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Mullite/glass/nano aluminum nitride (AlN) filler (1–10 wt% AlN) composites were successfully fabricated for the low‐temperature co‐fired ceramics applications that require densification temperatures lower than 950°C, high thermal... more
Mullite/glass/nano aluminum nitride (AlN) filler (1–10 wt% AlN) composites were successfully fabricated for the low‐temperature co‐fired ceramics applications that require densification temperatures lower than 950°C, high thermal conductivity to dissipate heat and thermal expansion coefficient matched to Si for reliability, and low dielectric constant for high signal transmission speed. Densification temperatures were ≤825°C for all composites due to the viscous sintering of the glass matrix. X‐ray diffraction proved that AlN neither chemically reacted with other phases nor decomposed with temperature. The number of closed pores increased with the AlN content, which limited the property improvement expected. A dense mullite/glass/AlN (10 wt%) composite had a thermal expansion coefficient of 4.44 ppm/°C between 25 and 300°C, thermal conductivity of 1.76 W/m.K at 25°C, dielectric constant (loss) of 6.42 (0.0017) at 5 MHz, flexural strength of 88 MPa and elastic modulus of 82 GPa, that are comparable to the commercial low temperature co‐fired ceramics products.
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Page 1. Fabrication and Electrical Properties of Textured Sr0.53Ba0.47Nb2O6 Ceramics by Templated Grain Growth Cihangir Duran, Susan Trolier-McKinstry,V and Gary L. MessingV Materials Science and Engineering Department ...
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Textured Sr0.53Ba0.47Nb2O6 ceramics with a relative density of >95% were fabricated using templated grain growth (TGG). Acicular KSr2Nb5O15 template particles synthesized via a molten salt process were aligned by tape casting in a... more
Textured Sr0.53Ba0.47Nb2O6 ceramics with a relative density of >95% were fabricated using templated grain growth (TGG). Acicular KSr2Nb5O15 template particles synthesized via a molten salt process were aligned by tape casting in a mixture of solid-state-synthesized SrNb2O6 and BaNb2O6 powders. The resulting ceramics possessed strong fiber texture along the polar axis ([001]) of the strontium barium niobate. Samples with 15.4 wt% templates attained a textured fraction of 0.82 after sintering at a temperature of 1450°C for 4 h. These materials showed peak dielectric constants of 7550 at 1 kHz, remanent polarizations of 13.2 mC/cm 2 , saturation polarizations of 21 mC/cm 2 (60%‐ 85% of the single-crystal value), piezoelectric strain coefficients of 78 pC/N (70%‐ 85% of the single-crystal value), and room-temperature pyroelectric coefficients of 2.9 3 10 22 mCz(cm 2 z°C) 21 (52% of the single-crystal value). These results show that TGG is a viable option for accessing single-crystal properties in polycrystalline ceramics.
Research Interests: Materials Science, Strontium, Grain Growth, Fabrication, Ceramic, and 3 moreNiobium, Oxygen, and Barium
SiO2‐Al2O3‐CaO‐based glass (10–60 wt%)/mullite composites were investigated for the LTCC and radome applications. The optimum densification temperatures decreased from 1550°C (10 wt% glass) to 1400°C (30 wt% glass) by means of... more
SiO2‐Al2O3‐CaO‐based glass (10–60 wt%)/mullite composites were investigated for the LTCC and radome applications. The optimum densification temperatures decreased from 1550°C (10 wt% glass) to 1400°C (30 wt% glass) by means of liquid‐phase sintering, and to 850°C–825°C (50–60 wt% glass) by means of viscous phase sintering. XRD analysis showed that mullite was the main phase as well as in situ crystallized anorthite after 825°C. The composite with 20 wt% glass was a suitable candidate for the radome applications (bulk density = 2.86 g/cm3 after sintering at 1450°C, dielectric constant (loss) = 7.12 (0.0025) at 5 MHz, thermal expansion coefficient = 4.27 ppm/°C between 25°C and 800°C, thermal shock resistance parameter = 162°C), and the composite with 50 wt% glass was a suitable candidate for the low‐temperature cofired ceramic applications (bulk density = 2.64 g/cm3 after sintering at 850°C, dielectric constant (loss) = 6.79 (0.0043) at 5 MHz, thermal conductivity = 2.11 W/m⋅K at 25°C, and thermal expansion coefficient = 3.93 ppm/°C between 25°C and 300°C).
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Abstract Effect of crystal anisotropy on thermoelectric properties of textured KSr 2 Nb 5 O 15 ferroelectric ceramics is studied for the first time. Temperature dependent conductivity and Seebeck coefficient were measured in directions... more
Abstract Effect of crystal anisotropy on thermoelectric properties of textured KSr 2 Nb 5 O 15 ferroelectric ceramics is studied for the first time. Temperature dependent conductivity and Seebeck coefficient were measured in directions parallel and perpendicular to the c direction. A transition in electrical conduction from semiconductor to metallic behavior was observed at around 610 K. The power factor was remarkably improved depending on measurement directions such that it was 390 μW/mK 2 in parallel and 283 μW/mK 2 in perpendicular to the c direction at 1120 K. Textured KSr 2 Nb 5 O 15 ceramics are promising candidates to be used as n-type thermoelectric materials at high temperatures and oxidizing environments.
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Pb(Yb/sub 1/2/Nb/sub 1/2/)-PbTiO/sub 3/ (PYbN-PT) ceramics at the MPB composition (50:50) with a relative density /spl ges/98% were reactively sintered. The ceramic had a remanent polarization of 40 /spl mu/C/cm/sup 2/, a maximum... more
Pb(Yb/sub 1/2/Nb/sub 1/2/)-PbTiO/sub 3/ (PYbN-PT) ceramics at the MPB composition (50:50) with a relative density /spl ges/98% were reactively sintered. The ceramic had a remanent polarization of 40 /spl mu/C/cm/sup 2/, a maximum dielectric constant of 23,000 at T/sub c/ =363/spl deg/C, and a piezoelectric charge coefficient, d/sub 33/, of 472 pC/N. These values are higher than the conventionally sintered samples reported in the literature, which makes reactive sintering an attractive process for fabricating PYbN-PT.
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Mullite is an attractive material for advanced ceramic applications, but its low fracture toughness prevents it from widespread industrial applications. Therefore, mullite/zirconia composites were prepared from a reactive mixture of... more
Mullite is an attractive material for advanced ceramic applications, but its low fracture toughness prevents it from widespread industrial applications. Therefore, mullite/zirconia composites were prepared from a reactive mixture of alumina and zircon with additives of TiO 2 and MgO to ...
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... Therefore, ZnO is very effective as TiO 2 in photocatalytic degradation processes under UVradiation. ... Other advantages of ZnO have also been claimed that it had absorption capacity with larger fraction ... To evaluate the... more
... Therefore, ZnO is very effective as TiO 2 in photocatalytic degradation processes under UVradiation. ... Other advantages of ZnO have also been claimed that it had absorption capacity with larger fraction ... To evaluate the efficiency of the plates in the degradation of model azo dye ...
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ABSTRACT Nanostructured silicon nitride and aluminium nitride powder mixtures have been successfully produced by high-energy mechanical activation. Subsequent high sintering activity and b-sialon formation at low temperature resulted from... more
ABSTRACT Nanostructured silicon nitride and aluminium nitride powder mixtures have been successfully produced by high-energy mechanical activation. Subsequent high sintering activity and b-sialon formation at low temperature resulted from activation milling at high acceleration. Densification of the samples prepared from the activated powders commenced at temperatures by about 200 1C lower, as compared with the samples prepared from the non-activated powder mixture. 27 Al MAS NMR spectra clearly showed the effect of mechanical activation on the structural changes and phase evolution of the sialon precursor during heat treatment. After pressureless sintering at 1600 1C for 60 min, b-sialon samples had a Young's modulus of 281 GPa, microhardness of 12.8 GPa, fracture toughness of 4.6 MPa m 0.5 and flexural strength of 632 7 129 MPa. The unique structure and bi-modal grain size distribution that is retained after conventional sintering at 1600 1C opens up new possibilities for tailoring the microstructure and related properties of these materials.
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Al2O3/glass/hBN composites were successfully fabricated for the LTCC applications. Alignment and homogeneous distribution of the platelet hBN particles during tape casting allowed high hBN (5 wt%) loading as well as facilitated... more
Al2O3/glass/hBN composites were successfully fabricated for the LTCC applications. Alignment and homogeneous distribution of the platelet hBN particles during tape casting allowed high hBN (5 wt%) loading as well as facilitated densification at 800°C (density of 2.65 g/cm3, apparent porosity of 0.7%). XRD results proved that hBN neither chemically reacted with the other phases nor decomposed with temperature, which was critical to increase thermal conductivity and at the same time to decrease dielectric constant. Dielectric constant of the dense composites decreased (or, alternatively, enhanced) with increasing hBN content from 7.3 for the 0 wt% hBN to 6.55 for the 5 wt% hBN at 5 MHz. In addition, hBN addition strongly improved the mean thermal conductivity from 1.86 W/m·K for the 0 wt% hBN to 2.43 W/m·K for the 5 wt% hBN between 75°C and 250°C. Therefore, the hBN phase itself effectively optimized both dielectric and thermal properties at the same time and made the Al2O3/glass/hBN ...
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Bu calismada Mn ile katkilanmis Pb(Mg1/3Nb2/3)O3-Pb(Yb1/2Nb1/2)O3-PbTiO3 (PMN-PYbN-PT) esasli piezoseramiklerin dielektrik ve elektromekanik ozellikleri arastirilmistir. %1 mol MnCO3 iceren 0,2875PMN-0,2875PYbN-0,425PT kompozisyonu... more
Bu calismada Mn ile katkilanmis Pb(Mg1/3Nb2/3)O3-Pb(Yb1/2Nb1/2)O3-PbTiO3 (PMN-PYbN-PT) esasli piezoseramiklerin dielektrik ve elektromekanik ozellikleri arastirilmistir. %1 mol MnCO3 iceren 0,2875PMN-0,2875PYbN-0,425PT kompozisyonu 1100˚C’de sinterlenerek uretilmistir. %98 goreceli yogunluga ve tamamen perovskit faza sahip bu numunelerin eTpC/N, d31 = -103 pC/N, Qm = 467, kp = %40, k31 = %24, k33 = %49 ve Tc = 275˚C olarak olculmustur. Benzer ozellikler Mn katkisi yapilmamis ve 1000˚C’de sinterlenerek uretilmis numunelerde eT2380, tanδ = %1,95, d280˚C olarak olculmustur. Mn ilavesi nedeniyle ozellikle sistemdeki tanδ azalmis, Qm ise artmistir. Muhtemelen Mn2+/Mn3+ iyonlari perovskit yapidaki oksijen oktahedralin merkezindeki B-konumu iyonlari ile yer degistirerek alici (acceptor) iyon olarak davranmaktadir ve kusur ciftleri olusturmaktadir. Bu kusur ciftleri ise yapidaki domain duvar hareketlerini engellediginden sistemdeki dielektrik ve mekanik kayiplar azalmakta boylece sistem “se...
Abstract 0.62[0.75(Pb(Mg 1/3 Nb 2/3 )O 3 )–0.25(Pb(Yb 1/2 Nb 1/2 )O 3 )]–0.38(PbTiO 3 ) ceramics were successfully textured in [001] (Lotgering factor of 0.91) using plate-like BaTiO 3 templates, for the first time. Samples were densified... more
Abstract 0.62[0.75(Pb(Mg 1/3 Nb 2/3 )O 3 )–0.25(Pb(Yb 1/2 Nb 1/2 )O 3 )]–0.38(PbTiO 3 ) ceramics were successfully textured in [001] (Lotgering factor of 0.91) using plate-like BaTiO 3 templates, for the first time. Samples were densified to 98% of the theoretical density. Significantly higher levels of strain (0.33%) and low-field ( 33 coefficient (1340 pm/V) together with a narrower hysteresis level (7.7%) at 50 kV/cm have been achieved in the textured ceramics. These results are very promising for high performance transducer and actuator applications without severe temperature restriction due to their higher T c values (214 °C) and also open up new opportunities for the concept of domain engineering in the textured ceramics.
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ABSTRACT Most ceramics are produced as particle assemblages made dense by firing. Since the fine ceramic particles usually possess poor formability, the addition of considerable amount of organic binders in the forming stage is... more
ABSTRACT Most ceramics are produced as particle assemblages made dense by firing. Since the fine ceramic particles usually possess poor formability, the addition of considerable amount of organic binders in the forming stage is unavoidable at the present time. However, the pyrolysis of the organic binders can result in the emission of carbon dioxide or other hydrocarbon gases. A reduction in the emission gases is one aim of current ceramics industry. A novel ceramic-forming process was developed that involves immobilizing reactive molecules on the surfaces of the ceramic particles, which on subsequent external stimuli, form bridges that bind the entire particle assembly together. The chemical forces involved produce strong bonds, resulting in a reduction in the amount of organic binder that is required to maintain the shape of the ceramic green body. The obtained green body with covalent bondings is also available for debinding methods not relaying on pyrolysis. The methods will help to decrease emission gases produced from pyrolysis of the organic additives.
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ABSTRACT The formation of ZrO2 nanopowders under various hydrothermal conditions such as temperature, time, autoclave rotation speed, heating rate and particularly assistance of ball milling during reaction was investigated. Full ZrO2... more
ABSTRACT The formation of ZrO2 nanopowders under various hydrothermal conditions such as temperature, time, autoclave rotation speed, heating rate and particularly assistance of ball milling during reaction was investigated. Full ZrO2 formation (with monoclinic phase) from zirconium solution was completed at shorter times with increasing temperature such as after 4 h at 150 °C, 2 h at 175 °C and less than 2 h at 200 °C. Crystallite size increased from 2.9 to 4 nm with increasing reaction temperature from 125 °C to 200 °C, respectively. Ball milling assisted hydrothermal runs were performed to understand the effect of mechanical force on phase formation, crystallinity and particle size distribution. Monoclinic ZrO2 was formed in both milled and non-milled runs when zirconium solution was used. Mean particle size for the 2 M solution was measured to be 94 nm for the milled and 117 nm for the non-milled powders. However, when amorphous aqueous zirconia gels (precipitated at pH 5.8) were used, tetragonal phase was also formed in addition to monoclinic phase. Mean particle size was measured to be 0.7 μm (d90≅1.3 μm) for the milled and 7.9 μm (d90≅13 μm) for the non-milled powders. Ball milling during hydrothermal reactions of both zirconium solution and aqueous zirconium gel resulted in smaller crystallite size and mean particle size and, at the same time, effectively controlled particle size distribution (or agglomeration) of nanopowders.