燃烧辅助合成LiNi0.05Mn1.95O4粉体及其性质研究

以醋酸锂、醋酸锰、硝酸镍、柠檬酸、乙二醇为原料,采用燃烧辅助合成锂离子电池正极材料LiNi0.05Mn1.95O4。采用X射线衍射、扫描电子显微镜、循环伏安、恒电流充放电等技术对合成产物进行物相、形貌及电化学性能分析与测试。结果表明:采用燃烧辅助合成LiNi0.05Mn1.95O4过程中,前驱体在空气中点燃后已形成单一尖晶石相,经750℃热处理4 h后得到的LiNi0.05Mn1.95O4粉末X射线衍射峰尖锐,结晶性好,晶粒尺寸均匀。该法合成的LiNi0.05Mn1.95O4粉末首次放电比容量为117.5 mAh.g-1,经50次充放电循环后的容量保持率为95.1%,合成的LiNi0.05Mn1.95O4粉末具有良好的电化学性能。     

Combustion synthesis of magnesium ferrite as liquid petroleum gas (LPG) sensor: Effect of sintering temperature

We report synthesis of Spinel type magnesium ferrite (MgFe₂O₄) material by a simple, inexpensive combustion method with glycine as a fuel and their application as a gas sensor for reducing gases (LPG, Acetone, Ethanol, Ammonia). The dependence of reducing gas sensing properties on the structural and surface morphological properties has been studied as an effect of sintering temperatures. The structural and surface morphological properties were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The MgFe₂O₄ were highly oriented along (311) with the spinel type crystal structure. The SEM observation reveals that porous morphology decreases due to the grain growth as sintering temperature increases. The mechanism of reducing gas sensing by the MgFe₂O₄ pellets is explained on the basis of adsorbed oxygen on the sensor surface. The selectivity and maximum response of 71% to 2000 ppm of LPG was observed at 698 K with the (MgFe₂O₄) material sintered at 1173 K.     

Supersonic combustion and hypersonic propulsion

50 多年的努力和曲折经历证明了超声速燃烧冲压发动机概念的可行性. 本文对影响超燃冲压发动机技术成熟的主要因素作了扼要的分析. 高超声速推进的首要问题是净推力, 利用超声速燃烧获得推力遇到各种实际问题的制约, 它们往往互相牵制. 几次飞行试验表明高超声速飞行需要的发动机净推力仍差强人意, 液体碳氢燃料(煤油) 超燃冲压发动机在飞行马赫数5 上下的加速和模态转换过程, 成为高超声速吸气式推进继续发展的瓶颈. 研究表明, 利用吸热碳氢燃料不仅是发动机冷却的需要也是提高发动机推力和性能的关键举措, 燃料吸热后物性改变对燃烧性能的附加贡献对超燃冲压发动机的净推力至关重要.当前, 实验模拟技术和测量技术相对地落后, 无法对环境、尺寸和试验时间做到完全的模拟. 计算流体动力学(Computational Fluid Dynamics, CFD) 逐渐成为除实验以外唯一可用的工具, 然而, 超声速燃烧的数值模拟遇到湍流和化学反应动力学的双重困难. 影响对发动机的性能作正确可靠的评估.提出双模态超燃冲压发动机模态转换、吸热碳氢燃料主动冷却燃料催化裂解与超声速燃烧耦合、燃烧稳定性、实验模拟技术与装置、内流场特性和发动机性能测量、数值模拟中的湍流模型、煤油替代燃料及简化机理等研究前沿课题, 和未来5~10 年重点发展方向的建议.     

基于扩散近似法和双通量法耦合的多孔介质内燃烧辐射换热计算方法

将Rosseland辐射模型和双通量法结合,对瓦斯气体在泡沫陶瓷中预混燃烧辐射换热计算方法进行研究.数值模拟的结果与试验结果吻合比较好,证明提出的辐射换热计算方法是有效的.     

Design studies on the 4π γ-ray calorimeter for the ETF experiment at HIRFL-CSR

A high detection efficiency calorimeter which is used to detect γ-rays with energies from 1 MeV up to 10 MeV as well as light charged particles has been proposed.Design of the geometry,results of the crystal tests and Monte Carlo simulations are presented in this paper.The simulation results confirm that the calorimeter can obtain high detection efficiency and good energy resolution with the current designed geometry.And the calorimeter is competent for the future External Target Facility(ETF)experiments.     

融合波长选择和异常光谱检测的天然气燃烧过程定量分析方法

针对天然气燃烧过程的近红外光谱数据,采用了一种融合波长选择和异常光谱检测的定量分析方法。该方法根据偏最小二乘(PLS)模型的系数及预测误差的统计分布,在实现波长选择的同时,完成异常光谱样本的检测。与PLS、先用留一法将异常样本删除后PLS建模(LOO-PLS)、基于PLS的无信息变量消除法(UVE-PLS)以及先用留一法将异常样本删除后使用UVE-PLS建模(LOO-UVE-PLS)相比较,该方法将甲烷预测模型的预测均方根误差(RMSEP)分别降低了14.33%,14.33%,10.96%和12.21%;将一氧化碳预测模型的RMSEP分别降低了67.26%,72.58%,11.32%和4.52%;将二氧化碳预测模型的RMSEP分别降低了5.95%,19.7%,36.71%和4.04%。实验表明,该方法建立的分析物预测模型具有较高的预测能力和较好的稳健性,在大大减少所选波长数量,降低模型复杂度的同时,还能有效地检测出异常光谱样本,减小两者之间的相互影响。     

Synthesis and optical properties of Ce-doped Y3Mg2AlSi2O12 phosphors

Y_3−xMg₂AlSi₂O₁₂:Ce_x³⁺ (x=0.015, 0.03 and 0.06) phosphors possessing garnet crystal structure were synthesized by the sol–gel combustion technique. The samples were characterized by application of powder X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, thermal quenching (TQ) and scanning electron microscopy (SEM). Moreover, luminous efficacies (LE), color points and quantum efficiencies (QE) were calculated. Optical properties were studied as a function of Ce³⁺ concentration and annealing temperature. XRD analysis revealed that sintering of polycrystalline Y₃Mg₂AlSi₂O₁₂:Ce³⁺ powders at 1550 °C results in nearly single-phase garnet materials. Phosphors showed broad emission band in the range of 500–750 nm and had the maximum intensity at 600 nm, which results in strongly red-shifted phosphors compared with conventional YAG:Ce phosphors emitting at 560 nm. However, strong concentration quenching has also been observed, probably due to increased Stokes shift.     

O_2/CO_2气氛燃煤半焦孔隙特性分析

在沉降炉上制备了不同燃烧气氛、不同燃尽程度的半焦,采用低温氮吸附仪和扫描电子显微镜测定了其孔隙结构和表面形态.结果表明,所取的半焦试样均具有完整且连续的孔结构体系;但在相同的操作条件下,O_2/CO_2气氛下半焦试样的孔结构参数及其分形维数均小于相同O_2浓度的O_2/N_2气氛下的情况;两种气氛下煤焦的燃尽过程中,孔隙结构参数(S_(BET)、V_(BJH)和d_(pore))随燃尽率的增加均呈减小趋势;SEM图像的定性分析结果与N_2吸附的定量测量吻合较好.研究结果为深入认识O_2/CO_2气氛下煤粉的孔隙结构与其燃烧特性的关系提供了基础.     

煤中钠元素赋存形态对亚微米颗粒物形成的影响研究

将原煤通过三步化学提取实验(水洗,NH_3OAc洗,HCl洗),然后通过浸溶实验(Impregnation Experiment),将煤中羧基(-COOH)中的H离子置换成Na离子.并将原煤、提取实验后煤和浸溶实验后的三种煤样在沉降炉中热解和燃烧,研究煤中钠的有机/无机赋存形态对其气化特征和亚微米颗粒物形成的影响.实验结果发现:提取实验后的煤样,Na元素大部分以硅酸盐形式存在,两种煤在沉降炉中的热解结果表明以硅酸盐形式存在于煤中的钠元素很难气化.浸溶实验后的煤样中,Na元素大部分以羧酸(COO-Na)的形式存在,两种煤在沉降炉中的热解实验结果表明以有机结合态存在于煤中的钠元素非常易气化.Na元素赋存形态对其燃烧过程中气化有重要影响,最终表现在亚微米颗粒物中的含量上.