Physical properties of a boreal clay soil under differently managed perennial vegetation

The physical properties of surface soil horizons, essentially pore size, shape, continuity and affinity for water, regulate water entry into the soil. These properties are prone to changes caused by natural forces and human activity. The hydraulic properties of the surface soil greatly impact the generation of surface runoff and accompanied erosion, the major concern of agricultural water protection. The general target of this thesis was to improve our understanding of the structural and hydraulic properties of boreal clay soils. Physical properties of a clayey surface soil (0 - 10 cm, clay content 51%), with a micaceous/illitic mineralogy subjected to three different management practices of perennial vegetation, were studied. The study sites were vegetated buffer zones located side by side in SW Finland: 1) natural vegetation with no management, 2) harvested once a year, and 3) grazed by cattle. The soil structure, hydraulic properties, shrinkage properties and soil water repellency were determined at all sites. Two distinct flow domains were evident. The surface soil was characterized by subangular blocky, angular blocky and platy aggregates. Hence, large, partially accommodated, irregular elongated pores dominated the macropore domain at all sites. The intra-aggregate pore system was mostly comprised of pores smaller than 30 μm, which are responsible for water storage. Macropores at the grazed site, compacted by hoof pressure, were horizontally oriented and pore connectivity was poorest, which decreased water and air flux compared with other sites. Drying of the soil greatly altered its structure. The decrease in soil volume between wet and dry soil was 7 - 10%, most of which occurred in the moisture range of field conditions. Structural changes, including irreversible collapse of interaggregate pores, began at matric potentials around -6 kPa indicating, instability of soil structure against increasing hydraulic stress. Water saturation and several freezethaw cycles between autumn and spring likely weakened the soil structure. Soil water repellency was observed at all sites at the time of sampling and when soil was dryer than about 40 vol.%. (matric potential < -6 kPa). Therefore, water repellency contributes to water flow over a wide moisture range. Water repellency was also observed in soils with low organic carbon content (< 2%), which suggests that this phenomenon is common in agricultural soils of Finland due to their relatively high organic carbon content. Aggregate-related pedofeatures of dense infillings described as clay intrusions were found at all sites. The formation of these intrusions was attributed to clay dispersion and/or translocation during spring thaw and drying of the suspension in situ. These processes generate very new aggregates whose physical properties are most probably different from those of the bulk soil aggregates. Formation of the clay infillings suggested that prolonged wetness in autumn and spring impairs soil structure due to clay dispersion, while on the other hand it contributes to the pedogenesis of the soil. The results emphasize the dynamic nature of the physical properties of clay soils, essentially driven by their moisture state. In a dry soil, fast preferential flow is favoured by abundant macropores including shrinkage cracks and is further enhanced by water repellency. Increase in soil moisture reduces water repellency, and swelling of accommodated pores lowers the saturated hydraulic conductivity. Moisture- and temperature-related processes significantly alter soil structure over a time span of 1 yr. Thus, the pore characteristics as well as the hydraulic properties of soil are time-dependent.

Dilute solution properties of methyl methacrylate—acrylonitrile copolymer (MA2)

This article deals with studies of the dilute solution properties of methyl methacrylate-acrylonitrile (MMA-AN) copolymer of 0.415 mole fraction (mf) of acrylonitrile composition. Mark—Houwink parameters for this copolymer have been evaluated in acetonitrile (MeCN), 2-butanone (MEK), dimethyl formamide (DMF), and γ-butyrolactone (γ-BL). The Mark-Houwink exponent a in all four solvents at all temperatures is larger than the corresponding values of the parent homopolymers. The solvent power is in the order of DMF < γ–BL < MEK < MeCN; [η] decreases with an increase in temperature, which is behavior characteristic of polymers in good solvent. The unperturbed dimensions (K0) values, obtained by the Stockmayer–Fixman method, are lower than those for the parent homopolymers and depend on solvent as well as temperature. The solute—solvent interaction parameter X1 values are close to 0.5; X1 is independent of temperature. The excess interaction parameter XABvalues are negative. The results for this copolymer system in regard to low second virial coefficient A2, large X1, and high a values suggest that the large extension of these copolymer chains is due to the unusual short-range interactions.

Thermodynamic properties of strontium titanates Sr2TiO4, Sr3Ti2O7, Sr4Ti3O10, and SrTiO3

The chemical potentials of SrO in two-phase fields (TiO2 + SrTiO3) (SrTiO3 + Sr4Ti3O10) (Sr4Ti3O10 + Sr3Ti2O7) and (Sr3Ti2O7 + Sr2TiO4) of the pseudo-binary system (SrO + TiO2) have been measured in the temperature range (900 to 1250) K relative to pure SrO as the reference state using solid-state galvanic cells incorporating single crystal SrF2 as the electrolyte The cells were operated under pure oxygen at ambient pressure The standard Gibbs free energies of formation of strontium titanates SrTiO3 Sr4Ti3O10 Sr3Ti2O7 and Sr2TiO4 from their component binary oxides were derived from the reversible electromotive force (EMF) of the cells For the formation of the four compounds from their component oxides TiO2 with rutile structure and SrO the standard Gibbs free energy changes are given by Delta G((ox))(SrTiO3) +/- 89/(J mol(-1)) = -121878 + 3 881(T/K) Delta G((ox))(Sr4Ti3O10) +/- 284/(J mol(-1)) = -409197 + 14 749(T/K) Delta G((ox))(Sr3Ti2O7) +/- 190/(J mol(-1)) = -285827 + 10 022(T/K) Delta G((ox))(Sr2TiO4) +/- 110/(J mol(-1))= -159385 + 3 770(T/K) The reference state for solid TiO2 is the rutile form The results of this study are in good agreement with Gibbs free energy of formation data reported in the literature for SrTiO3 but differ significantly with data for Sr4Ti3O10 For Si3Ti2O7 and Si2TiO4 experimental measurements are not available in the literature for direct comparison with the results obtained in this study (C) 2010 Elsevier Ltd All rights reserved

Wide Ranged La Modification in CCTO Ceramics Through Sol-Gel: Effect on Microstructure and Dielectric Properties

Sol-Gel method was employed to synthesize pure and wide ranged La-modified CaCu3Ti4O12 ceramics using mixed acetate-nitrate-alcoxide individual metal-ion precursors. SEM pictures revealed that grain size monotonously decreases with the extent of La incorporation. All the prepared ceramics manifested dielectric constant in the range similar to 10(3)-10(4). Dielectric loss was found to decrease with La incorporation and got optimized for 20% La3+ while retaining its high dielectric constant which may be industrially important. Room temperature Impedance spectroscopy suggested that decrease in grain resistance is responsible for reduction in dielectric loss according to Internal Barrier Layer Capacitor (IBLC) model.

Texture and grain-size dependence of tensile properties in warm rolled cadmium

The development of crystallographic texture and the change in the grain size during warm rolling (300 deg K) and their effect on the tensile yield strength at 77 and 300 deg K are studied in 99.9% pure Cd. Both longitudinal and transverse specimens are tested. The yield strength obeys the Hall--Petch relation. The Hall--Petch slope, k, is lower and the intercept sigma o is higher in the warm worked material in comparison with the corresponding values for annealed Cd. The differences are attributed to the change in 1013 < and 0001 textures that are developed during warm rolling.26 refs.--AA

Phase relationships in the system Ni-W-O and thermodynamic properties of NiWO,

The phase diagram of the Ni-W-O system at 1200 K was established by metallographic and X-ray identification of the phases present after equilibration at controlled oxygen potentials. The oxygen partial pressures over the samples were fixed by metered streams of CO+CO2 gas mixtures. There was only one ternary oxide, nickel tungstate (NiWO4), in the Ni-W-O system at a total pressure of 1 atm, and this compound decomposed to a mixture of Ni+WO2.72 on lowering the oxygen potential. The Gibbs' free energy of formation of NiWO4 was determined from the measurement of the e.m.f. of the solid oxide galvanic cell, Pt, Ni+NiWO4+WO2.72/CaO-ZrO2/Ni+NiO, Pt and thermodynamic properties of tungsten and nickel oxides available in the literature. For the reaction, NiO(s)+WO3(s)rarrNiWO4(s) DeltaG°=–10500–0.708 T (±250) cal mol–1.

Mechanical Properties of Al-Mica Particulate Composite Material

Cast aluminium alloy mica particle composites of varying mica content were tested in tension, compression, and impact. With 2.2 percent mica (size range 40µm – 120µm) the tensile and compression strengths of aluminium alloy decreased by 56 and 22 percent, respectively. The corresponding decreases in percent elongation and percent reduction are 49 and 39 percent. Previous work [2] shows that despite this decrease in strength the composite with 2.5 percent mica and having an UTS of 15 kg/mm2 and compression strength of 28 kg/mm2 performs well as a bearing material under severe running conditions. The differences in strength characteristics of cast aluminium-mica particle composites between tension and compression suggests that, as in cast iron, expansion of voids at the matrix particle interface may be the guiding mechanism of the deformation. SEM studies show that on the tensile fractured specimen surface, there are large voids at the particle matrix interface.

Donor properties of some flexidentate hydroxyimino-β-diketones in their rhodium(III) complexes

A series of rhodium(III) complexes of certain hydroxyimino-beta-diketones were synthesised and their structures assigned on the basis of elemental analyses and i.r. and1H n.m.r. spectral studies, The complexes exhibit coordination through carbonyl oxygen and nitrogen of the hydroxy-imino groups in the ligands.1H and13C n.m.r. studies show that the ligands exist in the isonitroso form in CDCl3.