Micro-/nanostructure evolution of C/SiFeO(N,C) polymer-derived ceramic papers pyrolyzed in a reactive ammonia atmosphere

SiFeO(N,C)-based ceramic papers were prepared via a one-pot synthesis approach by dip-coating a cellulose-based paper template with a polymeric perhydropolysilazane precursor modified with iron(III)acetylacetonate. The preceramic composites were subsequently pyrolyzed in ammonia atmosphere at 500, 700, and 1000°C, respectively, and the characteristics of the three resulting ceramic papers were comparatively investigated. Scanning electron microscopy revealed that in each sample, the morphology of the template is successfully transferred on the ceramic system, with the cellulose-derived fibers being converted to elemental carbon encased by a SiFeO(N,C) coating. Electron transparent cross-sectional samples for transmission electron microscopy (TEM) were prepared from the ceramic papers, employing a standard ultramicrotomy slice cutting procedure, allowing for a detailed characterization of their in situ generated micro-/nanostructure as well as occurring crystalline phases. TEM imaging and diffraction revealed that depending on pyrolysis temperature a different microstructure with a distinct phase assemblage is generated in the polymer-derived ceramic papers. Crystallization from the polymer precursor starts with the precipitation of wüstite (Fe_(1-x)O) nanoparticles at 700°C inside the ceramic coating and secondary ε-Fe_xN at the fiber-coating interface. Upon pyrolysis at 1000°C however, the sample primarily accommodates metallic α-iron nanocrystals that impart ferromagnetic characteristics to the ceramic paper. The results show that the template-assisted polymer-derived ceramic route is a feasible approach in the production of complex ceramic compounds with fibrous paper-like morphology. By adjusting the pyrolysis temperature, microstructure and phase composition of the ceramic paper can be conveniently tailored to the needs of its respective application.     

Characterization of plastic-bonded explosives by pyrolysis gas chromatography and multivariate data analysis. Part I: Setup of the method

A further development of the procedure based on pyrolysis gas chromatography (Py-GC) for the characterization of plastic-bonded explosives (PBX's) is described. After grinding, the PBX samples were pressed on a pyrolysis wire followed by Py-GC analysis. The peak areas obtained were normalized and subsequently submitted to multivariate data analysis. The use of principal component analysis (PCA) was tested on five samples which differed slightly in composition and age. The results were promising and showed that PCA is a powerful tool for the differentiation between PBX samples. The pyrolysis conditions were examined and optimized. A dependency was found between the sample loading (mass) and the position of the samples in a PCA score plot and indicates that control of the sample loading is important in obtaining reproducible results. For PBX samples an optimum pyrolysis temperature was determined around 540°C, close to the previous selected pyrolysis temperature of 610°C. In examining the pyrolysis at lower temperatures it was found that RDX or HMX is pyrolyzed independently from the binder. It appeared that PBX samples were inhomogeneous despite a thorough mixing of the constituents during preparation.     

Synthesis,characterization, and pyrolysis of ferrocenyl unit containing organosilicon polymers

New polyferrocenylsiloxanes (PFSXs) and polyferrocenylsilazanes (PFSZs) with linear or linear‐cyclic structure were prepared. The ceramic yields of the polymers were estimated by thermogravimetric analysis (TGA) and bulk pyrolysis, which closely depend on molecular structures. Compared with that of their linear counterparts having comparable molecular weights, the ceramic yields of linear‐cyclic PFSX and PFSZ were much higher. The pyrolysis process was investigated by lysis character is (TGA) highly depend on their molecular weights and structures, infrared spectra, and pyrolysis‐gas chromatography‐mass spectra (Py‐GC‐MS) analysis. The results indicated rather amount of ferrocene‐based small molecules were formed during the pyrolysis of linear polymers in the range of 25–300°C, whereas the existence of crosslinking or branched structure in the linear‐cyclic polymers prohibited this transformation, and therefore, dramatically improved the ceramic yields. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of nano-aluminum filler on the microstructure of SiOC ceramics

Ceramic SiC-mullite-Al₂O₃ based nanocomposites were successfully obtained at temperatures below 1500 °C after pyrolysis and annealing of green compacts prepared by cross-linking and shaping in a warm press step of commercial poly(methylsilsesquioxane) MK polymer mechanically mixed with aluminum filler having nanoparticle size. The heat treatment takes place under the exclusion of oxygen (inert argon atmosphere) and temperatures as low as 800 °C initiate the crystallization of a silicon carbide phase. The influence of the nano-aluminum filler and of the pyrolysis temperature on the crystallization behavior of the materials has been investigated. It was confirmed that an appropriate amount of nano-aluminum filler leads to a cristobalite free bulk SiOC ceramic. In consequence, the received ceramic samples have to be considered as a nano/micro-ceramic composite consisting of crystals of mullite (average dimension in the range of 200 nm), silicon carbide (20 nm) and α-alumina (50 nm).     

Preparation of Silicon Carbonitrides from an Organosilicon Polymer: I, Thermal Decomposition of the Cross-linked Polysilazane

The conversion of a solid copolymer (ViSiHNH)_x─(MeSiHNH)_y into a ceramic was studied in the 20–1450°C temperature range under different atmospheres (inert or oxidative). The ceramic yield, the ceramic composition, and the gaseous evolution directly depend on the heating rate, the pyrolysis atmosphere, and the duration of pyrolysis. The implications of these observations to the pyrolysis mechanism are discussed. The silicon carbonitride obtained after pyrolysis is amorphous up to 1400°C with high carbon content. It will be shown in Parts II and III that either SiC or Si₃N₄ could be selectively crystallized depending upon processing conditions.     

Process characteristics investigation of simulated circulating fluidized bed combustion combined with coal pyrolysis

A poly-generation process of simulated circulating fluidized bed (CFB) combustion combined with coal pyrolysis was developed in a laboratory scale. Pyrolysis characteristics of three bituminous coals with high volatile contents were investigated in a fixed bed with capacity of 10 kg solid samples. The effects of initial temperature of solid heat carrier, pyrolysis holding time, blending (ash/coal) ratio and coal particle size on gas and tar yields were studied experimentally. The results indicate that the initial temperature of the heat carrier is the key factor that affects the gas and tar yield, and the gas composition. Most of the gas and the tar are released during the first few minutes of the pyrolysis holding time. For caking coal, the amount of char agglomerating on the pyrolyzer inner wall is reduced by enhancing the blending ratio. The experimental results may provide basic engineering data or information for the process design of CFB combustion combined with coal pyrolysis in a large scale.     

Ceramization of Reflux-Treated Polymethylsilane Precursors to Silicon Carbide

The pyrolysis of polymethylsilane (PMS) in an argon gas environment with a flow rate of 1 L/min was investigated as a standard pyrolytic process, and the investigation showed SiSi network formation at 573 K. Subsequently, various condensed PMS resins were prepared by adjusting pre-heat-treatment or reflux conditions in the temperature range of 423–723 K. The effect of pre-heat treatment or refluxing on the ceramic yield at 1273 K was quantitatively evaluated. Structural evolution in the PMS resins prepared under various reflux conditions was investigated during pyrolysis up to 1873 K. The X-ray diffraction patterns of the pyrolysis products revealed crystallite growth of β-SiC and silicon at 1273–1473 K. ²⁹Si solid-state nuclear magnetic resonance with the single-pulse method was also conducted on the pyrolysis products at 1273 K.     

Understanding the influence of microwave on the relative volatility used in the pyrolysis of Indonesia oil sands

In this paper, pyrolysis of Indonesian oil sands(IOS) was investigated by two different heating methods to develop a better understanding of the microwave-assisted pyrolysis. Thermogravimetric analysis was conducted to study the thermal decomposition behaviors of IOS, showing that 550 °C might be the pyrolysis final temperature. A explanation of the heat–mass transfer process was presented to demonstrate the influence of microwave-assisted pyrolysis on the liquid product distribution. The heat–mass transfer model was also useful to explain the increase of liquid product yield and heavy component content at the same heating rate by two different heating methods. Experiments were carried out using a fixed bed reactor with and without the microwave irradiation. The results showed that liquid product yield was increased during microwave induced pyrolysis,while the formation of gas and solid residue was reduced in comparison with the conventional pyrolysis. Moreover, the liquid product characterization by elemental analysis and GC–MS indicated the significant effect on the liquid chemical composition by microwave irradiation. High polarity substances(ε N 10 at 25 °C), such as oxyorganics were increased, while relatively low polarity substances(ε b 2 at 25 °C), such as aliphatic hydrocarbons were decreased, suggesting that microwave enhanced the relative volatility of high polarity substances. The yield improvement and compositional variations in the liquid product promoted by the microwave-assisted pyrolysis deserve the further exploitation in the future.     

热解温度及AAEM元素对生物质快速热解焦油的影响

生物质热解受热解温度、热解速率和碱金属及碱土金属(AAEM)元素影响显著。利用热裂解气相色谱质谱联用法(Py-GC/MS)针对热解温度及AAEM元素对生物质快速热解焦油的影响展开深入研究,通过样品热解前后的失重情况分析了热解温度及AAEM元素对生物质(稻壳和木屑、酸洗稻壳和酸洗木屑)热解特性的影响规律,利用气相色谱质谱仪(GC/MS)对热解焦油组分及含量进行了在线半定量分析,并对热解焦油组分分子量分布情况展开了讨论。结果表明生物质Py-GC/MS快速热解实验,酸洗脱除AAEM元素致使热解失重率减小。500~900℃范围内随温度的升高,大分子焦油成分逐渐减少,逐渐转化为轻质组分。AAEM元素限制了焦油前体的聚合,进一步抑制了含氧杂环类碳环(糠醛等)的生成。稻壳的热解焦油的相对分子质量主要分布在110~129。木屑快速热解焦油产率明显高于稻壳,且热解焦油中分子量分布广泛,含有更多较大分子量(150~209)的化合物成分。     

Phenolic compounds from vacuum pyrolysis of wood wastes

Various softwood and hardwood bark residues, primary sludges and softwood sawdust residues were processed by vacuum pyrolysis in a laboratory scale batch reactor. The pyrolysis oil, water, charcoal, and gas were recovered and analyzed. The pyrolysis oils were analyzed in details for their content in phenolic compounds after derivatization to their acetyl derivatives. The influence of temperature, heating rate, feedstock bed thickness, particle size and feedstock water pretreatment on the yield of phenols was investigated. The highest yield of phenols was obtained when hardwood bark was soaked in water for 48 hours and pyrolyzed at a temperature of 450°C and a heating rate of 10°C/min. Pyrolysis performance was evaluated in terms of total phenolic yield and composition.     

Investigation of Strut Crack Formation in Open Cell Alumina Ceramics

An investigation was made into the source of strut cracking during the fabrication process of open cell ceramics that are produced by coating a polymeric foam. Several sources for the stress that produces these cracks were considered, viz., differential drying, thermal expansion mismatch between the polymer and the green ceramic coating, and the gas pressure produced by pyrolysis of the organic skeleton. Thermogravimetric analysis of the polymeric foam was used to estimate the gas evolution rate associated with the pyrolysis process, but this was found to be very low compared to the pressures required to cause strut damage. SEM observations on samples taken by interrupting the fabrication procedure showed the cracks were not produced during drying but rather at a temperature near the melting/decomposition point of the polymer and prior to pyrolysis. It was then deduced that the differential thermal expansion between the polymer and the ceramic coating was the source of the stress. The strut cracking is observed to occur primarily in the region of the highly curved strut edges of the polymer foam, at which the ceramic coating is often rather thin. Techniques to change the processing procedure to overcome the strut cracking are discussed.     

The effect of mineral matter on the physical and chemical activation of low rank coal and biomass materials

The effect of inorganic constituents on the thermal behaviour of low rank coals, as well as agricultural and forestry by-products, during pyrolysis and combustion processes was investigated. Selective demineralization of each fuel with acids was used. Raw and demineralized samples were analyzed for ash content and composition (mineralogical and chemical), surface area and porosity, as well as thermal conversion characteristics in inert and air atmospheres. Reactivity and kinetic experiments were performed by non-isothermal thermogravimetry, over the temperature range of 25–850 °C, at a heating rate of 10 °C/min and with a material particle size of −250 μm. The extent of mineral matter removal from the materials studied, ash composition and structural characteristics depended upon the type of the fuel and the method of acid treatment. Generally, calcium, magnesium, potassium and silicon minerals acted as inert materials, inhibiting the pyrolysis and combustion rates of the samples. However, they increased the sensitivity of the reactions, by lowering the peak temperatures. A first-order parallel reactions model for pyrolysis and a power low model for combustion fitted the experimental results accurately. Mineral matter had a small influence on the kinetic parameters of biomass samples, but appeared to hinder the overall process in the case of the coals.     

Pyrolysis of polystyrene-poly(2,6-dimethyl-1,4 phenyleneoxide) mixtures and graft copolymers

The influence of poly(2,6-dimethyl-1,4-phenyleneoxide) [PPO] on the thermal degradation of polystyrene [PS] has been investigated over the whole range of admixed homopolymer contents and for selected compositions of grafted copolymers of PS chains on PPO. The styrene yield on pyrolysis at 350–650°C was measured. The results are discussed in terms of the miscibility of the system and its influence on the course of pyrolysis, i.e., on participation of competitive processes in the overall mechanism of PS degradation. On the basis of the data, regression equations for the dependence of styrene concentration on the composition of the mixture were determined and the results show that the styrene content at pyrolysis near 500°C does not depend on the molecular interaction of the PS-PPO system. It is demonstrated that pyrolysis and gas chromatography can be used for determination of the composition of polymer mixtures and of copolymers.     

Influence of carbon enrichment on electrical conductivity and processing of polycarbosilane derived ceramic for MEMS applications

An analysis about the effect of carbon enrichment of allylhydridopolycarbosilane SMP10^® with divinylbenzene (DVB) as a promising material for electrical conductive micro-electrical mechanical systems (MEMS) is presented. The liquid precursors can be micropipetted and cured in polytetrafluoroethylene (PTFE) molds to produce 14 mm diameter disc shaped samples. The effect of pyrolysis temperature and carbon content on the electrical conductivity is discussed. The addition of 28.7 wt.% of DVB was found to be the optimum amount. Carbon was preserved in the microstructure during pyrolysis and the ceramic yield increased from 77.5 to 80.5 wt.%. The electrical conductivity increased from 10⁻⁶ to 1 S/cm depending on the annealing temperature. Furthermore, the ceramic samples obtained with this composition were found to be in many cases crack free or with minimal cracks in contrast with the behavior of pure SMP10. Using the same process we demonstrate that also microsized ceramic samples can be produced.     

The effect of hydrothermal pretreatment on the structure and fast pyrolysis behaviors of ShengLi lignite

The structure and composition of coal determine its fast pyrolysis characteristics,and the study of the relationship between them can play an important role in the efficient and clean utilization of coal.So,in this work,hydrothermal pretreatment was used to artificially change the structure and composition of ShengLi (SL) lignite,which was used to investigate the influence of structural changes on pyrolysis.The physicochemical structure and composition of samples were characterized by X-ray diffraction,specific surface area and porosity analyzer,solid-state 13C nuclear magnetic resonance,Fourier transform infrared spectroscopy,and elemental analyzer.Pyrolysis experiments were carried out in a powder-particle fluidized bed reactor,and the distribution and composition of the pyrolysis products were ana-lyzed.The gasification activity of char was investigated by thermogravimetric analysis with a CO2 atmo-sphere.The results show that hydrothermal pretreatment (HTP) can destroy the cross-linking structure of SL lignite,and affect its aromaticity,pore structure,functional group,and carbon structure to change the distribution and composition of pyrolysis products of SL lignite,especially the composition of tar.Finally,the structure-activity relationship between the structure,composition,and pyrolysis characteristics of coal was comprehensively studied.     

Structure–property relationship in copolymers of methacrylic acid esters. I. Thermal behavior

This article describes the synthesis and thermal characterization of copolymers of methyl methacrylate (MMA) and alkyl methacrylates. The copolymerization was carried out using different mol fractions (0.05–0.25) of alkyl methacrylates, i.e., octyl methacrylate (OMA)/decyl methacrylate (DMA)/lauryl methacrylate (LMA)/stearyl methacrylate (SMA), in the initial feed at 80°C. The copolymer composition was determined from ¹H-NMR. The thermal stability of the copolymers was investigated by thermogravimetric analysis and pyrolysis gas chromatography. A two/three-step degradation was observed in the copolymer samples. The monomers were the major product of degradation in most of the copolymers except in SMA/MMA copolymers where the product of side-group elimination was also observed. An attempt was also made to determine the yield of the monomers during degradation and then to evaluate the copolymer composition. © 1994 John Wiley & Sons, Inc.     

Upgrading of derived pyrolysis vapors for the production of biofuels from corncobs

A bubbling fluidized bed pyrolyzer was integrated with an in-situ honeycomb as a catalytic upgrading zone for the conversion of biomass to liquid fuels. In the upgrading zone, zeolite coated ceramic honeycomb (ZCCH) catalysts consisting of ZSM-5 (Si/Al=25) were stacked and N₂ or recycled non-condensable gas was used as a carrier gas. Ground corncob particles were fast pyrolyzed in the bubbling bed using fine sand particles as a heat carrier and the resulting pyrolysis vapors were passed on-line over the catalytic upgrading zone. The influence of carrier gas, temperature, and weight hourly space velocity (WHSV) of catalyst on the oil product properties, distribution and mass balance were studied. Using ZCCH effectively increased the hydrocarbon yield and the heating value of the dry oil, especially in the presence of the recycled noncondensable gas. Even a low usage of zeolite catalyst at WSHV of 180 h⁻¹ was effective in upgrading the pyrolysis oil and other light olefins. The highest hydrocarbon (≥C2) and liquid aromatics yields reached to 14.23 and 4.17 wt-%, respectively. The undesirable products including light oxygenates, furans dramatically decreased in the presence of the ZCCH catalyst.     

TG-FTIR characterization of coal and biomass single fuels and blends under slow heating rate conditions: Partitioning of the fuel-bound nitrogen

The devolatilization behavior of a bituminous coal and different biomass fuels currently applied in the Dutch power sector for co-firing was experimentally investigated. The volatile composition during single fuel pyrolysis as well as during co-pyrolysis was studied using TG-FTIR characterization with the focus on the release patterns and quantitative analysis of the gaseous bound nitrogen species. It was shown that all investigated biomass fuels present more or less similar pyrolysis behavior, with a maximum weight loss between 300 and 380 °C. Woody and agricultural biomass materials show higher devolatilization rates than animal waste. When comparing different fuels, the percentage of fuel-bound nitrogen converted to volatile bound-N species (NH₃, HCN, HNCO) does not correlate with the initial fuel-N content. Biomass pyrolysis resulted in higher volatile-N yields than coal, which potentially indicates that NO_x control during co-firing might be favored. No significant interactions occurred during the pyrolysis of coal/biomass blends at conditions typical of TG analysis (slow heating rate). Evolved gas analysis of volatile species confirmed the absence of mutual interactions during woody biomass co-pyrolysis. However, non-additive behavior of selected gas species was found during slaughter and poultry litter co-pyrolysis. Higher CH₄ yields between 450 and 750 °C and higher ammonia and CO yields between 550 and 900 °C were measured. Such a result is likely to be attributed to catalytic effects of alkali and alkaline earth metals present in high quantity in animal waste ash. The fact that the co-pyrolysis of woody and agricultural biomass is well modeled by simple addition of the individual behavior of its components permits to predict the mixture's behavior based on experimental data available for single fuels. On the other hand, animal waste co-pyrolysis presented in some cases synergistic effects in gas products although additive behavior occurred for the solid phase.     

毒重石制氢氧化钡的热分解实验研究

毒重石的热分解率严重影响氢氧化钡的收率。研究了高温分解毒重石钡矿,经热水浸取制备氢氧化钡工艺条件,考察了温度、压力、粒径、添加剂和气氛对分解率的影响。结果表明,毒重石钡矿颗粒粒径较小时,有利于降低分解温度,粒径在150 μm以下时,理想分解温度为1 373.15 K;通过加入石墨等含碳添加剂能大幅提高碳酸钡分解率;通入氩气来改善炉膛的气氛,减小反应生成的一氧化碳、二氧化碳浓度对提高毒重石分解率效果不大,当通入氩气流量为0.5 m³/h时,分解率仅提高2.55%。在真空烧结炉中（绝对压力5 Pa）煅烧钡矿能大幅提高分解率和降低分解温度,最佳分解温度为1 273.15 K,钡转化率达82.3%。较低的分解压力和较少的二氧化碳气氛有利于毒重石热分解。     

Investigation on initial stage of rapid pyrolysis at high pressure using Taiheiyo coal in dense phase

Rapid pyrolysis of Taiheiyo coal was investigated with a laboratory-scale batch type reactor (BTR), which was specially developed to study various gasification processes at the conditions close to an industrial entrained bed gasifier. The experiments were carried out in helium at 1073 K, 7.1 MPa, varying reaction times from 1 to 80 s and coal/gas ratios in the range of 0.41-1.65 g/l. Extents of pyrolysis and profiles of product formation were discussed based on the results of char yield, gas and tar formation characteristics. It was observed that reaction of pyrolysis was significantly affected by coal/gas ratio. At high coal/gas ratios, pyrolysis was found to be retarded at initial stage. Pyrolysis products can be roughly divided into two groups. One is the ultimate products such as methane, carbon oxides, hydrogen, and benzene and the other is the intermediate products such as ethylene and toluene. Heat supply inside BTR was examined and the influence of thermal properties of atmospheric gases was investigated by carrying out pyrolysis in nitrogen and by comparing the results with that in helium. As a result, the heat capacity of atmospheric gas has less influence on pyrolysis process whereas heat conductivity of atmospheric gas as well as mixing conditions of gas and coal sample significantly affect the pyrolysis reaction.