Non-oxidizing Acid Research Articles

Sex Differences in Energy Metabolism: A Female-Oriented Discussion.

The purpose of this review is to delineate aspects of energy metabolism at rest and during exercise that may be subject to sex differences and the potential underlying mechanisms involved. It focuses on distinct aspects of female physiology with an oriented discussion following the reproductive life stages of healthy, eumenorrheic females, including premenopausal time frames, pregnancy, perimenopause, and menopause. Finally, this review aims to address methodological challenges surrounding sexual dimorphism in energy metabolism investigations and confounding factors in this field. During resting conditions, females tend to have higher rates of non-oxidative free fatty acid clearance, which could contribute to lower respiratory exchange ratio measures. At the same time, carbohydrate energy metabolism findings are mixed. In general, females favor lipid energy metabolism during moderate-intensity exercise, while men favor carbohydrate energy metabolism. Factors such as age, dietary intake, genetics, and methodological decisions confound study findings, including properly identifying and reporting the menstrual cycle phase when female subjects are eumenorrheic. Pregnancy presents a unique shift in physiological systems, including energy metabolism, which can be observed at rest and during exercise. Changes in body composition and hormonal levels during the post-menopausal period directly impact energy metabolism, specifically lipid metabolism. This change in physiological state factors into the evidence showing a reduction in our understanding of sex differences in lipid metabolism during exercise in older adults. This review reveals a need for a focused understanding of female energy metabolism that could help exercise and nutrition professionals optimize female health and performance across the lifespan.

Methanesulfonic acid (MSA) in clean processes and applications: a tutorial review.

This Tutorial Review acquaints chemists and metallurgists with the properties and industrial applications of methanesulfonic acid (MSA, CH3SO3H). Over the past quarter-century, MSA has garnered increasing interest as a reagent for green chemistry due to its strong acidity, while circumventing many of the challenges associated with handling concentrated sulfuric acid, hydrochloric acid, or nitric acid. Concentrated MSA is a non-oxidizing reagent, exhibiting high chemical stability against redox reactions and hydrolysis, as well as high thermal stability and limited corrosivity towards construction materials. It is colorless, odorless, and possesses a very low vapor pressure. MSA combines commendable biodegradability with low toxicity. It is extensively utilized as a Brønsted acid catalyst for esterification or alkylation reactions, and is employed in biodiesel production. The high solubility of its metal salts, the high electrical conductivity of its concentrated solutions, coupled with the high electrochemical stability of MSA and its anion, make MSA-based electrolytes beneficial in electrochemical applications. Examples include the electrodeposition of tin-lead solder for electronic applications and the high-speed plating of tin on steel plate for food cans. MSA-based electrolytes are used in redox flow batteries (RFBs). MSA offers a much safer and environmentally friendlier alternative to electrolytes based on fluoroboric or fluorosilicic acid. A novel application area is as a strong acid in extractive metallurgy, where it may contribute to the development of circular hydrometallurgy. MSA is being explored in lithium-ion battery recycling flowsheets, as well as in other applications in the field of metal recovery and refining. However, this review is not solely about the advantages of MSA for green chemistry or clean technologies, as there are also some potential drawbacks. Apart from its higher price compared to regular strong acids, MSA has only minor advantages for applications where sulfuric acid performs well. Since methanesulfonate biodegrades into sulfate, the same emission restrictions as for sulfate should be considered. In conclusion, MSA is the acid of choice for applications where metal sulfates cannot be used due to poor solubility or where concentrated sulfuric acid is too reactive towards organics.

The Effect of Sample Preparation and Measurement Techniques on Heavy Metals Concentrations in Soil: Case Study from Kraków, Poland, Europe

Accurate and reliable laboratory results are an extremely important and integral part of conducting scientific research. Many factors influence the results obtained, including the type of determination method, accuracy and precision of measurements, and laboratory equipment used for the tests. This paper presents the results of measurements of heavy metal concentration in soil using two methods for adding soil components into solution and different laboratory methods and types of measuring equipment. The first method used was hot digestion of soil samples with a mixture of concentrated HNO3 and HClO4, after prior ashing of organic matter (IUNG method). The second method was a two-stage decomposition, where soil samples were hot digested, initially with oxidizing acid (HNO3) and subsequently with non-oxidizing acid (HF) (two-stage decomposition). The concentrations of selected heavy metals (Cr, Cu, Fe, Mn, Ni, Pb and Zn) were determined in solutions obtained by both digestion methods. The solutions obtained from soil decomposition were determined twice using atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP MS) methods in different laboratories using different types of spectrometers. In most cases, the measured concentrations of heavy metals are the highest for the two-stage solution samples and the measurements of their concentrations carried out using ICP. The exceptions are the measurements of Cu and Ni concentrations. In the case of Cu, lack of significant differentiation in concentrations of this metal may result from different forms of occurrence of Cu in soil than in the case of other metals. For Ni, however, a reversal of the trends seen for the other metals is observed and the type of spectrometer used for measurements is important. There may be an interference of the spectrometric spectrum of Ni with the spectra of the other determined metals. However, this is not clear at the present stage of the study. In conclusion, the results of this study indicate that the choice of soil sample preparation and the type of spectrometer used for measurements can, in many cases, determine the value of laboratory results, even if it is in an expected range of standard material. Research of published papers proved that most of them show only results based on one selected course of methodology without comparison with others. The novelty of the paper is the comparison of the measurements of heavy metal concentration in soil using two methods for adding soil components into solution and different laboratory methods and types of measuring equipment. Additionally, the article includes a discussion of the importance of methodology. We believe that the conclusions may help to better understand how sample preparation and measurement methods applied may influence the results obtained.

An Analysis of Copper Concentrate from a Kupferschiefer-type Ore from Legnica-Glogow Copper Basin (SW Poland)

ABSTRACT This study involved the chemical and detailed mineralogical analysis of the final copper concentrate produced at the Lubin Concentrator, one of the concentrating plants of the Mining–Smelting Complex KGHM Polska Miedz SA. The KGHM Complex mines and processes are one of the world’s biggest stratiform-type copper deposits. The ore processed in the Lubin Concentrator is the poorest in metals from the ores mined in the KGHM mines and is difficult for upgrading. The copper flotation concentrates produced at the Lubin Concentrator are characterized by polymetallic (Cu-Ag-Pb), polymineral and fine-grained composition, with the lowest content of copper (below 14%) among three concentrator plants of the KGHM. The total content of sulfide minerals is about 33%. The main sulfides are chalcopyrite, bornite, galena, and pyrite with marcasite. The aim of this study is an attempt to explain the causes of the low quality of concentrates produced in the Lubin Concentrator. For this purpose, a detailed quantitative mineral analysis of a commercial concentrate sample was performed. There were also performed operations consisting in non-oxidative acid leaching of gangue minerals followed by flotation of the concentrate with the use of a depressant. The obtained results are important and promising for the smelting use of these concentrates.

A mechanism study of acid-assisted oxidative stabilization of asphaltene-derived carbon fibers

The development of inexpensive carbon fiber precursors is necessary to meet the future demands of carbon fibers. This work shows how asphaltenes, which are obtained as a by-product in bitumen production, can play an important role as such inexpensive carbon fiber precursors. To synthesize carbon fibers from asphaltene, stabilization by means of oxidizing acids (HNO3 and H2SO4) was developed. Stabilization could not be achieved by a non-oxidizing acid (HCl). The reactions leading to fiber stabilization was investigated for nitric acid treatment, which led to oxidation and the incorporation of nitro-groups. Further thermal treatment caused an increase in C/H ratio that was related to decomposition of nitro-groups, which facilitated air oxidation and other reactions leading to the loss of volatile hydrogen-rich products, such as light hydrocarbons. Additionally, the influence of the acid concentration during treatment on fiber properties, such as fiber diameter, composition, tensile strength and elastic modulus, has been examined. The application of the acid treatment leads to carbon fibers with good tensile properties, with a tensile strength and elastic modulus of 811 MPa and 32.7 GPa, respectively. The overall yield of carbon fibers is 37 – 38 wt.%.

Electrolyte Based Modeling of Corrosion Processes in Sulfuric Acid Mixtures, Part 1: Nonoxidizing Conditions

The corrosion behavior of stainless steels and Ni-based alloys in nonoxidizing sulfuric acid mixtures at concentrations below approximately 30 mol/kg H2O is modeled. The redox potential in sulfuric acid across a broad concentration range, from 0 to 80 mol% (0 to 95.6 wt%), is determined by the proton reduction reaction. Thus, in the absence of other oxidizing species, sulfuric acid behaves as a nonoxidizing (reducing) acid. The calculated corrosion rates, using an electrochemical model up to about 30 mol/kg H2O (about 75 wt%), are in agreement with experimental values. The predicted polarization curves of anodic and cathodic processes show that the alloys in these environments are in active dissolution regime, consistent with experimental data. The model predictions of corrosion rates in H2SO4+HCl, H2SO4+HF, and H2SO4+HCl+HF mixtures are in agreement with weight-loss corrosion data. The corrosion rate of alloys in the nonoxidizing sulfuric acid mixtures correlated to an equivalent alloy composition given by (Ni0.7-Cr0.1+Mo+0.5 W). The effect of alloying elements under these conditions may be related to their beneficial effect on active dissolution and proton reduction reaction rates.

Mst1 knockdown alleviates cardiac lipotoxicity and inhibits the development of diabetic cardiomyopathy in db/db mice

Diabetic cardiomyopathy (DCM) accounts for increasing deaths of diabetic patients, and effective therapeutic targets are urgently needed. Myocardial lipotoxicity, which is caused by cardiac non-oxidative metabolic fatty acids and cardiotoxic fatty acid metabolites accumulation, has gained more attention to explain the increasing prevalence of DCM. However, whether mammalian Ste20-like kinase 1 (Mst1) plays a role in lipotoxicity in type 2 diabetes-induced cardiomyopathy has not yet been illustrated. Here, we found that Mst1 expression was elevated transcriptionally in the hearts of type 2 diabetes mellitus mice and palmitic acid-treated neonatal rat ventricular myocytes. Adeno-associated virus 9 (AAV9)-mediated Mst1 silencing in db/db mouse hearts significantly alleviated cardiac dysfunction and fibrosis. Notably, Mst1 knockdown in db/db mouse hearts decreased lipotoxic apoptosis and inflammatory response. Mst1 knockdown exerted protective effects through inactivation of MAPK/ERK kinase kinase 1 (MEKK1)/c-Jun N-terminal kinase (JNK) signaling pathway. Moreover, lipotoxicity induced Mst1 expression through promoting the binding of forkhead box O3 (FoxO3) and Mst1 promoter. Conclusively, we elucidated for the first time that Mst1 expression is regulated by FOXO3 under lipotoxicity stimulation and downregulation of Mst1 protects db/db mice from lipotoxic cardiac injury through MEKK1/JNK signaling inhibition, indicating that Mst1 abrogation may be a potential treatment strategy for DCM in type 2 diabetic patients.

A quick analytical approach to estimate both free versus sorbed hydrocarbon contents in liquid-rich source rocks

Free and sorbed low-to-medium molecular weight thermovaporized hydrocarbons (<C20) are the main organic compounds released at the temperature range corresponding to the Rock-Eval® Shale PlayTMSh0 parameter (100°C–200°C), whereas medium and high molecular weight thermovaporized compounds (< C30) are the predominant components that are thermal released in the temperature range corresponding to the Shale Play Sh1 parameter (200°C–350°C). Now, an analytical methodology is proposed here to predict the quantity of free versus sorbed hydrocarbons still present in any liquid-rich sedimentary rock. The method compares shale play parameters (Sh0 and Sh1) obtained from both whole-rock samples and their corresponding organic matter (OM) concentrates isolated by standard nonoxidizing acid treatments and drying procedures. The hydrocarbon content obtained from whole rock (HCTotal,rock) is mainly considered as the total amount of free liquid hydrocarbons (HCFree) and sorbed liquid hydrocarbons (HCSorbed,OM) still contained in the investigated rock sample. The hydrocarbon content obtained from OM concentrates, however, only reflects the sorbed liquid hydrocarbons. In these equations, TOCrock is the total organic carbon of the rock sample; TOCOM corresponds to the TOC content of the OM concentrate sample; Massrock is the initial mass of the rock sample; MassOM is the initial mass of the OM concentrate sample; FIDsignalrockSh0+Sh1 is the flame ionization detection (FID) signal that corresponds to the global surface area under each thermal peak (Sh0 and Sh1) generated by the Rock-Eval FID; FIDsignalOMSh0+Sh1 corresponds to the global surface area under each thermal peak (Sh0 and Sh1) measured by the Rock-Eval FID between 100°C and 350°C after the themovaporization of the OM concentrate sample. Free liquid hydrocarbons are finally calculated as the difference between these last two values (HCFree e HCTotal,rock − HCSorbed,OM). This paper illustrates the application of this methodology on rock samples derived from the Vaca Muerta Formation (Argentina). Along the selected vertical profile, the lower rock interval contains approximately 60% of sorbed liquid hydrocarbons, whereas the upper sample contains more than 90% free liquid hydrocarbons. The parameters FreeHCSh0 and FreeHCSh0+Sh1 could be used to identify potential producible free liquid hydrocarbons intervals in early exploration campaigns.

Nanoporous Gold Formation by Free Corrosion Dealloying of Gold-Silver Alloys in Nonoxidizing Acids Driven by Catalytic Oxygen Reduction Reaction

Highly concentrated nitric acid (molarity ~ 15 M), a strong oxidizing agent, has been extensively used to produce nanoporous gold by free corrosion dealloying of gold-silver alloys. This is because, kinetically, silver dissolution in dilute nitric acid with molarity 5 M (or lower) is not favorable at ambient temperature and pressure. We recently reported (Deng and Detsi in Nanoscale 9:11858, 2017; Fu et al. in ACS Appl Nano Mater 1(8):4164, 2018) on the use of catalytically driven reduction reactions to enhance the rate of nanoporous silver and nanoporous gold formation at ambient temperature and pressure by free corrosion dealloying in hydrochloric acid, a nonoxidizing acid. Here, we further elucidate these findings by combining our experimental studies with the mixed potential theory of corrosion to shed more light on the reaction mechanisms associated with free corrosion dealloying of silver-aluminum alloys, and gold-silver alloys in various corroding media and in the presence of a catalyst used to enhance the dealloying rate.

A comparative study of graphene oxide: Hummers, intermediate and improved method

Among 2-D nanostructures, graphene oxide is considered as the most attractive precursor nanomaterial for the utility of graphene in a variety of applications. There are problems associated with its mass production, which demands development of better and easier synthetic protocols. In addition, a chemical approach with a better control over degree of oxidation and nature of functionalities is simultaneously crucial for designing their structural modifications and the corresponding applications. Herein, three types of GOs are prepared by Hummers’, Intermediate and Improved method. A primary reaction step in GO synthesis is the formation of graphite intercalation compounds (GICs). The efficiency of oxidation and intercalant efficiency, non-oxidative Bronsted acid H3PO4/H2SO4 and H2SO4 are studied and properties are compared with the classical intercalant, H2SO4/NaNO3. A modulation in degree and nature of oxidative defects, flake size and stability of aqueous dispersion is observed, as supported by various analytical techniques. Depending upon the reaction conditions, the synthesized GOs revealed predominance of different type of oxidative functionalities and thereby reflected in associated physical properties, which is helpful to guide their usage for specific applications.

Modeling of Electrocatalytic Dinitrogen Reduction on Microstructured Electrodes

AbstractOne major challenge of electrocatalytic dinitrogen (N2) reduction is the competition between nitrogen reduction reaction (NRR) and hydrogen evolution reaction (HER). While experimental development of selective NRR catalysts is indispensable, the aim is to derive insights of catalyst design by developing a model that includes both the kinetics of competing reactions on the electrode and the mass transport of reactants in solution. The developed microkinetic model is reported here and it is applied to evaluate NRR selectivity on planar and microstructured electrodes. As a proof‐of‐principle, the model is numerically simulated under an aqueous electrolyte of 0.1 m nonoxidizing strong acid. The analysis indicates that while the first electron transfer to N2 is rate‐limiting in most cases, under certain scenarios the impact of subsequent proton transfer on the reaction rate can be prominent. The microstructure of electrodes can pose a limit of N2 mass transport and intriguingly cast a negative impact on the selectivity of N2 fixation. Overall, the developed model interfaces the kinetics on electrode surfaces with the mass transport in the solution, and will serve as a general platform for the design and optimization of electrochemical N2‐fixing process.

Leaching of yttrium, europium and accompanying elements from phosphor coatings

The aim of this work was to study and describe leaching behaviour of Y, Eu and accompanying elements (Zn, Cd) from the phosphors of waste cathode ray tube (CRT) screens in low concentrated sulphuric acid solutions under both non-oxidizing and oxidizing conditions (H2O2). Thermodynamic study showed that non-oxidizing acid leaching leads to elemental sulphur and hydrogen generation followed by formation of H2S(g). In the presence of oxidant in the leaching system SO2(g) or H2SO4 formation is possible. PbSO4 was formed during leaching independently from the presence of the oxidant. Y, Eu and Zn dissolution without using H2O2 in 0.4M H2SO4 at 80°C attained 6, 9 and 8% respectively. The appropriate content of H2O2 in leaching solution was determined as 3.9v/v %. The highest leaching efficiency of Y and Eu (around 90–95% after 20min) was achieved by using the leaching solution (400ml 0.4M H2SO4, 60ml 30v/v % H2O2) at 80°C and L/S ratio 23. Under these conditions Zn extraction was relatively low (20%) in comparison with Cd extraction (80%). The study also reveals that high leaching efficiency of both Y and Eu (around 90%) was achieved with even more diluted leaching solution (400ml 0.05M H2SO4, 60ml of 30v/v % H2O2) at 60°C, L/S ratio 23 after 20min of leaching. Zn and Cd extractions reached 20% and 55% respectively. Activation energy values calculated for Y and Eu leaching in the solution (400ml 0.4M H2SO4 with 60ml of 30v/v % H2O2) refer to diffusion mechanism in the range 40–80°C (Ea=14.85kJ/mol and 16.47kJ/mol respectively). In contrast, Ea values for Y and Eu leaching in the solution (400ml 1M H2SO4, 60ml of 30v/v % H2O2) suggest a mechanism change at the temperature around 40°C. The leaching of Y as well as Eu up to 40°C is controlled by diffusion and at higher temperatures by chemical reaction.

From ascorbic acid to furan derivatives: the gas phase acid catalyzed degradation of vitamin C.

Furan derivatives, potentially carcinogenic to humans, can be formed, in addition to carbohydrates and other sources, from the degradation of ascorbic acid (AA). At present, the mechanisms involved in the ascorbic acid degradation are not yet fully understood. In this study, we reported a gas-phase investigation, performed using Triple Quadrupole (TQ/MS) and Ion Trap Mass Spectrometry (QIT/MS) together with quantum mechanical calculations at the B3LYP/6-31+G(d,p) level of theory, on the non-oxidative degradation mechanism of l-ascorbic acid (AA) to furan derivatives. Gaseous protonated ascorbic acid ions, the AAH+ ionic reagents, were generated by Electrospray Ionization (ESI) of an aqueous AA solution added with a mild protonation reagent. The Collisionally Induced Dissociation (CID) mass spectra of the AAH+ ions displayed gaseous fragment ions corresponding to the degradation intermediates and reaction products, which were structurally characterized and identified. Precise mechanistic insights were achieved by using l-[1-13C]-AA. On the basis of experimental and computational results, the gas phase non-oxidative acid catalyzed degradation mechanism of ascorbic acid is proposed, a benchmark point for the comprehension of the mechanism in the condensed phase.

HosA, a MarR Family Transcriptional Regulator, Represses Nonoxidative Hydroxyarylic Acid Decarboxylase Operon and Is Modulated by 4-Hydroxybenzoic Acid.

Members of the Multiple antibiotic resistance Regulator (MarR) family of DNA binding proteins regulate transcription of a wide array of genes required for virulence and pathogenicity of bacteria. The present study reports the molecular characterization of HosA (Homologue of SlyA), a MarR protein, with respect to its target gene, DNA recognition motif, and nature of its ligand. Through a comparative genomics approach, we demonstrate that hosA is in synteny with nonoxidative hydroxyarylic acid decarboxylase (HAD) operon and is present exclusively within the mutS-rpoS polymorphic region in nine different genera of Enterobacteriaceae family. Using molecular biology and biochemical approach, we demonstrate that HosA binds to a palindromic sequence downstream to the transcription start site of divergently transcribed nonoxidative HAD operon and represses its expression. Furthermore, in silico analysis showed that the recognition motif for HosA is highly conserved in the upstream region of divergently transcribed operon in different genera of Enterobacteriaceae family. A systematic chemical search for the physiological ligand revealed that 4-hydroxybenzoic acid (4-HBA) interacts with HosA and derepresses HosA mediated repression of the nonoxidative HAD operon. Based on our study, we propose a model for molecular mechanism underlying the regulation of nonoxidative HAD operon by HosA in Enterobacteriaceae family.

Electrophilic amination of aromatics with sodium azide in BF3–H2O

Boron trifluoride monohydrate is an excellent Brønsted acid catalyst system for a wide range of reactions. It is a non-oxidizing acid catalyst prepared easily by bubbling BF3 into water. We have found boron trifluoride monohydrate/sodium azide combination to be an efficient reagent system for aromatic electrophilic amination. The present method avoids the use of expensive superacids such as trifluoromethanesulfonic acid and provides a facile access to aromatic amines directly from aromatics.

A NOVEL BLACKENING METHOD OF PREPARING ULTRA-BLACK Ni–P COATINGS: EFFECT OF PROCESS PARAMETERS ON MORPHOLOGY AND OPTICAL PROPERTY

Ni – P ultra-black coatings were prepared by a novel blackening method of anodic oxidation in nonoxidizing acid media. The effect of the applied voltage, concentration of H 3 PO 4 and anodization time on the microstructure and optical property of blackened coatings was investigated. The results show that the applied voltage plays the most important role during the formation of the ultra-black coatings. The concentration of H 3 PO 4 is the next-important factor, then anodization time. The optimum process parameter for obtaining ultra-black coatings is at 0.9 V in 3 mol/L for 40 min, in which the reflectance is only 0.14–0.21% in the visible region. The low reflectance is mainly attributable to the unique array structure of conical cavities ranging 1–3 μm in size, in which the innumerable tiny pits distribute on the cavity wall. In contrast, the black coatings etched by chemical etching method by strong oxidizing acid ( HNO 3) have larger conical cavities (10–20 μm) with smooth cavity wall, and thus lead to higher reflectance of 0.69–2.44%.

Insulin Protects Pancreatic Acinar Cells from Palmitoleic Acid-induced Cellular Injury

Acute pancreatitis is a serious and sometimes fatal inflammatory disease where the pancreas digests itself. The non-oxidative ethanol metabolites palmitoleic acid (POA) and POA-ethylester (POAEE) are reported to induce pancreatitis caused by impaired mitochondrial metabolism, cytosolic Ca(2+) ([Ca(2+)]i) overload and necrosis of pancreatic acinar cells. Metabolism and [Ca(2+)]i are linked critically by the ATP-driven plasma membrane Ca(2+)-ATPase (PMCA) important for maintaining low resting [Ca(2+)]i. The aim of the current study was to test the protective effects of insulin on cellular injury induced by the pancreatitis-inducing agents, ethanol, POA, and POAEE. Rat pancreatic acinar cells were isolated by collagenase digestion and [Ca(2+)]i was measured by fura-2 imaging. An in situ [Ca(2+)]i clearance assay was used to assess PMCA activity. Magnesium green (MgGreen) and a luciferase-based ATP kit were used to assess cellular ATP depletion. Ethanol (100 mM) and POAEE (100 μM) induced a small but irreversible Ca(2+) overload response but had no significant effect on PMCA activity. POA (50-100 μM) induced a robust Ca(2+) overload, ATP depletion, inhibited PMCA activity, and consequently induced necrosis. Insulin pretreatment (100 nm for 30 min) prevented the POA-induced Ca(2+) overload, ATP depletion, inhibition of the PMCA, and necrosis. Moreover, the insulin-mediated protection of the POA-induced Ca(2+) overload was partially prevented by the phosphoinositide-3-kinase (PI3K) inhibitor, LY294002. These data provide the first evidence that insulin directly protects pancreatic acinar cell injury induced by bona fide pancreatitis-inducing agents, such as POA. This may have important therapeutic implications for the treatment of pancreatitis.

A Study on the Passivation Behavior and Semiconducting Properties of Gamma Titanium Aluminide in 0.1 N H2SO4, HNO3, and HClO4 Acidic Solutions

The study focuses on the passivation behavior of single-gamma-phase titanium aluminide in acidic solutions with a particular emphasis on the role of oxidizing strength in characteristics of passive layer. The report includes potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies along with Mott-Schottky analysis in order to determine the corrosion behavior of the alloy and the semiconducting properties of the scale formed during exposure to acidic environment. Passive current density measured from potentiodynamic polarization curve, polarization resistance (R p) estimated by EIS, defect density, and flatband potential drawn from Mott-Schottky analysis are mainly used in estimating the ability of passive film formed on alloy in protecting it against high corrosion rates in Sulfuric acid (a non-oxidizing acid), perchloric acid, and nitric acid (oxidizing acid with different oxidizing strength). The results show that passive current density (i pass) in Sulfuric acid is 2.67 × 10−5 A cm−2, which is 2.5 and 3 times greater than the values obtained in perchloric acid (i pass = 9.91 × 10−6) and nitric acid (i pass = 7.98 × 10−6), respectively. EIS data reveal that the value of R p in sulfuric acid (20 kΩ cm2) is about three and five times smaller than that its value in perchloric acid and Nitric acid, respectively. Mott-Schottky analysis shows that the passive layer exhibits an n-type semiconducting characteristics irrespective of acidic environment. The greatest and the smallest values of donor density (N D) are obtained for the passive scale formed in sulfuric acid (N D, H2SO4 = 18.36 × 1019) and nitric acid (N D, HNO3 = 13.13 × 1019), respectively. The report concludes that characteristics of the passive scale are directly affected by reduction potential of the acid, which is the criterion of its oxidizing strength. An increase in the oxidizing strength of the acidic solution results in formation of more protective and less conductive layer on γ phase titanium aluminide.

Influence of the structural and surface characteristics of activated carbon on the catalytic decomposition of hydrogen iodide in the sulfur–iodine cycle for hydrogen production

Coal-based activated carbon (AC-COAL) catalysts subjected to acid treatment were tested to evaluate their performance on hydrogen-iodide (HI) decomposition for hydrogen production in sulfur-iodine (SI or IS) cycle. The effects of acid treatment on catalysts and the relations between sample properties and catalytic activities were discussed. The AC-COAL obtained by non-oxidative acid treatments had the best catalytic activity. However, the catalytic activity of AC-COAL decreased after the treatment of nitric acid. Higher surface area, higher carbon contents, lower ash contents and fewer surface oxidation groups contributed to the catalytic activity of ACs. HI decomposition on the AC surface itself may be due to high densities of unpaired electrons associated with structural defects and edge plane sites with similar structural ordering. Moreover, the oxygen-containing groups reduced the electron transfer capability associated with the basal plane sites.

Polyimide as a versatile enabling material for microsystems fabrication: surface micromachining and electrodeposited nanowires integration

The interest of using polyimide as a sacrificial and anchoring layer is demonstrated for post-processing surface micromachining and for the incorporation of metallic nanowires into microsystems. In addition to properties like a high planarization factor, a good resistance to most non-oxidizing acids and bases, and CMOS compatibility, polyimide can also be used as a mold for nanostructures after ion track-etching. Moreover, specific polyimide grades, such as PI-2611 from HD Microsystems™, involve a thermal expansion coefficient similar to silicon and low internal stress. The process developed in this study permits higher gaps compared to the state-of-the-art, limits stiction problems with the substrate and is adapted to various top-layer materials. Most metals, semiconductors or ceramics will not be affected by the oxygen plasma required for polyimide etching. Released structures with vertical gaps from one to several tens of μm have been obtained, possibly using multiple layers of polyimide. Furthermore, patterned freestanding nanowires have been synthesized with diameters from 20 to 60 nm and up to 3 μm in length. These results have been applied to the fabrication of two specific devices: a generic nanomechanical testing lab-on-chip platform and a miniaturized ionization sensor.