Reaction rate and product morphology in carbon composite iron ore pellets with and without Portland cement

The aim of this work is to study the reaction rate and the morphology of intermediate reaction products during iron ore reduction when iron ore and carbonaceous materials are agglomerated together with or without Portland cement. The reaction was performed at high temperatures, and used small size samples in order to minimise heat transfer constraints. Coke breeze and pure graphite were the carbonaceous materials employed. Portland cement was applied as a binder, and pellet diameters were in the range 5.6-6.5 mm. The experimental technique involved the measurement of the pellet weight loss, as well as the interruption of the reaction at different stages, in order to submit the partially reduced pellet to scanning electron microscopy. The experimental temperature was in the range 1423-1623 K, and the total reaction time varied from 240 to 1200 s. It was observed that above 1523 K the formation of liquid slag occurred inside the pellets, which partially dissolved iron oxides. The apparent activation energies obtained were 255 kJ mol(-1) for coke breeze containing pellets, and 230 kJ mol(-1) for those pellets containing graphite. It was possible to avoid heat transfer control of the reaction rate up to 1523 K by employing small composite pellets.

Study on Iron Formation During the Carbothermic Reduction of Iron Ore in Carbon Composite Pellets in the Temperature Range 1423 K-1623 K

The aim of this work is to study the reaction rate and the morphology of the intermediary reaction products during reduction of iron ore, when iron ore and carbonaceous material are agglomerated together as a carbon composite iron ore pellet. The reaction was performed at high temperatures, and in order to avoid heat transfer constraints small size samples were used. The carbonaceous materials employed were coke breeze and pure graphite. Portland cement was employed as a binder, and the pellets diameter was 5.2 mm. The experimental technique involved the measurement of the pellets weight loss, as well as interruption of the reaction at different stages in order to submit the partially reduced pellet to scanning electron microscopy. It has been observed that above 1523 K there is the formation of liquid slag inside the pellets, which partially dissolves iron oxides. The apparent activation energies obtained were 255 kJ/mol for coke breeze containing pellets, and 230 kJ/mol for those pellets containing graphite. It was possible to avoid heat transfer control of the reaction rate up to 1523 K by employing small composite pellets.

Fretting fatigue in overhead conductors: Rig design and failure analysis of a Grosbeak aluminium cable steel reinforced conductor

The performance optimisation of overhead conductors depends on the systematic investigation of the fretting fatigue mechanisms in the conductor/clamping system. As a consequence, a fretting fatigue rig was designed and a limited range of fatigue tests was carried out at the middle high cycle fatigue regime in order to access an exploratory S-N curve for a Grosbeak conductor, which was mounted on a mono-articulated aluminium clamping system. Subsequent to these preliminary fatigue tests, the components of the conductor/clamping system, such as ACSR conductor, upper and lower clamps, bolt and nuts, were subjected to a failure analysis procedure in order to investigate the metallurgical free variables interfering on the fatigue test results, aiming at the optimisation of the testing reproducibility. The results indicated that the rupture of the planar fracture surfaces observed in the external At strands of the conductor tested under lower bending amplitude (0.9 mm) occurred by fatigue cracking (I mm deep), followed by shear overload. The V-type fracture surfaces observed in some At strands of the conductor tested under higher bending amplitude (1.3 mm) were also produced by fatigue cracking (approximately 400 mu m deep), followed by shear overload. Shear overload fracture (45 degrees fracture surface) was also observed on the remaining At wires of the conductor tested under higher bending amplitude (1.3 mm). Additionally, the upper and lower Al-cast clamps presented microstructure-sensitive cracking, which was folowed by particle detachment and formation of abrasive debris on the clamp/conductor tribo-interface, promoting even further the fretting mechanism. The detrimental formation of abrasive debris might be inhibited by the selection of a more suitable class of as-cast At alloy for the production of clamps. Finally, the bolt/nut system showed intense degradation of the carbon steel nut (fabricated in ferritic-pearlitic carbon steel, featuring machined threads with 190 HV), with intense plastic deformation and loss of material. Proper selection of both the bolt and nut materials and the finishing processing might prevent the loss in the clamping pressure during the fretting testing. It is important to control the specification of these components (clamps, bolt and nuts) prior to the start of large scale fretting fatigue testing of the overhead conductors in order to increase the reproducibility of this assessment. (c) 2008 Elsevier Ltd. All rights reserved.

Pellets prepared with mechanically activated iron ore

This work analyses pellets prepared with iron ore that has been mechanically activated by high energy ball milling. Pellet feed iron ore was submitted to high-energy ball milling for 60 minutes, and the resulting material was analysed through measurements of particle size and specific surface area, as well as X-ray diffraction. Pellets were prepared from this material. The pellets were heated at temperatures ranging from 1000 to 1250 degrees C in a muffle furnace, and submitted to the maximum temperature during 10 - 12 minutes. The samples were then tested regarding crushing strength, densification and porosity, and were examined in a scanning electronic microscope. The results were compared to those obtained with similar samples made from non-milled pellet feed. It has been shown that through high-energy ball milling of iron ore it is possible to achieve pellets presenting high densification and compressive strength at firing temperatures lower than the usual ones.

Technological characterization of phosphate ore types from the Salitre Alkaline Complex, MG - Fosfertil Area

The present study was carried out on six different ore types from the Salitre Alkaline Complex aiming to determine their mineralogical composition and the major features that are relevant in the mineral processing. The P(2)O(5) grades vary from 9 to 25%. The slime content (-0, 020 mm) varies between 20 and 34% (w/w) and carries 17-22% of the P(2)O(5) content. The samples essentially consist of apatite, iron oxi-hydroxides, ilmenite, clay minerals, carbonate, quartz, pyroxene, perovskite, secondary phosphates and other minor accessory minerals. Below 0.21 mm, apatite essentially occurs in free particles showing a clean surface or a weak coating of it-on oxi-hydroxides; the highly covered apatite (not recoverable by flotation) varies from 6 to 9%. In the deslimed fraction (above 0.020 mm) more than 97% of the total phosphor content occurs as apatite; the estimated P 2 0 5 potential recovery in flotation concentration is over 90% (71-76% overall recovery).

Evaluation of aluminium tolerance in grapevine rootstocks

Aluminum (Al) toxicity is a major worldwide agricultural problem. At low pH, Al speciates into the soluble and phyto-toxic form Al(3+), inhibiting the root growth and affecting plant development. In Brazil, agriculture in acidic soils with elevated concentration of Al has significantly increased in the last decades. Therefore, in order to achieve efficient agriculture practices, the selection of plant cultivars with improved Al resistance has become crucial in this type of soils. In this work we have evaluated the Al resistance of six genotypes of grapevine rootstocks. The grapevine hardwood cuttings were grown in nutrient solution in the absence and presence of 250 and 500 mu M Al at pH 4.2. The phenotypic indexes of relative root growth, fresh and dry root weight, root area, hematoxylin staining profile, and Al content were evaluated for all six genotypes. These phenotypic indexes allowed us to identify the `Kober 5BB`, `Gravesac`, `Paulsen 1103`, and `IAC 766` grapevine rootstocks genotypes as the ones with the highest resistance to Al. Likewise, `IAC 572` and `R110` genotypes were the most Al-sensitive cultivars. We evaluated the root organic acid exudation profile in the most Al-resistant (`Kober 5BB`) and most Al-sensitive (`R110`) in plantlets cultivated in vitro in the absence and presence of 100, 200, and 400 mu M of Al. Among several compounds detected, citrate was the only organic acid related to the Al resistance phenotype observed in the `Kober 5BB` genotype. The high constitutive citrate exudation observed in `Kober 5BB` strongly suggests that exudation of this particular organic acid may impart Al-resistance/a melioration in grapevine.

Rhizotoxicity of aluminate and polycationic aluminium at high pH

Although monomeric Al species are often toxic in acidic soils, the effects of the aluminate ion (Al(OH)4-) on roots grown in alkaline media are still unclear. Dilute, alkaline (pH 9.5) nutrient solutions were used to investigate the effects of Al(OH)4- on root growth of mungbean (Vigna radiata L.). Root growth was reduced by 13 % after 3 d growth in solutions with an Al(OH)4- activity of 16 μM and no detectable polycationic Al (Al13). This decrease in root growth was associated with the formation of lesions on the root tips (due to the rupturing of the epidermal and outer cortical cells) and a slight limitation to root hair growth (particularly on the lateral roots). When roots displaying these symptoms were transferred to fresh Al(OH)4- solutions for a further 12 h, no root tip lesions were observed and root hair growth on the lateral roots improved. The symptoms were similar to those induced by Al13 at concentrations as low as 0.50 μM Al which are below the detection limit of the ferron method. Thus, Al(OH)4- is considered to be non-toxic, with the observed reduction in root growth in solutions containing Al(OH)4- due to the gradual formation of toxic Al13 in the bulk nutrient solution resulting from the acidification of the alkaline nutrient solution by the plant roots.

Freeform fabrication of functional aluminium prototypes using powder metallurgy

Freeform fabrication methods allow the direct formation of parts built layer by layer, under the control of a CAD drawing. Most of these methods form parts in thermoplastic or thermoset polymers, but there would be many applications for freeform fabrication of fully functional metal or ceramic parts. We describe here the freeforming of sinterable aluminium alloys. In addition, the building approach allows different materials to be positioned within a monolithic part for an optimal combination of properties. This is illustrated here with the formation of an aluminium gear with a metal-matrix composite wear surface. (C) 1999 Kluwer Academic Publishers.

The effect of solidification rate on the structure of magnesium-aluminium eutectic grains

A magnesium-aluminium alloy of eutectic composition was solidified under two different cooling conditions, producing a low and a high growth rate of the eutectic solid-liquid interface. The high growth rate specimen contained smaller eutectic grains and cells, with a smaller interphase spacing compared with the low growth rate specimen. The high growth rate specimen also contained some primary Mg17Al12 dendrites, suggesting that the coupled zone is skewed towards the Mg phase with increased undercooling, A lamellar eutectic morphology was observed in the low growth rate specimen, while the morphology was fibrous in the high growth rate specimen.

Aluminium alloys - their physical and mechanical properties: Grain formation in AlSi7Mg0.35 foundry alloy at low superheat

Hypoeutectic AI-Si alloys represent the most widely used alloy system for cast aluminium applications. This system has a unique behaviour with respect to grain formation where an increase in silicon content results in a transition to larger grain sizes after a minimum at an intermediate concentration. As a result of the already large solute content, grain refinement by solute additions is inefficient and nucleant particles from the common aluminium grain refiners are not as effective as in wrought alloys. However, casting conditions, such as a low pouring temperature, that promote the formation of wall crystals tie. crystals nucleated in the thermally undercooled layer at or next to mould walls) are very effective in yielding a small grain size. This paper presents results of an investigation of the effect of low superheat and mould preheat temperature on grain size. It was found that pouring temperature controls the effectiveness of the wall mechanism while mould preheat has little effect until high preheat temperatures at which a large increase in grain size occurs. The observed changes in grain size are explained in terms of the balance between nucleation rate and survival rate of crystal nuclei resulting from changes in superheat and mould temperature.

Mesoporous silica-immobilized aluminium chloride as a new catalyst system for the isopropylation of naphthalene

Mesoporous MCM-41 silica immobilized aluminium chloride shows high catalytic activity and selectivity in the Friedel-Crafts alkylation of naphthalene with isopropanol.

Subduction of the Nazca Ridge and the Inca Plateau: Insights into the formation of ore deposits in Peru

A large number of ore deposits that formed in the Peruvian Andes during the Miocene (15-5 Ma) are related to the subduction of the Nazea plate beneath the South American plate. Here we show that the spatial and temporal distribution of these deposits correspond with the arrival of relatively buoyant topographic anomalies, namely the Nazca Ridge in central Peru and the now-consumed Inca Plateau in northern Peru, at the subduction zone. Plate reconstruction shows a rapid metallogenic response to the arrival of the topographic anomalies at the subduction trench. This is indicated by clusters of ore deposits situated within the proximity of the laterally migrating zones of ridge subduction. It is accordingly suggested that tectonic changes associated with impingement of the aseismic ridge into the subduction zone may trigger the formation of ore deposits in metallogenically fertile suprasubduction environments. (c) 2005 Elsevier B.V All rights reserved.

Shear deformation at 29% solid during solidification of magnesium alloy AZ91 and aluminium alloy A356

Partially solid commercial Al-Si and Mg-Al alloys have been deformed in shear during solidification using vane rheometry. The dendritic mush was deformed for a short period at 29% solid and allowed to cool naturally after deformation. Both alloys exhibited yield point behaviour and deformation was highly localised at the surface of maximum shear stress. The short period of deformation was found to have a distinct impact on the as-cast microstructure leading to fragmented dendrites in the deformation region of both alloys. In the case of the Mg-Al alloy, a concentrated region of interdendritic porosity was also observed in the deformation region. Concentrated porosity was not observed in the Al-Si alloy. (c) 2005 Elsevier B.V. All rights reserved.