Abstract

Pipe pulverizer is a part of a coal mill machine that has a function to direct the coal dust from the grinding mill to the turbine combustion chamber of the steam power plant. The pipe material is mild steel. The process of sulfidation and erosion of coal dust can cause a decrease in pulverizer pipe performance, thus its service life also reduces. The pipe deterioration can be anticipated from the beginning of the pipe manufacturing so that it can avoid production time due to maintenance. The ceramic coating overlay on the surface of the mild steel is one of the best ways to protect the steel from erosion and sulfidation. This research is aimed to perform a ceramic coating over the surface of the mild steel to improve its erosion resistance by using the alumina-phosphate ceramic compound. The coating technique using a dipping method. The coating layer is formed by the reaction between monoaluminum phosphate (MAP, Al(H2PO4)3) as a binder and aluminum oxide (Al2O3) particle. It transforms to berlinite layer on the mild steel surface when heated in the phase transformation temperature. The observation of the coating performance is carried out with the variation of the binder composition Al:P 25:75, 28:72, 30:70 and the Al2O3/MAP slurry is given at 40/60. Optical emission spectrometry (OES) is applied to analyze the chemical composition of the mild steel, energy dispersive spectrometry (EDS) and scanning electron microscopy (SEM) is used to characterize the contents of the particle, analyze the morphology and also the microstructure of the coating. X-ray diffraction (XRD) is applied to investigate phase of the binder compound of monoaluminum phosphate. Erosion resistance properties of the coating are characterized by the gas erosion jet test. From the test result, it can be concluded that the erosion resistance of mild steel with an alumina-phosphate ceramic coating increasing four times compared to the condition without coating. Its performance is mainly influenced by the binder composition.

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