This paper demonstrates how the combination of inorganic and organic polymers can be used to form bicontinuous porosity in ceramics with pore sizes larger than 5
μm. Spinodal phase separation of ...pseudo-binary polymer mixtures allows to form larger bicontinuous pore structures than spinodal phase separation of inorganic glasses. Addition of salts allows even more complex compositions of ceramics and glasses to be formed. Here, bioactive glasses are presented that were produced via sol–gel processing of a pseudo-binary mixture of an inorganic and an organic polymer. Due to the addition of an organic polymer to the gelling sol and the spinodal phase separation at a specific equilibrium temperature, both an inorganic polymer ceramic phase and organic polymer-rich phase are formed. The evaporation of the solvent and the burnout of the organic polymer produce a microstructure of interconnected and nearly uniform porosity, which can be controlled by several processing parameters. The dependency of pore size and connectivity is best predicted by polymer phase separation rather than glass melt separation. Results suggest that polymer spinodal phase separation could be useful for the manufacture of a variety of porous ceramics.
Lead zinc niobate (PZN)–lead zirconate titanate (PZT) ceramics were produced by the reaction-sintering process. The specimens were prepared directly from a mixture of their constituent oxides without ...any calcination step. When 50% PZN was added to tetragonal Pb(Zr
0.47Ti
0.53)O
3 ceramics, the densities and electrical properties were found to be optimal (
ρ
=
7.91
g/cm
3,
K
=
1947 at 1
kHz and room temperature,
d
33
=
530
pC/N,
k
p
=
0.61). However, the specimen containing more than 50% PZN showed reduced density and decreased electrical properties, due to the formation of pyrochlore phases. The improved densification behavior of the reaction-sintering process was attributed to the enhanced diffusion of lattice defects, which were created by differences in the ionic valence of the B-sites ions of the perovskite structure.
The formation mechanisms of barium titanate particles from an amorphous TiO
2 gel during synthesis in aqueous solution at temperatures between 20 and 80°C have been investigated. It was found that ...barium ions diffuse into the gel almost immediately, with nanocrystalline BaTiO
3 particles being formed after heating to just 40°C. These particles grew to dimensions of about 100 nm as the temperature was increased to 80°C, consuming the remaining TiO
2 gel. Some remnants of gel were found on particle surfaces in a sample taken at this temperature but after holding the sol at 80°C for 2 or 4 h, the particle surfaces became “cleaner” and more rounded. It is proposed on the basis of these observations that the BaTiO
3 particles were formed by an in-situ transformation of the amorphous TiO
2 gel. The mechanism by which (i) the particles were then rounded off and (ii) the final gel fragments were incorporated into the main BaTiO
3 particles was, however, less clear.
A novel low-clay translucent whiteware body, using mostly non-plastic prefired materials and only a small amount of clay, was fabricated by slip casting and the effect of slip's solid content and ...sintering temperature on the mechanical behaviour was investigated. The degree of densification in the sintered specimens was determined by measuring the bulk density. The mechanical behaviour was determined by measuring the flexural strength and fracture toughness. Young's modulus and hardness were also measured. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies were carried out to analyse the microstructure.
The flexural strength and fracture toughness increase with both increasing the slip's solid content and the sintering temperature up to a certain level, but further increase in solid content and sintering temperature had an adverse effect on the properties. The maximum flexural strength (∼135
MPa) and fracture toughness (∼1.85
MPa
m
1/2) values were attained with specimens produced from a slip having 45
vol.% solid content at a sintering temperature of 1350
°C. It was found that the amount and distribution of closed pores, their size and possible link with each other control the flexural strength and fracture toughness of the low-clay translucent whiteware.
Rhombohedral LaMnO3+delta powders, prepared by two different soft chemistry routes (co-precipitation and hydrothermal synthesis), are sintered at 1400 C for 2 h in air. Measurements of internal ...friction Q(-1)(T) and shear modulus G(T), at low frequencies from -180 to 700 C under vacuum, evidence three structural transitions of nearly stoichiometric orthorhombic LaMnO3+delta. The first one, at 250 or 290 C, depending on the processing followed, is associated to either a Jahn-Teller structural transition or a phase transformation from orthorhombic to pseudo-cubic. The second one at 610 or 630 C is related to a phase transformation from pseudo-cubic or orthorhombic to rhombohedral. Below the Neel temperature, around -170 C, a relaxation peak could be associated, for samples prepared according to both processing routes, to the motion of Weiss domains.
Glass and metals on crystalline oxides Ravishankar, N.; Gilliss, Shelley R.; Carter, C.Barry
Journal of the European Ceramic Society,
2003, 2003-1-00, Volume:
23, Issue:
15
Journal Article, Conference Proceeding
Peer reviewed
Wetting and dewetting of liquid metals and glasses on ceramic substrates has been investigated using a combination of microscopy techniques. The influence of surface structure on dewetting behavior ...and the influence of the dewet droplets on the morphology of surface steps has been shown with the aid of experimental observations from many systems. The role of chemistry and kinetics on the wetting behavior has also been demonstrated. Finally, the possibility of exploiting reconstructed ceramic surfaces for nanopatterning of metal particles has been illustrated.
Pb(Zn
1/3Nb
2/3)O
3 (PZN) is a well known relaxor ferroelectric with excellent dielectric properties for capacitor applications and electromechanical properties for sensor and actuator applications. ...The perovskite structure stabilization of PZN based ceramics and their respective thin films has limited their applications in these devices. The crystallization behavior and the development of the perovskite structure in PZN with the addition of Pb(Zr
0.47Ti
0.53)O
3 (PZT) thin films were investigated using a metal–organic decomposition technique. When the annealing temperature was higher than 600 °C, the perovskite phase crystallized together with a pyrochlore phase. The fractions of the perovskite structure were kept at approximately 80% if the annealing temperature was higher than 700 °C. Otherwise, a new phase appeared when the annealing temperature was approximately 900 °C. Using a lead oxide upper-layer coating technique, a highly 〈111〉 oriented PZN based thin film with ∼96% perovskite was prepared. The electrical properties of this thin film were characterized with the remnant polarization,
P
r=25 μC/cm
2, and the dielectric constant,
ε′=712, respectively.
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