Acicular Mullite Crystals in Vitrified Kaolin

The microstructure of vitrified kaolin ceramic tapes has been studied via scanning and transmission electron microscopy (SEM and TEM). The sintered samples contained crystalline phase of predominantly stoichiometric mullite (3Al₂O₃·2SiO₂), which consisted of high aspect ratio, acicular crystals that are often referred to as secondary mullite. These crystals were interlocked and embedded in an aluminosilicate glass matrix of inhomogeneous composition. The glass matrix contained an average of ∼3.63 wt% K as determined by energy-dispersive X-ray analysis (EDS), whose composition could be approximated to 5Al₂O₃·16SiO₂·0.1MgO·0.3K₂O·0.15TiO₂·0.12Fe₂O₃. The acicular crystals have approximately the stoichiometric composition of Al₂O₃:SiO₂= 3:2. They have grown along a specific crystallographic orientation along the [001] axis. The crystal growth front exhibited facetting on the {110) planes with microfacetting on both the {100) and {010) planes.     

Water: a responsive small molecule

Unique among small molecules, water forms a nearly tetrahedral yet flexible hydrogen-bond network. In addition to its flexibility, this network is dynamic: bonds are formed or broken on a picosecond time scale. These unique features make probing the local structure of water challenging. Despite the challenges, there is intense interest in developing a picture of the local water structure due to water's fundamental importance in many fields of chemistry. Understanding changes in the local network structure of water near solutes likely holds the key to unlock problems from analyzing parameters that determine the three dimensional structure of proteins to modeling the fate of volatile materials released into the atmosphere. Pictures of the local structure of water are heavily influenced by what is known about the structure of ice. In hexagonal I(h) ice, the most stable form of solid water under ordinary conditions, water has an equal number of donor and acceptor bonds; a kind of symmetry. This symmetric tetrahedral coordination is only approximately preserved in the liquid. The most obvious manifestation of this altered tetrahedral bonding is the greater density in the liquid compared with the solid. Formation of an interface or addition of solutes further modifies the local bonding in water. Because the O-H stretching frequency is sensitive to the environment, vibrational spectroscopy provides an excellent probe for the hydrogen-bond structure in water. In this Account, we examine both local interactions between water and small solutes and longer range interactions at the aqueous surface. Locally, the results suggest that water is not a symmetric donor or acceptor, but rather has a propensity to act as an acceptor. In interactions with hydrocarbons, action is centered at the water oxygen. For soluble inorganic salts, interaction is greater with the cation than the anion. The vibrational spectrum of the surface of salt solutions is altered compared with that of neat water. Studies of local salt-water interactions suggest that the picture of the local water structure and the ion distribution at the surface deduced from the surface vibrational spectrum should encompass both ions of the salt.     

Synthesis and polymerization of liquid crystalline α-oxiranes containing 4-cyanobiphenyl andp-methoxyphenyl benzoate mesogenic groups

Summary The synthesis of a new series of -oxiranes containing 4-cyanobiphenyl andp-methoxyphenyl benzoate mesogenic groups and the phase behaviour of synthesized compounds are described. Polymerization of -oxiranes with BF₃.O(C₂H_{5 2}) and Et₃Al/H₂O/Acetyl acetone as initiators was carried out. The first initiator produced oligomers displaying liquid crystalline properties while the second gave crystalline polymers with a high degree of polymerization.     

The Role of Ozone in Improving Drinking Water Quality in London and Oxford

In recent years, drinking water quality has become a major subject for public and political debate, with the issue of pesticides in drinking water receiving much attention. The EC Drinking Water Directive included a limit of 0.1?µg/1 for individual pesticides, a standard far more stringent than health-based minimum levels set by such bodies as the World Health Organizations and the US EPA. With traditional treatment processes such as chemical coagulation, flocculation, filtration and slow sand filtration unable to meet the stricter pesticide standard, an additional method of treatment was required. Consequently, ozone and granular activated carbon (GAC) have been installed at all the major water treatment works (WTWs) in London and Oxford treating river Thames water. Groundwater WTWs, deemed to be at risk from pesticides, have GAC filters only. Computational Fluid Dynamics (CFD) was investigated as a tool for optimizing the design of ozone contractors. The aim was to distribute ozone flow uniformly so that maximum contact would be made between the water and gas. However, the application of ozone in water treatment processes remains expensive when compared to conventional treatment. Consequently, a cost benefit analysis of continuous versus intermittent ozone operation was carried out. Operational data was obtained and compared for two Thames Water UK and Ireland (TWUKI) surface water treatment works (one conventional (chemical) works and the second based on biological processes).     

Effect of waves on reaeration

Mechanically generated surface waves and their influence on oxygen transfer were investigated. The experiments were conducted in a reaeration column (Reynolds number from 125–937). The water surface was set in oscillatory motion to simulate periodic surface level fluctuation. The wave frequency used ranged from 0.125 Hz to 0.425 Hz for various wave heights ranging from 0.15 cm to 1.5 cm. After bleeding the water column with nitrogen, dissolved oxygen concentration was measured over time below the water surface. A modified surface renewal model was proposed and found to describe the oxygen transfer phenomenon well. In addition, it was found that the mean film thickness δ_D, may be used as the characteristic length to describe the reaeration process under the influence of small perturbation and surface water waves. The proposed model was also extended to include the reaeration process under larger waves reported by other researchers. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4839–4845, 2013     

Surface-Enhanced Raman Analysis of some Polycyclic Aromatic Dyes used in the Cosmetics and Food Industries

Abstract

The Surface-Enhanced Raman spectra of three important polycyclic aromatic dyes used in the food and cosmetic industries. Erythrosine, Eosine, and Phloxine, are recorded for the first time. The ability of the Surface-Enhanced Raman scattering techniques to detect these dyes at trace level is demonstrated. Such techniques minimize the fluorescence background in these highly fluorescing dyes, bringing out the Surface-Enhanced Raman Spectra features. The Normal Raman Spectra of erythrosine and phtalazine were also recorded and compared with their Surface-Enhanced Raman Spectra to illustrate the fluorescence suppression in Surface Enhanced Raman Spectra. The vibrational spectra features of the three dyes are discussed in terms of their molecular structure and the vibrations of the aromatic rings.     

Bonding microwave absorbing ferrites to thermal conducting copper

In the present study, the thermal characteristics of spinel ferrites are reported. The thermal expansion coefficient of ferrites is slightly larger than that of silicon; furthermore, these ferrites all demonstrate capability to absorb microwave. Nevertheless, their thermal conductivity is relatively low. A copper plate is bonded to ferrite to provide a backing for heat spreading. Microstructure observation at the interface reveals no reaction phase. The thermal resistance at the copper-ferrite interface is low. With the bonding of metallic copper, the heat generated in ferrites by microwave absorbing is possible to be removed by the backing copper layer.     

Net Shape Manufacturing of Three-Dimensional SiCN Ceramic Microstructures Using an Isotropic Shrinkage Method by Introducing Shrinkage Guiders

The two-photon cross-linking (TPC) process using ceramic precursors is recognized as a unique fabrication means of real three-dimensional (3D) ceramic microstructures. These structures can be applied to various microscale devices that are used in harsh conditions that demand high strength, high temperature endurance, and good chemical corrosion properties. However, the large shrinkage amount of 3D structures during pyrolysis is a serious limitation to the practical application of these structures; during pyrolysis, asymmetric distortion and shrinkage occur intrinsically. In an attempt to address this, a method is proposed for the precise fabrication of 3D ceramic microstructures that utilize shrinkage guiders to lead to isotropic shrinkage. SiCN ceramic woodpile structures were fabricated to show the efficiency and usefulness of the proposed method. In the results, the woodpiles showed no distortion after pyrolysis.     

Influence of ball milling on the sintering behaviour of ZnO powder

A high purity ZnO powder was milled with either YSZ or Al₂O₃ balls. The weight losses of YSZ and Al₂O₃ balls after milling for 4 h are 10 and 40 ppm, respectively. The debris of the milling media acts as sintering aid to the ZnO powder. As a result, the grain size of the sintered ZnO specimens is reduced. The ratio of the grain boundary energy over surface energy is also decreased.     

Identification of the plastic deformation characteristics of AL5052-O sheet based on the non-associated flow rule

This study aims to determine the plastic deformation characteristics of aluminum 5052-O based on non-associated flow rule. To achieve this goal, a new strain hardening model named as Kim-Tuan hardening model is proposed to perfectly describe the stress-strain relation of the studied material in terms of the uniaxial tensile test and to predict the material’s post-necking behavior. Additionally, the plastic behaviors of AL5052-O sheet are described by two approaches: the associated flow rule with YLD2000-2d yield function and the non-associated flow rule with Hill's quadratic function (NAFR-Hill48). The parameters of these functions were derived from the material properties that were obtained from uniaxial tensile tests and bulge test. The flow curve based on Kim-Tuan model and plastic behaviors obtained from two above-mentioned approaches were imported into a finite element analysis code to simulate the hydraulic bulge test for this material to confirm the precision of material characteristics achieved before. The simulation results based on the NAFR-Hill48 match well with the experiment results of bulge test while the YLD2000-2d provides highly accurate predictions for anisotropy of this material.