Synthesis of free template ZSM-5 catalyst from rice husk ash and co-modified with lanthanum and phosphorous for catalytic cracking of naphtha

ZSM-5 catalysts were synthesized from rice husk ash without using template and their catalytic activity has been investigated in catalytic cracking of light naphtha. Effect of hydrothermal temperature (170, 180 and 190?°C) on physicochemical properties of catalysts was investigated by BET, FE-SEM, FTIR, XRD and TGA-DTG analyses. The XRD analysis showed that hydrothermal temperature had great influence on crystalline structure of ZSM-5. Sample which was synthesized at 180 °C showed high crystllinity without any undesired alumina-silicate phases. The FE-SEM analysis showed that synthesis of ZSM-5 at 180?°C led to showed micro-scale hexagonal-shaped morphology. Furthermore, the textural properties of synthesized samples depend on the synthesis temperature drastically. Results of catalytic activity test showed that the synthesis temperature has great influence on the activity of ZSM-5 and the sample which synthesized with at 180?°C showed the highest catalytic activity. Furthermore, in order to improve the catalyst performance and the stability, both of Lanthanum and Phosphorus were used in catalytic cracking of naphtha. 2.5La–3P/ZSM-5 produced the highest light olefins yield. Catalyst modification of ZSM-5 by La and P, increased the ratio of propylene/ethylene from 1 to 2.     

Mechanical and biological performance of rainbow trout collagen-boron nitride nanocomposite scaffolds for soft tissue engineering

We aim to investigate the potential of collagen extracted from rainbow trout for tissue engineering applications. In this regard, nanocomposite scaffolds based on the extracted collagen reinforced with various concentrations of boron nitride (BN) nanoparticles (0, 3, 6, 9, and 12 wt%) were developed. In addition, the role of various concentrations of BN nanoparticles and two-step cross-linking process on the physical and chemical properties of nanocomposite scaffolds were investigated. Our results demonstrated the isolation of Type I collagen with excellent thermal stability but with some structural and chemical differences compared to other sources. The synergic role of BN nanoparticles and two-step cross-linking process resulted in a noticeable improvement in the mechanical properties of collagen-BN scaffolds. Noticeably, incorporation of 6 wt% BN along with a two-step cross-linking process significantly increased the compressive strength (9.5 times) and elastic modulus (four times) of the collagen scaffold. Besides, nanocomposite scaffolds significantly improved proliferation and spreading of MG-63 cell line, confirming their biocompatibility. The results suggested that the incorporation of BN nanoparticles along with a two-step cross-linking process not only could promote the mechanical and thermal performances of collagen scaffolds, but also enhanced high cell viability, and proliferation supporting their potential in tissue engineering applications.     

Synthesis and structural characterization of nanocrystalline (Ni,Fe)3Al intermetallic compound prepared by mechanical alloying

Synthesis of (Ni, Fe)₃Al intermetallic compound by mechanical alloying (MA) of Ni, Fe and Al elemental powder mixtures with composition Ni₅₀Fe₂₅Al₂₅ was successfully investigated. The effects of Fe-substitution in Ni₃Al alloy on mechanical alloying process and on the final products were investigated. The structural changes of powder particles during mechanical alloying were studied by X-ray diffractometry, scanning electron microscopy and microhardness measurements. At the early stages, mechanical alloying resulted in a Ni (Al, Fe) solid solution with a layered nanocrystalline structure consisting of cold welded Ni, Al and Fe layers. By continued milling, this structure transformed to the disordered (Ni, Fe)₃Al intermetallic compound which increased the degree of L1₂ ordering upon heating. In comparison to Ni–Al system, Ni (Al, Fe) solid solution formed at longer milling times. Meanwhile, the substitution of Fe in Ni₃Al alloy delayed the formation of Ni (Al, Fe) solid solution and (Ni, Fe)₃Al intermetallic compound. The microhardness for (Ni, Fe)₃Al phase produced after 80 h milling was measured to be about 1170HV which is due to formation of nanocrystalline (Ni, Fe)₃Al intermetallic compound.     

Mechanochemical synthesis of Al2O3/Co nanocomposite by aluminothermic reaction

In this work, Al₂O₃/Co nanocomposite was successfully prepared by mechanochemical reaction between Co₃O₄ and Al powders in a planetary high energy ball mill. The mechanism of the reaction was dealt using X-ray diffraction (XRD), differential thermal analysis (DTA), and thermodynamics calculations. It was found that Co₃O₄ reacts with Al through a self-sustaining combustion reaction after an incubation period of 50 min and the reaction between Co₃O₄ and Al involves two steps. First, Co₃O₄ reacts with Al to form CoO and Al₂O₃ at the temperature around melting point of Al, and at higher temperature, CoO reacts with remaining Al to form Co and Al₂O₃. Mechanical activation process decreases the reaction temperature from 1041 °C for as-received Co₃O₄ and Al powder mixture to 869 °C for 45 min milled powders. After annealing of powder milled for 12 h, no phase transformation has been detected. The crystallite sizes of both α-Al₂O₃ and Co remained in nanometeric scale after annealing at 1000 °C for 1 h.     

Mechanical properties of nanostructured Al2024–MWCNT composite prepared by optimized mechanical milling and hot pressing methods

Nanostructured Al2024–multiwall carbon nanotubes (MWCNTs) composites were produced using optimized mechanical milling and hot pressing methods. Nanostructured Al2024 powder was first prepared through 30 h mechanical milling of the alloy powder. MWCNTs up to 3 vol.% were added to the milled Al2024 powder and milled for different times. Differential thermal analysis (DTA) and X-ray diffraction (XRD) were used to assess the structural changes and thermal behavior during mechanical milling and hot pressing. Hardness and compression tests were applied on bulk samples to evaluate their mechanical properties. Mechanical milling applied on Al2024 powders for 30 h resulted in the grain refinement to ～30 nm. DTA analysis showed an endothermic peak at ～632 °C due to Al2024 melting and an exothermic peak between 645 and 658 °C related to Al and MWCNTs reaction. Mechanical milling of nanocomposite powder for 4 h and following hot pressing at 500 °C under a pressure of 250 MPa for 0.5 h were selected as optimized conditions for bulk nanocomposite preparation. With MWCNTs addition up to 2 vol.%, relative density remained at 98%, and hardness increased to 245 HV. Compressive strength of nanocomposites found a maximum value of 810 MPa at 2 vol.% MWCNTs addition which is 78%, 34% and 12% greater than that for Al2024–O, Al2024–T6 and nanostructured Al2024, respectively.     

Development of Al-Al3Ni Nanocomposite by Duplex Processing of Flame Spray and Friction Stir Processing,and Evaluation of Its Properties

Metallurgical and Materials Transactions A - In this study, Al-Al3Ni nanocomposite was fabricated by friction stir processing (FSP) of a nickel-deposited Al6061-T6 plate. X-ray diffraction results...     

A numerical study on the damping capacity of metal matrix nanocomposites

In the present study, the damping capacity of metal matrix nanocomposites (MMNCs) is predicted using a micro-mechanical modeling approach. The model is based on finite element analysis of a unit cell, which mimics a pure metallic lattice with stiff reinforcing nanoparticles. The dissipated energy of nanocomposite is predicted numerically by applying a harmonic load on the unit cell model. The influences of the grain size, boundary phase thickness and reinforcement size on the energy dissipation were calculated by the developed finite element model. Also, the damping capacities of three typical particulate reinforced nanocomposites have been simulated by the proposed model. The relationship between damping capacity and dislocations were also discussed with respect to the Granato–Lücke (G–L) theory. The results calculated from the developed model show good agreement with the G–L theory, which demonstrates the feasibility of damping calculation with the proposed method.     

Design of a Flexible Pilot Plant Reactor for the Steam Cracking Process

A design technique for a pilot plant reactor of single diameter is presented to scale up or down steam cracking coils of different configurations like mono‐tubular, classical, and reversed splits. Using dimensional analysis, two criteria are selected in establishing partial similarity between different scales, the mean residence time, and the axial pressure profile in the reactor, in addition to preserving the flow pattern within the turbulent region. The sensitivity and accuracy of the proposed method is compared to another conceivable alternative that focuses on the lateral gradients. The pilot reactor coil is adapted for any large‐scale reactor by the adjustment of feed flow rate and the effective length exposed to the firebox heat flux. Simulation results for naphtha cracking in a commercial split coil and also the equivalent pilot plant reactors are used for verification and validation of this method.     

The Effect of Crystallinity of Carbon Source on Mechanically Activated Carbothermic Synthesis of Nano-Sized SiC Powders

The relevance of the structure of carbon materials and milling on the carbothermic reduction of silica to produce nano-sized silicon carbide (SiC) was studied. Graphite (crystalline) and metallurgical coke (mainly amorphous) were chosen as carbon precursors that were mixed with amorphous pure nano-sized SiO₂ and milled for different times. The SiC yield at 1450 °C for l h was influenced by the degree of milling. Extending the milling time increased SiC formation in both cases. Although some extensive milling converted both sources of carbon into amorphous phase, the amount of synthesized SiC from graphite was about 4.5-3 times higher than coke with increased extent of milling. Graphite is converted from stable crystalline state into the amorphous phase, so it absorbs more activation energy of milling and fresher active centers are created, while the already amorphous coke absorbs less energy and thus less fresh active centers are created. This energy difference acts as a driving force, resulting in higher yield of nano-sized SiC when graphite is used as carbon source.