Ceramic Precursors Research Articles

Study on the sintering behavior of the ceramic precursor Daqiuni clay

Daqiuni clay is an aluminosilicate clay with unique properties that make it a promising ceramic precursor. Understanding its sintering behavior is crucial for quality control in manufacturing. This study aimed to investigate the phase evolution, densification process, and reaction kinetics during sintering of Daqiuni clay. A combination of X-ray diffraction (XRD), simultaneous thermogravimetric-differential scanning calorimetry (TG-DSC), scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques were employed to comprehensively analyse the phase transformations. The densification behavior, apparent activation energies, and reaction mechanisms were elucidated through thermodilatometric analysis conducted at varying heating rates. Four stages were identified during sintering including dehydration, dehydroxylation, mullite formation, and partial melting. The maximum shrinkages at each stage were measured. Kissinger analysis yielded apparent activation energies of 122.90, 258.40, 361.98 and 348.69 kJ/mol for the dehydroxylation, mullite nucleation, mullite growth, and partial melting stages, respectively. The dehydroxylation and partial melting processes followed the mechanisms of 3rd order reaction and 3D diffusion. Mullite formation was a two-step nucleation and growth process following the JMA model. This study clarified the phase evolution of Daqiuni clay during sintering.

Nanoparticles‐doped polymer‐derived SiCN ceramic with enhanced mechanical properties and electromagnetic wave absorption

AbstractPolymer‐derived ceramics (PDCs) have become promising candidates for electromagnetic wave (EMW) absorption due to their high thermal stability, design flexibility, and versatile functionality. However, the inevitable porous structure formed during pyrolysis greatly limits its mechanical performance. In this work, Ni–Fe–C/HfO2/SiCN ceramic was prepared by simultaneously doping nickel and iron‐containing metal‐organic framework (Ni–Fe–MOF) nanoparticles and hafnium dioxide (HfO2) nanoparticles into the ceramic precursor, thereby improving its intrinsic brittle structure while granting it extraordinary EMW absorption performance. The flexural strength, flexural modulus, and Vickers hardness of Ni–Fe–C/HfO2/SiCN ceramic were 101.06 MPa, 40.19 GPa, and 13.31 GPa, respectively. These values were 1 132%, 749%, and 191% higher than those of the initial SiCN ceramics. In addition, by optimizing the content of Ni–Fe–MOF, the Ni–Fe–C/HfO2/SiCN ceramic demonstrated satisfying EMW absorption performance from 25°C to 500°C. At 25°C, the minimum reflection loss (RLmin) and effective absorption bandwidth (EAB) were −54.07 dB and 3.95 GHz, covering 94% of the X‐band at a thickness of 2.27 mm. At 500°C, the RLmin and EAB were −33.72 dB and 1.82 GHz, still covering 43% of the X‐band at a thickness of only 1.65 mm. This work provides valuable insight into the integration of mechanical and EMW absorbing functions of PDC materials.

Additive manufacturing of high-quality tritium breeding pebbles using ceramic precursors

In this study, the fabrication of advanced lithium orthosilicate (Li4SiO4) ceramic tritium breeding pebbles through photopolymerization using ceramic precursors (i.e., SiO2 and Li2CO3) is reported for the first time. The pebbles exhibit excellent mechanical and physical properties. Through optimization of manufacturing parameters and a geometrical correction model to compensate printing deviations, the printing accuracy of the pebbles was enhanced. The resulting pebbles had a diameter of approximately 1 mm, a sphericity of 1.01, a uniformly distributed pore structure, a phase purity > 95%, and a satisfying relative density reaching 91.39%. The average crush load 25.7 ± 0.3 N, surpassed that achieved by previously reported methods. Furthermore, the thermal conductivity was enhanced compared to that of solid-phase synthesized Li4SiO4 powder, facilitating the tritium release process for fusion applications. This study may serve as a guidance for designing appropriate ceramic breeders, providing a cost-effective approach applicable to produce other high-precision ceramic components with complex compositions.

In Situ Ceramization of Nanoscale Interface Enables Aerogel with Thermal Protection at 1950 °C.

Conventional carbon fiber felt-reinforced aerogel composites are often used as lightweight thermal protection systems (TPSs) for aerospace craft. However, due to their poor oxidation resistance, they have gradually failed to handle increasingly harsh thermal environments. In this work, a nanoscale composite coating interface of SiC-ZrC ceramic precursor is first constructed on the fiber surface. Subsequently, using the coated fiber felt as a three-dimensional skeleton and through polymerization-induced phase separation, an aerogel composite with excellent thermal protection in extreme thermal environments is prepared. Owing to the in situ ceramization of this nanoscale interface at ultrahigh temperatures, the back temperature of the 12 mm thick aerogel is only 147 °C after exposure to an oxyacetylene flame at 1950 °C for 70 s. Meanwhile, the central region of the aerogel recedes by only 7%. Not only does this work provide a way to enhance aerogels by constructing a self-ceramizable nanoscale interface it is also expected that the developed aerogel composite can be applied in the ultrahigh-temperature thermal protection of future aerospace craft.

Hybridization of layered double hydroxides with functional particles.

Layered double hydroxides (LDHs) are a class of materials with useful properties associated with their anion exchange abilities as well as redox and adsorptive properties for a wide range of applications including adsorbents, catalysts and their supports, electrodes, pigments, ceramic precursors, and drug carriers. In order to satisfy the requirements for each application as well as to find alternative applications, the preparation of LDHs with the desired composition and particle morphology and post-synthetic modification by the host-guest interactions have been examined. In addition, the hybridization of LDHs with various functional particles has been reported to design materials of modified, improved, and multiple functions. In the present article, the preparation, the heterostructure and the application of hybrids containing LDHs as the main component are overviewed.

Rapid fabrication of porous metakaolin-based geopolymer via microwave foaming

Microwave foaming was used for the first time to rapidly fabricate the metakaolin-based porous geopolymers. Mechanical, thermal, and microstructural (optical and scanning electron microscope) investigations coupled with X-ray diffraction, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance techniques were conducted to characterize the obtained foams. High porosity metakaolin-based porous geopolymers could be obtained at 4 min of foaming/curing. The effect of the sodium silicate solution content on the total porosity as well as the mechanical and thermal properties was investigated. The total porosity decreased firstly and then increased in the range of ∼74 to ∼84 vol% with the increase of Na2SiO3 content. The foams with 47.7 wt% Na2SiO3 exhibited the lowest thermal conductivity (0.104 W/mK) and the highest total porosity (83.2 vol%). The fabrication time, mechanical, and thermal properties were compared with those of foams obtained by the conventional direct foaming method. With this approach, the preparation time can be greatly reduced, and the compressive strength (1.89–2.04 MPa) and thermal conductivity (0.104–0.155 W/mK) of the materials obtained were not inferior to similar components obtained by other foaming routes. The rapidly obtained porous geopolymers with high porosity and high strength as well as low thermal conductivity can be employed as thermal insulation materials and ceramic precursors.

Carborane-Containing Polymers: Synthesis, Properties, and Applications.

Carboranes are an important class of electron-delocalized icosahedral carbon-boron clusters with unique physical and chemical properties, which can offer various functions to polymers including enhanced heat-resistance, tuned electronic properties and hydrophobicity, special ability of dihydrogen bond formation, and thermal neutron capture. Carborane-containing polymers have been synthesized mainly by means of step-growth polymerizations of disubstituted carborane monomers, with chain-growth polymerizations of monosubstituted carborane monomers including ATRP, RAFT, and ROMP only utilized recently. Carborane-containing polymers may find application as harsh-environment resistant materials, ceramic precursors, fluorescent materials with tuned emissive properties, novel optoelectronic devices, potential BNCT agents, and drug carriers with low cytotoxicity. This review highlights carborane-containing polymer synthesis strategies and potential applications, showcasing the versatile properties and possibilities that this unique family of boron compounds can provide to the polymeric systems.

Bionic sweat high temperature self-lubricating coating based on ceramic precursor polysilazanes

Bionic sweat high temperature self-lubricating coating were prepared using ceramic precursor polysilazane and MoS2, Ag and BaF2 as fillers through high temperature chemical reaction to produce ceramic adhesive and molybdate solid lubricants. And the addition of active ZrB2 filler converted into ZrO2 and B2O3 through high temperature oxidation reaction not noly solved the cracking issues caused by the pyrolysis of polysilazane, but also enhances the tribology property due to the excellent fluidity and lubricity of the molten B2O3 through phase transition at high temperature through bionic sweat. Furthermore, the coating treated at 700 °C has the best lubrication performance at 500 °C, 2 N and 100 rpm that the friction coefficient was 0.223 and the wear rate was 1.53 × 10−4 mm3/N·m, respectively. Synergistic effect of solid lubricants and molten B2O3 leads to excellent lubrication property.

Effect of Temperature and Ratio for the Immobilization of Zinc Oxide in Aluminium Rich Ceramics

Zinc is one of the dangerous elements that is frequently present in municipal solid waste incinerator ash. When exceeding specific limits, there are various diseases and disorders caused by accumulation of zinc in nature as their characteristics is not biodegradable. By using zinc oxide to imitate zinc sludge, this study reveals the immobilization mechanisms that occur when zinc and ceramic precursors are used as waste-to-resources strategies. From the result, immobilization occur better at higher temperature at 10000C where the formation of Al2O4Zn is higher. Meanwhile, ratio 1:1 of ZnO and Al2O3 shows a better result of formation Al2O4Zn. Hence, it is possible to use the sintering process with precursors to turn hazardous wastes into secure products where the heavy metals can form phases that can demonstrate adequate stability due to irreversible phase transformation.

Additive manufacturing Cf/SiC composites with high fiber content by stereolithography combined with precursor infiltration and pyrolysis

A photocurable ceramic precursor slurry with a carbon fiber content of up to 25 vol% was prepared and carbon fiber reinforced SiC ceramic matrix composites (Cf/SiC composites) were successfully fabricated by stereolithography (SLA) combined with precursor infiltration and pyrolysis (PIP). The photocuring ability of the precursor composite slurry was investigated. The calculated result showed that the penetration depth of the slurry prepared with polycarbosilane (PCS) powder and chopped carbon fiber was 59.98 μm, which was suitable for stereolithography. In addition, the bulk density, porosity, flexural strength and micromorphology of the green body, debinding body and final Cf/SiC composites were analyzed in detail. After eight cycles of PIP, the bulk density and flexural strength of final Cf/SiC composites were 2.03 ± 0.04 g/cm3, 109.99 ± 15.05 MPa, respectively. This work provides a reference for additive manufacturing of Cf/SiC composites by stereolithography.

Preparation and properties of a porous ZrO2/SiZrBOC ceramic matrix composite with high temperature resistance and low thermal conductivity

In this study, porous ZrO2/SiZrBOC and SiZrBOC ceramic matrix composites were produced via vacuum impregnation method, using SiZrBOC ceramic precursor as a matrix, ZrO2 fiber prepared via electrospinning as the reinforcing agent and polyurethane foam as a skeleton. Polyurethane foam with open porosity is rather a substrate for the creation of a skeletal 3D structure. The preparation process and pyrolysis mechanism of ZrO2/SiZrBOC polyurethane foam impregnated with a precursor solution were expounded. The thermal conductivity tests and mechanical property measurements show that the lowest thermal conductivity (0.0378 W m−1 K−1) was achieved in the ZrO2/SiZrBOC ceramic matrix composite at the pyrolysis temperature of 800 ℃, being much inferior to that of the SiZrBOC composite (0.0861 W m−1 K−1). At 1400 ℃, the maximum compressive strength of the porous ZrO2/SiZrBOC ceramic matrix composites reached a value of 1.37 MPa, while that of the SiZrBOC composites was 0.22 MPa only. Therefore, the addition of ZrO2 fibers improved the compressive strength and thermal insulation properties of the composites.

Preparation of silicon-nitride ceramic fibers with hafnium compounds loaded on the surface and the high temperature properties

The surface and core are composed of heterogeneous fiber materials that are endowed with excellent properties due to the unique structure. In this work, polysiloxane (PSZ) was used as the ceramic precursor and hafnium carbide (HfC) was used as the hafnium source, and Si–N–C–O-Hf hybridized ceramic fibers were obtained using electrostatic spinning and pyrolysis. After the primary fibers were pyrolyzed at 1400 °C, hemispherical particles were found on the surface of the ceramic fibers. And the average fiber diameters were around 3 μm. Thermogravimetric analysis (TGA) showed that the mass of the cured fibers decreased to 67 % below 1650 °C in an argon atmosphere. The mass of the ceramic fibers remained almost unchanged in the high temperature aerobic environment. Meanwhile, the thermal conductivity of the specimens has remained relatively low. Analytical tests confirmed that the hafnium-containing hemispherical protective layer gave the specimens excellent thermal stability, oxidation resistance, and high temperature insulation. In addition, the excellent mechanical properties make it suitable for a wide range of applications. The optimized high-temperature performance and mechanical properties indicate that metal-hybridized silicon-based ceramic fibers herein are suitable for ultra-high-temperature environments.

DLP–printable hyperbranched polyborosilazane for microwave absorbing SiBCN(O) ceramic metastructure

This work introduces a novel digital light processing (DLP) printable SiBCN(O) ceramic precursor (UV-hPBSZ), derived through a straightforward aminolysis approach. The unique hyperbranched molecular structure of UV-hPBSZ leads to remarkable UV curing efficiency, excellent printability, satisfied ceramic yield, and consistent shrinkage ratio. UV-hPBSZ also exhibits superior resistance against cracking and collapse during the polymer-to-ceramic process, thus enabling the fabrication of intricate SiBCN(O) ceramic structures. Upon pyrolysis at 1200 °C, the resulting SiBCN(O) ceramic demonstrates outstanding electromagnetic wave (EMW) absorption performance, achieving full coverage in the X band (RLmin = -36.68 dB). To showcase the design flexibility, a distinctive metastructure is proposed and successfully fabricated using DLP printing technique. This SiBCN(O) metastructure absorber enables impressive EMW absorption in the Ku band (94.6 % coverage), attributed to surface resonance effects and multiple internal reflections. Moreover, SiBCN(O) ceramics exhibit excellent high-temperature stability, with less than a 1.63 % total mass change from room temperature to 1400 °C. UV-hPBSZ offers a simple but versatile way to control dielectric properties, which opens up new possibilities for multifunctional integrated EMW absorbers suitable for both ambient and high-temperature conditions.

Ablation behavior of 3D PyC-Cf/SiHfBOC Composites under an oxyacetylene torch environment above 2000 °C

A high-pressure assisted precursor impregnation pyrolysis method (PIP) was used to prepare 3D PyC-Cf/SiHfBOC composites. Its anti-ablation properties were tested in an oxygen-acetylene torch ablation environment exceeding 2000 °C. They revealed the ablation behavior and mechanism of SiHfBOC ceramics, carbon fiber, and the PyC interface layer. Under the action of Hf modification, a dense HfO2-SiO2 oxide layer was formed in situ on the surface of 3D PyC Cf/SiHfBOC composites, effectively preventing further ablation of the composite's matrix by high-temperature oxidation gases. During the ablation process of an oxyacetylene torch at 2000 °C, it still exhibits excellent anti-ablation properties (linear ablation rate of 1.10 × 10−4 mm s−1). This work enriches the system of hafnium containing ultra-high temperature ceramic precursors and their composites, which provides beneficial exploration for their application in the ultra-high temperature field.

In-situ synthesis of hierarchically high porosity ZrB2 ceramics from carbon aerogel template with excellent performance in thermal insulation and light absorption

This work introduces an innovative methodology combining the in-situ boron/carbon thermal reduction (BCTR) reaction and replication carbon aerogel template to synthesize hierarchically high porosity ZrB2 ceramics. The meticulously designed ceramic liquid-phase precursor ensures higher solubility of solutes while reducing the temperature requisite for boron/carbon thermal reduction. An additional carbon source is incorporated in the precursor to ensure the uniformity of resulting ZrB2 grains, concurrently maintaining ZrB2 phase purity. The ultimate prepared ZrB2 porous ceramics present a uniform microstructure, with grain sizes at the hundred-nanometer scale, and exhibit a hierarchical pore structure. The ZrB2 porous ceramics exhibited high porosity (85.4–92.9%), low density (0.264–0.482 g/cm3), reasonable compressive strength (0.26–0.51 MPa), low thermal conductivity (0.103–0.212 W/m·K), and efficient light absorption in the range of 400–2000 nm (>94%). The fabricated ZrB2 porous ceramics hold significant promise for applications in high-temperature insulation and light absorption within elevated-temperature environments.

Pyrolysis process and formation mechanism of water-based ZrC ceramics studied through a combined experimental and theoretical calculational method

ZrC has an important application in the field of supersonic aircraft, hypersonic spacecrafts and rocket engines. Normally, the toxic metal chelators and toxic organic reagents are used to prepare the ZrC ceramic precursors. In this paper, an environmentally friendly water-based ZrC ceramic precursors were synthesized in aqueous solvent via the combination of metal ion chelator and carbon source. Moreover, the water-based ZrC precursor was prepared by Tartaric Acid (TA) system can obtain high-purity ZrC ceramics. The experiment results indicated that the best Zr/C molar ratio in the precursor was 1:4. The synthetic mechanism of ZrC was Zr atoms reacted in situ to form ZrC. In addition, the effect of metal chelator carbon source assisted glucose carbon source on water-based ZrC precursors can provide a certain experimental basis for subsequent research on water-based carbide precursors.

Using flexible hydrothermal carbon-coated continuous carbon fiber to fabricate Cf/ZrB2-SiC composites by fused deposition modeling and precursor infiltration pyrolysis

In additive manufacturing of continuous fiber reinforced ceramic composites, the carbon fiber is difficult to give full play to its toughening effect without interface, and the high-viscosity resin, ceramic precursors or slurry is hardly to fully infiltrate into fiber bundles, which are not conducive to obtain high-performance ceramic composites. In this work, sugar-derived carbon acts as interface was deposited on continuous carbon fiber by hydrothermal reaction. Flexible hydrothermal carbon-coated continuous carbon fiber is appropriate for 3D printing. Continuous carbon fiber/ZrB2-polycaprolactone(PCL) filaments used for fused deposition modeling (FDM) was prepared by pre-impregnation-coating process. Ultrasound significantly improves the impregnation effect of ceramic slurry into fiber bundles. Cf/ZrB2-PCL billets with different fiber orientations were fabricated by FDM of continuous Cf/ZrB2-PCL filaments. The Cf/ZrB2-PCL billets were further densified by infiltration and pyrolysis of SiC precursor. The flexural strength and fracture toughness of Cf/ZrB2-SiC composites could reach 218.1 ± 21.3 MPa and 9.40 ± 1.45 MPa m1/2, respectively.

Thermodynamics aided design of hBN-capsulated diboride powders from novel nitrate precursors for high entropy ceramics

Hexagonal BN-coated powders have been widely used in various engineering sectors, however, their productions are restricted by the complexity of gas-solid reactions. In this study, guided by thermodynamics, a novel approach to synthesize Layer-structured hexagonal BN (hBN)-coated high entropy diboride powders in vacuum was developed, using metal salt Zr(NO3)4·5H2O, HfCl4, NbCl5, TaCl5, C16H36O4Ti, boric acid, and sucrose as raw materials. By adjusting the ratio of carbon to metal source (C/M), powders only consisting of two boride solid solutions and hBN were finally obtained, under an optimal processing condition of C/M = 5.5 and synthesis temperature of 1400 °C. Parts of hBN were found to coat on high-entropy metal diborides ceramic (HEB) particles, corresponding formation mechanism for core-shell structured powders was investigated, together with the liquid precursor assisted boro/carbothermal reduction process. Starting from as-synthesized core-shell powders, (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2–11 vol% hBN ceramics were densified at 1900 °C under 50 MPa without holding, with a high relative density of 97.3%.

Anti-cracking coating with wrinkled morphology for enhancing oxidation resistance of carbon-based fiber aerogel

In our previous work, ceramic precursor coating with wrinkled morphology was obtained by cross-linking gradient generated from ultraviolet and cross-linking agent to improve the anti-cracking of the coating in the pyrolysis. However, the cross-linking gradient was difficult to control with ultraviolet and cross-linking agent. Herein, a simple method was proposed to form the wrinkled morphology of the coating by the steady-state temperature gradient field generated from constant temperature pre-treatment. Composite aerogels were prepared by pyrolysis at high temperature. The thermal insulation and oxidation resistance of the composite aerogels were explored. The heat transfer behavior within the composite aerogels was analyzed by simulation. The results showed that the stored strain of wrinkled morphology counteracted the shrinkage of ceramic precursor polymer during the pyrolysis, which prevented the cracking of the coating. Compared with the aerogels of our previous work, the composite aerogels of this work demonstrated improved thermal insulation and oxidation resistance.

3D Printing of Liquid‐Metal‐in‐Ceramic Metamaterials for High‐Efficient Microwave Absorption

AbstractThis work reports a gallium indium alloy (EGaIn)‐doped SiBOC ceramic that possesses a unique liquid‐metal‐in‐ceramic feature. The low‐viscosity liquid nature of gallium‐based liquid metals (Ga‐LMs) and the reactive core‐shell structure provide possibilities for phase engineering inside polymer‐derived ceramics. As a demonstration, EGaIn nanoparticles (NPs) are directly mixed with a UV‐curable ceramic precursor (UV‐PBS) to obtain a resin suitable for digital light processing 3D‐printing. After pyrolysis at 800–1200 °C, SiBOC ceramics with uniformly distributed EGaIn NP domains (Si(GaIn)BOC) are obtained. EGaIn plays a key role in promoting carbonization and preventing crack formation during the polymer‐to‐ceramic process, resulting in an increase in both ceramic yield and mechanical strength. EGaIn NPs are also found to have a core‐shell structure (EGaIn@(GaxIn1‐x)2O3@SiBOC) inside the SiBOC matrix, which significantly enhances the dielectric properties and improves the interfacial polarization. As a result, an excellent electromagnetic wave absorption performance is achieved across the C, X, and Ku bands, respectively. Through rational design, a novel metastructure design based on the Schwarz P minimal surface is proposed, which exhibits an ultrawide effective absorption band extending up to 11.36 GHz (within C‐Ku bands).