Water availability in +2°C and +4°C worlds

While the parties to the UNFCCC agreed in the December 2009 Copenhagen Accord that a 2°C global warming over pre-industrial levels should be avoided, current commitments on greenhouse gas emissions reductions from these same parties will lead to a 50?:?50 chance of warming greater than 3.5°C. Here, we evaluate the differences in impacts and adaptation issues for water resources in worlds corresponding to the policy objective (+2°C) and possible reality (+4°C). We simulate the differences in impacts on surface run-off and water resource availability using a global hydrological model driven by ensembles of climate models with global temperature increases of 2°C and 4°C. We combine these with UN-based population growth scenarios to explore the relative importance of population change and climate change for water availability. We find that the projected changes in global surface run-off from the ensemble show an increase in spatial coherence and magnitude for a +4°C world compared with a +2°C one. In a +2°C world, population growth in most large river basins tends to override climate change as a driver of water stress, while in a +4°C world, climate change becomes more dominant, even compensating for population effects where climate change increases run-off. However, in some basins where climate change has positive effects, the seasonality of surface run-off becomes increasingly amplified in a +4°C climate.     

Regional temperature and precipitation changes under high-end (≥4°C) global warming

Climate models vary widely in their projections of both global mean temperature rise and regional climate changes, but are there any systematic differences in regional changes associated with different levels of global climate sensitivity? This paper examines model projections of climate change over the twenty-first century from the Intergovernmental Panel on Climate Change Fourth Assessment Report which used the A2 scenario from the IPCC Special Report on Emissions Scenarios, assessing whether different regional responses can be seen in models categorized as 'high-end' (those projecting 4°C or more by the end of the twenty-first century relative to the preindustrial). It also identifies regions where the largest climate changes are projected under high-end warming. The mean spatial patterns of change, normalized against the global rate of warming, are generally similar in high-end and 'non-high-end' simulations. The exception is the higher latitudes, where land areas warm relatively faster in boreal summer in high-end models, but sea ice areas show varying differences in boreal winter. Many continental interiors warm approximately twice as fast as the global average, with this being particularly accentuated in boreal summer, and the winter-time Arctic Ocean temperatures rise more than three times faster than the global average. Large temperature increases and precipitation decreases are projected in some of the regions that currently experience water resource pressures, including Mediterranean fringe regions, indicating enhanced pressure on water resources in these areas.     

Pendent drop measurements of the polypropylene/polystyrene interfacial tension between 220°C and 270°C

The interfacial tensions of molten polypropylene/polystyrene have been measured using the pendent drop method between 220°C and 270°C. The obtained tension values are comparable with those of most of the molten polymer pairs, though their linear decrease as a function of temperature is steeper. The interaction parameter of Good and Girifalco lies within the range of values for all other polymer pairs.     

Sintering of 6H(α)-SiC and 3C(β)-SiC powders with B4C and C additives

The sintering behavior of three fine industrial SiC powders (two 6H()-type and one 3C()-type) has been comparatively investigated. The powders were pressureless sintered with B₄C and C additives between 1950°C and 2250°C in a high temperature dilatometer with flowing Ar atmosphere. The densification and shrinkage rate curves, polytype content, and grain growth were correlated with physical and chemical characteristics of starting powders. One of 6H()-type powders presented good sinterability only after extensive milling, even though it presented small average particle size, narrow particle size distribution and high specific surface area. The main difference in densification behavior among powders was the narrower shrinkage rate curve of -SiC powder, with its maximum shifted to higher temperature. Grain growth and phase transformation simultaneously occurred. In -SiC, 6H polytype partially transformed to 4H. This transformation was favored by aluminum impurity and resulted in a microstructure with more elongated grains. In -SiC, 3C transformed mainly to 6H, 15R and 4H, introducing many stacking faults which resulted in elongated SiC grains.     

Self-repairing poly(phenylenesulfide) coatings in hydrothermal environments at 200 °C

Usefulness of hydraulic calcium aluminate (CA) fillers, containing monocalcium aluminate (CaO.Al₂O₃) and calcium bialuminate (CaO.2Al₂O₃) reactants as the major phases, in healing and repairing micro-sized cracks generated on the surfaces of poly(phenylenesulfide) (PPS) coating was evaluated by exposing the cleaved coatings to a simulated geothermal environment. CA fillers with a grain size of <40 μm were incorporated into the PPS coatings. The cleaved PPS coatings containing fillers then were exposed for up to 20 days in a 200 °C CO₂-laden brine. The decalcification–hydration reactions of the CaO.Al₂O₃ and CaO.2Al₂O₃ reactants disclosed in the cracks led to the rapid growth of boehmite crystals, while the crystalline calcite phase formed by the carbonation of these reactants was leached out of cracks because of the formation of water-soluble calcium bicarbonate. During exposure for 24 h, the block-like boehmite crystals, ∼4 μm in size, densely filled and sealed the open cracks; this was reflected in an increase in pore resistance to two orders of its magnitude compared with that of cleaved coatings without fillers. Extending the exposure time to 20 days resulted in no change in pore resistance, suggesting that the sealing of the cracks by boehmite crystals played an essential role in reconstituting and restoring the function of the failed coatings as corrosion-preventing barrier. Therefore, CA-filled PPS coatings are able to self-heal and -repair cracks generated on the surfaces of coating films in hydrothermal environments.     

Photoemission studies of the vicinal SiC(100) 4° surface and the Cs/SiC(100) 4° interface

Photoemission studies of the electronic structure of the vicinal SiC(100) 4° surface, which was grown using a new substrate atom substitution method, and the Cs/SiC(100) 4° interface have been performed for the first time. The modification of spectra of the valence band and C 1s and Si 2p core levels in the process of formation of the Cs/SiC(100) 4° interface was analyzed. The suppression of the surface SiC state with a binding energy of 2.8 eV and the formation of a cesium-induced state with a binding energy of 10.5 eV were observed. The modification of the complex component structure in the spectrum of C 1s core level has been detected and examined for the first time. It was found that Cs adsorption on the vicinal SiC(100) 4° surface results in intercalation of graphene islands on SiC(100) 4° with Cs atoms.     

Nondestructive Characterization and Evaluation of Embrittlement Kinetics and Elastic Constants of Duplex Stainless Steel SAF 2205 for Different Aging Times at 425°C and 475°C

In this work, an experimental study was carried out to evaluate the potential of the ultrasonic technique, with ultrasonic velocity and attenuation measurements, to assess the heat aging effects on duplex stainless steel SAF 2205, at temperatures of 425°C and 475°C for time periods of 12 h, 24 h, 50 h, 100 h and 200 h, as well as in the as received state of the material. Velocity measurements were calculated for both longitudinal and transversal waves. The elastic constants, Young’s modulus and shear modulus, of the material were computed from the relationship between longitudinal and transversal velocities. For the ultrasonic attenuation, only longitudinal waves were considered. Despite the large scatter measurements, both ultrasonic velocity and attenuation increased with the heat aging time, particularly at 475°C. Thus, it may be concluded that the technique used is promising and provides relevant contributions to an accurate characterization of materials and evaluation of their mechanical properties in a non-destructive manner.     

Compressive deformation of an Mg-Al-Si-RE alloy between 120 and 180 °C

The deformation behaviour of an Mg-Al-Si-RE (ASE210) alloy between 120 and 180 °C was investigated by means of uniaxial compression tests to identify possible differences in the deformation response compared with uniaxial tensile data. Early fracture was observed in the low-temperature/high strain rate regime, fracture occurring by crack propagation at 45° with respect to the compression axis. In the high-temperature/low strain rate regime, the flow curves exhibited the typical shape that is usually observed in materials where deformation is controlled by recovery of substructure. The peak flow stresses obtained in this regime of temperature and strain rate were compared with other data obtained by testing the same alloy in tension. The strength of the alloy was found to be slightly greater in compression than in tension, this difference gradually disappearing as strain rate decreased.     

Interferometric 45° and 60° strain rosettes measuring

A laser-based technique, referred to as interferometric strain rosettes for measuring three in-plane strains, is presented. The strain rosette consists of three microindentations produced on a specimen surface and can be of two separate forms. The two forms are 45° and 60° rosettes for indentations located at the vertices of a 45° right triangle and an equilateral triangle, respectively. The three indentations for either form can be grouped into three pairs. When the indentations are illuminated with laser light, each pair of indentations acts like a two-point source generating a pair of Young's interference fringe patterns. The fringe spacing is inversely proportional to the separation of the indentations. Because strains cause the separation to change, the fringe spacing also changes. The fringe change is monitored with linear-array diodes and collected real time through a microcomputer system. The three strain components in the directions of the indentation pairs can then be obtained.     

About the iron carbonyl complex with C60 and C70 fullerene: [Fe(CO)4(η2C60)] and [Fe(CO)4(η2C70)]

The iron carbonyl complexes with C₆₀ and C₇₀ fullerenes were synthesized in high yield by photochemical irradiation of solutions of C₆₀ and C₇₀ in presence of Fe(CO)₅. The resulting complexes were studied by FT-IR, Raman and electronic absorption spectroscopy. All the data are consistent with the structures [Fe(CO)₄(η²C₆₀)] and [Fe(CO)₄(η²C₇₀)]. The thermal stability and decomposition reaction of the two complexes were studied by TGA-FTIR and Differential Scanning Calorimetry (DSC). Both complexes decompose at moderate temperatures releasing CO and Fe(CO)₅ in the vapor phase leaving a residue of metallic iron and free C₆₀ or C₇₀ fullerenes that can be recovered by solvent extraction of the decomposition residue.     

1700°C热校准风洞

1700°C热校准风洞是一台高温、高速的稳态与动态温度校准装置.本文介绍了1700°C热校准风洞的主要性能和特点,以及为此而采取的保温与冷却相结合的结构设计、高温内壳设计和其它一些技术方法.     

Alumina formation and microstructural changes of aluminized CoNiCrAlY coating during high temperature exposure in the temperature range 925°C–1075°C

Abstract

MCrAlY (M = Ni, Co) coatings are commonly used on gas-turbine components as oxidation resistant overlay coatings and bondcoats for thermal barrier systems. In the present work the microstructural features and oxidation behavior of an aluminized Co-base MCrAlY-coating on a Ni-based superalloy have been investigated in the temperature range 925–1075 °C. Microstructural studies of the oxidized coatings by SEM/EBSD were complemented with numerical thermodynamic calculations using the software package ThermoCalc. In the as-received condition the outer part of the coating consisted mostly of β-(Ni,Co)Al. Formation of σ-CoCr was observed at the interface between the β-layer and the inner initial CoNiCrAlY. During high-temperature air exposure alumina based surface scales were formed but the oxidation induced Al depletion of the aluminized coating did not result in formation of the γ’-(Ni₃Al) phase. Rather, the subscale formation of Co/Cr-rich phases was observed and a direct transformation of β- into γ-Ni phase after longer times. It is expected that these subscale microstructural changes thus affect the alumina formation and growth as well as the critical aluminum depletion in a different manner as in the case of corresponding β-NiAl coatings, although a direct comparison between various coating systems was not possible on the basis of the present results.     

Oxidation kinetics of zirconium in water vapour between 750 and 1250°C

The zirconium oxidation has been followed in H₂/H₂0 gas mixtures by microgravimetry and morphological observations between 750 and 1250°C. The reaction rate is governed by a mixed regime of oxygen diffusion through multiplex oxide layers of zirconia and an oxygen solid solution. After the metal core has disappeared the reaction proceeds by direct oxidation of the solid solution. Different kinetic behaviours have been shown according to the phase couples present.     

Buffer Solutions of Potassium Dihydrogen Phosphate and Sodium Succinate at 25 °C

A buffer mixture consisting of equal molalities (m) of potassium dihydrogen phosphate and sodium succinate is proposed as a useful reference point in the study of acid-base equilibria, bridging the present gap between pH 5.5 and pH 6.8. The p(a_Hγ_Cl) at 25 °C has been determined by electromotive-force measurements for five buffer solutions in which m varied from 0.005 to 0.025. The conventional pa_H of each solution has been derived and found to be in good agreement with that calculated from existing data for the two equilibria concerned. The pa_H varies from 6.251 at m=0.005 to 6.109 at m= 0.025. The buffer mixture has been used successfully for the determination of the dissociation constants of 2-nitro-4-chlorophenol and 2,6-dichlorophenol.     

Mechanical and structural characterisation of Nicalon SiC fibres up to 1300°C

The resurgence of interest in metal matrix composites has been fuelled by the development of new fibres with high temperature characteristics. The new family of continuous fine ceramic fibres based on SiC or Al₂O₃ offers the possibility of producing high temperature composites with metal or ceramic matrices. The toughening of ceramics by these fibres is a particularly interesting prospect.Two types of continuous silicon carbide Nicalon monofilaments (NLP 101 and NLM 102) have been tested in air and argon up to 1300°C. Tensile and creep tests have shown that the tensile strength falls and the fibres creep above 1000°C. Different behaviour was found for the two types of fibres. The NLM 102 fibre was stronger and crept less at high temperature under small strains. However its creep lifetime was less than that of the NLP 101 fibres.These differences have been interpreted with the aid of a microstructural study. The fibres were found to contain silicon, carbon and oxygen (electron microphobe and Auger spectrometer) and SiC was also detected (X-ray diffraction and transmission electron microscopy). The modification of the amorphous and microcrystalline structures during creep have been investigated. A fine segregation of free carbon particles was detected (X-ray diffraction and ESR) and was seen to disappear during heat treatment in both types of environment studied.     

(AlCrTaTiZr)N/(AlCrTaTiZr)N0.7 bilayer structure of high resistance to the interdiffusion of Cu and Si at 900 °C

In this study, a multi-component (AlCrTaTiZr)N/(AlCrTaTiZr)N_0.7 bilayer structure of about 15 nm thick was developed as a diffusion barrier material for Cu interconnects. The as-deposited (AlCrTaTiZr)N_0.7 layer was characterized to be an amorphous structure, and the (AlCrTaTiZr)N layer was a nanocomposite structure. After annealing at a high temperature of 900 °C, the Si/(AlCrTaTiZr)N/(AlCrTaTiZr)N_0.7/Cu film stack structure with the bilayer diffusion barrier remained stable. Only a slight amount of Cu penetrated into the top (AlCrTaTiZr)N_0.7 layer. However, neither interdiffusion of Cu and Si through the (AlCrTaTiZr)N layer occurred, nor did any silicides form, indicating the excellent diffusion resistance of the bilayer structure.     

R-curves of an yttria- and alumina-doped hot-pressed silicon nitride ceramic at 1200°C and room temperature

An energy approach has been utilized to measure theR-curves of an Y2O3~A3-doped hot-pressed silicon nitride ceramic at 1200C in an argon atmosphere in three-point bending. In order to evaluate theR-curves at 1200C, a low constant displacement rate of =5 m min^–1 was applied in cyclic loading to obtain the cyclic loading/ unloading-displacement curves during controlled-crack propagation. Propagated crack lengths were measured directly by a microscope and they were compared to compliance-calculated crack lengths. After digitizing the cyclic load-displacement and crack length-displacement curves, crack-resistance parameters,R-curves andK-curves, were calculated by computer. At 1200C this material behaved non-elastically and the crack parameters, obtained here, represent the non-elastic ones. For comparison, at room temperature, continuous loading was applied to obtain the load-displacement curves. At room temperature, linear-elastic fracture mechanics behaviour was observed.