Supercritical direct extraction of neodymium using TTA and TBP

Extraction of a metal ion from its oxide using ligand assisted supercritical carbon dioxide (SC CO₂) comprises namely ionisation of metal oxide, in-situ chelation of metal cation with the ligand to form metal chelate/adduct and subsequently its extraction. Understanding of the mass transfer of chelate/adduct is very important in deciding the overall performance of the in-situ supercritical fluid extraction (ISCFE) process. For the present study neodymium (Nd) is selected as a model metal ion for its extraction from oxide using a mixed ligand system containing thenoyl tri-fluoroacetone (TTA) and tri-butylphosphate (TBP). Extraction studies have been performed at 35 MPa and 60°C for the prepared Nd-TTA-TBP adduct as well as for neodymium oxide (Nd₂O₃). The rate of dissolution starting from oxide and TTA-TBP adduct of Nd have been calculated and compared with the equilibrium values based on dissolution studies at the same conditions of temperature and pressure. During the extraction starting from oxide, the ligands TTA and TBP are also co-extracted with the adduct as these are highly soluble in SC CO₂. Mass transfer coefficient has also been estimated for the steady state during the dynamic extraction. It is observed that the rate of extraction and mass transfer coefficient increase with flow rate of SC CO₂.     

The performance of lateritic stones as concrete aggregates and road chippings

Laterites and Lateritic Stones abound in the tropical and semi-tropical areas of the world, more than the igneous and other standard rocks which are used as concrete aggregates and road chippings. The paper studies the properties relevant to the use of lateritic aggregate as road chippings and concrete aggregates, and compares the results to those obtained by the use of an igneous control aggregate. The strength growth pattern of concrete made with lateritic stones, the variation of the tensile strength of the concrete (both flexural and split); the reproducibility of the strength pattern, despite the known variability in the properties of the lateritic aggregates; the influence of the iron and aluminium oxide contents of the aggregates on concrete made with them etc., are some of the parameters investigated in detail to assess the suitability of lateritic stones and crusts as concrete aggregates and road chippings. The results show that lateritic aggregates are good materials for road chippings and concrete aggregates although they give results slightly inferior to those obtained from igneous aggregates. There does not appear to be any simple relation between the iron and aluminium oxide contents or the sesquioxide contents of lateritic aggregates and the properties of the resulting concrete, although the sesquioxide contents of the lateritic stones give very broad indications of their quality.

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Résumé Les latérites et les pierres latéritiques abondent dans les zones tropicales et semi-tropicales. Leur utilisation comme matériau de construction a été contrariée dans le passé par un manque de définition valable. Dans ce rapport qui utilise une définition internationale récemment admise d'après la composition chimique du béton, on examine et on évalue, par rapport à celles d'un granulat igné, les propriétés, qui les rendent aptes à la construction, de sept échantillons de pierres latériques. On étudie l'influence des propriétés chimiques des latérites sur leur performance en tant que granulats du béton et produits de concassage routiers. Les résultats concordants sont soumis à des tests statistiques pour éviter des conclusions erronées. En outre, on a coulé des éprouvettes de béton pour étudier le développement de la variation des propriétés de bétons confectionnés avec des pierres latéritiques. On s'est efforcé d'étudier la variation de la résistance à la compression, à la flexion, à la traction, etc.; les indices obtenus à partir de rapports tels que résistance à l'écrasement de cubes/résistance à la traction par fendage, résistance de 7/28 jours, résistance à la flexion/résistance à la traction par fendage; les équations correspondant à ces rapports; la comparaison entre les relations les équations, etc, et les résultats obtenus pour des granulats de roche ignés. On a également fait des essais sur la reproductibilité du béton de pierres latéritiques et l'aptitude de ces pierres à produire des bétons de moyenne et haute résistance en utilisant deux méthodes de calcul du dosage. Les résultats montrent que, d'une manière générale, quelques unes des propriétés des pierres latéritiques dépendent de leur contenu en sesquioxyde, et que le béton et les matériaux routiers résultants sont de bonne qualité mais ne conviennent pas pour des constructions de grande qualité, des environnements abrasifs, etc. où il convient de considérer leur dureté, leur densité et leur contenu en sesquioxyde pour éviter des revêtements très médiocres. Les résultats montrent essentiellement que, dans le béton produit, le développement de la variation de la résistance, comme les rapports résistance/autres propriétés à des ages variables est semblable à celui rencontré dans des bétons obtenus à partir des granulats courants.

     

An economic design for optimum maintenance float policy

This paper introduces a cost model to solve for optimum maintenance float policy. The model is based on an iterative solution developed for closed queuing maintenance networks. The use of this approach makes it possible to solve and obtain closed form solutions to maintenance float problems when all the centers in the network are exponentially distributed. A computer program is developed for the cost model. The program searches through a three-dimensional cost surface for the optimum solution. On reaching the optimum, the optimum policy as well as the maintenance float performance measures are generated. The computer program offers a decision support mechanism for the maintenance manager by making maintenance float information readily available, providing a more expedient alternative to simulation.     

Optimization of energy and manpower requirements in Nigerian bakeries

A study on energy and manpower requirements for the bakery industry in Nigeria was carried out, covering 90 bakeries representing 75% of total registered bakeries in Onitsha city. Analysis of the energy and manpower related time series data, using engineering and statistical tools, resulted in the development of empirical model for the estimation of capacity, manpower and energy requirements in the bakery industry. This empirical model can be used for the design of a new bakery or expansion of existing one. The conditions for optimum inventory and design were determined through this optimization and the results were compared with existing system. The study revealed a huge capital investment which amounts to 5.6 billion Naira annually, a correlation between capacity of the bakery plants and resource usage (manpower, raw materials and energy use), and jobs creation potentials for 960 persons for Onitsha city alone. Diesel contributes 66.75% of total heating energy need, followed by firewood, 22.57% and petrol, 10.68%. Application of optimization techniques could result in 61% savings in inventory costs and cut in energy by about 7.4% with overall cost reduction of 8%.     

Cerium oxide dispersed multi walled carbon nanotubes as cathode material for flexible field emitters

Nanomaterials based electron sources are omnipresent in modern flat panel displays. Multi walled carbon nanotubes (MWNT) are the well studied electron emitter among the carbon materials. Since the surface modification of MWNT with low work function materials would have a positive impact on the field emission property of MWNT, cerium oxide (CeO2) nanoparticles dispersed multi walled carbon nanotubes (CeO2/MWNT) were synthesized by catalytic chemical vapour deposition followed by chemical reduction and its field emission property was investigated. The high-purity MWNT as well as CeO2/MWNT showed crystalline structure conformed by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Further characterisation was done with Raman spectroscopy, UV-Visible absorption spectra and Fourier transform IR spectroscopy (FT-IR). The morphology and structural details of CeO2/MWNT composite was probed by field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDX). The direct evidence of the formation of CeO2/MWNT composites was given by transmission electron microscopy (TEM). The synthesized sample was coated over a flexible carbon paper using spin coating technique. The experiment was performed under a vacuum of 1 x 10(-6) Torr and Fowler-Nordheim equation was used to analyse the data. The turn-on voltage for the cerium oxide dispersed MWNT was found for a current density of 10 microA/cm2. The emission current density from the CeO2 nanoparticles dispersed MWNT reached 0.2 mA/cm2 at a reasonable bias field of 2.58 V/microm. The results were compared with those of pure MWNT and pure CeO2 nanoparticles with literature values.     

Carbon nanostructure grown using bi-metal oxide as electrocatalyst support for proton exchange membrane fuel cell

A novel carbon nanostructure grown by catalytic chemical vapour deposition technique has been applied as an electrocatalyst support for oxygen reduction reaction in proton exchange membrane fuel cell. The growth of carbon nanostructure (CNS) is carried over a low cost bi-metal oxide catalyst (Fe–Sn–O) synthesized by sol–gel technique. Platinum nanoparticle decoration on Fe–Sn–O incorporated CNS (CNS-FSO) is performed by ethylene glycol reduction method. The structural as well as morphological analysis confirms the formation of CNS-FSO and platinum decoration on CNS-FSO. The electrochemically active surface area (ECSA) of platinum decorated CNS-FSO (Pt/CNS-FSO) is 68 m² g⁻¹, as revealed from cyclic voltammetry. Polarization studies are carried out at different temperatures (40 °C, 50 °C and 60 °C) to exploit the oxygen reduction reaction activity of Pt/CNS-FSO. A maximum power density of 449 mW cm⁻² (without back pressure) at 60 °C shows the potential of this novel CNS-FSO as an electrocatalyst support in proton exchange membrane fuel cell.     

Intrinsically Formed Trivalent Titanium Ions in Sol–Gel Titania

Electron paramagnetic resonance (EPR) room-temperature observation of trivalent titanium in sol–gel titania has been reported. This unprecedented detection of stable paramagnetic signals in this titania, which was treated at 200°–800°C, occurred regardless of whether the atmosphere was reducing, inert, or oxidating. The possibility that the paramagnetic signals may originate from an metal impurity other than titanium was completely excluded by analyzing the samples using three different ion-beam-analysis techniques: Rutherford backscattering spectroscopy, particle-induced X-ray emission resonance, and energy-recoil detection analysis. The paramagnetic signals appeared at precisely the temperature range of the sample dehydroxylation, which suggests a mechanism for explaining these Ti³⁺ EPR spectra.     

A school-based schistosomiasis and intestinal helminthiasis control programme in Nigeria: acceptability to community members

In a population with high prevalences in schoolchildren of infection with hookworm (32.4%), Ascaris (22.9%) and Trichuris (2.5%), visible haematuria (17.9%), micro-haematuria (17%) and proteinuria (47.3%), the knowledge about transmission of schistosomiasis and acceptability of a school-based control programme were assessed. The community perceived schistosomiasis (80.6%) and intestinal helminthiasis (66.5%) as important health problems in school-age children and most people would prefer placement of the control programme in school because it would eliminate transportation cost to the health facility. They welcomed the idea of using teachers for detection of infection and drug administration. The health staff, on the other hand, were willing to work with teachers, but emphasized that teachers should be limited to organizational and supervisory roles while they do tests and administer the drug. This view was also shared by the officials in the state ministries of health and education.