Rainer Schuhmann

New Dielectric Sensors and Sensing Techniques for Soil and Snow Moisture Measurements

Measurements of material moisture are essential in fields such as agriculture or civil engineering. Electromagnetic techniques, more precisely dielectric methods, have gained wide acceptance in the last decades. Frequency or Time Domain methods take advantage of the high dielectric permittivity of water compared to dry materials. This paper presents four new dielectric sensors for the determination of soil or snow water content. After a short introduction into the principles, both the hardware and operating mode of each sensor are described. Field test results show the advantages and potentials such as automatic measurement and profiling, state-of-ground detection or large-scale determination. From the results it follows that the presented sensors offer promising new tools for modern environmental research.

Natural mixture of silica and smectite as a new clayey material for industrial applications

Abstract The main physico-chemical properties of a new smectitic clay containing large amounts of amorphous material are reviewed and potential industrial applications of this type of clay are discussed. Due to a 34% amorphous material content (natural silica gel), the investigated clay has very high porosity and can be used as it is or in acid-impregnated form for oil bleaching or phosphate reduction in edible oil. In the field of biodiesel purification, the new clay can be used to remove, in particular, mono-, diglycerides and glycerol. The natural silica-smectite mixture is also suitable as a carrier for liquid ingredients, for example in animal feeds, and might serve as a partial or complete substitute for synthetic precipitated silicas. In the field of bioseparation processes, the clay can be used as an adsorbent for protein separation by means of cation exchange. Due to the suppressed swelling (compared with smectite alone), it can be packed in columns which can be regenerated.

CHARACTER AND AMOUNT OF I-S MIXED-LAYER MINERALS AND PHYSICAL-CHEMICAL PARAMETERS OF TWO CERAMIC CLAYS FROM WESTERWALD, GERMANY: IMPLICATIONS FOR PROCESSING PROPERTIES

The industrial assessment of ceramic clays commonly consists of the determination of just two parameters, the particle-size distribution and the chemical composition; other parameters may also be important, however. The aim of the present study was to show that a careful determination of the mineralogical phase content provides valuable additional information on the processing behavior of ceramic clays.Two ceramic clays (W1 andW2) from theWesterwald area, Germany, were evaluated as being the same with respect to industrial screening criteria, but showed different processing properties. In order to elucidate the different behaviors, both clays were investigated comprehensively using a multi-method approach combining physical-chemical and mineralogical methods.Different aggregation characteristics for the two clays were revealed by determining the grain-size distribution with and without Na-pyrophosphate as a dispersant. In addition, W1 showed a greater electrical conductivity and soluble-salt concentration which promoted dispersion behavior.The phase content was identified both for bulk materials and for several grain-size fractions by X-ray diffraction (XRD) and Rietveld analysis. The quantitative phase content was crosschecked with the chemical composition by X-ray fluorescence (XRF) analysis. Additional information was gathered by thermal analysis, cation exchange capacity (CEC) measurements, Mössbauer spectroscopy, and optical microscopy. While bulk samples of W1 and W2 showed nearly the same mineralogical and chemical compositions, investigation of the clay-size fractions (0.6–2 μm, <0.6 mm) revealed differences in the composition of the 2:1 layer silicates. The percentages of smectite in the mixed-layer I-S, as well as the amount of kaolinite, discrete illite, and smectite were determined by one-dimensional XRD profile fitting (ODPF). Best-fitting results for W1 were achieved for a physical mixture of an illite-rich I-S mixed-layer mineral (R3 I(0.9)-S) with discrete smectite, whereas W2 was characterized by a greater proportion of smectite in the mixed-layer (R1 I(0.8)-S), without discrete smectite. Based on the different structural features of the swellable clays, a qualitative delamination model for the 2:1 layer silicates during processing of the clays was derived. The model provides a further approach, aside from aggregation characteristics, to help understand the clay-processing behavior, which was found to be different for the two ceramic clays investigated.

CATION EXCHANGE REACTIONS OF VERMICULITE WITH Cu-TRIETHYLENETETRAMINE AS AFFECTED BY MECHANICAL AND CHEMICAL PRETREATMENT

The cation exchange capacity (CEC) is a characteristic property of expandable clay minerals, such as smectites and vermiculites. The aim of this work was to examine the cation exchange behavior of vermiculite using the Cu-triethylenetetramine (Cu-trien) CEC method and the influence of mechanical and chemical pretreatment, with the ammonium acetate method serving as a reference. The Cu-trien method makes rapid and direct CEC measurements possible. Three different kinds of mill were used to grind a vermiculite sample from Russia, in order to reduce the particle size to <10 µm. The Netzsch CGS 10 dry mill reduced the particle size more effectively than the other grinding methods. Chemical pretreatments were used to remove carbonates, organic matter, Fe oxides, and divalent exchangeable cations from vermiculite samples prior to CEC measurements. Subsamples of ground and chemically pretreated vermiculite samples were saturated with Na, Li, Mg, Ca, and Cu cations to determine the effect of exchangeable cations on measured CEC values. Chemical pretreatment, monovalent cation pretreatment, and 48 h of shaking time were needed to measure vermiculite CEC values effectively using the Cu-trien method.

Mineralogical and physicochemical characterization of a natural bleaching earth containing sepiolite suitable for fast filtration and bioseparation

Abstract A clay from the Mediterranean area classified as natural bleaching earth was comprehensively characterized and the quantitative phase content was determined. Morphology and surface characteristics were determined by environmental scanning electron microscopy (ESEM) and nitrogen adsorption. The BET surface area was >200 m2 g-1 and the average mesopore diameter was >10 nm. Thus the clay is suitable for bioseparation of larger proteins. X-ray diffraction (XRD), X-ray fluorescence (XRF), cation exchange capacity (CEC), layer charge measurement and simultaneous thermal analysis (STA) were used for mineralogical characterization. Determination of the phase content by Rietveld analysis was possible only after Sr2+ saturation, while Rietveld analysis of XRD patterns from Na+-saturated clay resulted in a strong overestimation of the amorphous content and masking of the sepiolite. The clay consists of sepiolite, dioctahedral smectite with high layer charge and low stack height, X-ray amorphous matter (probably mainly SiO2) and accessory feldspars.

Correlation Between the Extent of Catalytic Activity and Charge Density of Montmorillonites

The clay mineral montmorillonite is a member of the phyllosilicate group of minerals, which has been detected on martian soil. Montmorillonite catalyzes the condensation of activated monomers to form RNA-like oligomers. Extent of catalysis, that is, the yield of oligomers, and the length of the longest oligomer formed in these reactions widely varies with the source of montmorillonite (i.e., the locality where the mineral is mined). This study was undertaken to establish whether there exists a correlation between the extent of catalytic property and the charge density of montmorillonites. Charge density was determined by saturating the montmorillonites with alkyl ammonium cations that contained increasing lengths of alkyl chains, [CH₃-(CH₂)(n)-NH₃](+), where n = 3-16 and 18, and then measuring d(₀₀₁), interlayer spacing of the resulting montmorillonite-alkyl ammonium-montmorillonite complex by X-ray diffractometry (XRD). Results demonstrate that catalytic activity of montmorillonites with lower charge density is superior to that of higher charge density montmorillonite. They produce longer oligomers that contain 9 to 10 monomer units, while montmorillonite with high charge density catalyzes the formation of oligomers that contain only 4 monomer units. The charge density of montmorillonites can also be calculated from the chemical composition if elemental analysis data of the pure mineral are available. In the next mission to Mars, CheMin (Chemistry and Mineralogy), a combined X-ray diffraction/X-ray fluorescence instrument, will provide information on the mineralogical and elemental analysis of the samples. Possible significance of these results for planning the future missions to Mars for the search of organic compounds and extinct or extant life is discussed.

Determination of Hydraulic Conductivity Based on (Soil) - Moisture Content of Fine Grained Soils

The chapter will be divided into the subchapter material, processes and systems. The first one will focus on the physical, chemical and dynamic material properties and their measuring methods. The second specifies the dynamic of the surface moistening and fluid flow. The comprehensive characterization of materials is prerequisite to understand processes in large (geo)-technical systems and their manipulation. The transition from nano (material) via meso (processes) to macro scale (systems) will be illustrated with an example in the third chapter.

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.

Impact of Intrinsic Structural Properties on the Hydration of 2:1 Layer Silicates

Several 2:1 layer silicates comprising di- and trioctahedral smectites of different layer charge between 0.2 and 0.4 per formula unit and a trioctahedral vermiculite were studied by an in situ method that allowed Fourier transform infrared spectroscopy (FTIR) spectra and water vapor sorption isotherms to be obtained simultaneously. The particle size and shape of the selected materials were determined using X-ray diffraction and gas adsorption analyses, which provided an estimate of the particle size with resulting edge site proportion. The aim of this study was to elucidate the hydration mechanism in 2:1 layer silicates during desorption and adsorption of water vapor. Domains in the desorption and adsorption of water vapor of the smectite samples with a slightly increasing slope were explained by a heterogeneous layer charge distribution, which enables the coexistence of different hydration states even under controlled conditions. Whereas hysteresis was observed over the entire isothermal range of the smectites, the isotherm of the vermiculite sample only showed hysteresis in the transition from the monohydrated state (1W) to the bihydrated state (2W). We also revealed that hysteresis is a function of the layer charge distribution, the achieved water content, and the particle size with resulting edge site contribution. Increasing the edge site proportions led to an increased hysteresis. The findings from the experimental FTIR/gravimetric analysis showed that the transition from 2W to 1W and backward is visible using infrared spectroscopy. The shifting of δ(H-O-H) was influenced by the layer charge and octahedral substitutions. As a final point, we use water as a sensor molecule to describe the OH groups of the octahedral sheet and show that the observed shifts result from a change in the tilting angle. Our experimental results were supported by ab initio thermodynamic simulations that revealed the different shifting behavior of δ(H-O-H) and δ(M x+-OH-N y+) related to the differences in surface charge density and octahedral compositions.