896 resultados para Ultrafine grains
Resumo:
Lipeä on vahva emäs, jonka on havaittu lisäävän hemiselluloosan ja ligniinin hydrolyysiä pötsissä. Näin ollen lipeäkäsittelyllä on mahdollista korvata viljan mekaaninen litistys ja jauhatus. Seosrehuruokinnalla, jonka osana on lipeäkäsitelty vilja, on mahdollista vähentää liiallisesta tärkkelyksestä aiheutuvia metabolisia ongelmia pötsissä. Tämän tutkielman tarkoituksena oli selvittää lipeäkäsitellyn vehnän vaikutusta lypsylehmien syöntiin ja tuotokseen ad libitum seosrehuruokinnoilla. Ruokinnoissa korvattiin kuivaa murskattua vehnää asteittain kokonaisella lipeäkäsitellyllä vehnällä. Kontrollina oli perinteisesti käytetty kuiva, murskattu ohra-kaura seos. Koe tehtiin Ruotsin maatalousyliopiston (SLU) maataloustieteiden laitoksella Uumajassa. Koe alkoi syyskuussa ja päättyi joulukuussa 2010. Kokeessa oli 17 useamman kerran poikinutta lehmää ja 6 ensikkoa (Ruotsin punainen -rotu). Lehmät olivat lämpimässä pihattonavetassa, jossa seosrehun syöntiä mitattiin vaakakuppien avulla. Koekäsittelyt olivat murskattu ohra-kaura seos (1:1), murskattu kuiva vehnä (1:0), murskatun kuivan vehnän ja kokonaisen lipeävehnän seos (1:1) ja kokonainen lipeävehnä (1:0). Ruokintojen kuiva-ainepitoisuudeksi asetettiin 370 g/kg ja raakavalkuaispitoisuudeksi 180 g/kg kuiva-ainetta. Näennäinen ravintoaineen sulavuus määritettiin happoon liukenemattoman tuhkan avulla. Typen hyväksikäyttöä arvioitiin laskennallisen typpitaseen avulla. Koe toteutettiin 4x4 latinalaisen neliön koemallin mukaisesti ja käsittelyjen väliset tilastolliset erot testattiin kontrastien avulla. Kuiva-aineen (PQ=0,02) ja orgaanisen aineen (PQ=0,02) syönnit lisääntyivät, samalla kun niiden sulavuudet paranivat korvattaessa puolet kuivasta vehnästä lipeävehnällä. Ruokintojen välillä ei ollut tilastollisesti merkitsevää eroa maitotuotoksessa eikä energiakorjatussa maitotuotoksessa. Maidon rasvatuotos lisääntyi vähän (PQ=0,04) ja rasvapitoisuus selvästi (PQ=0,004), kun kuivasta vehnästä korvattiin puolet lipeävehnällä. Kun kaikki kuiva vehnä korvattiin lipeävehnällä, maidon valkuaispitoisuus väheni (PL<0,001). Samoin kävi maidon ureapitoisuudelle (PL=0,002). Lipeäkäsittely ei tuottanut tässä kokeessa taloudellisesti kannattavaa tulosta, sillä maidon valkuaispitoisuus väheni ja syönti lisääntyi maitotuotoksen pysyessä samana. Vehnäruokinnoista paras tuotosvaste saatiin kuivan vehnän ja lipeävehnän seoksella.
Resumo:
The long-wavelength hydrodynamics of the Renn-Lubensky twist grain boundary phase with grain boundary angle 2pialpha, alpha irrational, is studied. We find three propagating sound modes, with two of the three sound speeds vanishing for propagation orthogonal to the grains, and one vanishing for propagation parallel to the grains as well. In addition, we find that the viscosities eta1, eta2, eta4, and eta5 diverge like 1/Absolute value of omega as frequency omega --> 0, with the divergent parts DELTAeta(i) satisfying DELTAeta1DELTAeta4=(DELTAeta5)2, exactly. Our results should also apply to the predicted decoupled lamellar phase.
Resumo:
The present work describes the evolution of a strong, single-component rotated-Brass ((1 1 0) < 5 5 6 >) texture in an Al-Zn-Mg-Cu-Zr alloy by an uneven hot cross-rolling with frequent interpass annealing. This texture development is unique because hot rolling of aluminum alloys results in orientation distribution along the ``beta-fibre''. It has been demonstrated that the deformation by cross-rolling of a partially recrystallized grain structure having rotated-Cube and Goss orientations, and the recrystallization resistance of near-Brass-oriented elongated grains play a critical role in development of this texture. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Resumo:
Nanocomposites of Al?In, Al?Pb, and Zn?Pb have been prepared and characterized using rapid quenching techniques and the nature of superconducting transitions in them has been studied by resistivity measurements. The precipitated second phases (In and Pb) have particle sizes (d) of a few tens of nanometers such that ?0?d?dmin, where ?0 is the superconducting zero temperature coherence length and dmin is the minimum particle size that supports superconductivity. The onset of superconductivity generally starts in samples with d??0 and progressively other grains with d??0 become superconducting. We suggest that the proximity effect of the matrix plays a significant role. In an Al?In system, even with 40?wt.% In, the zero resistivity state is obtained at T?1.33 times the Tc of Al. But in Al?Pb and Zn?Pb, the zero resistivity state is obtained at T?4 and 5 times the Tc of Al and Zn with only 10�15 wt?% Pb, respectively.
Resumo:
Microstructural and superconducting properties of YBa2Cu3O7-x thin films grown in situ on bare sapphire by pulsed laser deposition using YBa2Cu3O7-x targets doped with 7 and 10 wt% Ag have been studied. Ag-doped films grown at 730 degrees C on sapphire have shown very significant improvement over the undoped YBa2Cu3O7-x films grown under identical condition. A zero resistance temperature of 90 K and a critical current density of 1.2 x 10(6) A/cm(2) at 77 K have been achieved on bare sapphire for the first time. Improved connectivity among grains and reduced reaction rate between the substrate and the film caused due to Ag in the film are suggested to be responsible for this greatly improved transport properties.
Resumo:
The characteristics of hot deformation of INCONEL alloy MA 754 have been studied processing maps obtained on the basis of flow stress data generated in compression in the temperature range 700-degrees-C to 1150-degrees-C and strain rate range 0.001 to 100 s-1. The map exhibited three domains. (1) A domain of dynamic recovery occurs in the temperature range 800-degrees-C to 1075-degrees-C and strain rate range 0.02 to 2 s-1, with a peak efficiency of 18 pct occurring at 950-degrees-C and 0.1 s-1. Transmission electron microscope (TEM) micrographs revealed stable subgrain structure in this domain with the subgrain size increasing exponentially with an increase in temperature. (2) A domain exhibiting grain boundary cracking occurs at temperatures lower than 800-degrees-C and strain rates lower than 0.01 s-1. (3) A domain exhibiting intense grain boundary cavitation occurs at temperatures higher than 1075-degrees-C. The material did not exhibit a dynamic recrystallization (DRX) domain, unlike other superalloys. At strain rates higher than about 1 s-1, the material exhibits flow instabilities manifesting as kinking of the elongated grains and adiabatic shear bands. The material may be safely worked in the domain of dynamic recovery but can only be statically recrystallized.
Resumo:
The hot deformation characteristics of IN 600 nickel alloy are studied using hot compression testing in the temperature range 850-1200-degrees-C and strain rate range 0.001-100 s-1. A processing map for hot working is developed on the basis of the data obtained, using the principles of dynamic materials modelling. The map exhibits a single domain with a peak efficiency of power dissipation of 48% occurring at 1200-degrees-C and 0.2 s-1, at which the material undergoes dynamic recrystallisation (DRX). These are the optimum conditions for hot working of IN 600. At strain rates higher than 1 s-1, the material exhibits flow localisation and its microstructure consists of localised bands of fine recrystallised grains. The presence of iron in the Ni-Cr alloy narrows the DRX domain owing to a higher temperature required for carbide dissolution, which is essential for the occurrence of DRX. The efficiency of DRX in Ni-Cr is, however, enhanced by iron addition.
Resumo:
The physico-chemical, photo-physical and micro-structural properties responsible for the strikingly different photocatalytic behavior of combustion-prepared TiO2 (c.TiO2) and Degussa P25 (d.TiO2) samples are elucidated in this study. Electron microscopy and selected area electron diffraction micrographs revealed that the two samples exhibited different morphologies. The grains of c.TiO2 were spherical and comprised of 5-6 nm size primary particle. On the other hand, d.TiO2 consisted of large (0.5-3.0 mu m) size and irregular shape aggregates having primary particles of 15-40 nm cross-sectional diameter. The ESR study revealed that the presence of certain defect states in c.TiO2 helped in stabilization of O-. and Ti3+-OH type species during room-temperature UV-irradiation. No such paramagnetic species were however formed over d.TiO2 under similar conditions. C1s and Ti 2p XPS spectra provide evidence for the presence of some lattice vacancies in c.TiO2 and also for the bulk Ti4+ -> Ti3+ conversion during its UV-irradiation. Compared to d.TiO2, c.TiO2 displayed considerably higher activity for discoloration of methyl orange but very poor activity for splitting of water, both under UV and visible light radiations. This is attributed to enhanced surface adsorption of dye molecules over c.TiO2, because of its textural features and also the presence of photo-active ion-radicals. On the other hand, the poor activity of c.TiO2 for water splitting is related to certain defect-induced inter-band charge trapping states in the close vicinity of valence and conduction bands of c.TiO2, as revealed by thermoluminescence spectroscopy. Further, the dispersion of nanosize gold particles gave rise to augmented activity of both the catalysts, particularly for water splitting. This is explained by the promotional role of Au-0 or Au-0/TiO2 interfacial sites in the adsorption and charge-adsorbate interaction processes. (C) 2011 Elsevier B.V. All rights reserved.
Resumo:
Mullite-zirconia composite powders were prepared by the combustion of an aqueous heterogeneous redox mixture consisting of Al(NO3)(3), Zr(NO3)(4)/ZrO(NO3)(2), silica fume and urea/diformyl hydrazine at 500 degrees C. X-ray diffraction data showed that a large amount of tetragonal zirconia existed in the composite powders in spite of high temperature calcination. Milled composite powders showed enhanced densification compared to the unmilled powders and the microstructure of the sintered (1600 degrees C) compacts showed the presence of spherical zirconia grains in intergranular positions along with elongated mullite grains.
Resumo:
Nebulized spray pyrolysis provides a good low?temperature chemical route for preparing thin films of PbTiO3, (Pb0.9,La0.1)TiO3 and Pb(Zr0.52,Ti0.48)O3. The films are a? or c? axis oriented, with spherical grains of ?30 nm and give satisfactory P?E hysteresis loops. © 1995 American Institute of Physics.
Resumo:
The technique of nebulized spray pyrolysis has been explored to find out whether oriented films of certain important oxides can be produced on single-crystal substrates by this relatively gentle method. Starting with acetylacetonate precursors, oriented films of metallic LaNiO3 containing nearly spherical grains (30 nm) have been obtained. Films of near-stoichiometric La4Ni3O10 and La3Ni2O7 showing metallic conductivity have been obtained by this method. This is indeed gratifying since it is difficult to prepare monophasic and stoichiometric bulk samples of these materials. Films of La2NiO4 show the expected semiconducting behavior. In the La-Cu-O system, starting with acetylacetonates, we have obtained films mainly comprising semiconducting La2Cu2O5, which is generally difficult to prepare in bulk form. More interestingly, nebulized spray pyrolysis gives excellent stoichiometric films of Pb(Zr0.52Ti0.48)O-3 consisting of nearly spherical grains (30 nm) which show ferroelectric behavior. The present investigation demonstrates that nebulized spray pyrolysis provides a useful and desirable route to deposite oriented films of complex oxide materials on single-crystal substrates.
Resumo:
Allergens from the pollen of Parthenium hysterophorus (American feverfew), responsible for high incidence of allergic rhinitis, were found by immunoprint analysis to be localized on the surface of the pollen grains. The allergens were released very rapidly when extracted in vitro. The allergenic activity of the rapid (10 s) and slowly (20 h) released pollen proteins was comparable by in vivo skin test and ELISA inhibition assay. The isoelectric focusing patterns of the rapid and slowly released proteins, were also identical. SDS-PAGE and Western blot analysis revealed that all the major pollen allergens with molecular weight 14, 28, 31, 37 and 45 kDa were eluted within 10 s of extraction. Periodate-Schiff staining showed that the 28, 31 and 45 kDa components of the pollen extract are glycoproteins. The pollen allergens released after different periods of extraction lost 75% of IgE binding activity when subjected to in situ sodium m-periodate oxidation under controlled conditions, while 80% of the allergenic activity was still retained after extensive proteolysis. Our results support the clinical observation of a rapid onset of symptoms of allergic rhinitis in patients sensitive to Parthenium pollen, mediated predominantly by glycoproteins.
Resumo:
Rapid solidification of a ternary Al-Cu-Zr alloy results in a nanocomposite microstructure. In this study, melt spinning a Al82Cu15Zr3 alloy has resulted in the combined occurrence of, (a) 0.5 mu m sized grains of Al solid solution and (b) fine grains (10-20 nm) of intermetallic Al2Cu (theta) and alpha-Al, along side each other. The larger alpha-Al grains contain nanometric GP zones, with the Zr addition resulting in a grain refinement. In the other type of microstructure Zr promotes simultaneous nucleation of nanosized grains of the two equilibrium phases, Al2Cu and alpha-Al. Both these lead to a very high hardness of similar to 540 VHN for this alloy and can be used as a candidate for a high strength alloy with good ductility at a low strain rate.
Resumo:
Stabilization of nanocrystalline grain sizes by second phase particles can facilitate superplasticity at high strain rates and/or low temperatures. A metastable single phase nano-Ni-P alloy prepared by electrodeposition, with a grain size of similar to 6 nm, transforms to a nanoduplex structure at T> 673 K, with similar to 4 vol.% Ni3P particles at triple junctions and within Ni grains. The nanoduplex microstructure is reasonably stable up to 777 K, and the growth of Ni grains occurs in a coupled manner with the growth of Ni3P particles such that the ratio of the two mean sizes (Z) is essentially constant. High temperature tests for a grain size of 290 nm reveal superplastic behavior with an optimum elongation to failure of 810% at a strain rate of 7 x 10(-4) s(-1) and a relatively low temperature of 777 K. Superplastic deformation enhances both grain growth and the ratio Z, implying that grain boundary sliding (GBS) significantly influences the microstructural dynamics. Analysis of the deformation processes suggests that superplasticity is associated with GBS controlled by the overcoming of intragranular particles by dislocations, so that deformation is independent of the grain size. The nano-Ni-P alloy exhibits lower ductility than nano-Ni due to concurrent cavitation caused by higher stresses. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Resumo:
Thin films of barium strontium titanate (BST) including BaTiO3 and SrTiO3 end members were deposited using the metallo-organic decomposition (MOD) technique. Processing parameters such as nonstoichiometry, annealing temperature and time, film thickness and doping concentration were correlated with the structural and electrical properties of the films. A random polycrystalline structure was observed for all MOD films under the processing conditions in this study. The microstructures of the films showed multi-grains structure through the film thickness. A dielectric constant of 563 was observed for (Ba0.7Sr0.3)TiO3 films rapid thermal annealed at 750 degrees C for 60 s. The dielectric constant increased with annealing temperature and film thickness, while the dielectric constant could reach the bulk values for thicknesses as thin as similar to 0.3 mu m. Nonstoichiometry and doping in the films resulted in a lowering of the dielectric constant. For near-stoichiometric films, a small dielectric dispersion obeying the Curie-von Schweidler type dielectric response was observed. This behavior may be attributed to the presence of the high density of disordered grain boundaries. All MOD processed films showed trap-distributed space-charge limited conduction (SCLC) behavior with slope of similar to 7.5-10 regardless of the chemistry and processing parameter due to the presence of main boundaries through the film thickness. The grain boundaries masked the effect of donor-doping, so that all films showed distributed-trap SCLC behavior without discrete-traps. Donor-doping could significantly improve the time-dependent dielectric breakdown behavior of BST thin films, mostly likely due to the lower oxygen vacancy concentration resulted from donor-doping. From the results of charge storage density, leakage current and time-dependent dielectric breakdown behavior, BST thin films are found to be promising candidates for 64 and 256Mb ULSI DRAM applications. (C) 1997 Elsevier Science S.A.