Chude Feng

Formation of porous alumina with oriented pores

Abstract Adopting the theories describing the bubble forming in the metal–hydrogen solidification process, porous alumina with oriented pores was prepared by combining a foaming method with sol-gel technology. The bubble forming process in the sol-gel is different from that in the metal–hydrogen system. Samples were calcined at temperature from 800 to 1200C. The volume-shrinkage and compressive-strength increased with increasing calcination temperature. The porous alumina exhibited a bimodal pore structure when prepared below 1200°C.

Formation of columbite-type precursors in the mixture of MgO-Fe2O3-Nb2O5 and the effects on fabrication of perovskites

Abstract All possible combinations of the three oxides, MgO, Fe 2 O 3 and Nb 2 O 5 have been investigated to trace the phase development during calcination by means of X-ray diffraction (XRD). It has been found that for the ternary system MgO–Fe 2 O 3 –Nb 2 O 5 , the phase evolvement in the process of calcining is not the simple superimposition of the three binary systems MgO–Fe 2 O 3 , MgO–Nb 2 O 5 and Fe 2 O 3 –Nb 2 O 5 . The reaction existing in the binary system MgO–Fe 2 O 3 no longer appears in the ternary system. Furthermore, Mg 4 Nb 2 O 9 , as a by-product of the binary system MgO–Nb 2 O 5 , does not form in the ternary system. Different precursors have different influence on the fabrication of perovskites. The possible mechanisms are discussed in detail.

Dielectric properties and dielectric aging of 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 doped with CaO

Abstract The relaxor ferroelectric, 0.9Pb(Mg 1/3 ,Nb 2/3 )O 3 –0.1PbTiO 3 (0.9PMN–0.1PT) doped with different concentrations of CaO, was studied. Doping with CaO can increase the grain size of 0.9PMN–0.1PT ceramics. The dielectric properties and dielectric aging of this ceramic were studied. The maximum value of dielectric constant decreased and the degree of diffuse phase transition (DPT) enhanced with CaO doping. Also, obvious aging effects were found in the 0.9PMN–0.1PT doped with CaO. Through the analysis, it can be expected that Ca 2+ ions enter the lattice partly substituting for the Nb 5+ or Ti 4+ ions at B-sites.

Microstructure and mechanical properties of small amounts of In2O3 reinforced Pb(ZrxTi1−x)O3 ceramics

Piezoelectric Pb(Zr{sub x}Ti{sub 1-x})O{sub 3} (PZT) ceramics with small amount (0.5-2.0 wt.%) of In{sub 2}O{sub 3} are prepared by conventional sintering method. Based on X-ray diffraction analysis, the tetragonality of PZT matrix decreases with In{sub 2}O{sub 3} content, indicating that In{sub 2}O{sub 3} diffuses into PZT matrix. The microstructure of PZT matrix is significantly refined by doping small amounts of In{sub 2}O{sub 3}. The grain size reduction and the matrix grain boundary reinforcement are the probable mechanism responsible for the high strength and hardness in the PZT/In{sub 2}O{sub 3} materials. The enhancement in Youngs modulus is attributed to In{sup 3+} substitution. The decreased tetragonality with In{sub 2}O{sub 3} addition results in less crack energy absorption by domain switching and, hence, causes the small reduction in fracture toughness.

A novel preparation of porous alumina with parallel channels

Abstract A porous alumina with parallel channels has been prepared by combining a foaming method and sol–get technology. Samples were calcined at 800°C, 1000°C and 1200°C, respectively. The volume shrinkage and compressive strength increased with calcination temperature. The porous alumina exhibited a bimodal pore structure when calcined below 1200°C. The formation mechanism for porous alumina with parallel channels is discussed.

Effects of Processing Routes on Structures and Dielectric Properties of Lead Iron Niobate-Lead Magnesium Niobate Binary System

The binary system of lead magnesium niobate [Pb(Mg1/3Nb2/3)O3, PMN] and lead iron niobate [Pb(Fe1/2Nb1/2)O3, PFN] has been chosen to investigate the influence of different preparation routes on the microstructures and properties by means of X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersion spectrometer (EDS) and dielectric measurements. It is found that for the binary system (1-x)PFN–xPMN, the change in Curie temperature is approximately linear with respect to PMN content in the range of x=0 to 0.5. With the increase in x, the Curie points shift to lower temperatures. Both calcining and sintering conditions have a non-negligible influence on the microstructure and the dielectric properties. The dielectric and other properties of samples prepared by single-step and two-step precalcination routes are compared and the possible mechanisms are discussed. Samples mixed-sintered at an appropriate temperature exhibit a different dielectric behavior, which is also discussed in detail in this paper.

Effects of Different Dopants on Diffuse Phase Transition and Ordering Degree in Lead Magnesium Niobate

This work is based on the relaxor ferroelectrics lead magnesium niobate (PMN) system. The influences of different dopants (Li+, Sr2+, Y3+) on diffuse phase transition and ordering degree were studied. X-ray diffraction (XRD), high-resolution electron microscopy (HREM), selected area electron diffraction (SAED) and Raman spectroscopy were used to study small changes of ordering degree in PMN systems. Results showed that diffuse phase transition (DPT) is caused by the formation of an ordered structure at B-sites (Mg2+:Nb5+=1:1). The degree of DPT can be contrasted from dielectric properties, and has a direct relation with ordering degree of the microstructure. It also showed that, when doping with an element of one valence (Li+), the ordering degree of PMN was decreased; when doping with Sr2+ and Y3+, the ordering degree was enhanced to different extents.

The effect of different dopants on diffuse phase transition and ordering degree in PMN

This work is based on PMN system. The influences of different dopants (Li/sup +/, Sr/sup 2+/, Y/sup 3+/) on diffuse dielectric properties and micro-structure were studied. HREM, SAED, Raman spectra and XPS were used to study small changes of ordering degree of PMN systems. The research proved that diffuse phase transition (DPT) is caused by the formation of ordered structure at B site (Mg/sup 2+/:Nb/sup 5+/=1:1). The degree of DPT can be contrasted from dielectric properties, and has direct relation with ordering degree of microstructure. It also showed when doping with element of one valence (Li/sup +/), the ordering degree of PMN lowered; when doping with Sr/sup 2+/ and Y/sup 3+/, the ordering degree enhanced to different extent.