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Afterloading brachytherapy is conducted by the stepwise movement of a radioactive source through surgically implanted applicator tubes where at predefined dwell positions calculated dwell times optimize spatial dose delivery with respect to a planned dose level. The temporal exposure pattern exhibits drastic fluctuations in dose rate at a given coordinate and within a single treatment session because of the discontinuous and repeated source movement into the target volume. This could potentially affect biological response. Therefore, mammalian cells were exposed as monolayers to a high dose rate 192Ir source by utilizing a dedicated irradiation device where the distance between a planar array of radioactive source positions and the plane of the cell monolayer could be varied from 2.5 mm to 40 mm, thus varying dose rate pattern for any chosen total dose. The Gammamed IIi afterloading system equipped with a nominal 370 GBq (10 Ci) 192-Ir source was used to irradiate V79 Chinese hamster lung fibroblasts from both confluent and from exponential growth phase with dose up to 12 Gy (at room temperature, total exposure not exceeding 1 h). For comparison, V79 cells were also exposed to 6 MV x-rays from a clinical linear accelerator (dose rate of 2.5 Gy min−1). As biological endpoint, cell survival was determined by standard colony forming assay. Dose measurements were conducted with a diamond detector (sensitive area 7.3 mm2), calibrated by means of 60Co radiation. Additionally, dose delivery was simulated by Monte Carlo calculations using the EGSnrc code system. The calculated secondary electron fluence spectra at the cell location did not indicate a significant change of radiation quality (i.e. higher linear energy transfer) at the lower distances. Clonogenic cell survival curves obtained after brachytherapy exhibited an altered biological response compared to x-rays which was characterized by a significant reduction of the survival curve shoulder when dose rate fluctuations were high. Therefore, also for the time scale of the present investigation, cellular effects of radiation are not invariant to the temporal pattern in dose rate. We propose that with high dose rate variation the cells activate less efficiently their DNA damage response than after continuous irradiation. more...

Sulfur diffusion D S is reported on a technical alkali-poor barium alumoborosilicate glass melt at 900-1400°C and on three further Na 2 O-modified glass melts at 900°C, using a radioactive tracer method. Whereas D s for the base glass melt amounts to ≈ 1 x 10 -15 m 2 /s at 900°C, it increases nearly exponentially with increasing Na 2 O content from 0 to 15 mol% by almost three orders of magnitude. Similar to other glass melts, the sulfur diffusion obtained in these melts is also closely related to the Eyring diffusivity D n derived from viscosity. The diffusion controlling species in oxidized melts seems to be SO 2- 4 , in reduced melts S 2- . SO 2- 3 does obviously not play any role in this transport process. more...

The structure of two compositional series of ZrF4-LaF3-BaF2-MF (M = Li or Na) glasses has been examined by 19F magic-angle spinning (MAS)-NMR spectroscopy. From a detailed lineshape analysis, the fractions of corner-bridging (CBF) and non-bridging fluoride (NBF) species were extracted. With increasing LiF (or NaF) content, the fraction of NBF increases significantly, producing an increased spectral contribution of the low-frequency lineshape components. 19F{7Li} rotational echo double resonance (REDOR) experiments reveal that this part of the MAS-NMR lineshape interacts most closely with the 7Li nuclei. The compositional dependence of the NBF fractions is discussed in the context of various scenarios, describing the transformation of CBF units into NBF units, and affecting the average coordination number of the Zr ions. The results indicate that the evolution of the NBF fraction cannot be described by a single scenario over the entire composition range. more...

Glass bricks are important transparent building materials. They are produced by joining two halves of glass pressings at 600-700 °C. During this production process alkali oxides evaporate and are redeposited at the cooler inner front surfaces of the bricks. This surface layer reacts with H 2 O and CO 2 from the residual brick atmosphere, leading to the formation of an alkali-rich silicate-hydrate layer of ≥ 50 nm thickness, which could be evidenced leading to a reduced nano-hardness of similar thickness, and from which NaHCO 3 crystals can finally grow. Climate chamber experiments (repeated cooling between at -8 and -14 °C and reheating to 0 to 15 °C) resulted in reversible NaHCO 3 crystallization and redissolution, presumably influenced by water evaporation or condensation and driven by the NaHCO 3 supersaturation of the silicate-hydrate layer. Depending on the time-temperature schedule, different crystal morphologies became visible in this closed system, e.g. isolated spherical crystals, crystals arranged in chains and in double-chains, respectively, which can limit already the transmittance of the glass bricks. When a crack occurs or the brick is opened, the hygroscopic NaHCO 3 crystals take up more H 2 O from the ambient, react irreversibly with the glass surface, finally leading to a total loss of transmittance. more...

Sol-gel coatings composed of SiO2, SiO2-TiO2, SiO2-ZrO2 and SiO2-TiO2-ZrO2 were prepared on different technical enamels as substrates. Thin (from 80–300 nm) and thick (up to 2 μm) films were deposited by the dip coating method. The chemical durability of the coated and uncoated enamels was tested against acidic and basic attack in accordance with DIN ISO standards. The experimental results show that the thin SiO2 coatings increase the chemical resistance of the coated enamels against oxalic acid attack by a factor of 4 to 22 compared to the uncoated ones. Especially efficient were SiO2 films of 1 μm thickness, based on MTEOS-TEOS solutions. SiO2 films do not protect the enamels against NaOH attack; however, an SiO2-ZrO2 coating on a non-resistant low-network former enamel significantly increases its stability against this basic attack. SNMS in-depth profiles show that in this case Na, Ca and Ba diffuse from the enamel substrate into the sol-gel layer, apparently stabilizing it. more...

Sodium aluminophosphate samples with composition 43.8Na2O⋅12.5Al2O3⋅43.8P2O5 were prepared by the sol–gel route using different precursors and working in different pH ranges from pH 10. The structures of the gels and of the corresponding glasses were investigated by solid state NMR and compared to that of a glass with the same composition prepared by a traditional melting process. In addition to bulk materials, thin films were deposited by dip coating on silica glasses. Applying secondary neutral mass spectrometry (SNMS), the expected elements and residual carbon were identified. The surfaces of the coatings and fracture surfaces of bulk material were investigated using atomic force microscopy (AFM). Solid state NMR revealed that samples prepared via a lactate route exhibited local Al and P environments closest to that of the melt-prepared glass, with the highest extent of Al-O-P connectivity. more...

Gels and glasses along the compositional tie line Na2O–AlPO4 have been synthesized using an aqueous sol-gel route, using aluminum lactate, sodium phosphate, H3PO4 and sodium acetate (NaAc) precursors. The structural evolution from the solution to gel and the final glass is monitored ex-situ by multinuclear high-resolution liquid and solid state NMR techniques. The results indicate that the aluminophosphate network structure initially formed in solution is preserved in the gel and only subsequently disrupted upon annealing above 350 °C. A structural model of the AlPO4 network modification for these glasses has been developed on the basis of compositional trends observed in the 23Na, 27Al, and 31P single and double resonance NMR spectra. Addition of the Na2O network modifier to the tetrahedral AlPO4 network reduces the extent of Al–O–P connectivity, resulting in the increased formation of Na-bound phosphate species and aluminum in higher coordination states (AlO5 and AlO6 units). more...

Differently prepared SiO2, Na2O–SiO2, and Duran borosilicate glass surfaces were imaged by atomic force microscopy (AFM), both with an air-AFM and an ultra-high vacuum-AFM. The images of both microscopes display a nanostructure of SiO2 glass with a ripple pattern and a domain pattern, respectively, with coinciding sizes of several 10 nm. These domains show clusters of ⩾1 nm in diameter, in accordance with Bruckner’s SiO2 glass model of preordered regions. Inspecting glass fracture surfaces, prepared and imaged under ultra-high vacuum conditions, reveals structural features like interatomic distances, groupings of atoms, network holes, distribution of atomic distances, percolation paths, and topological connectivities of the glass structures. more...

Silica, silicate, borosilicate and heavy metal fluoride glasses were fractured under UHV conditions. The fracture mirror surfaces then were imaged by atomic force microscopy. The atomically resolved images display a fully interconnected random network arrangement for the silica glass, modified random network geometries with percolation paths for the silicate glasses, a structure with higher connectivity with some short percolation paths only for the borosilicate glass and a strongly interconnected structure for the heavy metal fluoride glass, probably with some chain- and ring-like geometric elements. Sodium diffusion, which is supposed to follow mainly these percolation paths, is qualitatively in line with the number, length and width of these paths. more...

The effect of different new sol-gel BaO—TiO2—SiO2 and CaO—BaO—TiO2—SiO2 coatings on long-term durability of glass fiber reinforced cement (GRC) was examined. Flexural strength of GRC was measured after curing for 7 to 150 days. Significant improvement was observed for coated GRC in this study and discussed in terms of the hydrate formation at interface. Concerned with the alkali resistance, CaO—BaO—TiO2—SiO2 coating was more effective than BaO—TiO2—SiO2 coating. In special, the 10CaO—10BaO—60TiO2—20SiO2 coating, prepared by sol-gel method, was recommended for the highest flexural strength of GRC and least corrosion at surface of E-glass fiber. more...

There are two anomalies at the tin bath side of silicate float glasses caused by the in-diffusion of tin into the glass melt, the tin hump in the micrometer region and the phenomenon of bloom, a microscopic wrinkling at the glass surface after reheating in air. A diffusion–reaction model is developed to explain the tin hump and it is shown that it occurs only for Fe 2 O 3 -rich (> 0.5 wt%) silicate float glasses. The bloom effect, on the other hand, is found only for Fe 2 O 3 -poor ( more...

Al-doped zinc oxide (ZnO:Al) films were deposited on glass substrates using a reactive midfrequency magnetron sputtering process. The optical transmission and reflection as well as the electrical resistivity of the films prepared on an area of 1000x600 mm(exp 2) were determined at different locations. Films with a uniform distribution of resistivity between 2.9x10(exp -4) and 3.6x10(exp -4) Omega cm and transmittance up to 88% in the visible spectral range were obtained. The ellipsometric spectra of the films were also analyzed using the Drude-Lorentz model. The calculated thicknesses of the films agreed well with those measured by a step profilometer. Secondary neutral mass spectrometry depth profiling showed uniform contents of Zn and O elements, while a slight periodic variation of the Al content was observed at different depths inside the film. A transition zone of 35-55 nm in width between the films and glass substrates due to the interdiffusion was also observed. more...

Atomic force microscopy was used to study the surface morphology of sol-gel derived Al2O3-TiO2-SiO2 coatings on microscope glasses. The coatings freshly annealed at 500°C for 1 h were homogeneous on a nanoscale and showed typical glass pattern. After 10-month storage in air either before or after annealing, tetragonal-like crystallites were observed in coatings. The effects of chemical compositions and the storage process on the surface topography and the crystallization of anatase were studied and discussed in combination with the XRD results of corresponding annealed gels. more...

A glass of composition 53ZrF4–20BaF2–4LaF3–3AlF3–20NaF (Tg=260°C) was prepared by careful crucible melting. High-resolution atomic force microscopy of fracture surfaces displayed the presence of nano-pores with diameters of 20–50 nm, being 4–10 nm deep, in all glasses. It was further found that only glasses without annealing and glasses with an annealing step considerably below Tg showed a distinct pattern, i.e. ripples of ≈20 nm in diameter and an rms roughness of ≈0.6 nm. Glasses annealed either near Tg or at the temperatures of maximum nucleation or maximum crystal growth rates showed both regions with the ripple pattern and regions with nano-hillocks, growing in size with increasing annealing temperature and time. Thus these hillocks nearly reach micro-dimensions of ≈270 nm in diameter and ≈65 nm in height following a 90 min annealing step at 343°C, the temperature of maximum crystal growth. These findings give evidence that the glass system, which is thought to be one of the most suitable for fiber drawing, is much less stable against nucleation and crystallization than anticipated. more...

The introduction of dynamic intensity modulation into radiotherapy using conventional photon beams or scanning particle beams requires additional and efficient methods of dose verification. Dose measurements in dynamically generated dose distributions with a single ionization chamber require a complete application of the treatment field for each single measurement. Therefore measurements are performed by simultaneous use of multiple ionization chambers. The measurement is performed by a computer controlled system and is comprised of the following steps: (a) automated positioning of the ionization chambers, (b) measurement at these points, (c) a comparison with the calculated dose from the treatment planning system, and (d) documentation of the measurement. The ionization chambers are read out by a multichannel electrometer and are densely packed into a mounting of polymethylmetacrylate, which is attached to the arm of a three-dimensional motor-driven water phantom. The measured and planned dose values are displayed numerically as well as graphically. The mean deviation between measured and planned doses as well as their standard deviation are calculated and displayed. Through printouts complete documentation of the measurement is obtained and a quick decision can be made whether the dose distribution is acceptable for the patient. The system is now routinely used for dose verification at the heavy ion therapy project at the Gesellschaft für Schwerionenforschung in Darmstadt. Up to now 242 measurements have been performed for heavy ion treatment of 30 patients. The system allows efficient verification and documentation of carbon ion fields and is in principle also applicable to intensity-modulated photon beams. more...

Atomic force microscopy (AFM) was used to study the performance of ≈80 nm thick Al2O3-TiO2-SiO2 sol-gel coatings on glass substrates following corrosion in 1 M NaOH solutions at 60°C. The as-prepared coatings were homogeneous on a nanoscale and displayed the “glass pattern” before corrosion. Layers with different compositions behaved differently during the corrosion process. Thus, TiO2 or TiO2-dominated layers had tetragonal-like crystals on their surfaces after corrosion, possibly of anatase composition. On the other hand, layers with a molar ratio Al2O3 : SiO2 near 1 : 2 displayed a pseudo-hexagonal morphology, possibly with a nepheline (Na2O · Al2O3 · 2SiO2) composition. Layers of 5Al2O3-40TiO2-55SiO 2 were corroded is a stepwise fashion and had no special surface morphology. more...

Atomic force microscopy (AFM) provides high resolution images of surfaces even if they are non-conducting. Thus, glass can be investigated without conductive preparation or other complicated preparation techniques. So far, the great advantage of this microscopy in ambient atmosphere impeded atomic resolution on vitreous surfaces. However, AFM proved to be an appropriate tool for imaging the structure on a nanometre scale, of glasses, glass ceramics and coatings on glass. AFM serves to detect surface defects and changes in the overall surface topology after different treatments, such as polishing, cleaning, aging and corroding. With the help of suitable preparation, volume properties can also be investigated with a spatial resolution in the nanometre range. AFM contributions to glass research fields like fracture mechanics, crystallization, interfaces and gel consolidation are reviewed in this paper. more...

Thick Fe2O3−SiO2 sol-gel coatings with 30 wt%Fe2O3 were prepared on glass substrates under different conditions. These were investigated by scanning electron and atomic force microscopies. The performance of the layers depended also on the way the substrate surface was pretreated. Annealed bulk gel pieces showed phases like FeCl2×2H2O and presumably C9Fe2O9 (300°C); at higher annealing temperatures, hematite, cristobalite and magnetite could be found. more...

After having been exposed to space radiation on the experimental platform Eureca (European Retrievable Carrier) for almost eleven months, different optical glasses were examined to determine radiation effects. For the 500 km high orbit with low inclination a radiation dose of 10 3 Gy is assumed. Using electron paramagnetic resonance (EPR) spectroscopy spectral components due to radiation effects were detected at room temperature. Oxygen hole centers (OHCs) were indicated in borosilicate glass, soda lime glass, phosphate crown glass, fluor crown glass and lanthanum crown glass, Ti 3+ was found in borosilicate glass. All investigated materials — excluding fused silica and fluoride glass — had differing intensities of Fe 3+ components caused by iron impurities in the samples. Comparing these results to earth specimen used in a simulation program, specially developed in preparation for the Eureca mission, the same type of radiation induced defects were identified. This confirms the validity of the simulation program as an appropriate tool to predict the performance of glass materials before space missions. more...

Textured glass ceramics of Li2O · 2SiO2 composition were prepared with a highly oriented microstructure. This orientation was achieved by surface crystallization and by volume crystallization moving the glass through a temperature gradient. The microstructure was determined by scanning electron microscopy. Quantitative texture investigations were performed by X-ray pole figure measurements, calculations of orientation distribution functions and inverse pole figures. The degree of orientation was calculated for randomly oriented bulk material, surface-crystallized material and material crystallized in the temperature gradient. The (0 0 2) planes of the surface-crystallized and of the temperature-gradient-crystallized materials resulted in a strong fiber texture parallel to the surface of the sample with a texture intensity about 40 times that of random material in the normal direction. more...

With a view to the protection of fluoride glasses, a water-resistant oxide glass with a transformation temperature, T g , of 227°C and a thermal expansion coefficient, α, of 20.6 × 10 −6 K −1 was developed. The hydrolytic resistance was comparable with that of commercial soda-lime silicate glasses for corrosion times up to 12 h. Additions of tungsten oxide to the phosphate glass cause a shift in the viscosity-temperature curves to higher temperatures and therefore fluoride glasses with T g values in the range of 260–340°C may be coated with the glass system mentioned. The thermal expansion coefficient of the overclad could be varied in the range from 16.9 to 20.6 × 10 −6 K −1 . Further, it could be shown that an appropriate oxide-fluoride composite can be produced in a fiber drawing process. more...

Using a hole-bushing drawing process, oxynitride glass fibers could be produced successfully in three different compositions. Although this method has resulted thus far in fibers on non-constant diameters only, several physical and chemical properties could be determined. Fibers of the glass system MgO-Al 2 O 3 -Y 2 O 3 -SiO 2 with an N content of 15.8 at.% partly displayed tensile strengths up to 13 GPa (20 μm diameter fibers), a Young's modulus of 200 GPa and an extremely high chemical resistance against 1N NaOH solution. Despite the scatter in the reported data, these oxynitride fibers seem to be the most stable glass fibers investigated thus far. more...

Space offers some unusual possibilities for experiments. Most space investigations executed thus far used the microgravity of 10−3–10−5g (g = gravitational acceleration on Earth), which influences experiments where gas, liquid or melt phases are involved. On Earth, distortion mainly by convective transport processes comes from buoyancy forces, whereas in space these forces are suppressed. Experiments thus yield intrinsic data according to pure atomic or molecular transport. Some of the glass experiments conducted thus far by the author's group are briefly reviewed: gas bubbles in glass melts, interdiffusion in glass melts, and homogeneity of glasses. Further, a recent experiment is presented, where glasses and glass ceramics are exposed to the unfiltered radiation in space. The macroscopic and microscopic defects induced by this radiation are discussed. more...

Secondary neutral mass spectrometry (SNMS) has been used to profile coatings of the systems SiO2 and 65SiO2.20TiO2.15ZrO2 (STZ). The coatings have been deposited on float glass and heat insulating glass by dip coating from alkoxide solutions. The microporous gel coatings have been densified by heat treatment. The SBM method (separate bombardment mode) has been applied to characterize the systems and the HFM method (high frequency mode) to check for matrix effects in the SBM depth profiles. Both methods show sodium diffusion from the float glass substrate into the STZ coating and no significant sodium diffusion into the SiO2 coating. Measurements of the coatings on the heat insulating glass indicate that the SnO2 interlayer acts as a diffusion barrier. The diffusion of sodium from the float glass substrate into the STZ coating during consolidation has been analyzed by SBM-SNMS. The sputtering rate decreases with increasing consolidation. Due to large differences between sputtering rates of the substrate and of the microporous coatings, the calibration of sodium intensities from time to depth at the interface has not been possible. However, a correlation between the final temperature of heat treatment and the depth of the Na2O depletion in the substrate surface under the coating can be obtained. more...

Glass ceramics of the composition Li2O⋅2SiO2.were prepared with an oriented microstructure. The oriented crystalline phase is orthorhombic lithium disilicate. This orientation was achieved by crystallization of glass fibers and bulk glasses in a temperature gradient and under isothermal conditions. Both bulk and surface crystallization were achieved. Further, oriented crystalline films were prepared on glassy and crystalline substrates by a sol-gel method. Scanning electron microscopy and atomic force microscopy were used to characterize the microstructure. The degree of orientation was investigated by X-ray pole figure measurements from which orientation distribution functions and inverse pole figures were calculated. The (002) plane of the surface crystallized material shows a strong fiber texture parallel to the surface of the sample. more...

Optical and electron optical methods were used to study the homogeneity of some Libyan Desert glass (LDG) samples which displayed dark brown bands and streaks. These inclusions contained Fe 2 O 3 , and wollastonite (CaSiO 3 ) and cristobalite (SiO 2 ) crystals were also found in them. Electron microprobe line analyses showed inclusions which, under the assumption that peak-like element distribution curves can be interpreted as diffusion profiles, led to the conclusion that high-temperature dissolution processes may have had some importance during the genesis of LDG. more...

New alkali resistant BaO-TiO2-SiO2 coatings have been developed via the sol-gel process. In the solutions and in the gels (T

Using Ag as a nucleating agent, the processes of controlled nucleation and crystal growth could be investigated for a ZrF 4 BaF 2 YF 3 AlF 3 glass by means of scanning electron microscopy. A two-stage heat treatment procedure was applied. Interestingly, the crystal phase distribution is bimodal. The fine-grained crystal phase has an extremely high maximum nucleation rate of 3.8 × 10 9 cm −3 s −1 , which is about six orders of magnitude higher than that for the coarse-grained β-BaZrF 6 phase. This phase is obtained for Ag and was also obtained previously for Pt and Se as nucleating agents. Using proper experimental conditions a crystal fraction of up to 100% could be developed in a controlled way. more...

Glasses containing up to 3.3 wt% nitrogen were prepared in the system MgO-Al[sub 2]O[sub 3]-SiO[sub 2]-AlN-Si[sub 3]N[sub 4]. Glass transition temperature, density, and elastic properties increased with increasing nitrogen content. Resistance against aqueous alkaline solutions was determined by weight loss measurements, solution and surface analysis. The good durability of both oxide and oxynitride glasses is caused by a protective surface layer. The introduction of nitrogen decreases the alkaline attack. The data suggest that nitrogen is incorporated as Si-N bonds. more...

A project has been set up to study the effect on a radiotherapy patient of the neutrons produced around the LINAC accelerator head by photonuclear reactions induced by the gamma radiation above ~8 MeV. These neutrons may reach directly the patient, or they may interact with the surrounding materials until they become thermalised, scattering all over the treatment room and affecting the patient as well, contributing to the peripherical dose. Spectrometry was performed with a set of Bonner spheres at 50 cm from the isocenter and at the place where a digital device for measuring neutrons will be located the treatment room. Exposures have taken place in six linac accelerators with different energies (from 6 to 23 MV). A summary of the spectrometry results and of the neutron doses received by the patient is presented. more...

Using a trace of Pt as a nucleating agent, several ZrF 4 –BaF 2 –YF 3 –AlF 3 glasses could be transformed to some extent to glass-ceramics by controlled nucleation and crystallization. The thermal expansion coefficient was decreased and the density and Young's modulus were increased with increasing crystal fraction, and also the water resistance was enhanced. more...

N-containing Li2OSiO2 glasses were prepared by different melting and sol-gel processes. The nitrogen was incorporated into the glasses by adding BN at different stages of the procedure. Thus it was possible to include nitrogen up to 0.34 wt%. Despite this low content the nitrogen influences some physical and chemical properties. For example, glass transition temperature and microhardness are increased and the chemical durability in water is improved. This indicates a tightening of the glass structure by the nitrogen. more...

Soda-lime glass samples with fresh fracture surfaces were treated in H 2 O and D 2 O for 15, 30, 60, and 120 min at 60°C and 85°C. The depth profiles of sodium and calcium in the leached layers were determined by NPB-SIMS, a technique which avoids surface charging by using neutral primary particles. When the glass is subjected to irreversible deformation occurring in the ‘plastic zone’ around the crack tip, a great number of siloxane bonds are broken, and therefore rapid diffusion pathways may be created. The influence of the deformed layer on the leaching kinetics was taken into account by a simple mathematical model. Starting from the assumption that the rapid pathways may be represented by pervading pores, a simple ion exchange between the water which quickly penetrates into the pores and the surrounding network is supposed. From the model of McClintock and Irwin, the thickness of the altered layer was estimated at about 15 nm. Considering the simplest case that hydronium ions are incorporated into the network at a constant rate, the mathematical description of the diffusion process reduces to a boundary value problem which is accessible to an analytical solution by the Laplace transform method. The calculated Na 2 O concentration profiles are in good agreement with the concentration profiles determined after a treatment in D 2 O at 60°C. The fit was based on an interdiffusion coefficient of D = 1 × 10 −15 cm 2 s −1 which holds for the network of the porous layer as well as for the unaltered glass. more...

Fracture surfaces of Suprasil 2, Herasil 2, AR glass and Duran glass rods have been studied by an atomic force microscope (AFM) in the contact mode. They could be characterized in the fracture mirror, the mist and the hackle zones. The RMS (root mean square) roughness in the fracture mirror of all glasses investigated increased with growing distance from the origin of the fracture. On several fracture surfaces of different glasses steps have been observed, due to fracture in shear mode. Furthermore changes in the fracture surfaces during scanning have also been observed. They are thought to stem from reactions of the freshly broken glass surface with the surrounding atmosphere and forces between the scanning tip and the soft surface. more...

Scratch resistant coatings on glasses and plastics are very important for the automobile industry. The windscreen in particular is exposed to considerable influences such as particle impact and abrasion through dust by the windscreen wiper or an ice scratcher. An increase of damage to the windscreen leads to light scattering, which reduces the driver’s view and endangers the security of all the road-users. more...

The Young's modulus, E, and the fracture toughness, KIc, were investigated for the glass series Te2Se7−xAsxI (x = 0−6), Te3−xSe6AsxI (x = 0−2.5), and Te5−xSe3AsxI2 (x = 0−4), respectively. For the glass series Te2Se7−xAsxI, E increased from ∼13 GPa to ∼19 GPa and K Ic from ∼0.15 MN m −3 2 to ∼0.3 MN m sol−3 2 for x = 0−6 . For the other two glass series E and KIc decreased to some extent with increasing As content. An attempt is made to discuss this dissimilar concentration dependence of the mechanical stability by structural models. more...

Hostile environments created by short wavelength elcctromagnetic radiation, for example UV. X-ray and γ-radiation, or from particle fluxes, for example α-particles. s-particles. protons and neutrons, can produce defects within optical glasses. This loss of transmission is detrimental to the performance of the optical system and must eliminated or reduced to a manageable level. For applications within these hostile environments, radiation-stabilized optical glasses have been developed. Radiation test results will be presented, discolouration of stabilized and not stabilized glasses will be compared and colour-centers will be discussed. more...

Atomic force microscopy has been used to investigate the topology of alkoxide gel dip coatings on different substrates. Results of SiO 2 -TiO 2 -ZrO 2 (STZ) coatings are presented on float glass, on polished fused silica, on commercially coated insulating flat glass, and on PtRh. (1) Consolidated STZ coatings display the so-called glass pattern with ripples equal or less than 2 nm high. The same pattern is seen on partially dense STZ coatings, as soon as the surface is stiff enough for scanning, and also on the bottom of a 50 nm deep sputtering crater in the consolidated coating. (2) The vitreous STZ coating on the fire side of the float glass is as flat as the float glass itself. It has the same tendency to contamination. 100 nm wide and 50 nm deep polishing grooves on fused silica have been filled up with the 80 nm thick coating, only dips of a few nm remain. The trenches between the SnO 2 crystallites on the insulating flat glass were filled up and the roughness of the substrate was partially reduced. PtRh sheet remained rough even after the coating. (3) On the partially densified STZ coating, sputtering generates a grained surface. more...

The aim of this study was to produce far-IR transmitting chalcogenide glass- ceramics, doped by appropriate nucleants. These materials, with improved thermal and mechanical properties, are to be applied as passive optical components in infrared systems and in high-power laser systems. By replacing light elements such as S or Se by a heavier element Te, the cut-off of the glasses shifted further into the IR region up to 16 jim. A base glass composition Ge32Se40Te28, which was found to be stable, was doped with a suitablenucleator, ZrSe2, and heat-treated in order to obtain glass-ceramic materials. The percentage of transmission of an undoped glass heated at 350°C (80°C above Tg) for 6 hours, dropped to 10% in the spectral range 8.O-l4.Oim, while thetransmission of a similar glass composition doped with 0.5 mole% of ZrSe2 was almost uneffected when heat-treated under the same conditions.So far, no remarkable improvement in the mechanical properties was detected. 2. INTRODUCTION more...

Up to 3.3 wt% nitrogen can be incorporated into Na2O-B2O3 glass melts. The melting procedure is described, and structure models are given. In contrast to N-containing silicate glasses, the borate glasses were transparent; however, micrographs of their fracture surfaces showed some crystallinity. Properties were determined as a function of the N and Na2O contents of the glasses. Compared with N-containing silicate glasses, the properties of borate glasses are much less changed by the nitrogen introduced. more...

The viscosities and surface tensions of three MgO-Al2O3-Y2O3-SiO2-based oxynitride glass melts were measured. Glass transition temperature, Littleton temperature, and sink-in temperature were obtained, and by using the Vogel-Fulcher-Tammann equation the viscosities were calculated from Tg (820° to 940°C) to 1600°C. The surface tensions were measured by the drop weight and the drop geometry methods and displayed values between about 500 and 600 N.mm−1. These values are about a factor of two higher than the surface tensions of oxide glass melts. more...

The strong influence of chemically dissolved nitrogen on the physical properties of oxynitride glasses based on the system Na2OCaOSiO2 has been investigated considering that three different modes of nitrogen incorporation in the glass network or combinations of these modes might be possible. Based on the theoretical calculation of Young's modulus of oxynitride glasses from their chemical compositions, one mode of nitrogen incorporation was determined to be the most probable. This conclusion was confirmed by considerations of the experimental data concerning the viscosity of oxynitride glass melts, the activation energy of viscosity, infrared spectra and ESCA measurement. This mode of incorporation proposes the nitrogen to be bonded to three silicons of the oxynitride glass network which, therefore, attains a higher degree of linkage than in pure oxide glass. more...

Glass melts of the metallic alloy system Pd10–70Ni10–70P14–26 were saturated with helium gas during the melt-spinning process. Some melts with platinum substituted for palladium; manganese, iron or cobalt for nickel; and boron for phosphorus could also be saturated. The helium could be extracted from the glasses and the amount of gas was quantitatively measured with a mass spectrometer. The helium solubilities, obtained between 750 and 1250° C, varied between about 2 and 45 (μl He per mol glass) (T/273). These solubilities turned out to be strongly composition-dependent. This fact is discussed in terms of different short-range order structure units which are directly related to the free volume available for the gas solution process. more...

Different glasses of the chalcogenide systems SeGeAs and SeSnAs were prepared. Fracture surfaces were investigated by scanning electron microscopy. All glasses displayed a microstructure which was similar for both systems. These inhomogeneities, consisting in most cases of globular particles with a “tail”, were enriched in Ge and Sn, respectively. Their numbers and diameters were dependent on the quenching rate and on the pre-annealing of the samples. Most probably their origin may be understood by a segregation process. more...

Thirty different glass compositions of the system SeSnAs were prepared. The glasses were then characterised by measuring the properties: glass transition temperature, T g ; density, p ; elastic constants, E , G , K and μ; load-independent microhardness, L 2 VH; and elastic recovery, r . In most cases the dependence between property and chemical composition is non-linear. This effect is discussed with respect to different structural units in the glasses. more...

Se, As and Ge self-diffusion were investigated in three different glasses of the chalcogenide system SeGeAs by means of the radioactive tracers 75 Se, 73 As and 71 Ge. All D values (Se between 200 and 290°C, As between 240 and 290°C and Ge between 280 and 295°C) lay between 10 −14 and 5 × 10 −16 cm 2 s −1 . The diffusion profiles were analyzed using a chemical micro-etching technique. Roles of glass structure and possible diffusion mechanism are discussed. more...

The microhardness of chalcogenide glasses of the system Se-Ge-As was investigated for twelve different compositions. An apparatus was constructed which was capable of recording loading and unloading curves, and the results evaluated according to the method of Frohlich and Grau. The Vickers microhardness valuesL 2(vh) obtained were independent of load and are thought to be material constants. TheseL 2(vh) values varied between 700 and 1400 N mm−2 in the Se-Ge-As system and showed a non-linear dependence on composition. This is explained structurally by the existence of varying proportions of different short-range order units in the different glasses. The elastic recovery after unloading varied between 45 and 61% for a maximum load of 1.96 N. more...