新型保护层对自保护膏剂渗硼效果的影响

以石英粉、粉煤灰和煤矸石为主要成分的3种配方的自保护膏剂,对 20钢试样进行了渗硼试验,并观察了渗硼层的显微组织.研究结果表明,采用石英粉、粉煤灰和煤矸石的保护层在渗硼温度下具有强度高、密封性好且易剥落,都能获得较好的渗硼效果;在3种自保护膏剂中,石英粉掺量为10%、粉煤灰掺量为20%、煤矸石掺量为10%时,渗硼效果最好.     

铬渣堆场污染土壤中重金属铬的存在形态

采用Tessier连续提取ICP-AES法对湖南某厂铬渣堆场土壤中重金属铬的存在形态(水溶性铬、交换态铬、碳酸盐结合态铬、有机结合态铬、铁锰结合态铬和残渣态铬)进行分析.研究结果表明,铬渣堆场土壤铬污染严重;铬渣堆场下土壤中大部分铬以铁锰结合态形式存在,在铬渣堆场周围和离铬渣堆场5 km处未污染土壤中铬大部分以残渣态的形式存在;交换态铬和碳酸盐结合态铬在土壤各剖面层次的含量相差不是很大,而可溶性铬和残渣态铬在0~40 cm土层富集,有机结合态铬和铁锰结合态铬在40~60 cm土层富集.     

酸性土壤腐蚀

1酸性土壤的腐蚀性1 1酸性土壤的形成所谓的酸性土壤是指缺乏碱金属、碱土金属而大量吸附Ｈ+ 的ｐＨ <5的土壤 ,其酸性来源有 :(1 )雨水中的碳酸(2 )微生物和植物根部代谢产物(3 )有机物分解过程中产生的有机酸(4 )硫化亚铁氧化生成的硫酸(5 )化肥分解一旦形成酸性环境 ,吸附在粘土和腐植质上的碱性金属离子和Ｈ+ 替换而引起土壤中这些金属离子的缺乏 ,因此土壤呈酸性 .1 2金属在酸性土壤中的腐蚀机理金属在土壤中的腐蚀 ,绝大多数是电化学腐蚀 ,在酸性土壤中也是如此 .金属在酸性土壤介质中也必然和在其它土壤介质一样同时存在阴极和阳极…     

伊朗东北部萨卜泽瓦尔蛇绿岩带Baghejar铬铁矿周边土壤的镍、铬污染分析与评估（英文）

主要分析伊朗东北部萨卜泽瓦尔蛇绿岩带Baghejar铬铁矿(BCM)周边土壤的镍、铬浓度,采用污染指数评估土壤污染程度。土壤样品(深度为0~20cm)采于距BCM矿不同距离的地点。采用原子吸收光谱测定土壤样品中重金属(铬和镍)含量。绘制等高线图描述重金属的空间分布,同时对金属污染程度进行了量化。结果表明,采样地土壤受到铬和镍污染。铬和镍的相应浓度分别达到(156.19±24.45)和(321.7±133.27)mg/kg,超出对应的土壤最大允许浓度。各种指数显示出铬铁矿周边土壤显著受到铬和镍污染,超出正常范围数倍之多。研究表明,重金属浓度随着与矿区距离增加而增加。采矿产生的污染可以迁移到距源头较远的地方。     

土壤中重金属的污染与危害

<正> 土壤无机污染物中以重金属比较突出,主要是由于重金属不能为土壤微生物所分解,而易于积累,转化为毒性更大的甲基化合物,甚至有的通过食物链以有害浓度在人体内蓄积,严重危害人体健康。 土壤重金属污染物主要有汞、镉、铅、铜、铬、砷、镍、铁、锰、锌等,砷虽不属于重金属,但因其行为与来源以及危害都与重金属相似,故通常列入重金属类进行讨论。就对植物的需要而言,可分为两类:一类是植物生长发育不需要的元素,而对人体健康危害比较明显,如Ca、Hg、Pb等;另一类是植物正常生长发育所需     

宁国市城市远景规划区土壤重金属积累特征及其污染评价

通过在宁国市城市远景规划区进行土壤采样及测试分析,研究了该地区0～20 cm表层土壤中Cu、Pb、Zn、Cr、Cd、As和Hg 7种典型重金属的累积状况,并采用单项指数法与内梅罗综合指数法对土壤重金属的污染进行评价.结果表明:参照安徽省土壤背景值,宁国市城区土壤中Cd积累明显,超过土壤背景值的195.08％;单项污染指...     

紫铜在土壤浸出液中的电化学腐蚀行为研究

采用电化学阻抗谱(EIS)和动电位扫描研究了紫铜在酸性和碱性土壤浸出液中的腐蚀行为,并用频率调制(EFM)方法测量了紫铜的腐蚀电流密度Icorr。结果表明:紫铜在腐蚀过程中表面生成了钝化膜,溶液中Cl-,NO3-和SO42-等离子会延长钝化膜的生长期;在酸性介质中,靠近溶液侧的钝化膜会转化成结构疏松的外层,膜层的转化使钝化膜的保护作用减弱;腐蚀20 d后,碱性介质中紫铜的Icorr为4μA/cm2左右,酸性介质中Icorr约为25μA/cm2,紫铜耐酸蚀性较差。     

X70管线钢在模拟土壤介质中裂纹扩展量化模型

试验研究了X70管线钢在模拟土壤介质中，循环载荷下的裂纹扩展特性和宏观规律．结果表明，裂纹扩展主要受裂尖应力强度因子幅△K的控制；在模拟高pH值(pH=9．3)土壤介质中，加载频率(0．1Hz～10Hz)对裂纹扩展速率无明显影响；在模拟近中性土壤介质中，裂纹扩展速率随加载频率的降低而升高，呈现明显的频率效应．结合裂纹扩展特性，分别建立了X70管线钢在模拟高pH值和近中性土壤介质中，加载频率为0．1Hz～10Hz的裂纹扩展量化模型。     

堆肥对重金属污染的水稻根际土壤细菌群落的剂量依赖性影响（英文）

在复合重金属污染的水稻土壤中分别添加1%、5%和10%(质量分数)的堆肥，150 d后观察土壤微生物群落的结构和组成变化。研究发现，堆肥对根际细菌群落的影响表现出剂量依赖效应。低等(1%)和中等(5%)堆肥添加量对根际细菌群落结构的影响比对非根际细菌群落的影响更大。根际土壤细菌多样性在添加堆肥后明显低于非根际土壤细菌多样性。冗余分析(RDA)结果表明，根际和非根际细菌群落对土壤理化性质(如p H、Pb、Cd和Cu含量)变化的响应不同，可能是根际和非根际细菌群落差异的原因之一。因此，在农业管理中应该考虑堆肥的施加对根际微生物的影响。     

广西某历史遗留矿区铅污染特征及风险评价

广西某历史遗留矿区选矿厂建设于20世纪70年代，初期铅锌矿浮选工艺落后，选矿产生的废水无序排放导致周边水体重金属超标，存在严重环境与安全隐患。对选矿厂地块土壤及地下水重金属铅进行调查，通过专业布点法采集样品，并应用单因子指数法、ALM模型评价法对选矿厂土壤重金属及地下水铅污染特征进行分析及评估。结果表明：调查范围内，地块土壤Pb含量为人体的风险不可接受，污染程度主要为中度、轻度和轻微度，且主要集中在垂向0～2 m表层，最大污染深度6 m。地下水中单因子指数区间为0.000 8～0.557 0,均<1,表明地下水对人体的健康风险在可接受范围内，地下水环境风险可控。     

Extraction of aluminium as aluminium sulphate from thermal power plant fly ashes

Valuable metal extraction technology from thermal power plant fly ash is limited. In the present study, aluminium is extracted from fly ash as highly pure aluminium sulphate (>99.0%) by leaching with sulphuric acid, followed by pre-concentration and successive crystallization. Two types of fly ashes from different sources, i.e., Talcher Thermal Power Station (TTPS) and Vedanta Aluminium Company Limited (VAL) were chosen for comparative study on the extraction of aluminium as aluminium sulphate. The product is characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Purity of aluminium sulphate was also investigated by inductively coupled plasma–optical emission spectrometry (ICP–OES). The extraction efficiency of aluminium depends on the varied solid-to-liquid ratio (fly ash : 18 mol/L H₂SO₄, g/mL) and particle size of fly ashes. Physico-chemical analysis indicates that the obtained product is Al₂(SO₄)₃·18H₂O, having low iron content (0.08%).     

SHS synthesis of Si-SiC composite powders using Mg and reactants from industrial waste

Si-SiC composite powders were synthesized by self-propagating high-temperature synthesis (SHS) using reactants of fly ash-based silica, sawdust-based activated carbon, and magnesium. Fly ash-based silica and sawdust-based activated carbon were prepared from coal mining fly ash and Para rubber-wood sawdust, respectively. The work investigated the effects of the synthesis atmosphere (air and Ar) on the phase and morphology of the SHS products. The SHS product was leached by a two-step acid leaching processes, to obtain the Si-SiC composite powder. The SHS product and SHS product after leaching were characterized by X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray spectrometry. The results indicated that the SHS product synthesized in air consisted of Si, SiC, MgO, and intermediate phases (SiO₂, Mg, Mg₂SiO₄, Mg₂Si), whereas the SHS product synthesized in Ar consisted of Si, SiC, MgO and a little Mg₂SiO₄. The SiC content in the leached-SHS product was higher when Ar was used as the synthesis atmosphere. As well as affecting the purity, the synthesis atmospheres also affected the average crystalline sizes of the products. The crystalline size of the product synthesized in Ar was smaller than that of the product synthesized in air. All of the results showed that fly ash and sawdust could be effective waste-material reactants for the synthesis of Si-SiC composite powders.     

A study on the passive state stability of steel embedded in activated fly ash mortars

The main reason for the premature failure of reinforced concrete structures (RCS) is corrosion of the reinforcements. The use of new mortars based on activated fly ash, an alternative to conventional portland cement, requires extensive research in order to check its passivating properties for reinforcements and the instability or permanence of the passive state achieved. The present paper studies this objective, analysing the passivating capacity of specimens manufactured with three different fly ash mortars treated with three activators and the stability of the passive state under the effect of 0%, 0.2%, 0.4% and 2% chloride additions in relation to the binder material, in an environment of apparently constant humidity and in humidity cycles. The evolution with time of corrosion potential (E_corr) and polarisation resistance (R_p) was studied. Polarisation curves and time constants (τ) were also assessed for some specimens using short duration galvanostatic pulses.     

Microwave Power Absorption in Materials for Ferrous Metallurgy

The characteristics of microwave power absorption in materials for ferrous metallurgy, including iron oxides (Fe₂O₃, Fe₃O₄ and Fe₀.₉₂₅O) and bitumite, were explored by evaluating their dielectric loss (Q _E) and/or magnetic loss (Q _H) distributions in the 0.05-m-thick slabs of the corresponding materials exposed to 1.2-kW and 2.45-GHz microwave radiation at temperatures below 1100°C. It is revealed that the dielectric loss contributes primarily to the power absorption in Fe₂O₃, Fe_0.925O and the bitumite at all of the examined temperatures. Their Q _E values at room temperature and slab surface are 9.1311 × 10³ W m^?3, 23.7025 × 10³ W m^?3, and 49.5999 × 10³ W m^?3, respectively, showing that the materials have the following heating rate initially under microwave irradiation: bitumite > Fe_0.925O > Fe₂O₃. Compared with the other materials, Fe₃O₄ has much stronger power absorption, primarily originated from its magnetic loss (e.g., Q _H = 1.0615 × 10⁶ W m^?3, Q _H/Q _E = 2.4185 at 24°C and slab surface), below its Curie point, above which the magnetic susceptibility approaches to zero, thereby causing a very small Q _H value at even the surface (Q _H = 1.0416 × 10⁵ W m^?3 at 880°C). It is also demonstrated that inhomogeneous power distributions occur in all the slabs and become more pronounced with increasing temperature mainly due to rapid increase in permittivity. Characterizing power absorption in the oxides and the coal is expected to offer a strategic guide for improving use of microwave energy in ferrous metallurgy.     

Chloride-induced steel corrosion in alkali-activated fly ash mortar: Increased propensity for corrosion initiation at defects

Chloride contents at the steel–mortar interface that initiate steel corrosion were determined for carbon steel in alkali-activated fly ash mortar for three different exposure conditions: exposure to 1 M NaCl solution; leaching in deionized water and then exposure to 1 M NaCl solution; and leaching in deionized water, aging in air at 20°C and natural CO₂ concentration, and then exposure to 1 M NaCl solution. For comparison, a Portland cement mortar, exposed to 1 M NaCl solution, was studied. The median values of the corrosion-initiating chloride contents (average over the full length of the rebar) in the alkali-activated fly ash mortar varied between 0.35 and 1.05 wt% Cl with respect to binder, consistently lower than what was obtained for the Portland cement mortar, but with no clear trend regarding the exposure conditions. For most of the alkali-activated fly ash mortar specimens, preferential corrosion at the connection between the working electrode and the external measurement setup was observed, while preferential corrosion did not occur for the Portland cement mortar. Scanning electron microscopy and auxiliary experiments in synthetic solutions indicated that this behavior was caused by inhomogeneities at the steel–mortar interface in the alkali-activated mortar, likely due to its peculiar rheological properties in the fresh state.     

Dilithium dialuminium trisilicate Crystalline Phase Prepared from Coal Fly Ash

The dilithium dialuminium trisilicate phase Li₂Al₂Si₃O₁₀ was prepared using coal fly ash and lithium hydroxide monohydrate LiOH·H₂O as precursors. The influences of various preparation conditions on Li₂Al₂Si₃O₁₀ forming were investigated. The results showed that the optimum additive amount of LiOH·H₂O was about 20%. The onset of calcining temperature and time was identified as 980?°C and 1?h, respectively. XRD analysis indicated that the content of Li₂Al₂Si₃O₁₀ phase increased at the expense of quartz and mullite, with calcining temperatures increasing and time extending. SEM observation revealed that the calcined samples were drastically interlocked together with the prolonging of time. The obtained Li₂Al₂Si₃O₁₀ phase was well crystallized and with small grain size.     

Microstructure and corrosion resistance of vanadium films deposited at different target-substrate distance by HPPMS

High power pulsed magnetron sputtering（HPPMS）, a novel physical vapor deposition technology, was applied to prepare vanadium films on aluminum alloy substrate in this paper. The influence of target–substrate distance（Dt–s）（ranging from 8 to 20 cm） on phase structure, surface morphology, deposition rate, and corrosion resistance of vanadium films was investigated. The results show that the vanadium films are textured with a preferential orientation in the（111） direction except for that fabricated at 20 cm. With Dt–sincreasing, the intensity of（111） diffraction peak of the films decreases and there exists a proper distance leading to the minimum surface roughness of 0.65 nm. The deposition rate decreases with Dt–sincreasing. All the V-coated aluminum samples possess better corrosion resistance than the control sample. The sample fabricated at Dt–sof 12 cm demonstrates the best corrosion resistance with the corrosion potential increasing by 0.19 V and the corrosion current decreasing by an order of magnitude compared with that of the substrate. The samples gain further improvement in corrosion resistance after annealing, and if compared with that of annealed aluminum alloy, then the corrosion potential of the sample fabricated at 20 cm increases by 0.415 V and the corrosion current decreases by two orders of magnitude after annealed at 200 °C. If the annealing temperature further rises to 300 °C, then the corrosion resistance of samples increases less obviously than that of the control sample.     

Laboratory‐simulated fuel‐ash corrosion of superheater tubes in coal‐fired ultra‐supercritical‐boilers

The corrosion behaviour of a number of Ni‐base alloys of different composition together with a highly‐alloyed austenitic stainless steel has been investigated with and without coating of the samples with alkali‐containing synthetic coal ash. The effects of various parameters have been studied, namely the Cr content (from 20 to 28 mass % Cr), the test temperature (700 and 775°C), the SO₂ content in the gas (1 vol% and 0.25 vol % SO₂) and the alkali sulphate content of the ash (10 and 30 mass%). The results can be explained on the basis of the differences in corrosion mechanisms resulting primarily from the composition of the alloys tested.     

A unified interpretation of threshold stresses in the creep and high strain rate superplasticity of metal matrix composites

The flow behavior of metal matrix composites is characterized by the presence of a threshold stress under both creep conditions at intermediate temperatures and in high strain rate superplasticity (HSR SP) at very high temperatures near the onset of partial melting. Experiments show the measured threshold stresses decrease with increasing temperature and this trend has been interpreted using an Arrhenius-type relationship incorporating an energy term, Q₀. Typically, the experimental values reported for Q₀ are ∼20–30 kJ/mol under creep conditions but up to ∼100 kJ/mol in experiments associated with HSR SP. This report resolves this apparent dichotomy by demonstrating that both sets of results become consistent when the analysis is extended to incorporate an additional dependence on temperature associated with load transfer and substructure strengthening.     

Directional solidification of TiAl–Si alloys using a polycrystalline seed

Directional solidification (DS) process of Ti–43Al–3Si alloys has been studied. Successful DS ingots having not only fully lamellar microstructure parallel to longitudinal axis but also rotated columnar grains with respect to longitudinal axis were obtained using a polycrystalline seed material. Successful seeding and growing require plane-front solidification condition during the entire DS process. Fracture toughness of the DS alloys were superior to the PST alloys, with a value of K_Q=21.7–31.7 MPa (m)^1/2 for the crack arrest/divide mode and K_Q=7.4–19.0 MPa (m)^1/2 for the short transverse mode. The orientation dependence of fracture toughness for the crack arrest/divide mode was improved in the DS alloy compared to the PST alloy.