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Organisationseinheit der BAM
Stable crack growth was measured for nominal dry and water-bearing (6 wt%) soda-lime silicate glasses in double cantilever beam geometry and combined with DMA studies on the effects of dissolved water on internal friction and glass transition, respectively. In vacuum, a decreased slope of logarithmic crack growth velocity versus stress intensity factor is evident for the hydrous glass in line with an increase of b-relaxation intensity indicating more energy Dissipation during fracture. Further, inert crack growth in hydrous glass is found to be divided into sections of different slope, which indicates different water related crack propagation mechanism. In ambient air, a largely extended region II is observed for the hydrous glass, which indicates that crack growth is more sensitive to ambient water.
We measured and collected literature data for the crystal growth rate, u(T), of µ-cordierite (2MgO · 2Al2O3 · 5SiO2) and diopside (CaO · MgO · 2SiO2) in their isochemical glass forming melts. The data cover exceptionally wide temperature ranges, i.e. 8001350 °C for cordierite and 7501378 °C for diopside. The maximum of u(T) occurs at about 1250 °C for both systems. A smooth shoulder is observed around 970 °C for µ-cordierite. Based on measured and collected viscosity data, we fitted u(T) using standard crystal growth models. For diopside, the experimental u(T) fits well to the 2D surface nucleation model and also to the screw dislocation growth mechanism. However, the screw dislocation model yields parameters of more significant physical meaning. For cordierite, these two models also describe the experimental growth rates. However, the best fittings of u(T) including the observed shoulder, were attained for a combined mechanism, assuming that the melt/crystal interface growing from screw dislocations is additionally roughened by superimposed 2D surface nucleation at large undercoolings, starting at a temperature around the shoulder. The good fittings indicate that viscosity can be used to assess the transport mechanism that determines crystal growth in these two systems, from the melting point Tm down to about Tg, with no sign of a breakdown of the StokesEinstein/Eyring equation.
Crystallization behavior in different atmospheres (air, Ar, and 7% H2/Ar) of lithium iron phosphate glass (33Li2O33Fe2O31Nb2O5–33P2O5 (LFNP)) powders with different sizes of 2–1000 µm was examined. The crystallization peak temperature (Tp) in Ar and 7% H2/Ar decreased with decreasing the particle size of glass powders, but the value of Tp in air was independent of particle size. The crystallized glass obtained by heating to Tp showed the formation of the α-Li3Fe2(PO4)3 and LiFePO4 crystalline phases. Fe2O3 crystals were formed only in the inside of crystallized glass plates in the heating in air. The crystallization of LiFePO4 was largely enhanced in the particle size of <2 µm during the heating in Ar and 7% H2/Ar atmospheres. The main crystallization mechanism in LFNP glass was found to be surface crystallization. Significant shrinkages were observed for glass compacts (pellets) in the heating in 7% H2/Ar. These results suggest that controlling particle sizes and atmospheres enables the design the morphology of LiFePO4 crystals in LFNP glass.
The effect of structural water on density, elastic constants and microhardness of water-bearing soda-lime-silica glasses of up to 21.5 mol% total water is studied. It is found that the Poisson ratio and the water content are positively correlated, while density and the elastic moduli decrease with increasing water content. Vickers hardness decreases by approximately 27% from the dry to the most hydrous glass. For water fractions <3 mol%, the dependencies are non-linear reflecting the non-linear change in the concentrations of OH and H2O molecules dissolved, whereas for water fractions >3 mol% linear dependencies are found. To distinguish the effect of structural water and environmental water, indentations were performed in toluene, nitrogen gas and air. Timedependent softening was evident for testing dry glasses in humid atmospheres as well as for tests of hydrous glasses in dry atmospheres. This indicates that the response times of dissolved water species are effectively equal in both scenarios.
Electric contacts based on silver-glass dispersions are key components in optoelectronic microsystems and control modules for medical, information & communication and energy technology in our networked society. Driven by the complexity of modern production processes and ever shorter time-to-market requirements, the fast and specific development of tailored silver-glass dispersions has become a bottleneck of technology development. Nevertheless, the underlying mechanisms of silver dissolution, transport, and reprecipitation, and the resulting micro structure evolution during firing are poorly understood. The broad literature on the precipitation of colloidal silver particles and the related processes of silver dissolution and diffusion mostly refer to very small volume fractions of silver. Transferring these results to the sintering of glass-containing silver dispersions, is therefore highly questionable. In this case, silver dissolution, electrical contact between silver particles, transport and reprecipitation take place under special conditions. This includes short diffusion lengths (particle size < 10 μm), the presence of three-phase contacts silver - glass - sintering atmosphere, as well as silver reprecipitation at the sintering contacts as the driving force of silver transport. Here, a dynamic balance of the silver concentration can be expected to result from the ratio between silver dissolution and reprecipitation. The aim of the project is to gain basic insight into the mechanisms of dissolution, transport and reprecipitation of silver in sintering silver glass dispersions. In this context, the main focus is on gaining basic knowledge about the dissolution of metallic silver in low melting oxide glasses as the limiting factor of the sintering of silver-glass composites. In particular, we will strive to gain insight into the effect of the oxygen content of the sintering atmosphere, of the oxygen dissolved in the silver particles, of silver oxide on the surface of the silver powder, of the electric contact between the silver particles, as well as the basicity of the glass. Furthermore, we strive for insights into the silver mobility and the silver concentration that can be attained (silver solubility) in oxide glasses with a low melting point. Summing up all these aspects, a closed explanatory model for silver dissolution, transport and reprecipitation during the sintering of glass silver dispersions will be introduced.
Electric contacts based on silver-glass dispersions are key components in optoelectronic microsystems and control modules for medical, information & communication and energy technology in our networked society. Driven by the complexity of modern production processes and ever shorter time-to-market requirements, the fast and specific development of tailored silver-glass dispersions has become a bottleneck of technology development. Nevertheless, the underlying mechanisms of silver dissolution, transport, and reprecipitation, and the resulting micro structure evolution during firing are poorly understood. The broad literature on the precipitation of colloidal silver particles and the related processes of silver dissolution and diffusion mostly refer to very small volume fractions of silver. Transferring these results to the sintering of glass-containing silver dispersions, is therefore highly questionable. In this case, silver dissolution, electrical contact between silver particles, transport and reprecipitation take place under special conditions. This includes short diffusion lengths (particle size < 10 μm), the presence of three-phase contacts silver - glass - sintering atmosphere, as well as silver reprecipitation at the sintering contacts as the driving force of silver transport. Here, a dynamic balance of the silver concentration can be expected to result from the ratio between silver dissolution and reprecipitation. The aim of the project is to gain basic insight into the mechanisms of dissolution, transport and reprecipitation of silver in sintering silver glass dispersions. In this context, the main focus is on gaining basic knowledge about the dissolution of metallic silver in low melting oxide glasses as the limiting factor of the sintering of silver-glass composites. In particular, we will strive to gain insight into the effect of the oxygen content of the sintering atmosphere, of the oxygen dissolved in the silver particles, of silver oxide on the surface of the silver powder, of the electric contact between the silver particles, as well as the basicity of the glass. Furthermore, we strive for insights into the silver mobility and the silver concentration that can be attained (silver solubility) in oxide glasses with a low melting point. Summing up all these aspects, a closed explanatory model for silver dissolution, transport and reprecipitation during the sintering of glass silver dispersions will be introduced.
The sintering of Low Temperature Co-fired Ceramics prepared from alumoborosilicate
glass- and Al2O3 powders of similar small particle size was studied by dilatometry, heating microscopy,
microstructure analysis, glass- and effective viscosity measurements. The steric effect of
Al3O3 inclusions was studied using a gnon-reactiveh model composite. With increasing Al3O3 volume
fraction (Φ ≤ 0.45), sintering decelerates and its final stage shifts to higher temperature. The
attainable shrinkage is reduced as Al2O3 particle clusters bearing residual pores become more frequent.
The kinetics of sintering could be described formally superposing the weighed contributions
of differentially sized and randomly composed glass-crystal particle clusters and assuming a sintering
rate controlled by the effective matrix viscosity, which increases with Φ and with progressive
wetting of Al2O3 particles during densification. The "reactive" model composite shows significant
dissolution of Al2O3 into the glass, which has two opposed effects on sintering: reducing Φ and increasing
glass viscosity. For the present case (Φ = 0.25), the latter effect dominates and sintering is
retarded by Al2O3 dissolution. Crystallization of wollastonite starts after full densification. Dissolution
of Al2O3 was found to promote the subsequent growth of anorthite.
Two fluorescent dyes were incorporated into sol-gel derived SiO2 matrices. The dye was added to SiO2 precursors of different degrees of pre-condensation and the spectroscopic properties of the immobilized dye were measured at various aging and drying stages of the resulting gels. The significant influence of the processing parameters on the spectroscopic properties is manifested in the relative intensity of a second red shifted emission band (550560 nm), which was observed besides the typical coumarin emission band (495 nm). The appearance of this long wavelength emission might be attributed to dye aggregation or to other reactions with the ambient matrix forced by micro porosity phenomena.
Evidence is provided that the tridymite component observed in the X-ray diffraction patterns of some sewage sludge ashes (SSAs) should not be interpreted as the tridymite modification of SiO2 but as the tridymite form of AlPO4. This proof is based on a combined X-ray Powder Diffraction (XRD), X-ray fluorescence (XRF) and Mossbauer spectroscopy investigation of two SSAs produced at two fluidized bed incineration facilities, located in different municipalities and operated differently. The structural and chemical characterization was carried out on the 'as received' SSA samples as well as on the residues of these two SSAs pretreated by leaching in citric acid. In addition, direct proof is presented that the tridymite form of AlPO4 does crystallize from X-ray amorphous precursors under conditions that mimic the huge heating rate and short retention time (just seconds at T ≈ 850 °C) typical for fluidized bed incinerators.
Barium silicate glass powders 4 h milled in CO2 and Ar and sintered in air are studied with microscopy, total carbon analysis, differential thermal Analysis (DTA), vacuum hot extraction mass spectroscopy (VHE-MS), Fourier-transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary-ion mass spectrometry (TOF-SIMS). Intensive foaming of powder compacts is evident, and VHE studies prove that foaming is predominantly caused by carbonaceous species for both milling gases. DTA Shows that the decomposition of BaCO3 particles mix-milled with glass powders occurs at similar temperatures as foaming of compacts. However, no carbonate at the glass surface could be detected by FTIR spectroscopy, XPS, and TOF-SIMS after heating to the temperature of sintering. Instead, CO2 molecules unable to rotate identified by FTIR spectroscopy after milling, probably trapped by mechanical dissolution into the glass bulk. Such a mechanism or microencapsulation in cracks and particle aggregates can explain the contribution of Ar to foaming after intense milling in Ar atmosphere. The amount of CO2 molecules and Ar, however, cannot fully explain the extent of foaming. Carbonates mechanically dissolved beneath the surface or encapsulated in cracks and micropores of particle aggregates are therefore probably the major foaming source.
Glasses stand out by their wide and continuously tunable chemical composition and large variety of unique shaping techniques making them a key component of modern high technologies. Glass development, however, is still often too cost-, time- and energy-intensive. The use of robotic melting systems embedded in an ontology-based digital environment is intended to overcome these problems in future. As part of the German research initiative MaterialDigital, the joint project GlasDigital takes first steps in this direction. The project consortium involves the Fraunhofer ISC in Würzburg, the Friedrich Schiller University Jena (OSIM), the Clausthal University of Technology (INW), and the Federal Institute for Materials Research and Testing (BAM, Division Glasses) and aims to combine all main basic components required for accelerated data driven glass development. For this purpose, a robotic high throughput glass melting system is equipped with novel inline sensors for process monitoring, machine learning (ML)-based, adaptive algorithms for process monitoring and optimization, novel tools for high throughput glass analysis and ML-based algorithms for glass design, including software tools for data mining as well as property and process modelling. The talk gives an overview how all these tools are interconnected and illustrates their usability with some examples.
lasses stand out by their wide and continuously tunable chemical composition and large variety of unique shaping techniques making them a key component of modern high technologies. Glass development, however, is still often too cost-, time- and energy-intensive. The use of robotic melting systems embedded in an ontology-based digital environment is intended to overcome these problems in future. As part of the German research initiative MaterialDigital, the joint project GlasDigital takes first steps in this direction. The project consortium involves the Fraunhofer ISC in Würzburg, the Friedrich Schiller University Jena (OSIM), the Clausthal University of Technology (INW), and the Federal Institute for Materials Research and Testing (BAM, Division Glasses) and aims to combine all main basic components required for accelerated data driven glass development. For this purpose, a robotic high throughput glass melting system is equipped with novel inline sensors for process monitoring, machine learning (ML)-based, adaptive algorithms for process monitoring and optimization, novel tools for high throughput glass analysis and ML-based algorithms for glass design, including software tools for data mining as well as property and process modelling. The talk gives an overview how all these tools are interconnected and illustrates their usability with some examples.
Glasig-kristalline Werkstoffe für Schlüsseltechnologien - Prozessbegleitende Prüfung und Simulation
(2017)
Eigenschaftsprofile und Kennwertstreuungen keramischer und glaskeramischer Komponenten und Bauteile werden durch ihren Herstellungsprozess wesentlich mitbestimmt. Prozessbegleitende Prüf- und Simulationsmethoden gewinnen so wachsenden Einfluss auf die Erschließung neuer Applikationsfelder dieser Werkstoffe. Eine wichtige Rol¬le spielen hierbei oft thermokinetische Prozesse, die u. a. Wärmetransport- und Diffusionsvorgänge, Phasengrenzflächenreaktionen, das rheologische Verhalten heterogener Systeme sowie deren Gefügeevolution beim Sintern umfassen. Ziel des Vortrages ist es, diesen Trend anhand ausgewählter Bei-spiele aus der Arbeit des Fachbereichs Glas der BAM zu illustrieren.
Glass powders are promising candidates for manufacturing a broad diversity of sintered materials like sintered ¬glass-ceramics, glass matrix composites or glass bonded ceramics with tailored mechanical, thermal, electrical and optical properties and complex shape. Its wide and precise adjustability makes this class of materials a key component for advanced technologies. Processing of glass or composite powders often allow even more flexibility in materials design. At the same time, however, processing can have substantial effects on the glass powder surface and sinterability. Thus, mechanical damage and surface contamination can strongly enhance surface crystallization, which may retard or even fully prevent densification. Whereas sintering and concurrent crystallization have been widely studied, partially as cooperative effort of the TC7 of the ICG, and although glass powder sintering is predominantly applied for glasses of low crystallization tendency, sintering is also limited by gas bubble formation or foaming. The latter phenomenon is much less understood and can occur even for slow crystallizing glass powders. The lecture illustrates possible consequences of glass powder processing on glass sintering, crystallization and foaming.
Glass powders are promising candidates for manufacturing a broad diversity of sintered materials like sintered glass-ceramics, glass matrix composites or glass bonded ceramics with tailored mechanical, thermal, electrical and optical properties and complex shape. Its wide and precise adjustability makes this class of materials a key component for advanced technologies. Processing of glass or composite powders often allow even more flexibility in materials design. At the same time, however, processing can have substantial effects on the glass powder surface and sinterability. Thus, mechanical damage and surface contamination can strongly enhance surface crystallization, which may retard or even fully prevent densification. Whereas sintering and concurrent crystallization have been widely studied, partially as cooperative effort of the TC7 of the ICG, and although glass powder sintering is predominantly applied for glasses of low crystallization tendency, sintering is also limited by gas bubble formation or foaming. The latter phenomenon is much less understood and can occur even for slow crystallizing glass powders. The lecture illustrates possible consequences of glass powder processing on glass sintering, crystallization and foaming.
The viscosity of silica glasses with different water contents was measured by penetration of sapphire microspheres in the range from 1012-1014·7 Pas at ambient pressure. Commercial silica glasses were used together with hydrous silica glasses, which were prepared by melting glass powder plus water in an internally heated pressure vessel at 2-3 kbar and 1350-1450°C. The temperature dependence of the viscosity of silica glasses with total water contents Cw of 5·4×10-4, 7·0×10-4, 1·00×10-2, and 1·55×10-2(Cw in mass fractions) can be described by Arrhenius equations. From the results, the linear dependence of the T12 isokom (K) with the logarithm of the water content was determined as T12=192-409 logCw. The analysis of the compositional dependence of the T12 isokom in the H2O-Na2O-SiO2 system reveals a temperature depression of up to 200 K for mixed water- and sodium-bearing glasses compared to H2O-SiO2 and Na2O-SiO2 glasses with same molar silica content. From these findings we conclude that protons may contribute significantly to the mixed alkali effect in glasses.
Gläser zeichnen sich durch eine breite und kontinuierlich abstimmbare chemische Zusammensetzung sowie einzigartige Formgebungstechniken aus, was sie oft zur Schlüsselkomponente moderner Hochtechnologien macht. Die Glasentwicklung ist jedoch oft noch zu kosten-, zeit- und energieintensiv. Der Einsatz von robotergestützten Schmelzsystemen, eingebettet in eine Ontologie-basierte digitale Umgebung, soll diese Probleme in Zukunft überwinden. Im Rahmen der BMBF Forschungsinitiative MaterialDigital unternimmt das Verbundprojekt GlasDigital „Datengetriebener Workflow für die beschleunigte Entwicklung von Glas“ erste Schritte in diese Richtung. Das Projektkonsortium, an dem das Fraunhofer ISC in Würzburg, die Friedrich-Schiller-Universität Jena (OSIM), die Technische Universität Clausthal (INW) und die Bundesanstalt für Materialforschung und -prüfung (BAM, Fachgruppe Glas) beteiligt sind, will alle wesentlichen Basiskomponenten für eine beschleunigte datengetriebene Glasentwicklung zusammenführen. Zu diesem Zweck wird ein robotergestütztes Hochdurchsatz-Glasschmelzsystem mit neuartigen Inline-Sensoren zur Prozessüberwachung, auf maschinellem Lernen (ML) basierenden adaptiven Algorithmen zur Prozessüberwachung und -optimierung, neuartigen Werkzeugen für die Hochdurchsatz-Glasanalyse sowie ML-basierten Algorithmen zum Glasdesign, Data Mining sowie Eigenschafts- und Prozessmodellierung ausgestattet. Der Vortrag gibt einen Überblick darüber, wie all diese Komponenten miteinander verzahnt sind, und veranschaulicht ihre Nutzbarkeit anhand einiger Beispiele.
Advanced methods for 3D green density characterization like computed tomography and 3D FE sinter modeling can be utilized for increasing the reliability of sintered components. The experimental in situ observation of sintering, however, is currently restricted to silhouette methods, i.e. heating microscopy. For complex shaped samples, in situ shape screening during shrinkage would allow much better validation of 3D sinter simulation models. Further, by revealing temporary sinter warpage, 3D high-temperature shape screening allows to locate potential defects of complex sintered components. Against this background, BAM developed a testing device for in situ 3D high-temperature shape screening for ceramic and glass-ceramic tapes up to 1000°C [1-3]. Current work is focused on dropping this restriction in sample shape and temperature. The poster illustrates the current state of this work and possible applications of the method e.g. in detecting sinter warpage of metallized glass-ceramic LTCC tapes.
Advanced ceramics are promising key components for microsystems
engineering, communication Technology and medical engineering.
Driven by steadiiy increasing demands on dimensional accuracy of
components and Integration density, sintering has to be controlled at
an unprecedented degree of precision.
Being most crucial for components of complex shape, graded or heterogeneous-composed parts like LTCC multilayers for microsystems, precise control of sintering has a decisive influence on the dimensional accuracy, mechanical integrity and reliability of sintered components.
Thus, permanent or temporary shape distortions or warping during sintering may result from spatially heterogeneous microstructure and
temperature distribution, e.g. during the co-firing process of green
multilayer Stacks printed with metallization and other functional pastes.
Whereas permanent warping can be easily measured after sintering, temporary warping during firing is more difficult to measure. Nonetheless, this effect may cause latent failures later, which often limit the applicability of ceramic components.
Hochleistungssinterwerkstoffe spielen eine wachsende Rolle in derzeitigen Schlüsseltechnologien wie der Mikrosystem-, Informations-, Kommunikations- und Medizintechnik.
Dabei steigen die Anforderungen an die präzise Steuerung der Sinterung. Besonders für komplexe, gradierte oder heterogen zusammengesetzte Formkörper wie zum Beispiel keramische LTCC-Multilayer für die Mikrosystemtechnik hat die exakte Beherrschung dieses Prozessschrittes wesentlichen Einfluss auf die Maßhaltigkeit, mechanische Integrität und Zuverlässigkeit der gesinterten Bauteile. Bedingt durch die Heterogenität der mehrlagigen und mit Leit- und anderen Funktionspasten bedruckten Sinterkörper hinsichtlich ihrer sinterphysikalischen oder thermischen Eigenschaften können bleibende
oder temporäre Verwerfungen beim Schrumpfungsprozess auftreten, wobei letztere unter Umständen Ursache latenter Fehler im späteren Bauteil sind.
Es wurde ein Gerät zur In-situ-Kontrolle des Sinterns keramischer Bauteile mit Hilfe der Hochtemperatur-Lasertriangulation aufgebaut. Durch Rotation der Probe und gleichzeitiger Positionierung des Laserabstandssensors erfolgt die dreidimensionale Erfassung der Topografie der Probenoberfläche. Derzeit können flache Proben mit den Maßen < 20 cm x 20 cm x 1 cm bis 1000 °C untersucht werden. Die örtliche Wiederholpräzision des verwendeten Lasersensors beträgt 10 µm bei 20 °C und 15 µm bei 1000 °C. Die lineare Positioniergenauigkeit des Sensors liegt bei 1 µm, die Winkelauflösung der Drehung des Probentellers beträgt 0,0025 °. Daten für ein 3D-Oberflächenprofil werden in etwa 2 bis 3 Minuten erzeugt. Spezielle Linienprofile erhält man bei einer Messzeit von wenigen Sekunden.