Percolative Mechanism of Aging in Zirconia‐Containing Ceramics for Medical Applications

Abstract

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...

Critical influence of alumina content on the low temperature degradation of 2–3mol% yttria-stabilized TZP for dental restorations

“…27,35 This explanation might be true when the amount of alumina addition is high, 12,27,35,36 but it cannot explain the degradation kinetics in this study for Y-TZPs containing a small amount of alumina. The area of zirconia exposed to water should be smaller as the alumina fraction was increased from 0.25 wt.% to 2 and 5 wt.%, but 0.25 wt.% alumina had a higher degradation retarding effect than 2 and 5 wt.% of alumina addition, which had a comparable effect.…”

Percolative mechanism of sliding wear in alumina/zirconia composites

“…Therefore, the alumina matrix grain size is the main factor in characterizing the wear resistance of the composite materials at these loads, as has been determined previously for alumina materials. 20 Pecharromán et al 21 using IR reflectance measurements have stablished that the percolation threshold of alumina/3Y-TZP composites is located at 16 vol.% for 3-YTZP. In the case of compositions above this percolation threshold (AL22TZY), the wear rate at relatively low contact pressure of 20 N (1.1 GPa) was found to be around two orders of magnitude higher than the ones corresponding to 14 and 7 vol.% zirconia content, and very similar to the one obtained at higher loads (Fig.…”

Key role of processing to avoid low temperature ageing in alumina zirconia composites for orthopaedic application

“…15 However, it is clearly impossible to completely avoid the transformation in a material where zirconia is the main phase. 18 Moreover, it has been shown that the zirconia level should be lower than the percolation threshold (16 vol.%) to avoid ageing propagation from grain to grain. 18,19 At last, even under the percolation threshold, significant transformation level can be observed at the beginning of some ageing experiments.…”

“…18 Moreover, it has been shown that the zirconia level should be lower than the percolation threshold (16 vol.%) to avoid ageing propagation from grain to grain. 18,19 At last, even under the percolation threshold, significant transformation level can be observed at the beginning of some ageing experiments. 19 Zirconia aggregates are suggested to be responsible for this transformation, but no study assessed clearly this issue.…”