Sharif Digital Repository

The effects of intermediate nickel layer on seal strength and chemical compatibility of seal glass and interconnect materials for solid oxide fuel cells (SOFCs) were investigated. Two types of samples (metal/glass/metal sandwiches and glass coated metals) were prepared with the sheet of AISI 430 (nickel plated and uncoated) and slurry of compliant silicate sealing glass (SCN-1). The joined and coated samples were heated at 850 °C for different time durations (0.5-100 h). Tensile and impact tests were performed and SEM micrographs were used to analyze the glass/metal interaction. The results indicate that nickel plated AISI 430 shows higher adhesion strength at short durations of heating due... 

The possible interactions near the triple-phase boundaries (TPB) metal/glass/air, and their effects on joint strength are investigated. Two types of samples (joined couples and glass coated coupons) are prepared with the coupon of AISI 430 (nickel plated and uncoated) and a slurry of compliant silicate sealing glass (SCN-1). The joined and coated samples are heated at 850 °C for 1000 h in air. The joined couples are cooled using two different schedules and then tested in uniaxial tension. For investigating the metal-oxides precipitation procedure in glass near the TPB, glass coated coupons are either cooled at the rate of 5 °C min−1 or water-quenched from aging temperature. The mechanical... 

A torsion test recently implemented for solid oxide fuel cell sealant materials is analyzed as a method for measuring the shear strength of sealant for solid oxide fuel cells. The finite element method is used to simulate the stress distribution in the hourglass-shaped steel specimens with intermediate sealant layer with different specimen's dimensions and configurations. Also, it is analyzed how stress concentration changes if the sealant does not completely fill the gap or is squeezed out of gap. The reduction of seal thickness to outer radius ratio results in an increase in stress concentration at the outer edge of sealant. The developed specimens with a hollow halve steel plate as well... 

Interactions between the metal interconnect and glass sealant in the solid oxide cells stack are critical to retaining the system integrity. To address this issue, in the current study, 8YSZ coating is applied on the Crofer22 APU steel via sol-gel and dip-coating method. Dense and continuous 8YSZ coatings are obtained on Crofer22 APU substrates. X-ray diffraction and Raman spectroscopy results show that both cubic and tetragonal structures of 8YSZ are formed. A glass-based sealing paste is applied on bare and 8YSZ coated Crofer22 APU steel. The interfacial compatibility and chemical stability of steel/glass and steel/8YSZ/glass joint couples are investigated using SEM and EDS line scan... 

The structural integrity of the sealant material is critical for the reliability of solid oxide fuel/electrolysis stacks. In the current study, a torsion test is implemented to evaluate and compare its shear strength with a partially crystallized glass sealant at room- and operation relevant high-temperatures. Hourglass-shaped specimens with different configurations of hollow- and full-halves are utilized for testing. The fracture surfaces are visualized via optical microscopy and complementary scanning electron microscopy. In addition, cyclic loading is used to investigate potential subcritical crack growth effects in the sealants. Both, the specimens with a hollow-half as well as the ones... 

Assessment of mechanical properties of glass/metal joints is a challenging process, especially when the application relevant conditions of the joints have to be considered in the test design. In this study, a finite element method (FEM) is implemented to analyze a torsional shear strength test designed for glass-ceramic/steel joints aiming towards solid oxide fuel/electrolysis cells application. Deviations from axial symmetry of the square flanges (ends) of respective hourglass-shaped specimens and also supporting and loading sockets of the test set-up are included in the model to simulate conditions close to reality. Undesirable tensile stress and also shear stress concentration appear at... 

The structural integrity of the sealant is critical for the reliability of solid oxide cells (SOCs) stacks. In this study, elastic modulus (E), hardness (H) and fracture toughness (KIC) of a rapid crystallizing glass of BaO–CaO–SiO2 system termed “sealant G” are reported as determined using an indentation test method at room temperature. A wide range of indentation loads (1 mN–10 N) was used to investigate the load-dependency of these mechanical properties. Values of 95 ± 12 GPa, 5.8 ± 0.2 GPa and 1.15 ± 0.07 MPa m0.5 were derived for E, H and KIC using the most suitable indentation loads. An application relevant annealing treatment of 500 h at 800 °C does not lead to a significant change of... 

The structural integrity of the sealant is critical for the reliability of solid oxide cells (SOCs) stacks. In this study, elastic modulus (E), hardness (H) and fracture toughness (KIC) of a rapid crystallizing glass of BaO–CaO–SiO2 system termed “sealant G” are reported as determined using an indentation test method at room temperature. A wide range of indentation loads (1 mN–10 N) was used to investigate the load-dependency of these mechanical properties. Values of 95 ± 12 GPa, 5.8 ± 0.2 GPa and 1.15 ± 0.07 MPa m0.5 were derived for E, H and KIC using the most suitable indentation loads. An application relevant annealing treatment of 500 h at 800 °C does not lead to a significant change of... 

The conventional relations for calculating the fracture stresses consider only elastic deformation but ignore viscoelastic and viscoplastic behaviors. Measuring the joining strength of a composite glass sealant-metallic interconnect specimen at solid oxide cell application relevant at high temperatures is a case where such effects can become significant. In the current study, three-point and four-point bending test results were analyzed using the finite element method (FEM) to assess systematic and random errors. It is shown that plastic deformation of the steel interconnect material at high temperature, although having a large effect on the stress distribution in the... 

A pulsed Nd:YAG laser welding of 1 mm thick Ti (grade 2) to 0.5 mm thick AA3105-O was performed by a ring-like spot joining. A 0.15 mm thick Al-12Si-2.5 Mg alloy was used as a filler metal. Intermetallic compounds of Ti3Al, Ti2Al, TiAl, Ti(Al,Si)3 and Mg2Si were observed respectively from Ti towards Al sides at the fusion zone. Si and Mg increased the strength of the Al re-solidified zone near the Ti-Al interface because of their easy dissolution in the Al. Exothermic effect of the Mg addition resulted in porosity in the welding zone. Joint strength of up to 98% of the Al base metal was obtained, which was much 14% higher than that achieved by autogenous welding. © 2019 Elsevier GmbH  

In this study, a pulsed Nd:YAG laser welding method is implemented to join Ti-G2 (1 mm thick) to AA3105-O (0.5 mm thick) via a ring of spots filled with AlScZr alloy (0.15 mm thick). The filler material improved the weld’s microstructure and mechanical properties by reducing the undesirable intermetallic compounds (IMCs) such as TiAl2 and TiAl3 in the aluminium re-solidified zone near the titanium/aluminium interface. The joints having AlScZr filler were mostly failed at Al heat affected zone (HAZ) during the tensile shear test. The addition of zirconium to binary Al–Sc system formed a substitutional solid-solution in which 50 wt% Zr+10 wt% Ti replaced Al3(Sc,Zr,Ti). Scandium had a...