Mechanical Properties Of Ceramics Research Articles

Robust, thermally insulating, and high-temperature resistant phosphate-enhanced mullite fiber porous ceramic composites

Porous mullite ceramics with high porosity and low thermal conductivity are urgently required as high-temperature thermal insulators in harsh environments. How to improve the strength of Porous mullite ceramics dramatically under the premise of no sacrificing its thermal insulating properties has remained an extremely challenging. Inspired by the freezing rain phenomenon in nature, high-strength and high-temperature resistant phosphate coatings were applied to the surface of mullite fibers, which significantly improved the mechanical properties of porous mullite ceramics without significantly increasing their thermal conductivity. The Al(H2PO4)3 solution concentration significantly affected the mechanical and thermal properties of the composite material, where the mechanical performance improved with an increasing Al(H2PO4)3 solution concentration. The phosphate coating phase stabilized with an increasing calcination temperature. The mechanical properties of the ceramics were improved by the excellent interfacial bonding strength between the coating and mullite fiber, and the forms of phosphate in the porous ceramics. The optimum composite preparation process increased its compressive strength by approximately nine-fold to 4.1 MPa and resulted in a thermal conductivity of only approximately 0.09 W/(m·K), demonstrating that the composite exhibited a significantly higher comprehensive performance than other previously reported porous ceramics and aerogels. Such new composites with excellent mechanical and thermal insulation properties exhibit excellent potential for high-strength thermal insulation in the chemical, metallurgical, pharmaceutical, aerospace, and other fields.

Translucency and Strength of Lithium Disilicate for Computer-Aided Design and Manufacturing at Different Thermal Temperatures and Thicknesses: An In Vitro Study.

To manufacture dental restorations composed of lithium disilicate (LD) through the computer-aided design and manufacturing (CAD/CAM) process, thermal refinement is an essential process that can affect the optical and mechanical properties of ceramics. In this study, we aimed to evaluate the translucency and flexural strength of lithium disilicate glass-ceramic for CAD/CAM using different thermal refinement schedules and thicknesses by measuring the total transmission of light through the specimen and calculating the peak load of the specimen until fracture in a piston-on-three-ball test, respectively. The results showed that a lower translucency was exhibited in thicker specimens, and the flexural strength decreased in the order of 1.0, 0.5, and 2.0 mm (p < 0.05). The lithium disilicates thermally refined at a heat of 820 degrees were shown to have the highest biaxial flexural strength (p < 0.05). These findings suggest that it is possible to adjust transparency and strength according to the clinical situation by choosing an appropriate thickness and thermal refinement process.

Introducing dislocations in ceramics by mechanical rolling: A first demonstration using SrTiO3 crystal

AbstractIt has long been known that dislocations can be used to tune the functional and mechanical properties of ceramics. However, introducing dislocations with controllable networks and densities into ceramics is difficult. In this study, a mechanical rolling technique was proposed to introduce dislocations into ceramics. Using a hard SiC ball with a diameter of 5 mm as a roller, plastic zones and dislocations were successfully produced in a SrTiO3 (STO) single crystal. The plastic zone area and dislocation densities were determined by the applied force (F) and number of rolling cycles. A force of 10 N produced a scalable plastic zone with an area of 140 µm × 5000 µm without crack formation after 100 rolling cycles. The dislocation density at the center of the plastic deformation zone can reach ∼1014 m2, which is an order of magnitude higher than that achieved previously by others. Increasing the applied force increased the density of the introduced dislocations, for example, ∼2 × 1014 m−2 under F = 30 and 35 N, however, lead to crack nucleation in the sample. The dislocations introduced significantly enhanced the mechanical properties of the STO crystal. The measured Vickers’ hardness and fracture toughness increased by 55%–60% and 23%–24%, respectively, compared to the crystal before rolling. This method can serve as a robust technique for engineering dislocations in ceramics, fulfilling the requirements of dislocation‐tuned mechanical and functional investigations.

Study of the Relationship between Changes in the Structural, Optical, and Strength Properties of AlN Ceramics Subjected to Irradiation with Heavy Xe23+ Ions.

The purpose of this study is to comprehensively analyze the influence of different fluences of irradiation with Xe23+ heavy ions on alterations in the structural, optical, and strength properties of AlN ceramics and to establish a connection between structural distortions and alterations in the optical and mechanical properties of the ceramics. X-ray diffraction, UV-Vis and Raman spectroscopy, and indentation and single-compression methods were used as research methods. During the study, it was demonstrated that at low irradiation fluences, the main role in the changes in the properties of the AlN ceramics is played by effects related to changes in their optical properties and a fundamental absorption edge shift, which characterizes changes in the electronic properties of the ceramics (changes in the distribution of electron density). A study of the variations in the optical properties of the examined samples in relation to the irradiation fluence showed that when the fluence surpasses 5 × 1011 ion/cm2, an extra-spectral absorption band emerges within the range of 3.38-3.40 eV. This band is distinctive for the creation of vacancy ON-VAl complexes within the damaged layer's structure. The presence of these complexes signifies structural deformations and the accumulation of defective inclusions within the damaged layer. An analysis of changes in the parameters of the crystal lattice showed that structural distortions in the damaged layer are due to the accumulation of tensile residual mechanical stresses, an increase in the concentration of which leads to the swelling and destruction of the damaged layer. Some correlations between the mechanical properties of ceramics and the irradiation fluence indicate the ceramics' remarkable resistance to radiation-induced brittleness and weakening. These effects become apparent only when structural damage accumulates, resulting in the swelling of the crystal lattice exceeding 2.5-3%.

Theoretical upper limit of dislocation density in slightly-ductile single-crystal ceramics

Upper limit of dislocation density without fracture is numerically calculated for slightly- ductile single-crystal ceramics for which the Griffith criterion for fracture and the Bailey–Hirsch type relationship between applied stress and the dislocation density are nearly valid simultaneously in order to obtain useful information to improve functional, electrical, and mechanical properties of ceramics by the introduction of appropriate dislocations. Two models of fracture as a function of dislocation density are constructed; simple model and probability model. If the diameter of pre-existing microcracks is sufficiently small, the dislocation density could be as high as the crystallographic limit ( m−2). Even if the typical diameter of pre-existing microcracks is not so small, there is some probability that the dislocation density could be as high as the crystallographic limit if the number of microcracks in the specimen is very small. Accordingly, the increase in ionic conductivity by several orders of magnitude without dendrite formation by introducing appropriate dislocations into single-crystal solid electrolytes with the dislocation density higher than about 1017 m−2 theoretically predicted by the authors may be practically possible.

Strengthening Mo2BC ceramic by a two-step sintering process

Mo2BC ceramic has potential application value in structural fields due to its high strength and hardness. However, the microstructures and mechanical properties of ceramics are greatly depended on the sintering process. In this paper, the effect of sintering temperature on microstructures and mechanical properties of Mo2BC ceramics has been studied. Mo2BC ceramic bulks were fabricated at the temperature varying from 1300 °C to 1600 °C under a pressure of 50 MPa by fast hot-pressing sintering method. It is well confirmed that the sintering temperature can remarkably influence microstructural evolution and mechanical properties. The results presented here provide an optimal sintering process to prepare Mo2BC ceramic bulks. It is established that the two-step sintering process is an effective method to refine the microstructures and improve the mechanical properties. Based on the two-step sintering process, the relative density of as-prepared Mo2BC ceramic bulk is as high as 98.5 %. Besides, the Vickers hardness, compressive strength, flexural strength and fracture toughness are all evidently improved, of which the values are 20.1 GPa, 4.95 GPa, 511.5 MPa and 4.7 MPa m1/2, respectively. The enhanced mechanical properties are mainly attributed to the refinement strengthening effect and high relative density.

Feasibility study on electrically conductive joining of MoSi2 electrodes for spark plugs

AbstractDespite the often outstanding functional as well as (high temperature‐) mechanical properties of ceramics, their usage is often limited due to their inherent brittleness. This also compromises the joining with metals, which is often indispensable for engineering applications. In this context, electrically conductive ceramics like MoSi2 are promising materials for the application as electrodes where high temperatures in harsh environments are present (e.g., in spark plugs for large gas engines). Due to the difficult joining of the respective materials, long‐term experiments are thereby often still pending. In this work, adhesive bonding, brazing, tungsten inert gas‐, and resistance welding were performed to evaluate their applicability for generating electrically conductive as well as mechanically reliable joints between MoSi2 and Inconel 600, aiming to utilize MoSi2 electrodes in spark plugs. Fractographic analyses are performed to understand cracks associated with the high (thermo‐) mechanical stresses. Additionally, a finite element model was set up for a deeper understanding of the observed fracture behavior. While adhesive bonding is acceptable for short‐term experiments at low temperatures, brazing and resistance welding may qualify for fast and reliable manufacturing of spark plugs with ceramic electrodes.

Novel TiC-based ceramic with enhanced mechanical properties by reaction hot-pressing at low temperature

Novel TiC-based ceramics were prepared by reactive hot-pressing at 1400–1600 °C using TiC, Si and ZrC powders as raw reactants for the first time. The effects of ZrC addition and temperature on the microstructure and mechanical properties of ceramics were investigated. The Ti3SiC2 phase existed when the content of ZrC was 10 mol%. The Zr-rich solid solution appeared and the Ti3SiC2 disappeared with 30 mol% ZrC addition. The flexural strength of ceramics was improved due to grain refinement by the pinned SiC, the formation of solid solutions and the Ti3SiC2 phase. The main toughening mechanism can be crack bridging by the layered Ti3SiC2 and crack deflection by the ZrSi particle. TiC-36 mol% Si-10 mol% ZrC (raw composition) exhibits good comprehensive mechanical properties (Vickers hardness of 21.8 GPa, flexural strength of 580 MPa, and indentation fracture toughness of 6.7 MPa m1/2), which reach or exceed most TiC-based ceramics in previous reports.

THE EFFECT OF MODIFYING ADDITIVES ON THE PROPERTIES OF THE CERAMIC COMPOSITION

The results of studies of the effect of modifying additives on the properties of ceramic masses are presented. It is shown that the complex activation of the ceramic mass by plasticizing additives in the form of bentonite and surfactants and using rice straw leads to a decrease in molding humidity and an improvement in the physical and mechanical properties of ceramics while reducing the firing temperature by 50-100 °C. The optimal composition of a ceramic composition containing low-plastic loam, bentonite, rice straw and surfactants for the production of ceramic bricks by plastic molding has been determined.

Mechanical Properties and Density Profile of Ceramics Manufactured from a Board Mixed with Sawdust and Mandarin Peels

In this study, the boards were manufactured according to the mandarin peels addition rate using sawdust and mandarin orange peel. After that, the mechanical properties and density profile of ceramics prepared by conditions through resin impregnation process and carbonization process were investigated. The bending and compression strengths of ceramics tended to increase as the resin impregnation rate increased. When the resin impregnation rate was 70%, the highest values were 8.58 MPa and 14.77 MPa, respectively. Also, the mechanical properties of ceramics according to carbonization temperature showed the highest values at 1,200°C for bending strength of 11.09 MPa and compression strength of 17.20 MPa. The bending strength and compression strength according to the mandarin peels addition rate showed the highest values at 8.62 MPa and 14.16 MPa, respectively, when the mandarin orange peel addition rate was 5%. The mechanical properties tended to decrease when the addition rate of mandarin orange was increased. The density profile of ceramics showed a similar tendency to the mechanical properties. It can be seen that the density distribution from the surface layer to the center layer is more uniform as the resin impregnation rate and carbonization temperature increase and the mandarin peels addition rate decreases.

Preparation and properties of anorthite‐based ceramics by using metallurgical solid waste and fly ash

AbstractA large amount of metallurgical solid waste accumulation poses a serious threat to the environment. Study on synergistic reinforcement of synthetic process of metallurgical solid waste‐based ceramics with fly ash is of great significance in reducing environmental pollution and resource utilization. A metallurgical solid waste‐based ceramic used as building ceramic was developed with the erosion part of used MgO–C bricks and fly ash as main raw materials, and the amount of solid waste added to the prepared ceramics was at least 60 wt% and up to 90 wt%. The effects of fly ash content and sintering temperature on the crystalline phase transitions, morphologies, and the main physical and mechanical properties of ceramics were investigated by X‐ray diffraction, scanning electron microscopy, and mechanical testing. The results show that the obtained ceramics presented maximum bending strength and minimum water absorption, 80.14 MPa and 5.04%, respectively, when the raw material proportions were the erosion part of used refractories accounted for 60 wt%, fly ash 20 wt%, pyrophyllite 10 wt%, and quartz sands 10 wt%, and the process parameters were the sintering temperature 1150°C, sintering time 120 min, and molding pressure 15 MPa.

The effect of natural fiber ratio on mechanical properties of kaolin/fly–ash at low temperature ceramics

This study aims to increase the feasibility of ceramics at low temperature using natural fibers. The ceramics (Ce) were prepared by mixing a powder of kaolin and fly–ash at an equal ratio of 50:50 wt.%. The mixture was milled by ball–milling technique. The natural fibers ceramics (CeNF) were created by adding local pineapple leaves to kaolin and fly–ash powder. Scanning electron microscopy (SEM) was used to amorphous observation and particle size determination. The compositions of Ce and CeNF were investigated by using X–ray diffraction (XRD) technique. The mechanical properties of ceramics were determined by hardness and density test. The results showed that the grinding of kaolin and fly–ash for 4 h produced the highest strength Ce. For the addition of local pineapple leaves at 2 wt.%, the strength could be increased from 92.9 kgf to 118.3 kgf.

Research of Microstructure, Phase, and Mechanical Properties of Aluminum-Dross-Based Porous Ceramics

In this study, the effect of sintering temperature and the addition of kaolin, a sintering agent, on the microscopic, phase, and mechanical properties of ceramics were investigated using secondary aluminum dross (SAD) as the main component in the manufacturing of ceramics. The basic phases of the ceramics were Al₂O₃, MgAl₂O₄, NaAl₁₁O₁₇, and SiO₂ without the addition of kaolin. The diffraction peaks of MgAl₂O₄, NaAl₁₁O₁₇, and SiO₂ kept decreasing while those of Al₂O₃ kept increasing with an increase in temperature. In addition, the increase in temperature promoted the growth of the grains. The grains were uniform in size and regular in distribution, with a shrinkage of 2.2%, porosity of 72.5%, bulk density of 1.076 g/cm³, and compressive strength of 1.12 MPa. When the sintering temperature was 1450°C, the basic phases of the ceramic after the addition of kaolin were Al₂O₃, MgAl₂O₄, NaAl₁₁O₁₇, and SiO₂. With the increase of kaolin, the diffraction peaks of NaAl₁₁O₁₇ and SiO₂ decreased until they disappeared, while the diffraction peaks of Al₂O₃ increased significantly. When kaolin was added at 30 wt.%, the ceramics obtained had shrinkage of 18%, a porosity of 47.26%, a bulk density of 1.965 g/cm³, and compressive strength of 31.9 MPa. Cracks existed inside the ceramics without the addition of kaolin, while the addition of kaolin significantly changed this defect. It is shown that SAD can obtain porous ceramics with good properties at a sintering temperature of 1450°C and a kaolin addition of 30 wt.%.

Cure behaviour and mechanical properties of Si3N4 ceramics with bimodal particle size distribution prepared using digital light processing

Digital light processing is a vital additive manufacturing technology used for manufacturing ceramic parts. The particle size distribution of ceramic suspensions significantly affects the cure behaviour and mechanical properties of ceramics. In this study, the cure behaviour and mechanical properties of Si3N4 ceramics with a bimodal particle size distribution were studied. The results indicated that the suspension with coarse particles had a higher cure depth for a lower absorbance but poor mechanical properties. The bending strength of the samples with the optimal ratio (coarse:fine particles = 3:7) reached a maximum of 728.7 ± 10.33 MPa, which is 16.5% higher than that of the samples prepared using only fine particles.

Cold sintering constructed in situ drug-loaded high strength HA-PLA composites: Potential bone substitution material

Hydroxyapatite (HA) is widely used as bone substitute material in repairing bone defects and injuries. However, the high brittleness and low fatigue strength of HA make it difficult to satisfy the long-term service requirements of implants. In general, the mechanical properties of ceramics can be improved by sintering which usually operated above 1000 °C. The high temperature not only brings huge energy consumption and environmental pollution, but also loss the surface-active sites on HA, which greatly limits the biological functions of the material, such as drug loading and degradation. A method that can achieve the densification of HA at a lower temperature is particularly important to improve mechanical and biological properties. In this work, a promising drug-loaded HA-polylactic acid (HA-PLA) composite with high densification and mechanical properties was prepared by cold sintering process at 80 °C, in addition, the relatively low operating temperature enables the material to realize in-situ loading of drugs. The cold-sintered composite with HA/PLA was 7/3 showed the best performance with significant biodegradation (16.8%) and drug release (95%) ability. Therefore, this study provides a simple and universal method for the preparation of biological composite material, which provides a useful platform for efficient in situ drug loading biomaterials.

Analysis of clay types and their binary systems

The objects of study were the Mali Budyshcha and Opishnia clays of two deposits in the Poltava region (Ukraine), binary systems of these clays, and ceramics based on them. It is noted that the efficiency of the practical use of these clays can be increased taking into account the peculiarities of their mineralogical composition. The features of the qualitative mineralogical composition of clays were studied by the methods of chemical, X-ray phase and thermal analysis. The amount of rock-forming minerals was determined using the new computer program «Mineral». It has been established that with an increased content of quartz in both samples, the Mali Budyshcha clay is characterized by a combination of clayey rock-forming minerals – 18.8 % montmorillonite, 12.1 % kaolinite, 17.9 % feldspar and 7 % calcite. According to the intensity of characteristic diffraction peaks and the plane of the endothermic effect with a maximum at 550–575 °C, Opishnia clay is marked by a significantly higher content of kaolinite – 48.1 %. Large values of the quantitative ratio of oxides SiO2:Al2O3 and the content of alkaline earth and alkaline oxides of the RO+R2O type determine the ratio of Mali Budyshcha clay to the group of low-melting clays with a fire resistance of 1230 °C, in contrast to refractory clay (1620 °C). It has been established that in the range of maximum firing temperatures of 950–1100 °C, samples of Mali Budyshcha clay differ from Opishnia clay in changes in average density from 1.90 to 2.28 g/cm3 versus 2.00–2.09 g/cm3, a decrease in water absorption from 15.3 to 5.0 wt % versus 12.0–9.1 wt %. It is shown that the use of binary systems of the studied clays has a significant effect on the chemical and mineralogical composition, the degree of sintering, and the physical and mechanical properties of ceramics. When varying the quantitative ratio of clays from 4:1 to 1:1, the content of kaolinite changes the most – from 19.3 to 30.1 %. An increase in the content of kaolinite in binary systems leads to a gradual expansion of the possible temperature range of firing. At the same time, in comparison with Mali Budyshcha clay, Opishnia clay achieves a decrease in water absorption, an increase in density and strength.

Effect of Al(OH)3 addition on densification mechanism and properties of reaction-sintered mullite-corundum composite ceramics

ABSTRACT Mullite composite ceramics were fabricated by using mullite powder from waste coal gangue and Al(OH)3 as starting materials. The effects of sintering temperature and Al(OH)3 content on phase composition, microstructure, and mechanical properties of the ceramics were systematically investigated. Results show that the bulk density and flexural strength of composite ceramics increase as the temperature increases from 1480°C to 1560°C. The composite ceramics exhibit optimal performances with addition of 10 wt.% Al(OH)3 at 1560°C, a bulk density of 2.43 g/cm3 and a flexural strength of 124.28 MPa, respectively. Moreover, additional Al(OH)3 promotes a reaction between SiO2 and Al2O3 and forms more mullite phase. The increase in mullite content endows the composite ceramics with high mechanical properties. Scanning electron microscope images indicate that the mullite particles exhibit an interlocking structure, while the corundum phase is “pinned” within the mullite interlocking structure, contributing to the mechanical properties of composite ceramics.

Advanced Estimation of Compressive Strength and Fracture Behavior in Ceramic Honeycombs by Polarimetry Measurements of Similar Epoxy Resin Honeycombs.

Finding a non-destructive characterization method for cellular ceramics’ compressive strength and fracture behavior has been a challenge for material scientists for years. However, for transparent materials, internal stresses can be determined by the non-destructive photoelastic measurements. We propose a novel approach to correlate the photoelastic stresses of polymer (epoxy resin) prototypes with the mechanical properties of ceramics (alumina). Regular and inverse epoxy honeycombs were 3D-printed via stereolithography with varying structure angles from −35° to 35°, with negative angles forming an auxetic and positive hexagonal lattice. Photoelastic measurements under mechanical loading revealed regions of excess stress, which directly corresponded to the initial fracture points of the ceramic honeycombs. These honeycombs were made by a combination of 3D printing and transfer molding from alumina. The photoelastic stress distribution was much more homogeneous for angles of a smaller magnitude, which led to highly increased compressive strengths of up to 446 ± 156 MPa at 0°. By adapting the geometric structural model from Gibson and Ashby, we showed that we could use a non-destructive technique to determine the compressive strength of alumina honeycombs from the median photoelastic stress measured on similar epoxy honeycomb structures.

Effect of Phase Composition on Leaching Behavior and Mechanical Properties of Ceramics from Ferrochrome Slag and Tundish Slag.

Ferrochrome slag (FS) and tundish slag (TS) are two typical slags containing high contents of Cr2O3 (3.88 wt.%) and MnO (18.69 wt.%), respectively. In this study, batches of ceramics were prepared from FS and TS, and their Cr/Mn leaching behaviors, mechanical properties and microstructures were investigated. Results showed that ceramics with 80 wt.% FS or 85 wt.% TS had acceptable properties. By controlling its composition and sintering temperature, pyroxene or spinel phases could become the main crystalline phases of the fired ceramics containing either of the two slags. For both slag series, pyroxene phases contributed to higher bending strengths, whereas spinel phases led to lower Cr/Mn leaching rates. Both ceramic containing 20 wt.% FS and ceramic containing 85 wt.% TS had the main crystals of pyroxene phases and possessed the highest bending strengths (FS20: 114.52 MPa and TS85: 124.61 MPa). However, both ceramic containing 80 wt.% FS and ceramic containing 25 wt.% TS with main crystals from the spinel phases had the lowest Cr/Mn leaching rates (FS80: Cr 0.05% and TS25: Mn 0.43%). Therefore, optimum designs for the compositions of ceramics from different slags were achieved by changing the proportions of pyroxene and spinel phases to obtain a balance between the high strengths of materials and the stable retention of heavy metal ions. This study provides an important basis for long-term research on the large-scale reuse of heavy metal-containing slags in the ceramic industry.

Strengthening boron carbide by doping Si into grain boundaries

AbstractGrain boundaries, ubiquitous in real materials, play an important role in the mechanical properties of ceramics. Using boron carbide as a typical superhard but brittle material under hypervelocity impact, we report atomistic reactive molecular dynamics simulations using the ReaxFF reactive force field fitted to quantum mechanics to examine grain‐boundary engineering strategies aimed at improving the mechanical properties. In particular, we examine the dynamical mechanical response of two grain‐boundary models with or without doped Si as a function of finite shear deformation. Our simulations show that doping Si into the grain boundary significantly increases the shear strength and stress threshold for amorphization and failure for both grain‐boundary structures. These results provide validation of our suggestions that Si doping provides a promising approach to mitigate amorphous band formation and failure in superhard boron carbide.