Thermal ramp test

Thermal stabihty of ceUs can be studied by linear programmed heating to cell failure, sometimes called the Thermal Ramp Experiment [14]. In one Thermal Ramp Experiment, cells were heated at a programmed heating rate (5 °C min is typical) from room temperature to 250 °C, at which temperature the ceU failed by initiating thermal runaway. 

The use of DSC and ARC provides for characterization of the electrodes and cells and the response to thermal transients. Larger-scale calorimetry (e.g., oxygen 

For any system with a high prevalence of organic construction (plastic cases, separators) or organic solvent electrolytes (as in lithium-ion cell technologies), the rate of oxygen consumption may be directly correlated to the heat released based on a standard of 13.1 MJ kg oxygen consumed. A combination of radiant flux meters provides aU necessary data to support large-scale battery failure analysis. 

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Figure 27.1 Cell self-healing rate during forced thermal ramp test of Li-ion Gen 2 lithium-ion chemistry anode = MCMB electrolyte =1.2 M LiPFe In EC PC DMC I cathode = LiNio.gCoo.os AI0.05O2 I separator = Celgard 2325 trilayer (from Ref [15]).

Thermal shock testing is commonly used to test components, but it is not necessarily a substitute for thermal cycling. Because the temperature ramp is extremely rapid and the dwell at the extremes is generally short, there is little time for creep consequently, the number of cycles to failure is increased. Furthermore, the rapid temperature change can induce differential thermal stresses that may be larger than those experienced during thermal cycling. These stresses can induce early failures, particularly if the failure is not in the solder. 

The main drawback of thermal shock experiments lies in the fact that these types of tests tend to induce failure modes not observed in the field. Additionally, even if solder joint fatigue can be induced, it is very difficult to map the high ramp rates associated with thermal shock loading conditions to the more gradual thermal loading conditions that occur in the field. Consequently, this test technique is limited to relative comparisons between packages in which the failure modes have been shown to be comparable under the same thermal shock test conditions. 

The alloy, Sn-3.4Ag. 8Bi, developed and patented by Sandia National Laboratories, was determined in the NCMS Lead-Free Solder Project to exhibit outstanding fatigue properties for surface mount applications under both accelerated thermal cycle test conditions used in the NCMS study. Sandia performed ATC testing of this alloy to 10,000 cycles for 0-100°C with 10°C/min ramp rates and 5-min dwell times [9,10]. There were no electrical failures at end of test (10,000 cycles) for 68 I/O PLCCs, 241/0 SOICs, and 1206 chip capacitors on FR4 boards, no cracks after 5000 cycles, and only minor surface cracks after 10,000 cycles. The Sn-3.4Ag-4.8Bi alloy has demonstrated considerable promise for use in surface mount applications, exhibiting greater fatigue resistance than eutectic Sn-Pb and most other lead-free alloys. It should be... 

A thermomechanical fatigue screening test for the remaining 13 alloys was performed utilizing 44 I/O and 20 I/O leadless ceramic chip carriers (LCCC) on FR-4 PWB substrates under the thermal cycling test conditions of —55 to + 160°C, with a ramp rate of 10°C/min, temperature dwell of 10 min at each temperature extreme for a total cycle duration of 1 hr. The WeibuU results for the various alloys are presented in Figure 29. The seven alloys determined to be the best performers based on mean life are listed in Table 41 The alloy Sn-A.8Bi-3.3Ag... 

Some prototype components are already under development. One of them is a ramp for the intake of the hypersonic propulsion system. This rather complex structure with dimensions of about 500 x 600 x 80 mm (in one piece) is planned to be tested under simulated thermal loads in early 1993. 

A thermochemical method that simultaneously measures differences in heat flow into a test substance and a reference substance (whose thermochemical properties are already well characterized) as both are subjected to programmed temperature ramping of the otherwise thermally isolated sample holder. The advantage of differential scanning calorimetry is a kinetic technique that allows one to record differences in heat absorption directly rather than measuring the total heat evolved/... 

Thermal stability as measured by these ramped TGA experiments of the sort previously described are not the definitive test of a polymer s utility at elevated temperature. Rather, for a polymer to be useful at elevated temperatures, it must exhibit some significant retention of useful mechanical properties over a predetermined lifetime at the maximum temperature that will be encountered in its final end use application. While many of the bisbenzocyclobutene polymers have been reported in the literature, only a few have been studied in detail with regards to their thermal and mechanical performance at both room and elevated temperatures. Tables 7-10 show some of the preliminary mechanical data as well as some other physical properties of molded samples of polymers derived from amide monomer 32, ester monomer 40, diketone monomer 14 and polysiloxane monomer 13. The use of the term polyamide, ester etc. with these materials is not meant to imply that they are to be regarded as merely modified linear thermoplastics. Rather, these polymers are for the most part highly crosslinked thermosets. 

The catalytic activity of the prepared catalysts for methane combustion was tested in a flow reactor unit. Bottled methane (99.995 % purity from AGA, Sweden) and air were fed to the system using mass flow controllers, giving a methane concentration of 2 vol%. The space velocity in all experiments was 50,000 h". The catalysts were placed in a vertical tubular Inconel reactor situated in a tubular furnace. The exiting gases were analyzed by gas chromatography using a Packard model 427 GC, equiped with a Poraplot Q fused silica capillary column and a thermal conductivity detector. The temperature in the furnace was controlled to give a linear temperature ramp of 2 °C/min in all experiments. Hence, the conversion of methane to carbon dioxide and water was determined as a function of the gas inlet temperature. 

Thermal dynamic mechanical analysis (TDMA) was done on a Rheometric Scientific RSA II Solids Analyzer (Piscataway, NJ) using a film testing fixture (5, 6). A nominal strain of 0.1% was us in all cases, with an applied frequency of 10 rad/sec (1.59 Hz). A temperature ramp of 10°C/min was used in all cases. Nominal dimensions of the samples were 6.4 mm x 38.1 mm. The gap between the jaws at the beginning of each test was 23.0 mm. Data analyses were carried out using Rheometrics RHIOS and Orchestrator software. 

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