Jump relaxation in solid electrolytes

The attachment strategy based on catecholic chemistry has been arousing renewed interest since the work on polymerized catecholic amine (polydopamine) (Messersmith et al., Science, 2007, 318, 426) was published. Catechols and their derived compounds can self-assemble on various inorganic and organic materials, including noble metals, metals, metal oxides, mica, silica, ceramics and even polymers. It opens a new route to the modification of various substrates and the preparation of functional composite materials by simple chemistry. However, there is still not a full review so far about the attachment chemistry despite the dramatically increasing number of publications. This critical review describes the state-of-the-art research in the area: the design and synthesis of catecholic molecules, their adsorption mechanisms and the stability of assemblies in solution, and their applications etc. Some perspectives on future development are raised (195 references).

Bioinspired catecholic chemistry for surface modification.

Additive manufacturing (AM) is a technology which has the potential not only to change the way of conventional industrial manufacturing processes, adding material instead of subtracting, but also to create entirely new production and business strategies. Since about three decades, AM technologies have been used to fabricate prototypes or models mostly from polymeric or metallic materials. Recently, products have been introduced into the market that cannot be produced in another way than additively. Ceramic materials are, however, not easy to process by AM technologies, as their processing requirements (in terms of feedstock and/or sintering) are very challenging. On the other hand, it can be expected that AM technologies, once successful, will have an extraordinary impact on the industrial production of ceramic components and, moreover, will open for ceramics new uses and new markets.

Additive Manufacturing of Ceramics: Issues, Potentialities, and Opportunities

Drugs: A review of promising novel corrosion inhibitors

A hydrothermal method was used to synthesize nanocrystalline SnO2 particles with an average particle size of 3.0 ± 0.5 nm. Thermally treated SnO2 with an average diameter of 3.3 ± 0.6 nm was obtain...

Hydrothermal Synthesis of SnO2 Nanoparticles and Their Gas-Sensing of Alcohol

The preparation of aqueous α-Al 2 O 3 , α-SiO 2 and α-SiC suspensions with polyelectrolytes, i.e. the NH 4 + salt of polymethacrylic acid (PMA-NH 4 + ) and the acidic form of polyethylene imine (PEI-H + ), is investigated. It is based on the adsorption of these polyelectrolytes which in turn depends mainly on the nature of the polyelectrolyte, and the charge density that develops on the powder surface in water. The efficiency of these dispersants is primarily attributed to the electrostatic interaction between -COO − groups of PMA-NH 4 + and positive sites on the alumina surface at pH 8–9 as well as between -NH 2 + -groups of PEI-H + and negative sites of the silica surface or of the oxidized surface of silicon carbide in acidic media. Good dispersion and stability of dispersions are then obtained through electrostatic and steric stabilization. As an application, the preparation of an Al 2 O 3 -SiC aqueous mixed slurry was investigated as a preliminary step in the processing of Al 2 O 3 /SiC nanocomposites.

Processing of aqueous α-Al2O3, α-SiO2 and α-SiC suspensions with polyelectrolytes

The use of water-based systems represents an interesting alternative to the widespread non-aqueous tape-casting but the low strength of water-based binders generally limits their applicability. A tape-casting slurry is a complex system where each organic component has a substantial effect on the rheological behaviour. In this study the effect of the dispersant and binders in alumina aqueous tape-casting slurries were characterized with electrophoretic mobility and rheological measurements. In aqueous medium, a 4,5-dihydroxy-1,3-benzenedisul-fonic acid, was found to be a very effective dispersant for alumina. The amount of dispersant required to achieve a minimum of viscosity was equal to 0.2 wt%. Two aqueous emulsions of acrylic polymers were used as binders. These binders strongly affect the rheology of the suspensions. The best conditions to obtain a homogeneous stable slurry with a high powder loading suitable for tapecasting were determined in terms of order of component addition, rheological behaviour and ageing of the suspensions. Acrylic binders should act through a cohesive mechanism and lead to green tapes with good mechanical strength.

Aqueous suspensions for tape-casting based on acrylic binders

Mass loss, shrinkage, Young’s modulus evolution and stress development of aqueous (alumina + latex) tape cast suspensions were observed during drying. Mass loss showed a constant drying rate period, followed by a falling rate period. Concurrently a linear shrinkage rate has been observed in the thickness direction, up to a drying point after which shrinkage abruptly stops. End of constant drying rate and end of shrinkage were not necessarily concomitant and depend on the latex/alumina ratio in the tape. A Young’s modulus value appears in the tape cast suspensions at the transition from liquid to solid like state. Then an increase of Young’s modulus is observed corresponding to latex film formation. The stresses generated by drying in the tape exhibited a first period of increase due to capillary pressure in the pores, a small relaxation immediately followed by a second stress increase due to latex film formation, and a stress plateau at the end of latex coalescence. Alumina powder granulometry and surface tension of the liquid had a preponderant influence on the first stress maximum whereas the properties of the latex and the drying conditions dominated the second stress maximum. By increasing latex proportion up to 25 wt.% on alumina basis, it was possible to make the first and the second stress rise concomitant.

Drying mechanisms and stress development in aqueous alumina tape casting

The strength of alumina green samples prepared by uniaxial pressing of powders spray-dried with two binders such as poly(ethylene glycol) or poly(vinyl alcohol) is discussed in terms of (i) the adhesive properties of the polymer-rich external layer of spray-dried granules and (ii) the mechanical properties of this layer. A transition from intra- to intergranular fracture is observed when the glass transition temperature of the binder increases. The influence of the binder on the defect size distribution in the green products is investigated using the classical Weibull statistics.

Mechanical Properties of Dry-Pressed Ceramic Green Products: The Effect of the Binder

A high state of dispersion of alumina particles can be achieved by using molecules derived from Catechol 1,2(OH)2C6H4, such as Tiron (OH)2C6H2(SO3Na)2 which allows to obtain stable alumina suspensions. In the field of understanding the dispersion mechanism of Tiron and the contribution of each functional group grafted onto the benzene ring of the Tiron molecule, adsorption experiments and surface charge measurements were conducted by using several compounds, containing a benzene ring, and by varying the nature and the number of substituents. The influence of the size and of the charge of the counter ion, electrostatically attracted by a positive charged alumina surface, onto the suspension stability was also studied. Electrokinetic properties of the suspensions versus pH appear to be very useful to characterize the ion adsorption sequence for an oxide surface. With a high immersion heat, an alumina surface better adsorbs ions with a high structuring power for water molecules. This influences the charge developed onto the oxide surface.

J.F. Baumard

Papers

Processing of aqueous α-Al2O3, α-SiO2 and α-SiC suspensions with polyelectrolytes

Aqueous suspensions for tape-casting based on acrylic binders

Drying mechanisms and stress development in aqueous alumina tape casting

Mechanical Properties of Dry-Pressed Ceramic Green Products: The Effect of the Binder

Catechol derivatives and anion adsorption onto alumina surfaces in aqueous media: influence on the electrokinetic properties