JPS63159271A - Manufacture of ceramic foam - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a ceramic foam that can be used in a wide temperature range, has excellent heat resistance and insulation properties, is lightweight and has high strength. The present invention relates to a method of manufacturing a ceramic foam that can be easily manufactured into a shape at a low cost.

U Conventional technology and problems 1 Ceramic foams have traditionally been used as electrical insulation materials, heat storage materials for heat exchangers, etc., and are usually made from natural raw materials such as expanded shale, expanded clay, and natural glass. By utilizing the foaming phenomenon that occurs when the crystal water and gases contained in these raw materials are released at a temperature near the softening or melting temperature of these raw materials, these raw materials can be used alone or with other ceramic materials. It is manufactured as a mixture of However, since such foaming raw materials are naturally produced, it is difficult to obtain them with constant ingredients.
There is a problem in that the characteristics of the product vary widely, and therefore the range of its use becomes narrow.

For this purpose, a method has been proposed in which a ceramic foam is manufactured by mixing an industrially refined foaming agent with a ceramic material and firing the mixture at a high temperature.

However, all of these manufacturing methods require 1000
It is fired and foamed at a temperature of ℃ or higher,
There are problems such as high energy consumption, high production costs, and difficulty in obtaining products with uniform and constant ingredients.

In addition, several manufacturing methods have recently been proposed in which foaming is caused by a reaction between an aqueous solution of a water glass-based alkali silicate and metal powder. This method is a method of heat treatment at a temperature of 1000°C or less, so it is a preferable method from an energy-saving perspective. However, the resulting foam contains a fairly large amount of alkaline components. However, this method still has problems with heat resistance, chemical stability, etc.

[Means for Solving the Problems] The present inventors have solved the above-mentioned problems and have developed heat resistant and
We conducted extensive research to find a method to easily and inexpensively manufacture lightweight, high-strength ceramic foam with excellent heat insulation properties in arbitrary shapes using fixed ingredients, and by adding phosphoric acid to a mixture of ceramic powder and metal powder. The present inventors have completed the present invention by discovering that the object can be achieved by foaming, drying, solidifying, and heat-treating, and further, after foaming, by impregnating with a concentrated chromic acid aqueous solution and heat-treating. That is, the first aspect of the present invention is to add phosphoric acid to a mixture of ceramic powder and a small amount of metal powder to form a paste or slurry, fill it into a mold, foam it, and then dry and solidify it. The second invention is a method for producing a ceramic foam that undergoes heat treatment, and the second invention is to add phosphoric acid to a mixture of ceramic powder and a small amount of metal powder to form a paste or slurry, and then fill the mixture into a mold and foam it. and drying at 200 to 300°C to form a foam; and after impregnating the foam with a concentrated chromic acid aqueous solution, the foam is strengthened by heat treatment. It's a method.

As the ceramic powder used in the present invention, a wide range of raw materials from naturally occurring minerals to synthetic products can be used depending on the purpose of use. That is, for example, silicas, clay minerals, silicates such as sillimanite, pyroxene, and holsterite, alumina, mullite, copillite, zirconia, zircon, spinel, chromia, silicon carbide, silicon nitride, and mixtures thereof. Examples include, but are not particularly limited to. Furthermore, the particle size of the ceramic powder is not particularly limited, but is usually 44μ.
m or less powder, and particle size distribution width (particle size range)
It is preferable to keep the value narrow in order to uniformize the size and distribution of bubbles generated during manufacturing. Furthermore, it is also possible to use a powder mixed with some short fibers.

Examples of the metal powder include aluminum, iron, manganese, zinc, arbitrary mixtures thereof, and alloys containing intermetallic compounds having these as main components, and one or more of these may be used. Although the particle size of the powder is not particularly limited, it is preferably 15 μm or less.

Therefore, this metal powder is added and mixed in a small amount to the above-mentioned ceramic powder, and becomes a foaming agent for reacting with phosphoric acid added as described below at room temperature to generate hydrogen gas, and The aqueous solution of phosphate of the added metal produced by this reaction is combined with the ceramic powder by drying and heat treatment, thereby firmly binding the ceramic powders together to form a strong ceramic foam.

As a phosphoric acid aqueous solution, the concentration is 24-28%t+3po
.

(specific gravity 1.14 to 1.17) is suitable, and strengthens the foaming reaction and the bonding of the ceramic powder,
The concentration and amount of the phosphoric acid aqueous solution are determined experimentally so that it will have an appropriate viscosity when formed into a paste or slurry, and will form a strong bond for the foam when heat treated.

The ceramic powder, metal powder, phosphoric acid aqueous solution, etc. used in the second method of the present invention have exactly the same specifications as those described above.

The concentrated chromic acid aqueous solution used in the second invention method is
Dissolve 100 parts by weight of chromium trioxide (Cr(1,) in 75 parts by weight of water, dilute with a small amount of water, and adjust the specific gravity to 1.4 or more, preferably 1.45 to 1.6.) .Taki Chromic acid aqueous solution is used to strengthen the foam, and a solution with a specific gravity of 1.4 or less can also be used. It is preferable that the specific gravity is 1.4 or more, since it is necessary to repeat the treatment with a large number of depressions, which is inconvenient.

Next, the first method of the present invention using these materials is to first add 3 to 10 parts by weight of metal powder to 100 parts by weight of ceramic powder and prepare a well-mixed mixture by dry or wet method. do. If this mixing is done wet,
Mix the metal powder with a non-oxidizing solution such as alcohol or mineral spirits to prevent it from oxidizing.
It is preferable to remove these solutions after the mixing is completed.

Then, 6 to 6 parts of phosphoric acid was added to 100 parts by weight of the powder mixture.
Add 14 parts by weight, mix, fill in a mold of any shape as a paste or slurry, foam at room temperature, and heat to 100°C.
After drying and solidifying before and after, the mold is released. The time required for foaming, drying, and solidification varies depending on the size of the mold used and other conditions, but it is preferable to sufficiently foam, dry, and solidify.

A heat treatment is then carried out to obtain a ceramic foam product. The atmosphere and heating rate of this heat treatment are not particularly limited, but usually, in an oxidizing or neutral atmosphere, the heating rate is 4 to 700°C or higher, preferably 750 to 850°C.
It is fired for 0 to 60 minutes. This heat treatment allows the production of ceramic foams that are strongly bonded by thermally stable metal phosphates.

As mentioned above, the second method of the present invention consists of two steps: preparation of a mixture of ceramic powder and metal powder in the first step - addition of phosphoric acid - preparation of a paste-like or slurry-like material - transfer to a mold. The operations and conditions such as filling, foaming, drying and solidifying at around 100° C., and mold release are exactly the same as in the first invention method. Next, after releasing the mold, a drying process is further performed at 200 to 300°C for 30 to 60 minutes. This drying temperature is 20
If the temperature is below 0°C, it is inconvenient that when the foam is treated with concentrated chromic acid in the next step, it may react with the concentrated chromic acid and collapse.Heating above 300°C is disadvantageous because the ceramic bonds may be damaged by the chromic acid. Chromium oxide (Cr
203), so it is useless.

Next, in the second step, the foamed solidified body formed in the previous step is impregnated with a concentrated chromic acid aqueous solution. Impregnation is performed by an appropriate method such as immersing the foamed solidified material in a concentrated chromic acid aqueous solution or pouring it on by spraying, etc., and removes the excess concentrated chromic acid aqueous solution stuck in the pores of the foamed solidified material using a centrifugal separator, for example. and thoroughly dry this at 50 to 70°C.

Next, heat treatment is performed at 500° C. or higher, but the atmosphere is not limited.

In addition, in order to obtain a high-strength ceramic foam, the impregnation with the concentrated chromic acid aqueous solution and heat treatment are further repeated for 2 to 30 minutes.
Preferably, four repetitions are carried out, which makes it possible to produce a very strong ceramic foam.

[Effects of the Invention] The present invention mixes ceramic powder and metal powder, adds phosphoric acid, foams at room temperature, and heat-treats the mixture (first step).
(2nd invention), after foaming, it is dried and then impregnated with a concentrated chromic acid aqueous solution and heat treated (2nd invention), so it is possible to foam by the reaction of the metal powder and phosphoric acid, and at the same time, the metal produced by this reaction can be foamed. A strong bond of ceramics can be achieved by heat treatment of the phosphate, and further, in the second invention, due to the synergistic effect of the bonding by the metal phosphate and the bonding action of chromium oxide converted from chromic acid. It is possible to manufacture ceramic foams with even higher strength, and there are no particular restrictions on the raw material ceramic powder, and materials with characteristics depending on the purpose of use can be selected. It can be used as electrical insulation materials, resistance materials, heat storage materials for heat exchangers, filtration materials, and other industrial materials.

Furthermore, since it is foamed at room temperature, dried, hardened, and released from the mold, it is possible to mold any complex shape using a small mold, and has the advantage that there is almost no dimensional change due to expansion or contraction due to heat treatment. , the heat treatment temperature can be lower than 1000°C, it is energy saving, does not require sophisticated manufacturing equipment, the process is simple and the manufacturing cost is low, and it has extremely excellent effects. This is recognized as an extremely advantageous method for industrially producing ceramic foams.

[Example 1 Next, examples of the present invention will be described.

Example 1 Alumina powder (α-A1203, particle size range 5-20 μm
) 5 parts by weight of aluminum powder (particle size 15 μm or less) and ethanol were added to 100 parts by weight, mixed with the particles using a ball mill for 6 hours, and then dried at 120° C. for 40 minutes. To 100 parts by weight of this dry powder was added a phosphoric acid aqueous solution (27% H3P).
0. ) 8.5 parts by weight was added and kneaded to form a paste, which was then filled into a paper-lined mold and foamed for several minutes at room temperature, and dried at 85°C for 60 minutes to form a foamed solidified product. did. Next, after releasing this foamed solidified body from the mold, the temperature was increased using an electric furnace at a heating rate of 5.5°C/min, and heat treatment was performed at 850°C for 30 minutes to produce a ceramic foamed body.

It was observed that relatively uniform pores were formed in the obtained product ceramic foam, and the bulk density as a dry weight relative to the volume calculated from the outer diameter was 0.54.
g/cx”, compressive strength measured by Amsler pressure tester is 31 kg/cd, JTSA-1412
Thermal conductivity measured by the flat plate comparison method is 0.075K
cal 7m-h-'C.

Example 2 Copeillite powder (Synthetic 2M (Jo 2^1203
・Contains 5Si095% or more, particle size 40μm or less) 100
3 parts by weight of aluminum powder (15 μm or less) and 4 parts by weight of zinc powder (15 μm or less) were prepared in the same manner as in Example 1, and a phosphoric acid aqueous solution (27%+1
3PO4) Add 12 parts by weight and stir to form a slurry.
This was foamed, dried and heat treated in the same manner as in Example 1 to produce a ceramic foam.

Various tests were conducted on the obtained product in the same manner as in Example 1. As a result, the bulk density is 0.38g/csn
”, compressive strength 27kg/i, thermal conductivity 0.0068K
al 7m −h −°C.

Example 3 Clay chamotte powder (particle size 40 μm or less) 100 parts by weight, iron powder (carbon steel 15.czm or less) 10 parts by weight,
Using 8 parts by weight of an aqueous phosphoric acid solution (27% H3P0.'), the mixture was treated in the same manner as in Example 1 to form a slurry, and subjected to foaming-drying-heat treatment to produce a ceramic foam.

Various tests were conducted on the obtained product in the same manner as in Example 1. The results were that the bulk density was 0.43 g/13,
Compressive strength 36kg/cJ, thermal conductivity 0.088Kal/
It was m・h・℃.

Example 4 70 parts by weight of alumina powder (α-A120 3.5 to 20 μm), 30 parts by weight of naturally produced silica powder (amorphous, 20 μm or less)
A mixed powder was prepared in the same manner as in Example 1 using 7 parts by weight of manganese powder (15 μm or less), and an aqueous phosphoric acid solution (27% t13PO, > 7 parts by weight) was mixed with this to form a mixed powder as in Example 1. Similarly, foaming was performed in the mold, dried at about 80°C for 60 minutes, removed from the mold, and further dried at 250°C for 40 minutes to form a foamed solidified product.Next, this foamed solidified product was Concentrated aqueous chromic acid solution (H2C
rO4, specific gravity 1.5) to impregnate the pores of the foamed solidified body with the solution, and then use a centrifuge to remove excess solution clogging the pores. After drying at about 65°C for about 1 hour, the temperature was raised using an electric furnace at a heating rate of 6°C/min, and heat treatment was performed at 550°C for 30 minutes, followed by the concentrated chromic acid aqueous solution treatment and heat treatment described above. Repeat the same process twice to produce a finished ceramic foam.

Various tests were conducted on the obtained product in the same manner as in Example 1. The results were: bulk density 0.78g/piece3, compressive strength 85kg/clv, and thermal conductivity 0.094Kal/3.
It was m−h ·°C.

Example 5 100 parts by weight of zirconia powder (CaO stabilized Z r02, particle size 15 m trn or less), aluminum powder (15 μm
In the same manner as in Example 4, using 4 parts by weight of zinc powder (15 μm or less), 3 parts by weight of manganese powder (15 μm or less), and 10 parts by weight of phosphoric acid aqueous solution (27% H3P0.). A foamed solidified product was formed by performing the foaming, drying, mold release, and drying processes, and then impregnation with a concentrated chromic acid aqueous solution (specific gravity: 4) and heat treatment were repeated three times in the same manner as in Example 4. Manufacture products ceramic foam.

Various tests were conducted on the obtained product in the same manner as in Example 1. The results were: bulk density 0.96g/cs3, compressive strength 74kg10&, thermal conductivity 0.052Kal/m
-h -°C.

Example 6 Silicon carbide powder (GC-3iC1 particle size 20 μm or less) 1
Same as Example 4 using 00 parts by weight, 3 parts by weight of aluminum powder (15 μm or less), 3 parts by weight of iron powder (carbon steel, 15 μm or less), and phosphoric acid aqueous solution (27% 1I3PO, >9 parts by weight) A foamed solidified body was formed by performing the following treatments: foaming, drying, mold release, and drying.This was impregnated with a concentrated chromic acid aqueous solution (specific gravity 1.5) and heat treated for 3 times in the same manner as in Example 4. The process was repeated several times to produce a finished ceramic foam.

Various tests were conducted on the obtained product in the same manner as in Example 1. The result was a bulk density of 0.73g/cm”
, compressive strength 95kg/J, thermal conductivity 0.092Kal/
It was m−h·℃.

Claims (2)

[Claims] (1) A ceramic characterized by adding phosphoric acid to a mixture of ceramic powder and a small amount of metal powder to form a paste or slurry, filling it into a mold, foaming it, drying it, solidifying it, and heat-treating it. Method of manufacturing foam. (2) Phosphoric acid is added to a mixture of ceramic powder and a small amount of metal powder to form a paste or slurry, which is filled into a mold and foamed, and then dried at 200-300°C to form a foam. A method for manufacturing a ceramic foam, comprising the steps of: impregnating the foam with a concentrated aqueous chromic acid solution and then heat-treating the foam to strengthen the foam.