Optimization of process variables and corrosion properties of a multi layer silica sol gel coating on AZ91D using the Box–Behnken design

• Published in: Journal of sol-gel science and technology Vol. 59; no. 3; pp. 640 - 649
• Main Authors: Nikrooz, Bahaedin, Zandrahimi, Morteza
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.09.2011; Springer; Springer Nature B.V
• Subjects: Ceramics; Chemistry; Chemistry and Materials Science; Coating; Colloidal gels. Colloidal sols; Colloidal state and disperse state; Composites; Corrosion; Corrosion currents; Corrosion prevention; Dependent variables; Design factors; Design of experiments; Dilution; Electrochemistry; Exact sciences and technology; Fluorination; General and physical chemistry; Glass; Immersion coating; Independent variables; Inorganic Chemistry; Magnesium alloys; Magnesium base alloys; Materials Science; Morphology; Nanotechnology; Natural Materials; Optical and Electronic Materials; Optimization; Original Paper; Polarization; Precursors; Process variables; Response surface methodology; Scanning electron microscopy; Silica gel; Silicon dioxide; Sodium chloride; Sol gel process; Sol-gel processes; Substrates; Tetraethyl orthosilicate; MTES; TEOS; Box–Behnken design; Silica coating; Sintering temperature; AZ91D; Binary compound; Methodology; Precursor; Silica; Optimization; Design; Scanning microscope; Formulation; Silica gel; Dip coating; Scanning electron microscopy; Fluorine compound; Sodium chloride; Electron microscopy; Resistance; Substrate; Dilution; Corrosion; Experimental design; Sol gel process; Measurement technique; Sintering; Morphology; Magnesium alloy; Electrochemistry; Impedance; Box-Behnken design
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1007/s10971-011-2539-z

Anti-corrosion silica coating was prepared via the sol–gel method for AZ91D magnesium alloy using tetraethoxysilane and methyltriethoxysilane as precursors. Silica coating was deposited on fluorinated magnesium alloy substrates by dip coating. The surface morphology of the silica coating was characterized by scanning electron microscope (SEM). The corrosion properties were studied by electrochemical impedance measurements and polarisation technique in 3.5 wt% Sodium chloride solution. The results showed an improvement in the corrosion performance from these coatings. A three-factor, three-level design of experiment (DOE) with response surface methodology including a Box–Behnken design was run to evaluate the main and interaction effects of several independent formulation variables, which included precursor ratios MTES/TEOS (X 1 ), sintering temperature (X 3 ) and sol dilution (X 2 ) which measured the volume of the diluted sol divided by the initial volume of sol. The dependent variables included the corrosion current derived from the polarisation curve (i cor  = Y 1 ) and the coating resistance derived from the Nyquist curve (R coat  = Y 2 ). Optimizations were predicted to yield Y 1 and Y 2 values of 1.57018E–7A cm −2 and 14279 Ω cm 2 , when X 1 , X 2 , and X 3 were 3.36, 1.52 and 222, respectively.