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Patent
Title
Magnetisch abtrennbare Mikroartikel mit einer silikatischen Hülle, Verfahren zu ihrer Herstellung sowie ihre Verwendung
Other Title
MAGNETICALLY SEPARABLE MICROPARTICLES WITH A SILICATE SHELL, METHOD FOR PRODUCTION THEREOF AND USE THEREOF
Abstract
The invention relates to magnetically separable particles, each comprising a plurality of nanoparticles with reversible magnetic properties and a matrix having an inorganic portion between 70 and 100 wt%, relative to the weight of the matrix, wherein the inorganic portion of the matrix consists of 80 to 100 wt% SiO2, characterised in that a. the particles have an average diameter in at least one direction of at least 5 mum, b. the particles have a surface area (according to BET measurement) of at least 1 m2/g and a (cumulative) pore volume of less than 0.195 cm3/g (ml/g), c. there is a loss of material from the nanoparticles with reversible magnetic properties of less than 2 wt% when the magnetically separable particles are stirred for 12 hours in acidic and alkaline solutions with a pH value of 1 and 12 respectively. These particles can be produced by a method comprising the following steps: a. provision of a fluid magnetic sol which was peptised by lowering the pH value to a value of not more than pH 2.5 by adding an acid; b. stabilising the sol by adding an organic complexing agent; c. adding ammonia or a compound having at least one amine function, or releasing such a function under the effect of thermal energy, to the stabilised sol in a quantity such that - optionally after the effect of the necessary thermal energy - a pH value of at least 9 is achieved; and d. effecting a precipitation of the magnetically separable particles by adding a silicon dioxide-forming agent to the stabilised sol, wherein the organic complexing agent is selected from monomeric and oligomeric hydroxycarboxylic acids with 1 to 3 hydroxy and 1 to 3 carboxylic acid functions, di-or oligocarboxylic acids and bis- or oligoalcohols with at most 8 functional groups suitable for complex formation, or the organic complexing agent is selected in such a manner that, after addition of the ammonia in accordance with step c., a measured hydrodynamic radius of the particles present in the sol in the range from 200 to 2000 nm, preferably 500 to 2000 nm results.
Inventor(s)
Mandel, Karl
Hutter, Frank
Gellermann, C.
Patent Number
102012201774
Publication Date
2012
Language
German