高粱秸秆热解产物的研究

研究了热解温度、气体流量、加热速率和保温时间三个操作因素对高粱秸秆热解产物(生物油和残炭)分布的影响。结果表明,对高粱秸秆热解产物的分布有很大影响的因素是热解温度和气体流速。在热解升温速率为10℃/min、热解温度为450℃,氮气流速为100mL/min、保温时间为1h的条件下,液体收率最高。     

A meltable precursor for zirconium carbide ceramics and C/C-ZrC composites

For process simplification and rapid densification of ceramic composites, a meltable single-source ZrC precursor was prepared by condensing zirconium acetylacetonate (Zr(acac)₄) at 190?°C for 40–150?min. The preparation of ZrC precursor and the conversion from precursor to ceramics were investigated by using FTIR and NMR spectroscopies, GPC, DSC-TGA, XRD, SEM, EDS and TEM. The precursor had low viscosity (~ 10?mPa?s) and proper processing window (60?min) for precursor infiltration and pyrolysis (PIP). The ceramic yield at 1650?°C was 29.6%, and EDS revealed that the composition was (ZrC)_0.337(HfC)_0.0025(ZrO₂)_0.044C_0.1865. The ceramics were composed of 0.2–0.5?µm grains which aggregated to form a stacked structure surrounded by amorphous carbon. The preparation processes were designed, and C/C-ZrC composites with the density of 2.45?g/cm³ were successfully fabricated through 11 cycles of PIP with Zr(acac)₄. In conclusion, the synthetic method provides a simple and cheap route for precursors, and allows combined composite preparation with high efficiency.     

C_(60) 对 NC、RDX 热分解作用的探讨

通过ＤＳＣ热分析实验，探讨富集物、Ｃ６０、炭黑三种物质对ＮＣ、ＲＤＸ的热分解的影响，研究发现它们都不同程度地提高了ＮＣ、ＲＤＸ的分解热值，特别是球烯分子的富电特性有利于催化剂铅盐的活化，Ｃ６０和单质铅可能生成一种络合物，它既能作为气相反应中的催化载体，又具有良好的催化作用。     

Synthesis,characterization, and ceramization of a carbon-rich SiCw-ZrC-ZrB2 preceramic polymer precursor

A precursor (PBSZ) for SiC_w-ZrC-ZrB₂ hybrid powder was synthesized by chemical reaction of phenol, paraformaldehyde, zirconium oxychloride, boric acid and tetraethylorthosilicate. Results show that zirconium, silicon and boron atoms have been successfully introduced into the branched structure. Decomposition of PBSZ is completed at 800 °C, and it gives amorphous carbon, SiO₂, B₂O₃ and ZrO₂ with a yield of 38% at 1200 °C. During the pyrolysis process, ZrB₂ and SiC form at about 1500 °C, followed by the appearance of ZrC when the amount of B₂O₃ is limited. Highly crystallized ZrB₂–ZrC–C powder with ZrB₂ and ZrC grains evenly distributed in the carbon matrix together with randomly distributed SiC whiskers are obtained after heat-treated at 1800 °C. Further heated at 1900 °C, ZrB₂ and ZrC grains grow from 200 to 500 nm, while SiC whiskers show a much smaller diameter size and tend to grow on the ZrB₂–ZrC–C block surface. The morphology difference is caused by the larger gas supersaturation and accommodation coefficient of the pore channels on the block surface. In addition, defects of the carbon matrix are cumulated to the highest at 1500 °C and the structure-ordered carbon is obtained after heat treated at 1900 °C.     

Preparation and characterization of the carbonized material of phenol-formaldehyde resin with addition of various organic substances

We prepared carbonized materials of phenol-formaldehyde resins (PF) synthesized with the addition of organic substances such as ethylene glycol (EG), 1,6-hexanediol (1,6HD), polyethylene glycol (PEG), etc. We investigated the influence of the carbonization temperature, the organic additive species, and the additive ratio in synthesizing the PF resins on the pore structure of the carbonized PFs. Variation in the length of the added organic substance caused differences in the pore sizes of the carbonized PFs; when the length was short, the pore size of the carbonized PF became gradually smaller with increasing carbonization temperature, but when the length was long, the pore size gradually increased with increasing carbonization temperature. The difference in the additive organic species gave different pore sizes in the carbonized PFs such that the longer the length of the organic additive the greater the pore size in the carbonized PF. The additive ratio of EG did not give a large change in the pore size of the carbonized PF, but the variance in the average pore sizes were sharper than that of the carbonized PF without any additives. On the other hand, the pore sizes of the carbonized PFs with a high additive ratio of PEG20K were greater, and the carbonized PFs had mesopores. The BET surface area of the carbonized PFs with a 50% additive ratio of PEG20K was about 500 m²/g.     

Chemistry of the co-pyrolysis of an aromatic petroleum residue with a pyridine-borane complex

Synthesis of boron-doped mesophase by controlled co-pyrolysis of an aromatic petroleum residue and a pyridine-borane complex, PB, as a boron source, was carried out. Pyrolysis was performed at temperatures ranging from 400 to 440 °C, under 1 MPa nitrogen atmosphere. Soaking time was varied between 1.5 and 6 h, and the boron concentration in the pyrolysis mixtures ranged from 0 to 1 wt.%. The effect of the presence of boron upon solid yield, insoluble content, mesophase development and microstructure was studied. PB reacts with molecules of the petroleum residue and creates B-C bonds, B substituting C in the polyaromatic molecules, with sp² hybridisation, and probably also creating B crosslinking between polyaromatic units. The enhanced reactivity caused by B addition is reflected in an increment of viscosity; as a result, the development of mesophase is strongly increased, but the size of the mesophase structures is decreased to a mosaic texture; B also causes an increase of the interlayer spacing and a noticeable enhancement of insoluble material.     

油酸甲酯和硬脂酸甲酯热解特性及动力学研究

通过热重分析仪对油酸甲酯和硬脂酸甲酯的热解特性进行了研究,发现油酸甲酯相变硬脂酸甲酯具有较差的热安定性。在升温速率分别为10、15、20、30℃/min条件下,利用TG-DTG曲线分析了它们的基本热解特性。结果表明,随着升温速率的增加,它们的起始热分解温度、最大失重速率、最大失重速率峰值温度以及其他热分解参数均呈增大趋势。同时,用多元线性回归法求得相应的反应级数、活化能和指前因子,发现油酸甲酯和硬脂酸甲酯的热解反应机理函数不同,且反应活化能和指前因子之间表现出较好的动力学补偿效应。     

Synthesis,composition and spin-dynamics of FCC and HCP phases of pyrolysis derived Co-nanoparticles embedded in amorphous carbon matrix

We report the structure, magnetic domain state and spin dynamics of biphasic Co nanoparticles embedded in amorphous carbon matrix. Two types of samples were synthesized by heating the precursors (Co-acetylacetonate and toluene) from RT to the pyrolysis reaction temperature (800 °C) at two different heating rates, viz. ∼ 3 °C/min and ∼20 °C/min. We observe that the sample prepared at higher heating rate (∼20 °C/min) predominantly contains fcc-phase of Co in the Co-nanoparticles, whereas the sample synthesized at lower heating rate exhibits higher amount of the hcp-phase-content in the Co-nanoparticles. The Co-nanoparticles are surrounded by graphitic carbon layers forming core-shell type morphology. The hcp-phase of Co is characterized by a higher saturation magnetization and coercivity (higher magnetic hardness) than the fcc-phase. The nature of the measured hysteresis loop in combination with the estimated critical size for the particles to be in a single magnetic domain state suggest that both hcp and fcc-phases of Co coexist in the same particle and most of the particles are multidomain-particles. Furthermore, our results reveal that the dynamics of the spins present at the grain boundaries are the slowest followed by those in the fcc-phase and hcp-phase of Co. The dynamics of the spins present at the domain walls are slower than those inside the magnetic domains. The responsive nature of the spins on the domain walls in comparison to those inside the domains leads to the so called domain wall enhancement effect.     

Fabrication of ceramic particles from preceramic polymers using stop flow lithography

Stop flow lithography (SFL) combines aspects of microfluidic and photolithography to continuously fabricate particles with uniform planar shapes as dictated by a mask. In this work we aim to expand the palette of materials suitable for SFL processing by investigating the use of UV-crosslinkable preceramic polymers to make ceramic particles. A commercially available methacrylated-polysiloxane was used as the preceramic polymer and was mixed with 2.5 wt% Irgacure 651 photoinitiator. A simple SFL system was assembled to continuously fabricate UV-crosslinked preceramic polymer particles in the shape of hexagons, triangles, and gears with diameters ranging from 100 to 200 μm and thicknesses of 74 μm +/- 4 μm. Particles were harvested from the excess preceramic solution, cleaned and then pyrolyzed at 1000 °C to transform them into silicon oxycarbide ceramic particles. Particle shape was maintained during pyrolysis despite a ～80 % linear shrinkage due to the removal of acryl and methyl side groups, as confirmed via FTIR. After pyrolysis the outer diameters of the SiOC particles ranged from 20 to 40 μm with thicknesses of 10 μm–12 μm. Pyrolyzed particles were successfully recovered and dispersed in water. This work demonstrates a robust path for the fabrication of ceramic particles with specific shapes from preceramic polymers via SFL.