Pure Nitrogen Environments Research Articles

The effect of nitrogen on the isothermal oxidation of substoichiometric zirconium carbide: Microstructural and spectroscopic investigations

The oxidation behavior of hot-pressed sub-stoichiometric zirconium carbide was investigated through isothermal flow-tube furnace experiments at temperatures ranging from 1000 to 1600 °C. Auxiliary gas composition influence on the oxidation of ZrC0.63 was studied by introducing oxygen to substrates held under either pure argon or nitrogen environments. During furnace ramp-up, prior to isothermal oxygen exposure, nitrogen flow was found to infiltrate the substrate resulting in ZrCxNy formation which provided superior oxidation resistance to the as-received ZrC0.63. Ex situ investigation of ceramic-oxide interfacial regions revealed the presence of carbon precipitate in both material sets at treatment temperatures of up to 1400 °C, along with the presence of the ZrCxOy system. At sufficiently high test temperatures, resulting scale formations for the N2/O2 systems were found to be less porous than the Ar/O2 counterparts, with a higher degree of c-/t-ZrO2 crystallites present at room temperature attributed to nitrogen incorporation into the anion sublattice of ZrO2.

Anoxia Tolerance in Four Forensically Important Calliphorid Species

Forensically important blow flies, Diptera: Calliphoridae, are among the first organisms to colonize carrion. After eggs hatch, the larvae of most blow fly species feed in an aggregation or “mass”. While in this mass larvae may experience periods of hypoxia/anoxia, but the tolerance of blow fly larvae to anoxic conditions is poorly studied. We tested the anoxia tolerance of four species of calliphorids (Calliphora vicina, Cochliomyia macellaria, Lucilia sericata, and Phormia regina), by examining actively feeding third-stage larvae across five temperatures. Experiments were conducted by exposing larvae to pure nitrogen environments and determining mortality at set time intervals. All species show significant linear relationships between survival time and temperature under anoxic conditions. Of species tested, C. macellaria had the greatest tolerance to anoxia (LT50 of 9 h at 20 °C). In contrast, C. vicina was the least tolerant (LT50 of 2.2 h at 40 °C). With all species, survivorship decreased with increasing temperature. Unlike many other insects tested in severe hypoxia, the larvae of the calliphorids tested, which included members of three subfamilies, were not tolerant of anoxic conditions. From these findings, it seems likely that hypoxia is a significant limitation for maggots in a maggot mass, particularly when the mass temperature is high (>40 °C). Forensically, these data provide a limit on potential maggot survival on bodies that have been submerged or otherwise experience severe hypoxia before discovery.

Optical fiber carbon dioxide sensor based on colorimetric change of α-naphtholphthalein and CIS/ZnS quantum dots incorporated with a polymer matrix

This paper presents a new optical fiber carbon dioxide (CO2) sensor based on the emission wavelength shift of CuInS2/ZnS quantum dots (CIS/ZnS QDs) due to changes in the absorption of a pH indicator (α-naphtholphthalein) with a changing CO2 concentration. Using an LED with a central wavelength of 375 nm as the excitation source, it is shown that using the red emission of CIS/ZnS QDs allows for the detection of CO2 concentration over the range of 0-100%, and the associated wavelength shift was found to be 630 pm/%CO2. Moreover, the observed luminescence intensity from CIS/ZnS QDs at 578 nm increases as the CO2 concentration increases. The observed luminescence intensity change by CO2 is expressed as I100/I0, which I0 is used to represent the sensitivity of the optical fiber sensor, where I100 and I0 represent the steady-state luminescence intensities in pure carbon dioxide and pure nitrogen environments, respectively. The ratio I100/I0 of this optical fiber sensor is estimated to be 100. These results of the optical sensing method can be used in practice for detection of CO2 and could offer a new approach for developing novel types of optical fiber sensor.

Pressure‐Tunable Ambipolar Conduction and Hysteresis in Thin Palladium Diselenide Field Effect Transistors

AbstractFew‐layer palladium diselenide (PdSe2) field effect transistors are studied under external stimuli such as electrical and optical fields, electron irradiation, and gas pressure. The ambipolar conduction and hysteresis are observed in the transfer curves of the as‐exfoliated and unprotected PdSe2 material. The ambipolar conduction and its hysteretic behavior in the air and pure nitrogen environments are tuned. The prevailing p‐type transport observed at atmospheric pressure is reversibly turned into a dominant n‐type conduction by reducing the pressure, which can simultaneously suppress the hysteresis. The pressure control can be exploited to symmetrize and stabilize the transfer characteristics of the device as required in high‐performance logic circuits. The transistors are affected by trap states with characteristic times in the order of minutes. The channel conductance, dramatically reduced by the electron irradiation during scanning electron microscope imaging, is restored after an annealing of several minutes at room temperature. The work paves the way toward the exploitation of PdSe2 in electronic devices by providing an experiment‐based and deep understanding of charge transport in PdSe2 transistors subjected to electrical stress and other external agents.

THE INFLUENCE OF SOL-GEL COATED LENGTH AND WITHDRAWAL RATE ON PLASTIC OPTICAL FIBER CORE TOWARDS OXYGEN GAS SENSING SENSITIVITY

The fabrication and characterization of an optical fiber oxygen sensor based on oxygen fluorescence quenching are described. The sensors are prepared by coating the oxygen sensitive indicator (tris-BP ruthenium (II) chloride and platinum octaethylporphyrin) that is immobilized by the sol-gel route onto the uncladded middle portion of a multimode plastic optical fiber. A design of experiment based on two parameters which are the uncladded coated length and withdrawal rate was carried out in order to identify the optimum setting that gives the highest fluorescence emission which leads to better sensitivity. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio I0/I where I0 and Irepresent the fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. Both ruthenium and platinum coated fiber produced a linear Stern-Volmer relationship which indicate the homogeneous environment of the luminophore. The experimental result reveals that the optimized setting for ruthenium sol-gel coated fiber is 5 mm decladded length and 120 mm/min withdrawal rate while for platinum sol-gel coated fiber is 8 mm decladded length and 160 mm/min withdrawal rate.

Stimulative mineralization of p-fluoronitrobenzene in biocathode microbial electrolysis cell with an oxygen-limited environment

p-Fluoronitrobenzene (p-FNB) is a toxic compound and tends to accumulate in the environment. p-FNB can be effectively removed and defluorinated in a single-chamber bioelectrochemical system (BES). To verify the suppositionally integrated reductive and oxidative metabolism mechanism in the BES, an oxygen-limited environment was used, with pure oxygen and nitrogen environments used as two controls. Under the oxygen-limited condition, the most excellent performance was achieved. The defluorination rate and mineralization efficiency were 0.0132h−1 and 72.99±5.68% after 96h, with 75.4% of fluorine in the form of the fluoride ion. This resulted from the unique environment that allowed conventionally integrated reductive and oxidative catabolism. Moreover, the oxidation–reduction potential (ORP) had a significant effect on microbial communities, which was also an important reason for performance diversity. These results provide a new method for complete p-FNB treatment and a control strategy by ORP regulation for optimal system performance.

Highly sensitive fiber-optic oxygen sensor based on palladium tetrakis (4-carboxyphenyl)porphyrin doped in ormosil

A simple, low-cost technique for fabrication of highly sensitive fiber-optic oxygen sensor is described. An organically modified silicate (ORMOSIL) as a matrix for the fabrication of oxygen sensing film was produced. The technique is based on coating the end of a plastic optical fiber with ormosil composite xerogel film sequestered with luminophore palladium (II) meso-tetra(4-carboxyphenyl)porphyrin (PdTCPP) prepared by a sol–gel process. The composite xerogel studied is tetraethylorthosilane (TEOS)/n-octyltriethoxysilane (Octyl-triEOS). Result shows that, expect for PdTCPP-doped TEOS/Octyl-triEOS composite xerogel show the high sensitivity and linear Stern–Volmer relationship which indicate the homogenous environment of the luminophore. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio IN2/IO2, where IN2 and IO2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental result reveals that the PdTCPP-doped TEOS/Octyl-triEOS oxygen sensor has sensitivity of 153.

A new portable optical sensor for dual sensing of temperature and oxygen

A new simple, low-cost technique for the fabrication of a portable optical sensor for the dual sensing of temperature and oxygen is described. The sensing film is based on the oxygen sensing dye platinum tetrakis pentrafluoropheny porphine (PtTFPP) and 7-amino-4-trifluoromethyl coumarin (AFC) embedded in tetraethylorthosilane (TEOS)/n-octyltriethoxysilane (Octyl-triEOS) composite xerogels. The feasibility of coating a color sensor with the sensing film to fabricate a portable optical dual sensing device is investigated. The temperature and oxygen indicators can both be excited with an LED at a wavelength 405nm. The portable optical dual sensor has been tested with regard to monitoring different temperatures and oxygen concentrations, the oxygen response of which is quantified in terms of the ratio IN2/IO2, where IN2 and IO2 represent the detected phosphorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results reveal that the portable optical oxygen sensor has a response of IN2/I100O2=1.75. In addition, our results show that the luminescence properties of the temperature sensor are independent of the presence of the oxygen sensor, and have a uniquely good linear response in the 25–65°C range. Finally, the oxygen sensing scheme presented in this work is intended for use in temperature compensation, and the portable optical dual sensor is a cost-effective alternative to traditional electrochemical-based temperature and oxygen sensors and provides a platform for other optically based sensors.

Enhanced optical oxygen sensing property based on Pt(II) complex and metal-coated silica nanoparticles embedded in sol–gel matrix

This paper presents a metal enhanced optical oxygen sensor that comprises an optical fiber coated at one end with platinum (II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and silver metal-coated nanoparticles embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio IN2/IO2, where IN2 and IO2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity of 167. The response time was 2.6s when switching from pure nitrogen to pure oxygen, and 36s when switching in the reverse direction. The experimental results show that compared to oxygen sensor based on Pt(II) complex immobilized in the sol–gel matrix, the proposed optical fiber oxygen sensor has higher sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the metal-coated silica nanoparticles also increase the sensitivity because the metal-enhanced fluorescence. The proposed optical sensor has the advantages of low cost and high sensitivity for oxygen monitoring using a cheap LED as a light source.

Optical fiber oxygen sensor based on Pd(II) complex embedded in sol–gel matrix

A simple, low-cost technique for fabrication of high performance optical fiber oxygen sensor is described. An organically modified silicate (ORMOSIL) as a matrix for the fabrication of oxygen sensing film was produced. The technique is based on coating the end of an optical fiber with ormosil composite xerogel film sequestered with luminophore palladium (II) meso-tetrakis(pentafluorophenyl)porphyrin (PdTFPP) prepared by a sol–gel process. The composite xerogel studied is n-propyltrimethoxysilane (n-propyl-TriMOS)/tetraethylorthosilane (TEOS)/n-Octyltriethoxysilane (Octyl-triEOS). Result shows that, expect for PdTFPP-doped n-propyl-TriMOS/TEOS/Octyl-triEOS composite xerogel shows a high sensitivity and linear Stern–Volmer relationship which indicates the homogenous environment of the luminophore. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio IN2/IO2, where IN2 and IO2 represent the detected phosphorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental result reveals that the PdTFPP-doped n-propyl-TriMOS/TEOS/Octyl-triEOS oxygen sensor has sensitivity of IN2/I100O2=263.

Optical Fiber Oxygen Sensor Based on Ru (II) Complex and Porous Silica Nanoparticles Embedded in Sol-Gel Matrix

This paper presents a high-sensitivity oxygen sensor that comprises an optical fibre coated at one end with tris (4, 7-diphenyl-1, 10-phenanthroline) ruthenium (II) ([Ru (dpp)3]2+) and porous silica nanoparticles embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio IN2/IO2, where IN2 and IO2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity of 26. The experimental results show that compared to oxygen sensor based on Ru (II) complex immobilized in the sol-gel matrix, the proposed optical fibre oxygen sensor has higher sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the porous silica nanoparticles increase the sensitivity because a substantial number of aerial oxygen molecules penetrate the porous silica shell. The proposed optical sensor has the advantages of easy fabrication, low cost, fast response and high sensitivity for oxygen monitoring using a cheap LED as a light source.

Optical oxygen sensing properties of Ru(II) complex and porous silica nanoparticles embedded in solgel matrix

This paper presents a high-sensitivity oxygen sensor that comprises an optical fiber coated at one end with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) ([Ru(dpp)3]2+) and porous silica nanoparticles embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio IN2 /IO2 , where IN2 and IO2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity of 26. The response time was 2 s when switching from pure nitrogen to pure oxygen, and 7.7 s when switching in the reverse direction. The experimental results show that compared to an oxygen sensor based on Ru(II) complex immobilized in the solgel matrix, the proposed optical fiber oxygen sensor has higher sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the porous silica nanoparticles increase the sensitivity because a substantial number of aerial oxygen molecules penetrate the porous silica shell. The proposed optical sensor has the advantages of easy fabrication, low cost, fast response, and high sensitivity for oxygen monitoring using a cheap LED as a light source.

Portable optical oxygen sensor based on Ru(II) complex and dye entrapped core-shell nanoparticles embedded in sol-gel matrix coated on a photodiode

A simple low-cost technique for the fabrication of portable optical oxygen sensors is described. The sensing film is based on the oxygen sensing dye tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) {[Ru(dpp)3]2+} and dye-entrapped core-shell silica nanoparticles embedded in a sol-gel matrix. The feasibility of coating a photodiode with the oxygen sensing film to fabricate a portable optical sensing device is investigated. The sensitivity of the sensor is quantified in terms of the ratio IN2/IO2, where IN2 and IO2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental result reveals that the portable optical oxygen sensor has sensitivity of 41. The sensor exhibits a linear response for oxygen concentrations in the range 0 to 60%. A preparation procedure for coating photodiodes with the oxygen film that produces repetitive and reliable sensing devices is proposed. The developed optical oxygen sensor is portable, low-cost, highly sensitive, and lacks optical filter elements. The proposed sensor is a cost-effective alternative to traditional electrochemical-based oxygen sensors and provides a platform for other optically based sensors.

Highly sensitive and linear calibration optical fiber oxygen sensor based on Pt(II) complex embedded in sol–gel matrix

A simple, low-cost technique for fabrication of high performance optical fiber oxygen sensor is described. An organically modified silicate (ORMOSIL) as a matrix for the fabrication of oxygen sensing film was produced. The technique is based on coating the end of an optical fiber with ORMOSIL composite xerogel films film sequestered with luminophore platinum (II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) prepared by a sol–gel process. The composite xerogels studied are 3,3,3-trifluoropropyltrimethoxysliane (TFP-TriMOS) or n-propyltrimethoxysilane ( n-propyl-TriMOS)/tetraethylorthosilane (TEOS)/ n-octyltriethoxysilane (Octyl-triEOS). Results show that, expect for PtTFPP-doped TFP-TriMOS or n-propyl-TriMOS/TEOS/Octyl-triEOS composite xerogels show the high sensitivity and linear Stern–Volmer relationship which indicate the homogenous environment of the luminophore. The sensitivities of the two oxygen sensors are quantified in terms of the ratio I N2/ I O2, where I N2 and I O2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results reveal that the PtTFPP-doped TFP-TriMOS/TEOS/Octyl-triEOS and n-propyl-TriMOS/TEOS/Octyl-triEOS oxygen sensors have sensitivities of 101 and 155, respectively. The experimental results confirm that the current oxygen sensors exhibit the linear Stern–Volmer plots and high-sensitive based on the oxygen indicator embedded in TFP-TriMOS or n-propyl-TriMOS/TEOS/Octyl-triEOS composite xerogels.

Enhanced oxygen sensing properties of Pt(II) complex and dye entrapped core–shell silica nanoparticles embedded in sol–gel matrix

This paper presents a highly sensitive oxygen sensor that comprises an optical fiber coated at one end with platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and PtTFPP entrapped core–shell silica nanoparticles embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio I 0/ I 100, where I 0 and I 100 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity ( I 0/ I 100) of 166. The response time was 1.3 s when switching from pure nitrogen to pure oxygen, and 18.6 s when switching in the reverse direction. The experimental results show that compared to oxygen sensors based on PtTFPP, PtOEP, or Ru(dpp) 3 2+ dyes, the proposed optical fiber oxygen sensor has the highest sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the dye entrapped in the core of silica nanoparticles also increases the sensitivity because a substantial number of aerial oxygen molecules penetrate the porous silica shell. The dye entrapped core–shell nanoparticles is more prone to oxygen quenching.

High-performance fiber-optic oxygen sensors based on fluorinated xerogels doped with Pt(II) complexes

This paper develops two high-performance quenchometric fiber-optic oxygen sensors based on platinum complexes and studies their temperature effects. The sensors are fabricated by coating the ends of optical fibers with a microporous film prepared using an n-propyltrimethoxysilane ( n-propyl-TriMOS)/3,3,3-trifluoropropyltrimethoxysliane (TFP-TriMOS) composite xerogel doped with either platinum tetrakis pentrafluoropheny porphine (PtTFPP) or platinum octaethylporphine (PtOEP) luminophores. The sensitivities of the two sensors are quantified in terms of the ratio I N 2 / I O 2 , where I N 2 and I O 2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results reveal that the PtTFPP-doped and PtOEP-doped oxygen sensors have sensitivities of 68.7 and 82.5, respectively. Furthermore, both sensors yield linear Stern–Volmer plots. The response time of the PtTFPP-doped sensor is found to be 3.7 s when switching from a fully deoxygenated environment (i.e. 100% nitrogen) to a fully oxygenated environment, and 5.3 s when switching reversely. The corresponding response times of the PtOEP-doped sensor are 3.7 and 5.9 s, respectively. The experimental results confirm that the current oxygen sensors exhibit a better sensitive performance, a shorter response time than existing oxygen sensors based on ruthenium dye immobilized in various sol–gel matrixes.

Microstructural and Corrosion Evaluation of Laser Surface Nitrided Ti-13Nb-13Zr Alloy

The present paper reports on the microstructure, hardness, surface roughness, phases formed and corrosion behaviour of laser nitrided Ti-13Nb-13Zr biomedical alloy. Surface melting and nitriding of the alloy were carried out using a Nd:YAG laser in pulsed mode under dilute and pure nitrogen environments. Laser nitriding of the alloy resulted in a hardness of 1600 HV and 650 HV, respectively, for pure N2 and dilute N2+ Ar environments. Cracks were not observed either on the surface or in the vertical cross-section of the samples nitrided in both environments. X-ray diffraction analysis of the sample nitrided in a pure nitrogen environment confirmed the formation of TiN, TiN0.3, alpha and beta phases along with ZrN. Quantitative analysis using electron probe microanalysis (EPMA) showed the enrichment of Zr and Ti in the dendrites. Corrosion resistance of the laser nitrided samples in a simulated body environment (Ringer's solution) was evaluated using the potentiodynamic polarisation method, and was found to be significantly better for the laser nitrided conditions compared with the untreated alloy.

TG/MS of Poly (Methyl Methacrylate)

Thermogravimetric analysis coupled with quadrupole mass spectrometry was performed to study the effects of heating rate on the rate of gasification of gases evolving from 0.5 mm particles size industrial-grade PMMA. The controlled mass loss measurements and the evolved gases were conducted in pure nitrogen and various oxidative environments under heating rates of 2 to 5°C min-1. The results indicated major differences, in pure nitrogen, the rate of production of gases is steeper compared to those associated with oxidative environment. Furthermore as the heating rate is lowered, it appears that the gases emanating from the surface are more volatile in the sense that they burst more abruptly from the surface.

Neutralisation of static surface charges by a flow stabilized corona discharge ionizer in a nitrogen environment

The neutralisation of static-charges by a flow stabilized dc corona ionizer in pure nitrogen environments has been investigated experimentally. The ionizer consisted of a pair of hollow corona electrodes operated at different dc negative and positive voltages and placed in a grounded environmental chamber. The flow rate of gas and temperature in the chamber were from 6 to 10l/min. and from −72 to 167°C, respectively. Measurements of charge decay rate and charge imbalance were secured using a half-sphere, conductive probe located 7.2cm downstream from the ionizer. The results show that the neutralisation of objects can be achieved with adjusting positive and negative applied voltage of each electrode as well as gas flow rate of hollow electrodes even under pure nitrogen environments.

Laser Nitriding of Ti-5.0Al-2.i5Sn

Laser surface treatment provides excellent wear resistance with good oxidation and corrosion resistance. Laser surface nitriding is one such technique resulting in high surface hardness to a depth of a few microns. This can be carried out in pure nitrogen and dilute nitrogen environments. This paper investigates the effect of laser nitriding on Space Shuttle Main Engine (SSME) Ti-5.0Al-2.5Sn alloy under pure nitrogen environment. The nitriding was carried out using 3 kW CW CO2 laser at different laser powers 900 W, 1.0 kW, and 1.2 kW with scan speeds 0.5 m min-1, 1.0 m min-1 and 1.5 m min-1 respectively. Optical microscopic and Vickers hardness tests were conducted on the test specimen to reveal the effect of laser nitriding in melt zone of laser nitrided trail. The extra high surface hardness of 3785 VHN at 25-50 (m depth was observed using the laser variable 1.0 kW laser power, 1.0 m min-1 speed and 3 mm beam dia. This may be attributed to the TiN dendrite formation. The melt zone of laser nitrided trail at other processing parameters shows fine needlelike structure of alpha prime with larger grain size and alpha in the heat affected zone with smaller grain size, with an average hardness 450 VHN. This present investigation shows that the surface of the nitrided trail is free from any cracks, even under the pure nitrogen atmosphere for all laser processing conditions.