High-strength Glasses Research Articles

Epoxy Radiotechnical Hot Pressed Glass Fiber Plastics for Ship Aerial Fairings and Protection of Antennas in Radio Connection and Radio Location Systems

The present work is aimed at solving an urgent scientific problem of creation of high-strength and water-resistant dielectric glass-reinforced hot pressed glasses using bi- and polyfunctional epoxy amine binders and fiberglasses from alkalineless, quartz, and silica glasses, as well as their use in shipbuilding.

Hertzian Testing to Obtain Flaw Distributions in High Strength Glasses and Glass‐Ceramics

Hertzian testing is applied to obtain flaw distributions in two fusion‐drawn glasses and two glass‐ceramics. A tungsten carbide sphere (diameter either 1.0, 2.5, or 5.0 mm) was used to produce surface cracks (ring cracks and cone cracks). Two theoretical approaches were employed to describe the data. Both approaches are only descriptive for very high strength materials in which the surface flaw sizes are small (e.g., <1 μm). In the first, a Weibull distribution for strength was assumed, and an expression for the probability of fracture was derived based on the stress field around the indent contact area. The unique aspect of this is that the stress field used includes material that has been “probed” at loads below the fracture load. A Weibull plot with this expression shows a slope of m + 2, where m is the conventional Weibull modulus. For the four different materials, the Weibull modulus varied between 8.0 for β‐quartz glass‐ceramic to 14.2 for fusion drawn alumni silicate glass. The second theoretical approach employs a modification of the method of Poloniecki and Wilshaw (the PW Method) to describe the distributions of very small flaws. The modification removes the need to bin the flaw distribution data. The modified PW Method revealed distinct differences in the flaw distributions between the four materials. These differences are consistent with the different Weibull moduli determined by ranking the different materials according to flaw size. However, Hertzian testing only probes relatively small flaw sizes and thus may differ from typical tensile or bending tests; nevertheless, the method should be applicable for extremely high strength materials.

The properties of glass resistive plate chambers made of different glasses

Glass resistive plate chambers (GRPCs) have been proposed as the basic element for the JUNO top tracker detector. With good uniform performance and low cost, GRPCs are well suited for large area experiments. Glass RPCs used in underground experiments require specially designed cassette and gas flow systems, since the glass is fragile and easily corroded by acid generated by water entering the gas-filled chamber. High-strength and chemical-resistant glasses have been proposed for underground experiments. We present here the test results of four GRPC chambers made of different glasses: normal thin glass, two high-strength glasses, and a chemical-resistant glass. The chemical-resistant and high-strength glasses have good surface quality, but their volume resistivities are higher. Higher resistivities lead to a higher required voltage to reach plateau operation, meaning that these glasses can only work in a very low rate experiment.

Thermal poling of alkaline earth boroaluminosilicate glasses with intrinsically high dielectric breakdown strength

Per the rectification model of thermal poling, it has been proposed that intrinsic breakdown strength plays a strong limiting role in the internal DC fields supported by the glass from the poling process. One might therefore hypothesize proportionately larger second-order nonlinearity (SON) in glasses with intrinsically high dielectric breakdown strength. We test these ideas by thermal poling of two different commercial alkali-free alkaline-earth boroaluminosilicate display glasses—one with barium only (AF45 from Schott), and the other with a mixture of alkaline-earth ions (OA-10 G from NEG). Not only are such compositions relevant from a commercial standpoint, they are also interesting in that they have been recently shown to exhibit remarkably high intrinsic dielectric breakdown strengths of 11–14 MV/cm. Quantitative Maker fringe and stack Maker-fringe measurements provide an accurate evaluation of the poling-induced SON susceptibilities, and indicate maximum χ(2) values of 0.44 and 0.26 pm/V in these glasses. These values are comparable to those reported for silica and other multicomponent glasses. Thus, the hypothesis that higher χ(2) would be observed in high intrinsic breakdown strength glasses was not validated. Based on our application of the rectification model, internal fields of the order 2–4 MV/cm were calculated, which are well below the measured intrinsic breakdown strengths at room temperature. The most plausible explanation for these observations is nonlinear electronic conduction effects taking place within the depletion region at the poling temperature, limiting internal fields to a fraction of the breakdown field.

Numerical Studies on Effects of Cavity Width on Smoke Spread in Double-skin Facade

Double-skin façade is more and more popular in modern buildings in recently years due to it can provide the building with improved thermal and sound insulation compared with a traditional glazed facade. But fire safety is a problem, the inner glass wall broken during a fire would lead to the smoke and flame spread to the adjacent levels, this might be dangerous for the occupants in those areas. Many such projects failed to comply with the fire safety codes at present. Engineering approach similar to performance-based fire codes practicing in some countries was applied to demonstrate the design is safe. Fire hazard assessment should be supported by the further investigations on the smoke and fire spread in DSF. Cavity depth effects, one of the key factors which can influence the smoke flow in DSF would be studied by numerical method in this paper. By examining the results for cavity depth of 0.5, 1.0 and 1.5 m, it is found that a wider cavity might give better fire safety under the scenarios studied. The outer glass panel would be broken rapidly for the cavity of 0.5m deep. a Cavity depth of 1.0 m might be the most risky design comparing with the other two cavity depths studied, the inner glass panel might be broken before the outer panel, this might lead to the fire spread to the adjacent upper levels, high strength glasses should be used or other protection measures should be taken for the DSF design under this condition. Further studied should be required for an in-depth understanding the smoke and fire spread in DSF in the further.

Glass micro-container based hydrogen storage scheme

Glass is the material of choice for inertial confinement fusion (ICF) targets due to its high strength [Bartenev GM, Sanditov DS. The strength and some mechanical and thermal characteristics of high-strength glasses. J Cryst Solids 1982;48:405]. There exist many technologies for producing fusion grade glass microballoons (GMBs) also known as hollow glass microspheres (HGMS) and filling techniques up to 1000 bars. These glass micro-containers offer a novel scheme of hydrogen storage [Rambach GD, Hendricks C. Hydrogen transport and storage in engineered glass microspheres. In: Proceedings of the 1996 USDOE hydrogen program review meeting, Miami, National Renewable Energy Laboratory; 1996. p. 765]. A comparative evaluation of hydrogen storage efficiency has been done for high tensile strength GMBs at different radius to wall thickness ratio termed as aspect ratio. By experimental and theoretical calculations, we propose the use of high aspect ratio GMBs with storage efficiency from 15% to 25% w/w for GMBs at pressures below 500 bars. Such efficiencies are unique, being greater than large cryostat ( ∼ 14 % w/w), and safe compared to large pressure vessels, etc. For the pressure range 150–300 bars a prototype hydrogen filling system has been developed in our laboratory. We have experimentally attained gravimetric efficiency η = M H / ( M H + M S ) as 15–17% for the GMBs. The advantages and also some shortcomings of this technique are compared with other hydrogen storage methods such as metal hydrides, physisorption and chemisorption, etc.

Fabrication Method for Hollow Microspheres Made of High-Strength Glasses

AbstractLasting storage of hydrogen, its isotopes and other gases under high (1–2 thousand atm) pressure inside hollow microspheres as well as production of low-density syntaxis poroplasts to withstand high external loads - all these need hollow microspheres of high mechanical strength. By modern commercial technology the microspheres are mainly obtained from water- soluble alkali-silicate or alkali-boro-silicate glasses. These microspheres are not strong, their strength being 1000–1500 MPa.. Besides the low resistivity to hydrolysis and chemicals also restrict their applications. To gain strength 1.5–2 times higher the additional modification of microspheres is done either by leaching, or by annealing, or by ion exchange. Microspheres of stronger glasses being usually multi-component require a technology fitted to produce highly uniform glass [1,2].A new fabrication method is presented to produce hollow microspheres of various glasses. They include simple alkali and alkali-boro-silicate glasses as well as multi-component glasses of commercially available compositions, alkali-free, refractory, and high-strength glasses.

The characterization of high-strength surface-crystallized glasses

Controlled surface crystallization has become established as a method of significantly improving the mechanical strengths of glasses. Previous work has indicated that the surface state of the glass prior to crystallization can profoundly influence the microstructure of the surface-crystallized layer and thereby modify the mechanical strength of the material produced. The purpose of the present investigation was to study the effects of different surface-abrasion treatments, prior to crystallization, upon the microstructure of the surface-crystallized layer and the mechanical properties of two glasses. Indentation fracture was employed to characterize the glass surface and electron microscopy to investigate the microstructures that developed. For a calcium zinc aluminosilicate glass, although the microstructure of the surface-crystallized layer was dependent on the prior surface state of the glass, there was no clear cut relationship with the mechanical strength of the surface-crystallized glass. This was attributed to surface flow of the glass during heat-teatment. For a calcium aluminate composition, the microstructure of the crystallized layer was clearly dependent on the prior surface state of the glass and evidence was provided that flaws in the surface served to provide crystal nucleation sites. The mechanical strength of the surface-crystallized glass was markedly dependent on the microstructure and with a suitable surface treatment a mean modulus of rupture of 510 MN m−2 was achieved.

The strength and some mechanical and thermal characteristics of high-strength glasses

The calculation of the ultimate strength of the silicate glasses, based on the microheterogeneous structure of these systems, is presented. The ultimate strength is determined by the stress ( δ n = − U o / r 3 o ) required for certain configurational changes (quasi-breaking, local loosening) in the glass structure at the boundaries between the microheterogeneities (microblocks, complexes). The ultimate strength depends not only on the modulus of elasticity E = β/ r o , where β is the power factor, but also on Poisson's ratio μ, which depends, together withβ, on the disharmony of the bonds g. It is shown that the disharmony of the bonds plays an important role in certain cases in the process of the glass destruction (fracture). The interrelationship between the ultimate strength and microhardness, surface tension, thermal expansion coefficient, glass-transition temperature, internal molecular pressure, which all depend on the same, in nature, configurational changes of the structure in the boundary region, as those of the destruction, are presented.

Some recent developments in high-strength glasses and ceramics

Two areas of development in the field of glasses and ceramics have produced new materials with unusual combinations of properties. Glass-ceramics are melted and formed as glasses by conventional glass-forming techniques, but by a subsequent heat treatment, they are converted to fine-grained crystalline structures with new and useful combinations of properties. Products with thermal expansion coefficients approaching zero and flexural strengths ranging from 10 000 to 50 000 Lb./in. 2 have been made though not all combinations of low thermal expansion coefficients and high mechanical strengths are possible. The second area of development is in so-called Chemcor glasses. Such glass products can be preferentially pre-stressed by chemical means so as to produce an outer layer with high compressive stress and a bending strength in the finished product up to 100 000 Lb/in. 2 .

Producing high-strength glasses

Producing high-strength glasses