Nr 1/2009 ____________________ INŻYNIERIA MATERIAŁOWA ____________________________ 1 PAWźŁ JÓħWIK, ZBIGNIEW BOJAR, PIOTR WINIAREK Catalytic activity of Ni 3 Al foils in decomposition of select chemical compounds Aktywność katalityczna taśm Ni3Al w rozkładzie wybranych związków chemicznych ABSTRACT Ni3Al–based intermetallic alloys are a group of advanced materials with potential outstanding physical and chemical properties (such as high catalytic activity and structural stability in corrosive environments) which make them possible candidates for many high-tech applications. A selection of strictly given parameters of plastic working and heat treatment allowed to obtain from as cast coarse-grained sheet a thin foils with thickness approximately 50m. These foils can be manufactured both with nano- or microcrystalline structure. The main objective of this work is to investigate of catalytic properties of microcrystalline Ni3Al-based foils surface without any additional catalytic coatings. The examination has concerned to decomposition of methanol, hexane and additionally dibutyl sulphide as mustard gas imitator in a fixed-bed tube quartz reactor. The catalysis reaction of methanol decomposition has started effectively at about 450 O C with 90% conversion degree or higher. SEM analysis of Ni3Al foils surface after this process showed deposit with the large part of carbon nano-fibers and nano-nickel precipitates. Similar catalytic behavior was observed for hexane decomposition, with emphasis that up to temperature of 600 O C conversion was 100%. Catalytic tests for dibutyl sulfide also confirmed a possibility of decomposition of this compound by thermocatalytic reactions on the Ni3Al thin foils surface. STRESZCZENIE (IN POLISH LANGUAGE) Stopy na osnowie fazy międzymetalicznej Ni3Al należą do grupy zaawansowanych materiałów o unikalnych właściwościach fizycznych i chemicznych (m.in. wysoka aktywność katalityczna i stabilność strukturalna w środowiskach korozyjnych), które stanowią o ich dużych możliwościach aplikacyjnych w obszarze wysokich technologii. Dobór ściśle określonych parametrów obróbki plastycznej i cieplnej pozwolił na uzyskanie, z materiału o grubokrystalicznej strukturze, folii o grubości ok. 50m o budowie zarówno nano jaki i mikrokrystalicznej. Głównym celem niniejszej pracy są badania właściwości katalitycznych mikrokrystalicznych taśm ze stopu na osnowie fazy Ni3Al bez dodatkowej warstwy katalitycznej. Badania dotyczyły dekompozycji metanolu i heksanu oraz dodatkowo siarczku dibutylowego jako imitatora iperytu siarkowego. Potwierdzono, że reakcja katalityczna rozkładu metanolu rozpoczyna się efektywnie w temperaturze około 450 O C ze stopniem konwersji 90% lub wyższym. Analiza warstwy powierzchniowej folii po reakcji katalitycznej przeprowadzona za pomocą skaningowej mikroskopii elektronowej wykazała obecność depozytu w postaci nano-włókien węglowych i nano-wydzieleń niklu. W trakcie rozkładu heksanu obserwowano podobną aktywność katalityczną, z zaznaczeniem, że począwszy od temperatury 600 O C następuje całkowity rozkład analizowanego związku. Przeprowadzone dodatkowo badania rozkładu siarczku dibutylowego potwierdziły również możliwość rozkładu tego związku na drodze reakcji termo katalitycznej na powierzchni cienkich taśm Ni3Al. INTRODUCTION Alloys based on the Ni 3 Al intermetallic phase, as compared to competitive group of nickel–based super-alloys, exhibit high strength for high deformation velocity at elevated temperature, high resistance to oxidation and carburization at elevated temperature, and much better fatigue strength (they crack more slowly than other intermetallic phase-based alloys). However, common application of these alloys meets, quite a few technological drawbacks mainly related to insufficient plasticity and a tendency to brittle cracking [1-2]. Additionally, Ni 3 Al-based alloys can be used in the form of honeycomb structures, which have an advantage in lightweight, high- stiffness and high-strength over bulk Ni-based superalloys. Thus far, we have successfully fabricated Ni 3 Al thin foils by cold rolling of commonly casted ingots without any additional treatment. The proposed technology allows to obtain foils with thickness even below 50m and with micro- and nanograined structure [3,4]. Methanol is expected to become an alternative energy source (a fuel) in the near future. It can be easily synthesized from biomass, natural gas, coal etc. which are more abundant resources than crude oil [8,9]. Hexane, as the second analyzed compound in this field of research, is a component of many products related to the petroleum and gasoline industries. Nevertheless, as an effect of these applications, increasing amount of this compound is released to the atmosphere and possibility of hexane deactivations is important for environmental pollution reducing. Above mentioned mechanical properties of Ni 3 Al thin foils, and their additional good catalytic properties without any coating, allow to build micro-scale power sources and micro-reactors for air purification (e.g. MEMS, MECS) [3, 4]. The main purpose of this work was an assessment of catalytic effects observed while thermo-decomposition reactions of methanol and hexane run over Ni 3 Al foil surface. Preliminary trials of thermo- decomposition of dibutyl sulfide acting as an imitator of poisoning mustard gas catalyzed with Ni 3 Al active surface were also conducted. EXPERIMENTAL PROCEDURE Samples for catalytic investigation were made of Ni 3 Al foils with chemical composition showed in the table 1. The investigated material was prepared by cold rolling at room temperature for 95 % cold work, without any intermediate annealing, up to thickness approximately 50μm. Subsequently, foils were subjected to recrystallization annealing up to 1200 O C, for time up to 2 hours, in a high purity argon atmosphere [9, 10]. Finally, the Ni 3 Al microcrystalline foils were mechanically polished and their surface was smooth and shiny (Fig.1). Further details about fabrication procedure of thin intermetallic foils have been described previously [1,2]. Table 1. Chemical composition of investigated Ni3Al-based alloy Tabela 1. Skład chemiczny badanego stopu na osnowie fazy Ni3Al Chemical element [at.%] Al Zr B Ni 22,1 0,26 0,1 Balance ________________________ DSc Pawel Jozwik (pjozwik@wat.edu.pl), Prof. Zbigniew Bojar - Department of Advanced Materials and Technology, Military University of Technology, DSc Piotr Winiarek- Faculty of Chemistry Warsaw University of Technology Dr inż. Paweł JóĨwik (pjozwik@wat.edu.pl), Prof. dr hab. inż. Zbigniew Bojar Katedra Zaawansowanych Materiałów i Technologii, Wojskowa Akademia Techniczna, dr inż. Piotr Winiarek, Wydział Chemiczny, Politechnika Warszawska.