Tuning the metal-to-metal charge transfer energy of cyano-bridged dinuclear complexes

The metal-to-metal charge transfer (MMCT) transitions of a series of Class II mixed valence dinuclear complexes bearing cyano bridging ligands may be varied systematically by variations to either the hexacyanometallate(II) donor or Co-III acceptor moieties. Specifically, the new dinuclear species trans-[(LCoNCFe)-Co-14S(CN)(5)](-) (L-14S = 6-methyl-1,11-diaza-4,8-dithia- cyclotetradecane-6-amine) and trans-[(LCoNCRu)-Co-14(CN)(5)]-(L-14 = 6-methyl-1,4,8,11-tetraazacyclotetradecane-6-amine) have been prepared and their spectroscopic and electrochemical properties are compared with the relative trans-[(LCoNCFe)-Co-14(CN)(5)](-). The crystal structures of Na{trans-[(LCoNCFe)-Co-14S(CN)(5)]}.51/2H(2)O.1/2EtOH, Na{trans-[(LCoNCRu)-Co-14(CN)(5)]}.3H(2)O and Na{trans-[(LCoNCRu)-Co-14(CN)(5)]}.8H(2)O are also reported. The ensuing changes to the MMCT energy have been examined within the framework of Hush theory, and it was found that the free energy change between the redox isomers was the dominant effect in altering the energy of the MMCT transition.

Time-resolved spectroscopy of the metal-to-metal charge transfer excited state in dinuclear cyano-bridged mixed-valence complexes

Visible pump-probe spectroscopy has been used to identify and characterize short-lived metal-to-metal charge transfer (MMCT) excited states in a group of cyano-bridged mixed-valence complexes of the formula [(LCoNCMII)-N-III(CN)(5)](-), where L is a pentadentate macrocyclic pentaamine (L-14) or triamine-dithiaether (L-14S) and M is Fe or Ru. Nanosecond pump-probe spectroscopy on frozen solutions of [(LCoNCFeII)-Co-14-N-III(CN)(5)](-) and [(LCoNCFeII)-Co-14S-N-III(CN)(5)](-) at 11 K enabled the construction of difference transient absorption spectra that featured a rise in absorbance in the region of 350-400 nm consistent with the generation of the ferricyanide chromophore of the photoexcited complex. The MMCT excited state of the Ru analogue [(LCoNCRuII)-Co-14-N-III(CN)(5)](-) was too short-lived to allow its detection. Femtosecond pump-probe spectroscopy on aqueous solutions of [(LCoNCFeII)-Co-14-N-III(CN)(5)](-) and [(LCoNCFeII)-Co-14S-N-III(CN)(5)](-) at room temperature enabled the lifetimes of their Co-II-Fe-III MMCT excited states to be determined as 0.8 and 1.3 ps, respectively.

Pressure and temperature effects on metal-to-metal charge transfer in cyano-bridged Co-III-Fe-II complexes

The effects of pressure and temperature on the energy (E-op) of the metal-to-metal charge transfer (MMCT, Fe-II --> Co-III) transition of the cyano-bridged complexes trans - [(LCoNCFe)-Co-14(CN)(5)](-) and cis-[(LCoNCFe)-Co-14(CN)(5)](-) (where L-14 = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) were examined. The changes in the redox potentials of the cobalt and iron metal centres with pressure and temperature were also examined and the results interpreted with Marcus Hush theory. The observed redox reaction volumes can mainly be accounted for in terms of localised electrostriction effects. The shifts in E-op due to both pressure and temperature were found to be less than the shifts in the energy difference (E degrees) between the Co-III-Fe-II and Co-II-Fe-III redox isomers. The pressure and temperature dependence of the reorganisational energy, as well as contributions arising from the different spin states of Co-II, are discussed in order to account for this trend. To study the effect of pressure on Co-III electronic absorption bands, a new cyano-bridged complex, trans - [(LCoNCCo)-Co-14(CN)(5)], was prepared and characterised spectroscopically and structurally. X-Ray crystallography revealed this complex to be isostructural with trans -[(LCoNCFe)-Co-14(CN)(5)] center dot 5H(2)O.

Exploratory modelling of grinding pressure within a compressed particle bed

With increasing industry interest in high pressure roll grinding (HPGR) technology, there is a strong incentive for improved understanding of the nature of grinding pressure that exists in the interior of a compressed particle bed. This corresponds to the crushing region of the HPGR. The relationship between applied pressure (stress) to the particle bed and induced pressure (stress) within particles and at contact points between particles is of particular interest. A detailed parametric investigation is beyond the scope of this exploratory paper. However, this exploratory investigation does suggest some interesting behaviour. The compressed particle bed within an 80 turn diameter piston has been modelled using Particle Flow Code for three dimensions. PFC3D is a discrete element code. The total number of simulated particles was 1225 and 2450 for two beds of different thickness. Particle diameters were uniformly distributed between 4 and 4.5 mm. The results of the simulations show that stress intensity within the simulated particle beds and within the observed particles increased with increase of the applied stress. The intensity of the average vertical stress in the selected particles tended to be comparable with the intensity of the pressure applied to the surface of particle bed and was only occasionally higher. However, the stress at contact points between particles could be several times higher. In a real crusher, such high stress amplification at contacts will quickly decrease due to local crushing and a resultant increase the size of the contact area. Therefore, its significance is likely to be relatively small in an industrial context. The modelling results also suggest that failure within the particle bed will progress from the crushing surface towards the depth of the bed. (c) 2006 Elsevier Ltd. All rights reserved.

Microstructure and grain boundary microanalysis of X70 pipeline steel

Grain boundaries (GBs), particularly ferrite: ferrite GBs, of X70 pipeline steel were characterized using analytical electron microscopy (AEM) in order to understand its intergranular stress corrosion cracking (IGSCC) mechanism(s). The microstructure consisted of ferrite (alpha), carbides at ferrite GBs, some pearlite and some small precipitates inside the ferrite grains. The precipitates containing Ti, Nb, V and N were identified as complex carbo-nitrides and designated as (Ti, Nb, WC, N). The GB carbides occurred (1) as carbides along ferrite GBs, (2) at triple points, and (3) at triple points and extending along the three ferrite GBs. The GB carbides were Mn rich, were sometimes also Si rich, contained no micro-alloying elements (Ti, Nb, V) and also contained no N. It was not possible to measure the GB carbon concentration due to surface hydrocarbon contamination despite plasma cleaning and glove bag transfer from the plasma cleaner to the electron microscope. Furthermore, there may not be enough X-ray signal from the small amount of carbon at the GBs to enable measurement using AEM. However, the microstructure does indicate that carbon does segregate to alpha : alpha GBs during microstructure development. This is particularly significant in relation to the strong evidence in the literature linking the segregation of carbon at GBs to IGSCC. It was possible to measure all other elements of interest. There was no segregation at alpha : alpha GBs, in particular no S, P and N, and also no segregation of the micro-alloying elements, Ti, Nb and V. (C) 2003 Kluwer Academic Publishers.

SCC initiation for X65 pipeline steel in the "high" pH carbonate/bicarbonate solution

The initiation of stress corrosion cracking (SCC) was studied using scanning electron microscope observations of linearly increasing stress test specimens. SCC initiation from the following surfaces was studied: (i) initiation from the commercial pipe surface covered by the Zn coating, (ii) initiation from a mechanically polished surface with a deformed layer, and (iii) initiation from an electro-polished surface. SCC initiation involved different features for these surfaces as follows. (i) For the Zn coated commercial pipe surface, a crack in the Zn coating led to the dissolution of the deformed layer and when the deformed layer was penetrated, intergranular SCC initiation became possible. (ii) For a mechanically polished surface with a deformed layer, cracks in the surface oxide concentrated the anodic dissolution to such an extent that there was transgranular SCC in the deformed layer. SCC was intergranular when the deformed layer had been penetrated. Transgranular stress corrosion cracks were stopped at ferrite grain boundaries (GBs) oriented perpendicular to the SCC propagation direction. (iii) For an electro-polished surface, the surface oxide film was cracked at many locations, but intergranular SCC only propagated into the steel when the oxide crack corresponded to a GB. An oxide crack away from a GB is expected to be healed. The observed SCC initiation mechanism was not associated with simple preferential chemical attack of the ferrite GBs. (C) 2003 Elsevier Ltd. All rights reserved.

Stress crrosion cracking fracture mechanisms in rock bolts

Rock bolts have failed by Stress Corrosion Cracking (SCC). This paper presents a detailed examination of the fracture surfaces in an attempt to understand the SCC fracture mechanism. The SCC fracture surfaces, studied using Scanning Electron Microscopy (SEM), contained the following different surfaces: Tearing Topography Surface (TTS), Corrugated Irregular Surface (CIS) and Micro Void Coalescence (MVC). TTS was characterised by a ridge pattern independent of the pearlite microstructure, but having a spacing only slightly coarser than the pearlite spacing. CIS was characterised as porous irregular corrugated surfaces joined by rough slopes. MVC found in the studied rock bolts was different to that in samples failed in a pure ductile manner. The MVC observed in rock bolts was more flat and regular than the pure MVC, being attributed to hydrogen embrittling the ductile material near the crack tip. The interface between the different fracture surfaces revealed no evidence of a third mechanism involved in the transition between fracture mechanisms. The microstructure had no effect on the diffusion of hydrogen nor on the fracture mechanisms. The following SCC mechanism is consistent with the fracture surfaces. Hydrogen diffused into the material, reaching a critical concentration level. The thus embrittled material allowed a crack to propagate through the brittle region. The crack was arrested once it propagated outside the brittle region. Once the new crack was formed, corrosion reactions started producing hydrogen that diffused into the material once again. (C) 2003 Kluwer Academic Publishers.

Absorption and fluorescence spectroscopy of rhodamine 6G in titanium dioxide nanocomposites

A comparison has been made between the spectroscopic properties of the laser dye rhodamine 6G (R6G) in mesostructured titanium dioxide (TiO2) and in ethanol. Steady-state excitation and emission techniques have been used to probe the dye-matrix interactions. We show that the TiO2-nanocomposite studied is a good host for R6G, as it allows high dye concentrations, while keeping dye molecules isolated, and preventing aggregation. Our findings have important implications in the context of solid state dye-lasers and microphotonic device applications. (C) 2003 Elsevier B.V. All rights reserved.

Attaching unit costs to Australia's National Survey of Mental Health and Wellbeing

Background: In mental health, policy-makers and planners are increasingly being asked to set priorities. This means that health economists, health services researchers and clinical investigators are being called upon to work together to define and measure costs. Typically, these researchers take available service utilisation data and convert them to costs, using a range of assumptions. There are inefficiencies, as individual groups of researchers frequently repeat essentially similar exercises in achieving this end. There are clearly areas where shared or common investment in the development of statistical software syntax, analytical frameworks and other resources could maximise the use of data. Aims of the Study: This paper reports on an Australian project in which we calculated unit costs for mental health admissions and community encounters. In reporting on these calculations, our purpose is to make the data and the resources associated with them publicly available to researchers interested in conducting economic analyses, and allow them to copy, distribute and modify them, providing that all copies and modifications are available under the same terms and conditions (i.e., in accordance with the 'Copyleft' principle), Within this context, the objectives of the paper are to: (i) introduce the 'Copyleft' principle; (ii) provide an overview of the methodology we employed to derive the unit costs; (iii) present the unit costs themselves; and (iv) examine the total and mean costs for a range of single and comorbid conditions, as an example of the kind of question that the unit cost data can be used to address. Method: We took relevant data from the Australian National Survey of Mental Health and Wellbeing (NSMHWB), and developed a set of unit costs for inpatient and community encounters. We then examined total and mean costs for a range of single and comorbid conditions. Results: We present the unit costs for mental health admissions and mental health community contacts. Our example, which explored the association between comorbidity and total and mean costs, suggested that comorbidly occurring conditions cost more than conditions which occur on their own. Discussion: Our unit costs, and the materials associated with them, have been published in a freely available form governed by a provision termed 'Copyleft'. They provide a valuable resource for researchers wanting to explore economic questions in mental health. Implications for Health Policies: Our unit costs provide an important resource to inform economic debate in mental health in Australia, particularly in the area of priority-setting. In the past, such debate has largely, been based on opinion. Our unit costs provide the underpinning to strengthen the evidence-base of this debate. Implications for Further Research: We would encourage other Australian researchers to make use of our unit costs in order to foster comparability across studies. We would also encourage Australian and international researchers to adopt the 'Copyleft' principle in equivalent circumstances. Furthermore, we suggest that the provision of 'Copyleft'-contingent funding to support the development of enabling resources for researchers should be considered in the planning of future large-scale collaborative survey work, both in Australia and overseas.

Segmented polyurethane nanocomposites: Impact of controlled particle size nanofillers on the morphological response to uniaxial deformation

A series of TPU nanocomposites were prepared by incorporating organically modified layered silicates with controlled particle size. To our knowledge, this is the first study into the effects of layered silicate diameter in polymer nanocomposites utilizing the same mineral for each size fraction. The tensile properties of these materials were found to be highly dependent upon the size of the layered silicates. A decrease in disk diameter was associated with a sharp upturn in the stress-strain curve and a pronounced increase in tensile strength. Results from SAXS/SANS experiments showed that the layered silicates did not affect the bulk TPU microphase structure and the morphological response of the host TPU to deformation or promote/hinder strain-induced soft segment crystallization. The improved tensile properties of the nanocomposites containing the smaller nanofillers resulted from the layered silicates aligning in the direction of strain and interacting with the TPU sequences via secondary bonding. This phenomenon contributes predominantly above 400% strain once the microdomain architecture has largely been disassembled. Large tactoids that are unable to align in the strain direction lead to concentrated tensile stresses between the polymer and filler, instead of desirable shear stresses, resulting in void formation and reduced tensile properties. In severe cases, such as that observed for the composite containing the largest silicate, these voids manifest visually as stress whitening.