Age-hardening characteristics of aluminum alloy-hollow fly ash composites

The aging characteristics of aluminum alloy A356 and an aluminum alloy A356 containing hollow spherical fly ash particles were studied using optical microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, hardness tests, and compressive tests. The variation of hardness and compressive strength as a function of aging time for the composite have been reported. Since the density of the composite is lower than that of the base alloy due to the presence of hollow particles, the composites have a higher specific strength and specific hardness compared to the matrix. Even though the hardness of the as-cast composite was higher than that of the base alloy, no significant change in the aging kinetics was observed, due to the presence of spherical fly ash particles in the matrix. Aging times of the order of 10⁴ to 10⁵ seconds were required to reach the peak hardness (92 HRF) and compressive strength (376 MPa) in both the A356-5 wt pct fly ash composite and the matrix alloy. The possible effects of shape and hollowness of particles, the interface between the matrix and the particles, the low modulus of the particles, and the microcracks formed on the surface of hollow fly ash particles on the kinetics of the age hardening of aluminum alloy A356 are discussed.     

铝灰的综合利用

铝灰是一种对环境造成直接或间接危害的工业废弃物,但同时又是一种可综合利用的再生资源。本文综述了铝灰综合利用的主要工艺方法。     

The relationship between the quantity of heavy metal and PAHs in fly ash

Several species of the genus Haemophilus are well known etiological agents of pneumonia, meningitis, conjunctivitis, epiglottitis and chancroid. However, identification and speciation of Haemophilus is both time consuming and labor intensive. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI/TOF-MS) has been used by several investigators to profile proteins from intact and disrupted bacteria; consequently, MALDI/TOF-MS has emerged as a powerful tool in diagnostic bacteriology. This paper reports the use of MALDI/TOF-MS as a technique for the rapid identification and speciation of Haemophilus. This technique was used to not only identify the pathogen, H. ducreyi, but also to determine strain differences from different isolates. Mass spectral 'fingerprints' were obtained which permitted the rapid speciation of not only pathogenic forms of Haemophilus, but also those bacteria which are normally regarded as non-pathogenic and members of the normal flora. MALDI/TOF mass spectra can be acquired in 10 min, allowing the identification of Haemophilus spp. within 24 h rather than the 48 h or more needed for traditional bacteriological methods. In addition, these are the first mass spectral fingerprints available in the literature for many of these organisms.     

Influence of ash on interfacial reactions between coke and liquid iron

Interfacial reactions occurring between molten iron and carbonaceous materials are of great significance in the steel industry, and specifically, the reaction of iron with metallurgical coke is one of the key phenomena occurring during blast furnace ironmaking. Major operating parameters such as hot metal composition will be directly influenced by the reactions occurring between liquid iron and coke. In the current investigation, the interfacial reactions occurring between coke and liquid iron were studied at a temperature of 1550 °C using the sessile drop method to further the understanding of the fundamental reactions occurring at the interface between coke and iron. The formation of interfacial reaction products was observed, and time-dependent reactions were identified. The transfer of elements such as carbon, sulfur, and silicon was determined. The reduction of silica was determined as having a major influence on the transfer of both silicon and carbon into liquid iron. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

粉煤灰在建筑工程中的应用

根据赤峰地区优质粉煤灰在工程中的应用,说明利用“双掺”技术,通过活性混合材料,不同性能的外加剂及水泥矿物成分有机的超叠加作用,进行弥补负效应,使砼具有高性能,从而节约了水泥,降低了成本。     

Modeling of sequential reactions during micropyretic synthesis

A numerical model for a two-step sequential micropyretic reaction is reported. Such multiple reactions can take place during micropyretic synthesis of composite materials. The model was developed for the aluminothermic reaction between molybdenum oxide, aluminum, and silicon, which react to give molybdenum disilicide and aluminum oxide. The model was used to obtain the solution for the propagation of the combustion front. The melting of various constituents of reactants and products was incorporated into the model. The effect of the pre-exponential factor and the amount of diluent on the nature of propagation and temperature profile was investigated. Other conditions of propagation and synthesis for general two-step reactions were explored by changing the activation energy and heat release of each sequential reaction. A mapping procedure to characterize the types of sequential reactions is proposed and studied for several aluminothermic type reactions. Formerly Graduate Research Assistants, Department of Materials Science and Engineering     

EDTA滴定法测定铝灰中金属铝

铝灰是炼钢重要辅助材料之一,不仅能吸附钢水夹杂物而提高钢水质量,而且其中的金属铝能起到脱氧作用,从而降低钢中气体含量、减少钢中夹杂、提高钢的洁净度及机械性能。因此,将铝灰中金属铝与三氧化二铝物相分离,准确测定金属铝含量具有重要意义。采用三氯化铁溶液在电磁搅拌下溶解试样,将金属铝和三氧化二铝分离,金属铝以离子形式转入溶液中,强碱分离溶液中铁、锰等干扰元素,用过量的EDTA络合Al ³⁺,在pH 4.5～5.5以二甲酚橙为指示剂,用锌标准溶液滴定过量的EDTA后,用F^-置换出与Al ³⁺络合的EDTA,再用锌标淮溶液滴定释放出的EDTA,从而计算出金属铝含量。实验表明,通过正交试验,确定了三氯化铁溶液的质量浓度(100g/L)、用量(100mL)、样品质量(0.500 0g)、搅拌时间(60min)等溶样条件。结果表明,测得结果的相对标准偏差(RSD,n=8)为0.45%～0.78%;回收率为96%～101%。方法满足金属铝质量分数范围在10%～30%之间的铝灰检测要求。     

Salt roasting of suncor oil sands fly ash

Fly ash samples from 25 years of Suncor’s oil sands upgrading operations were tested to determine the effects of time, temperature, and salt addition on vanadium recovery by salt roasting and water leaching. The optimum roasting conditions for “carbon-free” ash were determined to be 2 to 3 hours roasting at 850 °C to 900 °C with NaCl additions of 20 to 30 pct that resulted in vanadium extractions of 75 to 85 pct for all samples tested. Leach solutions contained less than 150 mg/L Al, Fe, Ni, Si, and Ti and typically analyzed 12–20 g/L V, 0.3 to 0.6 g/L Mo, 3.2 g/L K, and 10 g/L Na. Sodium carbonate (100 g/L) was also a selective lixiviant for vanadium and produced 2 to 7 pct higher extractions than water leaching. Characterization tests showed that most of the mineral matter in the Suncor fly ash is initially present as a poorly crystalline aluminosilicate glass, but crystallizes on heating with NaCl to form distinct aluminosilicate (albite and hauyne) and iron-titanium (pseudobrookite and hematite) phases. Water-soluble vanadium and molybdenum compounds are likely formed by reacting with NaCl during this crystallization. These tests indicate that insoluble vanadium and molybdenum are associated with the aluminosilicates and that nickel is associated with the iron-titanium minerals.     

碱激发对粉煤灰活性的影响

研究了粉煤灰的物理化学特性,设计了四种方案对粉煤灰进行改性,旨在扩大粉煤灰的应用.通过对比改性前后Na₂SiO₃-粉煤灰试块的强度,使粉煤灰在改性前后的反应速度通过试块的强度得以体现.扫描电镜照片显示,在机械粉磨结合化学激发处理后,坚硬的外壳大部分被破坏.²⁷Al的核磁共振图谱显示宽峰变窄.²⁹Si的核磁共振谱表明,Q⁰消失,Q²增多,Q⁴减少.说明加入强碱并同时机械粉磨可有效破坏粉煤灰的玻璃微珠外壳及硅铝网络结构,可增强粉煤灰的潜在活性.     

Factors affecting the shrinkage of fly ash geopolymers

The shrinkage of fly ash geopolymers was studied in the present study.Fly ash was used as the source material for making the geopolymers.The effects of the concentration of Na0H,sodium silicate-to-NaOH ratio,liquid-to-ash ratio,curing temperature,and curing time on shrinkage were investigated.The geopolymers were cured at 25,40,and 600C,respectively.The results indicate that the shrinkage of geopolymers is strongly dependent on curing temperature and liquid-to-ash ratio.The increase in shrinkage is associated with the low strength development of geopolymers.It is also found that NaOH concentration and sodium silicate-to-NaOH ratio also affect the shrinkage of geopolymers but to a lesser extent.     

韶钢热电厂粉煤灰脱碳试验研究

针对韶钢热电厂产生粉煤灰烧失量偏高,难以在水泥和混凝土中推广应用而导致粉煤灰利用率低的问题,通过开展粉煤灰脱碳试验研究,寻找合适的浮选药剂等,将粉煤灰中的未燃尽碳分离出来,脱碳后的粉煤灰烧失量完全可以达到Ⅱ级粉煤灰标准,为韶钢粉煤灰资源化利用开辟了新的途径.     

Electrical conductivity and dielectric property of fly ash geopolymer pastes

The electrical conductivity and dielectric property of fly ash geopolymer pastes in a frequency range of 100 Hz-10 MHz were studied.The effects of the liquid alkali solution to ash ratios(L/A)were analyzed.The mineralogical compositions and microstructures of ash geopolymer materials were also investigated using X-ray diffraction(XRD)and scanning electron microscopy(SEM).The 10 mol sodium hydroxide solution and sodium silicate solution at a sodium silicate-to-sodium hydroxide ratio of 1.0 were used in making geopolymer pastes.The pastes were cured at 400C.It is found that the electrical conductivity and dielectric constant are dependent on the frequency range and L/A ratios.The conductivity increases but the dielectric constant decreases with increasing frequency.     

粉煤灰基多孔陶瓷过滤材料的制备和性能

以粉煤灰为骨料,采用添加造孔剂法制备粉煤灰基多孔陶瓷过滤材料,研究了造孔剂用量和烧结温度对其性能的影响.通过压汞仪、X射线衍射仪和场发射扫描电子显微镜等分析测试技术对试样进行了性能表征.结果表明:随着造孔剂用量的增加,显气孔率和吸水率升高,抗弯强度和密度下降.提高烧结温度可以有效提高抗弯强度,而不影响材料的主要物相组成;当烧结温度大于1175℃时,显气孔率和透气度显著下降.造孔剂用量为35%,烧结温度为1175℃时,可制得抗弯强度大、气孔发达及高比表面积的多孔陶瓷过滤材料.     

Development and properties of aluminium silicon alloy fly ash composites

Abstract

Aluminium (Al) silicon alloy fly ash composites were developed using powder metallurgy technique. Aluminium silicon alloy powder was homogenously mixed with various weight percentages of fly ash (5–15%) and uniaxially cold pressed at pressures ranging between 200 and 515 MPa, and the green specimens were sintered at temperatures between 575 and 625°C. The various properties of the Al alloy fly ash composites were studied and compared with that of base alloy. The density of Al alloy fly ash composites was lower than that of the base alloy. The sintered density of the Al alloy fly ash composites and Al alloy slightly decreased when compared to green density. The hardness of the Al alloy fly ash composites was higher than that of base alloy and it increased with the increase in weight percentage of fly ash content upto 12 wt-%. Compressive strength of the composites was lower than that of base alloy and it decreased with increasing weight percentage of fly ash. The electrical resistivity and corrosion rate of the composites were higher than that of base alloy and they increased with increasing weight percentage of fly ash. Scanning electron microscope was used to examine the microstructural characteristics of the composites. X-ray diffraction pattern was used to identify various phases present in Al alloy fly ash composites.     

Chemical stability of zirconia-stabilized alumina fibers during pressure infiltration by aluminum

Metal matrix composites composed of high-purity aluminum and Du Pont PRD-166 continuous zirconia-stabilized polycrystalline alumina fibers are fabricated by liquid metal infiltration using three different casting procedures. The microstructure of the composites is analyzed using optical and electron microscopy, including analytical electron microscopy. It is found that discrete faceted particles of ZrAl₃ form at the interface and grow into the matrix of samples processed above the melting point of the matrix for 13 minutes or more. The formation of this compound is in agreement with thermodynamic stability calculations. It is also found that there is a reaction between solid aluminum and the fibers at 913 K, yielding a reaction product which has the same morphology as that observed with molten aluminum. When the fibers are infiltrated with an initial preform temperature below the metal melting point and a solidifination time below 1 minute, no reaction products were visible in the composite using the scanning electron microscope (SEM). This leads to the conclusion that aluminum matrix composites can be cast with no apparent interfacial reaction product using these fibers provided that adequate processing parameters are chosen.     

碳还原粉煤灰制备SiC/Al2 O3系复合材料

在氩气气氛下,以粉煤灰为原料,石墨为还原剂,研究碳还原粉煤灰制备SiC/Al₂O₃系复合材料的反应过程,并探索其制备的工艺条件.利用X射线衍射分析还原产物的物相变化规律,使用扫描电镜和能谱仪观察复合材料的微观结构.结果表明:在1673 K粉煤灰中石英相与碳反应生碳化硅,1773 K莫来石相基本分解完全.随着反应温度的升高,生成碳化硅和氧化铝含量增加,较合适的温度条件为1773~1873 K;保温时间的延长,有利于碳化硅和氧化铝的生成,较好的保温时间为3~4 h;增加配碳量对碳化硅和氧化铝的生成有促进作用,较合适的C/Si摩尔比为4~5.在制备出的SiC/Al₂O₃复合材料中碳化硅在产物中分散较为均匀,并且粒度小于20μm.      

Diffusion bonding reactions between a SiC/SiC composite and two superalloys during joining by hot isostatic pressing

Diffusion reactions during solid state joining of a ceramic SiC/SiC composite to two superalloys, Hastelloy X and Incology 909, by hot isostatic pressing (HIP) have been investigated. The HIP pressure was 200 MPa in all joining cycles, and the temperature/dwell time were either 800°C/15 min, 900°C/1 h or 1000°C/ 1 h. The reaction zones formed consisted of a thin layer of carbides surrounded by several layers containing silicides and free carbon. The thickness of the reaction layers increased with increasing temperature, but were more affected by the composition of the alloy. With more carbide formers in the alloy, the thickness of the reaction layer decreased. The SiC composite was found to be considerably more prone to reactions with these superallys during HIP as compared to Si₃N₄ under similar conditions.     

Extraction of vanadium from athabasca tar sands fly ash

The production of refinery grade oil from the Alberta tar sands deposits as currently practiced by Suncor (formally Great Canadian Oil Sands Ltd.—GCOS) generates a substantial amount of petroleum coke fly ash which contains appreciable amounts of valuable metals such as vanadium, nickel and titanium. Although the recovery of vanadium from petroleum ash is a well established commercial practice, it is shown in the present work that such processes are not suitable for recovery of vanadium from the GCOS fly ash. The fact that the GCOS fly ash behaves so differently when compared to other petroleum fly ash is attributed to its high silicon and aluminum contents which tie up the metal values in a silica-alumina matrix. Results of experiments carried out in this investigation indicate that such matrices can be broken down by application of a sodium chloride/water roast of the carbon-free fly ash. Based on results from a series of preliminary studies, a detailed investigation was undertaken in order to define optimum conditions for a vanadium extraction process. The process developed involves a high temperature (875 to 950 °C) roasting of the fly ash in the presence of sodium chloride and water vapor carried out in a rotary screw kiln, followed by dilute sodium hydroxide atmosphereic leaching (98 °C) to solublize about 85 pet of the vanadium originally present in the fly ash. It was found that the salt roasting operation, besides enhancing vanadium recovery, also inhibits silicon dissolution during the subsequent leaching step. The salt roasting treatment is found to improve vanadium recovery significantly when the fly ash is fully oxidized. This is easily achieved by burning off the carbon present in the “as received” fly ash under excess air. The basic leaching used in the new process selectively dissolves vanadium from the roasted ash, leaving nickel and titanium untouched.