Structure,nucleation, growth and morphology of secondary carbides in high chromium and Cr-Ni white cast irons

Heat-treated high chromium and Cr-Ni white cast irons are widely used by the mining and mineral industries for impact and abrasion resistance. With certain heat treatments, Fe-Cr carbides are precipitated within the chromium- and carbon-rich austenitic matrix, thereby destabilizing the austenite which transforms substantially to martensite on subsequent cooling. The crystal structures of these carbides were determined indirectly by referring electron microprobe analyses of the austenitic matrix to the appropriate isothermal solid-state sections of the Fe-Cr-C phase diagram and directly by microprobe analyses of exposed secondary carbides. The nucleation, growth and morphology of these carbides were studied by a combination of selective removal of the austenitic matrix and subsequent scanning electron microscopy of the exposed carbides.     

Tension-tension fatigue of a cross-woven C/SiC composite

The tension-tension fatigue behavior of a cross woven C/SiC composite was studied in terms of damage modes and damage development. The fatigue stress versus life diagram (S-N) curve and an endurance limit of 320–340 MPa (about 80% tensile UTS) for 10⁶ cycles were obtained for the C/SiC composite. Different fatigue behaviors were found for samples that failed during fatigue and for samples that survived 10⁶ cycles. Seven fatigue damage modes were observed, the development of which were used to explain the different fatigue behaviors. For the fatigue-failed samples, the degrees of damage of the seven modes increased with increase of cycles, leading to an increase in elapsed strain and a decrease in composite modulus. For fatigue-survived samples, the development of all the damage modes except for fiber breaking caused an initial increase of elapsed strain and decrease of composite modulus, but at high cycles, fiber bundle realignment and straightening in these samples led to partial recovery of the modulus and cessation of the damage development.     

Validation of the Adolescent Drug Use Screening Inventory: Preliminary findings.

Documented the validity of the Substance Use and Psychiatric Disorder scales of the newly developed Drug Use Screening Inventory (DUSI). 25 adolescents (mean age 15.6 yrs) were administered the DUSI. Results were correlated with the Kiddie Schedule for Affective Disorders and Schizophrenia (K-SADS) and Diagnostic and Statistical Manual of Mental Disorders-III-Revised (DSM-III-R) substance abuse symptoms. Significant positive correlations were observed between number of symptoms on the DSM-III—R checklist and severity scores on the Substance Use, Health Status, Psychiatric Disorder, Social Skills, Family System, School, Work, and Peer Relations scales of the DUSI. Number of psychiatric symptoms reported on the K-SADS correlated with severity scores on the Substance Use, Behavior Problems, Health Status, and Psychiatric Disorder scales of the DUSI. Drug use was also related to psychosocial disturbances in this sample of adolescents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cyclic deformation behavior of high-purity titanium single crystals: Part I. Orientation dependence of stress-strain response

Randomly oriented single crystals of high-purity titanium were prepared by strain annealing and were subjected to multiple-step fatigue testing under strain-controlled conditions, in order to determine their cyclic stress-strain curves (CSSCs). These were found to fall into three groups, depending on orientation and the extent of slip and twinning. For those crystals oriented for single prismatic slip, a plateau was observed in the CSSCs, persistent slip bands (PSBs) occurred, and the plateau stress was 38 MPa. In a second group, oriented for prismatic slip but for which cross-slip and twinning was favored, the plateau was suppressed and the flow stresses were higher. In a third group, connected with orientations on the borders of the unit triangle, extensive hardening occurred, the CSSCs were steep, and there were multiple cases of slip and twinning. The results are interpreted in terms of maps in the stereographic projection recording the Schmid factors for the various deformation modes.     

Large-area organic photovoltaic module—Fabrication and performance

Here we describe the fabrication of the largest (233 cm² total area) organic photovoltaic (OPV) module (polymer:fullerene) to be certified by the National Renewable Energy Laboratory (NREL). OPV solar cells were fabricated at Plextronics by spin coating a blend of poly 3-hexylthiophene-2,5 diyl (P3HT) and [6,6] phenyl C₆₁ butyric acid methyl ester (PCBM) on top of our hole transport layer (HTL), Plexcore^® OC. In laboratory-scale devices (0.09 cm²), this system routinely exhibits power conversion efficiencies exceeding 3.7%. This P3HT:PCBM active layer and HTL ink system was used to scale up to the larger area module (15.2 cm×15.2 cm module size, i.e. 233 cm² total area; 108 cm² active area), which was certified by NREL as having 1.1% total area efficiency (3.4% active area efficiency).     

Finite element analysis of a laser-processed fracture specimen

Finite element analysis was used to simulate the static failure of a AISI 4140, three-point bend, Charpy specimen. Non-linear finite element models (FEM) were constructed to represent standard Charpy, fatigue-precracked Charpy, and laser-processed Charpy specimens. For the laser-processed Charpy FEM, a strain-based failure criterion was used to simulate crack propagation through the 0.5 mm thick laser-processed zone. For comparison, a 0.5 mm long crack was used in the fatigue-precracked FEM and similarly loaded. Results showed that the numerically calculated load for crack initation through this zone compared favorably to that reported in earlier experiments. Furthermore, after the crack had propagated through the laser-processed zone within the FEM-comparison of plastic strain contours for this model and that for a fatigue-precracked model showed that similar patterns exist around the crack tip. These results indicate that laser-processing and fatigue-precracking should provide a similar basis for fracture toughness measurements.     

Effective health and safety management

Since the introduction of COSHH, textile manufacturers have energetically set up new health and safety policies. But how much of this has been relevant? John Laird looks at the progress made so far and calls for better health and safety management in the future.     

Hydrolysis of chlorpyrifos in aqueous and colloidal systems

Hydrolysis of chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate] to TCP (3,5,6-trichloro-2-pyridinol) is an important degradation process influencing the fate of chlorpyrifos in aquatic environments. The effects of water chemistry and suspended colloids (smectites, humic acid, and river sediment) on the hydrolysis of chlorpyrifos were investigated in this study. Chlorpyrifos was incubated in various aqueous and colloidal systems at 23 ± 2 °C for up to 100 days, and aqueous phase concentrations of chlorpyrifos and TCP were determined using solid phase extraction-high performance liquid chromatography (SPE-HPLC). Chlorpyrifos degraded in the aqueous solutions with half-lives ranging from 27 to 158 days, depending on the initial concentration of chlorpyrifos and the chemistry of the aqueous solutions. The rate of degradation was slower in systems containing low concentrations of suspended colloids (1 g L⁻¹ in 0.01 M CaCl₂) than in the control (0.01 M CaCl₂, with no colloids), and negligible hydrolysis of chlorpyrifos was found for concentrated colloidal systems (20 g L⁻¹ in 0.01 M CaCl₂). Total recoveries of chlorpyrifos for the concentrated colloidal systems ranged from 78% to 97%, with a tendency to decrease with incubation time. The study indicates that the formation of chlorpyrifos-colloid complexes inhibits the hydrolysis of chlorpyrifos in aqueous systems and that chlorpyrifos-colloid complexes may act as a buffer by slowly releasing chlorpyrifos to the aqueous phase.     

Cancer epigenetics comes of age

The discovery of numerous hypermethylated promoters of tumour-suppressor genes, along with a better understanding of gene-silencing mechanisms, has moved DNA methylation from obscurity to recognition as an alternative mechanism of tumour-suppressor inactivation in cancer. Epigenetic events can also facilitate genetic damage, as illustrated by the increased mutagenicity of 5-methylcytosine and the silencing of the MLH1 mismatch repair gene by DNA methylation in colorectal tumours. We review here current mechanistic understanding of the role of DNA methylation in malignant transformation, and suggest Knudson's two-hit hypothesis should now be expanded to include epigenetic mechanisms of gene inactivation.