Characterization of surface properties of dry-coated anhydrous borax powders

Abstract

Dry particle coating of anhydrous borax (ANB) powders with hydrophobic stearic acid (SA) in the planetary ball mill was investigated. Two process parameters, the amounts of modifier agent and the processing periods, were selected to investigate their effects on solubility, wettability, dispersibility, and hydration properties of ANB powders. Each of the process parameters, i.e., SA amounts (0.5, 1, and 2 wt.%), and coating periods (30, 60, and 120 min), was set at three different levels. Structural changes in the dry-coated powders were characterised using X-ray diffraction (XRD) and photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), and Differential thermal and thermogravimetric analysis (DTA-TG). A discrete coating at an efficiency of 68% was acquired with SA amount of 1 wt.% at a coating period of 60 min, and, thus, resulted in a 31.4% decrease (from 40% to 8.6%) in water solubility of ANB. Moreover, this discrete SA coating made ANB more hydrophobic (99o) and prevented its further hydration. Furthermore, FT-IR and XPS results indicated that SA is coated over the surface of ANB via physical adsorption rather than chemical bonding. Thus, the effective dry coating could be applied to obtain surface-coated ANB, which offers controlled solubility in water-based suspensions.