化学气相沉积反应研究的量子化学方法及应用

量子化学方法在研究化学气相沉积反应体系的反应机理、动力学计算方面有很大的潜力.本文分析了化学气相沉积过程的特点,并对量子化学计算的主要方法进行介绍.在此基础上,针对气相和表面基元过程的量子化学研究现状进行总结和评述.     

含稀释剂的Al-Cr2O3体系燃烧合成反应热力学分析与反应模型

对含稀释剂Al2O3和Cr2O3的Al-Cr2O3体系燃烧合成反应进行了热力学计算与分析,讨论了起始反应温度T0、稀释剂Al2O3和Cr2O3的含量对绝热反应温度Tad的影响,并得出T0与Tad在特定温度段上的近似线性关系以及该关系在指导材料成分设计上的应用;揭示了反应驱动力--Gibbs自由能(ΔG)随反应温度(T)的变化关系,得出该体系的反应为扩散控制型反应;结合实验结果与分析,描述了该体系热爆反应的微观模型.     

高纯无水InCl3反应热力学机理

通过直接氯化法,制备高纯无水InCl3,得到实验最佳反应温度为600 ℃。以热力学平衡计算为理论依据,用吉布斯自由能函数和平衡分压对体系中的反应方向和限度进行数据分析,确定不同温度下反应得到的理论产物,并通过分子动力模拟计算,进一步揭示体系中反应温度和反应机理的关系。理论计算结果表明,在反应温度为665 ℃以下时,In与Cl2反应生成In2Cl6后再分解为InCl3和其他副产物,在反应温度为665 ℃以上时,可直接得到主要产物InCl3;而实验结果与理论计算存在的65 ℃误差,说明反应过程中平衡状态与非平衡状态间存在差异。     

丙烷CVI工艺热解炭沉积非均相反应动力学模拟

分别运用总括非均相反应机理和详细非均相反应机理,结合均相反应机理(包括285种气相组分,1 074个气相可逆基元反应)来模拟C_3H_8在CVI工艺条件下炭纤维表面热解炭的沉积过程,进而对实验中的气相组分和热解炭的形成过程进行预测。总括非均相反应机理对炭沉积反应进行了简化处理,气相中的烃组分直接在表面脱氢沉积为热解炭;而详细非均相反应机理则利用表面基元反应来描述热解炭沉积过程,包括66种表面组分和250个表面基元反应。本文以C_3H_8为炭源,N_2为稀释气体,温度1 173~1 323 K、低压(2.6 kPa)和滞留时间为0.5~4s条件下的连续搅拌釜反应器为模型进行模拟,气相组成和沉积动力学两方面的预测与实验结果都较好吻合。计算表明在该设定条件下热解炭的前驱体主要为不饱和小分子(C_2H_2和C_2H_4)和甲基,进而利用这些组分定量解释热解炭的沉积动力学。     

含稀释剂的A1-Cr2O3体系燃烧合成反应热力学分析与反应模型

对含稀释剂A12O3和Cr2O3的A1-Cr2O3体系燃烧合成反应进行了热力学计算与分析，讨论了起始反应温度T0、稀释剂A12O3和Cr2O3的含量对绝热反应温度Tad的影响，并得出T0与Tad在特定温度段上的近似线性关系以及该关系在指导材料成分设计上的应用；揭示了反应驱动力——GibbS自由能(△G)随反应温度(T)的变化关系，得出该体系的反应为扩散控制型反应；结合实验结果与分析，描述了该体系热爆反应的微观模型。     

生态复合墙结构动力反应分析模型研究

独特构造及多种材料的使用与嵌套,使生态复合墙结构的动力特性计算异常复杂,故需提出其简化动力计算模型。结合课题组前期研究成果及相关理论,提出生态复合墙结构在弹性阶段简化的动力反应分析模型;建立每层复合墙体分布参数体系的运动偏微分方程,计算其振型和频率;把每层顶点位移作为上一层支座激励,利用振型叠加法对每层复合墙体进行有阻尼动力反应分析;对整体复合墙体进行动力反应分析,并与前期振动台试验结果进行对比分析。理论与试验结果表明：该简化模型计算求得的各层加速度时程反应值与试验值吻合较好,具有一定的计算精度与实用性,为生态复合墙结构在弹性阶段的动力反应分析提供了一种较为简化、实用的计算方法。     

影响异氰酸酯双封端反应动力学的因素

对ＴＤＩ、ＭＤＩ、ＮＤＩ３种异氰酸酯进行了双封端反应,讨论了温度、催化剂及不同原料对异氰酸酯双封端反应速度常数的影响,结果表明,异氰酸酯双封端反应为二元基元反应,不同的反应物,反应速度常数不同,其中ＮＤＩ〉ＭＤＩ〉ＴＤＩ。催化剂量及温度与反应速度常数成正比关系。实验结果还表明,催化剂能降低反应活化能,有利于封端反应的进行。     

Gear方法模拟光化学烟雾形成反应

本文应用Ｇｅａｒ方法对一个简化的光化学烟者形成机理进行了数值模拟，模拟结果在定性上与观察及实验结果相吻合，验证了该简化机理的正确性与合理性。在计算程序中，利用反应物矩阵和生物矩阵解决了系统地构造速率函数和Ｊａｃｏｂｉ矩阵的问题，这对于处理复杂反应体系的动力学模拟具有重要的意义。     

DF化学激光器反应动力学模型的简化及其有效性分析

DF化学激光器涉及到多组分的高速化学反应流,组分、反应方程、速率常数的选择对计算结果有着重要影响.通过对DF化学激光器反应动力学模型的讨论,给出了简化模型的依据,并且分别运用几组简化反应模型进行数值模拟,分析与完全反应模型相比,简化对激光器小信号增益系数和DF激发态分子空间分布的影响.推荐了一个针对(NF_3+H_3+He)/D_2燃料体系,DF化学激光器"冷反应"系统的11组分23方程简化模型,在很大程度上减少了计算量,有利于反应流场数值仿真的编程实现.     

稀释剂Al2O3对NiO／Al体系燃烧速度的影响及其表观反应激活能计算

研究了Al2O3稀释剂添加量对NiO／Al体系燃烧速度及体系产物形貌的影响,结合绝热温度的计算结果,基于Merzhanov等提出的燃烧波速公式,根据体系In（v／Tnd）-1／Ld的Arrhenius图,测定了添加Al2O3后NiO／Al体系的反应激活能。研究结果表明：对于NiO／Al体系,在一定范围内（0～5％,25...     

Photostriction of CH3NH3PbBr3 Perovskite Crystals

Organic–inorganic hybrid perovskite materials exhibit a variety of physical properties. Pronounced coupling between phonon, organic cations, and the inorganic framework suggest that these materials exhibit strong light–matter interactions. The photoinduced strain of CH₃NH₃PbBr₃ is investigated using high‐resolution and contactless in situ Raman spectroscopy. Under illumination, the material exhibits large blue shifts in its Raman spectra that indicate significant structural deformations (i.e., photostriction). From these shifts, the photostrictive coefficient of CH₃NH₃PbBr₃ is calculated as 2.08 × 10^?8 m² W^?1 at room temperature under visible light illumination. The significant photostriction of CH₃NH₃PbBr₃ is attributed to a combination of the photovoltaic effect and translational symmetry loss of the molecular configuration via strong translation–rotation coupling. Unlike CH₃NH₃PbI₃, it is noted that the photostriction of CH₃NH₃PbBr₃ is extremely stable, demonstrating no signs of optical decay for at least 30 d. These results suggest the potential of CH₃NH₃PbBr₃ for applications in next‐generation optical micro‐electromechanical devices.     

Constitution of the Ni3Cr-Ni3Al-Ni3W system

Isothermal sections of the Ni-Cr-Al-W system have been investigated at 75 at % Ni and temperatures of 1523 and 1273 K, by means of phase compositional analysis, X-ray diffraction and microscopical examination. The alloys studied lay in the range 2.5 to 10 at % Cr, 12.5 to 20 at% Al, 2.5 to 6.25 at % W, The phases formed were, and the bcc solid solution based on tungsten (designated ₂). The maximum extent of the region was found to be 3 at % each of chromium and tungsten. Preferential partitioning of tungsten to occurred. Study of an Ni-10Cr-12.5Al-2.5W alloy aged at 1273 and 1073 K, after quenching from 1573 K, showed that changes in and compositions and lattice parameters occur as a function of ageing time.     

Crystal structure of Tl3AsSe3

The structure of Tl₃AsSe₃, which has been solved by the single-crystal x-ray method, is rhombohedral, with space group R3m and cell parameters $\text{a}\text{= 9.870(2)}\text{A}\text{?}\text{, c}\text{= 7.094(3)}\text{A}\text{?}\text{, z}\text{= 3}$. A full-matrix least-squares refinement gives weighted R = 0.058. The Se atoms form equilateral triangles around Tl at 3.178Å and around As at 2.207Å. The structure may be described in terms of units formed from three TlSe₃ triangles by corner-sharing. These units share corners to produce a helical arrangement along the c axis. The triangles of AsSe₃ are isolated from each other.     

3 Cr3 Mo3 VNb 在热冲孔中的应用研究

高合金钢热冲孔冲头寿命关系到模具与产品成本、生产效率、自动化设备的使用,因此,应注重冲头的选材、材料制备与冲头制造工艺。 用 3 Cr3Mo3 VNb 作为高合金钢热冲孔冲头,为提高模具寿命,在材料制备上,优化了成分,采用电渣重熔冶炼,减少杂质,毛坯锻造两次,用大锻造比锻造,冲头热处理用真空炉,三次回火,热处理硬度取 HRC42 ~ 46 ,冲头表面处理采用镀铬工艺,开展了热冲孔工艺试验。 结果表明,用3 Cr3Mo3 VNb 可使冲孔冲头寿命平均达到 800 件以上。     

(La2/3Ca1/3)(Mn(3-x)/3)Fex/3)O3体系磁电阻行为的研究

通过系统地测量（La_2/3Ca_1/3）（Mn_{（3-x）／3}Fe_x／3）O₃（x＝0、0.1、0．2、0．3的体系样品的电阻率-温度关系以及一定温度下磁电阻率与磁场的关系,发现随x的变化其磁电阻率峰和电阻率峰均发生位移,磁电阻率峰值增大,并伴生磁电阻率峰展宽效应．作者认为由于Fe的替代,引起体系中Mn³⁺／Mn⁴⁺比率及磁矩的变化,加之外场对磁有序结构的调制作用,从而影响了Mn³⁺－O^－Mn⁴⁺的双交换作用,最终导致磁电阻行为发生变化．     

Multicolor up-conversion emissions of Tm3+/Er3+/Yb3+ tri-doped YF3 phosphors

Tm3+/Er3+/Yb3+ tri-doped yttrium fluoride (YF3) phosphors were prepared by a facile hydrothermal method. X-ray topographic analysis found that the phosphors were crystallized products. Their sizes and morphologies were characterized by scanning electron microscopy (SEM, Hitachi S-4800), which indicated that most of the YF3 phosphors were hundreds of nanometers in size. Up-conversion (UC) spectra were recorded under 980-nm diode laser excitation at room temperature with a fluorescence spectrometer (Hitachi F-4500). Plenty of UC emissions of Tm3+ and Er3+ were observed from ultraviolet to red. For Tm3+ ions, a five-photon process (approximately 291 nm and approximately 347 nm), a four-photon process (approximately 362 nm and approximately 452 nm), and a three-photon process (approximately 475 nm) were identified in the UC spectra. The UC emissions from the Er3+ were: approximately 380 nm, approximately 408 nm, approximately 521 nm, approximately 537 nm, and approximately 652 nm. Therefore, cyan-white light can be observed by the naked eye at 980-nm excitation, even under low excitation power density. By comparing the UC spectra of the phosphors annealed at different temperatures, we found that the intensity of the UC luminescence increased as annealing temperature increased. Furthermore, the spectral dependencies on Tm3+ doped concentrations were studied. The energy transfer processes and fluorescence dynamics in the tri-doped system are currently being investigated.     

The Ni3Al-Ni3Cr-Ni3Mo section of the Ni-Cr-Al-Mo system

An investigation is reported of the constitution of the 75 at % nickel section of the Ni-Cr-Al-Mo system in the temperature range 1523 to 1073 K. Alloys in the region 10 to 20 at % Al were annealed at 1523, 1273, and 1073 K, respectively, and subjected to electron microprobe analysis, X-ray diffraction, and microscopical and hardness examination. Constitutional data are presented as partial isothermal sections and as vertical sections. At 1523 K the section consists only of fields containing ,+ and , the last mentioned phase being predominant. With decreasing temperature the and + fields increase in extent. Also, the NiMo and Ni₃Mo phases were encountered in the ternary Ni-Al-Mo alloy studied. The quaternary + alloys showed small lattice mismatch values, i.e. up to 0.25%. Raft like morphologies of were found in the quaternary alloys, resulting from directional coarsening. Observations of as-cast structures are also reported.     

Optically and thermally stimulated luminescence of KMgF3:Ce3 and NaMgF3:Ce3+

The potentialities of optically stimulated luminescence (OSL) for personal dosimetry of ionising radiation have stimulated the search for new synthetic materials with good dosimetric properties. The sensitivity of two new OSL materials KMgF3 and NaMgF3 doped with Ce3+ ions has been evaluated and found to be of the same order of magnitude as that of Al2O3:C. Several other characteristics have also been investigated. Promising results for KMgF3:Ce are the high sensitivity and the low fading. However, this material suffers from a high self-dose due to the presence of 40K. NaMgF5:Ce is sensitive as well but shows strong fading. Interesting information on the mechanism has been obtained by correlating the signals of OSL and TL. Furthermore, the different bleachabilities under blue LED illumination of the strongly overlapping glow peaks allowed the extraction of one single peak for KMgF3:Ce3+. The results demonstrate new possibilities offered by the combination of TL and OSL.