DE102013004101B4 - Composition, method of making a composite, use of the composition, and composite - Google Patents

Abstract

Composition suitable for producing a composite material containing - silicon carbide, the silicon carbide containing less than 0.3% by weight of free silicon and the proportion of silicon carbide in the composition being 60-90% by weight, - and at least one containing silicates inorganic binder, the silicates being at least partially water glass and the proportion of water glass in the composition being 2-40% by weight.

Description

The invention relates to a composition according to claim 1, containing 60-90 wt .-% of silicon carbide and at least one inorganic binder, which is suitable for the production of a composite material, wherein the inorganic binder is at least partially water glass.

Machine parts are regularly exposed to high stresses, which can lead to wear. This is especially true, for example, for pumps and pump parts when they are used to convey abrasive, erosive and / or corrosive media. In order to limit wear, it is generally possible to use high-alloy, corrosion-resistant steels. The service life can be further improved by using composite materials with which the machine parts subject to particularly high stress are coated. Possibly. Also, individual components themselves can be made from appropriate composite materials. Such composites, which is a mineral casting, are for example from the international patent application WO 95/17297 A1 known.

As a mineral casting here is a mixture of chemically resistant and temperature-resistant reaction resin used with suitable fillers. Particularly suitable as a filler is silicon carbide, typically the mineral casting has a total composition of 60-90 wt .-% filler and 10-40 wt .-% of the reaction resin. Epoxy resin, vinyl ester resin or polymethyl methacrylate (PMMA) has hitherto been used as the reaction resin or binder.

In principle, good wear and corrosion protection can be achieved in this way, but it has been found that under particularly high stress due to high temperature or due to chemicals, in particular acids, the corrosion resistance is in some cases not sufficient.

Based on the above-described prior art thus has the task of providing a composition which is suitable for the production of a composite material which has an even better resistance, in particular to high temperatures and acids.

This object is achieved by a composition according to claim 1.

Surprisingly, it has been found that the properties of a silicon carbide-based composite material can be further improved if silicate binders, in particular water glass, are used as the binder instead of an epoxy resin from the prior art. Water glass is glassy, amorphous sodium and / or potassium silicates. In contrast to other silicates, alkali silicates are water-soluble. The proportion of water glass is 6-40 wt .-%, preferably 11-40 wt .-% and particularly preferably 21-40 wt .-%.

The silicon carbide must have a reduced free silicon content of less than 0.3% by weight. Commercially available silicon carbide contains 0.7-1% by weight of silicon, but the reaction of silicon with basic silicate as a binder in the presence of water releases hydrogen, which is associated with bubbling. This can lead to cavities forming in the composite material. In order to avoid a porous structure of the composite, therefore, silicon carbide without free silicon must be used. The proportion of free silicon in the silicon carbide is preferably less than 0.1 wt .-%, more preferably less than 0.01 wt .-%.

Although they are in the European patent specification EP 0 675 862 B1 (German translation: DE 693 09 105 T2 ) already described fireproof compositions comprising a particulate refractory material, e.g. As silicon carbide and an inorganic binder such as a microencapsulated sodium silicate solution (water glass). Similarly, the German patent application mentions DE 31 33 354 A1 Wasserglaskitte, which may contain silicon carbide as a filler. The WO 2009/121888 A1 describes combination materials, in particular for prefabricated structural and civil engineering components, which contain at least one inorganic binder and one fiber material, with additives for increasing the wear resistance such as diamond and silicon carbide being possible. However, it was surprising according to the invention that the quality of the material obtained can be considerably improved if silicon carbide with reduced free silicon content is used.

The composition of the invention can be used for the production of complex components as well as for coatings that can be applied to particularly stressed surfaces, in particular metal surfaces. In the case of a coating application, it can be both a preventative protection and the restoration of eroded metal surfaces. In this case, the ready-applied composite is applied in uncured, spreadable form on the surfaces to be processed, where then the curing takes place in order to bring about the desired protective effect.

It has been found that even with layer thicknesses of only 3 mm high acid resistance and a water pressure resistance of 5 bar can be achieved. For example, a high resistance to concentrated inorganic acids such as nitric acid, hydrochloric acid, sulfuric acid or phosphoric acid, organic acids and solvents is achieved. The temperature resistance of the composite is normally at least 700 ° C and sometimes up to 1,350 ° C. In contrast, when using an epoxy resin binder, temperatures in excess of 130 ° C have proven problematic.

Also, the mechanical wear resistance is particularly high, which is related to the use of silicon carbide. This is a material with an extremely high degree of hardness, which reaches a value of 9.5 on the Mohs scale and thus comes close to the diamond (10.0). Basically, the wear resistance is improved by a high degree of filling of silicon carbide, which is why according to the invention at least 60 wt .-% silicon carbide are used. Preferred are proportions of 65-90, more preferably 70-90, in particular 75-85 wt .-%.

The water glass used may be both soda and potassium water glass as well as mixtures thereof. The ratio of Na ₂ O or K ₂ O to SiO ₂ is typically 1: 1 to 1: 4. The use of water glass as a binder is in principle known, for example from the EP 1 081 114 A1 However, the building material mix described here does not relate to silicon carbide based materials.

For the preparation of the composite silicate binder containing water glass is presented, preferably in powder form, mixed with silicon carbide, whereupon by adding water, a pourable and fachtelbare mass is generated. This can be further processed, for example, applied to the surfaces to be coated or used for the production of moldings. Besides pouring and filling, other methods of applying the compound, such as spraying, spraying, brushing or rolling, are also conceivable. The curing can be carried out at room temperature.

The composition may contain other ingredients as additives, for example, in addition to the water glass other silicates such as calcium silicate hydrate, blastfurnace, fly ash, trass, brick, oil shale, quartz sand, slag, glass or silica particles. The proportion of the total composite material of these additional constituents can be up to 38% by weight. With the help of these additives, the properties of the composite material can be adjusted as needed.

In addition to silicon carbide, the composition may also have other abrasion and corrosion resistance improving ingredients. These are, in particular, metal oxides, for example aluminum oxide or zirconium oxide. The additionally used metal oxide can also serve to increase the proportion of filler in materials with a high degree of hardness, as described in US Pat DE 102 47 280 A1 is described. In particular, silicon carbide particles of comparatively coarse grain size can be combined with metal oxide particles of finer grain size such that the metal oxide grains occupy the interstices between the silicon carbide particles. In this way, the proportion of high-abrasion resistant fillers can be increased without the processability passes under it. On spreading, the coarser particles of silicon carbide can slide along the finer, typically round, metal oxide particles, so as to obtain a composition that continues to be easy to process overall (see Example 2).

In this case, the metal oxide particles preferably have an average particle size of preferably ≦ 50 μm, more preferably ≦ 10 μm. in contrast, the grain size of the silicon carbide is usually higher. The mean grain size of the silicon carbide is typically less than 3 mm, preferably less than 1 mm, which information applies regardless of the use of an additional metal oxide. The proportion of the metal oxide in the composite may preferably be 10-20% by weight.

It is preferred to use silicon carbide different grains, in particular, the majority of the silicon carbide may have a relatively coarse grain, while a smaller amount of the silicon carbide has a finer grain size. In this way a similar effect is achieved as described above in connection with the metal oxides, i. H. The coarser particles of silicon carbide can slide along the fine particles of silicon carbide, which is associated with an improvement in processability and high content of silicon carbide as a whole. For example, 5-40%, preferably 10-30%, particularly preferably about 25% of the silicon carbide have a particle size ≤ 0.1 mm.

It is also possible to add to the composition fibers, in particular inorganic fibers, which further increase the strength. In particular, these may be glass fibers, but the use of metal fibers would also be conceivable.

In order to increase the ability to attach the composite, which may be advantageous in particular when used as a repair material, it is possible to add highly dispersed SiO ₂ . Particularly suitable is the known under the name Aerosil SiO ₂ . This increases the attachment ability of a mass, in particular on vertical surfaces. At the same time it is possible in this way to apply a mass in thicker layers without it running and losing its shape.

In addition to the composition according to the invention itself, the invention also relates to a method for producing a composite material as described above, the use of the composition and the composite itself. The composition is mixed with water before the mixture is cured. As a rule, the inorganic binder is introduced together with the silicon carbide before the water glass is dissolved in water. It makes sense to apply a vacuum during the preparation of the mixture or to degas the mixture before introduction into a casting mold in order to avoid undesired air pockets in the material. Conveniently, a negative pressure of less than 80, preferably less than 20 mbar is applied. The mixture can be further processed in various ways, for example, the mixture can be applied to a (metal) surface to provide or repair them with a protective layer, as well as with the aid of the mixture moldings can be made to complete components of the composite material manufacture. After processing, the curing takes place, this can be carried out at room temperature or alternatively in an annealing oven at elevated temperature. By supplying heat excess water is evaporated faster, so that the hardening process is accelerated. It can also be made a graded curing, as in the WO 95/17297 A1 described and to which reference is made.

A water glass hardener may be added to the mixture in the manufacture of the composite. This is in particular a phosphate, for example aluminum phosphate, which hydrolyzes slowly in the alkaline medium of the water glass, so that silica precipitates in a controlled manner and the mixture is cured. It is also possible to use an acid as a water glass hardener, which may be both organic and inorganic acids.

In order to influence the properties of the mixture, for example also during the curing, inhibitors, hydraulic and / or pozzolanic components can be added to the mixture. Through the use of inhibitors, the setting reaction, i. H. the curing is slowed down as needed, leaving more time for the user to process the mass. With the aid of (latent) hydraulic or pozzolanic components, the composite material can be optimized for use in an alkaline or acidic environment. To control the setting reaction and the addition of metal salts, in particular alkali metal salts is possible.

The invention also relates to the use of the composition for coating or repairing surfaces, in particular metal surfaces. Such a coating typically has a thickness of a few millimeters to a few centimeters. Moreover, the invention relates to the use of the composition for the production of moldings with high abrasion and corrosion resistance. In particular, the composite material for pump housing and pump components can be used. It is also possible to define an element of the composite material on a component indirectly via an anchoring element, as shown in the DE 103 27 494 A1 is described.

When lining components such. As pump housings with the composite material according to the invention, the treatment of the surface to be lined of the component prior to pouring with a release agent is advantageous. Due to the use of such a release agent, there is no firm connection between the composite material and the steel sheath after lining, so that no destruction of the composite material can occur due to temperature differences between the outer component and the inner lining or due to different expansion due to different coefficients of expansion. The deviating expansion caused by temperature differences or different coefficients of expansion can be absorbed by the gap between component and lining produced by the release agent. The use of such release agents is known from WO 2004/033919 A1 known.

Examples:

Example 1: According to one embodiment of the invention, 1 kg of composite material is produced by placing 300 g of waterglass, 620 g of silicon carbide of a coarse grading curve and 80 g of silicon carbide of a fine grading curve, wherein the silicon carbide has been freed of silicon. Since the rough grading curve also contains fine-grained silicon carbide, a total of about 25% of the silicon carbide has a particle size ≤ 0.1 mm. 200 g of water are added. After mixing, the material can be processed before it hardens. In the curing process, the water escapes almost completely, resulting in the pure, cured composite material.

The material obtained is highly resistant to chemicals, including aggressive nature. In addition, it is characterized by a high mechanical strength with high abrasion resistance and heat resistance up to 1350 ° C without cracking. The material adheres well to the substrate and can therefore be processed well.

Example 2: According to this embodiment of the invention, 1 kg of composite material is produced by presenting 214 g of silicate binder (especially waterglass), 643 g of silicon carbide and 143 g of Al ₂ O ₃ , the silicon carbide being freed of silicon. Added are 143 g of water. After mixing, the material can be processed before it hardens. In the curing process, the water escapes almost completely, resulting in the pure, cured composite material.

Compared to Example 1, by adding alumina, the filler content (SiC, Al ₂ O ₃ ) could be further increased and the binder content reduced, without affecting the processability of the composition.

Claims (14)

Composition suitable for the production of a composite material containing Silicon carbide, the silicon carbide containing less than 0.3% by weight of free silicon and the proportion of silicon carbide in the composition being 60-90% by weight, And at least one silicates-containing inorganic binder, wherein the silicates are at least partially water glass and the proportion of water glass in the composition is 2-40 wt .-%. A composition according to claim 1, characterized in that the proportion of water glass is 6-40, preferably 11-40, in particular 21-40, wt .-%. Composition according to Claim 1, characterized by a proportion of 65-90, preferably 70-90, in particular 75-85,% by weight of silicon carbide. Composition according to any one of Claims 1 to 3, characterized in that the silicon carbide contains less than 0.1% by weight, preferably less than 0.01% by weight, of free silicon. Composition according to any one of Claims 1 to 4, characterized in that the composition contains further silicates, blast furnace slag, fly ash, trass flour, brick dust, oil shale, quartz sand, slag, glass and / or silica particles. Composition according to any one of Claims 1 to 5, characterized in that the composition contains metal oxides, in particular aluminum oxide and / or zirconium oxide. Composition according to one of claims 1 to 6, characterized in that the mean grain size of the silicon carbide ≤ 3 mm, preferably ≤ 1 mm. Composition according to one of claims 1 to 7, characterized in that 5-40 wt .-% of the silicon carbide have a particle size ≤ 0.1 mm. A process for producing a composite, wherein a mixture is prepared which contains the composition according to any one of claims 1 to 8 and water, and the mixture is cured. A method according to claim 9, characterized in that the mixture is added to a water glass hardener. A method according to claim 9 or 10, characterized in that the mixture inhibitors, hydraulic, latent hydraulic and / or pozzolanic components are added. Use of a composition according to any one of claims 1 to 8 for coating or repairing surfaces. Use of a composition according to any one of claims 1 to 8 for the production of moldings having, due to the less than 0.3 wt .-% free silicon-containing silicon carbide, improved abrasion and corrosion resistance. The composite material according to any one of claims 9 to 11, which has improved abrasion and corrosion resistance due to the less than 0.3 wt% of free silicon-containing silicon carbide.