Deng Pan,Shufeng Li,Xin Zhang,Bo Pan,Shengyin Zhou,Yabo Fu,Katsuyoshi Kondoh
Strip-shaped W 2 B 5 reinforced B 4 C ceramic composites were prepared via in situ reaction of boron(B)-graphite(Gr)-WC system by powder metallurgy (P/M). In order to study the effect of the graphite content on the properties of the as-fabricated ceramic composites, the powder mixture of B-Gr-WC with various amounts of Gr powder were blended and consolidated by spark plasma sintering (SPS). The sintering parameters were shown as following: sintering pressure was set as 30 MPa; The three-step sintering temperature was 1100-1550-1700°C and the duration time was set as 5-5-6 minutes, respectively. In situ formed strip-shaped W 2 B 5 particles were dispersed homogeneously in B 4 C matrix, which resulted in a remarkable improvement on the fracture toughness and mechanical properties. Appropriate 5vol% residual Gr in the composite shows positive effect on the mechanical properties which achieved an optimal counter-balance of fracture toughness and hardness, the relative density was 99.8%, the Vickers hardness can reach 30.2 GPa, and the fracture toughness was 11.9 MPa·m 1/2 when the sintering temperature was set at 1700°C.
As one of the most successful aqueous zinc-based batteries, the alkaline Zn-MnO 2 batteries (AZMBs) suffer from the low utilization of MnO 2 . This work proposes a simple approach to address this issue by optimizing the graphite contents and microstructures in the cathode. It is found that the cathode of AZMB containing 9 wt% graphite exhibits the best electrochemical performances, achieving the discharge capacities of 240.6 mAh and 196.25 mAh at 10 and 25 mA, increasing by 7.7 % and 9.0 % compared to that of the commercial AZMBs, respectively. Additionally, by adopting the fully-expanded graphite with large specific surface area and thin thickness, the discharge capacities of AZMB increase by 8.7 % and 8.8 % at 10 and 25 mA, compared to that of the commercial AZMBs, respectively. The improving discharge properties of AZMBs with proper graphite content and microstructure can be ascribed to the high conversion rate of MnO 2 into the discharge product of MnOOH due to the improved conductive network. This work provides a valuable insight for the development of the aqueous Zn-based batteries.
Combining short-process reduction and vacuum hot pressing, copper matrix composites with the graphite volume fraction of 55% and 70% were prepared by cuprous oxide and spherical graphite (Cu 2 O-Gr composites). Transmission electron microscopic (TEM) results show that some graphite particles in Cu 2 O-Gr composites change from spherical to finer flocculent or acicular shape, and the interface between the matrix and graphite is partially coherent. The reaction enhances interface bonding and modifies the interface morphology of graphite, leading to the good mechanical performance of the composites. Compared with the Cu-Gr composites prepared by conventional hot pressing, the Cu 2 O-Gr composites present higher density and strength and lower friction coefficients and wear rates. In the current-carrying friction experiments, the wear rate of the Cu 2 O-55Gr is nearly 25% lower than that of the Cu-55Gr. The short-process reduction contributes to better self-lubricating behaviors of the Cu 2 O-Gr composites, reducing the adhesive wear and abrasion wear.
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