Structural,Mechanical and Dielectric Properties of Microwave-Assisted High-Energy Ball Milling Synthesis of Hydroxyapatite

Abstract

In the present work, the effect of high-energy ball milling (HEBM) of starting precursors of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂)/HA system on the processing temperature, morphological, mechanical, and electrical properties are highlighted. Calcination and sintering of HA system were carried out in microwave furnace. XRD study confirmed the evolution of HA phase and EDX analysis confirmed Ca/P ratio ～1.65. Grain size of HA samples, synthesized by using microwave-assisted HEBM technique was found to be in the order of 54–75?nm. Enhanced dielectric and mechanical properties were obtained in HA samples.     

Adaptive enhancement of compressed SAR images

Synthetic aperture radar (SAR) imagery is an important global all-weather surveillance and mapping satellite imagery system. As space-borne systems have a limited storage capacity, it is imperative to heavily compress SAR images, possible with lossy compression schemes. As a result, SAR images need to be enhanced in earth stations. The work reported in this paper aims to address the issue of compression artefact removal of SAR images in an adaptive manner. The SAR images, compressed using the JPEG utility at significantly low bit rates, are enhanced by adaptively removing coding artefacts and speckle noise. As edges carry significant information in satellite imagery, a significant edge image is used for edge enhancement with selective removal of noisy edges. Further, an image sharpness metric is proposed in this work to serve as an objective no-reference metric for measuring the sharpness of SAR images.     

Synthesis of gold and silver nanoparticles by electron irradiation at 5-15 keV energy

Thin coatings (～10?μm) made from a mixture of polyvinyl alcohol (PVA) and HAuCl(4) or PVA and AgNO(3) on quartz plates were irradiated with 5-15?keV electrons, at room temperature. The electron energy was varied from coating to coating in the range of 5-15?keV, but electron fluence was kept constant at ～10(15)?e?cm(-2). Samples were characterized by the UV-vis, XRD, SEM and TEM techniques. The plasmon absorption peaks at ～511 and ～442?nm confirmed the formation of gold and silver nanoparticles in the respective electron-irradiated coatings. The XRD, SEM and TEM measurements reveal that the average size of the particles could be tailored in the range of 130-50?nm for gold and from 150-40?nm for silver by varying the electron energy in the range of 5-15?keV. These particles of gold and silver embedded in the polymer could also be separated by dissolving the coatings in distilled water.     

Removal of sulfur from Assam coal by bacterial conditioning and froth flotation

Reduction of sulfur by bacterial leaching from a high sulfur‐bearing coal sample from Assam was attempted. Flotation of the sample with light diesel oil could not depress the pyrite and also the Thiobacillus ferrooxidans was found to be ineffective in leaching the sulfur from the flotation concentrate. Conditioning of the same coal sample with Thiobacillus ferrooxidans was found to assist in selectively depressing the pyrite, thereby reducing nearly 60% of the pyritic sulfur present in the sample. © 1999 Society of Chemical Industry     

Response surface analysis of extract yield and flavour intensity of Brazilian cherry (Eugenia uniflora L.) obtained by supercritical carbon dioxide extraction

This work evaluated the effect of pressure and temperature on yield and characteristic flavour intensity of Brazilian cherry (Eugenia uniflora L.) extracts obtained by supercritical CO₂ using response surface analysis, which is a simple and efficient method for first inquiries. A complete central composite 2² factorial experimental design was applied using temperature (ranging from 40 to 60 °C) and pressure (from 150 to 250 bar) as independent variables. A second order model proved to be predictive (p ≤ 0.05) for the extract yield as affected by pressure and temperature, with better results being achieved at the central point (200 bar and 50 °C). For the flavour intensity, a first order model proved to be predictive (p ≤ 0.05) showing the influence of temperature. Greater characteristic flavour intensity in extracts was obtained for relatively high temperature (> 50 °C). Therefore, as far as Brazilian cherry is concerned, optimum conditions for achieving higher extract yield do not necessarily coincide to those for obtaining richer flavour intensity.Industrial relevanceSupercritical fluid extraction (SFE) is an emerging clean technology through which one may obtain extracts free from organic solvents. Extract yields from natural products for applications in food, pharmaceutical and cosmetic industries have been widely disseminated in the literature. Accordingly, two lines of research have industrial relevance, namely, (i) operational optimization studies for high SFE yields and (ii) investigation on important properties extracts are expected to present (so as to define their prospective industrial application). Specifically, this work studied the optimization of SFE process to obtain extracts from a tropical fruit showing high intensity of its characteristic flavour, aiming at promoting its application in natural aroma enrichment of processed foods.     

Trans boundary transport of pollutants by atmospheric mineral dust

The transport of anthropogenic pollution by desert dust in the Eastern Mediterranean region was studied by analyzing major and trace element composition, organic species, and Pb isotope ratios in suspended dust samples collected in Jerusalem, Israel. Dust storms in this region are associated with four distinct synoptic conditions (Red Sea Trough (RS), Eastern High (EH), Sharav Cyclone (SC), and Cold Depression (Cyprus low, CD)) that carry dust mostly from North African (SC, CD, EH) and Arabian and Syrian (RS, EH) deserts. Substantial contamination of dust particles by Pb, Cu, Zn, and Ni is observed, while other elements (Na, Ca, Mg, Mn, Sr, Rb, REE, U, and Th) display natural concentrations. Sequential extraction of the abovementioned elements from the dust samples shows that the carbonate and sorbed fractions contain most of the pollution, yet the Al-silicate fraction is also contaminated, implying that soils and sediments in the source terrains of the dust are already polluted. We identified the pollutant sources by using Pb isotopes. It appears that before the beginning of the dust storm, the pollutants in the collected samples are dominated by local sources but with the arrival of dust from North Africa, the proportion of foreign pollutants increases. Organic pollutants exhibit behavior similar and complementary to that of the inorganic tracers, attesting to the importance of anthropogenic-pollutant addition en route of the dust from its remote sources. Pollution of suspended dust is observed under all synoptic conditions, yet it appears that easterly winds carry higher proportions of local pollution and westerly winds carry pollution emitted in the Cairo basin. Therefore, pollution transport by mineral dust should be accounted for in environmental models and in assessing the health-related effects of mineral dust.     

Radiation transfer in participating medium interacting with variable property natural convection subjected to collimated/diffused irradiation at boundary—A critical appraisal

The current study addresses the interaction phenomenon of combined natural convection with radiation in the presence of radiatively active gray medium inside a two‐dimensional enclosure. The left wall is radiatively considered to be semitransparent and is subjected to collimated irradiation. All gray walls of the enclosure are assumed to diffuse, except the semitransparent wall which is considered to be specular in nature. Investigation is done for the flow which is considered to be steady, laminar, and two‐dimensional. The variation of properties (k, ρ, μ) with temperature has been taken into consideration to make the investigation realistic. The radiation modeling has been done with the higher order discrete ordinate radiation method (DOM). The finite volume discretization has been adopted for numerical simulation. The effect of varying properties has been delineated and its due consideration while modeling has been realized. The results are depicted through isotherm and streamline patterns. The effects of influencing parameters on the Nusselt number have also been illustrated. A critical appraisal is made examining the suitability of the radiation models starting from S₄ to S₃₂, for different situations. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20403     

Synthesis and characterization of multi-walled carbon nanotubes functionalized with hyperbranched poly(urea-urethane)

Two types of hyperbranched poly(urea-urethane)-functionalized multi-walled carbon nanotubes (GHPU) have been synthesized in the presence of bis- and tris-hydroxy terminated carbon nanotubes (MWNT-OH). For comparison of the grafting efficiency on carbon nanotubes, pure hyper-branched poly(urea-urethane)s (HPUs) were also synthesized to prepare pristine carbon nanotubes-reinforced nanocomposites (HPNTs). Better MWNT dispersion in the polymer matrix was obtained for GHPU than for HPNT, and the effect was superior in the case of highly branched GHPU from tris-hydroxy-functionalized MWNTs, compared to GHPU from bis-hydroxy-functionalized MWNTs. TEM measurements for GHPUs clearly showed hyperbranched polymer-wrapped MWNT structures. Crystallization of hyperbranched polymers in GHPU was more developed than that of the HPNT nanocomposites, although MWNT-induced crystallization was observed for both the GHPU and HPNT samples. The hyperbranched polymer-grafting effect on MWNTs resulted in greater enhancement of the mechanical properties of GHPU at the same nanotube loading, compared to the case of HPNT nanocomposites. However, a too highly branched structure was found to lower the crystallization and mechanical properties of both the GHPUs and HPNTs.     

Applying process design software for capacity increase and revamp of distillation units

The paper presents the results of feasibility study for increase of crude processing capacity and improves of energy efficiency of crude oil distillation units. Results introduce that boosting up the distillation capacity was solved while keeping the flexibility of units for processing different type crude oils. Analysis of heat exchanger network resulted significant reduction in fuel consumption and in CO₂ emission (93 × 10⁶ GJ year⁻¹ and 3,030 tCO₂ year⁻¹, respectively). Modification of furnace of one of the distillation units showed 63 GJ kt_crude⁻¹ saving in energy and 4.5 tCO₂ kt_crude⁻¹ decrease in emission.     

Influence of Coating Granulation Process on Iron Ore Sinter Quality and Productivity

For better blast furnace performance, there has always been a need for better quality raw materials like sinter, lump ore, and pellets. Among these raw materials the usage of sinter in blast furnace is at higher side compared to other iron bearing materials. As the quality of sinter product improves, its usage in blast furnaces also increases. Iron ore fines are the main source for sinter making. To improve the sinter properties it is necessary to provide good quality of iron ore fines. Due to depletion of high grade iron ore resources, goethite and limonitic ore content in iron ore fines is expected to increase gradually. Usually limonitic and goethite ore are associated with higher alumina and LOI. The conventional sintering process is one of the well established processes for high quality hematite ore. It does not fully respond to the low grade iron ore associated with goethite and limonite. This has led to deterioration in sinter properties and productivity. In recent years the improvement in the quasi‐particle structure with the granulation process is an effective method for improving sinter quality and productivity. To improve the sinter quality and productivity for low grade iron ore fines, different granulation processes like the conventional one, and other two advanced granulation processes like coke breeze, and flux & coke breeze coating granulation were studied in detail by conducting laboratory pot grate sintering experiments. From the test results it was found that sinter productivity, physical and metallurgical properties of the sinter improved with flux & coke breeze coating granulation process compared to conventional and coke breeze coating granulation process. Proper selection of the granulation time is very important to achieve the desired sinter properties. In the present work detailed laboratory experiments have been carried out by varying the coating time from 30s to 110s to study the influence of flux & coke breeze coating granulation time on mineralogy, productivity, physical, and metallurgical properties of sinter. With a coating granulation time of 50s, higher productivity, higher yield, and stronger sinter (higher T.I) with lower RDI and ‐5mm size sinter were achieved.