Performance Of Different Materials Research Articles

Corrosion behaviour of steel ropes for snow and rockfall barriers

During service, steel ropes can suffer from corrosion, which can reduce their mechanical properties. This degradation is particularly important in the case of structural ropes, or barriers, for snow and rockfall protection because it is not easy to detect any significant degradation over time due to the locations of these structures, which are often difficult to reach. Moreover, rockfall barriers are frequently used in marine environments to reduce the instability of rocks and cliffs, where corrosive attack by chlorides can be very dangerous. This study has characterised the effects on corrosion of the geometrical configurations of the strands and wires in the ropes, and the benefits of zinc and zinc alloy protective coatings on the wires for reducing the degradation of structural ropes. The aim of the research was to obtain information useful for the design of high durability barriers and the selection of an appropriate rope and coating. An approach based on an electrochemical testing has been compared with one based on classical tests involving the exposure of ropes in aggressive environments (salt spray, humidity chamber, etc.) in order to find an electrochemical method able to distinguish the performance of different materials as well as to monitor the corrosion degradation of barriers in the field.Using electrochemical techniques it was possible to quantify the corrosion rate and demonstrate the better behaviour of ropes coated with zinc–aluminum alloys in comparison with pure zinc. Moreover it was possible to evaluate the actual reactive area, and therefore the protective geometry effect when comparing two ropes with different geometries. This approach should be extended to further kinds of ropes in order to improve basic corrosion understanding of this important structural component.

Characterization of Submillimeter Wave Absorbers from 200–600 GHz

This paper presents measurements of both specular and non-specular scattering from several submillimeter wave absorber materials designed for antenna testing and from low-cost carpet materials. The frequency range is 200–600 GHz in specular scattering, and 300–400 GHz in non-specular scattering measurements. The constructed bistatic test bench allows testing of the full continuous angular range of 0°–90°. The measurement results show large differences in performance of different materials. It is shown that reflectivities below −50 dB over limited angular ranges are possible with a correct alignment of the material. Also, low-cost carpet materials have lower than −15 dB reflectivities in most angles, and may be useful in non-critical parts of the antenna test range. The results can be used to optimise the absorber placement inside an antenna range, concerning both best performance and lowest cost.

Optimization of the fabrication of sealed capacitive transducers using surface micromachining

Processing issues for the fabrication of capacitive micromachined ultrasonic transducer (cMUT) arrays have been studied using surface micromachining. This work focuses on the critical steps of process fabrication such as membrane formation, sacrificial layer properties and vacuum sealing performance of cavity. We describe a four-mask process for the realization of sealed cMUT. We demonstrate that the use of a sacrificial layer with a columnar structure gives a fast etching rate (29 nm s−1) in a buffered hydrofluoric acid solution. The mechanical stress of LPCVD silicon nitride (SiNx), used as membrane, was evaluated. We compared the vacuum sealing performance of different materials in order to find the best material in terms of lateral deposition inside the cavity. Functional transducers have been obtained. We proposed an electrical test in order to evaluate the vacuum sealing of the cavity based on the collapse voltage determination. Laser interference measurements were used to characterize the dynamic displacement of the membrane.

Quantum well photoconductors in infrared detector technology

The paper compares the achievements of quantum well infrared photodetector (QWIP) technology with those of competitive technologies, with the emphasis on the material properties, device structure, and their impact on focal plane array (FPA) performance. Special attention is paid to two competitive technologies, QWIP and HgCdTe, in the long-wavelength IR (LWIR) and very-long-wavelength IR (VLWIR) spectral ranges. Because so far, the dialogue between the QWIP and HgCdTe communities is limited, the paper attempts to settle the main issues of both technologies. Such an approach, however, requires the presentation of fundamental limits to the different types of detectors, which is made at the beginning. To write the paper more clearly for readers, many details are included in the Appendix. In comparative studies both photon and thermal detectors are considered. Emphasis is placed on photon detectors. In this group one may distinguish HgCdTe photodiodes, InSb photodiodes, and doped silicon detectors. The potential performance of different materials as infrared detectors is examined utilizing the α/G ratio, where α is the absorption coefficient and G is the thermal generation rate. It is demonstrated that LWIR QWIP’s cannot compete with HgCdTe photodiodes as single devices, especially at higher operating temperatures (>70 K). This is due to the fundamental limitations associated with intersubband transitions. The advantage of HgCdTe is, however, less distinct at temperatures lower than 50 K due to problems inherent in the HgCdTe material (p-type doping, Shockley–Read recombination, trap-assisted tunneling, surface and interface instabilities). Even though QWIP is a photoconductor, several of its properties, such as high impedance, fast response time, long integration time, and low power consumption, comply well with the requirements imposed on the fabrication of large FPA’s. Due to a high material quality at low temperatures, QWIP has potential advantages over HgCdTe in the area of VLWIR FPA applications in terms of array size, uniformity, yield, and cost of the systems. The performance figures of merit of state-of-the-art QWIP and HgCdTe FPA’s are similar because the main limitations come from the readout circuits. Performance is, however, achieved with very different integration times. The choice of the best technology is therefore driven by the specific needs of a system. In the case of readout-limited detectors a low photoconductive gain increases the signal-to-noise ratio and a QWIP FPA can have a better noise equivalent difference temperature than an HgCdTe FPA with a charge well of similar size. Both HgCdTe photodiodes and QWIP’s offer multicolor capability in the MWIR and LWIR range. Powerful possibilities offered by QWIP technology are associated with VLWIR FPA applications and with multicolor detection. The intrinsic advantage of QWIP’s in this niche is due to the relative ease of growing multicolor structures with a very low defect density.

Modelling of Grinding in an Air Classifier Mill Based on a Fundamental Material Function

An approach to quantifying the impact grinding performance of different materials is presented. Based on a dimensional analysis and on fracture mechanical considerations, two material parameters, fMat. and Wm,min, are derived theoretically. fMat. characterises the resistance of particulate material against fracture during impact comminution. Wm,min gives the mass-specific energy which a particle can absorb without fracture. Using this approach, various materials over a wide size range, e.g. different polymers, crystalline substances, glass and limestone, can be characterised quantitatively. The derived material parameters are applied to the systematic modelling of grinding in impact mills. A population balance model is presented and the results of the simulation for an air classifier mill are shown. The developed model permits a clear separation of the influence of material properties, mill-specific features and operating conditions, thus enabling a deeper understanding of the impact grinding process.

QUANTUM WELL INFRARED PHOTOCONDUCTORS IN INFRARED DETECTORS TECHNOLOGY

Investigations of the performance of quantum well infrared photodetectors (QWIPs) as compared to other types of semiconductor infrared (IR) detectors are presented. In comparative studies both photon and thermal detectors are considered. More attention is paid to photon detectors and between them we can distinguish: HgCdTe photodiodes, InSb photodiodes, Schottky barrier photoemissive detectors, and doped silicon detectors. Special attention has been paid to competitive technologies in long wavelength IR (LWIR) and very LWIR (VLWIR) spectral ranges with emphasis on the material properties, device structure, and their impact on FPA performance. The potential performance of different materials as infrared detectors is examined utilizing the α/G ratio, where α is the absorption coefficient and G is the thermal generation. From the discussion results, LWIR QWIP cannot compete with HgCdTe photodiode as the single device especially at higher temperature operation(> 70 K) due to fundamental limitations associated with intersubband transitions. However, the advantage of HgCdTe is less distinct in the temperature range below 50 K due to problems involved in the HgCdTe material (p-type doping, Shockley–Read recombination, trap-assisted tunneling, surface and interface instabilities). Even though the QWIP is a photoconductor, several its properties such as high impedance, fast response time, long integration time, and low power consumption, well comply with requirements for large FPAs fabrication. Due to the high material quality at low temperature, QWIP has potential advantages over HgCdTe for VLWIR FPA applications in terms of the array size, uniformity, yield and cost of the systems. Both HgCdTe photodiodes and quantum well infrared photodetectors offer multicolor capability in the MWIR and LWIR range. Powerful possibilities of QWIP technology are connected with VLWIR FPA applications and with multicolor detection. QWIP FPAs combine the advantages of PtSi Schottky barrier arrays (high uniformity, high yield, radiation hardness, large arrays, lower cost) with the advantages of HgCdTe (high quantum efficiency and long wavelength response).

Wear rates and specific energies of some ceramic, cermet and metallic coatings determined in the Coriolis erosion tester

A series of ceramic, cermet and metallic coatings of known resistance to slurry jet erosion has been subjected to sliding bed wear using a 10 wt.% aqueous slurry of 80 grit crushed alumina particles in the Coriolis erosion tester. Wear scar cross-sections have been measured and specific energies for material removal calculated for these coatings as well as for some bulk solid materials for reference purposes. Thermal-sprayed coatings included high velocity oxygen-fuel (HVOF)-sprayed WC–12Co, Cr 3C 2/NiCr and 316L steel, plasma-sprayed (PS) Al 2O 3 and Al 2O 3/TiO 2 and arc-sprayed 440C steel. Pulsed laser clad coatings of two FeCrB based alloys were also tested. The Coriolis erosion tester consists of a 150 mm diameter rotor with a diametral passage in which a flat plate specimen is located on each side, equidistant from the rotation centre. Slurry, delivered to a central orifice, is constrained to flow outwards through the channel as the rotor is turned at speeds up to 7000 rpm, the erodent particles being pressed onto the test specimen surface by the Coriolis force. The cross-sectional area of the scar is measured as a function of distance from the rotation centre and, through a summation of an expression for frictional work done, a value for the specific energy for material removal (essentially a measure of erosion resistance) is calculated. The test method seeks to simulate the wear environment in slurry pumps and cyclones in which particles move rapidly over the test surface either singly or in a bed. The wear rate of a WC–Co cermet was found to be ∼1000 times lower than that of 316L stainless steel. The remarkable ability of the Coriolis erosion tester to discriminate in the erosion performance of different materials is discussed in terms of particle trajectories and the probable wear mechanism. Coriolis test results are compared with those for slurry jet erosion and the applicability of the two tests for erosion resistance ranking of hard coating materials is discussed.

Modelling slurry particle dynamics in the Coriolis erosion tester

The Coriolis erosion tester consists of a rotor with a diametrical passage in which two flat specimens are located equidistant from the centre. At high rotation speeds, slurry flows outwards from the centre by centrifugal force while the erodent particles are directed towards the specimen surfaces by the Coriolis force. This test mode offers a quick, simple and reproducible means of simulating the wear environment in slurry pumps and cyclones in which particles move rapidly over component surfaces either singly or in a bed, and clearly distinguishes between the erosion performance of different materials. A model is presented to describe particle trajectories and particle impact velocities quantitatively for both dilute slurries and those with relatively high solids concentrations flowing through the Coriolis erosion tester. Experiments using either angular alumina particles or glass beads suspended in water and a range of both coatings and solid specimens have provided information on damage modes and erosion resistance which shows that the predominant particle–test surface interaction in the Coriolis erosion tester is low-angle impact. The influence of rotational speed, particle size, particle density and concentration on impact angle and impact velocity are predicted by the model and these are consistent with observed wear patterns. The erosion resistance of a material depends critically on its elastic deformation, plastic deformation and fracture properties, and this material response is interpreted in terms of contact mechanics.

New fabrication method for nickel metal hydride electrodes by sintering alloy onto a foam substrate

A new method for fabricating nickel metal hydride electrodes has been investigated. A slurry consisting of hydriding alloy mixed with nickel powder was pasted onto nickel foam substrates. These were then roller pressed to 1.2 mm thickness and sintered in an inert atmosphere for 10 min at 800°C. The role of the different processing steps as well as the performance of different materials has been characterized. Initial cycles give an energy density comparable to that obtained with conventional methods and a much higher fast rate discharge capacity.

Continued Development of the Nimbus/University of Pittsburgh (UOP) Axial Flow Left Ventricular Assist System

Nimbus and the University of Pittsburgh (UOP) have continued the development of a totally implanted axial flow blood pump under the National Institutes of Health (NIH) Innovative Ventricular Assist System (IVAS) program. This 62 cc device has an overall length of 84 mm and an outer diameter of 34.5 mm. The inner diameter of the blood pump is 12 mm. It is being designed to be a totally implanted permanent device. A key achievement during the past year was the completion of the Model 2 pump design. Ten of these pumps have been fabricated and are being used to conduct in vitro and in vivo experiments to evaluate the performance of different materials and hydraulic components. Efforts for optimizing the closed loop speed control have continued using mathematical modeling, computer simulations, and in vitro and in vivo testing. New hydraulic blade designs have been tested using computational fluid dynamics (CFD) and flow visualization. A second generation motor was designed with improved efficiency. To support the new motor, a new motor controller fabricated as a surface mount PC board has been completed. The program is now operating under a formal QA system.

Optical absorption, absorption saturation and a useful figure of merit for chromium doped glasses

Chromium-doped aluminate and silicate glasses have been prepared in both inert and oxidizing atmospheres. Spectroscopic measurements indicate that some of the glasses incorporated the chromium ion in the +4 valence state. These Cr 4+ doped glasses exhibit a broad spectral emission covering the communication window and the eye safe region around 1.5 μm. Ten glass samples and two crystalline materials, were used to study the phenomenon of saturable absorption in the Cr 4+ ion. A figure of merit was defined to compare the performance of different materials as saturable absorbers. The preparing conditions that lead to a glass saturable absorber with better figure of merit have been investigated. A Q-switched Cr:LiSAF laser was used for the saturable absorption measurements.

Development and characterisation of electrochromic devices on polymeric substrates

The development of full solid-state electrochromic (EC) devices on polymeric substrate is underway within a CEC BRITE-EURAM project (Project “FREDOPS”, BE-4137) carried out by four industries, two universities and two research centers from Belgium, Denmark, France, and Italy. The specific goal of this project is to develop a Fast Response Electrochromic Device On Polymeric Substrate (FREDOPS); in order to satisfy the required range of specifications in terms of fast response, long term performance and high contrast ratio, several systems based on different materials have been tested. The full cells consist of an electrochromic material layer and a counter electrode, inserted between two PET/ITO layers and separated by a polymeric electrolyte. Different types of polymeric electrolytes, counter electrodes and electrochromic layers have been developed, studied and checked. Full devices have been assembled using different combinations. Voltammetric and spectrophotometric measurements have been executed to check the electrochromic behaviour of the developed layers in half and full cells. Comparison of the electrochromic performances of different materials based cells has led to the rejection of several solutions due to poor performance and incompatibilities between layers. Considering that the electrochromic devices are finalised for different uses (window, sunroof,…), some performance specifications for each application are defined. A testing bench for cycling and ageing was developed. The present paper discusses these results in order to indicate the best performance.

Performance of materials used for the venting system in WED's desalination plants (MSF)

The removal of non-condensable gasses (nitrogen, oxygen and carbon dioxide) is vital for the successful operation of all thermal desalination plants. Every plant is equipped with means for removing them. However, the majority of MSF evaporators use steam ejector connected to a condenser to release them. The nature of these gases is very aggressive because the Arabian Gulf water contains in addition to nitrogen, oxygen and carbon dioxide, the bromine gas [3–6] which can cause severe localized corrosion problems with conventional stainless steels. Such corrosion had been reported in some MSF plants [1–2]. The present investigation surveys the performance of different materials used for venting systems over the last 15 years in WED's MSF plants in different places in the Emirate of Abu Dhabi.

Materials selection for semiconductor gas sensors

Semiconducting oxides are employed as gas-sensitive resistors both for monitoring changes in oxygen partial pressure and for monitoring small concentrations of impurity gases in air. A review of the performance of different materials in this function focuses attention on the mechanisms by which responses are generated and provides an indication of the ultimate selectivity that is likely to be achievable between gases.

Studies on materials for traps for spiny lobsters

Studies were conducted along the south-west coast of India in order to identify suitable materials and preservative treatments for the fabrication of spiny-lobster traps. Traps were fabricated in different designs using different materials, such as bamboo splinters, coconut leaf stalk fibres, wood, polyethylene twines, Polystrap binding tape, mild steel rod, welded mesh, chicken wire netting and galvanised iron wire. As measures of preservation, the traps fabricated of iron materials were plastic-coated or painted with anti-corrosive paints, and bamboo traps were treated with ASCU (arsenic-copper-chrome composition) or creosote. To assess the performance of different materials and to recommend suitable materials and protective coatings, the traps were subjected to experimental fishing using an indigenous trap as a control. The results show that bamboo traps are weak and fragile and wooden traps are unwieldy and so are not favoured. Metal traps made of mild steel rods and welded mesh covered by complete plastic coating were found to perform efficiently and last longer.

Smile—A computer program for evaluating the lifetime of fusion reactor structural components

The choice of materials for one of the most critical structural components of fusion reactors, such as the first wall, is the result of a trade-off between different and often conflicting requirements. The problem of checking whether or not a material can withstand the design operating conditions requires taking into account the complete set of relevant properties. The programme SMILE, based on a simple one-dimensional model, was developed as part of a broader experimental activity focused on the first wall design problem of the NET/INTOR reactor. The purpose of the programme is: (i) to assess the behavior of the candidate structural materials; (ii) to identify the limiting failure mechanism and the critical value of the property involved; and (iii) to provide a reference procedure for evaluating the performance of different materials and the effects of the different operating conditions.

SMILE—A computer program for evaluating the lifetime of fusion reactor structural components

The choice of materials for one of the most critical structural components of fusion reactors, such as the first wall, is the result of a trade-off between different and often conflicting requirements. The problem of checking whether or not a material can withstand the design operating conditions requires taking into account the complete set of relevant properties. The programme SMILE, based on a simple one-dimensional model, was developed as part of a broader experimental activity focused on the first wall design problem of the NET/INTOR reactor. The purpose of the programme is: (i) to assess the behavior of the candidate structural materials; (ii) to identify the limiting failure mechanism and the critical value of the property involved; and (iii) to provide a reference procedure for evaluating the performance of different materials and the effects of the different operating conditions.

The noisiness of materials for fixed resistors

Current noise in fixed resistors is usually expressed empirically in terms of current and resistance, but performance of different materials from which resistors can be constructed must be specified in terms of current density, resistivity and geometry. It is argued from the theory of dimensions that there should be a relationship between the index of frequency dependence and the index of resistance dependence. It is not clear how this can be associated with an experimentally observed relationship between frequency index and voltage coefficient. Secondary effects arise from any local concentration of current, and the order of magnitude of the associated temperature rise can be estimated from the potential difference across the contact by Holm's theory of point contacts.