State Primary Standard of the Unit of Energy Flux of an Electromagnetic Field in the Range 0.3–78 GHz

We report the results of studies of the new measurement standards GÉT 160-00. The primary standard is to be used to reproduce and transfer the size of the unit of electromagnetic energy flux in the frequency range 0.3–78 GHz.     

Diopside–Ba disilicate glass–ceramic sealants for SOFCs: Enhanced adhesion and thermal stability by Sr for Ca substitution

This article reports on the influence of strontium for calcium substitution in diopside–Ba disilicate glass–ceramics on stabilization thermal parameters and improvement adhesion to interconnect material of SOFCs. Sr replaced 10, 20, 30 and 40% of Ca in the Ca_0.9MgAl_0.1La_0.1Si_1.9O₆ component of the parent glass having the following composition, mol.%: 22.14 CaO, 24.60 MgO, 0.52 BaO, 1.23 Al₂O₃, 1.23 La₂O₃, 47.79 SiO₂, 1.69 B₂O₃, 0.79 NiO. ²⁹Si–MAS–NMR and ²⁷Al MAS–NMR spectra of the glasses revealed irrelevant chemical shifts for silicon and aluminum atoms upon changing the SrO content. T_g decreased and coefficient of thermal expansion (CTE) increased by Sr for Ca substitution in pyroxene glasses. Additionally SrO-containing glasses exhibited a viscosity of ∼10⁶ dPa s at 900 °C, which is suitable for joining of SOFC metallic/ceramic components by glass/glass–ceramic sealing upon stack hermetization. Glass–ceramics revealed long term (up to 1000 h) thermal stability at 900 °C and suitable CTE values (10.0–11.3) × 10⁻⁶ K⁻¹, high electrical resistivity, good adhesion and minimal reactivity with SOFC components.     

Effect of strontium-to-calcium ratio on the structure,crystallization behavior and functional properties of diopside-based glasses

The role of Sr/Ca ratio, which was varied from 3/6 to 9/0, on the structure, crystallization behavior and properties of diopside-based glass and glass-ceramic sealants targeted to solid oxide fuel cell (SOFC) applications was evaluated. The structural changes undergone by glass-powder compacts during isothermal heat treatment at 850 °C for 1–1000 h were investigated using XRD (X-ray diffraction) analysis, including quantitative Rietveld refinement, and MAS-NMR (magic angle spinning nuclear magnetic resonance) techniques. The tendency towards crystallization was retarded with increasing Sr/Ca ratio. Diopside-based phases, strontium akermanite and magnesium silicate were developed under various heat-treatment conditions. MAS-NMR analysis of glasses heat treated for 1000 h revealed that with increasing Sr/Ca ratio, Q¹ and Q⁴ structural units were formed at the expenses of Q² units. The good thermal stability and chemical compatibility of the new glass-ceramic compositions coupled with their mechanical reliability and high electrical resistivity make them attractive for further experimentation as sealants for SOFCs.     

A Method of Reducing the Effect of Residual Reflections in an Anechoic Chamber on the Measurement Precision of the Group Delay in an Antenna

Measurement Techniques - It has been shown that methods currently being used for measuring group delay in an antenna in an anechoic chamber are limited in precision due to the effect of residual...     

SrO‐Containing Diopside Glass–Ceramic Sealants for Solid Oxide Fuel Cells: Mechanical Reliability and Thermal Shock Resistance

A series of glasses and glass–ceramics (GCs) aiming at applications as sealants for solid oxide fuel cells (SOFCs) were synthesized by partial substitution of Ca for Sr in the diopside‐Ba disilicate composition. X‐ray diffraction in conjunction with the Rietveld‐RIR technique were employed to quantify the crystalline (diopside and Sr‐diopside) and amorphous phases in the glasses sintered/heat treated at 850 °C in humidified 10%H₂–90%N₂ gas mixture for 250 h. Weibull modulus varied in the range 11.6–34.4 implying toward good mechanical reliability of synthesized GCs. Thermal shock resistance of model electrochemical cells made of yttria‐stabilized zirconia, gadolinia‐doped ceria, and lanthanum gallate based solid electrolytes, hermetically sealed by one diopside‐based composition, was evaluated employing quenching from 800 °C in air and water. Suitable thermal expansion coefficient, mechanical reliability, and strong adhesion to stabilized zirconia and metallic interconnects, are all suggesting a good suitability of the sealants for SOFC applications.