Research

20 pages, 7731 KiB

Open AccessArticle

Study of Lightweight Ceramic Matrix-Less Syntactic Foam Composed of Cenosphere Using Spark Plasma Sintering

by Toms Valdemars Eiduks, Reinis Drunka, Vitalijs Abramovskis, Ilmars Zalite, Pavels Gavrilovs, Janis Baronins and Vjaceslavs Lapkovskis

Materials 2024, 17(2), 450; https://doi.org/10.3390/ma17020450 - 17 Jan 2024

Viewed by 827

Abstract

The current investigation presents porous ceramic materials prepared with cenospheres (CS) by using spark plasma sintering. The impact of sintering temperature, mould diameter (20, 30 and 50 mm) and cenosphere size on the properties of the sintered material was investigated. Shrinkage of the [...] Read more.

The current investigation presents porous ceramic materials prepared with cenospheres (CS) by using spark plasma sintering. The impact of sintering temperature, mould diameter (20, 30 and 50 mm) and cenosphere size on the properties of the sintered material was investigated. Shrinkage of the samples during sintering started at 900 °C. Total sample shrinkage during sintering increases with increasing temperature and decreases with increasing mould size; increasing sample sintering temperature increases the apparent density of all sample series CS 63–150 µm in a 20 mm mould from 0.97 to 2.3 g·cm⁻³ at 1050–1300 °C; in a 30 mm mould, 0.81–1.87 g·cm⁻³ at 1050–1200 °C; in 50 mm mould, 0.54–0.75 g·cm⁻³ at 1050–1150 °C; while CS 150–250 µm in a 20 mm mould is 0.93–1.96 g·cm⁻³ at 1050–1200 °C. Total porosity decreases from 61.5% to 3.9% by increasing sintering temperature from 1050 to 1250 °C, while open porosity reduces at lower temperatures, with closed porosity being highest in samples sintered at 1150 °C. When the sintering temperature increases from 1050 to 1300 °C, the compressive strength of the CS 63–150 samples produced in a 20 mm mould increases from 11 MPa to 312 MPa. These results correlate with the Rice model, which describes an exponential dependence of compressive strength on material porosity and fully dense material compressive strength. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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14 pages, 4658 KiB

Open AccessArticle

Exploring the Influences of BaO Amount on the Wettability and Mechanical Behavior of Vitrified Bond Diamond Composites

by Bingjian Guo, Haifeng Kuang, Xiaopan Liu, Hongyi Jiang, Rong Tu, Meijun Yang and Song Zhang

Materials 2024, 17(2), 339; https://doi.org/10.3390/ma17020339 - 10 Jan 2024

Cited by 1 | Viewed by 602

Abstract

In recent years, the vitrified bond diamond grinding wheel has been applied widely in automotive, aerospace and machine tools of manufacturing industries. However, the main problems of low intensity and poor wettability between the vitrified bond and diamond abrasive limit its further application. [...] Read more.

In recent years, the vitrified bond diamond grinding wheel has been applied widely in automotive, aerospace and machine tools of manufacturing industries. However, the main problems of low intensity and poor wettability between the vitrified bond and diamond abrasive limit its further application. In this study, BaO was added into the basic SiO₂–B₂O₃–Al₂O₃–R₂O vitrified bond system, and the impact of BaO on the wettability, thermal and mechanical behavior of vitrified bond and vitrified bond diamond composites was systematically discussed, respectively. The test indicated that when the vitrified bond containing BaO of 6 wt.% was sintered with diamond abrasive at 750 °C, a continuous barium feldspar phase transition layer between diamond abrasive and the bond was generated, which ameliorated the wet property of the bond–diamond abrasive. The contact angle varied from 59° on the blank sample to 35°, and the expansion coefficient changed from 6.24 × 10⁻⁶/K to 5.30 × 10⁻⁶/K. The Rockwell hardness and flexural strength of the vitrified bond diamond composites achieved the peaks of 117.5 MPa and 113.6 MPa, respectively, which increased by 20.2% and 16.5% compared with that of sample without the addition of BaO. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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23 pages, 29797 KiB

Open AccessArticle

High-Temperature, Lightweight Ceramics with Nano-Sized Ferrites for EMI Shielding: Synthesis, Characterisation, and Potential Applications

by Vitalijs Abramovskis, Ilmars Zalite, Mikhail Maiorov, Janis Baronins, Ashish Kumar Singh, Vjaceslavs Lapkovskis, Saurav Goel and Andrei Shishkin

Materials 2023, 16(24), 7615; https://doi.org/10.3390/ma16247615 - 12 Dec 2023

Viewed by 1245

Abstract

The present study focuses on the synthesis and characterisation of a lightweight ceramic material with electromagnetic interference (EMI) shielding properties, achieved using mullite containing micrometre-sized hollow spheres (cenospheres) and CoFe₂O₄ nanoparticles. This research explores compositions with varying CoFe₂O [...] Read more.

The present study focuses on the synthesis and characterisation of a lightweight ceramic material with electromagnetic interference (EMI) shielding properties, achieved using mullite containing micrometre-sized hollow spheres (cenospheres) and CoFe₂O₄ nanoparticles. This research explores compositions with varying CoFe₂O₄ contents ranging from 0 up to 20 wt.%. Conventional sintering in an air atmosphere is carried out at a temperature between 1100 and 1300 °C. The addition of ferrite nanoparticles was found to enhance the process of sintering cenospheres, resulting in improved material density and mechanical properties. Furthermore, this study reveals a direct correlation between the concentration of ferrite nanoparticles and the electromagnetic properties of the material. By increasing the concentration of ferrite nanoparticles, the electromagnetic shielding effect of the material (saturation magnetisation (M_s) and remanent magnetisation (M_r)) was observed to strengthen. These findings provide valuable insights into designing and developing lightweight ceramic materials with enhanced electromagnetic shielding capabilities. The synthesized ceramic material holds promise for various applications that require effective electromagnetic shielding, such as in the electronics, telecommunications, and aerospace industries. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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12 pages, 3374 KiB

Open AccessArticle

Structural and Electrical Characterization of LaSrAl_1−xMg_xO_4−δ Layered Perovskites Obtained by Mechanical Synthesis

by Carlos Mariño, Daniel Serafini, Juan Basbus, José Antonio Alonso and Loreto Troncoso

Materials 2023, 16(24), 7564; https://doi.org/10.3390/ma16247564 - 08 Dec 2023

Viewed by 712

Abstract

This work presents the structural and electrical characterization of K₂NiF₄-type layered perovskites of LaSrAl_1−xMg_xO_4−δ composition to be used as oxide–ion electrolytes for a solid-oxide fuel cell (SOFC). These perovskites were prepared by mechano-chemical synthesis [...] Read more.

This work presents the structural and electrical characterization of K₂NiF₄-type layered perovskites of LaSrAl_1−xMg_xO_4−δ composition to be used as oxide–ion electrolytes for a solid-oxide fuel cell (SOFC). These perovskites were prepared by mechano-chemical synthesis (ball milling), an alternative to traditional synthesis methods such as citrate-nitrates and solid-state reaction. With these methods, two things are avoided: first, the use of nitrate salts, which are more environmentally harmful than oxide precursors, and second, it saves the series of long thermal treatments associated with solid-state reactions. After grinding the precursors, nanometric particles were obtained with a combination of crystalline regions and amorphous regions; this effect was determined by XRD and TEM, showing that Mg has a positive effect on the phase formation by only mechanical synthesis. R2C4: After sintering, it was found by XRD that the sample x = 0.1 only presents the diffraction peaks corresponding to the desired phase, which shows a phase purity greater than 97%, even higher than that of the standard undoped sample. For x = 0.2 and 0.3, there was a segregation of impurities, possibly by the local migration of La and Sr heavy cations; this was determined by SEM and EDS. The electrical characterization of the sintered pellets was carried out by electrochemical impedance spectroscopy, which determined that the incorporation of Mg in the structure improves the ionic conductivity by three orders of magnitude, obtaining conductivities of 1.6 mS/cm at 900 °C for x = 0.2. Although the improvement in conductivity is considerable, many challenges such as densification, the segregation of impurities, and the study of mechanical and thermal properties must be carried out on these materials to endorse them as solid electrolytes in SOFC. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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13 pages, 3281 KiB

Open AccessArticle

Synthesis and Investigation of Properties of Beryllium Ceramics Modified with Titanium Dioxide Nanoparticles

by Alexandr Pavlov, Zhuldyz Sagdoldina, Almira Zhilkashinova, Nurtoleu Magazov, Zhangabay Turar and Sergey Gert

Materials 2023, 16(19), 6507; https://doi.org/10.3390/ma16196507 - 30 Sep 2023

Viewed by 605

Abstract

Samples of beryllium ceramics, with the addition of micro- and nanoparticles TiO_2, have been obtained by the method of thermoplastic slip casting. The microstructure of batch ceramics, consisting of micropowders and ceramics with TiO₂ nanoparticles sintered at an elevated temperature, has [...] Read more.

Samples of beryllium ceramics, with the addition of micro- and nanoparticles TiO_2, have been obtained by the method of thermoplastic slip casting. The microstructure of batch ceramics, consisting of micropowders and ceramics with TiO₂ nanoparticles sintered at an elevated temperature, has been investigated. It was found that the introduction of TiO₂ nanoparticles leads to changes in the mechanisms of mass transfer and microstructure formation, and the mobility of TiO₂ at interfacial grain boundaries increases, which leads to the formation of elements of a zonal shell structure. The reduction of intergranular boundaries leads to an increase in density, hardness, and mechanical strength of ceramics. The whole complex of properties of the synthesized material, with the addition of TiO₂ nanoparticles in the amount of 1.0–1.5 wt.%, leads to an increase in the ability to absorb electromagnetic radiation in the frequency range of electric current 8.2–12.4 GHz. The analysis and updating of knowledge on synthesis, and the investigation of properties of beryllium ceramics modified by nanoparticles, seems to be significant. The obtained results can be used in the creation of absorbers of scattered microwave radiation based on (BeO + TiO₂) ceramics. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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14 pages, 1617 KiB

Open AccessArticle

Experimental vs. Theoretical Viscosity Determination of Aluminosilicate Glasses

by Anna Zawada, Malgorzata Lubas and Adrian Nowak

Materials 2023, 16(17), 5789; https://doi.org/10.3390/ma16175789 - 24 Aug 2023

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Abstract

The paper presents the results of studies on the viscosity of the glass mass in various temperature ranges, determining the basic technological parameter, very important from the point of view of melting and forming. For this purpose, six sets based on natural raw [...] Read more.

The paper presents the results of studies on the viscosity of the glass mass in various temperature ranges, determining the basic technological parameter, very important from the point of view of melting and forming. For this purpose, six sets based on natural raw materials such as basalt, dolomite, and amphibolite, modified with different amounts of float glass cullet, were melted. The melting process was carried out in an electric furnace at the temperature of 1450 °C for 2 h. Using the dilatometric method, high-temperature microscopy and theoretical calculation methods, the viscosity of the produced glasses was determined in various temperature ranges. Comparative analyses of the employed methods were carried out. The significance of the applied calculation methods for aluminosilicate glasses depending on the basic chemical composition of the glasses was presented. The relationship between the manner of incorporating amphoteric ions Al³⁺, Fe³⁺ and Mg²⁺ into the glass structure and the change in viscosity in the temperature range corresponding to the working point range at 10⁴ [dPa·s] viscosity and the relaxation range—T_g temperature at 10¹³ [dPa·s] viscosity was justified. It was justified that in order to plot the viscosity curve with the correct slope in the forming range for aluminosilicate glasses, it is appropriate to use the two-point method based on the fixed viscosity points of 10⁴ [dPa·s] and 10¹³ [dPa·s]. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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13 pages, 4524 KiB

Open AccessArticle

Enhanced Mechanical Properties of Al₂O₃ Nanoceramics via Low Temperature Spark Plasma Sintering of Amorphous Powders

by Dongjiang Zhang, Rui Yu, Xuelei Feng, Xuncheng Guo, Yongkang Yang and Xiqing Xu

Materials 2023, 16(16), 5652; https://doi.org/10.3390/ma16165652 - 17 Aug 2023

Cited by 1 | Viewed by 618

Abstract

In this work, Al₂O₃ nanoceramics were prepared by spark plasma sintering of amorphous powders and polycrystalline powders with similar particle sizes. Effective comparisons of sintering processes and ultimate products depending on starting powder conditions were explored. To ensure near-full density [...] Read more.

In this work, Al₂O₃ nanoceramics were prepared by spark plasma sintering of amorphous powders and polycrystalline powders with similar particle sizes. Effective comparisons of sintering processes and ultimate products depending on starting powder conditions were explored. To ensure near-full density higher than 98% of the Al₂O₃ nanoceramics, the threshold temperature in SPS is 1450 °C for polycrystalline Al₂O₃ powders and 1300 °C for amorphous powders. The low SPS temperature for amorphous powders is attributed to the metastable state with high free energy of amorphous powders. The Al₂O₃ nanoceramics prepared by amorphous powders display a mean grain size of 170 nm, and superior mechanical properties, including high bending strength of 870 MPa, Vickers hardness of 20.5 GPa and fracture toughness of 4.3 MPa∙m^1/2. Furthermore, the Al₂O₃ nanoceramics prepared by amorphous powders showed a larger dynamic strength and dynamic strain. The toughening mechanism with predominant transgranular fracture is explained based on the separation of quasi-boundaries. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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11 pages, 2805 KiB

Open AccessArticle

Solubility and Valence Variation of Ce in Low-Alkali Borosilicate Glass and Glass Network Structure Analysis

by Liu Yang, Yongchang Zhu, Jichuan Huo, Zhu Cui, Xingquan Zhang, Xuanjiang Dong and Jie Feng

Materials 2023, 16(14), 5063; https://doi.org/10.3390/ma16145063 - 18 Jul 2023

Viewed by 797

Abstract

Low-alkali borosilicate glass was used as the immobilization substrate, and Ce was used to replicate the trivalent and tetravalent actinides, in order to create simulated waste glass through melt heat treatment. The valence of Ce and solubility of CeO₂ in waste glass [...] Read more.

Low-alkali borosilicate glass was used as the immobilization substrate, and Ce was used to replicate the trivalent and tetravalent actinides, in order to create simulated waste glass through melt heat treatment. The valence of Ce and solubility of CeO₂ in waste glass were studied as well as its network structure and thermal and chemical stability. The solubility of Ce in waste glass was examined by XRD and SEM. The network structure was examined by Raman spectroscopy. The valence of Ce was determined by X-ray photoelectron spectroscopy. Thermal analysis and product consistency (PCT) were employed to determine the thermal and chemical stability of waste glasses. The results show that the solubility of cerium in low-alkali borosilicate glasses is at least 25.wt.% and precipitates a spherical CeO₂ crystalline phase when it exceeds the solid solution limit; Ce is immobilized in the glass by entering the interstices of the glass network. Depolymerization and the transition from [BO₃] to [BO₄] occurs when CeO₂ doping levels rise. About 60 percent of Ce⁴⁺ is converted to Ce³⁺, and the thermal stability of glass rises then falls with the increase of CeO₂. All samples exhibit strong leaching resistance, with the average mass loss of Ce at 28 days being less than 10⁻⁴ gm⁻²d⁻¹. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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13 pages, 3782 KiB

Open AccessArticle

Study of TiO₂ on the Voltage Holdoff Capacity of Cr/Mn-Doped Al₂O₃ Ceramic in Vacuum

by Dandan Feng, Xiaojing Wang, Shike Zhao, Baipeng Song and Guanjun Zhang

Materials 2023, 16(14), 5048; https://doi.org/10.3390/ma16145048 - 17 Jul 2023

Viewed by 585

Abstract

With the development of vacuum electronic devices toward high power, high frequency, and miniaturization, the voltage holdoff capacity of the insulation materials in devices has also been raised to a higher demand. Cr/Mn/Ti-doped Al₂O₃ ceramics were prepared, and the bulk [...] Read more.

With the development of vacuum electronic devices toward high power, high frequency, and miniaturization, the voltage holdoff capacity of the insulation materials in devices has also been raised to a higher demand. Cr/Mn/Ti-doped Al₂O₃ ceramics were prepared, and the bulk density, micromorphology, phase composition, resistivity, secondary electron emission coefficient, and surface flashover threshold in the vacuum of the Al₂O₃ were characterized. The results show that the addition of TiO₂ to the Al₂O₃ ceramic can promote the sintering of the ceramic. The Cr/Mn/Ti-doped Al₂O₃ ceramic with a homogeneous microstructure can be obtained by an appropriate amount of TiO₂ addition. In the process of the heat treatment, the TiO₂ in the ceramics was reduced to a certain degree, which had an impact on the microstructure of the Al₂O₃ ceramic. Adding a small amount of TiO₂ can improve the voltage holdoff performance in the vacuum. The value of the surface flashover threshold in the vacuum of the Cr/Mn/Ti-doped Al₂O₃ ceramic containing 1 wt.% TiO₂ reached a value of 33 kV, which is 32% higher than that of the basic Al₂O₃ ceramic. The preparation of Al₂O₃ ceramics with a high voltage holdoff capacity in a vacuum provides fundamental technical support for the development of vacuum electronic devices. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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16 pages, 13309 KiB

Open AccessArticle

A Novel Inorganic Aluminum Phosphate-Based Flame Retardant and Thermal Insulation Coating and Performance Analysis

by Guoshuai Cai, Jiaxuan Wu, Jiayi Guo, Yange Wan, Qingjun Zhou, Pengyu Zhang, Xiaolei Yu and Mingchao Wang

Materials 2023, 16(13), 4498; https://doi.org/10.3390/ma16134498 - 21 Jun 2023

Cited by 4 | Viewed by 1271

Abstract

Currently, most thin-layer expandable coatings are polymer-based, with very few inorganic expandable coatings. Due to the high environmental friendliness of inorganic coatings, studying new types of inorganic coatings is of great significance. A novel amorphous aluminum phosphate-based flame-retardant coating was prepared by modifying [...] Read more.

Currently, most thin-layer expandable coatings are polymer-based, with very few inorganic expandable coatings. Due to the high environmental friendliness of inorganic coatings, studying new types of inorganic coatings is of great significance. A novel amorphous aluminum phosphate-based flame-retardant coating was prepared by modifying it with nano-silica, hollow silica beads, hollow glass microspheres, and boron carbide. A comprehensive study was conducted on the flame retardancy and thermal insulation performance, composition and structural evolution under flame and physical and chemical properties, and the mechanisms of flame retardancy and thermal insulation were elucidated. Large-plate combustion testing, bonding strength testing, XRD, IR, TG-DSC, and SEM testing were all applied in this work. The synergistic effect of the four fillers was very obvious, and a series of AP22XY (nano-silica/silica beads/hollow glass microspheres/boron carbide = 2:2:0:4, 2:2:1:3, 2:2:2:2, 2:2:3:1, 2:2:4:0) coatings were prepared. The change in the ratio of glass microspheres to boron carbide had a significant impact on the composition and structural evolution of the coating, thus reflecting its effectiveness as a flame retardant and thermal insulation. Although decreasing the ratio would promote the formation of borosilicate glass and Al₁₈B₄O₃₃ and improve the thermal stability of coatings, the structure inside of the coating, especially the skeleton, would be dense, which is not conducive to thermal insulation. When the ratio of glass microspheres to boron carbide is 3:1, AP2231 shows the best fire resistance. Under the combustion of butane flame at about 1200–1300 °C, the backside temperature reaches a maximum of 226 °C at 10 min, and then the temperature gradually decreases to 175 °C at 60 min. This excellent performance is mainly attributed to three aspects: (1) the foaming and expandability of coatings when exposed to fire, (2) the multiple endothermic reactions the coating undergoes, and (3) the improvement effect of boron carbide. Additionally, AP2231 shows the best bonding performance with a strength of close to 4.5 MPa after combustion, because of the appropriate content matching between borosilicate glass, Al₁₈B₄O₃₃, and hollow glass microspheres. The coating has potential application prospects in the construction and transportation fields, such as the protection of structural steel, fire prevention in subways and tunnels, and the prevention of lithium battery fires. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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14 pages, 5431 KiB

Open AccessFeature PaperArticle

Effects of β-Si₃N₄ Seeds on Microstructure and Performance of Si₃N₄ Ceramics in Semiconductor Package

by Qiang Shen, Zhijie Lin, Junjie Deng, Hongxiang Chen, Xuan Chen, Jun Tian, Biliang Bao, Pinqiang Dai and Xudong Sun

Materials 2023, 16(12), 4461; https://doi.org/10.3390/ma16124461 - 19 Jun 2023

Viewed by 1131

Abstract

Among the various ceramic substrate materials, Si₃N₄ ceramics have demonstrated high thermal conductivity, good thermal shock resistance, and excellent corrosion resistance. As a result, they are well-suited for semiconductor substrates in high-power and harsh conditions encountered in automobiles, high-speed rail, [...] Read more.

Among the various ceramic substrate materials, Si₃N₄ ceramics have demonstrated high thermal conductivity, good thermal shock resistance, and excellent corrosion resistance. As a result, they are well-suited for semiconductor substrates in high-power and harsh conditions encountered in automobiles, high-speed rail, aerospace, and wind power. In this work, Si₃N₄ ceramics with various ratios of α-Si₃N₄ and β-Si₃N₄ in raw powder form were prepared by spark plasma sintering (SPS) at 1650 °C for 30 min under 30 MPa. When the content of β-Si₃N₄ was lower than 20%, with the increase in β-Si₃N₄ content, the ceramic grain size changed gradually from 1.5 μm to 1 μm and finally resulted in 2 μm mixed grains. However, As the content of β-Si₃N₄ seed crystal increased from 20% to 50%, with the increase in β-Si₃N₄ content, the ceramic grain size changed gradually from 1 μm and 2 μm to 1.5 μm. Therefore, when the content of β-Si₃N₄ in the raw powder is 20%, the sintered ceramics exhibited a double-peak structure distribution and the best overall performance with a density of 97.5%, fracture toughness of 12.1 MPa·m^1/2, and a Vickers hardness of 14.5 GPa. The results of this study are expected to provide a new way of studying the fracture toughness of silicon nitride ceramic substrates. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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13 pages, 4889 KiB

Open AccessArticle

The Influence of the Synthesis Method on the Characteristics of BaTiO₃

by G. N. Almeida, R. N. de Souza, L. F. S. Lima, N. D. S. Mohallem, E. P. da Silva and A. M. A. Silva

Materials 2023, 16(8), 3031; https://doi.org/10.3390/ma16083031 - 11 Apr 2023

Cited by 2 | Viewed by 1267

Abstract

In this work, barium titanate powders were produced by sol-gel and sol-precipitation methods from metal alkoxides. In the sol-gel method, tetraisopropyl orthotitanate was mixed with 2-propanol, acetic acid and barium acetate, and the gel samples obtained were calcined at 600 °C, 800 °C [...] Read more.

In this work, barium titanate powders were produced by sol-gel and sol-precipitation methods from metal alkoxides. In the sol-gel method, tetraisopropyl orthotitanate was mixed with 2-propanol, acetic acid and barium acetate, and the gel samples obtained were calcined at 600 °C, 800 °C and 1000 °C. Through the sol-precipitation method, tetraisopropyl orthotitanate was mixed with acetic acid and deionized water and precipitated by the addition of a concentrated solution of KOH. The products were calcined at various temperatures, and the microstructural and dielectric properties of the BaTiO₃ prepared for the two processes were analyzed and compared. The results of these analyses allowed us to observe an increase in the tetragonal phase and the dielectric constant (15–50 at 20 kHz) with increasing temperatures in the samples produced by the sol-gel method, while the sample obtained by sol precipitation was cubic. The presence of BaCO₃ is more evident in the sample produced by sol-precipitation, and the band gap of the products obtained did not show significant variation, changing the synthesis method (3.363–3.594 eV). Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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19 pages, 4674 KiB

Open AccessArticle

Preparation of High-Stability Ceramic Slurry with Gel Behavior for Stereolithography 3D Printing

by Ning Wang, Hai Chang, Chi Zhang, Yingna Wu, Rui Yang, Xing Zhang and Zirong Zhai

Materials 2023, 16(7), 2816; https://doi.org/10.3390/ma16072816 - 01 Apr 2023

Cited by 2 | Viewed by 2111

Abstract

Maintaining sufficient uniformity and stability of a ceramic slurry throughout the printing cycle is key to ensuring the performance of ceramic parts in ceramic-slurry stereolithography. In this study, a stable three-dimensional network structure was introduced into a slurry to achieve slurry uniformity and [...] Read more.

Maintaining sufficient uniformity and stability of a ceramic slurry throughout the printing cycle is key to ensuring the performance of ceramic parts in ceramic-slurry stereolithography. In this study, a stable three-dimensional network structure was introduced into a slurry to achieve slurry uniformity and stability based on rheology theory. The effects of the particle size, solid loading, dispersant content, and gelling agent content on the stability of the three-dimensional network structure in the slurry were analyzed. Relatively stable three-dimensional network structures were constructed to achieve 4-week stability of micron- and submicron-size particle slurries by adjusting the contents of the dispersant and gelling agent. Stabilization ideas for different particle size ranges are provided. In addition, an empirical stability model was obtained based on the experimental results. When the predicted empirical stability factor of A was less than 0.035, the slurry exhibited good stability. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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12 pages, 2542 KiB

Open AccessArticle

Facile Synthesis of Two-Dimensional Natural Vermiculite Films for High-Performance Solid-State Electrolytes

by Yan Xing, Xiaopeng Chen, Yujia Huang, Xiali Zhen, Lujun Wei, Xiqiang Zhong and Wei Pan

Materials 2023, 16(2), 729; https://doi.org/10.3390/ma16020729 - 11 Jan 2023

Viewed by 1512

Abstract

Ceramic electrolytes hold application prospects in all-solid-state lithium batteries (ASSLB). However, the ionic conductivity of ceramic electrolytes is limited by their large thickness and intrinsic resistance. To cope with this challenge, a two-dimensional (2D) vermiculite film has been successfully prepared by self-assembling expanded [...] Read more.

Ceramic electrolytes hold application prospects in all-solid-state lithium batteries (ASSLB). However, the ionic conductivity of ceramic electrolytes is limited by their large thickness and intrinsic resistance. To cope with this challenge, a two-dimensional (2D) vermiculite film has been successfully prepared by self-assembling expanded vermiculite nanosheets. The raw vermiculite mineral is first exfoliated to thin sheets of several atomic layers with about 1.2 nm interlayer channels by a thermal expansion and ionic exchanging treatment. Then, through vacuum filtration, the ion-exchanged expanded vermiculite (IEVMT) sheets can be assembled into thin films with a controllable thickness. Benefiting from the thin thickness and naturally lamellar framework, the as-prepared IEVMT thin film exhibits excellent ionic conductivity of 0.310 S·cm⁻¹ at 600 °C with low excitation energy. In addition, the IEVMT thin film demonstrates good mechanical and thermal stability with a low coefficient of friction of 0.51 and a low thermal conductivity of 3.9 × 10⁻³ W·m⁻¹·K⁻¹. This reveals that reducing the thickness and utilizing the framework is effective in increasing the ionic conductivity and provides a promising stable and low-cost candidate for high-performance solid electrolytes. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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12 pages, 2635 KiB

Open AccessArticle

Microstructure and Crystallization Kinetics of Silica-Based Ceramic Cores with Enhanced High-Temperature Property

by Xin Li, Shuxin Niu, Dongsheng Wang, Jie Li, Qi Jiao, Xinlong Guo and Xiqing Xu

Materials 2023, 16(2), 606; https://doi.org/10.3390/ma16020606 - 08 Jan 2023

Cited by 4 | Viewed by 1093

Abstract

Silica-based ceramic cores play key roles in the casting of aeroengine blades, but they are highly limited by the poor high-temperature mechanical property. Here, fused mullite (FM) and sintered mullite (SM) powders were modified in silica-based ceramic cores, and the microstructure evolution and [...] Read more.

Silica-based ceramic cores play key roles in the casting of aeroengine blades, but they are highly limited by the poor high-temperature mechanical property. Here, fused mullite (FM) and sintered mullite (SM) powders were modified in silica-based ceramic cores, and the microstructure evolution and crystallization kinetics of ceramic cores depending on mullite types were studied. The ceramic cores with FM showed a dense microstructure and superior mechanical properties compared to those with SM. The ceramic cores with 10 wt.% of FM showed a crystallization activation energy of 1119.5 kJ/mol and a crystallization exponent of 1.74, and the values of 938.4 kJ/mol and 1.86 as SM were employed; the decreased crystallization activation energy and the elevated crystallization exponent by SM suggested that the excess impurities of alkali oxides and alkaline-earth oxides significantly promoted the crystallization of cristobalite. Even though the ceramic cores with mullite powders decreased slightly in the room-temperature mechanical property, their high-temperature flexure strength and creep deformation resistance were enhanced. The ceramic cores with 10 wt.% of FM showed excellent comprehensive performance, with linear shrinkage of 0.69%, room-temperature strength of 18.9 MPa, and high-temperature strength of 15.5 MPa, which satisfied the demands for hollow-blade casting. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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19 pages, 3516 KiB

Open AccessArticle

Characterization and In Vitro Biocompatibility of Two New Bioglasses for Application in Dental Medicine—A Preliminary Study

by Andra Clichici, Gabriela Adriana Filip, Marcela Achim, Ioana Baldea, Cecilia Cristea, Gheorghe Melinte, Ovidiu Pana, Lucian Barbu Tudoran, Diana Dudea and Razvan Stefan

Materials 2022, 15(24), 9060; https://doi.org/10.3390/ma15249060 - 18 Dec 2022

Cited by 2 | Viewed by 1526

Abstract

Bioactive glasses (BGs), also known as bioglasses, are very attractive and versatile materials that are increasingly being used in dentistry. For this study, two new bioglasses—one with boron (BG1) and another with boron and vanadium (BG2)—were synthesized, characterized, and tested on human dysplastic [...] Read more.

Bioactive glasses (BGs), also known as bioglasses, are very attractive and versatile materials that are increasingly being used in dentistry. For this study, two new bioglasses—one with boron (BG1) and another with boron and vanadium (BG2)—were synthesized, characterized, and tested on human dysplastic keratinocytes. The in vitro biological properties were evaluated through pH and zeta potential measurement, weight loss, Ca²⁺ ions released after immersion in phosphate-buffered saline (PBS), and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) analysis. Furthermore, biocompatibility was evaluated through quantification of lactate dehydrogenase activity, oxidative stress, transcription factors, and DNA lesions. The results indicate that both BGs presented the same behavior in simulated fluids, characterized by high degradation, fast release of calcium and boron in the environment (especially from BG1), and increased pH and zeta potential. Both BGs reacted with the fluid, particularly BG2, with irregular deposits covering the glass surface. In vitro studies demonstrated that normal doses of the BGs were not cytotoxic to DOK, while high doses reduced cell viability. Both BGs induced oxidative stress and cell membrane damage and enhanced NFkB activation, especially BG1. The BGs down-regulated the expression of NFkB and diminished the DNA damage, suggesting the protective effects of the BGs on cell death and efficacy of DNA repair mechanisms. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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16 pages, 7074 KiB

Open AccessArticle

Effect of Thermal Growth Oxide Composition and Morphology on Local Stresses in Thermal Barrier Coatings

by Kunying Ding, Tao Zhang, Zhe Wang, Jun Yu, Wansen Guo and Yifei Yang

Materials 2022, 15(23), 8442; https://doi.org/10.3390/ma15238442 - 27 Nov 2022

Cited by 6 | Viewed by 1091

Abstract

The failure of thermal barrier coatings (TBCs) during operation depends mainly on the thermal mismatch between the ceramic top coat (TC) and the metal bond coat (BC). The thermal mismatch at the interface is influenced by the dynamic changes in the composition and [...] Read more.

The failure of thermal barrier coatings (TBCs) during operation depends mainly on the thermal mismatch between the ceramic top coat (TC) and the metal bond coat (BC). The thermal mismatch at the interface is influenced by the dynamic changes in the composition and morphology of the thermally grown oxide (TGO) between TC and BC during thermal cycling. This work focuses on the establishment of a TGO dynamic growth model, which considers the changes in TGO composition and morphology for investigating the effect of dynamic growth of TGO on local mismatch stresses during thermal cycling. The results show that the sharp locations at the TGO/BC interface are more prone to high tensile stresses during thermal cycling due to the uneven growth behavior of TGO, leading to crack initiation. The valley region of the interface is in a state of compressive stress σ_xx during the early stages of thermal exposure. The peak region preferentially forms a concentration of tensile stress σ_yy. Once large-scale “layer” (Ni, Co)Al₂O₄-based spinel-like mixed oxides(MO) growth occurs in TGO, the stress σ_xx changes from compressive stress to tensile stress in the valley region, eventually forming high tensile stress (Max: +158 MPa). The maximum tensile stress σ_yy in the peak region is increased to 256 MPa, which is more than two times larger than the early period of thermal exposure. As a result, the dramatic changes in local stresses seriously affect the time and location of microcracks. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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12 pages, 3877 KiB

Open AccessArticle

A Promising High-Entropy Thermal Barrier Material with the Formula (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂

by Zhanqiang Li, Junfeng Zheng, Wenjuan Zhang, Yong Zheng, Weijun Zhao, Liyan Xue, Fan Yang and Heng Chen

Materials 2022, 15(22), 8079; https://doi.org/10.3390/ma15228079 - 15 Nov 2022

Cited by 4 | Viewed by 1340

Abstract

YSZ has been widely used as a TBC material, but its phase change at high temperatures limits its development, thus the need for developing new thermal barrier materials resistant to high temperatures. Rare-earth aluminate ceramics with a garnet structure (Yb₃Al₅ [...] Read more.

YSZ has been widely used as a TBC material, but its phase change at high temperatures limits its development, thus the need for developing new thermal barrier materials resistant to high temperatures. Rare-earth aluminate ceramics with a garnet structure (Yb₃Al₅O₁₂) have been considered as a potential thermal barrier material. The melting point of Yb₃Al₅O₁₂ is 2000 °C, which has a potential high temperature application prospect. However, Yb₃Al₅O₁₂ has lower thermal expansion and higher thermal conductivity than YSZ, which is a widely employed thermal barrier coating (TBC) material. To overcome these obstacles, (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂, a high-entropy ceramic, was prepared by a solid-state reaction and pressureless sintering. The thermal conductivity of the (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂ was 3.48 W/(m·K) at 300 K, approximately 25.48% lower than that of the Yb3Al5O12 (4.67 W/(m·K)). The thermal expansion coefficient of the (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂ was 9.28 × 10⁻⁶ K⁻¹ at 673-1273 K, approximately 18.52% higher than that of the Yb₃Al₅O₁₂ (7.83 × 10⁻⁶ K⁻¹, 673-1273 K). When the (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂ was annealed at 1550 °C for 7 days, its average grain size only increased from 0.7 μm to 1.3 μm. Moreover, the (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂ exhibited better chemical stability and a lower grain growth rate than the Yb₃Al₅O₁₂. This study reveals that (Y_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂ is a promising candidate for the future generation of thermal barrier materials. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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13 pages, 7047 KiB

Open AccessArticle

Fire Extinguishing Performance of Chemically Bonded Struvite Ceramic Powder with High Heat-Absorbing and Flame Retardant Properties

by Zilong Liang, Zhiji Zhou, Yunqi Sun, Yujia Huang, Xinya Guo, Guoshuai Cai, Mingchao Wang and Haijun Zhang

Materials 2022, 15(22), 8021; https://doi.org/10.3390/ma15228021 - 14 Nov 2022

Cited by 5 | Viewed by 1381

Abstract

Struvite is a chemically bonded ceramic product in the pipeline of a sewage treatment plant. In order to explore the fire extinguishing potential of struvite, a new type of struvite ultrafine dry powder with excellent performance was prepared by a simple process, and [...] Read more.

Struvite is a chemically bonded ceramic product in the pipeline of a sewage treatment plant. In order to explore the fire extinguishing potential of struvite, a new type of struvite ultrafine dry powder with excellent performance was prepared by a simple process, and its fire extinguishing performance and mechanism were analyzed in depth. Under the same process conditions, the refinement degree (D50 = 5.132 μm) and the specific surface area (BET = 25.72 m²/g) of ultrafine struvite were larger than those of NH₄H₂PO₄ (D50 = 8.961 μm, BET = 13.64 m²/g), making struvite more suitable for fire extinguishing. Besides, the pyrolysis process of struvite was relatively concentrated and absorbed more heat in a short time. Its heat absorption (458.4 J/mg) was higher than that of NH₄H₂PO₄ (156.4 J/mg). Water, ammonia, and PO· were released during the pyrolysis of struvite, which effectively reduced fire temperature, diluted oxygen concentrations and captured free radicals. At the same time, the final products were magnesium orthophosphate and magnesium pyrophosphate, which formed a dense flame-retardant ceramic layer with good thermal insulation and environmental protection functions. In these cases, the fire extinguishing mechanism of struvite was determined to have three stages: the cooling effect, the asphyxiation effect, and the chemical effect. Correspondingly, the fire extinguishing time of struvite was three seconds faster than that of ammonium phosphate under 0.2 MPa based on the local oil basin test. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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12 pages, 4434 KiB

Open AccessArticle

Effect of Carbon Content on Mechanical Properties of Boron Carbide Ceramics Composites Prepared by Reaction Sintering

by Wenhao Sha, Yingying Liu, Yabin Zhou, Yihua Huang and Zhengren Huang

Materials 2022, 15(17), 6028; https://doi.org/10.3390/ma15176028 - 01 Sep 2022

Cited by 4 | Viewed by 1211

Abstract

In this study, different reaction-bonded boron carbide (RBBC) composites with a free carbon addition from 0 to 15 wt% were prepared, and the effect of the carbon content on the mechanical properties was discussed. With the free carbon addition increase from 0 to [...] Read more.

In this study, different reaction-bonded boron carbide (RBBC) composites with a free carbon addition from 0 to 15 wt% were prepared, and the effect of the carbon content on the mechanical properties was discussed. With the free carbon addition increase from 0 to 15 wt%, the residual silicon content in the RBBC composite decreased first and then increased. Meanwhile, the strength of the RBBC composite improved first and then worsened. In the RBBC composite without free carbon, the B₄C grains are obviously dissolved, the grains become facet-shape, and the grain boundary becomes straight. The microstructure of the composite was tested by SEM, and the phase composition of the composite was tested by XRD. The RBBC composite with the addition of 10 wt% free carbon has the highest flexural strength (444 MPa) and elastic modulus (329 GPa). In the composite with a 10 wt% carbon addition, the phase distribution is uniform and the structure is compact. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications)

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