共查询到20条相似文献,搜索用时 15 毫秒
1.
Gamil A. El-Shobaky Awad I. AhmedHassan M.A. Hassan Shaymaa E. El-Shafey 《Journal of Alloys and Compounds》2011,509(4):1314-1321
The effects of K2O and Li2O-doping (0.5, 0.75 and 1.5 mol%) of Fe2O3/Cr2O3 system on its surface and the catalytic properties were investigated. Pure and differently doped solids were calcined in air at 400-600 °C. The formula of the un-doped calcined solid was 0.85Fe2O3:0.15Cr2O3. The techniques employed were TGA, DTA, XRD, N2 adsorption at −196 °C and catalytic oxidation of CO oxidation by O2 at 200-300 °C. The results revealed that DTA curves of pure mixed solids consisted of one endothermic peak and two exothermic peaks. Pure and doped mixed solids calcined at 400 °C are amorphous in nature and turned to α-Fe2O3 upon heating at 500 and 600 °C. K2O and Li2O doping conducted at 500 or 600 °C modified the degree of crystallinity and crystallite size of all phases present which consisted of a mixture of nanocrystalline α- and γ-Fe2O3 together with K2FeO4 and LiFe5O8 phases. However, the heavily Li2O-doped sample consisted only of LiFe5O8 phase. The specific surface area of the system investigated decreased to an extent proportional to the amount of K2O and Li2O added. On the other hand, the catalytic activity was found to increase by increasing the amount of K2O and Li2O added. The maximum increase in the catalytic activity, expressed as the reaction rate constant (k) measured at 200 °C, attained 30.8% and 26.5% for K2O and Li2O doping, respectively. The doping process did not modify the activation energy of the catalyzed reaction but rather increased the concentration of the active sites without changing their energetic nature. 相似文献
2.
Fuhe Le Luxiang Wang Wei Jia Dianzeng Jia Shujuan Bao 《Journal of Alloys and Compounds》2012,512(1):323-327
A novel phosphor Sr2P2O7 co-doped with europium ion and chlorine ion was firstly synthesized by solid state reaction under air atmosphere. Its properties were systematically analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fluorescence spectra. The introduction of chlorine into the system was helpful and necessary to Eu3+ substitute Sr2+ site and subsequently to reduce Eu3+ to Eu2+, XPS results confirmed that some amount of Eu3+ ions could be reduced to Eu2+ ions under air atmosphere at high temperature. The reduction tendency of Eu3+ depends not only on the doping Cl− content, but also on the sintering temperature and time. Photoluminescence spectra also revealed that europium ions were present in divalent as well as trivalent oxidation states, the emission peak at 415 nm is ascribed to the typical 5d-4f transition of Eu2+, 592 nm and 613 nm assigned to the characteristic transitions of 5D0-7F1,2 of Eu3+. Such abnormal reduction was attributed to the electronegative defects formed by nonequivalent substitution of Eu3+ on the Sr2+ sites in the investigated phosphors. 相似文献
3.
Mn4+, La3+ and Ho3+ doped MgAl2Si2O8-based phosphors were first synthesized by solid state reaction. They were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray powder diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). The phosphors were obtained at about 1300 °C. They showed broad red and fuchsia-pink emission bands in the range of 610-715 nm and had a different maximum intensity when activated by UV illumination. Such a fuchsia-pink emission can be attributed to the intrinsic d-d transitions of Mn4+. 相似文献
4.
Prasit Thongbai Bundit PutasaengTeerapon Yamwong Santi Maensiri 《Journal of Alloys and Compounds》2011,509(27):7416-7420
Non-ohmic and dielectric properties of Ca2Cu2Ti4O12 (CaCu3Ti4O12/CaTiO3 composite) ceramics prepared by a polymer pyrolysis method (PP-ceramic samples) are investigated. The PP-ceramics show a highly dense structure and improved non-ohmic and dielectric properties compared to the ceramics obtained by a solid state reaction method (SSR-ceramic samples). ?′ (tan δ) of the PP-ceramic samples is found to be higher (lower) than that of the SSR-ceramic samples. Interestingly, the PP-ceramic sintered at 1050 °C for 10 h exhibits the high ?′ of 2530 with weak frequency dependence below 1 MHz, the low tan δ less than 0.05 in the frequency range of 160 Hz-177 kHz, and the little temperature coefficient, i.e., |Δ?′| ≤ 15 % in the temperature range from −55 to 85 °C. These results indicate that the CaCu3Ti4O12/CaTiO3 composite system prepared by PP method is a promising high-?′ material for practical capacitor application. 相似文献
5.
氧化铝/氧化铝复合材料(Al2O3/Al2O3)是20世纪90年代兴起的一类连续陶瓷纤维增强陶瓷基复合材料,已经发展为与SiC/SiC、C/SiC等非氧化物陶瓷基复合材料并列的一类陶瓷基复合材料。与非氧化物陶瓷基复合材料相比,Al2O3/Al2O3具有长时抗氧化、高温耐腐蚀、低成本等独特优势,已经在航空发动机、地面燃气轮机等军民两用热结构材料领域展现出广阔的应用前景。本文从材料应用的角度出发,系统分析阐述了目前在Al2O3/Al2O3占主导地位的多孔基体Al2O3/Al2O3(P-Al2O3/Al2O3)的增韧机制、成型工艺和性能特点,重点归纳了国外近年来P-Al2O3/Al2O3的工程化应用进展及前景,最后指出了P-Al2O3/Al2O3存在的局限性并展望了未来发展方向,旨在为国内Al2O3/Al2O3体系发展提供借鉴和参考。 相似文献
6.
Glasses with different Bi2O3 contents (37-42 mol%) have been prepared by conventional melt quench technique. The IR and Raman studies indicate that these glasses are made up of [BiO6], [BiO3], [BO3] and [BO4] basic structural units. The vibrations of [BiO3] and [BO3] become stronger as the content of Bi2O3 increases, which makes glass structure loosened. Viscosity of the glasses was measured by using a Rheotronic III paralleled plate rheometry, which shows that the viscosity of glass samples decreased when the content of Bi2O3 increased at the same temperature (400-460 °C). The temperature range which suits for glasses sealing was calculated by using the approximation of Arrhenian behaviour. The wetting performance of Bi2O3-ZnO-B2O3 glasses was described by using high-temperature microscope, which also proves that the structure of investigated Bi2O3-ZnO-B2O3 glasses become loosened due to the increasing of the content of Bi2O3. 相似文献
7.
Jiaxiu Guo Dongdong Wu Lei Zhang Maochu Gong Ming Zhao Yaoqiang Chen 《Journal of Alloys and Compounds》2008,460(1-2):485-490
A kind of nanometric CeO2–ZrO2–Nd2O3 (CZN) solid solution for a carrier in the automotive three-way catalysts was synthesized by a coprecipitation method and characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption–desorption (BET), scanning electron microscopy (SEM) and oxygen storage capacity (OSC). For the purpose of comparison, an unincorporated CeO2–ZrO2 (CZ) was also synthesized. The XRD measurements disclose the prepared CeO2–ZrO2–Nd2O3 have a face-centered cubic fluorite structure and nanoparticle sizes. According to the results of XPS, Nd3+ ions can enter the CZ lattice and form a homogenous solid solution. Oxygen storage capacity measurements reveal that CeO2–ZrO2–Nd2O3 display high oxygen mobility at a low temperature. The results of the activity tests show that the catalyst exhibits good three-way catalytic activity and fairly wide range of air-to-fuel ratios. 相似文献
8.
航空发动机的效率与转动叶片和机匣之间的间隙密切相关。为了控制转子和静子之间的间隙,需要在机匣表面制备可磨耗的封严涂层。在发动机的高温端,ZrO2-8wt% Y2O3涂层是经常采用的封严涂层基体。涂层中的孔隙可以增加涂层的可磨耗性。本文利用聚苯酯(PHB)增加等离子喷涂的ZrO2-8 wt% Y2O3涂层的孔隙率。为了避免聚苯酯在等离子喷涂过程中的烧损,利用溶胶-凝胶法在聚苯酯颗粒表面沉积一层TiO2层。文中将讨论采用此方法制成的涂层的形态、孔隙率、硬度和可磨耗性。结果表明,在喷涂粉末中混合包覆型的聚苯酯后,涂层的孔隙率将会得到提升,涂层硬度将会下降。磨耗试验的结果表明涂层的磨耗深度随着涂层孔隙率的增加而增加。 相似文献
9.
以La2O3粉、Al粉、CuO粉为反应物原料、纯铜为基体,采用原位合成技术和近熔点铸造法制备颗粒增强Cu基复合材料,研究La2O3对Al-CuO体系制备的Cu基复合材料组织及性能的影响。结果表明:添加La2O3可获得纳米Al2O3颗粒,且弥散分布于Cu基体中,制备的材料组织更加细小、均匀,其材料的电导率及摩擦磨损性能明显提高。当添加0.6%wtLa2O3,复合材料的电导率达到90.2%IACS,磨损量达到最小,相比未添加La2O3,其导电率提高10.1%,磨损量减小36.6%。 相似文献
10.
使用粉末冶金法将纳米级(70–80 nm)和微米级(500–600 nm)稀土氧化物(La2O3,Y2O3)与钨粉混合,随后通过冷等静压、中频感应烧结、旋锻、拉拔等一系列工艺制备了W-1.5La2O3-0.1Y2O3-0.1ZrO2(质量分数,%)材料。对含有纳米和微米尺寸稀土氧化物的阴极样品使用相同的焊接电流,分别进行了0.5、1、2 h的氩弧焊。结果表明,具有纳米级稀土氧化物的样品在焊接过程中表现出更高的工作稳定性,烧损同比降低了近85.4%。此外,随着工作时间的延长,阴极尖端不同区域的稀土氧化物聚集度显著增加。结合COMSOL Multiphysics温度模拟发现,第二相的扩散活化能降低了近34%。这是因为更为细小的第二相有效地控制了钨基体组织的演变,保留了大量晶界作为通道,促进了活性物质在电子发射过程中的扩散。 相似文献
11.
M.A. Khaghani-DehaghaniR. Ebrahimi-Kahrizsangi N. SetoudehB. Nasiri-Tabrizi 《International Journal of Refractory Metals and Hard Materials》2011,29(2):244-249
Alumina-titanium diboride nanocomposite (Al2O3-TiB2) was produced using mixtures of titanium dioxide, acid boric and pure aluminum as raw materials via mechanochemical process. The phase transformation and structural characterization during mechanochemical process were utilized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analyses (TG-DTA) techniques. A thermodynamic appraisal showed that the reaction between TiO2, B2O3 and Al is highly exothermic and should be self-sustaining. XRD analyses exhibited that the Al2O3-TiB2 nanocomposite was formed after 1.5 h milling time. The results indicate that increasing milling time up to 40 h had no significant effect other than refining the crystallite size. 相似文献
12.
Cagri Tekmen Yoshiki Tsunekawa Masahiro Okumiya 《Surface & coatings technology》2008,202(17):4170-4175
In-situ plasma spraying (IPS) is a promising process to fabricate composite coatings with in-situ formed thermodynamically stable phases. In the present study, mechanically alloyed Al-12Si, B2O3 and TiO2 powder was deposited onto an aluminum substrate using atmospheric plasma spraying (APS). It has been observed that, during the coating process, TiB2 and Al2O3 are in-situ formed through the reaction between starting powders and finely dispersed in hypereutectic Al-Si matrix alloy. Also, obtained results demonstrate that in-situ reaction intensity strongly depends on spray conditions. 相似文献
13.
Pure and Pr6O11-doped CaCu3Ti4O12 (CCTO) ceramics were prepared by conventional solid-state reaction method. The compositions and structures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of Pr-ion concentration on dielectric properties of CCTO were measured in the ranges of 60 Hz-3 MHz and 290-490 K. The third phase of Ca2CuO3 was observed from the XRD of CCTO ceramics. From SEM, the grain size was decreased obviously with high valence Pr-ion (mixing valence of Pr3+ and Pr4+) substituting Ca2+. The room temperature dielectric constant of Pr-doped CCTO ceramics, sintered at 1323 K, was an order of magnitude lower than the pure CCTO ceramics due to the grain size decreasing and Schottky potential increasing. The dielectric spectra of Pr-doped CCTO were flatter than that of pure CCTO. The loss tangent of Pr-doped CCTO ceramics was less than 0.20 in 2 × 102-105 Hz region below 440 K. The complex impedance spectra of pure and Pr-doped CCTOs were fitted by ZView. From low to high frequency, three semicircles were observed corresponding to three different conducting regions: electrode interface, grain boundary and grain. By fitting the resistors R and capacitors C, the activation energies of grain boundary and electrode contact were calculated. All doped CCTOs showed higher activation energies of grain boundary and electrode than those of pure CCTO ceramics, which were concordant with the decreasing of dielectric constant after Pr6O11 doping. 相似文献
14.
以Al(NO3)3?9H2O为包覆原料,通过燃烧法制备得到LiNi0.03Co0.05Mn1.92O4@Al2O3正极材料。通过X射线衍射(XRD),场发射扫描电子显微镜(FESEM)和透射电镜(TEM)等表征手段对材料的结构和形貌进行分析,并通过恒电流充放电、循环伏安(CV)、交流阻抗(EIS)等测试分析材料的电化学性能。结果表明,Al2O3包覆没有改变LiNi0.03Co0.05Mn1.92O4的尖晶石型结构,包覆层厚度约10.6nm。LiNi0.03Co0.05Mn1.92O4@Al2O3正极材料电化学性能得到了明显改善,1 C和10 C倍率下初始放电比容量分别为119.9 mAh?g-1和106.3 mAh?g-1,充放电循环500次后容量保持率分别为88.4%和78.2%,而未包覆的LiNi0.03Co0.05Mn1.92O4在1 C和10 C倍率下初始放电比容量分别为121.2 mAh?g-1和104.0 mAh?g-1,500次循环后容量保持率分别为84.1%和67.6%。LiNi0.03Co0.05Mn1.92O4@Al2O3活化能为32.92 kJ?mol-1,而未包覆材料的活化能为36.24 kJ?mol-1,包覆有效降低了材料Li+扩散所需克服的能垒,提高了材料的电化学性能。 相似文献
15.
C. Bjormander 《Surface & coatings technology》2006,201(7):4032-4036
Coloured Al2O3/ZrO2 multilayers have been deposited onto WC-Co based inserts by a CVD process. Through physical as well as optical analysis of such multilayers, colour is believed to originate from interference. The coatings are obtained with good process reproducibility. It was found that the ZrO2 process used in the multilayer, with ZrCl4 as the only metal chloride precursor, results in a mixture of tetragonal and monoclinic ZrO2 phases. However by adding a relatively small amount of AlCl3 during such a process results in ZrO2 layers being composed of predominantly tetragonal ZrO2 phase. Corresponding multilayers seem to have a more fine grained and smoother morphology whereas multilayers containing monoclinic ZrO2 phase seem to be less perfect with existence of larger grains of ZrO2 which are believed to scatter light and alter the reflectance of such a multilayer. In addition to this, such multilayers were found to be free of or with greatly reduced amount of thermal cracks, normally present in pure CVD grown Al2O3 layers.It is believed that, in the studied Al2O3/ZrO2 multilayers, the observed tetragonal ZrO2 phase is the result of a size effect, where small enough ZrO2 crystallites energetically favor the tetragonal phase. However as the ZrO2 crystallite size distribution is shifted to larger sizes it is believed that a mixture of crystallites with both stable and metastable tetragonal phases as well as a stable monoclinic phase is obtained. The proposed metastable tetragonal ZrO2 phase may in fact explain the absence of thermal cracks in such multilayers through a transformation toughening mechanism, well known in ZrO2 based ceramics. 相似文献
16.
本文采用甘氨酸-硝酸盐法(GNP)和溶胶凝胶法分别合成了Sm0.1Nd0.1Ce0.8O1.9(SNDC) 和La2Mo2O9(LAMOX)粉末,并用常压烧结的方法制备了不同比例的SNDC和LAMOX的复合材料,通过XRD和SEM等手段表征了不同复合比例样品的物相和表面形貌并测试了烧结样品的电导率。结果表明,复合样品的电导率在相变点前后随着复合量增加变化趋势相反,其中LAMOX含量为20mol%的样品在550℃时的电导率能达到0.01S/cm,高于同温度下SNDC电导率。 相似文献
17.
Chia-Che Chuang Hsing-I Hsiang Jenn Shyong Hwang Tai Shen Wang 《Journal of Alloys and Compounds》2009,470(1-2):387-392
Al2O3-Ce0.5Zr0.5O2 catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spectroscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al3+ ions affected the phase development, texture and oxygen storage capacity (OSC) of the Ce0.5Zr0.5O2 powder. Single phase of ACZ-C could be maintained without phase separation and inhibit α-Al2O3 formation up to 1200 °C. The specific surface area value of ACZ-C (81.5 m2/g) was larger than that of ACZ-M (62.1 m2/g) and Ce0.5Zr0.5O2 (17.1 m2/g) powders, which were calcined at 1000 °C. In comparison with ACZ-C and Al2O3, which were calcined at high temperature (900–1200 °C), it was found that the degradation rate of specific surface area of ACZ-C was lower than that of Al2O3. ACZ-C sample showed a higher thermal stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity property for Ce0.5Zr0.5O2 powders. 相似文献
18.
Bing Xu Dezhi WangZhuangzhi Wu Aokui SunQijun Cheng Xiuqi Zan 《International Journal of Refractory Metals and Hard Materials》2010
Sintered Mo with the addition of La2O3/MoSi2 was prepared via the process of solid–solid doping + powder metallurgy. X-ray diffraction experiment, hardness test, three-point bending test and high-temperature tensile test were carried out to characterize the samples. The XRD pattern of a typical sample shows that the sintered Mo was mainly composed of Mo, La2O3 and Mo5Si3. Mo5Si3 was probably formed through the reaction between MoSi2 and the Mo matrix. Densities and fracture toughnesses of both doped Mo and pure Mo were measured and contrasted. Sintered Mo with the addition of 0.2 wt% La2O3/MoSi2 has the highest toughness, while more addition of La2O3/MoSi2 has smaller effect on improving toughness or even embrittles Mo. The results of three-point bending test and high-temperature tensile test show that the bending strength and high-temperature tensile strength of doped Mo are both higher than those of pure Mo. The formation of Mo5Si3 improves the high-temperature strength. The La2O3/Mo5Si3 dispersed in the Mo matrix refined the grains, and thus strengthened the Mo matrix by dispersion strengthening and grain refinement. 相似文献
19.
Y3Al5O12 and ZrO2-Y2O3 (8 mol% YSZ) coatings for potential application as thermal barrier coatings were prepared by combustion spray pyrolysis. Thermal cycling of as deposited coatings on stainless steel and FeCrAlY bond coat substrates was carried out at 1000 °C and 1200 °C to determine the thermal fatigue response. Structural and morphological studies on Y3Al5O12 and 8 mol% YSZ coatings before and after thermal cycling have been carried out. It has been noted that the coatings on FeCrAlY substrates remain intact after 50 cycles between room temperature and 1200 °C, whereas the coatings on stainless steel show some minor damage such as peeling off near the periphery after 50 cycles at 1000 °C. Thermal diffusivity values of Y3Al5O12 and 8 mol% YSZ films were measured by using photo thermal deflection spectroscopy and the values are lower than those of coatings produced by conventional techniques such as EBPVD and APS. 相似文献
20.
程功金 周新磊 高明磊 常富增 滕艾均 邢振兴 宋翰林 高子先 汤卫东 赵备备 王金龙 赵丹 刘超 李兰杰 杨合 陈东辉 薛向欣 白瑞国 张卫军 《稀有金属材料与工程》2021,50(6):1990-1998
为了确定高钛型钒钛磁铁矿烧结过程中铁酸钙的生成是受TiO2还是TiO2和CaO形成的CaTiO3影响,首先利用Fe2O3和CaO的纯试剂合成了铁酸钙,并研究了TiO2和CaTiO3对钛铁酸钙 (FCT) 形成的影响。在Factsage 7.0软件进行热力学计算的基础上,通过在空气气氛下进行烧结,获得了在1023~1423 K温度范围内、不同烧结时间的不同样品。通过X射线衍射和扫描电镜-能谱分析等表征手段,对烧结样品的物相转变和微观结构变化进行了表征。发现FCT的形成过程主要分为2个阶段:前一阶段为1023~1223 K温度范围内Fe2O3与CaO之间的反应,合成产物为Ca2Fe2O5,反应方程式为“Fe2O3(s)+ 2CaO(s)= Ca2Fe2O5(s)”;后一阶段为1223~1423 K温度范围内Ca2Fe2O5和Fe2O3的反应,主要产物为CaFe2O4,反应为“Ca2Fe2O5(s)+ Fe2O3(s)= 2CaFe2O4(s)”,该阶段尤其是温度为1423 K时,反应速率显著加快,随温度的升高CaTiO3显著增加。然而,Ti元素在铁酸钙中的固溶很难实现,TiO2与铁酸钙之间的反应不是形成FCT的有效途径。随着保温时间的延长,CaTiO3和FCT相界中Fe元素含量增加。FCT主要是通过Fe组分在CaTiO3中固溶形成的,主要反应是“Fe2O3+CaTiO3(s)=FCT(s)”。 相似文献