The creep behaviour of ultra-high modulus polypropylene

The creep and recovery behaviour of highly drawn polypropylene monofilaments has been studied over the temperature range 20 to 50° C. A range of samples was examined to identify the influence of draw ratio and molecular weight. It is concluded that the permanent flow creep arises from the presence of two thermally activated processes, one of which relates to the -relaxation process and is associated with the crystalline regions of the polymer, and the second with the molecular network.     

Quantitative X-ray powder diffraction analysis of clay minerals in Australian coals using Rietveld methods

The mineralogy of clay-rich mineral matter isolated from a range of Australian bituminous coals has been evaluated in quantitative terms from X-ray powder diffraction (XRD) patterns using a Rietveld-based data processing technique. The chemical composition of coal ash derived from this mineral matter has been calculated and compared to the directly determined composition of the ash prepared from the same coal samples. Although there are some minor differences due in part to uncertainty regarding the actual composition of several minerals, the compositions indicated by the two methods show a relatively high correlation, suggesting that the Rietveld technique provides mineralogical analyses that are consistent with independently determined chemical data. Comparison of the normalised clay mineral percentages from the Rietveld analysis to quantitative interpretations based on a peak intensities in glycolated and heat-treated oriented aggregates of the respective clay fractions also shows a high correlation, confirming mutual consistency of the two different mineralogical analysis methods. Such quantitative mineralogical data are significant to a range of coal exploration, mining and utilization activities, including seam correlation, material handling and ash and slag formation in combustion processes.     

Determination of glass content and estimation of glass composition in fly ash using quantitative X-ray diffractometry

The proportion of amorphous or glassy material in a series of fly ashes has been evaluated by X-ray powder diffraction (XRD) using the Rietveld-based SIROQUANT software package. Several different sample preparation and processing methods were investigated, including XRD analysis of samples spiked with known masses of synthetic corundum and zinc oxide as well as techniques based on analysing the raw or unspiked fly ash directly using the SIROQUANT process. In the latter case, two different poorly crystallised silicate mineral patterns, metakaolin and tridymite, were used in the SIROQUANT processing of the raw ash XRD data to represent the amorphous constituents. The results of the different methods based on XRD of spiked samples were found to be mutually consistent, and also consistent with other published data for an international reference fly ash sample. SIROQUANT analysis of the unspiked fly ashes gave similar results, although different poorly crystallised silicate reference patterns seem to be more suited for ashes from Australian and North American sources.The mineralogy of the ashes, including the proportions of quartz, iron oxide and glassy constituents, appears to be related to the nature of the mineral matter in the relevant feed coals. Calculations based on subtracting the inferred chemistry of the crystalline minerals in the fly ashes from the total fly ash chemistry were also used to estimate the overall chemical composition of the glass fraction in each ash. The results indicate that ashes derived from lower-rank coals in the samples studied have different glass compositions to those derived from higher-rank (bituminous) materials. These different glass compositions appear to be related to several other ash properties, including particle density and particle surface area. Evaluation of glass content and composition may be significant in different aspects of ash utilisation, and also in evaluating interactions with water at ash disposal sites.     

Verifying anonymity in voting systems using CSP

We present formal definitions of anonymity properties for voting protocols using the process algebra CSP. We analyse a number of anonymity definitions, and give formal definitions for strong and weak anonymity, highlighting the difference between these definitions. We show that the strong anonymity definition is too strong for practical purposes; the weak anonymity definition, however, turns out to be ideal for analysing voting systems. Two case studies are presented to demonstrate the usefulness of the formal definitions: a conventional voting system, and Prêt à Voter, a paper-based, voter-verifiable scheme. In each case, we give a CSP model of the system, and analyse it against our anonymity definitions by specification checks using the Failures-Divergences Refinement (FDR2) model checker. We give a detailed discussion on the results from the analysis, emphasizing the assumptions that we made in our model as well as the challenges in modelling electronic voting systems using CSP.     

Engineering plastics from lignin. XV. Polyurethane films from chain-extended hydroxypropyl lignin

A series of polyurethane (PU) films was prepared from chain-extended hydroxypropyl lignins (CEHPL). In appearance, these films ranged from brittle and dark brown to rubbery and bronze. The thermal, mechanical, and network properties of these PUs were investigated by DMTA and DSC analysis. All films exhibited single T_g's which varied between ?53° and 101°C, depending on lignin content. From swelling experiments, molecular weight between crosslinks (M _c) was determined and found to vary over 2.5 orders of magnitude. The M _c's were related to the change in T_g that accompanied network formation. Stress–strain experiments showed a variation in Young's modulus between 7 and 1300 MPa. Most of the variation in material properties was related to lignin content and to a lesser extent to diisocyanate type, hexamethylene diisocyanate, or toluene diisocyanate. The source of the CEHPL had no effect on the observed properties. From these results it was concluded that the properties of PUs can be controlled and engineered for a wide variety of practical uses.     

Reactive Laser Ablation Synthesis of Nanosize Alumina Powder

An aluminum (Al) target was laser ablated in an oxygen (O₂) atmosphere, producing nanosize alumina (Al₂O₃) powder. The powder surface area decreased (and the particle size increased) with both increasing oxygen pressure and laser fluence. All powders produced had surface areas between 135 and 250 m²/g, corresponding to primary particle sizes ranging from 7 to 3 nm in radius. Phase evolution with temperature was studied via X-ray diffraction. These powders showed a direct transformation from γ- to α-alumina at approximately 1200°C, bypassing other transition alumina phases, while still maintaining small particle size ( 30 nm). Despite the nanosize particles, green densities equal to 54% of the skeletal density (i.e., true density of the solid phase) were obtained by uniaxial pressing at 40 MPa.     

Synthesis and electrochemical characteristics of Al2O3-coated LiNi1/3Co1/3Mn1/3O2 cathode materials for lithium ion batteries

LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials have been coated with Al₂O₃ nano-particles using sol-gel processing to improve its electrochemical properties. The X-ray diffraction (XRD) pattern of the as-prepared Al₂O₃ nano-particles was indexed to the cubic structure of the γ-Al₂O₃ phase and had an average size of ∼4 nm. The XRD showed that the structure of LiNi_1/3Co_1/3Mn_1/3O₂ was not affected by the Al₂O₃ coating. However, the Al₂O₃ coatings on LiNi_1/3Co_1/3Mn_1/3O₂ improved the cyclic life performance and rate capability without decreasing its initial discharge capacity. These electrochemical properties were also compared with those of LiAlO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ cathode material. The electrochemical impedance spectroscopy (EIS) was studied to understand the enhanced electrochemical properties of the Al₂O₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ compared to uncoated LiNi_1/3Co_1/3Mn_1/3O₂.     

Reactive Laser Ablation Synthesis of Nanosize Aluminum Nitride

An aluminum (Al) target was laser ablated in a nitrogen (N₂) atmosphere, producing aluminum nitride (AlN) powder. These powders were calcined at 900°C for 2 h. Powders were produced at various nitrogen pressures, and the calcined powders were tested for unreacted aluminum content, using differential thermal analysis (DTA). The AlN powder, produced at a laser fluence of 12 J/cm² and a nitrogen pressure of 10.0 kPa (75 torr), showed no evidence of unreacted aluminum by DTA and was phase-pure AlN by X-ray diffraction (XRD). The surface area of this powder is 82 m²/g, corresponding to a particle size of ∼11 nm, which is in good agreement with TEM observations.