Browse

101 - 110 of 1,161 items :

  • Materials Sciences x
  • Materials Sciences, other x
Clear All
Effect of pellet size and additive on silica carbothermic reduction in microwave furnace for solar grade silicon

Abstract

Silicon as a raw material for solar cells can be produced by numerous methods. The carbothermic reduction of silica using electric arc furnace is the most widely used process in silicon industry. This paper presents a new approach to produce solar grade silicon using microwave furnace. Pellets of different sizes were prepared from a mixture of silica and carbon using water and polyvinyl alcohol as binder agents. Raman spectra indicated a peak at about 515 cm−1 attributed to silicon in the pellets prepared with polyvinyl alcohol, and peaks at about 523 cm−1 and 794 cm−1 attributed to silicon and silicon carbide, in the pellets prepared with water. The pellet size affects the absorption of microwave energy emitted from the magnetrons. Polyvinyl alcohol as a binder agent is promising for the production of silicon using microwave furnace.

Open access
Effect of Sm concentration on optical and electrical properties of CdSe nanocrystalline thin film

Abstract

Present paper reports optical and electrical properties of samarium doped CdSe nanocrystalline thin film which was grown on a glass substrate by chemical bath deposition method (CBD). X-ray diffraction (XRD) analysis revealed that the deposited films were nanocrystalline with sphalerite cubic structure. The average crystallite size calculated from FWHM of XRD peaks was found to be 10.11 nm. The bandgap of the Sm doped CdSe nanocrystalline thin films was calculated to be 1.91 eV to 2.22 eV. The optical absorption edge of undoped (pure) and Sm doped CdSe films was obtained between 650 nm to 640 nm showing blue shift as compared to bulk CdSe. Sm doping further enhanced the photoconductivity of these films. The I-V characteristic confirmed the suitability of prepared films for photosensor applications.

Open access
Estimation of an Airfoil Drag at High Angles of Attack from PIV Data

Abstract

The paper presents application of Particle Image Velocimetry for determination of an airfoil’s drag coefficient in wind tunnel tests. The purpose of the study was to investigate the feasibility of using PIV as an alternative to pressure rake measurements, especially at high angles of attack. The integral momentum concept was applied for determination of fluid drag from experimental low speed wind tunnel data. The drag coefficient was calculated from velocity and pressure rake data for intermediate angles of attack from 5° to 10°. Additionally, the experimental results were compared to panel method results. After validating the procedures at low angles of attack, the drag coefficient was calculated at close to critical angles of attack. The presented study proved that PIV technique can be considered as an attractive alternative for drag coefficient determination of an airfoil.

Open access
Estimation of optical parameters of silicon single crystals with different orientations

Abstract

Optical properties of Si single crystals with different orientations (1 0 0) and (1 1 1) were investigated using spectrophotometric measurements in a spectral range of 200 nm to 2500 nm. The data of optical absorption revealed an indirect allowed transition with energy gap of 1.1 ± 0.025 eV. An anomalous dispersion in refractive index. The normal dispersion of the refractive index was discussed according to Wemple-DiDomenico single oscillator model. The oscillator energy Eo, dispersion energy Ed, high frequency dielectric constant ∈, lattice dielectric constant ∈L and electronic polarizability α e were estimated. The real ∈1 and imaginary ∈2 parts of dielectric constant were also determined.

Open access
Imitation and innovation in business environment

Abstract

The main aim of this article is to demonstrate that in a dynamically changing business environment, an organization should focus on embracing imitation strategies such as a safer form of building up its market position. The author addresses issues of innovation and imitation, provides definitions and defines realistic conditions and advantages of imitation strategies. Innovation does not guarantee a company's market success. The research conducted has shown that imitation is not only a commonly used strategy of creating competitiveness, but it is also the foundation of many firms’ success stories. Innovative imitation, technological diffusion, creative imitation should be treated equally as innovation – as a another development strategy, different form of strategy implementation, assuming less risk and wider market access with less risk and cost.

Open access
Influence analysis of the main types of defects and damages on bearing capacity in reinforced concrete elements and their research methods

Abstract

In current economic trends, changes in construction using are required. It usually leads to changes in value and type of the working load on building structures, with the requirement to rate the technical state and replace or strengthen the elements. An important aspect of determining the residual bearing capacity of damaged bending reinforced concrete elements is the research concerning the influence of difference defects and damages on the change of strength and deformability. In the article main types of damages and defects, methods of studies of damaged reinforced concrete elements and the expediency of usage of this elements are described. However, most methods are suitable only for certain defects and damages due to the large complexity of calculations and the consideration of multifactoriality. Significant complexity of a single method for calculating damaged elements depends on the possible changing stress strain state of an element in combination with certain defects and damages, the presence of a non-complete separation where during loading or alteration of the damaged element the fractions become included in the work, reinforced concrete is the composite material which carrying complexity in calculating the joint work of its components.

Open access
Influence of bath temperature on microstructure and NH3 sensing properties of chemically synthesized CdO thin films

Abstract

Cadmium oxide (CdO) thin films were synthesized using chemical bath deposition (CBD) method from aqueous cadmium nitrate solution. The bath temperatures were maintained at room temperature (25 °C) and at higher temperature (80 °C). The structural studies revealed that the films showed mixed phases of CdO and Cd(OH)2 with hexagonal/monoclinic crystal structure. Annealing treatment removed the hydroxide phase and the films converted into pure CdO with cubic, face centered crystal structure. SEM micrographs of as-deposited films revealed nanowire-like morphology for room temperature deposited films while nanorod-like morphology for high temperature deposited films. However, cube-like morphology was observed after air annealing. Elemental composition was confirmed by EDAX analysis. Band gap energies of the as-deposited films varied over the range of 3 eV to 3.5 eV, whereas the annealed films showed band gap energy variation in the range of 2.2 eV to 2.4 eV. The annealed films were successfully investigated for NH3 sensing at different operating temperatures and at different gas concentrations. The room temperature synthesized film showed a response of 17.3 %, whereas high temperature synthesized film showed a response of 13.5 % at 623 K upon exposure to 24 ppm of NH3.

Open access
LEAN Production issues in the organization of the company - results

Abstract

The key to the functioning of enterprises in today's market is the concept of flexibility, which is mainly associated with adapting to very dynamically changing customer requirements. The basis for this approach is, among others, the realisation of serial production, products created for the customer's order in the quantity and time defined in orders. The LEAN Managemnt and LEAN production approach is a solution dedicated to meeting market assumptions. The LEAN concept, which both in the organization of production and management is focused on dynamic response to changes in the environment. The term LEAN represents numerous improvements to the organization, tools and techniques used to reduce and eliminate individual processes (or parts thereof) that are unnecessary activities. The key to analysing entire processes and defining unnecessary activities is thorough observation and selection of dedicated solutions. In the set of LEAN tools, you can find a lot of possibilities, from organization of a workstation itself, to a thorough quantitative analysis of times and process sequences, from simple facilities to complex technological solutions. The article presents the results of the assembly process analysis, indicates the point of product differentiation (marking for the client) and presents the map of organizational and preparatory activities for this process. The presented results are part of the activities within organization of the LEAN approach, currently having priority for the Research entity organisation improvement team.

Open access
Modelling of electronic and optical properties of Cu2SnS3 quantum dots for optoelectronics applications

Abstract

Copper tin sulfide (Cu2SnS3) is a unique semiconductor, whose nanocrystals have attracted researchers’ attention for its tunable energy bandgap and wavelength in visible and near infrared range. Quantum dots which are fabricated from this material are highly suitable for optoelectronics and solar cell applications. This paper discusses the tunable energy bandgap, exciton Bohr radius and wavelength range of wurtzite structure of Cu2SnS3 quantum dots to assess the opportunity to use them in optoelectronics applications. The considerations show that the mole fraction of copper increases as energy bandgap decreases and tunable energy bandgap of this quantum dot material is inversely proportional to the wavelength.

Open access
Modelling of the Aerospace Structure Demonstrator Subcomponent

Abstract

Carbon-epoxy composite materials, due to their high strength in relation to mass, are increasingly used in the construction of aircraft structures, however, they are susceptible to a number of damages. One of the most common is delamination, which is a serious problem in the context of safe operation of such structures. As part of the TEBUK project, the Institute of Aviation has developed a methodology for forecasting the propagation of delamination. In order to validate the proposed method, an aerial structure demonstrator, modelled on the horizontal stabilizer of the I-23 Manager aircraft, was carried out. However, in order to carry out the validation, it was necessary to "simplify" the demonstrator model. The paper presents a numerical analysis conducted in order to separate from the TEBUK demonstrator model a fragment of the structure, which was used to study the delamination area, as an equivalent of the whole demonstrator. Subcomponent selection was carried out in several stages, narrowing down the analysed area covering delamination in subsequent steps and verifying the compliance of specific parameters with the same parameters obtained in a full demonstrator model. The parameters compared were: energy release rate values on the delamination front line and strain values in the delamination area. The numerical analyses presented in the paper were performed with the use of the MSC.Marc/Mentat calculation package. As a result of the analyses, a fragment of the structure was selected, which allows to significantly reduce the time and labour consumption of the production of the studied object, as well as to facilitate experimental research.

Open access