Very different materials are named “Glass,” with Young's modulus (E) and Poisson's ratio (ν) extending from 5 to 180 GPa and from 0.1 to 0.4, respectively, in the case of bulk inorganic glasses. Although glasses have in common the lack of long-range order in the atomic organization, they offer a wide range of structural features at the nanoscale and we show in this analysis that beside the essential role of elastic properties for materials selection in mechanical design, the elastic characteristics (E, ν) at the continuum scale allow to get insight into the short- and medium-range orders existing in glasses. In particular, ν, the atomic packing density (Cg) and the glass network dimensionality appear to be strongly correlated. Maximum values for ν and Cg are observed for metallic glasses (ν∼0.4 and Cg>0.7), which are based on cluster-like structural units. Atomic networks consisting primarily of chains and layers units (chalcogenides, low Si-content silicate, and phosphate glasses) correspond to ν>0.25 and Cg>0.56. On the contrary, ν<0.25 is associated with a highly cross-linked network, such as in a-SiO2, with a tri-dimensional organization resulting in a low packing density. Moreover, the temperature dependence of the elastic moduli brings a new light on the structural changes occurring above the glass transition temperature and on the depolymerization rate in the supercooled liquid. The softening rate depends on the level of cooperativity of atomic movements at the source of the deformation process, with an obvious correlation with the “fragility” of the liquid.

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Elastic Properties and Short-to Medium-Range Order in Glasses

The recognition that bulk nanoceramic materials, having grain sizes typically 100 nm or finer, possess appealing mechanical, physical and tribological properties has generated considerable recent research activity. A major challenge in the research on bulk nanoceramics and nanoceramic composites is concerned with the aspect of processing, in particular restriction of grain growth during sintering. In this regard novel processing techniques have been developed with the aim of fabricating bulk ceramic nanomaterials. The superior properties exhibited by these bulk nanoceramics and ceramic nanocomposites, compared with conventional ceramic materials, have opened up prospects for their use in applications demanding better mechanical properties. The present review highlights outstanding issues related with the processing of nanoceramics and ceramic nanocomposites, discusses the novel processing techniques currently used to develop these materials, critically analyses the property modifications resulting...

Consolidation–microstructure–property relationships in bulk nanoceramics and ceramic nanocomposites: a review

With unique and efficient narrow-band red emission and broadband blue light absorption characteristics, Mn4+-activated fluoride red phosphors have gained increasing attention in warm white LEDs (WLEDs) and liquid crystal display (LCD) backlighting applications, whereas the intrinsic hygroscopic nature of these phosphors have inevitably limited their practical applications. Herein, a waterproof narrow-band fluoride phosphor K2TiF6:Mn4+ (KTF) has been demonstrated via a facile superhydrophobic surface-modification strategy. With the use of superhydrophobic surface modification with octadecyltrimethoxysilane (ODTMS) on KTF surfaces, the moisture-resistance performance and thermal stability of the phosphor KTF can be significantly improved. Meanwhile, the absorption, and quantum efficiency did not show obvious changes. The surface-modification processes and mechanism, as well as moisture-resistance performances and luminescence properties, of the phosphors have been carefully investigated. It was found that the luminous efficiency (LE) of the modified KTF was maintained at 83.9% or 84.3% after being dispersed in water for 2 h or aged at high temperature (85 °C) and high humidity (85%) atmosphere (HTHH) for 240 h, respectively. The WLEDs fabricated with modified KTF phosphor showed excellent color rendition with lower color temperature (2736 K), higher color rendering index (CRI, Ra = 87.3, R9 = 80.6), and high luminous efficiency (LE = 100.6 lm/W) at 300 mA. These results indicate that hydrophobic silane coupling agent (SCA) surface modification was a promising strategy for enhancing moisture resistance of humidity-sensitive phosphors, exhibiting great potential for practical applications.

Waterproof Narrow-Band Fluoride Red Phosphor K2TiF6:Mn4+ via Facile Superhydrophobic Surface Modification.

Purpose: Purpose of this paper is the applying of new technology in injection moulding technique and investigation of reinforcement of PC as dispersed phase inside PP matrix (Table 1). Second aim of work is enrichment of those composites by nanoclay and analyzing mechanical behaviour of nanocomposites. Design/methodology/approach: According to design of experiments (DOE) specimens were injection moulded in the shape of rectangular bars. Additionally advanced technology of melt manipulation inside mold cavity after injection was used. To achieve this purpose Ferromatik Milacron injection moulding machine, equipped with externally controlled mold was used. Findings: Addition of nanoclay clearly presents highly reinforced system, especially for neat matrix. Evenly dispersed PC particles within PP majority show reinforcement as well. Inducement of shear rate in injection moulding radically improved absorption of energy in nanocomposite. Research limitations/implications: Different variation of material composition, such combination with other polymers and use of different reinforcements (flexible or either rigid) is required to be checked in the further work. Practical implications: Reinforcement obtained thanks to dispersed phase and nanofillers creates composites with improved mechanical properties. Originality/value: Morphology development reflects on mechanical behaviour. Its manipulation may affect and improve mechanical properties. Use of advanced technologies opens wide range of possibilities in processing of polymer based systems. At present there is limited number of research of processing-structure-properties relationships of polymer-polymer composites and nanocomposites.

Silicon nitride ceramics - review of structure, processing and properties

It has been shown that pressureless sintering of SiC to theoretical density is possible with sintering additives from the system AlN–Y2O3. While commonly a combination of oxides is used such as Al2O3–Y2O3 (–SiO2), the oxynitride additives offer the advantage that only a nitrogen atmosphere is required instead of a powder bed for thermochemical stabilisation at the sintering temperature. The thermal decomposition of AlN is suppressed quite effectively when a moderate nitrogen overpressure is applied, resulting in very small mass loss during densification which only depends on the oxygen content of the SiC starting powder. By varying the mass ratio of β-SiC to α-SiC and applying dedicated post-densification heat treatments, a platelet-strengthened microstructure is obtained which shows enhanced fracture toughness. The platelet formation is attributed to a solution / precipitation process with simultaneous phase transformation from β-SiC to α-SiC, followed by anisotropic grain growth of α-SiC. In the present work, recent progress in the mechanical properties of these materials is reported. By means of a simple surface treatment-annealing in air — it is possible to obtain four-point bending strengths in excess of 1 GPa in liquid phase sintered SiC. The strength retention at temperatures around 1200°C is significantly improved.

High-temperature effects in the fracture mechanical behaviour of silicon carbide liquid-phase sintered with AlN–Y2O3 additives

Silicon nitride-based ceramics contain oxynitride glass phases at the grain boundaries which can impair subsequent high temperature properties. Studies of bulk glasses in the Y-Si-Al-O-N system have been carried out and it has been shown that up to 10 atomic % N can be incorporated into these oxynitride glasses. Nitrogen increases the viscosity, hardness and glass transition temperature of the glasses. Heat treatments of Y-Si-Al-O-N glasses have been carried out and the crystalline phases formed are reported. Further improvements are possible if glass-ceramic processes using two-stage heat treatments are introduced. This paper reviews the development of oxynitride glasses, the effects of nitrogen on properties and reports on the glassceramic heat treatments.

Yttrium oxynitride glasses: Properties and potential for crystallisation to glass-ceramics

Structural determination of sintered Si3N4/SiC nanocomposite using the XPS differential charge effect

The compressive creep behaviours of a silicon nitride ceramic densified with yttria and alumina and of the same material containing 10 wt% SiC nanoparticles are compared in the 1250–1450°C temperature range under stresses ranging from 45 to 180 MPa The stress exponents are ∼0·8 and 1 and the apparent activation energies are 514 and 590 kJ mol −1 for the monolith and the composite, respectively No signs of cavitation are observed For both materials grain boundary sliding accommodated by diffusion through the intergranular glass phase is considered as the primary steady-state creep mechanism The higher creep resistance of the composite is connected to the presence of intergranular SiC nanoparticles which limit grain boundary sliding and to the difference in chemical composition of the intergranular glass phase Les comportements au fluage d’une ceramique de type nitrure de silicium densifiee avec de l’yttrine et de l’alumine et du me me materiau contenant 10% en masse de nanoparticules de SiC sont compares dans le domaine de temperature 1250–1450°C sous des contraintes variant de 45 a 180 MPa Les exposants de contrainte valent respectivement ∼0·8 et 1 et les energies d’activation 514 et 590 kJ mol −1 pour le monolithe et le composite Aucun signe de cavitation n’a ete observe Le glissement le long des joints de grains, accommode par la diffusion a travers la phase vitreuse intergranulaire, est considere comme le principal mecanisme agissant pendant le stade de fluage stationnaire La resistance au fluage plus elevee du composite est reliee a la presence de nanoparticules de SiC en position intergranulaire, qui limitent le glissement le long des joints de grains, et a la difference de composition chimique des phases vitreuses intergranulaires

Si3N4/SiCN Nanocomposites: influence of SiC nanoprecipitates on the creep behaviour

The oxidation behaviour of oxynitride glasses in M-Si-Al-O-N system (M = Nd, Y) has been studied in air and under various oxygen pressures. The influence of glass composition on the oxidation resistance was studied at 1075 °C by varying Y Al or Si Al ratios and also by substituting Y by Nd and by varying the nitrogen content. The reactivities in air of the YSiAlON system is studied in the temperature range of 1000–1150 °C. The oxidation resistance of YSiAlON glasses is better than for glasses containing Nd. A pressure law is determined for the YSiAlON system based upon data from oxidation at 1050 and 1075 °C at oxygen pressures in the range of 15–100 kPa. The nature and morphology of oxidised samples were characterised by optical microscopy, XRD and SEM. These investigations reveal that the oxidation of the studied oxynitride glasses is governed by a reaction process where the progress of the internal interface is the limiting step.

Oxidation behaviour of yttrium and neodymium oxynitride glasses

The compressive creep behaviour of a Si 3 N 4 /SiC nanocomposite densified with yttria and alumina is studied in the 1150–1350°C temperature range under stresses from 45 to 180 MPa The stress exponent equals 1 and the apparent activation enthalpy is 580 kJ mol −1  Grain boundary sliding accommodated by diffusion through the intergranular glass phase is considered as the primary steady-state creep mechanism It is argued that the diffusion step through the glass phase is the rate limiting step in the dissolution–diffusion–reprecipitation process The results are compared with those obtained in previous studies for an α-Si 3 N 4 rich monolith and a Si 3 N 4 /SiC micro-nanocomposite The high creep deformation is explained by the nanometric size of the Si 3 N 4 grains and the absence of grain growth in the temperature range explored It is showed that a post-sintering heat-treatment consisting in 5 h at 1750°C followed by 3 h at 1400°C enhances the creep resistance to a fair level It is concluded that the high ductility of the as-sintered material is suitable for hot-forging whereas the subsequent heat-treatment is able to provide shaped parts with a high creep resistance for structural applications at high temperature

P. Goursat

Papers

Yttrium oxynitride glasses: Properties and potential for crystallisation to glass-ceramics

Structural determination of sintered Si3N4/SiC nanocomposite using the XPS differential charge effect

Si3N4/SiCN Nanocomposites: influence of SiC nanoprecipitates on the creep behaviour

Oxidation behaviour of yttrium and neodymium oxynitride glasses

SiCN nanocomposite: creep behaviour