This paper considers the factors influencing the formation and development of stress corrosion defects detected during the inspection and overhaul of the main gas pipeline section. The surveyed gas pipeline is made of large diameter steel pipes made by controlled rolling, produced by various companies, with the predominance of pipes produced by the Khartsyzsk Pipe Plant (KhPP). The correlation between the geometric parameters of defects is described, which makes it possible to estimate the depth of cracks by external parameters. Mechanical tests by cyclic loading of samples containing cracks, based on the site operation data for the last 11 years, showed no crack growth in the absence of a corrosive medium. Micro-X-ray spectral analysis of metal and corrosion products showed no trace of the influence of hydrogen sulphide and nonmetallic inclusions (sulphides) on the development process of SCC. According to the results of the research, the process of development of stress corrosion on the main gas pipelines located in the European part of the Russian Federation is described. The organization operating the gas pipeline is recommended to take into consideration the results of this work during drawing up their repair plan.
The paper reports on the results of the studies of static and dynamic characteristics of 4H-SiC drift step recovery diodes (DSRDs) assembled in diode stacks. Switching performance of single dies has been simulated and experimentally confirmed. It was established that the switching process is determined primarily by the incomplete ionization of acceptors in 4H-SiC and by the bandgap narrowing in heavily doped emitters. Based on the simulation results the optimized die size has been selected. For DSRD stacks of 4 and 8 dies I-V and C-V measurements are reported. The stacks were dynamically tested in a special oscillator circuit. Repetitive voltage pulses of 10.5 kV with the leading edge length of 900 ps were demonstrated.
This paper presents the results of research and development of two types diode structures based on wide bandgap 4H-SiC: drift step recovery diodes (DSRDs) and field emission diodes (FED). Diodes’ structure and manufacturing methods are reviewed. Diode’s characteristics were obtained (static current-voltage characteristics and capacitor-voltage characteristic, switching properties’ characteristics for DSRDs). Field emission 4H-SiC structures illustrated high (≥102 А/сm2) current densities at electric field intensity of approximately 10V/um. 4H-SiC DSRDs in the generator structure with a single oscillating contour allowed to form sub nanosecond impulses at a load 50 Ohm and 1,5-2kV amplitude for a single diode (current density at V=2kV J= 4•103 А/сm2),what is significantly higher than similar DSRD’s parameters obtained for silicon.
The electrical properties of metal-oxide-semiconductor (MOS) devices fabricated using dry oxidation on phosphorus-implanted n-type 4H-SiC (0001) epilayers have been investigated. MOS structures were compared in terms of interface traps and reliability with reference sample which was produced by dry oxidation under the same conditions. The notably lower interface traps density measured in MOS capacitor with phosphorus concentration exceeding 1018 cm-3 at the SiO2/SiC interface was attributed to interface traps passivation by incorporated phosphorus ions.
The effect of the alternative nitridation process of the 4H-SiC/SiO2interface by introduction of a thin silicon nitride layer on the electrical properties of the gate oxide has been investigated.C-VandG-Vmeasurements on inversion-channel MOS devices revealed similar results to the conventional N2O oxidation. Higher field-effect mobility values are achieved due to lower interface roughness of the alternative nitridation process. However, insignificant degradation of the reliability was observed.
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