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.     

Numerical evaluation of optimal approaches for electro-osmosis dewatering

A newly developed numerical model is used to identify and evaluate optimum electrode configurations for electro-osmosis dewatering, as well as to evaluate approaches such as current intermittence and current reversal. Various electrode configurations, electrode spacings, and voltage gradients are studied numerically using 3D models with a cubic domain and vertically installed tube electrodes. The results indicate that, with more anodes installed, one can expect more water to drain out and a more uniform surface settlement, although a greater energy consumption is then required. A 2D square domain is used to study current intermittence and current reversal. Current intermittence allows more water to be drained out and has a higher energy efficiency compared to a continuous current, although it consumes more energy. Polarity reversal is also shown to be more efficient than a continuous current supply.     

Dewatering effect of vacuum preloading incorporated with electro-osmosis in different ways

The dredger fill dewatering effect of vacuum preloading incorporated with electro-osmosis in different ways was evaluated by implementing six laboratory tests. The results of these tests show that the asynchronous consolidation effect of vacuum preloading incorporated with electro-osmosis was better than the other tests. However, vacuum preloading and electro-osmosis will not be able to give full play to the drainage effect, if the alternate time is too short. Alternatively, the energy provided by vacuum preloading and electro-osmosis will not be able to make full use, if the alternate time is too long. There are some advantages when using vacuum preloading and electro-osmosis asynchronous reinforcement. The alternate time of vacuum preloading and electro-osmosis has to constantly adjust according to the water discharge or drainage rate in engineering application.     

Dewatering of drinking water treatment sludge by vacuum electro-osmosis

The objective of this research was to evaluate the dewatering of drinking water treatment sludge (DWTS) by vacuum electro-osmosis dewatering (VEOD) technology. DWTS has a high moisture content, with the water existing as free water, pore water, surface adhesion water and internal combined water. Vacuum filtration of 0.05 MPa can quickly dewater sludge and has low energy consumption, but can only remove free water and some pore water. The moisture content of the DWTS was reduced to below 79% by vacuum filtration technique alone. At this moisture content, all free water had been expelled by vacuum filtration. Electro-osmosis optimized for the experimental conditions (0.05 MPa, 2.5 V/cm) began after vacuum filtration ceased, and drew pore water and surface adhesion water to the cathode, where it was expelled through vacuum filtration. The VEOD process removed all free water. In addition, pore water and surface adhesion water were reduced by 60.2% and 15.9%, respectively.     

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.     

一种基于电渗析的空气直接富氧装置影响因素

随着全球气候环境问题不断显现,关于CO₂减排的问题受到社会各界越来越多的关注。其中,以燃烧矿物作为主要能源来源的火电厂是CO₂最大的排放源,减少火电厂CO₂排放对缓解温室效应也就具有重大意义,当前火电厂实现CO₂减排的有效措施为富氧燃烧,研究富氧技术对减少火力发电厂CO₂减排有着重要的实用价值。根据传统的电渗析溶液除湿技术,提出了一种新型的基于电渗析技术直接作用于空气的富氧方法,并根据理论分析发现：在电场强度小于50 kV的情况下提高空气湿度与电场强度能显著增加装置富氧效果。     

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.     

Cyclic swelling of clays

Changes in free swelling and swelling pressure of different types of clays in response to varying cycles of wetting and drying have been studied. It can be shown that cyclic tests lead to a gradual destruction of the durable contacts in the clay structure and their transformation into less durable ones. At the same time, a reconstruction of the structure of the clays takes place, manifested by the destruction of large micro-aggregates and by disorientation of structural elements. All these phenomena result in great swelling with increase in the number of wetting cycles. Between cycles 3 and 20 the expansibility is at its maximum and may be 1.3–10 times as much as that after one wetting cycle. Cyclic swelling leads to an overall equilibrium in the system, when the internal energy of the clay is minimal and the bound water content is at its maximum. Clay in this state exhibits its maximum moisture uptake (W′_s), the meaning of which is of thermodynamic character and depends neither on the initial soil density and moisture, nor on the scheme of cyclic tests adopted.     

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.     

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.