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Stoichiometric Composition (stoichiometric + composition)
Selected AbstractsEffects of increased temperature and nutrient enrichment on the stoichiometry of primary producers and consumers in temperate shallow lakesFRESHWATER BIOLOGY, Issue 7 2008M. VENTURA Summary 1. We studied the effects of increased water temperatures (0,4.5 °C) and nutrient enrichment on the stoichiometric composition of different primary producers (macrophytes, epiphytes, seston and sediment biofilm) and invertebrate consumers in 24 mesocosm ecosystems created to mimic shallow pond environments. The nutrient ratios of primary producers were used as indicative of relative nitrogen (N) or phosphorus (P) limitation. We further used carbon stable isotopic composition (,13C) of the different primary producers to elucidate differences in the degree of CO2 limitation. 2. Epiphytes were the only primary producer with significantly higher ,13C in the enriched mesocosms. No temperature effects were observed in ,13C composition of any primary producer. Independently of the treatment effects, the four primary producers had different ,13C signatures indicative of differences in CO2 limitation. Seston had signatures indicating negligible or low CO2 limitation, followed by epiphytes and sediment biofilm, with moderate CO2 limitation, while macrophytes showed the strongest CO2 limitation. CO2 together with biomass of epiphytes were the key variables explaining between 50 and 70% of the variability in ,13C of the different primary producers, suggesting that epiphytes play an important role in carbon flow of temperate shallow lakes. 3. The ratio of carbon to chlorophyll a decreased with increasing temperature and enrichment in both epiphytes and seston. The effects of temperature were mainly attributed to changes in algal Chl a content, while the decrease with enrichment was probably a result of a higher proportion of algae in the seston and epiphytes. 4. Macrophytes, epiphytes and seston decreased their C : N with enrichment, probably as an adaptation to the different N availability levels. The C : N of epiphytes and Elodea canadensis decreased with increasing temperature in the control mesocosms. Sediment biofilm was the only primary producer with lower C : P and N : P with enrichment, probably as a result of higher P accumulation in the sediment. 5. Independently of nutrient level and increased temperature effects the four primary producers had significantly different stoichiometric compositions. Macrophytes had higher C : N and C : P and, together with epiphytes, also the highest N : P. Seston had no N or P limitation, while macrophytes and epiphytes may have been P limited in a few mesocosms. Sediment biofilm indicated strong N deficiency. 6. Consumers had strongly homeostatic stoichiometric compositions in comparison to primary producers, with weak or no significant treatment effects in any of the groups (insects, leeches, molluscs and crustaceans). Among consumers, predators had significantly higher N content and lower C : N than grazers. [source] Preparation of Highly Dispersed Ultrafine Barium Titanate Powder by Using Microbial-Derived SurfactantJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2003Hidehiro Kamiya To uniformly disperse ultrafine BaTiO3 particles with a stoichiometric composition and several tens of nanometers in diameter to primary particles during the sol,gel synthesis process, a new aqueous surfactant with a high hydrophilic group density and special cis-structure was prepared from a microbial product and added to solution before the sol,gel synthesis reaction. Because of the rapid formation of large and porous aggregates which were 30,50 ,m in diameter in suspension without addition of this unique structural surfactant, the prepared ultrafine BaTiO3 particles caused rapid sedimentation in suspension. The addition of the surfactant in the range of 7.1 wt% for the synthesized BaTiO3 particles made it possible to decrease the size of the aggregates in suspension as well as the sedimentation velocity while maintaining the stoichiometric composition. The optimum additive content to obtain the minimum aggregate size of about 100,200 nm in diameter and the highest dispersion stability in suspension while maintaining the stoichiometric composition of prepared ultrafine BaTiO3 particles without other phases was determined at about 7.1 wt%. Because the excess addition of this surfactant at more than 8.5 wt% inhibited the uniform synthesis of BaTiO3 particles, an amorphous phase with a highly specific surface area and a BaCO3 phase formed in the synthesized particles. [source] Low-Temperature Sintering and Electromagnetic Properties of Copper-Modified Z-type HexaferriteJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2002Hongguo Zhang The influence of the substitution of copper for cobalt on the low-sintering densification, microstructure, lattice parameters, and electromagnetic properties of planar Z-type hexaferrites, which have a stoichiometric composition of Ba3Co2(10.8,x) -Zn0.4Cu2xFe24O41, were investigated. The experimental results show that densification of the copper-substituted hexaferrite is dependent on the amount of copper substitution and sintering temperatures. XRD analysis reveals that the solid solubility of copper in Z-type hexaferrite is limited to x, 0.30. At the same time, the lattice parameters (a and c) of Z-type hexaferrites with copper substitution showed a small change, that is, decrease of a parameter in the basal plane and increase of the c axial. Moreover, the microstructure becomes more homogeneous and intragranular pores decrease considerably, but the temperature-stable range of the Z-type phase formation is narrow. The copper-substituted hexaferrites, with x= 0.20 and sintered at ,1125°C for 4 h, resulted in a high density sample of ,4.68 g/cm3 as the optimal value, good magnetic properties, and the enormous potentiality for fabrication of multilayer chip inductors used in hyper-frequencies. [source] Sintering Behavior and Surface Microstructure of PbO-Rich PbNi1/3Nb2/3O3,PbTiO3,PbZrO3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001Masao Kondo The sintering behavior and surface microstructure of PbNi1/3Nb2/3O3,PbTiO3,PbZrO3 (PNiNb-PT-PZ) ceramics were investigated. The PNiNb-PT-PZ ceramics with the stoichiometric composition and the addition of excess lead oxide (PbO-rich ceramics) were sintered by liquid-phase sintering in accordance with the solution-reprecipitation mechanism at temperatures below the melting point of PbO. The temperature at which the liquid phase forms fell to near the eutectic point of the PbO,Nb2O5 and the PbO,TiO2 system (868°C) with the addition of 5 mol% PbO. As the calcination temperature influenced the sinterability of the stoichiometric PNiNb-PT-PZ ceramic, unreacted PbO was considered to be the source of the liquid phase in the sintering of the stoichiometric powder. The secondary phase was observed at the surface of PbO-rich ceramics and was suggested to be a liquid phase expelled from inside the ceramic. A sintering scheme of PNiNb-PT-PZ ceramics was proposed, and the high sinterability of PNiNb-PT-PZ ceramics was attributed to the low formation temperature of the liquid phase. [source] Chemical Diffusivity of BaTiO3,,: IV, Acceptor-Doped CaseJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2000Chang-Rock Song The chemical diffusivity of 1.8 mol% aluminum-doped BaTiO3,, was measured on single-crystal specimens, as a function of ambient oxygen partial pressure, in the range 10,18 atm ,PO2, 1 atm and at temperatures of 800°,T, 1100°C, via a conductivity-relaxation technique. As in the polycrystalline, undoped BaTiO3,, described in Part II of this work, the chemical diffusivity exhibited a maximum, of thermodynamic origin, approximately at the stoichiometric composition (,= 0). The measured diffusivity was analyzed, based on the defect structure proposed and Wagner's classic theory of chemical diffusion, and the mobilities of the electrons and holes, as well as all of the relevant defect-equilibrium constants, then were evaluated with no prior assumptions. The evaluated parameters were compared with those for the undoped BaTiO3,,. [source] Deformation Mechanism of Fine-Grained Magnesium Aluminate Spinel Prepared Using an Alkoxide PrecursorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000Takeshi Shiono Polycrystalline MgAl2O4 spinel with high purity and stoichiometric composition was prepared using alkoxide precursors. The average grain size of the polycrystal was fine (1.7 ,m). The deformation mechanism of the polycrystal was investigated in air at temperatures of 1300°,1400°C. At 1300°C, oxygen lattice diffusion controlled the deformation, despite the fine grain size; however, increases in the temperature and applied stress caused cavities to nucleate and grow. Spinel possessed better creep resistance than alumina of comparative grain size. The effective diffusion coefficient was determined as follows: [formula omitted] [source] Cover Picture: Laser Phys.LASER PHYSICS LETTERS, Issue 7 2010Lett. It's known that single crystals of germanate melilites, such as Ba2ZnGe2O7 and Sr2MgGe2O7, show a congruent melting behavior at about 1450 °C. Crystals of Sr2MgGe2O7 were grown from melt of stoichiometric composition by the Czochralski technique using a seed crystal orientation (and pulling direction) along [001], a pulling velocity of 2,3 mm/h and crystal rotation of 40,60 rad/min. For single crystal growth of Ba2ZnGe2O7 a melt with a surplus of ,4 wt.% BaO and ,5 wt.% GeO2 proved to be useful. Grown crystals are of dimensions up to 25 mm in length and 18 mm in diameter for Sr2MgGe2O7 and of up to 15 mm in length and in diameter for Ba2ZnGe2O7. In Cover picture an example of a grown crystal of Sr2MgGe2O7 is presented. (Cover picture: A.A. Kaminskii, L. Bohatý, et al., pp. 528,543, in this issue) (© 2010 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] X-ray photoelectron spectroscopy and tribology studies of annealed fullerene-like WS2 nanoparticlesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2008B. Späth Abstract The time dependent chemical changes occurring at the surface of inorganic fullerene-like (IF) nanoparticles of WS2 were investigated using X-ray photoelectron spectroscopy (XPS) and compared to those of bulk powder, 2H-WS2. It was possible to follow the long term surface oxidation and carbonization occurring at defects on the outermost surface (0001) molecular layers of the inorganic fullerene-like nanoparticles. Vacuum annealing was shown to remove most of these contaminants and bring the surface close to its pristine stoichiometric composition. In accordance with previous measurements, further evidence was obtained for the existence of water molecules, which were entrapped in the hollow core and interstitial defects of the fullerene-like nanoparticles during the synthesis. These water molecules were also shown to be removable by the vacuum annealing process. Chemically resolved electrical measurements (CREM) in the XPS showed that the IF samples had become less p-type after the vacuum annealing. Finally, tribological measurements showed that the vacuum annealed IF samples performed better as an oil additive than the non-annealed IF samples and the 2H-WS2 powder. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Microstructure of CuFeS2,,,CuInS2 alloysPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2009B. V. Korzun Abstract Two series of alloys of the (CuFeS2,,)1,x(CuInS2)x system with molar part of CuInS2 x = 0.01, 0.03, 0.125, 0.25, 0.375, 0.50, 0.625, 0.75, 0.95, 0.97 and 0.99 and , being 0 and 0.10 were prepared from the CuFeS2,, and CuInS2 starting ternary compounds. The samples were investigated by micro structural optics using freshly-polished samples and XRPD. The studies confirmed two phase coexistences with microstructures dependent on the chemical composition. The geometric-oriented arrangement of the ,-phase with the structure of CuInS2 is found in the (CuFeS2,,)1,x(CuInS2)x system up to x equalling 0.50. It was established that the solvus of CuFeS2,, exceeds 0.05 molar parts of CuInS2, while the solvus of CuInS2 does not exceed 0.03 molar parts of CuFeS2,,. Additionally, stoichiometric composition of CuFeS2 exhibits a mixture of 3 coexisting phases of CuFeS2,,, with , from 0.14 to 0.28, bornite Cu5FeS4 and pyrrhotite Fe1,xS. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Tetragonal CeNbO4 at 1073,K in air and in vacuoACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2004Stephen J. Skinner The structure of the high-temperature scheelite-type polymorph of cerium niobium tetraoxide, CeNbO4, has been determined using time-of-flight neutron powder diffraction data collected both in situ at 1073,K in air and in vacuo. In both cases, the structure was found to be tetragonal, with I41/a symmetry and without any significant deviation from the stoichiometric composition. [source] Effects of increased temperature and nutrient enrichment on the stoichiometry of primary producers and consumers in temperate shallow lakesFRESHWATER BIOLOGY, Issue 7 2008M. VENTURA Summary 1. We studied the effects of increased water temperatures (0,4.5 °C) and nutrient enrichment on the stoichiometric composition of different primary producers (macrophytes, epiphytes, seston and sediment biofilm) and invertebrate consumers in 24 mesocosm ecosystems created to mimic shallow pond environments. The nutrient ratios of primary producers were used as indicative of relative nitrogen (N) or phosphorus (P) limitation. We further used carbon stable isotopic composition (,13C) of the different primary producers to elucidate differences in the degree of CO2 limitation. 2. Epiphytes were the only primary producer with significantly higher ,13C in the enriched mesocosms. No temperature effects were observed in ,13C composition of any primary producer. Independently of the treatment effects, the four primary producers had different ,13C signatures indicative of differences in CO2 limitation. Seston had signatures indicating negligible or low CO2 limitation, followed by epiphytes and sediment biofilm, with moderate CO2 limitation, while macrophytes showed the strongest CO2 limitation. CO2 together with biomass of epiphytes were the key variables explaining between 50 and 70% of the variability in ,13C of the different primary producers, suggesting that epiphytes play an important role in carbon flow of temperate shallow lakes. 3. The ratio of carbon to chlorophyll a decreased with increasing temperature and enrichment in both epiphytes and seston. The effects of temperature were mainly attributed to changes in algal Chl a content, while the decrease with enrichment was probably a result of a higher proportion of algae in the seston and epiphytes. 4. Macrophytes, epiphytes and seston decreased their C : N with enrichment, probably as an adaptation to the different N availability levels. The C : N of epiphytes and Elodea canadensis decreased with increasing temperature in the control mesocosms. Sediment biofilm was the only primary producer with lower C : P and N : P with enrichment, probably as a result of higher P accumulation in the sediment. 5. Independently of nutrient level and increased temperature effects the four primary producers had significantly different stoichiometric compositions. Macrophytes had higher C : N and C : P and, together with epiphytes, also the highest N : P. Seston had no N or P limitation, while macrophytes and epiphytes may have been P limited in a few mesocosms. Sediment biofilm indicated strong N deficiency. 6. Consumers had strongly homeostatic stoichiometric compositions in comparison to primary producers, with weak or no significant treatment effects in any of the groups (insects, leeches, molluscs and crustaceans). Among consumers, predators had significantly higher N content and lower C : N than grazers. [source] Ways to Create New CHNO-Oxidizers for Stoichiometric Gas-Generating Compositions with Low Combustion TemperaturePROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 5 2007David Abstract The investigation is aimed to study the possibility of creation of new CHNO-oxidizers for smokeless gas-generating compositions for airbag inflators. For ensuring low amount of CO and nitrogen oxides in combustion products it is necessary to create stoichiometric compositions with a relatively low combustion temperature. Ways to create new oxidizers acceptable to this requirement are examined, mainly by introducing low-enthalpy oxygen-containing groups into the oxidizer molecule. Standard enthalpy of formation (,fH°) has been calculated for substances with unknown ,fH°, thermal stability has been qualitatively estimated, and combustion temperatures of stoichiometric compositions have been calculated. [source] | |||||||||||||