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Crack measurement after thermal shock is usually considered as a replacement because real-time observation of thermal shock experiments is difficult to achieve. This paper presents an experimental approach for real-time displaying thermal shock cracking using oxygen-acetylene flame and high-speed imaging of translucent ceramic. We capture the crack propagation process, calculate the crack propagation speed, discuss the effect of sample size and flame heat flux on the crack propagation, and analyze the difference between the crack propagation under cold shock and hot shock. This paper further improves the mechanism of thermal shock damage of ceramic materials.

It is generally agreed that the nuclei of eukaryotic cells at interphase are partitioned into disjointed territories, with distinct regions occupied by certain chromosomes. However, the underlying mechanism for such territorialization is still under debate. Here we model chromosomes as coarse-grained block copolymers and to investigate the effect of loop domains (LDs) on the formation of compartments and territories based on dissipative particle dynamics. A critical length of LDs, which depends sensitively on the length of polymeric blocks, is obtained to minimize the degree of phase separation. This also applies to the two-polymer system: The critical length not only maximizes the degree of territorialization but also minimizes the degree of phase separation. Interestingly, by comparing with experimental data, we find the critical length for LDs and the corresponding length of blocks to be respectively very close to the mean length of topologically associating domains (TADs) and chromosomal segments with different densities of CpG islands for human chromosomes. The results indicate that topological constraints with optimal length can contribute to the formation of territories by weakening the degree of phase separation, which likely promotes the chromosomal flexibility in response to genetic regulations.

The influence of a prefabricated crack on thermal-shock cracking during quenching is studied in real-time. The results show that after the thermal-shock crack extends to the prefabricated crack, the secondary crack may appear at the lower end of the prefabricated crack. The total vertical length of the crack and the probability of the secondary crack occurrence will gradually increase with the prefabricated crack angle. Besides, the influence of the prefabricated crack distance from the edge on thermal-shock crack growth is also considered. The simulation results of meso-damage mechanics are consistent with experimental observation. This article quantitatively investigates the effect of the prefabricated crack on the thermal-shock crack propagation in ceramics, expanding the research on the mechanism of thermal-shock failure.

The cell-supported lipid bilayer (SLB) adhesion system has been widely used as the model system to study the receptor-ligand interactions that occur at the membrane interface. The ligand-functionalized SLBs are deposited either directly on solids or on polymer cushions. An important question that arises is whether the geometry of the SLB affects the binding of cell adhesion receptors to the ligands. By using a mesoscopic mechanical model and Monte Carlo simulations, we have investigated the adhesion of a fluid membrane to a corrugated or egg-carton shaped SLB. We find that the nanoscale geometry of the SLB strongly affects the receptor-ligand binding. This effect results from the fact that the adhering membrane bends according to the SLB geometry in order for the adhesion receptors to bind ligands. The membrane bending couples with spatial distribution of the receptor-ligand complexes and membrane thermal undulations. Our results demonstrate that cell adhesion to SLBs can be controlled by tuning the nanoscale geometry of the SLB, and may have profound implications for future development of tissue engineering and regenerative medicine.

This study aimed to determine the susceptibility and the changes of bacterial agents of chronic dacryocystitis and determine the risk factors for bacterial prevalence and drug sensitivity to provide a reference for clinical selection of antibiotics. A case–control study was conducted using 112 patients with chronic dacryocystitis and 112 patients with non-infectious ophthalmopathy between August 2017 and April 2018. Lacrimal and conjunctival sac secretions were cultured for aerobic and anaerobic bacteria. Forty-five patients with chronic dacryocystitis between November 2014 and November 2015 were also included. Positive bacterial cultures were obtained from 61.9% and 50.9% of chronic dacryocystitis and non-infectious ophthalmopathy patients, but the detection rates for pathogenic bacteria were 18.3% and 2.7%, respectively (P > 0.001). Gram-negative and anaerobic bacteria were significantly more prevalent in the patient group compared with the control group (P = 0.001 and 0.005, respectively). Bacteria were detected at a significantly higher rate in patients with irritant symptoms (itch or foreign-body sensation) than in those without (OR = 9.333, P = 0.002), particularly Staphylococcus (OR = 9.783, P = 0.002). 11.6% (10/86) and 55.8% (48/86) showed resistance to levofloxacin and tobramycin, respectively. Compared with three years ago, the detection rate for Gram-positive cocci decreased from 51.1% to 27.8% (χ2 = 8.054, P = 0.005) Gram-positive cocci, Gram-negative bacilli, and anaerobic bacteria were the predominant pathogens. The prevalence of Gram-positive bacteria in cases of chronic dacryocystitis is decreasing.

The cell-supported lipid bilayer (SLB) adhesion system has been widely used as the model system to study the receptor-ligand interactions that occur at the membrane interface. The ligand-functionalized SLBs are deposited either directly on solids or on polymer cushions. An important question that arises is whether the geometry of the SLB affects the binding of cell adhesion receptors to the ligands. By using a mesoscopic mechanical model and Monte Carlo simulations, we have investigated the adhesion of a fluid membrane to a corrugated or egg-carton shaped SLB. We find that the nanoscale geometry of the SLB strongly affects the receptor-ligand binding. This effect results from the fact that the adhering membrane bends according to the SLB geometry in order for the adhesion receptors to bind ligands. The membrane bending couples with spatial distribution of the receptor-ligand complexes and membrane thermal undulations. Our results demonstrate that cell adhesion to SLBs can be controlled by tuning the nanoscale geometry of the SLB, and may have profound implications for future development of tissue engineering and regenerative medicine.

Summary The Laplace pressure is one of the most fundamental regulators that determine cell shape and function, and thus has been receiving widespread attention. Here, we systemically investigate the effect of the Laplace pressure on the shape and function of the cells during cytokinesis. We find that the Laplace pressure during cytokinesis can directly control the distribution and size of cell blebbing and adjust the symmetry of cell division by virtue of changing the characteristics of cell blebbing. Further, we demonstrate that the Laplace pressure changes the structural uniformity of cell boundary to regulate the symmetry of cell division. Our findings provide further insights as to the important role of the Laplace pressure in regulating the symmetry of cell division during cytokinesis., Graphical abstract, Highlights • The Laplace pressure controls the distribution and size of cell blebbing • The Laplace pressure helps to develop a more uniform cell boundary • The Laplace pressure regulates symmetry of cell division by way of blebs, Cell; Functional aspects of cell biology; Biophysics

This work utilized a combination of experimental evidence and fractal geometric method to assess the effect of crack extension concerning the thermal shock on residual strength of ceramics. Sintered alumina (Al2O3) ceramic slabs were bundled and quenched in water under different thermal shock temperatures. The fractal dimension of thermal shock crack patterns on the interior surface and the cooled surface was calculated by the Box-counting method. Fracture energy of a fractal pattern of microcracks in quasi-brittle solids was employed to explain the relationship between crack length and fractal dimensions. The results show that if the crack propagation has the same crack length but a larger fractal dimension, it will absorb more fracture energy. The thermal shock crack patterns of Al2O3 ceramics with different grain sizes were analyzed, and the smaller grain size ceramic had a higher fractal dimension of crack patterns than the larger one.

This paper introduced a method of rapid solid-phase bonding Al block with Ag as the intermediate layer by longitudinal ultrasonic vibration under eutectic temperature in the atmospheric environment. This method is suitable for the application of structural lightweight design. It was observed that Al and Ag diffuse with each other in the weld seam to form an intermetallic compound Ag2Al with close hexagonal structure. The effects of different reaction temperatures and ultrasonic vibration times on the microstructure and mechanical properties of intermetallic compound Ag2Al were discussed. The influence of the effect of ultrasonic softening waves on surface oxide film rupture and element diffusion was explored. With the increase of ultrasonic vibration time, the intermetallic compounds grew along with the interface and the thickness increased. When the welding temperature was 500 °C and the ultrasonic vibration was 20 s, the highest average strength of the welded joint reaches 46.68 MPa.

Purpose To evaluate the biomechanical efficacy and safety of in vivo microbial transglutaminase (Tgases)-induced corneal crosslinking in a rabbit model. Methods A total of 34 white New Zealand rabbits were divided into two groups, a biochemistry group and a photochemistry group. The right eye of every rabbit was treated and left eyes served as negative controls. In the biochemistry group, a 1 U/mL solution of crosslinking agent microbial Tgases (Tgases CXL) was applied to the corneal surface, while in the photochemistry group, clinical ultraviolet A-riboflavin crosslinking (UVA/RF CXL) was used. Efficacy and safety evaluated on the 14th day after the procedures. Twelve pairs of corneal strips were harvested from the eyes of 12 euthanized rabbits in every group, and uniaxial tensile tests were performed to evaluate ex vivo biomechanical effects. The CXL-treated eye to its corresponding untreated eye ratio of tangent modulus were calculated. Another five pairs of corneal button were excised from euthanized animals in every group for corneal stroma and endothelium staining to evaluate changes in keratocyte distribution and endothelial cell damage. Results In tensile tests, tangent modulus was statistically higher in the Tgases CXL groups under 1.0 MPa (26.59 ± 4.54 vs. 21.47 ± 4.72 MPa, P = 0.04) and 1.5 MPa (29.75 ± 5.01 vs. 20.47 ± 6.63 MPa, P = 0.00). The tangent modulus ratio of Tgases group (1.72 ± 1.0 vs. 1.05 ± 0.22, P = 0.04) was significantly higher than that of UVA/RF under 1.5-MPa stress. The distribution of keratocytes in the corneal stroma and the morphologies of endothelial cells were similar in Tgases CXL-treated and untreated corneas. However, in the UVA/RF CXL group, keratocytes in the anterior half of stromal thickness were lost, and clear endothelial cell apoptosis was observed. Conclusions Tgases-CXL effectively stiffened the cornea and caused no damage to the endothelium and keratocytes in the cornea. This crosslinking method could be useful as a next-generation treatment for corneal ectasia and could replace CXL of photochemistry. Translational relevance These findings may give a new hope to biomechanically compromised corneal disease due to mechanical forces, such as corneal ectasia and keratoconus. A next-generation treatment to these corneal diseases due to mechanical forces may be designed based on the new findings.

The effects of water quenching temperature and specimen size on the propagation speed of thermal shock crack are investigated in real time by water quenching of translucent ceramic and high-speed imaging. The results show that the crack growth rate increases with the increase of quenching temperature difference or specimen size. Within 100 ms, average crack speed is 20.3 mm/s at a temperature difference of 400 °C in 20 mm wide ceramic and is 11.9 mm/s at a temperature difference of 220 °C in 5 mm wide ceramic, respectively. Compare with specimen size, the influence of quenching temperature difference on the crack propagation speed is larger. The calculations based on meso-damage mechanics have similar results to those of experiments. This paper quantitatively studies the thermal-shock crack growth of ceramic in real time and expands the scientific understanding of thermal shock cracking phenomenon of ceramic.

A novel formation mechanism according to the oxidative dehydrogenation of organics has been proposed for the low-temperature preparation of carbon-based nanomaterials. Several typical organics including ethanol, 1-butanol, p-cymene and liquid paraffin are used as precursors to react with ammonium persulfate (APS) in an autoclave, and carbon particles are obtained as a validation. The reaction characteristics are comprehensively investigated by the differential scanning calorimetric and thermogravimetric analysis. The strongly exothermic oxidation reaction below 200 °C is a common feature during the process. The organic molecules are cleaved into small carbon species and further transform to amorphous carbon. When the organometallic compound is used as a reactant instead, such as magnesocene and allyltriphenyltin, carbon encapsulated MgO and SnS nanocrystals with core-shell structure are synthesized, respectively. A detonation introduced by the violent reaction occurs in the process with a very rapid liberation of heat and large quantities of thermally expanding gases. The large amounts of free atomic/radical species and reactive intermediates are generated as sources for the core-shell structure. It is a common strategy for the large scale production of carbon encapsulated oxide/sulfide nanocrystals by means of the moderate detonation process of the organometallic compound and APS in an autoclave.

A simple and highly efficient method is developed for in situ one-step preparation of carbon co-encapsulated anatase and rutile TiO2 nanocrystals (TiO2@C) with core-shell structure for lithium-ion battery anode. The synthesis is depending on the solid-phase reaction of titanocene dichloride with ammonium persulfate in an autoclave at 200 °C for 30 min. The other three titanocene complexes including bis(cyclopentadienyl)dicarbonyl titanium, cyclopentadienyltitanium trichloride, and cyclopentadienyl(cycloheptatrienyl)titanium are used instead to comprehensively investigate the formation mechanism and to improve the microstructure of the product. The huge heat generated during the explosive reaction cleaves the cyclopentadiene ligands into small carbon fragments, which form carbon shell after oxidative dehydrogenation coating on the TiO2 nanocrystals, resulting in the formation of core-shell structure. The TiO2 nanocrystals prepared by titanocene dichloride have an equiaxed morphology with a small diameter of 10–55 nm and the median size is 30.3 nm. Hundreds of TiO2 nanocrystals are encapsulated together by the worm-like carbon shell, which is amorphous and about 20–30 nm in thickness. The content of TiO2 nanocrystals in the nanocomposite is about 31.1 wt.%. This TiO2@C anode shows stable cyclability and retains a good reversible capacity of 400 mAh g−1 after 100 cycles at a current density of about 100 mA g−1, owing to the enhanced conductivity and protection of carbon shell.

It is difficult to observe the thermal shock cracking in real time so the measurement of the crack after thermal shock is considered as an alternative method. This paper proposes a new experimental method which can exhibit the thermal shock cracking in real time by water quenching of translucent ceramic and high-speed imaging. The crack propagation is captured and the crack growth rate is calculated. The results confirm the previous theoretical predictions of crack propagation under thermal shock. This paper expands the research on understanding the failure mechanisms of ceramic materials in thermal shock.

The biomechanical characteristics of porcine corneal stroma along the depth of cornea in different anatomical orientations were experimentally investigated and quantitatively analyzed. The porcine corneal stroma tested here was cut mechanically into the three layers along the thickness of the cornea for the first time. Based on the convenient uniaxial tensile extensometry, the Young’s moduli of each stromal layer in different anatomical orientations were proved to be equal to each other. By virtue of testing the mechanical behaviors of the different layers, the Young’s moduli of the stromal layers were found to decrease gradually from the anterior to posterior corneal surface. Thus, the stroma was proved to be mechanically transversely isotropic. Furthermore, based on the analysis of the experimental data, the change of stromal Young’s modulus along the depth of the cornea was determined to be linear and equal to - 2.79 ± 0.967 MPa/mm from the anterior to posterior corneal surface. Finally, the li...

A self-propagating reaction between ferrocene and iron nitrate nonahydrate that is initiated at room temperature is discovered. Amorphous carbon-encapsulated Fe

We study the difference in the maximum stress on a cylinder surface σmax using the measured surface heat transfer coefficient hm instead of its average value ha during quenching. In the quenching temperatures of 200, 300, 400, 500, 600 and 800°C, the maximum surface stress σmmax calculated by hm is always smaller than σamax calculated by ha, except in the case of 800°C; while the time to reach σmax calculated by hm (fmmax) is always earlier than that by ha (famax). It is inconsistent with the traditional view that σmax increases with increasing Biot number and the time to reach σmax decreases with increasing Biot number. Other temperature-dependent properties also have a small effect on the trend of their mutual ratios with quenching temperatures. Such a difference between the two maximum surface stresses is caused by the dramatic variation of hm with temperature, which needs to be considered in engineering analysis.

Gaining insights into the fluctuation-induced entropic pressure between membranes that mediates cell adhesion and signal transduction is of great significance for understanding numerous physiological processes driven by intercellular communication. Although much effort has been directed toward investigating this entropic pressure, there still exists tremendous controversy regarding its quantitative nature, which is of primary interest in biophysics, since Freund challenged the Helfrich’s well-accepted results on the distance dependence. In this paper, we have investigated the entropic pressure between fluctuating membranes in multilayer systems under pressure and tension through theoretical analysis and Monte Carlo simulations. We find that the scaling relations associated with entropic pressure depend strongly on the magnitude of the external pressures in both bending rigidityand surface tension-dominated regimes. In particular, both theoretical and computational results consistently demonstrate that, in agreement with Helfrich, the entropic pressure p decays with inter-membrane separations c as p~c–3 for the tensionless multilayer systems confined by small external pressures. However, our results suggest that the entropic pressure law follows to be p~c–1 and p~c–3, respectively, in the limit of large and small thermal wavelengths for bending fluctuations of the membranes in a tension-independent manner for the case of large external pressures.

The formation of gas bubbles presents a frequent challenge to microfluidic operations, for which fluids are geometrically confined to a microscale space. Here, to understand the mechanism of nucleating gas bubbles in microfluidic devices, we investigate the formation and stability of nanobubbles in confined solutions. Our molecular dynamics simulations show that while pinning of the contact line is a prerequisite for the stability of surface nanobubbles in open systems that can exchange gas with surrounding environment, in confined solutions, stable nanobubbles can exist even without pinning. In supersaturated condition, stable bubbles can be found in confined solutions with acute or obtuse contact angle, depending on the substrate hydrophobicity. We also demonstrate that when open to the bulk solution, the stable nanobubbles in closed systems would become unstable unless both supersaturation and pinning of the contact line are satisfied. Our results not only shed light on the design of novel heterogeneous surfaces for generating nanobubbles in confined space with controllable shape and stability but also address the crucial effect of gas exchange with the surroundings in determining the stability of nanobubbles.

The present work examines the size effect of thermal shock crack patterns in ceramics and develops quantitative predictions. A set of water-quenching experiments on thin ceramic specimens of different widths yielded two-dimensional, periodic and hierarchical readings of thermal shock crack patterns, which showed the strong size-dependence of the crack length and length hierarchy, and the size-independence of the crack spacing. Furthermore, the effective convective heat transfer coefficients inversely estimated from the crack spacing data were observed to be size-independent. Such a finding may help engineers to assess the thermal shock failure of practical ceramic components by designing specimens of standard size. Numerical simulations were conducted and the results are in good agreement with experimental data. Several interesting phenomena of the evolution of thermal shock crack patterns were revealed and discussed. The present study has led to a much improved scientific understanding of thermal shock cracking phenomenon of ceramics. (C) 2014 Elsevier Ltd. All rights reserved.

Gaining insights into the binding of membrane-anchored receptors and ligands that mediate cell adhesion and signal transduction is of great significance for understanding numerous physiological processes driven by intercellular communication. Lipid rafts, microdomains in cell membranes enriched in cholesterol and saturated lipids such as sphingomyelin, are believed to serve as the essential platforms to recruit protein molecules for biological functions. An important question remains how the lipid rafts affect the binding constant of membrane-anchored receptors and ligands. We have investigated the adhesion of multicomponent membranes by using Monte Carlo simulations of a mesoscopic model with biologically relevant parameters. We find that the preferential partitioning of membrane-anchored receptor and ligand proteins in the lipid rafts significantly increases the binding constant of those proteins, in cooperation with the shape fluctuations of the membranes caused by thermal excitations. The binding constant can even be greater than that of the same receptors and ligands anchored to two apposing supported, planar membranes without shape fluctuations. The membrane shape fluctuations facilitate the binding of the anchored receptors and ligands, in contrast to the case of homogeneous membranes. Our results suggest that cells might regulate the binding of membrane-anchored receptor and ligand proteins by modulating the properties of lipid rafts such as area fraction, size and the affinity of rafts to the proteins.

We analytically present the characteristic dimensional limit below which the thermal shock failure of ceramics never occurs. This limit, together with the critical temperature difference, separates the state space of the ceramics under thermal shock into two parts - the cracked and the uncracked. Based on the water-quench tests of ceramics, we experimentally proved that when the states of ceramics are in the uncracked region, the ceramics do not produce any cracks during thermal shock. The results provide a guide to prevent thermal shock failure in ceramic.

A simple and highly efficient method is developed for the one-step in situ preparation of carbon-encapsulated MoO2 nanocrystals (MoO2@C) with core-shell structure for high-performance lithium-ion battery anode. The synthesis is depending on the solid-state reaction of cyclopentadienylmolybdenum tricarbonyl dimer with ammonium persulfate in an autoclave at 200 °C for 30 min. The large amount of heat generated during the explosive reaction cleaves the cyclopentadiene ligands into small carbon fragments, which form carbon shell after oxidative dehydrogenation coating on the MoO2 nanocrystals, resulting in the formation of core-shell structure. The MoO2 nanocrystals have an equiaxial morphology with an ultrafine diameter of 2–8 nm, and the median size is 4.9 nm. Hundreds of MoO2 nanocrystals are encapsulated together by the worm-like carbon shell, which is amorphous and about 3–5 nm in thickness. The content of MoO2 nanocrystals in the nanocomposite is about 69.3 wt.%. The MoO2@C anode shows stable cyclability and retains a high reversible capacity of 443 mAh g−1 after 50 cycles at a current density of 3 A g−1, owing to the effective protection of carbon shell.

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.

An explosive reaction between zinc nitrate hexahydrate and ferrocene taking place below 200∘C is discovered, which is employed for the one-step preparation of carbon-encapsulated ZnFe2O4 nanocrystals (ZnFe2O4@C) with core–shell structure in an autoclave. The small-sized equiaxed ZnFe2O4 nanocrystals have a median diameter of 22.1[Formula: see text]nm. The uniform carbon shell of about 5[Formula: see text]nm in thickness is amorphous, and its content is 32.6[Formula: see text]wt.% in the nanocomposite. After 50 cycles, the ZnFe2O4@C anode still maintains a high specific capacity of 551[Formula: see text]mAh[Formula: see text]g[Formula: see text] at a current density of 50[Formula: see text]mA[Formula: see text]g[Formula: see text]. The efficient, energy-saving and environment-friendly method will be very attractive for preparing different kinds of carbon-encapsulated nanocrystals.

By gel casting with polymethylmethacrylate microbeads (PMMA) as pore-forming agent, porous boron nitride/silicon nitride (BN/Si3N4) composite ceramics were successfully prepared. The obtained ceramic shows bimodal hierarchical structures that composed of spherical-shaped micro pores depending on PMMA content and irregular sub-micro pores formed by the stacking of ceramic particles. Porosity of the porous BN/Si3N4 ceramics can be well controlled from 53.0 to 60.6 % by the PMMA content from 10 to 40 wt%, as well as the mechanical and dielectric properties. Effect of PMMA content on phase composition and the relationship between microstructure and the basic properties of the porous BN/Si3N4 ceramics was discussed in detail. Microstructure analysis reveals that the sub-micro pores acted as channels between micro pores. BN particles have a relatively denser distribution on the wall of spherical-shaped micro pores with a window between micro and sub-micro pores, and resulting in a half-closed micro pore structure, which is meaningful for material design with concentration of BN particles on the wall of pore structure.

The effect of porosity on the crack characteristics of ceramics after water-quenching is studied by measuring the cracks in ceramic sheets. The result reveals that the pore volume fraction has a slight effect on the enhancement of thermal shock resistance of ceramics when the porosity ranges from 0 to 20 %, because the length and density of the long crack in porous alumina are always slightly less than that in dense alumina. This result is in agreement with the prediction based on the minimum potential energy principle using experimentally measured data. Moreover, the proportion of the strength reduction in the third regime decreases significantly with increasing porosity, because the strength of unquenched specimens decreases more rapidly than that of quenched specimens with increasing porosity. The results of this study may help to further understand the thermal shock behavior of ceramics.

In this paper, we determined the surface heat transfer coefficient of Al2O3 ceramics quenched from different initial temperatures into a water bath at room temperature. By using the multipoint temperature measurement technique and the inverse heat conduction method, this coefficient was measured as function of surface temperature of the ceramics during the water quench. The obtained results indicate that the surface heat transfer coefficient largely depends not only on the initial quenching temperature and their evolution in quenching media but also on the sizes of tested specimens. In addition, brief discussion was completed on the rationality of the traditionally used approach, which considers the surface heat transfer coefficient as a joint constant of materials and quenching media, in previous studies on heat transfer and thermal stresses.

Heat treatment was carried out between 800 and 1200°C to investigate its effects on the microstructure and electrochemical properties of the hollow carbon spheres (HCSs) prepared in high-pressure argon. Samples were characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy and N2 adsorption-desorption isotherms. The graphitization of the HCSs was improved with increase of heat treatment temperature. Mesopores of ca. 4 nm in diameter were created on the HCSs after the heat treatment. The results of electrochemical performance measurements for the HCSs as anode material for lithium ion batteries indicate that the discharge capacity of the HCSs is improved after heat treatment at 800°C compared with the as-prepared HCSs and have a maximum value of 357 mAh/g and still retains 303 mAh/g after 40 cycles. However, the discharge capacity of the HCSs decreases and the cycling performance is improved with the increase of heat treatment temperature.

Porous silicon nitride/silicon oxynitride composite ceramics were fabricated by silica sol infiltration of aqueous gelcasting prefabricated Si3N4 green compact. Silica was introduced by infiltration to increase the green density of specimens, so suitable properties with low shrinkage of ceramics were achieved during sintering at low temperature. Si2N2O was formed through reaction between Si3N4 and silica sol at a temperature above 1550 degrees C. Si3N4/Si2N2O composite ceramics with a low linear shrinkage of 1.3-5.7%, a superior strength of 95-180 MPa and a moderate dielectric constant of 4.0-5.0 (at 21-39 GHz) were obtained by varying infiltration cycle and sintering temperature. (C) 2010 Published by Elsevier B.V.

A highly efficient and convenient strategy is developed for the one-step in-situ synthesis of carbon encapsulated Cr2O3 nanocrystals with core-shell structure (Cr2O3@C). The explosive reaction of chromocene with ammonium persulfate in an autoclave at 200[Formula: see text]C is crucial for the formation of this nanostructure. The Cr2O3 nanocrystals have a diameter of 5 to 20[Formula: see text]nm, which are entirely encapsulated by the amorphous carbon shell. The Cr2O3@C anode can retain a stable reversible capacity of 397[Formula: see text]mAh[Formula: see text]g[Formula: see text] after 50 cycles at a current density of 119[Formula: see text]mA g[Formula: see text].

A new method for fabricating porous silicon nitride ceramics has been developed by using fly ash cenosphere (FAC) with mean diameter of 87 μm as a pore-forming agent. Sintering was carried out at 1780 °C for 2 h under a nitrogen atmosphere. FAC can also act as a sintering aid besides a pore-forming agent. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies showed that YSiO2N forms instead of Y2Si3O3N4 when FAC is incorporated. Microstructural analysis revealed that large spherical cavities are scattered in a relative dense matrix. Porous Si3N4 ceramics with density of 2.17–2.30 g/cm3, Young’s modulus of 141–150 GPa and strength of 180–320 MPa were obtained by changing the FAC content.

Effects of gas pressure and temperature on the synthesis and formation mechanism of hollow carbon spheres (HCSs) prepared in argon atmosphere using ferrocene and ammonium chloride as reactants are investigated. The reactions occurred in the process as well as the formation mechanism of the HCSs is also studied. Samples are characterized by X-ray diffraction, field-emission scanning electron microscopy, differential thermal analysis, differential scanning calorimetry analysis and thermogravimetric analysis. It is found that the quasi-static atmosphere is crucial for the formation of the HCSs. The yield of HCSs can be enhanced by increasing the initial argon pressure and reaches a maximum value at 2 MPa. When the initial argon pressure is 2 MPa, HCSs can be fabricated at 450 °C and yield of the HCSs is increased with temperature up to 600 °C. However, the diameters of the HCSs are several micrometers and independent on the argon pressure and temperature in the given ranges. Several iron compounds, including Fe(NH3)2Cl2, Fe(NH3)6Cl2, (NH4)FeCl5, NH4FeCl3 and FeCl2, are formed in different temperature ranges. The spherical Fe(NH3)2Cl2 droplets formed in the process is thought to serve as the core templates for the formation of the HCSs.

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.

Silicon nitride/silicon oxynitride (Si3N4/Si2N2O) ceramic foams with tailored microstructures were prepared by a gelcasting process using fly ash cenosphere (FAC) as a pore-forming agent. The slurry has a suitable viscosity so that the floating velocity of FAC in the slurry is slow enough to avoid delamination between the FAC and the matrix during consolidation. Experimental observation showed that a uniform distribution of FAC was achieved in the matrix. Sintering was carried out at 1500°, 1600°, and 1700°C, respectively, for 1 h under a nitrogen atmosphere. X-ray diffractometry analysis indicated that Si2N2O was formed via the reaction between FAC and Si3N4. Microstructural analysis revealed that spherical-shaped pores obtained from FAC were uniformly dispersed in the composite. Si3N4/Si2N2O composite ceramic foams with apparent porosities of 62.0%–67.4% and a bending strength of 21–39 MPa were obtained eventually.

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.

Hollow carbon spheres encapsulating magnetite nanocrystals were obtained in high-pressure argon at 600 °C followed by hydrolysis of Fe(NH3)2Cl2 in the hollow interiors at room temperature and heat treatment in argon at 450 °C for 2 h. The structure, morphology, and properties of the products were characterized by x-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and vibrating sample magnetometry. The hollow carbon spheres have diameters of 1–10 μm and wall thicknesses of hundreds of nanometers; the wt% of magnetite nanocrystals in them is ∼13.2%. Equiaxed magnetite nanocrystals range in size from 15 to 90 nm, while acicular magnetite nanocrystals have diameters of ∼20 nm and lengths of 120–450 nm. The saturation magnetization value of the hollow carbon spheres encapsulating magnetite nanocrystals is 4.29 emu/g.