Applicable Temperature Range Research Articles

PO2 stability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ

ABSTRACTThe mixed-conducting perovskite oxide Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), given its outstanding oxygen ionic and electronic transport properties, is considered a promising material composition for oxygen transport membranes (OTM) operated at high temperatures.Its long-term stability under operating conditions is, however, still an important issue. Although the incompatibility of BSCF with CO2-containing atmospheres can be avoided by appropriate means (oxyfuel processes in the absence of carbon dioxide), the thermal as well as the chemical stability of BSCF itself are still under thorough investigation.This work is focused on the stability of BSCF in the targeted temperature range for OTM applications (700…900 °C) and in atmospheres with low oxygen contents. Previous studies in literature suggest limited chemical stability below oxygen partial pressures pO2 of around 10-6 bar.By using a coulometric titration method based on a zirconia “oxygen pump” setup, precise control of the oxygen partial pressure pO2 between 1 bar and 10-18 bar was facilitated. Combining electrical measurements on dense ceramic bulk samples performed as a function of pO2 with an XRD phase composition study of single phase BSCF powders subjected to various pO2 treatments, an assessment of the chemical stability of BSCF is facilitated as a function of oxygen partial pressure. It could thus be shown that the pO2 stability limit is considerably lower than previously assumed in literature.

Recent developments in the preparation of nano-gold composite coatings

New possibilities in the design of gold-containing electrochemical coating systems for electronic applications are given by the incorporation of gold-nanoparticles in metal-matrix-systems. The major problem for the application of nanoparticles is the strong agglomeration of the particles in the electrolyte solutions, preventing the incorporation of nanoscaled dispersants.A complete new concept for the deposition of nano dispersion layers, overcoming this agglomeration challenge, is the application of core shell systems. Using these systems, it becomes possible for the first time to incorporate metal nanoparticles into electrodeposited metal layers to form metal nanoparticle metal matrix systems (MNP-MMS). The advantage of such layers is to form nanocomposite materials far away from the thermodynamic equilibrium. Especially for the combination of gold nanoparticles with a nickel matrix, a way is shown for the manufacturing of temperature-stable nanocomposite structures, because at least in the temperature range of electronic applications no loss of the dispersive character by diffusion processes is expected. By incorporating the precious metal material into the nickel matrix as the main electrodeposit, and reducing the top gold layer thickness, a possible way of reducing the gold consumption and an economic use of gold resources is shown.

High Power Characteristics of (Ca,Ba)TiO3 Piezoelectric Ceramics with High Mechanical Quality Factor

(Ca0.1Ba0.9)TiO3 + x wt % MnCO3 [x=0, 0.2, 0.5, 1.0] (CBT-Mx) ceramics were prepared by conventional sintering, and their dielectric and piezoelectric properties were measured. The mechanical quality factor (Qm) of CBT was markedly enhanced by Mn addition and reached 2400 when x=0.5. The dielectric loss tangent (tan δ) was 0.0023 at room temperature. The Curie temperature (TC) was 133 °C. Then, the high power characteristics of CBT-M0.5 were investigated. The maximum vibration velocity (v0) of CBT-M0.5 was 1.1 m/s and was higher than that of Pb(Zr,Ti)O3-based ceramics (Hard-PZT). The heat generation of CBT-M0.5 was smaller than that of Hard-PZT at the same v0. The resonant frequency (fr) of CBT-M0.5 was stable up to v0 of 1.1 m/s. Additionally, the temperature stability of fr was investigated in the practical application temperature range (from -20 to 80 °C). The amount of change in fr for CBT-M0.5 was larger than that for Hard-PZT below 10 °C.

Anthraquinone-Based Discotic Liquid Crystals

The syntheses of six room-temperature discotic liquid crystals based on an alkoxy-anthraquinone (AQ) framework is described. Differential scanning calorimetry, X-ray diffraction (XRD), and cross-polarized microscopy were used to identify phases and confirm phase-transition temperatures. Cross-polarized microscopy results suggest columnar discotic structures at room temperature. However, the AQ derivatives also undergo mesophase-to-mesophase transitions, which are attributed to rectangular- to hexagonal-columnar discotic transitions based on XRD analysis. Furthermore, some of the compounds display remarkable liquid crystalline phase stability that spans from -50 to 150 degrees C, a useful temperature range for organic materials applications. The different AQ derivatives did not exhibit electronic perturbations, as all compounds have absorption onsets of approximately 400 nm. Finally, solution cyclic voltammetry of the AQ derivatives was carried out to determine the redox potentials, diffusion coefficients, and electron transfer rate constants. All AQ derivatives had E(1/2) values that ranged between -1.52 and -1.70 V vs Fc/Fc(+). Diffusion coefficients and electron transfer rates for all AQ derivatives ranged between 0.4 and 7.1 x 10(-6) cm(2) x s(-1) and 0.9 and 5.2 x 10(-3) cm x s(-1), respectively.

Fault-tolerant silicone dielectric elastomers

Soft silicone films have garnered a great deal of interest for use in dielectric elastomer transducers due to their excellent properties, including high elongation to rupture, low viscoelasticity, and broad application temperature range. However, silicone films generally have higher stiffness and lower dielectric strength than VHB acrylic elastomers, which limits the achievable actuation strain. Devices based on silicone dielectric elastomers always experience high rates of premature dielectric failure when operated at high strains. The premature failure is characterized by the loss of functionality or mechanical rupture of the material when operated below the material's dielectric strength and elongation to rupture. The use is reported of ultrathin coatings of single-walled carbon nanotubes (SWNTs) as the compliant electrodes, which can overcome the issue of premature failure. The self-clearing of the SWNT electrodes in the event of localized dielectric breakdown improves the apparent dielectric strength of the material by isolating the regions of reduced dielectric strength. The actuators may be operated at higher than 50% area strain with reasonably long lifetimes. High strains were measured between −40 and 80°C and in a broad frequency range up to 100 Hz. The fault tolerance introduced by the SWNT electrodes should broaden the application scope of silicone dielectric elastomers.

Temperature dependence of pin solar cell parameters with intrinsic layers made of pm-Si:H and low crystalline volume fraction μc-Si:H

A comparison of the temperature dependence of the IV characteristics parameters of hydrogenated silicon pin solar cells with intrinsic layers made of polymorphous silicon (pm-Si:H) and of μc-Si:H with low crystalline volume fraction has been performed. When using pm-Si:H, higher efficiency and higher filling factors are achieved over a wide temperature range. Diode quality factors of both types of cells show similar temperature dependence. Recombination processes over the whole intrinsic layer dominates the forward current. A change of the cell parameters under illumination is also observed. The transport mechanism of both cells is similar in the temperature range that is important for most applications. Due to its optical and transport properties, pm-Si:H poses a very interesting alternative to μc-Si:H and a-Si:H in the temperature range of normal terrestrial applications.

On the applicability of the equipartition theorem

Generalization of the equipartition theorem is presented for a broad range of potentials U(x) with quadratic minimum. It is shown, that the equipartition of energy in its standard form appears at the low temperatures limit. For potentials demonstrating the quadratic behavior for large displacements from the equilibrium the equipartition holds also in the high temperature limit. The temperature range of applicability of the equipartition theorem for the potential U = ax2 + bx4 was established.

Overview of High-Molecular-Weight Methacrylate for Sealing Cracks in Concrete Bridge Decks

Cracking in concrete bridge decks is widely regarded as a long-term durability and maintenance problem that requires attention. These cracks propagate through the deck and allow rapid ingress of moisture and chlorides into the concrete interior, leading to excessive deterioration from rebar corrosion. In California, high-molecular-weight methacrylate (HMWM) is frequently used as a crack sealer, with millions of dollars spent annually on maintenance applications of methacrylate on state-owned bridges. The work presented reviews previous research regarding the effectiveness of concrete bridge deck sealers and the results of a nationwide survey investigating the effectiveness and state of practice of using methacrylate as a crack and surface sealer. Although a wide range of application temperatures was reported in the literature, application temperatures between 7°C and 29°C are generally recommended. Cracks should be sealed as soon as possible to ensure that chloride concentrations do not reach the corrosion threshold value. For old decks, careful attention should be paid to the preparation method and cleanliness of both the deck surface and cracks. For areas not subjected to deicing chemicals and chloride-laden environments, HMWM can nearly restore the full bond and flexural strength if the cracks are narrow and free of contaminants.

Consequences of the peculiar intrinsic properties of [formula omitted] on its macroscopic current flow

The influence of two important features of magnesium diboride on the macroscopic transport properties of polycrystalline MgB2 is discussed in the framework of a percolation model. While two band superconductivity does not have significant consequences in the field and temperature range of possible power applications, the opposite is true for the anisotropy of the upper critical field. The field dependence of the critical current densities strongly increases and the macroscopic supercurrents disappear well below the apparent upper critical field. The common scaling laws for the field dependence of the volume pinning force are altered and Kramer’s plot is no longer linear, although grain boundary pinning dominates in nearly all polycrystalline MgB2 conductors. In contrast to the conventional superconductors NbTi and Nb3Sn, a significant critical current anisotropy can be induced by the preparation technique of MgB2 tapes.

A BRIEF REVIEW OF Sn2P2(SexS1-x)6 CRYSTALLINE FAMILY PROPERTIES

The Sn2P2S6 compound is a member of a large isomorphous ferroelectric family. This compound exhibits a strong piezoelectric effect, combining large photorefractive coefficients with a fast holographic response, a high pyroelectric coefficient and a bulk piezoelectric modulus, which make them promising materials in a wide temperature and pressure range for optical and acoustical applications and also interesting materials for sensor applications in modern electronics.

Void Formation Mechanism of Flip Chip in Package Using No-Flow Underfill

This paper investigates the void formation mechanism induced by chemical interaction between eutectic solder (Sn63/Pb37) wetting and no-flow underfill material curing during flip chip in package assembly. During the process, low weight molecular components, such as fluxing agents and water molecules, could be induced by the chemical interaction between solder wetting and underfill curing when these components are heated to melt and cure, respectively. The low weight molecular components become volatile with exposure to temperatures above their boiling points; this was found to be the main source of the extensively formed underfill voiding. This mechanism of chemically and thermally induced voids was explained using void formation study, differential scanning calorimetry thermogram comparison, and gas chromatography and mass spectroscopy chemical composition identification on the suggested chemical reaction formula. This finding can enhance understanding of the mechanism that drives no-flow underfill voiding and can develop a void-free flip chip assembly process using no-flow underfill material for cost effective and high performance electronics packaging applications. Furthermore, this study provides the design guideline to develop an advanced no-flow underfill having high performance at high temperature range for the lead-free application.

Influence of temperature on the electrorheological response of dielectric suspensions based on a water-containing filler

A study is made of the influence of temperature on the rheological properties of electrorheological fluids containing hydrated alumina in the form of pseudoboemite. It is shown experimentally that such electrorheological fluids possess thermal stability, preserving high indices of electrorheological activity (ER activity) up to 120°C. The use of pseudoboemite as a filler of electrorheological fluids will make it possible to ensure efficient operation of electrically controlled hydraulic devices with an extended temperature range of application.

Development of an amperometric micro-biodetector for pesticide monitoring and detection

An enzyme-based electrochemical biodetection system and its corresponding hand-held prototype were developed to monitor pesticide concentrations. By combining biocatalyzation and electrochemistry, the reaction rate of bioredox was transformed into a current signal. The relationship between pesticide concentration and current inhibition rate could therefore be deduced, and pesticide concentration could be determined from output current signals. Different methods were tried to immobilize enzyme onto the surfaces of platinum electrode and screen-printed carbon electrode (SPE). The best performance was obtained by electropolymerization, which provided sensitivity two times higher than the enzyme under a suspended condition. In order to increase sensitivity, the electron mediator, i.e. Prussian Blue (PB) “KFe IIIFe II(CN) 6 −” was pre-coated onto the electrode surface and gold nanoparticles were intermingled during enzyme immobilization. The system, therefore, had a detection limit as low as 1 μg/L with a pesticide incubation time of 10 min. Experimental data indicate that pH value, temperature, heavy metal ions and organic solvents exerted influences on sensor performance. Even though the applicable temperature range could be expanded to be 10–40 °C via compensation equations, a proper pretreatment was necessary to eliminate the effect of heavy metal ions, especially for copper ions. This micro-biodetector was successfully applied to determine the pesticide residue in tomato juice, and was proven to be serviceable as a general commodity for household use.

Oxidation and reduction behavior of pure indium

Fundamental knowledge on the oxidation behavior of pure indium, commonly used as a low-temperature, fluxless soldering material in micro-electro-mechanical system (MEMS) devices, is of importance as it influences the solder joint reliability. A thermodynamic model of the oxidation and reduction behavior of indium is developed by constructing an Ellingham diagram, and by using H2(g)reactions. Partial pressure (p) of H2O was shown to be the critical parameter in creating a reducing environment in the applicable solder reflow temperature range. Verification of the thermodynamic models was then carried out through heating and melting of indium in controlled glove box environments by adjustingp(H2)/p(H2O). The nanometer scale thickness of the oxide layer grown on indium was measured by a spectroscopic ellipsometer. The growth mechanism for oxidation in air below 220 °C follows Uhlig's logarithmic law where electron transport is the rate-controlling mechanism, implying that there is an incubation period for the onset of initial oxidation. Its activation energy was found to be 0.65 eV.

Applicability of moiré deflection tomography for diagnosing arc plasmas

The argon arc plasma whose central temperature, 1.90x10(4) K, is used as a practical example for an experiment to research the applicability of moiré deflection tomography in arc plasma flow-field diagnosis. The experimental result indicates that moiré deflection of the measured argon arc plasma is very small, even smaller than that of a common flame with the maximal temperature of nearly 1.80x10(3) K. The refractive-index gradient in moiré deflection tomography mainly contributes to the temperature gradient in essence when the probe wavelength and pressure are certain in plasma diagnosis. The applicable temperature ranges of moiré deflection tomography in the argon arc plasma diagnosis are given with the probe wavelength 532 nm at 1 atm in certain measuring error requirements. In a word, the applicable temperature range of moiré deflection tomography for arc plasma diagnosis is intimately related to the probe wavelength and the practical measuring requirements.

Microstructure and mechanical properties of the intermetallic alloy Ti-45Al-6(Nb, Mo)-0.2B

The microstructure and tensile properties of the intermetallic γ-TiAl + α2-Ti3Al alloy Ti-45Al-6(Nb, Mo)-0.2B are studied after various heat and thermomechanical treatments. Its cast state is found to be characterized by a homogeneous, relatively fine-grained structure in the cases of both a model 30-g ingot and a bulk laboratory ∅120 × 180-mm ingot. The cast material subjected to heat treatment with furnace cooling and aging at T = 1100°C exhibits strength properties at T = 20–900°C that are relatively high for cast γ + α2 alloys. Due to the rational choice of the alloy, its thermomechanical treatment is facilitated, a fine-grained structure can easily be formed upon hot deformation, and a superplastic state with elongations in the test-temperature range T = 900–1000°C that are very large for γ + α2 alloys is reached. However, the high contents of niobium and molybdenum in the Ti-45Al-6(Nb, Mo)-0.2B alloy hinder the formation of an equilibrium lamellar structure upon heat treatment, and an increase in the aging temperature to T = 1100°C leads to the development of the α2 → s(B2) phase transformation, which makes it impossible to reach a high level of the mechanical properties in the temperature range of the potential application of γ + α2 alloys. Our study has revealed that the compositions of the γ + α2 alloys need further optimization of the way of refining the niobium and molybdenum contents.

Increase in the refractoriness of carbon composite materials with use of heat-resistant ceramic coatings

The main directions are considered for increasing the refractoriness of structural graphite materials, carbon-carbon composite materials (CCCM), and structures made of them. Practical examples are proposed for increasing the refractoriness of materials based on carbon in the application temperature range from 1200 to 1700°C. Results are provided for experimental study of four types of increased refractoriness. It is demonstrated that the contemporary direction of domestic work for increasing the refractoriness of structural graphite materials and CCCM agrees on the whole with a series of overseas achievements in this field.

A poly(ethylene glycol)-based smart phase change material

A shape memory thermoplastic polyurethane (PU) as a phase change material (PCM) was synthesized by employing poly(ethylene glycol) (PEG) as the soft segment via bulk polymerization. Its phase separation structure, crystalline morphology, phase change behaviors, dynamic mechanical properties and melt-processing ability were investigated using polarizing optical microscopy, atomic force microscopy, differential scanning calorimetry, dynamic mechanical analysis, thermogravimetry and melt flow index. A well-formed phase separation structure in the PEG-based polyurethane (PEGPU) was found which accounts for most of the material phase change properties and shape memory effect. The PEG soft segment phase transition between crystalline and amorphous states resulted in heat storage and release of the PEGPU. Due to the hydrogen bonded hard segment phase serving as “physical cross-linking” restricted the free movement of the soft segments, at temperature above the PEG phase melting transition, the PEGPU was still solid. The differential scanning calorimetry results indicated that the PEGPU had high latent heat storage capacity of more than 100 J/g. The dynamic mechanical analysis results showed that it had a plateau elastic modulus about 40 MPa in the region above the PEG phase melting transition while below 150 °C. The thermogravimetry results suggested that the PEGPU had a much broader applicable temperature range compared with pure PEG. The melt flow index results indicated that the material had a good melt-processing ability. The material shape fixity ratio was more than 84% and shape recovery ratio up to 93.7% obtained from thermomechanical cyclic tensile testing.

A temperature-regulating fiber made of PEG-based smart copolymer

A poly(ethylene glycol) (PEG)-based thermoplastic shape memory polyurethane was synthesized via bulk polymerization. The corresponding fiber, as a temperature-regulating fiber, was fabricated via melt spinning. The prepared 100-dtex fiber had a tenacity of 0.7 cN/dtex and breaking elongation of about 488%. The fiber's phase change behaviors, crystalline morphology, dynamic mechanical properties, and temperature-resistant performance were investigated using polarizing optical microscopy, differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetry. The PEG soft segment phase transfer between crystalline and amorphous states resulted in heat storage and release. The hydrogen-bonded hard segment phase, serving as ‘physical cross-links,’ restricted the free movement of soft segments, hence at temperatures above the PEG phase melting transition, the fiber still possessed certain mechanical strength. The differential scanning calorimetry results indicated that the fiber had large latent heat-storage capacity of about 100 J/g with a crystallizing temperature of 20.9 °C and a melting temperature of 44.7 °C. The dynamic mechanical analysis results showed that the fiber has a plateau elastic modulus in the region above the PEG phase melting transition and below 160 °C. The thermogravimetry results suggested that the fiber had a much broader applicable temperature range compared to pure PEG. The thermo-mechanical cyclic tensile testing results showed that the fiber had good shape memory effect with the shape fixity ratio more than 85.8% and the recovery ratio above 95.4%.

Thermally stable nanostructured materials from severe plastic deformation of precipitation-treatable Ni-based alloys

We demonstrate a means of extending the temperature range for structural applications of nanomaterials through introduction of a dispersion of precipitates, whose thermal stability determines the temperature at which strength deteriorates. Precipitate-stabilized nanostructures created via severe plastic deformation of Inconel are shown to be stable even after heat treatment for 240 h at temperatures up to one-half of the melting point. This stability results from retention of both the fine microstructure and precipitate phases at high temperatures.