碳前驱体热解机理的理论研究──反应能量、自由基的轨道能级及相对稳定性

运用Ｇａｕｓｓｉａｎ ９８程序包中的 ＡＭ１方法,通过对间二甲苯系列化合物设定的８种热裂解过程的反应能量、生成自由基的轨道能级、自由基的相对稳定性的量子化学理论计算,研究了间二甲苯系列化合物的热反应活性及热裂解机理．计算结果表明：（１）各反应物的主反应路径均是苯环上甲基Ｃ－Ｈ键首先断裂．该结论与实验结果一致;（２）各反应物之间的热反应活性由大到小顺序为： Ｃ_８Ｈ_９ＯＨ（ｄ_１）＞Ｃ_８Ｈ_９ＳＨ（ｄ_２）＞Ｃ_８Ｈ_１０（ａ）＞ Ｃ_８Ｈ_９ＣＮ（ｄ_３）．同时亦说明,自由基前线轨道能级差及生成自由基的相对稳定性和热力学等理论参数一样,亦适合于研究间二甲苯系列反应物的热解机理和热反应活性．     

碳前驱体热解机理的量子化学理论研究几何结构、反应焓变、化学键和热反应活性

运用Gaussian98程序包中半经验的量子化学(AM1)方法,对间二甲苯系列化合物(苯环上引入不同取代基-OH、-SH、-CN时的化合物)的热裂解机理进行了研究,对设定的8种有自由基形成的热裂解过程中的反应物、产物的全优化几何构型和反应的热力学量的计算结果表明无论苯环上联接的是吸电子基团还是供电子基团,这些化合物的热裂解键,都是首先从苯环上甲基碳氢键开始,也就是说甲基碳氢键是这类化合物最易断裂的键,也是热裂解的最初反应过程,该结论与实验结果一致;间二甲苯上若联有供电子取代基(-OH,-SH),反应物的热反应活性将增大,若联有吸电子取代基(-CN),反应物的热反应活性将减小。间二甲苯系列化合物的热反应活性的顺序为d1＞d2＞a＞d3。     

碳前驱体热解机理的量子化学理论研究——几何结构,反应焓变,化学键和热反应

运用Ｇａｕｓｓｉａｎ９８程序包中半径验的量子化学（ＡＭ１）方法,对间二甲苯系列化合物（苯环上引入不同取代基－ＯＨ、－ＳＨ、－ＣＮ时的化合物）的热裂解机理进行了研究,对设定的８种有自由基形成的热裂解过程中的反应物、产物的全优化几何构型和反应的热力学量的计算结果表明：无论苯环上联接的是吸电子基团还是供电子基团,这些化合物的热裂解键,都是首先从苯环上甲基碳氢键开始,也就是说甲基碳氢键是这类化合物最易断裂的键,也是热裂解的最初反应过程,该结论与实验结果一致;间二甲苯上若联有供电子取代基（－ＯＨ,－ＳＨ）,反应物的热反应活性将增大,若联有吸电子取代基（－ＣＨ）,反应物的热反应活性将减小。间二甲苯系列化合物的热反应活性的顺序为：ｄ１〉ｄ２〉ａ〉ｄ３。     

一种碳前驱物热解反应的热力学和动力学研究

根据量子化学理论研究了碳前驱物CH3－Ar-CH2-NH2的热裂解机理,利用Gaussian98程序包听AM1法,用UHF计算对化合物五种可能的热裂解路径进行了热力学和动力计算,结果表明,碳前驱物CH3－Ar-CH2-NH2将首先发生生成自由基CH3－Ar-CH2和NH2．的热裂解主反应,活化能Ea=230.78kg/mol,而碳前驱物CH3－Ar-CH2-NH2的实验表观活化能Ea=206.78kg/mol.键能的计算值与实验值符合得比较好,通过分析优化的反应物及产物自由基的部分结构参数,了解了理论支持主反应原因,计算的产物自由基的空间构型表明主反应路径生成的产物自由基相互间若进行筒环缩合反应,获得得分子平面取向性很好的稠环芳烃产物。     

有机锡化合物催化氰酸酯树脂固化反应的研究--(Ⅱ)催化剂的生成反应及催化固化反应机理

用傅立叶变换红外光谱(FT-IR)法研究了有机锡化合物催化剂(H9C4)2Sn(NCO-R-OCN)2的反应生成过程,并提出了氰酸酯三嗪化催化聚合反应的机理。     

基于量子化学理论的热解温度对木质素二聚体热解产物分布的影响

为了探究热解温度对木质素热解产物分布的影响,本工作采用密度泛函方法 B3LYP/6-31G(d,p),以β-O-4型木质素二聚体为模化物,在不同热解温度下,对该模化物两种主要热解反应途径中的反应物、产物、中间体和过渡态进行了能量梯度全优化以及振动频率计算。根据计算结果中的动力学和热力学参数的变化规律,分析了热解温度对热解产物分布的影响。计算结果表明:C_β-O键均裂的反应是主要的反应路径,当热解温度低于700 K时,主要产物为化合物4、化合物7、化合物15以及小分子甲醛和乙烯,化合物10、化合物11、化合物13、化合物14和CO在产物中的含量所占比例相对较少;当热解温度高于700 K时,产物中化合物15和乙烯继续占据主要产物的地位,且含量持续升高,同时,化合物7和甲醛的含量所占比例减少,而化合物10、化合物11和CO含量增多,成为主要产物; C_α-C_β键均裂的反应是主要的竞争反应,随热解温度升高,其主要生成物化合物4和乙醛含量持续升高,而化合物25和甲醛在产物中所占比例变化不大,化合物20和CO的比例则明显减少。     

低温碳热还原法合成氮化铝陶瓷超细粉末

采用硝酸盐-有机物低温燃烧反应溶胶-凝胶工艺,以硝酸铝（Al（NO3）3·9H2O）、葡萄糖（C6H12O6·H2O）、尿素（CO（NH2）2）为原料,制备出粒度细小、混合均匀的铝源和碳源的混合前驱物,然后以该前驱物为原料进行碳热还原反应制备氮化铝粉末.研究表明,该前驱物具有较高的反应活性,氮化反应速率快,1550℃时仅用90min即可实现完全转化,SEM分析结果表明合成粉末为粒度分布均匀的纳米级（～100nm）粉末.     

分散剂对纳米LiBr溶液稳定性的影响

文章在论述分散剂增强纳米流体分散稳定性的基础上,通过添加E414和C6H5O7（NH4）,验证分散剂增强纳米LiBr溶液的分散稳定性,通过测量分别添加异辛醇（C8H18O）、壬醇（C9H20O）和癸醇（C10H220）基液的表面张力,发现分散剂也能增强纳米LiBr溶液表面张力的稳定性,主要因为表面张力和汽化成核临界功之间存在相关性,因此,分散剂同样能增强纳米LiBr溶液沸腾温度的稳定性。     

用反应球磨法制备NiAl-TiC复合材料

球磨Ni、Al、Ti和C粉末以合成NiAl-TiC复合材料，分析了反应合成机理。结果表明，NiAl和TiC的突然生成归结于两个爆炸反应：Ni Al→NiAl ΔH1,Ti 2C→TiC ΔH2。还研究了NiAl和TiC化合物球磨过程中晶粒细化的规律以及粉末颗粒度的变化规律。     

基于水热法合成BaTiO3纳米粉的溶液及前驱物研究

主要围绕片式叠层用PTC纳米粉体的水热制备方法进行研究，采用钛酸四丁酯和乙酸钡为反应原料，通过XRD分析了水热环境pH值、反应前驱物钡钛比、钡源添加形式等工艺因素对粉体晶相及杂质组成等性能参数的影响。通过化学沉淀和溶液滴定方法研究了反应前驱物的Ba／Ti比对生成粉体化学计量比的影响。实验结果表明：当水热反应的pH值为14时，将Ba（Ac）21Ti（OC4H9）4按照化学计量比为1配置的前驱物置于饱和氢氧化钡溶液构成的富钡环境下进行水热反应，合成了化学计量比为1．027、晶粒尺寸30nm左右的立方相钛酸钡纳米粉。     

Growth of carbon nanotubes using a thermal insulator investigated by in-situ mass spectroscopy

The low-temperature synthesis (500-560 °C) of carbon nanotubes (CNTs) on a triple-layered catalyst, Al/Fe/Mo was performed using complex hydrocarbon radicals which were produced from pyrolysis of C₂H₂. These radicals were produced using a high-temperature heater (~ 830 °C), but the substrate where the CNTs were grown was placed on a thermal insulator. This then enabled the substrate to be at a much lower temperature (500-560 °C). A simulated temperature distribution inside the chamber was also used to describe this low-temperature configuration. The synthesis of CNTs relies on the thermal dissociation and dissociative recombination of C₂H₂ for the formation of complex high-order radicals (i.e. C₆H₉, C₅H₉, and C₆H₁₃), and their presence was confirmed by in-situ mass spectroscopy. To explain this, a simple gas-phase radical chain process and a growth model are presented.     

化学气相沉积碳化硅的热力学分析

根据吉布斯自由能最小原理, 采用FACTSAGE计算软件, 重点对MTS/H₂体系化学气相沉积碳化硅进行了均相平衡计算,评价了体系中主要化合物对沉积碳化硅的作用. 结果表明,低温和高压下, SiCl₄和CH₄的含量最多, 不饱和物质和自由基的含量非常少, 温度的升高和压力的下降可显著提高不饱和物质和自由基的浓度; 高温和低压下, SiCl₂和C₂H₂可能是形成碳和硅的主要先驱体, 其它稳定物质如碳氢化合物、有机硅化合物和硅烷等由于浓度太小和表面反应粘结系数低, 对碳化硅的沉积可以不予考虑; 体系中几乎没有含Si--C和Si--Si键的物质, 说明碳化硅是经过碳和硅独立形成, 二者的相对速率决定了碳硅比.     

Thermophysical and Magnetic Properties of Carbon Beads Containing Nickel Nanocrystallites

Ferromagnetic and superparamagnetic nickel nanocrystallites, stabilized in a carbon matrix, were prepared by a three-step procedure including formation of a Ni acrylamide complex, followed by frontal polymerization and pyrolysis of the polymer at various temperatures. It was found that the procedure applied enables fabrication of magnetic beads containing metallic nanocrystallites embedded in a carbon matrix. The size of the crystallites, their morphology, volume fraction, and magnetic properties can be tailored by the pyrolysis temperature. The size of the crystallites affects their behavior in an external magnetic field, i.e., a heating process is the most effective for a sample pyrolyzed at 873 K. The revealed H ⁿ-type dependence of the temperature increase rate, (dT/dt) _t=0, on the amplitude of the magnetic field indicates the presence of both superparamagnetic and ferromagnetic particles in all the samples studied since n > 2. For the superparamagnetic particles, the heating mechanism is associated with Néel relaxation. For the lower values of the magnetic field amplitude, H <  H ₀, the relaxation losses dominate whereas for the opposite case, H >  H ₀, the magnetic hysteresis is the main source of thermal energy losses. The composites containing magnetic Ni nanocrystallites entrapped in a carbon matrix can be potentially applied for hyperthermia treatment.     

Chemical vapor deposition of pyrolytic carbon on SiC fibers

We carried out thermodynamic analysis of reactions underlying the preparation of pyrolytic carbon from a number of carbon-containing compounds and experimentally determined the optimal temperature range for the deposition of thin (1–3 μm) pyrolytic carbon layers onto continuous silicon carbide fibers. The results indicate that, among the compounds studied, the highest deposition rate of pyrolytic carbon is ensured by the pyrolysis of toluene and n-heptane. The slowest deposition rate is observed in methane pyrolysis. Rate data are used to determine the apparent activation energies for the pyrolysis of C₇H₈, C₇H₁₆, (CH₃)₂CO, CCl₄, and CH₄. Original Russian Text ? P.M. Silenko, A.N. Shlapak, V.P. Afanas’ev, 2006, published in Neorganicheskie Materialy, 2006, Vol. 42, No. 3, pp. 288–291.     

ABO3型钛铁矿结构化合物的容差因子

通过结构解析, 建立了ABO₃型钛铁矿的容差因子计算公式以评估结构的稳定性, 经过分析具有钛铁矿结构的MgTiO₃、NiTiO₃、CoTiO₃、ZnTiO₃以及(Zn_1-x, M_x )TiO₃(M为Mg、Ni、Co)复合钛铁矿的稳定性, 验证了容差因子公式的合理性; 通过对已发现的具ABO₃型钛铁矿结构的化合物的统计分析, 提出形成稳定钛铁矿结构的经验容差因子范围和经验电负性差值, 即: t>0.80, e>1.465.     

磷酸镍空旷结构材料的水热合成及其影响因素

在水热条件下,考察了1NiCl₂·6H₂O-mH₃PO₄-nNH₄F-pNH₃·H₂O-40H₂O(n=0、3) 体系中空旷结构过渡金属磷酸镍材料的合成影响因素(原料、pH值、Ni/P比、模板剂和矿化剂等),并给出了材料的晶化区域图.在实验过程中得到的产物包括已知结构的24元环微孔材料VSB-1^[1]和VSB-5^[2]、12元环微孔材料A、层状材料B^[3]、氢键型微孔材料C^[4].采用XRD、FT-IR和TG对所合成的材料进行了表征.所合成几种材料的XRD图都在较低的2θ角处出现了衍射峰,表明它们可能具有比较空旷的骨架结构.实验证明该体系中矿化剂、pH 值和Ni/P比对产物的影响较大.值得说明的是文献报道在没有F离子的情况下不能合成出VSB-1^[1],而我们在没有F离子的条件下合成了VSB-1.     

双草酸硼酸锂的制备新方法、表征及性能研究

详细介绍了一种锂离子电池电解质盐双草酸硼酸锂（LiBOB）的新制备方法——乙腈溶剂法. 制备过程采用硼酸、碳酸锂、草酸等作为原料, 首先采用P204萃淋树脂预处理锂源, 后将反应物置于乙腈溶剂中直接反应, 所得产品经过乙二醇二甲醚提纯后即得到产物. 产物通过红外光谱和X射线衍射检测手段定性, 用原子吸收和离子色谱检测手段定量, 证明所制备的LiBOB杂质含量少, 纯度达到99.95%. 并通过热分析证实其热稳定性优于一般商品用LiBOB, 整套实验方法优势明显.     

A Robust Molecular Porous Material for C2H2/CO2 Separation

A molecular porous material, MPM-2, comprised of cationic [Ni₂(AlF₆)(pzH)₈(H₂O)₂] and anionic [Ni₂Al₂F₁₁(pzH)₈(H₂O)₂] complexes that generate a charge-assisted hydrogen-bonded network with pcu topology is reported. The packing in MPM-2 is sustained by multiple interionic hydrogen bonding interactions that afford ultramicroporous channels between dense layers of anionic units. MPM-2 is found to exhibit excellent stability in water (>1 year). Unlike most hydrogen-bonded organic frameworks which typically show poor stability in organic solvents, MPM-2 exhibited excellent stability with respect to various organic solvents for at least two days. MPM-2 is found to be permanently porous with gas sorption isotherms at 298 K revealing a strong affinity for C₂H₂ over CO₂ thanks to a high (ΔQ_st)_AC [Q_st (C₂H₂) − Q_st (CO₂)] of 13.7 kJ mol⁻¹ at low coverage. Dynamic column breakthrough experiments on MPM-2 demonstrated the separation of C₂H₂ from a 1:1 C₂H₂/CO₂ mixture at 298 K with effluent CO₂ purity of 99.995% and C₂H₂ purity of >95% after temperature-programmed desorption. C-H···F interactions between C₂H₂ molecules and F atoms of AlF₆³⁻ are found to enable high selectivity toward C₂H₂, as determined by density functional theory simulations.     

Thermal, spectroscopic and magnetic properties of the CoxNi1−x(SeO3)·2H2O (x = 0, 0.4, 1) phases: Crystal structure of Co0.4Ni0.6(SeO3)·2H2O

The Co_xNi_1−x(SeO₃)·2H₂O (x = 0, 0.4, 1) family of compounds has been hydrothermally synthesized under autogeneous pressure and characterized by elemental analysis, infrared and UV-vis spectroscopies and thermogravimetric and thermodiffractometric techniques. The crystal structure of Co_0.4Ni_0.6(SeO₃)·2H₂O has been solved from single-crystal X-ray diffraction data. This phase is isostructural with the M(SeO₃)·2H₂O (M = Co and Ni) minerals and crystallizes in the P2₁/n space group, with a = 6.4681(7), b = 8.7816(7), c = 7.5668(7) Å, β = 98.927(9)° and Z = 4. The crystal structure of this series of compounds consists of a three-dimensional framework formed by (SeO₃)²⁻ selenite oxoanions and edge-sharing M₂O₁₀ dimeric octahedra in which the metallic cations are coordinated by the oxygens belonging to both the selenite groups and water molecules. The diffuse reflectance spectra show the essential characteristics of Co(II) and Ni(II) cations in slightly distorted octahedral environments. The calculated values of the Dq and Racah (B and C) parameters are those habitually found for the 3d⁷ and 3d⁸ cations in octahedral coordination. The magnetic measurements indicate the existence of antiferromagnetic interactions in all the compounds. The magnetic exchange pathways involve the metal orbitals from edge-sharing dimeric octahedra and the (SeO₃)²⁻ anions which are linked to the M₂O₁₀ polyhedra in three dimensions.