High Purity Nitrogen Research Articles

On Mixing of Gases in a Laminar Chemical-Vapor-Deposition Reactor

Introduction. Investigation of the effi ciency and time of mixing of gases in fi lling laminar chemical-vapor-deposition (CVD) reactors is a topical problem facing engineers and researchers. This issue is particularly important in the context of the development of a highly effi cient technology for production of carbon and silicon nanofi bers on metallic catalysts in CVD reactors [1–4]. A similar problem exists in cleaning the CVD-reactor atmosphere on completion of the step of nanofi ber growth. To produce nanofi bers, one must control gaseous mixing in a region smaller than a micron in size near the reactor wall. Clearly, in this case the existing engineering estimates of the time of cleaning or fi lling of the reactor volume are rough and inaccurate. Nonetheless, mixing in a region as small as this near the substrate is determined by the processes of convective heat and mass transfer and diffusion in the volume of the entire fl ow reactor. The present work seeks to experimentally and theoretically investigate isothermal and nonisothermal mixing in fi lling the atmosphere of a CVD reactor with the laminar gas-mixture fl ow. In the model experiments discussed here, nitrogen is a background gas in the reactor, and oxygen is a diffusing gas. Experimental Setup and Measurement Procedure. A diagram of the experimental setup is shown in Fig. 1. The setup is a classical fl ow CVD reactor. Hydrocarbon gas diluted with high-purity nitrogen (99.9 vol. %) is used as the raw material for production of carbon nanomaterials. The fl ow rate of each gas is prescribed in an independent manner using automatic controllers 1 (Omega FMA-5420 and FMA-5426 fl ow controllers). The fl ow-rate relation determines the concentration of the hydrocarbon raw material in the working mixture. The two gases are delivered by the common tube to the reactor, i.e., a quartz tube 3 passing through a furnace with electroresistive heaters 4. The length of the reactor is L = 0.738 m and the internal radius is R = 0.056 m. Inside the tube, at a prescribed value of the temperature within 600–900 o C we have the pyrolysis of the hydrocarbon gas and the liberation of carbon on a catalytic substrate 6 depending on the selected operating mode with the resulting formation of carbon nanotubes, nanofi bers, and virtually spherical nanoparticles. The spent gas mixture fl ows out of the reactor freely. The created control system makes it possible to hold prescribed values of the operating parameters and to carry out measurements in an automatic mode. Nitrogen is pumped through the reactor with a constant fl ow rate throughout the operating period of the setup, whereas hydrocarbon is only delivered in addition to it during the operating mode. Thus, in the initial step of the operating mode, we have the process of mixing of the gases on the way to the reactor and inside it. Analogously, once the delivery of hydrocarbon in the reactor is discontinued, the process of displacement of this gas by pure nitrogen occurs. The procedure of measurements for quantitative determination of the processes in question was as follows. To the channel of an empty reactor, we connected a Testo-350XL digital gas analyzer making it possible to continuously measure the concentration of a number of components of a gas mixture: O2, CO, CO2, NO, and others. An analysis of the concentration of

Elimination of Al<sub>4</sub>C<sub>3</sub> Phase in Al/SiC<sub>P</sub> Composites by HYSYCVD

This paper presents results of the microstructure characterization and evaluation of physical and mechanical properties of Al/SiCp composites intentionally containing the Al4C3 phase prepared by pressureless infiltration, as well as results of treating the composites by the hybrid system chemical vapor deposition (HYSYCVD) route using Na2SiF6 as solid precursor. It also contains thermodynamic feasibility calculations (using the HSC 6.1TM program) of possible reactions between the SiFx (x=1-4) gas species (produced during the thermal decomposition of Na2SiF6), Al4C3 and N2 in the atmosphere. The composites were fabricated using an L4 Taguchi experimental design, infiltrating SiCp porous preforms at 1100 and 1200 °C in ultra high purity (UHP) argon and nitrogen (ArN2) atmosphere for 90 and 120 min, with the Al-6Si-16Mg (wt. %) alloy. The specimens were characterized by XRD, SEM and EDS. Results show that the composites exhibit a surface hardness between 63.95 and 86.5 (HR30T) and Young´s modulus up to 118.2 GPa. Application of a post-processing stage by HYSYCVD led to the elimination of Al4C3 and the formation of a coating of stable phases on the composites surface. The experimental results confirm the thermodynamic feasibility of the proposed chemical reactions.

Influence Of Mixing Technique On Sintering response Of Binary Aluminium Alloy Powders

Aluminium powder metallurgy (Al-PM) alloys are finding promising applications in many areas such as household appliances, automotive vehicles and many other allied sections where reduction in weight is the primary constraint. In the proposed research, two binary alloy systems Al-X were studied by mixing elemental powders of Aluminium (Al), Tin (Sn) and Magnesium (Mg). Two types of mixing techniques were followed. In one case, elemental powders were blended in a mechanical mixer without any mixing media (A) and another case powders were blended with ball to powder ratio of 10:1 (B). The content in binary premix was varied from 0.4 to 0.8 % Sn (by wt.) and 0.5 to 2 % Mg (by wt.) with base of Aluminium. The blended powders was compacted at 450 MPa followed by sintering in ultra high purity nitrogen atmosphere in tubular sintering furnace at 600 o C. The mixing technique B showed significant influence on increase in hardness by two-

Measurement of the (pressure, density, temperature) relation of a (methane + nitrogen) gaseous mixture using an accurate single-sinker densimeter

A single-sinker magnetic suspension densimeter based on Archimedes’ buoyancy principle is described. Density measurements on high-purity nitrogen demonstrate the performance of the densimeter. Comprehensive (p,ρ,T) measurements at low densities on a gaseous mixture with mole fraction of (0.8977CH4+0.1023N2) were carried out on this densimeter at six temperatures from (170.586 to 270.054)K and at pressures ranging from (0.1333 to 1.5945)MPa. The overall uncertainty in density is estimated to be 0.1%. The uncertainty in temperature is estimated to be 5mK and that in pressure is 250Pa for (0 to 1.5)MPa and 390Pa for (1.5 to 3)MPa, respectively. The experimental results of the (methane+nitrogen) mixture were compared with REFPROP 9.0, which used GERG-2008 and AGA8 equations of state to predict thermophysical properties of natural gas. The absolute relative deviations of density measurements are all within 0.1%. Meanwhile the experimental results were correlated using the virial equation of state (Virial EOS) with three different mixing rules. The calculated results using the virial EOS combined with VDW mixing rule show good agreement with the experimental data.

Final report on EURAMET.QM-S8: Analysis of impurities in pure and balance gases used to prepare primary standard gas mixtures by the gravimetric method

This supplementary comparison (EURAMET.QM-S8) concerns the purity analysis of nitrogen as used in reference gas mixture preparation. This project was carried out without adding impurities to the gas used for this comparison, and is therefore more representative to evaluate the analysis of carbon monoxide, carbon dioxide, methane, oxygen, argon and water impurities in high-purity nitrogen. The analysis of the amount-of-substance fraction water was optional.Two 50 litre high purity nitrogen cylinders were purchased from a well-qualified supplier of specialty gases. The listed components were expected to be present in the pure nitrogen at the target levels as a result of the purification of the nitrogen. From the start of this comparison it was clear that the comparison may not lead to reference values for the constituents analysed.The results indicate that analyses of high purity gases are often limited by the limits of detection of analytical equipment used. The reports of the participating laboratories also indicate that there is no agreed method of determination of the uncertainty on a detection limit value. The results provide useful information on the performance of participants. For all analysed components there is reasonable agreement in results for LNE, VSL, METAS and NPL. For BAM only the argon result is in agreement.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Thermal Stability and Decomposition Kinetics of Polysuccinimide

The thermal stability and decomposition kinetics of polysuccinimide (PSI) were investigated using analyzer DTG-60 under high purity nitrogen atmosphere at different heating rates (3, 6, 9, 12 K/min). The thermal decomposition mechanism of PSI was determined by Coats-Redfern method. The kinetic parameters such as activation energy (E), pre-exponential factor (A) and reaction order (n) were calculated by Flynn-Wall-Ozawa and Kissinger methods. The results show that the thermal decomposition of PSI under nitrogen atmosphere mainly occurs in the temperature range of 619.15-693.15 K, the reaction order (n) was , the activation energy (E) and pre-exponential factor (A) were obtained to be 106.585 kJ/mol and 4.644 × 109 min-1, the integral and differential forms of the thermal decomposition mechanism of PSI were found to be and , respectively. The results play an important role in understanding the thermodynamic properties of polysuccinimide.

Inception and propagation of positive streamers in high-purity nitrogen: effects of the voltage rise rate

Controlling streamer morphology is important for numerous applications. Up to now, the effect of the voltage rise rate was only studied across a wide range. Here we show that even slight variations in the voltage rise can have significant effects.We have studied positive streamer discharges in a 16 cm point-plane gap in high-purity nitrogen 6.0, created by 25 kV pulses with a duration of 130 ns. The voltage rise varies by a rise rate from 1.9 to 2.7 kV ns−1 and by the first peak voltage of 22 to 28 kV. A structural link is found between smaller discharges with a larger inception cloud caused by a faster rising voltage. This relation is explained by the greater stability of the inception cloud due to a faster voltage rise, causing a delay in the destabilization. Time-resolved measurements show that the inception cloud propagates slower than an earlier destabilized, more filamentary discharge. This explains that the discharge with a faster rising voltage pulse ends up being shorter.Furthermore, the effect of remaining background ionization in a pulse sequence has been studied, showing that channel thickness and branching rate are locally affected, depending on the covered volume of the previous discharge.

Synthesis of β-Sialon/Ti(C,N) Composites Using Low and Middle Grade Bauxite and Ilmenite by Carbothermal Reduction-Nitridation

β-Sialon/Ti(C,N) composites were prepared using low and middle grade bauxite and ilmenite as raw material,while coke as reducing agent in high purity nitrogen atmosphere through carbothermal reducrion-nitridation(CRN).The main phases of low and middle grade bauxite are kaolinire(Al2O3•2SiO2•2H2O) and (Al2O3•H2O)2 and ilmenite mainly contain ilmenite(FeTiO3) and rutile(TiO2).The reaction products of bauxite are the β-Sialon(Z=3,Si3Al3O3N5) while those of ilmenite are TiC and Fe.The results showed that the main phases are β-Sialon,Ti(C,N),Al2O3 and Fe when the reaction temperature is at 1400°C holding for 4 hours(10wt% ilmenite and 90wt% bauxite as raw material).However,β-Sialon decomposes into 21R at 1450°C and into 15R and AlN at 1500°C.So 1400°C is selected as the proper temperature to synthesize β-Sialon/Ti(C,N) composites.At 1400°C,the β-Sialon crystals with the largest quantity grow well and show long column in shape.With the increase of the reacrion temperature β-Sialon begin to decompose,the β-Sialon crystals change to short columnar,with the number decreasing quickly.

Sublimation Kinetic Studies of the Zr(tmhd) 4 Complex

The thermal behaviour of tetrakis(2,2,6,6‐tetramethyl‐3,5‐heptanedionato)zirconium(IV), [Zr(tmhd)4] was investigated by nonisothermal and isothermal thermogravimetric methods in a high pure nitrogen atmosphere. The influence of the heating rate in dynamic measurements (6, 8, 10, and 12°C/min) on activation energy was also studied. The nonisothermal sublimation activation energy values determined following the procedures of Arrhenius, Coats and Redfern, Kissinger, and Flynn‐Wall yielded 76 ± 5, 92 ± 2, 81 ± 8, and 72 ± 7 kJ/mol, respectively, and the isothermal sublimation activation energy was found to be 87 ± 4 kJ/mol over the temperature range of 411–462 K. Different reaction mechanisms were used to compare with this value. Analysis of the experimental results suggested that the actual reaction mechanism was an Rn deceleration type.

On selective laser melting of ultra high carbon steel: Effect of scan speed and post heat treatment

AbstractSelective laser melting is a laser‐based additive manufacturing process applying layer manufacturing technology and is used to produce dense parts from metallic powders. The application of selective laser melting on carbon steels is still limited due to difficulties arising from carbon content. This experimental investigation aims at gaining an understanding of the application of the process on ultra high carbon steel, which is a special alloy with remarkable structural properties suitable for different industrial applications. The feedstock ultra high carbon steel (2.1% C) powder, 20 μm to 106 μm was prepared by water atomizing technique. This powder was used for the selective laser melting to build specimens 10×10×40 mm in dimensions. To decrease the thermal stresses during layer by layer building, laser scanning was done through 5×5 mm random island patterns while layer thickness was 30 μm. Laser beam diameter, maximum power output, layer thickness and scan speed range were 0.2 mm, 100 W, 30 μm and 50–200 mm/s respectively. The process was done inside high purity nitrogen environment, with less than 0.5% oxygen content. The results illustrate the influence of scan speed from 50 to 200 mm/s on product geometry and dimensions, surface roughness, internal porosity and cracks, microstructure and surface hardness. The effect of post heat treatment by heating and holding for one hour (annealing) at different temperatures of 700°C, 750°C, 950°C is studied. The results indicate that selective laser melting is able to produce near to 95% density of ultra high carbon steel parts with acceptable geometry and surface quality. Porosity cracks, and microstructure formed during the process could be controlled through proper selection of process parameters and post heat treatment. Industrial ultra high carbon steel products can be rapidly fabricated by selective laser melting.

Preparation of nanostructured porous carbon composite fibers from ferrum alginate fibers

AbstractNano‐microstructured porous carbon composite fibers (Fe2O3@C/FeO@C/Fe@C) were synthesized by the thermal decomposition of ferrum alginate fibers. The ferrum alginate fiber precursors were prepared by wet spinning, and calcined at 300–1000°C in high purity nitrogen. The resulting composite fibers consist of carbon coated Fe2O3/FeO/Fe nanoparticles and porous carbon fibers. All the prepared nanostructures were investigated using thermal gravimetry, X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscope (TEM), and nitrogen adsorption–desorption isotherm. The results show that there are five stages in the decomposition process of the ferrum alginate fibers. Transitions between the five stages are affected by the decomposition temperature. XRD results show that maghemite (Fe2O3), wüstite (FeO), martensite (Fe) nanoparticles were formed at 300–500°C, 600–700°C, 800–1000°C, respectively. Scanning electron microscopy and TEM results indicate that the composite fibers consist of nanoparticles and porous carbon. The diameter of the nanosized particles increased from 100 to 500 nm with increasing reaction temperature. The nitrogen adsorption–desorption results also show that the composite fibers have a micro‐ and mesoporous structure. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Electrical and NO2 sensing properties of liquid crystalline phthalocyanine thin films

Abstract In this study, the electrical and nitrogen dioxide (NO2) sensing properties of a series liquid-crystalline octakisalkylthiophthalocyanine (C6S)8PcM [M = 2H, Ni, Cu, Zn] thin film were investigated. The thin films were coated on to the Interdigital Transducer (IDT) with gold electrodes, using jet-spray technique in an inert ambient from a solution of phthalocyanines in chloroform. The electrical properties of liquid-crystalline phthalocyanines were studied within wide temperature range from 293 to 423 K under the high purity nitrogen (N2) flow and in the frequency range from 500 Hz to 1 MHz for ac electrical measurements. It was observed that the I–V curves of all phthalocyanines showed a significant hysteresis at low temperature and the maximum dc conductivity obtained for (C6S)8PcZn thin film. The ac conduction mechanism of all thin films could be explained with quantum-mechanical tunneling (QMT) model. The NO2 gas sensing measurements were done in the concentration range of 1–10 ppm at the temperatures of 100 °C and 150 °C. The maximum sensor response (%) was obtained as approximately 10,000 and the response time was observed to be a few seconds for (C6S)8PcH2 thin film at 150 °C.

Structure and magnetic properties of FeSiAl-based soft magnetic composite with AlN and Al2O3 insulating layer prepared by selective nitridation and oxidation

FeSiAl is widely used in switching power supply, filter inductors and pulse transformers. But when used under higher frequencies in some particular condition, it is required to reduce its high-frequency loss. Preparing a homogeneous insulating coating with good heat resistance and high resistivity, such as AlN and Al2O3, is supposed to be an effective way to reduce eddy current loss, which is less focused on. In this project, mixed AlN and Al2O3 insulating layers were prepared on the surface of FeSiAl powders after 30min exposure at 1100°C in high purity nitrogen atmosphere, by means of surface nitridation and oxidation. The results revealed that the insulating layers increase the electrical resistivity, and hence decrease the loss factor, improve the frequency stability and increase the quality factor, especially in the high-frequency range. The morphologies, microstructure and compositions of the oxidized and nitrided products on the surface were characterized by Scanning Electron Microscopy/Energy Disperse Spectroscopy, X-Ray Diffraction, Transmission Electron Microscopy, Selected Area Electron Diffraction and X-ray Photoelectron Spectroscopy.

Probing background ionization: positive streamers with varying pulse repetition rate and with a radioactive admixture

Positive streamers need a source of free electrons ahead of them to propagate. A streamer can supply these electrons by itself through photo-ionization, or the electrons can be present due to external background ionization. Here we investigate the effects of background ionization on streamer propagation and morphology by changing the gas composition and the repetition rate of the voltage pulses, and by adding a small amount of radioactive 85Kr.We find that the general morphology of a positive streamer discharge in high-purity nitrogen depends on background ionization: at lower background ionization levels the streamers branch more and have a more feather-like appearance. This is observed both when varying the repetition rate and when adding 85Kr, though side branches are longer with the radioactive admixture. But velocities and minimal diameters of streamers are virtually independent of the background ionization level. In air, the inception cloud breaks up into streamers at a smaller radius when the repetition rate and therefore the background ionization level is higher. When measuring the effects of the pulse repetition rate and of the radioactive admixture on the discharge morphology, we found that our estimates of background ionization levels are consistent with these observations; this gives confidence in the estimates.Streamer channels generally do not follow the paths of previous discharge channels for repetition rates of up to 10 Hz. We estimate the effect of recombination and diffusion of ions and free electrons from the previous discharge and conclude that the old trail has largely disappeared at the moment of the next voltage pulse; therefore the next streamers indeed cannot follow the old trail.

Synthesis of (α- and β-)Si 3N 4/Si 2N 2O into silicon particulate porous preforms by hybrid system CVI and direct nitridation

An investigation on the microstructure and mechanical properties of Si/Si 3N 4/Si 2N 2O porous ceramic composites, synthesized in a multi-step approach via hybrid precursor system chemical vapor infiltration (HYSYCVI) and direct nitridation (DN) has been conducted. Particulate silicon porous preforms were infiltrated in subsequent stages S1-1, S1-2 (both at 1300 °C for 70 min in high purity nitrogen (HPN) using Na 2SiF 6 as solid precursor) and S2 (1350 °C for 120 min in ultra high purity nitrogen (UHPN)). Chemical reactions that account for the formation of Si 2N 2O and Si 3N 4 are proposed. Results show that the microstructure of the composites was influenced by atmosphere type and processing stage, affecting kind, morphology and size (including nanometric size) of nitrides formed. Porous composites (43% porosity) with modulus of rupture (MOR) ≈ 43 ± 3.5 MPa (evaluated in four-point bending tests) and elastic modulus ( E) ≈ 29 GPa (determined by the pulse-echo ultrasonic method) are routinely obtained.

Positive corona discharge ion source with IMS/MS to detect impurities in high purity Nitrogen

We have applied the Ion Mobility Spectrometry/Mass Spectrometry (IMS/MS) and the Atmospheric Pressure Chemical Ionisation/Mass Spectrometry (APCI/MS) techniques to study the formation of the ions in the positive corona discharge (CD) in highly purified nitrogen with impurities at 100 ppt level. The main products observed were H3O+(H2O)n ions (reduced ion mobility of 2.15 cm2 V-1 s-1). Additionally, we have observed ions with reduced mobilities 2.42 cm2 V-1 s-1 and 2.30 cm2 V-1 s-1. The intensity of these ions was increasing with the increasing discharge current. We associated these peaks with NH4+ and NO+(H2O)n. The formation of these ions results from trace amounts of O2 and NH3 in nitrogen. The time evolution of the ions in corona discharge has been studied using the APCI/MS technique in the time windows ranging from 100 μs to 2 ms. The present work indicates the ability of the IMS technique equipped with CD ions source to detect impurities below 100 ppt level.

Slip Casting of α-Sialon/AlN/BN Powder Carbothermally Prepared by Boron-Rich Slag-Based Mixture

With boron-rich slag, silica fume, bauxite chalmette and carbon black as starting materials, α-sialon/AlN/BN powder was prepared by carbothermal reduction-nitridation. The powder was attrition milled to submicron size and suspended in water. The effects of yttrium oxide as a sintering aid, pH, and addition of deflocculant on the suspensions were studied. Optimum slip casting properties, i.e. lowest viscosity values, the highest absolute zeta potential values, the smallest floc size and sediment volume were found at pH=10 for the powder. The suspensions were used to slip cast discs which were sintered in a high purity nitrogen atmosphere at 1700 °C for 2 h. The strength was about 230 MPa, the toughness 3.6 MPa•m1/2 and the hardness about 13.8 GPa.

Preparation of Li9Cr3(P2O7)3(PO4)2 as cathode material for lithium ion batteries through sol–gel method

The compound Li9Cr3(P2O7)3(PO4)2 has been successfully synthesized using sol–gel method. X-ray diffraction Rietveld refinement analysis indicates that single phase Li9Cr3(P2O7)3(PO4)2 can be obtained under air condition and high purity nitrogen atmosphere. Scanning electron microscopy indicates that nanowires with lengths ranging from several to tens micrometers and diameters varying from 100nm to 500nm can be obtained in the Li9Cr3(P2O7)3(PO4)2 compound heated under air condition. The electrochemical properties of Li9Cr3(P2O7)3(PO4)2 sintered under N2 as cathode material is reported for the first time. The XRD patterns of the electrodes before and after 30 cycles indicate that the Li9Cr3(P2O7)3(PO4)2 keeps its original monodiphosphate structure.

Simultaneous determination of eight common odors in natural water body using automatic purge and trap coupled to gas chromatography with mass spectrometry

Production and fate of taste and odor (T&O) compounds in natural waters are a pressing environmental issue. Simultaneous determination of these complex compounds (covering a wide range of boiling points) has been difficult. A simple and sensitive method for the determination of eight malodors products of cyanobacterial blooms was developed using automatic purge and trap (P&T) coupled with gas chromatography–mass spectrometry (GC–MS). This extraction and concentration technique is solvent-free. Dimethylsulfide (DMS), dimethyltrisulfide (DMTS), 2-isopropyl-3-methoxypyrazine (IPMP), 2-isobutyl-3-methoxypyrazine (IBMP), 2-methylisoborneol (MIB), β-cyclocitral, geosmin (GSM) and β-ionone were separated within 15.3 min. P&T uses trap #07 and high-purity nitrogen purge gas. The calibration curves of the eight odors show good linearity in the range of 1–500 ng/L with a correlation coefficient above 0.999 (levels = 8) and with residuals ranging from approximately 83% to 124%. The limits of detection (LOD) (S/N = 3) are all below 1.5 ng/L that of GSM is even lower at 0.08 ng/L. The relative standard deviations (RSD) are between 3.38% and 8.59% ( n = 5) and recoveries of the analytes from water samples of a eutrophic lake are between 80.54% and 114.91%. This method could be widely employed for monitoring these eight odors in natural waters.

Multi-residue determination of 11 pesticides in Shengmaiyin prescription by gas chromatography

To determine the pesticide residues in Shengmaiyin. The residues were simultaneously identified and quantified by capillary gas chromatography. The capillary column was OV-1701(0. 32 mm x 30 m, 0.5 microm), splitless injection and Agilent 63Ni electron capture detector ECD were adopted. The carrier gas were high-pure nitrogen, the flow rate were 60 mL x min(-1), the injector temperature was 260 degrees C, and the detector temperature was 300 degrees C. It showed a good linear relationship between peak area and pesticide concentration for 11 kinds of pesticides in the detection concentration range. All correlation coefficients were higher than 0.996 2. The average recovery was 83.1% -114.7%. A simple and efficient monitoring method of pesticide residues is established which provides the foundation for the safe use and analysis of Shengmaiyin.