Hydrogen storage in nickel doped MCM-41

Hydrogen as an energy carrier is one of the best environmentally friendly alternatives to fossil fuel sources. The potential use of hydrogen results with increasing demand to hydrogen production and storage. Recent studies show that materials having high surface area, large pore size and high affinity to hydrogen have high hydrogen storage capacity. MCM-41 is silica based material having such properties and its hydrogen sorption properties can be improved by doping transition metals to the structure. Ni was chosen for this purpose as it is known with its hydrogen affinity. In this study, different amounts of Ni doped in MCM-41 that was produced by microwave heating to examine hydrogen storage capacity of Ni doped MCM-41 systems. The morphology and structure of the material was characterized by scanning electron microscope and X-ray diffraction analysis. Thermal stability of MCM-41 was examined by thermogravimetric analysis and it was seen that MCM-41s are hydrothermally stable. Surface area, pore size and adsorption capacity of MCM-41 were measured by Brunauer-Emmett-Teller (BET) method. It was observed that the material had large surface area around 1000 m2/g and roughly 2 nm pore size. It was found materials have uniform pore structure with hexagonal well-ordered arrangement. BET surface area, pore volume and pore diameters decreased as the metal loading increased. The hydrogen adsorption capacity measurements were achieved by the Intelligent Gravimetric Analyzer at room temperature and up to 10 bar pressure. It was observed that the hydrogen storage capacity of MCM-41 is strongly affected by metal doping

Analysis of damage and fracture formulations in cold extrusion

In forming processes, components generally undergo large deformations. This induces the evolution of damage, which can influence material and product properties. To capture these effects, a continuum damage mechanics (CDM) model, based on the work of Lemaitre [8] and Soyarslan [13, 14] as well as different fracture criteria according to Cockcroft and Latham [2], Freudenthal [4] and Oyane [10] are implemented and in- vestigated. While the CDM theory considers the evolution of damage and the associated softening, fracture criteria do not affect the results of the mechanical finite element (FE) analysis. However, a coupling is generally possible via element deletion, but material softening cannot be depicted in the simulation. Tensile tests with notched specimens are performed in order to obtain the material parameters associated with these models by inverse parameter identification processes. The optimized set of parameters is finally ap- plied to the damage and fracture models used for the FE simulations of a cold extrusion process, which are investigated in terms of damage evolution and material failure. It is demonstrated that the CDM model predicts the evolution of damage observed for differ- ent process parameters in cold extrusion quantitatively. The prediction of the failure by the fracture criteria does not agree well with the experiments

Comparison of gurson and lemaitre model in the context of blanking simulation of a high strength steel

The process of blanking takes place in a short band with high accumulated strain undergoing various stress triaxialities. Enhanced implementations for shear and compressive loads of Gurson’s and Lemaitre’s model are directly compared for the same blanking setup. For a dual phase steel DP600 the Lemaitre parameters are identified completely by an inverse strategy, while the parameters of the Gurson’s porous plasticity model are predominantly gained from analysis with a scanning electron microscopy (SEM). The models are validated by comparison of force-displacement curves, time point and location of crack initiation. Advantages and disadvantages of both approaches are discussed with respect to prediction accuracy and costs of parameter identification. Both of the models deliver an exact prediction for the location of the crack and a good prediction of the punch displacement at the onset of cracking

Hydrogen storage in single wall carbon nanotubes produced on iron catalyst

Hydrogen is a promising clean energy alternative to conventional energy sources. Hence, increasing demand on hydrogen as energy carrier enhances studies in hydrogen storage. Hydrogen should be safely and efficiently stored in order to overcome existing barriers in hydrogen usage. Single wall carbon nanotube (SWCNT) is an eligible material for hydrogen storage. In this study, SWCNTs were produced by catalytic chemical vapor deposition (CCVD) of acetylene (C2H2) on MgO powder substrate impregnated with Fe. Catalysts were prepared with Fe to MgO ratio of 5:100 using iron nitrate (Fe(NO3)3•9H2O) solution as Fe source. SWCNTs were synthesized at 800°C for 60 minutes. Nitric acid (HNO3), was used for purification of synthesized SWCNT. The aim of the research was to investigate hydrogen storage capacity of as produced and purified SWCNTs synthesized on Fe-MgO catalyst. The morphology and structure of the SWCNTs were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. Thermal gravimetric analysis (TGA), and Raman spectroscopy were used for further characterization. Hydrogen storage capacities of SWCNTs were measured by high pressure volumetric analyzer using volumetric method at the cryogenic temperature and gas pressure up to 90 bar. It was found that the hydrogen adsorption capacities of these materials were around 1.9 and 5.3 wt% for as produced and purified SWCNTs respectively. With the fact that DOE target for 2015 is 5.5 wt%, it was seen that SWCNTs produced on Fe-MgO catalyst have good potential as hydrogen storage material

Onuncu Sınıf Öğrencilerinin Tercih Ettikleri Öğrenme Stillerinin Biyoloji Başarılarına Etkisi

This study aimed to investigate the effect of learning styles on tenth grade Turkish students’ biology achievement. In order to investigate the specified purpose of the study, 980 tenth grade students were administered the Turkish version of the Learning Style Inventory and a Biology Achievement Test. Oneway analysis of variance indicated statistically significant mean differences across learning styles with respect to biology achievement. The results of the study revealed that majority of high school students had the assimilating type learning style. Assimilator students were found to be more successful than accommodators, divergers, and convergers.Bu çalışmanın amacı tercih edilen öğrenme stillerinin lise 2. sınıf öğrencilerinin biyoloji başarısına olan etkisini araştırmaktır. Bu amaç doğrultusunda 980 lise 2. sınıf öğrencisine Öğrenme Stilleri Envanteri ve Biyoloji Başarı Testi uygulanmıştır. Tek yönlü varyans analizi sonuçlan öğrencilerin tercih ettikleri öğrenme stilleri ile biyoloji başarıları arasında anlamlı bir fark olduğunu göstermiştir. Aynca, özümseyen öğrenme stiline sahip öğrenciler, aynştıran, değiştiren ve yerleştiren öğrenme stilene sahip olan öğrencilere göre daha başanlı bulunmuştur

Design of Hybrid Conductors for Electromagnetic Forming Coils

The use of hybrid coil turns made of steel (St) and copper (Cu) is originally motivated by the increased mechanical strength compared to monolithic copper conductors. Due to the differing electrical conductivities of the two materials, the hybrid design also changes the current density distribution in the conductor cross section. This affects crucial process parameters such as the magnetic pressure and the Joule heat losses. The effect of the hybrid conductor design on the process efficiency is investigated. An electromagnetic sheet metal forming operation using a one-turn coil with rectangular cross section is used as reference case. The copper layer (CuCr1Zr) was deposited on a tool steel substrate (X40CrMoV5-1) using a selective laser melting process. The copper layer thickness is varied ranging from a monolithic steel conductor to a monolithic copper conductor. The workpiece (EN AW-5083, t_w = 1 mm) is formed through a drawing ring so that the final forming height is a qualitative measure for the process efficiency. The experimental results prove that the efficiency in case of a properly designed hybrid conductor can exceed the efficiency of a monolithic copper coil. The current density distribution in the hybrid cross section is investigated by means of numerical simulations. This way a deeper insight into the physical effects of a varying copper layer thickness is gained. The results reveal that the optimum layer thickness is not just a function of the coil cross section and the current frequency. It is also affected by the coil length and the resistance of the pulse generator

Enhanced granular medium-based tube press hardening

Active and passive control strategies of internal pressure for hot forming of tubes and profiles with granular media are described. Force transmission and plastic deformation of granular medium is experimentally investigated. Friction between tube, granular medium and die as also the external stress field are shown to be essential for the process understanding. Wrinkling, thinning and insufficient forming of the tube establishes the process window for the active pressure process. By improving the punch geometry and controlling tribological conditions, the process limits are extended. Examples for the passive pressure process reveal new opportunities for hot forming of tubes and profiles.Comment: 4 pages, 11 figure