| abstract |
Core-shell particles containing crystalline iron oxide in the core and amorphous silica in the shell and in which a) the shell contains 5 to 40% by weight of silica, b) the core b1) 60 to 95% by weight of iron oxide and b2) 0.5 to 5 wt .-%, at least one doping component selected from the group consisting of aluminum, calcium, copper, magnesium, zinc and tin, c) wherein the percentages by weight refer to the core-shell particles and the sum of a) and b) is at least 98% by weight of the core-shell particles, d) the core has interplanar spacings of 0.20 nm, 0.25 nm and 0.29 nm, each +/- 0.02 nm, as determined by HR-TEM. |