Papers by Keyword: Low Temperature

Abstract: This study evaluates the effectiveness of EDIPA, an alkanolamine admixture, in improving the early age strength and durability of GGBFS blended mortars under low temperature (5°C) curing. The experimental program comprised compressive strength tests, SEM/XRD analyses, and durability assessments via accelerated carbonation and drying shrinkage. Mortars with EDIPA achieved higher early age and 28 day strengths and exhibited a denser, more refined hydration microstructure. Durability also improved, as evidenced by reduced carbonation depth and lower shrinkage strain. These results indicate that a low dosage EDIPA approach is effective for securing structural performance and durability of mortar in cold weather construction.

Abstract: In this work, a nitrogen plasma treatment process was employed on n-type 4H-SiC. Both the Si- and C-face were studied and treated with N₂ plasma. The surface concentration of nitrogen increased from 5×10¹⁸ cm^-3 to 5×10²¹ cm^-3 in both the Si-face and C-face as analyzed by secondary ion mass spectroscopy (SIMS). This shows that a simple plasma treatment process was able to incorporate very high concentration of nitrogen dopants otherwise done using high temperature implanters. Titanium-based Ohmic contacts were formed at ~800 °C thanks to the presence of high concentration nitrogen dopants. Specific contact resistance of (ρ_c ~1.5 × 10^-6 Ω.cm² and ~1.9 × 10^-6 Ω.cm²) was obtained on Si-face and C-face, respectively.

Abstract: The determination of the dependencies of the electrical resistivity of the thin film to temperature is of great importance both for understanding the conduction mechanism and for numerous technical applications of these films. In this work, to characterize, the electrical properties of thin films, a GM cryocooler-based automatic board temperature range electrical properties measurement system has been constructed. The system can measure multiple samples simultaneously. The cooling process was simulated using the time-discrete differencing to validate the optimized device design parameters and minimize heat losses. Furthermore, the temperature-dependent sheet resistance results were compared with the results from the physical property measurement system.

Abstract: In this paper, the effect of direct and pulsed current in the arc welding with the use of UONI 13/Moroz coated electrodes on the structure and properties of 10KhSND structural low-alloy steel joints was investigated. Welding was performed in winter at an ambient temperature of-40oС. This work is a continuation of the cycle of research on welding of structural steels, carried out by the authors for several years.

Abstract: The PEM fuel cell was examined using numerical simulation in varied circumstances. To restore the fuel cell performance, a 3D-based PEMFC model was designed employing COMSOL Multiphysics 5.1. The analysis validity was confirmed using the V-I curves derived from data analysis in varied operational circumstances. The continuity, momentum, species transport and charge equations were used to represent the cell transport phenomenon. The flow of permeable medium in the gas diffusion layer was defined by employing Brinkman equations. V-I curves were obtained using the Butler-Volmer equations. According to findings, the current supply in the cathode catalyst layer achieves an optimum one, functioning as mass transport, ionic and charge transport resistances. It indicates optimum current supply in the cell holds a feature of highest oxygen deprivation on the channel's output side.

Abstract: 3C-SiC films have been grown on [100] n-doped Si substrates in a horizontal cold wall CVD reactor. Without the use of plasma enhancement, the precursors silane and propane are used to deposit silicon carbide films at T < 1200°C. The structure of the grown films has been investigated via FESEM, XRD and Raman spectroscopy. It has been found that the growth rates are between 200 and 300 nm/h. Additionally, structural analysis give evidence of polycrystalline phases. Reasons for that could be insufficient cracking of the precursors and homogenous nucleation of Si species in the gas phase.

Abstract: One of the most common asphalt concrete pavement distresses is low temperature cracking, also known as thermal cracking. Characterizations of low temperature cracking and formulation for pavement design have taken a lot of effort. Asphalt binder has viscoelastic behaviour, so asphalt mixture behaviour changes as the temperature changes. At high and low temperatures, the asphalt binder shows viscoelastic plastic behaviour and elastic behaviour. Low temperature cracks that grow day by day due to the movement of vehicles are the most significant pavement cracks caused by cold climates. It needs early and premature repairs to build and expand low temperature cracks. The aim of this research is to perform Low Temperature Cracking analysis of asphalt materials (laboratory and analytical assessment), in light of the latest update of binder cracking temperature. The role of basic material properties in low-temperature cracking was studied in this work. As a result, statistical analysis in the cohesive failure condition revealed that the asphalt mixture aggregate's free energy was ineffective in this cohesion failure. Fly ash had been used in the other type of asphalt mixture. It was proven that the addition of fly ash as an additive can improves the low temperature resistance of the asphalt mix. The binder with 60/70 penetration grade was used. The different amount of fly ash (0%, 1%, 3% and 5%) was added to the asphalt mixture. Marshall Stability and flow, resilient modulus and dynamic creep were carried out to investigate the mechanisms of cracking at low temperature. From the results obtained, there are significant effect comes from the addition of the fly ash. The result show that the addition of 5% fly ash produce the best outcomes for the density, stability, stiffness, resilient modulus and dynamic creep. Thus, it can conclude that the existence of fly ash in the mixture is able to enhance the mechanical performance of the AC14 dense-graded asphalt.

Abstract: The 3 at% Al doped ZnO thin films were deposited on p-Si substrate with a native SiO₂ layer by spray pyrolysis method. Low temperature conduction behaviors were studied by analysis of impedance spectroscopy and low temperature ac conductivity. The results of impedance spectroscopy showed that the grain boundaries contributed to the resistivity of Al doped ZnO/SiO₂/p-Si heterojunction. The calculated activation energy was 0.073 eV for grain boundaries. The equivalent circuit to demonstrate the electrical properties of Al doped ZnO/SiO₂/p-Si heterojunction was a series connection of two parallel combination circuits of a resistor and a universal capacitor. Low temperature ac conductivity measurements indicated that the conductivity increased with temperature. Low temperature conductivity mechanism was electron conductivity, and the activation energy was 0.086 eV.

Abstract: In a previous research by authors, a methodology was developed to derive J-R curves for Hot Mix Asphalt (HMA) mixtures using an elastic-plastic approach where a comprehensive understanding of crack propagation regime could be achieved. In this research, the effect of crumb rubber modification of HMA binder is studied in terms of R-curves and crack propagation at low temperatures. Mode I Single edge notched beam (SE(B)) fracture tests were conducted in temperature levels of 0 °C, -10 °C, and -20 °C. PG58-22 and PG64-22 binders were used in the fabrication of HMA samples. Modified specimens consist of 20% crumb rubber along with the incorporation of 3% warm mix admixture. Crack growth resistance curves were obtained in SE(B) tests by means of image processing and recording of the progressive crack length. Elastic-plastic J-R curves revealed that crumb rubber modified mixtures exhibit higher crack growth resistance for each bitumen performance grade. As well, increased ductility and cohesive energy can be observed according to the R-curves as the mixtures are modified by crumb rubber.

Abstract: Storage battery is an indispensable energy storage device at present. It is widely applied to industries like electric automobiles due to its advantages such as safety, reliability, low cost, etc. However, like most storage batteries, lead-acid battery has a series of problems in the low temperature environment such as the plunge of capacity, difficulty of charge, and so on, which deeply influence its application effect. To improve the low temperature performance of lead-acid battery, carbon materials could be added to the cathode of lead-acid battery. By measuring the properties like HRPSoC cycle and dynamic charging under different carbon (graphite) content, this article concludes that the addition of carbon material could improve the low-temperature performance of lead-acid battery. When the carbon content is between 0.3% and 0.9%, the improvement effect is relatively better. The research result of this article has a reference function to the design and development of low-temperature lead-acid batteries.