Browsing by Author "Höland, Wolfram"

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    Crystallization, microstructure and properties of selected glasses and glass-ceramics in the SiO2-Li2O-ZnO-K2O-P2O5 system
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2002) Clausbruch, Sascha Cramer von; Schweiger, Marcel; Höland, Wolfram; Rheinberger, Volker
    The crystallization behavior of selected glasses in the multicomponent SiO2-Li2O-ZnO-K2O-P2O5 system was investigated using high-temperature X-ray diffraction and differential scanning calorimetry. Proceeding from a dental model glass with the molar composition 63.2 SiO2, 29.1 Li2O, 3.3 ZnO, 2.9 K2O and 1.5 P2O5, 20 glasses were melted, varying the concentrations of the single components systematically. Glass compositions mainly influenced the formations and dissolutions of metastable and stable phases in the temperature range of 480 to 1100 °C. In the majority of the glasses hthium disilicate (Li2Si2O5) precipitated as the main crystal phase during heating, while lithium metasilicate, lithium orthophosphate, cristobalite and quartz crystallized as secondary phases. After a one-step heat treatment microstructures of glass-ceramics and morphologies of Li2Si2O5 crystals were characterized by scanning electron microscopy. With few exceptions glass-ceramics showed a finegrained microstructure with interlocking, rodshaped Li2Si2O5 crystals with 0.5 to 10 µm in length. The corresponding glass-ceramics were processed by a hot-pressing technique to test samples for mechanical and optical measurements. Concentration variations of the base glasses caused bending strengths between 224 and 675 MPa. Within a comparison of translucency according to dental standard BS 5612 contrast ratios between 0.3 and 0.8 were determined.
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    Development of bioactive glass-ceramics
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Apel, Elke; Höland, Wolfram; Rheinberger, Volker
    A bioactive glass-ceramic with rhenanite, NaCaPO₄, was developed in the SiO₂ - Na₂O - CaO - P₂O₅ - F System. Crystallization and microstructure were determined by room temperature X-ray diffraction (RT-XRD) and scanning electron microscopy (SEM) methods. The surface properties of the monolithic material and its surface reactivity were investigated after immersion in simulated body fluid (SBF) for 1 to 10 days. The layer that formed was identified as hydroxyapatite (HA) using surface sensitive analytical methods. Ion exchange processes of Ca²⁺ and phosphate ions were determined. HA formed on the surface of the samples within 48 hours. An open-porous scaffold was prepared using the polymer sponge method. Based on the main results of the investigation, we conclude that rhenanite glass-ceramics possess very good bioactive properties.
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    Effect of ZnO on the crystallization, microstructure, and properties of glass-ceramics in the SiO2-Li2O-ZnO-K2O-P2O5 system
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2001) Clausbruch, Sascha Cramer von; Schweiger, Marcel; Höland, Wolfram; Rheinberger, Volker
    Six glasses in the SiO2-Li2O-ZnO-K2O-P2O5 system were prepared. Starting from a dental glass-ceramic model composition the ZnO content was varied from 0.0 to 8.3 mol% with the molar ratios of the other components being invariant. Crystallization processes of these glasses were investigated using high-temperature X-ray diffraction and differential scanning calorimetry. Crystal phases occurred in the temperature range of 500 to 1050 °C, while the main precipitated phase was lithium disilicate (Li2Si2O5). Lithium metasilicate, lithium orthophosphate, and cristobalite were secondary phases. Morphology and microstructure of the glass-ceramics were studied using scanning electron microscopy. Li2Si2O5 crystals in glass-ceramics had elongated shapes along the c-axis, crystal lengths ranging from 1 to 5 µm and aspect rados between 2 and 5. The lath-shaped Li2Si2O5 crystals were randomly oriented in the volume of the glass-ceramics and were responsible for the good mechanical properties. With increasing ZnO content a decrease of flexural strengths from 520 to 450 MPa was observed. It was concluded that the ZnO variation mainly influenced the translucency of the glass-ceramics. Relating to dental standard contrast ratios between 0.23 and 0.74, method limits of 0 and 1 provided, were determined.
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    Einfluß von Eisenoxiden auf Kristallisationskinetik und Eigenschaften glimmerhaltiger maschinell bearbeitbarer Glaskeramiken Teil 1. Phasentrennung, Keimbildung und Kristallisationskinetik
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1982) Höland, Wolfram; Dung, Nguyen Anh; Heidenreich, Erich; Tkalcec, Emiliya; Vogel, Werner
    Gläser des Systems SiO₂ - Al₂O₃ - MgO - K₂O - F⁻ neigen zur Phasentrennung, die durch den Einbau von Fe²⁺- und Fe³⁺ - Ionen verstärkt wird. Die Zunahme der Phasentrennung fördert Keimbildungs - und Kristallisationsvorgänge in den Gläsern. In Abhängigkeit von der Konzentration der Eisenoxide können durch in situ-Kristallisation infolge einer thermischen Behandlung der Gläser fluorophlogopitähnliche oder biotitähnliche Glimmer zur Ausscheidung gebracht werden. Der Ausscheidung dieser Glimmerkristalle sind die Kristallisation der Primärphase Magnetit und die Bildung verschiedener Spinell-Mischkristalle vorgelagert. Auf Grund der Glimmerausscheidung sind die resultierenden Glaskeramiken maschinell bearbeitbar. Influence of iron oxides on the crystallization kinetics and properties of machinable glass-ceramics containing mica Part 1. Phase separation, nucleation and crystallization kinetics Glasses in the system SiO₂ - Al₂O₃ - MgO - K₂O - F⁻ tend to show phase separation which is increased by incorporation of Fe²⁺ and Fe³⁺ ions. The increase of phase separation favores the phenomena of crystalformation and crystallization in the glasses. In situ crystallization of platelets like fluorophlogopite or biotite can be made out by suitable heat treatment, depending on the iron content. Separation of these mica crystals is preceded by crystallization of primary phase magnetite and of spinel mixed crystals. Because of the production of mica the resultant glass-ceramics are machinable. Influence d'oxydes de fer sur la cinétique de cristallisation et les propriétés de vitrocéramiques usinables renfermant du mica 1ère partie. Séparation de phases, nucléation et cinétique de cristallisation Les verres du système SiO₂ - Al₂O₃ - MgO - K₂O - F⁻ ont une tendance à la séparation de phases qui est renforcée par l'insertion des ions Fe²⁺ et Fe³⁺. La croissanc e de la séparation de phases favorise les processus de nucléation et de cristallisation dans les verres. Suivant la concentration de l'oxyde de fer, des micas de type fluor-phlogopite ou biotite peuvent précipiter par cristallisat ion in situ à la suite d'un traitement thermique des verres. La précipitation de ces cristaux de mica est précédée de la cristallis ation de la phase primaire de magnétite et de la formation de différents cristaux mixtes de spinelle. Les vitrocéramiques obtenues à partir de la précipitation du mica peuvent être usinées.
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    Einfluß von Eisenoxiden auf Kristallisationskinetik und Eigenschaften glimmerhaltiger maschinell bearbeitbarer Glaskeramiken Teil 2). Ferrimagnetische Eigenschaften
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1982) Höland, Wolfram; Dung, Nguyen Anh; Heidenreich, Erich; Tkalcec, Emiliya; Vogel, Werner
    In SiO₂-Al₂O₃-MgO-K₂O-F⁻-haltigen Gläsern können durch Zusätze von FeO und Fe₂O₃ und thermische Nachbehandlung der Gläser Glimmer- und Spinellkristalle zur Ausscheidung gebracht werden. An zahlreichen Beispielen wird gezeigt, wie sich die Zusammensetzung der Spinellkristalle in Abhängigkeit von den experimentellen Bedingungen ändert. Die durch thermische Nachbehandlung der Gläser erzeugten magnetithaltigen Glaskeramiken besitzen ferrimagnetische Eigenschaften. Es ist aber auch möglich, solche Glaskeramiken herzustellen, die unter Beibehaltung der maschinellen Bearbeitbarkeit Ferrimagnetismus zeigen. Letzteres wird durch die Kristallisation von Fe^(III)(MgFe^(III))O₄-Spinellkristallen erreicht. Experimentell ermittelte Kennwerte für ferrimagnetische Eigenschaften werden für die resultierenden maschinell bearbeitbaren Glaskeramiken angegeben. Influence of iron oxides on the crystallization kinetics and properties of machinable glass-ceramics containing mica Part 2. Ferrimagnetic properties Addition of FeO and Fe₂O₃ to SiO₂-Al₂O₃-MgO-K₂O-F⁻-Fglasses causes precipitation of mica and spinel crystals on heat treatment. Numerous examples are used to show the composition of the spinel crystals depends on the experimental conditions. Glass-ceramics containing magnetite, obtained by thermal treatment, have ferrimagnetic properties and it is also possible to produce machinable glass-ceramics which also retain ferrimagnetic properties. The latter are produced by crystallization of Fe^(III)(MgFe^(III))O₄ spinel. Measured values of the ferrimagnetic properties of the resulting machinable glass-ceramics are given. Influence d'oxydes de fer sur la cinétique de cristallisation et les propriétés de vitrocéramiques usinables renfermant du mica 2e partie. Propriétés ferrimagnétiques II est possible de faire précipiter des micas et des cristaux de spinelle dans les verres de SiO₂-Al₂O₃-MgO-K₂O-F⁻ par addition de FeO et Fe₂O₃ et traitement thermique. On montre sur de nombreux exemples comment varie la composition des cristaux de spinelle en fonction des conditions expérimentales. Les vitrocéramiques renfermant de la magnétite obtenues par traitement thermique des verres possèdent des propriétés ferrimagnétiques. Mais il est également possible de fabriquer des vitrocéramiques qui, tout en conservant leur usinabilité, présentent un ferrimagnétisme. Ge dernier est obtenu par la formation de cristaux de spinelle de Fe^(III)(MgFe^(III))O₄. Les valeurs expérimentales des propriétés ferrimagnétiques sont indiquées pour les vitrocéramiques usinables obtenues.
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    Fundamental research on twofold phase formation of apatite solid-solutions and leucite in glass-ceramics
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) van 't Hoen, Christian; Höland, Wolfram; Rheinberger, Volker
    In this study the phase formation of apatites in the multi-component SiO₂-Al₂O₃-Na₂O-K₂O-GaO/SrO-P₂O₅-F system was investigated. Based on a special composition GaO was partially and completely substituted by SrO. Room and high temperature X-ray diffraction (RT- and HT-XRD) and scanning electron microscopy (SEM) were used to characterize the phase formation. The results of this study showed a formation of two different apatite solid-solutions, Sr_(7.3)Ca_(2.7)(PO₄)₆F₂ and Sr₆Ca₄(PO₄)₆F₂ and Sr-apatite Sr₅(PO₄)₃F. Leucite formation is based on surface crystallization. The conclusion is a twofold volume and surface nucleation and crystallization mechanism.
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    Glass development and controlled crystallization in the SiO₂ - Li₂O - ZrO₂ - P₂O₅ System
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Höland, Wolfram; Frank, Martin; Schweiger, Marcel; Wegner, Susanne; Rheinberger, Volker
    The objective of this investigation was to analyze glass formation and crystaUization in t h e SiO₂ - Li₂O- ZrO₂ - P₂O₅ System for the development of high-strength glass-ceramics produced with glass powder. In the course of this study, it was found that the base glass or the semicrystalline glass-ceramic could be pressed to form glass-ceramic final products. The analysis of glass formation demonstrated that in a relatively large composition range, up to almost 30 wt%, ZrO₂ could be incorporated into the base glass and increased the glass forming tendency. Other additives were also tested. The presence of ZrO₂ crystals, ZrSiO₄ crystals and lithium phosphate crystals as well as other secondary phases in t he microstructure following heat treatment at approximately 1000 °C was estabhshed in SEM and XRD examinations. This glass-ceramic possesses fiexural strengths of 280 MPa. Translucency was observed in 0.5 mm thick layers. Growth rates of the main crystal phases were determined with cast monolithic samples in a semiquantitative kinetic evaluation of phase development. In contrast to the kinetics of mica crystal growth processes in machinable glass-ceramics, no time lags were observed.
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    Glass-ceramics and biomaterials with tailor-made properties
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Höland, Wolfram; Rheinberger, Volker; Apel, Elke
    Based on the fundamental theories of materials development by Professor Kreidl, the developments of the authors are presented four types of glass-ceramics as biomaterials used in dentistry. These materials have been developed since the Norbert Kreidl Symposium in 1994. They are leucite glass-ceramics with new properties, as well as high-strength glass-ceramics and materials with particular optical brilliance. Furthermore, new approaches using surface-active materials are discussed.
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    Microstructure formation and surface properties of a rhenanite-type glass-ceramic containing 6.0 wt% P2O5
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Höland, Marlies; Dommann, Alex; Höland, Wolfram; Apel, Elke; Rheinberger, Volker
    The aim of this report was to characterize the microstructure formation of a rhenanite, NaCaPO4, glass-ceramic and to determine its surface properties. The composition of the material was (in wt%) 58.0 SiO2, 6.0 P2O5, 22.8 Na2O, 12.9 CaO, and 0.3 F. Nucleation and crystallization of the monolithic base glass was carried out at temperatures between 650 and 1000°C for one hour. To characterize the different microstructures of the glass-ceramics using scanning electron microscopy (SEM), a special sample with phosphoric acid was prepared. The control of microstructure formation resulted in the precipitation of isolated α-rhenanite crystals with a crystal size of 40 nm up to 1 μm and a crystal number density of 20 to more than 2000 particles per 100 μm2. The α-phase transformed into the β-phase at approximately 690 °C. The surface properties were determined by soaking the specimens in simulated body fluid for up to 10 d. In the process, the glass-ceramics exhibited a high surface activity. Morphological investigations after soaking showed ball-shaped hydroxyapatite-type crystals consisting of two half shells. The authors concluded that rhenanite crystals acted as heterogeneous nuclei for hydroxyapatite on the surface of the bioactive glass-ceramics. Therefore, this material was assumed to have the ability to bond to living bone.