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排序方式: 共有177条查询结果,搜索用时 15 毫秒
31.
Keith Rozenburg Ivar E. Reimanis Hans-Joachim Kleebe Ron L. Cook 《Journal of the American Ceramic Society》2008,91(2):444-450
The sintering kinetics of a pure magnesium aluminate spinel, MgAl2 O4 , and that doped with LiF were determined through the use of the master sintering curve technique developed by Su and Johnson. 20 Powders with 0%, 0.5%, and 1.0% by mass LiF were densified in a vacuum hot press under a range of unaxial pressures. After the sintering mechanisms in each temperature and pressure regime were determined, an optimized vacuum hot-pressing schedule was formulated for spinel powders doped with 1.0% by mass of LiF. In addition to forming a transient liquid phase, the presence of LiF leads to the formation of oxygen vacancies that promote late-stage sintering in MgAl2 O4 . 相似文献
32.
Simon Ivar Andersen 《Petroleum Science and Technology》2013,31(11-12):1551-1577
ABSTRACT Solid petroleum asphaltenes have been fractionated according to solubility in toluene/n-heptane mixtures of increasing toluene content. A large hysteresis was observed between this dissolution and the precipitation from the crude oil. In order to shed light on the solution mechanism, the fractions obtained have been analyzed using size exclusion chromatography (SEC-HPLC-UV-vis), VPO, elemental analysis, UV-vis adsorption spectroscopy and phenol interaction values and methylene content by FTir. Less polar non-associating low molecular weight species are dissolved and a specific extraction of porphyrins is observed. An increased association in the insolubles is indicated. More basic interaction sites are available on the asphaltenes in both fractions relative to the native asphaltene. From the SEC chromatograms it was seen that the soluble fractions did not associate as the insoluble fractions even when making up more than 60 % of the total asphaltenes. 相似文献
33.
Artur Noole Maksim Oeka Tnis Pehk Mario
eren Ivar Jrving Mark R. J. Elsegood Andrei V. Malkov Margus Lopp Tnis Kanger 《Advanced Synthesis \u0026amp; Catalysis》2013,355(5):829-835
3‐Chlorooxoindoles have emerged as versatile precursors in the synthesis of spirocyclopropyl oxindoles. High enantio‐ and diastereoselectivity was attained under conditions of both iminium/enamine and H‐bonding catalysis. 相似文献
34.
35.
Lovaas (see record 1987-16420-001) has been criticized for overstating the outcome of an intensive behavioral intervention for young autistic children. Part of the criticism reflects skepticism of Lovaas's view that it is possible to overcome autistic children's deficits. However, Lovaas's study built on a substantial body of research that has suggested just such a possibility. It also contained a number of methodological features that provide evidence supporting his interpretation of the outcome, notably, unbiased control groups and multiple pretreatment and follow-up measures. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
36.
Ivar E. Reimanis John J. Petrovic Hisayuki Suematsu Terrence E. Mitchell 《Journal of the American Ceramic Society》1996,79(2):395-400
A composite consisting of elongated α-Si3 N4 crystallites (5–50 (Am in diameter) embedded in an amorphous Si3 N4 matrix was synthesized by chemical vapor deposition. The hardness and indentation fracture toughness of the amorphous matrix and of the composite have been evaluated at temperatures from ambient to 1200°C. It was found that the crystallites have relatively little influence on the hardness and indentation fracture toughness when the surrounding matrix is amorphous. However, a 1400°C heat treatment of the material results in a matrix consisting of small crystals (100 nm in diameter) surrounded by carbon-containing regions which appear to be amorphous in the TEM; TEM and EELS in nearby triple points revealed the presence of amorphous carbon. After heat treatment, the indentation fracture toughness at ambient and at 1200°C is increased due to extensive microcracking. The Vickers hardness at 1200°C also increased significantly as a result of the heat treatment. The relationship between the mechanical properties and the microstructure is discussed. 相似文献
37.
Plant availability of inorganic and organic selenium fertiliser as influenced by soil organic matter content and pH 总被引:11,自引:0,他引:11
Susanne Eich-Greatorex Trine A. Sogn Anne Falk Øgaard Ivar Aasen 《Nutrient Cycling in Agroecosystems》2007,79(3):221-231
The objective of the present study was to investigate the influence of soil organic matter content and pH on plant availability
of both inorganic and organic selenium (Se) fertilisers. Further, the risk of Se leaching after application of inorganic Se
fertiliser was evaluated. A new interpretation of an older field study at different sites in Southern Norway showed that organic
C was correlated with grain Se concentration in wheat, barley and oats, explaining up to 60% of the variation in Se concentration.
Pot experiments with a peat soil, a loam soil and a peat/loam soil mixture were conducted for the present study at a range
of pH values between pH 5 and 7. Below pH 6, Se uptake from added Se fertiliser was higher in the soil types with high organic
matter content than in the loam. The opposite occurred at a soil pH above 6, where Se uptake was higher in the loam than in
the peat soil. A simple leaching experiment after one growing season confirmed the findings of the pot experiments that Se
availability in the loam soil with a relatively low organic matter content increased with increasing pH, whereas it decreased
in the peat soil. Neither Se yeast, nor pure Se methionine, used as organic Se fertiliser, resulted in any significant uptake
of Se when added at concentrations similar to the inorganic Se applications. 相似文献
38.
Ivar Sagefors Per-Anders Daerga 《Tunnelling and Underground Space Technology incorporating Trenchless Technology Research》1996,11(3):279-285
Construction of underground storage chambers in rock has traditionally adopted a construction-oriented approach; the cavern design and the method of excavation have been governed by the capabilities of the equipment available. One example is oil storage in unlined horizontal caverns. Today, however, equipment is no longer a limiting factor. The time has come to integrate the construction and operational aspects in the design process. This paper presents a construction concept developed for large vertical rock caverns with a circular or elliptical horizontal cross-section. The method of excavation, called PBM (Pillar Blasting Method), is condensed into a few main operations which are geometrically separated but overlapping in time. PBM is characterized by two main working sites per cavern, and by long-hole bench-drilling, massive blasting rounds, continuous loading and easy ventilation. Recent developments in drilling and blasting techniques are incorporated, such as the water-driven in-the-hole hammer and the electronic ignition system. PBM enables a high rate of excavation and provides a satisfactory working environment with respect to labour safety and human health (a limited exposure to large openings, no exposure to oil mist and to combustion and explosive fumes, etc). Considerable construction cost savings and time savings may thus be achieved compared to conventional methods of excavation for vertical and horizontal caverns of equal storage volume. A preliminary PCT patent (application No PCT/SE95/00324) has been granted. Examples of applications are fresh-water reservoirs, natural gas reservoirs, subsurface hydroelectric pump power plants, and similar objects which require a large underground storage space in preferably unlined rock caverns. 相似文献
39.
Simon Ivar Andersen Carlos Lira-Galeana Erling H. Stenby 《Petroleum Science and Technology》2001,19(3):457-467
In the evaluation of experimental data as well as in calculation of phase equilibria the necessity of the application of mass balances is obvious. In the case of asphaltenes the colloidal nature of these compounds may highly affect the mass balance. In the present paper several experiments are performed in order to check the consistency of mass balances within asphaltene precipitation. Asphaltenes are precipitated in two step processes either by changing temperature or by changes in precipitant with increasing precipitation power. This has been performed for three different oils. The data indicates that in temperature experiments as well as in solvent series experiments the precipitation of heavy asphaltenes affects the following precipitation of lighter asphaltenes. In both cases the mass balance using standard separation techniques cannot be closed, as less material is precipitated in a two step process than in the direct process either at low temperature or by direct precipitation with one precipitant. The different fractions were subject to HPLC size exclusion chromtagraphy showing that the material remaining in solution in the stepwise process was of low molecular weight, and that the material in the second precipitation step was often of higher apparent molecular weight and had an increased overall absorbance coefficient. 相似文献
40.
Daniel D. Osterberg John Youngsman Rick Ubic Ivar E. Reimanis Darryl P. Butt 《Journal of the American Ceramic Society》2013,96(10):3290-3295
Polycrystalline 3C silicon carbide (SiC) was implanted at room temperature with 400 keV cesium ions to a dose of 1016 ions/cm2. The samples were annealed at 600°C–1000°C for times up to 48 h to observe changes in the implantation zone crystallinity and density. The implanted regions were characterized by transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) before and after annealing. It is shown that the implantation resulted in a 217 ± 2 nm amorphous region with microstructural damage extending to ~250 nm below the surface. Recrystallization of the amorphous region was observed to begin at 725°C. Densification was determined indirectly through changes in the measured implantation zone thickness. Measurable thickness, or densification, of the implanted region was not observed until temperatures greater than ~800°C. The SiC recrystallization began at the interface between the amorphous, damaged region, and the underlying polycrystalline material. Image analysis was used to quantify the fraction of crystalline phase as a function of time and temperature. The recrystallization kinetics exhibited Arrhenius dependency with an apparent activation energy of 480 kJ/mol. SIMS demonstrated that 60%–70% of the cesium was retained within the recrystallized microstructure after thermal annealing. 相似文献