scholarly journals Translucent zirconia polycrystals prepared from nanometric powders

2015 ◽  
Vol 9 (3) ◽  
pp. 175-180 ◽  
Author(s):  
Radosław Lach ◽  
Mirosław Bucko ◽  
Krzysztof Haberko ◽  
Marian Rączka ◽  
Kamil Wojciechowski
Keyword(s):  
Freeze Drying ◽  
Wave Length ◽  
Tetragonal Symmetry ◽  
Particle Sizes ◽  
Closed Porosity ◽  
Cubic Symmetry ◽  
Grain Sizes ◽  
Fine Powders ◽  
Two Factors ◽  
Powder Compacts

The aim of the present study was investigation of synthesis and sinterability of nanometric zirconia solid solution powders containing 8mol% and 3mol% of Y2O3. The powders were prepared by the hydrothermal treatment of the co-precipitated gels, which resulted in very fine powders with particle sizes <10 nm. The main problem in application of such fine powders is their tendency to form hard agglomerates. To overcome this obstacle, the aqueous suspensions of the powders were subjected to the freeze drying. It resulted in the powders composed of very weak agglomerates which were broken under pressure as low as ~1MPa. The powder compacts were sintered in oxygen atmosphere to the state of closed porosity and then HIP-ed at 1300?C to fully dense ceramics. The spectrophotometric investigations in the wave length range of 190-1100 nm indicated higher translucency of the 8mol% Y2O3-ZrO2 than the 3mol% Y2O3-ZrO2 ceramics. Most probably it should be related to the birefringence phenomenon which occurs in the latter case due to the tetragonal symmetry of this material. In the polycrystal containing 8mol% of Y2O3 this phenomenon does not occur due to its cubic symmetry. The other two factors which lead to the decreased optical transparency of the material containing 3mol% Y2O3 are its smaller grain sizes and the presence of some amount of the monoclinic phase.

scholarly journals THEORY AND MEASUREMENT OF VISUAL MECHANISMS

1941 ◽  
Vol 25 (2) ◽  
pp. 293-308 ◽  
Author(s):  
W. J. Crozier ◽  
Ernst Wolf
Keyword(s):  
Wave Length ◽  
Theoretical Interpretation ◽  
Rational Relation ◽  
Flicker Response ◽  
Foveal Region ◽  
Two Factors ◽  
Image Area ◽  
Real Test

The several parameters of the flicker response contour (F – log I) are considered as a function of wave-length composition (white, blue, and red) and light-time fraction, for an extra-foveal region (monocular, temporal retina). These data are compared with those secured for the same image area centrally fixated at the fovea. The systematic changes in the parameters are shown to be in rational relation to other relevant excitability data. Since for two retinal regions the primary contours are quite different, the systematic nature of the behavior of the parameters in the two cases is a real test of the power of the analysis proposed. Theoretical interpretation is required to deal with the properties of sets of performance contours under systematically varied conditions, and cannot rely simply on the comparison of (for example) two contours under the same arbitrary conditions at two retinal locations. In particular it is emphasized that a qualitative separation must be made of the two factors of (a) number of units and (b) the frequencies of their actions, before the wave-length problem can be dealt with effectively.

scholarly journals Effect of porosity and particle size on microwave heating of copper

2010 ◽  
Vol 42 (2) ◽  
pp. 169-182 ◽  
Author(s):  
A. Mondal ◽  
A. Shukla ◽  
A. Upadhyaya ◽  
D. Agrawal
Keyword(s):  
Particle Size ◽  
Particle Sizes ◽  
Metallic Materials ◽  
Bulk Materials ◽  
Microwave Furnace ◽  
Particulate Form ◽  
Heating Profiles ◽  
Powder Compacts ◽  
Heating Behavior ◽  
Difference Time

The present study investigates the effect of varying particle size and porosity on the heating behavior of a metallic particulate compact in a 2.45GHz multimode microwave furnace. Experiments on copper suggest that unlike monolithic (bulk) materials, metallic materials do couple with microwaves when they are in particulate form. The powder compacts having higher porosity and smaller particle sizes interact more effectively with microwaves and are heated more rapidly. A dynamic electromagnetic-thermal model was developed to simulate the temporal temperature distribution using a 2-D finite difference time domain (FDTD) approach. The model predicts the variation in temperature with time during heating of copper powder compacts. The simulated heating profiles correlate well with those observed from experiments.

scholarly journals Sintering of a fine-grained BaCeO3 powder obtained from a co-precipitation method

2018 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Precursor Powder ◽  
Coarse Grained ◽  
Precipitation Method ◽  
Fine Grained ◽  
Grain Sizes ◽  
Three Phase ◽  
Sintering Behaviour ◽  
Co Precipitation ◽  
Precursor Powders ◽  
Powder Compacts

The formation of BaCeO3 by a co-precipitation method is described herein. The coprecipitationroute leads to an orange (BaCe)-precursor powder (1). To improve the sinteringbehaviour, a small amount of Ge4+ was incorporated, leading to a (BaCe0.95/Ge0.05)-precursor(2). Both precursor powders results in fine-grained preceramic powders (1A, 2A) aftercalcination. The shrinkage and sintering behaviour of resulting powder compacts were studiedin comparison to a coarse-grained mixed-oxide BaCeO3 powder (3). Compacts of 2A reach arelative density of 90 % after sintering at 1350 °C with grain-sizes between 0.9−3.2 μm. Onthe other hand ceramics of 1A and 3 have, after sintering at 1500 °C (10 h), relative densitiesof 85 % and 76 %, respectively. Ceramic bodies of 1A consisted of phase-pure orthorhombicBaCeO3, whereas bodies of 2A show reflections of BaCeO3 and a Ba2GeO4 phase. DTAinvestigations of samples 1A and 2A reveal three phase transitions at 255 °C (1A) and 256 °C (2A) as well as 383 °C (1A) and 380 °C (2A). A very weak one can be obtained in the range880−910 °C

A MEASUREMENT OF ULTRASONIC ATTENUATION COEFFICIENT BY FREQUENCY RESPONSE IN STEELS WITH DIFFERENT GRAIN SIZES

2003 ◽  
Vol 26 (4) ◽  
pp. 389-402
Author(s):  
Kyung-Cho Kim
Keyword(s):  
Frequency Response ◽  
Attenuation Coefficient ◽  
Evaluation Method ◽  
Ultrasonic Attenuation ◽  
Wave Length ◽  
Structural Behavior ◽  
Response Property ◽  
Sound Waves ◽  
Grain Sizes ◽  
Plate Specimen

A new evaluation method of ultrasonic attenuation in materials is proposed based on the frequency response property of the material evaluated by employing the sound impulse of a wide frequency band. Borrowing from ordinary system theory, the material to be tested is considered to have a characteristic impulse response, representing its micro-structural non-uniformities and thus resulting in the sound attenuation of the material. The concept is resumed as an attenuation system that simulates the material’s micro-structural behavior. Experimental results on a series of specimens, having different grain sizes but all made of a single austenitic stainless steel, showed that the attenuation could properly be evaluated from a single bottom echo in a plate specimen. The attenuation coefficient α, was corrlated in this case to the grain size, D, by the equation, αD=H(πD/λ)n, where λ is wave length and H and n are constants. It was also shown that the micro structural change of materials could be evaluated by the energy loss of sound waves passing through the attenuation systems.

Using Flow Properties to Solve Flow Problems with Hard-to-Handle Powders in the Ceramics Industry

2008 ◽  
Vol 591-593 ◽  
pp. 620-627
Author(s):  
Herman Purutyan ◽  
Alfredo del Campo ◽  
Roger A. Barnum
Keyword(s):  
Titanium Dioxide ◽  
Cohesive Strength ◽  
Particle Sizes ◽  
Flow Properties ◽  
Handling System ◽  
Flow Problems ◽  
Fine Powders ◽  
Common Problems ◽  
Ceramic Manufacturing ◽  
Ceramics Industry

Many processes in ceramic manufacturing require handling of fine powders with particle sizes down to sub-micron range. Problems that are often experienced with these powders, such as stoppages and/or surges, can be predicted and prevented by first measuring relevant flow properties of these powders, and then using these properties to design a handling system. In this paper we will review common problems with handling such powders and the relevant flow properties tests, such as permeability, compressibility, cohesive strength and friction, as well as how these properties can be used to prevent and solve problems. Issues related to handling titanium dioxide (TiO2) will be used as an illustration.

scholarly journals Factors affecting warmth comfort and stuffiness in domestic rooms

1947 ◽  
Vol 45 (4) ◽  
pp. 434-442
Author(s):  
K. W. Yarnold
Keyword(s):  
Air Temperature ◽  
Large Scale ◽  
Wave Length ◽  
Field Work ◽  
The Body ◽  
Equivalent Temperature ◽  
Factors Affecting ◽  
Two Factors ◽  
Striking Change ◽  
The Subject

One object of the investigation was to determine the ideal contributions to warmth comfort in small ‘domestic’ rooms of air heating and radiation. It was soon found that in rooms heated by fires, subjects usually complained of cold backs when the equivalent temperature was in the region of 60–65° F., the accepted standard for buildings heated by convection, and preferred equivalent temperatures above 70° F.Since large-scale trials, using many observers, were clearly necessary, the reliability of 5 min. test periods was studied; these short periods were proved reliable so long as the subject had previously been in a comfortable room for an hour or so.It was found necessary, in rooms heated by fires, to treat separately the side of the subject facing the fire and remote from it. The cooler side must be exposed to an equivalent temperature not much less than 65° F., while radiation falling on the warm side is to be regarded as a very desirable, but nonessential, bonus. These conclusions were confirmed by field work in the subjects' own homes.The eupatheoscope and globe thermometer were modified to enable conditions acting on the two sides of the body to be assessed separately.The extent to which radiation acting on the front of the body could compensate for a cold back to produce what was called ‘minimum comfort’ was also studied. It was shown that down to back equivalent temperatures of about 56° F. an increase of 2° in front equivalent temperature will compensate for a fall of 1° in back equivalent temperature, but below 56° F. compensation fails.The physical basis of sensations of stuffiness and freshness were also investigated. Throughout these experiments care was taken to ensure that the subjects were neither too hot nor too cold. In these conditions, only two factors appear to be important. First, the air temperature should be as low as possible. To obtain warmth comfort with a low air temperature some high temperature source of radiation is generally necessary. The peak wave-length of the radiation emitted by the fire is also of great importance, a striking change in the personal sensations occurring, for example, as the wave-length increases from 2 to 3μ. In general, those wavelengths which are absorbed in the outer layers of the skin cause sensations of stuffiness, and those which are not give rise to feelings of freshness. Peaks at 3, 4·1 and 4·7 μ should therefore be avoided in the design of gas and electric fires.

Paramagnetic resonance of S -state ions in calcium fluoride

1958 ◽  
Vol 247 (1249) ◽  
pp. 141-151 ◽  
Keyword(s):  
Single Crystals ◽  
Calcium Fluoride ◽  
Covalent Bonding ◽  
Tetragonal Symmetry ◽  
Stark Splitting ◽  
Paramagnetic Resonance ◽  
Cubic Symmetry ◽  
Cubic Field ◽  
Hyperfine Structures ◽  
The Eu

Paramagnetic resonance has been observed in Mn 2+ , Eu 2+ and Gd 3+ ions in single crystals of calcium fluoride grown from the melt. The Mn 2+ ion has a very small cubic-field Stark splitting ( a = + 0.6 ± 0.4 x 10 -4 cm -1 ), and a fluorine hyperfine structure of overall splitting of about 60G due to some covalent bonding with the fluorine ligands. The Eu 2+ spectrum has cubic symmetry with splitting parameters b 4 = 57.9 + 0.2, b 6 = 0.5 + 0.2 ( x 10 -4 cm -1 ), but the Gd 3+ spectrum has tetragonal symmetry with much larger Stark splittings; neither ion shows a resolved fluorine structure. The manganese and europium hyperfine structures are closely the same as in other salts with small covalent bonding.

Structural Transformation in Nanowires CuAu I with Superstructure of L10 of Tetragonal Symmetry at Uni-Axial Tension Deformation

2013 ◽  
Vol 592-593 ◽  
pp. 51-54 ◽  
Author(s):  
Mikhail Starostenkov ◽  
Alexander Yashin ◽  
Nikita Sinica
Keyword(s):  
Structural Transformation ◽  
Low Temperatures ◽  
Tetragonal Symmetry ◽  
Cubic Symmetry ◽  
Axial Tension

This article deals with the research of the influence of the anisotropy of the alloys properties having non-cubic symmetry for example nanofibers CuAu I during deformation at low temperatures.

scholarly journals Microwave Emission From Snow and Glacier Ice

1976 ◽  
Vol 16 (74) ◽  
pp. 23-39 ◽  
Author(s):  
T.C. Chang ◽  
P. Gloersen ◽  
T. Schmugge ◽  
T.T. Wilheit ◽  
H.J. Zwally
Keyword(s):  
Accumulation Rate ◽  
Mie Scattering ◽  
Microwave Emission ◽  
Mean Annual Temperature ◽  
Particle Sizes ◽  
Grain Sizes ◽  
Glacier Ice ◽  
The Mean ◽  
The Individual ◽  
Two Parameters

AbstractThe microwave emission from a model snow field, consisting of randomly spaced ice spheres which scatter independently, is calculated. Mie scattering and radiative transfer theory are applied in a manner similar to that used in calculating microwave and optical properties of clouds. The extinction coefficient is computed as a function of both microwave wavelength and ice-particle radius. Volume scattering by the individual ice particles in the snow field significantly decreases the computed emission for particle radii greater than a few hundredths of the microwave wavelength. Since the mean annual temperature and the accumulation rate of dry polar firn mainly determine the grain sizes upon which the microwave emission depends, these two parameters account for the main features of the 1.55 cm emission observed from Greenland and Antarctica with the Nimbus-5 scanning radiometer. For snow particle sizes normally encountered, most of the calculated radiation emanates from a layer on the order of 10 m in thickness at a wavelength of 2.8 cm, and less at shorter wavelengths. A marked increase in emission from wet versus dry snow is predicted, a result which is consistent with observations. The model results indicate that the characteristic grain sizes in the radiating layers, dry-firn accumulation rales, areas of summer melting, and physical temperatures, can be determined from multispectral microwave observations.

The Location of Tantalum Atoms in Ni3Al

1988 ◽  
Vol 133 ◽  
Author(s):  
Hui Lin ◽  
David P. Pope
Keyword(s):  
Diffraction Method ◽  
Average Particle ◽  
Grinding Process ◽  
Particle Sizes ◽  
X Ray ◽  
Fine Powders ◽  
Superlattice Peak ◽  
Melt Spun ◽  
Simple Substitution ◽  
Melt Spun Ribbons

ABSTRACTAn X-ray powder diffraction method was used to determine the location of tantalum atoms in Ni3Al. A series of Ni3 (Al,Ta) alloys were produced with tantalum content ranging from 0.1 to 3.0 at%. Fine powders with average particle sizes less than 80 pm were made from melt-spun ribbons by a grinding process. The values of the superlattice peak intensities normalized to the intensity of the (200) fundamental peak agreed with the calculated values assuming that tantalum atoms substitute on aluminum sites, not on nickel sites. Thus it is concluded from our experiments that tantalum atoms substitute for aluminum in Ni3Al, except for Ta contents around 0.2 at% where the data can not be interpreted in terms of a simple substitution scheme.

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