The dependency of the critical contact angle for flotation on particle size - Modelling the limits of fine particle flotation

The flotation behaviour of fine particles is studied in this work. Fine methylated quartz particles within the size range from 0.2 to 50 μm, and with varying contact angles, were floated in a mechanical flotation cell. Results indicate that particles of a given size need to possess a minimum critical contact angle, which increases in value as particle size decreases, for flotation to be initiated. As a consequence, a non-floating component exists within a given size fraction. This is interpreted as a fraction consisting of particles below the critical contact angle for flotation for that size. The critical contact angle for flotation is explained in terms of the existence of an energy barrier for bubble-particle attachment. The flotation results are interpreted by means of [Scheludko et al., 1976] and [Drelich and Miller, 1992] models for the floatability of fine particles. The experimental data compared very well with calculations using the Drelich and Miller equation, allowing extension to the prediction of the critical contact angle for flotation down to particle sizes well below the previous limits investigated, bridging the gap existing in the literature.     

Synthesis of an information channel in planning goal functioning of space remote sensing systems according to quality criteria

Quality criteria for an image received from optic-electronic complexes of space remote sensing systems and methods of evaluating these quality criteria that allow one to choose parameters of elements of a ground space information channel together with orbital design of space remote sensing systems are considered.     

Superficial modification in recycled PET by plasma etching for food packaging

An oxygen plasma treatment has been used to improve the adhesion of amorphous hydrogenated carbon (a‐C:H) films onto surfaces of recycled poly(ethylene terephthalate) (PET). Modifications produced by the oxygen plasma on the PET surface in chemical bonds and morphology were investigated by X‐ray photoelectron spectroscopy and atomic force microscopy, respectively. Contact angle measurements were used to study the changes in the surface wettability. Adhesion of the a‐C:H film onto the PET surface was investigated by the tape test method. It was observed that the improvement in film adhesion is in good correlation with the increase in surface roughness, due to plasma etching, and with the appearance of oxygen‐related functional groups at the surface. The results of this study indicate that a‐C:H‐coated recycled PET can be used in food packaging. The a‐C:H film could be used as a functional barrier to reduce or prevent migration of contaminants from the polymer to the package content. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Assessment of dielectric behavior of recycled/virgin high density polyethylene blends

In this work, high density polyethylene (HDPE) incorporation in virgin resin was assessed as to its electrical performance with the use of volumetric resistivity, dielectric strength, and stress tracking measurements. HDPE post-consumer packaging was collected and submitted to a basic process of plastic recovering: washing, grinding, and drying. Formulations containing 0, 25, 50, 75, and 100% of recycled material in the virgin resin were reprocessed by extrusion and injection molding with stabilization. Dielectric strength test results were analyzed by the statistical distribution of Weibull, and the maximum likelihood method. The degree of crystallinity was measured by X-ray diffraction. Atomic absorption spectroscopy was also done to identify metallic residue present in the samples. From the results analyzed, it can be concluded that the HDPE derived from post-consumer packaging can be considered in electrical insulation systems for low voltage (up to 600 V) containing as much as 75% incorporated virgin resin.     

Using a new diffusivity model to accelerate the drying of biopolymer films

A model was developed to study the drying rate of biopolymer films. The diffusivity of water in this biopolymer film is an exponential function of the water concentration. This creates a situation where simply increasing gas velocity can decrease the actual drying rate. The model revealed that the main factor limiting the drying of the biopolymer film was a significant and rapid decrease in the diffusivity of water through the film as the film dried. To avoid this a pulsing scheme was proposed where the velocity of the drying gas would be varied during the experiment; this variation allowed for a compromise between a high overall drying rate and maintaining a high diffusivity within the film. It was found that the optimum combination of gas velocities was 0.8 and 0.6 m/s with a duration of 10 min at the high and low gas velocities.     

Accelerated aging and contact with food simulants in adhesion of amorphous hydrogenated carbon films obtained by the PECVD process from recycled PET from packaging

This work focuses principally on the influence of time, temperature, and contact with food simulants in adhesion of amorphous hydrogenated carbon (a‐C:H) films obtained by the plasma enhanced chemical vapor deposition process in recycled PET from packaging. Shelf life of packaging used in soft drinks, fruit juice, etc. is known to be ～ 6 months, with possible variations. The a‐C:H film, used in this study as a functional barrier against possible contaminants in recycled PET, was analyzed to determine possible alterations in its physical and chemical properties. The film underwent an accelerated aging test and was exposed to contact with food simulants listed by the FDA. In this case, adhesion is one of the properties most in need of conservation. This property was analyzed by means of the tape test and scanning electronic microscopy. Superficial chemical alterations resulting from both the accelerated aging test and contact with liquids were examined by the contact angle. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Upgrading of low-grade gold ore samples for improved particle characterisation using Micro-CT and SEM/EDX

There is a considerable challenge in accurate characterisation of gold (Au) particles in low-grade plant ore mineral samples. This is particularly true for automated mineralogical tools such as X-ray micro-computed tomography (Micro-CT) and scanning electron microscopy (SEM), where the need for statistically meaningful numbers of particles requires many sections to be analysed. Whiles the Vertical Gas Stream (VGS) elutriator is suitable for coarse particle upgrading (i.e. >38 μm), the performance is poor for finer particles (i.e. <38 μm). Consequently, the system has been modified to Vertical Water Stream (VWS) elutriator using higher density fluid (i.e. water) to enable analysis of Au particles below 38 μm. In this work, the VGS system was used to upgrade Au particles in the ?53 + 38 μm size fraction (in rougher concentrate, rougher tailings, regrind mill discharge and regrind cyclone underflow) and the VWS system was used to upgrade Au particles in the ?38 μm size fraction of the regrind mill discharge sample. The VWS elutriator was calibrated using galena (specific gravity, S.G. of 7.58) and quartz (S.G. of 2.65) particles of <38 μm size as model minerals. From the calibration tests, partition curves as a function of particle size were generated. Using these measurements, theoretical partition curves for Au (S.G. of 19.3) have been calculated. The VWS concentrate was characterised using Micro-CT and compared with SEM coupled with energy dispersive X-ray (EDX) analysis of ?53 + 38 μm ore size fraction of the VGS concentrate of the four sample streams. The Micro-CT analysis of VWS Au concentrate showed that sufficient particles (Au) can be upgraded. SEM/EDX results indicate that regrind does not affect changes in free Au particle morphology, aspect ratio and frequency of shearing damage in the ?53 + 38 μm size fraction. Cyclone classification of the regrind mill discharge in the ?53 + 38 μm size fraction appears to perform surface cleaning by exposing obscuring silver (Ag) surfaces on Au particles in the mill discharge sample.     

Influence of additives on the dielectric strength of high-densitypolyethylene

In this study, we present the results of the influence of chemical additives (antioxidant and UV stabilizer) and pigments (titanium dioxide and carbon black) on the short-term dielectric breakdown test of high-density polyethylene (HDPE). These additives and pigments are commonly added to polyolefins, which are used as insulating material for medium voltage cables. The incorporation was performed in a single screw extruder and thin films specimens were obtained by hot compression from extruded materials. For the dielectric breakdown test, an automated system has been used. A voltage ramp of 500 V/s was applied to specimens immersed in a silicon oil bath at room temperature. The degree of crystallinity and chemical modification of the formulations were evaluated by X-ray diffraction and Fourier transform infrared (FTIR), respectively. The dielectric breakdown results have been analyzed by a Weibull distribution. The shape and scale parameters of this distribution have been obtained by a graphic and maximum likelihood method. These results showed that the carbon black is the component that affects the dielectric strength, that the β shape parameter from the graphic method can be used to evaluate additive mixing conditions, and that the weakest point for formation of the rupture channel is on the carbon black agglomerate     

Vegard’s law and superstructural phases in Al<Subscript>x</Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>As/GaAs(100) epitaxial heterostructures

The lattice constants of Al_xGa_1?x As epitaxial alloys with various AlAs (x) contents are determined for AlxGa_1?xAs/GaAs(100) heterostructures grown by MOC-hydride epitaxy using X-ray diffractometry and an X-ray back-reflection method. An ordered AlGaAs₂ (superstructural) phase is found in epitaxial heterostructures with x ≈ 0.50. The lattice constant of this phase is smaller than the lattice constants of an Al_0.50Ga_0.50As alloy and GaAs single-crystal substrate.