Xiangong Deng

Effects of firing temperature on the microstructures and properties of porous mullite ceramics prepared by foam-gelcasting

Porous mullite ceramics were prepared at 1300–1600°C for 2 h via a foam-gelcasting route using industrial-grade mullite powders as the main raw material, Isobam 104 as the dispersing and gelling agent, triethanolamine lauryl sulphate as the foaming agent and sodium carboxymethyl cellulose as the foam stabilising agent. The effects of firing temperature on the sintering behaviour of green samples as well as microstructures and properties of final porous mullite products were investigated. With increasing the temperature from 1300 to 1600°C, linear shrinkage and bulk density values of fired samples increased, whereas their porosity decreased. Mechanical strength and thermal conductivity values of fired samples decreased with increasing their porosities. Even at a porosity level as high as 79.4%, compressive and flexural strengths of fired samples (with average pore size of 314 μm) remained as high as 9.0 and 3.7 MPa, respectively, and their thermal conductivity (at 200°C) remained as low as 0.21 W (m−1 K−1).

Carbon Nanotube Reinforced Ceramic Composites: A Review

Carbon nanotubes (CNTs) have been extensively studied over the last two decades because of their excellent properties. In particular, they have been considered as promising reinforcements for development of novel ceramic composites (CCs). In this paper, current researches on CNT-reinforced CCs are briefly highlighted and reviewed. CNT-reinforced CCs possess remarkable electrical and thermal properties as well as superior mechanical properties compared to conventional CCs without using CNTs.

Effects of TiO2 on the Microstructure of Synthesized Elongated Mullite

Elongated mullite was synthesized via an in situ solid-phase reaction using α-Al2O3 and SiO2 as the raw materials and TiO2 as an additive, and characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). On the basis of thermodynamic analysis of the reaction process, the effects of TiO2 content and reaction temperature on the phase composition, phase contents, and microstructure of the synthesized samples were investigated. The results showed that elongated mullite with a length of about 8.0 μm was formed for the sample with 7 mass-% TiO2 at 1873 K. The dosage of TiO2 exceeded its solid solubility limit in mullite which resulted in the anisotropic growth of mullite grains.

Synthesis of hierarchically porous mullite ceramics with improved thermal insulation via foam-gelcasting combined with pore former addition

ABSTRACT To further improve the thermal insulation performance of porous mullite ceramics used in important industrial sectors, a combined foam-gelcasting and pore-former addition approach was investigated in this work, by which hierarchical porous mullite ceramics with excellent properties, in particular, thermal insulation property, were prepared. Both mesopores (2–50 nm) and macropores (117.8–202.7 μm) were formed in porous mullite ceramics resultant from 2 h firing at 1300°C with various amounts of submicron-sized CaCO3 pore former. The former mainly arose from the decomposition of CaCO3, and the latter from the foam-gelcasting process. The porous samples prepared with CaCO3 addition had low linear shrinkage of 2.35–4.83%, high porosity of 72.98–79.07% and high compressive strength of 5.52–14.82 MPa. Most importantly, they also exhibited a very low thermal-conductivity, e.g. 0.114 W m−1 K−1 at 200°C, which was much lower than in the cases of their counterparts prepared via the conventional foam-gelcasting route.

Low-Temperature Catalytic Graphitization of Phenolic Resin Using a Co-Ni Bimetallic Catalyst

Using a Co-Ni bimetallic catalyst we investigated the catalytic graphitization of phenolic resin at 400, 600, 800, and 1000°C under an Ar atmosphere. The structure and morphology of the pyrolyzed resin were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the optimum catalytic graphitization temperature of phenolic resin is 800°C, both carbon nanotubes and carbon onions are formed in the final products.

Research Progress in Preparation of Porous Ceramics

Porous ceramics have been extensively studied during the last two decades because of their potential application in the fields of thermal insulators, gas filters, catalytic supports, separation membranes, kiln furniture, and biomedical substitutes for bone and teeth. The properties of porous ceramics are highly dependent on their method of preparation. This mini-review summarizes recent developments in innovative fabrication of porous ceramics such as three-dimensional printing, molten salt synthesis, and the sacrificial template and replica methods. Finally, we conclude with our personal perspectives and recommendations for future research in porous ceramics.

Large-Scale Preparation of Carbon Nanotubes via Catalytic Pyrolysis of Phenolic Resin at Low Temperature

Carbon nanotubes (CNTs) were prepared through catalytic pyrolysis of phenol resin at 600°C under Ar atmosphere using ferric nitrate as the catalyst precursor. The structure and morphology of pyrolyzed resin were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the optimum growth temperature of the CNTs is 600°C, and other heating temperatures lower or higher than 600°C are not suitable for large-scale preparation of CNTs. Moreover, the ferric nitrate experienced the following phase transformation: Fe3O4 at 400°C, catalytically active Fe at 600°C and catalytically inactive (Fe, C) carbide at 800 and 1000°C. Based on the SEM and TEM results, a four-step mode of Vapour-solid-solid (VSS) and tip growth mechanism was revealed for the formation of CNTs from catalytic pyrolysis of phenol resin.

Fabrication of Porous Ceramics by Direct Foaming

Porous ceramics have been extensively studied during the last two decades because of their application potentials in various fields including thermal insulators, radome materials, gas or molten metal filters, catalytic supports and biomedical substitutes for bone. This paper gives a brief review on the recent developments of preparation of porous ceramics by direct foaming method, it shows that the direct foaming method is a more effective way for preparation of high performance porous ceramics with high porosity, high mechanical strength and an even pore size distribution compared with conventional methods.