scholarly journals BaGeO3 as sintering additive for BaTiO3-MgFe2O4 composite ceramics

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Magnetic Measurements ◽  
Sol Gel ◽  
Dissipation Factor ◽  
Composite Ceramics ◽  
Composite Powders ◽  
One Pot ◽  
Fine Grained ◽  
Sintering Additive ◽  
Nano Crystalline ◽  
Sintering Behaviour

BaTiO3-MgFe2O4 composites (30 wt.% MgFe2O4) with a small addition of BaGeO3 as a sintering additive were synthesized by a one-pot Pechini-like sol-gel process. Nano-crystalline composite powders with a crystallite size of about 10 nm were obtained after reaction at 700 °C for 1 h. Magnetic investigations suggest that the nano-powder is in its superparamagnetic state at room temperature. The addition of BaGeO3 leads to an improved sintering behaviour. DTA measurements reveal the formation of a liquid phase at 1164(3) °C. Dense ceramic bodies (relative density > 90 %) were obtained after sintering for 1 h at 1150 °C. SEM investigations prove a 0-3 connectivity and show that the addition of BaGeO3 promotes the grain growth leading to particles up to 4 μm. In contrast, fine-grained composite ceramics with smaller particles up to 230 nm were obtained after a two-step sintering process. Magnetic measurements indicate a ferrimagnetic behaviour with coercivity values up to 70 Oe depending on the sintering procedure. Furthermore, addition of BaGeO3 results in an increase of the relative permittivity, whereas the dissipation factor slightly decreases.

scholarly journals Fine-grained magnetoelectric Sr0.5Ba0.5Nb2O6–CoFe2O4 composites synthesized by a straightforward one-pot method

2021 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Impedance Spectroscopy ◽  
Magnetic Measurements ◽  
Composite Ceramics ◽  
Composite Powders ◽  
One Pot ◽  
Driving Field ◽  
Fine Grained ◽  
Magnetoelectric Coefficient ◽  
Rc Circuit ◽  
Nanocrystalline Composite

Magnetoelectric (Sr0.5Ba0.5Nb2O6)1x(CoFe2O4)x (x = 0.2–0.6) composites were prepared by a one-pot softchemistrysynthesis using PEG400. Calcining at 700 ◦C resulted in nanocrystalline composite powders (dcryst. =24–30 nm) which were sintered between 1050 and 1200 ◦C to ceramic bodies with relative densities up to 98%.SEM investigations confirm the formation of composite ceramics with a 0–3 connectivity and variable grain sizesfrom 0.2 to 3.6 μm for sintering up to 1150 ◦C, while sintering at 1200 ◦C leads both to a change in themicrostructure and a considerable grain growth. Magnetic measurements at 300 K reveal ferrimagnetic behaviourwith saturation magnetization values smaller than bulk CoFe2O4 and coercivities between 790 and 160 Oe.Temperature-dependent impedance spectroscopy showed that the relative permittivities decrease both withrising frequency and CoFe2O4 fraction. The frequency dependence of the impedance can be well described usinga single RC circuit. Magnetoelectric measurements show the presence of pronounced field hystereses. Themaximum magnetoelectric coefficient (αME) depends both on the CoFe2O4 fraction (x) and sintering temperature.The composite with x = 0.3 exhibits the largest αME value of 37 μV Oe1 cm1 (@ 900 Hz). With rising frequencyof the AC driving field αME increases up to 300–400 Hz and is nearly constant until 1 kHz.

scholarly journals Fine-grained BaTiO3–MgFe2O4 composites prepared by a Pechini-like process

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Phase Formation ◽  
Low Temperatures ◽  
High Field ◽  
Composite Powders ◽  
One Pot ◽  
Fine Grained ◽  
Crystallite Sizes ◽  
Sintering Behaviour

The synthesis of BaTiO3–MgFe2O4 composite powders by a Pechini-like one-pot process and resultingceramic bodies is described herein. Phase formation during the decomposition of homogenous (Ba, Ti,Fe, Mg)-gels was monitored up to 1200 ?C. Composite powders consisting of BaTiO3 and MgFe2O4 wereobtained after decomposition at 700 ?C for 1 h resulting in crystallite sizes of about 10 nm. The shrinkageand sintering behaviour of compacted powders were examined. Sintering at >1200 ?C leads to theformation of hexagonal BaTiO3 only for composites with a MgFe2O4 content of >30 wt.%. SEM imagesof ceramic bodies reveal that the MgFe2O4 particles are surrounded by BaTiO3 crystallites. Magneticmeasurements of both powders and corresponding ceramic bodies show ferrimagnetic behaviour withlow coercivities. At high-field and low temperatures an additional small paramagnetic contributionwas observed which increases with decreasing MgFe2O4 content and should be considered by the calculationof the saturation magnetization.Finally, the

scholarly journals Magnetic, optical, dielectric, and sintering properties of nano-crystalline BaFe0.5Nb0.5O3 synthesized by a polymerization method

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Crystallite Size ◽  
Magnetic Measurements ◽  
Spontaneous Magnetization ◽  
Secondary Phase ◽  
Phase Evolution ◽  
One Pot ◽  
Nano Crystalline ◽  
Rc Circuit ◽  
Tan Δ ◽  
Polymerization Method

Full text also available at: http://rdcu.be/v7Fn A one-pot polymerization method using citric acid and glucose for the synthesis of nano-crystalline BaFe0.5Nb0.5O3 is described. Phase evolution and the development of the crystallite size during decomposition of the (Ba,Fe,Nb)-gel were examined up to 1100 °C. Calcination at 850 °C of the gel leads to a phase-pure nano-crystalline BaFe0.5Nb0.5O3 powder with a crystallite size of 28 nm. The shrinkage of compacted powders starts at 900 °C. Dense ceramic bodies (relative density ≥ 90%) can be obtained either after conventional sintering above 1250 °C for 1 h or after two-step sintering at 1200 °C. Depending on the sintering regime, the ceramics have average grain sizes between 0.3 and 52 μm. The optical band gap of the nano-sized powder is 2.75(4) eV and decreases to 2.59(2) eV after sintering. Magnetic measurements of ceramics reveal a Neel temperature of about 23 K. A weak spontaneous magnetization might be due to the presence of a secondary phase not detectable by XRD. Dielectric measurements show that the permittivity values increase with decreasing frequency and rising temperature. The highest permittivity values of 10.6 9 104 (RT, 1 kHz) were reached after sintering at 1350 °C for 1 h. Tan δ values of all samples show a maximum at 1–2 MHz at RT. The frequency dependence of the impedance can be well described using a single RC-circuit.

scholarly journals Crystallite growth, phase transition, magnetic properties, and sintering behaviour of nano-CuFe2O4 powders prepared by a combustionlike process

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Phase Transition ◽  
Calcination Temperature ◽  
Magnetic Measurements ◽  
Cubic Phase ◽  
Crystallite Growth ◽  
Nano Crystalline ◽  
Conventional Sintering ◽  
Formation And Evolution ◽  
Sintering Behaviour ◽  
Growth Phase Transition

The synthesis of nano-crystalline CuFe2O4 powders by a combustion-like process isdescribed herein. Phase formation and evolution of the crystallite size during thedecomposition process of a (CuFe2)-precursor gel were monitored up to 1000 °C. Phase-purenano-sized CuFe2O4 powders were obtained after reaction at 750 °C for 2 h resulting in acrystallite size of 36 nm, which increases to 96 nm after calcining at 1000 °C. The activationenergy of the crystallite growth process was calculated as 389 kJ mol−1. The tetragonal -cubic phase transition occurs between 402 and 419 °C and the enthalpy change (dH) wasfound to range between 1020 and 1229 J mol−1 depending on the calcination temperature. The optical band gap depends on the calcination temperature and was found between 2.03 and1.89 eV. The shrinkage and sintering behaviour of compacted powders were examined. Denseceramic bodies can be obtained either after conventional sintering at 950 °C or after a twostepsintering process at 800 °C. Magnetic measurements of both powders and correspondingceramic bodies show that the saturation magnetization rises with increasing calcination-/sintering temperature up to 49.1 emu g−1 (2.1 μB f.u.−1), whereas the coercivity and remanencevalues decrease.

Macrocellular Titanosilicate Monoliths as Highly Efficient Structured Olefin Epoxidation Catalysts

2019 ◽  
Author(s):  
Valentin Smeets ◽  
Ludivine van den Biggelaar ◽  
Tarek Barakat ◽  
Eric M. Gaigneaux ◽  
Damien Debecker
Keyword(s):  
Sol Gel ◽  
Silica Matrix ◽  
Flow Mode ◽  
Tetrahedral Coordination ◽  
Excellent Performance ◽  
One Pot ◽  
Templating Method ◽  
Porous Texture ◽  
Internal Phase ◽  
Epoxidation Of Cyclohexene

Self-standing macrocellular titanosilicate monolith foams are obtained using a one-pot sol-gel route and show excellent performance in the epoxidation of cyclohexene. Thanks to the High Internal Phase Emulsion (HIPE) templating method, the materials feature a high void fraction, a hierarchically porous texture and good mechanical strength. Highly dispersed Ti species can be incorporated in tetrahedral coordination the silica matrix. These characteristics allow the obtained ‘SiTi(HIPE)’ materials to reach high catalytic turnover in the epoxidation of cyclohexene. The monoliths can advantageously be used to run the reaction in continuous flow mode.<br>

scholarly journals Aqueous Sol-Gel Synthesis of Different Iron Ferrites: From 3D to 2D

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1554
Author(s):  
Justinas Januskevicius ◽  
Zivile Stankeviciute ◽  
Dalis Baltrunas ◽  
Kęstutis Mažeika ◽  
Aldona Beganskiene ◽  
...  
Keyword(s):  
Magnetic Measurements ◽  
Substrate Surface ◽  
Sol Gel ◽  
Synthesis Method ◽  
Xrd Analysis ◽  
Dip Coating ◽  
Yttrium Iron ◽  
Iron Garnet ◽  
Dip Coating Technique ◽  
Sol Gel Synthesis

In this study, an aqueous sol-gel synthesis method and subsequent dip-coating technique were applied for the preparation of yttrium iron garnet (YIG), yttrium iron perovskite (YIP), and terbium iron perovskite (TIP) bulk and thin films. The monophasic highly crystalline different iron ferrite powders have been synthesized using this simple aqueous sol-gel process displaying the suitability of the method. In the next step, the same sol-gel solution was used for the fabrication of coatings on monocrystalline silicon (100) using a dip-coating procedure. This resulted, likely due to substrate surface influence, in all coatings having mixed phases of both garnet and perovskite. Thermogravimetric (TG) analysis of the precursor gels was carried out. All the samples were investigated by X-ray powder diffraction (XRD) analysis. The coatings were also investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Mössbauer spectroscopy. Magnetic measurements were also carried out.

scholarly journals Effect of micro-notches on fatigue strength of electrodeposited nanocrystalline nickel thin films

2018 ◽  
Vol 165 ◽  
pp. 04011
Author(s):  
Keisuke Tanaka ◽  
Yuta Murase ◽  
Hirohisa Kimachi
Keyword(s):  
Thin Films ◽  
Fatigue Strength ◽  
Fatigue Limit ◽  
Stress Ratio ◽  
Fatigue Crack Initiation ◽  
Fatigue Tests ◽  
Fine Grained ◽  
Nickel Thin Films ◽  
Nano Crystalline ◽  
Fictitious Crack

The effect of micro-notches on the fatigue strength of nickel thin films was studied. Two types of thin films with 10 μm thickness were produced by electrodeposition using sulfamate solution without and with brightener: ultra-fine grained film (UFG) with the grain size of 384 nm and nano-crystalline grained film (NCG) with that of 17 nm. Micro-sized notches introduced by FIB had the width of 2 μm and various depths from 8 to 150μm. Fatigue tests were conducted under the stress ratio of 0.1. The fatigue strength decreased with increasing depth of notches. NCG had much higher strength than UFG compared at the same notch depth. Notches as small as 8μm did reduce the fatigue strength of both UFG and NCG. The fatigue limit was controlled by the initiation of cracks and no non-propagating crack was observed in specimens fatigued below the fatigue limit. A model of fictitious crack successfully predicted the reduction of the fatigue limit due to micro-notches. The characteristic crack length of NCG was much smaller than the UFG, while the fatigue strength of defect-free NCG was larger than that of UFG. SEM observation of fracture surfaces was conducted to reveal micromechanisms of fatigue crack initiation.

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