The aim of this critical review is to provide a broad but digestible overview of mechanochemical synthesis, i.e. reactions conducted by grinding solid reactants together with no or minimal solvent. Although mechanochemistry has historically been a sideline approach to synthesis it may soon move into the mainstream because it is increasingly apparent that it can be practical, and even advantageous, and because of the opportunities it provides for developing more sustainable methods. Concentrating on recent advances, this article covers industrial aspects, inorganic materials, organic synthesis, cocrystallisation, pharmaceutical aspects, metal complexes (including metal–organic frameworks), supramolecular aspects and characterization methods. The historical development, mechanistic aspects, limitations and opportunities are also discussed (314 references).

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Mechanochemistry: opportunities for new and cleaner synthesis

This review focuses on key aspects of the thermal decomposition of multinary or mixed hydride materials, with a particular emphasis on the rational control and chemical tuning of the strategically important thermal decomposition temperature of such hydrides, Tdec. An attempt is also made to predict the thermal stability of as-yet unknown, elusive or even unknown hydrides. The future of a particularly promising class of materials for hydrogen storage, namely the catalytically enhanced complex metal hydrides, is discussed. The predictions are supported by thermodynamics considerations, calculations derived from molecular orbital (MO) theory and backed up by simple chemical insights and intuition.

Thermal decomposition of the non-interstitial hydrides for the storage and production of hydrogen.

Bone is a hierarchically structured composite material which, in addition to its obvious biological value, has been well studied by the materials engineering community because of its unique structure and mechanical properties. This article will review the existing bone literature, with emphasis on the prevailing theories regarding bone formation and structure, which lay the groundwork for proposing a new model to explain how intrafibrillar mineralization of collagen can be achieved during bone formation. Intrafibrillar refers to the fact that growth of the mineral phase is somehow directed by the collagen matrix, which leads to a nanostructured architecture consisting of uniaxially oriented nanocrystals of hydroxyapatite embedded within and roughly [0 0 1] aligned parallel to the long collagen fibril axes. Secondary (osteonal) bone, the focus of this review, is a laminated organic–inorganic composite composed primarily of collagen, hydroxyapatite, and water; but minor constituents, such as non-collagenous proteins (NCPs), are also present and are thought to play an important role in bone formation. To date, there has been no clear understanding of the role of these NCPs, although it has been generally assumed that the NCPs regulate solution crystal growth via some type of ‘epitaxial’ relationship between specific crystallographic faces and specific protein conformers. Indeed, ‘epitaxial’ relationships have been calculated; but in practice, it has not been demonstrated that intrafibrillar mineralization can be accomplished via this route. Because of the difficulty in examining biomineralization processes in vivo , the authors of this article have turned to using in vitro model systems to investigate the possible physicochemical mechanisms that may be involved in biomineralization. In the case of bone biomineral, we have now been able to duplicate the most fundamental level of bone structure, the interpenetrating nanostructured architecture, using relatively simple anionic polypeptides that mimic the polyanionic character of the NCPs. We propose that the charged polymer acts as a process-directing agent, by which the conventional solution crystallization is converted into a precursor process. This polymer-induced liquid-precursor (PILP) process generates an amorphous liquid-phase mineral precursor to hydroxyapatite which facilitates intrafibrillar mineralization of type-I collagen because the fluidic character of the amorphous precursor phase enables it to be drawn into the nanoscopic gaps and grooves of collagen fibrils by capillary action. The precursor then solidifies and crystallizes upon loss of hydration waters into the more thermodynamically stable phase, leaving the collagen fibrils embedded with nanoscopic hydroxyapatite (HA) crystals. Electron diffraction patterns of the highly mineralized collagen fibrils are nearly identical to those of natural bone, indicating that the HA crystallites are preferentially aligned with [0 0 1] orientation along the collagen fibril axes. In addition, studies of etched samples of natural bone and our mineralized collagen suggest that the long accepted “deck of cards” model of bone's nanostructured architecture is not entirely accurate. Most importantly, this in vitro model demonstrates that a highly specific, epitaxial-type interaction with NCPs is not needed to stimulate crystal nucleation and regulate crystal orientation, as has long been assumed. Instead, we propose that collagen is the primary template for crystal organization, but with the important caveat that this templating occurs only for crystals formed from an infiltrated amorphous precursor. These results suggest that the 25-year-old debate regarding bone formation via an amorphous precursor phase needs to be revisited. From a biomedical perspective, in addition to providing possible insight into the role of NCPs in bone formation, this in vitro system may pave the way toward the ultimate goal of fabricating a synthetic bone substitute that not only has a composition similar to bone, but has comparable mechanical properties and bioresorptive potential as natural bone. From a materials chemistry perspective, the non-specificity of the PILP process and capillary infiltration mechanism suggests that non-biological materials could also be fabricated into nanostructured composites using this “biomimetic” strategy.

Bone structure and formation: A new perspective

!Received 19 December 2005; accepted 27 January 2006 "The deÞnitions for important Rietveld error indices are deÞned and discussed. It is shown that whilesmaller error index values indicate a better Þt of a model to the data, wrong models with poor qualitydata may exhibit smaller values error index values than some superb models with very high qualitydata. © 2006 International Centr e for Diffraction Data. #DOI: 10.1 154/1.2179804 $

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R factors in Rietveld analysis: How good is good enough?

SnO2: A comprehensive review on structures and gas sensors

The combined use of high-resolution solid state NMR techniques (both 1D and 2D) with synchrotron-based powder x-ray diffraction studies yields detailed information on the lattice structures of highly siliceous zeolites. The two methods are complementary, the former probing short range ordering and structures while the latter is sensitive to long range orderings and periodicities.

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Multitechnique Analysis of the Lattice Structures of Highly Siliceous Zeolites

Crystal structure of silica-ZSM-12 by the combined use of high- resolution mas nmr solid-state spectroscopy and synchrotron x-ray powder diffraction.

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D.E. Cox

Papers

Multitechnique Analysis of the Lattice Structures of Highly Siliceous Zeolites

Crystal structure of silica-ZSM-12 by the combined use of high- resolution mas nmr solid-state spectroscopy and synchrotron x-ray powder diffraction.

Multitechnique Analysis of The Lattice Structures of Highly Siliceous Zeolites