Journal of the American Ceramic Society

Bandyopadhyay, Amit; Bernard, Sheldon; Xue, Weichang; Bose, Susmita

doi: 10.1111/j.1551-2916.2006.01207.xpmid: N/A

Resorbable calcium phosphate (CaP)‐based biomaterials are important because they can significantly improve health care by shortening the time necessary for restoration of functional loading of grafted bones. Although synthetic CaPs show exceptional similarities to natural bone, however, they are deficient in one major area, in that they do not have the same mineral content of bone. The focus of our work is to understand the influence of dopants on the physical, mechanical, and biological properties of tricalcium phosphate (TCP) resorbable ceramics with special emphasis toward in vitro strength degradation and cell–materials interactions as a function of time. For this purpose, β‐TCP was doped with magnesia (MgO), zinc oxide (ZnO), and silica (SiO2). Those dopants were added as individual dopants, and their binary and ternary compositions. It was found that these dopants significantly influenced densification behavior and as sintered microstructures of TCP. In vitro mineralization studies in simulated body fluids (SBF) for 12 weeks showed apatite growth on the highly porous compositions either on the surface or inside. From scanning electron microscopic analysis it was evident that surface degradation occurred on all compositions in SBF. Compression strengths for samples up to 12 weeks in SBF showed that it is possible to tailor strength loss behavior through compositional modifications. The highest compression strength was found for binary MgO–ZnO doped TCP. Overall, samples showed either a similar strength level during the 12 weeks test period, or a continuous decrease or a continuous increase in strength depending on dopant chemistry or amount. In vitro human osteoblast cell culture was used to determine influence of dopants on cell‐materials interactions. All samples were non‐toxic and biocompatible. Dopant chemistry also influenced adhesion, proliferation, and differentiation of osteoblastic precursor cell line 1 (OPC1) cells on these matrices.

Liu, Jing; Shen, Zhijian; Nygren, Mats; Su, Bo; Button, Tim W.

doi: 10.1111/j.1551-2916.2006.01122.xpmid: N/A

Nano‐powders of BaTiO3, SrTiO3, Ba0.6Sr0.4TiO3 (BST64), and a mixture of the composition (BaTiO3)0.6(SrTiO3)04 with particle sizes in the range of 60–80 nm were consolidated by spark plasma sintering (SPS). An experimental procedure is outlined that allows the determination of a “kinetic window,” defined as the temperature interval within which the densification process can be kinetically separated from the grain growth one, enabling preparation of dense nanostructured ceramics. The width of this window varied from almost zero for BST64 to 125°C for the (BaTiO3)0.6(SrTiO3)0.4 mixture. During the densification (sintering) of the (BaTiO3)0.6(SrTiO3)04 mixture, BST64 is formed. The main part of this reaction occurs in a fully densified body through which suggesting that the constitutional phase(s) have a self‐pinning effect on the grain growth.

Bharadwaja, S. S. N.; Olszta, M.; Trolier‐McKinstry, S.; Li, X.; Mayer, T. S.; Roozeboom, F.

doi: 10.1111/j.1551-2916.2006.01123.xpmid: N/A

Ordered arrays of high aspect ratio (>10:1) ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) tube structures were fabricated by vacuum infiltration of macroporous silicon (Si) templates. Improved phase purity was achieved when PZT microtubes were pyrolyzed at 300°C and partially released from the Si template to prevent a chemical reaction between the Pb and the Si during subsequent high‐temperature crystallization. The free‐standing microtubes were crystallized by rapid thermal annealing at 750°C for 1–3 min. Perovskite phase formation was confirmed by X‐ray diffraction and transmission electron microscopy methods. Coaxial structures comprised of metallic LaNiO3, PZT, and Pd layers were also processed to enable future electrical characterization of the ferroelectric microtubes.

Wu, Yu‐Chuan; Lu, Hong‐Yang; McCauley, Daniel E.; Chu, Mike S. H.

doi: 10.1111/j.1551-2916.2006.01124.xpmid: N/A

Barium titanate (BaTiO3) base‐metal electrode multilayer ceramic capacitors of an X7R‐formulation, sintered at 1200°C under low oxygen partial pressures (of pO2≈10−9 and 10−11 atm, respectively), followed by annealing at 1000°C in an atmosphere containing a higher oxygen partial pressure (of pO2≈10−5–10−6 atm), have been analyzed for crystalline phases using X‐ray diffractometry, for microstructure using transmission electron microscopy, and for microchemistry using energy‐dispersive X‐ray spectroscopy and electron energy loss spectroscopy. The classical core–shell structure characterized by a core consisting of tetragonal ferroelectric {011) domains and featureless shell (designated type I) was observed only in sample A sintered in pO2≈10−9 atm. For sample B sintered in pO2≈10−11 atm, the core–shell structure is predominantly type II, consisting of a featureless shell similar to type I, but a core of modulated domains. The core of type II contained incommensurately modulated {111} superlattice domains along 〈111〉. The superlattice can be described by a displacive modulation with incommensurate wave vectors k1=0.58a*, k2=0.58b*, and k3=0.58c*. It is due to the ordering of defect associates , generated extrinsically from sintering in low pO2. Shell thickness was determined by the lattice diffusion of Ca2+ solute cations into BaTiO3 grains during sintering. The core–shell interface became less distinguishable in type II because defect associates , unlike those in type I, were not completely eliminated by re‐oxidizing in pO2≈10−5–10−6 atm, but became ordered along 〈111〉 and gave rise to structural modulation.

Jaglin, David; Binner, Jon; Vaidhyanathan, Bala; Prentice, Calvin; Shatwell, Bob; Grant, David

doi: 10.1111/j.1551-2916.2006.01127.xpmid: N/A

Silicon carbide fiber‐reinforced silicon carbide matrix composites (SiCf/SiC) have been produced using microwave heated chemical vapor infiltration. Preferential densification of the composite from the inside out was clearly observed. Although an average relative density of only 55% was achieved in 24 h, representative of an ∼26% increase over the initial fiber vol%, the center of the preform densified to 73% of the theoretical. The densification mechanisms were investigated using X‐ray absorptiometry and scanning electron microscopy. The initial inverse temperature profile obtained, which was found to result in the efficient filling of the intratow porosity, although not the intertow porosity, flattened out after approximately 6 h as the densification front moved outward toward the edges. Although not investigated directly, the evidence suggested that this was caused by changes in both the thermal conductivity and microwave absorption characteristics as the samples densified.

Kim, Chang Soo; Lombardo, Stephen J.; Winholtz, Robert A.

doi: 10.1111/j.1551-2916.2006.01131.xpmid: N/A

A method is described whereby thin ceramic shapes are induced to adopt a different shape at elevated temperature without the application of an external pressure. To achieve deformation, thin beams of alumina are coated with magnesia; at a high temperature, the strain mismatch that arises in the sample leads to deformation. Scanning electron microscopy and compositional profiling suggest that a bilayer structure forms. One layer contains both Mg and Al cations and the spinel phase is present, whereas the second layer consists predominantly of alumina. A mechanics model based on strain mismatch in bilayer systems indicates how the resulting curvature depends on the thickness of the two regions. A mechanistic model is derived that describes the strain mismatch in terms of the degree of conversion to spinel, the amount of differential sintering between layers, and the amount of residual porosity present in the two layers of the substrate.

Chung, Chau‐Chyun; Jean, Jau‐Ho

doi: 10.1111/j.1551-2916.2006.01135.xpmid: N/A

Protective magnesia coating on Y2O2S:Eu phosphor powders is formed by a layer‐by‐layer (LbL) method in aqueous solutions. The phosphor powders are first coated with a negative‐charged, anionic polyelectrolyte of ammonium salt of poly(acrylic acid) (PAA‐NH4), on which a second‐layer, positive‐charged magnesium hydroxide coating is then deposited by precipitation and heterocoagulation. A uniform and multiple Mg(OH)2/PAA‐NH4 bilayer coating on the phosphor powder is prepared by repeating the above coating processes. Protective magnesia coating on the phosphor powders, which is evidenced by insignificant degradation in optical properties after an extended period of electron bombardment, is formed by calcining.

Pohle, Dirk; Wagner, Matthias; Roosen, Andreas

doi: 10.1111/j.1551-2916.2006.01136.xpmid: N/A

Vias, cavities, and other cutouts are significant inhomogeneities in low temperature co‐fired ceramics (LTCC) tapes and lead to inhomogeneous shrinkage during sintering, which has a negative effect on the quality of the final multilayer device. The influence of such cutouts on the shrinkage behavior of LTCC tapes was investigated by an exact measurement of the geometry before and after sintering and by in situ observations with an optical dilatometer. The investigations show a strong influence of cutouts on the magnitude of shrinkage inhomogeneities. This effect is more pronounced, if the tapes become thinner, the dimensions of the cutouts become larger, or their position becomes less centric. It is shown that the most important factor on the occurrence of shrinkage inhomogeneities in tapes with cutouts is the static friction of the LTCC material on the setter. Severe warpage is caused by interlocking effects, which occur at bumps of the rough setter surface when the inner edges of the cutouts are pulled over the setter. By using a separating agent between the LTCC tape and the setter, the static friction could be minimized, which eliminates the sintering inhomogeneities.

Omura, Naoki; Hotta, Yuji; Sato, Kimiyasu; Kinemuchi, Yoshiaki; Kume, Shoichi; Watari, Koji

doi: 10.1111/j.1551-2916.2006.01142.xpmid: N/A

A wet jet milling process was used as a novel method to prepare Al2O3 slurries. The wet jet‐milled slurries showed very low viscosity compared with the ball‐milled slurries. Moreover, the viscosity of the wet jet‐milled slurries was constant for long times, whereas that of the ball‐milled slurries increased rapidly with time. Al2O3 particles after wet jet milling retained initial surface conditions, although Al2O3 particles after ball milling yielded more OH groups on the surface. Casting rate was sensitive to the solid content and preparation method of slurry. The relative density of the green bodies prepared from the wet jet‐milled slurries was about 65% or more and was independent of the slurry solid content. On the other hand, the relative density of the green bodies prepared from the ball‐milled slurries increased with increasing solid content and was higher than 60% at the solid content of 50% by volume. Linear shrinkage of the sintered bodies prepared from the wet jet‐milled slurries was very low and independent of the solid content of the slurry whereas that of the sintered bodies prepared from the ball‐milled slurries increased with decreasing solid content.

Wang, Pei; Wang, Chunming; Lin, Li; Zhu, Yuexiang; Xie, Youchang

doi: 10.1111/j.1551-2916.2006.01154.xpmid: N/A

A simple method is described to prepare submicrometer α‐alumina by burning carbon supported on the surface of γ‐alumina in oxygen flow at a temperature of 800°C. The burning of carbon generates a large amount of heat and leads to a rapid increase in the local temperature inside the pores of alumina. When the temperature is high enough for the phase transformation, α‐alumina is obtained in a very short time. It was found that, for carbon contents between 6 and 10 wt%, all the γ‐alumina could transform into α‐alumina after burning of carbon in oxygen for a short time, and the transformed particle sizes of α‐alumina were mostly no more than 1 μm.