Statistical continuum mechanics analysis of effective elastic properties in solid oxide fuel cell glass–ceramic seal material

Thermal and mechanical stability of lanthanide-containing glass–ceramic sealants for solid oxide fuel cells

“…29 Si MAS NMR spectra were recorded using a 7 mm probe employing a rotation speed of 5 kHz, using a 4.5 ms radiofrequency (RF) excitation pulse length with a RF eld strength of 56 kHz (90 ip-angle) and 60 s recycle delay. 27 Al and 11 B MAS NMR spectra were recorded using a 4 mm probe using a spinning rate of 14 kHz, 1 s recycle delay, 0.5 ms RF excitation pulse (equivalent to a p/18 ip angle) for 27 Al and 0.9 ms (equivalent to a p/12 ip angle) for 11 B. The ip angle pulses used for 27 Al and 11 B were optimized using an aqueous solution of Al(NO 3 ) 3 and H 3 BO 3 .…”

“…This sequence was used to remove the 11 B probe background, which is present in most commercial probe heads. 11 B MQMAS (Multiple-Quantum MAS) NMR experiments were performed using the split-t 1 z-lter pulse sequence 18 employing RF pulse lengths of 2.8 ms and 0.8 ms for the rst two hard pulses and a 5 ms 90 so pulse. A RF eld strength of 150 and 20 kHz was employed for the hard and so pulses, respectively.…”

“…The paramagnetic susceptibility (c p ) of lanthanide cations 19 is proportional to the square of the effective number of the Bohr magnetons (p), c p f p 2 . In the case of materials containing Nd 3+ (p ¼ 3.5) and Gd 3+ (p ¼ 8.0), the presence of paramagnetic species, with high p values, can strongly affect the T 2 relaxation times of 29 Si, 11 B and 27 Al nuclei, leading to very broad resonance lines, oen yielding spectra showing noise only. For the case of the lanthanide Ln 3+ (4f shell empty), there is no paramagnetic effect and thus no additional line broadening is expected.…”

“…However, these glasses tend to devitrify at 800-850 C resulting in the appearance of hexacelsian (BaAl 2 Si 2 O 8 ) crystalline phase in the GC which during gradual SOFC operation transforms into its monoclinic polymorph with low CTE, lowering the CTE values for the GC seal along with deterioration of its mechanical properties. 11 Similarly, severe chemical interactions have been observed at the interface between BaO-containing and alkalicontaining glass seals when joined with metallic interconnects of SOFCs. 12,13 A vast amount of literature available in this area depicting the failure of glass seals during long-term operation warrants a thorough investigation of long-term thermal and chemical stability of any proposed glass composition for high temperature sealing application.…”

Recent developments in the preparation, characterization and applications of glass- and glass–ceramic-to-metal seals and coatings

“…7 [67]. Reactions do, however, become extremely critical during fuel cell operation, and cell ageing is therefore an extremely important aspect [83,[99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114]. Alkali-containing glass-ceramics are generally to be avoided due to the likelihood of pronounced glassceramic-metal reactions during cell operation.…”