MATHEMATICAL MODELLING OF THE CONSTITUENTS’ CONCENTRATIONS OF AISI 304 STAINLESS STEEL SAMPLES THAT DIFFUSE INTO SIMULATED ACIDIC ENVIRONMENTS

Abstract

The purpose of this research was to study the mathematical modelling of dependence between testing parameters and some metallic elements diffused into simulated acidic environments. Diffusion processes occurring at the contact between AISI 304 stainless steel samples and simulated acidic environments were analyzed to fulfill this goal. In order to process the experimental data by statistical and mathematical methods, the following steps were taken: diffusion testing of Cr, Mn, ⁵⁶Fe and Ni elements from AISI304 stainless steel samples into solutions with concentration of 3%, 6% and 9% acetic acid; chemical analysis of corrosive solutions using mass spectrometry and inductively coupled plasma method (ICP-MS); the results were processed using ANOVA method and thus resulting the  mathematical models that describe the dependence between variables. A polynomial model with independent variables was used to obtain the mathematical models: temperature of acidic simulated solutions (X₁),  testing time (X₂), stirring grade of environment (X₃) and the dependent  variables (response function): Y₁ - concentration of chromium (Cr), Y₂ - concentration of manganese (Mn), Y₃ - concentration of iron (⁵⁶Fe) and Y₄ - concentration of nickel (Ni) found in corrosive  environments. After having made the analysis of variance ANOVA, a model having the lowest P value (critical probability) for all variables was chosen. The regression coefficient was determined to verify the validity of each mathematical model.