Mechanistic study of thermal behavior and combustion performance of epoxy resins: I homopolymerized TGDDM

Tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) undergoes homopolymerization on heating. Intramolecular reactions which compete with crosslinking favor the formation of cyclic structures with increasing thermal and fire resistance of the resin, whereas physical mechanical properties tend to decrease. The mechanism of thermal decomposition of TGDDM is studied by thermogravimetry, differential scanning calorimetry and thermal volatilization analysis with characterization of volatiles evolved and residue left. Thermal degradation of poly-(TGDDM) starts at 260°C with elimination of water from secondary alcoholic groups which is a typical pathway for epoxy resin degradation. Resulting unsaturations weaken bonds in the β-position and provoke the first chain breaking at allyl–amine and allyl–either bonds. With increasing temperature, saturated alkyl–ether bonds and alkyl carbon–carbon bonds are broken first, followed by the most stable alkyl–aryl bonds at T>365°C. The combustion performance of TGDDM is discussed on the basis of the thermal degradation behavior.     

The identification of tricyclic neuroleptics and sulphonamides by high-performance thin-layer chromatography

Circular high-performance thin-layer chromatography (HPTLC) has been used to differentiate a series of twelve tricyclic neuroleptics, using both normal phase and reverse phase procedures. The use of normal phase systems also allows the resolution of geometric isomers of chlorprothixene, clopenthixol and flupenthixol. Thirteen sulphonamides and Trirnethoprim may also be distinguished using HPTLC.     

Thermodynamic study of the three isomers of bromo and iodobenzoic acids. Part II

Using our technique of combustion of small amount of a substance, we determined by calorimetry the standard molar enthalpy of formation in the condensed state and atT=298.15 K of the three isomers of bromo and iodobenzoic acids. Associating to these values their standard molar enthalpies of sublimation previously measured, it was possible to determine their standard molar enthalpies of formation in the gaseous state and atT=298.15 K. The experimental values of the thermodynamic properties _f H _m ^o (cr, 298.15 K), _f H _m ^o (cr, 298.15 K), _sub H _m ^o (298.15 K), and _f H _m ^o (g, 298.15 K) are given for the two series. From the experimental value of the standard molar enthalpy of atomization, it was possible to determine an enthalpy value for the C_b-Br and C_b-I bonds. The experimental and theoretical values of the resonance energy of bromo and iodobenzoic acids are compatible. The relative stability of some monosubstituted derivatives of benzoic acid studied in our laboratory is also discussed.Part I is concerned with Ref. 22 (for bromobenzoic acids) and with Ref. 23 (for iodobenzoic acids).     

The mean spherical model in a random external field and the replica method

We provide a quick elementary solution of the mean spherical model in a random external field. This also allows an immediate proof of the self-averaging property of the free energy. We calculate the free energy by means of the replica method, i.e., for any (not necessarily integer) replica numbern, and show that when a phase transition occurs the limits andn 0 are not interchangeable.     

Mode selective directional couplers for overmoded waveguide systems

Two types of directional couplers for transverse electric (TE) modes are described: short and multihole couplers, respectively. They selectively pick one mode out of a mode mixture in an overmoded circular waveguide system. Unwanted modes are either statistically kept at low level or are suppressed by destructive interference in the coupling waveguide. Mode selectivity and directivity in multihole couplers oscillate up and down with an increasing number of holes, finally reaching a minimum of approximately 20 dB, unless there are competing modes with rational fractions of the beat wavelength. A multihole coupler for the TE₀₂ mode (28 GHz, 63.4 mm waveguide diameter, 41 holes) and a length of 1.6 m shows a calculated directivity of 68 dB and suppresses the unwanted modes TE₀₁ with 34 dB (24 dB), TE₂₂ with 37 dB (45 dB), and further modes TE_m (<5, m<6) with 17 dB to 34 dB in forward direction (figures in parentheses are for unwanted modes propagating in backward direction).A short directional coupler for the TE₀₁ mode (28 GHz, 63.4 mm waveguide diameter) with 16 holes and a length of 230 mm shows a directivity of 55 to 100 dB between 27.9 and 28.1 GHz, suppressing the TE₀₂ mode with 35 to 80 dB, the TE₀₃ mode with 30 to 65 dB, and the TE₂₂ mode with 30 to 70 dB.     

石油焦与煤混合燃料热重分析研究

石油焦与煤混合燃烧是高效处理石油焦的有效方法，作者对选用的石油焦和煤不同配比的混合燃料进行了热重分析研究。使用常压高温热天平研究、分析了各配比混合燃料的热解特性和燃烧特性。并根据化学动力学方法计算了各过程的化学动力学参数，即活化能E和频率因子A0。结果表明，各混合燃料热解起始温度大致相同，随煤焦比减小，挥发分析出速率变缓，最大释放速度所对应的温度升高，最终失重率减小，挥发分释放特性指数减小；随煤焦比增大，混合燃料着火温度和燃尽温度逐渐降低，最大燃烧速率所对应的温度降低，燃烧特性指数增大；随煤焦比减小，活化能和频率因子增大。     

Cu-Mg/Al复合氧化物催化碳颗粒物燃烧性能的研究

恒定二价与三价阳离子比为3(nM2+/nM3+=3),采用共沉淀法制备不同Cu含量的系列水滑石前驱物, 800 ℃焙烧4 h形成复合氧化物(CuO质量百分数分别为0％、5％、10％、15％、20％、30％、40％)用作柴油车排放碳颗粒物燃烧的催化剂,并采用XRD、BET、TG-DSC、FT-IR、TPR等表征手段研究了Cu、Mg含量对材料前驱物物化性能的影响及对其衍生复合氧化物催化碳颗粒物燃烧性能的影响．结果表明,Cu、Mg含量对材料的热稳定性、比表面和催化氧化活性有显著的影响. Mg有助于提高催化剂的热稳定性; Cu含量增加,催化剂比表面下降,但比表面不是影响催化剂活性的主要因素. CuO含量为15％时,催化剂具有最好的催化活性和稳定性,碳颗粒物的起燃温度(T10)和半转化温度(T50)分别为336 ℃和409 ℃.在CuO含量≤30％时可以形成结构完整的水滑石前驱物, CuO含量为40％时出现Cu(OH)2杂相; CuO含量< 20％时,经高温焙烧可得到均匀的复合氧化物, CuO含量≥20％时出现CuO偏析． TPR结果表明焙烧温度和复合氧化物的组成决定了材料的可还原性能．     

Thermodynamics of phenylated polyphenylene between 0 and 340 K

In an adiabatic vacuum calorimeter, the temperature dependence of the heat capacity C _p of phenylated polyphenylene and initial comonomer 1,4-bis(2,4,5-triphenylcyclopentadienone-3-yl)benzene was studied between 6 and 340 K with an uncertainty of about 0.2%. In a calorimeter with a static bomb and an isothermal shield their energies of combustion DUcomb were measured. From the experimental data, the thermodynamic functions C _p ⁰ (T), H ⁰(T)-H ⁰(0), S ⁰(T)-S⁰(0), G ⁰(T)-H ⁰(0) were calculated from 0 to 340 K, and standard enthalpies of combustion ΔH _comb ⁰ and thermodynamic parameters of formation-enthalpies ΔH _f ⁰, entropies ΔH _f ⁰, Gibbs functions ΔG _f ⁰ - of the substances studied were estimated at T=298.15 K at standard pressure. The results were used to calculate the thermodynamic characteristics (ΔH _f ⁰ ,ΔS _f ⁰, ΔG _f ⁰) of phenylated polyphenylene synthesis in the range from 0 to 340 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Combined study of thermochemical properties of nitroform and its salts

A combined method for determination of the standard enthalpies of formation of nitroform and its salts was proposed. The enthalpies of dissolution of nitroform and its ammonium, hydrazinium, guanidinium, and potassium salts in water were measured. The enthalpy of combustion of hydrazinium salt of nitroform was determined by a combustion calorimetry, and its standard enthalpy of formation was calculated. The enthalpy of formation of trinitromethyl anion in indefinitely diluted aqueous solution −24.94±0.79 kJ mol⁻¹, was calculated on the basic of the data obtained for enthalpies of formation and dissolution of ammonium and hydrazinium salts of nitroform. Standard enthalpies of formation of nitroform and its salts were calculated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2451–2454, December, 1998.     

Studies on the Binding Mode of Pinacyanol Chloride to Nucleic Acids

The interaction of pinacyanol chloride(PC) with nucleic acids has been investigated by a series of experiments.Extensive hypochromism,appreciable peak shifts,isosbestic points and new peaks of the product of binding to nucleic acids in the spectra were observed.They showed that the interaction between PC and nucleic acids occurred.The results from absorption spectra of DNA,DNA melting,electrophoresis and fluorescence polarization studies have indicated that PC binds to DNA in nonintercalative way.Consistent with the nonintercalation,the studies of fluorescence titration and absorption titration specified that the binding of PC to nucleic acids occurred by an outside stacking binding,in which nucleic acids served for acting templates,The fact that the new absorption peaks of bound PC at ca,485nm are just close to the absorption bands of Haggregate of PC at high concentrations without DNA further supports the outside stacking binding mode,In addition,other evidence indicated that the interaction between PC and nucleic acids is not purely electrostatic.