Endre søk
Begrens søket
1 - 24 of 24
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Akhtar, Farid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Luleå University of Technology, Sweden.
    Ceramic reinforced high modulus steel composites: processing, microstructure and properties2014Inngår i: Canadian metallurgical quarterly, ISSN 0008-4433, E-ISSN 1879-1395, Vol. 53, nr 3, s. 253-263Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ceramic reinforced steel matrix composites are materials for automotive, aerospace, wear and cutting applications. Such metal matrix composites (MMCs) combine attractive physical, mechanical and wear properties with ease of fabrication and low cost. The review focuses on the current state of the art of producing these metal matrix composites, ceramics reinforcements, composition of steel matrix, microstructure evolution and parameters influencing the mechanical and wear properties. Processing methods to fabricate ceramic reinforced steel matrix composites are discussed to produce these composites with low number of defects, homogeneous microstructure and high mechanical and wear performance. The influence of chemical nature of ceramic reinforcements and composition of steel matrix on the microstructure, mechanical and wear properties is presented. The strengthening mechanisms and parameters controlling wear performance of steel MMCs are described as a function of the content of ceramic reinforcements, microstructural design and structure of the steel matrix. Keeping in view the stability of ceramics in steels, suitable ceramic reinforcements and steel matrix materials are discussed. Moreover, the importance of microstructure and interface between ceramic reinforcement and steel matrix in controlling the mechanical properties of steel MMCs is highlighted. The review identifies area of research for development to fully appreciate and tailor the properties of these industrially important composites.

  • 2.
    Akhtar, Farid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Ali, Liaqat
    Peizhong, Feng
    Shah, Jawad Ali
    Enhanced sintering, microstructure evolution and mechanical properties of 316L stainless steel with MoSi(2) addition2011Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 509, nr 35, s. 8794-8797Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sintering 316L stainless steel to near full density with an appropriate sintering additive can ensure high mechanical properties and corrosion resistance. We present here a sintering approach which exploits the dissociation of ceramics in steels at high temperatures to activate sintering densification to achieve near full dense 316L stainless steel materials. MoSi(2) ceramic powder was used as a sintering additive for pre-alloyed 316L stainless steel powder. Sintering behavior and microstructure evolution were investigated at various sintering temperatures and content of MoSi(2) as sintering additive. The results showed that the sintering densification was enhanced with temperature and MoSi(2) content. The distribution of MoSi(2) was characterized by XMAPs. It was found that MoSi(2) dissociated during sintering and Mo and Si segregated at the grain boundaries. Excess Mo and Si were appeared as separate phases in the microstructure. Above 98% of theoretical density was achieved when the specimens were sintered at 1300 degrees C for 60 min with 5 wt.% MoSi(2) content. The stainless steel sintered with 5 wt.% MoSi(2) exhibited very attractive mechanical properties.

  • 3.
    Akhtar, Farid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Andersson, Linnea
    Ogunwumi, Steven
    Hedin, Niklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Structuring adsorbents and catalysts by processing of porous powders2014Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 34, nr 7, s. 1643-1666Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Microporous materials such as zeolites, metal organic frameworks, activated carbons and aluminum phosphates are suitable for catalysis and separation applications. These high surface area materials are invariably produced in particulate forms and need to be transformed into hierarchically porous structures for high performance adsorbents or catalysts. Structuring of porous powders enables an optimized structure with high mass transfer, low pressure drop, good heat management, and high mechanical and chemical stability. The requirements and important properties of hierarchically porous structures are reviewed with a focus on applications in gas separation and catalysis. Versatile powder processing routes to process porous powders into hierarchically porous structures like extrusion, coatings of scaffolds and honeycombs, colloidal processing and direct casting, and sacrificial approaches are presented and discussed. The use and limitations of the use of inorganic binders for increasing the mechanical strength is reviewed, and the most important binder systems, e.g. clays and silica, are described in detail. Recent advances to produce binder-free and complex shaped hierarchically porous monoliths are described and their performance is compared with traditional binder-containing structured adsorbents. Needs related to better thermal management and improved kinetics and volume efficiency are discussed and an outlook on future research is also given.

  • 4.
    Akhtar, Farid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Andersson, Linnéa
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Keshavarzi, Neda
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Colloidal processing and CO2 capture performance of sacrificially templated zeolite monoliths2012Inngår i: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 97, s. 289-296Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Sacrificial templating of suspension cast and subsequently thermally treated zeolite monoliths with glassy carbon spheres and fibers yielded zeolite 13X and silicalite-1 monoliths with macroporosities up to 50 vol%. Homogeneous distribution of the macroporosity in hierarchically porous monoliths was obtained by tailoring the surface chemistry of the carbon particles by polyelectrolyte-assisted adsorption of zeolite particles. The effect of amount of kaolin binder and temperature for the thermal treatment on the monoliths strength, surface area and CO2 uptake was studied by diametral compression tests, electron microscopy, X-ray diffraction and gas adsorption. Cyclic adsorption and regeneration measurements showed that zeolite 13X monoliths display a high CO2 uptake while the silicalite-1 monoliths could be regenerated with a relatively low energy penalty.

  • 5.
    Akhtar, Farid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Colloidal Processing and Thermal Treatment of Binderless Hierarchically Porous Zeolite 13X Monoliths for CO2 Capture2011Inngår i: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 94, nr 1, s. 199-205Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Adsorbents with high surface area are potential candidates forefficient postcombustion CO2 capture. Binderless zeolite 13Xmonoliths with a hierarchical porosity and high CO2 uptakehave been produced by slip casting followed by pressurelessthermal treatment. The zeolite powder displayed an isoelectricpoint at pH 4.7 and electrostatically stabilized suspensions couldbe prepared at alkaline pH. The volume fraction-dependentsteady shear viscosity could be fitted to a modified Krieger–Dougherty model with a maximum volume fraction of 0.66. Thenarrow temperature range where monoliths could be producedwithout significant loss of the microporous surface area wasidentified and related to the phase behavior of the 13X material.Slip casting of concentrated suspensions followed by thermaltreatment of the powder bodies at a temperature of 8001Cwithout holding time resulted into strong hierarchically porouszeolite 13X monolith that displayed a CO2 uptake larger than29 wt%.

  • 6.
    Akhtar, Farid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Luleå University of Technology, Sweden.
    Keshavarzi, Neda
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shakarova, Dilshod
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Cheung, Ocean
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Hedin, Niklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Aluminophosphate monoliths with high CO2-over-N2 selectivity and CO2 capture capacity2014Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, nr 99, s. 55877-55883Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Monoliths of microporous aluminophosphates (AlPO4-17 and AlPO4-53) were structured by binder-freepulsed current processing. Such monoliths could be important for carbon capture from flue gas. TheAlPO4-17 and AlPO4-53 monoliths exhibited a tensile strength of 1.0 MPa and a CO2 adsorption capacityof 2.5 mmol g1 and 1.6 mmol g1, respectively at 101 kPa and 0 C. Analyses of single component CO2and N2 adsorption data indicated that the AlPO4-53 monoliths had an extraordinarily high CO2-over-N2selectivity from a binary gas mixture of 15 mol% CO2 and 85 mol% N2. The estimated CO2 capturecapacity of AlPO4-17 and AlPO4-53 monoliths in a typical pressure swing adsorption (PSA) process at 20C was higher than that of the commonly used zeolite 13X granules. Under cyclic sorption conditions,AlPO4-17 and AlPO4-53 monoliths were regenerated by lowering the pressure of CO2. Regeneration wasdone without application of heat, which would regenerate them to their full capacity for CO2 adsorption.

  • 7.
    Akhtar, Farid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Liu, Qingling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Hedin, Niklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Strong and binder free structured zeolite sorbents with very high CO2-over-N-2 selectivities and high capacities to adsorb CO2 rapidly2012Inngår i: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 5, nr 6, s. 7664-7673Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mechanically strong monoliths of zeolite NaKA with a hierarchy of pores displayed very high CO2-over-N-2 selectivity. The zeolite monoliths were produced by pulsed current processing (PCP) without the use of added binders and with a preserved microporous crystal structure. Adsorption isotherms of CO2 and N-2 were determined and used to predict the co-adsorption of CO2 and N-2 using ideal adsorbed solution theory (IAST). The IAST predictions showed that monolithic adsorbents of NaKA could reach an extraordinarily high CO2-over-N-2 selectivity in a binary mixture with a composition similar to flue gas (15 mol% CO2 and 85 mol% N2 at 25 degrees C and 101 kPa). Structured NaKA monoliths with a K+ content of 9.9 at% combined a CO2-over-N-2 selectivity of >1100 with a high CO2 adsorption capacity (4 mmol g(-1)) and a fast adsorption kinetics (on the order of one minute). Estimates of a figure of merit (F) based on IAST CO2-over-N-2 selectivity, and time-dependent CO2 uptake capacity, suggest that PCP-produced structured NaKA with a K+ content of 9.9 at% offers a performance far superior to 13X adsorbents, in particular at short cycle times.

  • 8.
    Akhtar, Farid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Ojuva, Arto
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Wirawan, Sang Kompiang
    Hedlund, Jonas
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Hierarchically porous binder-free silicalite-1 discs: a novel support for all-zeolite membranes2011Inngår i: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 21, nr 24, s. 8822-8828Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermal expansion mismatch between the zeolite film and the support is an important cause for the formation of defects and cracks during the fabrication and use of zeolite membranes. We have studied how silicalite-1 discs with a permeability comparable to commercially available alumina supports can be produced by pulsed current processing (PCP) as a novel substrate for all-zeolite membranes. Hierarchically porous and mechanically strong membrane supports where the surface area and crystallography of the silicalite-1 particles were maintained could be obtained by carefully controlling the thermal treatment during PCP consolidation. In situ X-ray diffraction and dilatometry showed that the coefficient of thermal expansion (CTE) of the silicalite-1 substrate was negative in the temperature range 200-800 degrees C while the commonly used alumina substrate displayed a positive CTE. The critical temperature variation, Delta T, and thicknesses for crack-free supported zeolite films with a negative CTE were estimated using a fracture energy model. Zeolite films with a thickness of 1 mu m can only sustain a relatively modest Delta T of 100 degrees when supported onto alumina substrates while the all-zeolite membranes can support temperature variations above 500 degrees.

  • 9.
    Akhtar, Farid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Rehman, Yaser
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology Lahore, Pakistan.
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    A study of the sintering of diatomaceous earth to produce porous ceramic monolithswith bimodal porosity and high strength2010Inngår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 201, s. 253-257Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Diatomite powder, a naturally occurring porous raw material, was used to fabricate ceramic materials withbimodal porosity and high strength. The effect of the sintering temperature on the density and porosity ofdry pressed diatomite green bodies was evaluated using mercury porosimetry and water immersionmeasurements. It was found that the intrinsic porosity of the diatomite particles with a pore size around0.2 μm was lost at sintering temperatures above 1200 °C. Maintaining the sintering temperature at around1000 °C resulted in highly porous materials that also displayed a high compressive strength. Microstructuralstudies by scanning electron microscopy and energy-dispersive X-ray analysis suggested that the porecollapse was facilitated by the presence of low melting impurities like Na2O and K2O.

  • 10.
    Akhtar, Farid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Sjöberg, Erik
    Korelskiy, Danil
    Rayson, Mark
    Hedlund, Jonas
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Preparation of graded silicalite-1 substrates for all-zeolite membranes with excellent CO2/H-2 separation performance2015Inngår i: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 493, s. 206-211Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Graded silicalite-1 substrates with a high gas permeability and low surface roughness have been produced by pulsed current processing of a thin coating of a submicron silicalite-1 powder onto a powder body of coarser silicalite-1 crystals. Thin zeolite films have been hydrothermally grown onto the graded silicalite-1 support and the all-zeolite membranes display an excellent CO2/H-2 separation factor of 12 at 0 degrees C and a CO2 permeance of 21.3 x 10(-7) mol m(-2) s(-1) Pa-1 for an equimolar CO2/H-2 feed at 505 kPa and 101 kPa helium sweep gas. Thermal cracking estimates based on calculated surface energies and measured thermal expansion coefficients suggest that all-zeolite membranes with a minimal thermal expansion mismatch between the graded substrate and the zeolite film should remain crack-free during thermal cycling and the critical calcination step.

  • 11.
    Akhtar, Farid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Vasiliev, Petr
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Hierarchically Porous Ceramics from Diatomite Powders by Pulsed Current Processing2009Inngår i: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 92, nr 2, s. 338-343Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hierarchically porous ceramic monoliths have been fabricated by pulsed current processing (PCP) of diatomite powders. The partial sintering behavior of the porous diatomite powders during PCP or spark plasma sintering was evaluated at temperatures between 600 degrees and 850 degrees C. Scanning electron microscopy and mercury porosimetry measurements showed that the PCP method was able to bond the diatomite powder together into relatively strong monoliths without significantly destroying the internal pores of the diatomite powder at a temperature range of 700 degrees-750 degrees C. Little fusion at the particle contact points occurred at temperatures below 650 degrees C while the powder showed partial melting and collapse of both the interparticle pores and the internal structure at temperatures above 800 degrees C.

  • 12.
    Andersson, Linnéa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Akhtar, Farid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Ojuva, Arto
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Colloidal processing and CO2-capture performance of hierarchically porous Al2O3-zeolite 13X composites2012Inngår i: Journal of Ceramic Science and Technology, ISSN 2190-9385, Vol. 3, nr 1, s. 9-16Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hierarchically porous composites for CO2-capture have been produced by coating the inner walls of foam-like macroporous alumina monoliths, produced by templated synthesis, with microporous zeolite 13X particles. Homogeneous and dense coatings of the particulate adsorbent were obtained when the impregnation process was performed at a pH above 9. At this pH-level the colloidally stable suspensions of the negatively charged zeolite 13X particles could fill all the voids of the highly connected pore space of the alumina supports and attach to the monolith walls, which had been pre-coated with poly(ethylene imine). A CO2-uptake as high as 5 mmol CO2/g zeolite 13X was achieved for alumina-zeolite 13X composites through minimisation of the added inorganic binder, kaolin, to only 3.0 wt% with respect to zeolite content, and through optimisation of the thermal treatment.

  • 13. Avila, M.
    et al.
    Burks, T.
    Akhtar, Farid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Gothelid, M.
    Lansaker, P. C.
    Toprak, M. S.
    Muhammed, M.
    Uheida, A.
    Surface functionalized nanofibers for the removal of chromium(VI) from aqueous solutions2014Inngår i: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 245, s. 201-209Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polyacrylonitrile (PAN) nanofibers functionalized with amine groups (PAN-NH2) were prepared using a simple one-step reaction route. The PAN-NH2 nanofibers were investigated for the removal of chromium(VI) from aqueous solutions. The adsorption and the kinetic characteristics were evaluated in batch process. The adsorption process showed pH dependence and the maximum Cr(VI) adsorption occurred at pH = 2. The Langmuir adsorption model described well the experimental adsorption data and estimated a maximum loading capacity of 156 mg/g, which is a markedly high value compared to other adsorbents reported. The kinetics studies indicated that the equilibrium was attained after 90 min and the experimental data followed a pseudo-second order model suggesting a chemisorption process as the rate limiting step. X-ray Photoelectron Spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) revealed that the adsorption of Cr(VI) species on PAN-NH2 was facilitated through both electrostatic attraction and surface complexation. High desorption efficiency (> 90%) of Cr(VI) was achieved using diluted base solutions that may allow the reuse of PAN-NH2 nanofibers.

  • 14. Binbin, Song
    et al.
    Peizhong, Feng
    Jianzhong, Wang
    Yuan, Ge
    Guangzhi, Wu
    Xiaohong, Wang
    Farid, Akhtar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Luleå University of Technology, Sweden.
    Oxidation properties of self-propagating high temperature synthesized niobium disilicide2014Inngår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 85, s. 311-317Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    NbSi2 monoliths were prepared by self-propagating high temperature synthesis (SHS) and hot pressing (HP) and their oxidation behavior was investigated at various temperatures (823-1123 K) in air. The combustion mode of SHS reaction was steady state combustion, and the combustion product was single-phase NbSi2. Oxidation studies show that the highest mass gain was 0.95675 kg m(-2) at 1023 K. In cyclic oxidation, the oxidation rate was reduced and the mass gain was only 0.15507 kg m(-2). A dense protective amorphous SiO2 scale formed at 823 K and 923 K whereas a porous multilayer SiO2 and alpha/beta-Nb2O5 oxide scales formed at and above 1023 K and spalled off. Pest oxidation of NbSi2 monoliths was not observed in hot pressed NbSi2 monoliths.

  • 15. Burks, T.
    et al.
    Avila, M.
    Akhtar, Farid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Gothelid, M.
    Lansaker, P. C.
    Toprak, M. S.
    Muhammed, M.
    Uheida, A.
    Studies on the adsorption of chromium(VI) onto 3-Mercaptopropionic acid coated superparamagnetic iron oxide nanoparticles2014Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 425, s. 36-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Chromium (Cr) in the form of Cr(VI) is deemed toxic in water due to its mutagenic and carcinogenic properties. For the successful removal of Cr(VI), we demonstrate a novel adsorbent consisting of superparamagnetic iron oxide nanoparticles (SPION) functionalized with 3-Mercaptopropionic acid (3-MPA). Fourier transform infrared spectroscopy (FT-IR) confirmed the functionalization of nanoparticles and presence of sulfonate groups. Batch adsorption experiments showed that the functionalized adsorbent recovered 45 mg of Cr(VI)/g of 3-MPA coated SPION at initial concentration of 50 mg/L aqueous solution at pH 1 with less than 1% of Fe dissolution from SPION. The results from X-ray photoelectron spectroscopy confirmed that Cr(VI) chemisorbed onto the adsorbent. Hence, the XPS spectra did not indicate any reduction of Cr(VI) to Cr(III) upon adsorption. The adsorption data were better fitted for the Freundlich model. Moreover, the Cr(VI) adsorption kinetics on functionalized SPION followed a pseudo-second order rate, revealing chemisorption as the dominant mechanism. The high Cr(VI) removal, rapid adsorption kinetics and stability of adsorbent indicate that 3-MPA coated SPION could be an efficient adsorbent for the removal of Cr(VI).

  • 16.
    Cumpstey, Ian
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Frigell, Jens
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Pershagen, Elias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Akhtar, Tashfeen
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Moreno-Clavijo, Elena
    Robina, Inmaculada
    Alonzi, Dominic S.
    Butters, Terry D.
    Amine-linked diglycosides: Synthesis facilitated by the enhanced reactivity of allylic electrophiles, and glycosidase inhibition assays2011Inngår i: Beilstein Journal of Organic Chemistry, ISSN 2195-951X, E-ISSN 1860-5397, Vol. 7, s. 1-9Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Diglycose derivatives, consisting of two monosaccharides linked at non-anomeric positions by a bridging nitrogen atom, have been synthesised. Conversion of one of the precursor monosaccharide coupling components into an unsaturated derivative enhances its electrophilicity at the allylic position, facilitating coupling reactions. Mitsunobu coupling between nosylamides and 2,3-unsaturated-4-alcohols gave the 4-amino-pseudodisaccharides with inversion of configuration as single regio- and diastereoisomers. A palladium-catalysed coupling between an amine and a 2,3-unsaturated 4-trichloroacetimidate gave a 2-amino-pseudodisaccharide as the major product, along with other minor products. Derivatisation of the C=C double bond in pseudodisaccharides allowed the formation of Man(N4-6)Glc and Man(N4-6)Man diglycosides. The amine-linked diglycosides were found to show weak glycosidase inhibitory activity.

  • 17.
    Cumpstey, Ian
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ramstadius, Clinton
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Akhtar, Tashfeen
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Goldstein, Irwin J
    Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI .
    Winter, Harry C
    Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI .
    Non-glycosidically linked pseudodisaccharides: thioethers, sulfoxides, sulfones, ethers, selenoethers, and their binding to lectins2010Inngår i: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, nr 10, s. 1951-1970Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrolytically stable non-glycosidically linked tail-to-tail pseudodisaccharides are linked by a single bridging atom remote from the anomeric centre of the constituent monosaccharides. Some such pseudodisaccharides with sulfur or oxygen bridges were found to act as disaccharide mimetics in their binding to the Banana Lectin and to Concanavalin A. A versatile synthetic route to a small library of such compounds is described

  • 18. Feng, Peizhong
    et al.
    Liu, Weisheng
    Farid, Akhtar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Wu, Jie
    Niu, Jinan
    Wang, Xiaohong
    Qiang, Yinghuai
    Combustion synthesis of (Mo1-xCrx)Si-2 (x=0.00-0.30) alloys in SHS mode2012Inngår i: Advanced Powder Technology, ISSN 0921-8831, E-ISSN 1568-5527, Vol. 23, nr 2, s. 133-138Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Combustion synthesis was adopted to successfully synthesize molybdenum-silicon-chromium (Mo-Si-Cr) alloys by the mode of self-propagating high-temperature synthesis (SHS). The experimental study of combustion synthesis of Mo-Si-Cr alloys was conducted on elemental powder compacts. Powder compacts with nominal compositions including MoSi2, (Mo0.95Cr0.05)Si-2, (Mo0.90Cr0.10)Si-2, (Mo0.85Cr0.15)Si-2, (Mo0.80Cr0.20)Si-2, (Mo0.75Cr0.25)Si-2 and (Mo0.20Cr0.30)Si-2 were employed in combustion synthesis experiments. The combustion mode, combustion temperature, flame-front propagation velocity and product structure were investigated. The results showed that Mo-Si-Cr alloys were synthesized by an unsteady state combustion mode with a spiral-trajectory reaction front. The peak combustion temperature reduced with the addition of Cr to Mo-Si system. The flame-front propagation velocity decreased with an increase in Cr content of the powder compact. The X-ray diffraction (XRD) results showed that the crystal structure of the combustion product changed from CIIb-type structure (Mo0.90Cr0.10)Si-2 to C40-type structure (Mo0.80Cr0.15)Si-2 with increase in Cr content of Mo-Cr-Si alloys. The intensities of diffraction peaks of the C40-type phase gradually increased with increase in Cr content.

  • 19.
    Keshavarzi, Neda
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Akhtar, Farid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Chemical durability of hierarchically porous silicalite-I membrane substrates in aqueous media2013Inngår i: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 28, nr 17, s. 2253-2259Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Zeolite-based supports for inorganic membranes intended for gas separation have the potential to increase the resistance to thermal shock-induced cracking compared with ceramic or metallic substrates. We have studied the effect of exposure at 90 degrees C of hierarchically porous silicalite-I substrates to aqueous solutions at pH 2.0, 10.6, and 13.0 for periods up to 168 h. Silicalite-I supports were produced in binder-free form by pulsed current processing and using clay-binders by conventional thermal treatment. Long-term (168 h) acid and alkali treatment of the silicalite-I substrates results in a slight removal of silicon (in acid) and aluminum (in alkali) and does not affect the specific surface area and the crystalline microporous structural features but broadens the size distribution of the macropores. The mechanical strength remains unchanged after exposure to both alkaline and acidic solutions and the binder-free substrates display more than 20 times higher strength than the binder-containing materials.

  • 20.
    Ojuva, Arto
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Akhtar, Farid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tomsia, Antoni P.
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Laminated Adsorbents with Very Rapid CO2 Uptake by Freeze-Casting of Zeolites2013Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 5, nr 7, s. 2669-2676Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Structured zeolite 13X monoliths with a laminated structure and hierarchical macro-/microporosity were prepared by freeze-casting aqueous suspensions of zeolite 13X powder, bentonite, and polyethylene glycol. Colloidally stable suspensions with a low viscosity at both room temperature and near freezing could be prepared at alkaline conditions where both the zeolite 13X powder and bentonite carry a negative surface charge. Slow directional freezing of the suspensions led to the formation of well-defined and thin lamellar pores and pore walls while fast freezing resulted in more cylindrical pores. The wall thickness, which varied between 8 and 35 mu m, increased with increasing solids loading of the suspension. Thermal treatment at 1053 K of the freeze-cast bodies containing between 9 and 17 wt % bentonite resulted in mechanically stable zeolite 13X monoliths. The monoliths displayed a carbon dioxide uptake capacity of 4-5 mmol/g and an uptake kinetics characterized by a very fast initial uptake where more than 50% of the maximum uptake was reached within 15 s. Freeze-cast laminated zeolite monoliths could be used to improve the volumetric efficiency and reduce the cycle time, of importance in, for example, biogas upgrading and CO2 separation from flue gas.

  • 21.
    Ojuva, Arto
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Jarvelainen, Matti
    Bauer, Marcus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Keskinen, Lassi
    Valkonen, Masi
    Akhtar, Farid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Luleå University of Technology, Sweden.
    Levanen, Erkki
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Mechanical performance and CO2 uptake of ion-exchanged zeolite A structured by freeze-casting2015Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 35, nr 9, s. 2607-2618Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Zeolite 4A has been freeze-cast into highly porous monoliths with a cylindrical shape. The brittle monoliths, with lamellar or columnar pores and wall thicknesses between 8 and 35 mu m, show a compressive mechanical response along the main pore axis that could be modeled by a buckling behavior. The failure strength is proportional to the density and the amount of transverse bridging across lamella, which was shown to be related to the pore cross-sectional aspect ratio. Monoliths with highly anisotropic pores with a cross-sectional aspect ratio higher than 3 yielded sequentially from the top surface, whereas monoliths with a pore aspect ratio lower than 3 were found to delaminate into longitudinal splinters. The freeze-cast monoliths show a sharp gas breakthrough front with a 1:9 mixture of CO2 and N-2, indicating rapid uptake kinetics of the lamellar structures.

  • 22.
    Shakarova, Dilshod
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Ojuva, Arto
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Akhtar, Farid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Luleå University of Technology, Sweden.
    Methylcellulose-Directed Synthesis of Nanocrystalline Zeolite NaA with High CO2 Uptake2014Inngår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 7, nr 8, s. 5507-5519Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Zeolite NaA nanocrystals with a narrow particle size distribution were prepared by template-free hydrothermal synthesis in thermo-reversible methylcellulose gels. The effects of the amount of methylcellulose, crystallization time and hydrothermal treatment temperature on the crystallinity and particle size distribution of the zeolite NaA nanocrystals were investigated. We found that the thermogelation of methylcellulose in the alkaline Na2O-SiO2-Al2O3-H2O system played an important role in controlling the particle size. The synthesized zeolite nanocrystals are highly crystalline, as demonstrated by X-ray diffraction (XRD), and scanning electron microscopy (SEM) shows that the nanocrystals can also display a well-defined facetted morphology. Gas adsorption studies on the synthesized nanocrystalline zeolite NaA showed that nanocrystals with a size of 100 nm displayed a high CO2 uptake capacity (4.9 mmol/g at 293 K at 100 kPa) and a relatively rapid uptake rate compared to commercially available, micron-sized particles. Low-cost nanosized zeolite adsorbents with a high and rapid uptake are important for large scale gas separation processes, e.g., carbon capture from flue gas.

  • 23.
    Vasiliev, Petr
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Akhtar, Farid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Grins, Jekabs
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Mouzon, Johanne
    Andersson, Charlotte
    Hedlund, Jonas
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Forming strong hierarchically porous zeolite monoliths by PCP-induced local amorphizationArtikkel i tidsskrift (Fagfellevurdert)
  • 24.
    Vasiliev, Petr Olegovich
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Akhtar, Farid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Grins, Jekabs
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Mouzon, Johanne
    Department of Applied Chemistry and Geosciences, Division of Chemical Engineering, Luleå University of Technology.
    Andersson, Charlotte
    Department of Applied Chemistry and Geosciences, Division of Chemical Engineering, Luleå University of Technology.
    Hedlund, Jonas
    Department of Applied Chemistry and Geosciences, Division of Chemical Engineering, Luleå University of Technology.
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Strong Hierarchically Porous Monoliths byPulsed Current Processing of Zeolite PowderAssemblies2010Inngår i: American Chemical Society, ISSN 1944-8244, Vol. 2, nr 3, s. 732-737Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Binderless hierarchically porous monoliths have been produced from silicalite-1 and ZSM-5 zeolite powders by a rapidand facile powder processing method where the zeolite powders are assembled in a graphite die and subjected simultaneously to acompressive pressure and a pulsed current. Pulsed current processing (PCP) or, as it is commonly called, spark plasma sintering,enables rapid thermal processing of zeolite powder assemblies with heating and cooling rates at 100 °C/minute or more, which resultsin the formation of strong powder bodies without any addition of secondary binders. Nitrogen adsorption measurements show thatit is possible to form strong zeolite monoliths by PCP that maintain between 85 and 95% of the surface area of the as-received silicalite-1and ZSM-5 powders. Line-broadening analysis of X-ray powder diffraction data by the Rietveld method and high-resolution electronmicroscopy showed that the formation of strong interparticle bonds is associated with a local amorphization reaction at the interfacialcontact points between the zeolite particles. The PCP-treated binderless ZSM-5 monoliths display a high selectivity in xylene isomerseparation.

1 - 24 of 24
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf