Control Of Nitrogen Content Research Articles

A Study of the Effect of Alloying Elements and Temperature on Nitrogen Solubility in Industrial Stainless Steelmaking

The role of nitrogen varies in different stainless steels from a harmful impurity to a valuable alloying element. Therefore, the strict control of nitrogen content is a very important issue in the steel making process. Better understanding about the thermodynamics of nitrogen solubility is the basis for this control. The aim of this study was to determine whether the nitrogen solubility at atmospheric pressure at any given composition and temperature in an Argon Oxygen Decarburization (AOD) converter could be reliably predicted. This was done by comparing different equations for nitrogen solubility to industrial measurements of several different steel grades with a wide range of compositions and temperatures. The test set consisted of 100 heats to ensure reproducibility and sufficient variability. The focus was on examining the effect of the main alloying elements (Cr, Ni, Mo, Mn) and temperature on nitrogen solubility. Nitrogen solubility is increased most by the chromium content, followed by manganese and molybdenum, whereas nickel decreases the solubility. The interaction effect of an alloying element on nitrogen declines at increasing temperatures, resulting in a negative temperature dependence, i.e., the maximum nitrogen solubility is obtained near the liquidus temperature. The study showed that most of the examined thermodynamic equations predicted the nitrogen solubility quite well in common stainless steels and even in high alloyed steels. On the other hand, clear discrepancies were observed for steels with a high manganese content as well as with strongly deviating temperatures. Therefore, based on the present measurements and the literature data, a new equation was developed for predicting the solubility of nitrogen in a wide range of stainless steels. This equation can be coupled with the existing process models to control the AOD process.

Control of nitrogen content and its effects on the electrochemical behavior of nitrogen-doped carbon nanofibers

Nitrogen-doped carbon nanofibers (N-CNFs) with different nitrogen contents were synthesized from vaporized acetonitrile as a simultaneous carbon and nitrogen source via the chemical vapor deposition method. N-CNF synthesis was conducted at 640°C for 2h, and the ratio of nitrogen and hydrogen mixture as reactant gas was adjusted to control the nitrogen content in the N-CNFs. The amount of hydrogen in the reactant gas was varied in the range from 0 to 40mLmin−1. The physical and electrochemical properties of the N-CNFs were characterized. The content of introduced nitrogen decreased with the ratio of supplied hydrogen, as opposed to the growth yield of the N-CNFs. Additionally, the nitrogen content and chemical states of the N-CNFs were examined and compared to reveal their correlations with the electrochemical behavior. The N-CNFs were found to have a noticeable electrochemical behavior such as capacitance and oxygen reduction reaction activity that was determined by the total nitrogen contents, especially those of pyridinic-nitrogen.

Development of Improved Materials for Structural Components of Sodium-Cooled Fast Reactors

Austenitic stainless steels (SS) with appropriate mechanical and irradiation-resistant properties are crucial for realizing sodium-cooled fast reactors (SFRs). In PFBR, with 40-years design life, 316LN SS with 0.02–0.03 wt-% C and 0.06–0.08 wt-% N, is used for structural components operating above 700K. For further improving high-temperature mechanical properties of 316LN SS, various heats with different nitrogen contents of 0.07, 0.14 and 0.22 wt-% were investigated. Detailed evaluation of tensile, creep, low cycle fatigue, creep-fatigue interaction and weldability, led to development of nitrogen-enhanced 316LN SS with 0.12–0.14 wt-% N having better combination of mechanical properties. Matching composition electrodes with 0.14 wt-% N have also been developed for its welding. The creep strength of fusion welded joints of modified 9Cr-1Mo (P91) steel, used for constructing the steam generators of PFBR, is considered to be a life limiting factor as a high percentage of the failures have been reported to occur in the inter-critical heat-affected zone, which is referred as Type-IV cracking. Micro-alloying the P91 steel with boron coupled with control of nitrogen content is considered as a possible way of reducing the strength disparities across the weld joint that enables minimising, if not eliminating, the Type-IV cracking problem. To optimize the boron and nitrogen contents, three heats of boron-added P91 steel, with 60-100ppm boron and 47-110ppm nitrogen, have been investigated. The weld joints of the boron-added P91 steel, with 60ppm boron and 110ppm nitrogen, exhibit better resistance to Type-IV cracking, with the creep rupture life of these weld joints being twice that of the weld joints of boron-free P91 steel.

Fine Control of Nitrogen Content in N-doped Titania Photocatalysts Prepared from Layered Titania/Isostearate Nanocomposites for High Visible-Light Photocatalytic Activity

In this contribution, high photocatalytic activity under visible-light irradiation realized by means of the fine control of the nitrogen content in doped titania photocatalysts is reported. The photocatalyst samples were prepared from a layered titania/isostearate nanocomposite as precursor, and the fine control of nitrogen content was achieved by the adjustment of the amount of hybridized isostearate in the nanocomposite, preserving the crystallinity and specific surface area of the final samples. Photocatalytic activity under the UV-light irradiation (290 and 350 nm) decreases with nitrogen content. Under visible-light irradiation (470 nm), a maximum value of photocatalytic activity was observed at [N]/[Ti] = 0.0145, whereas the absorbance in the visible-light region increases with nitrogen content. Fine control of the doped-nitrogen content provides a possible route to achieving high visible-light photocatalytic activity where the maximum value of the apparent quantum yield under 470 nm light irradiation exceeds 2%.

Control of nitrogen content and porosity in gas tungsten arc welding of high nitrogen steel

In welding of high nitrogen steel (HNS), it is essential to control the nitrogen content and porosity in the weld metal. In this paper, the influence of shielding gas composition and heat input on the nitrogen content and porosity in the weld metal of HNS was investigated by gas tungsten arc welding. The experimental results indicate that the weld nitrogen content increases as N2 in the shielding gas is increased in the same heat input of welding. The weld nitrogen content decreases with increasing the heat input for pure argon used as a shielding gas, whereas it increases with increasing the heat input for the shielding gas including some nitrogen. The nitrogen pore can be avoided when the nitrogen content in the shielding gas is <4% in the heat input range of 528–2340 J mm–1.

In-situ Control of Nitrogen Content and the Effect on PL Properties of SiNx Films Grown by Ion Beam Sputter Deposition

AbstractStrong visible luminescence was observed in silicon nitride (SiNx) thin films grown by ion beam sputter deposition (IBSD) using nitrogen ion as a sputtering source. Nitrogen content (x) of the films was controlled by variation of the sputtering N2 ion flux and analysed by in-situ x-ray photoelectron spectroscopy (XPS). Relative sensitivity factors of Si and N peaks could be calculated by Rutherford backscattering spectroscopy. The photoluminescence (PL) spectra of the post-annealed samples showed visible luminescence at blue-green region. PL energy showed a blue-shift due to quantum confinement with decreased excess Si and intensity showed a maximum value near x = 1.1. These PL properties are well correlated with the formation of Si nanocrystals (nc-Si). We found that there is a great increase of PL energy of SiNx thin films compared with SiOx thin films, which indicate that the surface state of Si nanocrystals plays an important role to increase PL energy and intensity.

Determination of the Relative Nitrogen Doping Level of Tantalum Nitride Resistor Film by Means of the Seebeck Effect

Summary Tantalum film reactively sputtered in nitrogen is extensively used as a thin film resistor material in film integrated circuits. The control of nitrogen content is very important, since the nitrogen content of the film determines the aging characteristics, anodizability, sheet resistance, and temperature coefficient of resistance (TCR) of the film. A suitable method of identifying the nitrogen doping level of film immediately after sputtering is highly desirable. This paper describes the design and use of a diagnostic instrument called the “Seebeck apparatus,” which has been developed for this purpose. The film parameter measured is the so-called “Seebeck ratio @,” a quantity directly related to the Seebeck coefficient of the material. The instrument is capable of making measurements on as-sputtered film deposited on high resistivity substrates. The measurement is contacting but nondestructive, fast, and simple. Determination of the Seebeck ratio of film can be reproducibly made in less than 1 min and the ratio is presented as a direct digital readout. Using the Seebeck apparatus, the relationship between the Seebeck ratio and the nitrogen concentration in reactively sputtered tantalum nitride films has been examined. The nitrogen doping level of the films was controlled by varying the partial pressure of nitrogen in the sputtering system. Other material properties, such as resistivity (p), TCR, and aging were concurrently .‘examined and correlated with the Seebeck ratio. The results show that the Seebeck ratio of tantalum nitride films is a very rapidly varying function of the nitrogen doping level in the range suitable for resistor fabrication. Because of this functjonal relationship, it has been found that a measurement of the Seebeck ratio provides a much more sensitive test of whether film is suitably doped than the joint measurements of p and TCR alone.