Uniform Grain Size Research Articles

Preparation of zirconia-toughened mullite with dissociated zircon

A method for the preparation of zirconia-toughened mullite using dc plasma is presented. An indigenously developed 50-kW thermal plasma reactor is used for the preparation of zirconia-toughened mullite using a dissociated zircon and alumina mixture. Both XRD and SEM studies of the product confirmed the formation of mullite and zirconia. The zirconia grew as equiaxed grains of uniform size (~5 μm) in a mullite matrix.

Preparation of nano-crystalline SrTiO 3 powder in sol-gel process

SrTiO 3 nano-powder in the sol-gel process was prepared with Sr(NO 3) 2 and Ti(C 4H 9O) 4 materials in order to acquire uniform size grains and even doping. The thermal treating conditions were selected out through DTA/TGA analysis of the powder. The crystallinity and purity of the powder were studied with X-ray diffraction spectrometer. The size and the distribution of SrTiO 3 grains were tested by transmission electron microscope (TEM). The effects of CH 3COOH and water concentration on the qualities of SrTiO 3 powder were studied and the proper process preparing powder was optimized.

NRM intensity of altered oceanic basalts across the MAR (21°N, 0-1.5 Ma): a record of geomagnetic palaeointensity variations?

Summary During cruise Tammar (May 1996) of R/V Nadir and submersible Nautile, 66 basaltic rock samples were collected along two long cross-sections encompassing the oceanic crust between 0 and 1.5 Myr at the centre of the mid-Atlantic ridge segment located at 21°N. This dense sampling provides a means to investigate natural remanent magnetization (NRM) variability with age using rock magnetic studies (high-field and k–T experiments, palaeofield intensity determinations by the original Thellier method) together with the good geophysical and geological knowledge of this peculiar segment. NRM intensities range from 1.3 to 25.4 A m−1 but do not display any rapid exponential decay with age, as expected. Despite the scatter, they seem to present short-wavelength variations consistent on both flanks of the two lines. Because of the relative uniformity in grain size (i.e. single domain, SD), ulvospinel content (i.e. x = 0.6) and amount of magnetic minerals in Tammar samples, the observed across-axis NRM intensity variations may be due either to oxidation degree variations or to geomagnetic field intensity changes. Curie temperatures display no increase towards the flanks nor a clear relationship with NRM intensities, suggesting that oxidation degree is not the major process controlling the NRM variations. Half of the collected samples, either fresh or highly altered, provide good-quality palaeointensity determinations. Depending on the alteration degree of samples, two major types of NRM/TRM diagrams are observed. For relatively fresh materials, only one line segment and the major part of NRM is used for field intensity calculations. For moderately or highly altered specimens, two line segments are observed with the first most probably corresponding to thermal demagnetization of the original remanence, and the second to the product resulting from chemical modification (i.e. inversion). Despite the difference in the amount of NRM that can be thermally demagnetized, samples of similar age but of different non-stoichiometric degree give coincident palaeofield strengths. Palaeofield values, from 15 to 62 µT (i.e. VADM from 3.4 to 13.6 × 1022 A m2), are in good agreement with the global palaeointensity database, and display coherent short-wavelength undulations with age, consistent (assuming a 1-km-wide neo-volcanic zone and steady, symmetrical spreading) with the relative palaeointensity record deduced from sediment core analysis (Guyodo & Valet 1999). Comparison between NRM and field intensity variations with age reveals a remarkable coincidence between both signals, suggesting that the NRM intensities are more sensitive to the field intensity than to the alteration degree. These observations suggest that magnetic particles are titanomaghemites, generated during the initial magma cooling and storing a durable record of the geomagnetic field intensity. The type of remanence is either (1) a chemical remanent magnetization that closely mimics the properties of the initial NRM or (2) a thermoremanent magnetization (the maghemitization precedes the TRM acquisition) or (3) a mixture of both.

Improved properties of polycrystalline GaN grown on silica glass substrate

Much improved optical properties are obtained for the polycrystalline GaN layers grown on amorphous silica glass substrate by gas source molecular beam epitaxy using an ion removed electron–cyclotron resonance radical cell. Photoluminescence (PL) spectrum shows a strong band edge emission with a full-width at half-maximum (FWHM) as less as 60 meV at room temperature. 8K PL spectrum has only two sharp peaks at 3.49 eV (FWHM 17 meV) and at 3.44 eV (FWHM 30 meV). X-ray diffraction rocking curve indicates C-axis orientation. Atomic force microscopy image shows a strongly oriented uniform-size grain structure surface morphology. Clear correlations between the PL properties and the crystalline structures (qualities) are observed.

A Study on the Suitability of Unmalted Sorghum as a Brewing Adjunct

Grain samples of thirteen sorghum cultivars with diverse chemical composition were assessed for their suitability as brewing adjuncts based on proximate analysis. Sieving analysis of the grain as well as hot water extractables (HWE), hot water extractable protein (HWEP) and free amino nitrogen (FAN) were also determined. Cultivars with high starch and amylose contents together with low protein and fat percent are better suited as adjuncts depending on their hot water extracts and hot water extractable protein yields. Large variations in the uniformity of grain size were found, two of these cultivars (CSV-14R and M 35-1) had highest grain size. Cultivars CSH-5, CSV-11 and CSV-13 among the released cultivars were identified as better adjuncts which could be used along with barley malt for brewing lager beers.

Distribution and fractionation of heavy metals in the surface sediments of the Ganges- Brahmaputra-Meghna river system in the Bengal basin

The lower Ganges-Brahmaputra-Meghna (G-B-M) drainage basin occupies the total Bengal Basin, which is one of the unique basins of the world because of its location and size, density of population, and catastrophic deposition of sediments. The increased heavy metal concentration in the 63 m fraction of surface sediments shows similarity among major segments of the G-B-M system in the basin, which reflects the homogenization of lithologic and chemical diversity of the greater denudation regime by the river processes. The differences in heavy metal concentation in the lower G-B-M system with that of its upper and middle counterpart is mainly related to the contrast between Himalayan rivers and the other major South Asian rivers, and may be due to the geological differences of their denudation regime. Heavy metals in the Lower G-B-M system have an affinity towards the clay fraction of the sediments. The correlation matix of heavy metals in the lower Brahmaputra and Meghna suggests the importance of Fe-Mn oxyhydroxides in their accumulations. Iron, Ti and Mn are higher in the Meghna main channel, Zn is higher in the Meghna tributaries, and Cr is higher in both the Brahmaputra and Meghna compared to the value for standard shale. The enrichment factor is ≤1 for most of the metals except Mn which is relatively higher in the Meghna and lower Ganges main channels. The geoaccumulation index (Igeo) for most of the heavy metals lies below grade zero, suggesting unpolluted sediment quality. The lower Ganges system shows relatively higher concentration in the nondetrital fraction of heavy metals, probably due to the presence of petroleum refinery, industrial and mining effluents, and agricultural runoff in the drainage basin. The relative uniformity in concentration of heavy metals in vertical profiles may be due to the uniformity in sediment grain size and catastrophic deposition of sediments, where the time period represented by the vertical sediment column is not enough to reflect the cultural accumulation of heavy metals. The Bengal basin thus represents a relatively unperturbed alluvial basin with regards to heavy metal pollution.

Natural Low-Frequency Riblets

A turbulent flow at modest Reynolds numbers (26,000–32,000, as defined in the text) over flat erodible sandy beds was investigated. The beds were composed of sand grains of uniform size with a diameter smaller than the viscous sublayer of the flow. When a modest sand transport (1.2 × 10-3–8.5 × 10-3 g/s·cm) was present, the near-wall coherent structures of the flow produced a bed form with a streaky longitudinal pattern. This pattern had a lateral spacing of about 100 viscous units and had less drag than a flat wall.

Electrodeposited CIS-Based Solar Cell Materials

AbstractWe have been investigating the synthesis of novel materials and device structures based on CuInSe2 or CIS system We are interested in developing CIS for use in thin film photoltaic solar cells used in space power systems. Non-stoichiometric native defects allow CIS to be selectively doped n or p type by controlling the Cu to In ratio. The Cu to In ratio of an electrodeposited CIS thin film is shown to be directly proportional to the deposition voltage. This behavior has allowed us to deposit different semiconductor-type films, pn junctions, and multilayer structures from the same aqueous solution. The affect of annealing in an Argon atmosphere and the addition of a wetting agent to our deposition solutions on the structural and electrical behavior of our films was measured. A dramatic improvement in the crystallinity, which was proportional to the annealing temperature was observed. The addition of a wetting agent to the solution was shown to improve the surface morphology and provide uniformity in the grain size. The electrical characterization of Schottky barriers on the CIS showed a decrease in several orders of magnitude of the carrier density with annealing. The ability to incorporate our CIS-based films in pn junction devices using CdS window layers was demonstrated by the rectifying current versus voltage behavior of these junctions.

Shear wave dispersion and attenuation in fine‐grained synthetic olivine aggregates: Preliminary results

Low‐frequency torsional forced oscillation tests have been performed on a fine‐grained olivine polycrystal to determine shear wave dispersion and attenuation. The specimen was a dense hot‐pressed San Carlos olivine aggregate with uniform grainsize of about 50 µm, < 0.1 vol.% of melt and minor amount of hydroxyl (∼100 ppm). Mechanical tests were conducted under 200 MPa hydrostatic pressure, low oscillation frequencies (0.01–1 Hz) and within the linear regime of strain (amplitude < 5 × 10−5). The specimen was first annealed at 1300°C, and subsequently measured at a series of progressively lower temperatures. At 1300°C evidence was obtained of marked viscoelastic relaxation: the shear modulus G is relatively low and strongly frequency‐dependent and the attenuation Q−1 is high (G ∼ 33 GPa, Q−1 ∼ 0.14 for 1 Hz). In the temperature range 1100–1300°C, G depends strongly on temperature with |∂G/∂T| several times greater than the value measured in ultrasonic experiments at MHz frequencies. Q−1 varies with temperature and frequency as Q−1=A0 [ωeE/RT]−n with activation energy for the relaxation rate E=420±30 kJ/mol and exponent n=0.31±0.02. The presence of thermal cracks complicates the interpretation of data obtained at temperatures below 900°C. Grainsize‐sensitive processes may be responsible for much of the observed viscoelastic relaxation. The strong temperature sensitivity of the shear modulus suggests much smaller thermal anomalies than are commonly inferred to be responsible for the variability of seismic wave speeds in the upper mantle.

Ｐｒ系ＺｎＯバリスタのエネルギー耐量に及ぼす焼成雰囲気の影響 （ＩＩ）

Effect of sintering atmosphere on maximum-energy capability of Pr-doped ZnO varistor has been studied with special reference to the microstructure. It is shown that maximum-energy capability and non-linearity are effectively improved by both introducing N2 at the heating up process of sintering and annealing at 1200°C under O2 atmosphere at cooling process. Maximum-energy capability strongly depends on the uniformity of grain size . According to the complex impedance analysis, it was found grain-boundary resistance increased and grain resistance decreased with N2-Air-O2 sintering. TEM-EDS, C-V characteristics and ICTS analysis showed that non-linearity depended on acceptor concentrations N3 which were mainly contributed by adsorbed-oxygen on Pr2O3 at grain boundaries. Interface state was calculated as 0.78eV. It was clarified by V-I characteristics of one grain boundary that grain boundary contributes varistor characteristics.

Ｐｒ系ＺｎＯバリスタのエネルギー耐量に及ぼす焼成雰囲気の影響

Effect of sintering atmosphere on maximum-energy capability of Pr-doped ZnO varistor has been studied with special reference to the microstructure. It is shown that maximum-energy capability and non-linearity are effectively improved by both introducing N2 at the heating up process of sintering and annealing at 1200°C under O2 atmosphere at cooling process. Maximum-energy capability strongly depends on the uniformity of grain size . According to the complex impedance analysis, it was found grain-boundary resistance increased and grain resistance decreased with N2-Air-O2 sintering. TEM-EDS, C-V characteristics and ICTS analysis showed that non-linearity depended on acceptor concentrations N3 which were mainly contributed by adsorbed-oxygen on Pr2O3 at grain boundaries. Interface state was calculated as 0.78eV. It was clarified by V-I characteristics of one grain boundary that grain boundary contributes varistor characteristics.

Grains in shocks in weakly ionized clouds - II. Magnetic field rotation in oblique shocks

A four-fluid treatment of oblique C-type shocks in magnetized dark molecular clouds is presented. The four fluids are those consisting of neutrals, ions, electrons and negatively charged spherical grains of uniform size and composition. The charged particles couple to the neutrals by frictional interaction and their motion is described by the drift approximation. In an oblique shock, a current is set up which has a component parallel to the magnetic field component transverse to the shock velocity; this component of the current induces rotation of the magnetic field around the shock propagation direction. We give steady solutions for oblique C-type shocks for which the propagation speed is only slightly above the coupled Alfvén speed of about 2.2 km |$\text s^{-1}$|⁠. in these shocks, the magnetic field component transverse to the shock velocity rotates by |$180^\circ$| through the shock. The rotation occurs for the upstream perturbations chosen in previous studies of steady oblique shocks in molecular clouds. it is possible that the set of upstream perturbations that do not lead to large rotation in these shocks is nonempty, but we find that the set is limited. We also find that, for reasonable dark cloud parameters, the rotation ill a shock with a speed of a few km |$\text s^{-1}$| or more is sufficient to cause the velocity component parallel to the shock velocity of at least one of the charged fluids to drop sharply to zero in the shock frame.

Modeling of subsidence and stress-dependent hydraulic conductivity for intact and fractured porous media

This study investigates the changes in deformation and stress dependent hydraulic conductivities that occur as a result of underground mining in intact and fractured porous media. The intact porous medium is assumed to be comprised of regularly packed spherical grains of uniform size. The variation in grain size or pore space due to the effect of changing intergranular stresses results in a change in rock hydraulic conductivity. A model is developed to describe the sensitivity of hydraulic conductivity to effective stresses through Hertzian contact of spherical grains. The fractured porous medium is approximated as an equivalent fracture network in which a single fracture is idealized as a planar opening having a constant equivalent thickness or aperture. Changes in fracture aperture as a result of changes in elastic deformation control the variation of hydraulic conductivity. A model is presented to illustrate the coupling between strain and hydraulic conductivity. Subsidence induced deformations that result from mining induced changes in hydraulic conductivity in both intact and fractured media. These changes are examined and compared with results from a mining case study.

Integral evaluation of the uniformity of aggregate grain size of a concrete mix

A change to a four-component composition equalizes the nonuniformity of the fractions and raises the authority of the standard. Thus, an integral evaluation of the uniformity of the aggregate grain size in a concrete mix make it possible to refine the requirements imposed by GOST on ready-mix fractions as a function of the structure of the composition of concrete, in particular, to increase the standardized yield of pure fraction 5–20 mm with consideration of the gravel content of sand under conditions of three-component concrete.

Nanocrystalline structures from amorphous precursors

The characteristics and production of nanocrystalline materials are briefly discussed, followed by a consideration of the use of an amorphous phase as a precursor to formation of a nanostructured material. The surprising stability of nanostructured grains can be attributed to the uniformity of grain size and pinning by solute, inclusions/pores and triple junctions.

Poly-Silicon Thin-Film Transistors with Uniform Performance Fabricated by Excimer Laser Annealing

Uniform performance in poly-Si thin-film transistors (TFTs) has been successfully achieved by excimer laser annealing. Mobility and its uniformity over a substrate were 59±3 cm2/V·s for n-channel TFTs and 45±5 cm2/V·s for p-channel types. To achieve uniform performance, we combined step annealing that uses two energy levels, and small-pitch annealing that moves a beam forward by a small pitch. The proposed method can improve surface morphology and uniformity of grain size in poly-Si. A 400-stage CMOS shift register composed of these TFTs could operate at 5 V, and attained the speed of 1 MHz at 8 V.

Modélisation du charriage en écoulement fluvial

Modeling of bed load sediment transport for fluvial flow The mathematical modeling choices of bed load transport in rivers must be confirmed by precise data. Collection of field data is long and difficult. Besides, the parameters of natural flows, such as discharge cannot be controlled. For these reasons a 50 m long flume was set up. It makes possible with the help of precise data, no study independantly some of the important physical phenomena involved in bed load transport, such as hydraulic resistance, influence of non uniformity of grain-size, spatial lag effects. This study has been carried out as part of the convention EDF-Ministeres of July 23, 1965.

Statistical considerations on uniform grain size

The distribution of grain size was determined in four alloys: ferritic steel, austenitic steel, zinc, and ferrite-pearlitic steel, using samples that can be considered as having uniform grain size (UGS), in order to delimit this term. It was found that the grain volume distribution in the four samples was log-normal. The concept of UGS was related to the characteristics of the distribution obtained and, specifically, to the value of the standard logarithmic deviation which was equal to 1 in the four samples studied. This enables us to know the volume distribution exactly by knowing only the mean geometric volume of the grain.

Applicability of the Biot theory. II. Suspensions

The Biot theory is used to compute compressional wave speeds and attenuation in fluid–solid suspensions. The frame moduli are estimated from the self-consistent theory of composites, assuming needle-shaped pores and spherical or ellipsoidal grains of uniform size. The permeability is computed from the Kozeny–Carman equation. The attenuation data are matched by assuming that all losses are caused by viscous absorption in the fluid.For suspensions of kaolinite, polystyrene beads, and glass beads in various fluids, the Biot model agrees with experimental sound speed data at least as well as do other models. For aqueous suspensions of kaolinite, of attapulgite, and of hydrous aluminum silicate pigments, the Biot model generally is in better agreement with attenuation data than are other models.

Theoretical Models of Porosity Reduction by Pressure Solution for Well-Sorted Sandstones

ABSTRACT The reduction of due to pressure solution is analyzed for some theoretical models consisting of aggregates of spherical grains of uniform size. The analysis is carried out for all six of the stable regular packing arrangements suggested by Graton and Fraser (1935). For each regular packing arrangement, two limiting cases are considered, one with all of the dissolved material removed from the system and the other with all of the material locally precipitated. Even for the most compact packing arrangement and complete local precipitation, the amount of vertical shortening for total reduction is found to exceed 26 percent. A comparison of the amount of reduction due to solution and the additional reduction due to precipitation of the dissolved material as cemen indicates that for all cases, solution is more important in the early stages while cementation becomes more effective in the later stages. The exact relationship also varies according to the packing arrangement and its orientation with respect to the direction of compaction. Cases 1 and 6 show the maximum cementation-solution ratio while Case 3 shows the minimum ratio. The results obtained from studies of regular geometric arrays of spherical grains can be used to estimate the importance of pressure solution as compared to other porosity-reducing mechanisms in the diagenesis of well-sorted sandstones of uniform grain size. Any initial in the sandstone can be represented by combinations of different volume proportions of the various packing arrangements. By comparing the minus cement porosity in a sandstone with the volume of cement predicted by a theoretical model, the role of pressure solution and the minimum volume of cement that has entered or left the system can be estimated.