Study on the Formulation and Performance of High Aluminum Powder Coatings

[China Aluminum Network] The preferred refractory fillers for foundry coatings are fused mullite powder and chemically purified zirconium dioxide powder (ZrO2>99.5%), corundum powder and zirconium powder. However, fused mullite powder and pure zirconia powder are expensive, and corundum powder and zirconium powder are also expensive. This article describes the high aluminum powder coating, its refractory filler high aluminum powder source rich, cheap, paint performance and use of the effect can be zirconium powder coating, corundum powder coating is comparable, is worth promoting a cast steel, cast iron with shallow Color paint. 1· Coating composition The coating consists of 5 parts: refractory filler, liquid carrier, suspending agent, binder and various additives. 1.1 Fire-resistant fillers The refractory fillers are the main part of the coating. Their physical and chemical properties have a decisive influence on the coating effect, especially on the refractoriness and thermochemical stability of the coating. The performance of several commonly used materials is shown in Table 1. As can be seen from Table 1, corundum powder, zircon powder, bauxite powder, chromite powder, quartz powder and graphite powder are all high in refractoriness, but corundum powder is expensive; chromite ore and graphite are both Black, serious pollution to the environment, and the chromite ore powder is poor in domestic resources and needs to be imported from abroad. Graphite is likely to cause carbon increase in the production of steel castings. Although quartz powder is white, it is easy to make quartz dust in the process of sand removal. Workers have silicosis; zirconium powder (rice white) and bauxite powder (light yellow) are all light-colored, have high refractoriness and low sintering point, and are easy to obtain sintering and peeling coatings. This paper chooses bauxite powder as a refractory filler instead of zirconium powder. Bauxite powder, also known as high aluminum powder, is a silicon-aluminum refractories. It is a corundum bauxite clinker obtained from the high-alumina bauxite ore by high-temperature calcination at 1300-1500°C, and is then ground into powder. The main mineral composition of bauxite is corundum (α-Al2O3) and mullite (3Al2O3·2SiO2). The refractoriness of bauxite clinker increases with the increase of Al2O3 content and the increase of calcination temperature, and its refractoriness ≥ 1770 °C. Bauxite does not generate a low-melting point substance with the metal oxide at the pouring temperature, and at the same time, the wettability of the high-aluminum powder by the molten steel and its oxide is relatively low. Therefore, it can be used as a good anti-adhesion effect for the coating. When using high-alumina powder as refractory filler, it must pay attention to its purity, Al2O3 content should be ≥85%, impurity content should be less. 1.2 Liquid carriers generally use ethanol. Ethanol is non-toxic, odorless, volatile, and combustible. It is an economical and safe carrier liquid. The purity of industrial ethanol is about 95%. It is difficult to ignite and burn the paint, and it is difficult to fully burn. Adding a certain amount of methanol can be used in combination to improve its combustion performance. Methanol is more volatile than ethanol and burns faster, but methanol is more toxic. It is harmful to ocular nerve stimulation and should be used with caution. 1.3 Suspension Bentonite is the more commonly used suspending agent in paints. The bentonite particles are very small (less than 0.1 μm). The carrier is wetted by the carrier and the carrier not only adsorbs on the surface of the particles but also enters into the colloidal layer between its crystal layers to make the carrier fluid into a colloidal solution. The bentonite particles form a spatial network structure in the colloidal solution, so that the bentonite slurry has a yield value, and the particles of the refractory filler particles do not easily sink. This paint uses lithium bentonite as a suspending agent. Lithium bentonite is obtained by ion exchange treatment of natural calcium bentonite. It cannot fully swell in ethanol and can only form colloids. Therefore, water must be added to make it fully swell, and then bentonite slurry is made by diluting with ethanol. Use after ~3 days.