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The physical mechanisms between residual strength and crack characteristic of ceramics after water-quenching are studied by statistically measuring the cracks in ceramic sheet. The result herein reveals that in the joint action of long crack length and density, the residual strength is maintained at the same level within a temperature range above the critical thermal shock temperature difference (Δ TC). The result presented herein forms a further comprehension to the ceramics behaviors of and the theoretical approaches to thermal shock. [ABSTRACT FROM AUTHOR]

The crack patterns generated in a real ceramic plate and in a plate stacked by ceramic slabs under quenching are experimentally studied. The results here reveal that there are some distinct differences between the two crack patterns. The reasons that caused the differences are the size and boundary effects of the slabs. These crack patterns are very useful to understand the failure mechanisms of ceramic materials in thermal shock. [ABSTRACT FROM AUTHOR]

Various carbon encapsulated nanocrystals, including MnS and MnO, Cr2O3, MoO2, Fe7S8 and Fe3O4, and ZrO2, are prepared in one step and in situ by a simple and highly efficient synthesis approach. The nanocrystals have an equiaxed morphology and a median size smaller than 30 nm. Tens and hundreds of these nanocrystals are entirely encapsulated by a wormlike amorphous carbon shell. The formation of a core–shell structure depends on the strongly exothermic reaction of metal π-complexes with ammonium persulfate in an autoclave at below 200 °C. During the oxidation process, the generated significant amounts of heat will destroy the molecular structure of the metal π-complex and cleave the ligands into small carbon fragments, which further transform into an amorphous carbon shell. The central metal atoms are oxidized to metal oxide/sulfide nanocrystals. The formation of a core–shell structure is independent of the numbers of ligands and carbon atoms as well as the metal types, implying that any metal π-complex can serve as a precursor and that various carbon encapsulated nanocrystals can be synthesized by this method. [ABSTRACT FROM AUTHOR]

Objectives: Knowledge of the mechanical behaviour of root dentine can facilitate better understanding of spontaneous vertical root fracture (VRF), an age-related disease initiated mainly at the root apex. We tested the hypothesis that the biomechanical properties of root dentine change with ageing. Methods: Sixteen human premolars were divided into ''old'' (17-30 years) and ''young'' (50- 80 years) groups. The elastic modulus, nano-hardness, micro-hardness, elemental contents, tubular density/area of root dentine in cervical, middle and apical root regions were evaluated using atomic force microscopy-based nano-indentation, Knoop indentation, scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. Results: The apical dentine showed a lower nano-hardness, a lower elastic modulus, a lower calcium content, a lower calcium-to-phosphorus ratio and a smaller tubular density/area than the cervical dentine in both age groups, whereas spatial differences in micro-hardness were observed only in old roots. Compared with young dentine, old dentine showed a greater hardness, a higher elastic modulus, a greater mineral content and a smaller tubular size in the cervical portion, whereas the age-induced changes in tubular density were insignificant. Finite element analysis revealed that due to its higher elastic modulus, old apical dentine has a higher stress level than young dentine. Conclusions: The intrinsic material properties of root dentine have spatial variations, and they are altered by ageing. The higher stress level in old apical dentine may be one reason, if not the most important one, why spontaneous VRFs are more likely to occur in the elderly population. [ABSTRACT FROM AUTHOR]

Abstract  Hollow carbon microspheres (HCMs) are prepared in a sealed quartz tube via the reaction between ferrocene and ammonium bromide. The morphology and microstructure of the product are characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, focused ion beam workstation, transmission electron microscopy, and differential scanning calorimetry analysis. The diameter of the HCMs ranges from 1 to 13 μm and the thickness of shells ranges from 70 nm to 450 nm. It is concluded that the self-generated spherical droplets of iron amine bromide serve as the core templates for the formation of HCMs. [ABSTRACT FROM AUTHOR]

Hollow and solid carbon spheres were prepared by the reaction of ferrocene and ammonium carbonate in a sealed quartz tube at 500°C. The morphology and microstructure of the product were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The carbon spheres are amorphous and their diameters range from 0·8-2·8 μm. The shell thickness of the hollow carbon spheres is not uniform and ranges from 100-180 nm. It is suggested that ammonium carbonate is crucial for the formation of carbon spheres and its amount also influences the morphology of the product. The method may be suitable for large scale preparation of carbon spheres. [ABSTRACT FROM AUTHOR]

A self-propagating reaction between ferrocene and iron nitrate nonahydrate that is initiated at room temperature is discovered. Amorphous carbon-encapsulated Fe3O4 nanocrystals (Fe3O4@C) can be one-step prepared in an autoclave through this reaction. The equiaxed Fe3O4 nanocrystals have typical dimensions in the range of 5–60 nm with a median size of 24.1 nm, and their weight percent is up to 82.3%. The course of the reaction is recorded, and the formation mechanism of Fe3O4@C with the core–shell structure is proposed. The scaling-up synthesis is also achieved, and 52.1 g of the Fe3O4@C can be obtained in a single batch. The shock wave appeared in the fast gas release self-propagating reaction in confined space plays a decisive role in the preparation of homogeneous Fe3O4@C with a core–shell structure. The Fe3O4@C anode shows excellent capacity retention with a high specific capacity of 494 mAh g−1 at 1 A g−1 in the 200th cycle. [ABSTRACT FROM AUTHOR]