Materials Literature
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A numerical technique has been used to predict eutectic compositions of some liquid crystal mixtures; good agreement was found with experimental results on mixtures of 4′-n-alkyl- and 4′-n-alkoxy-4-cyanobiphenyls some of which are nematic over the range 0–60 °C.
Natural diamond was implanted with 40 keV argon ions at room temperature and with fluences 6.1013 − 2.4.1015 cm−2. The crystal structure of implanted layers has been studied and the results are presented.
Après un bref rappel des travaux de Grandjean et de Cano, il est démontré que, lorsqu'un clivage dans un cristal, ou l'espace compris entre deux verres frottés est rempli par un liquide cholestérique, les cloisons apparaissant dans le milieu sont en fait des fils, ainsi que l'avait déjà noté Friedel (1922). Les fils s…
Certain peculiarities of photoconductivity in ferroelectrics are discussed. On the example of the ferroelectric SbSI, the nature of anomalies in electrical conductivity and photoconductivity in the Curie temperature region is discussed. For the first time the photoconductivity in certain ferroelectric niobates and the…
Abstract The heat capacity of SnCl2·2H2O and SnCl2·2D2O crystals, substances with layer structure, was measured from 13 to 300 K. Anomalies due to ordering of the hydrogen (deuterium) position were observed at TC(H2O)=217.94 K and at Tc(D2O)=234.47±0.05 K. The total entropy change of the transition was estimated to be…
A discussion is given of the dielectric properties of some nematic phenyl benzoates with the structure For n = 2 the dielectric anisotropy Δ∊=∊‖– ∊⊥ is found to be positive. For n = 1, however, the sign depends on the para substituents In particular, replacement of an alkyl group by an alkoxy group shifts Δ∊ towards n…
The anomalous ultrasonic attenuation and velocity variation caused by the critical fluctuation of spins near the Curie and Néel temperatures are theoretically investigated and found to be strongly affected by an application of magnetic field. In the random phase approximation, the attenuation coefficient is expressed…
Homolysis of the C–Mn bond of [RMn(CO)5] or [RCOMn(CO)5] under u.v. irradiation has been studied using nitrosodurene as a spin-trap for both the radicals formed; irradiation of various metal–metal bonded compounds (LM–ML, M = Mn, Re, Fe, Mo, or Co) gives rise to metal-centred radicals which can similarly be trapped.
Rates of oxidative vaporization of on preoxidized resistively heated chromium were determined in flowing oxygen at a pressure of 0.115 Torr for temperatures from 1000° to 1300°C. Reaction controlled rates were obtained from experimental rates by a gold calibration technique, and these rates were shown to agree with th…
The influence of the addition of mainly 1st row of transition elements on the resistivity anomaly of BaTiO3 semiconducting ceramics has been examined. The results showed that Mn ion is the most effective in increasing the PTC anomaly by up to a factor of 109. The high temperature chemical behaviour of the ceramics was…
A survey is given of the results of five years electron fractography as conducted at the National Aerospace Laboratory N.L.R. and of the contribution of this work to the comprehension of fatigue cracking, ductile fracture, cleavage and stress corrosion.
W A Wooster Oxford: University Press 1973 pp x + 344 price £7 'The reader who died of boredom' is a built in hazard for the authors of books on group theory, and Dr Wooster sets his own critical standards when he confesses that he has difficulty in keeping awake while reading such books. As a fellow sufferer, I am hap…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStereochemistry of low-spin cobalt porphyrins. III. Crystal structure and molecular stereochemistry of bis(piperidine)-.alpha.,.beta.,.gamma.,.delta.-tetraphenylporphinatocobalt(II)W. Robert ScheidtCite this: J. Am. Chem. Soc. 1974, 96, 1, 84–89Publication Date (Print):Janua…
The contrast in many-beam lattice images from very thin crystals of 4Nb2O5. 9WO3 is shown to be directly related to its known structure. On the basis of this correlation, the structure of 2Nb2O5.7WO3 is derived from the observed image contrast; it is an ordered intergrowth of the ReO3 and tetragonal tungsten bronze st…
Crystals of the title compound are monoclinic, space group C2/c, a= 18·14(1), b= 18·62(1), c= 18·51 (1)Å, β= 95·9(5)°, Z= 4. The heavy atoms were located by direct methods and the oxygen and sodium atoms by difference Fourier analyses, with block-diagonal least-squares refinement to R 0·083 for 2781 independent reflec…
SummaryTin coatings and some tin alloy coatings from various plating baths and on several substrates have been kept under observation for spontaneous whisker growth for periods up to 20 years. A review of the results and of information obtained elsewhere suggests that, although assured immunity from whiskers may be di…
The partial pressures of the gaseous species in equilibrium with solid silicon in the Si‐H‐Cl system are presented as a function of temperature for different Cl/H ratios and total pressures. Computations were performed using our recently determined value of Δ Hf ° 298 ( SiHCl 3 , g ) = − 116.9 kcal / mol . Experimenta…
The steady-state distribution of mobile point defects in a monatomic solid under irradiation has been calculated for a semi-infinite solid and for a foil. The calculation was performed for defect annihilation by mutual recombination, at internal sinks, and by diffusion to the surface. Simple approximations, accurate t…
Conditions for the nucleation of recrystallized grains are briefly reviewed with emphasis placed on the orientation-dependent aspects. Distinction is drawn between nucleation sites within grains, at grain boundaries, and at transition bands. These sites are shown to have different orientation dependences. The role of…
The inherent characteristics of the instrumented impact test are discussed. The hammer energy is reduced by deforming the test specimen, accelerating the specimen from rest, Brinell-type deformation at the load points, vibrations of the hammer assembly, and elastic deformation within the machine. The limitations of th…