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Running-in Period During Sliding Wear of Austenitic Steels

The running-in period during dry sliding wear might determine the evolution to steady-state wear behaviour. To this end, the running-in period during sliding wear of austenitic stainless steel, AISI 316L stainless steel, and Hadfield steel were studied through the testing pin (flat-ended)-on-disk configuration. The effects of the normal load, sliding speed, and alloy type were assessed, and the specific wear rate and strain hardening characteristics were determined. The wear rate was correlated with wear mechanism, friction coefficient, hardening, and roughness to characterize the changes occurring during the running-in period. These changes could influence the responses of these materials to wear during the steady-state period. The stabilization of the specific wear rate and hardness was noted to align with the end of the running-in period.Graphical

Activating MnO2 nanosheet arrays for accelerated water oxidation through the synergic effect of Ni loading and O vacancies

Birnessite (δ-MnO2), inspired by biological photosynthesis, holds promise as oxygen evolution reaction (OER) catalysts in water electrolysis for clean energy. Given that Mn3+ serves as the active sites, various strategies have been employed to increase the Mn3+ content to boost the OER activity. To surpass the limitations of the traditional adsorbate evolution mechanism (AEM), we have adopted an electrochemical reduction method to introduce metallic Ni and enrich oxygen vacancies onto δ-MnO2 nanosheets. The resulting Ni/MnO2v/CC exhibits exceptional OER performance, with a reduction in overpotential by 190 mV (from 478 mV to 289 mV) at 10 mA cm−2 and a Tafel slope as low as 45 mV dec-1, indicating accelerated catalytic activity. Experimental and theoretical analyses attribute this enhancement to a transition from the traditional AEM to lattice oxygen mechanism (LOM) mechanism. Moreover, the dual modification also enhances electronic conductivity, electrochemical surface area, and charge transfer ability of δ-MnO2. Our work offers a pathway to overcome conventional limitations in OER electrocatalysts, applicable not only to Mn-based catalysts but also to a range of other transition metal oxides.

Examining the effects of cognitive load on information systems security policy compliance

PurposeEnforcing employee compliance with information systems security policies (ISSP) is a herculean task for organizations as security breaches due to non-compliance continue to soar. To improve this situation, researchers have employed fear appeals that are based on protection motivation theory (PMT) to induce compliance behavior. However, extant research on fear appeals has yielded mixed findings. To help explain these mixed findings, the authors contend that efficacy formation is a cognitive process that is impacted by the cognitive load exerted by the design of fear appeal messages.Design/methodology/approachThe study draws on cognitive load theory (CLT) to examine the effects of intrinsic cognitive load, extraneous cognitive load and germane cognitive load on stimulating an individual’s efficacy and coping appraisals. The authors designed a survey to collect data from 359 respondents and tested the model using partial least squares.FindingsThe analysis showed significant relationships between cognitive load (intrinsic, extraneous, and germane) and fear, maladaptive rewards, response costs, self-efficacy and response efficacy.Originality/valueThis provides support for the assertion that fear appeals impact the cognitive processes of individuals that then in turn can potentially affect the efficacy of fear and coping appraisals. These findings demonstrate the need to further investigate how individual cognition is impacted by fear appeal design and the resulting effects on compliance intention and behavior.

Upcrossing‐based time‐dependent resilience of aging structures

The time-dependent resilience of an in-service aging structure provides quantitative measure of the structural ability to prepare for, adapt to, withstand and recover from disruptive events. Resilience models have been proposed in the literature to evaluate the resilience of aging structures subjected to discrete load processes, which are, however, not applicable to handle resilience problems considering continuous load processes. In this paper, a new method is developed to evaluate the time-dependent resilience of aging structures subjected to a continuous load process. The proposed method serves as the complement of the existing resilience models addressing discrete load processes, and takes into account the aging effects of the structural resistance/capacity and the nonstationarity in loads as a result of climate change. A structure suffers from a damage state upon the occurrence of an upcrossing of the load effect with respect to the resistance/capacity, leading to the reduction of the performance function, followed by a recovery process that restores the performance. The proposed method enables the time-dependent resilience to be evaluated via a closed form solution. It is also revealed that, the proposed resilience model takes an extended form of the existing formula for upcrossing-based time-dependent reliability, thus establishing a unified framework for the two quantities. The applicability of the proposed method is demonstrated through examining the time-dependent resilience of a residential building subjected to wind load. The effects of key factors on resilience, including the nonstationarity and correlation structure of the load process, as well as the resistance/capacity deterioration scenario, are investigated through an example. In particular, the structural resilience would be overestimated if ignoring the potential impacts of climate change, which is a relatively non-conservative evaluation.

Consideration of the effects of frost heave force and train loads on the cracks and propagation pattern of ballastless track slabs in cold regions

The construction of ballastless railway tracks in cold regions is susceptible to frost heave forces, which may particularly impact the stability of track slab cracks and lead to crack propagation. In this paper, the frost heave tests are conducted on the concrete specimens with prefabricated cracks to observe the evolution of the frost heave force within the cracks. The frost heave force is subsequently applied to the finite element model of the concrete specimens to calculate the stress intensity factors (SIFs). In addition, the CRTS III ballastless track model is established to investigate the crack propagation patterns under frost heave and train loads. The results show that the frost heave force in concrete cracks during freezing and thawing is divided into five stages, which produces two peaks of frost heave force. Train loading caused the SIFs of the crack tips to open and close alternately and to rise significantly under the coupling effect of frost heave load. The SIF increases approximately linearly with crack width and is higher for transverse cracks than for longitudinal cracks. Small size cracks do not possess sufficient SIF values to exceed fracture toughness, implying no crack propagation. However, as the crack width is constantly increasing, the SIF will eventually exceed the fracture toughness. Therefore, strict control over track slab's crack width is necessary for CRTS III ballastless tracks.

The Effect of Thermocycling and Mechanical Loading on the Fracture Resistance of Graphene and All-Ceramic Anterior Crowns.

Introduction Fixed prosthodontic treatment involves the replacement of missing tooth structures with a variety of materials. Several newer metal-free ceramics have been developed in recent years to meet patients' aesthetic needs. The long-term performance of all ceramics, however, is unknown, necessitating a continuous evaluation of the materials' strength. Aim The aim of this study was to compare and evaluate the fracture resistance of IPS E max pressable crowns and graphene crowns, which are luted with Rely X U200 self-adhesive resin cement on the respective dies, as well as thermocycling of IPS E max pressable crowns and thermocycling of graphene crowns. The current review was conducted as an in vitro examination at the Division of Prosthodontics, GSL Dental School, Rajahmundry, Andhra Pradesh, India. Materials and methods On a typodont tooth, a shoulder finish line design was prepared and incisal reduction was performed. The tooth was scanned, designed, and milled to produce 18 metal dies made of cobalt-chrome alloy. These metal dies produced a total of (n=36) all-ceramic crowns, which were divided into two groups based on crown type: 18 IPS E max crowns and 18 graphene crowns. The participants were once again divided into two subgroups within each group, with the purpose of assessing fracture resistance. This evaluation was conducted using a universal testing machine both before and after subjecting the specimens to thermocycling. The obtained data were sent for statistical analysis. Results Fracture resistance values were reduced after thermocycling of both IPS E max and Graphene crowns. Without thermocycling, the fracture resistance values of IPS E max crowns were higher than those of graphene crowns. Conclusions The fracture resistance of IPS E max crowns exhibited a statistically significant increase when compared to graphene crowns. Additionally, it was shown that the fracture resistance of both materials was reduced upon exposure to thermocycling.

Tribological evaluation of thermoplastic polyurethane-based bearing materials under water lubrication: Effect of load, sliding speed, and temperature

Polymers are widely used in bearing applications. In the case of water-lubricated stern tube bearings, thermoplastic polyurethane (TPU)-based composites are used due to their excellent wear resistance, corrosion resistance, and tunable mechanical properties. Their tribological performance, however, depends on operating conditions. In this work, TPU was blended with carbon fiber, graphene platelet, and ultra-high molecular weight polyethylene (UHMWPE). Friction tests of TPU based-composites against copper countersurface were carried out in water to mimic the actual operating conditions of the bearing. Most of the resulting contacts were in the boundary lubrication regime, in which friction was attributed to both contact mechanics of asperities as well as water lubrication. Our results show that the viscoelasticity of TPU has a considerable impact on its tribological performance. Water lubrication at 50 °C promotes the softening of polymer surface material during sliding, resulting in higher fluctuation in the coefficient of friction and wear loss. This is attributed to the reduced thermomechanical properties. In addition, Schallamach waviness is observed on worn surface. The tribological properties of TPU are significantly improved by the inclusion of carbon fiber, graphene platelet, and UHMWPE. The formation of graphene transfer-layers and UHMWPE transfer film reduces friction and wear loss, while the inclusion of carbon fiber enhances wear resistance due to improved mechanical properties and load bearing capacity.

Integrating phase-change thermal storage into the indirect dry-cooling system of a thermal power unit and optimal operation strategy

Extreme conditions (high ambient temperature and crosswind speed) reduce the cooling efficiency of dry cooling towers, consequently impairing the thermal performance of thermal power units (TPUs). Phase-change material thermal storage equipment (PCMTSE) is integrated into an indirect dry-cooling system of the TPU to realize a partial cooling load of the cooling tower, thereby stabilizing and improving the thermal performance of the TPU. A model of the TPU and numerical model of the hybrid indirect dry-cooling system are established and coupled, with the inlet cooling water temperature of the condenser serving as the iterative criterion. Two integration schemes are proposed, one with the PCMTSE downstream (Scheme A) and the other with it upstream (Scheme B) of the dry cooling tower. The results show that Scheme A is recommended owing to its superior efficiency in terms of coal savings. The effects of the unit power load on the coal-savings efficiency of the PCMTSE during its charging and discharging processes have been revealed. Operating the PCMTSE at higher power loads aids in improving the thermal efficiency of the TPU during the PCMTSE charging and discharging processes. The charging process should be started at the “three high” working conditions: a high ambient temperature, crosswind speed, and unit power load. The working conditions that allow only one cooling water pump to operate should first be considered for the discharging process, and the “three high” working conditions should then be selected. The TPU equipped with the PCMTSE can save 11.42 tons and 12.74 tons of coal in two typical extreme daily conditions with the implementation of the proposed operating strategy.

Freeze‐Casting of Arbitrary‐Shaped Porous Ceramics

Porous ceramics hold the great potential in the field such as bone tissue engineering, superinsulation material, and energy storage. However, it is quite challenging to fabricate them with arbitrary shape using conventional processes. Herein, a method to fabricate arbitrary‐shaped porous ceramic structure is presented by combining traditional freeze‐casting process and indirect three‐dimensional printing technology. Various polydimethylsiloxane (PDMS) soft molds are prepared for freeze‐casting, and diverse‐shaped porous ceramics are fabricated. It proves that PDMS molds are ideal choices for freeze‐casting of porous ceramics with complex geometries. The freeze‐casting process of a complex‐shaped model with PDMS is simulated by finite element analysis. The effect of the solid loading of the alumina suspension on the microstructure and compressive strength of the as‐fabricated porous ceramics are investigated. The present study provides a strategy to fabricate complex‐shaped porous ceramic structure that can be used in a wide variety of applications.

Fluid Structure Interaction Analyses of Elevated Storage Tank under Seismic Load

Elevated storage tanks are used to store fresh and waste water, cereal, oil and petrochemical materials. Therefore they serve in a wide area of utilization in this day and age. Analysis of a half full with water elevated storage tank is performed in the scope of this study. The structure is composed of a steel circular storage tank and frame typed steel stager. The structure is under the effect of earthquake loads as well as operational ones. Numerical model is generated by Finite Elements Analysis (FEA) software including fluid and structure parts. The interaction of the parts is provided by Coupled Eulerian Lagrangian (CEL) technique. While the structure constitutes the Lagrangian part, the fluid constitutes the Eulerian part. Interaction of Eulerian and Lagrangian parts are provided by general contact algorithms. Free surface movement of the water, maximum displacements and natural frequency values with related mode shapes of the structure are obtained after numerical analysis. Numerical results are verified by semi-analytical model, where the structure is modelled as single degree of freedom system. The accordance between results is numerically and visually obtained. The turbulent movement of water under the influence of an earthquake is modelled by utilizing the CEL technique. So, the effect of the dynamic pressure induced by the turbulence on the tank and the structural system has been taken into consideration.

Post-buckling behavior of variable-arc-length elastica pipe conveying fluid including effects of self-weight and pressure variation

This paper investigated the post-buckling behaviors of a variable-arc-length (VAL) elastica pipe caused by internal transporting fluid motion, accounting for the effects of the self-weight and variation of internal fluid pressure. Both weak-form and strong-form formulations of the VAL elastica pipe were developed. The weak-form formulation was derived by the virtual work principle, and later solved using the nonlinear finite element method (FEM). The strong-form formulation was derived using equilibrium of the force and moment equations, the geometrical relationship of the differential pipe segment, and the energy conservation of the transported fluid. Because of the large displacement analysis, the variation in the internal pressure inside the pipe was considered, which was taken into account by energy conservation based on the Bernoulli principle. Then, the set of nonlinear governing first-order differential equations, corresponding to the two-point boundary value problem, was conveniently solved using the shooting optimization method (SOM). The numerical results obtained from the presented FEM and SOM analyses independently verified each other, with good agreement between these two methods. The parametric study considered the effects of gravity load (pipe and fluid self-weights) and internal fluid pressure on the post-buckling characteristics of the VAL pipe. The numerical results showed that without the pipe and internal fluid weights, the transporting fluid exerted an axial compressive force on the pipe, causing post-buckling phenomena. Beyond the critical state, the support rotation and the length of the VAL pipe increased as the internal fluid velocity decreased. Finally, by including the effect of self-weight, the mode exchange of the odd buckling modes (1st and 3rd modes) was found from the load-displacement path.

Optimization of the Traffic Load Model for Suspenders of a Super-Long-Span Suspension Bridge Considering Influence Line Geometry and Extreme Load Effect Scenarios

Optimization of the Traffic Load Model for Suspenders of a Super-Long-Span Suspension Bridge Considering Influence Line Geometry and Extreme Load Effect Scenarios

Experimental study of quaternary blends with diesel/palm-oil biodiesel/ethanol/diethyl ether for optimum performance and emissions in a light-duty diesel engine using response surface methodology

Quaternary fuel blend consisting of diesel, palm-oil biodiesel (POB), diethyl ether (DEE), and ethanol is a promising low-carbon fuel solution for diesel engines. In this study, the effects of DEE, ethanol, and engine load on the brake specific fuel consumption (BSFC), nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (UHCs) emissions of a light-duty diesel engine were statistically analyzed using analysis of variance (ANOVA). Desirability-based response surface methodology (RSM) optimization was then employed to determine the optimum quaternary fuel blend. The desired optimum quaternary fuel blend was found to be 6.78 vol% DEE and 20.00 vol% ethanol at an operating engine load and speed of 31.36 % and 2000 rpm, respectively. The engine out responses of BSFC and NOx, CO, and UHCs emissions for the optimal solution were 490.58 g/kWh, 326.84 ppm, 0.300 vol%, and 156.95 ppm, respectively. Validation of the optimized parameters was conducted through actual engine experiments and the errors were less than 5 %. The results suggest that the optimum quaternary blend can be a cleaner alternative for light-duty diesel engine applications.

Numerical Simulation of Structural Performance in a Single-Tube Frame for 12 m-Span Chinese Solar Greenhouses Subjected to Snow Loads

To address the structural concerns of a 12.0 m-span landing assembled single-tube frame (LASF) for Chinese solar greenhouses subjected to snow loads, the internal forces and deformations of LASF and its reinforced counterpart (RLASF) were numerically simulated to determine the ultimate bearing capacities (Lu) and the failure loads (Lf). During the simulations, steel tubes were modeled as beam188 elements and cables as link180 elements. The frame constraints and the connections were assumed to be fixed supports and rigid, respectively. The loads were determined according to the Chinese standard (GB51183-2016). Simulations revealed that the LASF and RLASF primarily withstand bending moments and are prone to strength failures under snow loads. Both exhibited lower Lu and Lf under non-uniform snow loads than under uniform snow loads. The results also indicated that crop loads could deteriorate the structural safety of the LASF and RLASF. Lu and Lf were found to be proportional to the section modulus of the tubes. The effects of wind loads and initial geometry imperfections on Lf of the LASF and RLASF can be neglected. Furthermore, the RLASF exhibited higher Lf compared to the LASF. Steel usage of the RLASF could be further reduced by replacing circular tubes with rectangular tubes, making the RLASF a feasible option for constructing Chinese solar greenhouses.

Influence of graphene oxide additives on the NF separation of triazine-based H2S scavenging compounds using advanced membrane technology

This work proposes an innovative approach for the membrane separation of spent and unspent H2S scavengers (SUS) derived from the application of MEA-triazine in offshore oil and gas production. Modified nanofiltration membranes were fabricated by incorporating graphene oxide (GO) and polyvinyl alcohol (PVA) into a thin film composite (TFC) to obtain a thin film nanocomposite (TFN) with enhanced permeability. In addition, various immobilization strategies for GO were investigated. The performance of the membranes and the effect of the GO loading were evaluated in terms of permeability, fouling propensity, and rejection of key components of the SUS, i.e., MEA-triazine (unspent scavenger), dithiazine (spent scavenger), and monoethanolamine, operating on a sample of SUS wastewater obtained from an offshore oil and gas platform. Various characterization techniques, such as contact angle, FTIR, XRD, SEM, TGA, and AFM, were employed to evaluate the structure, composition, and hydrophilicity of the membrane. The results show a remarkable increase in permeability (from 0.22 Lm-2 h−1 bar−1 for the TFC to 5.8 Lm-2 h−1 bar−1 for the TFN membranes), due to the enhanced hydrophilicity from GO incorporation. The strong interfacial interaction between GO and PVA within the TFN membrane results in negligible nanofiller leaching. The incorporation of GO moderately increases the rejection of the unspent scavenger (63%–73%, 62%–79%, 62%–80%, and 68%–76%), while drastically increasing the rejection of the spent scavenger, which is approximately null for the TFC membrane without GO and increases up to 58% in the TFN membrane with GO. Therefore, while the proposed membranes cannot be used for the selective separation of the unspent form the spent scavenger, they can achieve substantial recovery of all the key components contained in the SUS to avoid their discharge into the sea.

PAU Smart Seeder: a novel way forward for rice residue management in North-west India

In winter, the paddy residues become wet during morning and late evening due to dew, which restricts the operation of sowing machines (Happy Seeder and Super Seeder) into paddy residues, as wet residues do not slide on furrow openers/tines. A PAU Smart Seeder (PSS) was developed and evaluated for a four-wheel tractor that can sow wheat with optimum crop establishment in combined harvested rice fields. The PSS were evaluated for its performance under varying straw load, forward speed, and rotor speed in terms of fuel consumption, field capacity, seed emergence, and grain yield. The crop establishment and wheat yield of PSS was also compared with the existing straw management machines Happy Seeder (HS) and Super Seeder (SS) under heavy paddy residue conditions. The effect of the straw load was more pronounced on dependent variables than the effect of the speed index. PSS performance was best at a forward speed of 2.6 km h−1, rotor speed of 127.5 rpm, and a straw load of 6 t ha−1. Average fuel consumption using PSS was lower than SS but higher than HS. Wheat emergence was higher by 15.6 and 25.7% on the PSS plots compared to HS and SS, respectively. Average wheat grain yield in PSS plots was significantly higher by 12.7 and 18.9% than SS and HS, respectively in one experiment, while the grain yield was similar for both PSS and HS in other experiments. PSS has a novel mechanism to manage paddy straw and simultaneously sow wheat into a heavy straw load (> 8 t ha−1) mixture of anchored and loose straw. In conclusion, PSS showed promise for in-situ management of rice straw as it eliminates most of the operational problems encountered by the existing seeders (HS and SS).

#2268 Dialysis patients survival in HD centres from Belgium, Estonia, Spain, and Sweden—association with BMI and hypocalcemia

Abstract Background and Aims Several factors are known to influence the morbidity and mortality of ESKD patients, among them cardiovascular disease, nutritional status, delivered dialysis dose, uremic toxins levels, and infectious diseases. This observational study aimed to analyse factors that impact the survival of ESKD patients on haemodialysis. Method We analysed 3- and 5-year survival of 76 patients during the period of 2018-2023 (17 females, 59 males, aged 63.6 ± 15.9 years) from four separate dialysis centres from countries with diverse life expectancies, renal replacement therapy incidences, and kidney transplant rates: North Estonia Medical Centre, Tallinn, Estonia (21 patients); Linköping University Hospital, Linköping, Sweden (21 patients); Ghent University Hospital, Ghent, Belgium (14 patients) and Fundación Jiménez Díaz University Hospital Health Research Institute, Madrid, Spain (20 patients). We included stable chronic haemodialysis patients receiving three times per week post-dilution ol-HDF treatment. Patients with central dialysis catheter, acute coronary syndrome or stroke within three months were excluded. Cox proportional-hazard regression analysis was used to detect the factors affecting the survival of patients. In the Cox model, the 3-year survival was set as a dependent parameter. Age, gender, BMI, and serum levels of creatinine, phosphate, calcium, total protein, and uric acid were set as independent parameters. Kaplan-Meier survival analysis was performed to study survival in the subgroups of patients. Results Out of 76 patients, 22 died in 3-years and 34 in five years (Fig. 1a and b). Our Cox model (adjusted with the age, gender, creatinine, phosphate, total protein, and uric acid serum levels) indicated patients' body mass index (BMI, p = 0.014) and calcium (p = 0.033) levels as statistically significant factors in 3-year survival. Kaplan-Meier survival analysis showed statistically significant increased survival in the group where BMI was higher than 27.6 kg/m2 (Fig. 2a) and in the group where serum calcium levels were higher than 2.25 mmol/L (Fig. 2b). Conclusion This study shows that among prevalent haemodialysis patients 3-year survival is about 65% and 5-year survival 45%, and a higher risk of mortality could be associated with low BMI and low serum calcium levels. Our findings are in accordance with previous studies, where survival benefit for haemodialysis patients with higher BMI is shown [1, 2]. It is proposed that this phenomenon among advanced CKD patients with higher BMI could be due to better nutritional reserve that helps resist chronic inflammation and wasting. The negative effects of excess calcium load for haemodialysis patients are well known, and nowadays, non-calcium-based phosphorus binders, calcimimetics, and low-calcium concentrates in haemodialysis are used more often, thus putting the patients at risk of hypocalcaemia. Though less studied, long-term hypocalcaemia is shown to increase mortality among haemodialysis patients [3], as concurs with our results. Safe calcium concentration limits for these patients are still debatable and need further investigation.

A comprehensive evaluation on particles breakage characteristics of waste argillaceous gangue as subgrade filler

Reutilising waste argillaceous gangue (AG) in road engineering is crucial to reducing its environmental pollution. To effectively control settlement and long-term performance of subgrade filled with AG, the effects of humidification and loading on the particle crushing evolution of AG were investigated. The effects of dry-wet cycles, compaction work, and initial coarse grain content (CGC) on the breakage characteristics were evaluated. The relationship among fractal dimension D and compaction work, initial CGC, and breakage index Bg was established. The results show that the initial CGC and compactness are essential factors affecting the breakage characteristics of AG. It is recommended that the CGC be controlled at 50% when AG is used as subgrade filler. The fractal dimension increases logarithmically with the increase of compaction work and decreases linearly with the rise of CGC. Fractal dimensions D and Bg can effectively evaluate the breaking process of AG and the gradation after compaction.

Fracture resistance of additively or subtractively manufactured resin-based definitive crowns: Effect of restorative material, resin cement, and cyclic loading

ObjectiveTo evaluate how restorative material, resin cement, and cyclic loading affect the fracture resistance of resin-based crowns fabricated by using additive or subtractive manufacturing. MethodsA right first molar crown standard tessellation language (STL) file was used to fabricate 120 crowns from one subtractively manufactured polymer-infiltrated ceramic network (SM) and two additively manufactured resin composites (AM-B and AM-S) (N = 40). These crowns were randomly divided into 4 groups within each material according to the dual-polymerizing resin cement to be used (RX and PN) and the aging condition (n = 10). After cementation, the crowns without cyclic loading were subjected to fracture testing, while the others were first cyclically loaded (1.7 Hz, 1.2 million cycles, and 49-N load) and then subjected to fracture testing. Data were analyzed with generalized linear model analysis (α = .05). ResultsFracture resistance of the crowns was affected by material, resin cement, and cyclic loading (P ≤ .030). However, none of the interactions significantly affected fracture resistance of tested crowns (P ≥ .140). Among tested materials, SM had the highest fracture resistance, whereas AM-B had the lowest (P ≤ .025). RX led to higher fracture resistance, and cyclic loading decreased the fracture resistance (P ≤ .026). SignificanceTested materials can be considered reliable in terms of fracture resistance in short- or mid-term (5 years of intraoral simulation) when used for single molar crowns with 2 mm occlusal thickness. In the long term, polymer-infiltrated ceramic network crowns cemented with RelyX Universal may provide promising results and be less prone to complications considering higher fracture resistance values obtained.

Bio-based composite from chitosan waste and clay for effective removal of Congo red dye from contaminated water: Experimental studies and theoretical insights

Water pollution due to dyes in the textile industry is a serious environmental problem. During the finishing stage, Congo red (CR) dye, water-soluble, is released into wastewater, polluting the water body. This study explores the effectiveness of utilizing a composite composed of Safi raw clay and chitosan to remove an anionic dye from synthetic wastewater. The chitosan was extracted from crab shells. Its removal performance was compared to that of natural clay. Both the composite and raw clay were used to remove target pollutant. The effects of the chitosan load in the composite, size particles, initial dye concentration, contact time, pH, and temperature on the dye's elimination were tested in batch modes. The composite with 30% (w/w) of chitosan exhibited the highest dye removal. At pH 2, an adsorption capacity of 84.74 mg/g was achieved, indicating that the grafting of the polymer onto clay surface enhances its efficacity and stability in acidic environments. This finding was supported by characterization data obtained from X-ray diffraction (XRD), scanning electron microscopy (SEM), dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FT-IR) analyses. Under optimized conditions of 20 mg dose, pH 2, 30 min of reaction time, and 20 mg/L of dye concentration, about 92% of dye removal was achieved. The Langmuir isotherm model represents dye adsorption by the composite, while dye removal was controlled by pseudo-second-order model. Thermodynamic data of the adsorption (ΔH = +8.82 kJ/mol; ΔG <0) suggested that the dye adsorption was spontaneous and endothermic. The findings provide insights into the dye elimination by the adsorbent, indicating that the removal occurred via attractive colombic forces, as confirmed by density functional theory (DFT) analysis. Overall, the composite of natural clays and chitosan waste is a promising and innovative adsorbent for treating wastewater containing recalcitrant dyes.