Fenter,P., Lee,S.S., Park,C., Catalano,J.G., Zhang,Z. and Sturchio,N.C.(2010): Probing interfacial reactions with X-ray reflectivity and X-ray reflection interface microscopy: Influence of NaCl on the dissolution of orthoclase at pOH 2 and 85℃. Geochimica et Cosmochimica Acta, 74, 3396-3411.

『X線反射法およびX線反射界面顕微鏡法で界面反応を探る:pOH 2および85℃でのオルソクレース(正長石)の溶解に対するNaClの影響』


Abstract
 The role of electrolyte ions in the dissolution of orthoclase (001) in 0.01 m NaOH (pOH〜2) at 84±1℃ is studied using a combination of in-situ X-ray reflectivity (XR) and ex-situ X-ray reflection interface microscopy (XRIM). The real-time XR measurements show characteristic intensity oscillations as a function of time indicative of the successive removal of individual layers. The dissolution rate in 0.01 m NaOH increases approximately linearly with increasing NaCl concentration up to 2 m NaCl. XRIM measurements of the lateral interfacial topography/structure were made for unreacted surfaces and those reacted in 0.01 m NaOH/1.0 m NaCl solution for 15, 30 and 58 min. The XRIM images reveal that the dissolution reaction leads to the formation of micron-scale regions that are characterized by intrinsically lower reflectivity than the unreacted regions, and appears to be nucleated at steps and defect sites. The reflectivity signal from these reacted regions in the presence of
NaCl in solution is significantly lower than that calculated from an idealized layer-by-layer dissolution process, as observed previously in 0.1 m NaOH in the absence of added electrolyte. This difference suggests that dissolved NaCl results in a higher terrace reactivity leading to a more three-dimensional process, consistent with the real-time XR measurements. These observations demonstrate the feasibility of XRIM to gain new insights into processes that control interfacial reactivity, specifically the role of electrolytes in feldspar dissolution at alkaline conditions.』

1. Introduction
2. Experimental details
 2.1. Sample preparation and experimental conditions
 2.2. X-ray reflectivity (XR)
 2.3. X-ray reflectivity interface microscopy (XRIM)
3. Results
 3.1. In-situ observations of orthoclase dissolution vs. electrolyte concentration
 3.2. Ex-situ observations of orthoclase (001) dissolution with XRIM
  3.2.1. Freshly cleaved surface
  3.2.2. 15 min reaction
  3.2.3. 30 and 58 min reactions
4. Discussion
 4.1. Dissolution rate enhancement with added electrolyte
 4.2. Effect of NaCl on the dissolution process
 4.3. Interpretation of the XRIM images
5. Conclusions
Acknowledgments
Appendix A.
 A.1. XRIM image processing to correct for different illumination conditions
 A.2. Reflectivity signal vs. interfacial topography and roughness
  A.2.1. Single-layer roughness
  A.2.2. Multiple layer roughness
References



戻る