Kaj Fröberg

A structural approach to bone adhering of bioactive glasses

Abstract Some silicate glasses exhibit the property of bonding to bone. In vivo tests show that a layer of silica gel is always formed on the glass surface when the bonding is successful. From a comparison with the silicon chemistry of diatoms and connective tissues it is apparent that silicate chelates form an essential step in the formation and mineralization of hard tissues. The same kind of chelating is also demonstrated for silicate anions in binary melts. It is suggested that in implants, the silica gel formed on the glass surface not only acts as a chelating agent, but also is flexible enough to supply the correct atomic distances required by the crystal structure of bone apatite. The phosphate phase used in most bioactive glasses is suggested to act as a source for a phosphate buffer, which adjusts the surface acidity of the glass implant.

Electrochemically controlled surface morphology and crystallinity in poly(3,4-ethylenedioxythiophene) films

Abstract The degree of crystallinity and surface morphology of poly(3,4-ethylenedioxythiophene) PEDOT, films was tuned by electrochemical synthesis. The films were produced by cyclic voltammetry in TBAPF6–acetonitrile medium. The films were characterized by X-ray diffraction and by scanning electron microscope.

Effect of shading the zirconia framework on biaxial strength and surface microhardness

Objective. Zirconia ceramics for frameworks of fixed partial dentures can be color shaded to better match the shade of veneering porcelain. The aim of this study was to evaluate the effect of color shading the green-stage zirconia ceramic on some mechanical properties. Material and Methods. Zirconia disks (diameter 19 mm, thickness 0.8 mm) were divided into 10 groups of 10 disks each according to the color shade of the zirconia ceramic. The disks were shaded with the same color liquid using either the recommended shading time (3 s) or prolonged shading time (60 s). Nine control disks were tested without color. Composition of the color liquids was determined with EDX analysis. All the disks were sintered at 1500°C and their biaxial flexural strength was measured dry and at room temperature. Surface Vickers microhardness was measured. Data were evaluated using ANOVA analysis. Results. Disks of shade D4 (Vita Classic-scale) revealed the highest strength (1007 MPa) of the shaded disks, but the strength did not differ statistically from that of the control group (1132 MPa). Other color shades had values of A3: 898 MPa, B1: 918 MPa, C4: 885 MPa, and D2: 897 MPa. Prolonging the shading time from 3 s to 60 s lowered the strength even more. Shading time had no effect on microhardness, but there were some differences among the different color shade groups (p<0.05). EDX analysis showed slight differences between compositions of different color liquids. Conclusions. Some variation was found in strength and surface hardness of zirconia that had been color shaded to different shades.

Effect of sintering time on biaxial strength of zirconium dioxide.

OBJECTIVES Aim of this study was to evaluate effect of sintering time on mechanical properties of yttrium partially stabilized zirconia (Y-TZP) (ICE Zirkon, ZirkonZahn, Italy). METHODS Fifty-six zirconia discs were divided into two groups. Discs of the first group were sintered in sintering oven (ZirkonZahn) at 20-1500 degrees C temperature using rise time of 3 h and kept at 1500 degrees C for 2 h. Discs of the second group were sintered at 20-1500 degrees C using rise time of 1h 40 min and kept at 1500 degrees C for 1 h. Half of the discs (n=15) from both groups were thermocycled in distilled water for 20000 cycles (5-55 degrees C). Biaxial flexural strength of the discs (diameter 19.0 mm, thickness 1.6 mm) were measured dry at room temperature. Surface microhardness (VHN) was also measured. X-Ray diffraction analysis was performed to evaluate the ratio of tetragonal to monoclinic phase in thermocycled discs. The data was calculated using Weibull and ANOVA analysis. RESULTS No statistically significant difference (p>0.05) was found between the groups in terms of sintering time or thermocycling. The biaxial flexural strength of the groups varied from 995MPa to 1127MPa. Surface microhardness varied from 1478 to 1532. The relative amount of the monoclinic phase was higher when zirconia was thermocycled and stored in water compared to control discs, which had no monoclinic phase at all. SIGNIFICANCE Variation in the sintering time from 1.6h to 3.0 h did not influence mechanical properties of Y-TZP zirconia.

Durability of Mat Glazes in Hydrochloric Acid Solution

The influence of composition on durability of fast-fired mat raw glazes in hydrochloric acid was studied with several different methods. The appearance of the corroded glazes was classified according to a standardised visual method. The surface composition of the glaze was studied by SEM/EDXA. The crystalline phases in the glaze were identified by XRD. Changes in surface topography on micro-range were observed by AFM, while macro-range related changed were examined by a non-contact optical profiler. The concentration of dissolved ions in the acid solution after the corrosion test was analysed by ICPS. The results indicate that besides chemical composition also phase composition and surface morphology should be taken into account in corrosion studies of mat glazes. Corrosion of both amorphous and crystalline phases could be detected. The proportion of unreacted raw material in the glaze also strongly affected the corrosion behavior.

Structural units in silicate glasses

Abstract When stoichiometric constraints are considered, incorporating three-, four- and six-rings of silica tetrahedra simultaneously into a structure restricts the number of alternatives to two sequences, a cristobalite-like for Na- and a tridymite-like for K- and Cs-silicates. It is suggested that only three- and six-rings are present in Li-silicate structures, which leads partly to clusters of less defined sizes and partly to mono- and disilicate ions. These sequences are supported by voltammetric measurements in melts and give a structural basis for the interpretation of Raman and NMR data of solid glasses.

On the structure of silicate melts

Abstract A striking similarity is obtained between the structure of binary silicate melts and the Qn distribution in the corresponding glasses. The former are deduced from voltammetric measurements, the latter from published Raman and NMR data. A closer analysis of Raman data based on the proposed neutralisation and depolymerisation scheme for anions in melts is therefore suggested.

Melting Behaviour and Surface Structure of Glazes Containing Wollastonite and Dolomite

The influence of wollastonite and dolomite on melting behaviour and crystallization was studied for 25 raw glazes. The melting behaviour was observed by hot-stage microscopy. The glazes were also fired industrially both in a fast-fired gas kiln for floor tiles (50 min) and in a traditional gas kiln for sanitaryware (25 hours). The surface composition and structure of the glazes were studied by SEM/EDXA. The crystalline phases in the glazes were identified by XRD. Main crystalline phases found in the glazes were wollastonite and diopside. Fusibility and surface structure on the raw glazes containing wollastonite and dolomite as raw materials depended both on the total content and the ratio of CaO and MgO in the glaze. Low content of alkaline earths gave incomplete fusion, while high content gave extensive crystallization. The results can be applied to tailor raw glaze compositions for a desired surface structure to be fired at a certain fusion temperature.