Residual effects of successive exposure of soybean Bradyrhizobium strains to aluminium on solid defined medium

The aim of these studies was to investigate whether residual toxic effects of exposing soybean root nodule bacteria to Al in a solid defined media (SDM) alter tolerance to Al, survival, sensitivity to antibiotics, N2 fixation effectiveness and genetic diversity of Bradyrhizobium strains. After being exposed four times to Al, strains showed variation in Al tolerance but there was no evidence of change in their original Al tolerance, sensitivity to the antibiotics or genetic diversity. Exposure of Bradyrhizobium strains to SDM plus Al did not alter biological N2 fixation effectiveness of five strains. Strain SEMIA 587 showed a reduction in its N2 fixation effectiveness but it seems that it was just a superficial toxic effect because one single passage through the plant eliminated this effect. Residual Al did not cause increases in Al tolerance and reductions in the survival and N2 fixation effectiveness of Bradyrhizobium strains USDA 143, SEMIA 586, SEMIA 5019, SEMIA 5039 and SEMIA 5073. It also did not alter the resistance to antibiotics of strains USDA 143, SEMIA 5039 and SEMIA 5073, and the genetic diversity of the strains SEMIA 587 and SEMIA 5019.

Nd:YAG Laser Welding of 5083 Aluminium Alloy using Filler Wire

High reflectivity and high thermal conductivity, high vapour pressure of alloyingelements as well as low liquid surface tension and low ionisation potential, make laser welding of aluminium and its alloys a demanding task.Problems that occur during welding are mainly process instabilities of the keyhole and the melt pool, increased plasma formation above the melt pool and loss of alloying elements. These problems lead to unwanted metallurgical defects like hot cracks and porosity in the weld bead andother problems concerning the shape and appearance of the weld bead. In order to minimise the defects and improve the weld quality, the process and beam parameters need to be carefully adjusted along with a consideration concerning the use of filler wire for the welding process. In this work the welding of 3,0 mm thick grade 5083 aluminium alloy plates using a 3,0 kW Nd:YAG laser with grade 5183 filler wire addition is investigated. The plates were welded as butt joints with air gap sizes 0,5 mm, 0,7mm and 1,0 mm. The analysis of the weld beads obtained from the weldedsamples showed that the least imperfections were produced with 0,7 mm air gaps at moderate welding speeds. The analysis also covered the calculation of the melting efficiency and the study of the shape of the weld bead. The melting efficiency was on average around 20 % for the melting process of the welded plates. The weld beads showed the characteristic V-shape of a laser weld and retained this shape during the whole series of experiments.

Effect of Shielding Gases in Laser Welding of Aluminium Alloys

High reflectivity to laser light, alloying element evaporation during high power laser welding makes aluminium alloys highly susceptibility to weld defects such as porosity, cracking and undercutting. The dynamic behaviour of the keyhole, due to fluctuating plasma above the keyhole and the vaporization ofthe alloying elements with in the keyhole, is the key problem to be solved for the improvement of the weld quality and stabilization of the keyhole dynamics isperhaps the single most important development that can broaden the application of laser welding of aluminium alloys. In laser welding, the shielding gas is commonly used to stabilize the welding process, to improve the welded joint features and to protect the welded seam from oxidation. The chemicalcomposition of the shielding gas is a key factor in achieving the final qualityof the welded joints. Wide range of shielding gases varying from the pure gasesto complex mixtures based on helium, argon, nitrogen and carbon dioxide are commercially available. These gas mixtures should be considered in terms of their suitability during laser welding of aluminium alloys to produce quality welds. The main objective of the present work is to study the effect of the shielding gascomposition during laser welding of aluminium alloys. Aluminium alloy A15754 was welded using 3kW Nd-YAG laser (continuous wave mode). The alloy samples were butt welded with different shielding gases (pure and mixture of gases) so that high quality welds with high joint efficiencies could be produced. It was observed that the chemical composition of the gases influenced the final weld quality and properties. In general, the mixture gases, in correct proportions, enabled better utilisation of the properties of the mixing gases, stabilized the welding process and produced better weld quality compared to the pure shielding gases.

Aluminium fouling and its impact on activated carbon based dioxin and furan removal in a wet scrubber at a co-incineration plant

Dioxins and furans, PCDD/Fs, are highly toxic substances formed in post combustion zones in furnaces. PCDD/F emissions are regulated by a waste incineration directive which relates also to co-incineration plants. Several observations of dioxin and furan enhancements in wet scrub- bers have been reported previously. This is thought to be due to the so-called "memory effect" which occurs when dioxins and furans absorb into plastic material in scrubbers and desorb when ambient circumstances alter significantly. At the co-incineration plant involved, dioxins and furans are controlled with a wet scrubber, the tower packing of which is made of plastic in which activated carbon particles are dispersed. This should avoid the memory effect and act as a dioxin and furan sink since dioxins and furans are absorbed irreversibly into the packing ma- terial. In this case, the tower packing in the scrubber is covered with a white layer that has been found to be mainly aluminium. The aim of this thesis was to determine the aluminium balance and the dioxin and furan behaviour in the scrubber and, thus, the impacts that the foul- ing has on dioxin and furan removal. The source of aluminium, reasons for fouling and further actions to minimize its impacts on dioxin and furan removal were also to be discovered. Measurements in various media around the scrubber and in fuels were made and a profile analysis of PCDD/F and mass balance calculations were carried out. PCDD/F content de- creased in the scrubber. The reduced PCDD/F was not discharged into scrubbing water. The removal mechanism seems to work in spite of the fouling, at least with low PCDD/F loads. Most of the PCDD/F in excess water originates from the Kymijoki River which is used as feeding water in the scrubber. Fouling turned out to consist mainly of aluminium hydroxides. Sludge combusted in the furnace was found to be a significant source of aluminium. Ways to minimize the fouling would be adjustment of pH to a proper lever, installation of a mechanical filter to catch the loose material from the scrubbing water and affecting the aluminium content of the sludge.

Dehydration and volatilization non isothermic kinetic of the solid state aluminium 8-hydroxyquinolinate

Al(C9H6ON)3.2.5H2O was precipitated from the mixture of an aqueous solution of aluminium ion and an acid solution of 8-hydroxyquinoline, by increasing the pH value to 9.5 with ammonia aqueous solution. The TG curves in nitrogen atmosphere present mass losses due to dehydration, partial volatilisation (sublimation plus vaporisation) of the anhydrous compound followed by thermal decomposition with the formation of a mixture of carbonaceous and residues. The relation between sublimation and vaporisation depends on the heating rate used. The non isothermic integral isoconventional methods as linear equations of Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose (KAS) were used to obtain the kinetic parameters from TG and DTA curves, respectively. Despite the fact that both dehydration and volatilisation reactions follow the linearity by using both methods, only for the volatilisation reaction the validity condition, 20<= E/RT<= 50, was verified.

Synthesis, characterization and thermal behaviour of solid state compounds of 2-chlorobenzylidenepyruvate with trivalent aluminium, gallium, indium and scandium metals

Solid state compounds M-2-Cl-BP, where 2-Cl-BP is 2-chlorobenzylidenepyruvate and M represents Al, Ga, In, and Sc were prepared. X-ray powder diffractometry, infrared spectroscopy and simultaneous thermogravimetry-differential thermal analysis (TG-DTA), have been used to characterize and to study the thermal behavior of these compounds. The results provided information concerning the stoichiometry, crystallinity, thermal stability and thermal decomposition of the compounds.

Synthesis and thermal studies of solid state 2-chloro-benzylidenepyruvic acid and its compounds with sodium, aluminium (III), gallium (III) and indium (III) cations

The synthesis of sodium 2-chlorobenzylidenepyruvate and its corresponding acid as well as binary, binary together with it's acid or hydroxo-2-chorobenzylidenepyruvate of aluminium (III), gallium (III) and indium (III), were isolated. Chemical analysis, thermogravimetry, derivative thermogravimetry (TG/DTG), simultaneous thermogravimetry-differential thermal analysis (TG-DTA) and X-ray powder diffractometry have been employed to characterize and to study the thermal behaviour of these compounds. The results provided information concerning the stoichiometry, crystallinity, thermal stability and thermal decomposition.

Performance of high power fibre laser cutting of thick-section steel and mediumsection aluminium

Cutting of thick section stainless steel and mild steel, and medium section aluminium using the high power ytterbium fibre laser has been experimentally investigated in this study. Theoretical models of the laser power requirement for cutting of a metal workpiece and the melt removal rate were also developed. The calculated laser power requirement was correlated to the laser power used for the cutting of 10 mm stainless steel workpiece and 15 mm mild steel workpiece using the ytterbium fibre laser and the CO2 laser. Nitrogen assist gas was used for cutting of stainless steel and oxygen was used for mild steel cutting. It was found that the incident laser power required for cutting at a given cutting speed was lower for fibre laser cutting than for CO2 laser cutting indicating a higher absorptivity of the fibre laser beam by the workpiece and higher melting efficiency for the fibre laser beam than for the CO2 laser beam. The difficulty in achieving an efficient melt removal during high speed cutting of the 15 mmmild steel workpiece with oxygen assist gas using the ytterbium fibre laser can be attributed to the high melting efficiency of the ytterbium fibre laser. The calculated melt flow velocity and melt film thickness correlated well with the location of the boundary layer separation point on the 10 mm stainless steel cut edges. An increase in the melt film thickness caused by deceleration of the melt particles in the boundary layer by the viscous shear forces results in the flow separation. The melt flow velocity increases with an increase in assist gas pressure and cut kerf width resulting in a reduction in the melt film thickness and the boundary layer separation point moves closer to the bottom cut edge. The cut edge quality was examined by visual inspection of the cut samples and measurement of the cut kerf width, boundary layer separation point, cut edge squareness (perpendicularity) deviation, and cut edge surface roughness as output quality factors. Different regions of cut edge quality in 10 mm stainless steel and 4 mm aluminium workpieces were defined for different combinations of cutting speed and laserpower.Optimization of processing parameters for a high cut edge quality in 10 mmstainless steel was demonstrated

Spectroscopic monitoring during laser welding of aluminium alloy

The mechanical properties of aluminium alloys are strongly influenced by the alloying elements and their concentration. In the case of aluminium alloy EN AW-6060 the main alloying elements are magnesium and silicon. The first goal of this thesis was to determine stability, repeatability and sensitivity as figures of merit of the in-situ melt identification technique. In this study the emissions from the laser welding process were monitored with a spectrometer. With the information produced by the spectrometer, quantitative analysis was conducted to determine the figures of merit. The quantitative analysis concentrated on magnesium and aluminium emissions and their relation. The results showed that the stability of absolute intensities was low, but the normalized magnesium emissions were quite stable. The repeatability of monitoring magnesium emissions was high (about 90 %). Sensitivity of the in-situ melt identification technique was also high. As small as 0.5 % change in magnesium content was detected by the spectrometer. The second goal of this study was to determine the loss of mass during deep penetration laser welding. The amount of magnesium in the material was measured before and after laser welding to determine the loss of magnesium. This study was conducted for aluminium alloy with nominal magnesium content of 0-10 % and for standard material EN AW-6060 that was welded with filler wire AlMg5. It was found that while the magnesium concentration in the material changed, the loss of magnesium remained fairly even. Also by feeding filler wire, the behaviour was similar. Thirdly, the reason why silicon had not been detected in the emission spectrum needed to be explained. Literature research showed that the amount of energy required for silicon to excite is considerably higher compared to magnesium. The energy input in the used welding process is insufficient to excite the silicon atoms.

Weldability of high strength aluminium alloys

The need for reduced intrinsic weight of structures and vehicles in the transportation industry has made aluminium research of interest. Aluminium has properties that are favourable for structural engineering, including good strength-to-weight ratio, corrosion resistance and machinability. It can be easily recycled saving energy used in smelting as compared to steel. Its alloys can have ultimate tensile strength of up to 750 MPa, which is comparable to steel. Aluminium alloys are generally weldable, however welding of high strength alloys like the 7xxx series pose considerable challenges. This paper presents research on the weldability of high strength aluminium alloys, principally the 7xxx series. The weldability with various weld processes including MIG, TIG, and FSW, is discussed in addition to consideration of joint types, weld defects and recommendations for minimizing or preventing weld defects. Experimental research was carried out on 7025-T6 and AW-7020 alloys. Samples were welded, and weld cross sections utilized in weld metallurgy studies. Mechanical tests were carried out including hardness tests and tensile tests. In addition, testing was done for the presence of Al2O3 on exposed aluminium alloy. It was observed that at constant weld heat input using a pulsed MIG system, the welding speed had little or no effect on the weld hardness. However, the grain size increased as the filler wire feed rate, welding current and welding speed increased. High heat input resulted in lower hardness of the weld profile. Weld preheating was detrimental to AW- 7020 welds; however, artificial aging was beneficial. Acceptable welds were attained with pulsed MIG without the removal of the Al2O3 layer prior to welding. The Al2O3 oxide layer was found to have different compositions in different aluminium alloys. These findings contribute useful additional information to the knowledge base of aluminium welding. The application of the findings of this study in welding will help reduce weld cost and improve high strength aluminium structure productivity by removing the need for pre-weld cleaning. Better understanding of aluminium weld metallurgy equips weld engineers with information for better aluminium weld design.

Analyse avantages-coûts de la réglementation visant l'accroissement du montant de consignation à 10¢ sur les contenants de boissons gazeuses composés d'aluminium.

Rapport de recherche

Étude critique de la densité électronique et des températures (excitation et ionisation) d'un plasma d'aluminium induit par laser

La caractérisation de matériaux par spectroscopie optique d’émission d’un plasma induit par laser (LIPS) suscite un intérêt qui ne va que s’amplifiant, et dont les applications se multiplient. L’objectif de ce mémoire est de vérifier l’influence du choix des raies spectrales sur certaines mesures du plasma, soit la densité électronique et la température d’excitation des atomes neutres et ionisés une fois, ainsi que la température d’ionisation. Nos mesures sont intégrées spatialement et résolues temporellement, ce qui est typique des conditions opératoires du LIPS, et nous avons utilisé pour nos travaux des cibles binaires d’aluminium contenant des éléments à l’état de trace (Al-Fe et Al-Mg). Premièrement, nous avons mesuré la densité électronique à l’aide de l’élargissement Stark de raies de plusieurs espèces (Al II, Fe II, Mg II, Fe I, Mg I, Halpha). Nous avons observé que les densités absolues avaient un comportement temporel différent en fonction de l’espèce. Les raies ioniques donnent des densités électroniques systématiquement plus élevées (jusqu’à 50 % à 200 ns après l’allumage du plasma), et décroissent plus rapidement que les densités issues des raies neutres. Par ailleurs, les densités obtenues par les éléments traces Fe et Mg sont moindres que les densités obtenues par l’observation de la raie communément utilisée Al II à 281,618 nm. Nous avons parallèlement étudié la densité électronique déterminée à l’aide de la raie de l’hydrogène Halpha, et la densité électronique ainsi obtenue a un comportement temporel similaire à celle obtenue par la raie Al II à 281,618 nm. Les deux espèces partagent probablement la même distribution spatiale à l’intérieur du plasma. Finalement, nous avons mesuré la température d’excitation du fer (neutre et ionisé, à l’état de trace dans nos cibles), ainsi que la température d’ionisation, à l’aide de diagrammes de Boltzmann et de Saha-Boltzmann, respectivement. À l’instar de travaux antérieurs (Barthélémy et al., 2005), il nous est apparu que les différentes températures convergeaient vers une température unique (considérant nos incertitudes) après 2-3 microsecondes. Les différentes températures mesurées de 0 à 2 microsecondes ne se recoupent pas, ce qui pourrait s’expliquer soit par un écart à l’équilibre thermodynamique local, soit en considérant un plasma inhomogène où la distribution des éléments dans la plume n’est pas similaire d’un élément à l’autre, les espèces énergétiques se retrouvant au cœur du plasma, plus chaud, alors que les espèces de moindre énergie se retrouvant principalement en périphérie.