Microwave Sintering of Pure and Doped Nanocrystalline Alumina Compacts

1996 ◽  
Vol 430 ◽  
Author(s):  
R. W. Bruce ◽  
A. W. Fliflet ◽  
L. K. Kurihara ◽  
G.-M. Chow ◽  
P. E. Schoen
Keyword(s):  
Grain Growth ◽  
Room Temperature ◽  
Microwave Sintering ◽  
Sol Gel ◽  
Single Mode ◽  
Nanocrystalline Powders ◽  
Sintering Process ◽  
Effect Of Additives ◽  
Microwave Furnace ◽  
Nanocrystalline Alumina

AbstractA single-mode cavity microwave furnace, operating in the TE103 mode at 2.45 GHz is being used to investigate sintering of pure and doped nanocrystalline alumina. The purpose of these experiments is to determine the effect of additives on the sintering process in the nanocrystalline regime. Using the sol-gel method, high purity Al2O3 nanocrystalline powders were synthesized. These powders were calcined at 700°C and then CIP'ed to 414 MPa, producing 0.4 in. diameter, 0.25 in. high cylindrical compacts. The compacts were heated in the microwave furnace to temperatures between 1100°C to approximately 1800°C and were then brought back to room temperature using a triangular heating profile of about 30 minutes duration. A two-color IR pyrometer was used to monitor the surface temperature of the workpiece. The additives tested in this work lowered the temperature needed for densification but this effect was offset by increased grain growth. Initial grain growth from < 5 nm to ∼ 50 nm was closely correlated with the γ to α-alumina phase transition.

Microwave Processing of Silicon Nitride

1990 ◽  
Vol 189 ◽  
Author(s):  
T. N. Tiegs ◽  
J. O. Kiggans ◽  
H. D. Kimrey
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Microwave Heating ◽  
Grain Growth ◽  
Microwave Power ◽  
Microwave Sintering ◽  
Microwave Processing ◽  
Microwave Furnace

ABSTRACTMicrowave sintering of Si3N4—based materials showed improved densification as compared to samples heated conventionally under similar conditions. Accelerated nitridation of Si in the microwave furnace to produce Si3N4 was also observed. Dense Si3N4, annealed by microwave heating, exhibited enhanced grain growth; however preferential coupling of the microwave power to the grain—boundary phases in the present experiments resulted in their degradation.

Elongated Grain Growth Mechanism of Alumina Ceramics with Additives

2010 ◽  
Vol 105-106 ◽  
pp. 844-847
Author(s):  
Yong Chang Zhu ◽  
Shou Fan Rong ◽  
Ji Wei Guo ◽  
Jun Gang Li
Keyword(s):  
Grain Growth ◽  
Growth Mechanism ◽  
Second Phase ◽  
Pressureless Sintering ◽  
Sintering Process ◽  
Alumina Ceramics ◽  
Effect Of Additives ◽  
Sintering Properties ◽  
Columnar Grain

The elongated grain evolution of alumina ceramics doping with Al2O3-CaO-SiO2(CAS), Nb2O5, and 3Y-TZP was studied under pressureless sintering. From in-situ growth elongated grain cooperating with second phase to toughen the alumina ceramics, microstructure and sintering properties were firstly studied systematically. The effect of additives on the alumina ceramics with columnar grain were analyzed by means of TEM, SEM, XRD, etc. Basing on the analyzed sintering process by the principle of dynamics, the elongated grain growth mechanism was further studied.

Pulsed 35 Ghz Gyrotron with Overmoded Applicator for Sintering Experiments

1996 ◽  
Vol 430 ◽  
Author(s):  
A. W. Fliflet ◽  
R. P. Fischer ◽  
A. K. Kinkead ◽  
R. W. Bruce
Keyword(s):  
Microwave Sintering ◽  
Pulse Length ◽  
Microwave Furnace ◽  
Set Up ◽  
Nanocrystalline Alumina

AbstractThe microwave sintering of nanocrystalline alumina compacts is currently under investigation at NRL. This paper will discuss an overmoded microwave furnace based on a 35 GHz pulsed gyrotron which is currently being set up to extend ongoing microwave sintering experiments at 2.45 GHz to 35 GHz. The gyrotron operates at 70 kV and currents up to 10 A. It is driven by a hard tube, variable pulse length (1–15 μs) modulator at repetition rates up to 1 kHz. The gyrotron can produce peak powers up to 100 kW at an efficiency of 20%, and average powers up to 200 W. The gyrotron output is transported via pressurized Ka-Band waveguide to an overmoded resonator containing the workpiece. In initial experiments, the resonator will consist of a piece of WR-284 waveguide. The operation of the system in preliminary sintering experiments is described.

Preparation and Thermoelectric Properties of (Ca1-x-yKxBiy)3Co4O9 Ceramic

2008 ◽  
Vol 368-372 ◽  
pp. 559-561 ◽  
Author(s):  
Hao Ming Hu ◽  
Yuan Deng ◽  
Jian Li ◽  
Guang Sheng Wang
Keyword(s):  
Electrical Conductivity ◽  
Seebeck Coefficient ◽  
Transport Properties ◽  
Thermoelectric Properties ◽  
Power Factor ◽  
Room Temperature ◽  
Raw Materials ◽  
Sol Gel ◽  
Sintering Process ◽  
Conventional Sintering

The precursor of (Ca1-x-yKxBiy)3Co4O9 was synthesized by sol-gel method using nitrate salts as raw materials and citrate acid as agent. The final product was obtained after the precursor was calcined at 800°C for 4 h. The polycrystalline bulk samples were fabricated by a conventional sintering process at 900°C for 12 h. XRD and SEM were used to characterize the microstructures and the composition of the samples. The transport properties of the samples at room temperature were determined by measuring electrical conductivity and Seebeck coefficient. The Bi and K-doped samples show an excellent transport properties even at room temperature. The value of power factor of (Ca0.90K0.075Bi0.025)3Co4O9 reaches 1.42×10-4Wm-1K-2 at 293K, close to the performance of pure Ca3Co4O9 at 1000K.

scholarly journals Microwave Sintering of SiAlON Ceramics with TiN Addition

Materials ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1345 ◽  
Author(s):  
Özgür Sevgi Canarslan ◽  
Roberto Rosa ◽  
Levent Köroğlu ◽  
Erhan Ayas ◽  
Alpagut Kara ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Vickers Hardness ◽  
Microwave Sintering ◽  
Single Mode ◽  
Nominal Composition ◽  
Indentation Fracture ◽  
Microwave Furnace ◽  
Indentation Fracture Toughness ◽  
Difference Time

α-β SiAlON/TiN composites with nominal composition of α:β = 25:75 were fabricated by microwave sintering. The effect of titanium nitride addition on the phases, microstructure, microwave absorption ability and mechanical properties (Vickers hardness and fracture toughness) of the SiAlON-based composites were studied. Finite Difference Time Domain (FDTD) software was used for the numerical simulation in order to assess the most suitable experimental setup. Sintering trials were performed in a single mode microwave furnace operating at 2.45 GHz and a power output of 660 W, for a reaction time of 30 min. SiC blocks were used as a susceptor to accelerate the microwave processing by hybrid heating, with reduced heat losses from the surface of the material of the α-β SiAlON/TiN composites. The optimum comprehensive mechanical properties, corresponding to a relative density of 96%, Vickers hardness of 12.98 ± 1.81 GPa and Vickers indentation fracture toughness of 5.52 ± 0.71 MPa.m1/2 were obtained at 850 °C when the content of TiN was 5 wt.%.

Afterglow and thermoluminescence of ZrO2 nanopowders

Open Physics ◽  
2014 ◽  
Vol 12 (6) ◽  
Author(s):  
Laurits Puust ◽  
Valter Kiisk ◽  
Kathriin Utt ◽  
Hugo Mändar ◽  
Ilmo Sildos
Keyword(s):  
Room Temperature ◽  
Sol Gel ◽  
Nanocrystalline Powders ◽  
Careful Study ◽  
Heating Rates ◽  
Luminescence Centre ◽  
Temperature Range

AbstractA careful study of the phosphorescence afterglow and the thermoluminescence (TL) of sol-gel-prepared m-ZrO2 nanocrystalline powders in an extended temperature range −100 to 300 °C was carried out. Wavelength-resolved TL proved the existence of a single active luminescence centre in this temperature range. A TL method based on various heating rates was used to derive more reliable trap depths of 0.75, 0.95, 1.25, 1.46 and 1.66 eV whereas deconvolution methods provided somewhat lower values. The most intense room-temperature afterglows (that were easily observable beyond 1000 s) were obtained from samples annealed at 1250 and 1500 °C, and were attributed mainly to depopulation of the 1.25 eV traps.

Colossal Magnetoresistance Effects of La1-xSrxMnO3

2007 ◽  
Vol 353-358 ◽  
pp. 1826-1828
Author(s):  
Shao Qun Jiang ◽  
Xin Xin Ma ◽  
Ming Ren Sun ◽  
Gang Wang ◽  
Guang Ze Tang
Keyword(s):  
Colossal Magnetoresistance ◽  
Room Temperature ◽  
Sintering Temperature ◽  
Sol Gel ◽  
Sintering Process ◽  
Gel Method ◽  
Sol Gel Method

Polycrystal samples of La1-xSrxMnO3 (x=0.2, 0.3) have been synthesized using a sol-gel method. The effect of sintering process on the sample microstructure and Sr doping on the magnetoresistance for La1-xSrxMnO3 have been investigated. The results show that the increase of sintering temperature and time can promote the crystallization of samples and reduce the content of impurity. The additive of Sr makes Mn ion in materials relatively compact, and this causes the distorted deformation of the materials structure. The magnetoresistance (MR) changes with the Sr doping. When x=0.2, the maximum MR% of sample is about 43% and keep about 40% between 10~150K. At room temperature, the MR% will decrease to about 6.5%. When x=0.3, the order magnetoresistance (OMR) effect occures above the room temperature.

Effect of MgO doping on densification and grain growth behavior of Gd2Zr2O7 ceramics by microwave sintering process

2019 ◽  
Vol 125 (8) ◽  
Author(s):  
Junjing Duan ◽  
Zhangyi Huang ◽  
Chen Shi ◽  
Yao Yang ◽  
Jianqi Qi ◽  
...  
Keyword(s):  
Grain Growth ◽  
Microwave Sintering ◽  
Growth Behavior ◽  
Sintering Process ◽  
Grain Growth Behavior

Microwave Sintering of Zirconia Toughened Mullite (ZTM)

1994 ◽  
Vol 347 ◽  
Author(s):  
J. Cai ◽  
C. Y. Song ◽  
B. S. Li ◽  
X. X. Huang ◽  
J. K. Guo ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Microwave Sintering ◽  
Single Mode ◽  
Microwave Processing ◽  
Toughening Mechanism ◽  
Conventional Sintering

ABSTRACTMicrowave sintering of zirconia toughened mullite (ZTM) has been performed in a single mode applicator. In comparison with conventional sintering, microwave processing of ZTM leads to a higher density and finer grain size. Microstructure of microwave sintered ZTM was characterized by TEM and HRTEM techniques. The pinning of intergranular ZrO2 dispersoids retarded the grain growth of mullite matrix. The observation of a considerable number of trans-granular microcracks indicates that microcracking toughening is the main toughening mechanism for ZTM.

Size-controlled synthesis of nanocrystalline BaTiO3 by a sol-gel type hydrolysis in microemulsion-provided nanoreactors

1998 ◽  
Vol 13 (11) ◽  
pp. 3174-3180 ◽  
Author(s):  
Ch. Beck ◽  
W. Härtl ◽  
R. Hempelmann
Keyword(s):  
Particle Size ◽  
Room Temperature ◽  
Sol Gel ◽  
Controlled Synthesis ◽  
Sintering Process ◽  
Line Broadening ◽  
X Ray ◽  
Transmission Electron ◽  
Hydrolysis Of ◽  
Size Controlled

Using the hydrolysis of appropriate alkoxide mixtures in water-in-oil microemulsions, nanocrystalline BaTiO3 has been prepared in the form of nonaggregated, cube-shaped crystals at room temperature without any sintering process as is demonstrated by means of x-ray diffractograms and transmission electron micrographs. By variation of the length of the hydrophilic part of the surfactant molecules, the diameter of the water droplets in the microemulsions could be tuned to values between 8 and 55 nm as determined by dynamic light scattering. The size of the resulting nano-BaTiO3 (6 nm ≤ 〈d〉vol ≤ 17 nm) was evaluated from the line broadening of x-ray reflections and correlates to the droplet size. The particle size distribution is very narrow, and in some cases nearly monodisperse.

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