Microstucture And Heat Resistance Of Coated Iron Oxide Pigments

The development of inorganic pigments with high colour intensity, low oil absorption, ultrafine, easily dispersed, multi function, temperature resistance, non-toxic, granulation, and other technology has attracted great attention. As the first majority colour pigment of inorganic pigments, Iron oxide pigment is widely used in building materials, paint, rubber, plastics, paints and other coloring area. To develop special requirements of iron oxide pigments of high quality and performance have attracted extensive attention. Coating treatment as one kind of traditional modification technology of iron oxide pigments has been initial industrialization. Among them, the hydrothermal coating method under the condition of high temperature and high pressure in a closed system, demanding advanced equipments and high energy consumption, thus limiting its large-scale production and application. Silicon dioxide, magnesium or aluminum hydroxide, and other available material can be used in precipitation method. Dehydration performance of iron oxide yellow pigment coated with silicon dioxide is stronger, but it's oil absorption value become larger significantly, thus impair it's dispersion ability in plastics and paints; Heatment resistance of iron oxide yellow pigment coated with magnesium or aliuminum hydroxide can improve to a high temperature, but the pH value of magnesium hydroxide is high?reach 9¹0?, limiting its application. As the aluminum hydroxide can decomposite under the effect of both acid and alkaline solution, the coated product's pH value near neutral and it's oil absorption value basically unchanged, will be able to accommodate the requirements of pigment application. This study synthesized the coating iron oxide yellow pigments with aluminum hydroxide as compact coating layer by a precipitation method using aluminum sulfate and sodium hydroxide as raw material for the first time to improve its heat resistance ability. Focusing on the relationship between construction of micro coating layer and heat resistance ability of the products synthesized under the different reaction temperature, the amount of coating, the crystallization time and pH value; secondly in the coated process we using phosphoric acid as a modifier to further improve the heat resistance of products and we analysised the micro stucture of the coated layer; finally, the study takes iron oxide yellow coating with aluminum hydroxide synthesised under different pH as precursor value as coating layer, and the samples was synthesized by baking.?1? Using iron oxide yellow as precursor, iron oxide yellow pigments coating with aluminum hydroxide were synthesized by a precipitation method. Structures of the composite pigments are characterized using XRD, FT-IR, TG-DTA, SEM&EDS and TEM. The effect of reaction temperature, the amount of coating, the crysta llization time, the pH value on structure and heat resistance of the pigments was inv estigated.It is obtained that optimized coating conditions of heat-resistant yellow pigment consist of reaction temperature is 80?, coating amount is 15%, the crystal ization time is more than 4 h, the pH value is 8 or 10, and the color difference value of pigments after treatment at 240? for 30 min is low owing to the surface coating layer. All results show that iron oxide yellow coating layer is amorphous aluminum hydroxide when the pH value is 4. The surface coating layer is boehmite phase when the pH value increases to 6, 8 and 10. After coating, the iron oxides yellow pigment maintains the original acicular structure, and pigment does not aggregate. The heat resistance of coated yellow iron oxide pigments is greatly improved.?2? Iron oxide yellow pigments coating with aluminum hydroxide were synthesized by a precipitation method using yellow iron oxide as precursor and H3PO4 as treatment agent, the synthesis pH value is 8. Structure of the composite pigment is characterized using XRD, FT-IR, TG-DTA, SEM-EDS. The effect of H3PO4 on structure and heat resistance of the pigments was investigated. XRD?FT-IR?EDS characterization results show that coating layer of sample is boehmite phase when the H3PO4 is not used.The heat resistance of the sample is improved and its coating layer is boehmite phase, and the phase of coating layer changed into amorphous aluminum phosphate when H3PO4 changed the coating layer. TG-DTA and heat-resistance test show that the heat-resistance of the samples changed with amount of H3PO4. When the using amount of H3PO4 reached 5.75 g, the ?E of sample before and after baking is 3.21, displaied good thermal stability. SEM test show that excessed H3PO4 modification will make the coating effect become poor in the reaction process, it is concluded that the reason for the heat resistance of the modified sample is decreased with excessed H3PO4 modification.?3? The application of iron oxide red pigment in ceramic coloring is limited due to its poor thermal stability. This paper takes coated iron oxide yellow as a precursor by using aluminum hydroxide as coating layer, and the samples are synthesized by firing at different temperature. Structure of the composite pigments is characterized using XRD, FT-IR, SEM, et al. The effect of pH value on the structure and thermal stability of precursor is investigated. XRD and FT-IR results show that precursor coating layer is ?-Al₂O₃ or amorphous aluminum hydroxide when the firing temperature is 400??600??800?, et al. While the firing temperature increases to 1100?, the surface coating layer of p H4/Al?p H8/Al is ?-Al₂O₃ and ?-Al₂O₃, respectively. But the crystal structure of surface coating layer of p H6/Al and p H10/Al is the mixture of two crystals. SEM test shows that anti-sintering property of Fe₂O₃/Al₂O₃ composite pigment is promoted by means of coating.The firing tests show that the iron oxide red samples have excellent thermal stability after coating. When p H=6, the color change ?E of samples fired at 1100 ? is 0.84 compared at 800?, displaying a great thermal stability.