Explosion investigation of asphalt-salt mixtures in a reprocessing plant

Cause investigation of a fire and explosion at the nuclear fuel waste reprocessing plant indicated that self-heating ignition of an asphalt-salt-waste, bituminized, mixture (AS) caused the disaster. A 220l drum was filled with the AS at a temperature of about 180 degrees C. About 20h later the drum ignited and burned as it was being cooled. It is estimated that the AS contained approximately 55wt.% blown asphalt, 25wt.% NaNO(3), 5wt.% NaNO(2), 8wt.% Na(2)CO(3), 2wt.% NaH(2)PO(4), 1wt.% Ba (OH)(2), 1wt.% K(4)[Fe(CN)(6)], and possibly 3wt.% of other materials. To determine the reaction promoting factors and pertinent chemical reaction rates, self-reaction of the AS has been investigated by the use of a C80D heat flux reaction calorimeter. The oxidizing reactions with asphalt are ruled by NaNO(2) rather than by NaNO(3), in spite of a lower concentration of NaNO(2). The kinetic rates of the interfacial reaction between salt particles and asphalt for the reaction controlled and diffusion controlled steps have been formulated as a function of salt particle size for both NaNO(2) and NaNO(3). Numerical solution of the heat balance equations formulating the heterogeneous reaction scheme indicates that a runaway reaction occurs when the AS-filling temperature is 208 degrees C for a drum filled with an AS mixture produced under standard operating conditions. Molecules containing intramolecular hydrogen, such as Na(2)HPO(4) and NaHCO(3), do not oxidize asphalt directly, however, their presence chemically promotes the oxidizing reaction of NaNO(2). Moreover, NaHCO(3) decomposition which produces gases creates many micro holes in the interior of the salt particles. This in turn promotes the oxidizing reactions that are diffusion controlled. Finally, the consequence of a runaway reaction at 180 degrees C or lower is qualitatively explained by taking into account the chemical effect of intramolecular hydrogen and the physical effect of the NaHCO(3) decomposition gases.     

Experimental determination of the minimum onset temperature of runaway reaction from a radioactive salt disposal in asphalt

In order to clarify the reason for the most hazardous explosion in the history of the Japanese nuclear power development by a radioactive salt disposal in asphalt, an adiabatic process was developed using a Dewar vessel to minimize the temperature difference between the reactants and the surroundings. By this means, the heat evolution from a reaction which is readily lost can be detected at a lower temperature imitating the accidental condition. A series of ambient temperature-tracking Dewar experiments on asphalt salt mixtures were conducted under different initial ambient temperatures, such as 230, 210, 190, and 170 °C, respectively. As a result, it was observed that from 190 °C the sample's temperature rose until a runaway reaction occurred. The minimum onset temperature for the runaway reaction of the asphalt salt mixture was determined to be 190 °C, which is close to the initial temperature of approximately 180 °C, the same temperature as the real accident. This implies that at near this operational temperature, initial faint chemical reactions may occur and lead to further rapid reactions if heat is accumulated at this stage.     

Thermal characteristics of lysine tri-isocyanate and its mixture with water

The thermal reactivity of lysine tri-isocyanate (LTI, 2-isocyanatoethyl-2,6-diisocyanato caproylate) and its mixture with 1% water was investigated after the occurrence of a runaway reaction at a plant. By using a sensitive thermal calorimeter, C80, and an adiabatic calorimeter, ARC, an onset reaction of LTI was observed at 70-100 degrees C and it became vigorous at 175-200 degrees C. The reaction is considered as co-polymerization at this stage, which causes a second decomposition reaction at 200 degrees C if the heat generation is accumulated in the vessel. On the other hand, the presence of water can catalyze LTI at much lower onset temperature and lead to a moderate reaction at 50 degrees C since carbamine is produced and in turn it induces decarbonization of the LTI molecule with significant release of CO2 gas which was detected by a gas chromatography and an FT-IR gas analyzer.     

Catalytic hydrotreating of 2,4'-DDT and 4,4'-DDT

The results of catalytic hydrotreating of a commercial mixture of 2,4'-DDT and 4,4'-DDT are reported. Experimental runs were carried out in a batch reactor (300 cm3) at constant hydrogen pressure (PH2 = 20 bar) and temperature. Temperature levels 150, 180, 200 and 230 degrees C were tested. A commercial sulphide Ni-Mo catalyst was adopted. The reacting medium was hexadecane. The kinetic constant and reaction order of the destruction reaction of 2,4'-DDT and 4,4'-DDT have been evaluated at temperature of 180, 200 and 230 degrees C. Destruction and removal efficiency (DRE) at T = 230 degrees C has been calculated.     

Using the poker-chip test for determining the bulk modulus of asphalt binders

The properties of asphalt binders strongly influence the overall mechanical response of asphalt mixture composites. A thorough understanding of the mechanistic behavior of asphalt binders is important in order to fully and accurately characterize the behavior of the asphalt mixture. The mechanical properties of the asphalt binder, the matrix in the asphalt mixture composite, are time and temperature dependent and have a lower stiffness compared to the inclusions (aggregate particles). However, computational methods used to model the micromechanics of asphalt mixtures typically assume a constant bulk modulus or Poisson’s ratio for asphalt binders. This research investigates the time-dependence of the bulk modulus of asphalt binders. Several approaches for measuring the bulk modulus were explored and the poker-chip geometry was found to be the most suitable one. The boundary value problem for the poker-chip geometry was solved to determine the bulk modulus and Poisson’s ratio of asphalt binders as a function of time. The findings from this research improve our understanding of the viscoelastic behavior of asphaltic materials, and also guide important assumptions that are typically made during computational modeling of asphaltic materials.     

考虑老化的温拌沥青混合料低温性能

为明确温拌沥青混合料中温拌剂和热老化对混合料低温性能的影响,对原样、短期老化、长期老化的沥青混合料,利用UTM-100进行了0℃、-10℃和-20℃下的小梁弯曲试验和小梁弯曲蠕变试验。研究结果表明：可用蠕变试验数据拟合出伯格斯模型参数,计算出温度应变能密度,进而由弯曲和蠕变试验结果预估出温拌沥青混合料的开裂温度,作为评价温拌沥青混合料低温性能的一个综合指标;可以用延时拌和法表征沥青混合料在短期老化过程中达到平均老化程度的热老化方法;沥青混合料在不同温度、不同老化程度下低温性能发生变化是由于拟合参数发生了变化;温拌剂在一定程度下增加了沥青混合料的抗短期老化性能;发现加入有机降黏型RH温拌剂会降低沥青混合料的低温性能,而益路温拌剂对沥青混合料的低温性能有利,故在寒冷地区推荐使用益路温拌剂。     

Thermal conductivity of reclaimed asphalt pavement (RAP) and its constituents

Up to the present, most work on the use of reclaimed asphalt pavement (RAP) has been empirical in nature. Very recent advances have demonstrated that finite-element techniques can be effectively used for modelling asphalt mixing drums in order to optimise the relative proportions of new and recycled materials and to determine the amount of time required to achieve full melting inside of the drum. A necessary prerequisite for the modelling is a definitive knowledge of the thermal conductivities of RAP and its components. This need motivated the present experimental work which encompassed RAP particles, RAP particles with the asphalt binder removed, and pure asphalt binder of different degrees of ageing. Also evaluated were taconite tailings, residual rock from the processing of iron-containing ore, and sand. The tailings have been mentioned as a candidate aggregate. The conductivity results for the solid media were related to three metrics: (a) the size ranges of the solids, (b) the density of the sample as a whole and (c) the porosity of the sample. All of the conductivity results for the investigated solid media fell in the range from 17 to 30 W/m °C. The measured conductivities of the binder ranged from 0.17 to 0.19 W/m °C.     

Effects of heating rate, temperature and iron catalysis on the thermal behaviour and decomposition of 2-nitrobenzoyl chloride

Runaway reactions arising from the decomposition of thermally unstable materials are a concern in industry due to the potentially devastating effects that they yield. Studies into the occurrence of thermal runaway incidents have shown the most likely cause to be a result of an inadequate investigation of the process prior to its operation on a large-scale. The chlorination of ortho-nitrated carboxylic acids is an industrially important reaction in the fine and agrochemical industries. The products of these reactions, ortho-nitrated acid chlorides, have been involved in runaway incidents that have resulted in violent explosions; hence, their thermal stability must be studied. Previous studies [S.D. Lever, M. Papadaki, Study of condition-dependent decomposition reactions: the thermal behaviour and decomposition of 2-nitrobenzoyl chloride, Part I, J. Hazard. Mater. 115 (2004) 91-100] showed that the decomposition of the parent molecule, 2-nitrobenzoyl chloride, is highly condition-dependent with the sample heating rate and temperature of decomposition playing a preponderant role in the course of the decomposition. Here, we present the results of studies of the decomposition of 2-nitrobenzoyl chloride, when the sample is subjected to various heating treatments, temperatures and in the presence of iron. As the temperature of decomposition was increased from 150 to 162 degrees C, the heat of decomposition was reduced from -215 to -90 kJ/mol. As the heat up rate applied in bringing the sample to the decomposition temperature increased, the heat of decomposition also increased. An increase in the heat up rate from 2 to 7.5 degrees C/min resulted in an increase in the heat of decomposition from -90 to -215 kJ/mol. The presence of iron and silver was observed to lower the heat of decomposition from -185 to -160 and -110 kJ/mol, respectively. Under most conditions investigated, the temperature at which gas flow was initiated was 147-150 degrees C. The presence of iron reduced this temperature to 140 degrees C. Decomposition was observed to take place over two stages, where the sample was heated directly from 40 degrees C at the required heat up rate. Where the sample was heated in stages and where calibrations had been carried out preceding decomposition, the decomposition took place in one stage alone.     

Numerical study of size-driven segregation of binary particles in a rotary drum with lower filling level

Discrete element method (DEM) simulations of size-driven segregation of binary particles in a rotary drum were conducted to investigate the influence of filling level, size ratio, and rotation speed on the segregation performance. Segregation experiments with different filling levels were used to verify the DEM model and analyze the influence of filling levels on segregation. The granular bed was divided into five layers to study the axial segregation in the rotary drum. The total velocity fluctuation was used to discuss the granular behavior from a mesoscopic perspective. A segregation index was adopted to quantify the segregation performance with different parameters. It was found that binary particles in the drum with different filling levels have different segregation patterns. A core of small particles was formed in the middle of granular bed for the case with a higher filling level, while there is no core formed for the case with a lower filling level. Results obtained indicate that the size-driven segregation in the drum with lower filling level increases with the increase of size ratio. Within the rolling regime, the rotation speed has little influence on the final segregation index of particles.     

Maximum Gauge Pressure in Dangerous Goods Packagings Under Normal Conditions of Carriage – Comparison of Direct Measurement and Calculation

The objective of this work was to determine the maximum gauge pressure in the vapour phase above the liquid in different design types of dangerous goods packagings under normal conditions of carriage. The design types investigated were steel and plastic packagings with a volume of approximately 6 l. Two different methods were applied. In method 1, the pressure inside the packaging filled with a certain filling substance (dichloromethane) was directly measured under simulated conditions of carriage (degree of filling: 90%; filling temperature: 15°C; temperature during storage: 31°C). The maximum measured gauge pressures were between 89 mbar for a light plastic jerrican and 336 mbar for a steel drum. In method 2, the gauge pressure was calculated. The consideration of a rigid packaging combined with the assumption of a vapour pressure of zero during filling and sealing can serve as a worst case scenario. The calculated gauge pressure is approximately 1061 mbar. This procedure leads to the highest safety factor and does not require any experimental investigations. For a more realistic approximation of the gauge pressure of a non‐rigid packaging, a packaging‐specific function of relative expansion can be used, which is determined by a hydraulic pressure test. The calculated values ranged from 105 to 347 mbar. Method 2 provides conservative results. No hazardous filling substance is needed, and it allows a prediction of gauge pressure for other temperatures, substances and filling degrees. Therefore, this method could serve as alternative to UN Model Regulations 6.1.5.5.4 (a). Copyright © 2014 John Wiley & Sons, Ltd.     

Kinetic model and tests for runaway thermally initiated styrene polymerization

An iterative analysis is presented which permits the step-by-step computation of the reaction rates, conversions, temperatures, pressures, and other variables during the runaway stage of a thermally initiated styrene polymerization contained in a sealed reactor. The highlight of this analysis is a derivation for the reaction rate as a function of reactant temperature and conversion.Based on a heat transfer analysis of some tests conducted at ambient temperatures ranging to 200°C, the iterative analysis predicted the observed reaction rates, pressures, rates of pressure rise, and temperatures within order-of-magnitude accuracies. We feel that this type of analysis may be extended to some other monomer-polymer systems.     

Numerical study of the motion behaviour of three-dimensional cubic particle in a thin drum

The motion of three-dimensional cubic particles in a thin rotating drum is simulated by the SIPHPM method. The drums with frictional or smooth front and rear walls, and the particles of cubic and spherical shapes, and different particle numbers are considered to study the effect of cubic particle shape, end-wall frictions and filling levels. Different flow patterns of cubic particles are observed, which are significantly dominated by the friction from the end-walls. The probability density function of velocity components, the flatness factors are used to analyze the motion behaviour of cubic particle. The Froude number, ensemble mean and time averaged particle velocities are also analyzed. A primary and secondary mode of driving from the end-wall frictions are indicated and the mechanisms on the influences of wall friction, particle shape and filling levels are fully explained.     

Electrical resistivity of hot-pressed silver-polystyrene powder mixture

Electrical volume resistivity and bulk density during hot-pressing were measured simultaneously on silver-polystyrene equal-sized binary powder mixture under three different conditions: (1) at constant rate of temperature increase under constant pressure; (2) at constant temperature and pressure, and (3) at constant temperature and constant rate of pressure increase. Volume resistivity decreased with increasing pressure at all temperatures studied (50 to 164° C). Above the softening temperature of polystyrene (101° C) volume resistivity under the constant pressure increased with time even after the bulk density of the compact became constant. Judging from the scanning electron micrographs, contiguity of silver particles seems to be gradually hindered due to the penetration of thin films of polystyrene between silver particles after the onset of softening of polystyrene. A new method of preparing plastic-based composites with desired electrical resistivity is therefore possible through appropriate hot-pressing of metal-polymer powder mixture.     

活化煤矸石改性沥青胶浆流变性能实验研究

煤矸石是我国目前排放量最大的工业固体废弃物之一,以粉体煤矸石为填料对沥青进行改性在国内外鲜有研究涉及。采用锥入度实验、动态剪切流变实验(DSR)和弯曲梁流变实验(BBR),研究了不同粉胶比条件下活化煤矸石改性沥青胶浆的剪切强度及高、低温流变性能变化规律,并与矿粉改性沥青胶浆进行对比;在此基础上,初探了活化煤矸石改性沥青胶浆作用机理。结果表明,采用活化煤矸石替代矿粉后,沥青胶浆的抗剪强度和高温性能大幅提高,低温性能则基本相当。研究成果为活化煤矸石替代矿粉作为沥青混合料填料的可行性提供了依据。     

Evaluation of low-temperature performance of asphalt paving mixtures

Low temperature cracking is the major damage in asphalt pavement, and many test methods have been used to evaluate the anti-cracking property of asphalt mixture. This paper evaluates the low temperature performance of asphalt mixture using four tests namely: beam bending test, indirect tensile test, contraction coefficient test and thermal stress restrained specimen test. Five types of asphalt mixtures namely: A, B, C, D and E were evaluated. Results show that compared with the thermal stress restrained specimen test, beam bending test, indirect tensile test and contraction coefficient test are not appropriate for the evaluation of asphalt mixtures low temperature performance. Moreover, results of gray relational analysis demonstrate that the bending strain energy density is significantly correlated to fracture temperature. It is reasonable to adopt the critical values of bending strain energy density to evaluate the low temperature performance of asphalt mixture in the absence of fracture temperature.     

国产环氧沥青混合料固化强度增长规律研究

研究了环氧沥青混合料的强度形成机理,在此基础上对影响环氧沥青混合料强度的两个重要因素即混合料的容留时间、养生温度进行了研究,确定了不同温度下环氧沥青混合料的容留时间范围及强度增长规律;采用差示扫描量热法（DSC）测得环氧沥青结合料在不同升温速率下的动态DSC曲线,通过非线性回归求得固化动力学关键参数,建立环氧沥青结合料的固化反应模型。研究结果可以指导环氧沥青混合料的生产与施工,同时对铺装层开放交通时间的确定有参考意义。     

Synthesis of LiYF4, BaYF5, and NaLaF4 optical nanocrystals

This paper reports the synthesis of high quality LiYF4, BaYF5, and NaLaF4 nanocrystals by high-temperature co-decomposition of precursors in organic solvents. Their bulk counterparts have long been used as efficient luminescent hosts for various applications including lasers, upconversion fluorescence, and quantum cutters. The particles were characterized using TEM, XRD, dynamic light scattering (DLS), and fluorescence spectrometry. Trifluoroacetic acid (CF3COOH) and the reaction temperature were crucial for the formation of NaLaF4 and LiYF4 nanoparticles. NaLaF4 was not formed without using CF3COOH, only LaF3 and NaF mixture was formed. NaLaF4 nanoparticles were obtained only when CF3COOH was added in the reaction solution and the temperature was > or =330 degrees C. For the synthesis of LiYF4,, in the absence of CF3COOH in the reaction, a mixture of YOF and LiYF4 nanoparticles was formed. Pure LiYF4 particles were obtained only until CF3COOH was added in the reaction at 340 degrees C or above. The nanoparticles were easily dispersed in organic solvents include hexane, toluene, and chloroform and formed transparent colloidal solutions. The ease of doping of these as-synthesized host nanoparticles for designed optical properties was assessed. The LiYF4, BaYF5, and NaLaF4 nanoparticles, co-doped with 20% Ytterbium (Yb) and 2% Erbium (Er), showed bright upconversion fluorescence upon 980 nm NIR excitation, confirming the high quality of as-synthesized nanoparticles. These nanoparticles are potential candidates for nano-optical devices, thin films, telecommunication, and bio-probes.     

Fe/C复合纳米炭粉的制备及其磁学性能研究

以高温煤焦油沥青为原料,以体积比7∶3的浓硫酸和浓硝酸混合酸为氧化剂,制备水性中间相沥青;采用溶胶-凝胶法先形成碳基溶胶,加入FeCl3后进一步形成复合Fe/C凝胶;凝胶经醇水交换、常温干燥和900℃炭化制备出Fe/C复合磁性纳米炭粉。利用FT-IR、XRD、TG和TEM等对水性中间相沥青、磁性纳米炭原粉以及磁性纳米炭粉进行表征。结果表明:采用溶胶-凝胶和常温干燥的方法可以制备出粒度均匀、形状近似于椭圆形的Fe/C复合磁性纳米炭;其磁性纳米炭粉的平均粒径约5 nm,以聚集成粒度为20 nm～30 nm的团聚体形式存在。磁性纳米炭粉中的碳以无定型结构的形式存在,Fe元素以α-Fe、Fe2O3和Fe3C的形式存在,Fe/C复合磁性纳米炭粉具有软磁性和较高的磁响应性。     

Effect of KCl, NaCl and CaCl2 mixture on volume combustion synthesis of TiB2 nanoparticles

Preparation of titanium diboride (TiB₂) nanoparticles was carried out by volume combustion synthesis. TiO₂, B₂O₃ and elemental Mg were mixed with 0-60% salt mixture of KCl, NaCl and CaCl₂ with increment of 15% as a low melting temperature diluent. Compressed samples were synthesized in a tubular furnace at a constant heating rate under argon atmosphere. Thermal analysis of the process showed that the addition of the low melting temperature salts mixture led to a significant decrease in ignition and combustion temperatures. Synthesized samples were then leached by nitric and hydrochloric acids to remove impurities. The samples were examined by XRD, SEM and DLS analysis. The results showed the formation of fine deagglomerated particles with the addition of the salts mixture. The results revealed that 45% salts mixture had the smallest average particle size of about 90 nm.     

基于DMA方法的玻璃态转变温度与沥青混合料低温性能研究

为进一步探究沥青与沥青混合料玻璃态转变温度与沥青混合料低温性能的相关性,以交通运输部公路科学研究院足尺环道(RIOHTrack)为依托,采用动态力学分析仪在弯拉受力模式下用沥青和沥青混合料试件进行温度扫描试验,通过函数拟合确定材料的玻璃态转变温度,进而比较不同定义方式下材料的玻璃态转变温度的变化趋势,探究沥青与沥青混合料相态转变温度的相关性。最后通过与低温弯曲小梁试验的实验结果的相关性和灰关联度分析,讨论利用沥青与沥青混合料的玻璃态转变温度评价沥青混合料低温性能的可行性。结果表明:(1)对于同一种材料,不同的玻璃态转变温度定义下获得的玻璃态转变温度之间存在良好的相关性;(2)在相同级配和相同试验条件下,沥青是影响沥青混合料玻璃态转变温度的主要因素;(3)在弯拉受力模式下沥青与沥青混合料的玻璃态转变温度与材料的低温性能相关性良好,但通过灰关联度分析发现采用沥青混合料的玻璃态转变温度评价混合料的低温性能更加合理。