Effect of Ammonia Addition on the Growth of an AlO(OH) Film during Steam Coating Process

Naotaka Itano,Ai Serizawa,So Yoon Lee

doi:10.3390/coatings12020262

Naotaka Itano, Ai Serizawa + Show 1 more

Open Access

https://doi.org/10.3390/coatings12020262

Copy DOI

Journal: Coatings	Publication Date: Feb 16, 2022
License type: CC BY 4.0

Affiliation: Shibaura Institute of Technology

Abstract

Al alloys possess excellent physical and mechanical properties, such as low density, high specific strength, and good ductility. However, their low corrosion resistance limits their use in corrosive environments. The steam coating process has attracted considerable attention as a new coating technology that can improve the corrosion resistance of Al alloys. This surface treatment technology uses steam to form a corrosion-resistant film on Al alloys. However, a decrease in the processing time, which can result in a lower cost, is needed for the practical application of the steam coating process. In this study, an Al-Mg-Si alloy is used as the base material, and ammonia is added to the steam source to increase the film formation rate. By adding ammonia (0.5 mol/L) to the steam source, the rate constant, K, for film formation increases 1.82 times compared to that of the pure-water-only treatment. Field emission scanning electron micrographs of the film surface confirms that the crystal morphologies of the crystals change from rectangular to parallelepiped shape with increasing process time by ammonia addition. Furthermore, X-ray diffraction patterns show that AlO(OH) crystals are successfully synthesized without byproducts, even when ammonia is added.

Highlights

In recent years, lightweight materials, including aluminum, magnesium, plastics, and composite materials, have been attracting increasing attention for reducing vehicle weight and improving fuel efficiency [1]
This study was focused on the steam coating process, which uses steam generated in a pressure vessel to form a dense anticorrosive film on the metal surface [28,29]
Ammonia was added to the steam source to increase the film formation rate, which was demonstrated by observing the surface morphology and cross-section of the film

Summary

Introduction

Lightweight materials, including aluminum, magnesium, plastics, and composite materials, have been attracting increasing attention for reducing vehicle weight and improving fuel efficiency [1]. There is a strong demand for environmentally friendly means of treating Al alloys Based on these factors, this study was focused on the steam coating process, which uses steam generated in a pressure vessel (autoclave) to form a dense anticorrosive film on the metal surface [28,29]. This study was focused on the steam coating process, which uses steam generated in a pressure vessel (autoclave) to form a dense anticorrosive film on the metal surface [28,29] The advantage of this surface technology is that it is environmentally friendly, as only water is used in the process. Ammonia was added to the steam source to increase the film formation rate, which was demonstrated by observing the surface morphology and cross-section of the film

Materials and Methods

The standard of pH measurements andtreatment after treatment at each time are

Surface Observation

Relationship between pH and the Surface Morphology

Conclusions