| 1. |
- Aguilar-Mamani, Wilson, et al.
(författare)
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Solution-mediated growth of NBA-ZSM-5 crystals retarded by gel entrapment
- 2018
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 487, s. 57-64
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of flat tablet-shaped ZSM-5 crystals from a gel using metakaolin as aluminosilicate source and n-butyl amine as structure directing agent was investigated. The evolution inside the solid phase was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetry and mass spectrometry. A kinetic study indicated that the nucleation of the majority crystals occurred concurrently with the formation of the gel upon heating the starting liquid suspension. Microstructural evidences undeniably showed that the gel precipitated on ZSM-5 crystals and mineral impurities originating from kaolin. As a result, crystal growth was retarded by gel entrapment, as indicated by the configuration and morphology of the embedded crystals. The results presented herein are harmonized with a solution-mediated nucleation and growth mechanism. Our observations differ from the autocatalytic model that suggests that the nuclei rest inside the gel until released when the gel is consumed. Our results show instead that it is crystals that formed in an early stage before entrapment inside the gel that rest inside the gel until exposed at the gel surface. These results illustrate the limitation of the classical method used in the field to determine nucleation profiles when the crystals become trapped inside the gel.
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| 2. |
- Akhtar, Farid, et al.
(författare)
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A study of the sintering of diatomaceous earth to produce porous ceramic monolithswith bimodal porosity and high strength
- 2010
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Ingår i: Powder Technology. - Amsterdam, Netherlands : Elsevier B.V.. - 0032-5910 .- 1873-328X. ; 201, s. 253-257
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
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| 4. |
- Akhtar, Farid, et al.
(författare)
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Aluminophosphate monoliths with high CO2-over-N2 selectivity and CO2 capture capacity
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:99, s. 55877-55883
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Tidskriftsartikel (refereegranskat)abstract
- Monoliths of microporous aluminophosphates (AlPO4-17 and AlPO4-53) were structured by binder-free pulsed current processing. Such monoliths could be important for carbon capture from flue gas. The AlPO4-17 and AlPO4-53 monoliths exhibited a tensile strength of 1.0 MPa and a CO2 adsorption capacity of 2.5 mmol g-1 and 1.6 mmol g-1, respectively at 101 kPa and 0°C. Analyses of single component CO2 and N2 adsorption data indicated that the AlPO4-53 monoliths had an extraordinarily high CO2-over-N2 selectivity from a binary gas mixture of 15 mol% CO2 and 85 mol% N2. The estimated CO2 capture capacity of AlPO4-17 and AlPO4-53 monoliths in a typical pressure swing adsorption (PSA) process at 20°C 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 was done without application of heat, which would regenerate them to their full capacity for CO2 adsorption.
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| 5. |
- Akhtar, Farid
(författare)
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Ceramic reinforced high modulus steel composites : processing, microstructure and properties
- 2014
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Ingår i: Canadian metallurgical quarterly. - 0008-4433 .- 1879-1395. ; 53:3, s. 253-263
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Akhtar, Farid, et al.
(författare)
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Colloidal processing and CO2 capture performance of sacrificially templated zeolite monoliths
- 2012
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 97, s. 289-296
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 7. |
- Akhtar, Farid, et al.
(författare)
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Colloidal Processing and Thermal Treatment of Binderless Hierarchically Porous Zeolite 13X Monoliths for CO2 Capture
- 2011
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 94:1, s. 199-205
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Tidskriftsartikel (refereegranskat)abstract
- 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%.
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| 8. |
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| 9. |
- Akhtar, Farid, et al.
(författare)
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Enhanced sintering, microstructure evolution and mechanical properties of 316L stainless steel with MoSi(2) addition
- 2011
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 509:35, s. 8794-8797
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
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