Showing papers on "Dissolution published in 1979"

Corrosion micromorphology of noble metal alloys and depletion gilding

Abstract: Noble metal alloys commonly undergo selective dissolution during anodic corrosion whereby the less noble component is dissolved preferentially. This is particularly interesting, as it leads to a depletion of the less noble species not only at the surface of the metal but also at an appreciable depth within it, implying that a mass transport of atoms is occurring either through the bulk of the crystal lattice or across the surface to support the continuing dissolution. Experiments in which the micromorphology of silver–gold alloys is observed during such corrosive treatment have shown that surface diffusion of gold plays an important part in this process. As surface silver atoms are dissolved the residual gold atoms reform into gold-rich islands so that fresh silver atoms are continuously exposed to the environment layer by layer. These observations will be described in detail elsewhere1. Here the mechanism of surface re-arrangement is considered, which leads to the accumulation of gold-rich surface regions, and throws a new light on the ancient craft of depletion gilding.

Electrochromism in Anodic Iridium Oxide Films II . pH Effects on Corrosion Stability and the Mechanism of Coloration and Bleaching

Abstract: The oxidation state of iridium ions in an oxide film, grown electrochemically on an Ir metal reflector electrode, can be rapidly and reversibly modulated according to the electrochromic redox reactionBy suitable choice of electrolyte composition and potential limits, the coloration and bleaching processes can be effected without causing oxide film growth or dissolution, or electrolyte decomposition. Color‐bleach (c‐b) cycles exhibit reflectance contrast changes, , and charging times, τ, suitable for electrooptic display devices, e.g., for a film 320 nm thick, at and . Long term corrosion stability is obtainable in mildly acidic sulfate electrolytes, e.g., at pH 3.5. Sulfate electrolytes are also apparently unique in preventing degradation of c‐b response times owing to changes in film structure. East write‐erase times are made possible by the highly porous and hydrated nature of the oxide film and the ready availability of the protons required for bleaching from an 'internal' source—free molecules in the electrolyte contained within the film pores and/or bound or OH groups on the oxide surface. The kinetics and mechanism of the electrochromic reaction in anodic iridium oxide films are discussed with particular reference to the requirement for preserving electroneutrality within the bulk oxide. Recent claims that this redox reaction can occur without exchange of protons with the electrolyte are shown not to be substantiated. Attractive features of the electrochromic iridium oxide system for display devices include: (i) broad spectral absorption; (ii) good contrast ratio; (iii) fast response; (iv) good corrosion stability; (v) good open‐circuit memory in the presence of water and dissolved ; (vi) suitable threshold and switching voltage levels; and (vii) the ability to grow and reform the oxide layer in situ in the electrooptic display cell. The charge (~20 mC cm−2) and energy (~30 mJ cm−2) required for coloration and bleaching are similar to those required for other electrochromic oxide systems, e.g., the tungsten bronzes.

Loss of additives from polymers: A theoretical model

Abstract: The rate at which an additive is lost from the surface of its solution in a polymer is considered to depend upon three factors—the solubility of the additive, the rate at which it volatilizes from the polymer surface, and its diffusion coefficient within the bulk of the polymer. By adapting the mathematics of heat flow in a solid, the loss of additive from a polymer is mathematically modeled in terms of these three variables for bulk polymer and for film and fiber samples. Two cases are considered—loss of additive by volatilization or dissolution from the polymer surface and loss by precipitation on the surface from a supersaturated solution of the additive. The results are applied to a discussion of the relative importance of the three parameters under various conditions occurring or expected in practical application of additives as oxidation stabilizers for polyethylene and polypropylene.

Rate of dissolution of diatom silica walls in seawater

Abstract: The solubility and dissolution rate of silica were investigated using cell walls prepared from two species of diatoms, Thalassiosira decipiens and Rhizosolenia hebetata forma semispina. The solubility (Ce) as a function of temperature (T, °C) can be described by the following equation: Ce (SiO2 mg l-1)=67.8+1.48 T. The first-order reaction equation without the surface-area term was considered to be reasonable in estimating the dissolution rate of biogenic silica in the ocean system. The rate of dissolution differed not only from one species to another but also from one portion to another portion of the same wall. The rate constants of dissolution in the ocean system were estimated to range in the order of from 10-1 to 10-9 per hour.

The initial kinetics of the dissolution of vitreous silica in aqueous media

Abstract: The initial kinetics of the dissolution of vitreous silica was measured in aqueous solutions as a function of pH (5–11) and ionic content ((Na,Mg) Cl x :0.1–3.5 M ) at 25°C. The apparent rate constant of silica dissolution, k 1 , increased by a factor of 360 from pH 5 to pH 11 at NaCl = 0.70 M . The addition of Mg 2+ to NaCl solutions, where the total ionic strength was maintained constant, had no effect on k 1 at pH 8 but k 1 decreased by about 30% at pH 9 (Mg 2+ = 0.055 M ). In NaCl solutions, k 1 is shown to be an explicit function of surface charge. A plot of log 10 (dissolution rate) vs log 10 (surface charge) is linear at lower surface charge with a slope of 1.94, suggesting that two surface excess OH − 's are in the transition state of the rate-determining step of silica dissolution.

Molecular interactions and macroscopic properties of polyacrylonitrile and model substances

Abstract: The relationships between intra- and intermolecular forces in polyacrylonitrile on the one hand, and the macroscopic behavior of the polymer and fibers thereof on the other, are reviewed Characteristic properties such as the very high polymerization rate constant in water, the dissolution of the polymer in concentrated inorganic salt solutions, the high melting point, the strong depression of melting point and glass transition temperature by water, the plasticization by polar additives, etc, are traced back to their molecular origins, in particular to the strong intra- and intermolecular noncovalent bonding caused by the highly polar nitrile group The effects of dipole-dipole interaction, hydrogen bonding and electron-donor-acceptor complex formation are discussed separately

Process for making amine oxide solution of cellulose

Abstract: A process is provided for making a solution of cellulose in an amine oxide In accordance with one aspect of the invention, a solid precursor of a solution of cellulose in a tertiary amine oxide in the form of a chip or the like which has been prepared by suspending cellulose in a mixture containing a tertiary amine oxide and water is heated in the barrel of an extruder to dissolve the cellulose, and the resulting solution is extruded to provide an extrudate adapted to be shaped into a cellulosic product In another aspect, a tertiary amine oxide solvent for cellulose can be added directly to the extruder where mixing and dissolution take place under the application of heat and pressure It is further advantageous, in either case, where a non-solvent for the cellulose, compatible with the tertiary amine oxide and water, is employed

Solid phase formation in Au: Ge/Ni, Ag/In/Ge, In/Au: Ge GaAs ohmic contact systems

Abstract: Solid phase epitaxy formation in Au: Ge/Ni, Ag/In/Ge, and In/Au:Ge contacts to GaAs has been identified utilizing micro-spot Auger spectroscopy and selected area electron channeling. It is shown that the lateral extent of solid phase formation directly controls the value of the specific contact resistivity. Solid phase growth occurs as a result of dissolution of GaAs by the contact constituents in the vicinity of the eutectic temperature. Solid phase growth also results in regions free of oxide layers and contaminants and hence a lower contact resistivity.

Geochemistry of Colloid Systems: For Earth Scientists

Abstract: 1. What is Colloid Science?.- 2. Classification of Colloid Systems.- 2.1 Based on States of Matter.- 2.2 Based on Chemical Properties of the Components.- 3. Crystal Chemistry of Silicates.- 3.1 Island Structure.- 3.2 Chain and Ribbon Structures.- 3.3 Layer Structure.- 3.4 Three-dimensional Network.- 4. Water.- 4.1 Fine Structure of Water.- 4.2 Fine Structure of Aqueous Inorganic Salt Solutions.- 4.3 Fine Structure of Aqueous Solutions of Small Non-polar Molecules and Radicals.- 4.4 Liquid Boundary Layer.- 4.5 Aqueous Solutions of Hydrophilic Colloids.- References.- 1 Some Geologic Colloid Systems.- 1. Mineralogy of Colloids in the Sedimentary Cycle.- 1.1 Structure of the Common Clay Minerals.- 1.2 Hydrous Oxides of Aluminum and Iron.- 2. Soils and Sediments as Colloid Systems.- 2.1 Solid Fraction in Soils and Sediments.- 2.2 Water in Soils and Sediments.- 2.3 Gases in Soils and Sediments.- 2.4 Organic Matter in Soils and Sediments.- 3. Fluidized Beds.- 4. Magma as a Colloid System.- 4.1 Magmaphilic Polymeric Structures.- 4.2 Magmaphobic Colloids.- 4.3 Emulsions of Immiscible Liquids.- 4.4 Foam of Volatiles.- 5. Colloid Systems in Volcanic Eruptions.- 5.1 Lava.- 5.2 Volcanic Smokes.- 6. The Ocean as a Colloid System.- 6.1 Air-Water Interface.- 6.2 Gas Bubbles in the Ocean.- 6.3 Suspended Inorganic Solids in the Ocean.- 6.4 Organic Compounds in the Ocean.- 7. The Atmosphere as a Colloid System.- 7.1 Tropospheric Aerosols.- 7.2 Stratospheric Aerosols.- References.- 2 Physical Chemistry of Surfaces.- 1. Thermodynamics of Heterogeneous Systems.- 1.1 Thermodynamic Properties and Quantities of the Interface.- 1.2 Pressure Dependence of Chemical Potential and of Water Migration in Compacting Sediments.- 1.3 Surface Tension, the Strength of Intermolecular Forces and Cleavage of Mineral Crystals.- 1.4 Capillary Pressure.- 1.5 Contact Angle of a Liquid at a Boundary of Three Phases and the Wetting Process.- 2. Liquid Surface.- 2.1 Liquid Surface Tension.- 2.2 Evaporation.- 3. Sorption.- 3.1 Sorption of Gases and Vapors by Solids.- 3.2 Sorption by Solids from Solutions.- 3.3 Sorption onto a Liquid-Gas Interface.- 3.4 Gas Exchange Across a Gas-Liquid Interface.- 3.5 Ion Exchange.- 3.6 Sorption and Surface Tension.- 4. Electrochemistry of Heterogeneous Systems.- 4.1 Electric Double Layer at a Solid-Liquid Interface.- 4.2 Electrokinetic Phenomena.- 4.3 Theory of Electrokinetic Phenomena.- 4.4 Electric Properties of Dust Storms.- References.- 3 Formation of Aqueous Solutions and Suspensions of Hydrophobic Colloids.- 1. Condensation Process (Formation of New Phases).- 1.1 Chemistry of Aluminum in Natural Waters.- 1.2 Chemistry of Iron and Manganese in Natural Waters.- 2. Dispersion Process.- 2.1 Physical Weathering.- 2.2 Chemical Weathering.- 2.3 Detachment of Particles Caused by Rainfall.- 2.4 Peptization.- References.- 4 Surface Coatings on Rocks and Grains of Minerals.- 1. Incongruent Dissolution of Silicates.- 2. Sorption from Aqueous Solutions onto Mineral Surfaces.- 2.1 Sorption by Long-range Interactions.- 2.2 Sorption by Short-range Interactions.- 3. Alteration of Minerals by Abrasion.- 3.1 Abrasion of Silica and Silicate Minerals.- 3.2 Abrasion of Calcite.- 3.3 Abrasion pH Values of Minerals.- 4. Surface Structures of Gibbsite and Goethite.- References.- 5 Kinetic Properties of Colloid Solutions.- 1. Kinetic Properties of Particles Dispersed in Still Fluids.- 1.1 Brownian Movement.- 1.2 Diffusion.- 1.3 Sedimentation.- 2. Kinetic Properties of Particles in Flowing Fluids.- 2.1 Laminar and Turbulent Flow.- 2.2 Fluid Drag.- 2.3 Dispersion of Particles in a Turbulent System.- 2.4 Entrainment of Sediment.- References.- 6 Colloid Geochemistry of Silica.- 1. Surface Chemistry of Silica.- 1.1 Functional Groups on Silica.- 1.2 Functional Groups on Silica-Alumina.- 1.3 Opals.- 2. Silica in Aqueous Solutions.- 2.1 Polymerization and Depolymerization of Silicic Acid.- 2.2 Solubility of Silica.- 2.3 Silica Sorption by Minerals.- 2.4 Silica in Natural Waters.- References.- 7 Colloid Geochemistry of Clay Minerals.- 1. Functional Groups on Clay Minerals and Ion Exchange Reactions.- 1.1 "Broken-bond" Surfaces.- 1.2 Interlayer Space of 2:1-Type Clay Minerals.- 1.3 The Flat Oxygen and Hydroxyl Planes.- 2. Interaction Between Clay Minerals and Organic Compounds.- 2.1 Sorption of Organic Ions by Clay Minerals.- 2.2 Sorption of Organic Polar Molecules by Clay Minerals.- 2.3 Organic Reactions Catalyzed by Clay Minerals.- 3. Solubility of Clay Minerals.- 4. Environmental Effects on Clay Mineralogy.- 4.1 Origin of Primary-stage (Neoformation) Clay Minerals and Their Related Environment.- 4.2 Environmental Relationships of N + 1 Stage Clay Minerals.- References.- 8 Interaction Between Solid Particles Dispersed in Colloid Systems.- 1. Interaction Between Solid Particles Dispersed in a Gaseous Phase.- 1.1 Van Der Waals-London Forces Between Disperse Particles.- 1.2 Electrostatic Forces Between Disperse Particles.- 1.3 Effect of Adsorbed Water Monolayer on Desert Varnish.- 2. Aggregation of Particulate Matter in the Hydrosphere.- 2.1 Interactions Between Solid Particles Dispersed in a Liquid Medium.- 2.2 Stability of Aqueous Hydrophobic Colloid Solutions and Suspensions.- 2.3 Coagulation in Natural Waters.- 3. Soil Aggregates.- 3.1 Interaction Between Clay Particles.- 3.2 Interaction Between Sand Grains.- 3.3 Reactions of Humic Substances with Mineral Soil Components.- 3.4 Pore Space in Soils.- 3.5 Stability of Aqueous Soil Dispersions and the Migration of Soil Constituents.- References.- 9 Rheology of Colloid Systems.- 1. Flow Behavior of Suspensions.- 2. Rheology of Dispersions in the Hydrosphere.- 2.1 Rheology of Dilute Dispersions.- 2.2 Rheology of Concentrated Dispersions and Muds.- 3. Rheology of Sediments of Silicate Minerals.- 3.1 Wet Sediments of Sand Grains.- 3.2 Argillaceous Sediments.- 4. Viscosity of Magmas.- References.- 10 Colloid Geochemistry of Argillaceous Sediments.- 1. Microstructure of Argillaceous Sediments.- 1.1 Microstructure of Fresh Sediments.- 1.2 Microstructure of Compacted Sediments.- 2. Aging and Diagenetic Alteration of Smectites in Argillaceous Sediments.- 3. Surface Chemistry of Solutes Flow Through Argillaceous Sediments.- 3.1 Nature of Pores in Shales.- 3.2 Effect of Migrating Water on the Migration of Solutes.- 4. Diagenesis of Organic Matter and Oil Generation in Argillaceous Sediments.- 4.1 Petroleum Origin Related to Kerogen.- 4.2 Generation of Hydrocarbons.- References.- Author Index.- Mineral Index.

Analytical treatment of the role of surface oxide layers in the sintering of metals

Abstract: The role played by a surface oxide layer in the kinetics of sintering of metallic particles is analysed quantitatively. Application of the analysis to metals with thermodynamically stable oxides gave results which are consistent with experimental observations. The presence of oxides which tend to dissolve in the metal at the sintering temperatures gives rise to an incubation period before the onset of sintering. Comparison with experimental results indicates that the oxide dissolution process is kinetically controlled at the oxide-metal interface.

Crystalline Oxide Solid Solutions in Oxygen Potential Gradients

Abstract: Abstract The steady state demixing of an initially homogeneous oxide solid solution (A, B)O in an oxygen potential field is studied theoretically and experimentally. In case that DA > DB ≫ D0, the crystal is shifted with respect to the oxide lattice system toward the higher oxygen potential and is enriched in A at the side of the higher oxygen potential, while the transport of oxygen in the crystal is negligible. A numerical solution of the transport problem is presented, and the predicted effect is verified experimentally

Dissolution of Phosphate Rock in Acid Soils as Influenced by Nitrogen and Potassium Fertilizers

Abstract: The dissolution in two acid soils (Weston, pH 4.5; Davidson, pH 5.2) of phosphorus from North Carolina phosphate rock, a highly reactive rock, was decreased by additions of (NH4)2SO4 or their mixtures, but increased by the addition of urea. The effect of urea was decreased by addition of KCI. It is concluded that urea hydrolyzes the organic matter of the soil and that the products of hydrolysis chelate calcium ions and so increase the dissolution of phosphorus from the rock. (NH4)2SO4 and KCI, on the other hand, increase the phosphorus-sorption capacity of the soil and so decrease the water-soluble phosphorus in the soil. The results suggest that the beneficial effects of nitrogen and potassium fertilizer salts on the uptake of phosphorus by plants may result from stimulation of plant growth and not from solubilization of phosphate rock.