Changes in compositional fluctuation during sintering of PZT ceramics were studied both for ordinary sintering and for the spark plasma sintering (SPS) method. Generally, sintering is established by diffusion at high temperatures. In ordinary sintering, compositional fluctuation decreased with increasing bulk density. In contrast, compositional fluctuation changed little with increasing bulk density during SPS.
A surface-modified α-FeOOH (denoted α-FeOOH[S]) was prepared by adsorption of stearate ion onto an α-FeOOH powder. The non-surface-modified α-FeOOH (denoted simply α-FeOOH) and α-FeOOH[S] powders contained particles of almost identical shape and size. When ferrite NiFe2O4 compacts were prepared by sintering the mixed powders of the surface-modified α-FeOOH[S] and NiO at 1573 K for 1 h, the total porosity of the NiFe2O4 compacts was 14.8% less than that found for compacts prepared by sintering the mixed powders of the non-surface-modified α-FeOOH and NiO. Although the morphology of the α-FeOOH and the α-FeOOH[S] was the same, the use of the α-FeOOH[S] powder accelerated densification of the NiFe2O4 compacts. The mixed powder containing α-FeOOH[S] and MO (M = Co, Zn) also formed denser ferrite compacts than when the powder containing the non-surface-modified α-FeOOH was used. The α-Fe2O3 and α-Fe2O3[S] powders were prepared by firing the non-surface-modified α-FeOOH and the α-FeOOH[S] powders, respectively, at 873 K for 1 h. The XPS O 1s and Fe 2p spectra of the α-Fe2O3 and α-Fe2O3[S] indicated that the surface of the α-Fe2O3[S] powder had a greater Fe3O4-like phase with oxygen vacancy than that of the α-Fe2O3 powder. The temperature dependence of the electrical conductivity of the α-Fe2O3 and α-Fe2O3[S] powder compacts also indicated the presence of an Fe3O4-like phase with a mixed-valence state of Fe3+ and Fe2+ on the surface. This Fe3O4-like phase plays an important role in the sintering and densification of ferrite compacts.
A study was undertaken concerning the kinetics and mechanism of the phosphidation of silver at 450°C in phosphorus vapor at 44.0 to 80.0 kPa. X‐ray diffraction patterns and an electron probe microanalysis of the reaction products demonstrated that the films were composed of single layers of . A marker experiment indicated that silver was apparently the component that diffused across these films. In the early stage, the phosphidation obeyed a linear rate law and its rate‐determining process was regarded as the surface reaction; that is, the chemisorption of molecules generated by dissociation of a molecule. When the thickness of a phosphide layer reached a critical value, the reaction kinetics exhibited a gradual transition from the linear to the parabolic rate law as a result of the rate‐determining process changing from adsorption to solid‐state diffusion.
La-doped lead magnesium niobate (Pb1-xLax[Mg(1+x)/3Nb(2-x)/3]O3, PLMN, x=0.1, 0.2) was prepared by a polyethylene glycol-based process (PEG method) as follows: PEG-cation (La3+, Mg2+, Nb5+) complex was oxidized and the obtained oxide was mixed with PbO. This oxide mixture was fired to obtain PLMN. This PEG method enabled to prepare the single phase of perovskite structure of PLN at 1023K. This temperature is lower than that used in the solid state reaction method. The PLMN prepared by the PEG method had quite little compositional fluctuation and structural strain. PLMN has an ordering domain with the super lattice structure of B site cations in the perovskite structure. The crystallite size of the ordering domain in the PLMN obtained by the PEG method increased when the molecular weight of the initial PEG increased (from 150 to 7500). The formation process of the ordering domain was under the influence of the cation distribution in the PEG-cation complex.
Diffusion in multi-compositional 0.9PbZrO3−xPbTiO3-(0.1–x)Pb(Zn1/3Nb2/3)O3 (PZ-PT-PZN) ceramics prepared by spark plasma sintering was investigated through measuring the pyroelectric properties. The strong dependence of pyroelectric properties on composition x provides a useful method to investigate the diffusion between the different compositions. In addition to the post heat-treatment, the calcination conditions and the existence of Ti4 + were found to play very important roles on the diffusion. The diffusion decreases with increasing calcination temperature, while the presence of Ti4 + significantly increases the diffusion between the different compositions.
