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Eingeladener Vortrag
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The effect of hydration on the kinetic fragility of soda-lime-silica glasses was investigated by viscometry in the glass transition range. Water-bearing glasses were prepared from industrial float glass (FG) and a ternary model glass (NCS = 16Na2O 10CaO 74SiO2 in mol%) by bubbling steam through the melt at 1480 °C and up to 7 bar. Additionally, a sodium borosilicate glass (NBS = 16Na2O 10B2O3 74SiO2 in mol%) was hydrated under equal conditions. As detected by infrared spectroscopy water dissolves in the glasses exclusively as OH-groups. The hydration resulted in a total water content CW up to ~ 0.2 wt% for FG, NCS and NBS glasses. Kinetic fragility, expressed by the steepness index m, was determined from the temperature dependence of η at the glass transition. Viscosity data from previous studies on hydrous float glasses (CW > 1 wt%) were surveyed together with literature data on the (H2O)Na2OCaOSiO2, (H2O)Na2OSiO2 and (H2O)SiO2 systems to expand the range of water concentration and bulk composition. We could demonstrate that m decreases for all glasses although water is dissolved as OH and should depolymerize the network. An empirical equation of the general type m = a - b logCW where a, b are fitting parameters, enables m to be predicted, for each glass series as function of the water content CW. The enlarged data base shows that the parameter B of the Arrhenius viscosity-temperature relation decreases much stronger than the isokom temperature at the glass transition.
We studied sintering of LTCC-type glass matrix composites (GMCs) consisting of small glass and alumina particles of equal size. Primarily, crystals act as rigid inclusions, decelerating the densification rate. In later stages, they also dissolve, partially increasing the viscosity. Release of alumina finally induces crystallization of alumosilicates, which enables post-firing stability. To study both effects, two model GMCs were prepared: an α-Al2O3 + barium alumoborosilicate glass (BABS)GMC, which shows neither significant dissolution nor crystallization, and an α-Al2O3 + calcium alumoborosilicate glass (CABS)GMC, which dissolves readily and promotes crystallization. The kinetics of shrinkage for both GMC were modeled by utilizing Frenkel theory for the early stage and MackenzieShuttleworth theory for the late stage, assuming that sintering is superimposed by the weighted contributions of triparticle glasscrystal clusters, their random occurrence (ideal mixing), and a shrinkage rate controlled by the GMC effective viscosity. In agreement with modeling, the experimental results showed that the shrinkage rate of BABSGMC decreases progressively for crystal volume fractions Φ > 0.15. The attainable shrinkage is reduced by up to 8% for Φ = 0.45. For the CABSGMC with Φ = 0.25, a reduction of Φ to 0.20 was evident due to partial α-Al2O3 dissolution. This effect was found able to increase the sintering temperature by ~5060 K.
Inconel 718 is a precipitation strengthened, nickel-based super alloy of interest for the Additive Manufacturing (AM) of low volume, complex parts to reduce production time and cost compared to conventional subtractive processes. The AM process involves repeated rapid melting, solidification and reheating, which exposes the material to non-equilibrium conditions that affect elemental segregation and the subsequent formation of solidification phases, either beneficial or detrimental. These variations are difficult to characterize due to the small length scale within the micron sized melt pool. To understand how the non-equilibrium conditions affect the initial solidification phases and their critical temperatures, a multi-length scale, multi modal approach has been taken to evaluate various methods for identifying the initial phases formed in the as-built Inconel 718 produced by laser-powder bed fusion (L-PBF) additive manufacturing (AM). Using a range of characterization tools from the bulk differential thermal analysis (DTA) and x-ray diffraction (XRD) to spatially resolved images using a variety of electron microscopy tools, a better understanding is obtained of how these minor phases can be properly identified regarding the amount and size, morphology and distribution. Using the most promising characterization techniques for investigation of the as-built specimens, those techniques were used to evaluate the specimens after various heat treatments. During the sequence of heat treatments, the initial as-built dendritic structures recrystallized into well-defined grains whose size was dependent on the temperature. Although the resulting strength was similar in all heat treated specimens, the elongation increased as the grain size was refined due to differences in the precipitated phase distribution and morphology.
The crystallization of 11BaO-25CaO-64SiO2 mol% glass powders and related effects of glass powder milling have been studied by X-ray diffraction (XRD), light and scanning electron microscopy (SEM) and differential thermal analysis (DTA). Glass powders were made by ZrO2 crushing with subsequent sieving or sedimentation or alternatively made by milling with agate, corundum and tungsten carbide. Although surface crystallization was detectable during late sintering, all powders fully sintered. Wollastonite was found as primary crystal phase followed by cristobalite and sanbornite precipitation. The latter crystallization steps caused a second DTA-peak for fine powders. DTA-peak temperatures shifted to lower temperature with decreasing particle size in any case. No significant effects of milling materials on DTA-peak temperatures were evident. As an exception, however, milling in agate caused strongly decreased temperatures of the second DTA-peak. This observation can be explained by the progressive mechanical damaging, which results from the required prolonged milling time with agate due to its small materials density, and the fact that diamond made scratches did promote surface crystallization of cristobalite. The present study thus shows that even for glass powders with excellent sinterability, milling can affect microstructure evolution.
The crystallization proceeds by the advance of the crystal faces into the disordered phase at the expense of the material excess, the supersaturation. Using a conservation constraint for the transformation ratio α∈[0,1] as complementing the rescaled supersaturation to 1 and a kinetic law for the normal growth velocity as function of the supersaturation raised to power g, the growth order, we derive an equation for the rate of transformation dα/dt. We integrate it for the six combinations of the three spatial dimensions D = 1, 2, 3 and the two canonical values of g = 1, 2 towards obtaining expressions for αDg. The same equation, with g = 1 and D = n (n is the so called Avrami exponent) is obtained when taking only the linear in α term from the Taylor’s expansion around α = 0 of the model equation of Johnson-Mehl-Avrami-Kolmogorov (JMAK). We verify our model by fitting datasets of α21 and α31 (from α = 0 to αupper = 0.999) with JMAK to obtain from the fit n = 1.725, 2.43, resp. We show
further how the values of n depend on the value of αupper to which the fit is performed starting always from 0. Towards building a validation protocol, we start with validating α21 with published results.
This paper reports the first successful synthesis and the structural characterization of nanocrystalline and stacking-disordered β-cristobalite AlPO4 that is chemically stabilized down to room temperature and free of crystalline impurity phases. Several batches of the title compound were synthesized and thoroughly characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy mapping in SEM, solid-state 31P nuclear magnetic resonance (31P-NMR) spectroscopy including the TRAPDOR method, differential thermal analysis (DTA), gas-sorption methods, optical Emission spectroscopy, X-ray fluorescence spectroscopy, and ion chromatography. Parameters that are critical for the synthesis were identified and optimized. The synthesis procedure yields reproducible results and is well documented. A high-quality XRD pattern of the title compound is presented, which was collected with monochromatic copper radiation at room temperature in a wide 2θ range of 5°–100°.
The fundamental processes of nucleation and crystallization are widely observed in systems relevant to material synthesis and biomineralization; yet most often, their mechanism remains unclear. In this study, we unravel the discrete stages of nucleation and crystallization of Fe3(PO4)2·8H2O (vivianite). We experimentally monitored the formation and transformation from ions to solid products by employing correlated, time-resolved in situ and ex situ approaches. We show that vivianite crystallization occurs in distinct stages via a transient amorphous precursor phase. The metastable amorphous ferrous phosphate (AFEP) intermediate could be isolated and stabilized. We resolved the differences in bonding environments, structure, and symmetric changes of the Fe site during the transformation of AFEP to crystalline vivianite through synchrotron X-ray absorption spectroscopy at the Fe K-edge. This intermediate AFEP phase has a lower water content and less distorted local symmetry, compared to the crystalline end product vivianite. Our combined results indicate that a nonclassical, hydration-induced nucleation and transformation driven by the incorporation and rearrangement of water molecules and ions (Fe2+ and PO4 3−) within the AFEP is the dominating mechanism of vivianite formation at moderately high to low vivianite supersaturations (saturation index ≤ 10.19). We offer fundamental insights into the aqueous, amorphous-to-crystalline transformations in the Fe2+−PO4 system and highlight the different attributes of the AFEP, compared to its crystalline counterpart.
Up to now, oriented surface crystallization phenomena are discussed controversially, and related studies are restricted to few glasses. The vast majority of previous work does not consider possible effects of surface preparation and surrounding atmosphere. Moreover, very few observations of surface crystal orientation were made on separately grown crystals.
The aim of our project is to advance the basic understanding of oriented surface crystallization, e.g. whether preferred orientation of surface crystals results from oriented nucleation or reorientation mechanisms during early crystal growth. In both cases, crystal orientation may reflect the orientation of the glass surface or that of anisotropic active surface nucleation sites. Therefore, we focus on orientation of surface crystals separately growing under controlled conditions.
First results on diopside (MgCaSi2O6) and walstromite (BaCa2Si3O9) crystals growing from 18BaO·22CaO·60SiO2 and MgO·CaO·2SiO2 glass surfaces, respectively, indicate that different orientation mechanisms may occur.
Neighbored walstromite crystals were found to gradually reorient themselves when they are going to impinge each other during stepwise isothermal treatments (log η = 4,5 Pa*s) of polished glass samples. Nevertheless, no preferred crystal orientation was evident for separate crystals.
For diopside crystals growing from polished glass surfaces (1 μm diamond lapping foil), strong preferred orientation was observed for 3.5 to 85 min annealing at 850 °C. Electron Backscatter Diffraction (EBSD) studies showed that the c-axis of surface crystals is oriented parallel to the glass surface and that separated diopside crystals as small as 600 nm are already oriented. Studies on glass surfaces, polished with diamond lapping foils starting from 16 μm down to 1 μm grain, revealed that crystal orientation may scatter arround this preferential orientation and that this scatter progressively decreases with decreasing polishing grain size.
A glass of the composition 37BaO·16CaO·47SiO2 wt% produced on an industrial scale is crystallized at 970 °C for times ranging from 15 min to 2 h. The crystallization at the immediate surface as well as the crystal growth into the bulk are analyzed using scanning electron microscopy (SEM) including energy dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD) as well as X-ray diffraction in the Θ–2Θ setup (XRD). The immediate surface shows the oriented nucleation of walstromite as well as the formation of wollastonite and an unknown phase of the composition BaCaSi3O8. All three phases also grow into the bulk where walstromite ultimately dominates the kinetic selection and grows throughout the bulk due to a lack of bulk nucleation. Walstromite shows systematic orientation changes as well as twinning during growth. A critical analysis of the XRD-patterns acquired from various crystallized samples indicates that their evaluation is problematic and that phases detected by XRD in this system should be verified by another method such as EDXS.
Oriented surface crystallization on polished diopside glass surfaces has been studied with scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy and laser scanning microscopy.
An orientation preference of [001] parallel to the glass surface was detected for separately growing diopside crystals even as small as 700 nm in size. This finding shows that crystal orientation occurs in the outermost surface layer without crystal-crystal interaction and indicates that the crystal orientation is a result of oriented nucleation. Depending on surface preparation, monomodal crystal orientation distributions with [100] perpendicular to the surface or bimodal distributions with [100] and [010] perpendicular to the glass Surface were detected. It was also shown that the degree of crystal orientation increases with decreasing Surface roughness. The observed orientation of diopside crystals could be explained in terms of the interfacial energies of different crystal faces.
Green compacts of ceramics, glass ceramic composites and sinter glass ceramics contain
different amounts of organic materials added as pressing aids or binders. Before sintering, these
organics have to burn out completely. In oxidising atmospheres, the debindering process is mostly
exothermic and therefore difficult to control. This uncontrolled heat production due to locally enhanced
debindering and respective gas release may cause damages in the green compact microstructure.
Therefore, debindering is usually operated with very low heating rates (< 3 K/min) which requires
long processing times of many hours. In this paper, we will show that it is possible to reduce
the processing time for debindering dramatically by using the decomposition rate of the organic
binder, detected by the weight loss of the sample, as a control factor of the furnace.
Sample preparation for analytical scanning electron microscopy using initial notch sectioning
(2021)
A novel method for broad ion beam based sample sectioning using the concept of initial notches is presented. An adapted sample geometry is utilized in order to create terraces with a well-define d step in erosion depth from the surface. The method consists of milling a notch into the surface, followed by glancing-angle ion beam erosion, which leads to preferential erosion at the notch due to increased local surface elevation. The process of terrace formation can be utilized in sample preparation for analytical scanning electron microscopy in order to get efficient access to the depth-dependent microstructure of a material. It is demonstrated that the method can be applied to both conducting and non-conducting specimens. Furthermore, experimental parameters influencing the preparation success are determined. Finally, as a proof-of-concept, an electron backscatter diffraction study on a surface crystallized diopside glass ceramic is performed, where the method is used to analyze orientation dependent crystal growth phenomena occurring during growth of surface crystals into the bulk.
Sintering and foaming of barium and calcium silicate glass powder compacts have been studied for different powder milling. Sintering was measured by means of heating microscopy backed up by XRD, DTA, Vacuum Hot Extraction (VHE) and electron microscopy. Foaming intensity strongly increased with decreasing glass partiefe size. Although powder compacts were uniaxially pressed and sintered in ambient air, foaming was affected by the milling atmosphere and most intensive for milfing in C02. Conformingly, VHE studies revealed that foaming of fully sintered samples was mainly driven by C02, even for powders milled in technical air, Ar and N2. Prolonged storage of air milled barium silicate glass powders in ambient air before pressing and sintering caused further increase of foaming intensity. These findings indicate that carbonaceous species are preferentially trapped to or close beneath the powder surface during milling and later storage. The temperature range of C02 degassing from fully sintered barium and calcium silicate g/ass powder compacts fits the temperature ranges of decomposition of BaC03 and CaC03 mix-milled with the respective barium and calcium silicate glass powders.
The manufacture of sintered glasses and glass-ceramics, glass matrix composites, and glass-bounded ceramics or pastes is often affected by gas bubble formation. Against this background, we studied sintering and foaming of barium silicate glass powders used as SOFC sealants using different powder milling procedures. Sintering was measured by means of heating microscopy backed up by XPD, differential thermal analysis, vacuum hot extraction (VHE), and optical and electron microscopy. Foaming increased significantly as milling progressed. For moderately milled glass powders, subsequent storage in air could also promote foaming. Although the powder compacts were uniaxially pressed and sintered in air, the milling atmosphere significantly affected foaming. The strength of this effect increased in the order Ar ≈ N2 < air < CO2. Conformingly, VHE studies revealed that the pores of foamed samples predominantly encapsulated CO2, even for powders milled in Ar and N2. Results of this study thus indicate that foaming is caused by carbonaceous species trapped on the glass powder surface. Foaming could be substantially reduced by milling in water and 10 wt% HCl.
Glass powders are promising candidates for manufacturing a broad diversity of sintered materials like sintered glass-ceramics, glass matrix composites, glass bonded ceramics or pastes. Powder processing, however, can substantially affect sinterability, e.g. by promoting surface crystallization. On the other hand, densification can be hindered by gas bubble formation for slow crystallizing glass powders. Against this background, we studied sintering and foaming of silicate glass powders with different crystallization tendency for wet milling and dry milling in air, Ar, N2, and CO2 by means of heating microscopy, DTA, Vacuum Hot Extraction (VHE), SEM, IR spectroscopy, XPS, and ToF-SIMS. In any case, foaming activity increased significantly with progressive milling. For moderately milled glass powders, subsequent storage in air could also promote foaming. Contrarily, foaming could be substantially reduced by milling in water and 10 wt% HCl. Although all powder compacts were uniaxially pressed and sintered in air, foaming was significantly affected by different milling atmosphere and was found most pronounced for milling in CO2 atmosphere. Conformingly, VHE studies revealed that foaming is mainly driven by carbonaceous species, even for powders milled in other gases. Current results of this study thus indicate that foaming is caused by carbonaceous species trapped on the glass powder surface.
We report the sintering of 3D-printed composites of 13-93 bioactive glass and hydroxyapatite (HAp) powders. The sintering process is characterized on conventionally produced powder compacts with varying HAp content. A numeric approximation of the densification kinetics is then obtained on the basis of Frenkel, MackenzieShuttleworth, and EinsteinRoscoe models, and optimized sintering conditions for 3D-printed structures are derived. Fully isotropic sintering of complex cellular composites is obtained by continuous heating to 750°C at a rate of 2 K/min for a HAp content of 40 wt%. The approach can readily be generalized for printing and sintering of similar glass-ceramic composites.
Sintering of LTCC
(2008)
Low Temperature Co-fired Ceramic materials (LTCC) have attracted growing interest in recent years since they are promising candidates for highly integrated ceramic packaging. This paper surveys materials concepts of related glass ceramic composites (GCC) and discusses unsolved problems and challenges. The densification of GCC based on "viscous sintering" may be affected by steric effects and partial dissolution of dispersed crystal particles, crystallization and phase boundary reactions.
Sol-gel preparation of calcium titanium phosphate: viscosity, thermal properties and solubility
(2012)
Calcium titanium phosphate (CTP) was prepared by the sol–gel route in order to prepare suitable coatings. This work addresses the question of how to prepare stable CTP sols. Their rheological properties as a function of process parameters like solid loading and water content are investigated. It was found that an increased solid loading as well as an increased water content lead to an increased initial viscosity as well as a more pronounced ageing induced viscosity rise. In addition, the thermal behavior of the resulting xerogels was analyzed. Furthermore, we studied the ion release behavior of the xerogels when brought in contact with water. Results suggest that calcium titanium phosphate shows a diffusion controlled ion release mode with a preferential release of Ca.
Dissolved water has major impact on the physical and chemical properties of phosphate glasses. In the present study we have investigated the structural response to water incorporation for glasses in the system Li2O–MgO–Al2O3–P2O5.
Glasses containing 0–8 wt% H2O were synthesised at 500 MPa confining pressure in internally heated gas pressure vessels at 1323 K (LMP, Al-poor glass) and 1423 K (LMAP, Al-enriched glass). Water contents of glasses were determined by pyrolysis and subsequent Karl-Fischer titration (KFT) and/or by infrared spectroscopy. Density varies nonlinearly with water content implying large structural changes when adding up to 2 wt% H2O to the dry glass. Glass Transition temperatures measured by differential thermal analysis (DTA) continuously decrease with water content. The trend can be explained by depolymerisation of the phosphate network. Near-infrared spectroscopy shows that even in Al poor glasses only a minority of dissolved water is present as H2O molecules, but the largest amount is present as OH Groups formed by hydrolysis of P–O–P bonds. The network is stabilised by aluminium which is predominantly six-coordinated in these glasses as shown by 27Al MAS NMR spectroscopy. With increase of Al in the glasses, breaking up of the Phosphate network through hydrolysis is depressed, i.e. much lower OH Contents are formed at same total water content.
Network depolymerisation upon addition of H2O is evident also from 31P MAS NMR spectroscopy. While Phosphate tetraheda are crosslinked by two to three bridging oxygen in dry glasses, diphosphate Groups are dominant in glasses containing 8 wt% H2O.
The structural properties of a borosilicate glass with nominal 16 mol% Na2O, 10 mol% B2O3 and 74mol% SiO2 and water contents between 0 and 8wt% H2O (0–22 mol% H2O)were investigated with IR, Raman and 11BMAS NMR spectroscopy. In addition to the pronounced OH stretching vibration band of weakly H-bonded species at 3580 cm−1 the MIR spectra show a triplet at 2900, 2350 and 1750 cm−1, similar as observed in water-bearing silicate glasses. These bands are assigned to OH groups and water molecules which are strongly H-bonded, to non-bridging oxygen. Water species contents determined from absorption bands in the NIR at 5200 cm−1 (molecular H2O), 4700 cm−1 (B\\OH), and 4500 cm−1 (Si\\OH) indicate that hydroxyl groups dominate up to ~6 wt% total H2O. Based on the absorption coefficients known from literature for silicate and borate glasses the B\\OH/Si\\OH ratio is estimated to be ≈0.8.
As indicated by density, Raman and NMR data the incorporation ofwater has strong structural impacts in particular at low water contents up to 3 wt% H2O. While the nominally dry glasses still contain a significant fraction (12%) of three-fold coordinated boron, almost all boron is four-fold coordinated in hydrous glasses. The increase of band components in the Raman spectra near 900 cm−1 relative to the region N 1050 cm−1 gives evidence for depolymerization of the network upon hydration. Fitting of the spectra with Gaussians implies that silica tetrahedra with two non-bridging oxygen (Q2) are preferentially formed by reactionwithwater on expense of tetrahedra linked to four tetrahedra (Q4).
Borosilicate glasses (16Na2O–10B2O3–74SiO2, NBS) with water contents up to 22 mol% H2O were prepared to study the effect of water on structural relaxation using DTA, viscometry and internal friction measurements. The results show that the glass transition temperature Tg of DTA and the isokom temperature T12, of viscometry are in excellent agreement, confirming the equivalence of enthalpy and viscous relaxation for NBS glass. Combining Tg data with water speciation data demonstrates that OH groups are mainly responsible for the decrease of Tg with increasing hydration, while molecular water plays only a minor role. Internal friction spectra at 7.125 Hz confirm the decisive influence of water on mechanical relaxation. The temperature range of α-relaxation (glass transition) strongly decreases while two β-relaxation peaks (sub-Tg) progressively appear with increasing water content. A high temperature β-relaxation peak, attributed to the presence of OH groups, shifts from 670 to 450 K as total water content increases from 0.01 to 5 wt%. A low temperature β-relaxation peak, attributed to molecular water, appears at 380 K and 330 K in glasses containing 3 and 5 wt% H2O, respectively. These findings suggest that relaxation mechanism of different hydrous species at low temperature may contribute to fatigue of stressed glasses.
Water plays an important role for the depolymerization of silicate glasses which becomes noticeable by a distinct decrease of glass transformation temperature, Tg. Thus, it has a considerable influence on aging and fatigue as well as on sub-critical crack growth in glasses. In this connection also sub-Tg relaxation processes play a major role, but they are poorly investigated in glasses with high contents of structural bonded water. Therefore, soda-lime-silicate and sodium-borosilicate glasses with water contents up to 5 wt.% H2O were investigated by differential thermal analysis and sphere penetration viscometry, as well as internal friction measurements. The latter was applied to study network related relaxation mechanisms (α-relaxation) in the range of glass transition, as well as faster relaxation modes occurring at lower temperatures (β-, γ- relaxation). Total water content and concentrations of H2O molecules (CH2O) and OH groups (COH) in the glasses were determined by infrared spectroscopy.
For low water contents two sub-Tg internal friction peaks were observed and assigned to the low-temperature motion of alkali ions (γ-relaxation) and cooperative movements of dissimilar mobile species under participation of OH at higher temperature (βOH relaxation).
For large water contents, where significant amounts of molecular water are evident, a low temperature shoulder appears on the β-relaxation peak. This emerging relaxation mode (βH2O relaxation) was assigned to the motions of H2O molecules.
Wasser hat einen starken Einfluss auf die Depolymerisation des Glasnetzwerks silikatischer Gläser, was sich durch eine deutliche Senkung der Glasübergangstemperatur, Tg, bemerkbar macht. So hat Wasser einen großen Einfluss auf die Alterung, Ermüdung und das unterkritische Risswachstum in Gläsern. Sub-Tg Relaxationsphänomene spielen hier ebenfalls eine große Rolle, sind aber für Gläser mit hohen Gehalten an strukturell gebundenem Wasser kaum untersucht. In dieser Arbeit wurden daher Kalk-Natron-Silikat (NCS) und Natrium-Borosilikat (NBS) Gläser mit Wassergehalten von bis zu 8 Gew.% mittels Differentialthermoanalyse (DTA), Mikropenetration und vor allem dynamisch mechanischer Thermoanalyse (DMTA) zur Charakterisierung netzwerkbedingter Relaxationsmechanismen (alpha-Relaxation) im Bereich des Glasübergangs sowie weiterer schnellerer sub-Tg Relaxationsmechanismen (beta-, gamma-Relaxation) bei tieferen Temperaturen untersucht. Mit Hilfe der IR-Spektroskopie wurde der Gesamtwassergehalt und die Speziation des Wassers als molekulares Wasser oder als OH-Gruppe in den Gläsern bestimmt.
Für niedrige Wassergehalte treten zwei sub-Tg Verlustpeaks auf, die der Bewegung von Alkali bei tiefen Temperaturen (gamma-Relaxation) und einer kooperativen Bewegung verschiedener mobiler Spezies unter Beteiligung von OH bei höherer Temperatur (betaOH- Relaxation) zugeordnet werden können. Bei hohen Wassergehalten, bei denen ein messbarer Anteil an molekularem Wasser im Glas vorliegt, ist ein weiterer Verlustpeak zu beobachten, der mit der Bewegung von molekularem Wasser im Glasnetzwerk in Verbindung gebracht werden könnte (betaH2O-Relaxation).
The crystallization behavior of sodium ion conductive Na2MnP2O7 glass was examined to clarify the crystallization mechanism. The formation of thermodynamically metastable phase, layered Na2MnP2O7, at the surface of the glass occurred. Heat treatment at 430 °C for 3 h lead to surface crystals of Na2MnP2O7 oriented with the (101) direction perpendicular to the sample surface. As the heat treatment temperature increased, the glass-ceramic samples deformed, and the presence numerous micro bubbles due to dissolved water was detected.