216,663 research outputs found
Clay minerals in South Australian Holocene basaltic volcanogenic soils and implications for halloysite genesis and structure
No full textThe clay mineralogical composition was determined of 8 soils formed from pyroclastic ejecta (tephra) from adjacent 5000-year old basaltic volcanoes at Mounts Gambier and Schank in South Australia. Both nanocrystalline (short-range order) and crystalline aluminosilicates and also Fe oxides and hydroxides were identified in the soils. Allophane generally occurred to a greater extent in the 4 soils derived from glass-rich Mt Schank tephra than in most of those from glass-poor Mt Gambier tephra. Ferrihydrite occurred along with allophane. Smectite, kaolinite, illite, and an interstratified kaolinite-smectite comprised the crystalline minerals in these soils. There was no evidence for halloysite. Unlike in New Zealand, decreased leaching resulted in Si-rich allophane, rather than halloysite, forming in place of the Al-rich form of the same mineral. This result may indicate that ferrous iron is an essential impurity in halloysite. It was likely absent from these soils because their high pH due to underlying calcareous rocks precludes its occurrence. The probable requirement of Fe(II) as an essential component of halloysites may have been overlooked because of oxidation consequent upon the inevitable drying of samples prior to analyses
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
[Copy of Letter from John Keeney to William L. Clay - April 25, 1975]
No full textCopy of a letter from John Keeney informing William L. Clay that the Department of Justice (DOJ) doesn't need to formally reply to a letter to the Attorney General, but they will notify Clay of the results of the investigation into narcotics allegations
[Copy of Letter from Laurence Silberman to William L. Clay - February 11, 1975]
No full textCopy of a letter from Laurence Silberman informing William L. Clay that he referred Clay's letter to John C. Keeney who is the Acting Assistant Attorney General
[Copy of Letter from William L. Clay to John Keeney - April 29, 1975]
No full textCopy of a letter from William L. Clay to John Keeney reviewing the points of a previous letter from Clay's colleagues regarding the circumstances in which the name William Clay was included in a narcotics trial brief
Recommended from our members
Letter from Edith Clay to William C. Brice, August 13, 1959
No full textEdith Clay gives a brief report of the status of archaeology excavations in progress for the season, including Sinclair Hood and John Evans at Knossos and Lord William Taylor at Laconia and Mycenae.Classic
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
Clay mineralogy of tephras and associated paleosols and soils, and hydrothermal deposits, North Island [New Zealand]
No full textTour themes and itinerary
The tour centres on the occurrence and genesis of clay minerals, especially allophane, halloysite, and ferrihydrite, associated with both Quaternary rhyolitic airfall tephra (volcanic ash) deposits and volcanogenic alluvium, and on mineralisation and thermal activity in hydrothermal fields. After a brief overview of the basaltic volcanoes of Auckland City, our route essentially traverses the Central Volcanic Region by way of a large loop with overnight stops at Rotorua (2 nights), Tokaanu, and Auckland (Fig. 0.1). We have around five stops planned for each day (including lunch), three of these being scientific stops except on Day 4 when we have only one scientific stop because of the need to travel greater distances.
Our route takes us progressively towards the locus of the most recently active volcanic centres of the Central Volcanic Region, and so the surficial tephra deposits and buried paleosols become successively younger and generally less weathered: tephras at the Mangawara section (Day 1) span c. 1 Ma; at Tapapa (Day 2), c. 140 ka; at Te Ngae (Day 2), c. 20 ka; and at De Bretts, c. 10 ka, and Wairakei, c. 2 ka (Day 3). Interspersed with these tephra-paleosol sections are stops to examine an allophane-halloysite soil drainage (leaching) sequence on volcanogenic alluvium (Day 1), hydrothermal activity and mineral deposits at Whakarewarewa (Day 2) and Waiotapu (Day 3), and pure ferrihydrite seepage deposits in Hamilton (Day 4). Following introductory and detailed background review material, the tour guide has been arranged on a day-by-day basis and includes an outline of the route and stops, and several pages describing the stratigraphy, mineralogy, chemistry, and pedology of the deposits or features at each of the main stops. We will attempt to point out and describe geological and other features as appropriate during travel periods.
Other activities
Examples of New Zealand's distinctive fauna and flora, including kiwis and tuataras, will be seen at close quarters at Rainbow Springs (Day 2), where we will also enjoy an agricultural farm show. In Rotorua we will partake in a Maori hangi (steam-cooked feast) and concert including traditional dance forms (hakas) and songs (Day 2). In Tokaanu, hot pools will be available to relax in near the slopes of Mt Tongariro (Day 3). At Waitomo, we will visit the Waitomo Cave and in Hamilton spend a short time at the Waikato Museum of Art and History (Day 4). Finally, the tour will conclude with a farewell dinner in Auckland
Effects of temperature, pH, and iron/clay and liquid/clay ratios on experimental conversion of dioctahedral smectite to berthierine, chlorite, vermiculite, or saponite
No full textIn deep geological repositories for high-level nuclear wastes, interactions between steel canisters and clay-rich materials may lead to mineralogical transformations with a loss of the confining properties of the clays. Experiments simulating the conversion of smectite to Fe-rich clay phases in contact with Fe metal have been carried out to evaluate such a possibility by taking into account the effects of a series of critical parameters, including temperature, pH, and Fe/clay (Fe/C) and liquid/clay (L/C) ratios. The mineralogical and chemical transformations observed in these experiments have been compared with data from the literature, and subsequently used to propose a conceptual model for the main mineralogical transformations which can be expected in clay formations surrounding high-level nuclear waste repositories. In the presence of Fe metal and under low oxygen fugacity ( 5: dioctahedral smectite (di-sm) → 7 A° Fe-rich phase (berthierine, odinite-cronstedtite) for large Fe/C ratios (>0.5), or di-sm → Fe-rich di-sm + Fe-rich trioctahedral smectite (tri-sm) for small Fe/C ratios (0.1); (2) up to 150C, under alkaline pH (10-12), and L/C > 5: di-sm → Fe di-sm (±palygorskite) for a small Fe/C ratio (0.1); (3) at 300°C, Fe/C = 0.1, and L/C > 5: di-sm → Fe-rich saponite → trioctahedral chlorite + feldspar + zeolite (near-neutral pH); di-sm → Fe-rich vermiculite + mordenite (pH 10-12). Low temperatures (<150°C) and large L/C and Fe/C ratios seem to favor the crystallization of the serpentine group minerals instead of Fe-rich trioctahedral smectites or chlorites, the latter being favored by higher temperatures. The role of L/C and Fe/C ratios and the competition between them at different temperatures is a crucial point in understanding the transformation of smectite in contact with Fe metal
International Clay Conference, 1978 : proceedings of the VI International Clay Conference 1978 held in Oxford, 10-14 July, 1978 /
No full textInternational Clay Conference, 1978.Includes bibliographical references and indexes.Print version record.section 1. Crystal chemistry and structure -- section 2. Colloidal properties and surface chemistry -- section 3. Geology and sedimentology -- section 4. Genesis and synthesis -- section 5. Applied clay mineralogy -- section 6. Non-crystalline and accessory minerals -- section 7. Kaolin investigations.Electronic reproduction.Master and use copy. Digital master created according to Benchmark for Faithful Digital Reproductions of Monographs and Serials, Version 1. Digital Library Federation, December 2002.digitizedInternational Clay Conference, 1978.Elsevie
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