The surge of interest in and scientific publications on the structure and properties of nanocomposites has made it rather difficult for the novice to comprehend the physical structure of these new materials and the relationship between their properties and those of the conventional range of composite materials. Some of the questions that arise are: How should the reinforcement volume fraction be calculated? How can the clay gallery contents be assessed? How can the ratio of intercalate to exfoliate be found? Does polymerization occur in the clay galleries? How is the crystallinity of semi-crystalline polymers affected by intercalation? What role do the mobilities of adsorbed molecules and clay platelets have? How much information can conventional X-ray diffraction offer? What is the thermodynamic driving force for intercalation and exfoliation? What is the elastic modulus of clay platelets? The growth of computer simulation techniques applied to clay materials has been rapid, with insight gained into the structure, dynamics and reactivity of polymer-clay systems. However these techniques operate on the basis of approximations, which may not be clear to the non-specialist. This critical review attempts to assess these issues from the viewpoint of traditional composites thereby embedding these new materials in a wider context to which conventional composite theory can be applied. (210 references).

Chemiosmotic coupling is universal: practically all cells harness electrochemical proton gradients across membranes to drive ATP synthesis, powering biochemistry. Autotrophic cells, including phototrophs and chemolithotrophs, also use proton gradients to power carbon fixation directly. The universality of chemiosmotic coupling suggests that it arose very early in evolution, but its origins are obscure. Alkaline hydrothermal systems sustain natural proton gradients across the thin inorganic barriers of interconnected micropores within deep-sea vents. In Hadean oceans, these inorganic barriers should have contained catalytic Fe(Ni)S minerals similar in structure to cofactors in modern metabolic enzymes, suggesting a possible abiotic origin of chemiosmotic coupling. The continuous supply of H2 and CO2 from vent fluids and early oceans, respectively, offers further parallels with the biochemistry of ancient autotrophic cells, notably the acetyl CoA pathway in archaea and bacteria. However, the precise mechanisms by which natural proton gradients, H2, CO2 and metal sulphides could have driven organic synthesis are uncertain, and theoretical ideas lack empirical support. We have built a simple electrochemical reactor to simulate conditions in alkaline hydrothermal vents, allowing investigation of the possibility that abiotic vent chemistry could prefigure the origins of biochemistry. We discuss the construction and testing of the reactor, describing the precipitation of thin-walled, inorganic structures containing nickel-doped mackinawite, a catalytic Fe(Ni)S mineral, under prebiotic ocean conditions. These simulated vent structures appear to generate low yields of simple organics. Synthetic microporous matrices can concentrate organics by thermophoresis over several orders of magnitude under continuous open-flow vent conditions.

Suspensions of fine alumina powder in a paraffin wax have been successfully formulated with viscosity values sufficiently low to allow ink-jet printing using a commercial printer. A commercial-grade paraffin wax, with stearylamine and a polyester, were used as the dispersant system. Suspensions with powder loadings up to 40 vol% were passed through the ink-jet printer head. Unfired ceramic bodies with a feature size of <100 m have been successfully fabricated with waxes that had a powder loading of 30 vol%. The influence of suspension fluid properties on the ink-jet printing process has been studied, and the importance of the acoustic resonance within the ink-jet printing apparatus has been demonstrated.

The modulus-volume fraction relationship for a poly( -caprolactone)-montmorillonite nanocomposite follows composite materials theory provided the clay volume fraction is correctly calculated. Thus, for interpretation of mechanical properties, nanocomposites do not have to be treated as a separate class of material. The tensile modulus of biodegradable poly( -caprolactone) was increased by 50% at 8 wt % clay addition (as corrected for surfactant), but the more dramatic improvement was in tensile elongation at break which increased from 165% to 550% for additions of up to 10 wt % clay. Poly( -caprolactone) nanocomposites with various clay volume fractions were produced with two organo-modified montmorillonites. Untreated montmorillonite was used as an experimental control to compare the properties with a conventional composite over the same clay volume fraction range, The composites were confirmed and characterized by XRD, DSC, NMR, and TEM.

No abstract

The scientific community relies upon the veracity of the scientific data in handbooks and databases. In a previous work, the authors developed a systematic, intelligent, and potentially automatic method to detect errors in such resources based on artificial neural networks (ANNs). This method revealed variations from (10 to 900) % in tables of property data for elements in the periodic table and pointed out the ones that are most probably correct. In this paper, we focus on the details of employing this method for analyzing the data of boiling points and enthalpies of vaporization recorded in different handbooks. The method points out the values that are likely to be correct. To verify the method employed, a detailed discussion of the data with reference to the original literature sources is given as well as factors that may affect the accuracy of the prediction.

No abstract

troversially that some processes may be materials speci c. It seems that the taxonomy of manufacturing Solid freeforming is a genus of manufacturing processes is not well organised from the student's processes in which three-dimensional objects are assembled by point, line or planar addition of point of view and awaits completion. In the casting material. Confining surfaces, such as mould or die category, which embraces sand casting, die casting, walls, are absent. The shape is built by adding injection moulding, solvent casting, slip casting and rather than subtracting material. Solid freeforming microcasting methods such as LIGA (Lithogra ehas come to be computer controlled over the past Galvanoformung-Abformung), a change of state two decades in parallel with the expansion of the occurs against con ning surfaces that de ne the shape. data handling capacity of personal computers. It The range of state change methods includes phase can be used for rapid prototyping but also offers change, solvent evaporation, chemical reaction and mass production pathways in which individuation phase separation. In deformation methods, dies, rolls is possible. It is of particular interest for the and formers are used for compaction, drawing, creation, inter alia, of prosthetics that can be individually built from modified X-ray computed forging, rolling and spinning. Most of these processes tomographic data. Some routes offer the are now enhanced by computer control. Machining additional capability to control, from the computer, operations include carving, turning, milling, electronot just the shape but also the composition discharge machining, laser machining and etching, throughout a component. Thus, three-dimensional while joining methods such as welding, soldering, functional gradients in multiphase ordered brazing, adhesive bonding and the use of fasteners composites become possible. The concept of allow prefabricated components to be assembled to 'design' now embraces the integration of the achieve a higher level of complexity. spatial variation of composition, microstructure Some processes are missing from this list. The and hence of properties together with the shape creation of a coiled pot from clay can be dated to the parameters for multifunctional materials. This is a vast and expanding field in which the first 5th millennium BC.7 It does not t these categories textbooks are emerging. A review of this type must but is the historical antecedent of a solid freeforming necessarily be focused. The emphasis here process known as 'fused deposition modelling' (q.v.) therefore is placed on ceramic processing. This in which the computer controlled travel of an extruder review attempts to set out the taxonomy of solid nozzle builds a shape from linear extrudate.8 It is also freeforming in an historical context, disentangling not quite so easy to classify brickwork. Houses are the multiplicity of process names that have arisen not made by building a large block of masonry and over the past two decades. Special emphasis is machi...