N2O5/HNO3体系中硝解DADN的反应动力学

采用高效液相色谱跟踪检测了不同温度条件下N₂O₅/HNO₃体系硝解DADN时反应底物、中间体和产物浓度随时间的变化情况。通过对303、313、323、333 K温度下实验数据的分析,计算得到各步的反应速率常数,并最终求得DADN到SEX和SEX到HMX两步的反应活化能分别为2.3996×10⁴ J·mol^-1和1.6598×10⁴ J·mol^-1,指前因子分别为2.2000×10⁴ h^-1和6.5178×10² h^-1。同时,通过柱分离得到的中间产物经结构鉴定为SEX,对其硝基机理进行了分析,实验证明DADN的硝解反应分两步进行,是一级连串反应过程,控制步骤是SEX到HMX。     

Diffusion coefficients of Br2, HNO3 and PdCl2 in graphite

Diffusion coefficients of HNO₃ and Br₂ from near-saturated vapor into highly oriented pyrolytic graphite at 30°C are respectively, 203 × 10^?6 cm²/min and 1.47 × 10^?6 cm²/min, and that of PdCl₂ is 0.52 × 10^?6 cm²/min at 450°C. Rapid diffusion of HNO₃ is attributed to its intercalation as a two-dimensional liquid, whereas bromine and PdCl₂ intercalate as two-dimensional solids. Estimated diffusion coefficients of alkali graphites, which also intercalate as two-dimensional solids, are smaller than those for Br₂ or PdCl₂, but transition metal chlorides which intercalate from the vapor above the bulk melting temperature have estimated diffusion coefficients comparable to those of HNO₃. Rates of intercalation are linear functions of $\text{(time)}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ until intercalation by HNO₃ is 80% complete and intercalation by Br₂ is at least 23% complete, and indicate that a single diffusion process controls each reaction even though gross compositions corresponding to the formation of discrete crystallographic “stages” are exceeded. This result accords well with structural models of intercalation compounds in which monolayer “rafts” of intercalant take up ordered positions throughout the bulk of a graphite crystal, but not with models, in which intercalant monolayers continuously cover basal planes. The apparent activation energy for diffusion of PdCl₂ in graphite, 35 kcal/mole, is attributed to a process which precedes diffusion.     

硝酸-硝酸铵体系中DPT硝解制备HMX工艺研究

在硝酸-硝酸铵体系硝解3,7-二硝基-1,3,5,7-四氮杂双环[3,3,1]壬烷(DPT),制备HMX,通过正交实验确定最佳工艺条件。结果表明,最佳工艺条件为:10 mL硝酸与3 g硝酸铵配制硝解液,控制5℃下加入0.735 g DPT,保温溶解30 min,升温至25℃,反应40 min,HMX的平均收率为61.2%;各因素对HMX产率的影响顺序为:硝酸铵加入量>DPT加料温度>反应时间>反应温度。采用HPLC离线监测最佳工艺条件下的硝解反应,得到DPT和HMX浓度的变化规律,并对相关反应过程进行了推测。     

Stabilisation of low softening point petroleum pitch fibres by HNO3

This paper deals with the stabilisation of low softening point pitch fibres obtained from petroleum pitches using HNO₃ as oxidising agent. This method presents some advantages compared with conventional methods: pitches with low softening point (SP) can be used to prepare carbon fibres (CF), the stabilisation time has been reduced, the CF yields are similar to those obtained after general methods of stabilisation, and the initial treatments to increase SP when low SP pitches are used to prepare CF, are avoided. The parent pitches were characterised by different techniques such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), elemental analysis and solvent extraction with toluene and quinoline. The interaction between HNO₃ and the pitch fibres, as well as the changes occurring during the heat treatment, have been followed by DRIFTS.     

The surface analytical characterization of carbon fibers functionalized by H2SO4/HNO3 treatment

A systematic, time-dependent, surface-sensitive study has, for the first time, given new insights into the mechanism of the often-used, but unexplained, sulfuric/nitric acid oxidation of graphene-containing materials, such as carbon fibers and carbon nanotubes. We used X-ray photoelectron, photoacoustic FTIR and Raman spectroscopies to follow the evolution of the functionalization of carbon fibers sonicated in a 3:1 (v/v) mixture of concentrated acids at 60 °C. The study has revealed that oxidation occurs subsequent to acid attack, the attack serving to prepare sites for the ensuing oxidation, as witnessed by the presence of four O1s, two N1s and two S2p XPS peaks during the site preparation process. Their intensities varied discontinuously with treatment time, particularly in the early stages, rather than constantly increasing with time. Two of the O1s, and all the S2p and N1s peaks diminished in intensity with treatment time, eventually disappearing. The only nontransitory oxidized carbon functionality was COOH, confirmed by the two remaining O1s XPS peaks, which continued to increase long after the disappearance of the transitory species. This slow carboxylic acid production indicates that COOH formation is the rate-controlling step of the process, occurring subsequent to the site preparation initiated by the transitory species.     

The influence of process parameters on desulfurization of Mezino coal by HNO3/HCl leaching

Coal desulfurization prior to usage is a preprocessing in order to achieve clean fuel and reduce environmental impacts such as acid rain. Desulfurization of Tabas Mezino coal was conducted with two consecutive steps of froth flotation at ambient temperature followed by leaching at various conditions. Reducing the ash content of Mezino coal by 35.7 wt.% and its total sulfur content by 36.9% using froth flotation process was successful. HCl and HNO₃ were used, separately, to leach the floated coal, and the effectiveness of each acid on Mezino coal desulfurization was investigated. Nitric acid was found to be much more effective than HCl and the effects of reaction time, acid concentration and temperatures as well as stirring speed were studied as major parameters in the nitric leaching process. Taguchi orthogonal experiment with the above mentioned parameter elements; one at three levels was used to optimize the experiment parameters by the analysis of variances. Applying of the Taguchi technique significantly reduced the time and cost required for the experimental investigation. The findings indicated that acid concentration, with a high contribution, had the most dominant effect on desulfurization performance, followed by temperature, stirring speed and time. Accordingly, the optimum condition was obtained as, temperature: 90 °C., acid concentration: 30%., and stirring rate: 1000 rpm. The total sulfur and ash removal after flotation and leaching at optimum condition reached to 75.4 and 53.2% respectively that is a remarkable result compared to the previous works.     

The intercalation of C60-containing PEO into layered MnPS3

This paper reports the synthesis and magnetism of a new polymer-inorganic intercalation nanocomposite based on a C₆₀-containing poly(ethylene oxide) (C₆₀-PEO) into layered MnPS₃, which is characterized by XRD, IR and thermal analyses. The lattice expansion (Δd) of the intercalation nanocomposite is about 9.3 Å indicating the successful intercalation. And the charge balance is maintained by K⁺ ions coordinating with PEO chain of C₆₀-PEO polymer, which come from the pre-intercalation compound Mn_1−xPS₃[K_2x(H₂O)_y]. Magnetic measurements indicate that the intercalation nanocomposite (C₆₀-PEO/MnPS₃) exhibits a magnetic phase transition from paramagnetism to ferrimagnetism at about 40 K. And the distinctive hysteresis of M-H relationship further confirms that it is a low temperature ferrimagnetic nanocomposite.     

Electrostatic interactions during the intercalation of Li in Lix TiS2

A model for the electrostatic interactions between the Li⁺ ions and the conducting electrons in the layered compound Li_xTiS₂ is developed. Li_xTiS₂ is considered as a sandwich structure consisting of layers of a homogeneous dielectric separated by conducting planes. The Li⁺ ions intercalated in the van der Waal gaps are treated as point charges in the dielectric and their charges are screened by the conducting planes. By image technique the interaction energy can be calculated as the Madelung energy of an ionic crystal. Assuming an effective dielectric constant of 30 good agreement between the calculated and the experimental emf-x reaction is obtained. On this basis it is concluded that the strong deviations from ideality observed during intercalation of Li⁺ in Li_xTiS₂ are due to electrostatic forces screened by the conduction electrons.     

Synthesis and structural investigation of new graphite intercalation compounds containing the perfluoroalkylsulfonate anions C10F21SO3, C2F5OC2F4SO3, and C2F5(C6F10)SO3

The preparation of graphite intercalation compounds (GIC’s) of three perfluorinated alkylsulfonate anions, C₁₀F₂₁SO₃⁻, C₂F₅OC₂F₄SO₃⁻ and C₂F₅(C₆F₁₀)SO₃⁻ is described for the first time. Pure stage 2 GIC’s are obtained by chemical oxidation of graphite with K₂MnF₆ in a solution containing hydrofluoric and nitric acids for 72 h. One-dimensional electron density maps derived from powder diffraction data are fit to obtain models for the intercalate interlayer regions (galleries) structures: the structure models provide details on anion concentrations, orientations, and conformations. In all cases, anion bilayers are observed with anion sulfonate headgroups oriented towards graphene sheets. Compared with structures calculated for the isolated anions, the intercalated anion conformations show changes in dihedral angles, involving rotations about C-C or C-O bonds. For the GIC containing C₂F₅(C₆F₁₀)SO₃⁻, the anion conformation change is related to the more efficient packing of anions in the intercalate gallery.     

Preparation of Porous BaTiO3 PTC Thermistors by Adding Graphite Porosifiers

Using an ordinary ceramic processing technique, a new method of preparing porous BaTiO₃, PTC thermistors is introduced. Adding proper graphite powders into calcined BaTiO₃, powder can increase porosity and enhance the PTC effect of the sintered sample. When the graphite addition is about 1.0 wt%, the resisivity of samples from low-purity raw materials decreases to 20 Σ·cm at room temperature, while the PTC resistivity ratio is over 10⁵ and 1–2 orders higher than that of samples without the porosifier. The porosifier has increased the reproducibility of resistivity from 60% up to 90%. In addition, the porous thermistor has a fast response to overcurrent and shows some improvement in heat resistance. With the aid of the Heywang model and the Kuwabara conclusion, the influence of graphite on grain surfaces is discussed. The experimental results show that this method is a useful technique to prepare good PTC thermistors from low-purity raw materials.     

Carbon-based catalytic briquettes for the reduction of NO: Effect of H2SO4 and HNO3 carbon support treatment

The influence of treating carbon with sulphuric and nitric acids on the activity of a carbon-based briquette catalyst for NO reduction with NH₃ was examined in a fixed-bed reactor at low temperature (150 °C). The briquette catalysts were prepared from a low-rank coal and a commercial tar pitch. The active phase was impregnated from a suspension of ashes of coke petroleum by means of an equilibrium adsorption method. The catalytic behaviour of NO reduction over acid treated briquettes was found to vary with the surface characteristics of the carbon support. This suggests that the number of oxygen-containing sites as well as vanadium load and dispersion affect the reaction activity. In the presence of oxygen, the SCR activity is enhanced with a nitric acid treatment, activity is promoted by the presence of acidic surface groups such as carboxyl and lactone, which can help not only to create a reservoir of reactants on the catalysts surface but also to improve the dispersion or even increase the amount of vanadium loading. Therefore, the results of this study suggest that the formation of acidic sites on the surface is an important step for NO reduction with NH₃ over carbon-based catalysts. Additional techniques such as XPS and TPD to characterize the oxygen surface and those such as N₂ adsorption to characterize the textural properties were also used in this study.     

Improvement of structural and electrochemical properties of commercial LiCoO2 by coating with LaF3

Commercial LiCoO₂ has been modified with LaF₃ as a new coating material. The surface modified materials were characterized by X-ray diffraction (XRD), transmission electronic microscopy (TEM), field emission scanning electron microscopy (FE-SEM), auger electron spectroscopy (AES) and galvanostatic charge–discharge cycling. The LaF₃-coated LiCoO₂ had an initial discharge specific capacity of 177.4 mAh g⁻¹ within the potential ranges 2.75–4.5 V (vs. Li/Li⁺), and showed a good capacity retention of 90.9% after 50 cycles. It was found that the overcharge tolerance of the coated cathode was significantly better than that of the pristine LiCoO₂ under the same conditions – the capacity retention of the pristine LiCoO₂ was 62.3% after 50 cycles. The improvement could be attributed to the LaF₃ coating layer that hinders interaction between LiCoO₂ and electrolyte and stabilizes the structure of LiCoO₂. Moreover, DSC showed that the coated LiCoO₂ had a higher thermal stability than the pristine LiCoO₂.     

Controlled generation of oxygen functionalities on the surface of Single-Walled Carbon Nanotubes by HNO3 hydrothermal oxidation

The surface chemistry of Single-Walled Carbon Nanotubes is finely tailored by a HNO₃ hydrothermal method. Temperature Programmed Desorption analysis is used to determine the nature and amount of different oxygenated functionalities, which are introduced in a controlled mode. The degree of oxygen functionalization is correlated with HNO₃ concentration through a mathematical function. Operating temperature and HNO₃ concentration are key parameters in the modification of the surface chemistry, in accordance with previous results obtained with a carbon xerogel subjected to the same hydrothermal treatment. A detailed comparison between the results obtained with both materials indicates that the yield of the HNO₃ hydrothermal functionalization strongly depends on the texture of the carbon material that is used.     

Critical Surface Energies of Al2O3 and Graphite

Based on the wetting properties of a -Al₂O₃, and pyrolytic graphite by liquid metals, the critical surface energy for spreading was determined and compared with the surface energy of the ceramics. The surface energy γ-₈ (ergs/cm²) of the (0001) surface of a -Al₂O₃ is estimated to be 892–0.12 T (°C), that of the c plane of pyrolytic graphite 1139–0.13 T (°C), and that of the a plane of pyrolytic graphite 1300–0.17 T (°C). Also, the liquid-solid interfacial energies were calculated and found compatible with the values reported in the literature. The surface energy of liquid Ag or liquid Cu is not significantly affected by carbon.     

Influence of HNO3 oxidation on the structure and adsorptive properties of corncob-based activated carbon

An investigation of the impact of strong oxidation with HNO₃ on the porosity and adsorption characteristics of char and activated carbons, derived from corncobs, is presented. Texture parameters, as obtained from N₂ adsorption at 77 K, showed a considerable decrease in surface area of the activated carbons with enhanced pore widening. The extent of porosity modification was found to depend on the scheme of activation of the precursor, simple carbonization, steam pyrolysis, steam gasification of the char, or chemical activation with H₃PO₄. Surface-chemical changes were detected by FTIR spectroscopy, where absorption bands assigned to carboxyl, carboxylate, carbonyl, and phenolic groups were observed. A SEM study demonstrated the erosive effect of HNO₃, detected by the presence of disintegration of the carbon grains, with the porous structure probably containing very large macropores. As a consequence of the oxidation process, elemental analysis showed high contents of O, H and N, and TG confirmed that the weight loss distribution in the thermogram becomes slower at higher temperatures. The removal of phenol decreased as a result of the formation of oxygen functionalities. Mono-nitrophenols were adsorbed in smaller amounts than phenol, and p-nitrophenol showed a relatively higher uptake than the other two mono-nitrophenols, whereas the uptake of Methylene Blue was improved. Removal of Pb²⁺ from aqueous non-buffered solution was considerably enhanced by chemical oxidation, which may be related to pore widening, increased cation-exchange capacity by oxygen groups, and the promoted hydrophilicity of the carbon surface.