Characterization of anisotropic gas permeability and thermomechanical properties of highly textured porous alumina

Porous alumina with a highly textured microstructure was fabricated by pulse electric current sintering (PECS) using alumina platelets. Highly oriented porous alumina with a porosity of 3%–50% was obtained by a pressure-controlled method of PECS. The properties of the highly textured porous alumina were measured in two directions. The nitrogen gas permeance and thermal conductivity at room temperature were higher in the direction along the platelet length due to the higher continuity of pores and the connectivity of alumina platelets, respectively. The anisotropy of the thermal conductivity at room temperature was investigated and explained by the effect of grain size of platelets as well as morphology and orientation of pores. The bending strength was higher with the loading direction along the platelet thickness. The thermal shock strength was clearly different in the two directions. The difference in the thermal shock strength was investigated by the measurement of properties and thermal stress analysis.     

Application of Cr3C2/C composite powders synthesized via molten-salt method in low-carbon MgO–C refractories

High-performance and low-carbon MgO–C refractories are important refractories for smelting ultra-low carbon steel and clean steel. Based on this, Cr₃C₂/C composite powders were synthesized by the molten-salt method, and used as an additive to prepare low-carbon MgO–C refractories under nitrogen atmosphere. The phase, morphology and oxidation kinetics of Cr₃C₂/C composite powders were studied. In addition, the effect of Cr₃C₂/C composite powders on the morphology, mechanical properties, thermal shock resistance, and corrosion resistance of MgO–C refractories was investigated. The results indicated that the Cr₃C₂/C composite powders exhibited superior oxidation resistance than flake graphite. Moreover, the Cr₃C₂/C composite powders were introduced into the MgO–C refractories. Compared with the sample without Cr₃C₂/C composite powders, the introduction of 1 wt% Cr₃C₂/C composite powders significantly improved the thermomechanical properties and corrosion resistance of the material, its CMOR, CCS before and CCS after thermal shock were 9.06 MPa, 50.40 MPa and 32.60 MPa, respectively, and the corrosion index was significantly reduced from 44.6% to 26.5%.     

A comparative study on the effect of carbon-based and ceramic additives on the properties of fiber reinforced polymer matrix composites for high temperature applications

Ablative composites have been in use for thermal protection of space vehicles for decades. Carbon-phenolic composites have proven to perform exceptionally well in these applications. However with development in aerospace industry their performance needs improvement. In this field, different carbon-based and ceramic additives have been introduced into ablative composite systems. This review article gives a comparative analysis of researches done in this field in the recent past. Density, ablative, thermal and mechanical properties of ablative composites with different ultra-high temperature ceramic particles i.e. ZrSi₂, Cenosphere, nano-SiO₂, BN etc. and carbon-based nanoparticles i.e. CNTs, nano-Diamonds, Graphene oxide etc. used as additives, have been compared and discussed. Emphasis is put on carbon-phenolic composite systems although some epoxy matrix systems have also been discussed for comparison.     

Deformation-induced bonding of polymer films below the glass transition temperature

Bonding between polymers through interdiffusion of macromolecules is a well-known mechanism of polymer adhesion. A new polymer bonding mechanism in the solid state, taking place at ambient temperatures well below the glass transition value (T_g), has been recently reported; in this mechanism, bulk plastic compression of polymer films held in contact led to adhesion over timescales of the order of a fraction of a second. In this study, we prepared various blends of plasticized polymer films with desirable ductility from amorphous and semicrystalline powders of hydroxypropyl methylcellulose and polyvinyl alcohol derivatives; then, we observed the bonding of these polymers at ambient temperatures, up to 80 K below T_g, purely through mechanical deformation. The deformation-induced bonding of the polymer films studied in this work led to interfacial fracture toughnesses in the range of 1.0–21.0 J/m² when bulk plastic strains between 3% and 30% were imposed across the films. Scanning electron microscopy observation of the debonded interfaces also confirmed that bonding was caused by deformation-induced macromolecular mobilization and interpenetration. These results expand the range of applicability of sub-T_g, solid-state, deformation-induced bonding processes.     

Stabilization of 6H-Hexagonal SrMnO3 Polymorph by Al2O3 insertion

We demonstrate the structural evolution of polymorphic phases in Al₂O₃-inserted SrMnO₃ ceramics synthesized by solid state reaction. While the 4H-hexagonal phase is predominant in pure SrMnO₃ ceramics, a small amount of 6H-hexagonal polymorph is identified in addition to the primary 4H-hexagonal SrMnO₃ and the secondary hexagonal SrAl₂O₄ phases in the as-sintered ceramics, evidenced by x-ray diffraction and subsequent Rietveld refinement analyses. The existence of the 6H-hexagonal SrMnO₃ phase is corroborated using Raman spectroscopy. The chemical compositions and electronic structures of the Al₂O₃-inserted SrMnO₃ compounds are also examined using energy dispersive spectroscopy and x-ray photoelectron spectroscopy, respectively. The first-principles calculations reveal that there is no clear difference between the total energies of 4H- and 6H-hexagonal polymorphs regardless of the presence/absence of Sr and oxygen vacancies. Possible origins are discussed with the estimation of actual strain based on the refined lattice parameter of 6H SrMnO₃.     

From enfant terrible to problem-solver? Tracing the competing discourse to explain blockchain-related technological diffusion

Since the inception of blockchain-related technologies over a decade ago, investors’ uptake of the technologies has grown rapidly. But even with the advancement in standing from conceptual beginnings to real-world experimentation, mainstream adoption of the technologies in either organizational or individual contexts has yet to eventuate. To resolve this paradox, we examine progression of the technologies’ diffusion instead, and in the process, seek to uncover the underlying dynamics of sentiments at play. Diffusion involves multiple actions by different parties, with social discourses via diverse media playing an essential role. In demonstrating the interplay of support to resistance via media framing and the diffusion of innovation theory, findings from our paper contribute to the technology adoption literature. Understanding resistant behavior toward a new technology area could help resolve potential issues that may arise. This would hopefully lead to better technological implementation outcomes in future.     

Cyclic thermal shock resistance of h-BN composite ceramics with La2O3–Al2O3–SiO2 addition

The effects of La₂O₃–Al₂O₃–SiO₂ addition on the thermal conductivity, coefficient of thermal expansion (CTE), Young's modulus and cyclic thermal shock resistance of hot-pressed h-BN composite ceramics were investigated. The samples were heated to 1000 °C and then quenched to room temperature with 1–50 cycles, and the residual flexural strength was used to evaluate cyclic thermal shock resistance. h-BN composite ceramics containing 10 vol% La₂O₃–Al₂O₃ and 20 vol% SiO₂ addition exhibited the highest flexural strength, thermal conductivity and relatively low CTE, which were beneficial to the excellent thermal shock resistance. In addition, the viscous amorphous phase of ternary La₂O₃–Al₂O₃–SiO₂ system could accommodate and relax thermal stress contributing to the high thermal shock resistance. Therefore, the residual flexural strength still maintained the value of 234.3 MPa (86.9% of initial strength) after 50 cycles of thermal shock.     

One-step preparation of the superhydrophobic Al alloy surface with enhanced corrosion and wear resistance

Corrosion and wear failures are bottlenecks for restricting applications and developments of Al-based functional materials. As a new lubrication technology, superhydrophobic preparation provides an effective way to settle Al alloy corrosion. The preparation methods of superhydrophobic Al alloys are mainly multistep strategies. In this study, superhydrophobic Al alloy, has been prepared by an efficient one-step electrochemical etching process. Meanwhile, its micromorphology has been observed by a scanning electron microscope. The wettability has been measured by video optical contact angle meter. The corrosion behavior has been tested by electrochemical workstation, and wear performance has been characterized by friction tester. The results show that the micro-nanoterraced concave–convex structure has been fabricated and an as-prepared surface exhibits excellent superhydrophobic behavior. Further electrochemical and tribological tests show that corrosion resistance and wear resistance have also been significantly improved. This study provides a new method to prepare wear-resistant and corrosion-resistant Al alloy for widening applications of multifunctional Al-based engineering materials.     

The thermochromic characteristics of Zn-doped VO2 that were prepared by the hydrothermal and post-annealing process and their polyurethane composite films

In this paper, Zn-doped VO₂ nanoparticles have been successfully fabricated by a two-step hydrothermal-annealing process, and the thermally induced visible light transmittance enhancement of Zn-doped VO₂ has been studied for the first time. It is found that Zn-doped VO₂ not only exhibits excellent solar modulation ability (ΔT_sol = 15.27%) but also can reduce the phase transition temperature and increase the visible light transmittance after the heat-induced phase transition (ΔT_lum=+5.78%). Moreover, with the increase of Zn doping concentration, the phase transition temperature (T_c) and phase transition hysteresis (ΔT) both decrease. It is shown that the Zn-doped VO₂-PU films not only have good solar light modulation ability and properties of improving visible light transmission after phase transition, but also have good durability. The research result is of great significance for improving the visible light transmittance after phase transition and realizing the practical application of VO₂ in the field of smart windows.