Aggressive Media Research Articles

Generalized implicit solution of ITZ percolation threshold and its effect on the diffusivity of concrete: Influence of aggregate shape- and size-polydispersities

Concrete is usually assumed to be a three-phase particulate composite composed of aggregate, cement paste and interfacial transition zone (ITZ) around the aggregate. Due to the high porosity of the ITZ, the transport of aggressive media in the ITZ is more rapid than that in the cement paste. However, it is still unclear how concrete components, like ITZ thickness and aggregate shape- and size-polydispersities affect the ITZ percolation threshold. This paper develops a generalized implicit solution to establish the quantitative relationship between the ITZ percolation threshold and concrete components using an analogy between lattice and continuum percolation. The reliability of the generalized implicit solution is confirmed by comparing the theoretically calculated ITZ percolation thresholds with the numerical results in this work and other literature. The concrete diffusivity is also predicted by combining the obtained ITZ percolation threshold with the differential effective medium approximation and the multi-component percolation-based effective medium model.

Microstructure and Mechanical Behavior of Modern Universal-Chromatic and Bulk-Fill Resin-Based Composites Developed to Simplify Dental Restorative Procedures.

One of the recent trends in the development of resin-based composites (RBCs) focuses on universal coloring to avoid time-consuming color matching and RBC layering for a clinically appropriate esthetic impact. We evaluated an experimental material for posterior restorations combining universal coloring with the possibility of bulk-fill placement. Clinically established materials were analyzed as a reference, including a bulk-fill and a universal chromatic RBC. Microstructural features were described using scanning electron microscopy and related to macroscopic and microscopic mechanical behavior. Standards to be met before market launch were supplemented by fractography, Weibull analysis, and aging behavior assessment. Quasi-static and viscoelastic behavior were evaluated on a microscopic scale, incorporating a large number of parameters and increasingly aggressive immersion media. All materials complied with the standard requirements even after aging. The latter had little impact on the measured parameters, except for strength. Strength, modulus of elasticity, and hardness parameters on the one hand and damping behavior on the other were mutually exclusive. Despite considerable differences in the microstructure and type of filler, an increased filler amount remained critical for better mechanical properties. The lower proportion of inorganic fillers was directly transferred to the elastic modulus values, which, in turn, restricts the experimental material in its clinical applications to smaller occlusal fillings.

A study on resistance of asphalt concrete exposed to the effect of mycelial fungi

Introduction. In recent years, the issue of improving the quality and service life of road surfaces has been relevant in Russian and worldwide. The main reasons for the early destruction of road surfaces is the quality of individual components and the imperfect composition of asphalt concrete that has pre-set durability. The results of studies, characterizing changes in the roadway surface properties, are of practical value. In this case, we consider the surface hardness of asphalt concrete specimens of various types, subjected to microbiological destruction, which is the property to be studied. The purpose of the work is to study the microbiological resistance of various asphalt concretes, to select and substantiate methods for assessing the biological stability of asphalt concrete subjected to mycelial fungi.
 
 Materials and methods. Asphalt concrete specimens contain BND 60/90 bitumen that has the following characteristics: needle penetration depth 0.1 mm at 25 °С – 85; needle penetration depth 0.1 mm at 0 °С — 35; ring and ball softening point 0 °С — 48; extensibility — 83 cm; penetration index — 0.6. Mineral powder, glass cullet powder, and food flour are used as fillers. MP-1 inactivated mineral filler, made of carbonate rock, having the true and average density of 2.71 and 1.71 g/cm3, respectively, was also used. Glass powder was obtained by grinding the waste glass of JSC “Lisma”, Saransk. The chemical composition of glass waste is (in percent for weight): SiO2 — 68.75–72.90; Na2O — 11.9–16.7; K2O — 1.2–3.8; CaO — 5.0–6.0; BaO — 2.2–5.5; MgO — 3.2–3.8; Fe2SO4 — 0.1–0.12; Al2O3 — 1.0–1.5. Food flour was considered as an additive that serves as the nutritional medium for mycelial fungi. Some other components, added to the studied specimens of asphalt concrete, are discussed in the work. The studied property, or hardness, was identified using the Hoppler consistometer. Testing results are provided in the paper. Linear interpolation of experimental data was conducted to identify hardness at the intermediate points to rank the tested asphalt concrete, the standard error between the hardness curve during the exposure and the straight line for the same exposure points. The results of the proposed method are explained graphically using the experimental data. It is assumed that the smaller the root-mean-square error, the more resistant the corresponding composition of asphalt concrete to the effect of mycelial fungi.
 
 Results. As a result of the studies and the application of the proposed hardness control methods, the best compositions were identified in terms of resistance to the effects of mycelial fungi. Each group of specimens and compositions of asphalt concrete under study was broken down by their resistance to the effects of the external environment, or mycelial fungi.
 
 Conclusions. The results of this research project enable the authors to evaluate the quality of asphalt concrete compositions exposed to the biological environment. The proposed approach to assessing the quality of asphalt concrete compositions can be applied to other building materials and products subjected to certain aggressive media.

Antimicrobial properties dependence on the composition and architecture of copper-alumina coatings prepared by plasma electrolytic oxidation (PEO)

This study presents environmentally friendly and low-cost synthetic routes to produce antimicrobial coatings over 5052 Al alloy based on plasma electrolytic oxidation (PEO) technology. Two methodologies were explored: the decoration with copper and anodic doping with copper ions. The porous oxide layers produced in silicate media presented two porous layers consisting of γ-Al2O3 crystalline phase and amorphous phases of aluminosilicate, silica, and Al(OH)3. Small amounts of copper (<0.3 at.%) were detected in the PEO films. In the Cu-decorated film, copper clusters composed of Cu0 and Cu2+ species were observed visually as small black dots on the surface. In the Cu-doped film, the Cu2+ and Cu+ species were homogeneously distributed on the surface. The copper content affected the corrosion performance in aggressive corrosive media. The PEO coatings showed a remarkable antimicrobial activity after 24 h in standard tests. The antimicrobial effectiveness of the Cu-decorated sample was higher against S. aureus, while the Cu-doped sample was more effective against E. coli. The results demonstrated that differences in the PEO coating architecture can affect the material composition and, consequently, the bacterial inactivation mechanism. These findings can serve as a guide to tailor aluminum alloys for specific antimicrobial surfaces.

AGNETRON SPUTTERING OF PROTECTIVE COATINGS ON PARTS OF SURFACES OF PRODUCTS AND TOOLS USING MULTIELEMENT TARGETS MANUFACTURED USING A NEW TECHNOLOGY

Recently, the use of magnetron sputtering for the deposition of protective coatings has been intensively developed. The great prospect of using this method is due to the possibility ofapplying high-entropy coatings, which are used to protect surfaces that are simultaneously exposed to elevated temperatures, aggressive media and various types of wear. However, the use of the method of creating high-entropy coatings greatly hinders the absence in many cases of the required alloys, which have not only a certain qualitative elemental composition, but also a quantitative one. We managed to solve this problem by creating multi-element targets, with the help of which it becomes possible to create not only almost any elemental composition, but also to regulate the quantitative composition of elements. In this paper, we have proposed a method for manufacturing new types of targets for magnetron sputtering, with a detailed description of the technological chain of their manufacture. The novelty lies in the possibility of applying multi-element coatings when using one target. This is due to the fact that the number of different elements in the target can be measured in tens. The paper also presents the obtained positive result of using a target, which included five different metals, during magnetron sputtering.

The Significant Effect of Mechanical Treatment on Ceramic Coating for Biomedical Application

Titanium and its alloys are commonly preferred materials used for biomedical implants. However, these alloys have issues related to corrosion resistance as a result of the aggressive attack of human body fluids. Several researchers have attempted to produce a ceramic coating via physical vapour deposition (PVD). A PVD layer consists of pores, pinholes, and columnar growth that attack the substrate as an aggressive medium. The aim of this research is to evaluate the influence of ultrasonic vibration parameters on a TiN-coated biomedical Ti-13Zr-13Nb alloy. This study used TiN to formulate and coat disk-type samples in a fixed condition. Ultrasonic vibration at fixed frequencies was applied to TiN-coated samples for three sets of exposure times. The findings revealed that all TiN-coated samples exposed to ultrasonic vibration had improved corrosion resistance compared to untreated samples. Field emission scanning electron microscopy (FESEM) was employed to analyse sample’s microstructures. The top parameter (16 kHz and 11 min) yielded the most compact coating. Ultrasonic vibration’s hammering effect decreased the size of microchannels in the lining and reduced the rate of corrosion attack. The nanoindentation test showed that coated ultrasonic treated samples had a higher hardness/elasticity (H/E) ratio than untreated samples.

Failure Risk Assessment of Coal Gasifier Based on the Integration of Bayesian Network and Trapezoidal Intuitionistic Fuzzy Number-Based Similarity Aggregation Method (TpIFN-SAM)

The coal gasifier is the core unit of the coal gasification system. Due to its exposure to high temperatures, high pressures, and aggressive media, it is highly susceptible to serious accidents in the event of failure. Therefore, it is important for the gasifier to perform failure-risk assessment to understand its safety status and provide safety measures. Bayesian networks (BNs) for risk analysis of process systems has received a lot of attention due to its powerful inference capability and its ability to reflect complex relationships between risk factors. However, the acquisition of basic probability data in a Bayesian network is always a great challenge. In this study, an improved Bayesian network integrated with a trapezoidal intuitionistic fuzzy number-based similarity aggregation method (TpIFN-SAM) is proposed for the failure-risk assessment of process systems. This approach used the TpIFN-SAM to collect and aggregate experts’ opinions for obtaining the prior probabilities of the root events in the BN. In the TpIFN-SAM, the intuitionistic fuzzy analytic-hierarchy-process method (IF-AHP) was adopted to assign the expert weights for reducing subjectivity or the bias caused by individual differences. To clarify the suitability of the proposed method, a case study of a coal gasifier was demonstrated, and both prediction and diagnosis analyses of the BN were performed; finally, the weak links of the gasifier were identified.

Influence of Sulphuric Acid on the Compressive Strength of Ternary Blended Geopolymer Mortar

The deteriorating effect of acid media on cement based constructions has become a worrying problem all over the world. These media generally occur as solutions in various branches of the industry, acid rains and mists, and acid ground-waters. A very popular form of acid attack on concrete that is usually referred to as biogenic sulphuric acid attack also occurs in both industrial and urban sewer systems. The emergence of new cementitious materials, like geopolymer cements, during the past decades necessitates detailed experimental work and research activities to investigate their durability in aggressive acid environments. The study therefore explored the development of alkali-activated CPA-SHA-MK ternary blended geopolymer mortar (GPM) using sodium silicate (Na2Si3) and sodium hydroxide (NAOH) solutions with 9M constant concentration as alkaline activators under both the aggressive and ambient-temperature curing media. The mass ratio of sodium silicate to sodium hydroxide (NS: NH) and as well as the binder to fine aggregate were fixed at 2.5 and 0.8 respectively. The durability of the ternary blended geopolymer mortar was examined through acid resistance test using 50 mm cubes after 28, 56 and 90 days of curing. The results revealed that the setting time prolonged as the replacement levels of RHA-MK increased at a decrease in the replacement levels of CPA. The results also showed that both the PCM and GPM samples studied suffered mass and strength losses in the acid solution and the loss increases at an increase in the hydration periods. The strength losses were observed to be higher in PCM mix (12.19 N/mm2 at 90 days) as compared to the GPMs (6.67 N/mm2 at 90 days) while the mix incorporated 50% CPA, 33% MK and 17% RHA (C50M33R17) was observed to be better compared to other mixes in durability behaviour. The study therefore recommends C50M33R17 mix proportion for good durability performance.

Bond performance of basalt FRP bar against aggressive environment in high-strength concrete with varying bar diameter and bond length

• Bond Performance of Basalt FRP Bars with high strength concrete is investigated. • The bond strength of FRP bars was found to be higher than that of steel bars. • FRP bars provide a cost-effective solution for corrosion mitigation of steel reinforcement bars in RC structures. • Higher Bond Strength retention was observed in alkaline environment in comparison to sea water. Concrete is a porous material and prone to attacks by aggressive media such as sulphates, carbonates, and alkali-silica reactions. These aggressive media penetrate the reinforced concrete members and not only damage the concrete but also the steel reinforcement. It has been observed that the bond between the ordinary steel rebars and concrete degrades significantly over time besides reducing the mechanical properties of the rebar. As a result, the service life of concrete structures reduces significantly and adversely impacts their overall structural behavior, hence, raising safety issues that are expensive to repair. Recently, Basalt Fiber Reinforced Polymer (BFRP) bars are found to be an emerging solution that could alleviate the issue of steel reinforcement corrosion in aggressive environments. This research comprises a detailed investigation of bond strength reduction between concrete and BFRP bars through pull-out testing. Since FRP rebar’s bond behavior is expected to differ from that of steel, therefore, to evaluate the bond performance of BFRP bars, the concrete specimens reinforced with BFRP bars having varying parameters, i.e., different bar diameters and development lengths, were exposed to the alkaline solution and sea water for three months. The results showed that both aggressive media triggered the bond strength reduction between the concrete and BFRP bars, however, a slightly higher bond strength retention was observed in comparison to steel rebars, i.e., 86% and 82% of bond strength retention was observed in the case of alkaline and seawater exposure, for three months respectively. The future bond strength retention for BFRP bars was lastly evaluated using the Fib bulletin model.

Mechanical and chemical analysis of structural silicone adhesives with the influence of artificial aging

Structural sealant glazing systems, or bonded glazing, refers to façades in which the glass is structurally bonded to a façade frame and which is typically used in large façades for office buildings. The structural silicone bond lines are an essential element of such façades and a variety of environmental influences and aggressive media interact with the adhesive and may affect its performance. The ETAG 002 is commonly used for the verification of the technical applicability taking these effects into account. In this study, samples of an approved standard silicone adhesive and a high-modulus silicone adhesive are artificially aged according to ETAG 002 and exposed to a climate change test. The aim of this study is to determine the essential mechanical properties and to explain the changes due to aging by means of chemical analysis. Polymer degradations are determined by evaluating the molecular structure with Fourier-transform Infrared Spectroscopy and Thermo-Gravimetric analysis. In addition, water absorption is investigated with Karl Fischer titration. Changes in the chemical structure are particularly identified after aging in SO2 atmosphere as well as after UV exposure. Increased water contents are detected for all specimens conducted to high moisture. The mechanical properties as well as their characteristic temperature ranges are determinate by the Dynamic Mechanical Analysis and Differential Scanning Calorimetry. The results of the study show significant loss of the adhesive stiffness up to 30% after artificial aging, mainly after storage in cleaning agent and after climate change test. However, there are no significant chemical effects of both aging methods on the adhesives. On the other hand UV-radiation as well as the acid attack, interact with the polysiloxane and the filler of the adhesive. This shifts the crystallization temperature a bit but it does not influence the adhesive stiffness at room temperature. Finally, tensile tests and shear tests are performed on both reference and aged bonded glass–aluminum specimens. These test confirm the good durability of silicone adhesives and the results meet the requirements of the ETAG 002.

Effect of Solution Heat Treatment by Induction on UNS S31803 Duplex Stainless Steel Joints Welded with the Autogenous TIG Process

In the oil and gas industry, the manufacture of equipment using materials that resist aggressive media is one of the greatest challenges. UNS S31803 duplex stainless steel is widely used for this purpose owing to its good combination of mechanical and corrosion resistance. The objective of this work was to evaluate the effect of induction solution heat treatment using autogenous TIG welding on UNS S31803 DSS sheets. Sheet samples were subjected to two different treatment parameters for a duration of 10 s and at temperatures of 1050 and 1150 °C. The results obtained with the treatments were compared with those of the as-welded condition, which was the reference condition. Quantitative and qualitative analyses of the samples were carried out, in addition to microstructural characterization using confocal microscopy and a corrosion resistance study as per ASTM G48 standard. We observed that the best results were obtained with a treatment of 10 s at 1150 °C, which was able to eliminate chromium nitrides and re-establish the proper balance of the ferrite and austenite phases. In addition, the treatment was able to reduce hardness and provide welds free of cracks and discontinuities, also presenting a low corrosion rate.

ПЕРСПЕКТИВЫ ИСПОЛЬЗОВАНИЯ ПЛЕНКООБРАЗУЮЩИХ АЭРОСПЕРСНЫХ СИСТЕМ ПРИ ЗАКРЕПЛЕНИИ СТОМЫ

Abstract. The potential of spray film-forming systems for prevention and therapy of peristomal complications is highly significant. The advantages of the dosage form include creation of protective skin barrier, prolonged release of active substances of anti-inflammatory, antiseptic, regenerative spectrum of action, etc. Polymeric compositions can delay and partially prevent the aggressive media impact released by stomas via osmotic action and neutralize the allergic potential of adhesives for attachment of stoma and pouching system. A flexible and thin film can be created via controlled spraying that follows the skin texture, interrupting the irritation "vicious circle". The pH of the composition will reduce the pH of the irritated skin and related microbial contamination. Creation of such form will significantly improve stoma patients’ life quality, prevent some peristomal complications and facilitate skin care surrounding stoma, especially in difficult postoperative periods. The aim was to establish the potential of spray film-forming systems and the prospects of drug development in such a new dosage form to prevent peristomal complications as maceration, allergic dermatitis, and infection complications of mechanical injuries of bacterial and fungal nature, to determine the main properties required from the resulting film, as well as relevant active substances spectrum. In addition, two types of medications were suggested to help patients with self-diagnosis of stoma discharge on the surrounding skin and partially prevent irritation until the problem is detected.

In situ growth of Ca-Zn-P coatings on the Zn-pretreated WE43 Mg alloy to mitigate corrosion and enhance cytocompatibility

Magnesium (Mg) alloys are potential materials for orthopedic fixation devices but rapid degradation of the materials restricts wider clinical applications. Herein, zinc-incorporated calcium phosphate (Ca-Zn-P) coatings are prepared on the Zn-pretreated WE43 Mg alloy by a hydrothermal technique under relatively stable and favorable conditions. The hydrothermal coating consists of a compact bottom layer of CaZn2(PO4)2∙2 H2O and ZnO granular crystals and a jagged upper layer of CaHPO4. The Zn coating reduces the corrosion current density of WE43 to (3.49 ± 1.60) × 10−5 A cm−2, whereas the Ca-Zn-P/Zn composite coating further reduces it by 3 orders of magnitude in the simulated body fluid (SBF). The charge transfer resistances of the Zn-coated and Ca-Zn-P/Zn-coated alloys increase by 49 and 7176 times to 835 and 1.22 × 105 Ω cm2, respectively. The 7-day immersion results reveal that the Zn coating cannot provide long-term protection to WE43 in SBF because of the formation of galvanic couples between the Zn coating and WE43. In contrast, Ca-Zn-P/Zn-coated WE43 remains intact after soaking for 7 days and furthermore, the Ca-Zn-P coating self-repairs and continues to grow despite dissolution. The compact and adherent Ca-Zn-P bottom layer plays a major role in mitigating corrosion of WE43 by hindering penetration of the aggressive medium and charge transfer of the corrosion reactions resulting in only slight corrosion of the Zn layer. Biologically, the Zn coating reduces attachment and proliferation of MC3T3-E1 pre-osteoblasts on WE43, but the composite coating fosters cell adhesion and proliferation which stems from the good biocompatibility of the hydrothermal layer and relatively stable surface conditions avoiding severe corrosion.

Degradation mechanism of cement-based materials under the effects of stray current, chloride and sulfate

When infrastructure is exposed to a complicated environment containing stray current, chloride and sulfate, it may be subjected to severe degradation. In order to analyze the interaction of different factors and the degradation mechanism of cement-based materials in a complicated environment, the blended solution with four molar concentration ratios of Cl-/SO42- (0, 0.5, 1, and 2) were prepared to simulate a range of aggressive medium. Meanwhile, 40 V DC (direct current) electrical field was applied to cement-based materials to simulate stray current. After exposure, the transport properties, macro-properties, and microstructures of specimens were observed and measured. Additionally, the types and amounts of degradation products were tested to further analyze the degradation mechanism of cement-based materials. Experimental results show that chloride in the blended solution could inhibit SO42- transport into cement-based materials, causing the SO42- concentration in a specimen to decrease with the increase of Cl-/SO42- ratio. Therefore, the specimens appeared less degraded in terms of macro-properties. But the results of microstructural analysis showed that degradation products and cracks were generated in the interior of specimens. Friedel’s salt was detected in the specimens exposed to the solutions containing chloride. The formation of Friedel’s salt consumed calcium aluminate hydrate, which caused the amount of Al-phase involved in the formation of ettringite to reduce. Consequently, the amount of ettringite was reduced, and the degradation of compressive strength and appearance was also reduced. Additionally, an electrical field could induce the ion concentration in pore solution to change and even break the ion chemical equilibrium, which resulted in the decomposition of ettringite and Friedel’s salt. However, Friedel’s salt can also transform into ettringite at a specific condition. Therefore, the amounts of ettringite and Friedel’s salt in specimens were changed over the exposure time.

Monitoring and mitigating corrosion in geothermal systems

AbstractIn terms of current needs for renewable resources, geothermal energy is one of the future solutions for heat and electricity generation. However, geothermal plants are exposed to very aggressive media (high‐temperature [HT], salt‐rich fluid, etc.), leading to extensive corrosion of the metallic parts. Should the corrosion inhibitors work at HT, their injection would be mandatory to ensure the reasonable lifetime of geothermal plants. The first part of this review concerns the degradations observed in geothermal plants, which depend on the site properties and the methods for evaluating the corrosion intensity of such systems. Autoclave experiments, although rarely used for geothermal applications, maybe the most appropriate to measure the representative corrosion rate, that is, under use temperature and pressure conditions. In the second part, clues to evaluate the performance and mechanism of corrosion inhibitors are mentioned, and molecules already used to protect steel are reported. However, this review also highlights the lack of data on HT inhibitors, especially for geothermal applications, where the efficiency of a given molecule is strongly related to the real medium. Thus, the protection of new geothermal plants where HT is reached requires the search for products that are stable and efficient under such conditions.

Розробка датчика диференційного тиску для авіакосмічного застосування. Метрологічне забезпечення і вибір первинного перетворювача

The main requirements for the differential pressure sensor developed by JSC "Element" by SE "DB" Yuzhnoye" order are given. It is shown that the most important criteria when choosing a primary transducer were the requirements, firstly, to control the pressure of chemically aggressive medium – rocket fuel, and secondly, to perform measurements of relatively low differential pressure under operating overpressure (linear) pressure. The upper limit of changes in linear pressure is an order of magnitude higher than the limit of the measured differential, and it is necessary to minimize the additional error due to the effect of operating overpressure. Information search data are given, because of which the primary transducers that best meet the specified requirements are selected, namely, Keller PD-10L series sensors. A sensor developed and manufactured on the basis of the selected primary transducer is briefly described. The main attention is paid to the description of metrological support of transducer development and testing and the results of experimental studies of its characteristics in terms of long-term stability and the effect of operating overpressure on the output signal when changing the controlled differential pressure in the measurement range. The given information concerns the creation of a specialized stand for the study of this effect, equipped with an imported meter that provides control of differential pressure from zero to 16 bar under the influence of operating overpressure 150…166 bar with an error of not more than ± 0,1 %. It is explained that the need to create a stand at the enterprise is due to the lack of such equipment and measuring equipment in the Ukrainian centers of metrology and standardization. Based on the results of the analysis of requirements for the application of the developed sensor performed together with the customer, a rational way of presenting the transformation function was selected, which minimizes the measurement error in the most responsible conditions.

Insight into the anti-corrosion performance of synthesized novel nano polymeric material of SiO2 for the protection of J55 steel in 3.5 wt% NaCl solution saturated with carbon dioxide

The oil and gas industry faces a great challenge and loss due to corrosion in the sweet aggressive medium. To overcome this effect addition of corrosion inhibitors, especially eco-friendly ones, are the prime additive. The description in this paper includes the synthesis of nano-sized novel polymeric composite material of SiO2, i.e., n-SiO2/P (ANA), and its application as a sweet corrosion inhibitor (3.5 wt% NaCl saturated with CO2) for J55 steel. The characterization of synthesized n-SiO2/P (ANA) was done via spectroscopic techniques. The chemical and electrochemical methods were used to evaluate the inhibitive performance. The surface texture of both protected and corroded samples was analyzed via scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM). The results of EIS and PDP reveal the increase in Rct values with the rising amount of n-SiO2/P (ANA) and the anodic nature of n-SiO2/P (ANA) inhibiting action. The maximum inhibitive performance result is 92% at 400 mg/L. The Langmuir plot supports the best fitting experimental data. The surface study supports the n-SiO2/P (ANA) covering onto J55 steel.

Corrosion inhibitors for AA6061 and AA6061-SiC composite in aggressive media: a review

Abstract The unique features of aluminium alloy (AA6061) and its composite (AA6061-SiC composite) and their distinct advantages over aluminium metal have made them popular in many engineering applications such as automotive, aerospace, and structural components. However, aggressive media like acid, alkaline or chloride media reduces their corrosion and fatigue resistance, hence the workability of these materials. There is no evidence available in the literature about the systematic review of corrosion and inhibition of these materials in aggressive acid, alkaline and chloride media. Hence, the present review paper gains significant importance. One of the most feasible strategies for managing material corrosion is the addition of an inhibitor to an aggressive medium. A critical review of the inhibition performance of reported organic and inorganic compounds as inhibitors against the corrosion of AA6061 and AA6061-SiC composite in acid, alkaline and chloride media is summarised in this paper. A correlation between the chemical structure and inhibition of the activity of the inhibitors is discussed. The details of the types of inhibition process and the general mechanism of inhibition involved have been discussed.

Optimization of coating parameters for fabrication of robust superhydrophobic (SHP) aluminum and evaluation of corrosion performance in aggressive medium

The huge interest in superhydrophobic surfaces originates from their potential engineering applications in corrosion protection, antifouling, oil recovery, self-cleaning, anti-adhesion, anti-icing, medical dressing, drag reduction and radiative cooling. Despite the progress made in developing superhydrophobic (SHP) coatings, a key challenge is the ability to fabricate mechanically robust SHP surfaces and a proper understanding of the corrosion performance of SHP surfaces in aggressive conditions. Here, we report a simple, rapid, inexpensive, scalable and eco-friendly method for fabrication of mechanically durable superhydrophobic (SHP) aluminum surfaces with self-cleaning properties using a scalable dip-coating method. The coating parameters were optimized to obtain a robust coating with desirable properties such as water contact angle (WCA), sliding angle, self-cleaning, abrasion and corrosion resistance. To obtain good adhesion between the substrate and the coating, chemical etching and hydroxylation of the Al surface were used. At an optimal withdrawal speed of the substrate in the precursor solutions, a maximum WCA of 172.3° ± 1.1° (SA ~ 1° ± 1°) was achieved. The hierarchical micro-nano roughness and the presence of the Si-(CH3)3 group were responsible for the superhydrophobic behavior. The existence of a covalent bond between the Al surface and the middle connecting layer and –O-Si-CH3 groups on the surface of the SHP Al are confirmed by LRS and XPS, respectively. The electrochemical studies in 3.5 wt% NaCl solution show that the Rct value of SHP Al during the initial state was ~2 orders higher than that of the bare sample. The Cdl value of SHP Al was 6 orders less than that of bare after 1 h of exposure in chloride solution. On the SHP surface, a droplet with an impinging velocity of 0.36 m/s showed approximately 7 bounces. The superhydrophobicity of the SHP sample was preserved up to 150 cm abrasion distance. The hierarchical surface morphology and superhydrophobicity (WCA ~151°) were retained by the SHP samples even after 120 h of immersion in 3.5 wt% NaCl, which indicates its suitability in seawater applications such as ships, underwater instruments and pipelines and marine structures. Further, our work provides a framework to develop mechanically robust SHP coating for various applications.

Manufacturing Technology of Sliding Bearings from Ferro-Graphite Compositions

Introduction. The development of modern technology imposes increasingly stringent requirements on materials operating under conditions of high pressures, speeds, deformations and aggressive media. The use of powder metallurgy methods in the creation of new materials makes it possible to provide a rational combination of production technology, structural and performance characteristics. Powder steels used in mechanical engineering are of great interest among the materials obtained by powder metallurgy. The article explores the possibility of manufacturing porous bearings made of iron powder for fan motors of domestic air conditioners instead of porous bearings made of bronze graphite.Problem Statement. To ensure long-term operation of fan motors from metal powders, it is necessary to create porous bearings without alloying additives with the required mechanical properties. This requires a series of experimental work to determine the dependences of mechanical and technological properties on the sintering temperature, compacting pressure and the porosity of samples.Theoretical Part. As a theoretical description, the use of a mold with an additional draining gap, which provides high bearing density at low compacting pressure, is analyzed. The effect of compacting pressure on the strength of sliding bearings under mechanical deformations depending on the sintering temperature is also considered.Conclusions. It was established in the work that during the sintering of sliding bearings at a temperature of 800-1100°C, a significant charge carburization occurs due to the decomposition of zinc stearate in closed pores. As a result, a ferritepearlite structure is formed, due to which the bearings are well calibrated and have high wear resistance when paired with a steel shaft. Optimum sintering modes and compacting pressures were selected, which showed high reliability and durability of the products obtained from pure iron powder.