Effect of in-situ formed MgO on the microstructure of thixomolded AZ91 magnesium alloy

ABSTRACT

In-situ magnesium matrix nano-composites were produced through a reaction of CO₂ with the AZ91 alloy at a semi-solid temperature range. The process was performed at 595°C, which corresponded to about 10% of solid fraction, under shear and mixing conditions generated by a screw-barrel system. As a result, nano-scale native MgO (30–50?nm) and a small amount of Al₄C₃ carbide within an eutectic consisting of α(Mg), β-Mg₁₇Al₁₂ were formed. Homogeneously distributed α(Mg) globular grains with volume 8–12% were visible. AZ91 composites revealed yield strength of 220?MPa at compression strength of 460?MPa and hardness 103?±?2?HV.     

Thermal and electrical properties of copoly(1,3,4‐oxadiazole‐ethers) containing fluorene groups

A series of aromatic copolyethers containing 1,3,4‐oxadiazole rings and fluorene groups was prepared by nucleophilic substitution polymerization technique of 9,9‐bis(4‐hydroxyphenyl)fluorene, 1 , or of different amounts of 1 and an aromatic bisphenol, such as 4,4′‐isopropylidenediphenol or phenolphthalein, with 2,5‐bis(p‐fluorophenyl)‐1,3,4‐oxadiazole. The polymers were easily soluble in polar solvents like N‐methylpyrrolidone, N,N‐dimethylacetamide, N,N‐dimethylformamide, and chloroform and can be cast from solutions into thin flexible films. They showed high thermal stability, with decomposition temperature being above 425°C. The polymers exhibited a glass‐transition temperature in the range of 195–295°C, with a reasonable interval between glass‐transition and decomposition temperature. Electrical insulating properties of some polymer films were evaluated on the basis of dielectric constant and dielectric loss and their variation with frequency and temperature. The values of the dielectric constant at 10 kHz and 20°C were in the range of 3.16–3.25. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characterization of new reworkable thermosetting coatings obtained by cationic and anionic curing of DGEBA and some Meldrum acid derivatives

Rare earth metal triflates, BF₃·MEA and N,N-dimethylaminopyridine (DMAP) were used as cationic and anionic initiators to cure mixtures of diglycidylether of bisphenol A (DGEBA) and Meldrum acid (2,2-dimethyl-4,6-dioxo-1,3-dioxane) derivatives in several proportions. The copolymerization process led to poly(ether-ester) three-dimensional networks. The linear ester groups in the final materials were evaluated by Fourier transform infrared in the attenuated-total-reflection mode (FTIR/ATR).     

Quantification of particle number and mass emission factors from combustion of Queensland trees

The quantification of particle emission factors under controlled laboratory conditions for burning of the following five common tree species found in South East Queensland forests has been studied: Spotted Gum (Corymbia citriodora), Blue Gum (Eucalyptus tereticornis), Bloodwood (Eucalyptus intermedia), Iron Bark (Eucalyptus crebra), and Stringybark (Eucalyptus umbra). The results of the study show that the particle number emission factors and PM2.5 mass emission factors depend on the type of tree and the burning rate. For fast burning conditions, the average particle number emission factors are in the range of 3.3-5.7 x 10(15) particles/kg for woods and 0.5-6.9 x 10(15) particles/kg for leaves and branches, and the PM2.5 emission factors are in the range of 140-210 mg/kg for woods and 450-4700 mg/kg for leaves and branches. For slow burning conditions, the average particle number emission factors are in the range of 2.8-44.8 x 10(13) particles/kg for woods and 0.5-9.3 x 10(13) particles/kg for leaves and branches, and the PM2.5 emissions factors are in the range of 120-480 mg/kg for woods and 3300-4900 mg/kg for leaves and branches.     

Effect of emulsifiers on shortenings

The quality of a shortening depends on its physicochemical characteristics. These include amount of solids, texture and melting behavior, among others. The type of shortening, the processing and storage conditions strongly affect these characteristics. Different strategies can be used to formulate shortenings with low trans fatty acids content while maintaining their physicochemical characteristics. This article describes some of these strategies and aims to provide information about the different variables that need to be controlled to obtain a high quality shortening.     

From Fault-Tree To Fault-Identification

A practical way is given of identifying actual faults, by using a fault tree's complete system of minimal cutsets. For instance, for a fault tree where 20 cutsets are considered with 30 possible primal events, any of them can be found in at most three steps by the proposed FID-algorithm.     

The effect of changing from secondary to primary safety belt enforcement on police harassment

The purpose of the study was to investigate whether changing Michigan's safety belt law from secondary to primary (standard) enforcement resulted in police harassment. The study investigated safety-belt-enforcement-related harassment by considering three measures: citizen complaints arising from enforcement of the safety belt law; citation over-representation, that is, a statistical determination of whether certain groups received more citations than would be expected based upon their presence in the driving population and their rate of violating the safety belt use law; and self-reported harassment among the population of people who receive safety belt citations. Safety-belt-related harassment complaints were very uncommon both before and after primary enforcement. Implementation of primary enforcement did not lead to an increase in citation over-representation, and, therefore, safety-belt-related harassment by sex, race, or age. The vast majority of people receiving safety belt citations reported officer behavior as professional and did not feel that they were singled out for their citation. However, a sizeable minority of Blacks and young people report perceptions of safety-belt-related harassment. Results suggest that states with secondary enforcement should continue their efforts to change to primary enforcement, but should also make a strong effort to educate both law enforcement and the public about the harassment issue.     

Effect of UV radiation on chromatic parameters in serpentinites used as dimension stones

Bulletin of Engineering Geology and the Environment - Colour is an important parameter that must be taken into account if aesthetic homogeneity in both construction and restoration work is to be...     

Strengthening of reinforced concrete beams in flexure by partial jacketing

This work investigates the structural behaviour of reinforced concrete beams strengthened in bending by the addition of concrete and steel on their tension sides using expansion bolts as shear connectors, technique here denominated partial jacketing. The experimental program comprised tests on eight full-scale reinforced concrete beams, simply supported, with rectangular cross section (150 mm × 400 mm) and 4,500 mm length. Five of these beams were strengthened in bending by partial jacketing, while the other three did not receive any strengthening and served as reference beams. The flexural reinforcement ratio in the beams varied between 0.49% and 2.33% and the beams target concrete strength was 35 MPa. On the basis of the obtained test results, the studied strengthening technique proven to be efficient in terms of increasing the resistance and stiffness of the beams. The used expansion bolts as shear connectors proven to be practical and added ease to the application of this technique.