Ppm In Solution Research Articles

Synergistic Effect of Opuntia ficus-indica Cladode mucilage on Physicochemical and Rheological properties of HPAM polymer solutions for EOR Application

This study focuses on the synthesis of a series of mixtures of a partially hydrolyzed polyacrylamide (HPAM), noted (H), and a cladode Opuntia ficus-indica mucilage (M). The main objective is to minimize the exclusive dependence of HPAM in the field of tertiary oil recovery, specifically in the process known as EOR.This study showed that a combination of 20% mucilage and 80% HPAM, for a total concentration of 800 ppm in solution, gives rheological performance equivalent to a solution of HPAM alone at 6000 ppm. The resulting mixture which is characterized by viscoelastic liquid behavior, exhibits remarkable flow and elasticity properties.This characteristic is considered favorable for extracting trapped oils from pores under effect of the normal stress. Spectral analysis revealed the presence of silica groups in the mixture, elements widely used in researchers in association with HPAM. Thermogravimetric analysis (TGA) demonstrated that mucilage decomposition only occurs at temperatures above 200 °C. As the main conclusion, all the physicochemical and rheological data argue in favor of the integration of mucilage in HPAM in order to minimize its concentration in Enhanced Oil Recovery (EOR) applications.

Estimates of Inhaled and Deposited Doses following Exposure to Humidifier Disinfectant Containing Polyhexamethylene Guanidine (PHMG)

We estimated the inhaled and deposited dose in humans using the International Commission on Radiological Protection (ICRP) and multiple-path particle dosimetry (MPPD) models following exposure to humidifier disinfectant containing polyhexamethylene guanidine (PHMG). The disinfectant has caused at least 1,810 deaths, with an odds ratio of lung injury of 47.3 (95% confidence interval: 6.1–369.7), because of its application in Korea. In this study, the Oxy product, which is regarded as the causative agent of most lung diseases, was sprayed into a cleanroom at normal (6.5 ppm in solution) and worst case (65 ppm in solution) dilutions; the airborne aerosol was monitored with direct reading instruments. Areas of deposition were divided into the head airway, tracheobronchial, and alveolar regions. Four dose scenarios were considered in this study: adults and children in both daily average and sleep conditions. Most PHMG aerosols were smaller than PM1 (96%). Number-based concentration analysis showed that <100 nm nanoparticles comprised 81% and 69% of the aerosol when the 6.5 and 65 ppm solutions were used, respectively. In all scenarios, the number-based deposited dose increased in the order of alveolar, tracheobronchial, and head airway regions; the mass-based deposited dose increased in the order of the head airway, alveolar, and tracheobronchial regions. The deposited dose per unit body weight was higher in children than in adults in terms of both number- and mass-based concentrations. When the humidifier was sprayed, the highest number-based concentration was found at a particle size of 15.4 nm; the highest deposition fraction or dose by PM1 was observed in the pulmonary and head airways in both models.

Anthocyanin-induced color changes in bacterial cellulose nanofibers for the accurate and selective detection of Cu(II) in water samples

The environment and our health are negatively impacted by heavy metal ions, like Cu(II). The present study developed a green and effective metallochromic sensor that detects copper (Cu(II)) ions in solution and solid state using anthocyanin extract from black eggplant peels embedded in bacterial cellulose nanofibers (BCNF). Cu(II) is quantitatively detected by the sensing method with detection limits between 10-400 ppm and 20–300 ppm in solution and solid state, respectively. In the solution state, we depicted a sensor for Cu(II) ions in aqueous matrices in the pH range from 3.0 to 11.0, with the capability to produce a visual color change from brown to light blue and dark blue depending on the Cu(II) concentration. Additionally, BCNF-ANT film can act as a sensor for Cu(II) ions in the pH range of 4.0–8.0. Neutral pH was selected from the standpoint of high selectivity. It was found that visible color changed when Cu(II) concentration was increased. Bacterial cellulose nanofibers modified with anthocyanin were characterized with ATR-FTIR and FESEM. Various metal ions, including Pb2+, Co2+, Zn2+, Ni2+, Al3+, Ba2+, Hg2+, Mg2+, and Na+, were used to challenge the sensor to determine its selectivity. Anthocyanin solution and BCNF-ANT sheet were employed in the actual tap water sample successfully. The results also clarified that the various foreign ions did not significantly interfere with Cu(II) ions detection at optimum conditions. Compared to previously developed sensors, no electronic components, trained personnel, or sophisticated equipment were needed to apply the colorimetric sensor developed in this research. Cu(II) contamination in food matrices and water can be monitored on-site easily.

Photocatalytic activity of sol-gel self-combustion derived MCr2O4 (M= Mg, Ni) spinel chromites for photodegradation of organic dyes

Herein, MCr2O4 (M= Mg, Ni) chromite photocatalysts were synthesized via sol-gel self-combustion route and sintered at 1000 °C. The Rietveld refined X-ray powder diffraction profiles confirmed the single-phase formation of MgCr2O4 (MCO) and NiCr2O4 (NCO) chromites crystalized in the face-centered cubic and tetragonal spinel structures having Fd3̅m and I41/amd space group symmetries, respectively. The polyhedral geometrical shape and sizes of the grains were determined by the surface micrographs obtained from the field emission scanning electron microscopy (FESEM). The oxidation states and cations distribution investigated by the x-ray photoelectron spectroscopic (XPS) analysis professed the charge balance in the compounds. The photocatalytic performance of the chromite nanoparticles was examined using malachite green (MG) and crystal violet (CV) organic dyes at 5 ppm in solutions irradiated under sunlight. The photodegradation studies revealed the degradation efficacy of 70% and 85% for MCO, and 90% and 95% for NCO catalysts for the degradation of the MG and CV dye pollutants within 120 min, without utilizing H2O2. Furthermore, the kinetic studies were carried out and the experimental equilibrium data were observed to follow the pseudo-second-order and intraparticle diffusion models which described the synergetic adsorption-photodegradation procedures. Thus, NCO exhibited a high percentage for the removal of MG and CV organic pollutants compared to MGO, indicating that the tetragonally distorted NiCr2O4 nanocatalyst is an efficient candidate for the potential environmental purification of toxic organic contaminants.

A Novel 3D-Morphology Pyrene-Derived Conjugated Fluorescence Polymer for Picric Acid Detection.

Aggregation-induced quenching (ACQ) is a hard problem in fluorescence material, leading to a poor utilization rate of fluorophores. In this work, 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) was synthesized and used as a precursor to build two kinds of fluorescence polymer. The TFFPy molecule with D2h symmetry can easily form polymers with C3 symmetry amines through the Schiff base reaction, making the resulting polymer a 3D amorphous material. Thus, ACQ of fluorophore can be reduced to minimum, making the most usage of the fluorescence of pyrene core. Fluorescence titration and DFT calculation can clearly prove this conclusion. The resulting CPs showed a highly sensitivity to picric acid, down to 3.43 ppm in solution, implying its potential in explosive detection.

The Evaluation for Salvinia sp. Adaptation to Iron Concentration on Nutrient Solution and Tidal Swamplands Soil Growing Media

Salvinia sp. is an alternative aquatic plant that is abundant in the swamplands and can be used for bioremediation of water contaminated with metals. The objectives of the experiment were (1) to evaluate the adaptation of Salvinia sp. to the iron (Fe) concentration in nutrient solution and tidal swampland soil growing medium and (2) to obtain Fe-adaptive Salvinia sp. as indicated by having rapid growth and high biomass. The experiment has been carried out in Cikabayan greenhouse IPB University, Bogor. Salvinia sp. was evaluated in a 4-liter plastic container with Hoagland nutrient solution that was supplemented with Fe based on the experimental treatments. The 10 accessions of Salvinia sp. were selected and evaluated using a pot filled with soil from tidal swampland. The results showed that increasing Fe concentration from 7 to 14 ppm in solution inhibited the growth, reduced the fresh weight, and delayed the doubling time of Salvinia sp. The selection of Salvinia sp. on 7 ppm Fe obtained 4 Salvinia sp. accessions with high biomass weights and fast doubling time, namely S. Kambat, Murung Karamat, Gambut, and Muning Tengah. Among the 4 accessions, the best two were S. Kambat and Murung Karamat with a fast doubling time of about 7.9 days and were adaptive in the tidal swampland.

Hydrogen embrittlement of API 5L X65 pipeline steel in CO2 containing low H2S concentration environment

The basic corrosion mechanisms in CO2 environments are widely investigated and reported by scientific community. However, cracking failure mechanisms in CO2 environment or in environments where CO2 coexist with other gases need a better understanding. Cracking susceptibility of API 5L X65 in pure CO2 was recently reported and the basic mechanism was attributed to hydrogen embrittlement. The influence of hydrogen permeation and the detrimental effect of cathodic polarisation support the assumption of hydrogen embrittlement as the determining factor for the loss of plasticity and strength. The loss of strength of an API 5L X65 steel when CO2 and H2S coexist in the same environment is the focus of the present work. Hydrogen embrittlement (HE) and hydrogen induced cracking (HIC) of pipeline steels are failures modes expected to occur in CO2 with traces of H2S environments. The present work aims to approach the performance in laboratory of an API 5L X65 steel in CO2 with traces of H2S environment (slightly sour), using as baseline the performance of the material in pure CO2 environment (sweet), already reported. Hydrogen permeation and Slow Strain Rate Tests (SSRT) were carried out in CO2 environment containing low concentration of H2S. It was observed that traces of H2S in CO2 environment promote much more intense hydrogen permeation, much higher than in purely CO2 environment. Loss of ductility was also much more severe than in CO2 environment, with and without the influence of cathodic polarisation. Hydrogen generation enhancement promoted by traces of H2S in solution, corresponding to an average content of 21 ppm in solution, had a heavy effect on hydrogen embrittlement of the steel, confirmed by the lower ratio of reduction in area (RRA) and time to fracture in comparison with sweet service conditions.

Visible light active, magnetically retrievable Fe3O4@SiO2@g-C3N4/TiO2 nanocomposite as efficient photocatalyst for removal of dye pollutants

Magnetically retrievable and visible light active Fe3O4@SiO2@g-C3N4/TiO2 core-shell microsphere nanocomposite photocatalyst was successfully synthesized. It comprises Fe3O4@SiO2 magnetic core and g-C3N4/TiO2 nanocomposite as an outer shell. The core-shell structure imparts reusability by magnetic retrieval and at the same time SiO2 encapsulated core acts as an efficient host for g-C3N4/TiO2 composite photocatalyst. The photocatalytic performance was examined using Rhodamine B (Rh B) and Methyl Orange (MO) at 10 ppm in solution. Photodegradation studies show the 10 wt.% g-C3N4/TiO2 a composite catalyst can degrade over 91% of both cationic and anionic dyes. The rate constant of reaction determined to be 3.2 fold higher for Rh B and 27.7 fold higher for MO in comparison to TiO2 thus proving its utility as useful photocatalyst for cationic dyes and as a high rate remover of anionic dyes. Free radical scavenger test shows superoxide and hydroxyl radical species play a major role in the degradation.

Photocatalytic ozonation for sea water decontamination

Polluted sea water is a common problem in coastal cities, but its decontamination remains a big challenge due to the existence of salt ions, which may invalidate many prevailing treatment methods originally developed for waste fresh water. This work presents the first attempt to decontaminate the polluted sea water by synergizing two separate processes: photocatalysis and ozonation. For low cost and human safety, the ozone concentration is kept to be < 60 ppm in the pumping gas (0.026 ppm in solution). Mechanism studies and experimental comparisons show that the photocatalysis, the ozonation and the photocatalytic ozonation (PCO) all have lower efficiencies in sea water than that in fresh water, and the PCO is always more efficient than only the photocatalysis or only the ozonation. More specifically, the PCO has a reaction rate constant about 23 times higher than only the ozonation. In addition, the sea water shows a positive synergistic effect of photocatalysis and ozonation and reaches the maximum when the pumping gas has an ozone concentration of 50 ppm in gas. In contrast, the fresh water shows a negative synergistic effect. Mechanism study using experiments infers that the dissolved ozone can enhance and stabilize the photocurrent by rapidly scavenging the photoelectrons. This work may pave the way to practical applications of sea water decontamination with high efficiency and low cost.

Resorcinol Functionalized Gold Nanoparticles for Formaldehyde Colorimetric Detection.

Gold nanoparticles functionalized with resorcinol moieties have been prepared and used for detecting formaldehyde both in solution and gas phases. The detection mechanism is based on the color change of the probe upon the aggregation of the nanoparticles induced by the polymerization of the resorcinol moieties in the presence of formaldehyde. A limit of detection of 0.5 ppm in solution has been determined. The probe can be deployed for the detection of formaldehyde emissions from composite wood boards.

Four new luminescent-organic frameworks exhibiting highly sensing of nitroaromatics: An experimental and computational insight

Four new metal–organic frameworks (MOFs) namely {[Cd(L)(bpp)]·H2O}n (1), {[Zn(L)(bpp)]·H2O}n (2), {[Cd(L)(bpz)]·H2O}n (3), [Zn(L)(bib)(H2O)]n (4), (H2L = 1,4-bis(4-carboxylbenzyl)piperazine acid; bpp = 1,3-bis(4-pyridyl)propane; bpz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole, bib = 1,4-bis(imidazol-1-yl)butane)) have been designed, synthesized and characterized. The MOFs 1 and 2 are isostructural and possess 4-connected dia topology with rare 8-fold interpenetrating network. In 3, the dianionic ligand L and bpz ligands link binuclear Cd(II) centres to generate a 2D layer framework with a double stranded chain. While in 4, the Zn(II) centres are bridged by L and bib ligands to furnish a 2D framework, which further generates a 3D supramolecular structure through the hydrogen bonding interactions formed between coordinated water molecules and carboxylate groups. The MOF 1 have been utilized as a possible luminescent sensor to detect nitroaromatic compounds (NACs). The results indicates that 1 showed good sensitivity towards p-nitrophenol (PNP) in comparison to other NACs by the decline in its luminescent intensity. The detection limit for PNP was found to be extremely low (1.27 ppm in solution) which represents one of the most efficient MOF-based sensors for PNP. The most plausible mechanism associated with sensing have been explained with the aid of theoretical calculations which indicated that a simultaneous electron/energy transfer phenomenon operating between 1 and NACs contributes toward the decline in the luminescence intensity.

Purification of industrial grade lithium chloride for the recovery of high purity battery grade lithium carbonate

Due to lithium’s high energy along with other exceptional characteristics, lithium demand across many industries is rising, specifically for Li-batteries. Therefore, a sufficient supply of high purity lithium is vital in order for these significant technologies to develop. In the current work, industrial grade lithium chloride has been successfully treated with four simple precipitation steps to obtain a high purity battery grade lithium carbonate of >99.95%. The LiCl starting solutions contained K, Na, Mg, Ca, Cu, Ni, and Fe chloride contaminants and solutions of 2.5 to 10 M were simulated. The heavier metals and the majority of Mg were removed in a single step with an increase in pH. The removal of Ca and remaining Mg was executed by sodium oxalate addition where the calcium levels of the 10 M were able to be reduced to 5–6 ppm in solution. It appeared that the higher molarity and ionic strength of the LiCl solution aided in obtained higher degrees of impurity removal. Finally, high purity Li2CO3 was obtained by first precipitating from brine solution, followed by a second purification step with pressurized CO2. The second step allowed for the removal of entrapped Na and K after the first precipitation, resulting in >99.95 wt% purity Li2CO3.

Experimental Assessment of The 100 mV Polarization Shift Criterion for Cathodic Protection Systems of the Prestressed Concrete Cylinder pipes

In this work, an experimental study was carried out to evaluate the 100 mV polarization shift criterion for confirming the effectiveness of applied cathodic protection viz via zinc sacrificial anodes to arrest progress of corrosion in uncorroded or partially corroded high tensile grade prestressing steel wires of the same grade as the one used to manufacture the prestressed concrete cylinder pipes (PCCP). Total number of 14 wire samples were placed under constant tension approximately 55% of their ultimate tensile strength by the use of specially designed and fabricated holding metal frames. All samples were individually immersed in glass vessels filled with alkaline solutions of pH around 12 and variable chloride ions concentration ranging from 500 to 3000 ppm. With the exception of one wire sample left unprotected; the remaining samples were cathodically protectedby systems of zinc sacrificial anodes such that an average measured polarization shift near 100 mV with variable chloride content in solution was maintained for 9 samples and near 75, 50, and 25 mV with constant chloride content of 3000 ppm. Evaluation of mechanical properties of wire samples suggested that 100 mV criterionand more than sufficient to confirm the adequacy and effectiveness of zinc sacrificial anodes cathodic protection system to arrest progress of corrosion of partially corroded and uncorroded prestressing steel wires in alkaline passivating environment contaminated with chloride ions up to 3000 ppm in solution and for shifts in polarization as low as 25 mV. It was also evident that corrosion progress in the prestressing steel wires can not be arrested in the 3000 ppm chloride environment without the application of cathodic protection.

Boron Doped Ultrananocrystalline Diamond Films on Porous Silicon: Morphological, Structural and Electrochemical Characterizations

Boron doped ultrananocrystalline diamond (BDUND) films were grown and characterized on porous silicon (PS) substrates. PS samples were prepared from n-type monocrystalline silicon wafers (100) with 1-20 Ω.cm of resistivity, by electrochemical etching, using HF-acetonitrile solution as electrolyte. BDUND films were grown by Hot Filament Chemical Vapor Deposition using CH4, H2 and Ar. The doping process consisted of an additional hydrogen line, passing through a bubbler containing B2O3 dissolved in methanol, with boron/carbon ratio of 20000 ppm in solution. Raman spectroscopy and X-Ray diffraction were used to evaluate the quality of the films. Scanning electron microscopy was used for morphological characterization, and confirmed that the films covered the pores without filling them. Electrochemical response and capacitance behavior of the electrodes were explored, by cyclic voltammetry. Samples presented high capacitance, confirming that BDUND/PS electrodes are promising for application as electrochemical capacitors.

Bicinchoninic acid-based colorimetric chemosensor for detection of low concentrations of cyanide

Bicinchoninic acid (BCA) is reagent that is widely used to determine the concentration of proteins in solutions through the colored complex it forms with Cu(I) and the proteins. In this report, we present a new use for BCA, where a highly sensitive method for detection of cyanide ions in solutions by using Cu2+–BCA complex as the chemosensing agent is demonstrated. The detection of cyanide ions is achieved by taking advantage of the nucleophilic attack of the Cu2+–BCA complex by cyanide ions. Upon the addition of cyanide ions, the Cu2+–BCA complex undergoes transformations to free BCA via a series of equilibriums and, as a result, forms different Cu(II)–(BCA)x(CN)y species depending on the concentrations of cyanide ions in the solution. These different Cu(II)–(BCA)x(CN)y species, in turn, give different metal-to-ligand charge transfer electronic spectra and colors that are easily detectable both with naked eyes and UV–vis spectroscopy. As the cyanide ion concentration increases, the color of the solution containing the complexes changes from green to purple, red, yellow, and finally colorless, giving a corresponding blue shift in the absorption maxima on their UV–vis spectra. Through this process, the complexes enable detection of cyanide ions with a detection level of up to 0.06ppm in solutions. Thus, this colorimetric technique based on Cu2+–BCA can make low concentrations of cyanide detectable, well before the concentrations possibly reach lethal amounts. Furthermore, the method is shown to give fast detection response with no interference from other anionic and cationic species and has the potential to be adopted for accurate and convenient analysis of cyanide ions in drinking water sources as well as industrial effluents.

New Synthesis Strategies for Luminescent YVO4:Eu and EuVO4 Nanoparticles with H2O2 Selective Sensing Properties

Nowadays, because of safety demands, the controlled design of efficient and selective sensors for hydrogen peroxide is paramount. Therefore, we develop herein new strategies of aqueous synthesis of crystalline YVO4:Eu and EuVO4 nanoparticles based on a rigorous control of the pH and of the nucleation step via microwave heating. These routes allow a precise control of composition, nanostructure, and surface states of the resulting luminescent nanoparticles that are structurally and optically characterized via a large set of modern techniques. Moreover, these nanoparticles exhibit reproducible optical responses that are highly selective to hydrogen peroxide and present excellent detection thresholds as low as 0.05 ppm in solution. These remarkable performances allow the design of a new family of H2O2 sensors, which surpass state-of-the-art inorganic optical sensors in liquid phase detection tests.

Photocatalytic Degradation of Methylene Blue Over Nanosized TiO&lt;SUB&gt;2&lt;/SUB&gt; Particles Prepared Using the Self-Propagating High-Temperature Synthesis Method

In order to reutilize the spent metallic titanium chips, TiO2 photocatalysts were prepared using the self-propagating high-temperature synthesis (SHS) method, and were characterized by N2 gas adsorption, X-ray diffraction, and scanning electron microscope, particle size distribution. Also, their photocatalytic activities were evaluated using methylene blue as a model organic compound. It was confirmed that the crystal structure of TiO2 prepared by SHS method was relatively homogeneous powder of rutile type. Optimum conditions for photocatalytic degradation of methylene blue under UV-C irradiation were methylene blue 9.5 ppm in solution and at amount of TiO2 added of 0.02 g/L. In addition, it was found that the photocatalytic activity for methylene blue degradation over the prepared TiO2 particles was positively related with BET specific surface area.

Characterization of Noninnocent Metal Complexes Using Solid-State NMR Spectroscopy: o-Dioxolene Vanadium Complexes

(51)V solid-state NMR (SSNMR) studies of a series of noninnocent vanadium(V) catechol complexes have been conducted to evaluate the possibility that (51)V NMR observables, quadrupolar and chemical shift anisotropies, and electronic structures of such compounds can be used to characterize these compounds. The vanadium(V) catechol complexes described in these studies have relatively small quadrupolar coupling constants, which cover a surprisingly small range from 3.4 to 4.2 MHz. On the other hand, isotropic (51)V NMR chemical shifts cover a wide range from -200 to 400 ppm in solution and from -219 to 530 ppm in the solid state. A linear correlation of (51)V NMR isotropic solution and solid-state chemical shifts of complexes containing noninnocent ligands is observed. These experimental results provide the information needed for the application of (51)V SSNMR spectroscopy in characterizing the electronic properties of a wide variety of vanadium-containing systems and, in particular, those containing noninnocent ligands and that have chemical shifts outside the populated range of -300 to -700 ppm. The studies presented in this report demonstrate that the small quadrupolar couplings covering a narrow range of values reflect the symmetric electronic charge distribution, which is also similar across these complexes. These quadrupolar interaction parameters alone are not sufficient to capture the rich electronic structure of these complexes. In contrast, the chemical shift anisotropy tensor elements accessible from (51)V SSNMR experiments are a highly sensitive probe of subtle differences in electronic distribution and orbital occupancy in these compounds. Quantum chemical (density functional theory) calculations of NMR parameters for [VO(hshed)(Cat)] yield a (51)V chemical shift anisotropy tensor in reasonable agreement with the experimental results, but surprisingly the calculated quadrupolar coupling constant is significantly greater than the experimental value. The studies demonstrate that substitution of the catechol ligand with electron-donating groups results in an increase in the HOMO-LUMO gap and can be directly followed by an upfield shift for the vanadium catechol complex. In contrast, substitution of the catechol ligand with electron-withdrawing groups results in a decrease in the HOMO-LUMO gap and can directly be followed by a downfield shift for the complex. The vanadium catechol complexes were used in this work because (51)V is a half-integer quadrupolar nucleus whose NMR observables are highly sensitive to the local environment. However, the results are general and could be extended to other redox-active complexes that exhibit coordination chemistry similar to that of the vanadium catechol complexes.

Glycolic Acid Ethoxylate 4-Tert-Butylphenyl Ether as Drag Reducing Agent in Aqueous Media Flow

Glycolic acid ethoxylate 4-tert-butylphenyl ether was used as investigated anionic surfactants in this experimental work. A built up rig with ratio of pipe length to diameter (L/D) is equal to 59 was used to achieve the purpose of this work which is to investigate the drag reduction in turbulent flow with different flow rates and concentration of additive. In the present study, the concentrations (ppm) of additive were analyzed starting from 200, 300, 400, 500 and 600, respectively. The flow rates (Re) of the solution were from 11235, 22470, 33705, 44940, 56175, 67410 and 78645, respectively. It was found that glycolic acid ethoxylate 4-tert-butylphenyl ether is capable to reduce the drag less than 10 %. The highest drag reduction is 8 % was achieved in 600 ppm of solution for turbulent flow with Re within the range 44940 to 56175. The results of experimental work shows that this anionic surfactant perform as a poor drag reducing agent due to its drag reduction values increases only 1 to 3 % even though the concentration of solution was added about 100 ppm. This occurred probably because of the formation of micelle in the solution which is not in a fully threadlike forms and the micelle networks are not fully established in solution to surpassed the degree of turbulent flow.

Effect of low nitrogen content on work hardening and microstructural evolution in Hadfield steel

Nitrogen content in austenitic manganese steels is usually not reported nor standardized. The present work has found that it typically ranges between 130 ppm and 200 ppm in solution. Microstructural evolution has been studied by optical microscopy, using mainly differential interference contrast mode. Work hardening was analyzed under compression conditions using Hollomon's fitting and Vickers microindentation hardness measurements at different deformation levels. Even low contents of nitrogen in solution exhibit a significant effect on the slope of stress–strain curves, with strain-hardening exponent values of 0.7, 0.57 and 0.41 for 720 ppm, 130 ppm and 71 ppm of nitrogen, respectively. It was also found that the nitrogen content influences the microstructure of deformed coarse grained polycrystalline austenite, leading to twining and shear bands at the upper level of nitrogen, while it was not clearly found in the samples with lower nitrogen content.