WO1992000928A1

WO1992000928A1 - High-temperature resistant, porous aggregates, process of producing the same and moulded parts made therefrom

Info

Publication number: WO1992000928A1
Application number: PCT/AT1991/000086
Authority: WO
Inventors: Harald Seifert; Ernst Schlegel
Original assignee: Magindag Steirische Magnesit-Industrie Aktiengesellschaft
Priority date: 1990-07-13
Filing date: 1991-07-12
Publication date: 1992-01-23
Also published as: DD296477A5

Abstract

A high-temperature resistant, porous aggregate, a process for producing the same and products made therefrom are disclosed, which are useful to prepare highly effective heat insulators available as mixtures or as moulded products that have applications in the construction of industrial ovens and of high-temperature installations. The aggregate on the basis of calcium aluminates and/or magnesium aluminates and/or their mineral derivatives having one or several components contains 0.20 to 0.95 parts in volume of micropores, whereas more than 60 % of the micropores have less than 40 νm in diameter. The porous aggregate is produced by mixing the corresponding oxidic or hydroxidic finely ground raw materials with 0.1 to 4.0 parts in mass of water, in relation to one part in mass of dry raw materials. The homogeneous mixture is then treated by autoclave at temperatures higher than 125 °C, for 1 to 25 hours, the solidified mass is dried, then sintered at temperatures equal to or higher than 1000 °C for 1 to 25 hours and the sintered product is transformed into aggregates.

Description

High temperature resistant oorous aggregates. Process for their production and molded parts made therefrom

c The invention relates to a porous aggregate that is resistant to high temperatures, a process for its production and molded parts produced therefrom. The high-temperature-resistant porous additives are the basis for the production of highly effective thermal insulation materials in the form of batches or shaped products which are used in industrial furnace construction and for high-temperature systems.

Heat and high temperature resistant materials that are used for thermal insulation in industrial furnace construction and for all high temperature systems are diverse and 5 are manufactured using different technological processes. This applies to batches, lightweight fire concrete and burned lightweight fire bricks. The high proportions of pores required for thermal insulation are achieved by using granular burnout materials, by blowing gas or by using foaming agents or similar measures. Likewise, the use of natural or technological _^ won highly porous Vormateria¬'s lien, such as expanded clays, expanded shale that are processed in a granular form is known. These technological measures lead to macropores. For example, the Gassilicatbeton-Rohgemenges formed in the pore formation by addition of metallic aluminum by the reaction of aluminum with water with evolution of hydrogen pores with a Poren¬ size of 10 ^{~ 3} to 10 ^"4 m with a proportion 80-90% of the total porosity. These large pores are disadvantageous for thermal insulation at high temperatures, because experience has shown that they lead to "radiation breakthrough" and there is no longer any thermal insulation effect, which is independent of the overall porosity.

Lightweight concrete that is characterized by the highest possible porosity and by micropores (below 10 ^{~ δ} m) can be used advantageously at medium to high temperatures.

With the help of autoclave treatment, it is possible to do this to meet both requirements (Silikattechnik 36 (1985) Issue 7, page 212). The hydrothermal process is known for the production of calcium silicate thermal insulation materials and of thermal insulation materials with a calcium aluminate bond. A disadvantage of the calcium silicate thermal insulation materials is that the application temperature is at most 1100 ° C. for material reasons. Is that in the later Hochtemperatureinsätz designating to verzeich¬ shrinkage the application of such materials in 120Q ° C is limited, and only the addition of prebaked microporous lightweight aggregates to increase the temperature limit allowed ^'(DD 206 142) A disadvantage of the thermal insulation materials with Calciumaluminatbindung. When using the unfired, merely hydro-thermally solidified body directly as thermal insulation material in thermal engineering plants, cracking results as a result of the sudden water release, the insufficiently high gas permeability of the matrix and the high thermal insulation effect of the material itself.

The aim of the invention is to improve the thermal insulation effect of thermal insulation materials at high temperatures and thus to reduce the energy consumption of industrial furnaces and other high-temperature systems.

The invention is based on the technical problem of developing a high-temperature-resistant additive with a variable total porosity on a different material basis, this additive using known binders and using known processes to produce highly effective thermal insulation materials with a largely proportional behavior of heat transport and temperature even at high temperatures to give molded parts , such as Shaped stones should be processable.

The technical problem is solved by a porous additive based on calcium aluminates and / or magnesium aluminates and / or one-component or multi-component derived therefrom

Mineral forms according to the invention solved in that the porous

Aggregate 0.20 to 0.95 parts by volume micropores, where > 60% of the micropores have a pore diameter of <40 μm.

c The porous additive is produced according to the invention in that the corresponding oxidic or hydroxide finely divided raw materials are mixed with 0.1-4.0 parts by mass of water, based on a mass fraction of the dry raw materials, the homogeneous mixture at temperatures from> 125 ° C to an autoclave treatment with a holding time of 1 to 25 hours, preferably 8 to 12 hours, the solidified mass is dried, then at temperatures of> .1000 ° C and holding times of 1 - 25 hours, preferably 3 - 5 hours, sintered and the sintered product is worked up to the additive. 5

Aluminum oxide, calcium oxide, calcium hydroxide, magnesium oxide, magnesium hydroxide, calcium magnesium oxide and / or calcium magnesium hydroxide can be used as oxidic or hydroxide raw materials, depending on the desired composition of the porous additive. The process conditions in hydrothermal synthesis depend on the mineral to be formed. For the compounds (aluminates) formed later, advantageous conditions are treatment temperatures of 125-350 ° C., preferably 175-225 ° C., with holding times 1-25

Hours, preferably 8-12 hours.

The substances newly formed in the autoclave under hydrothermal conditions have a widespread network of hydrates with stored water. This water is expelled by the subsequent drying process and a solid framework with a high proportion of pores remains in the form of micropores. A further thermal pretreatment with higher, depending on the type of material and later application temperature of the intended end product, variable firing temperatures leads to the further formation of micropores. The chemically bound water is driven out and the sintering with the parallel compression and solidification is terminated at the suitable temperature and holding time to be determined individually for each material combination. For magnesium aluminates, firing temperatures of 1000-2000 ° C., preferably 1350-1650 ° C., with holding times of 1-25 hours, preferably 3-5 hours, are for calcium aluminates and for calcium magnesium aluminates, firing temperatures of 1000 to 1700 ° C, preferably from 1200 to 1600 ° C with holding times from 1 to 25 hours, preferably from 2 to 6 hours, particularly suitable. The firing temperatures are determined by the later application temperature. The firing temperature should be at least 50 K above the application temperature. The highly porous materials with a microporous structure are then subjected to various comminution processes and the material is classified into the desired additives. These additives can be mixed with all suitable binders, such as, for example, a hydrothermal type, a hydraulic, a chemical, a ceramic, or an organic as well as various combinations, and different from those that can be processed at the construction site

Manufacturers are deformed by casting, shaking, pressing or else combined processes to form shaped articles of varying size and geometry. Further use in the industrial units can be carried out without or after such thermal treatments as setting, drying, annealing or sintering. The advantage of the production process according to the invention is that the material variability, including the water-solid ratio, means that the application temperatures and the overall porosity, and therefore also the structural strength, are varied, using the high-temperature-resistant porous additive Impact fabricated thermal insulation materials is given. Due to the large number of solid walls, this microporous structure offers greater resistance to the passage of heat from the steel, so that the thermal insulation capacity is considerably improved at high temperatures. The invention is illustrated by the following examples:

5

Example 1:

The raw materials aluminum hydroxide and calcium oxide or calcium hydroxide are mixed with such high water proportions, which are 150%, based on the dry weight, that very easily pourable but stable suspensions with a very high water content are formed. With regard to the ratio of aluminum oxide to calcium oxide, the solid is selected and adjusted such that so-called calcium hexaaluminate or at least in the desired proportions is formed after the high-temperature treatment.

The highly water-containing suspension is finely ground in a grinder, poured into molds, in an autoclave

. hardened at least 190 ° C and a holding time of 10 hours.

Z _u _Λ The hardened molded body is dried at 110 ° C and at

Sintered temperatures of> 1250 ° C. The sintered shaped body is then divided into predetermined grain classes by conventional comminution processes and classification processes. A certain variation of certain parameters is due to the amount of

Firing temperature, which is particularly important for the application

_- * -. technical properties, such as the overall porosity, the grain strength and the volume stability, are of influence. Using a variety of binders, a wide range of highly effective thermal insulation materials can be produced from the aggregate produced according to the invention using typical methods of refractory technology. Column 1 of Table 1 shows the quality parameters of an aggregate after pre-firing at 1350 ° C with a very high overall porosity. These additives form the basis for the thermal insulation materials and moldings to be manufactured, it being possible to use different binders and shaping processes 5. Example 2:

Analogously to Example 1, the water content is reduced so that it is 30%, based on the dry matter, and that a

Working mass with a pudding-like consistency is created.

This mass, homogenized only in the high-speed mixer, is shaken into the molds and furthermore according to the example

1 treated. After the fire at 1350 ° C there is an aggregate with high porosity, the quality characteristics of which are in column 2 of

Table 1 are shown.

These additives form the basis for the thermal insulation materials and moldings to be manufactured, whereby different binders and molding processes can be used.

Example 3

Analogously to Example 1, the water content, based on the dry matter, is reduced to 10%, so that a working mass which is suitable for dry pressing molding is formed. This working mass, which is only moistened in a conventional compulsory mixer, is processed into moldings by conventional pressing, which can then be cured freestanding in the autoclave and further treated in accordance with Example 1. After the fire at 1350 ° C., an aggregate with medium porosity arises, the quality values of which are set out in column 3 of the table.

These additives form the basis for the thermal insulation materials and moldings to be manufactured, it being possible to use different binders and shaping processes. Example 4:

The raw materials aluminum hydroxide and magnesium oxide or magnesium hydroxide are mixed with a water content, based on the dry content, of 150%, so that very easily pourable but stable suspensions with a very high water content are formed. With regard to the ratio of aluminum oxide to magnesium oxide, the solid is selected and adjusted so that so-called spinel or at least in desired proportions is formed after the high-temperature treatment.

This product is processed in an autoclave at temperatures of 175 ° C and a holding time of 10 hours. The additive is produced analogously to Example 1. Column 4 of the table shows the quality parameters of the surcharge after pre-firing at 1400 ° C.

Analogous to Examples 2 and 3, the porosity to be provided can be varied by differently designed water components and shaping processes for these products.

These additives form the basis for the thermal insulation materials and molded parts to be produced, it being possible to use different binders and shaping processes.

Example 5;

A microporous calcium aluminate aggregate (bulk density of the material about 0.5 g / cm, which corresponds to a total porosity of> 80%; pre-firing in an industrial tunnel kiln at 1500 ° C) is processed with high-tone cement according to the vibrating technology to a lightweight fire concrete. This lightweight fire concrete has the following quality values:

- Gross density after setting and drying about 1.0 g / c. ³

- Compressive strength after 14 days of storage about 1.0 MPa

- Shrinkage after 12 hours at 1400 ° C 2.40% (at 1300 ° C / 12 hours: elongation of 0.3%) - thermal conductivity

RT 0.300 W / mK 300 ° C 0. 305 W / mK

600 ° C, 305 W / mK

900 ° C, 305 W / mK

1000 ° C 0.325 W / mK

Example 6:

Example 6 applies to a microporous calcium aluminate additive (bulk density of the material approximately 1.25 g / cm ³ , which corresponds to a total porosity of>60%; pre-firing in an industrial bell-type furnace at 1600 to 1700 ° C) and a similar type BinderSuspension thermal insulation material produced according to vibrating technology and subsequent hardening in an autoclave (10 hours at 191 ° C), which as a result of its increased strength has constructive properties and can be described as a special refractory concrete with hydrothermal bond.

The thermal insulation material has the following quality properties:

- Bulk density after curing and drying 1.24 g / cm - Compressive strength after curing and drying 12.4 MPa

- Shrinkage after 12 hours at 1500 ° C 4.04%

- thermal conductivity

Example 7:

Example 7 applies to a microporous calcium aluminate aggregate (bulk density of the material approx. 1.0 g / cm ³ , which corresponds to a total porosity of>70%; pre-firing in an industrial tunnel kiln at 1500 ° C) and a similar binder suspension the damp presses and subsequent hardening in an autoclave (10 hours at 191 ° C.) produced thermal insulation material which is not prebaked.

The following quality properties are determined:

- Density after curing and drying 1.14 g / cm ³ , which corresponds to a total porosity of approximately 70%.

- compressive strength after curing and ^'drying 1.6 MPa, a prefiring enhances the strength as follows:

800 ° C 4.85 MPa 1350 ° C 10.90 MPa 1500 ° C 14.28 MPa

- Shrinkage after 12 hours at 1500 ° C 1.40%

- thermal conductivity

Example 8:

Example 8 applies to one made of a microporous aggregate of the "Spinel" type (bulk density of the material approximately 1.45 g / cm ³ , which corresponds to a total porosity of>50%; pre-firing in the laboratory furnace at 1550 ° C.) and one A similar suspension type after casting-vibrating shaping and subsequent hardening in an autoclave (6 hours at 180 ° C.) produced thermal insulation material which is not prebaked. The following quality properties are determined:

- density after hardening and drying approx. 1.0 g / cm ³ , which corresponds to a total porosity of approx. 70% - compressive strength after hardening and drying at least 1.5 MPa; a pre-bake at 1550 ° C increases the strength to at least 10.0 MPa.

- The thermal conductivity of the primary material after pre-firing at 1100 ° C is:

Table 1: Quality parameters of microporous aggregates

Property Example Example Example Example 1 2 3 4

Bulk density (g / cm- ³ ) 0.4-0.6 0.8-1.2 1.8-2.4 0.6-0 ,.

Total porosity (%) SO - 80 80 - 60 50 - 35 80 - 70

Proportion of micropores below 40 μm (%)> 80> 70> 60

At least minimum tensile strength at least mmα.

(MPa) 0.5 1.5 2.5 0.25

Application temperature * at least at least at least minα. (° C) 1250 1300 1300 1350 * The application temperature of the finished products using these tensile impact substances depends on the level of the pretreatment temperature and can generally be stated up to a maximum of 50 K below this if the respectively suitable binders are used.

Claims

Claims:

1. High-temperature-resistant porous aggregate based on calcium aluminates and / or magnesium aluminates and / or single or multi-component mineral forms derived therefrom, characterized in that the porous aggregate contains 0.20 to 0.95 parts by volume of micropores, with> 60% the micropores have a pore diameter> 40 μm.

2. Process for the production of a high-temperature-resistant porous additive based on calcium aluminates and / or magnesium aluminates and / or mineral forms derivable therefrom, the corresponding oxidic or hydroxide raw materials being used, characterized in that the oxidic or hydroxide raw materials with 0.1 to 4.0 parts by mass of water, based on a part by mass of dry raw material, after a homogenizing mixture, subjected to an autoclave treatment at temperatures> 125 ° C. and the solidified mass, then dried at temperatures of _ 1000 ^C C sintered at holding times of 1 to 25 hours and the sintered product is worked up into aggregates by customary comminution and classification processes.

3. The method according to claim 2, characterized in that are used as oxidic or hydroxide raw materials aluminum hydroxide, calcium oxide, calcium hydroxide, magnesium oxide, magnesium hydroxide, calcium magnesium oxide and calcium magnesium hydroxide according to the desired composition of the porous aggregate.

4. The method according to claim 2, characterized in that in a target product based on magnesium aluminates, the hydro-thermal treatment at temperatures of 125 to 350 ° C and holding times of 1 to 25 hours and the Ξinterprocesses Temperatures of 1000 to 2000 ° C and holding times of 1 to 25 hours can be carried out.

5. The method according to claim 2, characterized in that in a target product based on calcium aluminates, the hydro thermal treatment at temperatures from 125 to 350 ° C and holding times from 1 to 25 hours and the sintering process at temperatures from 1000 to 1800 ° C and holding times from 1 to 25

Hours.

6. The method according to claim 2, characterized in that for a target product based on calcium magnesium aluminates, the hydrothermal treatment at temperatures from ^' 125 to 350 ° C and holding times from 1 to 25 hours and the sintering process at temperatures from 1000 to 1800 ° C and holding times of 1 to 25 hours.