不同炭化温度制备的C/0.5Al2O3-0.5P2O5-100SiO2凝胶玻璃的光学性质

通过醇盐不完全水解制备了含有有机基团(O—C2H5)的C/0.5Al2O3-0.5P2O5-100SiO2凝胶，在氮气中加热到300,v700。C使其中的有机基团炭化，得到镶嵌在凝胶玻璃中不同尺寸的碳纳米颗粒。利用高分辨电镜、X射线衍射和喇曼光谱研究了碳纳米颗粒的结构，发现凝胶玻璃中的碳颗粒为非晶碳纳米颗粒。测试了它们的吸收光谱，发现了由于量子限域效应引起的吸收边的移动。在532nmNd：YAG激光的激发下镶嵌有碳纳米颗粒的凝胶玻璃有一强的室温发光，发光峰在586nm左右。发光峰几乎不随碳纳米颗粒尺寸的变化而变化，这种发光产生于碳纳米颗粒的表面或碳颗粒和凝胶网络的界面。     

Ni0.5Zn0.5Fe2O4粉末化学镀铜前后的电磁性能

本文用溶胶-凝胶自燃烧法制备了Ni0.5Zn0.5Fe2O4粉末颗粒,以甲醛为还原剂在Ni0.5Zn05Fe2O4颗粒表面进行了化学镀铜,制备了Cu/Ni0.5Zn0.5Fe2O4复合粉体.用扫描电镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)对镀铜前的Ni0.5Zn0.5Fe2O4颗粒以及镀铜后的复合纳米颗粒进行了表征.对镀铜前的Ni0.5Zn0.5Fe2O4粉体和不同镀铜量的Cu/Ni0.5Zn0.5Fe2O4复合粉体进行了电磁性能的研究,结果表明镀铜后镍锌铁氧体的吸波性能明显提高,增重量为65%的Cu/Ni0.5Zn0.5Fe2O4复合粉体在频率为11GHz处反射率可达-12dB左右.     

Co_(0.5)Zn_(0.5)Fe_2O_4/SiO_2磁性纳米复合粉体的制备

采用溶胶-凝胶法以正硅酸乙酯和金属硝酸盐分别作为SiO2和铁氧体的前驱体成功制得Co0.5Zn0.5-Fe2O4/SiO2磁性纳米复合粒子.利用XRD、DSC-TG、Raman和SEM研究了热处理温度和酸添加量对样品晶体结构和晶粒尺寸的影响,并用谢乐公式估算平均晶粒尺寸.最后用振动样品磁场计(VSM)对样品的磁性能进行检测.结果表明,随热处理温度的升高,样品由非晶态转变成SiO2基体中结晶较完整的尖晶石结构的单相铁氧体纳米晶,晶粒尺寸为12.65nm.晶粒尺寸随热处理温度的升高和酸添加量的增加不断变大.对材料的磁性能的研究结果表明,合成的纳米Co0.5Zn0.5Fe2O4/SiO2,其比饱和磁化强度为9.17emu/g,矫顽力为67Oe.     

含纳米颗粒V2O5溶胶凝胶的制备技术

以片状工业V2 O5晶体为原料 ,采用无机途径的溶胶 -凝胶法成功地制取了V2 O5溶胶和凝胶。测试了V2 O5溶胶中颗粒大小 ,并研究了其粘度和 pH值的变化。结果表明 :溶胶中V2 O5颗粒呈针状 ,其径向尺寸为 5 0～ 60nm ;当V2 O5溶胶浓度在 2 0 g/L以上时极易形成凝胶 ,其粘度随放置时间增大较快 ,约 10天以后即失去流动性 ,其 pH值也同时发生类似的变化     

溶胶凝胶法合成La0.5Sr0.5Co0.8Mn0.2O3-δ钙钛矿及其催化性质

采用溶胶凝胶煅烧法合成了La0.5 Sr0.5 Co0.8 Mn0.2 O3-δ纳米粉,通过X射线衍射、电子显微镜、X射线光电子能谱和碘定量滴定等测试方法对合成物进行了表征,并以四溴双酚A为模型污染物,考察其催化性能.结果表明,合成的纳米La0.5 Sr0.5 Co0.8 Mn0.2 O3-δ具有钙钛矿R-3c结构,平均晶粒尺寸为40～70 nm.与通氮气煅烧的样品相比,弱氧化煅烧样品的非化学计量氧浓度适中,钙钛矿结构中B位离子平均价态相对较稳定,其催化性能较强且相对较稳定,可再生循环使用四次.     

Sn0.5Ti0.5O2固溶体薄膜的制备及其气敏特性研究

采用溶胶凝胶法制备了Sn0.5Ti0.5O2固溶体.用X射线衍射(XRD)和红外(IR)技术对材料的结构和热稳定性进行了分析表征.固溶体的热稳定性与起始反应温度有关,40℃水浴制备的凝胶经过1000℃烧结就发生了相分解,出现了富Sn、富Ti相,而80℃水浴制备的凝胶经过1200℃烧结也不发生相分解,仍以Sn0.5Ti0.5O2相存在.将胶体制成了薄膜元件并测试了元件的气敏性能,发现此元件对H2S气体有一定的灵敏度.     

铜铁氧体纳米晶的溶胶-凝胶自蔓延燃烧法合成和表征

以硝酸铜、硝酸铁、硝酸钴和柠檬酸为原料,采用溶胶-凝胶自蔓延燃烧法一步直接合成了单相Co0.5Cu0.5Fe2O4纳米晶.借助TG/DTA、IR、XRD和SEM等手段分别对溶胶-凝胶自蔓延燃烧机理、粉体在不同退火温度下的结构演化过程以及燃烧粉体的表面形貌进行了研究.结果表明,自蔓延燃烧过程是在硝酸根离子和羧酸根离子之间进行的热诱导阴离子氧化还原反应,其中,硝酸根离子作氧化剂,羧酸根离子作还原剂.干凝胶燃烧后,产物已经初步晶化,晶粒尺寸约20nm.经600℃,2h退火即可得到晶化较好的Co0.5Cu0.5Fe2O4纳米粉体,燃烧粉末为多孔结构,密度为2.9g/cm3.     

溶胶-凝胶法引入ZnO-2B2O3-7SiO2玻璃对BaO-Sm2O3-4TiO2陶瓷性能的影响

采用固相反应法合成BaO-Sm2O3-4TiO2 (BST)陶瓷粉体.系统研究了溶胶-凝胶法引入ZnO-2B2O3-7SiO2 (ZBS)玻璃对BST陶瓷烧结特性、物相组成、微观形貌及介电性能的影响.结果表明,添加ZBS玻璃的陶瓷试样主晶相仍为类钙铁矿钨青铜结构的BaSm2Ti4O12,次晶相为Sm2Ti2O7.通过溶胶-凝胶法添加6％(质量分数)的ZBS玻璃,可使BST陶瓷的烧结温度从1350℃降低到1050℃,在1050℃烧结3h所得BST陶瓷介电性能优良:εr=60.17,tanδ=0.004,τf=-7.9×10 6/℃.     

两步法中煅烧温度对Ni0.5Zn0.5Fe2O4电磁性能的影响

采用两步法(共沉淀法联合溶胶-凝胶法)制备Ni_(0.5)Zn_(0.5)Fe_2O_4纳米吸波材料,探究了溶胶-凝胶法中前驱体的煅烧温度对样品微波吸收性能的影响。利用X射线衍射(XRD)、原子力显微镜(AFM)以及矢量网络分析(VNA)等方法对样品的微观结构和电磁性能进行表征。XRD分析结果表明:当煅烧温度大于650℃时,能够得到纯Ni_(0.5)Zn_(0.5)Fe_2O_4纳米粉体;AFM结果表明:随着煅烧温度的提高,样品颗粒粒径趋于细小化和均匀化;VNA结果表明:在2～12.4GHz范围内,煅烧温度为650℃时,制备的Ni_(0.5)Zn_(0.5)Fe_2O_4表现出最佳的电磁特性,具有优异的微波吸收性能。样品的有效吸波频宽为4.9GHz,最大吸波强度达到-24.94dB。     

LiCo0.5Ni0.5 O2的恒流充放电容量模型研究

为研究LiCo0.5Ni0.5O2的充放电容量和电流间模型,用高温固相反应合成了性能优良的LiCo0.5Ni0.5 O2,用一维扩散控制方程Q=Qm-(I2/3·D)·I描述了LiNi0.5Co0.5O2的充放电容量与电流的关系,并用该模型计算了最大可逆容量和扩散系数.恒电流充放电过程的扩散系数和最大可逆容量随循环次数的增加而降低,且与循环次数间存在对数线性关系.     

Crystallization mechanism in amorphous material of 0.5LiMnO2-0.5B2O3

0.5LiMnO₂-0.5B₂O₃ glass has been prepared by quenching a melt of LiNO₃, MnO₂ and B₂O₃ at 1100°C to room temperature in air. The crystallization mechanism of this kind of glass was investigated by differential thermal analysis (DTA) and powder X-ray diffraction (XRD). It is shown that the substances crystallized from powder and bulk samples are different because manganese with lower valence in powder sample can be further oxidized by the oxygen penetrated through the large surface of powder sample. For a powder sample the glass transition endothermic peak in the DTA curve is overlapped by an exothermic reaction attributed to the oxidization of Manganese. LiMn₂O₄ can not be crystallized directly from the glass matrix but can be formed on the surface of glass particles by effect of oxygen in air near the glass transition temperature.     

Magnetic and optical properties of MgAl2O4-(Ni0.5Zn0.5)Fe2O4 thin films prepared by pulsed laser deposition

Abstract

Thin films composed of MgAl₂O₄ and (Ni_0.5Zn_0.5)Fe₂O₄ ([MA(100-x)-NZFx] films) were grown on fused SiO₂ substrates by pulsed laser deposition. X-ray diffraction measurements revealed that the films were polycrystalline, and that their lattice constant varied linearly with composition, indicating the formation of a solid solution. The film with x=60 was paramagnetic and those with x ≥ 70 were ferromagnetic. The films had a transparency above 75% in the visible range, but the transparency decreased with the x value. The optical band gaps were 2.95, 2.55, 2.30 and 1.89 eV for x=20, 40, 60, 80 and 100, respectively. The Faraday rotation angle increased with x in the visible range, and the film with x=70 exhibited a value of 2000 degrees cm^-1 at 570 nm, which is comparable to the rotation angle of Y₃Fe₅O₁₂. Owing to their high transparency, which extends into the visible range, the [MA(100-x)-NZFx] films can be used in novel magneto-optical devices.     

Magnetic and optical properties of MgAl2O4-(Ni0.5Zn0.5)Fe2O4 thin films prepared by pulsed laser deposition

Thin films composed of MgAl₂O₄ and (Ni_0.5Zn_0.5)Fe₂O₄ ([MA(100-x)-NZFx] films) were grown on fused SiO₂ substrates by pulsed laser deposition. X-ray diffraction measurements revealed that the films were polycrystalline, and that their lattice constant varied linearly with composition, indicating the formation of a solid solution. The film with x=60 was paramagnetic and those with x ≥ 70 were ferromagnetic. The films had a transparency above 75% in the visible range, but the transparency decreased with the x value. The optical band gaps were 2.95, 2.55, 2.30 and 1.89 eV for x=20, 40, 60, 80 and 100, respectively. The Faraday rotation angle increased with x in the visible range, and the film with x=70 exhibited a value of 2000 degrees cm^-1 at 570 nm, which is comparable to the rotation angle of Y₃Fe₅O₁₂. Owing to their high transparency, which extends into the visible range, the [MA(100-x)-NZFx] films can be used in novel magneto-optical devices.     

Isochoric Heat Capacity Measurements for 0.5 H2O+0.5 D2O Mixture in the Critical Region

The isochoric heat capacity C _V of an equimolar H₂O+D₂O mixture was measured in the temperature range from 391 to 655 K, at near-critical liquid and vapor densities between 274.05 and 385.36 kgm^–3. A high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter was used. The measurements were performed in the one- and two-phase regions including the coexistence curve. The uncertainty of the heat-capacity measurement is estimated to be ±2%. The liquid and vapor one- and two-phase isochoric heat capacities, temperatures, and densities at saturation were extracted from the experimental data for each measured isochore. The critical temperature and the critical density for the equimolar H₂O+D₂O mixture were obtained from isochoric heat capacity measurements using the method of quasi-static thermograms. The measurements were compared with a crossover equation of state for H₂O+D₂O mixtures. The near-critical isochoric heat capacity behavior for the 0.5 H₂O+0.5 D₂O mixture was studied using the principle of isomorphism of critical phenomena. The experimental isochoric heat capacity data for the 0.5 H₂O+0.5 D₂O mixture exhibit a weak singularity, like that of both pure components. The reliability of the experimental method was confirmed with measurements on pure light water, for which the isochoric heat capacity was measured on the critical isochore (321.96 kgm^–3) in both the one- and two-phase regions. The result for the phase-transition temperature (the critical temperature, T _{C, this work}=647.104±0.003 K) agreed, within experimental uncertainty, with the critical temperature (T _{C, IAPWS}=647.096 K) adopted by IAPWS.     

Low Temperature X-ray Diffraction Study of ZnCr2O4 and Ni0.5Zn0.5Cr2O4

Results of x-ray diffraction measurements are presented for ZnCr₂O₄ and Ni_0.5Zn_0.5Cr₂O₄. Splits of the x-ray diffraction spectrum are observed in ZnCr₂O₄ at 12 K. In Ni_0.5Zn_0.5Cr₂O₄ no clear split is observed, but a full width at half maximum (FWHM) shows a steep increase below about 20 K. It is found that the integrated intensity of the diffraction spectra shows a softening behavior at low temperatures in ZnCr₂O₄.     

Mechanical and Electrical Properties of (Cu0.5Tl0.5)-1223 Phase Added with Nano-Fe2O3

Superconducting samples of type (Cu_0.5Tl_0.5)-1223 added with nano-Fe₂O₃ (x=0.0, 0.1, 0.2, 0.4, 0.6 and 1.0 wt.%) were prepared by solid-state reaction technique. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) for phase analysis and microstructure examination. The elemental content of the prepared samples was determined using particle induced X-ray emission (PIXE), whereas the Oxygen-content of these samples was obtained using non Rutherford backscattering spectroscopy at 3 MeV proton beam. It was found that the Oxygen-content of (Cu_0.5Tl_0.5)-1223 phase was not affected with the addition of nano-Fe₂O₃. The electrical resistivity measurements showed that the superconducting transition temperature (T _c ) increases up to x=0.2 wt.%, followed by a systematic decrease for x>0.2 wt.%. In addition, room temperature Vickers microhardness (H _v ) measurements were carried out at different applied loads (0.49–2.94 N) to study the performance of the mechanical properties of samples. The experimental results of H _v were analyzed using different models such as elastic, energy dissipation, energy balance and modified energy balance models. It has been found that the energy dissipation model is in a good agreement with the microhardness data.     

Synthesis of Sr0.5Ba0.5Nb2O6 by urea method

A precipitate was formed when an aqueous solution of SrCl₂, BaCl₂, NbF₅ and urea in stoichiometric ratio (total metal cations to urea ratio is 5) is heated on a water bath.. This precipitate on decomposition at 750 °C yielded the nanocrystallites of ternary oxide, Sr_0.5Ba_0.5Nb₂O₆ (SBN) as confirmed by X-ray diffraction study (XRD). This is much lower temperature as compared to that prepared by traditional solid state method (1000 °C) as reported for the formation of SBN ceramics. Transmission electron microscope (TEM) investigations revealed that the average particle size is 100 nm for the calcined powders. The room temperature dielectric constant at 1 kHz is found to be 1050. The ferroelectric hysteresis loop parameters of these samples were also studied.     

Low temperature sintering of Al2O3 microwave dielectric ceramics co-doped with 1.5wt%CuO-3wt%Nb2O5-0.5wt%ZrO2

Journal of Materials Science: Materials in Electronics - In this paper, the sintering behavior, microstructure and microwave dielectric properties of Al2O3 ceramics co-doped with...