H. A. Øye

Raman spectra of AlCl3-AlkCl and trends in species formation

Abstract The Raman spectra of LiCl-AlCl3, KCl-AlCl3 and CsCl-AlCl3 melts in the concentration range 50–100 mol.% AlCl3 are presented. The melt structure of these systems are discussed in terms of the species AlCl4−, Al2Cl7−, Al2Cl6 and higher polymers. The relative stabilities of the different species are studied as a function of the cation environment. Perturbation of the AlCl4− and Al2Cl7− vibrations due to the alkali counterion is found and interpreted in terms of change of symmetry, force constants and masses. The bridge structure of Al2Cl7− is discussed.

A possible mechanism of sulphur-induced graphitization

Abstract Studies of the structural changes of sulphur-containing cokes heat treated in the region 1420 to 1945°C reveal sulphur-enhanced graphitization. The mechanism is assumed to be a decomposition process of interstitials between carbon layers. The (002) composite X-ray diffraction reflection profiles observed are ascribed to the enhancement of the mechanism by reaction between the interstitials and sulphur. The well-ordered structure formed may be the rhombohedral form of the lattice that converts to the more stable hexagonal form at higher temperatures.

IR Emission Spectroscopy of Molten Salts and Other Liquids Using Thick Samples as Reference

The IR emittance of liquids relative to a blackbody is dependent on the reflectivity at the surface of the sample. This dependency leads to distortions in the bandshapes except when the absorption coefficient or the sample thickness is very low. The use of an opaque (i.e. very thick) sample as a reference eliminates the distortions in the bandshapes. A new emittance ε* = (emission of a thin sample)/(emission of an opaque sample) has been introduced. A theoretical analysis as well as experimental work on chloroaluminate melts demonstrate that the emittance ε* gives a better representation of the ideal sample property of interest, i.e., the internal transmittance of the sample, than the usual emittance with a blackbody as a reference.

Rapoport–Samoilenko test for cathode carbon materials: I. Experimental results and constitutive modelling

Abstract The sodium expansion of semigraphitic commercial cathode material used for aluminium production has been measured on solid cylinder samples. Experimental results have been obtained for three current density values using the Rapoport–Samoilenko-type apparatus. A constitutive model for cathode carbon materials which is able to reproduce the relationship between the sodium expansion and time during the Rapoport–Samoilenko-type test has been proposed. Parameters required in the proposed model such as the sodium expansion after infinite time and the diffusion coefficient have been calculated from experimental data by a least-square minimization process. The distribution of sodium concentration, radial stress, tangential stress, axial stress, first principal stress and von Mises equivalent stress in the solid semigraphitic cylinder with time have been obtained.

The solubility of magnesium metal and the recombination reaction in the industrial magnesium electrolysis

Abstract The solubility and dispersion of Mg in the systems MgCl 2 , MgCl 2 -NaCl and MgCl 2 -KCl has been studied. An extensive study of Mg solubility in MgCl 2 did not show any influence on the content of MgO or added NaOH or Na 2 B 4 O 7 . At 750°C the solubility was found to be 0.16 mol%. The solubility increased with increasing temperature and decreased on the addition of NaCl or KCl. In 25 mol% NaCl-75 mol% MgCl 2 the solubility was as low as 0.02 mol% at 815°C. The amount of Mg dispersed was found to be negligible with the present experimental set-up. The results are discussed with reference to the back reaction between Mg and Cl 2 in the industrial electrolysis. It seems likely that the rate determining step in this reaction is the rate of formation of small metal particles in the melt.

Absorption of metallic sodium in carbon cathode materials

The absorption of sodium vapour in commercial cathode materials for aluminium electrolysis has been studied within the range 1020–1227 K and 3–600 Torr. The absorption increases strongly with decreasing degree of graphitization. The absorption of sodium in the commercial materials can be described as a BET isotherm with calculated surface area between 9 and 124 m2/g. The measured surface area by helium absorption, however, is less than 1 m2/g. Pure synthetic graphite behaves differently and a minimum sodium pressure is needed before absorption starts.

Gas complexes between aluminium chloride and vanadium chloride

Abstract The reaction between VCl2 and VCl3 with AlCl3 gas has been studied spectrophotometrically and the gas complexes V(II)Al3Cl11, V(III)AlCl6 and V(III)Al2Cl9 were found. An octahedral coordination of V2+ was established, while a distorted tetrahedral arrangement was tentatively assigned to V3+. The structure is described as being built up from vanadium ions surrounded by AlCl4− or Al2Cl7− groups. It is pointed out that the stability of Al2Cl7− containing complexes may possibly be due to a chelating effect. Based upon thermochemical cycles and acid-base properties, a general discussion of bonding between MeClx and AlCl3 is given. VCl4(g) is also observed spectrophotometrically and its vapour pressure calculated.

Viscosity and density of molten barium zirconate and related melts

Viscosity and density of molten ZrF 4 -BaF 2 mixtures have been measured using the oscillating cup method and the Archimedean method respectively. The viscosity had a marginal minimum around the composition BaF 2 .2ZrF 4 , and increased significantly towards the composition BaF 2 .ZrF 4 . The density of molten ZrF 4 -BaF 2 increased with the BaF 2 content, while the volume thermal expansion decreased. The effect of the valence of the counter cation on the viscosity was studied by substitution of the glass modifier BaF 2 with NaF or LaF 3 . The viscosity increased with the valence of the counter cation. These fragile glass-forming systems are more comparable to ionic glasses than typical network glasses. The physical properties of the molten fluorides are discussed in relation to complex formation and the ionic character of the melts

An automatic image analysis of coke texture

Abstract A method for automatic image analysis of coke texture has been developed. The method uses an optical polarizing reflecting light microscope, with automatic sample movement. A series of images sized 405 × 270 mm is captured using a CCD video camera. These images are subdivided into six squares at 135 × 135 mm each. For each of these squares an image displaying the contours of the optical domains is made. This contour image is based on either thresholding or a grey level gradient. The structure is then characterized by the mean density and preferred direction of the contours in these square images. The method thus yields two values: A coarseness index, and a fibre index. These values do not require any classification of the texture into a finite number of texture classes. Commercial anode cokes as well as needle and pitch coke have been characterized. Reproducible results were obtained after 100 images (600 squares) were analysed. The differences between the commercial anode cokes are small but reproducible, while the pitch and needle coke deviate strongly.

Viscosity of NaFAlF3Al2O3 melt mixtures

Abstract Melt viscosities for the system NaFAlF 3 Al 2 O 3 over the experimentally accessible range are reported, the limiting factors being the solubility of Al 2 O 3 and the vapour pressure. The temperature extends from the liquidus temperature to 1100°C. A recently developed precision oscillation viscometer is utilized. The results are discussed in a qualitative fashion.