scholarly journals On the question of using solid electrodes in the electrolysis of cryolite-alumina melts. Part 2. The mechanism of passivation and conditions of stable electrolysis

2021 ◽  
Vol 25 (1) ◽  
pp. 108-121
Author(s):  
Е. S. Gorlanov
Keyword(s):  
Titanium Diboride ◽  
Complex Analysis ◽  
Chemical Inhomogeneity ◽  
Dense Layer ◽  
Composite Electrodes ◽  
Electron Microscopic ◽  
Experimental Conditions ◽  
Inhomogeneous Surface ◽  
Carbon Cathode ◽  
Solid Electrodes

 The aim was to investigate the mechanism of passivation of polycrystalline cathodes and to justify experimentally the possibility of stable electrolysis when using solid electrodes. Under laboratory conditions, the mechanism of electrode passivation and the conditions for stable electrolysis were experimentally studied. To this end, the methods of X-ray phase analysis and electron-microscopic examination of the spent electrodes were employed. A study of the electrolysis of cryolite-alumina melts showed that, in the presence of surface micro- and microdefects on a solid cathode, a precipitate consisting of impurities and electrolyte components was gradually formed. Under the selected experimental conditions, the surface of carbon cathodes was passivated with a dense double-layer precipitate of CaB6 and electrolyte components. Using the example of a carbon cathode containing both metallic titanium and titanium oxides, a method for eliminating surface microdefects is presented. This method consists in electrochemical borating of a carbon-titanium cathode. The conducted spectral electron microscopic and energy-dispersive analysis found that, during a 45-hour laboratory experiment at 980 °C and under a current density of 0.7 A/cm2, the inhomogeneous surface of the cathode was homogenized with a titanium diboride layer. At stable electrolysis parameters, an aluminum layer is electrodeposited on the cathode. A complex analysis of the electrolysis conditions, the appearance of the initial and spent carbon cathodes, and the data of analytical studies confirmed that micro- and macrodefects of the electrode cause the formation of a dense layer of deposits on the cathode. The established mechanism of passivation of a carbon cathode as a polycrystalline product can be applied to all composite electrodes, including those based on titanium diboride. A logical condition for the practical application of solid cathodes is the development of an electrolysis process with continuous surface reconditioning to decrease the chemical inhomogeneity and microdefects of the surface across the entire technological sequence. 

scholarly journals On the question of using solid electrodes in the electrolysis of cryolite-alumina melts. Part 3. Electric field distribution on the electrodes

2021 ◽  
Vol 25 (2) ◽  
pp. 235-251
Author(s):  
E. S. Gorlanov ◽  
A. A. Polyakov
Keyword(s):  
Electric Field ◽  
Field Distribution ◽  
Edge Effect ◽  
Current Density ◽  
Molten Salts ◽  
Functional Relationship ◽  
Electric Field Distribution ◽  
Chemical Inhomogeneity ◽  
Electrolytic Process ◽  
Solid Electrodes

The aim of this work is to identify the theoretical limitations of molten salts electrolysis using solid electrodes to overcome these limitations in practice. We applied the theory of electric field distribution on the electrodes in aqueous solutions to predict the distribution of current density and potential on the polycrystalline surface of electrodes in molten salts. By combining the theoretical background of the current density distribution with the basic laws of potential formation on the surface of the electrodes, we determined and validated the sequence of numerical studies of electrolytic processes in the pole gap. The application of the method allowed the characteristics of the current concentration edge effect at the periphery of smooth electrodes and the distribution of current density and potential on the heterogeneous electrode surface to be determined. The functional relationship and development of the electrolysis parameters on the smooth and rough surfaces of electrodes were established by the different scenario simulations of their interaction. It was shown that it is possible to reduce the nonuniformity of the current and potential distribution on the initially rough surface of electrodes with an increase in the cathode polarisation, alumina concentration optimisation and melt circulation. It is, nonetheless, evident that with prolonged electrolysis, physical and chemical inhomogeneity can develop, nullifying all attempts to stabilise the process. We theoretically established a relationship between the edge effect and roughness and the distribution of the current density and potential on solid electrodes, which can act as a primary and generalising reason for their increased consumption, passivation and electrolytic process destabilisation in standard and low-melting electrolytes. This functional relationship can form a basis for developing the methods of flattening the electric field distribution over the anodes and cathodes area and, therefore, stabilising the electrolytic process. Literature overview, laboratory tests and theoretical calculations allowed the organising principle of a stable electrolytic process to be formulated -the combined application of elliptical electrodes and the electrochemical micro-borating of the cathodes. Practical verification of this assumption is one direction for further theoretical and laboratory research.

Clay particle sizing by electrically-induced birefringence

Clay Minerals ◽  
1982 ◽  
Vol 17 (3) ◽  
pp. 313-325 ◽  
Author(s):  
D. M. Oakley ◽  
B. R. Jennings
Keyword(s):  
Orientational Order ◽  
Decay Rates ◽  
Sufficient Information ◽  
Electron Microscopic ◽  
Experimental Conditions ◽  
Clay Particles ◽  
Electron Microscopic Data ◽  
Rate Of Decay ◽  
Geometry Measurement ◽  
Log Normal

AbstractUnder the influence of a pulsed field, dilute clay sols become birefringent as the particles undergo orientational order. The rate of decay of the birefringence on removal of the field is characteristic of the particle geometry. Measurement of the decay rates under two specific experimental conditions provides sufficient information from which the particle-size distribution can be evaluated in terms of a two-parameter function. Experimental data are reported and analysed in terms of a log-normal distribution of particle sizes for attapulgite (rods), kaolinite (discs) and halloysite (ellipsoids) sols and compared with success to electron microscopic data. The ability of the method to determine size distributions in terms of the major dimensions of the clay particles, rather than those of the often used equivalent sphere, is highlighted.

scholarly journals A procedure for light and electron microscopic intracellular immunolocalization of collagen and fibronectin in rat liver.

1985 ◽  
Vol 33 (5) ◽  
pp. 407-414 ◽  
Author(s):  
B Clement ◽  
M Rissel ◽  
S Peyrol ◽  
Y Mazurier ◽  
J A Grimaud ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Endoplasmic Reticulum ◽  
Rat Liver ◽  
Type Iii Collagen ◽  
Collagen Types ◽  
Electron Microscopic ◽  
Experimental Conditions ◽  
The Matrix ◽  
Matrix Components ◽  
Indirect Immunoperoxidase

Experimental conditions have been designed that permit both extracellular and intracellular immunolocalization of various collagen types and fibronectin in rat liver. The procedure involves paraformaldehyde fixation by perfusion of the organ, use of saponin as a membrane permeabilizing agent, and visualization of the matrix components by indirect immunoperoxidase. Intracellular demonstration of collagens was particularly sensitive to the composition of the fixative and the duration of fixation. Hepatocytes contained fibronectin and types I and IV collagen, whereas fat-storing and endothelial cells evidenced type III collagen in addition. All the components were specifically located in the endoplasmic reticulum and/or the Golgi apparatus.

scholarly journals Synaptic vesicles have two distinct recycling pathways.

1996 ◽  
Vol 135 (3) ◽  
pp. 797-808 ◽  
Author(s):  
J H Koenig ◽  
K Ikeda
Keyword(s):  
Active Zone ◽  
Time Course ◽  
Microscopic Analysis ◽  
Temperature Sensitive ◽  
Fast Time ◽  
Permissive Temperature ◽  
Electron Microscopic ◽  
Experimental Conditions ◽  
Vesicle Recycling ◽  
Two Populations

In this paper, evidence is presented that two distinct synaptic vesicle recycling pathways exist within a single terminal. One pathway emanates from the active zone, has a fast time course, involves no intermediate structures, and is blocked by exposure to high Mg2+/low Ca2+ saline, while the second pathway emanates at sites away from the active zone, has a slower time course, involves an endosomal intermediate, and is not sensitive to high Mg2+/low Ca2+. To visualize these two recycling pathways, the temperature-sensitive Drosophila mutant, shibire, in which vesicle recycling is normal at 19 degrees C but is blocked at 29 degrees C, was used. With exposure to 29 degrees C, complete vesicle depletion occurs as exocytosis proceeds while endocytosis is blocked. When the temperature is lowered to 26 degrees C, vesicle recycling membrane begins to accumulate as invaginations of the plasmalemma, but pinch-off is blocked. Under these experimental conditions, it was possible to distinguish the two separate pathways by electron microscopic analysis. These two pathways were further characterized by observing the normal recycling process at the permissive temperature, 19 degrees C. It is suggested that the function of these two recycling pathways might be to produce two distinct vesicle populations: the active zone and nonactive zone populations. The possibility that these two populations have different release characteristics and functions is discussed.

Influence of Nanocomposite Surface Coating on Biofilm Formation In Situ

2007 ◽  
Vol 7 (12) ◽  
pp. 4642-4648 ◽  
Author(s):  
M. Hannig ◽  
L. Kriener ◽  
W. Hoth-Hannig ◽  
C. Becker-Willinger ◽  
H. Schmidt
Keyword(s):  
Free Energy ◽  
Composite Coating ◽  
Surface Free Energy ◽  
Biofilm Formation ◽  
Tooth Surface ◽  
Dense Layer ◽  
Electron Microscopic ◽  
Nano Composite ◽  
Nano Composite Coating

Caries and periodontitis, the most wide-spread oral diseases around the world, are caused by bacterial adherence and biofilm formation onto the natural as well as restored tooth surface. One possible way to prevent the pathogenic consequences of intraoral biofilm formation might be the modification of the tooth surface by application of an anti-adhesive coating that interferes with the bacterial attachment and subsequent bacterial accumulation. The objective of this study was to investigate the effect of an experimental, low surface free energy nano-composite coating material on biofilm formation in situ. For this purpose, an organic/inorganic nano-composite coating (NANOMER®, INM, Saarbrücken, Germany) with a surface free energy of 18–20 mJ/m2 was applied to enamel as well as titanium specimens. The nano-composite coated specimens and un-coated controls were attached to removable intraoral splints and carried by volunteers over 24 h in the oral cavity. After intraoral exposure, specimens were processed for transmission electron microscopic analysis. On non-coated enamel and titanium control samples a multi-layer of adherent bacteria was found. In contrast, on nano-composite coated specimens strongly reduced biofilm formation was observed. In most areas of the surface-coated specimens only a 10–20 nm thick electron dense layer of adsorbed salivary proteins with adherent protein agglomerates of 20–80 nm diameter could be detected. In addition, detachment of the adsorbed biofilm from the nano-composite coated surfaces was evident in electron microscopic micrographs. The present investigation provides ultrastructural evidence that it is possible to cover enamel as well as titanium with a nano-composite coating revealing easy-to-clean surface properties that cause reduced biofilm formation and accelerated removal of adherent biofilms under oral conditions.

scholarly journals Hippocampal place cells encode local surface texture boundaries

2019 ◽  
Author(s):  
Chia-Hsuan Wang ◽  
Joseph D. Monaco ◽  
James J. Knierim
Keyword(s):  
Flat Surface ◽  
Cell Activity ◽  
Place Cell ◽  
Cognitive Map ◽  
Neural Representation ◽  
Place Field ◽  
Experimental Conditions ◽  
Inhomogeneous Surface ◽  
Physiological Basis ◽  
Circular Track

SummaryThe cognitive map is often assumed to be a Euclidean map that isometrically represents the real world (i.e. the Euclidean distance between any two locations in the physical world should be preserved on the cognitive map). However, accumulating evidence suggests that environmental boundaries can distort the mental representations of a physical space. For example, the distance between two locations can be remembered as longer than the true physical distance if the locations are separated by a boundary. While this overestimation is observed under different experimental conditions, even when the boundary is formed by flat surface cues, its physiological basis is not well understood. We examined the neural representation of flat surface cue boundaries, and of the space segregated by these boundaries, by recording place cell activity from dorsal CA1 and CA3 while rats foraged on a circular track or square platform with inhomogeneous surface textures. About 40% of the place field edges concentrated near the surface cue boundaries on the circular track (significantly above the chance level 33%). Similarly, the place field edges were more prevalent near the boundaries on the platforms than expected by chance. In both 1-dimensional and 2-dimensional environments, the population vectors of place cell activity changed more abruptly with distance between locations that crossed cue boundaries than between locations within a bounded region. These results show that the locations of surface boundaries were evident as enhanced decorrelations of the neural representations of locations to either side of the boundaries. This enhancement might underlie the cognitive phenomenon of overestimation of distances across boundaries.

Quantitative assessment of radiation damage in protein crystal

1983 ◽  
Vol 41 ◽  
pp. 356-359
Author(s):  
Wah Chiu ◽  
T.W. Jeng
Keyword(s):  
Single Crystal ◽  
Radiation Damage ◽  
Quantitative Description ◽  
Protein Crystal ◽  
Electron Microscopic ◽  
Experimental Conditions ◽  
Structural Calculation ◽  
Standard Set ◽  
Diffraction Patterns ◽  
Damage Study

Radiation damage is a well known phenomenon in the electron microscopic study of thin crystals of macromolecules. A quantitative description of radiation damage is essential for at least 3 reasons: (i) it can provide numerical parameters for evaluating the extent of specimen damage at various experimental conditions, (ii) it can provide an indicator as to the maximum number of diffraction patterns and images obtainable from a single crystal before the specimen is significantly altered, and (iii) since the specimen is being altered after the initial hit by the electrons, schemes are needed to make correction of the data prior to its use for structural calculation. This paper primarily deals with the methodology used to evaluate the quantitative aspects of radiation damage of thin protein crystals. The example of crystal used in this study was crotoxin complex embedded in glucose.A standard set of data recorded in a radiation damage study is a series of electron diffraction patterns from a single crystal. The important experimental variables include the exposure rate, the exposure time and the accumulating exposure between successive patterns.

Freeze-fracture Electron Microscopic observations on the effects of sulphydryl group reagents on human erythrocyte membranes

1990 ◽  
Vol 48 (3) ◽  
pp. 524-525 ◽  
Author(s):  
Gheorghe Benga ◽  
Anthony Brain ◽  
Victor I. Pop ◽  
John Wrigglesworth
Keyword(s):  
Human Erythrocyte ◽  
Freeze Fracture ◽  
Band 3 ◽  
Erythrocyte Membranes ◽  
Electron Microscopic ◽  
Experimental Conditions ◽  
Water Permeation ◽  
Human Erythrocyte Membranes ◽  
Erythrocyte Membrane Proteins

The intra-membrane particles (IMPs) observed on the fracture face of frozen erythrocyte membranes are thought to correspond primarily to “band 3” tetramers or dimers. Some recent studies correlating the inhibition of water diffusion in erythrocytes by p-chloromercuribenzene sulfonate (PCMBS) with the binding of 203Hg to erythrocyte membrane proteins has enabled band 3 and the polypeptides in band 4.5 to be identified as the proteins associated with the channels for water permeation in human erythrocytes. A further characterization of the effects of the incubation of human erythrocyte membranes with PCMBS and N-ethylmaleimide (NEM) has been performed as previously described. Experimental conditions have been previously described.A comparison was made of the appearance of freeze-etched membranes of control erythrocytes and erythrocytes with the sulphydryl reagents. It was found that on many of the control and NEM-treated cells, small (50-100 nm) elevated patches could be seen (Fig. 1, 2 and 3). These are present on both fracture and etch faces and are devoid of any intramembrane particles. The patch elevations were never observed in the membranes of PCMBS-treated cells (Fig. 4).

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