Magnesium and its alloys are extensively used for various industries such as aerospace, automobile and electronics due to their excellent properties such as low density, high strength and stiffness and electromagnetic shielding. However, the wide spread applications of these alloys are limited due to the undesirable properties such as poor corrosion, wear and creep resistance and high chemical reactivity. These alloys are highly susceptible to galvanic corrosion in sea water environment due to their high negative potential (-2.37 V vs SHE). The effective way of preventing corrosion is through the formation of a protective coating, which acts as a barrier between the corrosive medium and the substrate. Many surface modification methods such as electro/ electroless plating, conversion coating, physical and chemical vapour depositions, thermal spray coating etc., are available currently to improve the corrosion resistance of Mg alloys. Of these methods, the electroless nickel plating has gained considerable importance because of its excellent properties such as high hardness, good wear and corrosion resistance. The properties of binary electroless nickel coating have been further improved by the addition of a third element such as cobalt, tungsten, tin and copper etc. It has been reported that the addition of tungsten as the third element in the Ni-P improves the properties such as hardness, wear and corrosion resistance, thermal stability and electrical resistance. Magnesium alloys are categorized as a “difficult to plate metal”, because of their high reactivity in the aqueous solution. They react vigorously with atmospheric oxygen and water, resulting in the formation of the porous oxide/ hydroxide film which does not provide any protection in the corrosive environment. Further, the presence of this oxide film prevents the formation of a good adhesive bond between the coating and the substrate. The surface treatment process for removal of the oxide layer is very much essential before plating the Mg alloy. Currently two processes such as zinc immersion and direct electroless nickel plating are adopted to plate Mg alloys. Etching in a solution of chromate and nitric acid followed by immersion in HF solution to form a conversion film is necessary for direct electroless nickel (EN) plating of Mg alloy. However, strict environmental regulations restrict their usage because of hazardous nature. Expensive palladous activation treatment is a well-known process as a replacement for chromate-HF pretreatments for Mg alloys. It has been reported that EN plating has been carried out over Mg alloys by using conversion coating followed by HF treatment. Formation of an intermediate oxide layer by electrolytic methods is also one of the ways these toxic pretreatments can be avoided. Microarc oxidation (MAO) is an environment friendly surface treatment technique which provides high hardness, better corrosion and wear resistance properties for the Mg alloys. EN coating has been prepared on MAO layer for improving the corrosion resistance. These MAO/EN composite coatings have been prepared using chromic acid and HF pretreatment process. As the replacement for the chromate-HF pretreatment, SnCl2 and PdCl2 sensitization and activation procedures respectively were adopted over MAO layer for the deposition of Ni-P coating. From the above reported literature, it can be inferred that for the activation of inert MAO layer to deposit electroless nickel coating, the hazardous chromate/HF and highly expensive PdCl2 activation processes were followed. Therefore, there is a need for identifying an alternative simple and cost effective pretreatment process for the deposition of electroless nickel. It is well known that borohydride is a strong reducing agent that has been used for the deposition of Ni-B coatings. In the present study, an attempt has been made to utilize borohydride in the pretreatment process for the reduction of Ni2+ ions over the MAO interlayer, which provides the nucleation sites for the deposition of Ni-P coating. Ni-P and Ni-P/Ni-W-P duplex coatings were deposited from stabilizer free carbonate bath on AZ31B Mg alloy to improve the corrosion resistance of the base substrate. The conventional chromate and HF pretreatment processes were followed for the deposition of electroless nickel coating. In order to improve the corrosion resistance of the duplex coating, post treatments such as heat treatment (4 h at 150°C) and chromate passivation were adopted. EDX analysis of AZ31B Mg alloy showed the presence of 2.8 wt.% of Al and 1.2 wt. % Zn with the balance of Mg for AZ31B Mg alloy. After the chromic acid and HF treatment, the magnesium content was reduced from 90.0 wt % to 54.9 wt%, which could be due to the incorporation of chromium on the surface layer. The surface showed about 17.8 wt. % of F. The alloy exhibited the roughness of about 0.29± 0.01µm after mechanical polishing. The roughness value was significantly changed after the chromic acid treatment processes. The maximum roughness of about 1.28±0.06 µm was obtained after the HF activation. XPS analysis confirmed the existence of chromium in +3 oxidation state after the chromic acid treatment. The Ni-P coating thickness of about 25 microns was obtained in 1 h and 15 min. In the case of duplex coatings, Ni-P plating was done for 45 min. to obtain approx. 17 microns thickness and Ni-W-P plating was done for 1.15 h to obtain a thickness of approx. 10 microns, resulting in a total thickness of 25 ± 5 microns. Ni–P coating exhibited nodular morphology with porosity. The size of these cluster nodules were of about 10 µm in diameter. On the other hand, the duplex coating exhibited a less nodular, dense and smooth appearance. From the compositional analysis it was found that Ni–P coating contained about 6 wt. % P. In the case of duplex coating, the P content was reduced to 3 wt % due to the incorporation of about 2 wt% of tungsten. In corrosion studies, the potentiodynamic polarization data obtained for bare Ni-P coating in 0.15 M NaCl solution exhibited a higher current of about 218 μA/cm2 as compared to the substrate due to the porosity of the coating. However, the Ni-P/Ni-W-P duplex showed 55 times improvement in corrosion resistance, vis-a-vis Ni-P due to the dense nature of the coating. The corrosion resistance of the coatings increased in the following order: Ni-P < bare alloy < duplex < duplex-passivated < duplex-heat treated passivated. In EIS study, the Nyquist plot obtained for the bare substrate and Ni–P coating showed the presence of inductance behavior at the lower frequency region due to the adsorption of electroactive species over the substrate through the porous oxide layer. However, the passivated and duplex passivated coatings exhibited only capacitive behavior due to their compact nature. From the above, it can be concluded that, direct deposition of Ni-P coating over the chosen Mg alloy using chromic acid and HF pretreatment process resulted in porous morphology, which affected the corrosion resistance of the coating. As an alternative strategy, the microarc oxidation conversion coating was developed on Mg alloy and characterized. The MAO coating was developed using silicate electrolyte at three different current densities (0.026, 0.046 and 0.067 A/cm2) for about 15 min. With respect to the MAO coating, an increase in the current density increased the pore diameter and decreased the pore density. The surface of the coating became coarser and rough. The cross-sectional morphology of the coating showed two district layers namely the dense and thin inner layer and a porous thick outer layer. The thickness of the coating increased with increase in current density. MAO coating prepared at an intermediate current density of 0.046 A/cm2 exhibited a higher thickness of about 12 µm and a further increase in current density showed a decrease in thickness, due to the greater rate of dissolution of Mg, relative to the rate of deposition. The surface roughness of the MAO coatings also increased with increase in current density. The Ra value increased from 1.39±0.06 to 3.52±0.17 µm with increase in current density. XRD peaks obtained for the Mg substrates corresponded predominately to magnesium. However, the coated specimens showed the presence of peaks corresponding to Mg2SiO4 along with Mg and MgO. The corrosion measurements for the bare substrate and MAO coatings were carried out in 3.5% NaCl medium (0.6 M). Based on potentiodynamic polarization studies, the MAO coating prepared at 0.046 A/cm2 exhibited a lower corrosion current density with a higher Rp value, which was about five orders of magnitude higher than the bare substrate, due to the dense nature of the coating. In EIS study, MAO coatings were fitted with the two time constants equivalent circuit containing outer porous layer and inner barrier layer. The barrier layer resistance values were higher than that of porous layer resistance, which indicated that the resistance offered by barrier layer was higher than the porous layer. The total resistance value obtained for the coating prepared at 0.046 A/cm2 were higher compared to the other coatings, which attested to its better corrosion resistance. The electrochemical noise measurement was carried out for longer immersion durations upto 336 h in 3.5% NaCl solution. The noise resistance value obtained for the base Mg alloy was about 100 Ω at 1h immersion, whereas for the MAO coating prepared at 0.04 A/cm2 a maximum value of about 34.8 MΩ was achieved and it was retained even after 96 h of immersion. Mott–Schottky analysis showed that the oxide layer on magnesium substrate acted as a n-type semiconductor, whereas the MAO coatings exhibited p-type semiconductor behavior. The MAO coating obtained at an intermediate current density showed a higher acceptor density and the flat band potential, which resulted in the better performance of the coating in corrosive environment. In another set of investigations, the Ni-P and Ni-P/Ni-W-P coatings were deposited on AZ31B Mg alloy with MAO coating as an interlayer. The MAO layer was activated by a simple borohydride pretreatment process. During the pretreatment process, the MAO coating was subjected to mild alkali treatment, immersion in the Ni-P plating solution and finally immersion in borohydride solution. During each pretreatment step, the sample was characterized for their surface morphology and composition. The surface morphology showed the distribution of spherical particles over the surface of MAO coating after immersion in the Ni-P plating solution. EDX analysis showed the presence of 2.4 wt. % of Ni, which confirmed that Ni ions were adsorbed over the surface of the MAO coating during the pretreatment process. XPS analysis carried out after immersion in the Ni-P plating solution indicated that Ni existed in +2 oxidation state. The surface became smooth and uniform with flake- like morphology after the borohydride treatment, which indicated that the surface was etched by the borohydride solution. EDX analysis showed the presence of 1.8 wt.% of Ni after borohydride reduction. XPS analysis confirmed the reduction of nickel to the zero oxidation state. Additionally, MAO/Ni-P and MAO/Ni-P/Ni-W-P duplex coatings were developed on MAO coating after a simple borohydride pretreatment. Ni-P and duplex coatings showed uniform and dense nodular morphology without any defects, which clearly indicated that the borohydride treatment provided a uniform and homogeneous active surface for the deposition of electroless nickel based coatings. Borohydride pretreatment process resulted in excellent bonding between MAO/Ni-P layers in the cross section. Based on potentiodynamic polarization studies, the corrosion current values obtained for MAO/ Ni-P and MAO/Ni-P/Ni-W-P duplex coatings were about 1.44 and 1.42 µA/cm2, respectively. The coating showed about 97 times improvement in corrosion resistance compared to the bare substrate, attesting to the dense nature of the coating. In EIS study, the single time constant equivalent circuit was used for fitting the spectra, which pertained to the coating /electrolyte interface. The single time constant could be attributed to the pore-free dense, uniform coatings developed over the MAO interlayer. For the MAO/Ni-P and MAO/Ni-P-Ni-W-P duplex coatings, the charge transfer resistance of about 15 and 11 kΩcm2 were obtained for duplex and Ni-P coatings, which reinforce the better corrosion protective ability of the coating. The above investigation confirms that MAO coatings have good corrosion resistance in the aggressive chloride medium. Consequently, they can serve as an ideal interlayer for the deposition of the electroless nickel coating. Even if the electroless nickel coating is found to fail in harsh environments, the MAO interlayer can protect the base substrate due to its higher corrosion resistance. It is also noteworthy that the borohydride treatment provides better adhesion between the MAO/Ni-P interlayer.

A large number of advanced structural materials are based on metallic materials where alloying additions play a key role in imparting the required properties. Most of the commercially important aluminium alloys are classified by the nature of the alloying additions. Among them the 2219, 2618, 5086, and 7075 are important class of lightweight alloys that plays critical role in modern engineering application. However, despite having a series of commercially useful aluminum alloys for commercial applications the increasing need of improved performance requires newer development in particular for applications that require high strength at elevated temperatures and performance at extreme environments. Precipitations of the intermetallic compounds containing copper during thermal treatments play a very important role in developing high strength aluminium alloys. Although,these precipitates are stable at fairly high temperatures, the rapid coarsening of these second phase precipitates (e.g. Al2Cu), leads to loss of strength at elevated temperature. Several approaches are explored to overcome this problem. One of them is to utilize non-equilibrium solidification route, which can increase solid solubility and hence increasing the precipitate density. Nonequilibrium processing can also alter the selection pathway of the competitive phases and evolution of the microstructure. Recently, non–equilibrium solidification by suction casting technique is becoming increasingly popular for casting of metallic materials of any shape. In this technique solidification is effected by sucking the molten alloy into water cooled copper mold using a suction force resulting from the differences between the melting chamber in Argon gas pressure and casting chamber under vacuum. The present thesis aims to develop a set of newer alloys with small amount of alloying additions primarily based on nickel that can retain reasonable strength at high temperature by utilizing the non-equilibrium solidification route. In addition to Ni (≤ 0.10at.%), the thesis present results of the effect of minor addition of Sc and Zr as ternary and quaternary additions. Following a short review in chapter 2, Chapter 3 presents the experimental techniques adopted for both preparation of alloys and their characterization. Chapter 4 deals with the results of alloying of aluminum with minor amount of nickel. The Ni in the range of 0.05-0.20at% was used to develop a high temperature template, containing a set of hardening intermetallic compounds to increase the strength of the host matrix. The microstructural investigations of the suction cast alloys reveal a characteristic feathery microstructure. At higher magnification the microstructure reveals the presence of fine dispersions of a second phase. Both x-ray and transmission electron microscopy confirms the phase in the dispersions to be primarily crystalline Al9Ni2 phase having a monoclinic crystal structure. This phase does not exist in equilibrium phase diagram. Only at higher concentration one can observe equilibrium Al3Ni (Orthorhombic) particles. The size of the particle ranges from 50-200nm. Beyond~0.5at%Ni, the microstructure changes to normal cellular type solidification morphology with interdendritic space decorated by the eutectic network of Al-Al3Ni having a rod eutectic morphology. A careful observation of alloys with small amount of Ni reveals that the feathery structure is associated with the thin cells, which have grown by continuously splitting the tip yielding a fractal like dendritic morphology. The dispersoids form at the intercellular regions. We have presented clear evidence of their origin from the interdendritic liquid, which most likely underwent Rayleigh instability. The random distribution reflects the nature of the dendritic growth. We have argued that these inter-dendritic liquid droplets, which are enriched with Ni, get undercooled. The metastable Al9Ni2 phase nucleates and grows in this liquid. In order to confirm this scenario, we have carried out a phase field simulation for dendritic growth of aluminium solid solution in the alloy melt both under the condition of constraint growth and free growth. The observed distribution of the dispersoid is well reflected in the phase field simulation. The chapter also report the response of effect of direct ageing of suction cast alloy as one expect an extension solid solubility of Ni in Al. A small increase in hardness could be observed during ageing treatment. In order to determine the thermal stability of the intermetallic particles, the samples of the suction cast alloys were exposed at 200°C for 200h and 500°C for 100h respectively. No change in the microstructure could be observed excepting a slight coarsening indicating the dispersed particles are thermally stable. After exposure at two different temperatures the maximum retained hardness was measured to be 350MPa. We have also attempted to correlate the hardness with coarsening behavior of particles. The feathery morphology of the cast structures and fine dispersion of the intermetallic phase is expected to improve the tensile strength of the alloy. The tensile yield strength of cast alloys was determined to be 150MPa ± 20 for Al- 0.09at%Ni alloy. We have tried to estimate the expected strength of the alloy from quantitative microstructural parameters using possible hardening mechanism. The estimates are in good agreement to the observed values. The chapter 5 reports attempts to develop thermally stable precipitation strengthened aluminum alloys by retaining the dispersion template developed earlier alloyed with Ni. Then, the binary alloys were added with extremely low diffusivity element Zr. The element Zr is traditionally added in the aluminium alloys as grain refiner and as a powerful agent for inhibiting recrystallization especially for high strength aluminium alloys. However, in this work we have alloyed Zr for imparting precipitation hardening. An amount of 0.15at%Zr was added to the suction cast alloys of Al-0.05, 0.09 and 0.20at%Ni. The first two alloys exhibit the formation of metastable phase Al9Ni2 during solidification stage. Increase the concentration of the alloy to Al-0.20at% Ni with 0.15at%Zr additions exhibits combination of both stable Al3Ni and Al9Ni2 metastable phases. Microstructures of these alloys show columnar cells of ~200μm with dispersions of spherical nodules of Al9Ni2 and Al3Ni with varying size ranges from 200-500nm. Particle size distribution of Zr containing aluminium alloys with 0.05at% Ni is 595nm ± 20 while the alloy having the 0.09 at% Ni has the optimum size of 290nm. Further increase of Zr composition above 0.20at % led to columnar to equiaxed transition. The as cast alloys containing Zr does not show the improvement with limited yield strength of the order of 150MPa. The equivalent hardness of the samples has been measured to be about 370-420MPa. Heat-treated alloys however show the presence of Al3Zr (L12) precipitates with ~20nm size that are coherent with the matrix. Binary suction cast Al-0.15at%Zr alloy after ageing exhibits tensile yield strength of ~200MPa. With ternary aluminium alloy with minor additions Ni and Zr, The strength increases to ~300MPa. Additionally, the alloy continue retain a maximum hardness of 870-920MPa even after long hours of aging. The Zr containing alloys were proved to be stable. When the tests were carried out on a nominally alloyed sample of Al-0.09at%Ni-0.15at%Zr peak aged and exposed to 250°C for 200h, the yield strength under compression tests was found to be 280MPa. The chapter 6 of the thesis discusses the role of Sc with the ternary Al-alloys with Ni and Zr. Addition of small quantities 0.1 and 0.2at%Sc substantially reduces the inter-particle distance of precipitates by increasing volume fraction and number of nano-sized particles. It has been observed and presented in this thesis that the Sc addition provides the highest incremental strengthening per atom percent of any alloying element. Chill-suction cast samples show equiaxed cells in the samples with dispersions of particles inside and some segregated particles at the cell boundaries. To achieve a further increase in the number density of precipitates we processed the suction cast alloys with additional heat treatment at 375 and 450°C. All the suction cast alloys with varying Ni content and keeping the Sc and Zr constant at 0.10 and 0.15at% respectively exhibit formation of Al9Ni2 phase. The alloy Al-0.20at%Ni-0.10at%Sc-0.15at%Zr also contain stable phase of Al3Ni with an eutectic morphology. The DSC experiments in the dynamic mode with heating rate of 10°C min-1 exhibit two distinct exothermic peaks due to precipitates from solution at 375 and 450°C. The TEM analysis using STEMEDX has further confirmed the existence of nano-sized particles 30-50 nm of both phases of Al3Sc and Al3 (Sc, Zr). The tensile yield strength of the as cast alloy show 200MPa while after precipitation treatment, we observe improved yield strength 350-450MPa. Thermal stability of the alloys were tested after peak aged condition and exposed to 200°C for 250h. The results show that the yield strength is unaffected implying the coarsening resistance of the precipitate particles. Overall the thesis establishes that with minimum alloying additions, it is possible to design alloys that are expected to perform for high temperature applications by the formation of set of dispersions of Al9Ni2 (monoclinic) and precipitates of ordered cubic phases of (L12) structure of Al3Zr, Al3Sc and Al3 (Sc, Zr) with required number density of particles.

The aim of my diploma thesis was to explore the influence of manganese ions put into nickel nitrate structure. The attention was focused mainly on the stabilization of nickel nitrate a modification, which could not change into b modification. The theoretical part of my thesis focused on applied materials, kinds of acumulators, basic parameters of acumulators and the description of chosen methods of measurement employed. It contained the electrodeposition, the impedance spectroscopy and the cyclic voltammetry. The task of the experimental part was to measure the effect of manganese ions put into potassium hydroxide structure. Proportions of Ni (nickel nitrate) : Mn (manganese nitrate) 10:0, 7:3, 5:5, 6:1 and 6:4 were blended for the measurement. By means of the electrodeposition, there was a thin layer of nickel hydroxide with an admixture of manganese ions from nickel nitrate and manganese nitrate dilution put on the nickel plate. After the spread of the thin layer on the nickel plate, the measurement by the method of cyclic voltammetry followed. The next task consisted in trying to add KOH (potassium hydroxide) anionic and cationic surfactant into the dilution.

<p>Испитиван је утицај повећаних концентрација тешких метала, кадмијума, никла и<br />олова, на метаболизам и биопродукцију различитих генотипова (фамилија)<br />багрема <em>(Robinia pseudoacacia</em> L. 1753) у циљу дефинисања њиховог физиолошког и биохемијског одговора на различити степен загађења. Биолошки ефекат тешких метала испитиван је на биљкама гајеним на воденим хранљивим растворима и у земљишним културама. Истраживања су обухватила одређивања степена биопродукције (свежа маса корена, изданака и листова; висина биљака; укупна лисна површина), интензитет размене гасова (фотосинтеза и транспирација), садржаја фотосинтетичких пигмената (каротеноиди, хлорофил а и б), садржаја макроелемената у биљном ткиву (N, P и К) и акумулираних тешких метала, биохемијске физиолошке параметре (активност ензима нитрат-редуктазе, каталазе, аскорбат-пероксидазе, гвајакол-пероксидазе, интензитет липидне пероксидације (садржај MDA), садржај пролина) у ткивима коренова, изданака и листова.</p><p>Токсични ефекти примењених метала су зависили од испитиване фамилије багрема (генотипа) и врсте метала, а испољили су се у редукцији интензитета фотосинтезе и транспирације, као и у променама активности ензима укључених у антиоксидативне механизме заштите. Изразитити симптоми токсичности били су евидентни код биљака гајених методом водених култура, где је присуство метала у раствору довело до значајних поремећаја водног биланса у виду смањенетранспирације и проводљивости стома. Регистровано је такође&nbsp; сигнификантно смањење интензитета фотосинтезе биљака гајених на третману никлом. Активност ензима укључених у антиоксидативне механизме заштите показала се као поуздан индикатор стреса изазваног тешким металима. Хидропоним тестовима утврђен потенцијал испитиваних фамилија багрема за фитоекстракцију метала класификује их у категорију хиперакумулатора. Поред тога, значајна акумулација тешких метала у корену биљака указује на велики потенцијал ових фамилија у процесу фитостабилизације полутаната у земљишту. Поред наведеног, третмани са EDTA су указали на велики значај овог синтетског хелатора приликом фитоекстракције никла и кадмијума у земљиштима слабо базне реакције и ниске биодоступности метала.</p> / <p>Ispitivan je uticaj povećanih koncentracija teških metala, kadmijuma, nikla i<br />olova, na metabolizam i bioprodukciju različitih genotipova (familija)<br />bagrema <em>(Robinia pseudoacacia</em> L. 1753) u cilju definisanja njihovog fiziološkog i biohemijskog odgovora na različiti stepen zagađenja. Biološki efekat teških metala ispitivan je na biljkama gajenim na vodenim hranljivim rastvorima i u zemljišnim kulturama. Istraživanja su obuhvatila određivanja stepena bioprodukcije (sveža masa korena, izdanaka i listova; visina biljaka; ukupna lisna površina), intenzitet razmene gasova (fotosinteza i transpiracija), sadržaja fotosintetičkih pigmenata (karotenoidi, hlorofil a i b), sadržaja makroelemenata u biljnom tkivu (N, P i K) i akumuliranih teških metala, biohemijske fiziološke parametre (aktivnost enzima nitrat-reduktaze, katalaze, askorbat-peroksidaze, gvajakol-peroksidaze, intenzitet lipidne peroksidacije (sadržaj MDA), sadržaj prolina) u tkivima korenova, izdanaka i listova.</p><p>Toksični efekti primenjenih metala su zavisili od ispitivane familije bagrema (genotipa) i vrste metala, a ispoljili su se u redukciji intenziteta fotosinteze i transpiracije, kao i u promenama aktivnosti enzima uključenih u antioksidativne mehanizme zaštite. Izrazititi simptomi toksičnosti bili su evidentni kod biljaka gajenih metodom vodenih kultura, gde je prisustvo metala u rastvoru dovelo do značajnih poremećaja vodnog bilansa u vidu smanjenetranspiracije i provodljivosti stoma. Registrovano je takođe&nbsp; signifikantno smanjenje intenziteta fotosinteze biljaka gajenih na tretmanu niklom. Aktivnost enzima uključenih u antioksidativne mehanizme zaštite pokazala se kao pouzdan indikator stresa izazvanog teškim metalima. Hidroponim testovima utvrđen potencijal ispitivanih familija bagrema za fitoekstrakciju metala klasifikuje ih u kategoriju hiperakumulatora. Pored toga, značajna akumulacija teških metala u korenu biljaka ukazuje na veliki potencijal ovih familija u procesu fitostabilizacije polutanata u zemljištu. Pored navedenog, tretmani sa EDTA su ukazali na veliki značaj ovog sintetskog helatora prilikom fitoekstrakcije nikla i kadmijuma u zemljištima slabo bazne reakcije i niske biodostupnosti metala.</p> / <p>The influence of increased concentrations of heavy metals, cadmium, nickel and lead on the metabolism and bioproduction of different genotypes (half-siblings) of black locust (<em>Robinia pseudoacacia</em> L. 1753) was investigated in order to define their physiological and biochemical responses to different pollution levels. The biological effect of heavy metals was tested on plants grown in aquatic nutrient solutions and in soil cultures. Тhe investigations included determination of biological production degree (fresh weight of roots, stems and leaves, plant height, total leaf area), the rate of gas exchange (photosynthesis and transpiration), the photosynthetic pigments content (carotenoids, chlorophyll a and b), the contents of major macronutrients in plant tissue (N, P and K) and the accumulated heavy metals, physiological biochemical parameters (activity of the enzymes: nitrate reductase, catalase, ascorbate peroxidase, guaiacol peroxidase, lipid peroxidation (MDA content), the content of proline) in tissues of roots, stems and leaves. Toxic effects of applied treatments differed between tested plant genotypes and applied metal, resulting with depletion of the photosynthetic and transpiration rate, and further altering the activity of antioxidative enzymes. Major influence of applied metals were observed on plants grown in nutrient solution where the presence of heavy metals had caused water status disbalance, resulting with decrease in transpiration rate and stomatal conduction. Results related to the activity of enzymes involved in antioxidative protection indicated significance and relevance of these metabolic parametars in research of heavy metals stress in plants. Besides aforementioned , the potential forphytoextraction purposes was confirmed through hydroponic trials. Obtained results for heavy metal accumulation in plant tisuess have determined these families as heavy metal hyperaccumulators. Likewise, significant accumulation of metals in root tissues might be very promising for phytostabilization purposes. In addition, supplementation of EDTA have shown a great potential for phytoextraction of nickel and cadmium in soils with high pH and lower bioavailability of metals.</p>

Une alternative aux énergies fossiles comme vecteur énergétique peut se présenter sous la forme de l'hydrogène et de son stockage. Les hydrures métalliques sont une des options possibles pour le stockage de l'hydrogène. Les accumulateurs alcalins Ni-MH présentent une technologie intéressante pour les applications portables et pour le développement des véhicules électriques hybrides (HEV). Afin de répondre à la demande d'augmentation de la capacité massique des accumulateurs, de nouveaux composés intermétalliques hydrurables de type ABx (3etlt;xetlt;5) sont étudiés. Le groupe A est constitué de terres rares partiellement substituées par du magnésium, le groupe B contient du Ni. Après un état de l'art sur ce type de composés, le travail de cette thèse consiste à rechercher les conditions d'élaboration des composés A1-yMgyNix (3etlt;xetlt;5, 0etlt;yetlt;1, A= La, Pr, Nd) ainsi que de les caractériser d'un point de vue structural et physico-chimique (DRX, microsonde électronique, ICP) et de déterminer leurs propriétés vis-à-vis de l'hydrogène (réac tion solide-gaz et électrochimique). Durant ce travail de nouvelles phases ont été découvertes et caractérisées : les phases (A1-yMgy)5Ni19 / One solution to overcome the diminution of fossil fuel resources is to use hydrogen as an energy vector. The main issue concerning hydrogen systems is its storage. NiMH batteries are promising candidates for portable devices and hybrid vehicles (HEV) applications. In order to answer to growing need for higher capacity, new compounds such as ABx (3etlt;xetlt;5) are under investigation. A is a rare earth element that can be partially substituted by Mg. B is Ni. After careful examination of the state of the art on this family of compound, the synthesis routes to prepare A1-yMgyNix (3etlt;xetlt;5, 0etlt;yetlt;1, A= La, Pr, Nd) alloys were investigated and optimized during this PhD work. The structure and chemical composition of the samples were determined using X-ray diffraction, microprobe analysis and ICP. The hydrogen sorption properties (solid-gas and electrochemical reactions) were studied as well. During this work the (A1-yMgy)5Ni19 new phase s have been reported and characterized

Ni electrodeposition is a suitable process for producing thick deposits and thick metallic microstructures, especially for producing relatively deep micromoulds in Microsystems industry. Ni-P deposits, due to their better properties compared to Ni deposits – particularly high mechanical properties (hardness, wear resistivity), corrosion resistance, magnetic properties, a higher fatigue limit and lower macroscopic deformation – can be a very good alternative for producing Microsystems, especially for MEMS or Microengines. According to few limited literature and our primary investigations, dispersion coating and adding particle into the electrolyte can be considered as an approach in order to decrease the stress and ease the deposition of Ni-P galvanically. Although in the last decades the influence of particles embedment in the matrix by electroplating techniques have attracted the scientific interest, there are still contradictions among the research community concerning the influence of codeposited particles on the microstructure and strengthening properties of Ni-based composites coatings. In many cases, it is believed that the enhanced mechanical performance of the coatings is mainly caused by a change in the microstructure of the metal matrix and not so much by the presence of the particles themselves. In other words, the role of particle characteristics - like their nature, size and concentration - on the layer features and strengthening mechanism of electrodeposited Ni-based composite coating with different matrix is not cleared well. Furthermore, the incorporation of particles into the deposit is mainly considered as a key factor for determining the composite coatings properties. Despite of existing models of ECD, the mechanism of particle incorporation into the film under influence of different particle characteristics has not been well understood yet. Therefore, the main aim of this study is to shed light on the effect of particle characteristics (size, concentration, type) on the codeposition process, microstructure and strengthening mechanisms in Ni and Ni-P electrodeposited composite coatings.

Les applications portables et stationnaires des accumulateurs Ni-MH nécessitent sans cesse des autonomies de plus en plus importantes. Cet accroissement d’autonomie peut être obtenu en développant de nouveaux composés intermétalliques hydrurables de type ABx (3<x<4) de plus grande capacité massique. Le groupe A de ces composés est constitué de La partiellement substitué par du Mg, qui est beaucoup plus léger et diminue la masse molaire de l’alliage, et le groupe B contenant du Ni partiellement substitué par d’autres éléments de transition. Après une étude bibliographique approfondie, le travail de cette thèse consiste à rechercher tout d’abord les conditions optimales d’élaboration d’intermétalliques de composition La1-yMgyNix (0<y<1 ; 3<x<4). Puis ces composés sont caractérisés du point de vue structural et physico chimique (diffraction des rayons X et microsonde électronique), et leurs propriétés vis-à-vis de l’hydrogène (réaction solide-gaz et électrochimique) sont étudiées / Mobile and stationary applications for Ni-MH batteries require continuously more and more energy density. This increased autonomy can be obtained by developing new hydride-forming compounds of ABx-type (3<x<4) with larger weight capacities. The A element of these compounds is constituted of La partially substituted by light Mg, allowing a reduced molar weight. The B element is made of Ni that can be partially substituted by other transition metals. After an extensive bibliographic study, this thesis presents the research work to find optimum conditions for the synthesis of Mg-containing intermetallic compounds La1-yMgyNix (0<y<1; 3<x<4). These compounds are then characterized from the structural and chemical point of views (X-ray diffraction and microprobe analysis) and their hydrogen-related properties are studied and compared (solid-gas and electrochemical reactions)

Cette thèse vise à améliorer les propriétés d'alliage à mémoire de forme et de stockage d'hydrogène du TiNi par des substitutions chimiques sur le sous-réseau de Ni. L'effet de la substitution de Ni par Pd, Cu et Co sur les propriétés structurales, la transformation martensitique et les propriétés d'hydrogénation de TiNi, a été étudiée par des techniques structurales (diffraction des Rayons-X et des neutrons sur poudre), calorimétriques, par réaction solide-gaz et par mesure électrochimique. Des calculs de type DFT ont été effectués pour mettre en évidence les modifications de la structure électronique sur les propriétés d'hydrogénation. Les trois substitutions, TiNi1-zMz (M = Pd, Cu et Co; z ≤ 0,5), conduisent à la formation de composés pseudo-binaires. La substitution par Pd et par Cu augmentent le volume de la maille de TiNi, alors que celle par Co possède un effet inverse. Les températures de transformation martensitique suivent la même tendance que les changements de volume. Ils augmentent fortement pour M = Pd et légèrement pour M = Cu, tandis qu'elles diminuent pour M = Co. Les propriétés d'hydrogénation sont très sensibles à la nature chimique des substitutions. La capacité diminue fortement avec la substitution par Pd, modérément avec le Cu et reste stable pour le M = Co. Contrairement à l'effet attendu par des considérations géométrique, la substitution par Pd et par Cu diminuent la stabilité des hydrures. Les calculs DFT montrent qu'un effet électronique, et non géométrique, régit la stabilité des hydrures pour M = Pd. La substitution par le cobalt induit une formation de plusieurs hydrures par étapes successives, observée par mesure d'isothermes pression-composition en multiple plateaux. Pour les applications, la substitution de Ni par Cu avec une faible teneur (z = 0,2) augmente la capacité de décharge électrochimique de TiNi de 150 à 300 mAh/g en raison de la déstabilisation de l'hydrure. Cela ouvre de nouvelles perspectives pour l'utilisation d'alliages TiNi comme électrodes de batteries Ni-MH. En revanche, la substitution par Pd ou Cu (avec z = 0,5) est très efficace pour réduire la réactivité de TiNi avec l'hydrogène, et est donc intéressante pour des applications à mémoire de forme sous un environnement réducteur / The PhD thesis aims to improve shape memory and hydrogen storage properties of TiNi by chemical substitutions in the Ni sub-lattice. The effect of Pd, Cu and Co substitutions on crystal structure, martensitic transformation and hydrogenation properties of TiNi has been studied by structural (X-ray and neutron powder diffraction), calorimetric, solid-gas and electrochemical means. Ab initio DFT calculations were done to highlight electronic effects on hydrogenation properties. The three substitutions, TiNi1-zMz (M = Pd, Cu and Co; z ≤ 0.5), lead to the formation of pseudobinary compounds. Substitutions by Pd and Cu increase the unit-cell volume of TiNi, whereas the reverse effect occurs for Co. Martensitic transformation temperatures correlate with volume variations. They increase strongly for M = Pd and slightly for M = Cu, whereas M = Co decreases it. Hydrogenation properties are very sensitive to chemical elements substitution. The capacity decreases strongly for M = Pd, moderately for M = Cu and remains stable for M = Co. Contrary to expected effect by geometric model, both Pd and Cu substitutions decrease the stability of hydrides. DFT calculations show that electronic rather than geometric effects govern hydride stability for M = Pd. Co substitution induces step-wise formation of hydrides with a multi-plateau behaviour in pressure-composition isotherms. As concerns applications, low amount of Cu substitution (z =0.2) increases the electrochemical discharge capacity of TiNi from 150 to 300 mAh/g due to hydride destabilization. This opens new perspectives for using TiNi-based alloys in Ni-MH batteries. In contrast, Pd and high amount of Cu substitution (z = 0.5) are effective to decrease TiNi reactivity towards hydrogen, and therefore attractive for shape memory applications under reductive environment

Cette thèse porte sur l'étude des phénomènes qui se produisent lors de la réaction métal-silicium (siliciuration) en couches minces et dans des nanofils. En effet, les phénomènes tels que la germination, la croissance latérale, la croissance normale et la diffusion doivent être compris pour réaliser les contacts des futurs dispositifs de la microélectronique. La comparaison entre la siliciuration en couches minces et dans les nanofils est l'un des principaux aspects de ce travail. La distribution atomique en 3D des éléments chimiques dans les différentes siliciures de Ni a été obtenue par sonde atomique tomographique (SAT). Pour permettre l'analyse par SAT de différents types des nanofils à base de silicium, plusieurs méthodes originales de préparation des échantillons par faisceau d'ions focalisés ont été développées et testées. D'autre part, des mesures in situ et en temps réel de diffusion réactive par diffraction de rayons X ont permis de mettre en évidence l'importance de la germination dans la formation des phases et de déterminer les cinétiques de formation des siliciures de Ni allié en Pt, notamment des régimes de réaction aux interfaces et de croissance latérale. La forme caractéristique associée à la croissance latérale a été déterminée par des analyses ex situ de microscopie électronique en transmission et comparée aux modèles existants. La détermination par SAT de l'espèce qui diffuse majoritairement donne aussi des indications sur les mécanismes de formation des phases et de relaxation des contraintes dans les siliciures. / This thesis focuses on the phenomena that occur during the reaction between metal and silicon (silicide) on thin films and nanowires. Indeed, phenomena such as nucleation, lateral growth, normal growth and diffusion must be understood to make contacts for future microelectronic devices. The comparison between the silicide formation on thin films and nanowires is one of the main aspects of this work. Atomic distribution in 3D for the elements in different Ni silicide phase was obtained by atom probe tomography (APT). To enable the analysis of different types of silicon nanowires by APT, several original methods for sample preparation by focused ion beam has been developed and tested. On the other hand, in situ and real-time analysis by X-ray diffraction during the reactive diffusion helped to highlight the importance of the nucleation of a phase and to determine the kinetics of formation of Ni(Pt) silicides, including the reaction on the interfaces and the lateral growth. The characteristic shape associated with the lateral growth was determined by ex-situ transmission electron microscopy analyzes and was compared with the existing theoretical models. Moreover, the determination of the fastest diffusing species by APT provided information on the mechanisms of phase formation and stress relaxation in the silicide.

Face à l'augmentation générale de la consommation d'énergie, l'exploitation du Gaz Naturel Liquéfié (GNL) connaît un intérêt croissant, d'où un marché en forte expansion avec de nombreux projets d'installation de terminaux méthaniers. Les installations de gaz naturel liquéfié ont la particularité de fonctionner à très basses températures (~ -160°C), ce qui exige l'utilisation de matériaux particuliers présentant des caractéristiques adaptées aux températures extrêmes. Cette étude nous a permis d'évaluer le comportement structural de l'acier 9% Ni métal de base, consistant en une phase ferrique d'un grain martensitique en présence d'austénite, utilisé dans la construction du réservoir interne de stockage du GNL.Ce métal présente des domaines inhomogènes au niveau mésoscopique principalement formés par la phase austénitique riche en Ni mis en évidence par la diffusion des neutrons aux petits angles. Suite à une déformation mécanique, une augmentation du pourcentage de la phase austénitique est observée au niveau de la zone de déformation plastique. Ce phénomène est probablement dû à la diffusion préférentielle du Ni le long des dislocations au cours du traitement mécanique et son accumulation au niveau de cette zone. Au cours du processus de soudage, une diffusion intergranulaire du Ni au sein de la zone affectée thermiquement (ZAT) est observée. Ce phénomène permet de stabiliser la phase austénitique au niveau de la ZAT et d'améliorer les propriétés mécaniques au sein de cette zone. La déformation mécanique appliquée à basse température sur l'acier 9% Ni, ne détériore pas les propriétés structurales de ce matériau. / Due to the overall increase in energy consumption, the use of the Liquefied Natural Gas (LNG) is experiencing an increasing interest, resulting in a rapidly growing market with many LNG terminals installation projects. LNG installations have the particularity of operating at extremely low temperatures (~ -160°C), which requires materials with specific characteristics suitable to extreme temperatures. This study allowed us to evaluate the structural behavior of the base metal 9% Ni steel, consisting of a ferritic phase with a martensitic grain in the presence of residual austenite, used in the construction of the inner wall of LNG storage tank. This metal presents, at the mesoscopic level, non-homogeneous domains formed primarily by the Ni rich austenitic phase revealed by small angle neutron scattering. Due to a mechanical deformation, an increase in the percentage of the austenitic phase is observed at the plastic deformation zone. This phenomenon is probably due to the preferential diffusion of Ni along dislocations during the mechanical treatment and its accumulation at this area. During the welding process, a grain boundary diffusion of Ni in the Heat Affected Zone (HAZ) is observed. This phenomenon allows the stabilization of the austenitic phase at the HAZ and the improvement of the mechanical properties within this area. Mechanical deformation applied at low temperatures on the 9% Ni steel, does not deteriorate the structural properties of the material.