Good High Temperature Performance Research Articles

Temperature dependence of the relaxation resonance frequency of long-wavelength vertical-cavity lasers

The temperature dependence of the differential gain in AlInGaAs 1310-nm vertical-cavity lasers is investigated. The variations in differential gain and in relaxation resonance frequency are shown to depend on the room-temperature offset between the gain peak wavelength and the wavelength of the lasing mode. The tradeoff between high modulation bandwidth and good high-temperature performance for vertical-cavity lasers is analyzed. A cavity mode that is red-shifted about 25 nm from the gain peak is shown to minimize the variation in modulation bandwidth with temperature, and simultaneously allow for satisfactory high-temperature operation. Experimental results are presented and compared to calculated results with excellent agreement. Because of the change in gain-mode offset with internal temperature, the measured modulation current efficiency changed from about 2 to 4.8 GHz/mA/sup 1/2/ for an increase in drive current from 2 to 10 mA.

Improved High Temperature Properties of SiC‐Ceramics Sintered with Lu2O3‐Containing Additives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Improved high temperature properties of SiC-ceramics sintered with Lu2O3-containing additives

Abstract Liquid-phase (LPS) sintered silicon carbide ceramics with additive systems containing aluminium nitride and rare earth oxides in combination are candidate materials for good high temperature performance in terms of creep behaviour and oxidation resistance. In the present work, creep testing in four-point bending geometry and scanning electron microscopic observation of oxidized surfaces were performed on yttrium and lutetium sesquioxide containing materials, demonstrating that Lu2O3-containing sintering additives give rise to largely improved properties. In particular, strain rates of about 1 × 10−9 s−1 were measured at both 1400 °C/100 MPa and 1300 °C/300 MPa in air. Oxidation resistance of LPS-SiC sintered with Lu2O3 was measured in the temperature range 1200–1500 °C for 100 h and improved behaviour was observed as compared to other liquid phase sintered SiC with different additives.

Processamento de concretos refratários zero-cimento contendo alumina e microssílica

Os concretos auto-escoantes de reduzido teor de cimento aliam facilidade de aplicação a um bom desempenho em temperaturas elevadas. Estudos anteriores mostraram que a auto-escoabilidade e o empacotamento de partículas necessário para redução do teor de cimento são função da granulometria e do estado de dispersão da matriz do concreto. Bonadia e outros propuseram, então, uma metodologia de formulação de concretos baseada nestes dois conceitos, enfocando a otimização dos parâmetros granulométricos. Com a granulometria otimizada, Studart et al. geraram mapas de estabilidade, que fornecem as condições ideais para dispersão de uma matriz contendo apenas alumina. Com o auxílio destes mapas foi possível preparar concretos auto-escoantes isentos de cimento (zero-cimento). Devido à importância da microssílica como precursora da fase mulita no concreto, o objetivo deste trabalho foi gerar mapas de estabilidade para matrizes contendo alumina e microssílica. Os resultados mostraram uma correlação entre a fluidez dos concretos e as regiões de menor viscosidade e tensão de escoamento indicadas nos mapas.

Performance characteristics of Ultralife's solid polymer rechargeable batteries

Abstract Ultralife Batteries delivered the world's first commercial shipments of solid polymer rechargeable batteries in 1997. The battery consists of a Li x Mn 2 O 4 − based cathode, graphite anode and proprietary polymeric separator. Energy density of the batteries exceeds 120 W h kg −1 and 200 W h dm −3 at the C rate. Pulse capability up to 5 C has been demonstrated. More than 90% of the initial C rate capacity remains after 500 continuous cycles at room temperature. These solid polymer rechargeable batteries also show good low and high temperature performance and have good safety characteristics.

Design and realization of a buried-heterostructure tunable-twin-guide laser diode with electrical blocking regions

An InGaAsP-InP buried-heterostructure tunable-twin-guide (TTG) laser diode is presented, incorporating epitaxially regrown p-n-p-n current blocking regions to minimize current leakage around the active region in the ridge. The laser design is based on a theoretical model describing the mechanism of current leakage and the influence of electrical blocking regions by a two-dimensional computer simulation. The technological realization of the laser device reveals a way to achieve a self-aligned transverse blocking region and a lateral ridge contact in any desired depth by a two-stage epitaxial process. Completely processed TTG laser diodes with buried blocking regions exhibit very good high-temperature performance and a wavelength tuning range of around 4.5 nm under forward bias together with a maximum light output of as much as 25 mW at room temperature.

Phosphorous-containing nadicimide resins: synthesis and characterization

A series of phosphorous-containing nadicimide end-capped resins, having different backbone, were prepared by reacting endo-5-norbornene- 2,3-dicarboxylic anhydride (nadic anhydride), pyromellitic dianhydride (PMDA)/3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA) andtris [3-azo(4-aminophenyl)] phosphine oxide (TAZP) in dimethyl acetamide. Yields were essentially quantitative. Structural characterization of resins was done by elemental analysis, IR and1H-NMR. Thermal behaviour of the resins was investigated by differential scanning calorimetry and thermogravimetric analysis, which revealed good high temperature performance. Isothermal ageing studies done at 340°C for various time periods showed good thermo-oxidative stability.

Densification studies of SRBSN with unstabilized zirconia by means of dilatometry and electron microscopy

A correlation of densification behaviour and microstructural development of ZrO2-fluxed sintered reaction-bonded Si3N4 (SRBSN) is reported in the light of dilatometry and both high-resolution electron microscopy (HREM) and analytical electron microscopy (AEM). Two distinct dilatometer maxima were observed using a modified dilatometer with improved sensitivity. The relatively small first dilatometer maximum, at approximately 1750‡C, is due to the formation of a highly viscous silica-rich liquid phase at the initial stage of sintering. The second maximum, showing a more pronounced densification rate, is related to a radical change in secondary-phase chemistry at approximately 1900‡C. In the SRBSN system, ZrO2 acts as an effective sintering aid because of the increased sintering temperatures and high N2 overpressure during the second dilatometer event, which promotes active participation of ZrO2 in the liquid-phase formation process. Sintering cycles were interrupted at the temperatures corresponding to the two dilatometer maxima. From these specimens, thin TEM foils were prepared, which correspond to the microstructures of the two densification events. Conventional TEM and HREM observations revealed significant microstructural differences, which could be related to the densification behaviour of the SRBSN-ZrO2 system. The good high-temperature performance of the densified SRBSN material is due to (i) the formation ofin situ large-grown Β-Si3N4 grains, (ii) a completely crystallized secondary phase (m-ZrO2), and (iii) very thin amorphous phase- and grain-boundary films of approximately 1.0 and 0.5 nm, respectively.

Phosphorus-Containing Nadimide Resins: Synthesis and Characterization

A series of phosphorous-containing nadicimide end-capped resins, having different backbone, were prepared by reacting endo-5-norbornene- 2,3-dicarboxylic anhydride (nadic anhydride), pyromellitic dianhydride (PMDA)/3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA) andtris [3-azo(4-aminophenyl)] phosphine oxide (TAZP) in dimethyl acetamide. Yields were essentially quantitative. Structural characterization of resins was done by elemental analysis, IR and1H-NMR. Thermal behaviour of the resins was investigated by differential scanning calorimetry and thermogravimetric analysis, which revealed good high temperature performance. Isothermal ageing studies done at 340°C for various time periods showed good thermo-oxidative stability.

Channelled-substrate narrow-stripe GaAs/GaAlAs injection lasers with extremely low threshold currents

Channelled-substrate GaAs/GaAlAs injection lasers with very narrow current-confining stripe contacts are described. They have threshold currents less than half those previously reported for this type of device. The best devices had a room-temperature threshold current of only 12 mA pulsed and 14 mA c.w. The lasers also have very good high-temperature performance and c.w. operation has been obtained up to 160°C.