5 Werkstofftechnik
Filtern
Dokumenttyp
- Zeitschriftenartikel (50)
- Vortrag (47)
- Posterpräsentation (24)
- Buchkapitel (1)
- Beitrag zu einem Tagungsband (1)
- Sonstiges (1)
Schlagworte
- Glass (32)
- Sintering (16)
- Crystallization (15)
- Crack growth (12)
- DCB (9)
- Water speciation (9)
- Soda-lime silicate glass (7)
- Vickers (7)
- Water content (7)
- Glas (6)
Organisationseinheit der BAM
- 5.6 Glas (124) (entfernen)
Eingeladener Vortrag
- nein (47)
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.
The system Na2O.B2O3-SiO2 (NBS) is the basis of many industrial glass applications and therefore one of the most studied systems at all. Glass formation is possible over a wide compositional range, but the system also contains ranges of pronounced phase separation and crystallization tendency. Despite its importance, experimental data are limited to few compositional areas. The general understanding and modelling of glass formation, phase separation, and crystallization in this system would therefore be easier if small step melt series could be studied. The efficient melting of such glass series is now possible with the new robotic glass melting system at the Federal Institute for Materials Research and Testing (BAM, Division Glasses). Using three exemplary joins within this NBS system, the small step changes of glass transition temperature (Tg), crystallization behavior as well as glass density (Roh) was studied. Additionally, experimental Tg and Roh data were compared with their modeled counterparts using SciGlass and a newly developed DFT model, respectively.
The search for strong and tough oxide glasses is important for making safer, more environmentally friendly, thinner glass products. However, this task remains generally difficult due to the material’s inherent brittleness. In search for tougher glasses, fracture toughness (KIC) prediction models are helpful tools to screen for promising candidates.
In this work, a novel model to predict KIC via the fracture surface energy, γ, is presented. Our approach uses readily available crystallographic structure data of the glass’s isochemical crystal and tabled diatomic chemical bond energies, D0. The method assumes that γ of a glass equals the fracture surface energy of the most likely cleavage plane of the crystal. Calculated values were not only in excellent agreement with those calculated with a former well-working model, but also demonstrates a remarkable equivalence between crystal cleavage planes and glass fracture surfaces.
Finally, the effectiveness of fracture toughness enhancement by chemical substitution is discussed based on our results and alternative toughening strategies will be suggested.
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.