ferrous metal furnaces such as melting furnaces, fuel heating furnaces, insulation materials for ceramic furnaces such as glass melting furnaces, cement firing furnaces, refractory firing furnaces, or insulation materials for fuel cells, and these insulation materials It relates to the manufacturing method.

  As such a heat insulating material, a microporous heat insulating material containing a fumed raw material having a diameter of about several tens of nanometers is known. The microporous heat insulating material is a low heat conductivity material excellent in heat insulating properties with a heat conductivity of about 0.02 W / mK.

  The microporous insulation is usually composed of a siliceous or alumina fumed raw material, an infrared opaque material such as silicon carbide, titania or zircon, and a reinforcing fiber such as glass fiber or silica fiber, which is dry-molded. Is. Therefore, since there is no binder, the strength is low and it is easy to buckle. If strength is low, external force and heat stress cannot be resisted, workability is poor, and in the case of bracket fastening method, the heat insulation material buckles, so if the nut sinks or loosens during use, heat leak will occur However, there was a problem that the heat insulating property was lowered.

JP-A-56-73684 JP 2012-136891 A

As a solution to the problem that the strength of the microporous heat insulating material is low, Patent Document 1 discloses that a metal oxide compound of silicon and / or aluminum element having a BET specific surface area of 10 to 700 m ² / g, a mineral suspending agent, and , A technique of chemically reacting an insulating molded body composed of an element capable of generating a solid oxide having a reference generation enthalpy of −900 kJ / mol or less and a mineral fiber at about 200 to 900 ° C. is disclosed. According to this technique, the strength of the entire molded body is increased, and since the chemical reaction does not cause sintering, the heat insulating property, volume, and porosity are not changed, and water resistance is assumed.

  Patent Document 2 is obtained by mixing small particles containing silica of less than 5 to 50 nm, large particles containing silica of 50 to 100 μm, and one or more of alkali metal elements and alkaline earth elements. A technique for heating the above mixture at a temperature of 400 ° C. or higher is disclosed. According to this technique, the basic element is melted by the heat treatment, reacts with silica, is fused at the particle interface, and has a high compressive strength. On the other hand, the basic element content is reduced to 5% or less. It is said that a large fusion surface is not formed.

  However, as a result of heating the inventors at 750, 800, and 850 ° C. for 3 hours with respect to Example 1 of Patent Document 1 above, the shrinkage ratios of the former two were 0.1 and 2.2. However, it rapidly increased to 18.8% at 850 ° C. Moreover, about Example 1 of the said patent document 2, as a result of heating at 900,950,1000 degreeC for 3 hours, as for the shrinkage rate, the former two were 0.2, 1.5, but at 1000 degreeC, it is 12 at 1000 degreeC. 3%.

  If the heat insulating material is significantly contracted, a gap is generated in the construction portion of the heat insulating material along with the contraction, and heat leaks to the back side, so that the original heat insulating property cannot be exhibited. Therefore, for example, JIS stipulates that the shrinkage rate is 4 to 2% or less (JIS R3311) in the case of a fibrous heat insulating material, and less than ± 2% (JIS R2611) in the case of a fireproof heat insulating brick.

  The problem to be solved by the present invention is to provide a heat insulating material that exhibits a predetermined heat resistance even at a high temperature, specifically 1000 ° C.

  In order to solve the above problems, the heat insulating material of the present invention is characterized in that it has a microstructure having a pore volume of 27 vol% or more with a pore diameter of 100 nm or less.

  The heat transfer (thermal conductivity) of such a microporous heat insulating material is represented by the sum of heat transfer of gas molecules, conduction due to contact between solids, and radiation. Microporous insulation has a small amount of solid, and dry fumed silica and fumed alumina, which are generally produced by the gas phase method, which is the main raw material, are spherical particles with a diameter of about several tens of nanometers. Is very small, and the actual heat transfer is determined by the heat transfer and radiation of gas molecules. Heat transfer of gas molecules can be suppressed when the pore diameter is equal to or less than the mean free path, and radiation can be controlled by an infrared opaque material. In terms of heat transfer characteristics, the former is dominant in the low temperature range (about 400 ° C. or less), and the latter is in the high temperature range (about 600 ° C. or more). However, since heat transfer is a summation, if the heat insulation is poor at low temperatures, it deteriorates further at high temperatures where the movement of gas molecules becomes more active. Therefore, tissue control is important to suppress heat transfer of gas molecules. It becomes.

  Accordingly, the present inventors made test pieces having different pore diameter distributions and conducted various investigations on the relationship between the pore diameter and the pore volume and the thermal conductivity at 600 ° C. As a result, the pore volume with a pore diameter of 100 nm or less was 27 vol%. In the above case, it has been found that the thermal conductivity can be suppressed to 0.1 W / mK or less. In addition, it was also found that the volume of the pores is preferably 53 vol% or more in order to make the thermal conductivity 0.08 W / mK or less where the characteristics of the microporous heat insulating material easily appear.

As for the thermal conductivity of the microporous heat insulating material, a thermal conductivity at 600 ° C. of 0.1 W / mK or less is often useful in comparison with various types of heat insulating materials. Since 600 ° C is often used at a heating surface side temperature of about 1000 to 1100 ° C at the maximum and a back side temperature of about 40 to 300 ° C, it is usually used as an intermediate temperature. Temperature. Also, JIS
The measurement temperature of the thermal conductivity of the refractory insulating brick defined by R2611 is also 600 ° C.

  Secondly, the heat insulating material of the present invention is characterized in that the shrinkage after heating at 1000 ° C. for 3 hours is 4% or less. If the shrinkage rate exceeds 4%, heat leaks to the back side, and the original heat insulating performance cannot be exhibited. If the shrinkage rate is 2% or less, the effect of heat leakage can be neglected practically. Therefore, the shrinkage rate is preferably 2% or less.

Further, the heat insulating material of the present invention preferably has a secant elastic modulus at 0.1 proof stress of 8 N / mm ² or more. Below this value, buckling occurs, which may hinder the metal fitting operation.

  Here, “second elastic modulus at 0.1 proof stress” will be described. For a material having a non-linear elastic property, a value obtained by dividing the stress at an arbitrary point by a strain at a point on the curve of the stress-strain line is called a second elastic modulus. Here, the secant elastic modulus at a stress equivalent to 10% of the compressive strength is defined as the secant elastic modulus at 0.1 proof stress.

The manufacturing method of the present invention for manufacturing the heat insulating material of the present invention is characterized in that a molded body made of a raw material for heat insulating material is fired under firing conditions such that the shrinkage ratio after firing is 7 to 40%. . If the shrinkage after firing is less than 7%, sintering is insufficient and the secant elastic modulus at 0.1 proof stress is less than 8 N / mm ^2, which is not suitable for applications where buckling is a problem (buckling). It can be applied to applications where there is no significant problem.) The shrinkage rate of 40% is an inflection point with respect to the thermal conductivity. If the shrinkage rate exceeds 40%, the pore volume of 100 nm or less becomes less than 27 vol%, and the thermal conductivity increases significantly, so it should not exceed 40%. The reason why the thermal conductivity increases remarkably when the shrinkage ratio after firing exceeds 40% is that the pore diameter of the amorphous refractory raw material (fumed raw material) contained in the heat insulating material is increased with the progress of solid phase sintering. This is thought to be due to a significant increase and a reduction (disappearance) of the heat transfer suppression effect of gas molecules.

  In the present invention, when no alkali metal element or alkaline earth metal is added, rapid shrinkage during firing can be suppressed, but the shrinkage after heating at 1000 ° C. for 3 hours does not exceed 4%. No problem. When an appropriate amount of alkali metal element or alkaline earth metal is added within this range, the secant elastic modulus can be improved.

In order to ensure a pore volume of 27 vol% or more with a pore diameter of 100 nm or less, achieve a thermal conductivity of 0.1 W / mK or less, and ensure a secant coefficient of 8 N / mm ² or more at 0.1 proof stress, The BET specific surface area of the amorphous refractory raw material in the raw material is preferably 50 m ² / g or more, and the content thereof is preferably 30% by mass or more. More preferably, the content of the amorphous refractory raw material is 50% by mass or more and 90% by mass or less.

The material of the amorphous refractory raw material is not particularly limited and may be selected according to the maximum operating temperature to be designed, or may be used in combination as appropriate. Typically, siliceous or alumina fumed raw material (fumed silica) Alternatively, fumed alumina) can be used. In addition, titania and other metal oxides can be used as the fumed raw material, and materials manufactured by the wet method, arc method, and pyrolysis method are used other than the fumed raw material manufactured by the vapor phase method. be able to. Any amorphous refractory raw material preferably has a BET specific surface area of 50 m ² / g or more for the above reasons.

There are no restrictions on other raw materials that occupy the remaining 70% by mass as the heat insulating material (heat insulating material), and raw materials that do not interfere with the properties of the heat insulating material may be used. Normally, when used for high temperature, zircon (ZrSiO ₄ ), silicon carbide (SiC), titania (TiO ₂ ), etc. can be used in combination as an infrared opaque material. When these infrared opaque materials are used in a ratio of 10% by mass or more in total in the ratio of the total amount of the heat insulating material (heat insulating material), an effect can be obtained. Preferably, it is used in an amount of 10% to 50% by mass.

  Moreover, a mineral fiber can be used as needed. The material of the mineral fiber is not limited, but from the viewpoint of reducing the shrinkage rate, for example, silica fiber (also referred to as high-purity glass fiber), alumina fiber or the like having a small alkali component can be used. In consideration of carcinogenicity, the fiber diameter is usually about 7 μm. An effect is acquired when the usage-amount is 0.2 mass% or more from the point of the handleability after shaping | molding, and a reinforcement. Preferably, it is used at 0.2 mass% or more and 5 mass% or less.

  The heat insulating material of the present invention exhibits predetermined heat resistance even at 1000 ° C. Moreover, according to the manufacturing method of the heat insulating material of this invention, the said heat insulating material of this invention can be manufactured stably and the intensity | strength of a heat insulating material can also be ensured.

  The heat insulating material of the present invention can be produced by mixing the raw materials of the heat insulating material and then forming the material, and baking the formed body under the baking conditions that the shrinkage ratio after baking is 7 to 40%.

As described above, a material containing 30% by mass or more of an amorphous refractory material having a BET specific surface area of 50 m ² / g or more can be suitably used as the heat insulating material. As described above, an infrared opaque material or mineral fiber can be used for the remaining 70% by mass.

  Mixing and forming of these heat insulating materials can be performed by conventional methods. Moreover, although baking is performed on the baking conditions which the shrinkage rate after baking becomes 7 to 40%, the baking itself can be performed by a conventionally general method.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.

  The raw material powder of the heat insulating material shown in Table 1 is uniformly mixed using a high-speed mixer, the mixed powder is pressure-molded, the molded body is fired under the firing conditions shown in Table 1, and a sample of the heat insulating material is prepared. Produced. Firing was performed in an oxidizing atmosphere, and the shrinkage after firing was determined according to JIS R2613.

  For each sample, (1) shrinkage after heating, (2) pore volume, (3) thermal conductivity, (4) compressive strength, and (5) secant elastic modulus were evaluated as characteristics. The evaluation method of each characteristic is as follows.

(1) Shrinkage ratio after heating A test piece of width 40 × length 40 × thickness 20 mm is placed in an electric furnace and heated at 1000 ° C. for 3 hours. The width and length before and after heating are measured, the residual line change rate (JIS R2613) averaged from the width and length is obtained, and this is defined as the shrinkage rate after heating.

(2) Pore volume The test piece is an 8 mm cube. The pore distribution is measured with a mercury intrusion porosimeter, and the pore volume of 100 nm or less is determined from the relationship between the pore diameter and the cumulative pore volume.

(3) Thermal conductivity Measured according to JIS A1412-1 “Measuring method of thermal resistance and thermal conductivity of thermal insulation material—Part 1: Protection hot plate method (GHP method)”. The measurement temperature is 600 ° C.

(4) Compressive strength The shape of a test piece shall be width 40x length 40x thickness 20mm. The degree of compressive stress is 0.05 to 0.2 MPa / s. JIS R2206-2 "Test method for compressive strength of refractory bricks-Part 2
Part: method using packing ".

(5) Secant elastic modulus The shape of a test piece shall be width 40x length 40x thickness 20mm. The test piece is loaded at a loading speed of 0.01 mm / s and subjected to compression fracture. During this time, the stress-strain relationship is recorded. A secant elastic modulus at a stress equivalent to 10% of the compressive strength is obtained, and this is defined as a secant elastic modulus at a 0.1 proof stress.

In Examples 1 to 5 of Table 1, the shrinkage after firing was changed from 7.7% to 40% by changing the firing conditions. As the shrinkage after firing increases, the shrinkage after heating and the pore volume decrease, and the thermal conductivity, compressive strength, and secant elastic modulus tend to increase, but in all cases, the pore volume is 27 vol% or more, the thermal conductivity Of 0.1 W / mK or less, the shrinkage ratio after heating is 4% or less, and the preferred elastic modulus of 8 N / mm ² is also satisfied. In particular, in Examples 1 to 4 in which the pore volume is 53 vol% or more, the thermal conductivity is 0.08 W / mK or less, and more excellent heat insulation is obtained. In this respect, the pore volume is preferably 53 vol% or more.

  In Examples 6 and 7, a compound containing an alkali metal element is added to a heat insulating material. In Table 1, the amount of addition is shown as outer mass% with respect to 100 mass% of other raw materials. When an alkali metal element is added, sintering is promoted as compared with Example 1 without addition, and as a result, the shrinkage after heating is reduced and the secant elastic modulus is increased. It is obvious to those skilled in the art that similar results can be obtained when a compound containing an alkaline earth metal element is added.

Examples 8-11 change the BET specific surface area of the dry-type fumed silica which is an amorphous refractory raw material. Although all the examples satisfy the requirements of the present invention that the pore volume is 27 vol% or more, the thermal conductivity is 0.1 W / mK or less, and the shrinkage after heating is 4% or less, the BET specific surface area is 20 g / m. ^In Example 8 of ² , the secant elastic modulus was less than 8 N / mm ² . Considering together with the results of Example 9, it can be said that the BET specific surface area of the amorphous refractory raw material is preferably 50 g / m ² or more.

In Examples 12 to 15, the content of dry fumed silica, which is an amorphous refractory raw material, is changed. In any of the examples, the pore volume is 27 vol% or more, the thermal conductivity is 0.1 W / mK or less, and the shrinkage ratio after heating is 4% or less, but the content of dry fumed silica is satisfied. However, in Example 12, the ^second elastic modulus was less than 8 N / mm ² . Considering together with the result of Example 13, it can be said that the content of the amorphous refractory raw material is preferably 30% by mass or more.

In Example 16, dry fumed alumina was used in place of dry fumed silica as an amorphous refractory raw material. This Example 17 also satisfies the requirements of the present invention that the pore volume is 27 vol% or more, the thermal conductivity is 0.1 W / mK or less, and the shrinkage after heating is 4% or less, and the ^second elastic modulus is 8 N / mm ^2. The preferable requirement is also satisfied.

Examples 17-20 use silicon carbide or zircon instead of titania as the infrared opaque material. These Examples 17 to 20 also satisfy the requirements of the present invention that the pore volume is 27 vol% or more, the thermal conductivity is 0.1 W / mK or less, and the shrinkage after heating is 4% or less, and the second elastic modulus is 8N. The preferable requirement of / mm ² is also satisfied.

  Examples 18 and 19 are examples in which a compound containing an alkali metal element was added to Example 17. Since sintering can be moderately promoted, the firing time can be shortened although the shrinkage ratio after heating is slightly increased. However, the addition of an alkali metal element or alkaline earth metal makes it difficult to control the shrinkage rate after heating, so it is preferable to add no additive.

  Comparative Examples 1 and 2 use the same heat insulating material as in Examples 1 to 5 above, but Comparative Example 1 is fired under the condition of oversintering with a shrinkage ratio after firing of 42.2%. As a result, the pore volume was less than 27 vol%, and the thermal conductivity exceeded 0.1 W / mK. On the other hand, in Comparative Example 2, the shrinkage ratio after firing was 2.2% and the sintering was insufficient, and the shrinkage ratio after heating exceeded 4%.

  Comparative Example 3 corresponds to Example 1 of Patent Document 2 described above. The shrinkage rate after firing was 1.2%, the sintering was insufficient, and the shrinkage rate after heating exceeded 4%.

Claims (10)

  A heat insulating material having a pore volume of 27 vol% or more with a pore diameter of 100 nm or less, a thermal conductivity at 600 ° C of 0.1 W / mK or less, and a shrinkage rate of 4% or less after heating at 1000 ° C for 3 hours.   The heat insulating material according to claim 1, wherein a pore volume having a pore diameter of 100 nm or less is 53 vol% or more.   The heat insulating material according to claim 1 or 2, wherein a shrinkage ratio after heating at 1000 ° C for 3 hours is 2% or less. The heat insulating material according to any one of claims 1 to 3, wherein a ^second elastic modulus at a proof stress is 8 N / mm ² or more.   The heat insulating material in any one of Claim 1 to 4 which does not contain an alkali metal element and an alkaline-earth metal.   The heat insulating material in any one of Claim 1 to 5 which contains 30 mass% or more of amorphous refractory raw materials.   The heat insulating material according to any one of claims 1 to 6, comprising 10% by mass or more of any one or more of zircon, silicon carbide, and titania.   In the manufacturing method of the heat insulating material which manufactures the heat insulating material in any one of Claim 1 to 7, the molded object which consists of a raw material for heat insulating materials is baked on the baking conditions from which the shrinkage rate after baking becomes 7 to 40%. The manufacturing method of the heat insulating material characterized by the above-mentioned.   The manufacturing method of the heat insulating material of Claim 8 in which the said raw material for heat insulating materials contains 30 mass% or more of amorphous refractory raw materials. The method for producing a heat insulating material according to claim 9, wherein the amorphous refractory raw material is fumed silica or fumed alumina having a BET specific surface area of 50 m ² / g or more.