Journal of Materials
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Open Access journal
ISSN (Print) 2314-4866 - ISSN (Online) 2314-4874
Published by Hindawi Publishing Corporation [403 journals]
- MATLAB User Interface for Simulation of Silicon Germanium Solar Cell
Abstract: Nuclear fusion reaction on the sun is the largest source of energy. In this paper, qualitative investigation of the numerical model of silicon germanium heterojunction solar cell is performed using MATLAB graphical user interface. The heterostructure is designed as for speculative determination of appropriate germanium mole fraction to get the maximized thin-film solar cell efficiency (ή). Other characteristics such as absorption coefficient (α), energy band gap (), reflectivity (r), open circuit voltage (), and generation rate are also considered. This user interface will reduce the complexity of solving differential equation for the analysis of silicon germanium heterojunction cell.
PubDate: Mon, 17 Aug 2015 12:19:10 +000
- Tailoring Imprinted Titania Nanoparticles for Purines Recognition
Abstract: Molecular imprinted titania nanoparticles were developed for selective recognition of purines, for example, guanine and its final oxidation product uric acid. Titania nanoparticles were prepared by hydrolysis of titanium butoxide as precursor in the presence of pattern molecules. The morphology of synthesized nanoparticles is evaluated by SEM images. Recognition characteristics of imprinted titania nanoparticles are studied by exposing them to standard solution of guanine and uric acid, respectively. The resultant change in their concentration is determined by UV/Vis analysis that indicated imprinted titania nanoparticles possess high affinity for print molecules. In both cases, nonimprinted titania is taken as control to observe nonspecific binding interactions. Cross sensitivity studies suggested that imprinted titania is at least five times more selective for binding print molecules than competing analyte thus indicating its potential for bioassay of purines.
PubDate: Mon, 03 Aug 2015 06:12:59 +000
- Enhancing Roentgen Sensitivity of Gold-Doped CdIn2S4 Thiospinel for X-Ray
Abstract: The single crystals were grown from preliminarily synthesized polycrystals by the method of chemical transport reactions in a closed volume with iodine used as a carrier. The influence of doping CdIn2S4 single crystals by gold (3 mol %) on their X-ray dosimetric parameters is studied. It is found that the X-ray sensitivity coefficients of crystals increase 6–8 times compared with undoped CdIn2S4 at effective radiation hardness keV and dose rate R/min. Moreover, the persistence of the crystal characteristics completely disappears and the supple voltage of a roentgen detector decreases threefold. The dependence of the steady X-ray-induced current in on the X-ray dose is described by linear law. The studied crystals have a rather high room-temperature X-ray sensitivity ( (A·min)/(R·V)) and are attractive as materials for X-ray detectors.
PubDate: Wed, 29 Jul 2015 08:15:37 +000
- First-Principle and Experimental Study of a Gadolinium-Praseodymium-Cobalt
Pseudobinary Intermetallic Compound
Abstract: First-principles methods were used to determine the magnetic state of a simulated cobalt-based binary alloy (Gd,Pr)Co17 along with its corresponding lattice parameters and density. The resulting composition was fabricated using two methods arc-melting and induction-melting and compared with the calculated values. The induction-melted samples showed greater homogeneity and successfully produced the R2Co17 structure. Calculated values qualitatively predict ferromagnetic behavior and lattice parameters to be within a low percent. The development of magnetic alloys with the assistance of computational methods promises faster development of new functional materials.
PubDate: Sun, 28 Jun 2015 07:34:41 +000
- Solution-Processed rGO/AgNPs/rGO Sandwich Structure as a Hole Extraction
Layer for Polymer Solar Cells
Abstract: We found that inserting silver nanoparticles (AgNPs) between two layers of reduced grapheme oxide (rGO) has an effect on tailoring the work function of rGO. The utilization of rGO/AgNPs/rGO sandwich structure as the hole extraction layer in polymer solar cells is demonstrated. Solution-processable fabrication of this sandwich structure at the ITO/active layer interface facilitates the extraction of hole from active layer into ITO anode because of lowering the barrier level alignment at the interface. It results in an improvement of the short circuit current density and the overall photovoltaic performance.
PubDate: Thu, 11 Jun 2015 07:00:23 +000
- Thermal Spectroscopy and Kinetic Studies of PEO/PVDF Loaded by Carbon
Abstract: Nanocomposites of polyethylene oxide (PEO) and polyvinylidene fluoride (PVDF) without and with low content of single and multiwalled carbon nanotubes (SWCNTs-MWCNTs) were prepared and studied by thermogravimetric analysis (TGA) using different heating rate. TGA results indicate that the thermal stability of neat PEO/PVDF blend was improved with both heating rate and incorporation of carbon nanotubes (CNTs). The degradation temperature for neat blend was lower than those of the nanocomposites after adding both SWCNTs and MWCNTs. As increase of heating rate, the onset of decomposition is irregularly moved to higher temperatures. This indicates that the thermal stability of the polymeric matrices has been improved after addition of CNTs. The residual weight of the samples left increased steadily with adding of both SWCNTs and MWCNTs. Kinetic thermodynamic parameters such as activation energy, enthalpy, entropy, and Gibbs free energy are evaluated from TGA data using Coats-Redfern model. The values of all parameters irregularly decrease with increasing of heating rate due to increasing of heating rate temperature, the random scission of macromolecule chain in the polymeric matrices predominates and the activation energy has a lower value.
PubDate: Sun, 31 May 2015 12:32:52 +000
- Sodium Sulphate Effect on Cement Produced with Building Stone Waste
Abstract: In this study, the blended cements produced by using the building stone waste were exposed to sulphate solution and the cement properties were examined. Prepared mortar specimens were cured under water for 28 days and then they were exposed to three different proportions of sodium sulphate solution for 125 days. Performances of cements were determined by means of compressive strength and tensile strength tests. The broken parts of some mortar bars were examined with scanning electron microscope (SEM). Besides, they were left under moist atmosphere and their length change was measured and continuously monitored for period of 125 days. In blended cements, solely cements obtained by replacing 10–20% of diatomites gave similar strength values with ordinary Portland cement (CEM I 42.5R) at the ages of 7, 28, and 56 days. In all mortar specimens that included either waste andesite (AP) or marble powder (MP) showed best performance against very severe effective sodium sulphate solutions (13500 mg/L).
PubDate: Thu, 07 May 2015 12:19:29 +000
- Effect of Inert and Pozzolanic Materials on Flow and Mechanical Properties
of Self-Compacting Concrete
Abstract: This research investigates the fresh behaviour and mechanical properties of self-compacting concrete (SCC) containing high volume of limestone, metakaolin, silica fume, zeolite, and viscosity modifying admixture. Two fine aggregates with different fineness modulus were also utilized to evaluate the effect of sand’s gradation on the mechanical and flow properties of SCC containing inert and pozzolanic powder. Slump flow, V-funnel for fresh concrete and 5-minute-old concrete, J-ring, Orimet with and without J-ring, and L-box and U-box tests were performed on all 14 fresh concrete mixtures to examine the fresh properties of self-compacting concrete. Compressive strength of hardened specimens was measured at 7 and 35 days and tensile strength was also determined at the age of 28 days. The results show that sand grading significantly affects the fresh properties of SCC. It is also concluded that high volume of active powders including metakaolin, zeolite, and silica fume could not improve both the flow and mechanical properties of SCC at the same time. Limestone can be effectively used as filler in SCC in high volume content. A new set of limits for the L-box and U-box tests for SCC containing silica fume is also recommended as the existing criteria are not satisfactory.
PubDate: Tue, 31 Mar 2015 13:42:54 +000
- A Qualitative Study of Thermochemical Degradation Related with Concrete
and Mortar Strength
Abstract: The nondestructive methods applied to the evaluation of concrete use different parameters to be related in the estimated resistance of concrete or other properties. The conducted study has evaluated a qualitative method of thermochemical degradation in concrete and mortar using a solvent acid whose chemical energy is capable of degrading the material. The reported study consisted in performing laboratory tests on mechanical compressive strength of concrete and mortar and thermochemical tests performed on little cores of concrete or mortar immersed in hydrochloric acid contained in a calorimeter system, obtaining several parameters as the time of thermal equilibrium, increase of temperature, degradation energy, and mass loss due to the thermochemical reaction. From the obtained results, these variables were analyzed and served as a parameter to be related with the concrete or mortar strength. The best parameter proved to be a good estimator was the increase of temperature and its degradation energy, whose value was inversely proportional to the strength of the material. Also, it is found that the most significant mechanisms that influenced the thermochemical reaction are the calcium content and the water chemically bound in the cement paste to perform the thermochemical test.
PubDate: Thu, 26 Mar 2015 11:20:33 +000
- A Reconciliation of Packed Column Permeability Data: Deconvoluting the
Abstract: In his 1952 publication, Ergun made the following proclamation: “Data of the present investigation and those presented earlier have been treated accordingly, and the coefficients and have been determined by the method of least squares. The values obtained are and, , representing 640 experiments.” In this paper, we demonstrate that because his experimental methodology was flawed, the corrected values, which his experimental results would otherwise have established for these coefficients, are significantly higher. This is, in part, because Ergun’s reporting of his measured data was ambiguous with respect to the embedded coefficients and . In addition, this ambiguity made it difficult for any subsequent researcher to figure out the true meaning of his empirical results which, in turn, resulted in his choice of the values for these coefficients being accepted by default in the scientific community.
PubDate: Mon, 22 Sep 2014 05:39:17 +000
- From Garbage to Biomaterials: An Overview on Egg Shell Based
Abstract: The conversion of waste obtained from agricultural processes into biocompatible materials (biomaterials) used in medical surgery is a strategy that will add more value in waste utilization. This strategy has successfully turned the rather untransformed wastes into high value products. Eggshell is an agricultural waste largely considered as useless and is discarded mostly because it contributes to pollution. This waste has potential for producing hydroxyapatite, a major component found in bone and teeth. Hydroxyapatite is an excellent material used in bone repair and tissue regeneration. The use of eggshell to generate hydroxyapatite will reduce the pollution effect of the waste and the subsequent conversion of the waste into a highly valuable product. In this paper, we reviewed the utilization of this agricultural waste (eggshell) in producing hydroxyapatite. The process of transforming eggshell into hydroxyapatite and nanohydroxyapatite is an environmentally friendly process. Eggshell based hydroxyapatite and nanohydroxyapatite stand as good chance of reducing the cost of treatment in bone repair or replacement with little impact on the environment.
PubDate: Mon, 25 Aug 2014 09:29:39 +000
- Effect of Short Fiber Reinforcement on Mechanical Properties of Hybrid
Abstract: Fiber plays an important role in determining the hardness, strength, and dynamic mechanical properties of composite material. In the present work, enhancement of viscoelastic behaviour of hybrid phenolic composites has been synergistically investigated. Five different phenolic composites, namely, C1, C2, C3, C4, and C5, were fabricated by varying the weight percentage of basalt and aramid fiber, namely, 25, 20, 15, 10, and 5% by compensating with barium sulphate (BaSO4) to keep the combined reinforcement concentration at 25 wt%. Hardness was measured to examine the resistance of composites to indentation. The hardness of phenolic composites increased from 72.2 to 85.2 with increase in basalt fiber loading. Composite C1 (25 wt% fiber) is 1.2 times harder than composite C5. Compression test was conducted to find out compressive strength of phenolic composites and compressive strength increased with increase in fiber content. Dynamic mechanical analysis (DMA) was carried out to assess the temperature dependence mechanical properties in terms of storage modulus (), loss modulus (), and damping factor (tan δ). The results indicate great improvement of values and decrease in damping behaviour of composite upon fiber addition. Further X-ray powder diffraction (XRD) and energy-dispersive X-ray (EDX) analysis were employed to characterize the friction composites.
PubDate: Wed, 06 Aug 2014 07:33:11 +000
- Experimental Investigation of the Phase Equilibria in the Al-Mn-Zn System
Abstract: Al-Mn-Zn ternary system is experimentally investigated at 400°C using diffusion couples and key alloys. Phase relationships and homogeneity ranges are determined for binary and ternary compounds using EPMA, SEM/EDS, and XRD. Reported ternary compound T3 (Al11Mn3Zn2) is confirmed in this study and is denoted as τ2 in this paper. Two new ternary compounds (τ1 and τ3) are observed in this system at 400°C. τ1 is determined as a stoichiometric compound with the composition of Al31Mn8Zn11. τ3 has been found to have homogeneity range of AlxMnyZnz ( at%; at%; at%). The binary compounds Al4Mn and Al11Mn4 exhibit limited solid solubility of around 6 at% and 4 at% Zn, respectively. Terminal solid solution Al8Mn5 is found to have maximum ternary solubility of about 10 at% Zn. In addition, ternary solubility of Al-rich β-Mn′ at 400°C is determined as 4 at% Zn. Zn-rich β-Mn′′ has a ternary solubility of 3 at% Al. The solubility of Al in Mn5Zn21 is measured as 5 at%. Based on the current experimental results, the isothermal section of Al-Mn-Zn ternary system at 400°C has been constructed.
PubDate: Thu, 17 Jul 2014 09:55:30 +000
- Effect of Carbon Nanotube Size on Compressive Strengths of Nanotube
Reinforced Cementitious Composites
Abstract: Application of nanoscale science to construction material has already begun. In recent times, various nanofibers have raised the interest of researchers due to their exceptional mechanical properties and high potential to be used as reinforcement within cement matrix. Carbon nanotube (CNT) is one of the most important areas of research in the field of nanotechnology. The size and exceptional mechanical properties of CNT show their high potential to be used to produce high performance next generation cementitious composites. In this study, an attempt has been made to investigate the effect of size of CNTs on compressive strengths of CNT reinforced cement composites. Seven different sizes of multiwalled nanotubes (MWNTs) were used to produce MWNT-cement composites. A trend was observed regarding the effect of nanotube size on compressive strength of composites in most cases. MWNT with outside diameter (OD) of 20 nm or less exhibited relatively better performance. Smaller MWNT can be distributed at much finer scale and consequently filling the nanopore space within the cement matrix more efficiently. This in turn resulted in stronger composites.
PubDate: Thu, 17 Jul 2014 07:39:05 +000
- Structural Investigation of Photocatalyst Solid Ag1−xCuxInS2
Quaternary Alloys Sprayed Thin Films Optimized within the Lattice
Compatibility Theory (LCT) Scope
Abstract: CuxAg1−xInS2 solid thin films were fabricated through a low-cost process. Particular process-related enhanced properties lead to reaching a minimum of lattice mismatch between absorber and buffer layers within particular solar cell devices. First, copper-less samples X-ray diffraction analysis depicts the presence of AgInS2 ternary compound in chalcopyrite tetragonal phase with privileged (112) peak ( Å) according to JCPDS 75-0118 card. Second, when x content increases, we note a shift of the same preferential orientation (112) and its value reaches 1.63 Å corresponding to CuInS2 chalcopyrite tetragonal material according to JCPDS 89-6095 file. Finally, the formation and stability of these quaternaries have been discussed in terms of the lattice compatibility in relation with silver-copper duality within indium disulfide lattice structure. Plausible explanations for the extent and dynamics of copper incorporation inside AgInS2 elaborated ternary matrices have been proposed.
PubDate: Mon, 14 Jul 2014 12:11:36 +000
- Synthesis, Growth, and Characterization of Bisglycine Hydrobromide Single
Abstract: Single crystals of BGHB were grown by slow evaporation technique. The unit cell dimensions and space group of the grown crystals were confirmed by single crystal X-ray diffraction. The modes of vibration of the molecules and the presence of functional groups were identified using FTIR technique. The microhardness study shows that the Vickers hardness number of the crystal increases with the increase in applied load. The optical properties of the crystals were determined using UV-Visible spectroscopy. The thermal properties of the grown crystal were also determined. The refractive index was determined as 1.396 using Brewster’s angle method. The emission of green light on passing the Nd: YAG laser light confirmed the second harmonic generation property of the crystals and the SHG efficiency of the crystals was found to be higher than that of KDP. The dielectric constant and dielectric loss measurements were carried out for different temperatures and frequencies. The ac conductivity study of the crystals was also discussed. The photoconductivity studies confirm that the grown crystal has negative photoconductivity nature. The etching studies were carried out to study the formation of etch pits.
PubDate: Sun, 29 Jun 2014 12:48:22 +000
- Synthesis of Thin Films by Magnetron Sputtering
Abstract: In this work films were prepared by reactive magnetron sputtering at room temperature and deposited on a silicon wafer. It was found that the diffractograms of the nitrogen-rich rhenium film are consistent with those produced by high-pressure high-temperature methods, under the assumption that the film is oriented on the substrate. Using density functional calculations it was found that the composition of this compound could be ReN3, instead of ReN2, as stated on previous works. The ReN3 compound fits in the Ama2 (40) orthorhombic space group, and due to the existence of N3 anions between Re layers it should be categorized as an azide. The material is exceptionally brittle and inherently unstable under indentation testing.
PubDate: Wed, 18 Jun 2014 08:20:19 +000
- Synthesis of Nanocrystalline CdS by SILAR and Their Characterization
Abstract: A simple and cost effective chemical technique has been utilized to prepare cadmium sulphide (CdS) nanoparticles at room temperature. The sample is characterized with XRD (X-ray diffractometer), SEM (scanning electron microscope), TEM (transmission electron microscope), FTIR (Fourier transform infrared), EDX (energy dispersive X-rays), and UV-VIS (ultraviolet visible) spectrophotometer. The particle size estimated using X-ray line broadening method is ~21.5 nm. While particle size estimation, both instrumental and strain broadening was taken into account. The lattice strain was evaluated using Williamson-Hall equation. SEM illustrates formation of submicron size crystallites and TEM image gives a particle size of ~23.5 nm. The characteristic stretching vibration frequency of CdS was observed in the absorption band in FTIR spectrum. Optical absorption study exhibits a band gap energy value of about 2.44 eV.
PubDate: Tue, 17 Jun 2014 07:22:02 +000
- New Quasi-One-Dimensional Organic-Inorganic Hybrid Material:
1,3-Bis(4-piperidinium)propane Pentachlorobismuthate(III) Synthesis,
Crystal Structure, and Spectroscopic Studies
Abstract: The organic-inorganic hybrid compound (C13H28N2) BiCl5 was synthesized by solvothermal method. The crystal structure was solved by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic system space group Cmc21 with (4) Å, (6) Å, (3) Å, and . The crystal structure was refined down to . It consists of corrugated layers of [BiCl5]2− chains, separated by organic [H2TMDP]2+ cations (TMDP=1,3-Bis(4-piperidyl)propane = C13H26N2). The crystal cohesion is achieved by hydrogen bonds joining the organic and inorganic layers. The influence of the organic cations' flexibility is discussed. Raman and infrared spectra of the title compound were recorded in the range of 50–400 and 400–4000 cm−1, respectively. Semiempirical parameter model three (PM3) method has been performed to derive the calculated IR spectrum. The crystal shape morphology was simulated using the Bravais-Friedel and Donnay-Harker model.
PubDate: Mon, 02 Jun 2014 00:00:00 +000
- Evaluation of CoBlast Coated Titanium Alloy as Proton Exchange Membrane
Fuel Cell Bipolar Plates
Abstract: We investigated the potential of graphite based coatings deposited on titanium V alloy by a low-cost powder based process for bipolar plate application. The coatings which were deposited from a mixture of graphite and alumina powders at ambient temperature, pressure of 90 psi, and speed of 20 mm were characterised and electrochemically polarised in 0.5 M H2SO4 + 2 ppm HF bubbled with air and hydrogen gas to depict the cathode and anode PEM fuel cell environment, respectively. Surface conductivity and water contact angles were also evaluated. Corrosion current in the 1 μA/cm2 range in both cathodic and anodic environment at room temperature and showed negligible influence on the electrochemical behaviour of the bare alloy. Similar performance, which was attributed to the discontinuities in the coatings, was also observed when polarised at 0.6 V and −0.1 V with air and hydrogen bubbling at 70∘C respectively. At 140 N/cm2, the coated alloy exhibited contact resistance of 45.70 mΩ·cm2 which was lower than that of the bare alloy (66.50 mΩ·cm2) but twice that of graphite (21.29 mΩ·cm2). Similarly, the wettability test indicated that the coated layer exhibited higher contact angle of 99.63° than that of the bare alloy (66.32°). Over all, these results indicated need for improvement in the coating process to achieve a continuous layer.
PubDate: Wed, 28 May 2014 12:24:14 +000
- Optical Response of Metakaolin after Ultraviolet and High Energy Electron
Abstract: Metakaolin, which is part of a class of inorganic polymers called geopolymers, is being tested currently for its use as a lightweight mirror material in spacecraft applications. Metakaolin, as with most geopolymers, has the advantages of low initial coefficient of thermal expansion, easy preparation at room temperature and pressure, and high specific strength. Even though metakaolin has been known as a structural material for millennia, it has not been properly vetted for use as a material in spacecraft applications, especially with respect to exposure to its environments. This research highlights one particular aspect of response to the space environment; that is, how do the optical properties of metakaolin change after subjugation to bombardment by ultraviolet and high energy electron radiation' These two radiation sources are common in low earth orbit and a primary cause of degradation of organic polymers in space. Photospectroscopic analysis showed that ultraviolet in combination with high energy electrons causes changes in the metakaolin which need to be accounted for due to their potential impacts on the thermal management of a spacecraft and during application in composite mirror structures.
PubDate: Thu, 08 May 2014 09:32:50 +000
- Electrochemical Behavior of TiO2 Nanoparticle Doped WO3 Thin Films
Abstract: Nanoparticle TiO2 doped WO3 thin films by pulsed spray pyrolysis technique have been studied on fluorine tin doped (FTO) and glass substrate. XRD shows amorphous nature for undoped and anatase phase of TiO2 having (101) plane for nanoparticle TiO2 doped WO3 thin film. SEM shows microfibrous reticulated porous network for WO3 with 600 nm fiber diameter and nanocrystalline having size 40 nm for TiO2 nanoparticle doped WO3 thin film. TiO2 nanoparticle doped WO3 thin film shows ~95% reversibility due to may be attributed to nanocrystalline nature of the film, which helpful for charge insertion and deinsertion process. The diffusion coefficient for TiO2 nanoparticle doped WO3 film is less than undoped WO3.
PubDate: Tue, 06 May 2014 06:31:36 +000
- Essential Magnesium Alloys Binary Phase Diagrams and Their Thermochemical
Abstract: Magnesium-based alloys are becoming a major industrial material for structural applications because of their potential weight saving characteristics. All the commercial Mg alloys like AZ, AM, AE, EZ, ZK, and so forth series are multicomponent and hence it is important to understand the phase relations of the alloying elements with Mg. In this work, eleven essential Mg-based binary systems including Mg-Al/Zn/Mn/Ca/Sr/Y/Ni/Ce/Nd/Cu/Sn have been reviewed. Each of these systems has been discussed critically on the aspects of phase diagram and thermodynamic properties. All the available experimental data has been summarized and critically assessed to provide detailed understanding of the systems. The phase diagrams are calculated based on the most up-to-date optimized parameters. The thermodynamic model parameters for all the systems except Mg-Nd have been summarized in tables. The crystallographic information of the intermetallic compounds of different binary systems is provided. Also, the heat of formation of the intermetallic compounds obtained from experimental, first principle calculations and CALPHAD optimizations are provided. In addition, reoptimization of the Mg-Y system has been done in this work since new experimental data showed wider solubility of the intermetallic compounds.
PubDate: Wed, 30 Apr 2014 11:04:07 +000
- Synthesis, Characterization, and Use of Novel Bimetal Oxide Catalyst for
Photoassisted Degradation of Malachite Green Dye
Abstract: This work reports a simple, novel, and cost effective synthesis of nanobimetal oxide catalyst using cerium and cadmium nitrates as metal precursors. The cerium-cadmium oxide nanophotocatalyst was synthesized by coprecipitation method and characterized by X-ray powder diffraction method to analyze the particle size. XRD study reveals a high degree of crystallinity and 28.43 nm particle size. The photocatalytic efficiency of the synthesized nanobimetal catalyst was examined by using it for the photocatalytic degradation of malachite green dye. Experiments were conducted to study the effect of various parameters, such as the pH of the dye solution, concentration of dye, amount of catalyst, and light intensity on the rate of dye degradation. The progress of the dye degradation was monitored spectrophotometrically by taking the optical density of the dye solution at regular intervals. Experimental results indicate that the dye degrades best at pH 8.0 with light intensity 600 Wm−2 and catalyst loading 0.03 g/50 mL of dye solution. The rate constant for the reaction was 7.67 × 10−4 s−1.
PubDate: Wed, 30 Apr 2014 09:30:24 +000
- Aerogels as Promising Thermal Insulating Materials: An Overview
Abstract: Aerogels are solids with high porosity (<100 nm) and hence possess extremely low density (∼0.003 g/cm3) and very low conductivity (∼10 mW/mK). In recent years, aerogels have attracted more and more attention due to their surprising properties and their existing and potential applications in wide range of technological areas. An overview of aerogels and their applications as the building envelope components and respective improvements from an energy efficiency perspective including performance is given here. This overview covers thermal insulation properties of aerogels and studies regarding structural features which will be helpful in buildings envelope. The improvements of thermal insulation systems have future prospects of large savings in primary energy consumption. It can be concluded that aerogels have great potential in a wide range of applications as energy efficient insulation, windows, acoustics, and so forth.
PubDate: Sun, 27 Apr 2014 00:00:00 +000
- Thermal Transport between Graphene Sheets and SiC Substrate by
Abstract: Using nonequilibrium molecular dynamics, we investigate the mechanisms of thermal transport across SiC/graphene sheets. In simulations, 3C-, 4H-, and 6H-SiC are considered separately. Interfacial thermal resistances between Bernal stacking graphene sheets and SiC (Si- or C-terminated) are calculated at the ranges of 100 K~700 K. The results indicate, whether Si-terminated or C-terminated interface, the interfacial thermal resistances of 4H- and 6H-SiC have similar trends over temperatures. Si-terminated interfacial thermal resistances of 3C-SiC are higher than those of 4H- and 6H-SiC in a wide temperature range from 100 K to 600 K. But, for C-rich interface, this range is reduced from 350 K to 500 K.
PubDate: Wed, 23 Apr 2014 13:49:45 +000
- Preparation, and Structural and Magnetic Properties of Ca Substituted
Magnesium Ferrite with Composition MgCaxFe2−xO4 ( = 0.00, 0.01,
0.03, 0.05, 0.07)
Abstract: Calcium substituted magnesium ferrite with composition MgCaxFe2−xO4 (where = 0.00, 0.01, 0.03, 0.05, 0.07) was prepared by ceramic technique. These compositions were then subjected to detailed study for structural and magnetic properties. X-ray diffraction studies reveal the formation of single phase cubic spinel. The values of lattice constant increase with the increase in calcium concentration from = 0.00 to = 0.03 and then decrease. Scanning electron microscopic (SEM) technique was used to study the morphology of the grown materials. The grain size was calculated using average intercept line method. The elemental composition of pure and calcium substituted magnesium ferrite was obtained from energy dispersive X-ray analysis (EDAX) spectrum. The hysteresis loop confirms the magnetic behaviour of the prepared composition, which is then discussed on the basis of cation distribution. The parameters such as saturation magnetization, coericivity, and retentivity are calculated. The Curie temperature was found to decrease with increasing calcium content.
PubDate: Tue, 22 Apr 2014 00:00:00 +000
- Synthesis and Characterization of LPCVD Polysilicon and Silicon Nitride
Thin Films for MEMS Applications
Abstract: Inherent residual stresses during material deposition can have profound effects on the functionality and reliability of fabricated MEMS devices. Residual stress often causes device failure due to curling, buckling, or fracture. Typically, the material properties of thin films used in surface micromachining are not very well controlled during deposition. The residual stress, for example, tends to vary significantly for different deposition conditions; experiments were carried out to study the polysilicon and silicon nitride deposited by Low Pressure Chemical Vapor Deposition (LPCVD) method at wide range of process conditions. High temperature annealing effects on stress in case polysilicon are also reported. The reduced residual stress levels can significantly improve device performance, reliability, and yield as MEMS devices become smaller.
PubDate: Mon, 14 Apr 2014 00:00:00 +000
- A Reconciliation of Packed Column Permeability Data: Column Permeability
as a Function of Particle Porosity
Abstract: In his textbook teaching of packed bed permeability, Georges Guiochon uses mobile phase velocity as the fluid velocity term in his elaboration of the Darcy permeability equation. Although this velocity frame makes a lot of sense from a thermodynamic point of view, it is valid only with respect to permeability at a single theoretical boundary condition. In his more recent writings, however, Guiochon has departed from his long-standing mode of discussing permeability in terms of the Darcy equation and has embraced the well-known Kozeny-Blake equation. In this paper, his teaching pertaining to the constant in the Kozeny-Blake equation is examined and, as a result, a new correlation coefficient is identified and defined herein based on the velocity frame used in his teaching. This coefficient correlates pressure drop and fluid velocity as a function of particle porosity. We show that in their experimental protocols, Guiochon et al. have not adhered to a strict material balance of permeability which creates a mismatch of particle porosity and leads to erroneous conclusions regarding the value of the permeability coefficient in the Kozeny-Blake equation. By correcting the experimental data to properly reflect particle porosity we reconcile the experimental results of Guiochon and Giddings, resulting in a permeability reference chart which is presented here for the first time. This reference chart demonstrates that Guiochon’s experimental data, when properly normalized for particle porosity and other related discrepancies, corroborates the value of 267 for the constant in the Kozeny-Blake equation which was derived by Giddings in 1965.
PubDate: Tue, 01 Apr 2014 08:00:31 +000
- The Construction of the Dupin Cyclides in a Smectic A Polygonal Texture
Abstract: We report experimental observations with optical microscopy of the usual so-called polygonal texture. We have made simulations of the Dupin cyclides in one small region of the sample.
PubDate: Sun, 30 Mar 2014 11:31:26 +000