Chromic Acid Research Articles

Enhanced tensile ductility and sustainability of high-strength strain-hardening cementitious composites using waste cement kiln dust and oxidized polyethylene fibers

To improve the tensile performance and sustainability of high-strength strain-hardening cementitious composites (SHCC), waste cement kiln dust (CKD) was used, replacing 30% of ordinary Portland cement (PC), and polyethylene (PE) fibers were modified through chromic acid and plasma treatments. The chemical structure and morphology of the PE fiber surface were modified by exposure to chromic acid and plasma treatment with two gas types, argon (Ar) and oxygen (O2), at various power levels and frequencies. The effect of surface treatment method on enhancing the tensile performance of SHCC was investigated. The surface oxidation and increased roughness of the fibers were verified through X-ray photoelectron spectroscopy and atomic force microscopy analyses. The oxygen/carbon atomic ratio and surface roughness of the PE fibers increased by up to 5.3 and 2.4 times, respectively, by the O2 gas plasma treatment. With 30% of PC replaced by CKD, 12% higher energy absorption capacity prior to tension softening could be obtained. The tensile ductility and energy absorption capacity of SHCC were significantly enhanced by using PE fibers treated with chromic acid for 10 min, approximately 145% and 64%, respectively, although its tensile strength decreased. The Ar-gas plasma effectively improved the compressive strength and tensile performance of the SHCC relative to the O2-gas plasma given an identical power level and frequency. The SHCC containing O2-plasma-treated fibers under 300 W and 40 kHz exhibited the best tensile performance and absorbed the highest energy of 310 kJ/m3, approximately two to five times greater than those of ordinary SHCC materials.

Effects of Anodizing Conditions on Thermal Properties of Al 20XX Alloys for Aircraft

Anodizing was applied to improve the heat dissipation performance of aluminum (Al) alloys, by forming an oxide layer, such that they could be employed in aerospace applications. The methods employed were hard sulfuric acid (high hardness), soft sulfuric acid (low hardness), boric-sulfuric mixed acid, tin-sulfuric mixed acid, and chromic acid solutions. Each process was completed under optimized conditions. The surface morphology was observed using field emission scanning electron microscopy (FE-SEM) and a digital camera. For the determination of thermal performance, Fourier transform infrared spectroscopy (FT-IR) was used to measure the emissivity at 50 °C, and laser flash analysis (LFA) was utilized to analyze the thermal diffusivity at room temperature to 300 °C. The radiative property of metals is often ignored because of their low emissivity, however, in this research, the emissivity of the metal oxides was found to be higher than that of bare metal series. This study improved the heat dissipation properties by oxidization of Al via the anodizing process.

Is Urinary Chromium Specific to Hexavalent Chromium Exposure in the Presence of Co-exposure to Other Chromium Compounds? A Biomonitoring Study in the Electroplating Industry.

Electroplating processes are widely used in metal industries to improve the resistance properties of manufactured metal parts. Workers in this industry are potentially exposed both to hexavalent chromium (Cr(VI)) and to other chromium compounds [mostly trivalent chromium (Cr(III))], due to the use of chromic acid baths. The goal of this study was to validate urinary chromium as a Cr(VI) exposure biomarker in the presence of exposure to other chromium compounds. A biomonitoring study consisted in monitoring airborne chromium exposure and urinary chromium for one working week in 93 workers from nine electroplating companies. Chromium concentrations were measured in all urinations of each volunteer for the working week. Individual airborne soluble and insoluble Cr(VI) as well as Cr(III) concentrations were measured for all of the shifts of the week. The main statistical analysis consisted in modelling, in a Bayesian framework, the pre- and post-shift urinary chromium as a function of airborne Cr(III) and airborne Cr(VI), taking into account the day of the week and the time of collection of the urines (pre- or post-shift). Preliminary descriptions showed an increase in pre-shift urinary chromium during the working week. The model showed an increase in urinary chromium over the shift related to the shift-specific airborne Cr(VI) concentration as well as an increasing trend over the week and a relationship with the mean weekly Cr(VI) thought to reflect chronic exposure. Taking into account the Cr(VI) exposure, there was no evidence of an effect of Cr(III) exposure on urinary chromium. A biological limit value (BLV) was derived from the French occupational exposure limit for Cr(VI) of 1 µg m-3 and was estimated at between 1.9 and 2.6 µg g-1 creatinine for a urinary sample collected at the end of the shift on the last working day of the week. In the present context of mixed exposure to Cr(III) and Cr(VI) in electroplating, this study showed that urinary chromium depended only on airborne Cr(VI) concentrations, which justifies using a BLV for assessing workers' exposure. The estimated BLV was close to the recommended French BLV, which is 1.8 µg g-1 creatinine, in the electroplating industry.

A new perspective on pore growth in anodic alumina films

In this study, we use advanced analysis techniques to examine the nanostructures of anodic films formed on aluminum in various electrolytes, including oxalic acid and sulfuric acid, in the original state (without being chemically dissolved) and reveal that pores grow with radially branched nanopores. Nanopores are generated in the main pores for the same reason that initial small pores are generated on the film surface: nanopores are created when the electric field is reduced due to the presence of a thick barrier layer. These radially branched nanopores appear in a form characteristic of a film formed in chromic acid, producing a feather-like pore wall. As a representative model, the atypical porous structures created in the film formed in chromic acid were classified into five categories: initial small pores, branched pores, side holes, spherical voids, and radially branched nanopores. We demonstrate that these structures are not unique to chromic acid films but are a universal phenomenon, particularly radial nanobranching, which occurs naturally during the anodizing of most electrolytes.

Stock and stability of organic carbon in soils under major agro-ecological zones and cropping systems of sub-tropical India

We evaluated long-term impact of agro-ecological zones and cropping systems on stock and stability of organic C in soils along depth. Sixty geo-referenced soil samples were collected from Terai (TZ) and New Alluvial (NAZ) agro-ecological zones of Wet Bengal. In each zone, soil samples were drawn at 0−0.3, 0.3−0.6 and 0.6−0.9 m depth from rice-potato-jute (R-P-J), rice-vegetables-vegetables (R-V-V), vegetables-vegetables-vegetables (V-V-V) and rice-rice (R-R) cropping systems. Total organic C (TOC) in soils and its pools viz., easily oxidizable Walkley and Black C (CWB), very labile (CVL), labile (CL), less labile (CLL), non-labile (CNL), active (CAP), and passive (CPP) were measured separating on the basis of ease of oxidation with chromic acid for computing different indices of soil organic C (SOC). Among the cropping systems, on average, rice-based systems had higher TOC and CNL than non-rice (V-V-V) one, particularly in NAZ; while non-rice system had a higher per cent allocation of SOC in CVL. Again, a greater per cent of SOC occurred in CPP and CAP under rice-based and non-rice systems, respectively. Anaerobiosis thus facilitated formation of a higher proportion of SOC in recalcitrant pools. Stratification ratios of organic C were higher for soils under NAZ than those under TZ, and also for soils under rice-based systems than those under non-rice one indicating a better soil quality in the former than the latter zone and systems. This was again corroborated with higher values of carbon management index for NAZ than TZ and R-R than V-V-V systems. Further, the recalcitrant indices (RIs) of SOC were higher for soils of TZ than those of NAZ, contrary to the values of lability index (LI). Among the cropping systems, V-V-V had the highest LI values followed by R-V-V > R-P-J = R-R. Along depth, the values of RIs increased, but LI decreased. There was thus an overriding influence of rice and its ecology on the stock and stability of SOC masking the influence of its companion crops in rice-based systems. Therefore, rice-based systems, grown by default in many regions, had a better C economy in soils of this sub-tropical part of the world.

Preparation of Biocomposite Material with Superhydrophobic Surface by Reinforcing Waste Polypropylene with Sisal (Agave sisalana) Fibers

Nowadays, eco-friendly, renewable, and biodegradable biocomposites are among the most intensely sought materials of choice. Biocomposites have been widely used as substitutes for plastics due to their biodegradability. However, biocomposite materials absorb water and ultimately loss mechanical properties that affect service life. In this work, a biocomposite material with superhydrophobic surface was prepared by reinforcing waste polypropylene with sisal (Agave sisalana) fibers. The biocomposite was prepared by mixing waste polypropylene and sisal fiber with 5%, 10%, 15%, and 20% fiber loading. Based on characterization results, the composite with 15% fiber content is considered as optimum ratio. Physicochemical properties of composites were evaluated using standard American Society of Testing Materials including biodegradability test and chemical resistance test. The biodegradability of the composite before surface modification was determined by calculating weight loss and found to be 0.11%, 4.62%, 7.15%, and 10.97% for 0%, 5%, 10%, and 15% fiber loadings, and their tensile strength was 10.25 ± 0.05 , 14.47 ± 0.02 , 14.48 ± 0.02 , and 19.90 ± 0.09 MPa for 0%, 5%, 10%, and 15% fiber content, respectively. The surface of the composite was modified for hydrophobicity by etching the surface with chromic acid followed by treating with stearic acid. The FTIR and the SEM images of unmodified and modified (superhydrophobic) surface of composites clearly state the significant difference in chemical composition and surface structure, respectively. The superhydrophobicity of the surface-modified biocomposite was defined by its self-cleaning and low wet ability properties.

Determination of the activation parameters [∆H#] and [∆S#] via a kinetic study of substituted secondary alcohols oxidation by using polymer supported chromic acid in the presence of 1,4 dioxane as a promoter

Determination of the activation parameters [∆H#] and [∆S#] via a kinetic study of substituted secondary alcohols oxidation by using polymer supported chromic acid in the presence of 1,4 dioxane as a promoter

Highly ductile ultra-rapid-hardening mortar containing oxidized polyethylene fibers

This study aims to develop a strain-hardening ultra-rapid-hardening mortar (URHM). A mixture of calcium sulfoaluminate (CSA) cement, ordinary Portland cement (OPC), and gypsum was used to prepare the ultra-rapid hardening cement along with 2% (by volume) polyethylene (PE) fibers. The PE fibers were oxidized by plasma and chromic acid treatments to achieve a robust strain-hardening characteristic. Test results indicated that the tensile strain-hardening behavior of the URHM was achieved in only 4 h of air-drying curing and further improved through surface treatments. The compressive strength of the URHM with untreated PE fibers at 4 h and 28 d of air-drying curing was found to be 37.9 and 60.0 MPa, respectively, and it was slightly enhanced by using the treated PE fibers. Tensile strength and energy absorption capacity of about 5.1 MPa and 124.8 kJ/m3, respectively, were achieved for the URHM at an early age (4 h) using the plasma-treated PE fibers. The tensile performance of the URHM improved with the increase in the air-drying curing age and by using oxidized PE fibers. It was identified that the plasma treatments were more effective than the chromic acid treatment. Finally, the highest tensile strength and energy absorption capacity of approximately 9.95 MPa and 381.1 kJ/m3 were observed in the URHM containing oxygen-gas-treated PE fibers after 28 d of curing.

Local sclerotherapy with lauromacrogol versus chemical cautery with chromic acid in treatment of idiopathic recurrent anterior epistaxis

Introduction: Epistaxis is a very common medical problem affecting up to 60% of population at a point of their life. The classic lines of treatment of significant epistaxis include, vessel compression by packing or similar maneuvers, cauterization using various types of chemicals or heat and ligation or embolization of the bleeding vessel(s). Lauromacrogol is a relatively new compound that has been recently used as a sclerosing material in some vessel-related diseases like varicose veins and Hereditary Hemorrhagic Telengectasia. Objectives: This study compared the efficacy of local sclerotherapy with Lauromacrogol and chemical cautery with chromic acid as treatments for recurrent idiopathic anterior epistaxis in adults. Patients and Methods: Patients were grouped into 2 groups. In group A Lauromacrogol was injected in the submucosa. In group B Chromic acid was applied locally to the surface over the bleeding vessel(s). The primary outcome measure was bleeding control / recurrence during 3-months follow up. Secondary outcome measures were morbidity or complications and cost of both materials. Results: The overall epistaxis control was significantly higher in group A (Lauromacrogol group) than in group B (Chromic acid group). Less morbidity was also reported in group A. Lauromacrogol was relatively more expensive. Conclusion: Local sclerotherapy with Lauromacrogol is an effective mean for controlling recurrent idiopathic anterior epistaxis in adults. Better bleeding control with less morbidity were reported during 3-months follow up than Chromic acid cautery.

Development and certification of chromic acid-free anodizing process for aircraft grade aluminium alloys

Chromic acid (Cr 6+ ) anodization process is widely used for the corrosion protection of aircraft aluminium alloys. Hexavalent chromium being toxic in nature need to be phased out by eco-friendly alternatives. In the present study modified tartaric-sulphuric acid (TSA) process has been developed followed by sealing in permanganate based bath to obtain 4 to 6 µm thick anodic oxide layer on 2024-T3, 6061-T6 and 7075-T6 aluminium alloys. The process was carried out using a pilot scale anodizing plant. The anodized specimens were characterized for visual observation, thickness, adhesion, electrical breakdown voltage, corrosion resistance and tensile behaviour. All the tests were carried out as per MIL-A-8625F specifications. The specimens were also subjected for about 800 hrs to real time corrosion testing, 200 metres away from sea shore at Mandapam Camp, Rameshwaram, India. The performance of the permanganate sealed TSA anodized aluminium alloys are comparable with that of the conventional chromic acid anodized coatings. This chromic acid-free anodization process has been qualified to airworthiness regulating standards by Indian military certification authorities. Efforts are in progress to commercialize this technology for use on aero platforms.

Новые данные по вооружению терракотовой армии (технологический аспект)

This article presents the results of studying protection methods against corrosion in bronze weapons which were found in the Mausoleum of Qin Shihuangdi. Even during the first season of excavations, well-preserved weapons with traces of chromium on the surface were discovered. Based on these findings, it was suggested that the Qin artisans knew the chromium plating process, when protective film was applied by immersing a bronze item in a container with solution of chromic acid salts. However, this technology is very complicated; it was fully mastered only in the early 20th century. Moreover, less than a dozen weapons were presented as examples of such a technology already in the Qin period (late 2nd century BC), which is not enough for such large-scale conclusions. Therefore, nowadays, an international team of scholars led by M. Martinon-Torres attempted to find a solution to this problem. As a result of their multidisciplinary studies, it has been established that traces of chromium on the surface of weapons are not directly associated with its good preservation. Particles of this metal were contained in lacquered fittings (scabbard, overlays on the handle, etc.), from where they penetrated into the composition of bronze. In the composition of lacquer, chromium ions appeared from treatment with chrome alum, well known to the Qin leatherworkers who could also use it for accelerating polymerization of lacquer tree sap. As far as really good preservation of bronze weapons found in the excavations is concerned, it was explained primarily by specific features of soil in the Mausoleum area (low acidity, fine dispersion, small amount of organic matter, etc.).

Catalytic C–H Oxidation Enhances Polyethylene Bonding

Selectively adding functionality to commodity plastics is an abiding challenge in polymer science. In this issue of Chem, Hartwig and co-workers describe a selective, catalytic oxidation of polyethylene C–H bonds by using high-valent ruthenium-oxo species. The transformation increases polyethylene’s adhesive properties without significantly modifying its thermal stability or mechanical strength.

In Ukrainian

Development of methods for controlling the change in the functional cover and the energy composition of the surface of detonation synthesis diamond nanopowders is necessary to create stable suspensions and materials from them. The aim of this work is to study changes in the electrokinetic and electrophysical characteristics of the powder as a result of the modification of detonation synthesis diamond nanopowders using a liquid-phase thermochemical treatment. Diamond nanopowders of grades ASUD-75 - ASUD-99 with different sp2-hybridization carbon content, manufactured at the V.I. Bakul National Academy of Sciences of Ukraine from the product of detonation synthesis of diamond from the company "ALIT" (Zhytomyr) investigated. Diamond nanopowders of ASUD-90 grade after their modification by means of liquid-phase thermochemical treatment using: a melt of alkalis, a mixture of nitric and sulfuric acids, a mixture of chromic and sulfuric acids were investigated by electrophoresis using a device "Dzeta-potential-analizer" company "Mikromeritiks". Electrokinetic characteristics of diamond nanopowders: the magnitude and sign of the electrokinetic potential, electrophoretic mobility are determined. The methods were used to study the physicochemical characteristics of nanopowders: electrical resistivity, carbon content of sp2-hybridization, mass fraction of impurities in the form of an incombustible residue, and specific surface area. In this work, it was established by electrophoresis that the value of the electrokinetic potential and electrophoretic mobility of the powder decrease by 2-10 times with a decrease in the mass fraction of sp2-hybridization carbon from 23.6 to 0 wt%. Using the ASUD-90 nanopowder as an example, it is shown that the modification of the nanopowder by the liquid-phase method using thermochemical treatment with mixtures of oxidants leads to a decrease in the values ​​of electrophoretic mobility by 1.1-7.5 times and electrokinetic potential by 1.1-7.3 times. It was found by dielectric measurement that the tangent of the dielectric loss angle of diamond nanopowders of grades ASUD-90 - ASUD-99 is in the range 0.3046 - 0.3146. Modification of the ASUD-90 grade nanopowder using a liquid-phase thermochemical treatment leads to a change in the interval of the dielectric loss tangent, namely 0.2450-0.3249. According to the degree of increase in the ratio of the dielectric loss tangent from 0% humidity to 100% humidity, the methods for modifying nanopowders can be arranged as follows: modifying using a melt of alkalis (ASUD-90-1 sample, S = 12.8%) <mixture of chromic and sulfuric acids (sample ASUD-90-3, S = 13.8%) <mixture of nitric and sulfuric acids (sample ASUD-90-2, S = 20.8 %).

ESTIMATION OF SOIL ORGANIC CARBON PERCENTAGE IN ORGANIC FARMING SOIL SAMPLES OF TANUKU REGION, ANDHRAPRADESH, INDIA BY WALKLEY-BLACK CHROMIC ACID WET OXIDATION METHOD

The Estimation of Soil Organic Carbon (SOC) Percentage is done in Organic farming Soil samples from various places in Tanuku Region, Andhra Pradesh, India. It provides all the necessary information about, effect of Organic farming on the concentration of soil organic carbon and also assess the amount of organic matter in soil. The result depends on the quality of soil. The Soil samples were collected systematically from organic farming lands, Sieved the soil samples through 2mm sieves. The determination of SOC is based on the Walkley-Black Chromic acid Wet oxidatiom method. The method measures the amount of carbon in plant and animal remains, including soil humus but not charcoal or coal

Selective, Catalytic Oxidations of C–H Bonds in Polyethylenes Produce Functional Materials with Enhanced Adhesion

Summary The synthesis of functional and processable polyethylenes from simple vinyl monomers with controlled molecular weights and architectures has been a grand challenge of polymer chemistry. Post-polymerization modification of the homopolymers of ethylene is attractive for this purpose but has been hampered by the lack of efficient methods for the selective functionalization of C–H bonds in polyolefins. We report the selective, catalytic oxidation of C–H bonds in commodity polyethylenes with varying molecular weights and architectures. Remarkably, the functionalized materials, even at low levels of functionalization, exhibit physical properties that are absent in unmodified polyolefins, such as strong adhesion and the ability to be painted with common waterborne latex paint. Such observations indicate that selectively modified polyethylenes as described here may help to transform existing commodity plastics into more valuable and potentially more sustainable materials.

Influence of Organic Manures on Soil Physical Properties, Organic Carbon and Crop Yield in Okra-Dhaincha-broccoli Cropping Sequence

A study was conducted at Organic Farming Research Centre of SKUAST -Jammu during 2016 to 2017 to find out the impact of organic manures on soil organic carbon, physical and crop growth parameters Okra-Dhaincha-Broccoli cropping sequence. The Soil Organic Carbon was analyzed by Chromic acid wet digestion method. However, in soil physical properties Bulk density was analyzed by Core method, water holding capacity by Keen Rackzowski Method and Infiltration rate by Double Ring Method. In the experiment, soil organic carbon was found non-significant in experiment. Bulk density was found to be significant in year 2016 and 2017 as very captivating change was observed as compared to control; T8 as the lowest value treatment with value 1.26 g cm-3 was recorded. Water holding capacity was found to be significant in year 2016 and 2017 as very positive change was observed as compared to control as WHC with highest value 43.68% was noted in T8 in 2017. Infiltration rate was also found to be significant in year 2016-17 as very positive change was observed as compared to control. Significant improvement in root volume, root length was observed in Okra and same was noted in size of curd in broccoli as compared to control. The significant impact of organic manures on soil quality parameters will provide a new way to improve the soil health and productivity in a sustainable way.

(Keynote) Actual Pore Morphology of Anodic Alumina Films: Straight or Branching?

Anodic oxide film on aluminum has attracted attention as a starting structure for nanomaterials because of its nano-sized straight tube shape. In this case, a straight pore of the films formed in oxalic acid electrolyte or sulfuric acid electrolyte is generally used. On the other hand, a film with a branched pore structure, like a chromic acid film, is used for practical aluminum materials such as aircraft alloy containing silicon and copper. This is because the branching action of the pores has the effect of suppressing the inhibition of uniform film growth due to the non-uniform base composition of the alloy material. Although the branched structure of the chromic acid film is considered to be unique as anodic film, it has been revealed that when the solubility of the electrolyte is low, the pore branching often appears accompanied by minute dielectric breakdown [1, 2].Recently, however, the authors found that by performing detailed TEM observation of the pore wall of anodic films, considerable branching of the pores occurred even when electrolysis was performed at 40 V in oxalic acid electrolyte, which is the self-ordering condition. The branching of the pores stops at the early stage of the process and remains as traces in the pore walls as radial fine pores. When the subsequent anodic oxidation continues, these radial micropores disappear due to chemical dissolution reaction of the oxide to the electrolyte. In this study, the actual morphology and controlling factors of pore branching in not only chromic acid electrolyte, but also of pore branching found in films formed by other typical anodizing electrolytes such as sulfuric acid, oxalic acid and phosphoric acid will be reported.[1] S. Ono, S. Chiaki, T. Sato, J. Surf. Finish. Soc. Jpn, 26, 456 (1975) DOI:10.4139/sfj1950.26.456[2] S. Ono, T. Kawaguchi, H. Ichinose, Y. Ishida, N. Masuko, J. Surf. Finish. Soc. Jpn, 40, 1361 (1989) DOI:10.4139/sfj.40.1361

A Review on Anodizing of Aerospace Aluminum Alloys for Corrosion Protection

Aluminum alloys used for aerospace applications provide good strength to weight ratio at a reasonable cost but exhibit only limited corrosion resistance. Therefore, a durable and effective corrosion protection system is required to fulfil structural integrity. Typically, an aerospace corrosion protection system consists of a multi-layered scheme employing an anodic oxide with good barrier properties and a porous surface, a corrosion inhibited organic primer, and an organic topcoat. The present review covers published research on the anodic oxide protection layer principles and requirements for aerospace application, the effect of the anodizing process parameters, as well as the importance of process steps taking place before and after anodizing. Moreover, the challenges of chromic acid anodizing (CAA) substitution are discussed and tartaric-sulfuric acid anodizing (TSA) is especially highlighted among the environmentally friendly alternatives.

Influence of impregnation conditions on the activity of CrOx/Al2O3 catalysts in dehydrogenation of isobutane in fixed bed reactor

The development of catalysts for dehydrogenation of light paraffin hydrocarbons in a fixed bed reactor is of great importance for the world petrochemical industry. The preparation of granules (~3 mm in diameter) of CrOx/Al2O3 catalysts is hindered by such problems as homogeneous distribution of active component and modifiers, high strength of granules, etc. In this paper, the alumina support dissolution in the impregnating solution containing chromic acid and the opportunity to apply vacuum impregnation to minimize this effect in the preparation of CrOx/Al2O3 catalysts are discussed. A series of catalysts is synthesized at different impregnation pressures (1, 0.85, and 0.7 atm), characterized by a complex of physical–chemical methods (low-temperature N2 adsorption, SEM, XRD, TPR-H2), and tested in isobutane dehydrogenation. The use of vacuum impregnation is shown to lead to the reduction of the specific surface area of the catalysts from to 91 to 56 m2/g and the growth of content of CrOx phases that decreases the catalytic activity in dehydrogenation. The isobutylene yield at 610 °C decreases from 68% to 54% for the catalyst prepared at P = 0.7 atm as compared with the one prepared at atmospheric pressure. The high activity and stability are connected with the hierarchical structure of the alumina support and homogeneous chromia distribution on its surface.

Nissl. Die Hypothese der specifischen Nervensellenfundion. (Allg. Zeitschr. f. Psychiat. Bd. 54. pg. 1—107)

It is known that Nissle managed to use alcohol for compaction and by a simple staining method to prove a special structure in the nervous cells, unknown until then, opening new horizons in the histopathology of the nervous system. The old method of condensation by means of chromic acid artificially alters the nerve lumen and therefore is not applicable to the study of the structure of cells.