Liquid Air Temperature Research Articles

Herstellung von Feinkristallinen oder amorphen BeO-Schichten durch reaktive verdampfung von beryllium

Layers of BeO have been formed in an ultra-high-vacuum system by reactive evaporation of Be according to Auwärter at a partial O 2 pressure of 10 -2 Pa. The BeO layers, which were of an arbitrary thickness, show almost no absorption in the visible wavelength range and may be prepared with surface resistivities ( i.e. ratio of resistivity to thickness) greater than 10 13Ω. with decreasing thickness of the BeO layers and with decreasing temperature of the substrate the grain size becomes smaller. If the substrate is kept at liquid air temperature, amorphous BeO layers are obtained which are of interest for electron microscopical purposes because of their low mass thickness and high resistance to chemicals. Under intense electron bombardment, thin extended monocrystalline BeO foils are formed by recrystallization processes.

Raman and infrared spectra of copper formate tetrahydrate

The Raman and i.r. spectra of antiferroelectric copper formate tetrahydrate have been recorded. The i.r. spectrum of copper formate tetrahydrate at liquid air temperature (the phase transition is at −38·9°C) does not show any striking changes from the room temperature spectrum except for intensity variations. This is explained as due to the fact that the frequency of reorientation of the protons even in the paraelectric phase is much less than the optical frequencies.

Optical absorption spectrum of iron in garnet

The optical absorption spectrum of garnet has been studied at room and liquid air temperatures. For the first time the ion responsible for the bands has been identified from spectrochemical and Mössbauer spectral studies as Fe3+. The cubic field approximation with Dq = 1000 cm−1, B = 650 cm−1, and C = 4 B is found to give a good fit to the observed band positions. Das optische Absorptionsspektrum von Granat wurde bei Zimmertemperatur und der Temperatur der flüssigen Luft untersucht. Zum erstenmal wurde das Ion, das für die Banden verantwortlich ist, aus spektrochemischen Untersuchungen und Mößbauerspektren als Fe3+ identifiziert. Es wird gefunden, daß die kubische Feldnäherung mit Dq = 1000 cm−1, B = 650 cm−1 und C = 4 B gute Anpassung an die beobachteten Banden liefert.

Electrical properties of Te-Si heterojunctions†

The electrical properties of Te(p)-Si(n) hetorodiodes are investigated at room and liquid air temperatures. The heterojunotion is formed between an evaporated Te film and an n-type Si single crystal substrate. The forward and reverse characteristics are explained on the basis of an energy band diagram similar to Ge—GaAs and a tunnelling mechanism. The capacitativo eut-off voltage and current cut-off voltage, at room temperature, are found to be about 0·7 v. Preliminary indications are that such a heterojunction is sensitive to I.E. radiation.

Low temperature thermomagnetic effects in n‐type PbS

AbstractTransverse and longitudinal Nernst effects have been measured over the temperature range 1 to 80°K. Acoustical and optical phonons are confirmed as the main scattering mechanisms at liquid air temperatures. At low temperatures neither ionised nor neutral impurity scattering provide an explanation of the measurements. The results are tentatively explained in terms of localised spin scattering.

The Uses of Deuterium in the Study of Heterogeneous Catalysis

Abstract The discovery and isolation of deuterium in 1932 was followed almost immediately by applications to the study of heterogeneous catalysis which appeared in the classical papers of A. and L. Farkas, of Taylor and Morikawa, and of Horiuti and Polanyi. These were primarily studies of isotopic exchange between various hydrides and deuterium, e.g., between methane and deuterium, and between water and deuterium. These investigations provided, for the first time, secure information about the ease of bond cleavage and formation in hydrides: that the bond in H, was cleaved a t a detectable rate on many metals and on chromium oxide at the temperature of liquid air; that on metals the bonds in ammonia and water were readily cleaved although less easily than the H-H bond; that on nickel, for example, C-H bonds were usually more readily cleaved than C-C bonds; and that the rate of cleavage of C-H was in the order methane < ethane < pro-pane.

Thermodynamics of adsorption of organic vapours on carbon black

An apparatus for gas adsorption on solids has been described and with the help of this apparatus specific surface area of carbon black was calculated by the adsorption of nitrogen gas on carbon black at liquid air temperature.

The size analysis of polymer latices by electron microscopy using freeze‐etched preparations

AbstractA range of styrene–butyl acrylate copolymer latices has been studied in the electron microscope, using the freeze‐etching method of specimen preparation. This involves the rapid freezing of a small specimen, fracture of the frozen block, followed by replication of the fracture surface. The process of freezing rapidly to liquid air temperatures minimizes deformation of “soft” latex particles and allows their size to be determined. Certain latices were also investigated using a conventional method of specimen preparation, involving size measurements on dried, deformed particles. The particles observed in freeze‐etched preparations appeared to have slightly smaller diameters.

The stereochemistry of the nickel(II), cobalt(II), copper(II) and palladium(II) complexes of the tetradentate Schiff base derived from salicylaldehyde and isobutylenediamine

The ligand N,N′-bis(salicylidene)-1,1-(dimethyl)ethylenediamine (Sal 2- i-bn) and its complexes with divalent nickel, cobalt, copper and palladium have been synthesized for the first time. The magnetic properties of the complexes have been investigated between 310 and 80°K. The nickel and palladium complexes are diamagnetic. The cobalt complex is low-spin with a magnetic moment of 2·40 → 2·22 B.M. and the copper complex has a temperature independent magnetic moment of 1·81 B.M. Electron paramagnetic resonance spectra of the powders have been measured at room and at liquid air temperatures while the solution spectra of the complexes were studied at room temperature only. The magnetic moment of the copper complex agrees with that calculated from the paramagnetic resonance g 0 ≅ 2·09 at liquid air temperature. The molecular weights were determined by mass spectrometry and by osmometry. Both methods provide evidence for the monomeric nature of the complexes. The i.r., u.v. and visible spectra are very similar to those of other related complexes. The complexes in the solid state and in solution and presumably in the vapor state are square-planar.

Optical and electron spin resonance absorption spectra of manganate ions in alkali halides

Manganese doped potassium iodide crystals containing large amount of background CO 3 2− ions and KCl and KBr crystals grown from the melts containing deliberately added manganese and CO 3 2− ions are green in colour and show four optical absorption bands peaking at 600, 430, 340 and 290 nm. The 600 nm band shifts to ∼ 615 nm if the KI crystals are grown in argon atmosphere and their color becomes yellow-green. The green colored crystals do not show any ESR absorption in the temperature range liquid air temperature (LAT) to 300°C. The KI crystals grown in argon atmosphere show a Lorentzian ESR line with g = 1·980. The half width and intensity of the line is very sensitive to the temperature of measurement. The half width changes from 50G at LAT to 150G at 250°C. The spectra disappears at 300°C. Detailed analysis of these results shows that the manganese impurity is present in hexavalent state as MnO 4 2− oxyanion in these crystals. The manganese impurity reacts with the background CO 3 2− impurity present in the KI and deliberately introduced in KCl and KBr powders and MnO 4 2− ions are formed. In KI crystals grown in argon atmosphere some manganese impurity is present in tetravelent state also.

Optical absorption spectrum of iron in beryl

Abstract The optical absorption spectrum of Fe 3 in beryl has been studied at room and liquid air temperatures. The cubic field approximation with Dq = 1320 cm −1 , B = 720 cm −1 and C = 4.4 B is found to give a good fit to the observed band positions.

Some characteristics of deformation twins in crystalline mercury

Deformation twins have been produced at liquid air temperature by bending mercury single crystals of square cross-section and by indenting flat large-grained polycrystals. The twins all belong to the anomalous Type II mode, reported earlier, which has an irrational composition plane near {1̄3̄5}. They interact amongst themselves and with slip to produce several characteristic features. Thus four crystallographically distinct types of twin interaction arise. One of these, which is termed complementary, is particularly abundant due to a series of crystallographic accidents which enable the strains at the twin intersection to be accommodated almost exactly by a single slip system. These complementary interactions can also occur repeatedly to produce networks of twins. Nine possible interactions between slip and twin boundaries can occur in mercury. The possibility of slip penetrating the boundary in these cases is examined and the resulting twinning dislocations which are responsible for twin growth are discussed. It is concluded that at low temperatures only one of these reactions, which produces groups of four unit twinning dislocations can occur, and this has been conclusively observed in two distinct situations. Facets and indentations in twin boundaries are also investigated and found to have a characteristic crystallographic habit. The structure of this interface is studied in detail and shown to have a semi-coherent nature. The observations are compared with similar features associated with deformation twins in other metals.

Ground state vibrational levels of zinc uranyl acetate

Abstract The vibrational levels in the ground state of zinc uranyl acetate [Zn(UO2)2(CH3)COO)6·H2O] have been established for the first time from the investigations of Raman, infrared and fluorescence spectra of the compound and the fluorescence spectrum has been analysed on the basis of these vibrational frequencies. The Raman spectrum has been obtained with a helium-neon laser as the excitation source. The infrared absorption spectrum has been recorded by both Nujol mull and potassium bromide disc techniques. The fluorescence spectrum has been photographed with powder samples of the compound at liquid air temperature. Besides the uranyl frequencies, eleven fundamentals due to the acetate ion and three fundamentals due to the crystal lattice have been obtained in the infrared and fluorescence spectra. Good agreement has been obtained between the values of the various fundamental frequencies from the different investigations. The interpretation given for the fluorescence spectrum confirms the analysis proposed by Dieke and Duncan involving a single electronic transition from the lowest excited state of the uranyl ion to the various vibrational levels of the ground state.

High temperature superconductivity

AbstractThe critical temperature, Tc, for all presently known superconductors does not exceed 21'K. This fact obviously limits the range of applications of superconductivity in technology in a very fundamental way. On the whole, the reason why the value of Tc for “ordinary” superconductors would not exceed 20‐40oK is fairly well understood. At the same time, there apparently could exist high temperature superconductors for which Tc would reach liquid air temperature or even room temperatures. Possible means of producing high temperature superconductors are considered in this article which is based on the review published in Contemporary Physics, 9, 355 (1968), but includes also some new material. Special attention is paid to what can be called the exciton mechanism of superconductivity and its application to systems of the “sandwich” type and metallic conductors with layer structures.

Studies of water vapor dissociated by microwave discharges at low flow rates. I. Effect of residence time in the traversed volume on product yields at liquid air temperature

Studies of water vapor dissociated by microwave discharges at low flow rates. I. Effect of residence time in the traversed volume on product yields at liquid air temperature

Infrared spectra and rotational isomerism of mono-, di-, and tri-ethylene glycol monoalkyl ethers

Infrared spectra have been recorded of the following mono-, di-, and tri-ethylene glycol monoalkyl ethers: CnH2n+1OCH2CH2OH where n = 17 and 19; CnH2n+1(OCH2CH2)2OH where n = 17, 18, 19, and 22; and C18H37(OCH2CH2)3OH. Spectra of the pure liquids, solutions in CCl4, and the solids at room and liquid air temperatures have been studied. From a study of the CH2 rocking modes at 927–934, 889, 900, and 862 cm−1 during the liquid–solid transformation and from solution studies, it has been shown that both the OCH2CH2O groups in diethylene glycol monoalkyl ethers exist predominantly in the gauche conformation in liquid and in solution. However, in the solid, while the end OCH2CH2O group takes both trans and gauche forms, the OCH2CH2O group adjacent to the polymethylene chain appears to take a trans configuration. The long polymethylene chain is found to pack in a triclinic subcell in the solid state, while in the quenched liquid state an orthorhombic or monoclinic packing is indicated. The present investigation has led to the conclusion that the difference in the conformations of end CH2CH2CH2OH groups found between the odd and even chain n-alcohols is removed in mono- and diethylene glycol monoalkyl ethers by the introduction of one or two OCH2CH2 groups.

Behaviour and Mechanism of the Allotropic Transformation of Cerium

When cerium is subjected to the thermal cycling between room and liquid air temperatures, the amount of α phase increases after each cycle as the electrical resistance changes accordingly, where the changing manners of both factors are quite similar. However, although terminal temperatures of the thermal cycling are far different from the transformation temperature, the amount of phase change never attains 100%, but a certain equilibrium value. In this paper, the transformation mechanism of cerium was discussed theoretically, while an attempt was made to give a theoretical explanation upon the above mentioned attainment of an equilibrium, utilizing the theory of martensite formation in carbon steel by Cohen, et al, considering the size effect due to the subdivision of crystal grains by the formed martensite leaves. The experimental part of this study was previously reported by the author at Virginia Academy of Science meeting.

Solution hardening of lead single crystals at liquid air temperature

Single crystals of lead with either thallium, indium, bismuth, cadmium, mercury or antimony were tested in tension in liquid air. The critical resolved shear stress τ0 increases linearly with increasing solute content c in a limited concentration range. The increase Δτ0/ΔC is lowest for lead-thallium and highest for lead-antimony. When log Δτ0/ΔC is plotted against log (sf + elf) where sf*[(d1)Pb − (d1)sol/(d1)Pb]10Pb, d1 being the closest distance of approach, and elf = ΣEn, ΣEn being the sum of the electronegativities of solvent and solute, a straight line of slope 2 results. A similar result is obtained with data from the literature for single crystals of copper alloys and of magnesium alloys. However in these cases a different size factor has to be used.

Thermally Induced Strains in Diamond Cubic, Tetragonal, Orthorhombic, and Hexagonal Films

When thin films adhere to a substrate which has a different thermal expansion coefficient, changing the temperature of the composite will induce strains in both film and substrate. Calculations of strain and strain energy have been made for various polycrystalline diamond cubic, tetragonal, orthorhombic, and hexagonal films on substrates which are assumed to be undeformable and to have isotropic thermal expansion and elastic properties in directions parallel to the surface of the substrate. Computer programs were developed to calculate the above quantities for the diamond cubic semiconductors Ge and Si, the tetragonal metals Sn and In, the orthorhombic metal Ga, and the hexagonal metals Be, Cd, Co, Mg, Ti, Zn, and Zr. Each film was assumed to have been deposited on glass or on sodium chloride at room temperature and cooled to approximately liquid air temperature. The induced thermal strains and strain energies for many different crystallographically oriented grains were calculated. The particular (hkl) orientations chosen corresponded to the lowest order x-ray reflections from crystal planes parallel to the surface of the substrate. These calculations extend the authors' earlier work on adhering cubic metal films. Finally, in the case of nonadhering films having more than one thermal expansion coefficient, strains due to thermal expansion alone were calculated as a function of crystal orientation. Various applications of these results are discussed in the text.

Anharmonicity and hydrogen bonding: Isotopic substitution

The fundamentals and first overtones of the free and self-associated OH stretching bands of three alcohols and phenol were measured, the associated bands at liquid air temperature in rigid glasses. The dependence of the frequencies and anharmonicity constants on deuterium substitution was examined. The result is a new proof that hydrogen bonding has a profound influence on the anharmonicity of OH stretching vibrations.