This paper reports the development of a new process for the synthesis and sintering of forsterite nanopowder via microwave-assisted high energy ball milling of a powder mixture containing silica gel ...and Mg(OH)2. X-ray diffraction (XRD), FTIR spectrometer, BET, scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) techniques were utilized to characterize the as-milled and annealed samples. X-ray diffraction results showed that highly ordered forsterite can be obtained through the calcination of the as-milled powder over 900°C. In addition, SEM and TEM observations of the synthesized powders showed that the particle size of the powder lies in the nanometer range, also being compared with the BET results (about 45 to 64.5nm). Microwave sintering (MS) of the forsterite nanopowder produced with high energy ball milling and subsequent microwave heating resulted in remarkable enhancement in densification in comparison with conventional sintering (CS) at lower temperatures.
This paper reports the development of a new process for the synthesis of spinel nano powder via microwave assisted high energy ball milling of a powder mixture containing Al(OH)3 and Mg(OH)2. X-ray ...diffraction (XRD), Simultaneous thermal analysis (STA), FTIR spectrometer, BET and scanning electron microscopy (SEM) techniques were utilized to characterize the as-milled and annealed samples. X-ray diffraction results provide evidence for the formation of a completely amorphous phase after milling for 8h. It is found that highly ordered MgAl2O4 spinel can be obtained by calcination the as-milled powder over 800°C. Also, SEM observations of synthesized powders showed that the particle size of powders lies in the nano meter range compared with the BET results (about 28–149nm). The DTA–TG analyses were carried out to investigate the effect of microwave heating on the synthesis temperature compared to the conventional heat treatment by conventional furnace. Synthesis of powders with different heating methods showed that microwave heating reduces the synthesis temperature by about 200°C.
•We report a new dielectric system with near zero τf of about −1.6ppm/°C.•The dielectric has low sintering temperature (900°C).•The dielectric has a good chemical compatibility with Ag electrode.
The ...crystalline phases, microstructure, composition analysis and microwave dielectric properties of Li2TiO3–xvol.% Li2Zn3Ti4O12 (x=15–40) composite ceramics with 1–3wt.% Li2O–ZnO–B2O3 (LZB) glass addition prepared by solid-state reaction method have been investigated. A near zero temperature coefficient of resonant frequency (τf) of about −1.3ppm/°C was obtained in the Li2TiO3–30vol.% Li2Zn3Ti4O12 ceramic sintered at 1100°C for 2h with permittivity of 22.0, Q×f value of 38,900GHz. The microwave dielectric properties of Li2TiO3–20vol.% Li2Zn3Ti4O12 ceramics with 1–3wt.% LZB glass addition sintered at 900°C for 2h were characterized. The addition of 2.5wt.% LZB glass reduced the sintering temperature of the Li2TiO3–20vol.% Li2Zn3Ti4O12 ceramic from 1100°C to 900°C without obvious degradation of the microwave dielectric properties. The 2.5wt.% LZB glass-added Li2TiO3–20vol.% Li2Zn3Ti4O12 ceramic sintered at 900°C for 2h could reach a high relative density of 98% of the theoretical density of the Li2TiO3–20vol.% Li2Zn3Ti4O12 ceramic and exhibited microwave dielectric properties of ɛr=22.0, Q×f=28,407GHz, and a near zero τf value of −1.6ppm/°C. Moreover, this ceramic has a chemical compatibility with Ag electrode, making it a very promising candidate material for Low-temperature co-fired ceramic (LTCC) applications.
The nanocomposite powders of γ-alumina-carbon nanotube were successfully synthesized by a sol–gel process. The homogeneous mixture of carbon nanotubes and alumina particles was obtained by mixing the ...carbon nanotubes within alumina solution and followed by heating into gel. The resultant gel was dried and calcined at 200
°C into boehmite-carbon nanotubes composite powders. The mean particle size of synthesized boehmite was of the order of 4
nm. The boehmite-carbon nanotubes composite powders were calcined at different temperatures and XRD investigations revealed that as the amount of carbon nanotube increases, γ- to α-alumina phase transformation is completed at higher temperatures. The specific surface area and mean particle size of resultant nanocomposite powders increased and decreased, respectively by increasing the content of carbon nanotubes.
The effects of Li2O–ZnO–B2O3 (LZB) glass additive on the sintering behavior, phase composition, microstructure and microwave dielectric properties of Li2TiO3 (LT) ceramics have been investigated. The ...addition of a small amount of LZB glass can reduce the sintering temperature of LT ceramics from 1150°C to 900°C without obvious degradation of the microwave dielectric properties. Only a single-phase Li2TiO3 is formed in LT ceramic with LZB glass addition sintered at 900°C for 2h. Typically, the 2.5wt% LZB glass-added LT ceramic sintered at 900°C for 2h can reach a maximum relative density of 94.8% of the theoretical density and exhibits good microwave dielectric properties of εr=22.9, Qf=59,600GHz and τf=+23.7ppm/°C. The XRD, SEM and EDX analyses showed that the ceramic can be co-fired well with Ag electrode, which may be applied for LTCC application.
Mg
4
Nb
2
O
9
nanopowders were prepared from MgO and Nb
2
O
5
mixtures by using a high energy ball milling method, combined with subsequent annealing at low temperatures by microwave heating. After ...milling for 20 h, pure phase Mg
4
Nb
2
O
9
nanopowders with an average grain size of 127 nm were obtained at 850, 130 °C lower than that required by a conventional solid state reaction process. Mg
4
Nb
2
O
9
ceramics sintered at a low temperature of 1,300 °C using microwave heating showed almost full density and excellent microwave dielectric properties (ε
r
= 12.9, Q × f = 174,200 GHz and τ
f
= −68).
Al2O3-20 wt%Al2TiO5 nanocomposites were prepared by the reaction sintering of alumina and titania nanopowders. The nano-sized raw powders were reconstituted into nanostructured particles by ball ...milling and then the nanostructured reconstituted powders were pressed and pressureless sintered into bulk ceramics at 1300, 1400, 1500 C for 2 h. The phase composition and microstructures of reconstituted powders and as-prepared composites were characterised by XRD, SEM, TEM and EDS. The microstructural analysis of the ceramics showed that the average grain size of the alumina-aluminium titanate composites increased with increasing temperature. SEM proved the existence of an interface between Al2TiO5 and Al2O3 grains and preferential distribution of aluminium titanate particles at the grain boundaries. XRD analysis indicated the absence of rutile titania in the sintered composites ensuring complete formation of aluminium titanate. The hardness of the samples sintered at 1300, 1400, 1500 C were 4.8, 6.2 and 8.5 GPa, respectively.
Sintering behavior, microstructures and microwave dielectric properties of ZnNb
2
O
6
(ZN) ceramics prepared by reaction-sintering method were investigated. The X-ray diffraction patterns of the ...sintered samples revealed single-phase formation with a columbite structure after 1–5 h sintering at 1,025–1,125 °C. After sintering at 1,125 °C for 5 h, the ZN ceramics with the density of 5.56 g/cm
3
(98.9 % of the theoretical density) and good microwave dielectric properties of ε
r
= 23.9, Q × f = 51,000 and τ
f
= −62 ppm/°C were obtained. The obtained results demonstrated that the reaction-sintering process is a simple and effective method to prepare the ZN ceramics for applications on microwave dielectric resonators.
High density ZnNb2O6 ceramics were successfully fabricated by microwave sintering of ZnO–Nb2O5 and ZnNb2O6 nanopowders. Phase formation, microstructure and microwave electrical properties of the ...microwave sintered (MS) and microwave reaction sintered (MRS) specimens were examined using X-ray diffraction, field emission scanning electron microscopy and microwave dielectric properties measurement. Specimens were sintered in a temperature range from 950 to 1075°C for 30min at an interval of 25°C using a microwave furnace operated at 2.45GHz frequency, 3kW power. XRD pattern revealed the formation of pure columbite phase of ZnNb2O6. The SEM micrographs show grain growth and reduction in porosity of specimens with the increase in sintering temperature. Good combination of microwave dielectric properties (εr~23.6, Qf~64,300GHz and τf~−66ppm/°C and εr~24, Qf~75,800GHz and τf~−64ppm/°C) was obtained for MS- and MRS-prepared samples at 1000°C and 1050°C for 30min, respectively.
Ball-milling and subsequent conventional and microwave assisted heating processes have been applied to synthesize ZnNb
2
O
6
nanoceramic. X-ray diffraction, simultaneous thermal analysis, scanning ...electron microscope (SEM), transmission electron microscope (TEM) and BET techniques were utilized to characterize the as-milled and annealed samples. Characterization of synthesized powders revealed that in spite of the very short heating time in the microwave process without soaking time, the powder heated at 550 °C had all physical properties similar to powders synthesized in conventional heating at the 650 °C temperature with a heating rate of 10 °C/min and a soaking time of 1 h. In addition, SEM, TEM and BET observations of synthesized powders showed that the particle size of powders lies in the nano meter range.
