DE19735448B4 - Use of anhydrous acidic alkali metal phosphate as a melt binder - Google Patents

Abstract

Use of anhydrous acidic alkali metal phosphate having a molar ratio of alkali metal oxide to P ₂ O ₅ of 0.4 to 0.9 as dry-mixable inorganic binder for fusion.

Description

The This invention relates to the field of inorganic meltbinders Raw materials, especially for silicate, oxidic and mineral raw materials. Such binders is used in various industries, such as the refractory industry, ceramic industry, building materials industry, for insulating compounds, friction linings or Induction furnaces.

For example, from DE-A-21 19 668 refractory products of a refractory aggregate and binder are known, wherein the binder consists essentially of granular P ₂ O _5- containing material and fatty acid-containing pitch. A spray for dry spraying the lining of metallurgical furnaces, which contains as binders 10-30 wt .-% of organic components and 5-15 wt .-% of binding clay, magnesium sulfate, kaolin, bentonite or molasses, is known from DE-A-17 56 037 known. Such binders have the disadvantage of containing organics which are destroyed at higher temperatures and release harmful gases, thereby not only weakening the bond but also creating environmental stress.

The EP 399,728 B1 describes the use of trialkali phosphates as corrosion inhibitors in friction linings or in solid lubricant combinations for friction linings. This use has nothing to do with fusion bonding, and the phosphates used have very high melting points.

The WO94 / 14727 A1 describes self-curing Refractory materials using inorganic salts, the high proportions Contain crystal water. Although these salts are low melting, but their high water content has the disadvantage of causing hydration lead the raw materials used can and that you with temperature effect large Release quantities of water vapor. This water vapor can cause cracking to lead, what would make the refractories unusable.

From the DE 22 55 516 A For example, a refractory composition is known which consists essentially of a magnesia chrome ore grain material and is bound with a water soluble phosphate as a chemical binder. The claimed mass is processed as ramming mass or casting compound with the addition of water. Here, too, water vapor can form when heated, which leads to cracking.

In the DE 22 49 418 A are described with water cold setting refractory mass and mortar, using as binder a mixture of Portland cement and solid acidic phosphate.

The The object underlying the invention was therefore, melt binder for inorganic raw materials to get, which must contain no organic components, if possible are low melting, when temperature effect is not essential Develop amounts of water vapor and with the inorganic raw materials, that they are supposed to bind, react.

According to the invention, this object is achieved by using anhydrous acidic alkali metal phosphate having a molar ratio of alkali metal oxide to P ₂ O ₅ of 0.4 to 0.9 as dry-mixable melt binder for inorganic raw materials.

One Meltbinder for inorganic raw materials according to the application is a solid binder at room temperature, which has a melting temperature below the melting temperature the raw materials to be bonded, and when heating a mixture of raw materials to be bonded and melt binder above the melting temperature of the binder and then cooling down the mixture physically sets with solidification.

The said acidic alkali metal phosphates, in particular sodium or potassium phosphates, especially sodium phosphates, are purely inorganic and contain no organic constituents. Even in the case of being used in conjunction with lower levels of organic matter, as the main constituent of the hot melt binder, they offer the advantage of being purely inorganic. They have low melting points in the order of 50 ° C to 120 ° C, are free of water of crystallization, ie they contain a maximum of 10% water of crystallization and therefore develop when heated little or no water vapor, and finally they are highly reactive with a pH of about 2.2, so that they, for example, oxidic and si bind likatic raw materials well.

The inventive binder can Of course also be used in combination with other substances, wherein the bond over the melting process takes place. When used together with other binder components make sure that the above-described advantages of the melt binder according to the invention by the additional Components can not be canceled.

The acidic alkali metal phosphates used in the present invention suitably have a molar ratio of alkali metal oxide, especially sodium oxide, to P ₂ O ₅ in the range of 0.5 to 0.8, which means that they may be mixtures of acidic alkali phosphates. It is particularly expedient if the acidic alkali metal phosphate according to the invention consists of the water-free Me _0.5 H _2.5 PO ₄ , in which Me is Na or K, in particular Na, or this phosphate is mixed with other acidic alkali metal phosphates free of water of crystallization, such as Monosodium phosphate.

The acid alkali metal phosphates can According to the invention for the beginning mentioned applications are used, but in general for Bonding of mineral or ceramic raw materials, in particular to Binding of silicate or oxidic inorganic raw materials. there can the water-free acidic alkali metal phosphates in a wide Range, based on the total mass, used as a binder be functional in the area from 2-50 Wt .-%, preferably in the range of 5-15 wt .-%, based on the dry weight the bound mass, consisting of binder and inorganic Raw materials.

The acidic alkali metal phosphates used according to the invention are expediently obtained by crystallization of the stoichiometric mixtures of 75% strength phosphoric acid and, for example, 50% strength sodium hydroxide solution. For example, to obtain a molar ratio of Na ₂ O: P ₂ O ₅ of 0.525, assume 5228 grams of 75% phosphoric acid (40.0 moles) and 1680 grams (21.0 moles) of 50% NaOH.

The phosphoric acid is presented and the sodium hydroxide solution added. Then it is evaporated at 145 ° C. and cooled to <80 ° C. The formed crystals are separated and dried at 100 ° C.

Instead, but less preferred, the preparation of the acidic alkali phosphates by spraying of phosphoric acid carried out on monosodium phosphate. For example, 85 parts by weight submitted anhydrous monosodium phosphate and with 15 parts 85% phosphoric acid sprayed. The product will be without additional Drying ground.

Example 1:

A Mixture of quartz sand and quartz powder becomes dry with the sodium salt mixed. Without the addition of water, the mixture becomes a mold vibrated dry and then annealed at 150 ° C. The tempering takes place after the mixture in the mold in the cold Furnace was introduced. Subsequently, the oven was at 10 ° C per minute to 150 ° C heated. Subsequently is held for 3 hours. After the molding results in a strong solidified molding.

Example 2:

The in Example 1 mentioned mixture of quartz sand and flour is with dry mixed with the sodium salt. Without the addition of water will The mixture is dry-vibrated in a mold and then in a 200 ° C hot oven put and there for leave for two hours. After molding, the molding is solidified. cracking by gas pressure could not be observed.

Example 3:

In the refractory industry, high temperature resistant olivine, a naturally occurring raw material consisting of Forsterite (2MgO · SiO ₂ ) and Fayalit (2FeO · SiO ₂ ) mixed crystals is used. The raw material has a strong excess of forsterite of over 80%. In this example, an olivine mass of the composition 55% MgO, 37% SiO ₂ , 5% FeO, 2% Al ₂ O _{3 is} mixed dry with 5% of the sodium salt. Subsequently, the dry vibrated mass is placed in the cold oven and this brought at a heating rate of 100 ° C per 10 minutes quickly to 300 ° C. After one hour, it is cooled and molded. It creates a solid bond.

Example 4:

The Mixture from Example 3 is mixed with 10% of the sodium salt and at 200 ° C annealed. The heating rate is chosen at 50 ° C per 10 minutes. To cooling is formed.

Example 5:

perlite is mixed with the sodium salt volumetrically 1: 1. Subsequently, will the mixture is vibrated in a steel mold and by means of a steel punch compacted. Subsequently is the molding for 2 hours at 250 ° C annealed. After cooling is formed. The result is a lightweight body of good strength.

Example 6:

A mixture consisting of alumina-containing raw materials of the following composition is annealed at 150 ° C and at 300 ° C. The amount of addition of the sodium salt is varied between 5 and 15%. offset: Al ₂ O ₃ raw material of 1-3 mm grain size 42% Al ₂ O ₃ raw material of 0-1 mm grain size 32% Al ₂ O ₃ raw material of grain size DIN 70 20% Fireproof clay 6%

After this the mixture cooled are formed. In any case, a solid molded body, the is stable and can be handled. The forms could without break to be pulled.

Example 7:

One Friction lining mixture more common Kind consisting of metals, fillers, Lubricants, Faserarmierungsstoffen and resins is additionally with the sodium salt (5%). After pressing and annealing (150 ° C) is the Heated mold to a temperature of 600 ° C. Here is the Resin bond increasingly destroyed. It can be stated that the vitrified fusion bond of the salt the breaking resin bond intercepts and consolidates the friction lining even at high temperature.

Example 8:

A mixture of chamotte and clay is bound with 15% of the sodium salt. The offset was:
42% chamotte Otavi "Mono" 1-3 mm
32% chamotte Otavi "Mono" 0-1 mm
20% chamotte Otavi "Mono" DIN 70
6% fireproof clay DIN 70
15% semisodium hydrogen phosphate (= sodium salt)

The slightly compacted mass is annealed at 200 ° C. After cooling it will formed. The strength is very good.

Example 9:

One Offset of the following composition is mixed with 15% of the sodium salt bound. The offset consists of 70% tabular earth 0-0, 18 mm and 30% tabular earth 0-0, 15 mm. After annealing at 200 ° C is the have cooled down Molded part rated. The mixture shows a very strong bond.

Example 10:

90% of a coarse fused magnesia are mixed with 10% of the sodium salt. After thorough mixing, the mass is vibrated in a mold and slightly compacted. The mold is then placed in a cold oven and this slowly to 200 ° C heated. It is kept at this temperature for 3 hours and then slowly cooled. After forming, a solid bond is evident.

Example 11:

A Mass according to Example 3 becomes dry with the potassium salt (5%) mixed. Subsequently Place the dry vibrated mass in the cold oven and this at a heating rate of 100 ° C per 10 Minutes quickly to 300 ° C brought. After one hour, it is cooled and molded. It arises a solid composite.

Claims (7)

Use of anhydrous acidic alkali metal phosphate having a molar ratio of alkali metal oxide to P ₂ O ₅ of 0.4 to 0.9 as dry-mixable inorganic binder for fusion. Use of acidic alkali metal phosphate having a molar ratio of alkali metal oxide to P ₂ O ₅ of 0.5 to 0.8 according to claim 1. Use of Me _0.5 H _2.5 PO ₄ -containing alkali metal phosphate, wherein Me means Na or K, in particular Na, according to Claim 1 or 2. Use of by crystallization from an aqueous solution of phosphoric acid and caustic soda obtained acidic alkali metal phosphate according to one of claims 1 to 3. Use of by spraying phosphoric acid on Monosodium phosphate produced acidic alkali metal phosphate according to one of claims 1 to 3. Use of acidic alkali metal phosphate according to one of claims 1 to 5 for binding silicate or oxidic raw materials. Use of acidic alkali metal phosphate according to one of claims 1 to 6 in an amount of 2-50, preferably 5-15% by weight, based on the totality of melt binders and inorganic raw materials.