A Research On Surface Modification Of Ultra-Fine Oxide Iron Red Pigment

Powders, especially ultra-fine powders, which have many advantages, such as little particle size, large specific surface, high surface energy, large reactivity on other materials and special effect on light and electricity, are widely used. If powders agglomerate each other, particularly forming hard agglomeration, their reactivity will be apparently degraded and Ultra-fine effect and nano effect will disappear. So this will influence on their applied performances, especially for ultra-fine pigments. The dispersion of pigment particles influences on the applied performances of pigments: color, covering power, tinting power, oil absorption and so on. Therefore improving the dispersion properties of ultra-fine powders is one of the fields of powder engineering technical research and is of theoretic and practical significance.Iron oxide pigments are the second largest output and consumption inorganic pigments only next to titanium pigment and the largest volume colored inorganic pigments and are used widely in many fields. China is a major producer and the second largest exporter of iron oxide pigments only next to Germany. But compared with iron oxide pigments in developed countries, iron oxide pigments are mostly primary products, with price cheap and additive value low. So iron oxide pigments must be additionally treated to improve quality. Surface treatment technique is one of very important processing technique of Iron oxide pigments and can improve dispersion properties and applied performances of products. In iron oxide pigments, iron oxide red is the largest proportion, so in this paper surface modification of ultra-fine iron oxide red pigment is chose to study.By dry surface modification process, the optimal surface modification technical conditions: modifier D3008, optimal dosage 3.0%; assistant modifier precipitated amorphous silica, optimal dosage 4.0%; optimal experimental temperature 97-98 癈 are achieved, and on this base, ultra-fine iron oxide red pigments with good dispersion properties are made. Compared with raw material and similar products of Bayer company, the treated samples with the better stability of the dispersion, the smaller loose bulk density, thehigher f potential, have better dispersion properties in aqueous solution and in natural dry powders. In addition, tinting power is rather greatly improved. According to the characteristic of pigment powders in different applied fields, a viewpoint is put forward that the dispersion properties of powders should be divided into two parts: the dispersion properties in liquid phase and the dispersion properties in dry powders.By testing samples with IR, DTA/DTGA and ?potential, the modification mechanism of modifier D3008 is analyzed that D3008 not only reacts with hydroxide on the surface of iron oxide red particles, but also with Fe 桹 bonds in crystal lattice. Moreover, the adsorption model on the surface of particles is found that D3008 acts on the surface by chemical adsorption and physical adsorption and precipitated amorphous silica fills among iron oxide red particles. After samples are dispersed in aqueous solution, modifier D3008 endues the surface of particles with relatively high ?potential to enhance static repulsion, and forms steric stabilization or depletion stabilization on the surface. It improves the stability of the dispersion in aqueous solution. Precipitated amorphous silica adsorbed on the surface of particles degrades the liquid bridge force between particles and adds the space between particles and reduces agglomeration of particles to improve the dispersion properties of dry powders.