Materials Literature
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Encapsulation of platinum-group metals (Ru, Rh, Pd, Os, Ir, Pt) within carbon nanocapsules and synthesis of single-layered (SL) carbon nanotubes by arc evaporation of metal/carbon composites have been studied. Transmission electron microscopy revealed that all the platinum-group metals, forming small particles (10–200…
The intermediate‐temperature oxidation embrittlement, or ‘pest,’ effect found in ceramic‐matrix composites (CMCs) is shown to have features analogous to stress corrosion cracking. The behavior involves crack growth upon oxidation of the fibers or the fiber coatings to form an oxide that weakens the fibers. It has reac…
Abstract The iron(II) complex [Fe(bpp) 2 ]‐(CF 3 SO 3 ) 2 H 2 O (bpp = 2,6‐bis(pyrazolyl‐3‐yl)pyridine) shows a thermal spin transition associated with a hysteresis of approximately 140 K width. The transition temperatures T 1/2 (where the fraction of HS species γ HS = 0.5) are 147 K and ≈︁285 K in the cooling and hea…
Gold(III) ions in aqueous solutions of NaAuCl4 were reduced to form gold particles by ultrasonic irradiation. The rate of formation of gold particles was accelerated in the presence of certain organic additives such as surfactants, water-soluble polymers and aliphatic alcohols and ketones. The rates of formation of go…
Micromagnetic calculations using the finite-element method provide a quantitative understanding of demagnetization processes in nanocrystalline ferromagnetic materials. In these materials demagnetization processes are mainly determined by short-range exchange and long-range dipolar interactions, which sensitively depe…
High pulse energies of nanosecond-level fourth- and fifth-harmonic (4omega and 5omega) generation of a Nd:YAG laser have been obtained with a CsLiB(6)O(10) (CLBO) nonlinear crystal. 500 mJ of 4omega output with a conversion efficiency of 50% from the second-harmonic input was generated. 5omega output at 213 nm of as h…
The fictive temperature dependence of the relative abundances of three‐ and four‐coordinated boron was investigated in several sodium borate and borosilicate glasses using high‐resolution 11 B nuclear magnetic resonance (NMR). In the compositions with low sodium/boron ratios, no effect was observed, but in the borosil…
Abstract Hydrocracking of vacuum gas oil is an important chemical process involving complex reaction mixtures. The reaction is carried out in a trickle‐bed reactor, considering reaction kinetics along with such hydrodynamic effects as mass transfer, intraparticle diffusion, and partial wetting. Since reaction kinetics…
Silicon nitride was fabricated by tape casting of α‐Si 3 N 4 powder with 5 wt% Y 2 O 3 and 5 vol% rodlike β‐Si 3 N 4 seed particles, followed by tape stacking, hot pressing under 40 MPa, and annealing at 1850°C for 2‐66 h under a nitrogen pressure of 0.9 MPa. Silicon nitrides fabricated by this procedure exhibited a h…
The fracture behavior of multilayer Si 3 N 4 /BN ceramics in bending has been studied. The materials were prepared by a process of tape casting, coating, laminating, and hot pressing. The Si 3 N 4 layers were separated by thin, weak BN interlayers. Crack patterns in bending bars were examined with a scanning electron…
All articles of this category The synthesis and characterization of a variety of subphthalocyanines and subnaphthalocyanines are reported. The isomers of several trisubstituted subphthalocyanines were separated by HPLC. The physical properties of subphthalocyanines are investigated and their use as novel targets for N…
The mean first passage time for the close approach of the ends of a polymer is investigated by computer simulation of the Brownian dynamics of a Rouse model. There are N bonds, of length b, and the contact distance is a. The results for N=50, 75, and 100 are compared with theoretical predictions by Wilemski and Fixman…
The photoluminescence (PL) of amorphous hydrogenated carbon (a-C:H) has been investigated as a function of optical gap and excitation energy. The PL spectra exhibit a red shift when the excitation energy falls below the optical gap. The bandwidth of the PL spectra increases with the excitation energy but depends very…
The use of electron energy-loss spectroscopy for characterization of zirconium oxide pseudopolymorphs is investigated. The results demonstrate that spectroscopic ``fingerprints'' for each phase can be identified and the technique can be utilized for phase identification. The oxygen K-edge spectra are analyzed in detai…
Macroscopic particles of size a immersed in liquid crystalline solvents (e.g. polystyrene spheres in a lyotropic nematic) will exert long-range forces on each other by distorting the order-parameter field around them. As a first step towards a full theory of this novel class of suspensions, we show how to calculate th…
Temperature dependences of dielectric constants, specific heat and D – E hysteresis loops of Li-doped zinc oxide ceramics were investigated. A new dielectric anomaly was found at 330 K in Zn 1- x Li x O with x =0.17. A cusp-like anomaly was also found in specific heat. A ferroelectric D – E hysteresis loop was success…
The effects of growth processes on the chemical bond structure, microstructure, and mechanical properties of carbon–nitride (CNx) thin films, deposited by reactive magnetron sputtering in a pure N2 discharge, are reported. The film deposition rate RD increases with increasing N2 pressure PN2 while N/C ratios remain co…
Abstract The cornucopia of novel porhyrinoid macrocycles that ‐ as a result of a symbiotic link between annulene and porphyrin chemistry ‐ has emerged from the Cologne laboratory over the last decade is reviewed.
The dielectric and piezoelectric properties of solid solutions with compositions PbZr 1- x Ti x O 3 , x =0.200 to 0.750, with an 0.005Nb 2 O 5 additive prepared by modern ceramic technology were investigated, focusing on the morphotropic phase boundary (MPB, x =0.467). Relationships between the dielectric, piezoelectr…
The presence of two distinctly different local segmental mobilities found in the case of several phase mixed polymer blends by two-dimensional 2H-NMR, dielectric spectroscopy and depolarized dynamic light scattering is rationalized through a simple concentration fluctuation model. Our primary hypothesis is that, altho…