Franz Königer

Low-frequency dielectric properties of three bentonites at different adsorbed water states

Three bentonites of varying smectite content were investigated by dielectric spectroscopy in the frequency range 10(-4) to 10(6) Hz after storage at well-defined humidities. The identification of relaxation processes from complex permittivity measurements was difficult, since conductivity effects were superimposed on the underlying relaxations. Relaxation peaks revealed by the dissipation factor indicated the occurrence of interfacial processes between 10(2) and 10(6) Hz. The intensity of the polarization of the electrochemical double-layer at the clay-water interface was promoted by increasing water content and was shifted to higher frequencies the higher the water content in the bentonites. Below ~1 Hz, electrode polarization (EP) was shown to be a participating process with capacitance values ranging from 0.6*10(-3) to 7.3*10(-3)F due to the accumulated charges. An equivalent circuit model was introduced that successfully described the low-frequency dielectric behavior of bentonites at low moisture levels. An included series R-CPE connection was used to describe the double-layer relaxation. At water contents up to 17%, the bulk resistivity was mainly influenced by smectite content and cation exchange capacity, whereas at water contents of ≥19%, interlayer occupation and hydration state became more important.

High-density bimodal bentonite blends for hydraulic sealings at the Ibbenbüren coalmine

Abstract The two high-pressure water-retaining dams at the Ibbenbüren coalmine in Münsterland (Germany) have to perform reliably under the induced tension caused by further exploitation of the current mining area. The load-bearing and the sealing functions of the new barriers were separated and new sealing materials were developed. An innovative multilayer sealing system of bentonite and sandwiched equipotential layers (SANDWICH) supporting homogeneous swelling and sealing, independent of formation water (Nüesch et al., 2002), was applied in this project. A testing program of strain-controlled swelling pressure tests on compacted bentonite specimens and on a bentonite/sand mixture was conducted to ensure an adequate potential for swelling-pressure development. The measurements under constant volume for dry densities between 1.45 g/cm³ and 1.67 g/cm³ showed an evolving swelling pressure between 1.04 and 1.8 MPa for 100% bentonite samples. Strain-controlled oedometer tests for zero strain and step-wise applied strain up to 2% revealed that a sufficient magnitude of swelling pressure existed at maximum applied strain.

‘Free Line Sensing’, a new method for soil moisture measurements using high-voltage power lines

Large area integrated soil moisture measurement results are often required for meteorological studies as well as for geological, agricultural and natural disaster research. Commonly used sensors measure the soil moisture locally and exhibit a strong spatial variability due to the heterogeneity of most land surfaces. The new ‘Free Line Sensing’ technology uses existing high-voltage power lines to detect variations in soil moisture below the lines. The electromagnetic field of an additional radio-frequency signal in the range of 50–500 kHz on the line is influenced by changes in the electric properties of the soil, e.g., after rainfall. This has been simulated using high-frequency software, the result being that variations of electrical conductivity or dielectric coefficient of the soil will lead to a measurable effect with power line sections extending over several kilometres. Measurements have been conducted on a 13 km long high-voltage power line. The resulting signal is evaluated with respect to amplitude and phase. Measurement data demonstrate the capability of the ‘Free Line Sensor’ to monitor the integrated soil moisture of the Earth’s surface and near subsurface over the area covered by the power line. The resulting signal of the ‘Free Line Sensor’ strongly responds to precipitation events and the following drying of the soil. Comparison with soil moisture data obtained from gravimetric drying of soil samples reveals a good agreement.

Calcium Silicate Phases Explained by High-Temperature-Resistant Phosphate Probe Molecules

In this work, high-temperature-resistant phosphate molecules are applied to characterize ultrathin (100 nm) calcium silicate (C-S) phases. These C-S phases are synthesized on silicon wafers, and the interaction of phosphates with the C-S phases is studied by means of in situ transmission Fourier transform infrared (FTIR) spectroscopy. At room temperature, the chemistry of the system is dominated by the formation of calcium phosphates (C-P). In the case of temperature rising to 1000 °C, the C-S phases are regenerated. FTIR results are analyzed on the basis of first-principles calculations and further supported by complementary time-of-flight secondary ion mass spectrometry (ToF-SIMS) experiments. This study provides a detailed and self-consistent picture of the chemical and structural properties of interfaces such as the one between the atmosphere and ultrathin C-S phases (gas/C-S) and the one between them and silicon wafers (C-S/Si bulk). The material combination of ultrathin C-S phases grown on silicon wafers might in the future have great potential in selective chemistry, catalysis, and sensing technology as well as in semiconductor manufacturing.