Blowing Nitrogen Gas Research Articles

A corrosion failure analysis of a titanium tank used for production and storage of molten sodium sulfide

The corrosion failure of a titanium tank operating under high temperature of 220 °C for the production and storage of molten Na2S was thoroughly analyzed in this study. The various materialcharacterization methods, such as visual inspection, microscopic observation, chemical analysis, and mechanical assessment, demonstrated that hydride-inducedembrittlement plays a considerable role in the failure of the titanium tank. The key finding was that side products of H2, H2S, and Na2SO3 cause the destruction of the passive oxide film and, thus, provide the conditions for the absorption and penetration of atomic hydrogen, resulting in the formation of brittle TiH2 and subsequent flaking on the surface. To failure prevention of the titanium tank in such environments, the selection of tank material from Monel®400, blowing nitrogen gas into the system, and loading Na2CO3 into the reactive media were proposed. By complementary electrochemical investigations, it was clarified that Na2CO3 can stabilize the passive oxide film on the titanium surface and, therefore, enhance the resistance of the titanium tank against corrosion and failure. Notably, the present study can provide helpful references for enhancing the safety maintenance management of similar types of equipment.

Effect of surface characteristics on the axial fatigue properties and wear resistance of Ti-6Al-4V alloy nitrided by gas blow induction-heating

The effects of surface characteristics on the axial fatigue properties and wear resistance of the GBIH-nitrided titanium alloy were investigated to improve the fatigue strength and wear resistance of Ti-6Al-4V alloy rapidly nitrided by induction-heating in a nitrogen atmosphere with blowing nitrogen gas (GBIH-nitriding). The fatigue strength of the GBIH-nitrided Ti-6Al-4V alloy was lower than that of the mirror-polished specimen owing to the formation of a brittle nitrogen compound layer and grain coarsening. Fatigue tests using specimens prepared by combining GBIH-nitriding and particle collision treatments revealed that the formation of nitrogen diffusion layers at the outermost surface and the generation of compressive residual stress without forming surface asperities increased the fatigue strength of the GBIH-nitrided Ti-6Al-4V alloy. Moreover, the formation of a nitrided layer and suppression of surface asperities effectively improved the wear resistance of the Ti-6Al-4V alloy. Therefore, formation of a nitrogen diffusion layer and the introduction of compressive residual stress without grain coarsening, a compound layer, and surface asperities increased the fatigue strength and wear resistance of the GBIH-nitrided alloy.

Study on the Development of AlN Particles Synthesized by Gas/Liquid Reaction <i>In Situ</i>

AlN particles can be synthesized by blowing Nitrogen gas into liquid metal. At high temperature Nitrogen molecules decompose to atoms and react with Al to create AlN. EDX diffraction shows that weight ratio of the particles fully coincides with the ratio of standard atomic mass between Al and N (about 2), confirming that the particles are AlN. The SEM images show that AlN particles size varies from several hundred nanometers to some micrometers, depending on the contact time between gas bubbles and liquid metal. A simple model shows that the growth rate of the AlN particles (0.148 nm/s) at the early stage is only a half of that at finishing stage (0.305 nm/s), this may be due to the difficulty of the nucleation at the early stage. The formation rate of AlN was calculated based on the X-ray diffraction and shows the same tendency, as the growth rate.

Surface Modification of Titanium by Producing Ti/TiN Surface Composite Layers via FSP

In this paper, we report the use of blowing nitrogen gas for the successful fabrication of a composite layer composed of Ti/TiN on a substrate of commercially pure titanium (cp-2) using the friction stir processing technique. The prepared composite layer was characterized by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectrometry. The maximum microhardness of the Ti/TiN composite reached 1024 HV, which is 6.4 times higher than that of the titanium substrate. The results of wear test indicated that the Ti/TiN composite layer possesses excellent abrasive and adhesive wear resistance because of the formation of the TiN and its high hardness.

Gas Atomizer Making to Produce Tin Powders

The objective of this research is to make an economical laboratory-scale, horizontal gas atomizer for producing tin powders. The procedures were designing a furnace, gas chamber and cyclone, and 2-nozzle air tubes. All equipments were built and assembled to be a gas atomizer. The gas atomizer was trial run by blowing nitrogen gas to molten tins. It produced powders in many sizes. The trial run had been repeated in many conditions. The variable conditions were the molten tin temperature, the 2-nozzle air tubes angle, and the gas pressure. The best trial run resulted, tin powder smaller than 150 μm was 75.4 %. The best conditions of trial run result were 300 o C of molten tin temperature, 30 degree of 2-nozzle air tubes angle, and 200 psi of gas pressure. The tin powder particles were spherical shape. This research can produce an economical laboratory-scale, horizontal gas atomizer for learning metal powder.

Research on Kinetics Behavior of Nitrogen Gas Absorption in Fe-Cr-Mn(Mo) Alloy

The kinetics of nitrogen absorption in Fe-Cr-Mn (Mo) alloys under 0.1 MPa nitrogen pressure and 1873K was investigated by top blowing nitrogen gas into the steel melts. A thermodynamic model of nitrogen solubility was established. Also the effect of surface active elements oxygen and sulfur on nitrogen absorption was studied. The results show that Fe-Cr-Mn (Mo) melts achieve nitrogen saturation value within 50 minutes, the nitrogen solubility increases with the content of chromium and manganese, but the experiment values of nitrogen solubility are general lower than theoretical values because of the open nitrogen gas atmosphere and high surface active elements content in the steel melts. The nitrogen absorption can be described well by a second order reaction and the interfacial reaction is restrictive step. The rate of nitrogen absorption decreases by lowering the surface reaction constant due to oxygen and sulfur in the steel melts. The effect of the surface active elements oxygen and sulfur on nitrogen absorption can be described well as .

The Purification of ZL114A Alloy by Means of Bubble Floatation

According to the principle of bubble floatation, purification of ZL114 aluminum casting alloy has been studied by blowing nitrogen gas into the ZL114A alloy melt through the porous plug which can produce dispersed micro bubbles. 5 samples have been taken at 0 min, 2 min, 4 min, 6 min, 8 min and 10 min, respectively, to measure the hydrogen content through HYSCAN II hydrogen tester. The experiments results show that the removing effect of hydrogen is remarkable. The hydrogen removing efficiency reaches 85.7% when blowing lasts 4 minutes. The rate of hydrogen removing begins to decrease from 4 minutes to 10 minutes; the hydrogen removing efficiency gets to the maximum after 8 minutes. The inclusions are also removed with the removal of hydrogen.

Production of in-situ hard Ti/TiN composite surface layers on CP-Ti using reactive friction stir processing under nitrogen environment

Reactive friction stir processing was carried out on a commercially pure titanium substrate by blowing nitrogen gas into the stir zone. Surface layers were produced having non-uniform banded-type microstructures of TiN precipitates in a transformed titanium matrix. Using additional passes, near uniform dispersion of TiN precipitates (~2μm) in a matrix of fine grains (~4.5μm) with α′-Ti martensite sub-structure was achieved. Dissolution of nitrogen in the stir zone and formation of TiN-based structure were confirmed by energy-dispersive X-ray spectroscopy, X-ray and electron diffraction, respectively. The fabricated Ti/TiN (2.3vol.%) composite layer showed an average microhardness value of ~972HV, which is about six times greater than that of its underlying titanium substrate; this is attributed to the formation of hard TiN reinforcements at boundaries of fine dynamically restorated grains with α′-Ti martensite sub-structure.

The Antioxidant Transcription Factor Nrf2 Negatively Regulates Autophagy and Growth Arrest Induced by the Anticancer Redox Agent Mitoquinone

Mitoquinone (MitoQ) is a synthetically modified, redox-active ubiquinone compound that accumulates predominantly in mitochondria. We found that MitoQ is 30-fold more cytotoxic to breast cancer cells than to healthy mammary cells. MitoQ treatment led to irreversible inhibition of clonogenic growth of breast cancer cells through a combination of autophagy and apoptotic cell death mechanisms. Relatively limited cytotoxicity was seen with the parent ubiquinone coenzyme Q(10.) Inhibition of cancer cell growth by MitoQ was associated with G(1)/S cell cycle arrest and phosphorylation of the checkpoint kinases Chk1 and Chk2. The possible role of oxidative stress in MitoQ activity was investigated by measuring the products of hydroethidine oxidation. Increases in ethidium and dihydroethidium levels, markers of one-electron oxidation of hydroethidine, were observed at cytotoxic concentrations of MitoQ. Keap1, an oxidative stress sensor protein that regulates the antioxidant transcription factor Nrf2, underwent oxidation, degradation, and dissociation from Nrf2 in MitoQ-treated cells. Nrf2 protein levels, nuclear localization, and transcriptional activity also increased following MitoQ treatment. Knockdown of Nrf2 caused a 2-fold increase in autophagy and an increase in G(1) cell cycle arrest in response to MitoQ but had no apparent effect on apoptosis. The Nrf2-regulated enzyme NQO1 is partly responsible for controlling the level of autophagy. Keap1 and Nrf2 act as redox sensors for oxidative perturbations that lead to autophagy. MitoQ and similar compounds should be further evaluated for novel anticancer activity.

窒素ブロー方式による高送りミーリング時の工具寿命改善

If the cutting speed is high, the cutting temperature will also be high and that may reduce the tool life remarkably. However, use of a cutting fluid in high-cutting speed conditions will increase the thermal shock and can cause thermal cracks in the tool, thus resulting in increased tool wear. In this study, the heat generated by oxidation during cutting was suppressed by blowing nitrogen gas onto the cutting point in order to lower the cutting temperature and thus to prolong the tool life. As result, blowing nitrogen gas during cutting operations at high speeds and high feed rates, increased the tool life about two times, which allowed higher speeds and higher feed rates, thus reducing the total cutting time required. It was found that the blowing nitrogen gas makes it possible to improve productivity in a high-speed, high-feed rate milling operation.

Influence of Oxygen Concentration and Alkalinity on the Hydrogen Gas Generation by Corrosion of Carbon Steel

ABSTRACTA repository for low and intermediate level radioactive wastes will contain a great deal of carbon steel as reinforcement materials and waste containers. These steel components are expected to generate hydrogen gas due to reductive corrosion of carbon steel under repository condition. In this study, we have investigated the influence of the environmental factors such as oxygen concentration and pH in the solution on the rate of the gas generation. This rate was measured with a gas flow type test system under the controlled oxygen concentration, which simulates the redox conditions from initial to final environment in a repository. In addition, the corrosion mechanism was examined through the electrochemical tests.As a result, it has been found that pH in the solution and the oxygen concentration considerably affected the generation rate of hydrogen gas in various way. As to the influence of pH of the solution, it has been found that the gas generation rate increased with the increase of pH between 11.8 and 14. Further, as to the influence of the oxygen concentration, when the oxygen concentration in the blowing nitrogen gas was 2 ppm or more, the gas generation rate increased with the oxygen concentration. This trend was possibly caused by local decrease of pH due to localized corrosion. The gas generation rate was very low when the oxygen concentration was in the passive region. The rate was equal to 0.01 μm/y or less if the corrosion occurs with an equation: 3Fe+4H2O → Fe3O4 + 4H2 ↑ to 0.01 *m imcro;/y (hereafter we call this the equivalent corrosion rate). However the gas generation rate increased when the oxygen concentration was controlled to the extent that sufficient passive film cannot be produced and thus it shifts from passive state to active state.

Steep central islands after myopic photorefractive keratectomy

Purpose: To investigate the formation of steep central islands and their reduction under modified experimental conditions.Setting: University Eye Hospital Munster and Schwind Co., Kleinosthelrn, Germany.Methods: Corneas of enucleated intact bovine eyes were treated with the Schwind Keratom. All experimental conditions were repeated six tunes in six different corneas. Eight expehrriental groups were looked at. Fluence was 180 to 200 mJ/cm2. Ablation mode (phototherapeutic keratectomy [PTK] and standard myopic photorefractive keratectomy [PRK]), internal repetition rate (3 to 30 Hz), and ablation diameter (5 to 8 mm) and depth (4 to 15 diopters [D] in PRK) were varied. Modifications to reduce or avoid steep central islands included blowing nitrogen gas and aerosol over the cornea, cleaning the cornea of fluid, and using an anticentrai-island software program.Results: In PTK, an increase in the internal repetition rate resulted in a decrease in the height of the steep central island. In standard PRK; increasing refractive correction up to −8.0 D and increasing the ablation diameter resulted in an increase in steep central island polder. The anti-central-island program, blowing aerosol, and cleaning the comea reduced the formation of steep central islands and blowing nitrogen gas eliminated them.Conclusion: Steep central islands are created by a wide-field ablation process and are probably caused by many factors. Both software and hardware modifications can be used to reduce their formation.

The effect of surface movements on nitrogen mass transfer in liquid iron

Marangoni convection due to surface tension gradients set up in a nitrogen-liquid iron system at 1873K has been mathematically simulated and experimentally confirmed by measuring the rate of nitrogen absorption into liquid iron and by observing the free surface motion of liquid ironvia zirconium oxide particles using X-ray radiography. This surface flow was created by blowing nitrogen gas through a small lance over the free surface of the liquid iron contained in an alumina boat under resistance heating. Absorption measurements indicated that the mass-transfer coefficient of nitrogen in liquid iron due to Marangoni convection (km1>=1.5×10−4 m/s) is slightly less than that due to induction stirring (km1=2.1×10−4 to 1.5×10−4 m/s). The free surface velocity induced by the surface tension gradient, with an initial composition difference of 425 to 10 ppm, was found to be of the order of 0.05 to 0.11 m/s. Mathematical modeling was also carried out to determine the velocity and nitrogen concentration profiles in the alumina boat. It was found that Marangoni convection creates mildly turbulent flows in liquid iron. Good agreements between the experimentally obtained data (nitrogen concentration and surface velocity) and the computed results were attained when a constant eddy viscosity which was five times the molecular value was assumed. This prescription allows both the predicted apparent mass-transfer coefficient and the predicted surface velocity to match the experimental results simultaneously. Note that the transport coefficients in the momentum and the convective-diffusive equations are correlated by the turbulent Schmidt number. The dimensionless mass-transfer correlation obtained for the present N-Fe system at 1873 K under resistance heating was found to be Sh=0.104 Re0.7·Sc0.7 with Sc=79.5 (3500<Re<7700).

Corneal Wound Healing after Excimer Laser Ablation: Effects of Nitrogen Gas Blower

To examine the effects of blowing nitrogen gas over the cornea during photorefractive keratectomy. Excimer laser ablations for myopia were performed on rabbit corneas with or without the blowing of nitrogen across the surface of the cornea. All eyes underwent a 5-diopter myopic ablation; in 8 eyes, a ring was used to blow nitrogen gas across the cornea, and, in 8 eyes, the same ring was used, but no nitrogen gas was blown. Epithelial healing occurred more rapidly in the eyes that were not treated with the gas (3.8 +/- 1.3 days) than in the gas-treated group (6.1 +/- 0.8 days; P = 0.0025). Corneal haze was greater in the group treated with gas. Results of histologic examination showed the ablated area to have a smoother surface when nitrogen was not blown across the cornea surface. Superficial corneal deturgescence produced by the nitrogen gas appears to result in a rougher surface immediately postoperatively with undesirable effects on surface healing, but further studies will be necessary to determine the applicability of these results to humans.

Experimental study of a micro-rotor fabricated on a silicon wafer

This paper describes an experimental study of the fabrication of micro-mechanisms on a silicon wafer. Planar process technology developed in the industry of CMOS LSI was employed. The structural material is CVD-polycrystalline silicon with a thickness of 2.5 μm and the sacrificial material is CVD-SiO2 with a thickness of 1.0 μm. In the experimental study, micro-rotors with a shaft and a cap in an assembled form were fabricated on a silicon wafer. The self-alignment process gave a tolerance of 1.0 μm between the rotor and the shaft. The maximum rotation speed observed was 9 x 104 rpm by blowing nitrogen gas.

アトマイズ法によるＡｌ‐Ｐｂ合金粉末の凝固組織

By blowing nitrogen gas into the molten state of Al-5 to 50%Pb alloys, which was discharged from the molten metal nozzle at the bottom part of graphite crucible, powder was produced. The solidification structure and cooling rate of the powder were examined. The results obtained are summarized as follows: The particle shape was not spherical but tear-drop-like, and the particle size was from 10 to 500 μm. It was found that lead particles were dispersed in the aluminum matrix in all the cases. The cooling rate of this powder was from 50 to 5800 k/s. The value of the heat transfer coefficient at the powder-gas interface was from 89 to 577 J/m2.s.k.