Materials Literature
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Methane plasmas excited at 25 kHz and 13.56 MHz used for a-C:H deposition have been studied by optical emission spectroscopy. At 25 kHz the emitted bands and lines, namely CH (431.4 nm), H (486.1 nm) and H 2 (463.4 nm), have been found to result from dissociative excitation of the CH 4 molecule under electron impact.…
It is shown that, assuming first order kinetics and a frequency factor s(T) given by s(T)=s 0 T a with -2<or=a<or=2, it is impossible to determine the value of a from any combination of thermally stimulated luminescence (TSL) measurements alone, provided E/kT m is greater than about 20 (E is the activation energy, T m…
Traditionally, synthetic polymers have always been designed to be resistant to microbial attack and are usually stabilized with antioxidants, antiozonants, heat stabilizers and UV stabilizers in order to protect them from environmental degradation. The environmental stability of some polymeric materials, such as const…
Oligomers of synthetic polymers are biodegradable, whereas only few polymers are biodegradable. Polyethylene adipate with Mn 3000 and polycaprolactone with Mn 25,000 were completely degraded by Penicillium spp. Aliphatic and alicyclic polyesters, ester type polyurethanes (I), copolyamide-esters (II) and copolyesters (…
This overview is an attempt to briefly cover the history and recent developments in environmentally degradable commodity and specialty polymers and plastics. Degradation pathways are mentioned, polymer types, including blends, are reported and the limitations of current testing protocols raised. The chapter concludes…
Recent work on the synthesis, structure and some properties of macromolecules bearing furan rings is discussed. Two basic sources of monomers are considered, viz. furfural for monomers apt to undergo chain polymerization and hydroxymethylfurfural for monomers suitable for step polymerization. Within the first context,…
Using synchrotron x-ray-scattering measurements on ${\mathrm{NbSe}}_{3}$, we show that the diffuse scattering associated with the ${\mathit{q}}_{1}$ charge-density-wave fluctiations are rods perpendicular to the (a,b) planes reflecting a 2D regime of fluctuations with an in-plane anisotropy ${\ensuremath{\xi}}_{\mathi…
Large second hyperpolarizabilities, 〈γxxxx〉, have been measured in solutions of two recently prepared organic polymer superlattices. These compounds have period aromatic and quinoidal structures and differ from each other by a side group substituent. The values observed are 1.6×10−29 esu for the parent copolymer and 3…
Infinitely many lines of zero thickness may be adsorbed onto a plane without overlap, and it is shown that the number of lines adsorbed should scale as 1 3/, where is the number of adsorption trials per unit area of surface. This is confirmed by numerical simulation. The adsorption of ellipses with major and minor axe…
The special properties of calcium aluminate cements make them of value in the construction, mining and refractory industries. This book brings together new international research information on their performance. As well as a state-of-the-art review, it includes reports on studies of: mineralogy, hydration and microst…
Abstract The powders of Bombyx mori silk fibroin were prepared from aqueous solutions of silk fibroin by several kinds of the insolubilization methods, some of which used methanol. The insolubilization appeared to be effected by the conformational transition of silk fibroin from the random coil to antiparallel β‐sheet…
X-ray diffraction analysis (at 2.1-A resolution) of an acid alpha-amylase from Aspergillus niger allowed a detailed description of the stereochemistry of the calcium-binding sites. The primary site (which is essential in maintaining proper folding around the active site) contains a tightly bound Ca2+ with an unusually…
For pt.I see ibid., vol.21, p.3165 (1988). The density-functional theory of freezing is extended to the case of binary mixtures of hard discs viewed as a simple model for monolayers adsorbed on a smooth substrate. The theory is applied to the fluid-disordered crystal transition. The results are similar to those alread…
The long-range behaviour of the orientational fluctuations of a pair distribution function is studied. The existence of the instability of an isotropic liquid against formation of the state with bond orientational order is shown. The estimated for the instability points for a Lennard-Jones liquid are obtained, and a c…
The properties of the ferroelectric IV-VI semiconductor GeTe have been studied as a function of pressure up to 25 GPa at room temperature, by powder X-ray diffraction in a diamond anvil cell. In a truly hydrostatic medium, the transition from the rhombohedral to cubic NaCl-type structure was not observed up to 8 GPa w…
Pyrite films were prepared using the pure elements as source materials: thin iron films were evaporated on quartz substrates and exposed to a sulfur plasma. The process was controlled by a transmission measurement. X-ray spectroscopy was used to characterize the films and preliminary optical and electrical measurement…
The photoconductivity of vacuum-evaporated vitreous selenium films has been found to depend strongly on residual gases which exist in the vacuum chamber. Specific effects depend on whether these gases are the result of increased system outgassing or purge gas leaked into the evaporation chamber. Films that were evapor…
Different solid-state refining techniques can be used to decrease the interstitial impurity level of refractory and other high melting metals. Purification by external gettering is particularly effective for carbon, oxygen and nitrogen in vanadium and niobium. Oxygen and nitrogen can also be readily removed from niobi…
Abstract Yield strength of NaCl: Eu 2+ monocrystals was studied as function of both the dopant concentration and the annealing parameters. Main attention was paid to the strengthening mechanisms induced by the presence of europium related second phases the structure of which was controlled by means of optical methods.…
Abstract 29 Si‐NMR has been used to identify and analyze oligomeric mixtures of diorganyl cyclosiloxanes of the general formula F n D m − n (D = (CH 3 ) 2 SiO, F = CH 3 (CH 2 CH)SiO, m = 3–5 and n = 0 − m ). Chemical shift assignments were confirmed by comparing 29 Si‐NMR and GC‐MS results for composition of the mixt…