Guidelines For Selection Of Materials Research Articles

Controlling carrier accumulation and exciton formation in organic light emitting diodes

It is found that the device performance of organic light emitting diodes (OLEDs) can be significantly improved by separating the carrier accumulation zone from the exciton formation interface. The improvement is explained by suppression of exciton quenching caused by accumulated carriers at the exciton formation interface. It is also found that the position of the exciton formation interface in OLEDs correlates well with the interfacial dipole measured using ultraviolet photoelectron spectroscopy at the interface between a hole transport layer and an electron transport layer. The findings of this work provide useful material selection guidelines in designing high performance OLEDs.

Evaluation from the Environmental Conformity of Heat-Resistant Materials

In recent years, a considerable amount of discussion has taken place about the environmental problems on a worldwide scale. Environmental load gases, such as CO2, SOx, and NOx, are generated in the manufacturing process of metal materials, which cause environmental destruction. Thus, the generation of environmental load gases in the process of manufacturing various heat-resistant materials was estimated using an environmental load calculation system developed by Halada et al., and the indicator of the optimum material selection is discussed from the viewpoint of environmental conformity.Research was conducted with regard to the relationship between the environmental load gases of heat-resistant materials, and mechanical properties at high temperature were also investigated. Consequently, it was understood for the heat-resistant materials with many kinds of additional alloy element that there are generating considerable amount of the environmental Consequently, it was understood that heat-resistant materials with many kinds of additional alloy elements generate a considerable amount of environmental load gases during the manufacturing process. Moreover, the guidelines for material selection were established for the design of an apparatus used at high temperature on the basis of the optimal environmental conformity.

Failures of Chemical Injection Points in Upstream Facilities

Chemicals play an important role in the enhancement of oil and gas production and processing. They control corrosion, prevent organic and inorganic deposits, aid in phase separation and control microbial problems. Several factors can have significant impact on the safety, maintenance, operation, and service life of the chemical injection point. Failures encountered in the high pressure retrievable chemical injection points are presented. This paper also provides guidelines for materials selection and design of chemical injection points in upstream facilities.

COLOR IN DENTISTRY: MATCH ME, MATCH ME NOT

This Critical Appraisal focuses on defining color match in dentistry through determination of perceptibility and acceptability visual thresholds. Differences between in vitro and clinical conditions, monochromatic and polychromatic materials, and old and new Commission Internationale de l'Eclairage (International Commission on Illumination; CIE) formulas will be considered. Color difference thresholds can serve as a quality control tool and as guidelines for selection of dental materials and evaluation of their clinical performance.

Material environmental performance index method in green design

Materials selection decision-making in green design takes lifecycle environmental impact of materials as one of the most important objectives.Eco-Indicator'99 is adopted to analyze the holistic lifecycle environmental impact of materials and processes,in order to quantify the decision objective.Environmental performance index is presented based on performance index concept by M.F. Ashby.The environmental performance index analysis model for materials selection is established.The bottom panel design problem for air-conditioner is described.The minimal environmental impact of materials is given based on the stiffness constraint and strength constraint condition.As shown in the case study,the results of the decision-making analysis can provide useful design guidelines for materials selection in green design.

On the stress-assisted magnetic-field-induced phase transformation in Ni2MnGa ferromagnetic shape memory alloys

The effect of magnetic field on the martensitic phase transformation in Ni2MnGa single crystals was investigated under compression. Reversible and one-way stress-assisted field-induced phase transformations were observed under low field magnitudes. The total work output levels achieved during reversible stress-assisted field-induced phase transformation are similar to that attained using field-induced martensite reorientation in NiMnGa magnetic shape memory alloys (MSMAs). However, the actuation stress levels are an order of magnitude higher. Possible magneto-microstructural mechanisms and necessary magnetic and mechanical conditions to accomplish field-induced phase transformation are discussed. A thermodynamical description is introduced to understand magnetic energy contributions to trigger the phase transformation. Materials design and selection guidelines are proposed to search for this new mechanism in other ferromagnetic materials that undergo thermoelastic martensitic phase transformation. The present work output levels achieved in the Ni2MnGa MSMA and the possibility of further increase place MSMAs above many currently available high frequency active materials.

Role of Stabilized and Drainable Bases in Early-Age Cracking on Concrete Airfield Pavements

A strong body of emerging evidence shows that under certain circumstances concrete pavements constructed over certain types of bases have a higher risk of early-age, uncontrolled cracking. In some cases, this has resulted in the removal and replacement of up to 5% to 7% of the total number of slabs paved on a project–an expensive proposition for the stakeholders. An investigation of nearly two dozen airfield pavement sections in the United States identified several plausible factors that act either independently or in concert with other factors and lead to this phenomenon. This study attempted to explain the interaction between factors that trigger slab movements (triggers) and key design, material, and construction factors (variants) that aggravate the impact of these movements on early cracking risk. On the basis of this study, guidelines for design, materials selection, and construction of rigid pavements on stabilized and drainable bases were developed to mitigate the impact of various factors on the early-age cracking phenomenon. Revisions were suggested to the FAA's specifications for lean concrete, cement-treated, and hot-mix asphalt bases. New specifications were developed for permeable bases that balance stability with drainability.

Selection and maintenance of mine haul road wearing course materials

The drive for greater cost efficiencies in surface mining has led to the development of very large off highway trucks currently capable of hauling payloads in excess of 290 tons on mine haul road networks that have historically been designed empirically, relying heavily on local experience. With the trend in increasing truck size, haul road performance has become unpredictable, difficult to manage and costs of both maintaining the road and operating the truck have also increased prohibitively. Most surface mine operators agree that good roads are desirable, but find it difficult to translate this requirement into an effective and responsive road maintenance management system (MMS). The aim of the present paper is to present an overview of the wearing course material selection for mine haul road applications and to recommend appropriate wearing course material selection guidelines. Using the material performance models established, the paper then describes the development of a haul road MMS utilising mine haul truck operating cost models to derive an optimal frequency of road maintenance. Finally, a typical application is presented which illustrates the potential of the technique to manage maintenance as and where needed with resultant reduction in total road user costs and an improvement in service provided for the road user.

The Influence of a Surface Coating on the High-rate Fragmentation of a Ductile Material

A bifurcation analysis of a layered ductile structural element undergoing homogeneous, high-rate extension is presented. Formation of multiple strain localization sites provides a precursor to ductile fragmentation, and the objective of the analysis is to investigate the effect of an added surface layer on resistance of the structural element to fragmentation. The analysis shows that, in addition to dissipating plastic work, the outer layer can increase the total energy dissipation prior to fragmentation by increasing bifurcation strain. The analysis also shows that the strain hardening exponent of the outer layer plays an important role in increasing the bifurcation strain; higher values of hardening exponent result in higher bifurcation strain. Strength and density of the outer layer play a secondary role in increasing bifurcation strain. Once a material with a high hardening exponent is chosen for the outer material, its strength plays an important role in increasing the total dissipated energy. The analysis also reveals that, for certain combinations of strength and hardening exponent of the outer layer, the sandwich structure can dissipate more energy than a homogeneous core structure of the same total thickness and length. This is so even when the outer layer is weaker than the core. Energy dissipated per unit mass can be significantly improved by choosing a softer outer layer which displays high-strain hardening. Thus, the bifurcation analysis presented here provides a quantitative guideline for material selection in designing layered structures optimized for resistance to fragmentation.

Built-in Potential and Open Circuit Voltage of Heterojunction CuIn1-xGaxSe2 Solar Cells

AbstractThe reasons why the open circuit voltage (Voc) of high-x CuIn1-xGaxSe2 (CIGS)/ZnO solar cells remain low are discussed. Here it is shown that the Voc ceiling can be interpreted simply on the basis of a model that the valence-band energy (Ev) of CIGS is almost immovable irrespective of x. When the conduction-band energy (Ec) of ZnO is lower than that of high-x CIGS (DEc<0), the built-in potential (Vbi) of a CIGS/ZnO junction is equivalent to the flat-band potential (Vbi) that arises from the separation between the Fermi energies of the two materials. If the Ev (and therefore the Fermi energy) of p-type CIGS is constant with increasing x, the Vbi and Voc that follows the Vbi remain unchanged since the Fermi energy of ZnO is constant. This unchangeable Voc reduces the conversion efficiency of high-x CIGS cells in cooperation with reduced photocurrents due to a larger bandgap. A positive offset, ΔEc>o gives rise to a photoelectrons barrier in the conduction-band that partially cancels Voc, thus the Voc of a low-x CIGS cell is governed by the Ec of CIGS. Based upon this concept, a material selection guideline is given for the windows and transparent electrodes appropriate for high-x CIGS absorbers-based solar cells.

Effect of band offset on the open circuit voltage of heterojunction CuIn1−xGaxSe2 solar cells

The reasons behind why the theoretically estimated open circuit voltage (Voc) of CuIn1−xGaxSe2 solar cells with large x values has not been realized are discussed. Typically, the reduction in Voc is estimated only on the basis of the conduction-band offset between the absorber and the window material. The importance of the electron affinity difference between the window and the transparent electrode must also be taken into account. Based upon both of these factors, a material selection guideline is reported for the window and the transparent electrode layers suitable for high-x CuIn1−xGaxSe2 absorber-based solar cells.

Materials selection guidelines for membranes that remove CO 2 from gas mixtures

Membrane technology has been investigated for removing CO 2 from mixtures with light gases such as CH 4, N 2 and H 2, and optimal membranes with high CO 2 permeability and high CO 2/light gas selectivity are of great interest. This overview describes the material science approaches to achieve high CO 2 solubility and CO 2/light gas solubility selectivity by introducing polar groups in polymers. CO 2 solubility and CO 2/N 2 solubility selectivity in both liquid solvents and solid polymers containing a variety of polar groups are discussed. Optimum materials appear to have a solubility parameter of about 21.8 MPa 0.5 to achieve both high solubility and high solubility selectivity. However, the introduction of polar groups can decrease CO 2 diffusion coefficients and can make a material more size-selective, which is detrimental to, for example, CO 2/H 2 separation properties. So far, ether oxygens in ethylene oxide (EO) units appear to provide a good balance of CO 2 separation and permeation properties. One drawback of using pure poly(ethylene oxide) (PEO) is its strong tendency to crystallize. This report reviews strategies for incorporating high concentrations of EO units into polymers while suppressing crystallization. A simple model, based on free volume theory, is used to correlate a wide range of CO 2 permeability coefficients in PEO containing materials, and the results are satisfactory, particularly given the simplicity of the model. Crosslinked poly(ethylene glycol) acrylate (XLPEO) containing branches with methoxy end groups exhibit the highest CO 2 permeability (i.e. 570 Barrers) and highest CO 2/H 2 selectivity (i.e. 12) at 35 °C and infinite dilution among all PEO containing materials reported to date. Because such materials do not crystallize at typically accessible temperatures, CO 2/H 2 selectivity can be further improved by decreasing temperature. For example, at an upstream pressure of 4.4 atm, CO 2/H 2 pure gas selectivity reaches a value of 40 at −20 °C while maintaining a CO 2 permeability of 52 Barrers.

Collection development in California Indian tribal libraries

The tribal library is a community center that serves the unique information needs of a Native American community. A tribal library can be a kind of public library for the community, an education and literacy center, as well as an archive that records and preserves the heritage of a tribe. However, tribal libraries typically struggle with inadequate and unstable funding, and in California are often denied the benefits of resource‐sharing agreements within library networks. Tribal library collection development also presents special challenges in terms of identifying, locating and acquiring the materials most needed. This paper provides guidelines for selection of materials, suggestions for sources of Native American materials with an emphasis on California Indians, as well as selected titles for California tribal libraries.

Materials selection guidelines for low thermal conductivity thermal barrier coatings

Materials selection guidelines are desirable in identifying and developing alternative materials for higher-temperature capability thermal barrier coatings. Some relate to identifying candidate materials that exhibit particularly low values of thermal conductivity at high temperatures and others relate to thermodynamic stability in contact with the thermally grown oxides formed on bond-coat alloys and superalloys. By using existing theories of the minimum thermal conductivity, a materials parameter is developed that can be used to identify candidate alternatives to yttria-stabilized zirconia for high-temperature applications.

Weldability of thin sheet metals by small-scale resistance spot welding using high-frequency inverter and capacitor-discharge power supplies

An investigation has been conducted of the weldability of 0.2-mm-thick sheet aluminum, brass, and copper in small-scale resistance spot welding using a high-frequency inverter and a capacitor-discharge power supply. The results have been compared to those of previous investigations using a line-frequency alternating current power supply. The effects of electrode materials and process parameters on joint strength, nugget diameter, weld-metal expulsion and electrode-sheet sticking were studied. This work has also provided practical guidelines for selection of power supplies, process parameters (welding current/pulse energy, welding time/pulse width, electrode forces, etc.) and electrode materials for small-scale resistance spot welding of thin sheet aluminum, brass and copper.

Selection parameters for mine haul road wearing course materials

ABSTRACT The trafficability of unpaved surface mine haul roads is dictated to a large degree through the optimal choice, application and maintenance of locally available wearing course materials. Poor trafficability, or functional performance, results in decreased safety and operational efficiency and increasing road and vehicle maintenance requirements. The aim of this paper is to present an overview of the functional design method for mine haul roads and, through an analysis and quantification of existing wearing course material performance, to recommend appropriate wearing course material selection guidelines. The functional design technique has been applied at a number of mines and is illustrated by an application case study which demonstrates the potential improvements in wearing course trafficability and the associated reduced road maintenance requirements.

Review of solar-energy drying systems III: low temperature air-heating solar collectors for crop drying applications

The efficient design and construction of solar-energy air-heating collectors are critical to the overall performance of the distributed (indirect mode) and mixed-mode designs of either active or passive solar-energy crop dryers. A review of the various designs and the performance evaluation technique of flat- plate solar-energy air-heating collectors for low temperature (i.e. temperature elevations between 10°C–35°C above ambient) solar-energy crop drying applications are presented. The appropriateness of each design and the component materials selection guidelines are highlighted.

Gas separation using polymer membranes: an overview

AbstractThis overview article discusses fundamental principles of gas sorption and transport in rubbery and glassy polymers and material selection guidelines for gas separation membranes. Comparisons between the performance of membrane‐based gas separation systems and more conventional technologies in key commercial applications are provided. Companion articles in this special edition focus on state‐of‐the‐art reviews and descriptions of theoretical and experimental developments important in the technology of gas separations using polymeric membranes.

Performance of construction materials in multiphase liquid/solid flows

The transport of corrosive liquids containing solids, in conventional energy and process technology as, for example, in oil and gas production, places high demands on the selection of materials for plant construction. A discussion on the chemo-mechanical load demonstrates the significance of hydrodynamics in selecting the test method. Choosing a pipe with an abrupt expansion of cross-section as a flow model yields a new method of simulating operation conditions. By subjecting ferrous materials used for hydraulic machinery to representative media from three important industries, a broad spectrum of results can be obtained. Classification of the results leads to four basic types of mass loss behaviour in materials as functions of flow rate. These findings yield guidelines for the selection of materials and the dimensioning of flow equipment.

Diffusion bonding of ceramics

Diffusion bonding of ceramics to ceramics and to metals is reviewed, with primary emphasis on the effects of operational variables on joint strength. These include principal bonding parameters such as temperature, time and pressure. In addition, the influence of atmosphere, mismatch in coefficient of thermal expansion between the joint members, interlayers and surface structure are discussed. The mechanisms involved, i.e. plastic deformation, various forms of diffusion and power law creep, imply that temperature is the most important process parameter. Finally, a survey of variables employed in bonding of different ceramic-metal and ceramic-ceramic joints is included as a guideline for selection of materials and parameters.