Factors Affecting the Collision of Aerosol Particles with Small Water Drops

The factors influencing the collision of aerosol particles with small water drops at low collision efficiencies are examined. The gravitational force and velocity slip of air on the drop surface are found to affect the collision efficiency in the range of values of 10^?4–^?2. The efficacies of the different computational models are compared for ratios of particle radius to drop radius of less than 0.1. The accuracy of the numerical scheme in the trajectory model can be verified by comparing the efficiencies obtained for submicrometer particles with the convective-diffusion model.     

A Cough Aerosol Simulator for the Study of Disease Transmission by Human Cough-Generated Aerosols

Aerosol particles expelled during human coughs are a potential pathway for infectious disease transmission. However, the importance of airborne transmission is unclear for many diseases. To better understand the role of cough aerosol particles in the spread of disease and the efficacy of different types of protective measures, we constructed a cough aerosol simulator that produces a human-like cough in a controlled environment. The simulated cough has a 4.2 l volume and is based on coughs recorded from influenza patients. In one configuration, the simulator produces a cough aerosol containing particles from 0.1 to 100 μm in diameter with a volume median diameter (VMD) of 8.5 μm and a geometric standard deviation (GSD) of 2.9. In a second configuration, the cough aerosol has a size range of 0.1–30 μm, a VMD of 3.4 μm, and a GSD of 2.3. The total aerosol volume expelled during each cough is 68 μl. By generating a controlled and reproducible artificial cough, the simulator allows us to test different ventilation, disinfection, and personal protection scenarios. The system can be used with live pathogens, including influenza virus, which allows isolation precautions used in the healthcare field to be tested without risk of exposure for workers or patients. The information gained from tests with the simulator will help to better understand the transmission of infectious diseases, develop improved techniques for infection control, and improve safety for healthcare workers and patients.

Copyright 2013 American Association for Aerosol Research     

Erosion of atmospheric plasma sprayed rare earth oxide coatings under air suspended corundum particles

Atmospheric plasma sprayed (APS) zirconium oxide based coatings are used widely in aero engine components for providing thermal insulation, improving the corrosion and oxidation resistance. Despite its wide spread industrial use, little is known about the basic erosion behaviour and the mechanisms by which such coatings erode. In this paper, the erosive wear behaviours of Yttria Stabilized Zirconia (YSZ) coatings; Lanthanum Zirconate (LZ) coatings and Inconel 738 base material (BM) were studied and compared under air jet erosion conditions with corundum particles as erodent material. The erosion behaviour was studied with respect to the different porosity volume percentages of the coatings and the changes in velocity of erodent, impact angle of erodent and erodent particle flux. It was found that in solid particle erosion, the wear resistances of YSZ and LZ coatings were the best at their lowest porosity volume and it decreased with the increase in the percentage volume of porosity. There was a linear increase in the wear resistance with the increase in hardness. Further, relationships among the erosion parameters with respect to erosive wear loss were derived by using the response surface methodology and the erosion mechanisms were discussed adequately.     

The PZT system (PbZr1-xTixO3, 0.0≤x≤1.0): Specific features of recrystallization sintering and microstructures of solid solutions (Part 1)

This work is concerned with the specific features of sintering of solid solutions of the PZT system (PbZr_1?xTi_xO₃, 0.0≤x≤1.0) depending on composition. The microstructure of the solid-solution ceramics has been found to be a fairly homogeneous, mosaic, sufficiently close packing of isometric crystallites with a range of section from 3 to 11 μm, but there exists a number of special features related to the component and phase composition of the objects. It has been found that the changes in multifractal parameters of grain structure of these ceramics reflect with high sensitivity the processes of phase transformations in the solid solutions. The obtained results are useful in developing piezoelectric materials based on the PZT system.     

Effect of Deviation from Coaxiality between the Directions of Magnetization and Mechanical Strain on the Results of Magnetic Testing of Elastic Strain in Steels

The magnetoelastic effect in steels that are in the states of coercive force and residual magnetization in the saturation hysteresis loop is studied. The regularities of changes in the residual magnetization and coercive force under uniaxial tensioning and compression of specimens of 30KhGSA steel magnetized along the direction of strain application are established. It is shown that a variation in the direction of magnetization and complication of the strain pattern result in considerable deviations in the character of changes in the magnetic forces determined by a ferroprobe-type coercive force meter for elastically strained plates from St3 and R6M5 steels and for an St3 beam.     

Chelants to inhibit magnesia (MgO) hydration

Magnesium oxide (MgO) presents excellent refractoriness and high resistance to basic slag. However, in the presence of water, MgO undergoes an expansive hydration reaction generating Mg(OH)₂, which can lead to swelling and cracking. In this work, additives called chelants were added to dead burnt magnesia suspensions in order to check their effectiveness as inhibitors of the magnesium oxide hydration. Zeta potential, ionic conductivity, pH and temperature measurements were used to provide information related to the magnesia surface and the chelant adsorption. Assessment of the hydration degree and volumetric expansion provided indications of the amount of Mg(OH)₂ formed, as well as its likelihood to damage the ceramic bodies. The results showed that citric acid can inhibit hydration to some extent, whereas ethylenediamine tetraacetic acid (EDTA) was more effective in preventing volume expansion. An addition of 0.3 wt% of these chelants was sufficient to prevent hydration and avoid expansion.