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The densification behaviors of pure B4C and B4C-ZrO2 mixtures were compared during hot pressing. The results showed that in-situ formed ZrB2 effectively enhanced the densification process of B4C-ZrO2 mixtures, more significantly during the intermediate stage. Within the relative density ranging from 0.75 to 0.90, the B4C-15 wt%ZrO2 mixture (B15Z) achieved the maximum densification rate as twice much as that of pure B4C. The stress exponent n>3 indicated plastic deformation was the dominant densification mechanism of B15Z. The viscosities of plastic flow were evaluated using Murray-Rodger-William equation and the viscosity of B15Z was only a quarter of that in pure B4C. The sintering activation energy was calculated to be 305.9 kJ/mol for pure B4C and 197 kJ/mol for B15Z, respectively. It was proposed that the lower viscosity of plastic flow and activation energy accelerated the sliding and propagating motions of plastic flow, by which underlain the enhanced densification behaviors of B4C-ZrO2 mixtures.

Dense ultrafine-grained B4C ceramics with superhigh hardness and outstanding fracture toughness were fabricated via spark plasma sintering at 1700 °C and 80 MPa. This process used the ultrafine B4C powder prepared by high-energy ball milling as starting powder. During sintering, densification began earlier at 1050 °C and the maximum densification rate appeared earlier at 1500 °C under the influence of high pressure and high sintering activity of the powder. The B4C ceramics possessed ultrafine grains, with average grain size of 370 nm, which contributed to the superhigh hardness. Many small B4C grains with size of less than 200 nm were individually dispersed among large B4C grains or accumulated to form congregated areas. The small grains induced crack deflection, particle pullout and crack bridging, thereby enhancing the toughness of the ceramics. The relative density, Vickers hardness and fracture toughness of the B4C ceramics reached 99.4 ± 0.49%, 41.1 ± 0.9 GPa and 4.57 ± 0.12 MPa m1/2, respectively.

Dense ZrB2-SiC-ZrC composites with four different compositions were prepared using ZrC, B4C and Si powders as the starting materials by reactive spark plasma sintering (R-SPS). The evolutions in the phases and microstructures were investigated using XRD, Raman spectrum and SEM. It was found that the formation of ZrB2 and SiC involved two steps. Lower initial content of ZrC results in microstructural refinement and mechanical enhancement. The composite ZrB2− 47.9SiC-4.7ZrC prepared by 5 min sintering at 1800 °C under 30 MPa pressure exhibited the most satisfying combination of properties. The flexural strength, fracture toughness and Vickers hardness were 760 ± 19 MPa, 6.3 ± 0.3 MPa∙m1/2 and 22.7 ± 1.4 GPa, respectively.

Zirconium carbide (ZrC 0.84 O 0.13 ) nanopowders were consolidated using plasma activated sintering with 0–8 wt% ZrH 2 as the sintering additive to improve the sinterability. Compared with pure ZrC sintering, ZrH 2 additive led to the higher sintering kinetics and lower sintering temperature. This improvement was attributed to the increased carbon-vacancy concentration in the non-stoichiometric ZrC in the presence of ZrH 2 additive during the sintering process. Fully dense and fine-grained ZrC ceramics (1.3 ± 0.2 μm) were achieved at 1650 °C with 6 wt.% ZrH 2 . The final product exhibited the Vicker’s hardness of 21.2 ± 1.0 GPa and fracture toughness of 2.2 ± 0.3 MPa m 1/2 .

A commercial 3Y-TZP nanopowder was consolidated by spark plasma sintering (SPS) techniques. By special die-upset designs, each possible influence from the electric field, uniaxial pressure and heating rate was peeled to identify its contribution. Besides density and grain growth, the evolution of pore structure was consulted to clarify the relationships between microstructural development and densification kinetics. The results showed that neither electric current nor fast heating had no decisive contributions while external force was a necessity for the microstructural refinement. The authors proposed that the essentially underlying mechanism was the intensive particle rearrangement, which involves no grain growth but particle close-packing through grain rotation and sliding. The full advantages of this mechanism can be taken in rapid heating conditions, which combined with the application of higher pressures, make the SPS family of techniques to have advancement in the preparations of nanoceramics over their conventional counterparts characterized by slow heating features.

Confinement is common in biological systems and plays a critical role in the structure-forming process of biominerals. However, the knowledge of confinement effects on biomineralization is limited due to the lack of specific chemical structures and elaborate spatial distribution. In this article, we explore the confined mineralization of amorphous calcium carbonate (ACC) within collagen fibrils. Three issues of the confined mineralization of ACC within collagen fibrils were investigated, including the morphology and characteristics of the confined mineralization of ACC within collagen fibrils; the initiation and development of the confined mineralization of ACC within collagen fibrils; and the driving mechanism of ACC infiltration into collagen fibrils. Results show that the negatively charged ACC droplets were attracted to positively charged gap regions of collagen fibrils through electrostatic interactions, infiltrated into collagen fibrils, and then transformed into the crystalline phase. The observation of juxtaposed crystalline and amorphous phases on the surface of fibrils indicates that a secondary nucleation mechanism may be responsible for the co-orientation of calcite nanocrystals. Through modifying the wettability of amorphous calcium carbonate with magnesium ions, it is verified that the infiltration of ACC into collagen fibrils was driven by capillary forces. The present study not only provides evidence of the confinement effects in biomineralization but also facilitates the understanding of the in vivo bone formation process. It may also open up a new avenue in the bioprocess-inspired synthesis of advanced materials.

Al2O3/Y3Al5O12(YAG) eutectic ceramics are considered to be candidate materials for use in high temperature and oxidizing environments owing to their remarkable thermodynamic stabilities. Many techniques have been used to prepare eutectic ceramics, including the Bridgeman, edge-defined film-fed growth, micro-pulling-down, floating zone, and laser zone re-melting methods. However, these methods use complex high temperature equipment. In this work, simple equipment was used to achieve combustion reaction heating with the advantages of a high heating rate (2000℃/min), high temperature, and high cooling rate. Using this set-up we could melt and fabricate eutectic ceramics. The microstructure and physical properties of the obtained Al2O3/YAG eutectic ceramics were studied. The eutectic ceramics consisted of Al2O3 and YAG phases. The two phases exhibited coupled growth with well-matched and clean phase boundaries. Several special morphologies were obtained besides the typical Chinese script microstructure, and their formation mechanisms are discussed. The Vickers hardness of the eutectic ceramics was 20.52 GPa, which is higher than that previously reported for any binary eutectic ceramic system. The fracture toughness was 2.64 MPa m1/2, which is slightly higher than about 2 MPa m1/2 previously reported. The crack propagated in a straight line from the indentation corner and did not deflect at the interface between the Al2O3 and YAG domains, compared with the intergranular fracture in the hot-pressed sample. This weak interaction of the crack path with the microstructure was induced by the absence of residual stress and the excellent bonding between the eutectic phases. Samples treated at 1500℃ for 20 h exhibited no weight loss or obvious change in microstructure, indicating the high temperature stability of these eutectic ceramics.

Genetically engineered living organisms direct the synthesis of nanostructured anatase with nanoparticle, mesoporous structure and carbon coating characteristics which shows excellent lithium storage performance., Biomineral formation processes in nature are temporally and spatially regulated under the functions of biomolecules in a confined space. It is potentially very productive to rationally design a mineralized system by taking into account confined space as well as biomolecules. The laboratory technique of “bacterial cell surface display” is an ideal platform to host catalytically active proteins in a three-dimensionally confined space. In the present study, aiming to regulate the synthesis of nanostructured TiO2 anatase, repeating segments of silaffin were displayed on Escherichia coli surfaces through genetic manipulation. The displayed protein electrostatically interacted with a titanium source and catalyzed the hydrolysis of titanium dioxide precursors through hydrogen bonding interactions on the cell surface. In the subsequent calcination process, the genetically modified cells not only served as a framework for producing rod-shaped TiO2 assembled by nanoparticles, but also provided a carbon source in situ. The size of nanoparticles was controlled by changing the number of tandem repeats of the protein segment. The as prepared TiO2 anatase exhibited unique characteristics including nanosized anatase crystals, mesoporous structure and carbon coating. When tested as the anode electrode of a lithium-ion battery, it showed excellent lithium storage performance. The carbon coated anatase anode shows a higher specific capacity of 207 mA h g–1 after 200 cycles at a current rate of 1C and an ultra-long cycling lifetime of 5000 cycles with an outstanding retention capacity of 149 mA h g–1 at a higher rate of 10C. This bioprocess-inspired approach may help broaden the scope and impact of nanosized biominerals.