5 Werkstofftechnik
Filtern
Dokumenttyp
- Vortrag (56)
- Zeitschriftenartikel (54)
- Posterpräsentation (21)
- Buchkapitel (1)
- Beitrag zu einem Tagungsband (1)
- Sonstiges (1)
Sprache
- Englisch (134) (entfernen)
Schlagworte
- Glass (34)
- Sintering (16)
- Crystallization (15)
- Crack growth (12)
- Water speciation (9)
- DCB (8)
- Soda-lime silicate glass (7)
- Water content (7)
- Foaming (6)
- Robotic melting (6)
- Vickers (6)
- EBSD (5)
- Vickers indentation (5)
- Viscosity (5)
- Alkali ions (4)
- Alkali zinc borate glasses (4)
- Bioactive glass (4)
- Glas (4)
- Internal friction (4)
- Ontology (4)
- Orientation (4)
- Surface energy (4)
- Workflow (4)
- Coating (3)
- Corrosion (3)
- Crack healing (3)
- Crystal orientation (3)
- Data Space (3)
- Diopside (3)
- Fracture Toughness (3)
- Glass ceramic (3)
- Glass powder (3)
- NMR spectroscopy (3)
- Oxide Glasses (3)
- Scintillators (3)
- Silicate Glasses (3)
- Simulation (3)
- Surface crystallization (3)
- Al2O3 (2)
- Aluminosilicate glasses (2)
- Bioactive Glass (2)
- Bond energy (2)
- Diffusion coefficient (2)
- Diopsid (2)
- Elastic constants (2)
- Fluoride phosphate glasses (2)
- Fracture surface energy (2)
- Gender gap (2)
- Geothermal (2)
- Glass Digital (2)
- Glass composition (2)
- Glass transition (2)
- Glass-ceramic (2)
- Hydrogen permeation (2)
- IR (2)
- Infrared spectroscopy (2)
- Ionic porosity (2)
- Lead borate glasses (2)
- Martensitic steel (2)
- Mechanical properties (2)
- Microhardness (2)
- Microstructure (2)
- Multifunctional nanoparticles (2)
- Nanoparticles (2)
- Ontologie (2)
- Oriented surface crystallization (2)
- Permeability (2)
- Powder (2)
- Raman spectroscopy (2)
- Relaxation (2)
- SEM (2)
- Silver diffusion (2)
- Silver metallization paste (2)
- Silver-glass-metallization-paste (2)
- Soda-lime-silica glass (2)
- Sol-gel coating (2)
- Solubility (2)
- Stress intensity factor (2)
- Superconducting magnet (2)
- Surface Energy (2)
- Surface nucleation (2)
- Upconversion (2)
- 3D etching (1)
- 3D glass structure model (1)
- 3D printing (1)
- Acid-leaching (1)
- Alkali aluminosilicate glasses (1)
- Alkali and alkaline earth silicate and borate glass (1)
- Alkali zinc borate glass (1)
- Alumina coatings (1)
- Analytical scanning electron microscopy (1)
- Artificial weathering (1)
- Atomic packing factor (1)
- Automated analysis (1)
- BTS (1)
- Batch reactions (1)
- Behmite (1)
- Bioactive (1)
- Blähen (1)
- Borate (1)
- Borate glasses (1)
- Borosilicate glass (1)
- Brittle fracture (1)
- Brownian motion (1)
- Bubble formation (1)
- Calculated intrinsic fracture toughness (1)
- CdTe quantum dots (1)
- Cement (1)
- Ceramic multilayers (1)
- Co-firings (1)
- Coefficient of thermal expansion (1)
- Composite materials (1)
- Concrete (1)
- Crack growth in air (1)
- Crosslinking (1)
- Crystal growth (1)
- Crystal growth velocity (1)
- Crystal lattice (1)
- Crystal morphology (1)
- Cytocompatibility (1)
- DCB geometry (1)
- Data space (1)
- Degradation (1)
- Density (1)
- Dental ceramics (1)
- Differential scanning calorimetry (1)
- Diffusion (1)
- Diffusivity (1)
- Digital Twin (1)
- Digitalization (1)
- Dissolved water (1)
- Dynamic mechanical analysis (1)
- Dynamisch Mechanische Analyse (1)
- EPR (1)
- Efficiency (1)
- Epoxy resin (1)
- Exposed metal sites (1)
- FT-IR (1)
- Facilitated activation (1)
- Female noble prize winners (1)
- Ferrous phosphate hydrate (1)
- Flow Coefficient (1)
- Fluorescence spectroscopy (1)
- Fracture Mechanics (1)
- Fracture surface (1)
- Fracture toughness (1)
- Fragility (1)
- Fresnoit (1)
- Fresnoite (1)
- Gas permeation (1)
- Gasabgabe (1)
- Gasgehalt (1)
- Gd3+ (1)
- General Chemistry (1)
- Glass Ceramic (1)
- Glass capillaries (1)
- Glass crystallization stress (1)
- Glass forming melts (1)
- Glass liner (1)
- Glass manufacturing (1)
- Glass matrix composite (1)
- Glass melt (1)
- Glass melting (1)
- Glass scintillator (1)
- Glass screening device (1)
- Glass structure (1)
- Glass transformation temperature (1)
- Glass-ceramics definition (1)
- Glasses (1)
- Growth kinetics (1)
- Growth rate (1)
- Heißgasextraktion (1)
- High energy radiation (1)
- High pressure (1)
- High pressure gas storage (1)
- High temperature (1)
- High temperature corrosion (1)
- High-temperature corrosion (1)
- High-temperature oxidation (1)
- Host-guest hybrid materials (1)
- Hot stage microscopy (1)
- Hydrogen diffusivity (1)
- Hydrogen gas (1)
- Hydrogen permeability (1)
- Hydrogen storage (1)
- Hydrogen storage tank (1)
- Hydrous glass (1)
- IR spectroscopy (1)
- In situ synthesis (1)
- Inconel 625 (1)
- Indentation fracture toughness (1)
- Internal stresses (1)
- Ion beam erosion Sectioning (1)
- JMAK model (1)
- Kristallisation (1)
- Limestone Filler (1)
- Long-term calculation (1)
- Low expansion (1)
- MOF-74 (1)
- Martensitic steels (1)
- Master curve (1)
- Material Digital (1)
- Materials Chemistry (1)
- Materials Data Space (1)
- Mechanical Engineering (1)
- Mechanics of Materials (1)
- Metallic silver precipitates (1)
- Metals and Alloys (1)
- Metformin (1)
- Milling (1)
- Mixed-linkers (1)
- Modeling (1)
- Moisture (1)
- NMR (1)
- Nb3Sn (1)
- Noble metal nanoparticles (1)
- Non-desired foaming (1)
- Nucleation (1)
- Nucleation mode (1)
- Nucleation tendency (1)
- Nydrogen melting (1)
- Optical properties (1)
- Optical properties of glasses and ceramics (1)
- Optical spectroscopy (1)
- Optical tweezers (1)
- Oxidation protection (1)
- Oxide coatings (1)
- Oxide glass (1)
- Oxidglas (1)
- Oxyfuel (1)
- PMD (1)
- Particle Size Distribution (1)
- Persistent luminescence (1)
- Persistent luminescent (1)
- Phase Separation (1)
- Phase separation (1)
- Phase transformations (1)
- Phosphate (1)
- Phosphors (1)
- Photocatalysis (1)
- Photodynamic therapy (1)
- Photovoltaic modules (1)
- Physical properties (1)
- Plasmon enhancement (1)
- Polymer (1)
- Polyurethane (1)
- Precipitation (1)
- Property simulation (1)
- Protective coating (1)
- Quantum dots (1)
- Radiation-matter interaction (1)
- Raman (1)
- Real time growth control (1)
- Reference Material (1)
- Relaxationsphänomene (1)
- Resonance testing (1)
- Rheology (1)
- Risswachstum (1)
- Robot-assisted galss melting (1)
- Robotic glass melting (1)
- Robotische Glasschmelzanlage (1)
- Roughness (1)
- Sample preparation (1)
- Sand blasting (1)
- Scaffolds (1)
- Sensing (1)
- Shear thinning (1)
- Silicate glass (1)
- Silicatglas (1)
- Silicoborate glasses (1)
- Silver (1)
- Silver cluster (1)
- Silver glass paste (1)
- Silver precipitates (1)
- Silver-glass metallization paste (1)
- Sinter retardation (1)
- Sintering atmosphere (1)
- Sintern (1)
- Slow crack growth (1)
- Soda lime silicate glass (1)
- Soda-lime-silica (1)
- Sodium ion batteries (1)
- Sodium zinc borate glass (1)
- Sodiumborosilicate glasses (1)
- Spectroscopy (1)
- Stable crack growth (1)
- Steel (1)
- Steel P92 (1)
- Stress intensity (1)
- Stress-corrosion (1)
- Stress-strain behavior (1)
- Stress-strain-behavior (1)
- Structural defects (1)
- Structure (1)
- Structure property correlations (1)
- Structure-property correlation (1)
- Subcritical crack growth (1)
- Supersaturation (1)
- Surface Nucleation (1)
- Surface roughness (1)
- Synchrotron micro-tomography (1)
- TEM (1)
- Tb3+ (1)
- Theranostics (1)
- Thermal expansion (1)
- Thermo-optical measurement (1)
- Thermoanalytical Methods (1)
- Toughness (1)
- Transmission electron microscopy (1)
- Transmittance (1)
- Upconversion nanoparticles (1)
- Vacuum hot extraction (1)
- Viscose sintering (1)
- Viscous sintering (1)
- Vivianite (1)
- Volume Fraction (1)
- Volume changes (1)
- Wasser (1)
- Water (1)
- Water in glass (1)
- White light emitters (1)
- Women in science (1)
- X-ray diffraction (1)
- Young`s modulus (1)
- Young´s Modulus (1)
- Young´s modulus (1)
- Young’s Modulus (1)
- high pressure (1)
- hydrogen storage (1)
- infrared spectroscopy (1)
- phosphate glasses (1)
- water speciation (1)
Organisationseinheit der BAM
- 5.6 Glas (134) (entfernen)
Liquid phase sintering of glass bearing silver pastes used in photovoltaics and microelectronics is poorly understood. In particular, the role of different network modifiers acting in the glass component and the question of the most suitable atmospheric oxygen level during sintering are still under considerable debate. To tackle these issues, low-melting and lead-free X2O-ZnO-B2O3 glasses with X = Li, Na, K and Rb (LZB, NZB, KZB and RZB) were prepared. Infrared spectroscopy showed that the glass structure was similar to each other, while an increase of tetrahedrally coordinated boron with increasing field strength of the alkali was evident. In turn, the glass transition temperature (from differential thermal analysis) increased in the order: RZB (449 °C) < KZB (460 °C) < NZB (465 °C) < LZB (472 °C). Powders of each glass were mixed with organics to receive silver-glass-pastes containing 30 vol% glass and these were subjected to heating microscopy in air. Although similar onset temperatures of sintering were recorded for Ag-NZB and Ag-LZB glass pastes, and for Ag-RZB paste and KZB-Ag-paste, respectively, differences in the crystallization behavior and final densification were observed between the former and the latter group. These were translated in terms of differences in silver dissolution and reprecipitation among the two groups. Further, running the experiments in nitrogen gas showed that sintering of all pastes was considerably hampered. The slow-down of the sinter kinetics was found to be in line with the assumed lower oxidation and dissolution of silver ions into the glass-forming liquid.
Glasses in the systems Me2O-ZnO-B2O3 with Me = Li, Na, K, Rb (MeZB), Na2O-ZnO-CuO-B2O3 (NZCuB), CaO-ZnO-B2O3 (CaZB), and Li2O-PbO-B2O3 (LPbB) as a reference, were studied by differential thermal analysis, dilatometry, rotational viscometry, and heating microscopy. A decrease of viscosity and sintering range was found with decreasing number of fourfold coordinated boron. The viscosity of the alkali zinc borate glasses varies only slightly. LPbB and CaZB stand out by their reduced and increased viscosities, respectively. Sodium, potassium, and calcium zinc borate glasses possess a fragility above 76. All glasses were sintered to full density before crystallization. Mostly binary zinc borate phases govern crystallization. A ternary crystalline phase was detected only in the potassium containing sample. The Weinberg glass stability parameter ranges between 0.07 and 0.12. This is caused by the presence of several crystalline phases and varying melting points of even the same crystalline phase in different glass matrices.
Low melting Li2O-PbO-B2O3, Me2O-ZnO-B2O3, Me = Li, Na, K, Rb and CaO-ZnO-B2O3 glasses were studied with Raman and infrared spectroscopies to advance the structural understanding of zinc borate glasses as potential candidates for substitution of lead containing glasses. Although the effect of type of alkali ions on the number (N4) of fourfold coordinated boron (B4) in the glasses is small, the alkali ions direct the type of borate groups, i.e., pentaborate in lithium, sodium, and calcium zinc borate glasses, as well as diborate in potassium and rubidium containing ones. Both groups were simultaneously found in Li2O-PbO-B2O3. Alkali ions are mainly responsible for the formation of B4-units and metaborate. Zinc ions favorably compensate non-bridging oxygen and partially form ZnO4. With decreasing N4 and field strength of the alkali ions the atomic packing density, glass transition temper ature and Young’s Modulus also decrease. The coefficient of thermal expansion increases with decreasing N4.
Artificial bone replacement by individual customized three-dimensional resorbable bioactive glass has not yet been widely established in the clinical use. This is mainly due to the antagonism of sintering ability and suitable bioactivity. Competitive crystallization often prevents the generation of dense sintered bodies, especially for additive manufactured 3D structures. Previous studies of the fluoride-containing glass F3 have shown its potential to combine both sintering ability and suitable bioactivity. Furthermore, the occurring sintering blockade by surface crystallization of Na2CaSi2O6 was tunable by glass particle size.
In this study the glasses F3, F3-Cu with 1 mol% CuO added at the expense of CaO and the well-known 13-93 were chosen to determine the influence of surface crystallization on 3D printed sinter bodies. For this purpose, grain size fractions in range of smaller 32 µm to 315 µm in fraction size of 6-20 µm were sieved from jaw crushed glass frit as well as glass cubes were cut from casted blocks for all glasses. Sintering behavior of both pressed and printed powder compacts was observed via heating microscopy. Crystallization was determined by DTA and crystallization progress was monitored on fractured sinter bodies and polished cubes via electron and laser scanning microscopy as well as with diffractometry.
Depending on grain size the formation of crystalline support framework along former grain boundaries shows the capability to stabilize fully densified sinter bodies before softening. Beside of this, the generation of complex hierarchic porosity was possible as well.
Sintering, crystallization, and foaming of 44.8SiO2–2.5P2O3–36.5CaO–6.6Na2O–6.6K2O–3.0CaF2 (F3) and 54.6SiO2–1.7P2O3–22.1CaO–6.0Na2O–7.9K2O–7.7MgO (13–93) bioactive glass powders milled in isopropanol and CO2 were studied via heating microscopy, differential thermal analysis, vacuum hot extraction (VHE), Infrared spectroscopy, and time-of-flight secondary ion mass spectrometry. Full densification was reached in any case and followed by significant foaming.
VHE studies show that foaming is driven by carbon gases and carbonates were detected by Infrared spectroscopy to provide the major foaming source. Carbonates could be detected even after heating to 750◦C, which hints on a thermally very stable species or mechanical trapping. Otherwise, dark gray compact colors for milling in isopropanol indicate the presence of residual carbon as well. Its significant contribution to foaming, however, could not be proved and might be
limited by the diffusivity of oxygen needed for carbon oxidation to carbon gas.
We present an easy-to-apply method to predict structural trends in the internal nucleation tendency of oxide glasses. The approach is based on calculated crystal fracture surface energies derived from easily accessible diatomic bond energy and crystal lattice data. The applicability of the method is demonstrated on literature nucleation data for isochemically crystallizing oxide glasses.
The lecture focuses on the mechanisms of non-desired gas bubble formation and foaming during the sintering of glass powder compacts. It is shown that foaming is driven by carbon gases and that carbonates, encapsulated in micropores or mechaniacally dissolved beneath the glass surface, provide the major foaming source.
Crack growth velocity in alkali silicate glasses was measured in vacuum across 10 orders of magnitude with double cantilever beam technique. Measured and literature crack growth data were compared with calculated intrinsic fracture toughness data obtained from Young´s moduli and the theoretical fracture surface energy estimated from chemical bond energies. Data analysis reveals significant deviations from this intrinsic brittle fracture behavior. These deviations do not follow simple compositional trends. Two opposing processes may explain this finding: a decrease in the apparent fracture surface energy due to stress-induced chemical changes at the crack tip and its increase due to energy dissipation during fracture.
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.
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.
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.
The suitability of an Al2O3 coating for corrosion protection on X20Cr13 was evaluated in various artificial geothermal brines, focusing on the influence of different pH (4, 6 and 8) and their chemical compositions on the coating properties. All experiments were performed in the laboratory using autoclaves at 150 ◦C and 1 MPa in deaerated condition for 1 and 7 days. Results showed that the pH of geothermal waters is the most detrimental factor in the transformation of ɣ-Al2O3 and its protective abilities. Delaminations were found in the Coating exposed to geothermal brines with pH 4. FTIR spectra indicated a transformation of ɣ-Al2O3 to boehmite AlOOH after exposure to pH 4 and 6, and bayerite Al(OH)3 was formed after exposure to pH 8. Different Crystal structures of the hydrated Al2O3 also contribute to the stability of the coatings, observed by the SEM- EDX of the surface and cross-section of coatings. This study indicated that ɣ-Al2O3 sol-gel coating presents a promising aspect of corrosion protection in geothermal environment with a neutral pH.
Since decades electric contacts based on silver metallization pastes are key components of photovoltaics and advanced microelectronics. For the metallization of commercial Si solar cells, high conductive silver glass pastes are cost effectively applicated by screen printing. Nevertheless, silver pastes are still one of the most crucial and expensive none Si materials in solar cells. Ever shorter time to market as well as increasing demands on reduced Ag consumption and line width require the targeted development of silver-glass-pastes with increased sinter ability and electrical conductivity. As a main difficulty, however, the liquid phase sintering of silver glass pastes is poorly understood so far.
In the present study, the influence of different network modifier in alkali-zinc-borate paste glasses on liquid phase sintering of silver-glass-pastes was investigated. Low melting X2O-ZnO-B2O3 glasses with X = Na, Li and Rb (abbr. LZB, NZB, and RZB) were utilized to prepare silver-glass-composites containing 30 %Vol glass. Shrinkage behavior of the silver-glass-composites compared with that of pure silver and pure glass powder compacts was studied with heating microscopy. The powder compacts were uniaxially pressed and heated at 5 K/min to the glass softening temperature. Glass transformation temperature and viscosity of the glasses were respectively measured with dilatometry and rotational viscometry. The thermal behavior of the pure glasses was analyzed with thermal analysis. Additionally, the contact angle of glass on pure silver foil was determined by means of heating microscopy between room temperature and 830 °C.
Thermal analysis of the alkali-zinc-borate-glasses under study has shown transformation temperatures between 450 °C (RZB), 460 °C (LZB) and 465 °C (NZB). For all glasses crystallization was found to start approximately at about 550 °C. However, different peak areas hint on a different degree of crystallization. Conformingly, the sintering behavior, measured in terms of area shrinkage, significantly differed for the silver-pastes under study. For silver-pastes with NZB or LZB-glass, sintering starts at 464 °C for NZB Ag pastes and at 451 °C for LZB Ag pastes and ends at 597 °C for NZB Ag paste and at 594 °C for LZB Ag paste. The sintering of the RZB Ag paste proceeds between 426 °C and 703 °C. The final densification was retarded possibly due to crystallization or swelling. The low sinter onset at 426 °C seems to correlate with the good wetting behavior of the RZB glass. Thus, the lowest apparent contact angle between the just densified powder compact sintered at a silver substrate was found for this glass. Moreover, microstructure analyses of the various composites indicate differences in silver dissolution and reprecipitation.
Network modifier ions can decisively influence properties and structure of low melting alkali-zinc-borate glasses and thus cause complex effects on the liquid phase sintering of silver-glass metallization pastes. This effect was studied for X2O-ZnO-B2O3 (X = Li, Na, Rb) glasses for silver-glass metallization pastes. Viscosity and the glass transition temperature, Tg, were measured with rotational viscometry and dilatometry. Dried model pastes with 30 vol% LZB, NZB or RZB glass were prepared for sintering studies by means of heating microscopy measuring the silhouette area shrinkage of uniaxially pressed powder compacts during heating at 5 K/min. For comparison, the silhouette area shrinkage of pure glass and silver powder compacts were determined. Glass-silver wetting was investigated during heating of bulk glass cylinders placed on silver substrates. Glass RZB turned out to have the lowest viscosity among the glasses under study. Its glass transformation temperature, Tg, was found at 444 °C and it caused the lowest sintering onset for its glass and paste powder compacts. Slightly increased values of Tg were found for NZB and LZB (468 °C and 466 °C, respectively) and a slightly retarded sintering was found for both paste powder compacts. These results indicate that liquid phase sintering of silver-glass pastes under air atmosphere is mainly influenced by glass viscosity.
Low melting zinc borate glasses awake interest to replace lead borate glasses in the silver metallization pastes for solar cells or microelectronics. In the current study, characteristic properties of alkali zinc borate glasses (X2O-ZnO-B2O3, X = Li, Na, K, Rb) were compared to an earth alkali zinc borate glass (CaO-ZnO-B2O3). Additionally, zinc oxide is partially substituted by lead oxide or cooper oxide in the borate glasses (Li2O-PbO-B2O3, Na2O ZnO CuO-B2O3). The alkali zinc borate glasses indicate less differences in Raman spectra, and thus in structural properties, in comparison to the Ca and Pb ions influence. LPbB (Tg = 401 °C) has a lower viscosity than LZB (Tg = 468 °C) and CaZB has the highest glass transition temperature (Tg = 580 °C). The Angell plot for the alkali zinc borate glasses shows a high fragility m = 80. Besides Tg, the density measured by means of the Archimedean principle, molar volume, and coefficient of thermal expansion (CTE) of the glasses were investigated. Trends could be found according to alkali ions or intermediate oxides. The density increases with decreasing alkali ion size from KZB (2.632 g/cm3) to LZB (2.829 g/cm3) and increases from LZB to LPbB (3.764 g/cm3). CTE ranges between 7.09 10-6 K-1 for CaZB and 11.5 10 6 K 1 for KZB and RZB. The differential thermal analysis (DTA) and X ray diffraction (XRD) indicate crystallization of various crystalline phases during heating with 5 K/min in most cases.
In many late-breaking research fields as in photovoltaics, microelectronics, nuclear waste glasses or at least mirror glasses silver diffusion in glasses is relevant to the issues of high-level functionality and recycling. The present study is focused on silver diffusion in innovative, low-melting alkali zinc borate glasses (X2O-ZnO-B2O3, X = Li, Na, K, Rb) potentially usable for silver metallization-pastes in solar cells. The glasses were coated with a thin metallic silver layer and heat treatments in air and nitrogen close to Tg at 470 °C for 2 h were performed. After heat treatment under air and nitrogen atmospheres the coating thickness, measured by a white light interferometer, was about 1.8 µm thick. Silver depth profiles determined by means of secondary neutral mass spectrometry (SNMS) indicate the fastest silver diffusion to a depth of 3.5 µm for Li2O-ZnO-B2O3 (LZB) glass. Nevertheless, the influence of the different alkali ions on the silver diffusion is small. The oxygen availability determines the silver diffusion into the glasses. The oxygen promotes the oxidation of the silver layer enabling Ag+ to diffuse into the glass and to precipitate as Ag0. Both species were detected by x-ray absorption spectroscopy (XAS). The precipitated metallic silver particles in Na2O-ZnO-B2O3 (NZB) glass have a mean size of 5.9 nm ± 1.2 nm diameter, which was determined using transmission electron microscopy (TEM). Phase separation in zinc-rich and zinc-poor phases with a mean diameter of 75 nm ± 20 nm occurred in NZB glass after heat treatment. Ion diffusion of the glasses into the silver layer was suggested by EDX-line scans.
Al2O3 has been widely used as a coating in industrial applications due to its excellent chemical and thermal resistance. Considering high temperatures and aggressive mediums exist in geothermal systems, Al2O3 can be a potential coating candidate to protect steels in geothermal applications. In this study, γ-Al2O3 was used as a coating on martensitic steels by applying AlOOH sol followed by a heat treatment at 600 °C. To evaluate the coating application process, one-, two-, and three-layer coatings were tested in the artificial North German Basin (NGB), containing 166 g/L Cl−, at 150 °C and 1 MPa for 168 h. To reveal the stability of the Al2O3 coating in NGB solution, three-layer coatings were used in exposure tests for 24, 168, 672, and 1296 h, followed by surface and cross-section characterization. SEM images show that the Al2O3 coating was stable up to 1296 h of exposure, where the outer layer mostly transformed into boehmite AlOOH with needle-like crystals dominating the surface. Closer analysis of cross-sections showed that the interface between each layer was affected in long-term exposure tests, which caused local delamination after 168 h of exposure. In separate experiments, electrochemical impedance spectroscopy (EIS) was performed at 150 °C to evaluate the changes of coatings within the first 24 h. Results showed that the most significant decrease in the impedance is within 6 h, which can be associated with the electrolyte penetration through the coating, followed by the formation of AlOOH. Here, results of both short-term EIS measurements (up to 24 h) and long-term exposure tests (up to 1296 h) are discussed.
Al2O3 coatings are often used as protective layers on steels against electrochemical and high-temperature corrosion because they are chemically inert and stable at elevated temperatures. This study presents preliminary work on the possibilities of using Al2O3 sol-gel coatings for corrosion protection of martensitic stainless steels in geothermal environments. Al2O3 sol-gel coatings were applied on UNS S42000, which is known to be susceptible to uniform and localized corrosion. The coated steel specimens were then tested in two types of artificial geothermal water, which simulate the geothermal fluids found in Sibayak (SBY), Indonesia, and North German Basin (NGB), Germany, respectively. SBY has pH 4 and 1.5 g/L of chloride ions, whereas NGB has a pH of 6 and 166 g/L of chloride ions. All experiments were carried out in autoclaves at 150 °C and 1 MPa under the deaerated condition. Evaluations were performed by investigating the surface profiles of both uncoated and coated steels before and after the corrosion test using a Laser Scanning Microscope (LSM) and Scanning Electron Microscope (SEM). Finally, Electrochemical Impedance Spectroscopy (EIS) was performed to compare the corrosion resistance of Al2O3 coated steels in SBY and NGB solutions. It was observed from the corrosion test that Al2O3 coatings are more suitable for use in the geothermal water with a higher pH.
A double cantilever beam technique in air equipped with ultrasound modulation was used to measure the crack velocity v in borate and silicate glasses. In all glasses v and the stress intensity KI followed the empirical correlation v ~ KIn. Indicated by its smallest KI at v = 1 μm s − 1, KI* = 0.27 MPa m0.5, the silicoborate glass containing 70 mol% B2O3 was found most susceptible to stress-corrosion enhanced crack growth. Contrarily, the sodium calcium magnesium silicate glass appeared least susceptible with KI* = 0.57 MPa m0.5. No clear correlation is evident between KI*, reflecting the stress-corrosion susceptibility, and the hydrolytic resistance for all glasses under study, but values of n obtained from the present study and taken from previous literature for 35 glasses tend to decrease with increasing network modifier ion fraction. Energy dissipation during stress-corrosion enhanced crack propagation is assumed to cause this trend.
Physical storage of gaseous hydrogen under high-pressure in glassy micro-containers such as spheres and capillaries is a promising concept for enhancing safety and the volumetric capacity of mobile hydrogen storage systems. As very low permeation through the container wall is required for storage of compressed hydrogen, development of glasses of minimal hydrogen permeability is needed. For this purpose, one has to understand better the dependence of hydrogen permeability on glass structure. The paper points out that minimizing the accessible free volume is as one strategy to minimize hydrogen permeability. Based on previously measured and comprehensive literature data, it is shown that permeation is independently controlled by ionic porosity and network modifier content. Thus, ionic porosity in modified and fully polymerized networks can be decreased equally to the lowest hydrogen permeability among the glasses under study. Applying this concept, a drop of up to 30,000 with respect to the permeation of hydrogen molecules through silica glass is attainable.