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Nanocomposite LaNi5/Mg2Ni- and ZrV2/Mg2Ni-type hydrides

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Nanostructured metal hydrides are a new class of materials in which outstanding hydrogen sorption may be obtained by proper engineering of the microstructure and surface [1]. These materials will play an important role in the field of hydrogen storage. For the vehicle application, depending on the temperature of hydrogen absorption/ desorption below or above 150°C, the alloy hydrides can be distinguished in high and low temperature materials. The principal disadvantages of alloy hydrides, apart from the cost, are the low hydrogen content at low temperature (e.g. La-based alloys) and the difficulty of reducing desorption temperature and pressure of alloy hydrides having high hydrogen storage capacity and fast rated (e.g. Mg-based materials). To solve the above mentioned problems, the use of composite materials, starting from La-based alloys and of catalyzed metal (C, Ni, Pd) or Mg-based alloy hydrides has been proposed [1, 2]. An important process on the surface of hydrogenated material is the splitting of the hydrogen molecule into atoms. Many clean transition metal surfaces have the capability of dissociating hydrogen, but lose this property upon oxidation. It is well known, that the oxidation process causes the sealing of the surface to H2 in metals and compounds such as Nb, V, Ta, FeTi, and others [3]. On the other hand, in a surface layer of LaNi5, La segregates and Ni forms ferromagnetic precipitation’s [3, 4]. The lanthanum atoms binds the impurities as oxide or hydroxide and keeps the Ni metallic, which then is able to split the hydrogen molecule. Therefore, the surface segregation process of lanthanum in the presence of O2 or H2O explained the excellent hydrogenation properties of LaNi5 [4, 5]. The nanocrystalline metal hydrides offer a breakthrough in prospects for practical applications. Their excellent properties (significantly exceeding traditional hydrides) are a result of the combined engineering of many fa[...]

Modyfikacja tytanu mikroi nanoprekursorami proszkowymi metodą stopowania mikroplazmowego powierzchni

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Tytan i jego stopy wraz z jego unikatowymi właściwościami, do których można zaliczyć dużą wytrzymałość właściwą oraz bardzo dobrą odporność korozyjną, wypierają z niektórych obszarów aplikacyjnych stale konwencjonalne. Odpowiedni dobór składu chemicznego oraz stosowanych procesów obróbki cieplnej umożliwia uzyskiwanie struktury w zakresie pożądanych właściwości eksploatacyjnych [1, 2]. Znaczne koszty materiałowe w wielu obszarach przemysłu maszynowego, chemicznego, spożywczego, a także motoryzacyjnego, zbrojeniowego, lotniczego [3], czy wreszcie aplikacji medycznych [4], ustępują wzrostowi efektywności i żywotności użytkowania odpowiednio dobranych materiałów. Obecnie prowadzone badania dla tej grupy materiałowej są głównie ukierunkowane na poprawę własności eksploatacyjnych, w tym odporności na ścieranie, w znaczący sposób ograniczających dalszy rozwój możliwych obszarów aplikacyjnych [5]. Prezentowana praca opisuje metodę modyfikacji powierzchni czystego tytanu w celu wytworzenia warstwy powierzchniowej o odmiennym od podłoża składzie chemicznym. Zastosowany proces stopowania mikroplazmowego powierzchni za pomocą prekursorów proszkowych o określonej charakterystyce wejściowej umożliwia otrzymanie jednorodnych warstw powierzchniowych z trwałym połączeniem metalurgicznym zapewniającym gładkie przejście właściwości w kierunku podłoża. Takie podejście charakteryzuje znaczna grubość uzyskiwanych warstw powierzchniowych w odróżnieniu od procesów konwencjonalnego nawęglania, borowania, azotowania, utleniania, czy też ich kombinacji [6, 7]. Wspomnianie przykłady charakteryzuje płytkie wnikanie składnika dyfundującego, uzależnione w sposób istotny od temperatury procesu wywołującej najczęściej zmiany mikrostrukturalne w obszarze podłoża związane z rozrostem ziarna. Skokowa zmiana właściwości uzyskiwanych warstw o charakterze wewnętrznym jak i przyrostowym o nieznacznej grubości może być przyczyną powstawania niekorzystnych zjawisk [...]

Physical and chemical properties of Mg-based nanomaterials

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Magnesium-based hydrogen storage alloys have been considered to be possible candidates for hydrogen storage as well as for electrodes in Ni-MHx batteries [1÷3]. The chemical composition and microstructure of the metal alloys are one of the most important factors in the metal-hydrogen system. Substantial improvements in the hydriding-dehydriding properties of Mg-based hydrides could be possibly achieved by the formation of nanocrystalline structures by nonequilibrium processing technique such as mechanical alloying (MA) [4, 5]. As nonequilibrium processing method MA can be utilised to produce large quantities of materials at relatively low cost. Introducing metastable phases may result in totally different behaviour of the alloy. With current storage metallic materials it is not possible to exceed a capacity of 2 wt % H2. Nevertheless for instance, magnesium can store 7 wt % H2. Unfortunately MgH2 is too stable and too much energy has to be expended in releasing the hydrogen. Alloying magnesium with other elements could lower the stability of the hydride without reducing the capacity to an unacceptable value. Mg2Ni, one of the typical magnesium alloys, has great potential as a light hydrogen-storage alloy with high energy and is superior to the rare alloy of LaNi5-type and to the alloy of ZrV2-type with Laves phase in term of materials costs and the theoretical capacities. The theoretical capacity of the Mg2Ni alloy is about three times capacity of LaNi5 alloy. Mg2Ni alloy, however, can absorb and discharge hydrogen only at 200÷300°C and the speed of absorption and discharge is very slow. The electrochemical capacity of the microcrystalline Mg2Ni alloy is too low to be a hydrogen-storage alloy. On the other hand, Mg and Fe do not form an intermetallic compound; this results in difficulties in the preparation of its hydride phase. Recently, the direct synthesis of Mg2FeH6 by mechanical alloying in hydrogen atmosphere has been in[...]

Plasma surface alloying and post depositional electrochemical treatment of titanium as a new concept of biomaterial properties modification

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In past few years tremendous scope of advanced and interdisciplinary research at field of biomaterial properties was evaluated. Investigations particularly bring closer relations between ?gliving tissue?h and biomaterial surface [1]. Manipulation at the level of surface morphology its physical state and most of all chemical composition, brings direct impact on tissue-implant integration that was confirmed in different approaches [2?€4]. The tissue, for example, may improve cell proliferation in respond to proper chemical composition, energy state or surface roughness [5]. Its spreading and adhesion could also be dependent from the above factors and emerge ionic state for example may determine proper signalling and regulates a wide variant of biological functions [6]. Successful osseointegration of biomaterial and proper functioning after orthopaedic and trauma surgery, depends on various surface factors. Different research demonstrate that roughness influenced cell morphology and growth with topography that can change cell orientation and attachment strength. Surface reaction always takes (firstly) water molecule and protein adsorption. At this stage different electrochemical reactions on surface of biomaterial may occur. Following that consideration occurring reaction may lead to the formation of fibrous tissue also results from micromotion of implant or even inflammatory response of human body that ends with the rejection. Proper cellular interaction with surface energy results in cell adhesion, proliferation and differentiation that should lead to matrix production and calcification with expected expand osseointegration. Significance of above relations focused the researchers attention on surface properties without necessity of changing basis. The future of economic processes of surface properties enhancement seems to be high energy treatments employing lasers [7, 8], electron beam or plasma [9]. Problems of modifying [...]

Nanocrystallinie TiNi, Ti2Ni alloys for hydrogen storage

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In the last decade a great interest has been observed in the field of nanoscale materials. Mechanical alloying (MA) has been proved to be a novel and promising method for alloy formation, especially in the preparation of non-equilibrium materials of various systems [1÷7]. This technique has already succeeded in obtaining a wide range of alloy hydrides for energy storage or other energy related applications [2, 4÷11]. The advanced nanocrystalline intermetallics are representing a new generation of metal hydride materials with the following characteristics: high storage capacity, stable temperature- pressure cycling capacity during the life-time of the system, good corrosion stability and low costs. These materials exhibit quite different properties from both crystalline and amorphous materials, due to structure in which extremely fine grains are separated by what some investigators have characterized as "glass-like" disordered grain boundaries [3, 4]. Therefore, the hydrogenation behaviour of the amorphous structure is different than that of the crystalline material. Mechanical alloying has recently been used to make an amorphous and nanocrystalline TiFe, ZrV2-, LaNi5- and Mg2A-type alloys (A = Fe, Co, Ni, Cu) [6÷11]. These materials show substantially enhanced absorption and desorption kinetics, even at relatively low temperature [9, 10]. Among the different types of hydrogen forming compounds, Ti-based alloys are among the promising materials for hydrogen energy applications [6, 7, 12, 13]. For example, the TiNi alloy, which crystallizes in the cubic CsCl-type structure is lighter and cheaper than the LaNi5-type alloy. Nevertheless, the application of TiNi material in batteries has been limited due to poor absorption/ desorption kinetics in addition to a complicated activation procedure. To improve the activation of this alloy several approaches have been adopted. For example, ball milling of TiNi is effective for the improve[...]

Effects of mechanical alloying conditions on the properties of Mg-based nanomaterials DOI:10.15199/28.2015.5.5


  Various methods can be used to improve properties of Mg-based materials. These modifications include alterations of the chemical composition or microstructure modification. Nanostructured Mg-based alloy powders were produced by mechanical alloying method. The effect of different milling conditions on the microstructure evolution during mechanical alloying of Mg-type alloys with a nominal composition Mg-4Y-5.5Dy-0.5Zr, Mg-1Zn-1Mn-0.3Zr was studied. Bulk nanostructured Mg-type materials were finally obtained by the application of powder metallurgy. The evolution of microstructure and mechanical properties of Mg-based alloys were investigated. Compared to microcrystalline magnesium synthesized samples exhibit higher microhardness. This effect is directly associated with structure refinement and obtaining a nanostructure. Data concerning corrosion of nanostructured Mg-type alloys are scarce. In this paper, the corrosion behaviour of synthesized bulk Mg-based alloys containing different elements were investigated by immersion test in 0.1 M NaCl. The potentiodynamic corrosion test results indicate that addition of alloying elements shifts the corrosion potential to the less negative values. Nanocrystalline Mg-based alloy with enhanced mechanical and corrosion properties can be used in the automotive and marine industries. Key words: magnesium, mechanical alloying, nanostructure.1. INTRODUCTION Nanocrystalline materials produced by the application of non-equilibrium processing techniques, such as mechanical alloying (MA) or severe plastic deformation (SPD) demonstrate novel properties compared to conventional (microcrystalline) materials [1, 2]. Nanomaterials can include metals, ceramics, and composite materials, and they demonstrate novel properties compared to conventional (microcrystalline) materials because of their nanoscale features. Mechanical alloying is a powder processing technique that enables the production of nanomaterials starting [...]

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