Structural Design of Polymer‐Derived SiOC Ceramic Aerogels for High‐Rate Li Ion Storage Applications

SiOC ceramic aerogels with different porosity, pore size, and specific surface area have been synthesized through the polymer‐derived ceramic route by modifying the synthesis parameters and the pyrolysis steps. Preceramic aerogels are prepared by cross‐linking a linear polysiloxane with divinylbenzene (DVB) via hydrosilylation reaction in the presence of a Pt catalyst under highly diluted conditions. Acetone and cyclohexane are used as solvent in our study. Wet gels are subsequently supercritically dried with CO₂ to get the final preceramic aerogels. The SiOC ceramic aerogels are obtained after a pyrolysis treatment at 900°C in two different atmospheres: pure Ar and H₂ (3%)/Ar mixtures. The nature of the solvent has a profound influence of the aerogel microstructure in terms of porosity, pore size, and specific surface area. Synthesized SiOC ceramic aerogels have similar chemical compositions irrespective of processing conditions with ~40 wt% of free carbon distributed within remaining mixed SiOC matrix. The BET surface areas range from 215 m²/g for acetone samples to 80 m²/g for samples derived from cyclohexane solvent. The electrochemical characterization reveals a high specific reversible capacity of more than 900 mAh/g at a charging rate of C (360 mA/g) along with a good cycling stability. Samples pyrolyzed in H₂/Ar atmosphere show a high reversible capacity of 200 mAh/g even at a high charging/discharging rate of 20 C. Initial capacities were recovered after whole cycling procedure indicating their structural stabilities resisting any kind of exfoliations.     

Matrix‐Based Encapsulation of Construction Chemicals Using High‐Shear Agglomeration

Encapsulation of dry superplasticizers in matrix‐based encapsulation systems was investigated. As basic material, commercially available fly ash was granulated by high‐shear agglomeration. Due to a high variability of factors affecting the encapsulation process and later release of admixtures, the design‐of‐experiments method was applied to reduce the quantity of experiments. Statistical evaluation indicates that the particle characteristics of the agglomerates were mostly influenced by the binder viscosity during the investigations. The delayed admixture release was enhanced by high binder viscosity and low energy input during the agglomeration process due to a coating of the bigger superplasticizer particles by the smaller fly ash. These results will help to develop encapsulated construction chemicals with controlled admixture delivery for the future application in a wide range of different building materials.     

Low‐Temperature Co‐Fired Ceramic Substrates for High‐Performance Strain Gauges

Recent advances in the development of high gauge factor thin films for strain gauges prompt the research on advanced substrate materials. A glass ceramic composite has been developed in consideration of a high coefficient of thermal expansion (9.4 ppm/K) and a low modulus of elasticity (82 GPa) for the application as support material for thin‐film sensors. In the first part, constantan foil strain gauges were fabricated from this material by tape casting, pressure‐assisted sintering, and subsequent lamination of the metal foil on the planar ceramic substrates. The accuracy of the assembled load cells corresponds to accuracy class C6. That qualifies the load cells for the use in automatic packaging units and confirms the applicability of the low‐temperature co‐fired ceramic (LTCC) substrates for fabrication of accurate strain gauges. In the second part, to facilitate the deposition of thin‐film sensor structures to the LTCC substrates, pressure‐assisted sintering step is modified using smooth setters instead of release tapes, which resulted in fabrication of substrates with low average surface roughness of 50 nm. Titanium thin films deposited on these substrates as test coatings exhibited low surface resistances of 850 Ω comparable to thin films on commercial alumina thin‐film substrates with 920 Ω. The presented material design and advances in manufacturing technology are important to promote the development of high‐performance thin‐film strain gauges.     

Silicon Carbide Whisker‐Reinforced Ceramic Tape for High‐Power Components

An attempt to enhance both mechanical strength and thermal conductivity of glass‐based tapes is described. Flexural strength of ~420 MPa and thermal conductivity of ~10.3 W/m/K have been achieved in fully densified tape comprising calcium aluminoborosilicate glass, aluminum nitride, and silicon carbide whiskers. Silicon carbide whiskers aligned parallel to the casting direction contributed significantly to the reinforcement of the microstructure with accompanying extensive densification over a broad temperature range. These results are compared with the more typical alumina filler substituted for the aluminum nitride.     

Particle Motion in Simple Shear Flow with Gravity

The motion of aerosol particles in simple shear flow, subject to gravity, is analyzed. The combination of gravity and shear-induced lift is shown to give rise to particle drift. It is shown that in shear flow near a wall, when gravity points in the direction of flow, particles drift towards the wall, while for gravity pointing against the flow the drift is away from the wall. These results are also demonstrated experimentally, with fair qualitative agreement between analysis and experiments.     

Shear Modulus and Yield Stress Measurements of Attractive Alumina Particle Networks in Aqueous Slurries

The shear modulus and yield stress of attractive alumina particle networks in aqueous slurries was determined as a function of volume fraction (0.1 to 0.5), pH (2, 4, 5, 6, and 9), and salt (NH₄l) concentration (0.25M to 2.34) using both vane and couette rheological tools. Consistent with previous observations concerning the relative strength of attractive particle networks, the shear modulus increased to a plateau value with salt concentration. In this work we have shown that the salt concentration at which this plateau value is achieved is a function of the pH, and thus, the surface charge density. The values of the shear modulus [G'], yield stress [τ_y], and yield strain [γ_y] of the attractive networks can be described with power law functions for particle volume fraction [φ] (G'∝φ^4.75, τ_y∝φ^3.6, and γ_y∝φ^−1.1) and salt concentration [c] (G'∝ [c]^2.0, τ, ∝ [c]^1.15, and γ_y∝ [c]^−0.85).     

Surface Modification in Polycrystalline Y2O3 Under High‐Pressure/High‐Temperature Processing Conditions

A pressure‐induced phase transformation is used to refine the grain size of polycrystalline Y₂O₃, by a factor of 3000. A surface modification effect accompanies the observed grain refinement, which becomes more apparent with increasing holding time under high pressure. The surface‐modified layer exhibits lower hardness and lower oxygen content relative to the underlying material. Moreover, it possesses columnar‐grained structure with cubic symmetry, whereas the interior has a monoclinic structure.     

High‐Temperature Shear Strength and Bonding Mechanism of the Mullite Ceramic/Fiber Brick Component Joined by Phosphate Adhesive

The mullite ceramic/fiber brick system was bonded by two kinds of phosphate adhesives. The specimens were treated from 200 to 1400°C. The mechanical properties were tested at room temperature and at high temperature, and the relevant bonding mechanism was also discussed. The results show that the addition of silicon can greatly improve the adhesive's mechanical properties. The room‐temperature shear strength of the component bonded by adhesive with the silicon calcined at 800°C can reach 6.58 MPa. The shear strength of the adhesive with silicon tested at 800°C can reach 0.42 MPa.     

A Lead‐Free and High‐Energy Density Ceramic for Energy Storage Applications

In this work, we demonstrate a very high‐energy density and high‐temperature stability capacitor based on SrTiO₃‐substituted BiFeO₃ thin films. An energy density of 18.6 J/cm³ at 972 kV/cm is reported. The temperature coefficient of capacitance (TCC) was below 11% from room temperature up to 200°C. These results are of practical importance, because it puts forward a promising novel and environmentally friendly, lead‐free material, for high‐temperature applications in power electronics up to 200°C. Applications include capacitors for low carbon vehicles, renewable energy technologies, integrated circuits, and for the high‐temperature aerospace sector.     

Heat and Mass Transfer in Ceramic Lattices During High‐Temperature Oxidation

This work reports on the heat and mass transfer evolution of ceramic lattices during their oxidation at 1400°C and 1600°C in air. Si–SiC and Si–SiC–ZrB₂ systems were employed as skeleton material because they, previously produced as monolithic bars, showed promising oxidation behavior at high temperatures. Regular arrays of tetrakaidecahedra were first designed by CAD, then 3D printed and finally converted into ceramic by replica technique followed by reactive silicon infiltration. The surface area of each sample was calculated and specific weight variations were evaluated as a function of time. During oxidation, effective thermal conductivity and pressure drop of each sample were measured. Finally, results were correlated with the phenomena occurring during high‐temperature oxidation.     

Fine‐Scaled Piezoelectric Ceramic/Polymer 2‐2 Composites for High‐Frequency Transducer

A novel technique was utilized to fabricate fine‐scaled piezoelectric ceramic/polymer 2‐2 composites for high‐frequency ultrasonic transducers. Lead zirconate titanate (PZT) was used as raw material. Tape‐casted acetylene black tapes were used to define kerfs after sintering. A one‐directional supporter was utilized to avoid distortion of PZT elements. PZT elements with 20 ± 2 μm width exhibited good consistency in longitudinal direction. A resonant method was utilized to evaluate the piezoelectric and dielectric properties of the composites. A 72‐μm‐thick composite with an aspect ratio of ~3.6 exhibited a k_t of 0.61 with satisfied piezoelectric and dielectric properties. A prototype high‐frequency ultrasonic transducer was fabricated and evaluated by an underwater pulse‐echo test. The center frequency was found to be 23.75 MHz, with ?6 dB bandwidth of 5.5 MHz.     

Producing Large Complex‐Shaped Ceramic Particle Stabilized Foams

Highly porous ceramic foams can be produced by combining particle stabilized foams and gelcasting concepts. Sulfonate‐type surfactants are selected to weakly hydrophobize the alumina surface and stabilize air bubbles in suspensions containing gelcasting additives, polyvinyl alcohol (PVA), and 2,5‐dimethoxy‐2,5‐dihydrofurane (DHF). The aim of this work was to prepare large complex‐shaped ceramic foam objects with homogeneous microstructure and high porosity. A key to avoiding drying cracks is to strengthen the wet green body via gelcasting. The influence of the amount of gelcasting additives on the mechanical strength of the ceramic foam green bodies is investigated as well as the effect of using cross‐linking agent versus the addition of just a binder. The presence of a cross‐linked polymeric network within the green body increases its mechanical strength and minimizes crack formation during drying.     

Enhanced High‐Frequency Properties of NiZn Ferrite Ceramic with Co2Z‐Hexaferrite Addition

Significantly enhanced dielectric and loss characteristics have been observed in Ni_0.4Zn_0.6Fe₂O₄ ferrite with various Ba₃Co₂Fe₂₄O₄₁ (Co₂Z) addition (x). Compared with pure NiZn and Co₂Z ferrites, the composite ceramics obtain much refined grains and notable high‐frequency characteristics. With the introduction of Co₂Z into NiZn ferrite matrix, the resistivity is largely increased from the order of 10⁶ Ω cm to the order of 10⁸ Ω cm and the frequency stability of permittivity is dramatically enhanced. Co₂Z addition obviously improves the magnetic quality factor Q and reduces the dielectric loss of the ceramics at high frequency. For the samples with x = 20?30 wt%, permittivity ε′ is almost unchanged from 1 MHz to 1 GHz, Q is greater than 10 in a wide frequency range, and dielectric loss tan δ_ε is observed to be of the order of 10^?3 at 100 MHz, which is lower by two orders of magnitude compared with pure NiZn and Co₂Z ferrites. These characteristics are all desirable for magneto‐dielectric ferrites in high‐frequency applications.     

Sintering of High‐Performance Silicon Nitride Ceramics Under Vibratory Pressure

To improve mechanical behaviors of silicon nitride ceramics, here we introduced a novel external field—vibratory pressure into the sintering of Si₃N₄ ceramics with advantages of higher density, more uniform distribution of interfacial phase, higher sintering motivation in the width direction, and therefore more favorable mechanical properties than traditional sintering methods. Grain size and aspect ratio of the two ceramics were investigated with linear intercept method. Flexural strength of the vibratory‐assisted hot‐pressing (VAHP) specimen increased from 936 ± 27.2 MPa to 1247 ± 28.9 MPa, and an increase of 10% was achieved in fracture toughness. It is believed that such VAHP method can provide a universal approach and new opportunities for the fabrication of covalent‐bonded ceramics or composites with enhanced performances.     

Self‐Generating High‐Temperature Oxidation‐Resistant Glass‐Ceramic Coatings for C–C Composites Using UHTCs

Carbon–carbon (C–C) composites are ideal for use as aerospace vehicle structural materials; however, they lack high‐temperature oxidation resistance requiring environmental barrier coatings for application. Ultra high‐temperature ceramics (UHTCs) form oxides that inhibit oxygen diffusion at high temperature are candidate thermal protection system materials at temperatures >1600°C. Oxidation protection for C–C composites can be achieved by duplicating the self‐generating oxide chemistry of bulk UHTCs formed by a “composite effect” upon oxidation of ZrB₂–SiC composite fillers. Dynamic Nonequilibrium Thermogravimetric Analysis (DNE‐TGA) is used to evaluate oxidation in situ mass changes, isothermally at 1600°C. Pure SiC‐based fillers are ineffective at protecting C–C from oxidation, whereas ZrB₂–SiC filled C–C composites retain up to 90% initial mass. B₂O₃ in SiO₂ scale reduces initial viscosity of self‐generating coating, allowing oxide layer to spread across C–C surface, forming a protective oxide layer. Formation of a ZrO₂–SiO₂ glass‐ceramic coating on C–C composite is believed to be responsible for enhanced oxidation protection. The glass‐ceramic coating compares to bulk monolithic ZrB₂–SiC ceramic oxide scale formed during DNE‐TGA where a comparable glass‐ceramic chemistry and surface layer forms, limiting oxygen diffusion.     

High‐Temperature Strength of Boron Suboxide Ceramic Consolidated by Spark Plasma Sintering

The spark plasma sintering (SPS) of B₆O ceramics using a highly crystalline boron suboxide powder with a low oxygen deficiency level is reported. The monolithic boron suboxide ceramic exhibited a room‐temperature strength of 300 ± 20 MPa, which is comparable to the strength of monolithic boron carbide. With increasing flexural test temperature, the strength of the boron suboxide ceramics increased to 450 MPa at 1400°C. The increase in strength with the temperature is associated with the unique microstructure of boron suboxide grains, which allows intergranular “brittle” fracture along subgrains even at 1400°C. This suggests that even higher strengths can be achieved.     

Synthesis of High‐Temperature‐Stable TiO2 and its Application on Ag+‐Activated Ceramic Tile

The main purpose of study was to provide a common synergy using Ag⁺‐doped calcium phosphate powder and high‐temperature‐stable TiO₂ for antibacterial and photocatalytic tile applications. Thermally stable SiO₂‐modified TiO₂ active layer was deposited on Ag⁺‐activated ceramic tiles by spray coating. The results showed that a nearly 100% cleanability degree was detected for SiO₂‐modified TiO₂ (TS)‐coated antibacterial tiles when compared uncoated and unmodified TiO₂‐coated tiles. Antibacterial tests and colorimetric analyses indicated that ceramic tiles provide both antibacterial and photocatalytic properties simultaneously.     

PNN‐PZN‐PMN‐PZ‐PT Multilayer Piezoelectric Ceramic with Low Sintering Temperature

Multilayer piezoelectric ceramic material with a composition of 0.1Pb(Ni_1/3Nb_2/3)O₃‐0.35Pb(Zn_1/3Nb_2/3)O₃‐0.15Pb(Mg_1/3Nb_2/3)O₃‐0.1PbZrO₃‐0.3PbTiO₃‐4 mol% excess NiO (0.1PNN‐0.35PZN‐0.15PMN‐0.10PZ‐0.3PT‐0.04NiO) was fabricated by a roll‐to‐roll tape casting process and co‐fired with Ag/Pd electrode at low temperature of 950°C. Their dielectric, piezoelectric, and ferroelectric properties were evaluated. The effective piezoelectric coefficient d₃₃ of the obtained multilayer piezoelectric material was 412 pm/V, while d₃₃ for the ceramic pellet was 503 pm/V. Piezoelectric displacement measurements revealed small displacement hysteresis for the multilayer material. The combined characteristics of the multilayer piezoelectric material using the selected composition showed the potential for high power, high strain, and high force actuation applications. In addition, as the composition had a tetragonal phase, which substantially deviated from morphotropic phase boundary (MPB), the excellent properties may be more tolerant to stoichiometric fluctuation, which can allow larger processing and composition window as desired for scalable production.     

Effect of High‐Intensity Ultrasound on the Crystallization Behavior of High‐Stearic High‐Oleic Sunflower Oil Soft Stearin

The objective of this research was to evaluate the effect of high‐intensity ultrasound (HIU) and crystallization temperature (T_c) on the crystallization behavior, melting profile, and elasticity of a soft stearin fraction of high‐stearic high‐oleic sunflower oil. Results showed that HIU can be used to induce and increase the rate of crystallization of the soft stearin with significantly higher SFC values obtained in the sonicated samples, especially at higher T_c. SFC values were fitted using the Avrami model, and higher k_n and lower n values were obtained when samples were crystallized with sonication, suggesting that sonicated samples crystallized faster and through an instantaneous nucleation mechanism. In addition, the crystal morphology, melting behavior, and viscoelasticity were significantly affected by sonication.