Due to their high melting point, low density, and affordable price, TiC ceramics have emerged as one of the most promising ultrahigh temperature structural materials. However, its development and usage are severely constrained by its weak mechanical characteristics. The Ti2AlC-TiC and Ti3AlC2-TiC composites were synthesized by using the laminated metal-ceramic Ti2AlC/Ti3AlC2 as the binder, combined with high-temperature and high-pressure sintering technology (GPa order of magnitude confinement system). The thermal analysis shows that the exothermic heat of Ti/1.2Al/2TiC is less than that of 3Ti/1.2Al/2C, 2Ti/1.2Al/C, and 3Ti/1.5Al/C. The ratio of Ti/1.2Al/2TiC can suppress the thermal explosion phenomenon during the sintering process and improve the safety of the high-pressure sintering process. XRD results showed that the main composition of the sintered products was Ti2AlC-TiC at 2∼3.5 GPa and Ti3AlC2-TiC at 4∼5 GPa. As the sintering pressure increased from 2 GPa to 5 GPa, the bonding phase changed from Ti2AlC to Ti3AlC2. The thickness of the synthetic Ti3AlC2 layer is near 0.1 µm under 5 GPa. The average friction coefficient of Ti2AlC-TiC composites sintered 2 GPa with POM is as low as 0.1767, while the average friction coefficient of Ti3AlC2-TiC composites with POM increased to 0.3468∼0.3797. The wear width of Ti2AlC-TiC is lower than that of Ti3AlC2-TiC composites sintered under 4–4.5 GPa. The wear width of Ti3AlC2-TiC composites decreases following the rise of sintering pressure and is reduced to 0.3504 mm under 5 GPa. Ti2AlC-TiC and Ti3AlC2-TiC composites with PP ball counterparts have friction coefficients of 0.375 to 0.45 and worse wear resistance than that of POM balls. Ti3AlC2-TiC composites synthesized at 5 GPa with a Cu ball had the smallest friction coefficient (0.4558) and the smallest wear scar width (0.6289 mm). The friction coefficients and wear widths of synthetics with Al pairs ranged from 0.48–0.697 and 0.851–1.087 mm, respectively, and varied irregularly with increasing sintering pressure. Ti2AlC-TiC composites synthesized at 2 GPa with agate and glass pairs have coefficients of friction of 0.5 and 0.61, respectively. Abrasion widths of Ti2AlC-TiC composites synthesized at 2 GPa with agate and glass pairs were 1.3 mm and 0.72 mm, respectively. The friction coefficient of synthetics with agate and glass pairs increases with increasing sintering pressure. The magnetization and magnetization intensity of the Ti3AlC2-TiC composites are stronger than those of Ti3AlC2. Ti2AlC-TiC and Ti3AlC2-TiC composites held promise to serve in the field of ceramic grinding processing applications.
Triboelectric nanogenerator as new energy technology needs to develop new triboelectric semiconductor materials with excellent electrical transport properties and friction properties for better electric output performance. High manganese silicide Mn 4 Si 7 bulks were prepared from Mn powders and Si powders at 1273 K for 1 h. The residual Si phase and MnSi phase coexisted in the primary sintered Mn 4 Si 7 compacts. The fine Mn powder obtained from mechanical pulverization and secondary sintering can accelerate the formation of Mn 4 Si 7 bulks. MnSi disappeared and slight amount of Si phase remained in the secondary sintered Mn 4 Si 7 bulks. Due to the slight decrease in the resistivity, ZT of Mn 4 Si 7 bulks reached 0.43 at 813 K. The thermal conductivity of the secondary sintered Mn 4 Si 7 compact increased due to the pulverization of the primary Mn 4 Si 7 bulk and the growth of crystal grains. The thermoelectric properties of Mn 4 Si 7 compact are reduced after heat treatment. Secondary sintering can increase the density of Mn 4 Si 7 compact. For the friction property of Mn 4 Si 7 , secondary sintering and heat treatment can reduce the coefficient friction and mass loss of primary sintered Mn 4 Si 7 compact. Based on the excellent thermoelectric properties and low wear loss at low loads of Mn 4 Si 7 , it is possible to be employed as new triboelectric materials for triboelectric nanogenerator.
For this work, europium monosulfide (EuS) powders were prepared by sulfurizing Eu2O3 powder with CS2 gas. The synthesized EuS powders were sintered by SPS at temperatures in the 800–1600 °C range for 0.33–1 h at 50 MPa under vacuum conditions. The influences of Yb doping and sintering conditions on the magnetocaloric and mechanical properties of EuS were investigated systematically. An increase in sintering temperature caused the rise of lattice parameters of EuS, whereas Yb doping caused them to drop. SEM showed that the grain size of the EuS increased with sintering temperatures in the 1000–1400 °C range. Higher sintering temperatures can enlarge the magnetizability and saturation magnetization of EuS compact. On the contrary, Yb doping can weaken the magnetizability and saturation magnetization of EuS compact. All sintered polycrystalline EuS compacts had weaker thermomagnetic irreversibility and lower magnetic anisotropy.
LiTiO2 was prepared from tetraethoxy titanium and lithium ethoxide by a sol–gel process and then treated at 773 K and 973 K under oxygen atmosphere, respectively. Compared with LiTiO2 prepared at 973 K, LiTiO2 prepared at 773 K has better CO2 capture properties. XRD patterns of synthetic LiTiO2 before and after CO2 capture confirm that the intermediate product, LixTizO2, is produced during CO2 capture. CO2 absorption degree of LiTiO2 was determined to be 37% (293 K), 40.8% (333 K), 45.5% (373 K), and 50.1% (393 K) for 11.75 h, respectively. Repetitive CO2 capture experiment indicates that LiTiO2 has excellent cyclic regeneration behavior. The CO2 absorption degree of LiTiO2 increased with increasing CO2 concentration. At a concentration of 0.05%, the absorption degree of LiTiO2 had a stable value of 1% even after an absorption time of 1.4 h. LiBO2 was fabricated by the similar sol–gel method and treated at 713 K. Mass percentage and specific surface area of synthesized LiBO2 increased with the increasing absorption temperature. Evidently, the diffusion of the CO2 molecule through the reaction product, which had a low activation energy of 15 kJ·mol−1 and apparent specific surface value of 55.63 m2/g, determined the efficiency of the absorption reaction. Compared with the other sol–gel synthesized lithium-based oxides, LiTiO2 possessed higher absorption capabilities and lower desorption temperature.
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