G. Carl

Mechanical properties of oriented mica glass ceramic

Abstract The mechanical properties of extrusion oriented mica glass ceramic were studied. Anisotropy caused by the alignment of the basal planes of phlogopite crystals along the extrusion axis was observed. Fracture toughness varied in direction by about 350%, Knoop-microhardness by about 30% and Youngs modulus by about 15%. By comparison with the randomly oriented mica glass ceramic, an enhancement of the mechanical properties was measured in the direction perpendicular to the extrusion axis. The influence of the crystal alignment on mechanical properties and machineability is discussed.

Oriented fluoroapatite glass-ceramics

Abstract Glasses in the systems SiO 2 –Al 2 O 3 –CaO–P 2 O 5 –Na 2 O–F − and SiO 2 –Al 2 O 3 –CaO–P 2 O 5 –K 2 O–F − enable the formation of glass-ceramics with apatite crystals possessing needle-like morphology using high heating rates and a crystallization temperature of 1200°C. Extruding of these partially crystalline samples at high temperatures led to the formation of a highly oriented glass-ceramic. The apatite needles were aligned with their crystallographic c -axis along the extrusion direction. The orientation is demonstrated by scanning electron micrographs, X-ray diffraction patterns as well as pole-figures. By contrast to lithium disilicate, an orientation was not achieved by extruding the glassy sample and subsequent crystallization.

Viscous flow sintering of bioactive glass-ceramic composites toughened by zirconia particles

In order to widen the application fields of a bioactive glass-ceramic (Bioverit 1 I), the possibility of preparing a glass-ceramic matrix biocomposite, toughened by zirconia particles, was investigated. Two kinds of biocomposites were prepared, using as reinforcing phase tetragonal yttria-stabilised zirconia (ZrO2–3%Y2O3) and pure monoclinic zirconia particles, respectively. The composites were prepared by viscous flow sintering. The sintered composites were characterised by optical and Scanning Electron Microscopy (SEM), Energy Dispersion Spectroscopy (EDS) and X-Ray Diffraction (XRD). A mechanical characterisation of the sintered samples was carried out by means of Vickers indentations, Young’s modulus measurements, fracture toughness and compressive strength determinations. The chemical stability of the samples was evaluated by soaking them in Ringer solution. # 2002 Published by Elsevier Science Ltd.

Control of phase formation processes in glass-ceramics for medicine and technology

Abstract The control of phase separation processes in silicate glasses makes possible the control of nucleation and crystallization of base glasses. Ti(III,IV)-species influence the phase formation in SiO 2 –Al 2 O 3 –MgO glasses to form glass-ceramics based on s- and α-quartz solid solutions. Additions of Na 2 O, K 2 O and F in a specific composition range and heat treatment of the glass result in an new glass-ceramic with curved micas. The structure of these crystals shows a high tetrahedral rotation. Glasses of the SiO 2 –Al 2 O 3 –MgO–Na 2 O–K 2 O–P 2 O 5 –F system show a double phase separation. Apatites and micas grow as a result of controlled in situ crystallization. The material can be machined and has bioactive properties. Phosphate glasses show no glass-in-glass phase separation. However, the high supersaturation is cancelled by a thermal treatment of the glass and a primary crystal is formed. Apatite crystals grow in the primary phase.

Processing, microstructure and mechanical properties of extruded mica glass-ceramics

Abstract Glass-ceramics with oriented mica crystals have been produced by extrusion and subsequent thermal treatment of glasses of the system SiO 2 –Al 2 O 3 –MgO–Na 2 O–K 2 O–F. The formation of a ring-fiber texture of plate-like mica crystals was observed by electron microscopy and X-ray diffraction. The study of the crystallization behavior of glasses extruded at different temperatures revealed that subsequent heat treatments solely result in oriented crystal growth if mica nuclei or crystals have been formed during the extrusion process. The strongly textured material showed notable anisotropic properties. By comparison to mica glass-ceramic with randomly oriented crystals, fracture toughness and bending strength increased by about 100% upon texture introduction. The force of crack deflection increased with the angle between the crack front and the basal planes of mica crystals. The strengthening effect through crystal alignment is attributed to the occurrence of a centric ring-fiber texture, which reduces the size and number of surface flaws generated by the cleavage planes of mica crystals. Machinability, however, decreased by about 50% in the textured material.

Optimisation of the synthesis of glass-ceramic matrix biocomposites by the response surface methodology

Abstract In this work a Bioverit®III glass-ceramic matrix composite, containing Yttria-stabilised zirconia (Y-PSZ) particles as toughening phase, was prepared, with the aim of improving the glass-ceramic mechanical properties. In order to prepare the composite, a pressureless sintering process has been optimised. The aim of the work is to determine the best processing conditions, i.e. time and temperature of sintering. For this purpose traditional methods (thermal, morphological and mechanical analysis) have been supported by the statistical method called ”Response Surface Methodology” (RSM). On the basis of these studies two sintering series have been performed, so that we could determine the region where the best process conditions could be found.

Characterization of Bone-Glass Ceramic Interface

ABSTRACT Glass ceramics for bone substitution have been developed derived from the Si02-(A1203)-MgO-Na20-K20-(CaO)-(P205) glass forming system. The concentration of the ion content within the biomaterials could be varried in dependence of the indication. The glass ceramics are multiphase materials, they contain a glassy phase and crystalline phases. Machineable and bioreactive glass ceramics, containing apatite and mica-type crystals, show ion exchange reaction with body fluid. The interface reaction with living bone is limited in a depth of less than 15 ¨m. ESMA- and SIMS-investigations demonstrate the ion exchange and surface diffusion of the biomaterial.