Compliant Glass Research Articles

Compliant glass–polymer hybrid single ion-conducting electrolytes for lithium batteries

Compliant glass–polymer hybrid single ion-conducting electrolytes for lithium batteries

Compliant glass–polymer hybrid single ion-conducting electrolytes for lithium batteries

Despite high ionic conductivities, current inorganic solid electrolytes cannot be used in lithium batteries because of a lack of compliance and adhesion to active particles in battery electrodes as they are discharged and charged. We have successfully developed a compliant, nonflammable, hybrid single ion-conducting electrolyte comprising inorganic sulfide glass particles covalently bonded to a perfluoropolyether polymer. The hybrid with 23 wt% perfluoropolyether exhibits low shear modulus relative to neat glass electrolytes, ionic conductivity of 10(-4) S/cm at room temperature, a cation transference number close to unity, and an electrochemical stability window up to 5 V relative to Li(+)/Li. X-ray absorption spectroscopy indicates that the hybrid electrolyte limits lithium polysulfide dissolution and is, thus, ideally suited for Li-S cells. Our work opens a previously unidentified route for developing compliant solid electrolytes that will address the challenges of lithium batteries.

Electrical Properties of Alkali/Alkaline-Earth Borosilicate Glass Composite Sealants for Solid Oxide Fuel Cells

Development of a reliable sealant or sealing system remains one of the top priorities in planar solid oxide fuel cells (SOFCs) technology. Recently, a compliant glass seal such as an alkali silicate glass was proposed for SOFCs. In contrast to the conventional glass–ceramic sealant which develops a rigid or semi-rigid microstructure after sealing, the compliant glass shows so called “self-healing” behavior and will remain vitreous without substantial crystallization after sealing and during operation at elevated temperatures. The objective of this study was to investigate the relationship between sealant structure and high temperature electrical conductivities of glass composite sealants for SOFCs. Alkali/alkaline-earth borosilicate glass-based sealants, both with and without Al2O3 or ZrO2 fillers, were heat treated at various temperatures for periods of up to 48 h. The effects of filler type, densification of glass and alkali/alkali-earth oxide content in sealants on the electrical conductivities of the sealants were investigated. The results showed that the electrical conductivity of a glass composite sealant containing ZrO2 filler increased ten times after 48 hours of heat treatment. The electrical conductivity of a ZrO2 filler-containing glass after heat treatment was similar to that of an Al2O3 filler-containing glass. This was attributed to the densification of sealing glass by heat treatment.

Compliant alkali silicate sealing glass for solid oxide fuel cell applications: The effect of protective alumina coating on electrical stability in dual environment

An alkali-containing silicate glass was recently proposed as a potential sealant for solid oxide fuel cells (SOFC). The glass contains appreciable amount of alkalis and retains its glassy microstructure at elevated temperatures over time. It is more compliant as compared to conventional glass–ceramics sealants and could potentially heal cracks during thermal cycling. In previous papers the thermal cycle stability, thermal stability and chemical compatibility were reported with yttria-stabilized zirconia (YSZ) electrolyte and YSZ-coated ferritic stainless steel interconnect. In this paper, we report the electrical stability of the compliant glass with aluminized AISI441 interconnect material under DC load in dual environment at 700–800 °C. Apparent electrical resistivity was measured with a 4-point method for the glass sealed between two aluminized AISI441 metal coupons as well as plain AISI441 substrates. The results showed good electrical stability with the aluminized AISI441 substrate, while unstable behavior was observed for un-coated substrates. In addition, interfacial microstructure was examined with scanning electron microscopy and correlated with the measured resistivity results. Overall, the alumina coating demonstrated good chemical stability with the alkali-containing silicate sealing glass under DC loading.

Compliant alkali silicate sealing glass for solid oxide fuel cell applications: The effect of protective YSZ coating on electrical stability in dual environment

Recently, compliant sealing glass has been proposed as a potential candidate sealant for solid oxide fuel cell (SOFC) applications. In a previous paper, the thermal stability and chemical compatibility were reported for a compliant alkali-containing silicate glass sealed between anode supported YSZ bi-layer and YSZ-coated stainless steel interconnect. In this paper, we will report the electrical stability of the compliant glass under a DC load and dual environment at 700–800 °C. Apparent electrical resistivity was measured with a 4-ponit method for the glass sealed between two plain SS441 metal coupons or YSZ-coated aluminized substrates. The results showed instability with plain SS441 at 800 °C, but stable behavior of increasing resistivity with time was observed with the YSZ coated SS441. In addition, results of interfacial microstructure analysis with scanning electron microscopy will be correlated with the measured resistivity results. Overall, the YSZ coating demonstrated chemically stability with the alkali-containing compliant silicate sealing glass under electrical field and dual environments.

Compliant alkali silicate sealing glass for solid oxide fuel cell applications: Combined stability in isothermal ageing and thermal cycling with YSZ coated ferritic stainless steels

An alkali silicate glass (SCN-1) is being evaluated as a candidate sealant for solid oxide fuel cell (SOFC) applications. The glass contains about 17wt.% alkalis (K+Na) and has low glass transition and softening temperatures. It remains vitreous and compliant after sealing without substantial crystallization, as contrary to conventional glass–ceramic sealant. The glassy nature and low characteristic temperatures can reduce residual stresses and result in the potential for crack healing. In a previous study, the glass was found to have good thermal cycle stability and was chemically compatible with yttria stabilized zirconia (YSZ) coating during short term testing. In this study, the compliant glass was further evaluated in a more realistic way in that the sealed couples were first isothermally aged for 1000h followed by thermal cycling. High temperature leakage was measured. Chemical compatibility was also investigated with powder mixtures to enhance potential interfacial reaction. In addition, interfacial microstructure was examined with scanning electron microscopy and evaluated with regard to the leakage and chemical compatibility results. Overall the compliant sealing glass showed desirable chemical compatibility with YSZ coated metallic interconnect of minimum reaction and hermetic behavior at 700–750°C in dual environment.

Compliant alkali silicate sealing glass for solid oxide fuel cell applications: Thermal cycle stability and chemical compatibility

An alkali silicate glass (SCN-1) is currently being evaluated as a candidate sealing glass for solid oxide fuel cell (SOFC) applications. The glass containing ∼17mole% alkalis (K2O and Na2O) remains vitreous and compliant during SOFC operation, unlike conventional SOFC sealing glasses, which experience substantial devitrification after the sealing process. The non-crystallizing compliant sealing glass has lower glass transition and softening temperatures since the microstructure remains glassy without significant crystallite formation, and hence can relieve or reduce residual stresses and also has the potential for crack healing. Sealing approaches based on compliant glass will also need to satisfy all the mechanical, thermal, chemical, physical, and electrical requirements for SOFC applications, not only in bulk properties but also at sealing interfaces. In this first of a series of papers we will report the thermal cycle stability of the glass when sealed between two SOFC components, i.e., a NiO/YSZ anode supported YSZ bilayer and a coated ferritic stainless steel interconnect material. High temperature leak rates were monitored versus thermal cycles between 700 and 850°C using back pressures ranging from 1.4 to 6.8kPa (0.2–1.0psi). Isothermal stability was also evaluated in a dual environment consisting of flowing dilute H2 fuel versus ambient air. In addition, chemical compatibility at the alumina and YSZ interfaces was examined with scanning electron microscopy and energy dispersive spectroscopy. The results shed new light on the topic of SOFC glass seal development.

Study of geometric stability and structural integrity of self-healing glass seal system used in solid oxide fuel cells

A self-healing glass seal has the potential to restore its mechanical properties upon being reheated to the solid oxide fuel cell (SOFC) stack operating temperature. Such a self-healing feature is desirable for achieving high seal reliability during thermal cycling. Self-healing glass is also characterized by its low mechanical stiffness and high creep rate at SOFC operating temperatures. Therefore, the geometric stability and structural integrity of the glass seal system are critical to its successful application in SOFCs. This paper describes studies of the geometric stability and structural integrity of the self-healing glass seal system and the influence of various interfacial conditions during the operating and cooling-down processes using finite element analyses. For this purpose, the test cell used in the leakage tests for compliant glass seals, conducted at Pacific Northwest National Laboratory (PNNL), was taken as the initial modeling geometry. The effect of the ceramic stopper on the geometric stability of the self-healing glass sealants was studied first. Two interfacial conditions of the ceramic stopper and glass seals, i.e., bonded (strong) or unbonded (weak), were considered. Then the influences of interfacial strengths at various interfaces, i.e., stopper/glass, stopper/PEN, as well as stopper/IC plate, on the geometric stability and reliability of glass during the operating and cooling processes were examined.

Ultrathin Strained-SOI by Stress Balance on Compliant Substrates and FET Performance

Ultrathin, strained-silicon-on-insulator (s-SOI) structures without a residual silicon-germanium (SiGe) underlayer have been fabricated using stress balance of bi-layer structures on compliant borophosphorosilicate glass (BPSG). The bi-layer structure consisted of SiGe and silicon films, which were initially pseudomorphically grown on a silicon substrate and then transferred onto BPSG by a wafer bonding and SmartCut process. The viscous flow of the BPSG during a high-temperature anneal then allowed the SiGe/Si bi-layer to laterally coherently expand to reach stress balance, creating tensile strain in the silicon film. No dislocations are required for the process, making it a promising approach for achieving high-quality strained-silicon for device applications. To prevent the diffusion of boron and phosphorus into the silicon from the BPSG, a thin nitride film was inserted between the bi-layer and BPSG to act as a diffusion barrier, so that a lightly doped, sub-10-nm s-SOI layer (0.73% strain) was demonstrated. N-channel MOSFETs fabricated in a 25-nm silicon layer with 0.6% strain showed a mobility enhancement of 50%.

Relaxed SiGe Layers with High Ge Content by Compliant Substrates

AbstractRelaxed, high Ge content SiGe layers have been realized using stress balance on a compliant borophosphorosilicate glass (BPSG). A 30-nm fully-strained Si0.7Ge0.3 layer was transferred onto a 1 μm BPSG film by wafer-bonding and Smart-cut® processes, after which the continuous Si0.7Ge0.3 film was patterned into small islands to allow for lateral expansion. After the strain in Si0.7Ge0.3 islands was released by the lateral expansion resulting from the flow of the BPSG, a Si0.4Ge0.6 layer was commensurately deposited under compression. Upon equilibrium after an annealing, stress balance was formed between the SiGe films, resulting in a larger in-plane lattice constant than that of relaxed Si0.7Ge0.3. With a thiner (6 nm) Si0.7Ge0.3 starting film, an in-plane lattice constant equivalent to fully-relaxed Si0.45Ge0.55 has been obtained.

A one-dimensional viscoelastic model for lateral relaxation in thin films

This paper is dedicated to a one-dimensional model intended to describe the lateral relaxation in thin film bonded on a wafer via a compliant (viscous) glass. We analyze the partition of energy between the film and the template substrate and we show that if relaxation takes place, it will be initiated at the lateral boundary of the interface (template substrate)/(viscous glass). We extend the one-dimensional model to take into account the growth rate and show that the lateral relaxation is favored by a slow growth rate.

Ultra-low leak rate of hybrid compressive mica seals for solid oxide fuel cells

A novel hybrid compressive mica seal was developed that showed a reduction of leak rate by about 4300 times (compared to simple mica seals) at 800 °C. The hybrid compressive mica seal is composed of 2 compliant glass layers and a mica layer. Three commercially available micas were tested in hybrid compressive seals for solid oxide fuel cell applications. The best results were obtained using Muscovite single crystal mica. The normalized leak rate for this seal at 800 °C was only 1.55×10 −4 sccm/cm at a stress of 100 psi and a pressure gradient of 2 psi. Seals based on the other commercial micas (Muscovite and Phlogopite mica papers), also exhibited superior leak rates (∼0.011 sccm/cm) compared to simple mica seals without the compliant glass layer (about 6–9 sccm/cm). The microstructure of the mica was examined before and after the 800 °C leak tests using scanning electron microscopy. The cause for the substantial reduction of the leak rate was discussed. In addition, the effect of the compressive stresses was also investigated.

Measurement of nucleotide release kinetics in single skeletal muscle myofibrils during isometric and isovelocity contractions using fluorescence microscopy

Rabbit psoas muscle myofibrils, in the presence of the fluorescent nucleotide analog 2'(3')-O-[N-[2-[[Cy3]amido]ethyl]carbamoyl]-adenosine 5' triphosphate (Cy3-EDA-ATP), showed selective fluorescence staining of the A-band with a reduced fluorescence at the M-line. Addition of Cy3-EDA-ATP to a myofibril in the presence of Ca2+ caused auxotonic shortening against a compliant glass microneedle. These results indicate that Cy3-EDA-ATP is a substrate for myosin in the myofibril system. The kinetics of nucleotide release from a single myofibril, held isometrically between two needles, were measured by the displacement of prebound Cy3-EDA-ATP on flash photolysis of caged ATP. The A-band fluorescence of the myofibril decayed exponentially with a rate constant of 0.3 s(-1) at 8 degrees C, an order of magnitude faster than that for isolated thick filaments in the absence of actin. When a myofibril was imposed to shorten with a constant velocity by a piezoelectric actuator, the nucleotide displacement rate constant initially increased to 0.7 s(-1) with increasing shortening velocity and then declined with a further increase in shortening velocity. These results demonstrate that the displacement rates of Cy3-EDA-nucleotides bound to the cross-bridges in the contracting myofibril reflect a process that shows strain dependence.

An experimental fracture mechanics study of a strong interface: The silicon/glass anodic bond

The fracture behavior of the silicon/Pyrex glass anodic bond was investigated using the methods of linear elastic bimaterial fracture mechanics. Due to the high bond strength, interfacial cracks were invariably observed to kink away from the interface into the more compliant glass under approximately mode I remote tensile loading. Kink angles measured by profilometry increased from 14 to 28°as bonding temperature increased from 300 to 450 °C. A regime of stable cracking accompanied penetration of cracks into the glass, with maximum load and corresponding fracture toughness measurement occurring at a location significantly removed from the interface. Approximately mode I, near-interface, plane-strain fracture toughness values (KIC) measured by rising load testing of chevron-notched and straight-thru-cracked compact-tension specimens increased from 0.63 to 0.68 MPa-m1/2 and 0.66 to 0.75 MPa-m1/2, respectively, as bonding temperature increased from 300 to 450 °C. In addition, XPS measurements revealed a sodium depletion zone of decreasing size and depletion magnitude with increasing bonding temperature over the same range. The near-interface region of the glass also experiences compressive residual stresses which decrease linearly with distance from the interface according to linear elastic computations. These stresses increase in magnitude with increasing bonding temperature due to enhanced differential thermal contraction upon cooling to room temperature. It is proposed that the trends in toughness and in kink angle with bonding temperature can be at least partially accounted for by variation of crack-tip shielding with compressive residual stress magnitude, the effects of interfacial. crack-tip shear stresses induced by the thermal mismatch, and by an increase in Young's modulus of the near-interface glass accompanying sodium depletion.

Prediction of interfacial crack path: a direct boundary integral approach and experimental study

This paper presents the development of a higher-order direct boundary integral-displacement discon- tinuity method for crack propagation in layered elastic materials. The method is based on the dual boundary integral equations of linear elasticity which are solved by means of a quadratic boundary element formulation. The analytical solution for a point force within a bonded half-plane region is used to derive the kernel functions of the boundary integral equations. Square-root displacement-discontinuity elements are used to model the crack tips, and stress intensity factors may be computed using the numerically predicted values of the displacement discontinuity components at the midpoints of these crack-tip elements. An algorithm based on the maximum tensile-stress criterion is then developed and incorporated into the boundary element model to predict the paths of cracks propagating in layered elastic materials. In the experimental part of this study, crack profiles for straight-through-cracked, compact-tension specimens of the anodically bonded silicon/Pyrex glass system are measured by profilometry. The plane strain prediction of the crack-propagation path is compared with the experimentally measured crack profiles. Consistent with the prediction, the interfacial crack is observed to kink away from the strong, anodicaUy-bonded interface and propagate into the more compliant glass layer. The predicted initial kink angle of 26 ° agrees very well with the average measured value of 280 . The measured path of the crack is also in very good agreement with the predicted path over about the first 120 microns of crack growth with increasing deviation observed beyond that.