Gd、Zr双位掺杂Sm_2Ce_2O_7的热物理性能

以Sm_2O_3、Gd_2O_3、CeO_2和ZrO_2为原料,采用固相反应法制备了(Sm_(0.5)Gd_(0.5))_2(Ce_(0.7)Zr_(0.3))_2O_7陶瓷,采用X射线衍射法、扫描电子显微镜分析了其相结构及显微组织,采用激光脉冲法和推杆膨胀法测试了其热扩散及热膨胀性能。结果表明,本文成功合成了具有萤石结构的(Sm_(0.5)Gd_(0.5))_2(Ce_(0.7)Zr_(0.3))_2O_7陶瓷,其组织致密,且晶界清晰;小半径离子掺杂使其热膨胀系数小于Sm_2Ce_2O_7,但仍然满足热障涂层的要求;掺杂原子与基质原子之间质量及离子半径之间的差别使其具有较低的热导率。(Sm_(0.5)Gd_(0.5))_2(Ce_(0.7)Zr_(0.3))_2O_7有潜力用作新型热障涂层用陶瓷材料。     

Ce微量掺杂Sm_2Hf_2O_7氧化物的热物理性能

以高纯度Sm_2O_3、HfO_2和CeO_2为原材料,采用高温固相反应法制备了Sm_2(Hf_(1-x)Ce_x)_2O_7氧化物,对其相组成、热膨胀性能和热导率进行了研究。结果表明,成功合成了具有单一焦绿石结构的Sm_2(Hf_(1-x)Ce_x)_2O_7氧化物。由于元素掺杂所引起的声子散射加剧,该系列氧化物热导率随着Ce~(4+)含量增加而降低。由于Ce和Hf之间电负性差别,该系列氧化物的热膨胀系数随Ce~(4+)含量增加而降低。该系列氧化物的热膨胀系数和热导率满足热障涂层的要求。     

Ti~(4+)掺杂对Sm_2Ce_2O_7氧化物的热物理性能影响

以Sm_2O_3、CeO_2和TiO_2氧化物为原料,采用高温固相反应烧结工艺制备Sm_2(Ce_(1-x)Ti_x)_2O_7氧化物。使用X射线衍射仪和电子扫描显微镜分析样品的相组成和微观结构。采用激光脉冲法和推杆膨胀法测试样品的热导率和热膨胀系数。结果表明,Sm_2(Ce_(1-x)Ti_x)_2O_7氧化物具有单一的萤石结构,显微组织致密,晶界清晰。其热导率和热膨胀系数均随TiO2掺杂量的增加而降低,但仍能满足热障涂层的热性能要求。制备的Sm_2(Ce_(1-x)Ti_x)_2O_7氧化物具有用作新型热障涂层表面陶瓷层材料的潜力。     

热障涂层用氧化物稳定的ZrO2陶瓷材料研究现状

综述了氧化物稳定的热障涂层用ZrO2陶瓷的研究情况。指出氧化物稳定的ZrO2陶瓷材料主要适用于在1000℃左右工作的热障涂层,而不易用作新型高温热障涂层表面陶瓷层材料。随着航空发动机技术的发展,化学式为A^3＋ 2 B^4＋ 2 O7焦绿石结构的陶瓷材料有望替代氧化物稳定的ZrO2陶瓷,根据声子导热理论和晶体化学原理,选用合适的氧化物对A^3＋ 2 B^4＋ 2 O7型陶瓷材料进行掺杂进一步降低其热导率并改善热膨胀系数,将为热障涂层技术应用开辟广阔的空间。     

Sm_xCe_(1-x)O_(2-x/2)(x=0.05,0.1,0.15)陶瓷的热物理性能

以Sm_2O_3和Ce(NO_3)·6H_2O为原料,采用溶胶凝胶法和固相烧结法合成了Sm_xCe_(1-x)O_(2-x/2)陶瓷材料。研究了材料的相结构和显微组织,热导率和热膨胀。结果表明:合成的Sm_xCe_(1-x)O_(2-x/2)陶瓷纯净并具有单一的萤石结构。其显微组织致密,晶界清晰。Sm_2O_3掺杂能降低CeO_2的热导率,其1000℃时的热导率在2.2~2.6 W/m·K之间,与氧化钇部分稳定氧化锆的热导率相当;Sm_xCe_(1-x)O_(2-x/2)陶瓷的热膨胀随Sm_2O_3含量的增加而降低,其1200℃时的热膨胀系数大于13×10~(-6)/K。     

(Sm0.7Yb0.3)2Ce2O7陶瓷的热膨胀系数及热导率

以Sm2O3、Yb2O3和CeO2为原材料,采用固相反应法制备了(Sm0.7Yb0.3)2Ce2O7陶瓷材料,用X射线衍射(XRD分析了其相结构,采用扫描电子显微镜(SEM)和电子能谱(EDS)分析其显微组织和元素组成,用推杆膨胀法和激光脉冲法测试了其热膨胀系数和热导率.结果表明,所制备的(Sm0.7Yb0.3)2Ce2O7具有典型的萤石结构,其微观组织致密,晶界清晰.Yb3+离子较小的离子半径使其热膨胀系数低于Sm2Ce2O7,基质原子与取代原子之间质量及尺寸之间的差别,使其具有比Sm2Ce2O7更低的热导率,该材料有潜力用作新型热障涂层表面陶瓷层材料.     

稀土氧化物改性YSZ热障涂层材料热学性能研究

以Gd₂O₃、Yb₂O₃、Y₂O₃和ZrO₂为原料，通过固相合成法制备5Gd₂O₃-6Yb₂O₃-10YSZ热障涂层粉末，又称GYbYSZ。以X射线衍射仪(XRD)和场发射扫描电镜对材料相结构和显微组织进行表征。用激光热导率测试仪和热膨胀仪测试样品热导率和热膨胀系数。结果表明，1600℃制备材料物相为高温相c相；稀土氧化物改性后YSZ块体材料在1000℃下热导率达到1.51 W/(m·K);1200℃热膨胀系数为11.25×10^-6/K；在室温至1500℃范围内，不发生相变，高温稳定性优异。     

Y_2O_3掺杂对La_2Zr_2O_7陶瓷结构与热物理性能的影响

用Y2O3掺杂La2Zr2O7制备(La1–xYx)2Zr2O7(x=0,0.1,0.2,x为摩尔分数)陶瓷材料,利用X射线衍射仪、扫描电子显微镜、激光导热仪以及热膨胀仪分别对其物相结构、显微形貌、热导率及热膨胀性能进行表征。结果表明,(La1–xYx)2Zr2O7为立方烧绿石结构,显微结构致密,在室温至1 450℃范围内具有良好的高温相稳定性。La2Zr2O7掺杂小离子半径Y3+可提高其热膨胀系数(x=0.2),降低热扩散系数,并在高温下表现出类似于玻璃的超低热导率。1 000℃时,La1.6Y0.4Zr2O7的热导率为1.28 W/(m·K),平均热膨胀系数达到9.7×10–6/K。     

Sm_2Ce_2O_7-YSZ功能梯度热障涂层热冲击性能计算机模拟

采用有限元技术分析了Sm_2Ce_2O_7-YSZ功能梯度热障涂层的水淬热冲击性能,研究了金属基体材质及尺寸对其热冲击性能的影响。结果表明,在Sm_2Ce_2O_7/YSZ功能梯度热障涂层中存在较大的冲击热应力。涂层径向热应力从中心处到试样边缘逐渐递减。基体的热膨胀系数对涂层冲击应力影响最明显,涂层中热应力随基体厚度增加而增大,但基体厚度超过20 mm后热应力趋于稳定。基体半径超过14 mm后径向应力不再增大,基体半径超过10 mm后轴向应力和剪切应力不再降低。与Sm_2Ce_2O_7涂层相比,Sm_2Ce_2O_7-YSZ功能梯度涂层具有最大热应力,其结构仍需要进一步优化。     

(Y1-xLax)2O3透明陶瓷的制备及性能

采用传统陶瓷生产工艺制备了(Y1-xLax)2O3(x=0～0.125)透明陶瓷.研究了陶瓷的显微结构、硬度、透光性及热导率.结果表明:La2O3可以有效促进陶瓷烧结,抑制晶粒长大.La2O3添加后,陶瓷硬度由786MPa提高到878MPa,陶瓷热导率明显降低,由16.92W/(m·K)降为5.68W/(m·K).制备...     

Preparation and fine thermal insulation performance of Gd2Zr2O7/ZrO2 composite fibers

Gd₂Zr₂O₇/ZrO₂ (GZC) composite fibers were prepared by electro-spinning method. The XRD, XPS and Raman results showed that there were three crystalline phases, tetragonal phase ZrO₂, cubic phase ZrO₂ and defect fluorite phase Gd₂Zr₂O₇ in GZC composite fibers. GZC fibers remained an intact fiber texture up to 1400 °C according to SEM photographs. The thermal conductivity of GZC fibers was between 0.173 W/(m·K) at 400 °C and 0.309 W/(m·K) at 800 °C, which was lower than that of 7YSZ under the same experimental conditions. The fiber sheet with density about 3.5 g/cm³ has thermal shrinkage less than 3% at 1400 °C. Hence, GZC fibers could be used as refractories for heat protection.     

Enhancing the thermal insulating properties of lanthanum zirconate porous ceramics via pore structure tailoring

The potentially useful role of lanthanum zirconate (La₂Zr₂O₇, LZO) porous bulk ceramics has been rarely explored thus far, much less the optimisation of its pore structure. In this study, LZO porous ceramics were successfully fabricated using a tert-butyl alcohol (TBA)-based gelcasting method, and the pore structures were tailored by varying the initial solid loading of the slurry. The as-prepared ceramics exhibited an interconnected pore structure with high porosity (67.9 %–84.2 %), low thermal conductivity (0.083–0.207 W/(m·K)), and relatively high compressive strength (1.56–7.89 MPa). The LZO porous ceramics with porosity of 84.2 % showed thermal conductivity as low as 0.083 W/(m·K) at room temperature and 0.141 W/(m·K) at 1200 °C, which is much lower than the counterparts fabricated from particle-stabilized foams owing to its unique pore structure with a smaller size, exhibiting better thermal insulating performance.     

Elevated temperature thermal properties of ZrB2-B4C ceramics

The elevated temperature thermal properties of zirconium diboride ceramics containing boron carbide additions of up to 15 vol% were investigated using a combined experimental and modeling approach. The addition of B₄C led to a decrease in the ZrB₂ grain size from 22 µm for nominally pure ZrB₂ to 5.4 µm for ZrB₂ containing 15 vol% B₄C. The measured room temperature thermal conductivity decreased from 93 W/m·K for nominally pure ZrB₂ to 80 W/m·K for ZrB₂ containing 15 vol% B₄C. The thermal conductivity also decreased as temperature increased. For nominally pure ZrB₂, the thermal conductivity was 67 W/m·K at 2000 °C compared to 55 W/m·K for ZrB₂ containing 15 vol% B₄C. A model was developed to describe the effects of grain size and the second phase additions on thermal conductivity from room temperature to 2000 °C. Differences between model predictions and measured values were less than 2 W/m·K at 25 °C for nominally pure ZrB₂ and less than 6 W/m·K when 15 vol% B₄C was added.     

Effects of cerium doping on the microstructure,mechanical properties,thermal conductivity,and dielectric properties of ZrP2O7 ceramics

A two-step method, combined with cold isostatic pressing, was used to prepare CeO₂-doped ZrP₂O₇ ceramics, and their microstructure, mechanical properties, thermal conductivities, and dielectric properties were determined. It was found that CeO₂ doping could increase the Zr–P and P–O bond lengths, which in turn decreased the thermal conductivity of the ZrP₂O₇ matrix. Doping with 12 wt% CeO₂ simultaneously reduced the sintering temperature and improved the mechanical properties of the ZrP₂O₇ ceramics, while retaining its low thermal conductivity and good dielectric properties. The maximum cold modulus of rupture of a sample at 1250 °C was 75.91 MPa, which met most conditions for use at room temperature. A COMSOL model was used to predict the thermal conductivity, based on the microstructure, with a relatively high degree of accuracy. The thermal conductivity of the CeO₂-doped samples was lower than 1.083 W/(m·K). The dielectric constant was in the range of 5.93–6.52 at 20–40 GHz, and the dielectric loss was less than 4 × 10^?3. The ZrP₂O₇-doped ceramics have potential for application in millimetre wave technology, satellite communication, and vehicle radar fields, because they can meet the high thermal insulation requirements for these applications.     

Y3Ce7Ta2O23.5 and Yb3Ce7Ta2O23.5—Two kinds of novel ceramics for thermal barrier coatings

For the development of ceramic candidates for thermal barrier coatings, two kinds of new ceramics, Y₃Ce₇Ta₂O_23.5 and Yb₃Ce₇Ta₂O_23.5, were synthesized by sintering at 1873?K for 10?h. The obtained samples were composed of a single fluorite-type phase, and their relative densities are greater than 90%. Because of phonon scattering caused by the complex lattice, the large number of oxygen vacancies, and substituted atoms, the thermal conductivity is lower than that of 8YSZ. The coefficients of thermal expansion (CTEs) of these two products are located in the range of 10.22–12.57?×?10^?6/K and 9.62–12.66?×?10^?6/K, respectively, from 323?K to 1473?K, and they also exhibit excellent phase stability up to 1473?K. However, their thermal conductivities and CTEs are lower than those of RE₂Ce₂O₇ (RE?=?La, Nd, or Sm).     

Transparent polycrystalline Gd2Hf2O7 ceramics

We have successfully developed transparent polycrystalline Gd₂Hf₂O₇ ceramics with high in‐line transparency. A sol–gel process was used to synthesize the Gd₂Hf₂O₇ powder. Simultaneous thermal gravimetric analysis and differential thermal analysis (TGA/DTA) was used to identify the decomposition sequence as a function of temperature for the as‐synthesized sol–gel powders. The calcined powder is single phase and was formed with an estimated average particle size of 120 nm. Crystallization was confirmed by x‐ray diffraction (XRD) and a single phase was achieved by calcining at 1000°C. The calcined powders were hot‐pressed at 1500°C to achieve >95% theoretical density with closed pore structure followed by a hot isostatic pressing at 1500°C at 207 MPa to achieve a fully dense structure. Microstructural characterization shows a uniform grain size distribution with an average grain size of about 11 μm. In‐line transmission measurements revealed high transparency in the red and infrared. Dielectric properties remain stable with relative permittivity values around 180 and loss tangents less than 0.005 up to 350°C. Thermal conductivity was measured to be ~1.8 W/m°K at room temperature, decreasing to ~1.5 W/m°K by 500°C.     

Preparation and thermophysical properties of Sm2YbTaO7 and Sm2YTaO7

Sm₂YbTaO₇ and Sm₂YTaO₇ ceramics were synthesized by solid reaction method at 1600 °C for 10 h. Crystal phases have been identified by X-ray diffraction, and their thermal conductivities and thermal expansion coefficients were measured using a laser flash method and the pushing-rod technology, respectively. Results indicate that Sm₂YbTaO7 and Sm₂YTaO₇ exhibit a typical defect fluorite-type crystal structure. Compared to Sm₂YTaO₇, Sm₂YbTaO₇ has lower thermal conductivity due to the higher atomic weight difference between the substituted and substituting atoms. The thermal expansion coefficient of Sm₂YbTaO₇ is greater than that of Sm₂YTaO₇ due to its elongated average interionic distance. Their thermal conductivities are much lower than that of YSZ, and their thermal expansion coefficients are very close to that of YSZ. The synthesized ceramics also exhibit excellent phase stability in the temperature range from ambient to 1200 °C.     

Thermal and mechanical properties of Ta2O5 doped La2Ce2O7 thermal barrier coatings prepared by atmospheric plasma spraying

La₂Ce₂O₇ (LC) is a new promising thermal barrier coating (TBC) material for high-temperature applications. However, the sudden decrease of thermal expansion coefficient (TEC) at ∼623 K limits its application. In this study, the plasma-sprayed La₂Ce_1.7Ta_0.3O_7.15 (LCT) coating was developed by partial substitution of Ce⁴⁺ in LC with Ta⁵⁺. LCT coating shows lower thermal conductivity between 298 K and 1273 K (0.54–0.71 W/(m·K)) than LC coating (0.65–0.85 W/(m·K)) and the traditional yttria partially stabilized zirconia (YSZ) coating (1.53–1.72 W/(m·K)). It also exhibits excellent thermal stability at least up to 1573 K for 1000 h. What is more, the sudden TEC drop is suppressed owing to the reduced oxygen vacancy concentration governed by Ta⁵⁺-substitution content. As a result, LCT TBC shows an improved thermal cycling lifetime in an air furnace as compared to LC TBC.     

The dual effect of zirconia fiber on the insulation and mechanical performance of the fumed silica-based thermal insulation material

Inorganic fibers and opacifiers are indispensable for improving the strength and high temperature insulation performance of the fumed silica-based thermal insulation material. However, zirconia fiber enhances the strength of the fumed silica-based thermal insulation material and reduces the radiative heat transfer to replace the opacifier. The sample of fumed SiO₂/Al₂O₃ doped with 7% zirconia fiber (FZ7) has a lower density of 0.70 g/cm³ and a high porosity of 75.0%. In addition, the thermal conductivity of FZ7 at 800 °C is 0.077 W/(m·K), which is lower than the sample of fumed SiO₂/Al₂O₃ doped with 7% glass fiber (FG7) and 0.089 W/(m·K) at 800 °C. The effective extinction coefficient of the thermal insulation material containing zirconia fiber is larger than that of the glass fiber by Fourier transform infrared spectroscopy analysis and calculation, indicating that the zirconia fiber has a distinct absorption and scattering effect on infrared radiation to reduce the radiative heat transfer. Therefore, zirconia fiber enhances the strength and decreases the high temperature thermal conductivity of the composites with the dual effect on the insulation and mechanical performance of the fumed silica-based thermal insulation material.     

Structure evolution,thermal properties and sintering resistance of promising thermal barrier coating material La2(Zr0.75Ce0.25)2O7

Rare-earth doped zirconates are promising candidate materials for high-performance thermal barrier coatings (TBCs). The phase and microstructure stability is an important issue for the materials that must be clarified, which is related to the long-term stable work of TBCs at high temperatures. In this work, La₂(Zr_0.75Ce_0.25)₂O₇ (LCZ) ceramic coatings prepared by atmospheric plasma spraying present a metastable fluorite phase, which can transform into stable pyrochlore under high-temperature annealing. The detailed structure evolution of the ceramic coatings is characterized systematically by SEM, XRD and Raman. The associated thermal properties of LCZ ceramics were also reported. Results show that LCZ ceramic has an ultralow thermal conductivity (0.65 W/m·K, 1200 °C), which is only 1/3 of that of yttria-stabilized zirconia (YSZ). The thermal expansion coefficients of LCZ ceramic increase from 9.68 × 10^-6 K^-1 to 10.7 × 10^-6 K^-1 (300 - 1500 °C), which are relatively larger than those of La₂Zr₂O₇. Besides, Long-term sintering demonstrates that LCZ ceramic coating has preferable sintering resistance at 1500 °C, which is desirable for TBC applications.