MEAN LIVES OF POSITRONS IN ALUMINUM AND THE ALKALI METALS

1960 ◽  
Vol 38 (5) ◽  
pp. 652-664 ◽  
Author(s):  
M. H. Jørgensen ◽  
R. E. Bell
Keyword(s):  
Angular Correlation ◽  
Time Distribution ◽  
Alkali Metals ◽  
Fast Time ◽  
Sodium Potassium ◽  
Aluminum Lithium

The time distribution of positron annihilations in the metals aluminum, lithium, sodium, potassium, and cesium have been measured with a fast time-to-amplitude converter. The decay curves appear to be complex, with about 5% of the events having a mean life of approximately 5×10−10 sec. The main (95%) components of the decay curves show the following mean lives, in units of 10−10 sec: Al, 1.9 ± 0.2; Li, 2.9 ± 0.2; Na, 3.15 ± 0.2; K, 4.0 ± 0.2; Cs, 4.3 ± 0.2. The results for the alkali metals disagree with the previously published measurements of De Benedetti and Richings (1952). These results are discussed, and the lifetimes for other metals are predicted roughly from them and from the angular correlation measurements of other workers.

A Convenient Method of Distillation of the Alkali Metals

1927 ◽  
Vol 23 (8) ◽  
pp. 953-955 ◽  
Author(s):  
R. J. Clark
Keyword(s):  
Convenient Method ◽  
Alkali Metals ◽  
Mercury Vapour ◽  
Sodium Potassium

The alkali metals, sodium, potassium and rubidium can be distilled easily in a good vacuum and obtained reasonably free from occluded gas in the following way. As potassium is now used for the absorption of mercury vapour and many experiments are being done on the others, an account of a convenient way of preparing pure specimens may be of some service to experimenters.

The de Haas–van Alphen effect in alkali metals

1964 ◽  
Vol 281 (1384) ◽  
pp. 62-91 ◽  
Keyword(s):  
Fermi Surface ◽  
Field Dependence ◽  
Alkali Metals ◽  
Spherical Shape ◽  
Orientation Dependence ◽  
Sodium Potassium ◽  
Fermi Surfaces ◽  
Fixed Orientation ◽  
Absolute Amplitude ◽  
Structure Calculations

A new method for studying the de Haas–van Alphen effect in steady magnetic fields has been developed in which the field is modulated at frequency ω and a signal at frequency 2 ω is generated in a pick-up coil round the specimen because of the non-linear field dependence of magnetization. The rectified 2 ω signal is proportional to d 2 M /dH 2 and so shows de Haas–van Alphen oscillations either when H is varied for fixed orientation or when the orientation is varied in fixed H if the Fermi surface is anisotropic. Because the phase of oscillation is very high (of order 10 4 π ) even very slight anisotropy will produce a few oscillations when the orientation is varied and the method is therefore particularly sensitive for studying very nearly spherical Fermi surfaces. From the oscillations with H , values of the frequency F were found for sodium, potassium, rubidium and caesium which were close to those predicted for a free-electron sphere containing 1 electron per atom, though some small systematic deviations of order ½ % were observed which may be significant. From detailed study of the oscillations produced by rotation of single crystals in fixed H it was found possible to describe the orientation dependence of F (proportional to the area of cross-section of the Fermi surface) for potassium and rubidium consistently by a series of cubic harmonics and hence to deduce the small departures of the Fermi surfaces from spherical shape. The deviations from a sphere were found to be of the order of 1 part in 10 3 for potassium and a little less than 1 part in 10 2 for rubidium; these deviations are compared with those predicted by band structure calculations. Preliminary results for sodium suggest that it is appreciably less anisotropic than potassium. Some results are also reported on the temperature and field dependence and the absolute amplitude of the de Haas-van Alphen effect, and it is also shown how the effect can be used to measure very small variations of field with position.

A preliminary study of the influence of alkali-metal promoters on the selectivity and activity of vanadium catalysts in the oxidation of naphthalene

1981 ◽  
Vol 34 (6) ◽  
pp. 1325 ◽  
Author(s):  
NR Foster ◽  
MS Wainwright ◽  
DWB Westerman
Keyword(s):  
Alkali Metal ◽  
Partial Oxidation ◽  
Alkali Metals ◽  
Catalyst Activity ◽  
Fixed Bed ◽  
Oxidation Products ◽  
Metal Sulfate ◽  
Sodium Potassium ◽  
Fixed Bed Reactors ◽  
Preliminary Study

The oxidation of naphthalene over vanadia catalysts promoted by alkali- metal sulfates was studied in the temperature range 400-440°C. The effects of SO3 levels and alkali-metal sulfate promoter type on catalyst activity and selectivity were investigated in laboratory fixed-bed reactors employing integral conversions. ��� The relative promoting abilities of the alkali metals sodium, potassium, rubidium and caesium were investigated with laboratory catalyst preparations. Alkali metals of higher atomic number favoured selectivity to partial oxidation products with an associated loss in overall activity.

Pressure Dependence of Positron Annihilation in Alkali Metals

1975 ◽  
Vol 53 (5) ◽  
pp. 450-454 ◽  
Author(s):  
P. Kubica ◽  
M. J. Stott
Keyword(s):  
Positron Annihilation ◽  
Angular Correlation ◽  
Pressure Dependence ◽  
Alkali Metals ◽  
Correlation Data

The observed pressure dependence of the total positron annihilation rates in alkali metals has been studied. The observation that the rates increase more rapidly with pressure than the estimated valence annihilation rates alone has been explained in terms of increased positron penetration into the ion cores. This picture is shown to be consistent with observed changes with pressure in angular correlation data for Na.

scholarly journals Alkali Metal Re-Distribution after Oxidation of 4H-SiC

2016 ◽  
Vol 858 ◽  
pp. 677-680
Author(s):  
Margareta K. Linnarsson ◽  
Sethu Saveda Suvanam ◽  
Lasse Vines ◽  
Anders Hallén
Keyword(s):  
Alkali Metal ◽  
Alkali Metals ◽  
Main Part ◽  
Secondary Ion Mass Spectrometry ◽  
Minor Amount ◽  
Sodium Potassium ◽  
Alkali Atoms ◽  
A Minor ◽  
P Type ◽  
Secondary Ion

Relocation of alkali metals sodium, potassium and cesium during oxidation of 4H-SiC has been studied by secondary ion mass spectrometry. The alkali metal source has been introduced by ion implantation before oxidation into n-and p-type 4H-SiC samples. Dry oxidation of SiC has been performed at 1150 oC during 4, 8 and 16 h. In the formed oxide, the main part of the alkali metals diffuses out via the SiO2 surface. Close to the moving SiO2/SiC interface, a minor amount of alkali metals is retained. In the SiC material, the main amount of implanted alkali atoms is not redistributed during the oxidation, although a minor amount diffuses deeper into the samples. For p-type 4H-SiC, the diffusion deeper into the samples of the studied alkali metals decreases as the mass increases, Na+<K+<Cs+, but the sodium mobility is substantial already at 1150 °C.

A Study of Chemical Reactions in Molton Sodium-Potassium Hydrogen Sulfate Eutectic. IV. The Reaction of Eight Oxalates

1985 ◽  
Vol 38 (7) ◽  
pp. 1123
Author(s):  
JO Sabato ◽  
SA Tariq
Keyword(s):  
Alkali Metals ◽  
Alkaline Earth ◽  
Hydrogen Sulfate ◽  
X Ray Diffraction ◽  
Metal Sulfate ◽  
Chemical Methods ◽  
Sodium Potassium ◽  
X Ray ◽  
Potassium Hydrogen ◽  
Wet Chemical

The reactions of oxalates of ammonium, alkali metals (Li, Na and K) and alkaline earth metals (Mg, Ca, Sr and Ba ) with sodium-potassium hydrogen sulfate eutectic were investigated. Oxalic acid was found to be an intermediate product in all these reactions. Final products of the reactions as determined by thermogravimetry , differential thermal analysis, X-ray diffraction, infrared and 'wet' chemical methods consisted of a mixture of H2O, CO, CO2 and the corresponding metal sulfate. The stoichiometries of the reactions were elucidated.

Thermal and electrical conductivities of the alkali metals at low temperatures

1956 ◽  
Vol 235 (1202) ◽  
pp. 358-374 ◽  
Keyword(s):  
Alkali Metals ◽  
Current Theory ◽  
Thermal Resistivity ◽  
Free Electrons ◽  
Sodium Potassium ◽  
Electrical Conductivities ◽  
Semi Empirical ◽  
Thermal Vibrations ◽  
Temperature Resistivity ◽  
Good Agreement

Measurements of the thermal and electrical conductivities of very pure lithium, sodium, potassium, rubidium and caesium have been made down to temperatures as low as 2°K. The respective resistivities, W and ρ , may be written as the sum of an impurity resistance ( W 0 , ρ 0 ) and a so-called ‘ideal’ component ( W i , ρ i ) due to scattering by the thermal vibrations of the lattice. The terms in the thermal resistivity may be represented by W 0 = A / T and W 1 = B T n f o r T ≤ θ / 10 , where n ≃ 2 and A = ( ρ 0 /2⋅45) x 10 8 cm deg. 2 W -1 . Current theory predicts thatt he quantity C ≡ Bθ 2 / W ∞ N ⅔ should be constant, where N is the number of free electrons per atom and W is the measured high-temperature resistivity. Taking N = 1, the present experiments yield C ≃ 18 ± 4. The electrical resistance may be written ρ = ρ 0 + β T m f o r T < θ / 10 with m ≃ 5 except for sodium, where, below 8°K , m is found to increase to 6. The theoretical relationships which exist between the low-temperature ‘ideal’ resistivities and those at higher temperatures are discussed in conjunction with the measured values. It is concluded that with the existing theories, no common adjustment of θ can give satisfactory agreement of theory with experiment. A new simple semi-empirical expression is put forward for W i which provides rather good agreement with experiment.

Synthesis and Spectroscopic and Structural Investigations of the 2,3,4,5-Tetraethylarsolides and -stibolides of the Alkali Metals Sodium, Potassium, Rubidium, and Cesium

2004 ◽  
Vol 23 (14) ◽  
pp. 3417-3424 ◽  
Author(s):  
Matthias Westerhausen ◽  
Manfred W. Ossberger ◽  
Peter Mayer ◽  
Holger Piotrowski ◽  
Heinrich Nöth
Keyword(s):  
Alkali Metals ◽  
Sodium Potassium ◽  
Structural Investigations

Alkali Metals salts of a Tetracyanopyridine (TCPy) Derivative: Structure Characterization and Luminescence Properties

CrystEngComm ◽  
2021 ◽  
Author(s):  
Sergey Chunikhin ◽  
Oleg V Ershov ◽  
Aleksandr V. Yatsenko ◽  
Viktor Tafeenko ◽  
Natalia Evgenievna Dmitrieva ◽  
...  
Keyword(s):  
Solid State ◽  
Single Crystal ◽  
Alkali Metals ◽  
Diffraction Method ◽  
Structure Characterization ◽  
Luminescence Properties ◽  
X Ray Diffraction ◽  
Sodium Potassium ◽  
X Ray

Five new salts of 3,4-dicyano-2-(dicyanomethylene)-5-methyl-6-phenyl-2H-pyridin-1-ide anion (TCPy−) with lithium, sodium, potassium, rubidium and cesium cations were synthesized and structurally characterized by the single-crystal X-ray diffraction method. Solid state photoluminescence characteristics...

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