Influence of pyrolytic carbon coatings on complex permittivity and microwave absorbing properties of Al_2O_3 fiber woven fabrics

The pyrolytic carbon （PyC） coatings were fabricated on A1203 fiber fabrics by the method of chemical vapor deposition （CVD）. The microstructures of A1203 fibers with and without PyC coatings were characterized by SEM and Raman spectroscopy. The influence of deposition time of PyC on the DC conductivity （ad） of A1203 filaments and complex permittivity of fabrics at X band （8.2-12.4 GHz） were investigated. The values of Crd and complex permittivity increase with increasing deposition time of PyC. The electron relaxation polarization and conductance loss were supposed to be contributed to the increase of ε＇ and ε＂, respectively. In addition, the reflection loss （RL） of fabrics was calculated. The results show that the microwave absorbing properties of Al2O3 fiber fabrics can be improved by PyC coatings. The best RL results are for 60 min-deposition sample, of which the minimum value is about -40.4 dB at about 9.5 GHz and the absorbing frequency band （AFB） is about 4 GHz.

Effect of Catalyst Properties on Hydrocracking of Pyrolytic Lignin to Liquid Fuel in Supercritical Ethanol

The metal-acid bifunctional catalysts have been used for bio-oil upgrading and pyrolytic lignin hydrocracking. In this work, the effects of the metal-acid bifunctional catalyst prop- erties, including acidity, pore size and supported metal on hydrocracking of pyrolytic lignin in supercritical ethanol and hydrogen were investigated at 260 ℃. A series of catalysts were prepared and characterized by BET, XRD, and NHa-TPD techniques. The results showed that enhancing the acidity of the catalyst without metal can promote pyrolytic lignin poly- merization to form more solid and condensation to produce more water. The pore size of microporous catalyst was smaller than mesoporous catalyst. Together with strong acid- ity, it caused pyrolytic lignin further hydrocrack to numerous gas. Introducing Ru into acidic catalysts promoted pyrolytic lignin hydrocracking and inhibited the polymerization and condensation, which caused the yield of pyrolytic lignin liquefaction product to increase significantly. Therefore, bifunctional catalyst with high hydrocracking activity metal Ru supported on materials with acidic sites and mesopores was imperative to get satisfactory results for the conversion of pyrolytic lignin to liquid products under supercritical conditions and hydrogen atmosphere.

Effects of Preform and Pyrolytic Carbon Structure on Thermophysical Properties of 2D Carbon／Carbon Composites

Four kinds of carbon/carbon (C/C) composites, including the needled carbon fiber felt/the pyrolytic carbon (two different pyrolytic carbon microstructures), the chopped carbon fiber/the resin + pyrolytic carbon (PyrC), and the carbon cloth/PyrC, named as the composites 1#, 4#, 2#, and 3#, are prepared respectively. Effects of the preform and pyrolytic carbon structure on the thermophysical properties of 2D C/C composites are studied. The C/C composites possess low coefficient of thermal expansion (CTE). In a range of some temperatures, the negative expansion emerges in x-y direction for four C/C composites. From 0 to 900℃, the CTE is small and almost linear with the temperatures. The C/C composites have high thermal conductivities (TCs). As a function of temperature, TCs of the C/C composites are varied with the structures of preform and pyrc as well as the direction of heat transfer. In x-y and z direction, TCs differ greatly and that in x-y direction (25.6-174 W/m·K) is several times larger than that in z direction(3.5-50 W/m·K).

Intensification of adsorption process by using the pyrolytic char from waste tires to remove chromium(Ⅵ) from wastewater

Pyrolysis has the potential of transforming waste into valuable recyclable products. Pyrolytic char(PC) is one of the most important products from the pyrolysis of used tires. One of the most significant applications for pyrolytic char recovered is used for the removal of Cr(Ⅵ) in the wastewater effluent to control waste by waste. The surface chemistry properties of surface element distribution / concentration and chemical structure were examined for the pyrolytic char and the commercial activated carbon(CAC) respectively. The results showed that surfaces of PC possesses a large amount of ester and hydrocarbon graft, whereas there are mainly carbon functional components of C—OH, C O and COOH on the surface of CAC. Therefore the surface electronegativity of PC is lower than that of CAC in the water. The repulsive interactions between the surfaces of PC and the negatively charged Cr(Ⅵ) ion are weaker than that of CAC, which results in an intensification of the adsorption process by the utilization of PC. The adsorption isotherms of Cr(Ⅵ) ion on the two kinds of carbons were determined experimentally. The larger adsorption amount on the PC in the case of Cr(Ⅵ) may be attributed mainly to its special surface micro-chemical environment. The mechanism of the removal Cr(Ⅵ) from aqueous solution was assumed to be the integration of adsorption and redox reaction. The adsorption was the rate-controlled step for Cr(Ⅵ) removal. The adsorption of Cr(Ⅵ) was identified as pseudo-second-order kinetics. The rate constants of adsorption were evaluated.

Impact of impregnation pressure on desulfurization performance of Zn-based sorbents supported on semi-coke

High-pressure impregnation, a new preparation method for sorbents to remove H2S from hot coal gas, is introduced in this paper. Semi-coke （SC） and ZnO is selected as the support and active component of sorbent, respectively. The sorbent preparation process includes high-pressure impregnation, filtration, ovendry and calcination. The aim of this research is to primarily study the effects of the impregnation pressure on physical properties and desulfurization ability of the sorbent. The desulfurization experiment was carried out in a fixed-bed reactor at 500 ~C and a simulated coal gas used in this work was composed of CO （33 vol%）, H2 （39 vol%）, H2S （300 ppm in volume）, and N2 （balance）. Experimental results show that the pore structure of the SC support can be improved effectively and ZnO active component can be uniformly dispersed on the support, with the small particle size of 10-500 nm. Sorbents prepared using high-pressure impregnation have better desulfurization capacity and their active components have higher utilization rate. P20-ZnSC sorbent, obtained by high-pressure impregnation at 20 atm, has the best desulfurization ability with a sulfur capacity of 7.54 g S/100g sorbent and a breakthrough time of 44 h. Its desulfurization precision and efficiency of removing H2S from the middle temperature gases can reach 〈 1 ppm and 〉99.7%, respectively, before sorbent breakthrough.

Investigation on activated semi-coke desulfurization

An activated semi coke with industrial scale size was prepared by high pressure hydrothermal chemistry activation, HNO 3 oxidation and calcination activation in proper order from Inner Mongolia Zhalainuoer semi coke, which is rich in resource and cheap in sale. SO 2 adsorption capacity on this activated semi coke was assessed in the fixed bed in the temperature range of 60—170℃, space velocity range of 500—1300 h -1 , SO 2 concentration of 1000—3000 ppmv, and N 2 as balance. The surface area, elemental and proximate analysis for both raw semi coke and activated semi cokes were measured. The experimental results showed that the activated semi coke has a high adsorption capacity for sulfur dioxide than the untreated semi coke. This may be the result of increase of surface area on activated semi coke and surface oxygen functional groups with basicity characteristics. Comparison to result of FTIR, it is known that group of —C—O—C? ?may be active center of SO 2 catalytic adsorption on activated semi coke.

Combustion characteristics of Daqing oil shale and oil shale semi-cokes

Thermo-gravimetric-analysis(TGA) was used to analyze the combustion characteristics of an oil shale and semi-cokes prepared from it.The effect of prior pyrolysis and TGA heating rate on the combustion process was studied.Prior pyrolysis affects the initial temperature of mass loss and the ignition temperature.The ignition temperature increases as the volatile content of the sample decreases.TG/DTG curves obtained at different heating rates show that heating rate has little effect on ignition temperature.But the peak of combustion shifts to higher temperatures as the heating rate is increased.The Coats-Redfern integration method was employed to find the combustion-reaction kinetic parameters for the burning of oil shale and oil shale semi-coke.

Effects of ultrasound on the desulfurization performance of hot coal gas over Zn-Mn-Cu supported on semi-coke sorbent prepared by high-pressure impregnation method

Zn-Mn-Cu/SC（U） sorbent was hydrothermally synthesized by ultrasound-assisted high-pressure impregnation method with semi-coke（SC）as support and the mixed solution of zinc nitrate,manganese nitrate and copper nitrate as active component precursors.The desulfurization performances of hot coal gas on the prepared sorbent at a mid-temperature of 500°C were tested in fixed-bed reactor.Morphology and pore structure of the prepared sorbent were also characterized by TEM,N2adsorption/desorption isotherms and XRD.For comparison,the sorbent of Zn-Mn-Cu/SC prepared by conventional high-pressure impregnation was also evaluated and characterized in order to study the effects of ultrasound treatment.Zn-Mn-Cu/SC（U） sorbent prepared by high-pressure impregnation under ultrasound-assisted condition showed a better desulfurization performance than Zn-Mn-Cu/SC.It could remove H2 S from 1000×10-6m3/m3 to 0.1×10-6m3/m3 at 500°C and maintained for 12.5 h with the sulfur capacity of 7.74%,in which both the breakthrough time and sulfur capacity were about 32% and 51% higher than those of Zn-Mn-Cu/SC sorbent.The introduction of ultrasound during high-pressure impregnation process greatly improved the morphology and pore structure of the sorbent.The ultrasonic treatment made particle size of active components smaller and made them more evenly disperse on semi-coke support,which provided more opportunities to contact with H2S in coal-based gases.However,there were no any difference in compositions and existing forms of active components on the Zn-Mn-Cu/SC and Zn-Mn-Cu/SC（U） sorbents.

Characterization of pyrolytic lignins with different activities obtained from bio-oil

Pyrolytic lignin, the water-insoluble fraction in bio-oil, often shows a high content and has strong intermolecular interactions with other compounds in bio-oil. In order to obtain pure pyrolytic lignin and facilitate the utilization of aqueous phase obtained from water extraction of bio-oil, methanol–water extraction method was employed to further separate the bio-oil water-insoluble phase in this paper. Different technologies, including Fourier transform infrared spectroscopy, gel permeation chromatography, and nuclear magnetic resonance, were adopted to characterize the structures of pyrolytic lignins with different activities obtained through this method. Both the heating value and the polymerization degree of high-molecular-weight pyrolytic lignin were higher than those of low-molecular-weight pyrolytic lignin. The molecular weight distribution of high-molecular-weight pyrolytic lignin was relatively wider, among which the contents of dimers to pentamers all accounted for 12% –18%,while the low-molecular-weight pyrolytic lignin mainly consisted of trimers(75.38%). The pyrolytic lignins had similar basic structures, both of which contained syringyl and guaiacyl units, whereas the low-molecular-weight pyrolytic lignin had more abundant syringyl units, reactive carbonyl groups and hydroxyl groups. Meanwhile,thermogravimetric study revealed that the final char residue yield of low-molecular-weight pyrolytic lignin was lower than that of high-molecular-weight pyrolytic lignin.

Characterization of Pyrolytic Lignin Extracted from Bio-oil

Bio-oil is a new liquid fuel produced by fast pyrolysis,which is a promising technology to convert bio-mass into liquid. Pyrolytic lignin extracted from bio-oil,a fine powder,contributes to the instability of bio-oil. The paper presents the structural features of three kinds of pyrolytic lignin extracted from bio-oil with different methods(WIF,HMM,and LMM) . The pyrolytic lignin samples are characterized by Fourier transform infrared spectrometer(FTIR) and X-ray photoelectron spectroscopy(XPS) . FTIR data indicate that the three pyrolytic lignin samples have similar functional groups,while the absorption intensity is different,and show characteristic vibra-tions of typical lignocellulosic material groups O H(3340-3380 cm-1) ,C H(2912-2929 cm-1) and C O(1652-1725 cm-1) . Comparison in the region(3340-3380 cm-1) indicates that WIF has more O H stretch groups than HMM and LMM. The carbon spectra are fitted to four peaks:C1,C C or C H,BE 283.5 eV;C2,C OR or C OH,BE 284.5-285.8 eV;C3,C O or HO C OR,BE 286.10-287.10 eV;C4,O C O,BE 287.5-287.7 eV. The absence of C1,C C or C H indicates the dominant polymerization structure of aro-matic carbon in pyrolytic lignin samples. For HMM and WIF,C2a and C2b can not be separated,so there is no free hydroxyl group in the samples. The oxygen peaks are also fitted to four peaks:O1,OH,BE = 530.3 eV;O2,RC O,BE 531.45-531.72 eV;O3,O C O,BE = 532.73-533.74 eV;O4,H2O,BE 535 eV. The absence of O1 and O4 indicates that little hydroxyl groups and adsorbed water are present in the samples.

Microwave dielectric properties of Nextel-440 fiber fabrics with pyrolytic carbon coatings in the temperature range from room temperature to 700℃

Pyrolytic carbon(PyC) coatings are deposited on the Nextel-440 fiber fabrics by chemical vapor deposition(CVD).The dielectric properties of the Nextel-440 fiber fabrics with PyC coatings(Nextel-440/PyC) are investigated in a temperature range from room temperature to 700℃ in X-band. Compared with the permittivity of the original Nextel-440 received,the complex permittivity of the Nextel-440/PyC(the real part εand the imaginary part ε), is significantly improved: εof the Nextel-440/PyC has a positive temperature coefficient, in contrast, εof the Nextel-440/PyC exhibits a negative temperature coefficient. Moreover, the reflection loss in units of d B is calculated. The results indicate that the microwave absorbing properties of the Nextel-440/PyC coatings is enhanced at 700℃ compared with that at lower temperatures.

Effects of process parameters on pore structure of semi-coke prepared by solid heat carrier with dry distillation

The semi-coke was prepared by solid heat carrier with dry distillation in single factor method. The pore structures of raw coal and semi-coke were characterized by Brunauer-Emmett-Teller (BET) and scanning electron microscope (SEM). The results show that the adsorption and desorption isotherm of semi-coke are not coincident. There was a wide pore distribution on the semi-coke, in which mesopores and micropores account for a considerable proportion. Also there are many more secondary pores. With the increase of the final temperature of heat carrier and constant temperature, as well as the decrease of volume ratio of coal and hot carrier reactor, specific surface area and pore volume of semi-coke increased rapidly first and then decreased and finally increased, along with the rapidly reduction of average pore size. SEM photos show that the surface of semi-coke becomes increasingly rough and glossy.

Process optimization for treatment of methyltin mercaptide effluents using modified semi-coke

The central composite process optimization was performed by response surface methodology technique using a design for the treatment of methyltin mercaptide with modified semi-coke. The semi-coke from the coal industry was suitably modified by treating it with phosphoric acid, with a thermal activation process. The objective of the process optimization is to reduce the chemical oxygen demand （COD） and NH4＋-N in the methyltin mercaptide industrial effluent. The process variables considered for process optimization are the semi-coke dosage, adsorption time and effluent pH. The optimized process conditions are identified to be a semi-coke dosage of 80 g/L, adsorption time of 90 min and a pH value of 8.34. The ANOVA results indicate that the adsorbent dosage and pH are the significant parameters, while the adsorption time is insignificant, possibly owing to the large range of adsorption time chosen. The textural characteristics of modified semi-coke were analyzed using scanning electron microscopy and nitrogen adsorption isotherm. The average BET surface area of modified semi-coke is estimated to be 915 mE/g, with the average pore volume of 0.71 cm3/g and a average pore diameter of 3.09 nm, with micropore volume contributing to 52.36%.

The Electrocatalytic Activity of Bare Pyrolytic Graphite and Single Wall Carbon Nanotube Modified Glassy Carbon Sensors Is Same for the Quantification of Bisoprolol Fumarate

A comparison of voltammetric behavior of bisoprolol fumarate (BF) at edge and basal plane pyrolytic graphite electrodes (EPPGE/BPPGE) has been made with single wall carbon nanotube modified glassy carbon. The electrochemical properties are investigated exercising the cyclic voltammetry and square wave voltammetry (SWV). Enhanced peak current associated with bisoprolol fumarate oxidation at EPPGE is due to its better electron transfer property. Quantification of bisoprolol fumarate was carried out at pH 7.2 at both the pyrolytic graphite electrodes. Well-defined peak has been observed at ~ 792 and 954 mV at EPPGE and BPPGE respectively for bisoprolol fumarate oxidation. The detection limit is found to be 2.8 × 10–7 M and 7.3 × 10–7 M for EPPGE and BPPGE respectively. A comparison of common quantification parameters for bisoprolol at carbon nanotube modified glassy carbon electrode and bare BPPGE and EPPGE has been made and it is observed that carbon naotube modified glassy carbon exhibits sensitivity and detection limit close to that observed at bare basal plane pyrolytic graphite electrode. The method developed is applicable for determination of bisoprolol fumarate in pharmaceutical preparations and real samples.

Electrochemical preparation and characterization of gold-polyaniline core-shell nanocomposites on highly oriented pyrolytic graphite

A simple electrochemical method for the in situ preparation of homogeneously dispersed gold-polyaniline core/shell nanocomposite particles with controlled size on the highly oriented pyrolytic graphite(HOPG)was demonstrated.The HOPG surface was modified preferentially by covalent bonding of a two-dimensional 4-aminophenyl monolayer employing diazonium chemistry.AuCl4 -ions were attached to the Ar-NH2 termination and reduced electrochemically.This results in the formation of Au nuclei that could be further grown into gold nanoparticles.The formation of polyaniline as the shell wrap of Au nanoparticle was established by localized electro-polymerization.These core-shell nanocomposites prepared were characterized by AFM and cyclic voltammetry.The results show that the gold-polyaniline core-shell composites on HOPG have a mean particle size of 100 nm in diameter and the polyaniline shell thickness is about 15 nm.

Study on the Pyrolytic Carbon Generated by the Electric Heating CVD Method

A new method of fabricating C/C composite materials, namely electric heating CVD method, was used, which electrified the carbon fiber directly by using the conductivity of itself. Acetylene was used as the carbon source with nitrogen as dilution gas, and the pyrolytic carbon started to deposit on the carbon fiber surface when the deposition temperature was reached. The morphology of pyrolytic carbon was characterized by SEM, and the surface properties of carbon fibers before and after CVD were characterized by Raman spectroscopy. The experimental results show that the electric heating method is a novel method to fabricate C/C composite materials, which can form a dense C/C composite material in a short time. The order degree and the average crystallite size of the carbon fiber surface were decreased after the experiment.

Microstructure of carbon fiber preform and distribution of pyrolytic carbon by chemical vapor infiltration

The carbon/carbon composites were made by chemical vapor infiltration(CVI) with needled felt preform. The distribution of the pyrolytic carbon in the carbon fib er preform was studied by polarized light microscope(PLM) and scanning electroni c microscope(SEM). The experimental results indicate that the amount of pyrolyti c carbon deposited on the surface of chopped carbon fiber is more than that on t he surface of long carbon fiber. The reason is the different porosity between th e layer of chopped carbon fiber and long carbon fiber. The carbon precursor gas which passes through the part of chopped carbon fibers decomposes and deposits o n the surface of chopped carbon fiber. The pyrolytic carbon on the surface of lo ng carbon fibers is produced by the carbon precursor gas diffusing from the chop ped fiber and the Z-d fiber. Uniform pore distribution and porosity in preform are necessary for producing C/C composites with high properties.

Observations on Durability of a Pyrolytic Carbon Bileaflet Mechanical Heart Valve

This study aims to observe the durability of a pyrolytic carbon bileaflet mechanical valve prosthesis. The mechanical valves prosthesis was tested in vitro by the durability test instrument of valve prosthesis. Then in vivo, the durability of the implanted valves was observed with animal experiments and elinieal application. In the impact test for 5 min and durability test of 380 million eyeles in vitro, there was no the phenomenon of flyer, perforation and fracture observed, as well as no wear or pit found on the surface of valve leaflets. The valve leaflets could normally be turned on or off. The weight of the valve was（1.0031 ± 0.0004） g for 23 mm and（1.6003 ± 0.0002） g for 27 mm. The hydrodynamies test demonstrated that the valve prosthesis had still exeellent hemodynamic performance after the durability test. The animal autopsy showed that the valve leaflets could normally be turned on or off, and no wear was found. By follow-up of 62 patients implanted the valves, all patients had long-terms survival, no complication caused by valve was found. The age of the longest survival was more than 10 years. This study demonstrates that the new meehanieal valve prosthesis have excellent durable performance.

Electrochemical Determination of Epinephrine with a Pyrolytic Graphite Electrode in the Presence of Ascorbic Acid and Dopamine

A method for determination of epinephrine（EP） in the presence of ascorbic acid （AA） and dopamine （DA） with bare pyrolytic graphite electrodes has been described for the first time. In pH 7.0 phosphate buffer solution, the linear relationship was observed between the reduction peak current of EP and its concentration over the range from 1×10^-4 to 5×10^-7 mol/L, the related coefficient is 0.9992 （N=8）.

GROWTH CHARACTERSAND MODEL OF PYROLYTIC CARBON IN CHEMICAL VAPOR INFILTRATION PROCESS

Chemical Vapor Infiltration (CVI) processes are the essential techniques for fabrication of high performance carbon carbon composites. Based on the polarized light and scanning electron analysis, the authors study the micro morphology and texture characteristics of pyrolytic carbon deposited in CVI process, as well as the growth behavior of pyrolytic carbon. The research shows that Rough Laminar (RL) texture has the hierarchical and self similar structural features, which reflects the stage growth and self similar behavior during the growth course of pyrolytic carbon. According to the two growth features, a laminated growth model of pyrolytic carbon is proposed with the concept of Cone Growth Units (CGU). The laminated growth model can provide a fine description for the growth course of RL pyrolytic carbon. The model indicates that formation, developing and combination of local high order structures (such as CGU structures) are the essential factors for the growth of RL texture. Smooth Laminar (SL) texture and ISO carbon come into being with long range orderliness and isotropy structure respectively, which no local high orderliness intermediate involves in.