大粒径石灰石热分解动力学研究

主要研究大粒径石灰石的煅烧特性,采用热重分析仪研究了5种不同粒径石灰石的煅烧过程。石灰石粒径分布在0.5~10 mm,煅烧温度在900~1 050 ℃。研究结果表明,粒径越小温度越高石灰石分解速率越快,而且粒径和煅烧温度对石灰石热分解机理也有明显的影响。粒径小温度高时反应符合随机成核和随后生长机理模型,粒径大温度低时反应符合相界面反应机理。当粒径为0.5~1 mm时反应活化能很小,随着粒径的增大反应活化能有所增加,粒径在1~5 mm时活化能变化不大,粒径继续增大（5~10 mm）活化能增大了1倍。     

Effect of particle size on thermal decomposition and devolatilization kinetics of melon seed shell

Thermogravimetric analysis (TGA) and devolatilization kinetics of melon seed shell (MSS) at different particle sizes (150?µm and 500?µm) and at different heating rates (10, 15, 20, and 25?°C/min) were investigated with the aid of TGA. The results of the TGA analysis show that the TGA curves corresponding to the first and third stages for 150?µm particle sizes exhibited some bumps that developed at the first and third stages of pyrolysis. It was also observed that at constant heating rate, the maximum peak temperature increases as the particle sizes increase from 150 to 500?µm, whereas 500?µm particle sizes exhibited higher peak temperatures compared to 150?µm particle sizes. The resulting TGA data were applied to the Kissinger (K), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods and kinetic parameters (activation energy, E and frequency factor, A) were determined. The E and A obtained using K method were 74.27?kJ mol^?1 and 3.84?×?10⁵?min^?1 for 150?µm particle size, whereas for 500?µm particle size were 97.12?kJ mol^?1 and 3.74?×?10⁷?min^?1, respectively. However, the average E and A obtained using KAS and FWO methods were 82.35?kJ mol^?1, 1.29?×?10⁷?min^?1, and 88.50?kJ mol^?1, 1.32?×?10⁷?min^?1 for 150?µm particle sizes. While for 500?µm particle sizes, the E and A were 108.46?kJ mol^?1, 3.14?×?10⁹?min^?1, and 113.05?kJ mol^?1, 7.56?×?10⁹?min^?1, respectively. It was observed that E and A calculated from FWO and KAS methods were very close and higher than that obtained by K method. It was observed that the minimum heat required for the cracking of MSS particles into products is reached later at higher peak temperatures since the heat transfer is less effective as they are at lower peak temperatures.     

N-甲氧酰基-N'-氨基嘧啶硫脲的热分解动力学

文章合成了N-甲氧酰基-N'-氨基嘧啶硫脲,通过X-射线单晶结构分析法测定该化合物的分子结构和晶体结构.采用DSC,TG/DTG方法研究了化合物的热分解机理,并用5种积分法和1种微分法对其进行了非等温动力学研究.结果表明:化合物为三斜系,空间群为P-1.热分解机理为随机成核和随后生长机理,热分解反应的表观活化能为142...     

The dissolution kinetics of sand as function of particle size

The initial dissolution rate of sand into sodium hydroxide solution (12.5 mol/L) over a wide range of temperatures (150 to 220°C) and pressures (0.47 to 2.29 MPa) has been determined. A semi-empirical equation was found to fit the dissolution data obtained at different temperatures and at different particle sizes. The influence of temperature on the reaction extent led to the activation energy of the dissolution, E_a = 74.41 kJ/mol. Six samples of sieved silica having narrow particle size distribution 38–40, 100–125, 212–200, 400–500 and 850–1000 μm were reacted with 12.5 mol/L sodium hydroxide solution at 220°C. The effect of particle size, i.e., surface area of the grains, on the initial rate of dissolution (denoted v₀) has been described by an empirical equation. Evidence is given here showing that the general assumption of the simple proportionality between the rate of reaction and the exposed surface of solid is not always confirmed.     

纳米粒子分散状况对复合材料非等温结晶动力学行为的影响

采用低剪切应力下分散混合与普通熔融混合方法制备出聚丙烯／无机纳米粒子复合材料。使用扫描电子显微镜（SEM）观察其脆断表面发现;采用低剪切应力下分散混合方法制备的试样中纳米粒子以纳米尺度均匀分散于树脂基体中,而普通熔融共混方法制备的试样中,纳米粒子多以十几个以上的粒子团聚体形式存在。采用示差扫描量热（DSC）研究了聚丙烯及其复合材料的非等温结晶动力学,通过对t1/2、Zc、n和△E等结晶动力学参数的分析,证明了在同等含量下,纳米粒子以纳米尺寸均匀分散的聚丙烯／纳米碳酸钙复合材料更容易结晶,且结晶速率更快。     

粒径对微米级氢氧化镁热解动力学的影响

采用热重分析仪研究了氮气气氛下不同尺寸氢氧化镁颗粒(微米级)的非等温热解动力学。结果表明,氢氧化镁热解反应呈现阶段性特征,转化率达0.8以上的反应后期,其产物水蒸气扩散被氧化镁膜所阻碍,导致失重速率明显降低。针对转化率0~0.8的氢氧化镁主分解阶段,采用Starink法和联合动力学分析法拟合解析其过程动力学模型,发现颗粒尺寸对微米级氢氧化镁的热解过程动力学无显著影响,由此可知,所考察范围内的氢氧化镁热解过程为分解反应控制,颗粒热传导和产物水蒸气扩散的阻力作用弱,氢氧化镁热解主反应过程近似于均匀转化。模型拟合求解结果显示,微米级氢氧化镁热解反应活化能为129.4 kJ/mol,指前因子为1.820×1010 min?1,其热解反应过程服从随机成核和随后生长机理(A1.5)。     

原料粒径对石灰石热分解反应动力学影响

利用热同步分析仪,在纯二氧化碳气氛、升温速率为10~30 K/min的条件下,对4种不同粒径的石灰石进行热分解特性研究,并采用改进的双外推法求解石灰石的热分解反应动力学参数。数据分析结果表明：石灰石粒径与其分解所需的活化能成正比例关系,粒径越小所需要的活化能越小,反之越大;升温速率越快,对应的分解反应温度越高,达到同一转化率所需要的时间越短,说明反应进程越快;纯二氧化碳气氛下,4种不同粒径的石灰石热分解均遵循随机成核和随后生长模型,不同粒径的石灰石对应不同的反应级数,反应级数变化范围为1/2~2;不同升温速率下石灰石热分解反应速率不同,粒径范围为38~250 μm的石灰石热分解反应速率受界面化学反应控制。     

热重分析法研究氢氧化镁纳米粉体的非等温分解动力学

以白云石为原料,盐酸酸溶后得到CaCl₂-MgCl₂滤液,采用氨水直接沉淀法制备出符合HG/T 3607-2000Ⅰ型标准的六方片状的纳米氢氧化镁。六方片厚度为25～30 nm,直径为0.3～0.4 mm。利用热重分析法对纳米氢氧化镁在不同升温速率下的热分解动力学进行研究,以期深入了解纳米氢氧化镁热分解制备纳米氧化镁粉体过程的物理化学本质。采用Kissinger法和Ozawa法计算出氢氧化镁热分解反应活化能分别为115.47 kJ·mol^-1和126.04 kJ·mol^-1。对热重分析数据进行处理和拟合,判断纳米氢氧化镁粉体热分解反应机理函数为Avrami-Erofeev（n=1.5）的随机成核和随后生长机理。指前因子为3.077×10¹⁰ s^-1。纳米氢氧化镁经煅烧制备得到的氧化镁纳米球的直径为80～100 nm。     

悬浮态下温度对碳酸钙分解产物特性的影响

  摘 要：实际生产中,人们往往关注生料入窑分解率指标,而很少考虑生料分解后物料的自身特性。利用高温一维炉设备研究了悬浮态下不同温度条件对碳酸盐反应及产物活性的影响。结果表明：相同停留时间下,900 ℃下碳酸钙分解率为26.0%,1 150 ℃下碳酸钙分解率为67.1%;1 150 ℃下碳酸钙分解产物氧化钙累计水化放热是900 ℃的近4倍,水化活性大大增强。原因在于1 150 ℃下分解后的产物结晶细小,孔隙率较高,比表面积较大。因而可利用此特点进一步加快熟料烧成进程。     

Marked particle size and support effect of Pd catalysts upon the direct decomposition of nitric oxide

The catalytic behavior of beryllia-supported Pd catalyst for the direct decomposition of NO was compared with that of silica supported one. The TOF of NO decomposition was one order of magnitude larger in the case of Pd/BeO. Over Pd/SiO₂, the TOF was increased with the increase of the Pd particle size. On the contrary, over Pd/BeO smaller Pd particles exhibited higher TOF for NO decomposition suggesting some strong electronic or structural interaction between Pd and beryllia. TPD spectra of NO(a) over reduced catalysts indicated that NO was adsorbed on Pd/SiO₂ more strongly than on Pd/BeO, and dissociation of NO(a) was easier on the former catalyst. FT-IR spectra of adsorbed NO at room temperature followed by the evacuation at elevated temperatures confirmed this. TPD spectra of O₂ desorbed from oxidized surface indicated that adsorption strength of O(a) is one of the most important factors to determine the catalytic activity of NO decomposition over supported Pd catalysts.     

Thermal decomposition kinetics and compatibility of NH3OHN5

Hydroxylammonium cyclo-pentazolate (NH₃OHN₅), as one of the poly-nitrogen compounds, has a broad prospect in the field of energetic materials, due to its high specific impulse, high detonation velocity, and the pollution-free products. In this paper, the thermal decomposition behavior of NH₃OHN₅ was studied by differential scanning calorimetry (DSC) using four heating rates (2, 5, 8, 10 °C min⁻¹). The apparent activation energy (E_K,O=114.31 kJ mol⁻¹), the pre-exponential factor (A_K=4.78×10¹¹ s⁻¹) and the critical temperature of the thermal explosion (T_b=108.08 °C) of NH₃OHN₅ were calculated by Kissinger and Ozawa method under non-isothermal heating conditions. The compatibility of NH₃OHN₅ with 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaza-isowurtzitane (CL-20), ammonium perchlorate (AP), and hydroxy-terminated polybutadiene (HTPB) were tested and judged based on a standard agreement (STANAG-4147). The DSC results showed that NH₃OHN₅/HMX, NH₃OHN₅/RDX, NH₃OHN₅/CL-20, NH₃OHN₅/AP and NH₃OHN₅/HTPB had good compatibility.     

Metaettringite, a decomposition product of ettringite

Dehydroxylation of ettringite in an atmosphere of constant partial water vapour pressure (30-400 Torr) and controlled temperature (55-95 °C) yields an X-ray amorphous product containing 11-13 H₂O per ettringite formula unit. The X-ray amorphous product does, however, give electron diffraction patterns similar to those of ettringite but with a considerably reduced from ∼1.123 nm (ettringite) to 0.85 nm in the partially dehydroxylated product, termed metaettringite. The structure of metaettringite is closely related to that of fleischerite, Pb₃Ge[(OH)₆](SO₄)₂·3H₂O and the isostructural despujolsite, Ca₃Mn^IV(SO₄)₂(OH)₆·3H₂O. These minerals contain columnar units. The columnar structure is like that of ettringite but with closer packing of columns in the a direction, resembling metaettringite.The mechanism of collapse of ettringite to metaettringite, involving loss of water and motion of columns, cannot be achieved without scissoring and possibly rotation of individual columns; this and other defect-producing mechanisms result in loss of crystallinity of the metaettringite product.     

复分解法原位合成疏水球状球霰石纳米碳酸钙

以油酸为表面改性剂,利用复分解法原位合成了疏水性球形球霰石相纳米碳酸钙颗粒,并用扫描电镜、X射线衍射、红外光谱、接触角测试等先进测定方法对产物进行表征。研究了氯化钙浓度、乙醇含量对纳米碳酸钙的影响,结果表明,增大氯化钙浓度和乙醇含量,产物粒径更小,分散性更好,但对其晶型和产物形貌影响不大,均为球形球霰石相。同时分析得出纳米碳酸钙粒子的表面性质由亲水性转变为疏水性,并探究了其表面改性的原因。     

Studies on crystal morphology and crystallization kinetics of polypropylene filled with CaCO3 of different size and size distribution

Changes in the crystal morphology, crystallinity, and the melting temperature of thermoplastics resulted in significant changes in the mechanical behavior of composites containing them. For this reason, the research of crystal morphology and crystallization kinetics in thermoplastic composites became an important requirement. The thermoplastic filled with the filler of different size gradation was a new method for improving processability of thermoplastic composites. We have previously reported that the melt viscosity of polypropylene (PP) composites, which were filled with 30 wt % CaCO₃ of effective size gradation, could be evidently declined. In this study, two sizes of CaCO₃, 325 meshes and 1500 meshes, were blended by different proportions and filled into PP matrix with 30 wt %. Crystal morphology and isothermal crystallization kinetics of a series of composites were characterized by differential scanning calorimeter (DSC) and polarizing microscope. The results showed that composites filled with CaCO₃ of effective size gradation leaded to a well‐crystalline order and a large crystal size, while their isothermal crystallization kinetics and crystallization rate constant (k) were declined, and their Avrami exponents (n) and crystallization half‐life (t_1/2) were increased compared with the composites filled with single size CaCO₃. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2437–2444, 2006     

The effect of particle size on nitric oxide decomposition and reaction with carbon monoxide on palladium catalysts

The effect of palladium particle size on its catalytic activity was investigated by the decomposition of chemisorbed nitric oxide and the reaction of nitric oxide with carbon monoxide in flow conditions. Palladium particles (30–500 Å) were prepared on silica thin films (100 Å) which were supported on a Mo(110) surface. The reactivity of the supported palladium varied with the metal particle size. On large palladium particles, nitric oxide (NO) reacts to form nitrous oxide (N₂O), dinitrogen (N₂) and atomic oxygen during temperature-programmed reaction, whereas on small particles (< 50 Å), nitrous oxide is not formed. Similarly, reactions of NO with CO on large particles, in flow conditions produce N₂O, N₂ and CO₂, whereas N₂O is not produced on small particles. In addition, more extensive NO decomposition is observed on the smaller particles.     

Determination of the intrinsic rate constant and activation energy of CO2 gas hydrate decomposition using in-situ particle size analysis

Experimental data on the rate of decomposition of CO₂ gas hydrates has been obtained using a semi-batch stirred tank reactor, with an in-situ particle size analyser, at temperatures ranging from 274 to and pressures ranging from 1.4 to . A method for calculating the moments of the particle size distribution has been presented. The experimental data was analysed using the kinetic model of Clarke and Bishnoi (Determination of the intrinsic kinetics of gas hydrate decomposition kinetics using particle size analysis, Presented at the Third International Conference on Gas Hydrates, Salt Lake City, Utah, July 18-22, 1999; Chem. Eng. Sci. 55 (2000) 4869) in its differential form in order to account for the slight change in temperature during the decomposition of CO₂ hydrates. The applicability of the new instrument for measuring gas hydrate decomposition kinetics was examined by conducting experiments with ethane at conditions similar to those encountered by Clarke and Bishnoi (2000). It was seen that the previously obtained rate constants for ethane hydrate decomposition were able to predict the new obtained data. A new procedure for regressing the intrinsic rate constant and activation energy has also been described and it is seen that the activation energy is and the intrinsic rate constant is for CO₂ gas hydrate decomposition.     

Critical initiation-energy density as a function of single-crystal size in explosive decomposition of silver azide

The dependence of the critical initiation-energy density of explosive decomposition of silver azide on the sample size was studied experimentally for the first time. The dependence of the critical energy density was found to be determined by the diffusion of the reactants to the crystal surface, where their recombination rate far exceeds the bulk rate. The diffusion coefficient and the rate constant of bulk electron-hole recombination obtained for the explosive decomposition agree within the experimental error with those determined earlier in photoconductivity studies. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 76–78, March–April, 2008.     

Enhancement of gas absorption rate as a function of the particle size in slurry reactors

Exact relationships are given for the enhancement of gas absorption rate as a function of particle size in a three-phase slurry reactor. The solid-liquid mass transfer in the liquid film at the gas-liquid interface is considered as a transfer through spherical surface. The solid phase is the catalyst or reactant. The enhancement of the gas absorption rate calculated by the given equations are in very good agreement with the experimental data as a function of particle size and solid phase concentration.     

Colour control in fly ash as a combined function of particle size and chemical composition

This paper presents the results of an investigation on the combined effect of particle size and chemical composition on the colour of fly ash - a property that determines whether fly ash polymer composites can be engineered to have very light appearance satisfying the need for a wide range of commodity applications, particularly in the building material and computer housing industry. Four fly ash samples were collected from Tarong power plant Queensland, Australia, namely fly ash from first hopper (T59), classified fly ash from first hopper (T60), grinded and then classified fly ash from first hopper (T63) and fly ash from fourth hopper (T64). It was found that the particle size of T64 is smaller but still in the same order as T63. Colour measurement and chemical composition analysis of the different FA samples showed that there is a correlation between the particle size, chemical composition and colour of the fly ash. This information could be effectively used in fly ash recycling industry.     

Modelling of decomposition of a synthetic core of methane gas hydrate by coupling intrinsic kinetics with heat transfer rates

Decomposition of a synthetic core of methane hydrate has been modelled by Selim and Sloan (1985) and Ullerich et al. (1987) based on heat transfer considerations. In the present work, the decomposition is modelled by coupling intrinsic kinetics with heat transfer rates. Numerical simulation results are presented to show the effects of incorporating the intrinsic kinetic rate of decomposition. Simulation results indicate that by changing the system pressure we can move from a heat transfer controlled regime to a regime where both heat transfer and intrinsic kinetics have a significant effect on the global rate of decomposition.