A novel capacitor devicewith a high, frequency‐independent dielectric constant has been fabricated by a simple powder processing route. A mixture of microparticles of ferroelectric BaTiO3 and de‐passivated metallic nickel was sintered to yield percolative composites in which the system of conducting particles separated by insulator layers (see Figure for an SEM image) exhibits a dielectric constant higher than that of either component.

Changes in crystalline phases resulting from low-temperature ageing of different yttria doped and non-doped zirconia-toughened alumina composites and nanocomposites were investigated under controlled humidity and temperature conditions in autoclave. A classical powder mixing processing route and a new modified colloidal processing route were used to process the composites. Different compositions ranging from 2.5 wt.% zirconia in a matrix of alumina to pure zirconia (3Y-TZP) were studied. It was observed that Al2O3+yttria stabilised ZrO2 composites exhibited significant ageing. However, ageing was much slower than traditionally observed for Y-TZP ceramics, due to the presence of the alumina matrix. Ageing was clearly limited for zirconia content beyond 25 wt.%. On the other side of the spectrum, Al2O3+2.5 wt.% ZrO2 initially presented a monoclinic fraction but did not show any ageing degradation. These composites seem to represent the best choice between slow crack growth and ageing resistance.

tion of an ethanolic suspension of microspheres produces a colloidal crystal film that is of controlled thickness and essentially single-crystalline. The concentration of microspheres in ethanol was chosen to obtain a nominal thickness of 15 sphere layers.The synthesis of monomers 1, 2, and 3 was performed using previously published protocols [15,16,19]. Briefly 1,1¢-dilithioferrocene, synthesized from ferrocene and n-butyl lithium with N,N,N¢,N¢-tetramethylethylenediamine as catalyst, was treated with a 1.3 molar excess of methyltrichlorosilane, silacyclobutyldichlorosilane, or ethylmethyldichlorosilane (chlorosilanes were obtained from Gelest) in dry diethyl ether to give, respectively, crude 1, 2, and 3. Crude products were crystallized from dry hexanes, and pure monomers were obtained following two crystallization/sublimation cycles.Prior to infiltration of silica colloidal crystal films, these were dehydrated under vacuum at 200 C for 12 h to remove any adsorbed moisture, using a Schlenk tube inserted into a muffle furnace. Colloidal crystal films were then soaked in a 10 mg mL ±1 solution of 1 in dry hexanes for 30 min, then washed abundantly with dry hexanes. A drop of very concentrated solution (approximately 1.5 (g monomer) (mL benzene) ±1 ) of a mixture comprising 10 wt.-% crosslinker 2 and 90 wt.-% monomer 3 in dry benzene was then dropped onto the colloidal crystal film, and the solvent was removed by partial vacuum (300 torr). The monomer infiltrated colloidal crystal film, a sheet of clean, polished PTFE, and another glass slide were bound together with binder clips, and the sample thermally polymerized in a Schlenk tube under a positive nitrogen pressure at 190 C for 13 h. Once polymerized, a surgical blade was used to remove excess polymer on the sides of the sample and to carefully pry the PTFE cover from the sample. The produced sample was soaked in tetrahydrofuran overnight to remove any oligomers not covalently bound to the PFS network.Cross-sectional SEM images of the colloidal crystal samples were obtained on a Hitachi S-4500 field-emission scanning electron microscope operating at 15 kV, orienting the substrate parallel to the incident electron beam. Onto the sample was sputtered a thin layer of gold prior to imaging to eliminate charging.Transmission UV-vis-NIR spectra of samples were performed in a standard IR cell mount. (Wilmad, Cat No. 5321) with a rectangular quartz plate, PTFE spacer, and a quartz plate with two drilled holes allowing for injection and removal of solvent, constrained by a metal frame with a window and tightening screws. A 0.3 mm aperture was affixed to the cell in order to obtain spectra of a small sample area. Spectra were collected using a UV-vis-NIR spectrometer (Perkin-Elmer Lambda 900 model), orienting the sample perpendicular to the incident beam using alignment marks. A background spectrum of the cell mount with the affixed aperture was subtracted from the experimental spectra.Kinetics data for the chemomechanical optical response of the sample were obtained b...

The low temperature autoclave aging behavior of zirconia toughened alumina composites processed by a classical powder mixing processing route was analyzed using atomic force microscopy (AFM), scanning electron microscopy and X-Ray diffraction. The transformation was evaluated in terms of nucleation and growth, assessed by XRD. The time-temperature equivalency of the transformation was used to measure an apparent activation energy of the nucleation stage of the transformation of 78 kJ/mol. The microstructural features influencing the transformation were identified, and the influence of the alumina matrix on the transformation was investigated. Transformation progression grain by grain was observed by AFM. Transformation does not only occur in zirconia agglomerates but also in isolated zirconia grains. The matrix could partially inhibit the transformation. This behavior could be rationalized considering the constraining effect of the alumina matrix, shape strain accommodation arguments and microstructural homogeneity effects. INTRODUCTIONZirconia toughened alumina (ZTA) composites are of raising interest as far as biomedical applications are concerned, as an alternative to biomedical grade alumina and zirconia. Indeed, alumina is somewhat brittle, and recent serious problems have been reported 1,2 with yttria-stabilized zirconia aging degradation used in total hip replacement (THR). Aging is related to the tetragonal to monoclinic (t-m) phase transformation of zirconia 3,4 , 2 transformation promoted by mechanical and hydrothermal stresses 3,5,6 . This transformation is accompanied by a 4 vol.% increase and 16% shear, leading to microcracking, surface degradation and eventually grain pop-out. and concluded that either the martensitic theory needed to be modified to take into account bulk effects, or that twins formed subsequently as deformation twins to minimize the shape change of the particle due to transformation. It has since been demonstrated that twins in zirconia were self-accommodated martensitic variants 19 . This study raised the interest for taking into account bulk conditions, as opposed to the behavior of thin foils. Transformation was nonetheless stress-induced, and not autoclave-induced.Among the identified factors influencing the transformation behavior, the zirconia grain size is of prime importance. By limiting zirconia grain growth, it seems possible restricting the transformation. However, this was identified only for transformation occurring during heat treatment at high temperatures (>1200K) or during cooling after sintering 16 , which is different to autoclave aging conditions.Some of the microstructural features that could influence the autoclave aging behavior of zirconia remain ambiguous. Further understandings of these phenomena require local observation of the transformation at the 3 surface of bulk specimens. Recent developments of atomic force microscopy allow observing the transformation-induced surface relief modification at a nanometer scale 20 . The purpose of this paper i...

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The wear resistance of four Al 2 O 3 /SiC nanocomposites that contained SiC particles of varying average size (40, 200, and 800 nm) was studied under dry sliding conditions and compared with the results obtained in unreinforced alumina. The wear rate of the alumina and the nanocomposites of equivalent grain size increased as the contact load increased; however, the nanocomposite wear resistance at high contact loads was better than that of the alumina by a factor of 3-5. The wear resistance of the nanocomposites of submicrometer grain size was fairly independent of the contact load, and their wear resistance at high contact loads was up to two orders of magnitude better than that of the alumina. The mechanisms responsible for these behaviors were discussed in terms of the microscopic wear mechanisms that were observed on the worn surfaces.

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Objectives To assess the internal accuracy, mechanical behaviour under static load and screw loosening before and after cyclic loading of implant‐supported crowns restored with original components or with two compatible non‐original brands. Materials and Methods Sixty‐three dental implants were divided into three groups (n = 21 each): Group 1 used original components, and groups 2 and 3 used non‐original components. Internal accuracy was measured throughout a cross section of the sample groups (n = 8) using scanning electron microscopy (SEM) to evaluate the fit for implant–abutments, implant–crowns and crown–abutments. To evaluate load‐bearing capacity, eight samples from each group were loaded until fracture according to ISO Norm 14801. The removal torque value (RTV) was evaluated in the screws connecting the crown with the abutment and the abutment with the implant before and after cyclic loading (2 x 106 cycles) in five samples from each group. The data were analysed using the Kruskal–Wallis test (p < 0.05). Results Statistically significant differences were found among the mean crown–abutment gaps measured in Group 1 (9.3 μm), Group 2 (45.4 μm) and Group 3 (44.9 μm). Higher values for mean load‐bearing capacity were found in Group 1 (1,098 N) than in groups 2 and 3 (1,057 and 973 N, respectively); however, these differences were not statistically significant. Original abutment–implant screws exhibited lower percentages of torque reduction than the non‐originals. Conclusions Enhanced fit is expected when original components are used. The original abutments exhibited lower percentages of torque reduction after cyclic loading than non‐originals.