348,133 research outputs found
Polymer-clay Nanocomposites
No full textPhDPolymer-clay nanocomposites are attracting global interest principally because
property enhancements are obtained at low clay particle loadings (1-5 wt%).
However there is lack of fundamental understanding of such composites. The aim
of this work is to provide an insight into the interaction between polymer and clay.
This includes the driving force for intercalation, the reinforcement mechanisms and
property-volume fraction relationships.
Functionalised poly(ethylene glycol)-clay, poly(c-caprolactone)-clay and
thermoplastic starch-clay nanocomposites with a range of polymer molecular
weights, clay volume fractions and with different clays were prepared using
solution methods, melt-processing methods, and in situ polymerisation. A reliable
X-ray diffraction technique for low angle basal plane spacing of clay, the essential
parameter for structure determination, was established obtaining ±0.005 Mn
between three diffractometers. The basal plane spacing was found to be unaffected
by polymer molecular weight and preparation method but was affected by the
nature of the polymer and clay. Increasing clay loading could lead to a lower
spacing. As a cautionary observation, poly(ethylene glycol) with high molecular
weight (2: 10,000) was found to undergo degradation readily during preparation of
nanocomposites with and without clay.
Competitive sorption experiments for molecular weight showed that high
molecular weight fractions of polymer intercalate preferentially into clay during
solution preparation. Thermodynamic studies on the intercalation process found
that significant enthalpic change occurred during intercalation, which is coincident
with the observation that heat-treated clays without interlayer water can intercalate
polymer. The calculation of true volume fraction against nominal volume fraction
provided reasonable explanation of property enhancement and helps understand the
relation between nanocomposites and conventional composites. At a given clay
loading, nanocomposites with better dispersion gave more property enhancement
than those with lower dispersion or conventional composites. The crystallinity of
semicrystalline polymer was also affected by varying extents of dispersion of clay.
The use of X-ray diffraction with an internal standard was explored for quantitative
analysis of intercalation and exfoliation
Mineral acquisition from clay by Budongo Forest chimpanzees
No full textDate of Acceptance: 06/07/2015Chimpanzees of the Sonso community, Budongo Forest, Uganda were observed eating clay and drinking clay-water from waterholes. We show that clay, clay-rich water, and clay obtained with leaf sponges, provide a range of minerals in different concentrations. The presence of aluminium in the clay consumed indicates that it takes the form of kaolinite. We discuss the contribution of clay geophagy to the mineral intake of the Sonso chimpanzees and show that clay eaten using leaf sponges is particularly rich in minerals. We show that termite mound soil, also regularly consumed, is rich in minerals. We discuss the frequency of clay and termite soil geophagy in the context of the disappearance from Budongo Forest of a formerly rich source of minerals, the decaying pith of Raphia farinifera palms.Peer reviewe
Guide to the nature and methods of analysis of the clay fraction of tephras from the South Auckland region, New Zealand.
No full textThe manual outlines some of the more common laboratory procedures available for qualitatively and quantitatively analysing the composition of the tephric clays, many of which are difficult to determine because of their short range order or 'amorphous' nature. Techniques described and assessed in terms of their rapidity and quantitativeness include XRD, IR, DTA, TEM and SEM, sodium fluoride reactivity, chemical dissolution analyses, and surface area measurements. No one technique alone produces a definitive clay fraction analysis of tephric deposits. -from Author
Clay minerals and their gallery guests: an ab initio investigation into their interactions.
No full textClay minerals are ubiquitous and readily accessible in the natural environment and consequently have become an essential ingredient in the development of Western Society. Their structural properties are responsible for many of their uses, their layered-leaf composition enables the absorption of water and other solutes, for example. In this thesis, the focus of interest lies primarily in the chemical properties of the clay minerals, which is due to the large surface areas of varying atomistic environments comprising the mineral layers. Clay minerals offer a challenge to the electronic structure modeller as their atomistic composition is non-exact, consequently a number of constraints are automatically applied during the modelling process, the first being the choice of composition of the model. There are currently few examples of density functional theory studies using planewaves and the pseudopotential approximation, and the available experimental data is not necessarily directly applicable to theoretical data due in part, to the inexactness of the clay mineral composition. Consequently, in the studies presented in this thesis, as much time has been spent in considering the modelling methods as on the results obtained and the implication of these in the modelling environment chosen.
This thesis records investigations into the decarboxylation of a fatty acid into an alkane and CO with the modelling of a catalytic environment of an aluminium-bearing clay mineral; the identification of a transition state of this reaction pathway using lattice dynamics and finally, the mechanism of reduction within iron-bearing clay minerals
The engineering behaviour of the tropical clay soils of Dhaka, Bangladesh
No full textThis research has evaluated the engineering behaviour of the tropical clay soils of Dhaka, Bangladesh. Attempts have been made to show the relationship of mineralogy and fabric with engineering properties. The engineering behaviour has been investigated by comparing the soil properties in a natural and destructured state at the same void ratio. Consolidation behaviour of the soils are discussed, based on oedometer and triaxial tests. Undrained and drained mechanical behaviour have been evaluated from triaxial tests in terms of stress-strain curves, stress paths, bonding effects, critical state conditions, stiffness and yielding behaviour. A framework for the tropical clay soils of Dhaka is presented. The tropical clay soils of Dhaka are intermediate to high plasticity inorganic clay. These soils are mainly composed of illite,. kaolinite, chlorite and some non clay minerals mainly quartz and feldspar. It was observed that these sods showed a random open microfabric of silt and clay. There was also some evidence that aluminosilicates, iron compounds and silica formed bonds between and within the grains. An apparent preconsolidation pressure of 170 kPa to 250 kPa was estimated for the natural soils, which is likely to be due to the bonded structure of the soils. The compressibility of the soil is very low to medium. The consolidation results are consistent with the mineralogy of the soils. It is established that the tropical clay soils of Dhaka are bonded. Bonding has an influence on the development of stress-strain and stiffness of these soils. Under undrained shearing, samples initially showed peak positive values of excess pore water pressure followed by negative values at higher strains due to the tendency of the samples to dilate. No negative pore water pressures were observed at high confining pressures. Only a few samples at low confining pressures reach the critical state at very large strains approximately in excess of 20%. High confining pressure samples may not have reached the critical state due to the formation of distinct shear surfaces. A significant difference between the natural and destructured failure surfaces was observed due to the presence of bonds in the natural soils. Differences in failure type were observed between the natural and destructured soils of three boreholes. It was observed that stiffness values gradually decreased with increasing strain. For the natural soils, two yield points could be identified at low confining pressures below the final yield. It was also observed that bond breakdown would occur in isotropic compression for tests at high confining pressures. At the final yield, the soil looses almost all of its stiffness due to bonding. After final yield, a soil’s behaviour is controlled only by friction. It was observed that three zones of behaviour could be identified for these soils in the stress space
Interview with Robert E. Clay (on Goal 10)
No full textInterview with Robert E. Clay by Sy Adler on May 3, 2017 focused on Goal 10 of Oregon\u27s Statewide Land Use Planning Program. Bob Clay is a planning consultant in Portland, Oregon who has held senior management positions in urban planning for city, state, regional, and federal agencies since 1973.https://pdxscholar.library.pdx.edu/planoregon_interviews/1031/thumbnail.jp
Reactivity of the Clay Mineral Montmorillonite: A First Principles Study
No full textPhDThe recent development of clay-polymer nanocomposite materials has led to ail
increased interest in the structure and properties of clay minerals. In this thesis the
reactivity of the clay mineral montmorillonite is explored by means of density
functional theory based calculations. In particular three aspects are considered:
catalytic properties, cation migration and dehydroxylation.
The origin of the catalytic properties of the clay mineral is investigated in the
context of the synthesis of clay-polymer nanocomposite materials, by in sttu,
intercalative polymerisation. It is found that catalysis is most likely to occur at the
clay mineral lattice-edge where exposed aluminium atoms act as Lewis acid sites.
Migration of lithium cations into the clay mineral lattice is explored by
means of first principles molecular dynamics. Comparison of calculated hvdrox-vl
stretching frequencies, with those from experiment indicates that cations migrate to
vacant octahedral sites, as oppose to the ditrigonal cavities.
Dehydroxylation of the clay mineral is examined by consideration of a cis-vacant
pyrophyllite structure. It is shown that dehydroxylation leads to formation of a
tyan8-vacant structure, with aluminium in trigonal bipyramidal coordination and a
highly distorted tetrahedral layer. Differences in the dehydroxylation behaviour of
cm and tran8-vacant pyrophyllite are shown to be due to the fact that in the
former adjacent hydroxyl groups bridge different pairs of aluminium atoms,
while in the latter they are both bonded to the same pair.
Overall density functional theory based calculations are shown to be
a powerful tool for the studly of the structure and reactivity of clay minerals.Queen Mary University of London
W.R. Grace & Co
Thermal-Mechanical Properties of Polyurethane-Clay Shape Memory Polymer Nanocomposites
No full textShape memory nanocomposites of polyurethane (PU)-clay were fabricated by melt mixing of PU and nano-clay. Based on nano-indentation and microhardness tests, the strength of the nanocomposites increased dramatically as a function of clay content, which is attributed to the enhanced nanoclay–polymer interactions. Thermal mechanical experiments demonstrated good mechanical and shape memory effects of the nanocomposites. Full shape memory recovery was displayed by both the pure PU and PU-clay nanocomposites.
Electrophoretic mobility and clay mineralogy of some fragipan and non-fragipan soil horizons.
No full textThe physical properties of the horizons above and below the fragipan are different from those of the fragipan itself. Indeed, fragipans are characterized by massive, dense, and brittle consistence when moist, hard when dry, but their clods are completely disrupted when submerged in water. These physical characteristics have been related to the presence of clay and weak chemical binding, but there is no general agreement on the main process causing the development of this typical behaviour. We recently found that the low permeability and high bulk density of fragipans are linked to specific arrangements of particles: an open packing of the clay phase is associated to an extremely dense packing of silt and sand. This combination was not present in any other horizon of some Typic Fragiudalfs.
Since the packing arrangement of soil colloids depends on the flocculation/dispersion behaviour of clay particles, we evaluated the electrophoretic mobility (EM) and the mineralogical composition of the water dispersible clay fractions of fragipans and non-fragipan horizons. The EM was determined in a pH range from 4 to 6.5, and the hydrodynamic diameter was recorded. The mineralogy of the clay fraction was assessed by XRD.
The clay fraction was composed of a complex suite of minerals: vermiculite prevailed but, illite, chlorite, kaolinite and several interstratified minerals were also present. When clay was separated using only deionised water, the proportion of minerals varied. The EM data of non fragipan samples ranged between -1.2 and -3.3 μm cm s-1 V-1 as a function of pH, whereas fragipan samples had less negative values and varied from -0.7 to -2.3 μm cm s-1 V-1. In both cases, the permanent charge prevailed over the pH dependent, but the contribution of oxides to EM was greater in non fragipan. At the highest pH, when the electrostatic repulsion was higher, the hydrodynamic diameter was similar or slightly smaller in Bx than in non-Bx (0.7 μm and 0.7-0.9 μm, respectively). With decreasing pH, the changes in the electrophoretic mobility were accompanied by an increase in particle size in Bx horizons, up to 0.9-0.8 μm. At the lowest pH, the clay extracted from non-fragipans showed a smaller hydrodynamic diameter, suggesting repulsion within the clay-sized aggregate and confirming the role of oxides.
As Bx horizons were richer in pedogenic Fe oxides than non-fragipans, our results indicate that the open packing of the clay phase typical of fragipans is the result of water stable aggregation among layer silicates and oxides, combined with a poorly aggregated water dispersible clay
Egyptian Rose [music] /
No full textCaption title.; Photograph of singer Lee White and Clay Smith on cover.; "Sung by Lee White in her song show 'Let's go', produced by Clay Smith".; Also available online http://nla.gov.au/nla.mus-an6301513
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