Stepwise synthesis of a Zr–C–Si main chain polymer precursor for ZrC/SiC/C composite ceramics

Low valence state Cp2Zr(ii) was firstly obtained by a redox reaction of Cp2ZrCl2 with reductive Mg, which subsequently copolymerized with (CH3)2Si(CH2Cl)2 to form a Zr–C–Si main chain polymeric precursor of polyzirconosilane (PZCS).

Fine-grained magnetoelectric Sr0.5Ba0.5Nb2O6–CoFe2O4 composites synthesized by a straightforward one-pot method

Magnetoelectric (Sr0.5Ba0.5Nb2O6)1x(CoFe2O4)x (x = 0.2–0.6) composites were prepared by a one-pot softchemistrysynthesis using PEG400. Calcining at 700 ◦C resulted in nanocrystalline composite powders (dcryst. =24–30 nm) which were sintered between 1050 and 1200 ◦C to ceramic bodies with relative densities up to 98%.SEM investigations confirm the formation of composite ceramics with a 0–3 connectivity and variable grain sizesfrom 0.2 to 3.6 μm for sintering up to 1150 ◦C, while sintering at 1200 ◦C leads both to a change in themicrostructure and a considerable grain growth. Magnetic measurements at 300 K reveal ferrimagnetic behaviourwith saturation magnetization values smaller than bulk CoFe2O4 and coercivities between 790 and 160 Oe.Temperature-dependent impedance spectroscopy showed that the relative permittivities decrease both withrising frequency and CoFe2O4 fraction. The frequency dependence of the impedance can be well described usinga single RC circuit. Magnetoelectric measurements show the presence of pronounced field hystereses. Themaximum magnetoelectric coefficient (αME) depends both on the CoFe2O4 fraction (x) and sintering temperature.The composite with x = 0.3 exhibits the largest αME value of 37 μV Oe1 cm1 (@ 900 Hz). With rising frequencyof the AC driving field αME increases up to 300–400 Hz and is nearly constant until 1 kHz.

Effects of theTiB2-SiC Volume Ratio and Spark Plasma Sintering Temperature on the Properties and Microstructure of TiB2-BN-SiC Composite Ceramics

TiB2-BN composite ceramics combine excellent electrical conductivity, thermal shock resistance, high-temperature resistance, corrosion resistance, and easy processing of TiB2 and BN. However, in practical applications, their high-temperature oxidation resistance is poor and the resistivity distribution is uneven and changes substantially with temperature. A TiB2-BN-SiC composite ceramic with stable and controllable resistivity was prepared by introducing SiC into the TiB2-BN composite ceramics. In this work, spark plasma sintering (SPS) technology was used to prepare TiB2-BN-SiC composite ceramics with various TiB2-SiC ratios and sintering temperatures. The samples were tested by XRD, SEM, and thermal and mechanical analysis. The results show that as the volume ratio of TiB2-SiC was increased from 3:1 to 12:1, the resistivity of the sample decreased from 8053.3 to 4923.3 μΩ·cm, the thermal conductivity increased from 24.89 to 34.15 W/(m k), and the thermal expansion rate increased from 7.49 (10−6/K) to 10.81 (10−6/K). As the sintering temperature was increased from 1650 to 1950 °C, the density of the sample increased, the mechanical properties were slightly improved, and the resistivity, thermal expansion rate, and thermal conductivity changed substantially. The volume ratio and sintering temperature are the key factors that control the resistivity and thermal characteristics of TiB2-SiC-BN composite ceramics, and the in situ from liquid phases of FeB and FeO also promotes the sintering of the TiB2-BN-SiC ceramics.