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41.
《Ceramics International》2022,48(17):24471-24475
Al2O3–SiC composite powder (ASCP) was successfully synthesized using a novel molten-salt-assisted aluminum/carbothermal reduction (MS-ACTR) method with silica fume, aluminum powder, and carbon black as raw materials; NaCl–KCl was used as the molten salt medium. The effects of the synthesis temperature and salt-reactant ratio on the phase composition and microstructure were investigated. The results showed that the Al2O3–SiC content increased with an increase in molten salt temperature, and the salt–reactant ratio in the range of 1.5:1–2.5:1 had an impact on the fabrication of ASCP. The optimum condition for synthesizing ASCP from NaCl–KCl molten salt consisted of maintaining the temperature at 1573 K for 4 h. The chemical reaction thermodynamics and growth mechanism indicate that the molten salt plays an important role in the formation of SiC whiskers by following the vapor-solid growth mode in the MS-ACTR treatment. This study demonstrates that the addition of molten salt as a reaction medium is a promising approach for synthesizing high-melting-point composite powders at low temperatures. 相似文献
42.
43.
Haibin Sun Xue Guo Jiao Li Guochang Li Zanzhong Yang Hao Ding Weilu Yan Shuai Qi Peng Wang Youjie Song 《Ceramics International》2019,45(1):622-626
In order to clarify the effect of grain size on the electrical performance of BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) solid electrolytes with addition of NiO, microcrystalline (~1.5?µm) and ultrafine-grained (~280?nm) BZCYYb electrolytes (with 1?wt% NiO) were fabricated by the conventional and two-step sintering method, respectively. The results show that compared with microcrystalline electrolytes, the ultrafine-grained electrolytes have similar grain-interior conductivities, but much lower grain-boundary conductivities, illustrating that the grain boundary is not conducive for ionic transport. As a result, the electrical conductivity of microcrystalline electrolytes (1.9?×?10?2 S?cm?1 at 600?°C in wet air) is higher than that of ultrafine-grained electrolytes (1.1?×?10?2 S?cm?1 at 600?°C in wet air). In addition, the OCV (open-circuit voltage) values of electrolyte-supported single cells show that the undesired electronic conduction exists in the electrolytes due to the BaY2NiO5 impurity formed by the reaction of NiO and BZCYYb. The ultrafine-grained electrolytes show lower OCV values than that of microcrystalline ones, due to the prolonged electronic transport paths. Therefore, large-grained or grain boundary-free microstructure are necessary for improving the electrical performance of BZCYYb electrolytes. 相似文献
44.
Jia Liang Balaji Devakumar Liangling Sun Qi Sun Shaoying Wang Bin Li Daqin Chen Xiaoyong Huang 《Ceramics International》2019,45(4):4564-4569
Novel Mn4+-activated KLaMgWO6 red phosphors with different Mn4+ concentrations were successfully synthesized via a high-temperature solid-state reaction method. The phase formation, microstructure, photoluminescence properties, decay lifetimes and internal quantum efficiency were discussed to analyze the properties of the as-prepared phosphors. The samples belonged to monoclinic crystal system with enough WO6 octahedrons that provided suitable sites for Mn4+ ions. Upon the excitation of 348?nm, KLaMgWO6:Mn4+ phosphors gave bright far-red emission around 696?nm due to the 2Eg→4A2g transition of Mn4+ ions. The critical concentration of Mn4+ was 0.6?mol% and the concentration quenching mechanism belonged to electric multipolar interaction. Besides, the CIE chromaticity coordinates of the KLaMgWO6:0.6%Mn4+ phosphor were (0.7205, 0.2794) which located in deep red range, and its color purity reached up to 96.6%. The KLaMgWO6:0.6%Mn4+ sample also exhibited high internal quantum efficiency of 43%. All of the admirable optical properties indicate that the KLaMgWO6:Mn4+ phosphors can be applied to indoor plant growth illumination. 相似文献
45.
46.
Wenya Du Yunlong Ai Weihua Chen Wen He Jianjun Zhang Yaqi Fan Yuxing Gong 《Ceramics International》2019,45(6):6788-6794
xNb2O5–7.5La2O3-Al2O3 ceramic composites with in-situ-grown columnar Al2O3 crystals were successfully prepared by microwave sintering at 1450–1525?°C using α-Al2O3, Nb2O5, and La2O3 powders as raw materials. X-ray diffraction results indicated that the main phases were Al2O3, LaNbO4, and Nb2O5 in the prepared samples. A field emission scanning electron microscope (FESEM) showed that the Al2O3 crystals appeared as columnar in the structure. Moreover, the grain size of the columnar Al2O3 crystals increased with the Nb2O5 content. The ratio of the major axis to the minor axis of the crystals was largest when the Nb2O5 content was 15?vol%. Furthermore, the grain-growth kinetics index (n), growth activation energy (Q), and growth mechanism of the columnar Al2O3 crystals were studied. The results indicated that the Nb2O5 addition could promote formation and growth of columnar Al2O3 crystals, and the grain-growth activation energy indicated that the dissolution process controls the crystal growth. The growth mechanism of the columnar Al2O3 crystals was also studied. The present work demonstrated that Nb2O5 is a good additive for the preparation of Nb2O5–7.5La2O3-Al2O3 composite ceramics with columnar Al2O3 crystals. 相似文献
47.
ABSTRACTR-curve and controlled stable crack growth behaviour of ZrB2–17vol.-%SiC and ZrB2–45vol.-%SiC ceramic composites was studied on V-notched samples using four-point bending at room temperature. The rising K1R behaviour was determined as a function of the crack extension Δa with a crack bridging mechanism being dominant in such behaviour. Significant differences in crack growth rates were found within the same composition of ceramics simply as the crack length varied during crack growth processes. These differences are indicative of the significant influence of microstructural parameters of the ceramics on crack propagation. The peculiarities of stress intensity factor K1 and the crack growth-specific behaviour in ZrB2–SiC particulate ceramic composites are discussed. 相似文献
48.
Crushable volcanic soils are well-known for their distinctive texture, vesicular nature and grain fragility. These features of volcanic soils lead to difficulty in interpreting the results of laboratory and field testing because of the occurrence of particle crushing. Sands containing pumice particles are commonly found in the Hamilton Basin in the North Island of New Zealand. The pumice particles originated from a series of volcanic eruptions centered in the Taupo and Rotorua regions. As a result of flooding and erosion along the Waikato River, the pumice particles have become mixed with other materials and have been distributed over the Hamilton Basin; these mixtures are referred to herein as natural pumiceous (NP) sands. This paper initially investigates an appropriate technique for measuring the maximum dry density (MDD) of NP sands; then a modified MDD test is proposed for estimating the pumice contents of these sands. In order to examine the applicability of different standard methods for determining MDD, New Zealand and Japanese standards are employed. The results using the Japanese standard show consistent MDD values when repeating the tests due to negligible particle crushing. On the other hand, the results of MDD tests according to the New Zealand standard indicate that a significant amount of particle crushing occurs after each repeated test and, consequently, it is not possible to get the same result when the test is repeated. NP sands reach their ultimate potential breakage during the modified MDD tests (at least, for the level of loading applied) and they experience different levels of particle crushing which may be a function of their pumice content. As a way forward, the relative breakages of the materials tested are used to estimate the pumice contents of the NP sands. 相似文献
49.
目的:分析血小板源性生长因子(PDGF)/蛋白激酶B(AKT)通路在压力超负荷诱导的心室重构中的作用及机制。方法:选取C57BL/6雌性小鼠55只,建立主动脉弓缩窄模型,成功建模45只,小鼠随机数字表法分为假手术组、DMSO组和实验组,假手术组小鼠开胸后逐层缝合,不进行主动脉缩窄术(TAC),开胸24 h后给予PBS溶液200 μL加DMSO 50 μL,DMSO组TAC术后24 h给予PBS溶液200 μL加DMSO 50 μL,实验组TAC术后24 h给予PBS溶液200 μL加抑制剂AG1296 50 μL,观察小鼠心功能及心肌组织病理形态。慢病毒感染建立PDGF基因不同表达人脐静脉内皮细胞(HUVEC)细胞鉴定和培养,依据细胞不同处理方式分为对照组、PDGF组、shRNA组和PDGF+IMA组,检测p-AKT及t-AKT蛋白在HUVEC细胞内表达情况。结果:DMSO组小鼠左室收缩末期容积(LVESV)、左室舒张末期容积(LVEDV)、左室收缩末期内径(LVESD)及左室舒张末期内径(LVEDD)较假手术组升高,左室射血分数(EF)、左室短轴缩短率(FS)较假手术组降低。实验组LVESV、LVEDV、LVESD及LVEDD较DMSO组降低,EF、FS较DMSO组升高,差异有统计学意义(P<0.05)。假手术组小鼠心肌组织整齐排列,间隙正常;DMSO组小鼠形态不规整,炎性细胞浸润,细胞间隙变大,胞核深染。实验组小鼠膨大或坏死细胞减少,间隙变小,炎性浸润降低。DMSO组小鼠心肌细胞横截面积较假手术组升高,实验组小鼠心肌细胞横截面积较DMSO组降低,差异有统计学意义(P<0.05)。PDGF+IMA组细胞内p-AKT及t-AKT蛋白表达较PDGF组及shRNA组显著降低,差异有统计学意义(P<0.05)。结论:PDGF可加速压力超负荷诱导心室重构,促进形成心肌组织纤维化,而抑制PDGF/AKT通路可改善心肌细胞肥大。 相似文献
50.
Jian Wang Shuai Huang Mingyang He Peihua Wangyang Yangfan Lu Hongjian Huang Lei Xu 《Ceramics International》2018,44(7):7656-7662
The ceramic coatings on the surface of aluminum alloy substrates with micro-grooves have been successfully fabricated in the silicate solution via micro-arc oxidation (MAO) approach. Microstructure characterization showed that the larger main discharge channels were located in the center of micro-groove, the smaller secondary discharge channels were located on both sides of main discharge channel; and a few irregular micro-pores existed in the vicinity of all discharge channels, which were mainly cause by the rapid cooling and solidification of discharge channels hindering the removal of gases produced via reaction. Moreover, the growing direction of coating in the initial stage was mainly outward-growth and resulted in the formation of inverted triangle coating structure, which was due to the sharp-angled effect. But in the final growing stage, the inward-growth behavior played a key role owing to the spark transfer. According to above results and discussion, the formation of smooth, uniform and homogeneous ceramic coating on the surface of whole trapezoidal micro-groove substrate contained four stages: anodic oxidation growth, sharp corner rapid growth, coating homogenization and groove self-filling. 相似文献