An overview of electro-osmosis in fuel cell polymer electrolytes

Electro-osmosis, the transport of water with protons, in polymer electrolyte fuel cell membranes is important because it effects water management within an operating cell on both a global and local level. The electro-osmotic drag coefficient is the number of water molecules transported per proton and is a quantitative measure of the extent to which electro-osmosis occurs in a given polymer electrolyte. The methods for which electro-osmotic drag coefficients have been determined are reported. An effort is made to report proton electro-osmotic drag coefficients extensively, while a few non-proton cation electro-osmotic drag coefficients have been chosen for illustrative purposes. The results reported have implications for fuel cell performance and in the development and characterization of new polymer electrolyte membranes.     

Roles of clays in soils

In soil science, the term clay refers to all particles less than 2 μm in diameter. Thus it includes layer silicates, oxides and other minerals. Clays are the source of many of the chemical and physical properties of soils that make them a useful medium for the growth of plants and for the less common uses such as a medium for the disposal of wastes. Clays add much of the diversity found in soils. The minerals in soil clays frequently differ from their counterparts in commercial deposits. Also, the behavior of soil clays is influenced by the associated minerals in the coarser fractions. Organic matter is an important reactant with clays of some soils, but it is beyond the scope of this review.The cation exchange properties of clays are among their most important properties in retaining plant nutrient ions (e.g., NH₄⁺, K⁺, Ca²⁺, Mg²⁺, etc.). Cation selectivity of clays influences soils as a plant growth medium and as a disposal medium for wastes (e.g., radioactive and toxic metal ions). Native K in layer silicates of soils is the most important element provided to plants by illites and other micas. Clays contribute to the formation of soil structure by undergoing seasonal shrinking and swelling. Also, they are transported and form clay films that coat natural aggregates that characterize many friable soils. The dispersion and flocculation of clays are important reactions in the physical behavior of soils which in turn influence friability, water infiltration rate, erodibility and other behavioral properties.Vermiculite and smectite in soils frequently have Al³⁺ or polymeric Al on the cation exchange sites. Thus the behavior of these minerals is different from structurally similar minerals in natural deposits. The Fe oxides in soils occur largely as goethite and hematite. Yet they contain Al substituted in their structures, consequently the crystals are smaller and less soluble than their ideal counterparts. Iron oxides contribute to the color, aggregation, and adsorptive properties of soils. Manganese oxides in soils contribute to the retention of trace metals (Co, Zn, Ba, Ni, etc.) and to the oxidation of Fe. Lithiophorite forms in acid soils thus marking another group of minerals that occurs in soils and that is influenced by Al in the structure or in interlayer positions as a result of weathering.     

Reasons for the different effects of calcareous clays on strength properties of ceramics

It is demonstrated that the strength properties of ceramic products molded from poorly sintering polymineral low-melting argillaceous materials and calcareous clays improve due to an increasing content of the total montmorillonite component in the batch; due to organogenic calcite in calcareous clays, which in firing facilitates the formation of a local reducing medium that affects the transformation of Fe³⁺ to Fe²⁺ and facilitates earlier sintering of clay; and due to a gypsum impurity contained in calcareous clays, which is an intense flux.     

Thermoplastic polyurethane nanocomposites of reactive silicate clays: effects of soft segments on properties

This paper addresses the effects of soft-segment on clay particle exfoliation and resultant mechanical and thermal properties of nanocomposites of reactive layered silicate clay and thermoplastic polyurethanes (TPU). The composites were synthesized via a two-step bulk polymerization scheme from polyether- and polyesterpolyols of molecular weight 2000, diphenylmethanediisocyanate, butanediol, and up to 5 wt% reactive layered silicate clay. It was found that the extent of tethering reactions between polymer chains carrying residual -NCO groups and reactive clay particles was significant, although did not depend on the nature of polyol used. Nanocomposites were obtained only in the case of polyesterpolyol, which can be attributed to both clay-polymer reactions and higher viscosity in the clay-polymer mixing step. These nanocomposites showed 125% increase in tensile stress, 100% increase in elongation, and 78% increase in tensile modulus along with 130% increase in tear strength and a 60% reduction in volume loss in abrasion test. It was observed that hydrogen bonding did not influence the properties and the extent of hydrogen bonding was not affected by the clay particles.     

The effect of electro-osmosis on the synthesis of lead and tin fluoroborates

Pronounced electro-osmosis phenomena were observed during the anodic dissolution of lead and tin in fluoroboric acid with an anionic exchange membrane separating the anode compartment from the cathode compartment. The consequent volumetric increment of anolyte was influenced by the current density and the initial volume and concentration of catholyte. The selectivities (S _i) of the given membrane were found to be $$\begin{gathered} 50\% Sn(BF_4 )_2 solution: S_{BF^{4 - } } = 0.952; S_{Sn^{2 + } } = 0.048 \hfill \\ 50\% Pb(BF_4 )_2 solution: S_{BF^{4 - } } = 0.887; S_{Pb^{2 + } } = 0.113 \hfill \\\end{gathered}$$      

Firing Belkin clays in rotary kilns

Conclusions A technology for producing chamotte with a water absorption of 8% or less from Belkin Clays was developed and introduced. The optimum operating parameters (the kiln charge and the fuel oil or gas consumption) giving good-quality chamotte were determined.An analysis was carried out of some of the causes of the formation of fused deposits. It was established that this process is influenced in large measure by the chemical composition of the clay, more especially by a high TiO₂ content.Translated from Ogneupory, No. 1, pp. 19–26, January, 1976.     

The meaning of surface area and porosity measurements of clays and pillared clays

Pillared clays (PC) generally present textural complexity, geometrical constraints and possible chemical heterogeneity by pillaring. As far as surface area and porosity measurements by physical adsorption of nitrogen are concerned, this overall complexity introduces interpretation difficulties. We consider two aspects of this problem in pillared clays.The textural complexity stems from the distribution of charge density, from the deformation of the host layers and from their entanglement. The microtexture is controlled by the wet preparation chemistry, to a large extent by the drying method as examplified by the titanium pillared montmorillonites.The geometrical constraints arise from the fact that the interlamellar space of the PC is (so far) microporous or just mesoporous. The small distance between the layers, of the order of one or a few molecular diameters, is therefore expected to perturb the arrangement of the pore filling molecules. The molecular confinement is a major source of underestimation of the total pore volume in the interlamellar space. It makes the surface area determination difficult and of little physical significance. Probably microporosity values are more valuable criterion of pillaring as shown in the titanium pillared samples.In addition to these two aspects, one has also to consider a possible chemical heterogeneity arising from the simultaneous presence of pillars, exchangeable ions and precipitated species. This can lead to a complex behaviour of surface area and microporosity as examplified by the mixed aluminium-iron pillared laponites.     

Water content and shear strength evaluation of marine soil after electro-osmosis experiments

In this study, a series of electro-osmosis experiments were conducted using Dalian marine soil to evaluate the water content and shear strength of soil samples after electro-osmosis experimental treatment. The conditions that were considered in these experiments include voltage, preloading pressure, drainage direction, temperature, anode material, and processing duration. In comparing water content and shear strength, the different operational conditions were demonstrated to affect the results of electro-osmosis to a variable extent. For example, the shear strength of samples at 35°C improved by an average of 61.96% compared with room temperature samples. Also, water content under 12?V trials decreased by an average of 9.30% compared with 6?V. These results can be attributed to the difference in electro-dewatering capacities of the conditions mentioned above. Based on the data, two statistical relationships, which represent the relationship between experimental conditions and results, were also established.     

On loosening of refractory clays in roasting

Kaolin samples of the Malinovetskoe deposit are used to study the processes of loosening and bloating of clay rocks in roasting at a temperature exceeding the sintering one. It is shown that the bloating is a result of oxidation-reduction reactions between the admixtures contained in the clays when they are heated under the conditions of diminished viscosity of the glass phase. In addition to the possible influence of these factors the loosening is connected with crystallization of new phases. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 3, pp. 23–32, March, 2000.     

Color characteristics of low-melting clays

An unconventional method of determining the color of clay and ceramic materials in air-dry and calcined states in equal-color coordinates of the color space using the color characteristics (saturation, hue, yellow hue, lightness, color coordinate) is employed to classify clays from the Gzhel’ deposit. The method is recommended for adjusting the color range of ceramic articles.