Where the bulk terminates: Experimental evidence for restructuring, chemibonded OH − and H + , adsorbed water and hydrocarbons on calcite surfaces

Abstract

Better understanding of mineral surface reactivity can improve control of crystal growth and dissolution which is central to biomineralisation, design of advanced materials and preventing transport of toxic substances in the environment. Some experimental observations of fundamental processes on calcite using high-resolution techniques (AFM, XPS, TOF-SIMS, LEED) are summarised. Surfaces, cleaved in ultrahigh vacuum (UHV) in the absence of reactive species, relax. Cleavage in air results in hydration and hydrolysis, covering the surface with chemisorbed CaOH and CO 3 H. Water adsorbed from air promotes recrystallisation on apparently dry surfaces. Organic components can inhibit dissolution and precipitation; even in the cleanest laboratory, surfaces have at least a monolayer of hydrocarbons. On commercial calcite powders contaminated by organic additives during manufacture, we do not see layer-by-layer and atom-by-atom growth or dissolution and behaviour contradicts the theoretical models developed from macroscopic experiments with these materials. Instead, steps are rounded and many atomic layers high.

Keywords:

• Calcite
• Caco 3
• Surface Atomic Structure
• Solid Solution Interface
• Surface Processes
• Hydrolysis Species