Ultra-high Temperature Stability Research Articles

Ultrahigh temperature stability in heterovalent-ion doped PZT ceramics

We achieved ultrahigh temperature stability of the piezoelectric coefficient d33 by doping heterovalent ions in the PbZr0.54Ti0.46O3 ceramics at the A/B sites in the ABO3 lattice. The Sm3+-ion amount at the A-site remains constant, while the Ta5+-ion amount at the B-site changes. We utilized electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) to investigate the reduction of oxygen vacancies, which are closely associated with the defect dipoles formed by heterovalent doping. We utilized piezoresponse force microscopy (PFM), temperature-dependent X-ray diffraction (XRD) combined with Rietveld refinement, and temperature-dependent Raman spectroscopy to understand the mechanism of the temperature stability of the piezoelectric coefficient d33. When x = 0.01, the performance of xTa-0.01Sm-PbZr0.54Ti0.46O3 ceramic is optimal: d33 = 530 pC/N, electromechanical coupling factor kp = 0.72, Curie temperature TC = 343 °C, where the temperature stability of the piezoelectric coefficient is ultrahigh, and the d33 changes only 2.2 % over the 25–200 °C temperature range.

Ultrahigh thermal stability and piezoelectricity of lead-free KNN-based texture piezoceramics

The contradiction between high piezoelectricity and uniquely poor temperature stability generated by polymorphic phase boundary is a huge obstacle to high-performance (K, Na)NbO3 -based ceramics entering the application market as Pb-based substitutes. We possess the phase boundary by mimicking Pb(Zr, Ti)O3’s morphotropic phase boundary structure via the synergistic optimization of diffusion phase boundary and crystal orientation in 0.94(Na0.56K0.44)NbO3−0.03Bi0.5Na0.5ZrO3−0.03(Bi0.5K0.5)HfO3 textured ceramics. As a result, a prominent comprehensive performance is obtained, including giant d33 of 550 ± 30 pC/N and ultrahigh temperature stability (d33 change rate less than 1.2% within 25-150 °C), representing a significant breakthrough in lead-free piezoceramics, even surpassing the Pb-based piezoelectric ceramics. Within the same temperature range, the d33 change rate of the commercial Pb(Zr, Ti)O3−5 ceramics is only about 10%, and more importantly, its d33 (~ 350 pC/N) is much lower than that of the (K, Na)NbO3-based ceramics in this work. This study demonstrates a strategy for constructing the phase boundary with MPB feature, settling the problem of temperature instability in (K, Na)NbO3-based ceramics.

Effect of ultra-high temperature treatment on the rolled pure molybdenum for nuclear thermal propulsion

Molybdenum (Mo)-based uranium dioxide (UO2) fuel is considered one of the most promising fuel forms for deep-space exploration. The rolling process has been proposed for the preparation of Mo matrix due to its excellent performance. However, there has been limited research on the ultra-high temperature stability of Mo matrix used in nuclear thermal propulsion (NTP). Therefore, in this study, annealing experiments were carried out on rolled Mo plates within a relatively wide temperature range of 1200 to 2300 °C for 1 h to investigate the effects of temperature on the phase composition, microstructure, and mechanical property. The results showed that, despite the body-centered cubic structure of the Mo plates remaining unchanged without undergoing phase transition after high-temperatures, the intensity of the crystal diffraction peaks experienced a significant increase. The preferred growth orientation shifted from the (110) direction at lower temperatures to the (200) direction at 2300 °C. The grain shape of the rolled Mo plates changed from elongated to equiaxed after annealing, and the grain size increased from the initial 1 μm to tens of microns. No discernible surface pores or fracture bubbles were observed when annealed at 1200 to 2100 °C. However, subsequent annealing at 2300 °C revealed a proliferation of polyhedral bubbles, ranging in size from tens of nanometers to several microns, distributed both in grain boundaries and within grains. Nevertheless, there is no apparent change in the density from 1200 to 2300 °C. Bright-field TEM micrographs show that after annealing at 2300 °C, the dislocation density is significantly reduced, and the dislocation shape evolves from screw dislocation to long and straight line. In addition, the Vickers hardness value of the rolled Mo plates undergoes a significant decrease, from 247.1 to 199.6 Hv, after annealing at 1200 °C. Subsequently, in the temperature range of 1200 to 2300 °C, a gradual decline in the hardness value is observed. This work will deepen our understanding of the high-temperature resistance of rolled Mo plates and provide data to support their applications in ultra-high-temperature conditions.

Significantly enhancing high-temperature piezoelectric response and Tdr of BF-BT-based ceramics through multi-component optimization strategy

Phase boundary-domain engineering modulation with diverse group elements and coexistence of multiphase and composite domain structures is a good pathway that can be realized to simultaneously improve the piezoelectric properties of BF-BT ceramics and their thermal stability. Here, we propose a multicomponent optimization strategy. We innovatively introduce the 0.8(Bi0.5Na0.5)TiO3-0.2(Bi0.5K0.5)TiO3 (BNT-20BKT) component to 0.69BF-0.31BT ceramic, to build a morphotropic phase boundary (MPB) for enhancing d33. Meanwhile, Bi(Zn0.5Ti0.5)O3 with high Curie temperature and high tetragonal degree was introduced with the expectation of obtaining higher thermal stability along with high piezoelectric properties. The 0.69BiFeO3-0.31BaTiO3-0.005[0.8(Bi0.5Na0.5)TiO3-0.2(Bi0.5K0.5)TiO3]-xBi(Zn0.5Ti0.5)O3 (referred to as BF31BT-0.005(BNT-20BKT)-xBZT, 0.00 ≤ x ≤ 0.025) ceramics were successfully prepared. For the first time, an ultra-high piezoelectric performance of 749.6 pC/N was achieved at a real-time depolarization temperature (Tdr) of 395.6 °C, reflecting the real-time piezoelectric properties and ultra-high temperature stability of the ceramic at high temperatures. A two-phase coexisting structure of R and PC phases was produced in BF31BT-0.005(BNT-20BKT)-0.025BZT ceramic. TEM results showed the formation of nanodomains and a large number of polar nanoregions (PNRs). By adjusting the appropriate R/PC phase ratio, oxygen octahedral distortion, and optimizing the local domain engineering, an effective strategy is provided for simultaneously achieving ultra-high temperature stability and ultra-high piezoelectric response.

Realization of ultra-high temperature stability and excellent electrical properties in LTO-based ceramics via A/B-site co-doing

La2Ti2O7 (LTO) ceramics, ideal for ultra-high temperature applications with a Curie temperature near 1460 °C, were previously limited by a low piezoelectric coefficient (d33) of 1.5 pC/N. In this work, the incorporation of Bi3+ and V5+ dopants have been employed to augment the piezoelectric properties of LTO. An enhanced d33 ∼ 4.0 pC/N is achieved in La1.91Bi0.09Ti1.97V0.03O7 (LBTV9) ceramics, while maintaining an ultra-high Curie temperature of 1437 °C. This improvement is attributed to local heterogeneity in the lattice structure induced by the doping. LBTV9 ceramics also exhibit excellent high-temperature stability and insulation properties, maintaining a d33 at 4.0 pC/N after annealing at 1000 °C for 48 h and stabilizing at 4.2 pC/N across temperatures from 200 °C to 1600 °C, with a DC resistivity of 1.7 × 106 Ω·cm at 1000 °C. These enhancements make LBTV9 ceramics suitable for extreme condition applications, thus unlocking new possibilities for their use in ultra-high temperature piezoelectric devices.

Preparation method and industrialization of Ta-based ultra high temperature ceramic Tujia jar tea baking jar materials

The production materials of traditional Tujia jar tea often face problems such as poor high-temperature performance and poor durability. To improve the temperature resistance and durability of tea baking utensils, this study proposes a new type of TaC ultra-high temperature ceramic. TaC ceramics with excellent performance were prepared through powder metallurgy technology, including high-energy ball milling to ensure uniform mixing, followed by compression molding and high-temperature sintering. The test results demonstrated excellent mechanical properties, with a maximum depth of 948.67 nm and a contact depth of 954.45 nm, proving outstanding compressive and wear resistance. The hardness reached 21.4±0.5 Gpa, and the elastic modulus was 397.2±8.7 Gpa, both of which indicate its stability under high loads. In addition, the fracture toughness was 2.8±0.2 Mpa*m1/2. At a high temperature environment of 1000 °C, the oxidation rate constant of TaC ceramics was only 0.183 mg2 *cm−4 *h, which demonstrates its excellent high-temperature stability. The development of this TaC ceramic not only strengthened the traditional production process of Tujia teapots and tea roasting teapots, thereby improving the product’s service life, but also holds potential for other industrial applications that demand ultra-high temperature stability. These contributions provide new directions for the high-temperature application of ceramic materials and bring tangible economic and technological value to related industries.

Turning Ultra-Low Coercivity and Ultra-High Temperature Stability Within 897 K via Continuous Crystal Ordering Fluctuations.

High-performance soft magnetic materials are important for energy conservation and emission reduction. One challenge is achieving a combination of reliable temperature stability, high resistivity, high Curie temperature, and high saturation magnetization in a single material, which often comes at the expense of intrinsic coercivity-a typical trade-off in the family of soft magnetic materials with homogeneous microstructures. Herein, a nanostructured FeCoNiSiAl complex concentrated alloy is developed through a hierarchical structure strategy. This alloy exhibits superior soft magnetic properties up to 897K, maintaining an ultra-low intrinsic coercivity (13.6 A m-1 at 297 K) over a wide temperature range, a high resistivity (138.08µΩcm-1 at 297K) and the saturation magnetization with only a 16.7% attenuation at 897 K. These unusual property combinations are attributed to the dual-magnetic-state nature with exchange softening due to continuous crystal ordering fluctuations at the atomic scale. By deliberately controlling the microstructure, the comprehensive performance of the alloy can be tuned and controlled. The research provides valuable guidance for the development of soft magnetic materials for high-temperature applications and expands the potential applications of related functional materials in the field of sustainable energy.

Precursor-derived SiHfBCN ceramics with ultrahigh temperature stability: Facile preparation, phase evolution behavior, and mechanism of ultrahigh temperature thermal stability

SiHfBCN ceramics are the most promising candidates as ultrahigh temperature ceramics for aerospace applications. In this work, PHSNB precursors were synthesized by hydrosilylation reaction of polyborosilazane (PSNB) and polyhafnocenecarbosilane (PHCS), and then the SiHfBCN ceramics can be obtained from the PHSNB precursors through the precursor-derived ceramics (PDC) strategy. The structure, composition, pyrolysis process, and phase evolution behavior at high temperatures of the SiHfBCN ceramics were systematically investigated. The results show that the optimum SiHfBCN ceramic prepared in this study can remain stable until 1780 °C, and the weight loss at 1800 °C is only 0.8 wt%, demonstrating the excellent high temperature thermal stability of the SiHfBCN ceramics. The outstanding high temperature thermal stability of the SiHfBCN ceramics can be attributed to two reasons. Firstly, the formation of HfCxN1-x solid solution at high temperatures can greatly inhibit the formation of SiNx, so the carbothermal reduction reaction and thermal decomposition reaction of SiNx can be greatly inhibited. Secondly, the generated crystal phases at high temperatures are surrounded by the chaotic layered structures of B–C–N phase, which greatly restricts the decomposition process of the SiHfBCN ceramics. This work presents a convenient strategy in preparing multiphase ceramics (not only SiHfBCN) that can be applicable in various harsh environmental conditions.

Lightweight and large-scale rGO reinforced SiBCN aerogels with hierarchical cellular structures exposed to high-temperature environments

SiBCN ceramic aerogel is an ideal potential candidate for ultra-high temperature thermal insulation due to its unique microscopic pore structure combined with the excellent thermal stability of SiBCN ceramic. Here, reduced graphene oxide (rGO) modified SiBCN aerogels (rGO/SiBCN) were prepared through solvothermal, freeze-casting and pyrolysis, and the dimension of the aerogel is up to Φ130 mm × 28 mm. The density of the rGO/SiBCN aerogel is as low as 0.024 g/cm3 and the microstructural regulation is achieved by controlling the rGO content in the aerogel. The hierarchical cellular structure endows the aerogel with a high specific surface area (148.6 m2/g) and low thermal conductivity (0.057 W m−1 K−1). The 10 mm-thick sample exhibits excellent thermal insulation and ablation resistance, as evidenced by its ability to reduce the temperature from ∼1100 °C to ∼180 °C under the intense heat of a butane flame. Moreover, benefiting from the ultrahigh-temperature stability of SiBCN, the rGO/SiBCN aerogel exhibits good thermal stability up to 1200 °C in argon and short-oxidation resistance at 800 °C in air. Therefore, the rGO/SiBCN aerogel with superior overall performance could expand its practical application in high-temperature thermal insulation under extreme environments.

Ultra-high thermal stability InAs/GaAs quantum dot lasers grown on on-axis Si (001) with a record-high continuous-wave operating temperature of 150 °C.

Direct epitaxial growth of group III-V light sources with excellently thermal performance on silicon photonics chips promises low-cost, low-power-consumption, high-performance photonic integrated circuits. Here, we report on the achievement of ultra-high thermal stability 1.3 µm InAs/GaAs quantum dot (QD) lasers directly grown on an on-axis Si (001) with a record-high continuous-wave (CW) operating temperature of 150 °C. A GaAs buffer layer with a low threading dislocation density (TDD) of 4.3 × 106 cm-2 was first deposited using an optimized three-step growth method by molecular beam epitaxy. Then, an eight-layer QD laser structure with p-type modulation doping to enhance the temperature stability of the device was subsequently grown on the low TDD Si-based GaAs buffer layer. It is shown that the QD laser exhibits the ultra-high temperature stability with a characteristic temperature T0=∞ and T1=∞ in the wide temperature range of 10-75 °C and 10-140 °C, respectively. Moreover, a maximum CW operating temperature of up to 150 °C and a pulsed operating temperature of up to 160 °C are achieved for the QD laser. In addition, the QD laser shows a high CW saturation power of 50 mW at 85 °C and 19 mW at 125 °C, respectively.

Effect of Y2O3, La2O3 and ZrO2 dispersoid addition on ultra-high temperature stability of 95W–3.5Ni–1.5Fe heavy alloy

In this work, the effect of three different oxide dispersoids (Y2O3, La2O3, ZrO2) addition on densification, phase, microstructure evolution and high-temperature stability has been investigated thoroughly and compared with that of 95W-3.5Ni-1.5Fe (wt.%) heavy alloy (WHA). The heavy alloys were prepared by powder metallurgy process and consolidated by conventional sintering at 1500 °C in hydrogen atmosphere. The oxide additives did not improve the densification, however, enhanced the hardness of the sintered heavy alloys. Upon exposure to ultra-high temperature (2300 °C) for 10 s, the base alloy suffered significant damage and experienced mass loss due to evaporation of W-oxide. On the other hand, Y2O3, La2O3 and ZrO2-dispersed heavy alloys exhibit protective oxide layer formation. Furthermore, the XRD and FESEM analyses of the exposed surface affirm that no significant damage has incurred in the oxide dispersed WHAs despite identical experimental condition. Owing to the thermal stability of W-Y-O, W-La-O and W-Zr-O systems, the oxide-dispersed heavy alloys offer better structural stability at ultra-high temperature.

Synergistic reinforcement effects of ZrB2 on the ultra-high temperature stability of Cf/SiC composite fabricated by liquid silicon infiltration

A carbon fiber-reinforced silicon carbide (Cf/SiC) composite was fabricated with ZrB2 via the liquid silicon infiltration (LSI) method. A prepreg was prepared by impregnating the phenolic resin with the ZrB2 powder. The as-LSIed composites were tested for 5 min with an oxyacetylene torch to evaluate their ablation and oxidation properties under an ultra-high temperature environment. The ZrB2 powders and SiC matrix between carbon fiber bundles generated a dense ZrO2-SiO2 layer, which inhibited further oxygen diffusion into the composite and minimized the ablation and oxidation of the carbon fibers. Weight loss and linear ablation rate were further reduced with the addition of ZrB2 to the Cf/SiC composite; moreover, the synergistic effect of ZrB2 and SiC reinforced the ablation properties with increased ZrB2 content. ZrB2 also reduced the amount of residual silicon, which was detrimental to the mechanical properties of Cf/SiC composite.

Design of a gradient epsilon-near-zero refractory metamaterial with temperature-insensitive broadband directional emission

Gradient epsilon-near-zero (ENZ) metamaterials offer broadband directional control over thermal emission. Implementing this approach using materials that remain stable in harsh thermo-chemical environments would allow it to be broadly deployed in thermal photonics. Our prior work showed that heterostructures of rock salt MgO and perovskite BaZr0.5Hf0.5O3 (BZHO) are stable up to 1100 °C in air, with no discernible intermixing. In this work, we design a gradient ENZ metamaterial made from three lattice-matched refractory oxides: MgO, BZHO, and NiO. The miscibility of MgO and NiO makes it possible to linearly vary the ENZ frequency of the metamaterial layers. BZHO is used as a thin, interlayer diffusion barrier. We model the emissivity of our gradient ENZ metamaterial at 25 and 1000 °C to demonstrate that the spectral bandwidth of directional emission is preserved at high temperatures despite changes in the optical properties of each material. Finally, we discuss practical fabrication challenges associated with the back reflector and offer potential solutions based on advancements in hetero-integration. Overall, this work shows a pathway toward gradient ENZ metamaterials with ultrahigh-temperature stability.

Optimal active control for fast response of temperature oscillation suppression in cryostats

A fast response active temperature control method and ultra-high temperature stability in a cryostat are essential for the low-temperature primary gas thermometry. In this paper, numerical analysis models of the Proportional-Integral-Derivative (PID) active temperature control method on a cryocooler-based cryostat's performance with different coefficients are constructed. Furthermore, the heat capacity hysteresis is also considered to reduce temperature fluctuation further. The response of temperature oscillations under different PID modes is analyzed and compared to address the difficulty in accurately regulating the temperature oscillations. The system can quickly respond to the required temperature by predicting and optimizing the control coefficients. The flange temperature fluctuations are reduced by magnitude. We unfolded the temperature time series in phase portraits and Poincaré maps to identify the temperature fluctuation characteristics with different regulation coefficients. Numerical research in this paper realizes a faster response to disturbances with better temperature stability according to the dynamic characteristics of temperature fluctuation in the sample chamber. The pre-calculation of the control coefficient makes the heating power fluctuate in a small range, preventing overshoot and effectively reducing the percussion to the experimental equipment.

A promising layered thermoelectric metallic ceramic with ultra-high temperature stability: Mo2Ti2AlC3

As a structural ceramic, MAX phases have attracted the most attentions because of light weight, excellent machinability, good thermal shock resistance and thermal stability at ultra-high temperature. Herein, for the first time we reported the thermoelectric property of Mo2Ti2AlC3, one of MAX phases. It has similar resistivity (~2.3 μΩ·m) and higher Seebeck coefficient (−15μV/K) compared with Pt-Rh alloy. Mo2Ti2AlC3 has higher power factor (~46% improvement) and much lower thermal conductivity (6.2 W/(m·K), one-third) compared with SiC thermoelectric ceramics at 700 °C. The ZT value is about 0.0138 at 700 °C, which is three times as high as that of SiC-7%Si3N4 thermoelectric composite. These suggest that Mo2Ti2AlC3 and other MAX phases have an important application prospect in the field of thermoelectric generator and temperature sensor at ultra-high temperature. Meanwhile, although Mo2Ti2AlC3 ceramic shows metallic transport behavior, the electric thermal conductivity far deviates from traditional Wiedemann-Franz law, indicating that there are strong correlations or couplings between electrons and 2-D layered lattices, and Mo2Ti2AlC3 is a new strong related system with spin-orbital coupling.

Bigao3 Doped Bifeo3-Batio3 Lead-Free Piezoelectric Ceramics with High Piezoelectric Properties and Ultra-High Temperature Stability

Bigao3 Doped Bifeo3-Batio3 Lead-Free Piezoelectric Ceramics with High Piezoelectric Properties and Ultra-High Temperature Stability

Highly porous multicomponent (Hf1/3Ta1/3Nb1/3)C ultra-high temperature ceramic with low thermal conductivity

Fundamental requirements of ultra-high temperature ceramic (UHTC) thermal insulators are excellent thermal stability above 1800 °C, good thermal insulation capability, and high mechanical reliability. We report foam-gelcasting-freeze drying method to fabricate porous multicomponent (Hf1/3Ta1/3Nb1/3)C UHTC with superhigh porosity (90.0-94.0%). The as-prepared samples show low density (0.70–1.17 g/cm3), moderately high compressive strength (0.34–1.34 MPa), low thermal conductivity (0.089–0.098 W/(m•K)), and excellent ultra-high temperature stability (low shrinkage of < 1% after thermal cycles up to 2000 °C). Coordinative mechanisms of multicomponent induced phonon scattering enhancement and low solid skeleton thermal conduction are the main factors that provide excellent thermal insulation capability.

Ultra high temperature stability of milk protein concentrate: Effect of mineral salts addition

Reconstituted milk protein concentrate (RMPC) showed higher thermal stability than reconstituted skimmed milk powder (RSMP) at equal protein level (7.5%); heat coagulation time (HCT) 6.80 and 1.80 min, respectively. RMPC contained lower concentration of milk minerals as compared to RSMP. The total mineral content of RMPC was matched with RSMP using mineral salts, which decreased its HCT to 1.55 min. Individual Ca, Mg, Na and K content of RMPC were also matched. Addition of CaCl2·2H2O and MgCl2·6H2O to RMPC reduced it HCT and made it unsuitable to UHT processing. NaCl added RMPC was UHT stable (UHT run-time>120 min). KCl added samples showed diminished UHT stability (run-time 15 min) and lower overall heat-transfer coefficient. Addition of mineral salts increased protein aggregation. The reduced amount of minerals in RMPC as compared to RSMP, notably potassium content per protein unit, appeared to be responsible for its high heat stability.

Structure and mechanical properties of HNTs/SiBCN ceramic hybrid aerogels

SiBCN ceramic aerogels have excellent properties such as ultra-high temperature stability, low density and high thermal insulation. The aerogels have better potential applications in aerospace and other fields. However, similar to inorganic aerogels, the low mechanical strength of SiBCN ceramic aerogels are the main limitation of its application. Based on the principle of inorganic double network enhancement, the first network was constructed by PVA and HNTs, and HNTs/SiBCN dual network aerogels were constructed by SiBCN ceramic aerogels as the second network. The structure and mechanical properties were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), specific surface area analyzer and pressure tester. Compared with SiBCN ceramic aerogels, 6 wt% HNTs-SiBCN ceramic hybrid aerogels have better microscopic properties (maintaining basic porous network structure and structural stability) and mechanical properties.The continuous HNTs first network can effectively transfer the stress load and enhance the strength of SiBCN ceramic aerogels.

Excellent temperature stability with giant electrostrain in Bi0.5Na0.5TiO3-based ceramics

In this work, we report a giant strain (0.42%) in lead-free ceramics of (1–x) (0.79Bi0.5Na0.5TiO3–0.20 Bi0.5K0.5TiO3–0.01NaNbO3)–xSrTiO3 with x=0.03. Most importantly, ultra-high temperature stability was simultaneously achieved under this giant strain with the variation less than 10% in the range of 20 °C and 140 °C. Systematic temperature dependent Raman spectra measurements and Ginzburg–Landau–Devonshire thermodynamic theory analysis revealed that the intrinsic lattice strain and electric field induced relaxor-ferroelectric phase transition provide reverse strain response with the increase of temperature, jointly conducive to the ultra-high temperature stability of strain property. These materials are extremely competitive in practical application of actuators.