For most oxide/electrolyte systems potentiometric titration curves measured for different ionic strengths have a Common Intersection Point (CIP) which corresponds to the Point of Zero Charge (PZC). However, there are systems where a CIP exists but the surface charge at this point does not equal zero (PZC CIP). In this paper theoretical analysis of the systems in which the PZC and CIP do not coincide is presented. It is based on the well-known 2-pK surface charging approach and Triple Layer Model (TLM) as well as the Four Layer Model (FLM) of the electric double layer. The appropriate mathematical criterion for CIP existence was applied with detailed derivations, both for TLM and FLM. Having determined in this manner the parameter values, one can draw proper conclusions about the features of oxide/electrolyte adsorption systems, in which PZC and CIP do not coincide. The values of adsorption parameters are found by fitting simultaneously the obtained theoretical expressions to both of the experimental titration isotherms, and to the individual isotherms of electrolyte cation adsorption measured using radiometric methods. 相似文献
We review a direct dynamics method for the simulation of metal|water interfaces. The occupancy of on-top binding sites for water in this model as applied to a (100) surface of ‘copper' is very sensitive to potential. We suggest that this may account for some previously unexplained features of X-ray data on water structure and noble metal|water interfaces. We discuss the problem of statistical fluctuations on the occupancy of such tightly bound water molecules in such simulations. Though the problem is not too serious for charged interfaces, the problem of accounting for fluctuations at zero charge can be quite formidable, as we illustrate for the (100) surface of copper. 相似文献
Layer‐by‐layer (LbL) assembly has emerged as the leading non‐vacuum technology for the fabrication of transparent, super gas barrier films. The super gas barrier performance of LbL deposited films has been demonstrated in numerous studies, with a variety of polyelectrolytes, to rival that of metal and metal oxide‐based barrier films. This Feature Article is a mini‐review of LbL‐based multilayer thin films with a ‘nanobrick wall’ microstructure comprising polymeric mortar and nanoplatelet bricks that impart high gas barrier to otherwise permeable polymer substrates. These transparent, water‐based thin films exhibit oxygen transmission rates below 5 × 10‐3 cm3 m‐2 day‐1 atm‐1 and lower permeability than any other barrier material reported. In an effort to put this technology in the proper context, incumbent technologies such as metallized plastics, metal oxides, and flake‐filled polymers are briefly reviewed.
The steady state growth of porous anodic alumina films in oxalate solutions at various conditions was studied by chronopotentiometry,
mass balance and optical microscopy methods enabling determination of consumed Al, film mass and thickness, current efficiencies,
Al3+ and O2− transport numbers across barrier layer, etc. The film thickness growth rate was found to be proportional to O2− anionic current. A high field ionic migration model was developed. It predicted that, during anodising, the local oxide density
across barrier layer rises from 2.6 in Al|oxide to 4.59–5.22 g cm−3 in oxide|electrolyte interface with mean value ≈3.21–3.52 g cm−3. The field strength rises from the first to second interface. The mechanism of Al oxidation near the Al|oxide interface embraces
the transformation of the Al lattice to a transient, rare oxide one sustained by field with comparable Al3+ spacing parameter. The oxide near the Al|oxide interface and around the density maximum in the oxide|electrolyte interface
are under different levels of electro-restriction stresses. During relaxation, the oxide behaves like a solid-fluid material
suppressing the initial density distribution. 相似文献
Chemical dissolution of the barrier layer of porous oxide films formed on an aluminum foil (99.5% purity) in 1.5 M sulfanic
acid after immersion in a 2 mol dm−3 sulphuric acid at 50 °C was studied. The barrier layer thickness before and after dissolution was determined using a re-anodizing
technique. Re-anodizing was conducted in 0.5 mol dm−3 H3BO3/0.05 mol dm−3 Na2B4O7 solution. We found that the change in the porous oxide growth mechanism was observed at the anodizing voltage of 30 V. Taking
into account this result chemical dissolution behaviour of the barrier layer of porous films formed at 20 V and 36 V and also
the influence of annealing of oxide films at 200 °C were studied. We showed the interplay between the dissolution rates and
charge distribution across the barrier layer. We conclude that the outer and middle layers have negative space charges and
the inner layer has positive space charges. 相似文献
In this work, we offer a direct evidence to illustrate the synergistic effect of water layer and divalent metal ions in oil sands on bitumen liberation from solids surface. A model oil sand was constructed by coating bitumen on the glass surface with a water layer containing divalent metal ions inserted between them. The bitumen liberation behaviors were investigated by placing the model oil sands in various pH solutions. It was found that the water layer facilitated the bitumen liberation, while the presence of Ca2+ or Mg2+ in the water layer played a different role on the bitumen liberation depending on the solution pH. It was believed that the variation of the bitumen liberation was attributed to the changes of surface wettability arising from the adsorption of natural surfactants on the solids and bitumen surfaces. The preferential adsorption of Ca2+ or Mg2+ on the solids and bitumen surfaces acted as either a barrier to disturb the cationic surfactants adsorbing or a bridge to anchor the anionic surfactants. The findings in this work are important for understanding the bitumen liberation behaviors and give a guideline of how controlling the water chemistry when processing the oil sands by water-based bitumen extraction processes. 相似文献
The effect of several deposition parameters on the uniformity of copper electrodeposition through the alumina barrier layer into porous aluminum oxide templates grown in sulfuric or oxalic acid was systematically investigated. A fractional factorial design of experiment was conducted to find suitable deposition conditions among the variables: frequency, voltage, pulsed or continuous deposition, electrolyte concentration, and barrier layer thinning voltage. Continuous ac sine wave deposition conditions yielded excellent uniformity of pore-filling but damaged the porous aluminum oxide templates when deposition was continued to grow bulk copper on the surface. Pulsed electrodeposition yielded comparable uniformity of pore-filling and no damage to the porous aluminum oxide templates, even when bulk copper was deposited on them. Further optimization of pulsed deposition conditions was accomplished by comparing square and sine waveforms and pulse polarity. Pulsed square waveforms produced better pore-filling than pulsed sine waveforms. For sine wave depositions, the oxidative/reductive pulse polarity was more efficient than the commonly used reductive/oxidative pulse polarity. For square wave depositions into sulfuric acid grown pores, the reductive/oxidative pulse polarity produces more uniform pore-filling, likely as a result of enhanced resonant tunneling through the barrier layer and reoxidation of copper in faster filling pores. 相似文献
With the ever increasing miniaturization in microelectronic devices, new deposition techniques are required to form high‐purity metal oxide layers. Herein, we report a liquid route to specifically produce thin and conformal amorphous manganese oxide layers on silicon substrate, which can be transformed into a manganese silicate layer. The undesired insertion of carbon into the functional layers is avoided through a solution metal–organic chemistry approach named Solution Layer Deposition (SLD). The growth of a pure manganese oxide film by SLD takes place through the decoordination of ligands from a metal–organic complex in mild conditions, and coordination of the resulting metal atoms on a silica surface. The mechanism of this chemical liquid route has been elucidated by solid‐state 29Si MAS NMR, XPS, SIMS, and HRTEM. 相似文献