On the Mechanism of Natural Convection and Equiaxed Structure during Dendritic Solidification Processes

A new technique has been developed to generate dendritic‐equiaxed structures in aluminium alloy casting processes, not only to improve the mechanical properties but also to study the effect of crystal structure on the chemical and physical properties of alloys to be cast. The investigation combined laboratory experimental work, metallographic examination and mathematic modelling. The laboratory experimental work involved different superheats for Al‐4.5%Cu alloy in cast ingots. Measurements of temperature distributions were conducted to verify the solidification model. A metallographic study combined macro and micro structural evolution of cast ingot samples. Two‐dimensional mathematical models of fluid flow and heat transfer were developed to characterise the natural convection streams and thermal fields. The model predictions were compared to temperature and isotherms measurements where a good agreement was found. The formation of cast structure and columnar, equiaxed transition (CET) and macro segregation phenomena were studied and discussed, based not only on the theories of nucleation but also on the thermal effects in the mushy and liquid zones.     

PVD Coating of Mg–AZ31 by Thin Layer of Al and Al–Si

Although magnesium alloys have the advantage of high specific strength, they have poor atmospheric corrosion resistance. An important method of improving the corrosion resistance is by applying a coating layer. In this work, the physical vapor deposition (PVD) technique is used for coating a magnesium (Mg) AZ31 sheet substrate with a thin layer of high purity aluminum (Al) and Al–12.6% Si. Aluminum is expected to be suitable as a coating layer on Mg sheets, due to its corrosion resistance and its formability. Before coating, the substrate was subjected to several consecutive surface preparations, including sand-blasting, mechanical grinding, mirror-like polishing, ultrasonic etching, and finally ion etching by magnetron sputtering (MS). PVD coating was conducted using a PVD machine with max electron beam power and voltage of 100 kW and 40 kV, respectively. This was either with or without plasma activation, and with variable substrate speeds ranging between 10 and 70 mm/s. During MS ion etching and coating, the substrate temperature increased. The substrate temperature increased with the application of plasma activation and with lower substrate speeds. The coating-layer thickness varied inversely with substrate speed. A thinner coat with finer morphology was obtained in the case of plasma activation. Other results included coating layer characteristics, diffusion between the AZ 31 substrate and the Al coating layer, adhesion of the coating layer to the substrate, and corrosion resistance by a humidity test.     

The mystery of clustering in macromolecular media

Clustering occurs in most polar media such as water-soluble macromolecules. The true origin of clustering has been elusive despite a great deal of research effort. This paper uses the simplest water-soluble polymer, poly(ethylene oxide), dissolved in deuterated water to investigate the cause of clustering. The small-angle neutron scattering technique is used to separate out solvation effects from clustering effects and back out the various interaction parameters. It is found that clustering is related to attractive inter-chain interactions between hydrophobic groups which create physical crosslinks thereby causing clustering.     

Influence of organic liquids on the nanostructure of precipitated cellulose

Organic liquids have been used in pretreatments to improve the digestibility of lignocellulosic biomass, ultimately reducing the amount of enzyme required to digest the material to its constituent sugars. To understand the influence of these solvents on cellulose nanostructure, phosphoric acid was used to solubilize cellulose (PAS cellulose) followed by washing of the PAS cellulose with organic liquids previously demonstrated to aid pretreatment. PAS cellulose washed using methanol, ethanol, and ethylene glycol had gel‐like properties with disrupted nanostructures. PAS cellulose washed with acetone, 2‐propanol, and water yielded an opaque white precipitate. Small‐angle neutron scattering indicated the formation of loosely bundled rods of cellulose in the gel‐like material. Fourier transform infrared resonance of solvent‐washed, flash‐dried PAS cellulose suggested an increase in interchain hydrogen bonds in the gel‐like precipitates relative to the more obvious precipitates formed in other solvents. The optimal wash liquid was determined to be 40% by volume ethanol in water to induce a highly digestible, gel‐like material. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Study of the behavior of an organic coating applied on the storage reservoirs of oil in a medium of 3% NaCl solution and in marine environment

The paints are used extensively in various fields, especially for the protection of the oil installations such as the storage reservoirs of crude oil. Reducing possession cost and applying the new hygiene and security standards imply the necessity to deepen the knowledge of the physico‐chemical processes of ageing coatings in the first stage and their impact on the corrosion of the substrate. The tests have been carried out on a primer, and on painted steel plates completely immersed in a 3% NaCl solution. The survey of the water absorption and the kinetics deterioration of the paints have been achieved especially by means of electrochemical impedance spectroscopy under the test of salt spray. The barrier weakness of the primer paint, due to the existence of two capacitive loops observed on the Nyquist's diagrams has been put in evidence. While the study of the resistance of the complete system by the test accelerated in the salt spray shows that the system of painting presents a good resistance up to 196 hours, which is equivalent to 8 years of exposure.     

Ultra-High Resolution Inelastic Neutron Scattering

Two types of ultra high energy resolution neutron scattering instruments, the backscattering spectrometer and the spin echo spectrometer, are described. Examples of the types of research which can be done with these instruments are given and plans for a cold neutron backscattering spectrometer which will be built in the NIST Cold Neutron Research Facility (CNRF) are discussed. It is hoped that this information will be of use to researchers considering neutron scattering experiments at NIST.     

Preparation of TiO2-pillared montmorillonite as photocatalyst Part I. Microwave calcination, characterisation, and adsorption of a textile azo dye

Two photocatalysts based on TiO₂-pillared intercalated montmorillonite have been prepared by microwave for 10 min at 700 W or by furnace heating at 673 K. Montmorillonite pillaring with TiO₂ increased the basal spacing to 14.7 Å (conventional heating) and 17.6 Å (microwave heating). XRD patterns of both materials showed the presence of 100% anatase with a slightly higher rate of crystallinity obtained through microwave calcination than by conventional heating at 673 K. The BET specific surface area of the microwave prepared photocatalyst (151 m² g^− 1) was 3 fold higher than those of the Degussa TiO₂ P25. At pH = 5.8, the maximum adsorption capacity of Solophenyl red 3BL (a textile azo dye) on the TiO₂-pillared montmorillonite calcined by microwave was 185 mg g^− 1, whereas it was 1.4 and 3 fold lower on the TiO₂-pillared montmorillonite calcined at 673 K, and on the Degussa TiO₂ P25 respectively. The influence of pH on the adsorption of the dye depended on the pH_ZPC of the pillared montmorillonites.     

Indoor air quality assessment in dwellings with different ventilation strategies in Nunavik and impacts on bacterial and fungal microbiota

Indoor air quality is a major issue for public health, particularly in northern communities. In this extreme environment, adequate ventilation is crucial to provide a healthier indoor environment, especially in airtight dwellings. The main objective of the study is to assess the impact of ventilation systems and their optimization on microbial communities in bioaerosols and dust in 54 dwellings in Nunavik. Dwellings with three ventilation strategies (without mechanical ventilators, with heat recovery ventilators, and with energy recovery ventilators) were investigated before and after optimization of the ventilation systems. Indoor environmental conditions (temperature, relative humidity) and microbiological parameters (total bacteria, Aspergillus/Penicillium, endotoxin, and microbial biodiversity) were measured. Dust samples were collected in closed face cassettes with a polycarbonate filter using a micro-vacuum while a volume of 20 m³ of bioaerosols were collected on filters using a SASS3100 (airflow of 300 L/min). In bioaerosols, the median number of copies was 4.01 × 10³ copies/m³ of air for total bacteria and 1.45 × 10¹ copies/m³ for Aspergillus/Penicillium. Median concentrations were 5.13 × 10⁴ copies/mg of dust, 5.07 × 10¹ copies/mg, 9.98 EU/mg for total bacteria, Aspergillus/Penicillium and endotoxin concentrations, respectively. The main microorganisms were associated with human occupancy such as skin-related bacteria or yeasts, regardless of the type of ventilation.     

Batch sizes optimisation by means of queueing network decomposition and genetic algorithm

Batch sizes have a considerable impact on the performance of a manufacturing process. Determining optimal values for batch sizes helps to reduce inventories/costs and lead times. The deterministic nature of the available batch size optimisation models reduces the practical value of the obtained solutions. Other models focus only on critical parts of the system (e.g., the bottleneck). In this paper, we present an approach that overcomes important limitations of such simplified solutions. We describe a combination of queueing network analysis and a genetic algorithm that allows us to take into account the real characteristics of the system when benefiting from an efficient optimisation mechanism. We are able to demonstrate that the application of our approach on a real-sized problem with 49 products allows us to obtain a solution (values for batch sizes) with less than 4% relative deviation of the cycle time from the exact minimal value.     

Aminodiazine: A Molecular Compound of Sulfadiazine and Ethylenediamine

Aminodiazine, a sulfadiazine-ethylenediamine solid compound was prepared. This compound possesses a markedly higher aqueous solubility compared to sulfa-diazine. Equilibrium solubility and elemantal analysis data indicate a 1:1 molecular interaction. Investigation of the structure of aminodiazine in the solid state suggests strong association of the sulfonamido group of sulfadiazine with one of the basic groups of ethylenediamine probably through ionic and hydrogen bonding.

From a practical standpoint, aminodiazine exhibits a much higher dissolution rate than sulfadiazine. In solution with a slight excess of ethylenediamine, aminodiazine proves compatible with four intravenous solutions over a study period of 8 hours. Further, the compound shows quantitatively the same antibacterial activity as sulfadiazine against test organisms.