Key Engineering Materials Vol. 917

Abstract: The corrosion inhibition effect of Cocos nucifera (CN) surfactant inhibitor, has been inspected on 316L steel in 5 M HCl and H₂SO₄ solutions by weight loss (WL) method. The results revealed that the presence of alkanols, glycosides, steroids and terpenoids in CN surfactant supported the inhibitor by retarding corrosion effect to give an optimum inhibition efficiency of 93.71% in HCl and 89.66% in H₂SO₄ solutions after 504 h. Also, the regression values for both acidic solutions were close to unity after obeying Langmuir isotherm adsorption mechanism with 0.9971 for HCl and 0.9882 for H₂SO₄ solution. The result confirms that CN surfactant inhibitor performed better in HCl solution than in H₂SO₄ solution. Keywords: Corrosion inhibitor; active components; austenitic 316L material; weight loss method; adsorption isotherm.

Abstract: Biofouling is a severe problem in the marine environment, as all hard surfaces, including some macroorganisms, mostly get colonized by microorganisms existing in the maritime. In the past, some substances such as tributyltin and mercury have been used to combat this problem. These substances are still toxic and harmful to aquatic lives and even human beings, leading to these substances being banned globally. It is then highly important to produce anti-biofouling substances from natural products, which are sustainable, economical, environmentally friendly and applied on surfaces conveniently. The inspiration for using these natural substances came from the fact that the microorganisms, which are biofoulers, do not get attached or colonized on marine animals such as whales, dolphins and shellfishes. This review highlights some of the advances in natural and agro-based products that have been used as anti-biofouling. These natural substances are corals, fermented milk, pepper, marine biofilms, seaweeds and shellfishes.

Abstract: Arachis hypogaea (AH) and Cocos nucifera (CN) surfactant were examined as corrosion inhibitor for 316L steel in 9 M HCl solution by weight loss (WL) method. Observation from the results showed that the presence of the active components and functional groups were actually the reasons for strong adsorption performance of AH and CN inhibitors as the corrosion rate was drastically retarded with increment in percentage inhibitor concentrations. Though AH inhibitor showed better efficiency than CN inhibitor due to more active components as revealed by the phytochemical analysis test. ATF-FITR test demonstrated all the potential functional groups accountable for the excellent inhibitions of AH and CN inhibitors. Keywords: Organic compound; Corrosion rate; Active components; Functional groups. ATF-FTIR spectroscopy.

Abstract: The inhibition performance of citrus x aurantiifolia extract (CXA) on the corrosion of mild steel in 1.5 M H₂SO₄, 2 M H₂SO₄, 3 M H₂SO₄, and 4 M H₂SO₄ solutions was evaluated by weight loss, potentiodynamic polarization techniques, and scanning electron spectroscopy equipped with energy-dispersive X-ray spectroscopy. CXA inhibited the mild steel corrosion in the sulphuric acid solutionswith optimal inhibition results of 96.06% in 1.5 M H₂SO₄ and 86.57% in 4 M H₂SO₄ from weight loss measurement. Weight loss, potentiodynamic polarization, and scanning electron microscopy tests confirm the inhibitive performance of this compound and the increase in inhibitor efficiency increases with inhibitor concentration. The polarization data showed that the inhibitor acts as a mixed-type inhibitor, and fits the Langmuir adsorption isotherm. The adsorption studies clarify the excellent adsorption of this compound on the mild steel surface. The inhibited steel in the acid solution displayed improved surface morphology due to the surface protection effect of CXA molecules. The citrus x aurantiifolia studied here easily mitigates the effect of stress corrosion cracking on mild steel in a sulphuric acid environment. Keywords: Mild steel, Stress corrosion, Adsorption, Corrosion inhibitor, Sulphuric acid, Citrus X Aurantiifolia

Abstract: MnO₂ and TiO₂ composites have garnered substantial research interest for energy applications, including supercapacitor electrodes and photocatalysts. This study investigated the microstructures, densification behaviour, and microhardness of spark plasma sintered TiO₂-MnO₂ composites. TiO₂-MnO₂ composites with 10 wt.% MnO₂ and 30 wt.% MnO₂ were sintered at a temperature of 1000 °C and applied pressure of 25 MPa. To investigate the influence of annealing, the second batch of powders with similar compositions were pre-annealed at a temperature of 500°C for 5 minutes before consolidation. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the powders and compacts. The results revealed that the pre-annealing stage influences the microstructural constituents, densification, and microhardness. The formation of pores and a new phase was observed in SEM images and XRD patterns. The relative densities of the 10wt.%MnO₂ sample increased from 97.48 % to 97.71 %, whereas that of the 30wt.%MnO₂ composite increased from 96.11% to 96.46%. Similarly, the microhardness values in the pre-annealed 10wt.% MnO₂ and 30wt.%MnO₂ composites increased by 1.78% and 0.41%, respectively.

Abstract: The long-term viability of human civilization is heavily reliant on a sustainable energy supply, and fossil fuels have long been the most sustainable source of energy. However, since fossil fuels are a non - renewable energy source, their depletion is unavoidable and inevitable in this century. Renewable energy, notably solar energy (SE), has gotten a lot of attention as a solution to this problem because it transforms SE through technology into electrical power (EP) with no environmental impact. For its inherent low unit cost and simplicity of production, organic-solar cells (OSCs) have recently been the topic of investigation for both home and commercial uses. OSCs also have a weight and flexibility benefit over standard silicon-based crystalline solar cells (CSCs). Research has suggested that dye sensitized solar cells (DSSCs) are the most effective and simple to implement of all the OSCs. In this mini review, we survey the existing DSSCs literature and attempts made to improve its performance based on mangifera indica natural dye, an eco-friendly, cost-effective, easy to extract, source of natural dye with high conversion efficiency.

Abstract: In industry, synthetic zeolites are commonly used as ion-exchange materials, catalyst supports, and adsorbents. As a result, a more energy-efficient alternative for its synthesis from low-cost and accessible raw materials is needed. This study, presents the possibility of using class F South African coal fly ash (SACFA) from Lethaba thermal-power station as a precursor to produce zeolites via a microwave (MW) assisted synthesis route. The mineral content of synthetic materials was determined using X-ray florescence (XRF). Morphology was determined using a Scanning electron microscopy (SEM), elemental composition by energy dispersive spectrometer (EDS). X-ray diffractometry (XRD) was used to get structural characterization. Microwave (MW) irradiation time and intensity enhance the crystallization of the zeolite phase as a result of sufficient energy required to enable the solubility of alumina and silica from coal fly ash. The use of MW irradiation provides a green alternative to zeolite synthesis from fly ash (FA) than traditional thermal and fusion techniques, which uses a great deal of energy consumption and a longer reaction time.

Abstract: Enhanced treatment of river water was investigated by the modified coagulation-flocculation process for the application of self-cleaning filters (SCF’s) in the removal of turbidity using a combination of Alum and Sudfloc 3880. This study is aimed to improve the removal of iron and turbidity concentrations from river water and reduce water loss. This is achieved by piloting innovative water treatment technologies such as the SCF’s Plant. The new technology further assessed the effectiveness, efficiency, and operability of the SCF’s Plant by varying certain operational parameters such as water flow, differential pressures, coagulant, and flocculent dosages. The results established in this study critically analyze the feasibility of deploying water treatment technologies such as the SCF Plant in areas with similar environmental conditions and/or facing similar water treatment challenges. The removal efficiencies of turbidity were about 40 % and further optimization will be continued until 90 % to 100 % is achieved. The average removal efficiency of turbidity was 40 % and achieved at a 250 m³/h flow rate. The average removal across all flow rates was over 20 %. Further optimization of the RF14 will be carried out using other chemical combinations and formulations at various process settings while bypassing the PLF filters. The PLF elements will be brought into service to further reduce the turbidity after the optimization of the RF14. Keywords: Water, Treatment, Coagulation, Flocculation, Processes, Technologies, Filters ^*

Abstract: The sensing characteristics of pristine, Ni-doped, and C-vacancy graphene towards CO and NO₂ gas molecules were studied using density functional theory (DFT). The adsorption energies, electronic properties, charge transfer, and stable geometries were calculated to evaluate the gas-surface interaction mechanisms. Both pristine and vacancy graphene have smaller CO and NO₂ adsorption energies and charge transfer than the Ni-doped graphene, whereas the adsorption energy on Ni-doped vacancy graphene is higher than that of Ni-doped graphene. The results indicate that both CO and NO₂ gas molecules only attach to pristine graphene through weak physical adsorption. Stronger chemisorption occurs when the gas molecules adsorb on the surface of vacancy, Ni-doped, and Ni-doped vacancy graphene. Additionally, the results demonstrated that Ni-doped vacancy graphene has higher sensitivity and selectivity towards the NO₂.

Abstract: This study investigates transport process in circular tubes cross-flow Heat Exchanger (HEX) using water-CuO-nanofluids cooling media. The effects of nanoparticle volume fractions (Ø) and Reynolds number (Re) on the flow structure, coefficient of skin friction, isotherms and Nusselt number (Nu) are determined for steady laminar flow. The governing equations of continuity, momentum and energy are discretized over the flow domain and solved using SIMPLE method of the Finite Volume Method with ANSYS Fluent 16. The results show that the flow field for the conventional fluid is concentric around the inner tubes for Re up to 60 after which vortices evolve downstream behind the tubes, elongate and eclipse with the increase in Re. Vortex inception occurs at Re between 60 and 45 for 0 ≤ Ø ≤ 10%. The temperature fields are characterized by plume-like structure which envelopes the two inner cylinders between which heat transfer occurs. The average Nusselt number is correlated as Nu = 22.4 - 411,588س + 0.757Re + 1803.31/ln(Re) in which the interaction between Re and Nu has significant (p ≤ 0.05) effect. The addition of nanoparticles in the range 2 ≤ Ø ≤ 10% results in the increase in Nu from 0.55 to 5.84%. It follows that the thermal performance of the cross flow heat exchanger could be enhanced with CuO-based nanofluids.