Stability testing thermal cycling

Beyond a certain number of cycles there was stabilization in the mechanical properties. After the thermal cycling process was concluded the bars were measured for their Modulus of Rupture using a 3-point bend test method, with a span of 40mm between the suf rts and a crosshead speed of O.Smm/min (Tinius Olsen (Surrey, England) machine, model H25KS). This value of MOR was compared to the value for as-sintered samples. 

The long-term ASR behavior of MCO coated AL 441HP samples is shown in Figure 4. For the first 1600 hours the samples were tested at 800 °C, consistent with standard SOFC operating temperatures. The temperature was then increased to 900 °C to accelerate thermally driven failure mechanisms before the temperature was returned to 800 "C for thermal-cycling and long-term stability testing. 

Laminates based on Rhone Poulenc s Keramid 601 polyimide resin are fabricated in a conventional laminating press, and processed in a manner similar to that used for epoxies but with an extended cure cycle or post-cure. The room-temperature mechanical and electrical properties are similar to epoxy laminates, as shown in Table 9.4. At elevated temperatures, the polyimides exhibit exceptional stability. In particular, the thermal coefficient of expansion in the Z axis does not change significantly up to approximately 240°C, as shown in Fig. 9.11. Exhaustive tests have shown that polyimide-based multilayer boards can withstand repetitive thermal cycling at elevated temperatures (>150°C) without cracking of plated through holes. Similar excellent results were also obtained in solder shock tests (10 s at 288°C in molten solder). The thermal stability of these materials is retained at temperatures of approximately 200°C for continuous exposure in air, which has qualified them for military applications. 

Hot column stability testing is done by placing the test substrate with resistors on a hot stage at 400°C for 5 min, with a subsequent quench to room temperature. The shift in resistance values is then recorded. Stable resistors experience minimum change from this test. Stability of resistors after thermal shock is shown in Fig. 8.64. The stability of resistors can also be tested by subjecting them to a thermal cycle test which consists of 5 cycles of 5 min at-65°C, transfer within 10 s to-l-150°C, and a dwell of 5 min before transfer back to -65°C. The stability of commercial thick film resistors is considered acceptable if changes in resistance of less than +0.2 percent result from this test. 

To validate the Pxy-TFSI- RTIL mixtures as electrolytes for batteries Li-ion application, tests of cycling ability are required, after the determination of their electrochemical window. The quality of the passivating protective layer, and its stability at the graphite electrode, must be checked by mean of galvanostatic chronopotentiometric measurements. The Pxy-TFSI- RUL contents lower than 20 % (w/w) are not of a real interest, in spite of an ionic conductivity over the standard electrolyte one, because the phenomenon of self-extinguished flame becomes striking only from 20 % of Pxy-TFSI. For between 20 % and 30 % Pxy-TFSI- RUL, the performances are optimized from the point of view of the ionic transpxjrt, of the thermal stability and of the material wettability Beyond these contents, up to 50 %, the increase of the viscosity of mixtures can limit their applications at room temperature (mainly because of the decrease of the performances of ionic transport), but their use can be considered for higher temperature applications. 

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