Materials Literature
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Bayum hexaferrites are anisotropic iron oxides which can present high values of permeability. We have studied Ba(Co,Ti)xFe12-2xO19 ( M type) and Ba3Co2Fe24O41 (Z type) compositions. Powders are synthetized using a classical ceramic method (M type) or a chemical one (Z type) consisting in the coprecipitation of carbona…
Solution equilibria and optical spectra of several metallooctaethylporphyrin π-cation radicals have been examined in methylene chloride solution. The several π-cation radical species, [M(OEP • )]Y (M = Cu, Ni, Zn, Pd, or VO; Y = ClO 4 - or SbCl 6 - ), are found to dimerize to form [M(OEP • )] 2 2+ . These dimeric spec…
Small-angle light scattering and scanning electron microscopy (SEM) have been used to study morphology development in poly(methyl methacrylate) membranes formed by the thermal inversion method. Analysis of the early time behavior of the scattered intensity in terms of Cahn−Hilliard theory establishes spinodal decompos…
The Bacillus subtilis araC locus, mapped at about 294 degrees on the genetic map, was defined by mutations conferring an Ara- phenotype to strains bearing the metabolic araA, araB, and araD wild-type alleles (located at about 256 degrees on the genetic map) and by mutants showing constitutive expression of the three g…
The unusual magnetic properties of La0.5Ca0.5MnO3 were found to be associated with structural and magnetic ordering phenomena, resulting from the close interplay between charge, orbital, and magnetic ordering. Analysis of synchrotron x-ray and neutron powder diffraction data indicates that the anomalous and hysteretic…
Experiments were conducted to determine the effect of changing the acid volume, acid normality, and incubation time on in vitro solubility values of various test calcium samples. A 200 mL volume of 0.2N HC1 solution combined with 2.0 g sample size and 10 min incubation time at 42°C produced a limestone solubility rang…
Rate coefficients of the reaction of hydroxyl (OH) radicals with CH 3 OCH 3 ( k 1 ) and CH 3 OC(CH 3 ) 3 ( k 2 ) over an extended temperature range are reported. Measurements were performed using a laser photolysis−laser-induced fluorescence technique under slow flow conditions at a total pressure of 740 ± 10 Torr. Ar…
Experimental solubilities are reported at 25.0 °C for trans-stilbene dissolved in 28 different organic nonelectrolyte solvents containing methyl, ether, hydroxy, and tert-butyl functional groups. Results of these measurements are used to test the applications and limitations of expressions derived from Mobile Order th…
The nature of extrinsic point defects in lead zirconate titanate (PZT) ceramics of various compositions prepared by solution chemistry has been explored. Using electron paramagnetic resonance (EPR), several impurity sites have been identified in the as‐received materials, which include Fe 3+ oxygen vacancy (V O ‥ ) co…
Since the early study by Galasso and Pyle, the structure of complex perovskite compounds with 1:2 ordering of B-site ions, ordered perovskite compounds, has been thought to be Ba(Sr 1/3 Ta 2/3 )O 3 -type hexagonal. Recently, a structural phase transformation has been found in A-site substituted ordered perovskite comp…
Amorphous SixGeyOz alloy films of different chemical composition and SiOx/GeOy multilayers are prepared by dc magnetron sputtering. The formation of Ge nanocrystals in the alloy matrix is induced by annealing at temperatures ranging from 700 to 900 °C. In contrast, the crystallization in the Ge sublayers in the multil…
Abstract Absorption and fluorescence spectroscopies were applied to study the adsorption of rhodamine 6G on several smectite-type clays in aqueous suspension. The dye can be adsorbed as the monomeric and the dimeric forms on both the external and the interlamellar surfaces of the clay. The presence of these species an…
The influence of grinding on the thermal transformation of pyrophyllite to mullite is analyzed by 27 Al and 29 Si MAS NMR spectroscopies, using X-ray powder diffraction and thermal analysis (DTA-TG) as complementary techniques. Mechanical treatments by dry grinding produce partial destruction of pyrophyllite and rearr…
In lyotropic liquid crystalline polymers, flow is known to induce either director tumbling or flow alignment, depending on the shear rate. Recently the existence of an intermediate transition region, a “wagging” regime, has been predicted on the basis of molecular theories. Here, rheological and rheo-optical technique…
Rare-earth-metal ions (Pr 3+, Sm 3+, Eu 3+, Tb 3+, Dy 3+, and Er 3+ ) doped in KLaNb 2 O 7 with a layered perovskite structure showed photoluminescence by excitation of the two-dimensional host at 77 K. Dy 3+ - and Er 3+ -doped KLaNb 2 O 7 showed the luminescence of both rare-earth-metal ions and host. In contrast, Pr…
Abstract Sulfur cured SBR elastomers, devulcanized by high power ultrasonic irradiation, were revulcanized by using the same curing conditions as for virgin SBR. Crosslink density and gel fraction of virgin, devulcanized, and revulcanized elastomers were measured. Curing behavior of some model compounds based on virgi…
The mechanism of stain formation in the chemical etching reaction of silicon has been investigated in HF–oxidizing agent–H2O solutions. The chemical formula of the stain formed during the silicon etching reaction is K2SiF6. The concentration of holes on silicon surface increases with the increase of redox potential an…
In order to follow the insulator to conductor transition in a polymer when it is subject to a progressive degradation process, we have irradiated about 50 samples of poly(imide) Kapton with heavy ions and measured their conductivities as functions of temperature, electric field, and frequency. Electron spin resonance…
Synthesis of the phase formerly reported as Ba(5)Ga(6) succeeds only in the presence of hydrogen. The heavy atom structure of Ba(5)Ga(6)H(2) has been redetermined by single-crystal X-ray diffraction (trigonal P3c1, Z = 2, a = 7.7698(2) Å, c = 14.3902(7) Å), and the hydrogen positions have been elucidated by time-of-fl…
A model graft copolymer that has well-defined length, number, and position of grafts was prepared via anionic living polymerization. (4-Vinylphenyl)dimethylvinylsilane (VS) was anionically polymerized by cumylcesium in THF at −78 °C for 20 min under a pressure of 10 -5 mmHg, and subsequent addition of styrene (St) yie…