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HYDROGENATION PROPERTIES OF BALL-MILLED Mg-Ti-C-Zr COMPOSITE
Král, Lubomír; Čermák, Jiří; Roupcová, Pavla
2016 - anglický
The hydrogen storage properties of ball-milled Mg-Ti-Zr-C composite (1.8 wt.% Ti, 1.9 wt.% Zr and 0.2 wt.% C) were investigated. It has been previously shown, that the addition of Ti, Zr and C improved its storage properties. This beneficial effect of additives upon hydrogen storage properties can be explained by catalysis by the particles rich in Ti or Zr located on the surface of Mg grains. They provide effective pathways for the hydrogen diffusion into the MgH2. The morphological and microstructural characteristics were investigated by scanning electron microscopy and by X-ray diffraction. The hydrogen sorption was measured by Sieverts method using Setaram PCT-Pro device. In this paper, sorption behaviour of the composite after ball-milling and after aging on the air was compared. The ball-milled composite adsorbed 3.5 wt.% H2 within 10 min at 623 K. However, hydrogen storage capacity of the composite aged on the air for 7 months remarkably decreased: The aged composite adsorbed within 10 min only 2 wt.% H2 at 623 K and the sorption capacity decreased from 4.7 wt.% H2 to 2.1 wt.% H2.
Klíčová slova:
hydrides; hydrogen storage; Mg-alloys
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
HYDROGENATION PROPERTIES OF BALL-MILLED Mg-Ti-C-Zr COMPOSITE
The hydrogen storage properties of ball-milled Mg-Ti-Zr-C composite (1.8 wt.% Ti, 1.9 wt.% Zr and 0.2 wt.% C) were investigated. It has been previously shown, that the addition of Ti, Zr and C ...
Ab initio study of {101-2} twinning transition in magnesium
Káňa, Tomáš; Ostapovets, Andriy
2016 - anglický
Twinning is an important deformation mode in materials with the hexagonal close-packed (hcp) structures. The shear deformation combined with shuffling of atomic planes can lead to a transition between the Mg hcp structure and a twinned hcp structure. Studying such a transition by means of ab initio methods should bring more insight into the twinning mechanism in magnesium where the {1012} planes are the twinning planes. Comparison of ab initio results with those obtained using the semi-empirical embedded atom method is provided. It can help improve the fitted parameters of the embedded atom method.
Klíčová slova:
Ab initio; Magnesium; Shear deformation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Ab initio study of {101-2} twinning transition in magnesium
Twinning is an important deformation mode in materials with the hexagonal close-packed (hcp) structures. The shear deformation combined with shuffling of atomic planes can lead to a transition between ...
NUMERICAL SUPPORT FOR SPECIMEN LOADED BY BENDING AND WEDGE SPLITTING FORCES FOR MEASUREMENT OF CONCRETE PROPERTIES
Seitl, Stanislav; Liedo, R.; Holušová, T.
2016 - anglický
Fracture mechanical properties of silicate based materials are performed from various fracture mechanicals tests. For evaluation of parameters, the knowledge about calibration and compliance function is so important. Therefore, in contribution the compliance and calibration curves for a novel test based on combination wedge splitting test (WST) and three-point bend test (3PBT) are introduced. These selected variants exhibit significantly various stress state conditions at the crack tip, or, more generally, in the whole specimen ligament.
Klíčová slova:
Stress intensity factor; T-stress, constraint; wedge splitting test; three-point bend test; compliance function; COD
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
NUMERICAL SUPPORT FOR SPECIMEN LOADED BY BENDING AND WEDGE SPLITTING FORCES FOR MEASUREMENT OF CONCRETE PROPERTIES
Fracture mechanical properties of silicate based materials are performed from various fracture mechanicals tests. For evaluation of parameters, the knowledge about calibration and compliance function ...
Microstructural Study and Analysis of Hard Zinc
Luptáková, Natália; Pešlová, F.; Stodola, P.; Stodola, J.
2015 - anglický
The presented work is focused on the character and morphology of the input material for the production of metallic zinc which is used in the production of ZnO through indirect pyrometallurgical processes. The input material is the key parameter in the production of high-quality zinc oxide. For the prediction of a complex production process when problematic situation may occur, the systematic analysis of the input zinc raw materials is needed. Undesirable phases in the feedstock can be identified through profound recognition of the source material and the nature of its microstructure. Chemical composition of zinc metal and zinc additives helps to detect the phases occurring in the matrix. Undesirable phases in the feedstock can form hard and brittle compounds. If these compounds diffuse into the lining during thermal processes, they become the cause of stress in metallurgical ceramics. From the microstructure viewpoint, the heterogeneity of the grain size, various morphology of intermediate phases, their layout, arrangement, etc. can be expected. The results obtained by analysis are used to minimize waste-zinc slag and to eliminate the conditions which enable the formation of the undesired product, thereby increasing the productivity of the zinc oxide production. Moreover, another important knowledge could be used for modernization and effective the process of industrial production of ZnO in practical application in military technologies.
Klíčová slova:
zinc; zinc oxide; pyrometallurgical process; metallurgy; structural phase; intermediate phase; residual elements
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Microstructural Study and Analysis of Hard Zinc
The presented work is focused on the character and morphology of the input material for the production of metallic zinc which is used in the production of ZnO through indirect pyrometallurgical ...
Determination of mechanical properties of light alloys and composites by means of Small Punch Testing
Bártková, Denisa; Langer, J.; Dymáček, Petr; Válka, L.
2015 - anglický
Nowadays, in many testing areas a volume of experimental material is limited (laboratory-scaled volume, semidestructive approach). Therefore many testing techniques on miniature samples were devised. Principle of Small Punch Test (SPT) method is a penetration of small puncher through thin disc placed on a ring until the disc bursts. In dependence on loading mode it can provide information comparable to uniaxial tensile tests (UTT) and/or conventional constant load creep tests. However clarification of relations between SPT and conventional methods is difficult and empirical formulas are non-universal. The aim of this study is to i) evaluate mechanical properties of aluminium and magnesium alloys and its composites by means of SPT, ii) compare SPT results with UTT, iii) validate correlation formulas from literature, iv) propose more advanced approach to define correlation between UTT and SPT. Measurement were carried out at constant deflection rate (SPT-CDR) in two different laboratoires. Results from both laboratories were compared to evaluate the reproducibility of the method. Better results agreement was reached for the ultimate strength measurements. Yield strength results exhibited greater variance. An influence of pre-deformation of the sample on yield strength and deflection at maximum force was also identified. We can conclude, that for quantitative estimation of strength parameters we can use correlation formulas based on materials with similar composition and fracture behaviour.
Klíčová slova:
Small Punch Test; Magnesium Alloys; Aluminium Alloys Thin Disc
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Determination of mechanical properties of light alloys and composites by means of Small Punch Testing
Nowadays, in many testing areas a volume of experimental material is limited (laboratory-scaled volume, semidestructive approach). Therefore many testing techniques on miniature samples were devised. ...
Compressive creep testing of MoSi2-SiC nanocomposites
Luptáková, Natália; Ballóková, B.; Dymáček, Petr
2015 - anglický
The aim of this study is to investigate the creep resistance of molybdenum disilicide (MoSi2-SiC) based composites with different types of embedded particles. The materials were prepared via powder metallurgy using high temperature controlled reaction sintering (CRS). The creep experiments were performed in uniaxial compression at constant stress in the temperature range from 1273 K (1000 °C) to 1473 K (1200 °C) for applied stress from 50 to 100 MPa. Creep was tested by stepwise loading: in each step, the load was changed to a new value after steady state creep rate had been established. The applied stress dependences of the creep rate at different temperatures were analyzed in terms of stress exponent (n) and activation energy (Q). Possible rate-controlling mechanisms were suggested.
Klíčová slova:
MoSi2-SiC; creep test; compressive creep; stress exponent; activation energy
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Compressive creep testing of MoSi2-SiC nanocomposites
The aim of this study is to investigate the creep resistance of molybdenum disilicide (MoSi2-SiC) based composites with different types of embedded particles. The materials were prepared via powder ...
Stress analysis of modified compact tension specimens: K-calibration curves
Seitl, Stanislav; Viszlay, V.
2015 - anglický
Compact tension (CT) test is in engineering frequently used test for metallic materials to determiner fracture parameters/properties, e.g. fracture energy, fracture toughness, crack propagation rate, J-R curves etc. [20]. The modified compact tension (MCT) specimen for cement based composites has to be prepared due to negligible concentration around the holes for tenons. An accurate determination of fracture parameters requires the use of a valid calibration curves, there for in this contribution the stress analysis near the crack tip and calibration curve for modified compact tension test are introduced. The calibration curve is introduced for diameter 150 mm (the specimen could be easy made from the specimen for compression test) and includes all theoretical imperfections that results from preparation of the MCT specimens.
Klíčová slova:
Modified compact tension specimen; stress intensity factor; concrete; FEM
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Stress analysis of modified compact tension specimens: K-calibration curves
Compact tension (CT) test is in engineering frequently used test for metallic materials to determiner fracture parameters/properties, e.g. fracture energy, fracture toughness, crack propagation rate, ...
Stress relaxation in partially pyrolysed SiOC materials
Halasová, Martina; Chlup, Zdeněk; Černý, Martin; Strachota, Adam; Dlouhý, Ivo
2015 - anglický
This paper focuses on the difficulty with Vickers hardness evaluation of SiOC materials. To evaluate it, diagonals of an indent are crucial. Due to stress relaxation in experimental material it was not possible to evaluate it in the whole range of experimental temperatures. As experimental materials were used two types of commercialy available polysiloxane resins, pyrolysed in range from 400 to 1000°C.
Klíčová slova:
polysiloxane; resin; SiOC; glass; ceramics; Vickers hardness; 3D reconstruction; indent
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Stress relaxation in partially pyrolysed SiOC materials
This paper focuses on the difficulty with Vickers hardness evaluation of SiOC materials. To evaluate it, diagonals of an indent are crucial. Due to stress relaxation in experimental material it was ...
The Changes in Structure of Steel P91 after Short Annealings
Král, Lubomír; Čermák, Jiří; Král, Petr
2015 - anglický
Phase composition of the steel P91 during annealing was studied with the aim to reveal the evolution of new phases. In this paper, the precipitation was characterized using energy-dispersive X-ray spectroscopy (EDS) and electron diffraction in transmission microscopy (TEM). Only Nb-rich particles were found in the studied samples austenitized at 1423 °C for 20h and water cooled. After tempering at 673 °C for 2 h, the formation mainly M3C type carbides and after tempering at 873 °C for 2 h, the formation of M7C3 and M23C6 was observed. These structure changes play an important role for stability and also carbon diffusion.
Klíčová slova:
P91; carbides; carbon; precipitation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
The Changes in Structure of Steel P91 after Short Annealings
Phase composition of the steel P91 during annealing was studied with the aim to reveal the evolution of new phases. In this paper, the precipitation was characterized using energy-dispersive X-ray ...
HYDROGEN STORAGE IN Mg-In-C ALLOYS: EFFECT OF COMPOSITION AND AGEING
Čermák, Jiří; Král, Lubomír
2015 - anglický
Hydrogen storage in two Mg-In-C alloys with different In concentration, c In , was studied in the temperature range from 250°C to 350°C after five-years-ageing at room temperature. The both alloys show acceptable cycling stability, however, the storage capacity of the alloys decreased from about 5 wt. % H2 to about 2,5 and 3.1 wt. % H 2 by higher c In and lower c In , respectively after 5 years. The sorption kinetics degraded much more by high c In than by c In . PCT isotherms, TPS and DSC patterns were measured for both materials. It was found that the hydrides responsible for hydrogen storage in alloy with higher c In are slightly more stable.
Klíčová slova:
hydrogen; hydrogen storage; magnesium alloys
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
HYDROGEN STORAGE IN Mg-In-C ALLOYS: EFFECT OF COMPOSITION AND AGEING
Hydrogen storage in two Mg-In-C alloys with different In concentration, c In , was studied in the temperature range from 250°C to 350°C after five-years-ageing at room temperature. The both alloys ...
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