Nanocrystalline sintered bodies made from alpha aluminium oxide and method for production and use thereof
A nano-crystal, sintered body technology, applied in nanotechnology for materials and surface science, chemical instruments and methods, alumina/aluminum hydroxide, etc., can solve problems such as expensive and unsuitable for sintering corundum
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Embodiment 1
[0065] As α-Al for the preparation of nanocrystals 2 o 3 The starting material, used commercially under the name Locron L Basic aluminum chloride available from Clariant AG, Gersthofen (Germany). Basic aluminum chloride is supplied as a 50% aqueous solution and has the molecular formula corresponding to Al 2 (OH) 5 Clx2-3H 2 The chemical composition of O. It follows that a 50% aqueous solution of basic aluminum chloride contains about 23-24% Al 2 o 3 .
[0066] as for α-Al 2 o 3 -Starting material for crystal nuclei using WSK3000, an α-alumina from Treibacher Schleifmittel GmbH, Laufenburg (Germany), supplied as easily redispersible spray granules with a primary diameter of about 0.5 μm average particle size.
[0067] The WSK3000 is wet milled for about 3 hours in an agitator ball mill. The resulting suspension is subsequently processed in a clarifier, where about 95% of the solid fraction is separated off by centrifugation. The fine fraction left in the suspensi...
Embodiment 2
[0078] Preparation of a suspension of basic aluminum chloride mixed with crystal nuclei, subsequent drying and thermal conversion to α-Al 2 o 3 Proceed as in Example 1.
[0079] However, no stabilizer for the suspension was added in the subsequent approx. 3-hour deagglomeration in the stirred ball mill. Instead, the suspension was cast as a layer about 6 mm thick directly after the end of the deagglomeration, degassed in a vacuum oven (5 hours at 200 mbar) and subsequently dried at about 80° C. The dried material was pre-calcined at 500° C. for 30 minutes and subsequently comminuted to abrasive grain size (6 mm and finer). The final sintering was carried out as in Example 1 in a rotary furnace.
[0080] The abrasive grains thus obtained have a density of 98.8% of the theoretical density, Vickers hardness HV 0.2 The average primary particle size is 2190GPa and 70nm. Also like Example 1 above, Example 2 was tested in abrasives on a substrate and in bonded abrasives. The r...
Embodiment 3
[0082] Preparation of a suspension of basic aluminum chloride mixed with crystal nuclei, subsequent drying and thermal conversion to α-Al 2 o 3 Proceed as in Example 1.
[0083] In the subsequent approximately three-hour deagglomeration in an agitated ball mill, polyacrylic acid was used as a stabilizer for the suspension as a dispersion aid. A 10% aqueous suspension of polyvinyl alcohol (Mowiol 8-88, Kuraray Specialties Europe GmbH, Frankfurt, Germany) was subsequently admixed as binder into the suspension with a solids content of about 30% in an amount of about 0.05 wt. %, based on Al 2 o 3 content meter.
[0084] The suspension was subsequently sprayed in a fluidized bed spray granulator (AGT 150, Glatt GmbH, Binzen, Germany) at an air inlet temperature of 95°C, a bed temperature of 45°C, an injection pressure of 3 bar and an injection rate of 70 g / min Granulated. For the nucleation a fine-grained fraction with an average particle size of 0.2 mm was used which was obt...
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