Dilution Percentage Research Articles

Study of the rotating arc on the tribological behavior of hardbanding for oil drilling tubes

In this work, four welded coupons were evaluated with a welding speed of 5, 9, 11 and 13 mm/s. A semi-automatic welding process was used under gas protection, using a 1.6 mm diameter tubular wire. The chemical composition was analyzed on each welded coupon, the dilution percentage was determined, the dimensional of the beads was carried out and the microstructure was characterized by optical microscopy and scanning electron microscopy. In addition, the Vickers microhardness HV2 in the middle of the bead were measured. It was found that the dilution decreased up to 22% (a decrease of 80% compared to traditional welds). Furthermore, the beads presented less refusion with the base material, increasing their width and penetration. A microstructure formed by an “α matrix” was observed, with complex metallic carbides and carboborides which increased in quantity when considering the effects of the rotating arc method Also, it was observed a microstructure formed by a matrix α with complex metal carbides and carboborides that increased in quantity with the effect of the rotating arc. The hardness of the beads varied between 720 and 780 HV2. The weight loss and the friction coefficient decreased with the application of the arc rotation. These changes would be related to the increase in non-metallic phases.

Titanium surface functionalization via directed energy deposition of CuNiTi ternary alloy

Pure titanium is a soft material that tends to degrade quickly during service due to wear and microbiologically influenced corrosion. Therefore, current research aims at the deposition, microstructural characterization, and surface functionalization of the TiCuNi coatings on pure titanium substrate to improve its surface properties. Cu–Ni premixed elemental powders are deposited on the pure Ti by laser-directed energy deposition (LDED) using a novel method of extracting Ti from the substrate through melt pool convection. The single-track deposit geometry and integrity characterization using dilution percentage, heat-affected zone width (HAZ), and microhardness values show the sound metallurgical bonding with the substrate. The X-ray diffraction (XRD) pattern and microstructure image reveal the presence of NiTi binary (B2) and Ti2CuNi ternary (B19) hard phases and equiaxed dendritic morphology, respectively, demonstrating ternary alloy coating formation. The microhardness value of the coatings is thrice that of the substrate due to the presence of hard NiTi (B2) binary and Ti2CuNi (B19) ternary phases. The coating’s wear resistance is significantly (80%) higher than the substrate, owing to hard phases and Cu as a solid lubricant. The wear track consists of small grooves, adhered debris, and a smooth profile, mainly due to a significant reduction in adhesion and abrasion compared to the substrate. Moreover, the polarisation corrosion potential and current density are increased and decreased by 53% and 97%, respectively, displaying symbolic improvement in the corrosion resistance. Hence, this work has presented the LDED ability to enhance the pure Ti anti-wear and corrosion resistance properties by depositing CuNiTi ternary alloy coating for potential aerospace, marine, and biomedical applications.

Effect of heat input on ultrahard Fe-Cr-B-C-W-Mo-Nb hardfacing

Multicomponent alloys (Cr, Mo, W, Nb, C, B) nanostructured iron base with complex carboborides have been developed to provide great protection against abrasive wear to elements of agricultural and mining machines. These overlays are subject to severe material losses due to impact and abrasion of hard particles and therefore optimizing their wear resistance is critical when it comes to their lifespan, increasing it as a result. The objective of this work was to study the influence of heat input on the wear resistance through of the analysis of the solidification rate. In this sense, the increase of welding speed was produced a decrease of heat input and refined of microstructure. In order to explain these effects, an analysis was made of of the influence of welding speed on the geometry of the deposited metal, dilution with the base metal, microstructural evolution and hardness of iron-based nanostructured deposits with complex carbides. For this, four samples were welded with different speeds; these being 1, 2.5, 5 and 12 mm/s. A semi-automatic welding process was used with a 1.6 mm wire rope used to provide gas protection. The chemical composition was analyzed on a dilution free welded sample. For the each welded sample the dilution percentage was determined, the dimensional survey of the beads was carried out and the microstructure was characterized by X-ray diffraction and optical and scanning electron microscopy. In addition, Vickers microhardness tests were measured in the central area of the beads and the microhardness of phases were measured. The dilution of the deposited metals ranged from 17% to a maximum of 28%. A microstructure formed by a matrix with complex metal carbides and carboborides was observed. The hardness of the beads varied between 960 and 1350 HV2. The highest wear resistance was found in the sample with highest speed welding.

Effect of powder composition, PTAW parameters on dilution, microstructure and hardness of Ni–Cr–Si–B alloy deposition: Experimental investigation and prediction using machine learning technique

The implementation of hard-facing alloy on the existing materials caters the need for high-performance surfaces in terms of wear and high temperatures. The present research explore the effect of Plasma Transferred Arc Welding (PTAW) parameters and powder composition on dilution, microstructure and hardness of the commonly used hard-facing alloy Ni–Cr–Si–B powder. The hard-facing alloy was deposited with three weight proportions of boron (2.5 %, 3 % and 3.5 %). The statistical-based Grey Relational Analysis (GRA) followed by a Machine Learning Algorithm (MLA) was implemented to identify the ideal parameters and degree of significance of each parameter and for the prediction of the responses. The dilution percentage, microstructure analysis, and phase detection were estimated through elemental analysis, Scanning electron Microscopy (SEM) and X-ray Diffraction Analysis (XRD) respectively. The experimental and modelling results revealed that 400 mm/min of scanning speed, 8 gm/min of powder delivery, 14 mm of stand-off distance, and 120 A of current were the optimal parameters along with 3.5 wt% of boron powder composition to yield a better dilution, microstructure and hardness.

Ore dilution control when mining low-thickness ore bodies using a system of sublevel drifts

Purpose. The research is aimed at substantiating the optimal parameters of blast-hole ore breaking to reduce the rock mass destruction when mining low-thickness vein deposits using the mining system of sublevel drifts (SD). The focus is on analyzing the impact of blasting on the out-contour rock mass during the blast-hole breaking process. Methods. The three-dimensional block model is constructed using rating classifications of rocks based on studying their strength properties and structural peculiarities. The inelastic deformation zones around the stoping extraction are determined by numerical analysis using the finite element method in 2D formulation. Experimental blasts are assessed by varying the blast-hole drilling scheme depending on the stability rating. Findings. During the experimental-industrial tests, rational blast-hole drilling schemes have been substantiated, contributing to maintaining the stability of the host rocks when mining low-thickness veins. Originality. Effective methods for reducing the ore dilution have been substantiated, which take into account not only the strength properties and structural peculiarities of rocks, but also their seismic impact from blasting on the out-contour rock mass stability when mining low-thickness deposits using a system of sublevel drifts. Practical implications. Practical significance is in the possibility of minimizing the percentage of mineral dilution when mining low-thickness ore bodies using a system of sublevel drifts, which can significantly reduce the cost of mined minerals by reducing ore losses caused by the rock mass destruction during mining operations.

Surface Modifications of Silver Nanoparticles with Chitosan, Polyethylene Glycol, Polyvinyl Alcohol, and Polyvinylpyrrolidone as Antibacterial Agents against Staphylococcus aureus, Pseudomonas aeruginosa, and Salmonella enterica.

In medicine, the occurrence of antibiotic resistance was becoming a critical concern. At the same time, traditional synthesis methods of antibacterial agents often lead to environmental pollution due to the use of toxic chemicals. To address these problems, this study applies the green synthesis method to create a novel composite using a polymer blend (M8) consisting of chitosan (CS), polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and silver nanoparticles. The results show that the highest ratio of AgNO3:M8 was 0.15 g/60 mL, which resulted in a 100% conversion of Ag+ to Ag0 after 10 h of reaction at 80 °C. Hence, using M8, Ag nanoparticles (AgNPs) were synthesized at the average size of 42.48 ± 10.77 nm. The AgNPs' composite (M8Ag) was used to inhibit the growth of Staphylococcus aureus (SA), Pseudomonas aeruginosa (PA), and Salmonella enterica (SAL). At 6.25% dilution of M8Ag, the growth of these mentioned bacteria was inhibited. At the same dilution percentage of M8Ag, PA was killed.

Diluted contrast media combined with high-resolution C-arm CT for evaluating apposition of flow diversions in a porcine model.

In intracranial stenting, good stent apposition is crucial, and high-resolution C-arm computer tomography (CT) is utilized to assess whether stent apposition is complete. This study was aimed at finding optimal hypertonic or isotonic contrast media injection concentration for high-resolution C-arm CT to assess apposition of flow diversion (FD) after carotid artery stenting in swine. Twelve FD stents were implanted into the left carotid artery of Bama swine through the endovascular method. During high-resolution C-arm CT scanning, 6%, 8%, 10%, 12%, and 14% dilution percentages of hypertonic contrast media (iopromide 370 mg/ml) and 10%, 12%, 14%, 16%, and 18% dilution percentages of isotonic contrast media (iodixanol 320 mg/ml) were separately injected. A radiologist and a neuro-interventional specialist evaluated and qualitatively scored the post-processed images, and intravascular ultrasound (IVUS) was used to verify the accuracy of these images. Overall, 12 FD stents were implanted into the left common carotid artery of 12 swine, with a technical success rate of 100%. The best reconstructed images used to observe stent apposition were achieved with iopromide diluted to a concentration of 12% (all P < .05) or iodixanol diluted to a concentration of 16% (all P < .05). Malapposition was noted in one case, and good apposition was noted in 11 cases. These results were consistent with IVUS observations. Injecting iopromide or iodixanol diluted to 12% or 16% during high-resolution C-arm CT scanning, respectively, can help evaluate FD stent apposition and obtain optimal image quality.

Evaluation of immunomodulatory potential of probiotic conditioned medium on murine macrophages

Probiotics are a mixture of beneficial live bacteria and/or yeasts that naturally exist in our bodies. Recently, numerous studies have focused on the immunostimulatory effects of single-species or killed multi-species probiotic conditioned mediums on macrophages. This study investigates the immunostimulatory effect of commercially available active, multi-species probiotic conditioned medium (CM) on RAW264.7 murine macrophages. The probiotic CM was prepared by culturing the commercially available probiotic in a cell-culture medium overnight at 37 °C, followed by centrifugation and filter-sterilization to be tested on macrophages. The immunostimulatory effect of different dilution percentages (50%, 75%, 100%) of CM was examined using the MTT assay, proinflammatory cytokine (tumor necrosis factor TNF-alpha) production in macrophages, migration, and phagocytosis assays. For all the examined CM ratios, the percentages of cell viability were > 80%. Regarding the migration scratch, TNF-alpha and phagocytosis assays, CM demonstrated a concentration-dependent immunostimulatory effect. However, the undiluted CM (100%) showed a significant (p-value < 0.05) stimulatory effect compared to the positive and negative controls. The findings suggest that the secretions and products of probiotics, as measured in the CM, may be closely associated with their immune-boosting effects. Understanding this relationship between probiotic secretions and immune function is crucial for further exploring the potential benefits of probiotics in enhancing overall health and well-being.

Evaluation of Austenitic Stainless Steel ER308 Coating on H13 Tool Steel by Robotic GMAW Process

Within the drilling, petrochemical, construction, and related industries, coatings are used to recover components that failed during service or to prevent potential failures. Due to high stresses, such as wear and corrosion, which the materials are subjected to, industries require the application of coating between dissimilar materials, such as carbon steels and stainless steels, through arc welding processes. In this work, an austenitic stainless steel (ER308) coating was applied to an H13 tool steel substrate using the gas metal arc welding (GMAW) robotic process. The heat input during the process was calculated to establish a relationship between the geometry obtained in the coating and its dilution percentage. Furthermore, the evolution of the microstructure of the coating, interface, and substrate was evaluated using XRD and SEM techniques. Notably, the presence of martensite at the interface was observed. The mechanical behavior of the welded assembly was analyzed through Vickers microhardness, and a pin-on-disk wear test was employed to assess its wear resistance. It was found that the dilution percentage is around 18% at high heat input (0.813 kJ/mm) but decreases to about 14% with reduced heat input. Microhardness tests revealed that at the interface, the maximum value is reached at about 625 HV due to the presence of quenched martensite. Moreover, increasing the heat input favors wear resistance.

Optimization of a foot-and-mouth disease virus Southern African Territories-specific solid-phase competitive ELISA for small ruminant serum samples.

We optimized and verified a single-spot solid-phase competitive ELISA (ss-SPCE) to detect antibodies against structural proteins of Southern African Territories (SAT) serotypes of foot-and-mouth disease virus (FMDV) in small ruminants. Sera from goats vaccinated and experimentally challenged with a SAT1 FMDV pool were tested in duplicate at 4 dilutions (1:10, 1:15, 1:22.5, 1:33.8) to optimize the assay. To assess the performance of the assay in naturally infected animals, we evaluated 316 goat and sheep field sera collected during active SAT2 outbreaks. Relative to results of the virus neutralization test, the optimal serum dilution and cutoff percentage inhibition (PI) were 1:15 and 50%, respectively. At these values, the Spearman rank correlation coefficient was 0.85 (p < 0.001), and the sensitivity and specificity (95% CI) were 80.3% (72.6, 87.2) and 91.1% (84.1, 95.9), respectively. Relative to the liquid-phase blocking ELISA and the nonstructural protein ELISA, the ss-SPCE exhibited divergent performance characteristics between the goat and sheep field sera. Repeatability was better for goats, but the correlation and agreement among all 3 assays were better for the sheep sera. The prevalence of SAT2 FMDV infection in the sampled sheep was 23.6%; sampled goats were seemingly FMDV-free. The ss-SPCE is an appropriate FMDV detection tool to investigate the role of small ruminants in the epidemiology of FMD in Africa.

Possible Pollution of Surface Water Bodies with Tequila Vinasses

The aim of this study was to evaluate the water quality in two streams of the Valles region of Jalisco, Mexico and fully determine if they are being used as tequila vinasse disposal sites. Three sampling campaigns were carried out at eight different points of the two streams that run near tequila factories (TFs). Different physicochemical parameters of water quality were measured: chemical oxygen demand (COD); biochemical oxygen demand (BOD5); total suspended solids (TSSs); total phosphates; fats, oils, and grease (FOG); Kjeldal nitrogen; nitrite; nitrate; pH; conductivity; temperature; dissolved oxygen (DO); and turbidity. Also, the analysis of samples of tequila vinasses (TVs) diluted with tap water were carried out to have a reference for the level of pollution in the streams. Furthermore, due to the fact that COD could be considered the main indicator of pollution with TVs, a linear regression was performed between COD concentrations and the percentage of dilution of TVs (with tap water). A positive correlation was found between these two variables, and based on this analysis, the vinasse content was estimated at each sampling point of the streams. It was found that on average, a volume of 8.5 ± 6.3% and 11.5 ± 4.9% of TVs were present in each sampling point of the Atizcoa and Jarritos Streams, respectively. Additionally, it was found that, in general, the concentration of pollutants increased as the streams passed through the TFs, particularly the Atizcoa Stream. According to the Water National Commission criteria, most of the points would be classified as highly polluted, since they reach concentrations of COD and BOD5 up to 6590 mg/L and 3775 mg/L, respectively, temperature values up to 37 °C, and DO values of 0.5 mg/L. Therefore, it was confirmed that the streams are being used as tequila vinasse disposal sites. Due to the above, there is an urgent need for tequila companies to implement treatment systems for the vinasse generated, since under current conditions, the monitored streams are practically devoid of aquatic life.

Influence of input parameters to determine the shape of weld bead in cladding on 316L stainless steel using the Taguchi method

Background: The Cold Metal Transfer (CMT) process, with its low heat input, is selected for cladding carbon steel in demanding industries such as mining, oil, gas, offshore, steel, and metal. Limited research exists on the utilization of Taguchi's technique in welding and cladding processes. The main objective of the present research is to employ the Taguchi approach for determining the impact of CMT parameters on the cladding geometry of 316L stainless steel. Methods: The influence of process parameters on the weld bead was examined using both Signal-to-Noise (S/N) ratio and Analysis of Variance (ANOVA) by implementing an orthogonal array. A structural steel substrate was coated with nickel-based metal inert gas (MIG) welding wire using the CMT process while being shielded by a 99.9 percent pure argon gas. To attain the desired quality of weld bead, the CMT input parameters and geometry of the bead are separately and collectively optimized. Results: When the welding current (Iw) is set at 130A, welding speed (V) at 200 mm/min, and the distance between the nozzle and plate (X) at 5 mm, the Taguchi method indicates that the desired outcome is obtained with the following parameters: a penetration (P) of 1.115 mm, a reinforcement (R) of 1.51 mm, a bead width (W) of 4.265 mm, and a percentage of dilution (D) of 21.145%. Conclusions: The research findings indicate, under certain limitations, the techniques of the Taguchi method be utilized to efficiently manage the CMT cladding process parameters.

Effects of site dilution on Compensation in Ising Spin-1/2 trilayered triangular Ferrimagnets with non-equivalent planes

Using Monte Carlo simulations with the Metropolis algorithm, the magnetic and thermodynamic behaviours of a spin-1/2, trilayered ferrimagnetic system on triangular monolayers with quenched nonmagnetic impurities are studied. Two different theoretical atoms, A and B, make up the ABA and AAB types of distinct configurations. Like atoms (A-A and B-B) interact ferromagnetically, while unlike atoms (A-B) interact antiferromagnetically. Only the A-layers are randomly site-diluted with dilution percentages ranging from 5% to 45%. Such diluted magnetic thin systems exhibit magnetic compensation which depends sensitively on the concentration of impurities. The phase diagram in the Hamiltonian parameter space related to the occurrence of magnetic compensation phenomenon and the effect of site dilution is discussed in detail. Special attention is given to the mathematical dependencies of compensation temperature on the concentration of nonmagnetic impurities. Depending upon the concentration of nonmagnetic impurities, the compensation and critical points shift with the equilibrium magnetic behaviours changing between distinct ferrimagnetic behaviours. For each combination of the coupling strengths, with values of the impurity concentration above a threshold, compensation appears where previously was absent. Suggested mathematical formulae show how threshold impurity concentration relies on Hamiltonian parameters.

Optimization of single-pass geometric characteristics of IN718 by fiber laser via linear regression and response surface methodology

Direct laser deposition is among the critical processes for fabricating and reconstructing parts. This study investigated a single-pass laser coating of Inconel 718 superalloy powder on the same substrate using a continuous fiber laser. The linear regression method was used to establish the relationship between the main process parameters, including laser power (P), laser scanning speed (V), and powder feeding rate (F), as well as geometric characteristics of the single-pass cladding including width, height, dilution percentage, and single-pass wetting angle. In addition, drawing process maps by two methods of linear regression and the response surface method was investigated comprehensively. The results showed that the width of a single pass was directly related to the laser power and inversely related to the laser scanning speed. In addition, this parameter has a negligible association with the powder feeding rate. Furthermore, it was found that the height of a single pass has a direct and inverse relationship with the powder feeding rate and the laser scanning speed, respectively, but poorly correlated with the laser power. Dilution was directly and inversely related to laser scanning speed and powder feeding rate, respectively, while the trend was quite the opposite for the wetting angle.

Influence of Filler Material on the Microstructural and Mechanical Properties of 430 Ferritic Stainless Steel Weld Joints

Tungsten Inert Gas (TIG) welding is a commonly used welding technique for ferritic stainless steel, due to its ability to produce high-quality, clean, and precise welds. This welding method provides excellent control over the heat input, making it suitable for thin-walled, high-alloy materials such as ferritic stainless steel. The purpose of this study was to investigate the effect of using two different filler materials, 310 (austenitic) and 410 (ferritic), on the microstructural and mechanical properties of Tungsten Inert Gas (TIG) weld butt joints of 430 ferritic stainless steel (FSS). The results showed that the choice of filler material significantly impacted the dilution percentage, the chromium-nickel equivalent ratio, microstructure, microhardness, and tensile characteristics of the welded joint. The use of 310 filler resulted in a columnar microstructure, whereas the use of 410 filler resulted in a ferritic (acicular ferrite) microstructure with the presence of martensite and austenite. The sample welded with 410 filler demonstrated superior mechanical properties compared to the sample welded with 310 filler. These findings emphasize the importance of selecting the appropriate filler material in order to achieve the desired microstructural and mechanical properties in 430 FSS welded joints.

Effects of process variables on the quality and mechanical properties of 18%Ni-M350 maraging steel produced by direct energy deposition laser additive manufacturing

The characteristics, defects formation and mechanical properties of 18 wt% Ni M350 maraging (18%Ni M350) steel produced by the powder direct energy deposition (DED-p) laser additive manufacturing process is studied. Using a response surface methodology (RSM) based on Central Composite Design (CCD), the relationships between the DED-p process parameters and the resultant single-bead characteristic of the alloy are established. Mathematical models based on second-order polynomials are developed for predicting the bead aspect ratio and the percentage of dilution between the deposit and the base material, which are crucial for producing the bulk-multilayer additive-manufactured material. Multi-layer deposits of the 18%Ni M350 material are produced using optimized process parameters. X-ray computed tomography is used to study the extent of defects formation in the multi-layer material. The results show that the morphology, volume percent and size of defects during the DED-p process are controlled by the laser energy density. In particular, the morphology of defects is found to change from irregular lack-of-fusion defects to spherical gas porosity and keyhole porosity as the energy density increases from ∼14 J/mm2 to 48 J/mm2. A set of process parameters is achieved that significantly minimized the defects to produce high-density additive-manufactured material. Furthermore, the influence of the defects morphology in the 18%Ni-M350 material produced by DED-p on the tensile properties in as-processed and heat-treated conditions is evaluated and discussed in this paper.

Comparing and analysing the characterisation of laser cladding of CrNiW and CrNiFeAlZr powders on H13 tool steel

Cladding-based repair has been found to be superior than welding or flame spraying repair approaches in terms of extending die life. In this work, two different alloy powders, that is, CrNiW and CrNiFeAlZr were coated on H13 steel using laser cladding. The laser power, powder feed rate and scanning speed were varied and the clad dimensions, aspect ratio and dilution percentage were measured. The microhardness found in the CrNiW clad is 834 ± 20 HV0.5, which is higher than that of the CrNiFeAlZr clad (780 ± 20 HV0.5) as well as the substrate clad (548 ± 20 HV0.5). CrNiW clad has a higher microhardness than CrNiFeAlZr clad and substrate, indicating that CrNiW laser cladding has a significant impact on microhardness. The interface region for CrNiFeAlZr has 8.33% of C, which is less than the interface region for CrNiW (10.65% of C) so that the microhardness at the interface in CrNiW clad is high. The XRD patterns identified the common phase creation of Ni3C and Fe3C for CrNiFeAlZr and CrNiW coatings, while the oxide formation was only seen in CrNiFeAlZr coatings and the addition of carbon content in the CrNiW clad layer forms WC, Cr23C6, Ni3C and Fe3C. A response surface methodology with a Box-Behnken design is used in the optimisation process.

Research into the influence of the thin ore body occurrence elements and stope parameters on loss and dilution values

Purpose. Development of a methodology for determining the level of actual losses and dilution of ore based on the identified patterns of the influence of occurring ore body elements and the stope parameters when mining thin slope deposits using a system for delivering ore by the blasting force. Methods. The task set is solved using an integrated approach, including the analysis of literary sources and the existing practical experience on the issues of losses and dilution, conducting experimental-industrial experiments in the conditions of the Akbakai deposit to assess the recommended method effectiveness for determining the values of excess losses and dilution of ore, geomechanical assessment of the mass using the methods of limit equilibrium, numerical and probabilistic analyses. Findings. A methodology for determining losses and dilution when mining thin slope deposits using a system for delivering ore by the blasting force is proposed, which makes it possible to predict excess losses and dilution coefficients arising from stope roof caving and incomplete ore delivery. The actual losses and dilution of ores in the Akbakai deposit have been determined based on the proposed methodology and instrumental surveys. The developed methodology for determining the values of excess losses and dilution makes it possible to take preliminary measures to prevent the stope roof caving with the complete ore mass delivery using the blasting force. Originality. New dependences have been revealed for the conditions of the Akbakai deposit: logarithmic – the value of dilution depending on the angle of the ore body occurrence; polynomial – the stope maximum span depending on the ore body dip angle; exponential – ore losses depending on the angle of the ore body occurrence. Practical implications. The practical significance, confirmed in the course of pilot-experimental work, is in minimizing the percentage of loss and dilution of the useful component when mining thin slope ore deposits using a sublevel blast-hole stoping system with an open stope space, which makes it possible to reduce the cost of the produced mineral.

Flame Flashback Critical Damköhler Number for CO$$_2$$ Diluted CH$$_4$$ and C$$_3$$H$$_8$$ Mixtures with Air

The premixed laminar flame flashback phenomenon in tubes has been known and studied for several decades. However, the effect of the CO\(_2\) dilution has not been addressed, which is relevant for assessing the safety of oil-producing facilities. Furthermore, even if numerical studies have underscored the important role played by the mixture Lewis number (Le), these lack an experimental validation. For this reason, specific studies of premixed flame flashback in laminar flows have been undertaken. The objective is to assess the flame flashback critical conditions in mixtures of hydrocarbons — methane or propane diluted by various amounts of CO\(_2\) — with air. This is effected by determining the critical Damköhler number, which is computed using both experimental and numerical data. The former leads to the flashback critical velocity gradient, whereas the latter to a characteristic chemical time scale. The effect of different flame thickness definitions on the Damköhler number (Da) is examined, evidencing than an order of magnitude discrepancy may arise depending on the definition choice. For methane/air mixtures the critical Da increases with the equivalence ratio, whereas a decrease of nearly two orders of magnitude has been obtained for propane/air mixtures. The original results show that CO\(_2\) dilution increases Da only when the fuel dilution percentage is larger than 25 and 50%, for methane and propane, respectively, situations which correspond to flame extinction after flashback. The propane/air/CO\(_2\) mixture results exhibit a \(Da \propto Le^{5.06}\) dependency which closely follows the trend computed previously, whereas the methane/air/CO\(_2\) results evidence the thermal boundary condition at the tube wall influence.

Fate of fentanyl after formalin-fixed tissues: About an authentic case and a stability study

Death leads to various body modifications: lividities, rigidities, cyanosis, swelling, etc. In order to delay the degradation of a body and to keep it in a state close to living, formalin-fixed can be done, in order to stop invasive bacterial growth and slow down decomposition. Formalin is the main preservative liquid used. Formalin will modify the characteristics of the xenobiotics present in the organism: modification of the pH, dilution of the compounds and/or chemical transformations. Thus, the toxicological results after formalin-fixed are therefore not characteristic of the time of death. The difficulty lies in the interpretation of the results. The authors report the case of a 41-year-old man, found unconscious at his home. Resuscitation manoeuvers were unsuccessful and death was pronounced shortly after. An external examination of the body was carried out, revealing no lesion suggestive of violence or cause of death. Femoral blood was collected in a dry tube (blood 1). An autopsy, performed a few days later, also failed to identify a cause of death. In the interval between the external examination and the autopsy, body preservation treatments were carried out. After a deeper investigation of the circumstances, fentanyl transdermal patches (Durogesic®) were discovered at the home of the victim. It was envisaged that the victim died from an overdose of fentanyl, linked of transdermal patches misuse. A complete toxicological analysis was requested on the samples collected during the autopsy, including femoral blood (blood 2). A standard analysis of blood 2 was performed, using validated laboratory procedures. In addition, stability study of fentanyl was conducted in the presence of formalin to determine possible influence. A 30 mL pool of blank blood containing 1 mg/L of fentanyl was prepared and then aliquoted into 30 tubes of 1 mL. Except for the first tube, 20 μL of formalin (20%) was added to each tube. On day 1, the first set of tubes (without formalin) was extracted and analyzed on UPLC-MS/MS. The stability study was spread over 4 months, and each analysis was done in duplicate ( n = 2). The femoral blood 2 analyzes showed the presence of methanol (present in the preservative liquid), fentanyl at toxic concentration (30 ng/mL) and norfentanyl (4 ng/mL). No other compound was detected. It is possible that the concentrations measured in blood 2 were lower than those at the time of death, due to preservative treatment, without being able to evaluate the percentage of degradation or dilution. However, the stability study of fentanyl over 4 months did not show any fentanyl degradation in the presence of formalin, as the concentration remained stable throughout the study. The blood 1 collected during the external examination was also analyzed. Fentanyl and norfentanyl were measured at 16 ng/mL and 1 ng/mL, respectively. The differences in concentrations between the two femoral blood samples confirm that there is no degradation of fentanyl in presence of formalin. Moreover, the higher concentrations measured after preservative treatments are in favor of a redistribution of fentanyl from the skin where the patches were worn (relocation of fentanyl linked to preservation treatments operations). The results can also be explain by the breaking of the plasma protein binding of fentanyl to albumin (estimated at 80–85%) in presence of formalin, and thus a significant increase in the concentration of free-fentanyl. A stability study showed that fentanyl does not degrade in the presence of formalin. Nevertheless, other formalin-related phenomena can have an impact on the concentrations (transfer of molecules and breaking of protein bonds), making interpretation very difficult, if not impossible.