Skip to Main Content
Skip Nav Destination
GEOREF RECORD

Comparison of isoelectric points of single-crystal and polycrystalline alpha -Al (sub 2) O (sub 3) and alpha -Fe (sub 2) O (sub 3) surfaces

Yingge Wang, Per Persson, F. Marc Michel and Gordon E. Brown
Comparison of isoelectric points of single-crystal and polycrystalline alpha -Al (sub 2) O (sub 3) and alpha -Fe (sub 2) O (sub 3) surfaces
American Mineralogist (October 2016) 101 (10): 2248-2259

Abstract

The surface charging behavior as a function of pH and isoelectric points (IEPs) of single-crystal alpha -Al (sub 2) O (sub 3) (0001) and (1102) and alpha -Fe (sub 2) O (sub 3) (0001) was determined by streaming potential measurements using an electrokinetic analyzer. The IEPs of alpha -Al (sub 2) O (sub 3) (0001) and (1102) and alpha -Fe (sub 2) O (sub 3) (0001) were found to be 4.5, 5.1, and 6.5, respectively. These IEP values for oriented single crystals of alpha -Al (sub 2) O (sub 3) are in good agreement with literature values, whereas the new IEP value for alpha -Fe (sub 2) O (sub 3) (0001) is significantly lower than four reported values (IEP = 8-8.5) for single-crystal alpha -Fe (sub 2) O (sub 3) (0001) (Eggleston and Jordan 1998; Zarzycki et al. 2011; Chatman et al. 2013; Lutzenkirchen et al. 2013) and significantly higher than one (IEP = 4) recently measured by Lutzenkirchen et al. (2015) on a fresh alpha -Fe (sub 2) O (sub 3) (0001) surface. Most of the single-crystal IEP values measured recently are lower than IEP values reported for polycrystalline alpha -Al (sub 2) O (sub 3) and alpha -Fe (sub 2) O (sub 3) , which are generally in the pH range of 8 to 10. Calculations of the IEP values based on estimated K (sub a) values of alpha -Fe (sub 2) O (sub 3) and alpha -Al (sub 2) O (sub 3) surfaces in contact with water as a function of defect type and concentration suggest that highly reactive surface defect sites (primarily singly coordinated aquo groups) on the Fe- and Al-oxide powders are possibly a major source of the surface charge differences between polycrystalline samples and their oriented single-crystal counterparts studied here. The results of this study provide a better understanding of the surface charging behavior of Fe and Al-oxides, which is essential for predicting complex processes such as metal-ion sorption occurring at mineral/water interfaces.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 101
Serial Issue: 10
Title: Comparison of isoelectric points of single-crystal and polycrystalline alpha -Al (sub 2) O (sub 3) and alpha -Fe (sub 2) O (sub 3) surfaces
Affiliation: Stanford University, Department of Geological Sciences, Stanford, CA, United States
Pages: 2248-2259
Published: 201610
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 74
Accession Number: 2016-096608
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
Secondary Affiliation: Lund University, SWE, Sweden
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201647
Close Modal

or Create an Account

Close Modal
Close Modal