Materials

11 pages, 4905 KiB

Open AccessArticle

Hierarchically Graphitic Carbon Structure Derived from Metal Ions Impregnated Harmful Inedible Seaweed as Energy-Related Material

by Yun-Mi Song, Hui Gyeong Park and Jung-Soo Lee

Materials 2024, 17(18), 4643; https://doi.org/10.3390/ma17184643 (registering DOI) - 21 Sep 2024

Abstract

This study explored the development of hierarchical graphitic carbon structures (HGCs) from harmful inedible seaweed waste harvested in the summer. Elevated sea temperatures during the summer increase the cellulose content of seaweeds, making them unsuitable for consumption. By utilizing seaweed biomass, this study [...] Read more.

This study explored the development of hierarchical graphitic carbon structures (HGCs) from harmful inedible seaweed waste harvested in the summer. Elevated sea temperatures during the summer increase the cellulose content of seaweeds, making them unsuitable for consumption. By utilizing seaweed biomass, this study addresses critical marine environmental issues and provides a sustainable solution for promising electrode materials for energy storage devices. The fabrication process involved impregnating seaweed with Ni ions, followed by annealing to create a highly crystalline carbon structure. Subsequent etching produced numerous nano-sized pores and a large surface area (806 m²/g), significantly enhancing the number of electrically active sites. The resulting HGCs exhibited a high capacitance and maintained their capacity even after 10,000 cycles in fast-current systems. This innovative approach not only mitigates the environmental burden of seaweed waste but also offers a sustainable method for converting it into efficient energy storage materials. Full article

(This article belongs to the Special Issue Synthesis and Characterization Techniques for Nanomaterials)

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26 pages, 15136 KiB

Open AccessArticle

Experimental and Numerical Study on Lightweight-Foamed-Concrete-Filled Widened Embankment of High-Speed Railway

by Didi Hao, Changqing Miao, Shisheng Fang, Xudong Wang and Qiaoqiao Shu

Materials 2024, 17(18), 4642; https://doi.org/10.3390/ma17184642 (registering DOI) - 21 Sep 2024

Abstract

To study the performance of lightweight foamed concrete (LWFC) in widened embankments of high-speed railways, this study first conducted numerous strength, permeability, and water immersion tests to investigate the mechanical properties and water resistance of LWFC with designed dry densities of 550, 600, [...] Read more.

To study the performance of lightweight foamed concrete (LWFC) in widened embankments of high-speed railways, this study first conducted numerous strength, permeability, and water immersion tests to investigate the mechanical properties and water resistance of LWFC with designed dry densities of 550, 600, and 650 kg/m³. Secondly, a field test was performed to analyze the behavior of the deformation and the internal pressure within the LWFC-filled portions. Furthermore, a parametric study via numerical modeling was performed to investigate the effects of four key factors on the performance of the LWFC-filled, widened embankments. Results showed that LWFC possesses adequate bearing capacity and impermeability to meet high-speed railway embankment widening requirements. However, water seepage reduces LWFC strength. The additional pressure from LWFC filling increases initially but then decreases once dehydration occurs. The settlement induced by LWFC accounted for 71% of the total filling height, which is only 37.5% of the total settlement after construction. The parametric study results show that the maximum settlement of widened and existing portions induced by LWFC was 46.3–49.6% and 48.3–53.2% of those induced by traditional fillers due to the LWFC’s lower density as well as their better self-supporting ability. Making an appropriate reduction in the thickness of the retain wall installed against the LWFC-filled widened embankment of the high-speed railway generates a few variations in the lateral deformation of the wall. Furthermore, the effects of the pile offset on the deformation of the LWFC-filled embankment were more sensitive compared to the diameter of the piles. Full article

(This article belongs to the Section Construction and Building Materials)

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17 pages, 5338 KiB

Open AccessArticle

The Application of Machine Learning Algorithms to Bond Strength between Steel Rebars and Concrete Using Bayesian Optimization

by Huajun Yan, Nan Xie and Dandan Shen

Materials 2024, 17(18), 4641; https://doi.org/10.3390/ma17184641 (registering DOI) - 21 Sep 2024

Abstract

The purpose of this study is to estimate the bond strength between steel rebars and concrete using machine learning (ML) algorithms with Bayesian optimization (BO). It is important to conduct beam tests to determine the bond strength since it is affected by stress [...] Read more.

The purpose of this study is to estimate the bond strength between steel rebars and concrete using machine learning (ML) algorithms with Bayesian optimization (BO). It is important to conduct beam tests to determine the bond strength since it is affected by stress fields. A machine learning approach for bond strength based on 401 beam tests with six impact factors is presented in this paper. The model is composed of three standard algorithms, including random forest (RF), support vector regression (SVR), and extreme gradient boosting (XGBoost), combined with the BO technique. Compared to empirical models, BO-XGB`oost was found to be the most accurate method, with values of R², MAE, and RMSE of 0.87, 0.897 MPa, and 1.516 MPa for the test set. The development of a simplified model that contains three input variables (diameter of the rebar, yield strength of reinforcement, concrete compressive strength) has been proposed to make it more convenient to apply. According to this prediction, the Shapley additive explanation (SHAP) can help explain why the ML-based model predicts the particular outcome it does. By utilizing machine learning algorithms to predict complex interfacial mechanical behavior, it is possible to improve the accuracy of the model. Full article

(This article belongs to the Section Construction and Building Materials)

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16 pages, 574 KiB

Open AccessArticle

Thomson/Joule Power Compensation and the Measurement of the Thomson Coefficient

by Javier Garrido and José A. Manzanares

Materials 2024, 17(18), 4640; https://doi.org/10.3390/ma17184640 (registering DOI) - 21 Sep 2024

Abstract

The energy transported by the electric current that circulates a thermoelectric element (TE) varies with position due to the Joule and Thomson effects. The Thomson effect may enhance or compensate the Joule effect. A method for measuring the Thomson coefficient of a TE [...] Read more.

The energy transported by the electric current that circulates a thermoelectric element (TE) varies with position due to the Joule and Thomson effects. The Thomson effect may enhance or compensate the Joule effect. A method for measuring the Thomson coefficient of a TE is presented. This method is based on the total compensation of the Joule and Thomson effects. The electric current then flows without delivering power to the TE or absorbing power from it. For a TE, the global Thomson/Joule compensation ratio is defined as the ratio of the power absorbed by the current due to the Thomson effect and the power delivered by the current to the TE due to the Joule effect. It can be expressed as , where I is the electric current and is the zero-power current, a quantity that is proportional to the average Thomson coefficient. When , the Thomson effect exactly compensates the Joule effect and the net power delivered by the current to the TE is zero. Since the power delivered by the current is related to the temperature distribution, temperature measurements for currents around can be used as the basis for a measurement technique of the Thomson coefficient. With varying current, the difference between the temperatureat the center of the TE and the mean temperature between its extremes reverses its sign at the zero-power current, . This observation suggests the possibility of measuring the Thomson coefficient, but a quantitative analysis is needed. With calculations using the constant transport coefficients model for and , it is theoretically shown that a null temperature detector with a sensitivity of the order of 1 mK allows for the accurate determination of the Thomson coefficient. Full article

(This article belongs to the Special Issue Research Progress of Thermoelectric Materials, Modules and Applications)

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Graphical abstract

31 pages, 13227 KiB

Open AccessArticle

Notches and Fatigue on Aircraft-Grade Aluminium Alloys

by Valentin Zichil, Cosmin Constantin Grigoras and Vlad Andrei Ciubotariu

Materials 2024, 17(18), 4639; https://doi.org/10.3390/ma17184639 (registering DOI) - 21 Sep 2024

Abstract

The influence of notches and fatigue on the ultimate tensile strength and elongation at break of aluminium alloys (2024-T3, 6061-T4, 6061-T4 uncoated, 6061-T6 uncoated, 7075-T0, and 7076-T6) is presented in this study. A total of 120 specimens were used. On all specimens, notches [...] Read more.

The influence of notches and fatigue on the ultimate tensile strength and elongation at break of aluminium alloys (2024-T3, 6061-T4, 6061-T4 uncoated, 6061-T6 uncoated, 7075-T0, and 7076-T6) is presented in this study. A total of 120 specimens were used. On all specimens, notches were made using a CNC machine, with 60 of them subjected to low-cycle fatigue (LCF) before undergoing the tensile test. Based on the statistical examination of the measured data, mathematical prediction models have been established. Compared to their unscratched counterparts, the results indicate a significant decrease in the UTS and elongation at break for both notched and notched-fatigued specimens. The LCF pre-treatment contributes to the negative impacts of the notches, resulting in reduced values for the UTS and elongation at break, thus concluding that surface integrity is critical for maintaining the structural strength of aircraft components. Full article

(This article belongs to the Special Issue Advances in Fatigue Analysis and Numerical Simulation in Engineering Materials)

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17 pages, 8189 KiB

Open AccessArticle

Experimental Study on the Microstructure and Tribological Properties of Laser-Clad Ni60-WC Composite Coatings

by Yupeng Cao, Kai Yan, Weidong Shi, Rui Zhou, Bin Li and Jiaxin Qin

Materials 2024, 17(18), 4638; https://doi.org/10.3390/ma17184638 (registering DOI) - 21 Sep 2024

Abstract

To address the wear issues faced by the leg components of offshore platforms in harsh marine conditions, a Ni60-WC composite coating was fabricated on the surface of E690 high-strength steel using laser cladding. The microstructure, elemental distribution, microhardness, and tribological properties of the [...] Read more.

To address the wear issues faced by the leg components of offshore platforms in harsh marine conditions, a Ni60-WC composite coating was fabricated on the surface of E690 high-strength steel using laser cladding. The microstructure, elemental distribution, microhardness, and tribological properties of the composite coating were characterized and tested using XRD (X-ray diffraction), SEM (scanning electron microscopy), EDS (energy-dispersive spectrometry), a microhardness tester, and a multifunctional tribometer. The study focused on the microstructure and tribological properties of the Ni60-WC composite coating. The results show that the composite coating primarily consists of γ-(Fe, Ni), WC, W2C, M23C6, and M6C phases, with cellular and dendritic structures at the top. WC and W2C, along with M23C6 and M6C, are precipitated from the W and C elements. The average hardness of the composite coating reached 569.5 HV, representing a 103% increase over the substrate hardness. The prepared composite coating exhibited a 32.6% increase in corrosion potential compared to the substrate. Additionally, the corrosion current density was reduced by 62.0%, indicating a significant enhancement in the corrosion resistance of the composite coating. The friction coefficient of the composite coating was reduced by 17.4% compared to the substrate, and wear volume was reduced by 79%, significantly enhancing the tribological performance of the coating due to reduced abrasive wear and fatigue wear. Full article

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18 pages, 10988 KiB

Open AccessArticle

Thermal Annealing Effect on Elastoplastic Behaviour of Al/Cu Bimetal during Three-Point Bending

by Robert Uścinowicz

Materials 2024, 17(18), 4637; https://doi.org/10.3390/ma17184637 (registering DOI) - 21 Sep 2024

Abstract

This paper presents the results of experimental studies on the effects of temperature and time of annealing on the elastoplastic properties of bimetallic aluminium–copper sheets. Mechanical tests were carried out on flat samples previously heated to temperatures of 250, 350, 450, and 500 [...] Read more.

This paper presents the results of experimental studies on the effects of temperature and time of annealing on the elastoplastic properties of bimetallic aluminium–copper sheets. Mechanical tests were carried out on flat samples previously heated to temperatures of 250, 350, 450, and 500 °C for 40, 90, and 150 min. At the beginning of the tests, the elastic constants and internal friction energy were determined after thermal exposure using the impulse vibration exposure method. Further tests were carried out on the same samples using the three-point bending test. Based on the tests, the following quantities were determined and analysed: elasticity angles, translocations of the neutral axes of the cross-sections of samples, and changes in the values of bending moments plasticizing the extreme layers of bimetallic Al/Cu samples resulting from thermal interactions. The final part of this paper presents the results of measurements of the thickness of diffusion zones at the interface and their effect on the stability of the joint after annealing. The studies that were conducted indicate the dominant influence of the thermal factor on the properties of the Al/Cu bimetal above the temperature of 350 °C, which leads to the weakening of its strength and the degradation of the structure at the metallic phase boundary. Full article

(This article belongs to the Section Advanced Composites)

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12 pages, 4168 KiB

Open AccessArticle

Elastic Modulus Measurement at High Temperatures for Miniature Ceramic Samples Using Laser Micro-Machining and Thermal Mechanical Analyzer

by Zhao Zhang, Hai Xiao, Rajendra K. Bordia and Fei Peng

Materials 2024, 17(18), 4636; https://doi.org/10.3390/ma17184636 (registering DOI) - 21 Sep 2024

Abstract

In this paper, we demonstrate a method of measuring the flexural elastic modulus of ceramics at an intermediate (~millimeter) scale at high temperatures. We used a picosecond laser to precisely cut microbeams from the location of interest in a bulk ceramic. They had [...] Read more.

In this paper, we demonstrate a method of measuring the flexural elastic modulus of ceramics at an intermediate (~millimeter) scale at high temperatures. We used a picosecond laser to precisely cut microbeams from the location of interest in a bulk ceramic. They had a cross-section of approximately 100 μm × 300 μm and a length of ~1 cm. They were then tested in a thermal mechanical analyzer at room temperature, 500 °C, 800 °C, and 1100 °C using the four-point flexural testing method. We compared the elastic moduli of high-purity Al₂O₃ and AlN measured by our method with the reported values in the literature and found that the difference was less than 5% for both materials. This paper provides a new and accurate method of characterizing the high-temperature elastic modulus of miniature samples extracted from representative/selected areas of bulk materials. Full article

(This article belongs to the Special Issue Advanced Laser Ablation and Damage in Materials)

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22 pages, 2008 KiB

Open AccessReview

Recent Advancements in Fabrication of Metal Matrix Composites: A Systematic Review

by Pallab Sarmah and Kapil Gupta

Materials 2024, 17(18), 4635; https://doi.org/10.3390/ma17184635 (registering DOI) - 21 Sep 2024

Abstract

Metal matrix composites (MMCs) are essential materials in various industries due to superior properties, such as high strength-to-weight ratios, better corrosion resistance, improved wear resistance and adaptability, developed by continuous improvements in their fabrication methods. This helps to meet the growing demand for [...] Read more.

Metal matrix composites (MMCs) are essential materials in various industries due to superior properties, such as high strength-to-weight ratios, better corrosion resistance, improved wear resistance and adaptability, developed by continuous improvements in their fabrication methods. This helps to meet the growing demand for high-performance and sustainable products. The industries that stand to gain the most are automotive and aerospace, where MMCs are used for car parts, airplane frames, and jet engines that need to be strong and lightweight. Furthermore, MMCs are being extensively used in the biomedical industry for implants and medical equipment because of their suitable mechanical integrity and corrosion resistance. Applications in heavy construction, defense, and even space exploration are noteworthy. The advancements in fabrication of MMCs have revolutionized the composite industry with their improved mechanical, tribological, and metallurgical properties. This review article offers an introduction and thorough examination of the most recent advancements (mostly within the last five years) in fabrication methods of MMCs. The novelty and modernization in the traditional processes and advanced processes are covered, along with discussing the process parameters’ effects on the microstructure and properties of the composites. The review focuses on features and prospective applications of MMCs that have been greatly improved and extended due to such advancements. The most recent methods for developing MMCs, including friction stir processing (FSP), ultrasonic-assisted stir casting, and additive manufacturing, are discussed. Artificial intelligence and machine learning interventions for composite manufacturing are also included in this review. This article aims to assist researchers and scholars and encourage them to conduct future research and pursue innovations to establish the field further. Full article

(This article belongs to the Special Issue Experimental Testing, Manufacturing and Numerical Modelling of Composite and Sandwich Structures (Second Edition))

15 pages, 9219 KiB

Open AccessArticle

In Vitro Evaluation of Speed Sintering and Glazing Effects on the Flexural Strength and Microstructure of Highly Translucent Multilayered 5 mol% Yttria-Stabilized Zirconia

by Ji-In Jeong, Yong-Hoon Kwon and Hyo-Joung Seol

Materials 2024, 17(18), 4634; https://doi.org/10.3390/ma17184634 (registering DOI) - 21 Sep 2024

Abstract

This study aimed to investigate the impact of speed sintering and glazing on the flexural strength and microstructure of multilayered 5 mol% yttria-stabilized (5Y-) zirconia, which remains unknown. Bar-shaped specimens (N = 600) were fabricated from 5Y-zirconia (FX; Ceramill Zolid FX ML, ST; [...] Read more.

This study aimed to investigate the impact of speed sintering and glazing on the flexural strength and microstructure of multilayered 5 mol% yttria-stabilized (5Y-) zirconia, which remains unknown. Bar-shaped specimens (N = 600) were fabricated from 5Y-zirconia (FX; Ceramill Zolid FX ML, ST; Katana STML) by cutting, polishing, sintering (conventional and speed sintering), and then glazing. A flexural strength test (n = 30/group), field emission scanning electron microscopy (FE-SEM) observation (n = 2/group), and an X-ray diffraction (XRD) study with Rietveld refinement (n = 1/group) were performed. The flexural strength was analyzed using three-way ANOVA and a post hoc Scheffé test. The grain size was analyzed using the Kruskal–Wallis H test and Bonferroni–Dunn post hoc test. Flexural strength slightly decreased in the nonglazed FX after speed sintering (p < 0.05). Glazing with and without glazing paste did not affect flexural strength at both sintering speeds (p > 0.05). Speed sintering and glazing minimally changed the Weibull modulus and phase fraction, and did not affect grain size (p > 0.05). ST had a larger grain size and lower tetragonal phase content than FX and had a lower flexural strength than FX in most groups (p < 0.05). Overall, the multilayered 5Y-zirconia is considered suitable for dental application using speed sintering and glazing. Full article

(This article belongs to the Special Issue Advanced Materials for Oral Application (3rd Edition))

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11 pages, 11271 KiB

Open AccessArticle

Effect of Deformation Mode on Grain Characteristics and Strength–Toughness of Al-Zn-Mg-Cu Alloy

by Guohui Shi, Mingyang Yu, Kai Zhu, Weicai Ren, Kai Wen and Xiwu Li

Materials 2024, 17(18), 4633; https://doi.org/10.3390/ma17184633 (registering DOI) - 21 Sep 2024

Abstract

The Al-Zn-Mg-Cu alloy plate is a structural material widely used in aerospace, and its rolling process plays a crucial role in determining its performance. This study investigated the effects of different pass combinations of forward and spread rolling on the grain characteristics, strength, [...] Read more.

The Al-Zn-Mg-Cu alloy plate is a structural material widely used in aerospace, and its rolling process plays a crucial role in determining its performance. This study investigated the effects of different pass combinations of forward and spread rolling on the grain characteristics, strength, and fracture toughness of Al-Zn-Mg-Cu aluminum alloy plates under industrial conditions. The results show that initially using a small pass reduction followed by a larger one can improve the grain width and thickness on the Long Transverse–Short Transverse surface. Additionally, increasing the spread rolling pass enhances the grain width-to-thickness ratio on the TS surface. Performance tests indicate that grain characteristics have minimal influence on room-temperature tensile properties. However, a higher grain width-to-thickness ratio significantly improves the alloy’s fracture toughness. Full article

(This article belongs to the Special Issue Corrosion and Crack Behavior of Metallic Materials in High-Temperature Environment)

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25 pages, 6280 KiB

Open AccessArticle

Non-Propagating Cracks at the Fatigue Limit of Notches: An Analysis of Notch Sensitivity and Size Effect

by Mirco Daniel Chapetti

Materials 2024, 17(18), 4632; https://doi.org/10.3390/ma17184632 (registering DOI) - 21 Sep 2024

Abstract

The issues of the high-cycle fatigue resistance of notches and the role of non-propagating short cracks in defining the fatigue notch sensitivity and fatigue limit of the configuration are addressed. A fracture mechanics approach is employed to determine the threshold configuration that defines [...] Read more.

The issues of the high-cycle fatigue resistance of notches and the role of non-propagating short cracks in defining the fatigue notch sensitivity and fatigue limit of the configuration are addressed. A fracture mechanics approach is employed to determine the threshold configuration that defines the associated fatigue limit. The influence of notch sharpness, notch size, intrinsic fatigue limit, microstructural dimensions, and the threshold for crack propagation is examined. A simple expression is proposed to estimate the maximum fatigue notch factor, k_f^Max, which incorporates the influence of these non-propagating cracks. The fatigue limits for both blunt and sharp elliptical notches are analyzed and predicted based on experimental results reported in the literature. Additionally, shallow notches or small defects are analyzed, where it is found that the same hypothesis may not be applicable. Full article

(This article belongs to the Special Issue Advances in High Cycle Fatigue and Fracture Failure of Metallic Materials and Components)

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13 pages, 5579 KiB

Open AccessArticle

Melt Pool Changes Characterization in Laser-Processed H11 Hot Work Tool Steel Using Point-by-Point Scanning Mode towards LPBF Process Optimization

by Krzysztof Fryzowicz, Radosław Bardo, Rafał Dziurka, Jakub Kawałko, Grzegorz Cios, Andrzej Stwora and Piotr Bała

Materials 2024, 17(18), 4631; https://doi.org/10.3390/ma17184631 (registering DOI) - 21 Sep 2024

Abstract

Additive manufacturing techniques employing laser-based metal melting have garnered significant attention within the scientific community. Despite a decade of comprehensive research on the fundamentals of these techniques, there still remain unexplored facets related to heat flux impact on metallic alloys’ properties. Particularly, the [...] Read more.

Additive manufacturing techniques employing laser-based metal melting have garnered significant attention within the scientific community. Despite a decade of comprehensive research on the fundamentals of these techniques, there still remain unexplored facets related to heat flux impact on metallic alloys’ properties. Particularly, the effects of point-by-point laser operation on melt pool formation in metallic materials still remain unclear. Thus, this study focuses on the implications of laser metal melting, particularly investigating a point-by-point laser mode operation’s influence on melt pool formation and its geometry in the phase-transformation-sensitive material H11 hot work tool steel. To examine the melt pool, singular laser tracks with various laser parameters were scanned across H11 sheet metal, which allowed for the elimination of layer-by-layer heat cycles’ influence on the melt pool’s microstructure. Samples were examined by means of metallography, revealing significant differences in the melt pool’s depth, influenced mostly by exposure time rather than volumetric energy density. Heat-affected zone effects were found to have a limited range and thus potentially marginal effects in layer-by-layer manufacturing conditions. At the same time, retained austenite concentrations near fusion lines have been found within melt pools, suggesting potential micro-segregation of the alloying additions. The results present guidelines towards laser melting processes optimization. Full article

(This article belongs to the Special Issue Processing–Structure–Properties Relationships of Advanced Materials)

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11 pages, 2678 KiB

Open AccessArticle

Valorization of Iron (II) Oxalate Dihydrate Coming from Pickling Processes through Thermal Conversion

by Emiliano Salucci, Antonio D’Angelo, Antonio Fabozzi, Osvalda Senneca, Francesco Bellucci, Rosa Francesca, Henrik Grénman, Henrik Saxen, Martino Di Serio and Vincenzo Russo

Materials 2024, 17(18), 4630; https://doi.org/10.3390/ma17184630 (registering DOI) - 21 Sep 2024

Abstract

The valorization of industrial byproducts is an emerging practice that aims to transform waste materials generated during production processes into valuable resources. In this work, a preliminary study was carried out on the thermal conversion of an industrial solid byproduct resulting from the [...] Read more.

The valorization of industrial byproducts is an emerging practice that aims to transform waste materials generated during production processes into valuable resources. In this work, a preliminary study was carried out on the thermal conversion of an industrial solid byproduct resulting from the pickling of metal surfaces, mainly containing iron (II) oxalate. In a fixed-bed reactor, the thermal conversion was investigated as a function of the operating temperature and overall time. The starting material and the products obtained after heat treatment were characterized in detail, using numerous qualitative and semi-quantitative techniques. The aim of this research was to determine the optimal operating conditions for the transformation of the industrial byproduct into a high-quality product. By varying the operating conditions, it was found that complete conversion of iron (II) oxalate to magnetite was achieved at high temperatures (i.e., 773 K and 873 K) after one hour of treatment. The resulting product had a low degree of crystallization, which increased slightly with an increasing reaction time at a temperature of 873 K, reaching a maximum of about 11%. The magnetite obtained can be used in the future as a starting material for chemical looping processes as a chemical/energy carrier for the production of hydrogen. Full article

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23 pages, 5146 KiB

Open AccessArticle

Flame Retardancy and Thermal Stability of Rigid Polyurethane Foams Filled with Walnut Shells and Mineral Fillers

by Sylwia Makowska, Karolina Miedzińska, Agnė Kairytė, Jurga Šeputytė-Jucikė and Krzysztof Strzelec

Materials 2024, 17(18), 4629; https://doi.org/10.3390/ma17184629 (registering DOI) - 21 Sep 2024

Abstract

Recently, the influence of the concept of environmental sustainability has increased, which includes environmentally friendly measures related to reducing the consumption of petrochemical fuels and converting post-production feedstocks into raw materials for the synthesis of polymeric materials, the addition of which would improve [...] Read more.

Recently, the influence of the concept of environmental sustainability has increased, which includes environmentally friendly measures related to reducing the consumption of petrochemical fuels and converting post-production feedstocks into raw materials for the synthesis of polymeric materials, the addition of which would improve the performance of the final product. In this regard, the development of bio-based polyurethane foams can be carried out by, among other things, modifying polyurethane foams with vegetable or waste fillers. This paper investigates the possibility of using walnut shells (WS) and the mineral fillers vermiculite (V) and perlite (P) as a flame retardant to increase fire safety and thermal stability at higher temperatures. The effects of the fillers in amounts of 10 wt.% on selected properties of the polyurethane composites, such as rheological properties (dynamic viscosity and processing times), mechanical properties (compressive strength, flexural strength, and hardness), insulating properties (thermal conductivity), and flame retardant properties (e.g., ignition time, limiting oxygen index, and peak heat release) were investigated. It has been shown that polyurethane foams containing fillers have better performance properties compared to unmodified polyurethane foams. Full article

(This article belongs to the Special Issue Advances in Bio-Polymer and Polymer Composites)

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12 pages, 4010 KiB

Open AccessArticle

Effects of Tempering on Microstructure and Properties of Additive Manufacturing Cu-Bearing AISI 431 Steel

by Li Zhao, Baichun Li, Chaolin Tan and Hongmei Zhu

Materials 2024, 17(18), 4628; https://doi.org/10.3390/ma17184628 (registering DOI) - 21 Sep 2024

Abstract

AISI 431 martensitic stainless steels (MSS) with 2.5 wt% Cu were fabricated via laser-directed energy deposition additive manufacturing followed by single-step tempering treatment. The influences of different tempering times at 600 °C on microstructure and mechanical properties of the as-deposited 431-2.5Cu MSS have [...] Read more.

AISI 431 martensitic stainless steels (MSS) with 2.5 wt% Cu were fabricated via laser-directed energy deposition additive manufacturing followed by single-step tempering treatment. The influences of different tempering times at 600 °C on microstructure and mechanical properties of the as-deposited 431-2.5Cu MSS have been explored and analyzed. The as-deposited MSS specimen primarily consisted of lath martensite, austenite and M₂₃C₆ carbide. After the single-step tempering treatment at 600 °C, Cu-enriched (ԑ-Cu) nano-precipitates and reverse austenite can be formed and promoted by extending the tempering treatment. The microhardness, strength and elongation can be improved with increasing the tempering time up to 1.0 h, and subsequently reduced with the tempering time prolonging to 2.0 h. Compared to 431 MSS that requires a multiple-step heat treatment for excellent performance, the 431-2.5Cu MSS specimen presented superior tensile properties after single-step tempering at 600 °C for 1.0 h in the present work. The ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of one-hour tempered MSS were 1611 MPa, 1334 MPa and 16.3%, respectively. This study provides a quantitative theoretical reference and experimental basis for realizing short-process fabrication of the Cu-bearing MSS with high strength and ductility. Full article

(This article belongs to the Special Issue Development and Applications of Laser-Based Additive Manufacturing)

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23 pages, 1888 KiB

Open AccessArticle

An Experimental Study of Zinc Evaporation from Bottom Zinc Dross at Atmospheric Pressure and in Inert Atmosphere with Integrated CFD Modelling

by Katarína Pauerová, Róbert Dzurňák, Jarmila Trpčevská, Pavol Liptai and Tomáš Vindt

Materials 2024, 17(18), 4627; https://doi.org/10.3390/ma17184627 (registering DOI) - 20 Sep 2024

Abstract

In the present study, the recycling process of bottom zinc dross was performed by evaporation and subsequent condensation at 800 °C for 30 min with an observed argon flow rate of 100–400 mL/min to ensure an inert atmosphere, to observe the evaporation rate [...] Read more.

In the present study, the recycling process of bottom zinc dross was performed by evaporation and subsequent condensation at 800 °C for 30 min with an observed argon flow rate of 100–400 mL/min to ensure an inert atmosphere, to observe the evaporation rate and final form of the product. Under the set conditions of over 98% zinc purity, products in the form of nanofibres (thickness 500 nm), powder (size of spherical particles 2–5 μm), dendrites, and metallic forms were obtained. The employed mathematical modelling (via Ansys 2023R1 software) predicted the behaviour of the argon flow current in the quartz tube, as well as the temperature gradient in the quartz tube and in the close vicinity of the zinc sample. Via Inventor 2014 software, the rate of zinc sample heating was calculated. All the simulations were compared with the physical measurements and correlation was proven. Full article

(This article belongs to the Special Issue Development and Modification of New or Recycled Materials and Technological Processes toward Sustainable Development (Second Edition))

9 pages, 653 KiB

Open AccessArticle

Study on the Rheological Behaviors, Thixotropy, and Printing Characteristics of Screen Printing Slurry for Nd-Fe-B

by Xiaojun Sun, Xiao Lin, Yang Luo, Dunbo Yu, Wenlong Yan, Hongbin Zhang, Zilong Wang, Chaofan Zhang, Jiyuan Guo, Wendi Zhang, Weiguo Gao and Shan Huang

Materials 2024, 17(18), 4626; https://doi.org/10.3390/ma17184626 (registering DOI) - 20 Sep 2024

Abstract

The rheological behavior and printing characteristics of the screen-printing slurry for Nd-Fe-B grain boundary diffusion are key factors that determine the quality of printing and magnetic performance. However, few studies have focused on the organic medium, a crucial material for slurry. In this [...] Read more.

The rheological behavior and printing characteristics of the screen-printing slurry for Nd-Fe-B grain boundary diffusion are key factors that determine the quality of printing and magnetic performance. However, few studies have focused on the organic medium, a crucial material for slurry. In this paper, the rheology, thixotropy, and thermal decomposition behavior of the organic vehicle in Nd-Fe-B screen printing slurry were studied. The results show that the organic vehicle formed by terpineol and polyvinyl butyral (PVB) exhibits typical non-Newtonian fluid characteristics, with excellent rheology and thixotropy, ensuring that the slurry prepared from it has excellent static stability and printing consistency. Additionally, the carbon residue of the organic vehicle formed by terpineol and PVB is less than 0.1% at 900 °C, avoiding excessive carbon entering the magnet during the diffusion process. Moreover, studying the rheology and thixotropy of the organic vehicle through a rheometer can quickly screen the slurry system. This work provides valuable guidance for designing an organic vehicle for screen-printing slurry for Nd-Fe-B grain boundary diffusion in future research. Full article

22 pages, 1095 KiB

Open AccessArticle

The Effect of Incorporating Dimethylaminohexadecyl Methacrylate and/or 2-Methacryloyloxyethyl Phosphorylcholine on Flexural Strength and Surface Hardness of Heat Polymerized and 3D-Printed Denture Base Materials

by Njood F. AlAzzam, Salwa O. Bajunaid, Heba A. Mitwalli, Bashayer H. Baras, Michael D. Weir and Hockin H. K. Xu

Materials 2024, 17(18), 4625; https://doi.org/10.3390/ma17184625 (registering DOI) - 20 Sep 2024

Abstract

Background: A major disadvantage of polymethyl methacrylate (PMMA) acrylic resins is susceptibility to biofilm accumulation. The incorporation of antimicrobial agents is a reliable prevention technique. The purpose of this study is to investigate the effect of incorporating dimethylaminohexadecyl methacrylate (DMAHDM) and/or 2-methacryloyloxyethyl phosphorylcholine [...] Read more.

Background: A major disadvantage of polymethyl methacrylate (PMMA) acrylic resins is susceptibility to biofilm accumulation. The incorporation of antimicrobial agents is a reliable prevention technique. The purpose of this study is to investigate the effect of incorporating dimethylaminohexadecyl methacrylate (DMAHDM) and/or 2-methacryloyloxyethyl phosphorylcholine (MPC) into heat-polymerized (HP) and 3D-printed (3DP) denture base materials on the flexural strength, modulus of elasticity, and surface hardness. Methods: DMAHDM and/or MPC were mixed with the acrylic resin liquid of a heat-polymerized (ProBase Hot) and a 3D printed (NextDent Denture 3D) material at mass fractions of 1.5% and 3% and a combination of 3% MPC and 1.5% DMAHDM. Results: Significant differences in mechanical properties between the control and experimental groups have been detected (p-value < 0.0001). In HP materials, the addition of DMAHDM and/or MPC generally decreased the flexural strength, from (151.18 MPa) in G1 down to (62.67 MPa) in G5, and surface hardness, from (18.05 N/mm²) down to (10.07 N/mm²) in G5. Conversely, in 3DP materials, flexural strength was slightly enhanced, from (58.22 MPa) in G1 up to (62.76 MPa) in G6, although surface hardness was consistently reduced, from (13.57 N/mm²) down to (5.29 N/mm²) in G5. Conclusion: It is recommended to carefully optimize the concentrations of DMAHDM and/or MPC to maintain mechanical integrity. Full article

(This article belongs to the Special Issue Advances in Dental and Restorative Materials)

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