Glass and Glass-Ceramic Sealant Compositions

A glass composition for use as a sealant or otherwise bonded to a fuel cell component, including from about 40 mol % to about 60 mol % RO; from about 2 mol % to about 10 mol % M2O3; and from about 35 mol % to about 45 mol % SiO2. R is selected from the group including strontium, calcium, magnesium and zinc and combinations thereof. M is selected from the group including aluminum, boron, lanthanum, iron and combinations thereof. The glass includes at least about 5 mol % ZnO. Upon heat treatment, the glass at least partially crystallizes with the formation of at least one alkaline earth-zinc pyrosilicate crystalline phases

Corrosion-Resistant Glasses for Steel Enamels

A cementitious composite material wherein glass-coated steel rods are positioned in a cementitious matrix. The glass composition for coating the steel reinforcing rods includes between about 33-45 weight percent SiO2, 13.5-19.5 weight percent B2O3, 3.5-4.6 weight percent Al2O3, 4.0-13.5 weight percent K2O, 5.5-15.5 weight percent ZrO2, 8.6-15.9 weight percent Na2O, 4.6-5.1 weight percent CaO, 0.6-0.7 weight percent MnO2, 1.0-1.0 weight percent NiO, and 1.0-1.1 weight percent CoO. The glass composition is typically in compression on the rods at ambient temperatures, has a coefficient of thermal expansion of between about 12.5 and about 13.5, and has a softening temperature of between about 585 degrees Celsius and about 600 degrees Celsius

Corrosion-Resistant Glasses for Steel Enamels

A cementitious composite material wherein glass-coated steel rods are positioned in a cementitious matrix. The glass composition for coating the steel reinforcing rods includes between about 33-45 weight percent SiO2, 13.5-19.5 weight percent B2O3, 3.5-4.6 weight percent Al2O3, 4.0-13.5 weight percent K2O, 5.5-15.5 weight percent ZrO2, 8.6-15.9 weight percent Na2O, 4.6-5.1 weight percent CaO, 0.6-0.7 weight percent MnO2, 1.0-1.0 weight percent NiO, and 1.0-1.1 weight percent CoO. The glass composition is typically in compression on the rods at ambient temperatures, has a coefficient of thermal expansion of between about 12.5 and about 13.5, and has a softening temperature of between about 585 degrees Celsius and about 600 degrees Celsius

Resilient Sealing Materials for Solid Oxide Fuel Cells

This report describes the development of ''invert'' glass compositions designed for hermetic seals in solid oxide fuel cells (SOFC). Upon sealing at temperatures compatible with other SOFC materials (generally {le}900 C), these glasses transform to glass-ceramics with desirable thermo-mechanical properties, including coefficients of thermal expansion (CTE) over 11 x 10{sup -6}/C. The long-term (>four months) stability of CTE under SOFC operational conditions (e.g., 800 C in wet forming gas or in air) has been evaluated, as have weight losses under similar conditions. The dependence of sealant properties on glass composition are described in this report, as are experiments to develop glass-matrix composites by adding second phases, including Ni and YSZ. This information provides design-guidance to produce desirable sealing materials

Effects of Rare-Earth Doping on Femtosecond Laser Waveguide Writing in Zinc Polyphosphate Glass

We have investigated waveguide writing in Er-Yb doped zinc polyphosphate glass using a femtosecond laser with a repetition rate of 1 KHz. We find that fabrication of good waveguides requires a glass composition with an O/P ratio of 3.25. The dependence on laser writing parameters including laser fluence, focusing conditions, and scan speed is reported. Waveguide properties together with absorption and emission data indicate that these glasses can be used for the fabrication of compact, high gain amplifying devices

Coated Steel Rebar for Enhanced Concrete-Steel Bond Strength and Corrosion Resistance

This report summarizes the findings and recommendations on the use of enamel coating in reinforced concrete structures both for bond strength and corrosion resistance of steel rebar. Extensive laboratory tests were conducted to characterize the properties of one- and two-layer enamel coatings. Pseudostatic tests were performed with pullout, beam and column specimens to characterize mechanical properties and develop design equations for the development length of steel rebar in lap splice and anchorage areas. The splice length equation was validated with the testing of large-scale columns under cyclic loading. For corrosion properties, ponding, salt spray, accelerated corrosion, potentiodynamic and electrochemical impedance spectroscopy (EIS) tests were conducted to evaluate the corrosion resistance and performance of enamel-coated steel and rebar. Experimental procedures and observations from various laboratory tests are documented in detail. The corrosion performances of enamel and epoxy coatings were compared. It is concluded that a one-layer enamel coating doped with 50% calcium silicate has improved bond strengths with steel and concrete but its corrosion resistance is low due to porosity in the coating, allowing chloride ions to pass through. Based on limited laboratory tests, a two-layer enamel coating with an inner layer of pure enamel and an outer layer of enamel and calcium silicate mixture has been shown to be practical and effective for both corrosion resistance and bond strength. A coating factor of 0.85 is recommended to use with the current development length equations as specified in ACI318-08. The large-scale column tests indicated that the column-footing lap splice with enamel-coated dowel bars had higher load and energy dissipation capacities compared to uncoated dowel bars. When damaged unintentionally, chemically reactive enamel coatings limit corrosion to a very small area whereas epoxy coatings allow corrosion expansion in a wide area underneath the coating

Designing Sealing Glasses for Solid Oxide Fuel Cells

Thermal and chemical properties of invert glasses and glass-ceramics developed for hermetic seals for solid oxide fuel cells are described. The glasses crystallize to form thermally stable pyro- and orthosilicate phases with the requisite thermal expansion match to the Y-stabilized ZrO2 (YSZ) electrolyte. In addition, the glasses bond to Cr-steel substrates at 800-850 °C without forming extensive interfacial reaction products. The thermal expansion characteristics of the glass-ceramics remain essentially unchanged after 28 days at 750 °C. Compositions with lower (\u3c2 mol%) B2O3 contents exhibit the lowest volatilization rates when exposed to wet forming gas at 750 °C

Properties of Glass-ceramic Seals for Solid Oxide Fuel Cells

The thermal stability of invert glass-ceramics, based on crystalline pyro- and orthosilicate phases, developed for hermetic seals for solid oxide fuel cells (SOFC) are described. The effects of long-term (up to 60 days) high temperature (up to 800°C) heat treatments on the properties of the glass-ceramics in oxidizing and reducing environments were evaluated by dilatometric analyses, x-ray diffraction, weight loss measurements, and impedance spectroscopy. The glass-ceramics have thermal expansion coefficients in the range 9.5-11.5 × 10-6/°C and can be sealed to SOFC materials, including Y2O3-stabilized ZrO2 (YSZ) and Cr-steel interconnect alloys, at or below 900°C. The thermal expansion characteristics of some glassceramics remain essentially unchanged after \u3e40 days at 800°C, and the glass conductivity at 750°C remains constant (in the range 0.3-1.0 × 10-7 S/cm) in forming gas

Isothermal Crystallization of a Solid Oxide Fuel Cell Sealing Glass by Differential Thermal Analysis

The crystallization kinetics of a solid oxide fuel cell sealing glass were studied using a new isothermal differential thermal analysis (DTA) method. The weight fraction of glass crystallized after an isothermal heat treatment was determined from the DTA crystallization peak area and the crystallization kinetic parameters were determined using the classical Johnson-Mehl-Avrami equation. The glass, an alkaline earth-zinc-silicate composition, crystallized in the temperature range between 740° and 950°C. The activation energy for crystallization varied with glass particle size and decreased from 570±25 to 457±30 kJ/mol as the average particle size decreased from 425-500 to ∼10 μm. The activation energy for crystallization, E, increased from 520±20 to ∼600±20 kJ/mol when glass particles (45-53 μm) were mechanically mixed with 10 vol% of micrometer-sized Ni or YSZ powders. This increase in E reflects the effect of a second phase in composite seal systems, but is independent of the chemical nature of the additives. The measured values of the Avrami exponent (n) indicate that surface crystallization is the dominant crystallization mechanism for this glass, particularly for small particle sizes, e.g. n=0.9±0.1 for ∼10 μm