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In this paper, using only high alumina fly ash as raw material and MoO 3 as additive agent, the high-strength porous mullite ceramics were achieved by in situ mullite whisker growth via a calcination method. The influence of MoO 3 addition on pore structure and mechanical properties of as-prepared mullite ceramics was investigated. The mechanism of MoO 3 promoting the formation of mullite whiskers and improving the strength of matrix was elucidated. The porous mullite ceramic reached its best performance with a high porosity of 49.4% and an improved compressive strength of 13.03 MPa with 10 wt% MoO 3 addition calcinated at 1300 °C. Specifically, MoO 3 facilitated the mullite whisks growth mainly by reducing melting point of amorphous SiO 2 /quartz and changing crystal structure of Al 2 O 3. The larger aspect ratio of mullite grain at 1300 °C was easier to form an interlocking structure, which enhanced the strength of mullite ceramic while maintaining high porosity. [ABSTRACT FROM AUTHOR]

In this paper, the ceramics with composition of (0.98- x)(K 0.5 Na 0.5)(Nb 0.96 Sb 0.04)O 3 -0.02(Bi 0.5 Na 0.5)(Zr 0.8 Ti 0.2)O 3- x CaZrO 3 (abbreviated as (0.98- x)KNNS-0.02BNZT- x CZ, x = 0, 0.01, 0.015, 0.02, 0.025, 0.03) were prepared by a traditional solid-state reaction method. The effect of the additional amount of CaZrO 3 on the phase structure, microstructure, dispersion index, domain structure and piezoelectric properties of ceramics was systematically studied. Finally, the piezoelectric properties and thermal stability of ceramics could be controlled by adding different amounts of CaZrO 3. The addition of CaZrO 3 transferred the phase structure of the ceramics from orthogonal-tetragonal (O-T) coexistence phase to rhombohedral-orthogonal (R–O) coexistence phase, which could be demonstrated by XRD test, temperature-dependent Raman spectra and ε r ‐ T plot analysis. And when x = 0.02, the ceramics possessed the best piezoelectric and dielectric properties (d 33 = 253 pC/N, ε r = 1185, tan δ = 0.044). Such excellent electrical properties could be originated from the heterogeneous domain structure and small-size nano-domains of the ceramics. Moreover, with the increase of CaZrO 3 doping amount, the dispersion index of ceramics gradually increased from 1.404 to 1.871, which showed more obvious dispersion phase transition characteristics and improved the thermal stability of ceramics. Particularly, when x = 0.02, after annealing at a high temperature of 220 °C (close to its Curie temperature), the d 33 tested at room temperature remained above 85% of that without annealing. The results indicated that (0.98- x)KNNS-0.02BNZT- x CZ ceramic was a promising lead-free piezoelectric ceramic system. [ABSTRACT FROM AUTHOR]

The effect of CaF 2 addition (15.4, 20.4, 27.4 and 35.4 wt%) on the crystallisation ability and preparation of transparent glass ceramics (TGCs) containing CaF 2 nanocrystals was studied. It was found that samples with 15.4, 20.4, and 35.4 wt% CaF 2 are crystallised with multiple crystal phases, making the TGCs opaque. Only when the amount of CaF 2 added is increased to 27.4 wt%, TGCs with only CaF 2 nanocrystals can be successfully prepared by heat treatment at 630 and 730 °C for 2 h. The crystallisation activation energy of the sample with 27.4 wt% CaF 2 is 247.07 kJ mol−1, and the crystallisation energy barrier to be overcome corresponds to the formation of CaF 2 nanocrystals rather than the formation of aluminosilicates, whose size and distribution easily make the glass opaque. Similarly, the FT-IR and XPS results indicate that as the amount of CaF 2 added is increased to 27.4 wt%, the polymerisation degree of the sample is more suitable for the diffusion of calcium and fluorine atoms to form only CaF 2 nanocrystals; therein, the corresponding mole fractions of the bridging oxygen (Oo), non-bridging oxygen (O−), and free oxygen (O2−) are approximately about 0.12, 0.77 and 0.11, respectively. [ABSTRACT FROM AUTHOR]