Al2O3 and Si C

FRACTURE, STRENGTH AND DAMAGE TOLERANCE OF CERAMIC NANOCOMPOSITES

Objectives
The objectives of the project were to investigate ceramic “nanocomposites”, principally Al2O3 / SiC:
1. To identify strengthening and damage-tolerance mechanisms
2. To optimise design of nanocomposites
3. To optimise processing of nanocomposites
Substantial progress was made in all three of these areas. We now have a “recipe” for producing a sintered (rather than hot-pressed) Al2O3 / SiC “nanocomposite”, with improved strength, toughness, damage tolerance and wear resistance, and have made good progress in understanding the mechanisms of property improvement. Since the research program focused on the links between processing, microstructure, and mechanical properties, this report deals with processing issues first, followed by mechanical property investigations, finally dealing with the mechanisms linking the two via microstructure and leading to property improvements Processing Two aspects of processing were investigated: (a) the feasibility of using sintering to produce Al2O3 / SiC nanocomposites with enhanced properties, and (b) production of hot-pressed composites with very fine SiC particle size.

Sintering Previous investigations on Al2O3 / SiC nanocomposites by other workers suggested that it is difficult to obtain near fully dense products using the pressureless sintering route. However, the flexibility of this route (in terms of the geometrical complexity of manufactured products) and its relative costeffectiveness are compelling, so a main aim of the project was to investigate this method of fabrication. For a full report on this aspect of the project see [1].

Ultra-fine SiC composites. We have been able to fabricate a range of alumina/SiC nanocomposites with mean SiC particle sizes ranging from 12 nm to 120 nm. These were fabricated by two routes, the first a conventional powder processing and the second using a novel polymer precursor route where ultrafine SiC was generated by the pyrolysis of a polycarbosilane [2,3,4,5].

Publications
1. C.C Anya and S.G. Roberts, Pressureless sintering and elastic constants of Al2O3-SiC ‘nanocomposites’, J.Eur.Cer.Soc. in press.
2. B. Su and M. Sternitzke, A novel processing route for alumina/SiC nanocomposites by Si-polymer pyrolysis, 4th Europ. Ceram. Conv. (Ed. A. Bellosi), Vol. 4 p. 109-116 (1995).
3. L. Carroll, M. Sternitzke and B. Derby, Silicon carbide particle size effects in alumina based nanocomposites, Acta Mater. 44 (1996) 4543.
4. M. Sternitzke, E. Dupas, P. Twigg and B. Derby, Surface mechanical properties of alumina based nanocomposites, submitted to Acta Mater.
5. C.C. Anya and S.G. Roberts, Indentation fracture toughness & surface flaw analysis of sintered alumina/SiC ‘nanocomposites’ J.Eur. Cer.Soc. 16 (1996) 1107

http://www-sgrgroup.materials.ox.ac.uk/abstracts/J77542.pdf

Langmuir monolayers

A Langmuir–Blodgett film contains one or more monolayers of an organic material, deposited from the surface of a liquid onto a solid by immersing (or emersing) the solid substrate into (or from) the liquid. A monolayer is adsorbed homogeneously with each immersion or emersion step, thus films with very accurate thickness can be formed. This thickness is accurate because the thickness of each monolayer is known and can therefore be added to find the total thickness of a Langmuir-Blodgett Film. The monolayers are assembled vertically and are usually composed of amphiphilic molecules (see Chemical polarity) with a hydrophilic head and a hydrophobic tail (example: fatty acids). Langmuir–Blodgett films are named after Irving Langmuir and Katharine B. Blodgett, who invented this technique while working in Research and Development for General Electric Co. An alternative technique of creating single monolayers on surfaces is that of self-assembled monolayers.

Langmuir-Blodgett Films should not be confused with Langmuir films, which tends to describe an organic monolayer submersed in an aqueous solution .

http://en.wikipedia.org/wiki/Langmuir-Blodgett_film

Electron microscopy

Electron microscopy and microanalysis are an integral part of many research activities of other groups in the Department, including processing, polymers and ceramics, and there is a strong interaction with the modelling group.

In recent years the Oxford EM&M Group has undergone major growth, including expansion into the Begbroke site and the installation of the world's first double aberration-corrected TEM/STEM. The group includes Professors Cockayne and Kirkland and Drs Hutchison, Jenkins and Nellist as academic staff, and is expanding into new research areas, and seeking collaborations. It has a well-developed formal and informal postgraduate training programme, in modular form, and a seminar series. An innovative schools outreach programme has a remotely accessible SEM (Oxford CyberSEM), supported by modules aimed at the school curriculum. Collaborations with JEOL through the JEOL Applications Laboratory at the Begbroke Site of the University involve the new aberration corrected FEG(S)TEM and the remote microscopy project.

http://www-em.materials.ox.ac.uk/


flexural rigidity - a measure of the resistance of the lithosphere to bending on long (i.e. > 105 years) time-scales.

flexural response function - the wavenumber parameter that modifies the Airy response to loads to produce the flexural response.



Better photocells from bigger Buckyballs: Now, a group of scientists collaborating from several research institutions, namely the Georgetown University, Washington DC, Luna Innovations Inc., Virginia, the Friedrich-Alexander-Universität, Erlangen, Germany, the National Renewable Energy Laboratory, Colorado, and the University of Santa Barbara have developed a novel fullerene species for this application [Ross, et al., Nature Materials (2009), doi:10.1038/NMAT2379].

Au/CeOx/TiO2(110)

High catalytic activity of Au/CeOx/TiO2(110) controlled by the nature of the mixed-metal oxide at the nanometer level


Mixed-metal oxides play a very important role in many areas of
chemistry, physics, materials science, and geochemistry. Recently,
there has been a strong interest in understanding phenomena
associated with the deposition of oxide nanoparticles on the
surface of a second (host) oxide. Here, scanning tunneling microscopy,
photoemission, and density-functional calculations are used
to study the behavior of ceria nanoparticles deposited on a
TiO2(110) surface. The titania substrate imposes nontypical coordination
modes on the ceria nanoparticles. In the CeOx/TiO2(110)
systems, the Ce cations adopt an structural geometry and an
oxidation state (+3) that are quite different from those seen in bulk
ceria or for ceria nanoparticles deposited on metal substrates. The
increase in the stability of the Ce3+ oxidation state leads to an
enhancement in the chemical and catalytic activity of the ceria
nanoparticles. The codeposition of ceria and gold nanoparticles on
a TiO2(110) substrate generates catalysts with an extremely high
activity for the production of hydrogen through the water–gas
shift reaction (H2O+CO3H2+CO2) or for the oxidation of carbon
monoxide (2CO + O2 3 2CO2). The enhanced stability of the Ce3+
state is an example of structural promotion in catalysis described
here on the atomic level. The exploration of mixed-metal oxides at
the nanometer level may open avenues for optimizing catalysts
through stabilization of unconventional surface structures with
special chemical activity.

Park J et al, PNAS March 31, 2009 vol. 106 no. 13, 4975–4980

Nanoparticles LPSiNPs and TiO2

Researchers from California and Massachusetts have come up with a new type of non-toxic nanoparticle (NP) that is efficiently broken down and excreted by the kidneys once it has delivered its drug cargo to the target organ [Park, et al., Nat. Mater. (2009), doi: 10.1038/nmat2398].

There is already a significant amount of research on drug delivery using NPs, but some of these systems suffer from major drawbacks, such as the body’s immediate rejection of NPs before they can deliver their payload, or biodegradability and toxicity of the NPs or their by-products. However, the use of NPs for drug delivery remains of major interest because these small bodies have some exceptional properties. NPs have a large specific capacity for loading drugs, they are easily detected while they are in the body, and they are retained by the blood stream long enough for them to reach their target and offload the drug.

The new 126 nm luminescent porous Si NPs (LPSiNPs) are fabricated by electrochemical etching of single-crystal Si wafers, followed by ultrasonication and filtration to obtain NPs with 5-10 nm pore diameters. Silicon oxide grown onto the surface of LPSiNPs gives them an intrinsic photoluminescence at 650-900 nm. This makes them suitable for in vivo applications as organs and tissues exhibit very low adsorption in this region and any photoluminescence can be attributed to the LPSiNPs. The luminescent material is much more photostable than fluorescein or cyanin fluorophores and has a quantum yield comparable to other water-soluble luminescent silicon-silica NPs.

In vivo tests have been carried out by the researchers who incorporated an anti-cancer drug – doxorubicin – into LPSiNPs (DOX-LPSiNPs) and injected the DOX-LPSiNPs into mice. Photoluminescence indicates that the DOX-LPSiNPs reach the tumor, where they build up. Histology of the tissues also confirms the presence of the drug together with LPSiNPs inside the tumor. The LPSiNPs then break down, most probably into soluble silicic acid and are completely eliminated from the body by renal clearance within 1-4 weeks of injection, without any signs of toxicity in the major organs of the mice.

http://www.materialstoday.com/archive/2009/12-04/news01.html



TiO2 particles in various concentrations were added into culture plated with confluent cells. After incubation for 24 hours the cell viability was then quantified with Live/Dead cytotoxicity Viability stain (Molecular Probes). The cell viabilities were then normalized with cells without treatment. Vertical lines denote ± 1 SD (n = 4 for all test samples and cells). Significance of differences between cancer cells versus 3T3 cells: P < .05.



LLC cancer cells derived from mouse tumour tissues
JHU prostate cancer cells
B16F1 and B16F10 skin melanoma cancer cells
3T3 fibroblast cells (as control)



........we find that TiO2 nanoparticles have low cytotoxicity to B16F10 and B16F1 melanoma cells as well as 3T3 fibroblasts. These findings are in agreement with many recent published results. Specifically, various sizes and concentrations of TiO2 particles have been reported to be nontoxic in cell monolayer uptake models in vitro,[40] and [41] in vitro inhalation models,3 and in vivo models.[5] and [10] However, in the case of the JHU prostate tumor cells and LLC cells, we found that there are significant differences in viability levels for uncoated TiO2 particles at concentrations of 1 mg/mL for LLC cells and 0.1 mg/mL for JHU prostate tumor cells. Our results have shown that TiO2 particles possess cell-specific toxicity, depending on the concentrations and surface functionality of the particular particles.


Thevenot P et al, Univ of Texas, Surface chemistry influences cancer killing effect of TiO2 nanoparticles, Nanomedicine: Nanotechnology, Biology and Medicine, Volume 4, Issue 3, September 2008, Pages 226-236

Solar control glass reduce the amplitude of radio waves

It is a well known phenomenon that the amplitude of radio waves propagating through solar control glass is greatly reduced, because the electrical conductive film on the surface of solar control glass reflects the incident radio waves withfrequencies lower than that of the plasma oscillation of free electrons in the conductive film. As a result of the moment method analysis of the scattering problem in the spectral domain, it was found that the amplitude of radio waves was not damped when the conductive film was divided into discontinuous segments with a periodic array because the motion of free electrons induced by the magnetic field of incident radio waves is restricted in the divided film. The effect of dividing the conductive film of solar control glass has been examined experimentally in the television wave region.


H. Nakashima et al, Effect of segmentation of conductive coatings on the radio wave
transmission through solar control sheet glass,
Journal of Non-Crystalline Solids 178 (1994) 176-181

‘Casimir–Lifshitz’ force

Space is not completely empty; the vacuum teams with quantum mechanical energy fluctuations able to generate an attractive force between objects that are very close to each other. This ‘Casimir–Lifshitz’ force can cause static friction or ‘stiction’ in nanomachines, which must be strongly reduced. Until now only attractive interactions have been reported but in theory, if vacuum is replaced by certain media, Casimir–Lifshitz forces should become repulsive. This has now been confirmed experimentally. Repulsion, weaker than the attractive force, was measured in a carefully chosen system of interacting materials immersed in fluid. The magnitude of both forces increases as separation decreases. The repulsive forces could conceivably allow quantum levitation of objects in a fluid and lead to new types of switchable nanoscale devices with ultra-low static friction. Levitation depends only on the dielectric properties of the various materials. The cover illustrates repulsion between a tiny gold sphere and a silica substrate (left). Replace the silica with gold (right), and the force becomes attractive.

Quantum fluctuations create intermolecular forces that pervade macroscopic bodies1, 2, 3. At molecular separations of a few nanometres or less, these interactions are the familiar van der Waals forces4. However, as recognized in the theories of Casimir, Polder and Lifshitz5, 6, 7, at larger distances and between macroscopic condensed media they reveal retardation effects associated with the finite speed of light. Although these long-range forces exist within all matter, only attractive interactions have so far been measured between material bodies8, 9, 10, 11. Here we show experimentally that, in accord with theoretical prediction12, the sign of the force can be changed from attractive to repulsive by suitable choice of interacting materials immersed in a fluid. The measured repulsive interaction is found to be weaker than the attractive. However, in both cases the magnitude of the force increases with decreasing surface separation. Repulsive Casimir–Lifshitz forces could allow quantum levitation of objects in a fluid and lead to a new class of switchable nanoscale devices with ultra-low static friction13, 14, 15.


Measured long-range repulsive Casimir–Lifshitz forces, Nature 457, 170-173 (8 January 2009) |

Nanotech food

Maynard serves up the complexities of nanoscience in enticing, digestible, bite-size morsels. It is a friendly, funny, 25-minute travel guide to the technology that promises to ignite the next industrial revolution. In the video, Maynard shows products that use nanotechnology today. And he travels into the future to demonstrate how nanotechnology will change virtually everything—in medicine, energy, materials, travel and electronics.

Nanotechnology is the ability to measure, see, manipulate and manufacture things usually between 1 and 100 nanometers. A nanometer is one billionth of a meter. A human hair is roughly 100,000 nanometers wide.

http://penmedia.org/video/maynard.html

MY ASHMOLEAN

MY MUSEUM

This is an exciting time for the Ashmolean. In November 2009 we will unveil the Museum’s transformation, a redevelopment that is doubling our display space, and which the Oxford Times has called the ‘most significant’ in the Ashmolean’s 326-year history.

The My Ashmolean My Museum appeal has been launched to ask for your support as we reach the final stages of this historic expansion.

The architect of the new Ashmolean is Rick Mather, and the Guardian placed Rick’s ‘subtle yet major extension’ in its top five architectural highlights of 2009. His design has created 39 superb new galleries in which to display the Ashmolean’s rich and varied collections, as well as an Education Centre with its own entrance on St Giles, and Oxford’s first rooftop café.

These state-of-the-art facilities, together with inventive and engaging new displays, will allow us to build upon the position we occupy as a museum of local, national and international importance. Despite these momentous changes, entry to the Ashmolean will remain free.

The cost of the Ashmolean’s transformation is £61 million. So far we have raised nearly eighty per cent of that goal, thanks to the generous backing of the Heritage Lottery Fund, the Linbury Trust, and a number of other charitable trusts and individuals.

We are grateful to those who have already shown their support, and we hope that you will help us to reach our target. Every pound really does count.


http://www.ashmolean.org/appeal/