Papers by Keyword: Nitrogen

Abstract: Silicon carbide (SiC) is one of the ideal electronic materials for producing high-temperature, high-frequency, and high-power electronic devices. In the past 20 years, with the continuous improvement of silicon carbide material processing technology, its application have been expanding. Unlike Si devices, SiC devices cannot be directly fabricated on crude wafers. Instead, epitaxial films need to be deposited and grown on SiC wafers, then the epitaxial films will be used to produce devices. The doping concentration performance of the epitaxial layer can determine the device performance, making it the most important indicator of the epitaxial layer quality. For a long time, nitrogen has been used as the dopant in the production of SiC epi-wafers. Due to the difficulty of nitrogen cracking and its adsorption in graphite, the concentration is prone to significant drift, resulting in a decrease in yield and low production efficiency. In this research a vertical epitaxial equipment was used to consecutively grow 10 8-inch SiC substrate with nitrogen and ammonia as dopant separately. The concentration and thickness of the grown epitaxial films were measured and studied. The results indicate that compared to nitrogen as a dopant, the results of ammonia doping are significantly better in terms of intra-wafer concentration uniformity and inter-wafer consistency. Using nitrogen as the dopant, the doping concentrations uniformity of epi-layer ranges from 1.31% to 2.18%, and the deviation is between ± 8.0%. As a comparison, using ammonia as the dopant, the doping concentration uniformity of epi-layer ranges from 0.65% to 0.89%, and the deviation is between ± 1.0%. Meanwhile, the thickness performance is at the same level. Therefore, ammonia as a dopant can solve the concentration drift problem that has long been a headache in large-scale production of SiC epitaxy, greatly improving production efficiency. Its advantages are obvious. This study analyzed the possible reasons for the superior performance of ammonia gas as a dopant for 4H SiC epitaxy compared to nitrogen.

Abstract: Modified stainless steel grade X45CrNiW 18-9 has been developed through replacement of nickel by nitrogen. The modified steels have been produced in induction furnace under nitrogen pressure and were cast into round ingots with 100 mm diameter. The cast modified stainless steels were forged, followed by air cooling. The nitrogen contents were determined and compared with those calculated using Institute of Metal Science (IMS) equation: The results showed that there are great deviations between the actual nitrogen contents and predicted values through IMS equation. So, an equation has been derived based on chemical composition, pressure and temperature at 1600 °C. [N%] = 0.0078 + 0.0406*X, where X is function of chemical composition and nitrogen pressure. The derived equation has been used to calculate the nitrogen content of different stainless steels using published data. The results reveal the difficulty of deriving a general equation for the prediction of nitrogen content covering different steel compositions. So it is necessary to use narrow composition range. The phases of modified stainless steels have been investigated using Schaeffler diagram, dilatometer and microstructure observations. Both partial and total replacement of nickel using 0.33-0.50% nitrogen, are effective to produce a modified fully austenitic stainless steel grade X45CrNiW 18-9.

Abstract: The problem of using gaseous extinguishants to eliminate fire sources is to inhibit the active radicals of the flame, but at the same time it is necessary to take into account the change in the concentration of oxygen. Therefore, the object of research was the value of the extinguishing concentrations of both individual extinguishants and binary mixtures of halocarbons and inert gases during the elimination of heptanes burning. It has been proven that when nitrogen was supplied, gaseous combustion products were diluted and the relative radiation intensity of hydroxyl radicals decreased to 80 %; on the contrary, when pentafluoroethane (HFC-125) and heptafluoropropane (HFC-227ea) were supplied, the process of chemical inhibition of the combustion reaction took place which led to a significant reduction of the burning rate and, accordingly, the intensity of radiation of hydroxyl radicals by more than 4 times. The joint action of the inert gas and the combustion inhibitor in different ratios did not exceed the intensity of the radiation of hydroxyl radicals of the flame of the inhibitor itself. However, when an inert gas was introduced, the flame was being enriched with fuel and the number of hydroxyl radicals decreased, and the additional introduction of an inhibitor led to a more effective reduction of hydroxyl radicals in the flame. On the basis of the derived results of the experimental studies on the elimination of the fire source of a cup burner with binary mixtures of a halocarbon and an inert gas, it was established that a relatively small dilution of air with nitrogen led to a significant decrease in the extinguishing concentration of the combustion inhibitor. In particular, the extinguishing concentration of heptafluoropropane HFC-227ea for extinguishing n-heptane can be reduced by 2.0 times if, by adding nitrogen, the concentration of oxygen in the air is reduced from 20.5 to 19 % by volume, that is, by only 7 % (relative). The practical value lies in the fact that the derived results of determining the extinguishing concentration of halocarbons, nitrogen and their binary mixtures make it possible to establish the conditions for the elimination of fire sources.

Abstract: Recent studies indicate that bio-oil production from EFB is highly influenced by the temperature during pyrolysis. In this study the pyrolysis process was conducted at the optimum temperature of 500°C for 60 minutes and the nitrogen gas flowrate (N₂) was varied between 1 and 3 L/min. The bio-oil itself can be obtained from the condensed gas pyrolysis product. The characteristics of bio-oil were then identified based on biofuel quality standards. The bio-oil was then tested in order to determine its physical properties such as its density, water content, and acid number. Besides, the chemical components of the bio oil were identified by using GC-MS. The results show that the density of bio-oil is within the range of 0.9918 - 1.0083 g/cm³. The highest water content produced is 27.22% at a flow rate of 1 L/min. The acid number of bio oil is ranging from 124.9 – 139.6 mg KOH / g. According to GCMS test results, linoleic acid content is high at a flow rate of 1 L / min, while hexadecane content dominates by 15.79% at a 2 L / min rate. Further observation on the rate of 3 L / min shows that phenol content increases.

Abstract: Cement dust is principal industrial waste that exhibits detrimental effects on soil properties especially the nitrogen content of the soil. This study investigated the total Nitrogen and Nitrate value of the soil and dust collected in thirteen (13) different locations around Ewekoro Limestone Quarry and Cement Production. The results showed that the total nitrogen value ranges between 0.093ppm and 0.037ppm while the nitrate value ranged from 145.25ppm - 66.50ppm in the soil samples. Also, the total nitrogen in the dust particulate samples was from 0.950-0.100ppm while the nitrate value ranged from 63.00ppm-28.00pm. The value of total nitrogen value and nitrate around Ewekoro Quarry is relatively lower than the value obtained at Ososun, the control location which is about 10km away from Quarry. Duncann Multiple range tests revealed that soil samples collected from Alaguntan, Ajegunle, Arigbajo, Papa Lanto, Rail km 53, Waasinmi Alaafia, Apomu, Isofin Orile, Quarry, were significantly different in total nitrogen from the control sample (Ososun). In contrast, soil samples collected from Ayepe, Lapeleke, and Agbesi do not differ significantly in total Nitrogen from the soil sample. Also, the result of the correlation matrix indicated that there is a significant positive correlation between total nitrogen, conductivity, and depth at (<0.05), while there is a negative correlation but non-significant relationship between soil depth, pH, clay content, and total nitrogen. It is possible that the reduced level of nitrogen around the quarry location compared with the control site must have been due to the effect of cement duct particulates.

Abstract: Diamond and Silicon Carbide (SiC) are promising wide band-gap semiconductors for power electronics, SiC being more mature especially in term of large wafer size (200 mm). Nitrogen impurities are often used in both materials for different purpose: increase the diamond growth rate or induce n-type conductivity in SiC. The determination of the nitrogen content by secondary ion mass spectrometry (SIMS) is a difficult task mainly because nitrogen is an atmospheric element for which direct monitoring of N^± ions give no or a weak signal. With our standard diamond SIMS conditions, we investigate ¹²C¹⁴N^- secondary ions under cesium primary ions by applying high mass resolution settings. Nitrogen depth-profiling of diamond and SiC (multi-) layers is then possible over several micrometer thick over reasonable time analysis duration. In a simple way and without notably modifying our usual analysis process, we found a nitrogen detection limit of 2x10¹⁷ at/cm³ in diamond and 5x10¹⁵ at/cm³ in SiC.

Abstract: Biochar research has been gaining recent interest in agricultural applications because of its use as a soil amendment. Biochar is a porous carbonaceous solid produced from heat in the absence of any introduced oxygen (pyrolysis). It has relatively high surface area and slow-release properties that makes it suitable for fertilizer formulation. In this study, rice straw is used for biochar production using modified carbonizer at 600-650°C temperature range. After synthesis in the nanoscale level, the biochar produced was infused with nutrients such as nitrogen, phosphorus, potassium and zinc. The morphological characteristics were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and energy dispersive Xray spectrometry (EDS). Nutrients were incorporated in the biochar and analysis revealed concentrations of 4.96% N, 3.46% P, 2.25% K, and 10.90% OM. The nanoscale biochar-based fertilizer was then applied into rice production. Rice grown in soil amended with nanoscale biochar-based fertilizer showed higher yield than control treatments but with comparable result from the inorganic fertilizer treatments. This implies that biochar can be used as an alternative to chemical based fertilizer when infused with the essential nutrients needed by plants. Furthermore, the soil amended with the nanoscale biochar-based fertilizer was also found to have a higher nutrient and organic matter content after harvest. Therefore, it could preserve the soil fertility which is beneficial in the long term.

Abstract: The present study has been conducted in order to obtain iron nitrides layer on AISI4140 steel by using plasma nitriding treatment. As one of several parameters of this process, the nitrogen rate ranging from 10 to 70% with a step of 20% was chosen. The structure, the morphology, the thickness and the hardness of iron nitrides layer were investigated. As a result, the improvement of surface hardness of nitrided steel was identified related with the increase of compound layer thickness due to the increase of activation rate. The steel substrate treated at high activation rate presents hardness 3 times higher than that of untreated steel.

Abstract: Magnetic properties of the R₂Fe₁₇ compounds are sensitive to the atomic substitutions and interstitial absorption of nitrogen. In our work, both were combined and their effect on the magnetization behavior of Er₂Fe₁₇ compound in magnetic fields up to 58 T was studied. Er₂Fe₁₇N₂, Sm_1.2Er_0.8Fe₁₇N₂ and Sm_1.8Er_0.2Fe₁₇N_2.1 nitrides were prepared. Magnetization measurements were carried out, mainly on powder samples (excluding Er₂Fe₁₇ single crystal). Nanopowders of Sm_1.2Er_0.8Fe₁₇N₂ were obtained by mechanical grinding. The grinding time was varied from 0 to 60 minutes. The strength of the inter-sublattice coupling in samples is estimated by analyzing high-field magnetization data.

Abstract: Recently, the frequency of earthquakes has been increasing worldwide. As a result, steel reinforced with seismic performance that can satisfy the social needs to strengthen the existing seismic performance of existing infrastructure facilities and new buildings has become important. In general, to secure the yield strength of reinforcing bars and to reduce the production cost, reinforcing bars are produced by rolling the surface through a facility such as a Tempcore. In Korea, most of them have adopted the Tempcore process to ensure the mechanical requirements of the product. However, the use of a small amount of alloying elements and the application of Tempcore have limitations in producing reinforcing bars that require seismic performance. In recent years, remarkable progress has been made in the production and application of high strength rebars. Microalloying and fine-grain strengthening are the most effective methods in developing high strength rebars. That is, the precipitation of V (C, N) is promoted by the addition of V to improve the strength by precipitation strengthening of V-carbonitride. However, in V-microalloyed reinforcing bars, it was confirmed that the required strength did not increase proportional to the amount of V added. In this study, the effects of vanadium and other alloying elements on the mechanical properties and yield ratio of steel bars were investigated by tensile test results and microstructural evaluation.