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1.
Apatite-type lanthanum silicate (ATLS) electrolyte coatings for use in intermediate-temperature solid oxide fuel cells were deposited by atmospheric plasma spraying (APS). Plasma-sprayed coatings with typical composition La10(SiO4)6O3 exhibiting good densification and high oxide ionic conductivity were obtained by properly adjusting the spraying parameters, particularly the gun current. The highest obtained ionic conductivity value of 3.3 mS/cm at 1,173 K in air is comparable to other ATLS conductors. This work demonstrated empirically that utilization of the APS technique is feasible to synthesize dense La10(SiO4)6O3 electrolyte coatings using gun currents within an unusually broad range.  相似文献   

2.
The effects of La2O3 and HfO2 addition on thermal conductivity and thermal cycle life of EB-PVD YSZ coatings were investigated. La2O3 and HfO2 were selected as additives, because they significantly suppress the sintering of YSZ. The developed coating showed low thermal conductivity as well as high resistance to sintering. Burner rig tests confirmed that the developed coating have a superior thermal insulating effect and have a longer life than that of a coating with conventional composition.  相似文献   

3.
Multilayer particle assemblies that contained both Yb2O3 and SiO2 particles were prepared on Si substrates by layer-by-layer self-assembly (LBLSA) as a new non-line-of-sight avenue of producing dense and uniform Yb2O3-SiO2 coating microstructures. Morphological characteristics of the multilayer particle assemblies upon viscous sintering in the temperature range of 1300 to 1350 °C were evaluated in reference to those of multilayer assemblies that only contained SiO2 or Yb2SiO5 particles. A 4-layer 0.5-μm SiO2 particle assembly could be easily transformed to a dense and continuous coating structure after sintering. In contrast, a 4-layer 1.7-μm Yb2SiO5 particle assembly could not be consolidated and densified, as anticipated from the absence of the viscous sintering mechanism provided by the SiO2 phase. Most of the coatings produced from sintering of Yb2O3-SiO2 (0.5 μm) particles assemblies were dense and continuous with Yb2Si2O7 and Yb2SiO5 as two predominant phases. The results suggest the feasibility of producing dense and uniform silicate coating structures by integrating the LBLSA concept with the viscous flow sintering mechanism provided by the SiO2 particles.  相似文献   

4.
Different plasma electrolytic oxidation (PEO) coatings were prepared on AZ91D magnesium alloy in electrolytes containing various concentrations of (NaPO3)6. The morphologies, chemical compositions and corrosion resistance of the PEO coatings were characterized by environmental scanning electron microscopy (ESEM), X-ray diffractometer (XRD), energy dispersive analysis of X-rays (EDAX), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) test. The results showed that the PEO coatings were mainly composed of MgO, Mg2SiO4, MgAl2O4 and amorphous compounds. As the (NaPO3)6 concentrations increased from 0 to 10 g/l, the thickness and surface roughness of the coatings approximately linearly increased; the MgO and Mg2SiO4 phase increased within the concentration range of 0–3 and 0–5 g/l, and then decreased within the range of 3–10 and 5–10 g/l, respectively, while the MgAl2O4 phase gradually decreased. Moreover, the corrosion resistance of the coatings increased within the range of 0–5 g/l and then decreased within the range of 5–10 g/l. The best corrosion resistance coating was obtained in electrolyte containing 5 g/l (NaPO3)6, it had the most compact microstructure. Besides, a reasonable equivalent circuit was established, and the fitting results were consistent with the results of the EIS test.  相似文献   

5.
The microstructure and microwave dielectric properties of xLa(Mg1/2Ti1/2)O3–(1 − x)Ca0.6La0.8/3TiO3 ceramics system with ZnO additions (0.5 wt.%) investigated by the conventional solid-state route have been studied. Doping with ZnO (0.5 wt.%) can effectively promote the densification and the dielectric properties of xLa(Mg1/2Ti1/2)O3–(1 − x)Ca0.6La0.8/3TiO3 ceramics. 0.6La(Mg1/2Ti1/2)O3–0.4Ca0.6La0.8/3TiO3 ceramics with 0.5 wt.% ZnO addition possess a dielectric constant (r) of 43.6, a Q × f value of 48,000 (at 8 GHz) and a temperature coefficient of resonant frequency (τf) of −1 ppm/°C sintering at 1475 °C. As the content of La(Mg1/2Ti1/2)O3 increases, the highest Q × f value of 62,900 (GHz) for x = 0.8 is achieved at the sintering temperature 1475 °C. A parallel-coupled line band-pass filter is designed and simulated using the proposed dielectric to study its performance.  相似文献   

6.
New pyrophosphate Sn0.9Sc0.1(P2O7)1−δ was prepared by an aqueous solution method. The structure and conductivity of Sn0.9Sc0.1(P2O7)1−δ have been investigated. XRD analysis indicates that Sn0.9Sc0.1(P2O7)1−δ exhibits a 3 × 3 × 3 super structure. It was found that Sn0.9Sc0.1(P2O7)1−δ prepared by an aqueous method is not conductive. The total conductivity of Sn0.9Sc0.1(P2O7)1−δ in open air is 2.35 × 10−6 and 2.82 × 10−9 S/cm at 900 and 400 °C respectively. In wet air, the total conductivity is about two orders of magnitude higher (8.1 × 10−7 S/cm at 400 °C) than in open air indicating some proton conduction. SnP2O7 and Sn0.92In0.08(P2O7)1−δ prepared by an acidic method were reported fairly conductive but prepared by similar solution methods are not conductive. Therefore, the conductivity of SnP2O7-based materials might be related to the synthetic history. The possible conduction mechanism of SnP2O7-based materials has been discussed in detail.  相似文献   

7.
采用激光熔覆技术,利用CaHPO_4·2H_2O,CaCO_3,La_2O_3,SiO_2粉末和Ti粉在医用钛合金Ti-6Al-4V表面制备掺杂的质量分数分别为0%,5%,10%,15%SiO2的含La2O3梯度生物陶瓷涂层,并研究了SiO_2含量对涂层性能的影响。利用金相显微镜、扫描电镜、能谱仪、X射线分析仪分别对涂层进行显微结构、表面元素、物相组成分析,利用MTT细胞活性检测法对涂层上种植的小鼠破骨前体细胞(RAW264.7)进行细胞活性分析。结果显示:掺杂10%~15%的SiO_2后,涂层的裂纹明显减少,且厚度变均匀。涂层在模拟体液(SBF)中浸泡2周后,羟基磷灰石(HA)在掺杂10%SiO_2涂层表面的沉积量最多,涂层表面的金属元素含量稀少,这表明含10%SiO_2涂层在SBF中具备更加优良的沉积HA的能力,同时有效的阻碍了基体中重金属离子的析出。MTT结果表明,掺杂SiO_2的涂层对破骨前体细胞的活性有更加明显的抑制作用。  相似文献   

8.
Mechanism of charge compensation on lanthanum, (La3+) substitution on Ca site in calcium copper titanate (CaCu3Ti4O12), and its effect on resulting electrical and dielectric properties has been studied in the present investigation. For this purpose samples were prepared according to two stoichiometries viz. LaxCa(1−3x/2)Cu3Ti4O12 (x ≤ 0.09) and LaxCa(1−x)Cu3Ti4O12 (x = 0.03) by solid state ceramic route. The former represents ionic compensation while the later is in accordance with electronic compensation. Nature of charge carriers is identified by measuring Seebeck coefficient which is found to be negative in the entire range of measurement. In order to understand the mechanism of conduction, ac conductivity is measured as a function of temperature and frequency. Space charge polarization is the dominant polarization mechanism phenomenon at low frequency and high temperature while orientation polarization dominates at low temperature and high frequency. Impedance analysis confirms the formation of internal barrier layers which is responsible for high dielectric constant in these samples.  相似文献   

9.
In this paper, the dielectric properties of Ca1−xMgxLa4Ti5O17 ceramics at microwave frequency have been studied. The diffraction peaks of Ca(1−x)MgxLa4Ti5O17 ceramics nearly unchanged with x increasing from 0 to 0.03. Similar X-ray diffraction peaks of Ca0.99Mg0.01La4Ti5O17 ceramic were observed at different sintering temperatures. A maximum density of 5.3 g/cm3 can be obtained for Ca0.99Mg0.01La4Ti5O17 ceramic sintered at 1500 °C for 4 h. A maximum dielectric constant (r) and quality factor (Q × f) of Ca0.99Mg0.01La4Ti5O17 ceramic sintered at 1500 °C for 4 h are 56.3 and 12,300 GHz (at 6.4 GHz), respectively. A near-zero temperature coefficient of resonant frequency (τf) of −9.6 ppm/°C can be obtained for Ca0.99Mg0.01La4Ti5O17 ceramic sintered at 1500 °C for 4 h. The measurement results for the aperture-coupled coplanar patch antenna at 2.5 GHz are presented. With this technique, a 3.33% bandwidth (return loss <−10 dB) with a center frequency at approximately 2.5 GHz has been successfully achieved.  相似文献   

10.
Novel thermal barrier coatings based on La2Ce2O7/8YSZ double-ceramic-layer (DCL) systems, which were deposited by electron beam physical vapor deposition (EB-PVD), were found to have a longer lifetime compared to the single layer La2Ce2O7 (LC) system, and even much longer than that of the single layer 8YSZ system under burner rig test. The DCL coating structure design can effectively alleviate the thermal expansion mismatch between LC coating and bond coat, as well as avoid the chemical reaction between LC and Al2O3 in thermally grown oxide (TGO), which occurs above 1000 °C as determined by differential scanning calorimetry (DSC) analysis. The failure mechanism of LC/8YSZ DCL coating is mainly due to the sintering of LC coating surface after long-term thermal cycling.  相似文献   

11.
The as-sintered sinter skin of WC–11 wt% Co–0.71 wt% Cr3C2–0.06 wt% La2O3 cemented carbide was observed and analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. It was unexpectedly discovered that lanthanum which was added in the form of oxide could migrate directionally from the alloy to the sinter skin during the sintering process. As a result, La2O2S and LaCoO3 phases were formed in situ on the sinter skin. It is significant that both phases are characterized with layered-structure related self-lubricating function and high melting point. Noteworthily, La2O2S grains preferentially grew up along a group of parallel faces with orientation index [0 0 1] in the WC + β matrix. It was revealed that the alloy had a diffusion-resulted dual structure (i.e., core and skin structure), i.e., WC + β + η three-phase structure in the inner part and WC + β + La2O2S + LaCoO3 four-phase structure on the sinter skin. Cr3C2 with carbon-donation ability and the impurity elements from the sintering atmosphere with much bigger electronegative parameters than lanthanum are thought to be the driving force behind the directional migration.  相似文献   

12.
The P2O5 + ZnO, ZrO2 + TiO2, B2O3 and a low-melting-point CaO–B2O3–SiO2 glass (LG) are selected as the sintering additives, and the effect of their additions on the microwave dielectric properties, mechanical properties and microstructures of CaO–B2O3–SiO2 system glass ceramics is investigated. It is found that the sintering temperature of pure CBS glass is higher than 950 °C and the sintering range is about 10 °C. With the above additions, the glass ceramics can be sintered between 820 °C and 900 °C. The dielectric properties of the samples are dependent on the additions, densification and microstructures of sintered bodies. The major phases of this material are CaSiO3, CaB2O4 and SiO2. With 10 wt% B2O3 and LG glass additions, the CBS glass ceramics have better mechanical properties, but worse dielectric properties. The r values of 6.51 and 7.07, the tan δ values of 0.0029 and 0.0019 at 10 GHz, are obtained for the CBS glass ceramics sintered at 860 °C with 2 wt% P2O5 + 2 wt% ZnO and 2 wt% ZrO2 + 2 wt% TiO2 additions, respectively. This material is suitable to be used as the LTCC material for the application in wireless communications.  相似文献   

13.
A literature survey and recent results on phase relationships in the quasi-ternary systems RE2O3-Al2O3-SiO2 are given. The investigated systems exhibit extended ternary solid solutions, RE9.33+2x(Si1_xAlxO4)6O2 (withx up to ~0.33) and/or RE4Al2(1_X)Si2xO9+x (withx up to ~0.3), which are based on the quasi-binary phases RE9.33(SiO4)6O2 and RE4A12O9, respectively. The former is encountered only in systems with laige RE3+ ions (e.g., La3+), whereas the latter is found in systems with small RE3+ ions (e.g., Yb3+); in systems with medium-sized KE3+ ions (e.g., Gd3+) both types exist Quasi-ternary compounds are known only in the La, Ce, and Sc systems. Severe discrepancies in reported ternary eutectic temperatures led to a need for their accurate redeteimination.  相似文献   

14.
Dense aluminum nitride ceramics were prepared by Spark Plasma Sintering at a lower sintering temperature of 1700 °C with Sm2O3 as sintering additives. The effect of Sm2O3 content on the density, phase composition, microstructure and thermal conductivity of AlN ceramics was investigated. The results showed that Spark Plasma Sintering could fabricate dense AlN ceramics with superior thermal properties in a very short time. Sm2O3 not only facilitated the densification via the liquid-phase sintering mechanism but also improved thermal conductivity by decreasing oxygen impurity. Thermal conductivity decreased with increasing amount of Sm2O3 and the highest thermal conductivity was obtained for the AlN ceramics with 2 wt.% Sm2O3 content. During Spark Plasma Sintering process, only 2–3 wt.% sintering additives was enough to fabricate dense AlN ceramics, and the microstructures played a key role in controlling the thermal conductivity of AlN ceramics.  相似文献   

15.
Increased turbine inlet temperature in advanced turbines has promoted the development of thermal barrier coating (TBC) materials with high-temperature capability. In this paper, BaLa2Ti3O10 (BLT) was produced by solid-state reaction of BaCO3, TiO2 and La2O3 at 1500 °C for 48 h. BLT showed phase stability between room temperature and 1400 °C. BLT revealed a linearly increasing thermal expansion coefficient with increasing temperature up to 1200 °C and the coefficients of thermal expansion (CTEs) are in the range of 1 × 10− 5–12.5 × 10− 6 K− 1, which are comparable to those of 7YSZ. BLT coatings with stoichiometric composition were produced by atmospheric plasma spraying. The coating contained segmentation cracks and had a porosity of around 13%. The microhardness for the BLT coating is 3.9–4.5 GPa. The thermo-physical properties of the sprayed coating were investigated. The thermal conductivity at 1200 °C is about 0.7 W/mK, exhibiting a very promising potential in improving the thermal insulation property of TBC. Thermal cycling result showed that the BLT TBC had a lifetime of more than 1100 cycles of about 200 h at 1100 °C. The failure of the coating occurred by cracking at the thermally grown oxide (TGO) layer due to severe oxidation of bond coat. Based on the above merits, BLT could be considered as a promising material for TBC applications.  相似文献   

16.
The oxide-ion conductors (La1−xSrx)2Mo2O9−δ (x = 0.01–0.08) were prepared by means of a conventional solid-state reaction. The effects of Sr doping for La site on the structures, electrical and thermal expansion properties of the oxide-ion conductor La2Mo2O9 were investigated using X-ray diffraction, direct current four-probe method, thermal dilatometer and scanning electron microscopy, respectively. The results show that the lattice constants were first decreased, then increased, and decreased again with the increase of Sr doping content. The solid solubility of Sr in (La1−xSrx)2Mo2O9−δ is x = 0.07. The sinterability of samples is markedly improved with the increase of Sr doping content. The sintered density of sample x > 0.07 is higher than 96% of its theoretical density. When x > 0.02, doping Sr in La2Mo2O9 can inhibit the excessive growth of grains, thus increases the sintered density of samples. The structural transition temperature shifts to the low side with the increase of Sr doping content, and the phase transition is completely suppressed when the doping content reaches 0.07. The conductivity of sample increases with the increase of Sr doping content. The conductivity of sample x = 0.07 reaches a maximum of 0.078 S/cm and 0.101 S/cm at 800 °C and 850 °C, respectively. In this study, it was demonstrated that doping 7 mol% Sr for La site not only can completely suppress the structural phase transition in La2Mo2O9, but also can effectively enhance electrical conductivity of samples at higher temperature.  相似文献   

17.
Recently, doped hexagonal BaTiO3 (6h-BaTiO3) ceramics have been reported as potential candidates used in microwave dielectric resonators. However, similar to other common microwave ceramics, doped 6h-BaTiO3 ceramics require a high sintering temperature, greater than 1300 °C. In this study, the effect of sintering aids, including Bi2O3, B2O3, BaSiO3, Li2CO3, CuO, V2O5, 5ZnO·2B2O3, and 5ZnO·2SiO2, on the densification, microstructural evolution, and microwave properties of the 6h-Ba(Ti0.85Mn0.15)O3 ceramics was examined. Results indicate that among the fluxes studied, Bi2O3, B2O3, and Li2CO3 could effectively reduce the sintering temperature of 6h-Ba(Ti0.85Mn0.15)O3 ceramics through liquid phase sintering, while retaining the hexagonal structure and the microwave dielectric properties. The best results were obtained for the 6h-Ba(Ti0.85Mn0.15)O3 with the additions of 5 wt% Bi2O3 sintered at 900 °C (r: 54.7, Qfr: 1323, and τf:183.3 ppm/°C), 10 wt% B2O3 sintered at 1100 °C (r: 54.4, Qfr: 3448, and τf: 254.5 ppm/°C), and 5 wt% Li2CO3 sintered at 950 °C (r: 43.7, Qfr: 2501, and τf: −29.8 ppm/°C).  相似文献   

18.
Single-phase Bi0.85La0.1Ho0.05FeO3 multiferroic ceramics were prepared by a rapid liquid sintering method. The ceramics exhibited an obvious ferroelectric loop with a remnant polarization of 11.2 μC/cm2 and also showed weak ferromagnetism with the remnant magnetization of 0.179 emu/g at room temperature. A considerable enhancement of the polarization on magnetic poling and a dielectric anomaly in the vicinity of the antiferromagnetic transition temperature due to the intrinsic magnetoelectric coupling effect were observed in Bi0.85La0.1Ho0.05FeO3 ceramics. The dielectric constant for the Bi0.8La0.1Ho0.05FeO3 samples at room temperature decreases with increasing applied magnetic fields, and the coupling coefficient (?′(H) − ?′(0))/?′(0) reaches −1.04% at H = 10 kOe.  相似文献   

19.
Mg0.4Al2.4O4 single crystals with good optical quality were successfully grown by the Czochralski method. The transmission spectrum indicated that the absorption edge of the crystal was at 220 nm, while no apparent absorption peaks were found. The X-ray diffraction and DSC curve analysis showed that Mg0.4Al2.4O4 crystal was stable at room temperature. While after annealing in the air and hydrogen atmosphere at about 1200 °C, Mg0.4Al2.4O4 decomposed into Al2O3 and (MgO)0.4(Al2O3)x (0.4 < x < 1.2). The reaction mainly occurred on the crystal surface, barely inside.  相似文献   

20.
The corrosion-resistant ceramic coatings up to 80 μm thick were fabricated on SiCP/AZ31 magnesium matrix composite by microarc oxidation (MAO) technique in Na3PO4 + KOH + NaF solution. The microstructure, composition and phase constituent of ceramic coatings were analyzed by SEM and XRD, and the electrochemical corrosion behaviour of coatings was evaluated by the electrochemical polarization method. The thicker coating is compact and displays a good adhesion to the composite substrate. The ceramic coatings consist of MgO, Mg2SiO4, MgF2, Mg3(PO4)2, furthermore, a few residual SiC phases were also found in the coatings by means of SEM observation and EDX analysis. Most of SiC reinforced particles in the oxidized composite substrate have transformed into the oxides under microarc discharge sintering, but a few residual SiC reinforcements in the MAO coatings have not disrupted the continuity of coatings. So the corrosion resistance of the SiCP/AZ31 composite is greatly improved by MAO surface treatment, however, the corrosion resistance of coated composite also depends on the coating thickness.  相似文献   

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