Ceramic Composites Research Articles

Effect of sintering pressure on microstructure and mechanical properties of (TiB2–SiC)/B4C composite ceramics

Effect of sintering pressure on microstructure and mechanical properties of (TiB2–SiC)/B4C composite ceramics

The synthesis and characterization of alkaline niobate-based ceramic composites containing L-lysine Hydrochloride

Some lead-free piezoelectric ceramics are known to have high dielectric and piezoelectric properties but are limited by their brittle nature. A few amino acids have recently been reported to exhibit rather low dielectric and piezoelectric properties but have the advantage of being biocompatible and flexible. It would therefore be interesting to form a composite that will combine the inherent advantage of high dielectric properties from the ceramics and flexibility from the biomolecule. In this research, the properties of lead-free (K0.45Na0.51Li0.04)(Nb0.85Ta0.1Sb0.05)O3 (KNNLST) ceramics and L-lysine hydrochloride (L-LHCl) have been combined to produce dielectric composites. The samples were produced by mixing the constituents from 0 wt.% to 100 wt.%, pelletising and heat-treating them. Bulk density, X-ray diffraction, scanning electron microscopy, and dielectric characterisation were techniques used to determine the density, phases, morphology, and dielectric properties of the produced composites. The results show an increasing bulk density value from 1.2 g/cm3 for L-LHCl to 4.67 g/cm3 for the KNNLST ceramics. The morphology of the composite shows very tiny grains when small amounts of the ceramics were introduced. The L-LHCl transforms from an amorphous phase to a crystalline phase having the orthorhombic-tetragonal structure with the introduction of the KNNLST ceramics. The dielectric constant values increased with increasing KNNLST ceramics content from 10 @1 kHz to 200 for the composite with 80 wt%. KNNLST content. The dielectric loss values decreased for L-LHCl from 0.9 @1 kHz to 0.2 @1kHz. The electrical conductivity values increased with increasing KNNLST ceramics content. The results show that the composites produced from these constituents may be suitable for dielectric applications.

Hydraulic pressure resistance of the ceramic resin composite buoyancy materials based on cylindrical tube configuration

Due to high modulus, high strength and low water absorption of the 99.5% alumina ceramic, the tubular ceramic resin composite (TCRC) has been designed and fabricated, which can provide a potential option for the deep-sea buoyancy materials. The reliability and applicability of TCRC under hydrostatic pressure are systematically discussed by means of theory, experiment and simulation. Circumferential instability and strength failure are two possible failure modes of the TCRC through theoretical analysis. The study indicates that the load-bearing capacity of TCRC decreases with the increase of the number of vertical/horizontal tube arrays m, the ratio of the inner to outer radius r/Rc of the ceramic tube or the ratio of the length to the outer radius L/Rc of the ceramic tube. Conversely, the load-bearing capacity of TCRC increases with the increase in the modulus of matrix phase Er. In addition, TCRC with parameters of “r/R-0.93/0.91-3X3-L40-E3.18” has excellent performance through experimental verification. That is, the core density and hydrostatic strength of the TCRC are 0.67 g/cm3 and 150.6 MPa, respectively. Better stated, our designed buoyancy material can be applied in the deep-sea environment of 12000m, which is the deepest spot on the ocean floor ever explored. The excellent performance of TCRC verifies the feasibility of ceramic circular honeycomb configuration in the application of hydrostatic pressure environment. Meanwhile, the buoyancy materials used in different water depths can be designed by changing the L/Rc or r/Rc of the round tube in circular honeycomb.

Microstructure, interfacial and mechanical properties of SiC interphase modified C/C-SiC composites prepared by reactive melt infiltration

Interfacial modification can effectively regulate the interfacial properties of ceramic matrix composites. This paper reports on the effect of SiC interphase thickness on the microstructure, interfacial and mechanical properties of C/C-SiC composites. As the SiC interphase thickness increased to 2 μm, the flexural strength and modulus of the C/C-SiC composites increased up to 252 MPa and 40 GPa, an increase of 36 % and 40 %, respectively. Because the SiC interphase protected the carbon fibers from the corrosion of liquid silicon, thereby increasing the effective fiber volume fraction. Furthermore, the increased interfacial shear strength (IFSS) measured by the fiber push-in test improved the load transfer efficiency. Raman spectrum and transmission electron microscopy indicated that the damage process of the interface with high IFSS after the fiber push-in test showed fiber/pyrolytic carbon interface debonding, release of thermal residual stress, and larger upward rebound protrusion of carbon fibers without interface crushing.

Nanoindentation of B4C-HfB2 particulate ceramic composite doped with Cr–B compounds

Mechanical behavior of B4C - HfB2 particulate ceramic composite doped with CrB + Cr3B4 chromium boride compounds were studied by nanoindentation. Hardness, Young's modulus, and indentation stress - indentation strain behavior of B4C and HfB2 phases was computed. It was found that hardness and Young's modulus of B4C matrix phase in B4C - HfB2 doped with Cr - B was increased as compared to those hardness and Young's modulus of pure B4C. It was also found that indentation stress was relieved by “pop-in” events in some of the B4C grains, however, the “pop-in” discontinuous events were always observed upon indentation of HfB2 grains, that lead to a decrease in hardness of HfB2 from 40 to 50 GPa before “pop-ins” to 28–32 GPa after “pop-ins”. The obtained results can be further used in calculations of thermal residual stresses in B4C and HfB2 phases of B4C - HfB2 particulate ceramic composite.

The influence of B4C content on the pore structure of reaction-synthesized porous Ti3AlC2-TiB2 composite ceramics

Using a mixture of TiH2, Al, B4C, and graphite powders with a molar ratio of 3+2 m/1.2/m/2-m (where m ranges from 0 to 0.25, with increments of 0.05), porous Ti3AlC2-TiB2 composite ceramics were successfully synthesized through activated reaction sintering. The effect of B4C content on the phase composition, volumetric expansion, microstructure, and pore structure parameters (including pore size, porosity, and permeability) was systematically studied. When the molar ratio of B4C was less than 0.1, the volumetric expansion rate, average pore size, and permeability increased with the addition of B4C, reaching maximum values of −5.46 %, 2.23 μm, and 92.4 m3 m−2·10 kPa−1 h−1, respectively. Conversely, when the B4C molar ratio exceeded 0.1, the parameters related to the pore structure of the porous Ti3AlC2-TiB2 composite ceramics decreased, with minimum values of −10.40 %, 1.46 μm, and 68 m3 m−2·10 kPa−1 h−1, respectively. In addition, the pore formation mechanism of the porous Ti3AlC2-TiB2 composite ceramics was systematically explored. The revolution tendency of pores is related to the decomposition of TiH2, Kirkendall partial diffusion, diffusion between B and C, and the transition process of the final phase Ti3AlC2-TiB2. This research work could provide a reference for the preparation of the MAX phase composite porous materials.

Mass minimization approach for the optimal preliminary design of CMC inner liners in rocket thrust chambers

In the past decade, the world has witnessed a new space race, driven by a growing commitment to reducing the environmental impact of space missions. This has led to the widespread adoption of liquid-propellant rocket engines, which offer several advantages over their solid-propellant counterparts. One key advantage is their reusability, which not only helps to reduce the generation of space debris but also makes space exploration cheaper. To further enhance the performance of liquid rocket engines, researchers have been exploring innovative cooling techniques and advanced materials. Among these materials, Ceramic Matrix Composites (CMCs) have shown great potential in reducing the overall engine weight when used instead of high-tech metal alloys, resulting in lower fuel consumption and emissions during launches. This paper focuses on the mass minimization of inner liners made of CMCs in rocket thrust chambers. At this aim, a computationally efficient preliminary design approach, based on an analytical one-dimensional thermo-mechanical model, is proposed. A case study of mass minimization of an inner liner of rocket thrust chamber is also presented and discussed, by considering five different CMC materials.

Preparation and characterization of ZnO modified solid state sintered 45S5 bioactive ceramics

In this research, the traditional 45S5 bioactive glass powder was modified using ZnO (<20 μm) by powder metallurgy route. Five different bioactive ceramics compositions (45BC, 45BC1, 45BC3, 45BC5 and 45BC7) were formulated containing varied amounts of ZnO in the step of 1, 3, 5 and 7 wt % respectively. Each body was thoroughly mixed in a porcelain-lined ball mill to ensure proper homogenization followed by an addition of prepared 2 % PVA (Polyvinyl alcohol) and then again thoroughly mixed. The batch material was uniaxially pressed at 70 MPa using a cylindrical mould of 40 × 20 mm. A total of 20 samples from each body composition were produced and allowed to dry in an ambient temperature followed by sintering at 1000 °C for 2h at the rate of 5 °C/min. The samples were then allowed to anneal within the furnace to room temperature. Selected samples were later immersed inside simulated body fluid. Physical, mechanical, microstructure and phase evaluation were conducted to examine the developed bioactive ceramics. The results showed that the bulk density increased from 1.6 to 2.64 g/cm3 while porosity decrease from 95 % to 58 % across the series, with increasing ZnO addition. Sample 45BC7 showed maximum hardness and compressive strength of 7.98 GPa and 83.54 MPa respectively. The carbonate-hydroxyapatite/hydroxyapatite (CHA/HA) deposits were found to also increased with ZnO addition showing good bioactivity, which affirms that the developed bioactive ceramics can bond well with living tissues, thus its suitability for bone regeneration.

Enhancement of thermoelectric properties in Sr0.6La0.4Nb2O6-δ-based ceramics by addition of graphite

Oxide thermoelectric materials have a wide range of applications due to their excellent stability, low cost, and non-toxic properties. However, their low thermoelectric conversion efficiency limits their practical use. Therefore, improving the performance of oxide thermoelectric materials has become the focus of current research. Interface engineering is an important approach to enhance thermoelectric properties by optimizing electrical transport properties through multiphase composite regulation of phase interface structure. A series of Sr0.6La0.4Nb2O6-δ/x wt% graphite (x = 0, 0.6, 1.0, 1.5, 2.0) composite ceramics thermoelectric materials were prepared, and the mechanism for improving their thermoelectric properties was explored. Graphite serves as an electron momentum amplifier within the Sr0.6Ba0.4Nb2O6-δ matrix, thereby augmenting both conductivity and power factor values significantly. Notably, the incorporation of 1.5 wt% graphite led to a remarkable enhancement in the thermoelectric power factor at 1073 K, reaching an impressive value of 254.84 μW/K2m - representing a notable increase of approximately 51 % compared to the unmodified sample - primarily attributed to the elevated electrical conductivity.

Effect of applied load on wear of microwave sintered alumina-graphene ceramic composite material

The present work is mainly focussed on the preparation of alumina ceramic composite material reinforced with different weight proportions (wt%) of graphene ranging from 0.15 wt% to 0.45 wt% (with an interval of 0.1) and fabrication using microwave sintering method. Wear studies are performed on graphene reinforced alumina ceramic material samples using pin-on-disk apparatus at different loads of 5 N, 10 N, 15 N keeping speed of 0.8 m s−1 and sliding distance of 40 m constant. The obtained wear results are compared with wear performance of pure alumina samples which are prepared in the same condition. Wear tests even at higher load of 15 N revealed that the decrease in the wear rate of the ceramic composite samples reinforced with 0.35 wt% of grapheme is 35.14% and in the ceramic composite samples reinforced with 0.45 wt% of graphene is 34.85% when compared with the wear rate of samples prepared with pure alumina. The effect of different wt%s of graphene on wear properties of prepared ceramic composites is studied through SEM analysis, and observed that the abrasive wear phenomenon is found to be the dominant wear mechanism.

Towards high strength SrTiO3-based composites fabricated at room temperature

This paper explores the effect of the binder phase on the mechanical strength of room temperature fabricated (RTF) SrTiO3 ceramic composites. Lithium molybdate-strontium titanate (Li2MoO4-SrTiO3) and sodium silicate-strontium titanate (Na2SiO3-SrTiO3), along with their corresponding single-phase materials, were investigated. A comparison with single-phase high temperature sintered counterparts was also conducted. The biaxial strength of RTF Na2SiO3-SrTiO3 was seven times higher than that of Li2MoO4-SrTiO3 composites (i.e. 77 MPa to 11 MPa), resulting in ca. 40 % of the strength of single-phase SrTiO3 sintered at high temperature (i.e. ∼200 MPa). The relatively high strength of RTF Na2SiO3-SrTiO3 is related to the polycondensation of (SiO4)4- monomers in Na2SiO3 aqueous solution. This yields stronger bonding of Na2SiO3 with SrTiO3, as evidenced by wettability tests, supported by spectroscopy and fractographic analyses. The understanding of how the binder phase affects densification of ceramics fabricated at room temperature may lead to functional ceramic composites with enhanced structural integrity.

Transition mechanism and thermokinetic analysis of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics for nuclear waste forms based on in-situ synthesis

In this study, the novelly designed Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics were utilized as nuclear waste form to simultaneously immobilize simulated fission products Sr and actinide nuclides. The phase transition mechanism, thermokinetics and densification behavior of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics based on in-situ synthesis were systemically analyzed by XRD, in-situ XPS, TG-DSC, SEM and density measurements. The results demonstrate that the formation of Ce0.5Sm0.5PO4 solid solution phase preceded that of Sr0.5Zr2(PO4)3 phase, of which there is a valence change of Ce from Ce4+ to Ce3+ before 1023 K. Additionally, as for the exothermic crystallization enthalpy, change of exothermic crystallization enthalpy and activation energy, the values of Sr0.5Zr2(PO4)3 and Ce0.5Sm0.5PO4 phases in composite ceramics are 286.17 – 515.61 mJ, 19.11 – 35.38 J/g, 702.45 kJ/mol and 145.21 – 232.44 mJ, 9.26 – 15.44 J/g, 450.04 kJ/mol, respectively. It is then indicated that the formation of Ce0.5Sm0.5PO4 phase is definitely more favorable than that of Sr0.5Zr2(PO4)3 phase. Simultaneously, the relative densities of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics are more than 95 % when the sintering temperature exceeds 1273 K.

Radio frequency‐assisted zirconium carbide matrix deposition for continuous fiber‐reinforced ultra high temperature ceramic matrix composites

AbstractZirconium carbide (ZrC) is considered to be a potential candidate for ultra high temperature applications due to its high melting point, good chemical inertness, and ablation resistance, but the monolithic form suffers from low fracture toughness and hence poor thermal shock resistance. Reinforcing it using continuous carbon fibers (Cf) to create an ultra high temperature ceramic matrix composite is an obvious solution, however densifying ZrC requires the use of very high temperatures combined with significant pressure, such as obtained by using hot pressing or spark plasma sintering, which risks damaging fibers. In the present work, radio frequency‐assisted chemical vapor infiltration (RF‐CVI) has been investigated with a view to forming Cf/ZrC composites. These initial experiments revealed the ability to deposit pure, nano‐grained, and near stoichiometric ZrC with deposition occurring preferentially from the center of the sample due to the nature of the inverse temperature profile developed. The deposited ZrC grains were in the range of 4–9 nm in size and had a lattice parameter of 0.4750 nm. The work also showed that the use of RF‐CVI enabled the minimization of early pore sealing, a common problem for conventional CVI.

Microwave‐sintered mullite structural ceramics based on low‐grade bauxite applied for fracturing proppants

AbstractThis study aimed to assess the feasibility of manufacturing fracturing proppants by microwave sintering and using low‐grade bauxite as raw material. The effects of microwave hotspot SiC and sintering additive MnO2 content on the performance of the mullite‐based structural materials were studied, respectively. The optimum sintering condition was determined by single‐factor experiments. The sintering process and mechanism were explored based on the analysis of physicochemical properties, phase transitions, and microstructure. The results showed that (1) mullite ceramic composites could be successfully prepared only with SiC added and with poor interparticle bonding microstructure. (2) With the addition of MnO2 and CaO, the granular‐shaped mullite crystals transformed into rod‐like mullite crystals, forming a net structure. (3) As the input power increased, the overfast sintering rate would reduce proppants' mechanical properties, and it was also necessary to select a reasonable sintering time to avoid overburning. (4) When the mass ratio of MnO2:CaO:SiC:bauxite was 2:1.5:12:84.5 and under the sintering condition of 1000 W, 2 h, the performance (breakage ratio of 8.5% under 28 MPa closed pressure, apparent density of 2.58 g/cm3, turbidity of 52 FTU, and acid solubility of 6.77%) could meet the requirements of the Chinese Petroleum and Gas Industry Standard (SY/T 5108–2014). This study provides a powerful way for reducing the fracturing cost, which not only improves the low‐grade bauxite utilization scale within the ceramic industry, but also expands the application of microwave sintering technology in mullite structural materials for the petroleum and gas industry.

Effect of microwave drying on TiO2–Y2O3–ZrO2 composite ceramics and drying kinetic study

TiO2–Y2O3–ZrO2 composite ceramics exhibit excellent abrasion resistance, corrosion resistance, and high-temperature resistance, making them vital structural-functional materials in ceramics and refractories. The key to preparing high-quality TiO2–Y2O3–ZrO2 ceramic powders lies in controlling the agglomeration rate, which can be optimized by choosing an appropriate drying method. This study utilized microwave drying techniques to dehydrate TiO2–Y2O3–ZrO2 ceramic powders. It was found that the average drying rate is proportional to initial masses, initial moisture contents and microwave heating powers. To describe the drying process, four models—the Quadratic, Wang and Singh, Modified Page, and Page—were employed. The best model for the drying process was the Modified Page model. The specimens were analyzed to assess the alterations in the samples pre and post-drying by scanning electron microscopy and Fourier transform infrared spectroscopy. The findings revealed that microwaves can hasten the drying process of TiO2–Y2O3–ZrO2 and enhance its spread. Utilizing Fick's second law, the effective diffusion coefficient was ascertained, showing an inverse proportionality to the sample mass, and a proportionality to the microwave heating power and initial moisture content. Using the Arrhenius exponential model, it was ascertained that the microwave drying process's activation energy stands at 13.81834 W/g. This paper demonstrates that microwave drying effectively achieves efficient drying and lays the theoretical and experimental groundwork for the microwave heating and drying of other powdered materials.

Dielectric percolation in ceramic matrix composites

This paper presents the results of an experimental study of the percolation behavior of the complex dielectric constant of ceramic matrix composites (CMC). Samples of piezoactive CMC were obtained by joint sintering of synthesized PZT piezoceramic powder (matrix) and crushed particles of sintered PZT piezoceramics (filler) of different compositions. The experimental dependencies of real and imaginary parts of the complex dielectric constant of CMC on the porosity of piezoceramic matrix and volume content of ceramic filler particles were measured and analyzed. It was shown that the additional porosity of the ceramic matrix resulting from sintering of the CMC masks the dielectric percolation transition, that actually occurs at the volume concentration of ceramic filler close to percolation threshold (V ∼ 1/3).

Experimental Permeability and Porosity Determination of All-Oxide Ceramic Matrix Composite Material.

This paper presents an investigation into the water permeability of an all-oxide ceramic matrix composite. To determine the parameters and characterize the water permeability of the ceramic composite material, an experimental study was carried out in which a dedicated test rig was constructed and commissioned. A total of five different configurations of composite tubes were tested. They differed in fibre roving strength, winding angle, fibre bundle arrangement during winding, and matrix grain size distribution. To better understand the internal structure of the analysed ceramic matrix composite material, the experimental study used scanning electron microscopy for microstructure and porosity observation. The tested tubes will be used as liners in an oxy-combustion chamber in future studies. The experiments obtained new and interesting results regarding the water permeability of the ceramic matrix composite with different structural parameters. It was also observed that, as with some porous materials, the permeability of ceramic matrix composites decreases with time as more and more liquid is pressed through it.

Study on the giant dielectric response of Ca1-xSrxCu3Ti4O12/TiO2 composite ceramics with a hierarchical grain boundary structure

In this study, Ca1-xSrxCu3Ti4O12/TiO2 ceramics doped with different Sr/Ca ratios and an excess of 20% nano-scale TiO2 particles were prepared via the solid-state method (denoted as C1-xSxCTO/TiO2, where x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). The phase composition, microstructure, elemental distribution, elemental valence states, and electrical properties of the composite ceramics were systematically analyzed. XRD data confirmed the successful synthesis of CSCTO crystals in a series of CSCTO ceramics, and it was observed that the lattice parameters of the main phase increased as the Sr/Ca ratio in CSCTO/TiO2 increased. Ca0.8Sr0.2Cu3Ti4O12/TiO2 ceramics demonstrated a good dielectric constants (1 × 105, 1 kHz) at room temperature. Microstructure analysis revealed that the excess TiO2 hinders the composite ceramics' crystal growth, forming pomegranate-like structures. The structure leads to a hierarchical interfacial polarization, which results in the giant dielectric response in CSCTO/TiO2 composite ceramics.

A comprehensive study on the phase composition, mechanical properties and stability of Li4SiO4-Li2ZrO3 biphasic ceramics

Lithium orthosilicate (Li4SiO4) is regarded as a candidate for tritium breeding in fusion reactors. In this study, the Li4SiO4-Li2ZrO3 biphasic was developed to improve the sinterability, density, and mechanical properties of Li4SiO4. The Li4SiO4-xLi2ZrO3 (x = 0.5, 1) composite powders were prepared using solid-state reaction via in-situ method. Li6Zr2O7 existed in the ceramic powders at low calcination temperatures. When the calcination temperature was increased to 900 °C, Li6Zr2O7 was transformed into Li2ZrO3 due to the decomposition of Li6Zr2O7 at high temperatures. The TEM observation confirmed that the powders consisted of Li4SiO4 and Li2ZrO3. The Li4SiO4 and Li4SiO4-xLi2ZrO3 (x = 0.5, 1) pebbles were fabricated by the sol-gel method. The measurement results showed that the pebbles had a narrow size distribution and fine sphericity. The density of Li4SiO4-Li2ZrO3 pebbles reached 96.01% of the theoretical density when it was sintered at 1000 °C for 4 h. Compared with the Li4SiO4, the grain size of ceramic pebbles was significantly reduced. Owing to decreased grain size, 139.0 N crush load for the pebbles and 92.4 MPa bending strength for the sintered bodies were achieved. Besides, the ceramics with the Li4SiO4 to Li2ZrO3 ratio of 2: 1 exhibited preferable mechanical properties. Further, to investigate the chemical stability of biphasic ceramics, the structure and mechanical properties were examined under high temperatures and continuous inert gas purging, simulating the working condition of fusion reactors. It was shown that there was almost no change in phase composition and grain size after purging for 60 h at 650 °C. For the mechanical properties, the crush load was decreased initially due to the cracking in the surface region of the ceramic and then increased because the cracking was recovered.

Properties and transpiration cooling performance of Cf/SiC porous ceramic composite

Transpiration cooling have gradually become the lead candidate for thermal protection technology of hypersonic vehicle also due to its excellent cooling performance. The porous medium with exceptional properties can further improve thermal protection capability and reliability of transpiration cooling. This paper investigates the preparation and properties of Cf/SiC porous ceramic composite with low density and remarkable permeability, and probes the transpiration cooling performances of ceramic composites (mass ratio of silicon carbide particles and short chopped carbon fibers of 1:1) in the various heat flux conditions. The research results show that Cf/SiC porous ceramic composites prepared by adding short chopped carbon fibers have uniform pore size distributions (3～20 μm) and low densities (1.074 g/cm3 ～ 1.377 g/cm3), as well as outstanding wettability and permeability (6.07 × 10−8 mm2 ～ 12.22 × 10−8 mm2). Besides, The Cf/SiC porous ceramic composites (mass ratio of 1:1) display excellent transpiration cooling performance, meanwhile a new interesting phenomenon that the water pressure difference increases with the rising of heat flow is discovered. Such studies can provide an essential reference for developing porous medium in transpiration cooling technology.