Influence of pyrolysis temperature on structure and dielectric properties of polycarbosilane derived silicon carbide ceramic

β-SiC ceramic powders were obtained by pyrolyzing polycarbosilane in vacuum at 800-1200 °C. The β-SiC ceramic powders were characterized by TGA/DSC, XRD and Raman spectroscopy. The dielectric properties of β-SiC ceramic powders were investigated by measuring their complex permittivity by rectangle wave guide method in the frequency range of 8.2-18 GHz. The results show that both real part ε′ and imaginary part ε″ of complex permittivity increase with increasing pyrolysis temperature. The mechanism was proposed that order carbon formed at high temperature resulted in electron relaxation polarization and conductance loss, which contributes to the increase in complex permittivity.

Influence of pyrolysis temperature on ferroelectric properties of La and Mn co-doped BiFeO_3 thin films

Bi0.9La0.1Fe0.95Mn0.05O3 （BLFMO） ferroelectric thin films were fabricated on Pt/Ti/SiO2/Si/ substrates by the sol-gel process at different pyrolysis temperatures. The mass loss of BLFMO powder was investigated by thermo gravimetry analyser （TGA）, and the polycrystalline structure and smooth surface of BLFMO thin films were characterized by X-ray diffraction （XRD） and atomic force microscopy （AFM）, respectively. The remnant polarization （Pr） of the BLFMO films pyrolyzed at 420 ℃ is 21.2 μC/cm2 at the coercive field （Ec） of 99 kV/cm and the leakage current density is 7.1×10-3 A/cm2, which indicates that the BLFMO thin films display relatively good ferroelectric property at this temperature.

Effect of pyrolysis temperature and hold time on the characteristic parameters of adsorbent derived from sewage sludge

According to the Doehlert's matrix method, the adsorbent derived from sewage sludge was prepared through chemical activation under controlling the pyrolysis temperature and hold time. The characteristic parameters including the total yield, adsorption of methylene blue, adsorption of iodine, BET surface area, micro-pore volume are 35%—49%, 16.5—38 mg/g, 285—362 mg/g, 185—359 m2/g, and 0.112—0.224 m3/g, respectively. According to the experimental data, the multi-linear regression method was adopted to fit the relations between the characteristic parameters and influential factors. At final, through optimization method, the optimal adsorbent is obtained when using 62 min as hold time and 1105K as pyrolysis temperature. Under the conditions, the adsorbent was produced and compared the characteristic parameters with model forecast value, the coherence is satisfied.

Effect of pyrolysis temperature on properties of ACF/CNT composites

Activated carbon fiber/carbon nanotube(ACF/CNT) composites were fabricated by chemical vapor deposition(CVD) process.The effects of pyrolysis temperature on properties of ACF/CNT composites,including BET specific surface area,mass increment rate and adsorption efficiency for rhodamine B in solution,were investigated by scanning electron microscopy.The results show that the pyrolysis temperature is a key factor affecting the qualities of ACF/CNT composites.The mass increment rate and BET specific surface area sharply decrease with the increase of pyrolysis temperatures from 550 ℃ to 850 ℃ and the minimum diameter of CNTs appears at 750 ℃.The maximum adsorption efficiency of ACF/CNT composites for rhodamine B is obtained at 650 ℃.ACF/CNT composites are expected to be useful in adsorption field.

Electrical conductivity of wood biochar monoliths and its dependence on pyrolysis temperature

Biochar is traditionally used as solid fuel and for soil amendment where its electrical conductivity is largely irrelevant and unexplored.However,electrical conductivity is critical to biochar’s performance in new applications such as supercapacitor energy storage and capacitive deionization of water.In this study,sugar maple and white pine were carbonized via a slow pyrolysis process at 600,800 and 1000°C and conductivities of monolithic biochar samples along the radial direction were measured using the 4-probe method.Biochars were characterized using an elemental analyzer,scanning electron microscopy,X-ray diffraction and Raman spectroscopy.The solid carbon in biochar samples was found to consist primarily of disordered carbon atoms with small graphitic nanocrystallites that grow with increasing temperature.The bulk conductivity of biochar was found to increase with pyrolysis temperature-1 to~1000 S/m for maple and 1 to~350 S/m for pine,which was accompanied by an increase in carbon content-91 to 97 wt%and 90 to 96 wt%for maple and pine,respectively.The skeletal conductivity of biochar samples carbonized at 1000°C is about 3300 S/m and 2300 S/m for maple and pine,respectively(assuming solid carbon is amorphous);both values are above that of amorphous carbon(1250-2000 S/m).This work demonstrated the importance of carbonization and graphitization to electrical conductivity and suggested electron hopping as a likely mechanism for electric conduction in biochar-an amorphous carbon matrix embedded with graphitic nanocrystallites.

Combustion characteristics of semicokes derived from pyrolysis of low rank bituminous coal

Various semicokes were obtained from medium-low temperature pyrolysis of Dongrong long flame coal.The proximate analysis,calorific value and Hardgrove grindability index(HGI) of semicokes were determined,and the ignition temperature,burnout temperature,ignition index,burnout index,burnout ratio,combustion characteristic index of semicokes were measured and analyzed using thermogravimetry analysis(TGA).The effects of pyrolysis temperature,heating rate,and pyrolysis time on yield,composition and calorific value of long flame coal derived semicokes were investigated,especially the influence of pyrolysis temperature on combustion characteristics and grindability of the semicokes was studied combined with X-ray diffraction(XRD) analysis of semicokes.The results show that the volatile content,ash content and calorific value of semicokes pyrolyzed at all process parameters studied meet the technical specifications of the pulverized coal-fired furnaces(PCFF) referring to China Standards GB/T 7562-1998.The pyrolysis temperature is the most influential factor among pyrolysis process parameters.As pyrolysis temperature increases,the yield,ignition index,combustion reactivity and burnout index of semicokes show a decreasing tend,but the ash content increases.In the range of 400 and 450 °C,the grindability of semicokes is rational,especially the grindability of semicokes pyrolyzed at 450 °C is suitable.Except for the decrease of volatile content and increase of ash content,the decrease of combustion performance of semicokes pyrolyzed at higher temperature should be attributed to the improvement of the degree of structural ordering and the increase of aromaticity and average crystallite size of char.It is concluded that the semicokes pyrolyzed at the temperature of 450 °C is the proper fuel for PCFF.

Investigation of effective dimensionless numbers on initiation of instability in combustion of moisty organic dust

In this work, the effect of various effective dimensionless numbers and moisture contents on initiation of instability in combustion of moisty organic dust is calculated. To have reliable model, effect of thermal radiation is taken into account. One- dimensional flame structure is divided into three zones： preheat zone, reaction zone and post-flame zone. To investigate pulsating characteristics of flame, governing equations are rewritten in dimensionless space-time （（, r/, ~） coordinates. By solving these newly achieved governing equations and combining them, which is completely discussed in body of article, a new expression is obtained. By solving this equation, it is possible to predict initiation of instability in organic dust flame. According to the obtained results by increasing Lewis number, threshold of instability happens sooner. On the other hand, pulsating is postponed by increasing Damk6hler number, pyrolysis temperature or moisture content. Also, by considering thermal radiation effect, burning velocity predicted by our model is closer to experimental results.

Biochar-Induced Priming Effects in Young and Old Poplar Plantation Soils

The priming effect(PE)induced by biochar provides a basis for evaluating its carbon(C)sequestration potential in soils.A 60 days’laboratory incubation was conducted,which involved the amendment of biochar(1%of soil mass)produced from rice straw at 300℃(B300)and 500℃(B500)to young(Y)and old(O)poplar plantation soils,with the aim of studying the responses of biochar-induced PEs to poplar plantation ages.This incubation included six treatments:Y+CK(control),Y+B300,Y+B500,O+CK,O+B300,and O+B500.Carbon dioxide(CO_(2))emissions were significantly increased(p<0.05)in the B300 amended soils,while it was decreased in the B500 amended soils compared to the CK.The primed CO_(2) emissions were 2.35 times higher in the Y+B300 than the O+B300 treatments,which was measured to be 18.6 and 5.56 mg C·kg^(-1) with relative PEs of 12.4%and 3.35%,respectively.However,there was little difference between the primed CO_(2) emissions in Y+B500 and O+B500 treatments,which were measured to be-24.9 and-29.6 mg·C·kg^(-1) with relative PEs of-16.6%and-17.8%,respectively.Dissolved organic carbon(DOC)was significantly lower in the young poplar plantation soil than that in the old poplar plantation soil regardless of biochar amendment throughout the incubation,indicating greater C-limit of soil microorganisms in the young poplar plantation soil.Using ^(13)C isotope tracing,neither B300 nor B500 decreased native soil-derived DOC,which indicated that the negative B500-induced PEs were not due to a reduction in the availability of native soil-derived C.In conclusion,the response of biochar-induced PEs to poplar plantation age depends on biochar types while soil available C indirectly affects biochar-induced PEs.Further studies should focus on how the interactive effects between soil C availability and microbial community impacts biochar-induced PEs.

Effects of temperature on pyrolysis products of oil sludge

Temperature is the determining factor of pyro-lysis,which is one of the alternative technologies for oil sludge treatment.The effects of final operating temper-ature ranging from 350 to 550uC on pyrolysis products of oil sludge were studied in an externally-heating fixed bed reactor.With an increase of temperature,the mass fraction of solid residues,liquids,and gases in the final product is 67.00%–56.00%,25.60%–32.35%,and 7.40%–11.65%,and their corresponding heat values are 34.4–13.8 MJ/kg,44.41–46.6 MJ/kg,and 23.94–48.23 MJ/Nm 3,respectively.The mass and energy tend to shift from solid to liquid and gas phase(especially to liquid phase)during the process,and the optimum temperature for oil sludge pyrolysis is 500uC.The liquid phase is mainly com-posed of alkane and alkene(C_(5)–C_(29)),and the gas phase is dominantly HC S and H 2.

Preparation of Kenaf Biochar and Its Adsorption Properties for Methylene Blue

The toxic dyestuff's from printing and dyeing wastewater have caused serious damages to the ecological environ-ment,thus exploring effective methods to remove them having become a key topic.Here,a series of biochar sam-ples were synthesized form kenaf to adsorb methylene blue(MB),which was acted as the dye representative for the test of adsorption capacity due to the presence of abundant double bond and aroma tic heterocyclic ring.By tuning the raw materials and pyrolysis temperature,a super adsorption capacity about 164.21 mg·g^(-1) was obtained over the biochar that pyrolyzed at 700℃ with the kenaf fiber as raw material Through the physical adsorption,elemental analysis,FTIR spectra and NH_(3)-TPD,it was found the high surface area and pore volume of biochar played a key role in the adsorption of MB,and the acidic sites would also assist the adsorption process.Besides,the adsorption kinetic model was ftted and calculated,implying the MB physically adsorbed on the bio-char rapidly and then occurred chemical adsorption on the acidic sites.In addition,through KBC700 recycling experiments,it was found that kenaf biochar had a good binding force to MB,which effectively avoided secondary pollution.This work provides important insights for the adsorption mechanism of MB by biochar,also offers some guidance for the further synthesis of biochar from various biomass.

Biochar as a Soil Ameliorant: How Biochar Properties Benefit Soil Fertility—A Review

In recent years, biochar has received great attention among researchers worldwide. This carbon-rich material, mainly produced from residues from agriculture and forestry, holds a wide range of properties, e.g. large specific surface area, high cation exchange capacity, and substantial nutrient contents, that can have beneficial effects when added to soils. This review is giving a brief introduction to biochar properties and how feedstock, pyrolysis temperature, and time influence these properties. As the majority of studies concentrate on the soil amending effects of biochar, this review also provides an overview of how biochar affects the chemical, physical, hydrological, and biological properties of soils. For example, biochar addition to soils can raise the pH, increase the organic carbon content, enhance nutrient retention, foster porosity, augment the water-holding capacity, and increase microbial biomass. Consequently, biochar can contribute to soil fertility, increase yields, help closing nutrient cycles, and thus help secure food safety in a region. However, the knowledge about the long-term effects is still limited and should be broadened by a more systematic testing of biochar effects in the future to help bring the benefits of biochar into practice.

A granular-biomass high temperature pyrolysis model based on the Darcy flow

We established a model for the chemical reaction kinetics of biomass pyrolysis via the hightemperature thermal cracking of liquid products. We divided the condensable volatiles into two groups, based on the characteristics of the liquid prdoducts., tar and biomass oil. The effects of temperature, residence time, particle size, velocity, pressure, and other parameters on biomass pyrolysis and high-temperature tar cracking were investigated numerically, and the results were compared with experimental data. The simulation results showed a large endothermic pyrolysis reaction effect on temperature and the reaction process. The pyrolysis reaction zone had a constant temperature period in several layers near the center of large biomass particles. A purely physical heating process was observed before and after this period, according to the temperature index curve.

Spray Pyrolysis Deposition of ZnO Thin Films from Zinc Chloride Precursor Solution at Different Substrate Temperatures

ZnO films were prepared at different substrate temperatures through spraying pyrolysis deposition of zinc chloride precursor onto glass substrate. Substrate temperature affects surface morphology of films and therefore their optical and electrical properties. All films are polycrystalline with Wurtzite crystal structure and preferentially grow along c-axis direction. Formation of ZnO rods start at about 500 °C. The diameter and length of rods deposited at 500 °C are350–500 and 550–700 nm, respectively. By increasing substrate temperature, film becomes more coverage and diameter of the rods reduces to 250–300 nm but their length increases to 1,000–1,200 nm, respectively. Optical transmission in visible region decreases with increasing substrate temperature. An ultraviolet emission and two visible emissions at 2.82 and2.37 eV are observed for photoluminescence spectra at room temperature. The resistivity of ZnO films increases with increasing substrate temperature due to surface morphology.

Experimental Investigation of Pyrolysis Process of Woody Biomass Mixture

This paper describes an experimental investigation of pyrolysis of woody biomass mixture. The mixture consists of oak, beech, fir, cherry, walnut and linden wood chips with equal mass fractions. During the experiment, the sample mass inside the reactor was 10 g with a particle diameter of 5-10 mm. The sample in the reactor was heated in the temperature range of 24-650℃. Average sample heating rates in the reactor were 21, 30 and 54 ℃/min. The sample mass before, during and after pyrolysis was determined using a digital scale. Experimental results of the sample mass change indicate that the highest yield of pyrolytic gas was achieved at the temperature slightly above 650℃ and ranged from 77 to 85%, while char yield ranged from 15 to 23%. Heating rate has sig- nificant influence on the pyrolytic gas and char yields. It was determined that higher pyrolysis temperatures and heating rates induce higher yields of pyrolytic gas, while the char mass reduces. Condensation of pyrolytic gas at the end of the pyrolysis process at 650℃ produced 2.4-2.72 g of liquid phase. The results obtained represent a starting basis for determining material and heat balance of pyrolysis process as well as woody biomass pyrolysis equipment.

Effects of Temperature and Catalyst Concentration on the Growth of Aligned Carbon Nanotubes

The effects of preheating and pyrolysis temperatures and catalyst concentration on the synthesis of aligned carbon nanotubes （CNTs） using ferrocene as the catalyst and xylene as the carbon source in chemical vapor deposition were experimentally studied. The as-grown aligned CNTs were characterized by field emission scanning electron microscopy, transmission electronic microscopy, high-resolution transmission electronic microscopy, and Raman spectroscopy. The growth rate, the diameters, and the degree of crystal structure of the aligned CNTs were all found to depend on the preheating and pyrolysis temperatures and the catalyst concentration. The optimized conditions for the growth of aligned CNTs resulted in a rapid growth rate of 20.4 um/min, with the CNTs having a good, uniform crystal structure, and clean surfaces with little amorphous carbon. The results also show that higher preheating temperatures and lower ferrocene concentrations favor the growth of single-walled CNTs.

Biochar pyrolyzed at low temperature enhanced acidophilous plant growth by promoting rhizospheric microbes in a slightly alkaline urban soil

Biochar has been considered as a potential way to enhance acidophilous plant growth in alkaline soils.However,whether such enhancements are closely linked with biochar pyrolysis temperature and its improvements in rhizospheric soil fertility and microbial activities remains largely unknown.We performed a pot experiment to investigate changes in azalea(Rhodo-dendron)morphology and physiology,as well as its rhizosphere soil chemical and biological properties in a slightly alkaline urban soil under the amendment of biochars that pyrolyzed at three temperatures(i.e.,350,550 and 700°C).Our results showed that the effects of biochars on plant growth and soil properties depended on pyrolysis temperature.In comparison with the non-amended control,350 and 550°C biochars showed significant promotions on the azalea growth in terms of photosynthetic characteristics,biomass,root morphology,and N and P uptake.Whereas,700°C biochar showed an inhibi-tion effect on them.350°C biochar decreased soil pH and increased soil available P and K contents and the activities ofα-glucosidase,N-β-glucosaminidase,phosphatase and sulfatase.In addition,350°C biochar significantly enhanced bacterial 16S rRNA and fungal 18S rRNA gene abundances in the rhizosphere soil of azalea and mycorrhizal infection.Correlation analysis indicated that soil pH,available nutrients and fungal abundance had positive associations with the enhanced plant growth parameters.Therefore,our findings suggest that biochar produced at low temperature could be a feasible strategy for enhancing acidophilous azalea growth and improving urban soil quality.

Structural, optical and electrical properties of zinc oxide thin films deposited by a spray pyrolysis technique

Zinc oxide（ZnO） thin films were deposited on glass substrates by spray pyrolysis technique decomposition of zinc acetate dihydrate in an ethanol solution with 30 m L of deposition rate, the ZnO thin films were deposited at two different temperatures： 300 and 350℃. The substrates were heated using the solar cells method.The substrate was R217102 glass, whose size was 30×17.5×1 mm^3. The films exhibit a hexagonal wurtzite structure with a strong（002） preferred orientation. The higher value of crystallite size is attained for sprayed films at 350℃, which is probably due to an improvement of the crystallinity of the films at this point. The average transmittance of obtain films is about 90%–95%, as measured by a UV–vis analyzer. The band gap energy varies from 3.265 to 3.294 e V for the deposited Zn O thin film at 300 and 350℃, respectively. The electrical resistivity measured of our films are in the order 0.36 Ω·cm.

Electromagnetic wave absorbing ceramics composites made of polymer-derived SiC with BN@CNTs pyrolyzed higher than 1200℃

Polymer-derived ceramics(PDCs)pyrolyzed at high temperatures are promising electromagnetic wave(EMW)absorption materials for aerodynamically heated parts of aircraft under harsh environments.Nev-ertheless,high-temperature pyrolysis results in a significant increase of electrical and dielectric proper-ties of the ceramics,causing extensive reflection of EMW.To address this challenge,boron nitride-coated carbon nanotubes(BN@CNTs)were fabricated and introduced into polymer-derived SiC(PDC-SiC)by py-rolyzing its precursor higher than 1200℃to form SiC-BN@CNT ceramic composites.The fabricated com-posites with 3 wt.%BN@CNTs pyrolyzed at 1200℃have an effective absorption bandwidth(EAB)of 4.2 GHz(8.2-12.4 GHz)at a thickness of 3.4 mm and the minimum reflection loss(RL min)of-57.20 dB.The ultra-broad EAB of 12.62 GHz(5.38-18 GHz)is obtained by simulation through periodic structure design-ing.The RL of the metamaterials was also measured using an arch testing method at a frequency range of 2-18 GHz and an EAB of 11.52 GHz(6.48-18 GHz)is obtained.The excellent absorption is attributed to the BN layer that limits the electrical conduction of the ceramic composites while retaining the high loss of CNTs.The introduction of BN@CNTs causes the refinement of SiC grains,which provides plenty of interfaces and enhances the interface polarization loss.This work successfully solves the problem that PDCs pyrolyzed at elevated temperatures cannot be used as EMW absorption materials by applying BN coating on CNTs served as absorbers for PDC-SiC.The results of this work greatly broaden the application scope of the PDC systems for EMW absorption.

Use of Biochar as an Amendment for Remediation of Heavy Metal-Contaminated Soils:Prospects and Challenges

Biochar(BC), known as the new black gold, is a stable, novel carbonaceous by-product that is synthesized through pyrolysis of biological materials in the absence of O_2.Recently, an emerging interest in the application of BC as a robust soil amendment has given rise to a broad research area in science and technology.It is considered a promising remediation option for heavy metal(HM)-contaminated soils to reduce HM bioavailability to plants.Remediation efficacy of BC depends on the porosity, composition,pyrolysis temperature, feedstock, and residence time of pyrolysis.This review article aimed to present an overview of BC use in the immobilization of HMs, i.e., Cd, As, Pb, Zn, Ni, Cu, Mn, Cr, and Sb, in contaminated soils.The remaining uncertain factors, including the specific soil HM immobilization mechanisms, long-term beneficial effects, and potential environmental risks associated with BC application are analyzed.Future research must be conducted to ensure that the management of environmental pollution is in accord with ecological sustainability and adaptation of the black gold biotechnology on a commercial basis for immobilization of HMs in contaminated soils.

Sorption of ammonium and phosphate from aqueous solution by biochar derived from phytoremediation plants

The study on biochar derived from plant biomass for environmental applications is attracting more and more attention. Twelve sets of biochar were obtained by treating four phytoremediation plants, Salix rosthornii Seemen, Thalia dealbata, Vetiveria zizanioides, and Phragmites sp., sequentially through pyrolysis at 500 °C in a N2 environment, and under different temperatures(500, 600, and 700 °C) in a CO2 environment. The cation exchange capacity and specific surface area of biochar varied with both plant species and pyrolysis temperature. The magnesium(Mg) content of biochar derived from T. dealbata(TC) was obviously higher than that of the other plant biochars. This biochar also had the highest sorption capacity for phosphate and ammonium. In terms of biomass yields, adsorption capacity, and energy cost, T. dealbata biochar produced at 600 °C(TC600) is the most promising sorbent for removing contaminants(N and P) from aqueous solution. Therefore, T. dealbata appears to be the best candidate for phytoremediation application as its biomass can make a good biochar for environmental cleaning.