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Published on: October 21, 2016
BET Measurements: Outgassing of Minerals
1Department of Geology and Geotechnical Engineering, Technical University of Denmark, Lyngby, DK-2800, Denmark
Journal of Colloid and Interface Science
|June 22, 2000
Summary
Outgassing minerals before BET analysis requires careful temperature control. Low temperatures are best for poorly crystalline materials to prevent phase changes, with extended time improving accuracy for iron oxides.
Area of Science:
- Geochemistry
- Materials Science
- Analytical Chemistry
Background:
- Elevated temperatures during outgassing can alter mineral phases, impacting surface area measurements.
- Amorphous and poorly crystalline materials are particularly susceptible to thermal phase changes.
- The Brunauer, Emmett, and Teller (BET) method is crucial for determining specific surface areas of minerals.
Purpose of the Study:
- To assess the BET method's applicability under low outgassing temperature conditions.
- To investigate the impact of varying outgassing temperatures and times on mineral surface area measurements.
- To identify optimal outgassing parameters for diverse aquifer minerals.
Main Methods:
- Selected aquifer minerals (2-line ferrihydrite, goethite, lepidocrocite, quartz, calcite, alpha-alumina, kaolinite) were outgassed at different temperatures and durations.
- Specific surface areas were measured using the BET method.
- Scanning electron microscopy (SEM) was used to compare particle sizes derived from BET data with observed sizes.
Main Results:
- Iron oxide surface areas were highly sensitive to outgassing conditions, increasing by 170% with higher temperatures.
- Phase changes in poorly crystalline minerals occurred below 100°C.
- Stable BET values for iron oxides were achieved by increasing outgassing time, not temperature.
- Quartz, calcite, alpha-alumina, and kaolinite yielded stable BET values after 2 hours at 100-250°C.
- Outgassing at room temperature (20°C) for these minerals caused only minor errors if time was increased.
Conclusions:
- Low outgassing temperatures are preferable to minimize phase changes in minerals, especially for BET analysis.
- Increasing outgassing time can stabilize BET measurements for iron oxides without heating.
- Aquifer sediments with poorly crystalline components can be analyzed using BET at low temperatures with extended outgassing times.
- BET-derived particle sizes correlate well with SEM observations, validating the surface area measurements.
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