Surface-Charge Anisotropy of Scheelite Crystals

Area of Science:

• Surface science
• Colloid and interface science
• Materials chemistry

Background:

• Understanding surface charge is crucial for predicting colloidal interactions.
• Scheelite (CaWO4) is an important industrial mineral, and its surface properties influence processing.
• Crystallographic orientation significantly impacts surface characteristics.

Purpose of the Study:

• To measure colloidal interactions between silicon nitride and scheelite crystal surfaces at varying pH.
• To calculate surface-charge density and surface-potential for different scheelite crystallographic planes using the DLVO model.
• To investigate the relationship between surface charge anisotropy and surface atomic structure.

Main Methods:

• Atomic force microscopy (AFM) was used to probe force-distance curves.
• The Derjaguin-Landau-Verwey-Overbeek (DLVO) model was fitted to AFM data.
• Measurements were conducted in 1 mM KCl solutions across a range of pH values.

Main Results:

• Surface-potential values were negative for all measured crystallographic surfaces ({112}, {101}, {001}) in both acidic and basic conditions.
• The {101} surface exhibited the highest negative charge, followed by {112} and {001}.
• Surface potential of {001} was pH-insensitive, while {112} and {101} potentials increased with pH.

Conclusions:

• Surface charge anisotropy exists on scheelite crystals and is influenced by crystallographic orientation and pH.
• The density of active oxygen atoms on the surface correlates with surface charge, likely due to OH- adsorption.
• AFM and DLVO modeling provide valuable insights into the surface chemistry of scheelite.