Nature of Active Sites on Cu–CeO2 Catalysts Activated by High-Temperature Thermal Aging

ACS Catalysis ◽  
2020 ◽  
Vol 10 (21) ◽  
pp. 12385-12392
Author(s):  
Beibei Wang ◽  
Hui Zhang ◽  
Wei Xu ◽  
Xiaobao Li ◽  
Wei Wang ◽  
...  
Keyword(s):  
High Temperature ◽  
Thermal Aging ◽  
Active Sites

Structural/Texture Evolution During Facile Substitution of Ni into ZSM-5 Nanostructure vs. its Impregnation Dispersion Used in Selective Transformation of Methanol to Ethylene and Propylene

2020 ◽  
Vol 23 ◽  
Author(s):  
Parisa Sadeghpour ◽  
Mohammad Haghighi ◽  
Mehrdad Esmaeili
Keyword(s):  
High Temperature ◽  
Physicochemical Properties ◽  
Active Sites ◽  
Catalytic Performance ◽  
Fixed Bed Reactor ◽  
Light Olefins ◽  
Isomorphous Substitution ◽  
Impregnation Method ◽  
Hydrothermal Temperature ◽  
X Ray

Aim and Objective: Effect of two different modification methods for introducing Ni into ZSM-5 framework was investigated under high temperature synthesis conditions. The nickel successfully introduced into the MFI structures at different crystallization conditions to enhance the physicochemical properties and catalytic performance. Materials and Methods: A series of impregnated Ni/ZSM-5 and isomorphous substituted NiZSM-5 nanostructure catalysts were prepared hydrothermally at different high temperatures and within short times. X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray (EDX), Brunner, Emmett and Teller-Barrett, Joyner and Halenda (BET-BJH), Fourier transform infrared (FTIR) and Temperature-programmed desorption of ammonia (TPDNH3) were applied to investigate the physicochemical properties. Results: Although all the catalysts showed pure silica MFI–type nanosheets and coffin-like morphology, using the isomorphous substitution for Ni incorporation into the ZSM-5 framework led to the formation of materials with lower crystallinity, higher pore volume and stronger acidity compared to using impregnation method. Moreover, it was found that raising the hydrothermal temperature increased the crystallinity and enhanced more uniform incorporation of Ni atoms in the crystalline structure of catalysts. TPD-NH3 analysis demonstrated that high crystallization temperature and short crystallization time of NiZSM-5(350-0.5) resulted in fewer weak acid sites and medium acid strength. The MTO catalytic performance was tested in a fixed bed reactor at 460ºC and GHSV=10500 cm3 /gcat.h. A slightly different reaction pathway was proposed for the production of light olefins over impregnated Ni/ZSM-5 catalysts based on the role of NiO species. The enhanced methanol conversion for isomorphous substituted NiZSM-5 catalysts could be related to the most accessible active sites located inside the pores. Conclusion: The impregnated Ni/ZSM-5 catalyst prepared at low hydrothermal temperature showed the best catalytic performance, while the isomorphous substituted NiZSM-5 prepared at high temperature was found to be the active molecular sieve regarding the stability performance.

Thermal aging performance of glass fiber/polyphenylene sulfide composites in high temperature

2021 ◽  
pp. 50948
Author(s):  
Wenchao Wang ◽  
Xiaoman Wu ◽  
Chao Ding ◽  
Xianbo Huang ◽  
Nanbiao Ye ◽  
...  
Keyword(s):  
High Temperature ◽  
Glass Fiber ◽  
Thermal Aging ◽  
Polyphenylene Sulfide ◽  
Aging Performance

Characteristics and aging of SiC MOSFETs operated at very high temperatures

2014 ◽  
Vol 1693 ◽  
Author(s):  
Dean P. Hamilton ◽  
Michael R. Jennings ◽  
Craig A. Fisher ◽  
Yogesh K. Sharma ◽  
Stephen J. York ◽  
...  
Keyword(s):  
High Temperature ◽  
High Temperatures ◽  
Threshold Voltage ◽  
Thermal Aging ◽  
Ohmic Contacts ◽  
Stress Tests ◽  
Temperature Capability ◽  
Temperature Constant ◽  
Voltage Management ◽  
Very High

ABSTRACTSilicon carbide power devices are purported to be capable of operating at very high temperatures. Current commercially available SiC MOSFETs from a number of manufacturers have been evaluated to understand and quantify the aging processes and temperature dependencies that occur when operated up to 350°C. High temperature constant positive bias stress tests demonstrated a two times increase in threshold voltage from the original value for some device types, which was maintained indefinitely but could be corrected with a long negative gate bias. The threshold voltages were found to decrease close to zero and the on-state resistances increased quite linearly to approximately five or six times their room temperature values. Long term thermal aging of the dies appears to demonstrate possible degradation of the ohmic contacts. This appears as a rectifying response in the I-V curves at low drain-source bias. The high temperature capability of the latest generations of these devices has been proven independently; provided that threshold voltage management is implemented, the devices are capable of being operated and are free from the effects of thermal aging for at least 70 hours cumulative at 300°C.

Viscoplastic Constitutive Model for High Strain Rate Mechanical Properties of SAC-Q Leadfree Solder After High-Temperature Prolonged Storage

2018 ◽  
Author(s):  
Pradeep Lall ◽  
Vikas Yadav ◽  
Jeff Suhling ◽  
David Locker
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
High Strain Rate ◽  
Strain Rate ◽  
Thermal Aging ◽  
High Strain ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Aging Effects ◽  
Model Predictions

Electronics in automotive underhood and downhole drilling applications may be subjected to sustained operation at high temperature in addition to high strain-rate loads. SAC solders used for second level interconnects have been shown to experience degradation in high strain-rate mechanical properties under sustained exposure to high temperatures. Industry search for solutions for resisting the high-temperature degradation of SAC solders has focused on the addition of dopants to the alloy. In this study, a doped SAC solder called SAC-Q solder have been studied. The high strain rate mechanical properties of SAC-Q solder have been studied under elevated temperatures up to 200°C. Samples with thermal aging at 50°C for up to 6-months have been used for measurements in uniaxial tensile tests. Measurements for SAC-Q have been compared to SAC105 and SAC305 for identical test conditions and sample geometry. Data from the SAC-Q measurements has been fit to the Anand Viscoplasticity model. In order to assess the predictive power of the model, the computed Anand parameters have been used to simulate the uniaxial tensile test and the model predictions compared with experimental data. Model predictions show good correlation with experimental measurements. The presented approach extends the Anand Model to include thermal aging effects.

Characterization of Silicone Gel for High Temperature Encapsulation in High Voltage WBG Power Modules

2017 ◽  
Vol 2017 (1) ◽  
pp. 000312-000317
Author(s):  
Adam Morgan ◽  
Xin Zhao ◽  
Jason Rouse ◽  
Douglas Hopkins
Keyword(s):  
High Temperature ◽  
Thermal Aging ◽  
Dielectric Strength ◽  
Material Structure ◽  
Power Module ◽  
Leakage Currents ◽  
Test Vehicle ◽  
Silicone Gel ◽  
Power Modules ◽  
Silicone Gels

Abstract One of the most important advantages of wide-bandgap (WBG) devices is high operating temperature (>200°C). Power modules have been recognized as an enabling technology for many industries, such as automotive, deep-well drilling, and on-engine aircraft controls. These applications are all required to operate under some form of extreme environmental conditions. Silicone gels are the most popular solution for the encapsulation of power modules due to mechanical stress relief enabled by a low Young's modulus, electrical isolation achieved due to high dielectric strength, and a dense material structure that protects encapsulated devices against moisture, chemicals, contaminants, etc. Currently, investigations are focused on development of silicone gels with long-term high-temperature operational capability. The target is to elevate the temperature beyond 200°C to bolster adoption of power modules in the aforementioned applications. WACKER has developed silicone gels with ultra-high purity levels of < 2ppm of total residual ions combined with > 200°C thermal stability. In this work, leakage currents through a group of WACKER Chemie encapsulant silicone gels (A, B, C) are measured and compared for an array of test modules after exposure to a 12kV voltage sweep at room temperature up to 275°C, and thermal aging at 150°C for up to more than 700 hours. High temperature encapsulants capable of producing leakage currents less than 1μA, are deemed acceptable at the given applied blocking voltage and thermal aging soak temperature. To fully characterize the high temperature encapsulants, silicone gel A, B, and C, an entire high temperature module is used as a common test vehicle. The power module test vehicle includes: 12mil/40mil/12mil Direct Bonded Copper (DBC) substrates, gel under test (GUT), power and Kelvin connected measurement terminals, thermistor thermal sensor to sense real-time temperature, and 12mil Al bonding wires to manage localized high E-Fields around wires. It was ultimately observed that silicone gels B and C were capable of maintaining low leakage current capabilities under 12kV and 275°C conditions, and thus present themselves as strong candidates for high-temperature WBG device power modules and packaging.

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