Molecular Binder Research Articles

Assembly of thin mesoporous titania films and their effects on the voltammetry of weakly adsorbing redox systems

Titania (anatase) films composed of nanoparticulate building blocks are formed in a layer-by-layer deposition procedure followed by calcination. Field emission gun scanning electron microscopy (FEGSEM) and conducting probe atomic force microscopy (C-AFM) techniques are used to assess the topography and electrical conductivity of the resulting titania films in the dry state. Two types of molecular binder, cyclohexane hexacarboxylic acid and phytic acid, are employed in the deposition process. The surface charge of the resulting titania films is dramatically affected by the presence of phosphate (from phytic acid) after pyrolysis of the molecular binder. Voltammetric responses for the Ru ( NH 3 ) 6 3 + / 2 + redox system obtained at mesoporous titania coated electrodes immersed in aqueous KCl are strongly affected by the adsorption of Ru ( NH 3 ) 6 3 + in the presence of phosphate. In order to further investigate the effects of the mesoporous membrane on voltammetric features, an approximate adsorption and transport model supported by a simple numerical simulation (of explicit finite-difference type) with reversible adsorption/desorption equilibria is developed. Based on the comparison of experimental and numerical data, it is proposed that the electrical conductivity (electron diffusion) within the wet titania film in the potential range where the reduction of Ru ( NH 3 ) 6 3 + occurs is important in addition to ion transport.

Electrochemistry in the Presence of Mesoporous TiO2 Phytate Nanofilms

AbstractThin composite organic – inorganic membranes are formed at electrode surfaces via a layer‐by‐layer deposition process employing TiO2 nanoparticles and phytic acid as molecular binder. The mesoporous membranes form uniformly across platinum and glass surfaces and are shown via conducting atomic force microscopy (C‐AFM) to behave in dry state as electrically insulating films. Voltammetry at platinum electrodes of 1.5 mm, 100 μm, and 10 μm diameter is used to survey the effect of the composite membrane on electrochemical processes. The electrode diameter as well as concentration and nature of electrolyte have a considerable effect on the electrode process. For the one electron reduction of Ru(NH3)$\rm{ {_{6}^{3+}}}$ in aqueous media adsorption effects, mobility effects, and accumulation or ‘memory’ effects are observed. Similarly, protons or cationic molecules such as dopamine can be accumulated and ‘stored’ in the membrane and then transferred to a clean electrolyte for analysis.

Nanostructures from nanoparticles

This paper reviews recent experimental approaches to the development of surfacenanostructures from nanoparticles. The formation of nanowires by electron beam writing infilms of gold nanoparticles passivated with a specially designed class of ligand molecules(dialkyl sulfides) is presented, together with illustrations of practical nanostructures.Potential applications of this methodology are discussed. Another alternative to thecontrolled fabrication of arrays of nanoparticles, based on nanocrystals which containmolecular recognition elements in the ligand shell, is also surveyed. These particlesaggregate in the presence of specifically designed molecular dications which act asa molecular binder. Finally, recent work on the formation of nanoscale surfacearchitectures using x-ray patterning of self-assembled monolayers is introduced. Currentand potential future applications of these surface nanostructures are discussed.

Thermal debinding processing of 316L stainless steel powder injection molding compacts

The process of thermal debinding of injection molded water atomized 316L stainless steel powder compacts was studied in a vacuum and hydrogen atmosphere using a mercury porosimetry and the thermogravimetric analysis method. The vacuum debinding rate was investigated under the conditions of different binder compositions and temperature-increase rates, especially at the low temperature stage. The process of thermal debinding in the hydrogen atmosphere was compared with that in vacuum. It was found that the binder removal rate was much higher in vacuum than that in the hydrogen atmosphere under the same experimental conditions. The mercury porosimetry was used to measure the pore structure evolution. The results of the mercury porosimetry indicated that the pore structure evolution in injection molded compacts during thermal debinding in vacuum was greatly different from that in hydrogen atmosphere. A fine inter-connected pore structure developed as a result of the evaporation and removal of the low molecular binder components at the early stage of debinding. The reason for the difference in binder removal rate and the inter-connected pore structure in these two debinding environments lies in the difference of the vapor pressure drop, which was the vapor pressure difference between that in the molded compacts and that in the ambient environment. At the different thermal debinding stages and environments, the pore structure evolution and changes in the mean pore size in the thermally debound compacts were also different. From the low debinding temperature stage to the intermediate temperature stage of about 300 °C, the pores in the thermally debound compacts in the hydrogen atmosphere were finer and the pore size distribution was more homogeneous than that in the vacuum. At the final debinding stage, the pore size distribution was almost the same in the hydrogen atmosphere as in the vacuum.

Diisocyanates as novel molecular binders for monolayer assembly of zeolite crystals on glass.

Isocyanate groups readily form urethane linkages with surface hydroxy groups on glass and zeolites and this phenomenon was utilized in the assembly of monolayers of zeolite microcrystals on glass by employing diisocyanates as novel molecular binders.

Characterization of Porous AlN Separators for Batteries

AbstractA ceramic membrane of porous, sintered aluminum nitride (AIN) is under consideration for use as a separator in a Lithium-Metal Sulfide battery due to the corrosion resistance and thermal stability of AlN. The pore structure and electrolytic permeability of the membrane must be appropriate if AlN is to be used. Commercialization of these membranes can occur only after repeatability in the processing conditions can be assured. In this study, extensive permeability and porosity testing was performed on membranes prepared under various processing conditions. Attempts to correlate processing conditions with permeability were made in order to determine the optimum method for fabrication of the membranes. It was determined that membranes produced with a lower molecular weight binder will have a higher permeability, higher porosity, and a larger pore structure than membranes produced with a higher molecular weight binder.

The formation of isoprenoid sulfur compounds during diagenesis: simulated sulfur incorporation and thermal transformation

The mechanism of natural sulfur incorporation into organic matter during early diagenesis was studied by simulation reactions carried out with three isoprenoid aldehydes under phase transfer catalysis (PTC) of ammonium polysulfide at ambient temperatures. The adehydes were phytenal ( 4), an α,β-unsaturated aldehyde formed by mild oxidation of phytol ( 3), citral ( 5), a monoterpene dienal, and 2H-dihydrocitronellal ( 6), a saturated monoterpene aldehyde. All three aldehydes gave polysulfide cross-linked macromolecules. The structures of the macromolecular substances were studied by the analysis of the products formed by MeLi/MeI depolymerization. The structures of these products are similar to the products formed by the same method from sulfur-rich macromolecular structures identified in immature sediments. Thermal decomposition experiments of the macromolecular products of the α,β-unsaturated aldehydes gave the corresponding isoprenoid thiophenes. The C 20 isoprenoid thiophenes formed from 4 are found in many natural immature sediments. A mechanism for the formation of these thiophenes is presented. These results give additional chemical support to the important role of inorganic polysulfide anions as molecular binders in nature. The results suggest that thermal processes that follow the incorporation of sulfur may play an important role in transforming the early formed sulfur-containing compounds into thermally stable structures. The results also provide a possible new pathway for phytol degradation in sulfide-rich environments and for the formation of C 20 isoprenoid thiophenes.

The influence of powder loading and binder additive on the properties of alumina injection-moulding blends

The effects of powder loading and binder additive on the rheology, moulding, and sintered properties of alumina injection-moulding blends were studied. The melt viscosity increased with the powder loading, which enhanced the defect concentration of the moulded parts when the powder loading was higher than 0.54 volume fraction. This transitional powder loading was much smaller than the critical powder loading of 0.65 derived by fitting the rheological data with a mathematical model. The low molecular weight acidic binder additives used in this study effectively reduced the melt viscosity. However, additives that yielded a large quantity of burn-out residue deteriorated the sintered properties. A high powder-loading mixture having a low melt viscosity and good powder dispersion was achieved by eliminating powder agglomerates before mixing, and by using an appropriate binder additive.

Rheological Behavior of Injection‐Moldable Silicon Powder–Silicon Carbide Whisker Formulations

The rheological behavior of injection‐moldable formulations for reaction‐bonded Si3N4 toughened with silicon carbide whiskers was studied using capillary rheometry. The effects on rheology of the following parameters were examined: solids loading, powder/whisker volume ratio, particle size and type, and binder composition. Two important aspects of the flow behavior were delineated. First, corrections for end effects and slippage along the wall were made in order to interpret the experimental data properly. At high shearing rates (i.e., 103 s−1) slip may account for more than 50% of the total flow. Such slippage promotes flow into the smallest channels or corners of the mold and may appreciably facilitate molding. Consequently the careful study of slippage is an inherent requirement of the rheological characterization of these concentrated suspensions. Second, the suspension viscosities were delineated. An empirical equation for predicting relative viscosity was developed for formulations containing up to ∼30 vol% of silicon carbide whiskers (with more than 50 vol% total solids). Suspension viscosities generally increased with decreasing particle size and increasing whisker contents. Particle surface roughness appears to affect the shearing behavior. Binders of low molecular weight resulted in higher relative viscosities than higher molecular weight binders, indicating possibly better dispersion of solids when more viscous binders are employed.

The effects of binder on the mechanical properties of carbonyl iron products

Experiments have been conducted to examine the effects of binder composition on the mechanical properties of injection-molded, carbonyl iron sintered products. A solvent extraction debinding technique was used to quickly remove the binder and carefully control the carbon content. A high content of high molecular weight backbone binder component gives rise to a higher flow viscosity, but does not significantly enhance the green strength. The addition of a small amount of stearic acid can improve moldability by reducing the flow viscosity. A variance in sintered properties is related to the difference in carbon content and final grain size.

Amino acid sequence homology between human and bovine low molecular weight folate binding protein isolated from milk

The partial amino acid sequence of a low molecular weight folate binding protein from human milk has been determined from N-terminal sequencing of the native protein and isolated cyanogen bromide fragments. A molecular weight of approximately 30,000 is estimated on the basis of amino acid composition and sequence homology with the low-molecular weight folate binder isolated from cow's milk. Preliminary studies with a large molecular weight folate binding protein have shown that the N-terminal amino acid sequence is identical with that of the low molecular binder.