Characterization of surface properties of dry-coated anhydrous borax powders

Abstract

Dry particle coating of anhydrous borax (ANB) powders with hydrophobic stearicacid (SA) in the planetary ball mill was investigated. Two process parameters,the amounts of modifier agent and the processing periods, were selected toinvestigate their effects on solubility, wettability, dispersibility, and hydrationproperties 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 threedifferent levels. Structural changes in the dry-coated powders were characterisedusing X-ray diffraction (XRD) and photoelectron spectroscopy (XPS), Fouriertransform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM),and Differential thermal and thermogravimetric analysis (DTA-TG). A discretecoating at an efficiency of 68% was acquired with SA amount of 1 wt% at acoating period of 60 min, and, thus, resulted in a 31.4% decrease (from 40% to8.6%) in water solubility of ANB. Moreover, this discrete SA coating made ANBmore hydrophobic (99o) and prevented its further hydration. Furthermore, FT-IRand XPS results indicated that SA is coated over the surface of ANB via physicaladsorption rather than chemical bonding. Thus, the effective dry coating couldbe applied to obtain surface-coated ANB, which offers controlled solubility inwater-based suspensions.