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  • 1.
    Fu, Le
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Xia, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Highly translucent and strong ZrO2-SiO2 nanocrystalline glass ceramic prepared by sol-gel method and spark plasma sintering with fine 3D microstructure for dental restoration2017In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 37, no 13, p. 4067-4081Article in journal (Refereed)
    Abstract [en]

    Balance of better mechanical strength and good translucency for dental restorative materials is always a challenge. A translucent glass ceramic/ceramic with improved mechanical properties or a strong glass ceramic/ceramic with good translucency would therefore be interesting for dental application. Nanocrystalline glass ceramics (NCGC) attract a lot attention because of their superior optical and mechanical properties. This study aims to obtain ZrO2-SiO2 nanocrystalline glass-ceramic that possesses high mechanical strength as well as excellent translucency by controlling the content, size, and connection of nanocrystalline ZrO2 in a ZrO2-SiO2 glass-ceramic material. Toward this end, well-homogenized nano powders with three different compositions, 45%ZrO2-55%SiO2 (molar ratio, 45Zr), 55%ZrO2-45%SiO2 (55Zr), and 65%ZrO2-35%SiO2 (65Zr), were synthesized, followed by a fast sintering process. Highly translucent nanocrystalline glass ceramics composed of tetragonal ZrO2 were obtained. Samples with high zirconia content showed that the structure of the skeleton was predominately built by nano-sized ellipsoidal ZrO2 particles bonded by grain boundaries, with amorphous SiO2 filling the voids between the ZrO2 particles. The achieved flexural strength measured by piston-on-three-ball test was as high as 1014 MPa. To our knowledge, this is one of the highest flexural strength values of glass ceramics ever reported, which is higher than transparent zirconia and alumina ceramics. The 3D structure of nanocrystalline zirconia in silica matrix did enhance the flexural strength of the NCGC. The results of this study suggest that the new ZrO2-SiO2 NCGC has great potential of using as dental restoration.

  • 2.
    Fu, Le
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala university.
    Xia, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Highly translucent and strong ZrO2-SiO2 nanocrystalline glass ceramicprepared by sol-gel method and spark plasma sintering with fine 3Dmicrostructure for dental restoration2017In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 37, p. 4067-4081Article in journal (Refereed)
    Abstract [en]

    Balance of better mechanical strength and good translucency for dental restorative materials is alwaysa challenge. A translucent glass ceramic/ceramic with improved mechanical properties or a strongglass ceramic/ceramic with good translucency would therefore be interesting for dental application.Nanocrystalline glass ceramics (NCGC) attract a lot attention because of their superior optical andmechanical properties. This study aims to obtain ZrO2-SiO2 nanocrystalline glass-ceramic that possesseshigh mechanical strength as well as excellent translucency by controlling the content, size, and connectionof nanocrystalline ZrO2 in a ZrO2-SiO2 glass-ceramic material. Toward this end, well-homogenized nano-powders with three different compositions, 45%ZrO2-55%SiO2 (molar ratio, 45Zr), 55%ZrO2-45%SiO2(55Zr), and 65%ZrO2-35%SiO2 (65Zr), were synthesized, followed by a fast sintering process. Highly-translucent nanocrystalline glass ceramics composed of tetragonal ZrO2 were obtained. Samples withhigh zirconia content showed that the structure of the skeleton was predominately built by nano-sizedellipsoidal ZrO2 particles bonded by grain boundaries, with amorphous SiO2 filling the voids betweenthe ZrO2 particles. The achieved flexural strength measured by piston-on-three-ball test was as high as1014 MPa. To our knowledge, this is one of the highest flexural strength values of glass ceramics everreported, which is higher than transparent zirconia and alumina ceramics. The 3D structure of nanocrys-talline zirconia in silica matrix did enhance the flexural strength of the NCGC. The results of this studysuggest that the new ZrO2-SiO2 NCGC has great potential of using as dental restoration.

  • 3.
    Fu, Le
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Xia, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Spark plasma sintering of biodegradable Si3N4 bioceramic with Sr, Mg and Si as sintering additives for spinal fusion2018In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 38, no 4, p. 2110-2119Article in journal (Refereed)
    Abstract [en]

    Silicon nitride (Si3N4) bioceramics with standard sintering additives (Al2O3 and Y2O3) are used in spinal fusion. Alternative Si3N4 bioceramics with biologically beneficial sintering additives could lead to improved osseoin- tegrative properties. The aim of this study is to obtain dense and strong Si3N4 bioceramics by using SrO, MgO and SiO2 as sintering additives, and evaluate the effect of these sintering additives on microstructures and properties of Si3N4 bioceramics. Raw powders with 10 wt% and 18 wt% sintering additives were sintered by spark plasma sintering. Samples sintered at 1750 °C, with an applied pressure of 60 MPa and a holding time of 3 min, showed the highest content of β-Si3N4 (94.9%). The mechanical properties of the developed Si3N4 bio- ceramics are comparable to the mechanical properties of currently used structural Si3N4 ceramics sintered with standard sintering additives (Al2O3 and Y2O3). The highest flexural strength of the developed Si3N4 bioceramics reached 1079 MPa. Ion release results showed that Sr2+,Mg2+ and Si4+ ions kept leaching out within 10 days’ immersion. The degradable Si3N4 bioceramics with adequate strength and biologically beneficial sintering ad- ditives show the promise for load bearing biomedical applications, such as spinal fusion.

  • 4.
    Fu, Le
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wu, Chengtie
    Chinese Acad Sci, Shanghai Inst Ceram, State Key Lab High Performance Ceram & Superfine, 1295 Dingxi Rd, Shanghai 200050, Peoples R China..
    Grandfield, Kathryn
    McMaster Univ, Dept Mat Sci & Engn, Hamilton, ON, Canada.;McMaster Univ, Sch Biomed Engn, Hamilton, ON, Canada..
    Unosson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Chang, Jiang
    Chinese Acad Sci, Shanghai Inst Ceram, State Key Lab High Performance Ceram & Superfine, 1295 Dingxi Rd, Shanghai 200050, Peoples R China..
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Xia, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Transparent single crystalline ZrO2-SiO2 glass nanoceramic sintered by SPS2016In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 36, no 14, p. 3487-3494Article in journal (Refereed)
    Abstract [en]

    Transparent ZrO2-SiO2 glass ceramics show potential for application in the dental industry. The application of this material prepared by a sol-gel method was hindered by the difficulties in obtaining large dimension samples. Spark plasma sintering (SPS) offers the possibility of achieving transparent ZrO2-SiO2 glass ceramics. In this study, a ZrO2-SiO2 powder was prepared by the sol-gel method and subsequently sintered by SPS. Varied sintering temperatures and pressures were explored to achieve better mechanical strength and transparency. TEM results showed single crystalline ZrO2 spherical nanocrystals (approximately 20 nm) homogenously embedded in the SiO2 matrix. Tetragonal ZrO2 was the only crystalline phase in all specimens. With sintering conditions of 1200 degrees C and 30 MPa, a glass ceramic with fracture toughness of 4.13 MPa was obtained. This value is similar to the commercial dental glass ceramic of IPS e.max (R) Press. The studied transparent glass ceramic with high transparency and moderate mechanical strength shows promise for dental application.

  • 5. Iftekhar, Shahriar
    et al.
    Grins, Jekabs
    Svensson, Gunnar
    Lööf, Jesper
    Jarmar, Tobias
    Botton, Gianluigi A.
    Andrei, Carmen M.
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Phase formation of CaAl2O4 from CaCO3-Al2O3 powder mixtures2008In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 28, no 4, p. 747-756Article in journal (Refereed)
    Abstract [en]

    Calcium aluminate is the main constituent in calcium aluminate cements, used in a wide range of applications in construction and mining industries and recently also as biomedical implant. In applications that demand very precise reaction features, such as the biomedical ones, the phase purity is of very high importance. In this paper the formation of CaAl2O4 from CaCO3-Al2O3 powder mixtures has been studied, varying holding times between 1 and 40 h and temperatures between 1300 and 1500 degrees C. Phase formation was studied in samples both quenched from the holding temperatures and in samples slowly cooled. Samples were characterized by X-ray powder diffraction (XRPD), using Guinier-Hagg film data and the Rietveld method, and scanning (SEM) and transmission (TEM) electron microscopy. Samples for TEM with very high site accuracy were produced using focused ion beam microscopy. In addition to CA (CaAl2O4) the samples contained major amounts of CA(2) (CaAl4O7), C(12)A(7) (Ca12Al14O33) and minor amounts of un-reacted A (Al2O3). Trace amounts of C(3)A (Ca3Al2O6) were observed only for samples heated to 1500 degrees C. The amount of the Ca-rich phase C(12)A(7) was found to decrease with time as it reacts with A and, to a less degree, CA(2) to form CA. In agreement with previous studies the amount of CA(2) formed decreases comparatively slowly with time. Its un-reactivity is due to that it is concentrated in isolated porous regions of sizes up to 100 mu m. The formation of the Ca aluminates is found to be in response to local equilibriums within small inhomogeneous regions, with no specific phase acting as an intermediate phase. Samples quenched from 1500 degrees C were found to contain smaller amounts of poorly crystallized phases. A reaction between C and A takes place already at 900 degrees C, forming a meta-stable orthorhombic modification of CA. The orthorhombic unit cell with a = 8.732(2) b = 8.078(2) angstrom, c = root 3 center dot a = 15.124(4) angstrom was verified by electron diffraction, revealing frequent twinning and disorder of the crystallites.

  • 6. Krest'an, J.
    et al.
    Pritula, O.
    Smrcok, L'.
    Sajgalik, P.
    Lences, Z.
    Wannberg, A.
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, The Studsvik Neutron Research Laboratory.
    Monteverde, F.
    Corrosion of beta-sialon-based ceramics by molten steel2007In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 27, no 5, p. 2137-2143Article in journal (Refereed)
    Abstract [en]

    The corrosion resistance of sialons made from commercial powders (AlN, Al2O3 and Si3N4) and from powder precursor produced by carbothermal reduction and nitridation of raw aluminosilicate (pyrophyllite) in molten steel were investigated. The corroded zone in sialon made from raw pyrophyllite (P1) is more then two times deeper compared to the corroded zone of sialon made from commercial powders (C1). The corrosion zone of sample P1 is on the average 610 mu m deep, while in sample C1 it is only 260 mu m. The main corrosion products are gamma-Al2O3 and iron silicides. The phase compositions were estimated by neutron Rietveld refinement.

  • 7.
    Persson, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Unosson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Ajaxon, Ingrid
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Engstrand, Johanna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Xia, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Nano grain sized zirconia–silica glass ceramics for dental applications2012In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 32, no 16, p. 4105-4110Article in journal (Refereed)
    Abstract [en]

    Glass ceramics based on lithium disilicates are commonly used in dental veneers and crowns. Alternative materials with improved mechanical properties may be of interest for more demanding applications, e.g. bridgeworks. In this study, a sol-gel method was optimized to produce nano grain-sized zirconia-silica glass ceramics with properties adequate for dental applications. The material properties were compared to those of IPS e.max (R) CAD, a commercially available lithium disilicate. The zirconia-silica glass ceramic was found to be translucent, with a transmittance of over 70%, and possessed excellent corrosion resistance. It also presented a somewhat lower elastic modulus but higher hardness than the lithium disilicate, and with the proper heat treatment a higher fracture toughness was achieved for the zirconia-silica glass ceramic. In conclusion, the material produced in this study showed promising results for use in dental applications, but the production method is sensitive and large specimen sizes may be difficult to achieve.

  • 8.
    Pettersson, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Pakdaman, Zohreh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Liu, Yi
    Dept of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Shen, Zhijian
    Dept of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Östhols, Erik
    Sandvik Tooling, Stockholm.
    Spark plasma sintered beta-phase silicon nitride with Sr and Ca as a sintering aid for load bearing medical applications2012In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 32, no 11, p. 2705-2709Article in journal (Refereed)
    Abstract [en]

    Due to its inherent good physical and chemical properties silicon nitride has high potential to be used for load bearing implants. However, the standard sintering additives alumina and rare earth oxides are limiting the biocompatibility of the material. The aim of the current project is to exchange the additives for more biologically beneficial additives. Spark plasma sintered silicon nitride was manufactured with strontium or calcium as sintering aids. The ability of forming high strength beta-phase microstructure silicon nitride was investigated. Powders were prepared with 10 and 30 wt.% glass phase and sintered at 1600, 1650, 1700 and 1750 degrees C. X-ray diffraction demonstrated compositions with 10 wt.% glass phase with strontium as sintering aid to yield larger amount of beta-phase. The highest amount of beta-phase (96% of the crystalline structure) was obtained using SPS for strontium-doped silicon nitride at sintering temperature 1750 degrees C, resulting in the highest fracture toughness, 4.2 MPa m(1/2).

  • 9.
    Shang, Lin
    et al.
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Baben, Moritz To
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany.;GTT Technol, Kaiserstr 103, D-52134 Herzogenrath, Germany..
    Pradeep, Konda Gokuldoss
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Sandloebes, Stefanie
    Rhein Westfal TH Aachen, Inst Metallkunde & Metallphys, Kopernikusstr 14, D-52074 Aachen, Germany..
    Amalraj, Marshal
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Hans, Marcus
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Chang, Keke
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Music, Denis
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Schneider, Jochen M.
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Phase formation of Nb2AlC investigated by combinatorial thin film synthesis and ab initio calculations2017In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 37, no 1, p. 35-41Article in journal (Refereed)
    Abstract [en]

    The phase formation of Nb2AlC was studied by combinatorial thin film synthesis and ab initio calculations. Thin films with lateral chemical composition gradients were synthesized by DC magnetron sputtering at substrate temperatures of 710-870 degrees C. The lowest formation temperature for Nb2AlC is between 710 and 750 degrees C. A predominantly single phase Nb2AlC region where 99% of the X-ray diffraction intensity originate from Nb2AlC was identified. Furthermore, selected area electron diffraction analysis reveals the local formation of single phase Nb2AlC. The limited Al solubility in Nb2AlC compared with Cr2AlC can be understood by comparing the defect formation energy of Al substituting Nb and Cr in Nb2AlC and Cr2AlC, respectively. This methodology may serve as indicator for the magnitude of the A-element homogeneity range in M(n+1)AX(n) phases. The structural and elastic properties of Nb2AlC determined experimentally are in very good agreement with the ab initio calculated data.

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