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Zhang, H., Hedman, D., Feng, P., Han, G. & Akhtar, F. (2019). A high entropy B4(HfMo2TaTi)C and SiC ceramic composite. In: : . Paper presented at XVI ECerS CONFERENCE.
Open this publication in new window or tab >>A high entropy B4(HfMo2TaTi)C and SiC ceramic composite
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2019 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Refractory carbides HfC, Mo2C, TiC, TaC, B4C, and SiC were mixed with a molar ratio of 2:1:2:2:1:2 to fabricate multicomponent ceramic composite by pulsed current processing (PCP). From the starting materials that consist of face-centered cubic (FCC), hexagonal and rhombohedral crystal structures, the investigated carbide system is reported to form a single phase B4(HfMo2TaTi)C high-entropy ceramic (HEC) with SiC. The HEC phase contains uniform distribution of constitutional elements Hf, Mo, Ta, Ti, B and C, according to Energy dispersive X-ray spectroscopy (EDS) and wavelength dispersive X-ray spectroscopy (WDS) results.

The fabricated HEC phase displays a hexagonal crystal structure, with a high average lattice distortion of 8.26% (Figure 1). The HCP structure was observed by X-ray diffraction and selected area diffraction in transmission electron microscopy (TEM). Density-functional theory (DFT) optimization suggested that the hexagonal crystal structure has alternating layers of metal atoms and carbon/boron atoms, i.e. metal atoms of Hf, Mo, Ta and Ti were distributed on the (0001) plane in the hexagonal lattice, while the carbon/boron atoms formed hexagonal 2D grids on the (0002) plane in the hexagonal unit cell. Despite of the vast differences in the crystal structures and lattice parameters among the utilized carbides, the formation of the unique hexagonal lattice structure of B4HfMo2TaTi)C can be a result of independent diffusion of the metal and nonmetal atoms. The sintered HEC ceramic composite exhibits excellent oxidation resistance at mediate temperature, 900 ºC for 50h, and elevated temperature, 2000 ºC for 20 s. Nanoindentation test shows that the HEC phase has a high hardness of 35 GPa. The remarkable improvement compared to the theoretical hardness value estimated based on the rule of mixtures (23 GPa) was contributed by the severe lattice distortion in the hexagonal structure.

National Category
Materials Engineering
Identifiers
urn:nbn:se:ltu:diva-74894 (URN)
Conference
XVI ECerS CONFERENCE
Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2019-06-24
Zhang, H., Hedman, D., Feng, P., Han, G. & Akhtar, F. (2019). A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite. Dalton Transactions, 48(16), 5161-5167
Open this publication in new window or tab >>A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite
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2019 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, no 16, p. 5161-5167Article in journal (Refereed) Published
Abstract [en]

A multicomponent composite of refractory carbides, B4C, HfC, Mo2C, TaC, TiC and SiC, of rhombohedral, face-centered cubic (FCC) and hexagonal crystal structures is reported to form a single phase B4(HfMo2TaTi)C ceramic with SiC. The independent diffusion of the metal and nonmetal atoms led to a unique hexagonal lattice structure of the B4(HfMo2TaTi)C ceramic with alternating layers of metal atoms and C/B atoms. In addition, the classical differences in the crystal structures and lattice parameters among the utilized carbides were overcome. Electron microscopy, X-ray diffraction and calculations using density functional theory (DFT) confirmed the formation of a single phase B4(HfMo2TaTi)C ceramic with a hexagonal close-packed (HCP) crystal structure. The DFT based crystal structure prediction suggests that the metal atoms of Hf, Mo, Ta and Ti are distributed on the (0001) plane in the HCP lattice, while the carbon/boron atoms form hexagonal 2D grids on the (0002) plane in the HCP unit cell. The nanoindentation of the high-entropy phase showed hardness values of 35 GPa compared to the theoretical hardness value estimated based on the rule of mixtures (23 GPa). The higher hardness was contributed by the solid solution strengthening effect in the multicomponent hexagonal structure. The addition of SiC as the secondary phase in the sintered material tailored the microstructure of the composite and offered oxidation resistance to the high-entropy ceramic composite at high temperatures.

Place, publisher, year, edition, pages
Royal Society of Medicine Press, 2019
National Category
Materials Engineering Ceramics Composite Science and Engineering Other Physics Topics
Research subject
Engineering Materials; Applied Physics
Identifiers
urn:nbn:se:ltu:diva-72953 (URN)10.1039/C8DT04555K (DOI)000465328200037 ()30778490 (PubMedID)2-s2.0-85064521555 (Scopus ID)
Available from: 2019-02-20 Created: 2019-02-20 Last updated: 2019-05-14Bibliographically approved
Saeidi, K., Alvi, S., Lofaj, F., Petkov, V. I. & Akhtar, F. (2019). Advanced Mechanical Strength in Post Heat Treated SLM 2507 at Room and High Temperature Promoted by Hard/Ductile Sigma Precipitates. Metals, 9(2), Article ID 199.
Open this publication in new window or tab >>Advanced Mechanical Strength in Post Heat Treated SLM 2507 at Room and High Temperature Promoted by Hard/Ductile Sigma Precipitates
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2019 (English)In: Metals, E-ISSN 2075-4701, Vol. 9, no 2, article id 199Article in journal (Refereed) Published
Abstract [en]

Duplex stainless steel, 71 wt.% austenite, 13 wt.% ferrite and 16 wt.% sigma, was made upon heat treating of fully ferritic as-built selective laser melted (SLM) 2507 stainless steel at 1200 °C. Formation of sigma phase in the heat treated SLM 2507 was investigated using optical microscopy and scanning electron microscopy (SEM). The heat treated SLM 2507 demonstrated a yield strength of 686 MPa, ultimate tensile strength of 920 MPa and an elongation of 1.8% at room temperature with a brittle fracture morphology. Precipitation of sigma phase during heat treatment and slow cooling improved the mechanical and wear properties at high temperatures (1200 °C and 800 °C, respectively). The tensile strength and elongation of the heat treated SLM 2507 was measured 400 MPa and 20% as compared to casted duplex steel with 19 MPa and 30% elongation at 1200 °C. The 20 times higher mechanical strength as compared to casted duplex steel was attributed to sigma precipitates. Tribological behaviour of heat treated duplex SLM 2507 containing sigma at 800 °C showed very low wear rate of 4.5 × 10−5 mm3/mN compared to casted duplex steel with 1.6 × 10−4 mm3/mN.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
selective laser melting, duplex stainless steel, heat treatment, mechanical properties
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73183 (URN)10.3390/met9020199 (DOI)000460764700090 ()2-s2.0-85062367956 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-03-13 (johcin)

Available from: 2019-03-13 Created: 2019-03-13 Last updated: 2019-04-12Bibliographically approved
Zhang, H., Hedman, D., Feng, P., Han, G. & Akhtar, F. (2019). Correction: A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite. Dalton Transactions, 48(19), 6647-6647
Open this publication in new window or tab >>Correction: A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite
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2019 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, no 19, p. 6647-6647Article in journal (Refereed) Published
Abstract [en]

The authors regret that there is an error in writing the crystal structure in the article. The authors would like to address as follows:

The presented XRD and TEM results revealed a hexagonal crystal structure. The following analyses including the identification of the lattice parameters and the DFT calculation were based on a hexagonal lattice. Therefore, the HCP (hexagonal close-packed) structure mentioned in the article should be regarded as a hexagonal structure. The HCP term used in the introduction, where the article from Joshua Gild et al. was cited, should also be regarded as hexagonal AlB2 structure.

The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

Place, publisher, year, edition, pages
Royal Society of Medicine Press, 2019
National Category
Materials Engineering Ceramics Composite Science and Engineering Other Physics Topics
Research subject
Engineering Materials; Applied Physics
Identifiers
urn:nbn:se:ltu:diva-74978 (URN)10.1039/C9DT90099C (DOI)000472451000039 ()2-s2.0-85065896417 (Scopus ID)
Note

Coorection to: A high-entropy B 4 (HfMo 2 TaTi)C and SiC ceramic composite

(2019) Dalton Transactions, 48 (16), pp. 5161-5167.DOI:10.1039/c8dt04555k

Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-08-15Bibliographically approved
Hooshmand, S., Nordin, J. & Akhtar, F. (2019). Development of Ceramic Foams Containing Platinum Nanoparticles as the Catalyst. In: : . Paper presented at 10th EEIGM International Conference on Advanced Materials Research.
Open this publication in new window or tab >>Development of Ceramic Foams Containing Platinum Nanoparticles as the Catalyst
2019 (English)Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

The exhaust gases contribute significantly to global warming, but without a catalytic converter, exhaust gases would be even more polluting. Therefore, having a catalytic metal such as platinum nanoparticles on the surface of the pore walls in ceramic foams is a practical way to remove particulate matters and to have an effective catalytic converter in one. The porous structure of the foam filters the particulate matters and the high specific surface area of the Pt nanoparticles in the pores speed up the reactions. The role of platinum is to oxidize carbon monoxide (CO) and hydrocarbons (HC) to form carbon dioxide (CO2) and water vapor (H2O). In this study, The Pt nanoparticles were coated on the surface of the thermally expandable microspheres (Expancel). The Energy-dispersive X-ray spectroscopy (EDS) and Ultraviolet-visible spectroscopy (UV-Vis) confirmed the successful adsorption of Pt on the Expancel surface. In the next step, alumina foams prepared by the gel-casting technique using Pt-coated Expancels as the sacrificial template. The EDS confirmed the successful transfer of the Pt nanoparticles to the pore walls of the foam. The morphology and the porosity of the foams were studied using SEM and X-ray microtomography. Moreover, the compressive strength of the prepared sample in form of the green body, debinded and sintered was measured.  The results showed a promising way to design ceramic-based bi-functional foams for eliminating dust and converting harmful gases to nontoxic gases simultaneously.

National Category
Ceramics
Identifiers
urn:nbn:se:ltu:diva-74639 (URN)
Conference
10th EEIGM International Conference on Advanced Materials Research
Available from: 2019-06-17 Created: 2019-06-17 Last updated: 2019-06-17
Wenjing, Z., Narang, K., Salcedo, A. J., Dou, Y., Simonsen, S. B., Sørensen, M. G., . . . Kaiser, A. (2019). Electrospun nanofiber materials for energy and environmental applications. In: : . Paper presented at 10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, China (pp. 6723-6724). Elsevier, 158
Open this publication in new window or tab >>Electrospun nanofiber materials for energy and environmental applications
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2019 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Electrospinning is the one of the most versatile techniques to design nanofiber materials with numerous applications in the fields of energy conversion, catalytic chemistry, liquid and gas filtration.1 By electrospinning, complex structures can be designed from a rich variety of materials including polymers, metals, ceramics and composite, with the ability to control composition, morphology and secondary structure and tailor performance and functionality for specific applications. Moreover, with recent developments in the design of electrospinning equipment and availability of industrial-scale electrospinning technologies with production rates of several thousands of square meters per day new opportunities for electrospinning are imminent. With this, the advanced research on materials performed in our labs is getting closer to the commercialization of new products for applications in fields of energy and environment.

An overview will be given on electrospinning activities at DTU Energy that address the sizable challenges in energy and environmental applications by electrospinning: 1. Electrospun perovskite oxide nanofiber electrode for use in solid oxide fuel cells. In this application, a (La0.6Sr0.4)0.99CoO3-δ cathode was shaped into 3-dimensional thin-film by so-gel assisted electrospinning method combined with calcination and sintering; 2. Electrospun nanofiber materials for gas adsorption. Both the advantages and challenges of using electrospun nanofiber materials will be discussed, in terms of electrochemical performance, surface area, packing efficiency and mechanical stability.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73870 (URN)10.1016/j.egypro.2019.01.016 (DOI)
Conference
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, China
Available from: 2019-05-07 Created: 2019-05-07 Last updated: 2019-06-14Bibliographically approved
Liu, Y., Cai, X., Sun, Z., Zhang, H., Akhtar, F., Czujko, T. & Feng, P. (2019). Fabrication and Characterization of Highly Porous FeAl‐Based Intermetallics by Thermal Explosion Reaction. Paper presented at 2nd International Conference and Exhibition on Light Materials − Science and Technology(LightMAT2017), September 8-10, 2017, Bremen, Germany. Advanced Engineering Materials, 21(4), Article ID 1801110.
Open this publication in new window or tab >>Fabrication and Characterization of Highly Porous FeAl‐Based Intermetallics by Thermal Explosion Reaction
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2019 (English)In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 21, no 4, article id 1801110Article in journal (Refereed) Published
Abstract [en]

Porous FeAl-based intermetallics with different nominal compositions ranging from Fe–40 at% Al to Fe–60 at% Al are prepared by a novel process of thermal explosion (TE) mode. The results show that the Al content significantly affects the combustion behavior of the specimens, the ignition temperature of the Fe–Al intermetallics varies from 641 to 633 °C and the combustion temperature from 978 to 1179 °C. The porous materials exhibit uniform pore structures with porosities and average pore sizes of 52–61% and 20–25 µm, respectively. The TE reaction is the dominant pore formation mechanism regardless of the alloy composition. However, differences in the porosity and average pore size are observed depending on the Al content. The compressive strength of porous Fe–Al intermetallics is in the range of 23–34 MPa, duly applied as filters. Additionally, a surface alumina layer is formed at the early stage and both of the oxidation process and the sulfidation process follows the familiar parabolic rate law in the given atmosphere, exhibiting excellent resistance to oxidation and sulfidation. These results suggest that the porous Fe–Al intermetallics are promising materials for applications in harsh environments with a high-temperature sulfide-bearing atmosphere, such as in the coal chemical industry.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
FeAl intermetallics, microstructure, porous material, properties, thermal explosion
National Category
Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-72765 (URN)10.1002/adem.201801110 (DOI)2-s2.0-85060210181 (Scopus ID)
Conference
2nd International Conference and Exhibition on Light Materials − Science and Technology(LightMAT2017), September 8-10, 2017, Bremen, Germany
Note

Konferensartikel i tidskrift

Available from: 2019-02-01 Created: 2019-02-01 Last updated: 2019-06-26Bibliographically approved
Alvi, S. & Akhtar, F. (2019). High temperature tribology of CuMoTaWV high entropy alloy. In: Wear of Materials: . Paper presented at 22nd International Conference on Wear of Materials, April 14-18 2019, Miami, USA (pp. 412-419). , 426-427
Open this publication in new window or tab >>High temperature tribology of CuMoTaWV high entropy alloy
2019 (English)In: Wear of Materials, 2019, Vol. 426-427, p. 412-419Conference paper, Published paper (Refereed)
Abstract [en]

An equiatomic high entropy alloy (HEA) CuMoTaWV was designed for room temperature to high temperature wear applications using spark plasma sintering of elemental powder mixture at 1400 °C. The sintered solid solution showed uniform distribution of elements in a BCC high entropy alloy phase along with V rich solid solution phase with an average hardness of 600 Hv and 900 Hv, respectively. Room temperature (RT) dry sliding wear tests, against alloy steel (700–880 Hv) for 200 m sliding distance at 5 N normal load, showed negligible wear of 5 × 10−7 mm/N m and a coefficient of friction (COF) of 0.5. Sliding wear characterization of sintered CuMoTaWV alloy against Si3N4 (1550 Hv) counter body from RT to 600 °C showed an increasing average COF of 0.45–0.67 from RT to 400 °C and then reducing to 0.54 at 600 °C. The wear rate was found to be lower at RT (4 × 10−3 mm3/N m) and 400 °C (5 × 10−3 mm3/N m), and slightly higher at 200 °C (2.3 × 10−2 mm3/N m) and 600 °C (4.5 × 10−2 mm3/N m). The CuMoTaWV alloy showed wear mechanisms specific to the test temperatures. The wear of CuMoTaWV alloy was governed by adhesive wear at RT and 200 °C and oxidative wear at 400 °C and 600 °C. The analyses of wear surfaces showed that the low wear rate at RT was due to the high hardness of the HEA, presence of V rich zones and formation of W and Ta tribofilm. At 400 °C, the formation of CuO tribolayer reduced the wear and hindered oxidation of wear track. At 600 °C, the wear rate increased due to oxidation of Cu, Ta and W. Moreover, the formation of lubricating elongated magneli phase V2O5 in V rich regions of CuMoTaWV alloy reduced the COF to 0.54.

Keywords
Sliding wear, High temperature wear, Adaptive wear, High, Entropy alloy (HEA, ) Refractory, Tribology, Spark plasma sintering (SPS)
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73687 (URN)10.1016/j.wear.2018.12.085 (DOI)000464583700044 ()
Conference
22nd International Conference on Wear of Materials, April 14-18 2019, Miami, USA
Available from: 2019-04-17 Created: 2019-04-17 Last updated: 2019-06-14Bibliographically approved
Nikjoo, D., Perrot, V. & Akhtar, F. (2019). Laminated Porous Diatomite Monoliths for Adsorption of Dyes From Water. Environmental Progress & Sustainable Energy, 38(s1), 377-385
Open this publication in new window or tab >>Laminated Porous Diatomite Monoliths for Adsorption of Dyes From Water
2019 (English)In: Environmental Progress & Sustainable Energy, ISSN 1944-7442, E-ISSN 1944-7450, Vol. 38, no s1, p. 377-385Article in journal (Refereed) Published
Abstract [en]

Structured laminated diatomite monoliths with superior mechanical properties were prepared by controlled freeze-casting of the aqueous suspensions of diatomite powders for wastewater treatment. The directional freezing of suspensions with solids loading of 25, 30, and 37 wt % at cooling from 0.5 to 5 K/min resulted in the formation of lamellar pores and solid walls with the thickness of 12–30 and 14–39 μm, respectively. The increase in solid loading and freezing rate resulted in refinement of the porous structure. Durable monoliths with the mechanical strength of 5.3 MPa were obtained by thermal treatment of the freeze-dried green bodies at 1,373 K. Diatomite monoliths with a pore size of 29.6 μm showed the removal of model dye pollutant Rhodamine B from water by adsorption and long-term water stability. The dye uptake capacity of monolith changed from 1.38 to 17.04 mg/g for the initial dye concentrations between 1.0 and 12.5 mg/L at 298 K and pH = 6, respectively. The adsorption data analysis using Lagergren's pseudo-first-order, pseudo-second-order, and intra-particle diffusion models revealed that diatomite monoliths offered efficient mass transfer in the porous laminated scaffold and to the adsorption sites and bulk diffusion of dye molecules in water was the rate-limiting mechanism for dye removal. © 2018 American Institute of Chemical Engineers Environ Prog, 2018.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
porous ceramic, diatomite, freeze‐casting, adsorption, dye uptake
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-71352 (URN)10.1002/ep.13064 (DOI)000460576900040 ()2-s2.0-85054712187 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-03-08 (johcin)

Available from: 2018-10-26 Created: 2018-10-26 Last updated: 2019-04-12Bibliographically approved
Lal, G., Derakhshandeh, M., Akhtar, F., Spasyuk, D. M., Lin, J.-B., Trifkovic, M. & Shimizu, G. K. H. (2019). Mechanical Properties of a Metal−Organic Framework formed by Covalent Cross-Linking of Metal−Organic Polyhedra. Journal of the American Chemical Society, 141(2), 1045-1053
Open this publication in new window or tab >>Mechanical Properties of a Metal−Organic Framework formed by Covalent Cross-Linking of Metal−Organic Polyhedra
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2019 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, no 2, p. 1045-1053Article in journal (Refereed) Published
Abstract [en]

Overcoming the brittleness of metal-organic frameworks (MOFs) is a challenge for industrial applications. To increase the mechanical strength, MOFs have been blended with polymers to form composites. However, this also brings challenges, such as integration and integrity of MOF in the composite, which can hamper the selectivity of gas separations. In this report, an "all MOF" material with mechanical flexibility has been prepared by covalent cross-linking of metal-organic polyhedra (MOPs). The ubiquitous Cu 24 isophthalate MOP has been decorated with a long alkyl chain having terminal alkene functionalities so that MOPs can be cross-linked via olefin metathesis using Grubbs second generation catalyst. Different degrees of cross-linked MOP materials have been obtained by varying the amount of catalyst in the reaction. Rheology of these structures with varying number of cross-links was performed to assess the cross-link density and its homogeneity throughout the sample. The mechanical properties were further investigated by the nanoindentation method, which showed increasing hardness with higher cross-link density. Thus, this strategy of cross-linking MOPs with covalent flexible units allows us to create MOFs of increasing mechanical strength while retaining the MOP cavities.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73213 (URN)10.1021/jacs.8b11527 (DOI)000456350300045 ()30582892 (PubMedID)2-s2.0-85059781426 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-03-15 (svasva)

Available from: 2019-03-15 Created: 2019-03-15 Last updated: 2019-03-25Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4888-6237

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