Thermogravimetric analysis of peat decomposition under different oxygen concentrations

Smoldering combustion of peat is of global concern as a natural hazard to consume sequestered carbon and form wide-area haze. It is affected by thermal decomposition kinetics of peat and the diffusion and availability of oxygen. In this work, thermal decomposition behavior of peat was investigated using thermogravimetric analysis under the atmosphere with different oxygen concentrations. The results showed that thermal decomposition process of peat could be divided into three stages: dehydration, oxidative pyrolysis of organic matters into volatiles and char, and oxidation of the generated char. The apparent activation energies of peat decomposition under different oxygen concentrations were calculated by model-free methods of Kissinger, FWO, Starink, Gyulai, and Friedman. A two-step reaction model was proposed to describe thermal decomposition kinetics of peat (excluding dehydration stage) and the effect of oxygen concentration on the kinetic parameters was discussed. These results provide basic data for smoldering modeling of peat.     

Study of sorption and catalytic activity of peat-based composition material in relation to organic pollutants in waters

The effect exerted by modifying iron(III) chloride additive on the sorption and catalytic activity of granulated iron-containing peat composition in removal of oxalic acid was studied depending on the conditions of the solution treatment (ozone, UV radiation, and hydrogen peroxide). The conditions for virtually complete absorption of oxalic acid from model solutions were chosen.     

森林泥炭的热解特性及热解动力学

泥炭阴燃是森林地下火的主要燃烧形式之一, 研究泥炭的热解规律对认识其阴燃机理及地下火蔓延机理有重要意义. 本文使用荧光光谱分析技术测定了我国东北林区一种典型泥炭样品的主要元素组成, 并使用热重-差热分析(TG-DTA)技术研究了泥炭样品在惰性气氛中的热解规律. 实验结果表明, 泥炭样品主要由45种元素构成. 从常温到1073 K高温的升温过程中, 泥炭样品的质量损失过程可以分为三个阶段, 依次为水分损失阶段、有机质热解阶段和矿物质分解阶段. 对于泥炭阴燃密切相关的有机质热解阶段, 结合热分析动力学理论和优化计算方法, 建立了描述泥炭有机质热解动力学规律的三组分叠加反应模型.     

Impact of Heat Treatment on the Structure and Properties of Tomsk Region Peat

Botanical composition of terrestrial peat and fen peat with decomposition degree (R) ranging from 25% to 45% has been studied and technical analysis has been carried out. The effect of heat treatment on peat group composition alteration was evaluated. The peculiarities defined by the preliminary heat treatment were revealed. Optical properties of peat were studied by IR spectroscopy. Conclusions about the degree of heat treatment influence on the physicochemical properties of peat were made.     

The use of peat mineral hydrophobizers as anticlodding agents for powder nitrile butadiene rubbers

Problems of clodding of loose materials and the main techniques to prevent it are considered. The main characteristics of nitrile butadiene rubber are briefly overviewed. The principle of the synthesis of hydrophobic modifying additives by thermochemical destruction of the organic substance of peat is described. A research method for an anticlodding agent based on peat mineral compositions is detailed. Comparative analysis of the efficiency of anticlodding agents based on kaolin and chalk is performed. It is established that the use of hydrophobically modified chalk decreases the clodding ability of nitrile butadiene rubber by 22.5 times under the long-term storage.     

有机改性先驱体对含铕配合物的凝胶玻璃结构及性能的影响

分别采用γ-缩水甘油氧基三甲氧基硅烷(CH₂OCHCH₂O(CH₂)₃Si(OCH₃)₃) (GPTMS), 甲基三甲氧基硅烷(MTMS)和乙烯基三乙氧基硅烷(VTES)作为有机改性先驱体, 采用原位合成技术, 用溶胶-凝胶法制备了Eu^3＋, β-二酮噻吩甲酰三氟丙酮(TTA)及协同体1,10-菲啰啉(phen)共掺的三种有机改性二氧化硅(ormosil)玻璃. 测量了它们的发射光谱和红外光谱, 并进行了XRD, SEM和TG-DSC测试. 探讨了不同有机改性先驱体及热处理温度对原位合成的稀土有机配合物掺杂二氧化硅凝胶玻璃的发光性能、热稳定性及机械性能的影响. 结果表明, 有机改性先驱体能使凝胶玻璃结构致密, 但同时热稳定性降低; 对于荧光性能, MTMS和VTES可使其有一定的提高, 但它们的最大含量不能超过50%, 否则凝胶易失透, 而GPTMS能大幅提高凝胶的荧光性能. 通过综合比较, 选取出各种性能都较好的配方, 为今后制备较实用的具有较强荧光的含铕的凝胶玻璃提供了一定的依据.     

Transport processes in the sorption of colored ions by peat particles

A three-step model has been proposed for the adsorption of Astrazone Blue dye (Basic Blue 69) on peat. The initial rate of uptake of dye ions due to physical adsorption and chemisorption (ion exchange) has been correlated using a surface mass transfer coefficient. These coefficients have been determined and expressed in the dimensionless mass transfer form, Sh/Sc^0.33, as a function of agitation, initial dye concentration, peat particle size range, dye solution temperature, and mass of peat.     

On the use of a natural peat for the removal of Cr(VI) from aqueous solutions

A natural peat has been used as an adsorbent for the removal of hexavalent chromium from aqueous solution. The peat was firstly characterized in terms of particle size and chemical composition (ash content, pH of the point of zero charge, FT-IR and thermal analysis). Next, the kinetic and equilibrium aspects of the adsorption of Cr(VI) by this adsorbent were studied. The kinetic data were satisfactorily fitted to a kinetic law of partial order in C equal to one. The specific adsorption rates are around 10(-4)s(-1), increasing as temperature does. A noticeable influence of diffusion on the global adsorption process has been demonstrated. Finally, the equilibrium isotherms were satisfactorily fitted to a previously proposed model. The adsorption capacity of Cr(VI) was similar to some other previously reported and the affinity of Cr(VI) towards the active sites of the adsorbent increases as temperature rises.     

Cluster analysis of the elemental composition of five austrian peats

The elemental composition of peat depends on the plant residues from which the peat was formed. The concentrations of 45 elements were determined for five peat samples by plasma emission spectrometry. Literature data on the composition of three bogs was added. The elemental abundances of six rock or soil categories, the elemental compositions of several peat-forming plants, and the results of the elemental analyses of bog samples, were examined by the SIMCA method. A clear difference was found between fens and raised bogs. Factor analysis of the elemental compositions shows that the concentrations of most of the elements reflect their natural abundance in the surrounding region. Some concentrations are influenced by anthropogenic pollution, e.g. lead, and by plant metabolism. The cluster analysis together with the training sets shows the degree of the deposition of mineral material from adjacent rivers and the type of plant growth which formed the peat.     

General analysis of the measurements of the lateral crystal lattice moduli of semicrystalline polymers by x-ray diffraction and the application to nylon 6

A mathematical representation based on a linear elastic theory is proposed by which one may investigate the dependences of molecular orientation and crystallinity on the crystal lattice moduli and linear thermal expansion coefficients in the direction perpendicular to the chain axis as commonly measured by x-ray diffraction. In the theoretical calculation, a previously introduced model was employed in which oriented crystalline phase is surrounded by oriented amorphous phase and the strains of the two phases at the boundary are identical. The mathematical analysis indicated that the lateral crystal lattice moduli and linear thermal coefficients as measured by x-ray diffraction may be different from the intrinsic crystal moduli and linear thermal coefficients of a crystal unit cell, depending on the structure of the polymer solid. The numerical calculation was applied to nylon 6. As a result, it may be confirmed that the lateral crystal lattice moduli measured by x-ray diffraction are sensitive to the morphology of the bulk speciments and close to the intrinsic crystal moduli if the morphology of the test specimen can be represented by a parallel model with respect to the original stretching longitudinal direction.     

Direct determination of arsenic in acid digests of plant and peat samples using HG-AAS and ICP-SF-MS

A new analytical procedure for the reliable and direct determination of arsenic (As) in nitric acid digests of ombrotrophic peat samples in the low ng l⁻¹ range has been developed based on hydride generation-atomic absorption spectrometry (HG-AAS). The pre-reduction capabilities of KI/ascorbic acid and of l-cysteine in nitric acid digests of peat and plant samples for the conversion of As(V) to As(III) were tested systematically. Samples were digested with high purity nitric acid in a high-pressure microwave autoclave at 240 °C and subsequently measured using HG-AAS or ICP-SF-MS (inductively coupled plasma-sector field-mass spectrometry). Using KI/ascorbic acid as pre-reductant, the accuracy and precision were poor when digests of complex matrices, such as peat were analyzed for As by HG-AAS. However, 10 g l⁻¹ l-cysteine was successfully employed as pre-reductant in diluted nitric acid digests (3%, v/v) of peat samples prior to hydride generation of As with 0.5% (m/v) of NaBH₄ and 7 mol l⁻¹ HCl. The analytical procedure was critically evaluated by analyzing several certified plant reference materials, two in-house peat reference materials and by the determination of As in diluted digests of peat samples with ICP-SF-MS. The results for the determination of As in various peat and plant materials showed excellent agreement with the reference values. The method detection limits for the determination of As by the optimized HG-AAS procedure and by ICP-SF-MS were 23 ng g⁻¹ and 1.4 ng g⁻¹ in solid peat, respectively. The newly developed analytical procedure was applied to the determination of As in selected peat samples. Results for As in these peat samples obtained by the developed HG-AAS procedure and the optimized procedure for the determination of As with ICP-SF-MS were highly correlated (R² = 0.993, n = 12).     

Effect of Modifying Additives on the Sintering and Properties of SiC/SiC<Subscript>w</Subscript> Ceramic Composite Material

Spark plasma sintering and hot compaction methods were used to obtain experimental samples of a composite material of the SiC?SiC_w system with various modifying additives (AlN, B₄C, HfB₂, Y₂O₃, Al₂O₃, Si₃N₄). The effect of the modifying additives on the sintering process, physicomechanical, and thermal properties of the ceramic composite material was examined. The introduction of the modifying additives lowered the sintering temperature of silicon carbide produced by the hot compaction method by 200°C and that formed with spark plasma spark sintering by 300?450°C as compared with the sintering temperature of silicon carbide without additives.     

Extraction of humic acids and their fractions in poly(ethylene glycol)-based aqueous biphasic systems

The possibility of extraction and fractionation of humic acid (HA) in the aqueous biphasic systems (ABS) was shown for the first time. The 10% PEG-10% (NH₄)₂SO₄-H₂O and 5% PEG-7.5% dextran (or dextran sulphate, sodium salt)-H₂O systems were used. HA originated from peat, soddy-podzolic soil and chernozem were studied. The distribution coefficients were measured for HA of different origin, size of the molecules, molecular weights (MW) of the polymers and pH of the system. The PEG-(NH₄)₂SO₄-H₂O system was found to be better for preconcentration and isolation of HA, whereas the PEG-dextran-H₂O system is preferable for HA fractionation. The extractability of HA in ABS increases with increasing the MW of HA molecules. Peat HA are extracted in ABS with higher distribution coefficients compared with chernozem and soddy-podzolic soil HA. It is consistent with higher hydrophobicity of peat HA revealed by hydrophobic interaction chromatography. ABS are promising for HA separation into fractions that differ in their hydrophobic/hydrophilic properties as well as for comparing HA of different origin by their relative hydrophobicity.     

A study on the adsorption-exchange of UO2 2+,137Cs,169Yb and HPO4 2− on modified peat

The adsorption-exchange equilibrium time and the adsorption isotherms of UO₂ ²⁺,¹³⁷Cs,¹⁶⁹Yb and HPO₄ ²⁻ on modified peat have been investigated by batch experiments. The effect of pH on the adsorption-exchange percentage (E) and the distribution coefficients (K _d) was also examined. It was found that the adsorption-exchange of UO₂ ²⁺ and¹⁶⁹Yb on the modified peat was described well by Freundlich isotherm, whereas the adsorption-exchange of¹³⁷Cs and HPO₄ ²⁻ on modified peat corresponded to a Langmuir isotherm and the maximum adsorption capacities of the modified peat for¹³⁷Cs and HPO₄ ²⁻ ions were 4.4 and 4.1 μg/g respectively. The optimum pH for the adsorption-exchange of UO₂ ²⁺,¹³⁷Cs,¹⁶⁹Yb and HPO₄ ²⁻ on the modified peat was 7.0 at 25°C.     

Effect of mechanochemical modification on the surfactant and structural properties of humic and himatomelanic acids

The structural properties of humic and himatomelanic acids are studied by means of ¹Н NMR spectroscopy and differential thermal analysis after mechanochemical modification of peat. The relationship between the structural modification of humic and himatomelanic acids and their surfactant properties in aqueous solutions is established. It is shown that the critical micelle concentration of transformed himatomelanic acids is halved in comparison to the initial sample, while the adsorption equilibrium constant grows by 9 times.     

Modification of epoxy novolak resin with polyamic acid,investigation of cocuring mechanism

The processes of thermal curing in the epoxy novolak resin-polyamic acid system were investigated by means of high-temperature FTIR spectroscopy. It was shown that, under the conditions studied, the formation of copolymer took place, and the mechanism of cocuring changed depending on the concentration of modifying agent.     

Thermogravimetric analysis of thermal stability of poly(methyl methacrylate) films modified with photoinitiators

Films of poly (methyl methacrylate) (PMMA) were prepared by the addition of photoinitiator to the polymer. The influence of five organic photoinitiators on thermal stability of poly(methyl methacrylate) was studied by thermogravimetric analysis. Next, the PMMA films doped with these photoinitiators were UV irradiated and investigated in terms of changes in their thermal stability. It was found that the photoinitiators had accelerated thermal degradation of non-irradiated PMMA films due to the action of free radicals coming from the additives’ thermolysis. For UV-irradiated specimens, the effect of photoinitiator on PMMA thermal stability depended on the chemical structure of organic compound modifying the polymer. In general, thermal stability of irradiated samples was higher in the presence of additives. Thermal destruction of modified PMMA can be explained by the formation of resonance structures in aromatic photoinitiators and consumption of energy in dissipation processes.     

63Ni在泥煤-水体系中的吸附动力学

应用同位素示踪技术,简要地研究了63Ni在泥煤中的静态吸附行为。结果表明,5 min后泥煤对63Ni的吸附率可达69%,60min后达到吸附平衡;第1吸附阶段内镍吸附量随时间的延长而增加,不易解吸;从泥煤-水液固体系中泥煤的电离平衡和镍离子-氢离子之间离子交换平衡,以及物料平衡关系推导出泥煤平衡时63Ni的吸附量和氢离子的浓度、平衡时镍离子的浓度有关。溶液的pH值对镍的吸附和解吸有很大影响,随着溶液pH值增大,63Ni由水分室向泥煤分室转移的速率常数也逐渐增大,而由泥煤分室向水分室转移的速率常数逐渐减小,二者比值逐渐增大,pH=4.624 6时,2种可逆传递速率常数相等,为2.51。即适宜pH值范围内的pH值升高吸附量增大,低pH值不利于吸附。63Ni在泥煤-水体系中的动态变化可用封闭二分室进行描述,经拟合后的理论值与实验数据点具有较好的一致性。     

Kinetic analysis of the thermal oxidative degradation of upper peat

Differential thermogravimetric analysis was used to study the thermal oxidative degradation of peat samples from different districts of the Ivanovo Region. The study was performed in nonisothermic conditions. It was found that the thermal oxidative processes involve a few steps. Kinetic characteristics [activation energy (E_a), preexponential factor (ln A), and reaction order (n)] were estimated for each step. It was found that the limiting stage of the entire process is a chemical reaction. The resulting data can be used to develop prognostic models for peatbog combustion.     

Differentialthermoanalytische Untersuchungen verschiedener Brennstoffe in Spülgasen bei unterschiedlichen Drücken

Differential thermal studies of peat and brown coal are described at high gas pressures (0.3–2.1 MPa). The experiments were performed with samples of different particle size in nitrogen, hydrogen and carbon dioxide atmospheres. The total reaction heats were plotted vs. the carbon content and a decrease was observed above 68% carbon.