Effects of HfB2 and HfN Additions on the Microstructures and Mechanical Properties of TiB2-Based Ceramic Tool Materials
The effects of HfB2 and HfN additions on the microstructures and mechanical properties of TiB2-based ceramic tool materials were investigated. The results showed that the HfB2 additive not only can inhibit the TiB2 grain growth but can also change the morphology of some TiB2 grains from bigger polygons to smaller polygons or longer ovals that are advantageous for forming a relatively fine microstructure, and that the HfN additive had a tendency toward agglomeration. The improvement of flexural strength and Vickers hardness of the TiB2-HfB2 ceramics was due to the relatively fine microstructure; the decrease of fracture toughness was ascribed to the formation of a weaker grain boundary strength due to the brittle rim phase and the poor wettability between HfB2 and Ni. The decrease of the flexural strength and Vickers hardness of the TiB2-HfN ceramics was due to the increase of defects such as TiB2 coarse grains and HfN agglomeration; the enhancement of fracture toughness was mainly attributed to the decrease of the pore number and the increase of the rim phase and TiB2 coarse grains. The toughening mechanisms of TiB2-HfB2 ceramics mainly included crack bridging and transgranular fracture, while the toughening mechanisms of TiB2-HfN ceramics mainly included crack deflection, crack bridging, transgranular fracture, and the core-rim structure.
Microstructure and Mechanical Properties of ZrB2–HfC Ceramics Influenced by HfC Addition
ZrB2–HfC ceramics have been fabricated using the liquid phase sintering technique at a sintering temperature as low as 1750 °C through the addition of Ni. The effects of HfC addition on the microstructure and mechanical properties of ZrB2–based ceramics have been investigated. These ceramics were composed of ZrB2, HfC, Ni, and a small amount of possible (Zr, Hf)B2 solid solution. Small HfC grains were distributed among ZrB2 grain boundaries. These small grains could improve the density of ZrB2–based ceramics and play a pinning role. With HfC content increasing from 10 wt % to 30 wt %, more HfC grains were distributed among ZrB2 grain boundaries, leading to weaker interface bonding among HfC grains; the relative density and Vickers hardness increased, and flexural strength and fracture toughness decreased. The weak interface bonding for 20 and 30 wt % HfC contents was the main cause of the decrease in both flexural strength and fracture toughness.
Polymer-derived mesoporous SiOC/ZnO nanocomposite for the purification of water contaminated with organic dyes
Abstract Polymer-derived mesoporous SiOC/ZnO nanocomposite for water decontamination was prepared by a simple mechanical incorporation of ZnO nanopowders into the commercial vinyl-functionalized polysiloxane followed by pyrolysis at 700 °C for 2 h. The as-prepared nanocomposite was characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen physisorption measurement and UV–vis spectroscopy. The effects of pyrolysis temperature (700–900 °C) and ZnO content (0–20 wt.%) on the formation of SiOC/ZnO nanocomposite were investigated. The polymer-to-ceramic transformation of pure polymer resulted in the formation of an amorphous microporous SiOC ceramic (pore size S BET  = 398 m 2 /g) value with the pore size of S BET value of 220 m 2 /g with the pore size of ∼4 nm. The adsorption and photocatalytic properties of the as-prepared samples were evaluated by measuring the decrease in concentration of methylene blue (MB) after adsorption in the dark and photochemical reaction under UV irradiation, respectively. The lowest MB adsorption was noted for SiOC ceramic, and MB adsorption by SiOC/ZnO nanocomposite monotonically decreased with the increase in the ZnO content. The photocatalytic activity of porous SiOC ceramic for the degradation of MB is enhanced significantly by the incorporation of ZnO nanopowders into the SiOC matrix.