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Xiang, Sisi; Yang, Qirong; Lien, Hsu‐Ming; Shial, Keya; Gronske, Eric; Haber, Richard; Xie, Kelvin Y.
doi: 10.1111/jace.17062pmid: N/A
In this work, B4C, B4C + 5 at.% Al, B4C + B, and B4C + B + 5 at.% Al were arc melted, and the resultant solid products were characterized. Results from x‐ray diffraction and scanning electron microscopy showed that adding Al alone in B4C did not result in Al doping; adding Al and B in B4C led to Al doping. Al‐doping also changed the surface energy of boron carbide in the liquid state, thus altered the wettability. Transmission electron microscopy revealed that stacking faults are more likely to form in the Al‐doped sample, especially in the regions where the Al concentration is high.
Fu, Yanqin; Zhang, Yulei; Yin, Xuemin; Li, Tao; Zhang, Jian
doi: 10.1111/jace.17073pmid: N/A
Awl‐like hafnium carbide (HfC) nanowires were successfully synthesized on carbon cloth in a polymer pyrolysis route via Fe‐catalyzed for the first time. A detailed study of the HfC nanowire morphology was performed. X‐ray diffraction, scanning electron microscopy and transmission electron microscopy were used to investigate the morphology and microstructure of the obtained awl‐like HfC nanowires and the growth mechanism was also discussed in detail. Results show that HfC nanowires wrapped by amorphous HfO2 layer with ~10 nm in thickness display awl‐like structure and the nanowire's surface exhibit prismatic geometry. The diameter of the nanowire decreases from the bottom (~500 nm) to the top (~100 nm). The growth mechanism of the awl‐like HfC nanowires was mainly affected by the combination of bottom‐type vapor‐liquid‐solid (VLS) and solid‐liquid‐solid.
Zhang, Chaofan; Yuan, Baohua; Yang, Lixia; Bai, Liangjiu; Yang, Huawei; Wei, Donglei; Wang, Wenxiang; Liang, Ying; Wang, Qingyao; Chen, Hou
doi: 10.1111/jace.17076pmid: N/A
Solar steam generation has been considered as an effective way to solve the shortage of freshwater resources. In this paper, we have designed an interfacial evaporation device for efficient solar steam generation based on near infrared (NIR)‐absorbing lanthanum hexaboride (LaB6) nanoparticles and melamine sponge (MS) as the skeleton. LaB6 nanoparticles as a photothermal conversion material can absorb the NIR light and convert it into heat. Due to the porous 3D network and better hydrophilicity of MS, it can act as a substrate to support the LaB6 dispersed on the surface and transport the water by the capillary force. The evaporation rate of 1.13 kg m−2 h−1 and photothermal conversion efficiency of 60.7% under 1 kW m−2 solar illumination were achieved. Moreover, LaB6‐MS photothermal conversion device (LaB6‐MS PTCD), with excellent chemical stability could purify different water sources such as simulated seawater, strong acid, strong alkaline, and dyed methylene blue solution, exhibiting promising application in highly efficient solar energy‐driven seawater desalination and wastewater purification.
Gurnani, Luv; Kumar, Udit; Mukhopadhyay, Amartya
doi: 10.1111/jace.17049pmid: N/A
The role of coherency strain at the matrix/precipitate interface toward hardening of bulk polycrystalline “ceramic alloys” has been established here. Formation of “near ideal” bulk polycrystalline ceramic microstructure characterized by the presence of uniformly distributed coherent “ultra‐fine” MgCr2O4 particles (size: ~25 nm) within matrix (MgO) grains was achieved via solid‐state precipitation during aging treatment of bulk supersaturated MgO–Cr2O3 solid solutions (formed during pressureless sintering in air, followed by fast cooling). The as‐aged MgO–MgCr2O4 “ceramic alloys” exhibited hardness increment by ~73% over that of phase pure bulk MgO upon aging for just 10 hours at 1000°C in air. Evidences toward the presence of significant coherency strains across the MgO/MgCr2O4 coherent interfaces were obtained with transmission electron microscopy. Analysis based on hardening mechanisms and comparisons with MgO–MgFe2O4 system, having lesser hardening due to lower misfit strain at MgO/MgFe2O4 coherent interfaces (despite greater content of second‐phase particles), confirm the dominant role of coherency strains toward hardness enhancement in “ceramic alloys.”
Suzuki, Muneyasu; Kusaka, Yasuyuki; Tsuchiya, Tetsuo; Ushijima, Hirobumi; Akedo, Jun
doi: 10.1111/jace.17038pmid: N/A
Recently, the demand for flexible or stretchable Internet‐of‐things devices has increased with the rise in popularity of wearables. Also, research is progressing for the development of oxide‐based all‐solid‐state lithium‐ion batteries, which are expected to have improved safety and performance compared with current batteries. Room‐temperature processes for the production of oxide films would facilitate the development of such novel devices. Press forming is a simple room‐temperature process; however, conventional press forming cannot produce highly dense green compacts. Here, we developed a new press forming‐based, room‐temperature process, the mega‐press forming (MF) method, that produces highly dense aggregate oxide films at a pressure below 1 GPa, which is lower than that at which oxide particles fracture, by taking advantage of the differences in cohesive force between microsized and nanosized particles. We used our novel process to produce highly dense lead zirconate titanate aggregate films on aluminum foil at room temperature, and found that when impregnated with silicone oil, these films exhibited low leakage current density and saturated polarization hysteresis properties. Furthermore, we were able to produce films with a porosity of only 6%, which is much lower than that of films produced by conventional press forming (20%). Thus, the MF method will be useful for the development of novel functional composite ceramics that are difficult to fabricate using high‐temperature processes.
R. Lavagnini, Isabela; Campos, João V.; Ferreira, Julieta A.; A. Pallone, Eliria M. J.
doi: 10.1111/jace.17037pmid: N/A
The effect of a controlled current ramp during flash sintering (FS) on the densification and microstructural evolution of 3 mol% yttria‐stabilized zirconia was investigated. The samples were flash sintered using a current ramp control with six different current ramp rates and compared with samples sintered by FS without current ramp control. In both cases, maximum electric current densities of 100 and 200 mA mm−2 were used. The microstructure of cylindrical samples was observed, showing grain size heterogeneity between the curved surface and the core for the flash‐sintered (FSed) samples regardless of the maximum current density used. By contrast, the current ramp FSed samples exhibited a homogeneous grain size when the electric current density of 100 mA mm−2 was applied. Thus, controlling a current ramp during FS can be an alternative for avoiding grain size heterogeneity on ceramics sintered by this technique.
Costakis, William J.; Schlup, Andrew; Youngblood, Jeffrey P.; Trice, Rodney W.
doi: 10.1111/jace.17044pmid: N/A
Uniaxial warm pressing was used to align alumina platelet‐filled polyethylene‐based copolymer blends. The solids loading (30‐40 vol.%) and platelet diameter (1.2 and 11 μm) were varied to compare effects on viscosity, percent reduction, and final alignment. All ceramic‐filled thermoplastic polymer blends exhibited pseudoplastic behavior. Crystallographic alignment of green body samples was quantified by the orientation parameter (r) and grain misalignment angle (full width at half maximum, FWHM) obtained from rocking curve analysis. Blends with 11 μm diameter platelets displayed a higher temperature sensitivity constant, better flow properties, and higher alignment compared to blends with 1.2 μm diameter platelets. Optimal samples produced with blends containing 30 vol.% of 11 μm diameter platelets demonstrated an alignment of r = .251 ± .017; FWHM = 11.16° ± 1.16°. A sample with optimal alignment was hot‐pressed to transparency and obtained an in‐line transmission of 70.0% at 645 nm. The final alignment of this pre‐aligned hot‐pressed sample (r = .254 ± .008; FWHM = 11.38° ± 0.54°) improved when compared to a non‐pre‐aligned sample (r = .283 ± .005; FWHM = 13.40° ± 0.38°).
Yao, Qing; Zhang, Le; Gao, Pan; Sun, Bingheng; Shao, Cen; Ma, Yuelong; Zhou, Tianyuan; Li, Ming; Chen, Hao; Wang, Yun
doi: 10.1111/jace.17052pmid: N/A
Large and nondeforming Nd: YAG ceramic prepared by wet forming is of great importance as gain medium to obtain high‐power solid‐state lasers. However, it is difficult to achieve high‐quality laser ceramics due to insufficiency of the in‐depth understanding of transformation mechanism of gels viscoelasticity and effective control means during drying process. In this work, the rheological behaviors, viscoelastic characteristics, and mechanical strengths in classical acrylamide (AM) and novel Isobam (PIBM) gelcastings were systematically compared to explore the suitable route for the large‐sized 2% Nd: YAG transparent ceramics with high aspect ratio (>10). AM system exhibited a higher complex viscosity (1.82 × 105 Pa s), a shorter gel time (92.9 seconds), and a higher flexural strength (about 24.46 MPa) than PIBM system, and especially its ability to quickly gel was beneficial to the homogeneity of green body. In addition, the order of drying rates of wet gels in four drying media was observed as follows: 55℃ hot air> ethanol> solid desiccant> PEG‐11000 and the moisture diffusion coefficients were calculated and simulated to offer the deep consideration of drying kinetics. The “ethanol + 55℃ hot air” was regarded as an effective composite drying method to eliminate defect and to achieve φ8 mm × 160 mm Nd: YAG ceramic with the in‐line transmittance of 83% @1064 nm. Therefore, not only the cognition of gel process, but also the defects control strategy is proposed. More importantly, this work greatly promotes the application of wet forming and laser ceramics in high‐power lasers.
Nandha Kumar, Ponnusamy; Subramanian, Shangavi; Vijayalakshmi, Uthirapathy; Kannan, Sanjeevi
doi: 10.1111/jace.17056pmid: N/A
Structurally stable β‐Ca3(PO4)2/t‐ZrO2 composite mixtures with the aid of Dy3+ stabilizer were accomplished at 1500°C. The precursors comprising Ca2+, P5+, Zr4+, and Dy3+ have been varied to obtain five different combinations. The results revealed the fact that complete phase transformation of calcium‐deficient apatite to β‐Ca3(PO4)2 occurred only at 1300°C, whereas the evidence of t‐ZrO2 crystallization is obvious at 900°C. The dual occupancy of Dy3+ at β‐Ca3(PO4)2 and t‐ZrO2 structures was evident; however, Dy3+ initially prefers to occupy β‐Ca3(PO4)2 lattice until its saturation limit and thereafter accommodates at the lattice site of ZrO2. The typical absorption and emission behavior of Dy3+ were noticed in all the systems and, moreover, the surrounding symmetry of Dy3+ domains has been determined from the luminescence study. All the systems ensured paramagnetic response that is generally contributed by the presence of Dy3+. A gradual increment in the phase content of t‐ZrO2 in the composite mixtures ensured a significant improvement in the hardness and Young's modulus of the investigated compositions.
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