scholarly journals Aerosol synthesis and characterization of nanostructured particles of Y3Al5O12:Ce3+ and Y2O3:Eu3+

2007 ◽  
Vol 61 (3) ◽  
pp. 101-108
Author(s):  
Katarina Marinkovic ◽  
Ljiljana Veselinovic ◽  
Luz Gomez ◽  
Maria Rabanal ◽  
Lidija Mancic ◽  
...  
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Crystallite Size ◽  
Flow Reactor ◽  
Rietveld Method ◽  
Morphological Characteristics ◽  
Diffraction Method ◽  
Submicron Particles ◽  
Cubic Phase ◽  
Aerosol Synthesis

Nanostructured YAG:Ce3+ and Y2O3:Eu3+ were synthesized by low temperature (320?C) aerosol synthesis-LTAS and high temperature (900?C) aerosol synthesis-HTAS, respectively. The synthesis included aerosol generation from a nitrate precursor solution by an ultrasonic atomizer (1.3 MHz). The obtained aerosol was introduced into a tubular flow reactor, using air as the carrier gas, where successively, on a droplet level, evaporation/drying, precipitation and thermolysis occurred. The obtained powders were collected and thermally treated at different temperatures (900-1200?C). The phase development and the morphology were investigated by the X-ray powder diffraction method (XRPD) and scanning electron microscopy combined with energy dispersive spectrometry (SEM/EDS). Structural refinement was performed using the Rietveld method with the Fullprof and Koalariet programs. The average crystallite size for the Y2O3:Eu system was calculated using the Profit program. It was shown that 89 wt.% of Y3Ai5Oi2:Ce was obtained by annealing (1000?C/6 h) the as prepared, amorphous powder, synthesized by the low temperature aerosol method (LTAS). High temperature spray pyrolysis (HTAS) at 900?C led to the formation of the targeted cubic phase of Y2O3:Eu3+. The microstructural parameters of the asprepared samples of the Y2O3:Eu3+ system indicate the formation of nanostructures with crystallite size smallest than 20 nm. The substitution of luminescent centers (Ce3+, Eu3+) into a host lattice (YAG, Y2O3, respectively) was confirmed by changes in the crystal lattice parameters. Also, it was shown in both systems that good morphological characteristics (non-a?gglomerated, spherical, submicron particles) were obtained enabling improved luminescent characteristics.

A THERMOGRAVIMETRIC STUDY OF ORGANIC MATTER OF REPRESENTATIVE CANADIAN PODZOL SOILS

1964 ◽  
Vol 44 (1) ◽  
pp. 7-13 ◽  
Author(s):  
M. Schnitzer ◽  
R. C. Turner ◽  
I. Hoffman
Keyword(s):  
Organic Matter ◽  
High Temperature ◽  
Low Temperature ◽  
Morphological Characteristics ◽  
Inorganic Materials ◽  
Pronounced Effect ◽  
Thermogravimetric Study ◽  
Surface Materials ◽  
Organic Matter Addition ◽  
Podzol Soils

Differential thermogravimetric (DTG) curves of untreated peat, muck, and 10 different Podzol L–H materials showed peaks at approximately 100 °C (moisture), 280° (low-temperature band), and 370 to 390 °C (high-temperature band). The maxima at 280 °C were sharp and characteristic of all surface materials investigated. The DTG curves were essentially the same for all of the Podzol L–H materials investigated.The DTG curves for 12 organic matter preparations extracted from Podzol Bh, Bfh, Bhf, Bfl, and Btf horizons showed maxima at 100 °C and in the 420 to 520 °C region (high-temperature band). The peaks at 280 °C were virtually absent in these materials. This suggested differences in composition between L–H and B horizon organic matter of the Podzols studied. The variations in the positions of the high-temperature bands of the B materials were related to the morphological characteristics of these soils in the field. From this it appeared that thermogravimetry might be a useful aid in soil classification.Addition of inorganic materials did not affect the position of the low-temperature bands but had a pronounced effect on the high-temperature bands of both L–H and B organic matter. Addition of Na caused the peaks of the latter to shift to higher temperatures while addition of Al and Fe caused shifts to lower temperatures.

Study on stabilization of cubic Li7La3Zr2O12 by Ge substitution in various atmospheres

2016 ◽  
Vol 09 (06) ◽  
pp. 1642005 ◽  
Author(s):  
Masashi Kotobuki ◽  
Binngong Yan ◽  
Li Lu ◽  
Emil Hanc ◽  
Joanna Molenda
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Tetragonal Phase ◽  
The Other ◽  
Cubic Phase ◽  
Other Hand ◽  
High Temperature Xrd ◽  
Li Ion

Stabilization of high Li ion conductive cubic Li7La3Zr2O[Formula: see text] (LLZ) by Ge substitution in air, N2/O2 and N2 atmospheres are studied by high temperature XRD (HT-XRD) of Ge-added tetragonal LLZ (Ge-LLZ). A formation of low temperature cubic phase caused by CO2 absorption during storage of the Ge-LLZ is observed at about 160[Formula: see text]C in all atmospheres. Additionally, impurity formation of La2Zr2O7 and La2O3 also occurs in all atmospheres. On the other hand, stabilization of cubic phase by substitution of Ge is largely influenced by the atmosphere. The cubic phase is observed at 40[Formula: see text]C after heating Ge-LLZ to 700[Formula: see text]C in air while only tetragonal phase appeared after heating in N2/O2. It is concluded that the heating atmosphere largely influences substitution of Ge, resulting in stabilization of the high Li ion conductive cubic phase.

Phase Relations And Conductivity In ZrO2-Sc2O3-La2O3 System

1994 ◽  
Vol 346 ◽  
Author(s):  
Akihiko Yamaji ◽  
Takao Ishii ◽  
Masami Kanzaki
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Structural Transition ◽  
Ion Conductivity ◽  
Cubic Phase ◽  
Discontinuous Change ◽  
Ion Conductor ◽  
Oxygen Ion ◽  
Phase Stabilization ◽  
Oxygen Ion Conductor

ABSTRACTThe oxygen-ion conductor 0.88ZrO2-0.12Sc2O3 has a discontinuous change in ion conductivity at about 660°C. This change accompanies the structural transition from rhombohedral to cubic phase. Since the high temperature cubic phase shows large ion conductivity, it is of interest to examine whether or not the cubic phase stabilizes in the low temperature region by another dopant . By adding only 0.005 mole % La2O3, the cubic phase is stabilized below about 500 °C without any loss of conductivity compared with 0.88ZrO2-0.12Sc2O3. The ion conductivity of cubic stabilized ZrO2-Sc2O3-La2O3 system is around 1×10-1 S/cm at 800°C. Cubic phase stabilization using second dopant in a ZrO2-Sc2O3 system led to the finding of a fast oxygen-ion conductor in the ZrO2-Sc2O3-La2O3 system.

XRPD/TEM studies of model high-temperature shift catalysts

2006 ◽  
Vol 39 (4) ◽  
pp. 519-526 ◽  
Author(s):  
Rune E. Johnsen ◽  
Alfons M. Molenbroek ◽  
Kenny Ståhl
Keyword(s):  
High Temperature ◽  
Iron Oxide ◽  
Crystallite Size ◽  
Rietveld Method ◽  
Temperature Shift ◽  
Average Crystallite Size ◽  
Model Catalysts ◽  
Crystallite Sizes ◽  
Scherrer Equation

The combination of transmission electron microscopy (TEM) andin situX-ray powder diffraction (XRPD) for the investigation of four model high-temperature shift catalysts makes it possible to obtain and compare information concerning the crystallite and particle shapes and sizes before, during and after the reduction of the synthesized hematite-based model catalyst to the active magnetite-based catalyst. Two chromium-containing iron oxide model catalysts and two pure iron oxide model catalysts were synthesized from hydrated chloride or nitrate salts, resulting in particles with different shapes and sizes. The average crystallite sizes of four model catalysts were determined by XRPD using the Scherrer equation before and after the reduction. The crystallite sizes determined before the reduction were compared with particles sizes determined from TEM images of the same samples. These sizes were generally in good agreement. By using the Rietveld method combined with the Scherrer equation and the Lorentzian Scherrer broadening parameters, the development of the average crystallite size during thein situreduction was demonstrated. This showed that the average crystallite size of the remaining hematite increases when the reduction begins. Additionally, the average crystallite sizes of the reduced samples showed that the chromium-containing model catalysts have the smallest increase in the overall crystallite size.

Nanophase Copper Ferrite Using an Organic Gelation Technique

1996 ◽  
Vol 457 ◽  
Author(s):  
D. Sriram ◽  
R. L. Snyder ◽  
V. R. W. Amarakoon
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Crystallite Size ◽  
Polyacrylic Acid ◽  
Size Analysis ◽  
Copper Ferrite ◽  
Carboxylic Group ◽  
X Ray Diffraction ◽  
X Ray ◽  
Nano Size

ABSTRACTNanocrystalline copper ferrite (Cu0.5Fe2.5O4) was synthesized using a forward strike gelation method with polyacrylic acid (PAA) as a gelating agent. The dried gel was calcined at a low temperature of 400 °C to get the final powder. The effect of pH and the ratio of the cation to the carboxylic group in the initial gel were studied with respect to both the phases and the crystallite size of the final powders synthesized. Phase and crystallite size analysis were done using x-ray diffraction and TEM. Saturation magnetization results were obtained using a SQUID magnetometer. The reactions occurring in the nano-size copper ferrite, in air as a function of temperature, were tracked using adynamic high temperature x-ray diffraction (HTXRD) system.

Effects of Diffusion of Co/Ni Cations on Sol-Gel Derived ZrO2 Polymorphic Transformations

1995 ◽  
Vol 398 ◽  
Author(s):  
H.C. Zeng ◽  
M. Qian
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Tetragonal Phase ◽  
Sol Gel ◽  
Heating Process ◽  
Cubic Phase ◽  
Impregnation Method ◽  
Cooling Process ◽  
Polymorphic Transformations ◽  
Metal Diffusion

ABSTRACTTransition metal incorporated ZrO2 gel matrices have been prepared by impregnation method and investigated with FTIR/DTA/XRD. The metastable tetragonal - monoclinic -tetragonal - cubic phase transformations are revealed in the DTA heating process up to 1400°C for the studied gels. High-temperature tetragonal to monoclinic transition is also observed in the cooling process. It is found that the diffusing metal cations stabilize the low-temperature tetragonal phase. However, for high-temperature (900°C) calcined gels, both as-prepared and metal-stabilized tetragonal phases are reduced substantially. Correlations between metal diffusion and gel polymorphic stabilities are also demonstrated.

Gas-phase combustion synthesis of titanium boride (TiB2) nanocrystallites

1996 ◽  
Vol 11 (4) ◽  
pp. 948-954 ◽  
Author(s):  
R. L. Axelbaum ◽  
D. P. DuFaux ◽  
C. A. Frey ◽  
K. F. Kelton ◽  
S. A. Lawton ◽  
...  
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Combustion Synthesis ◽  
Gas Phase ◽  
Thermodynamic Analysis ◽  
Flow Reactor ◽  
Titanium Boride ◽  
Sodium Vapor ◽  
Vacuum Sublimation ◽  
Water Washing

Two techniques are described for synthesizing nanometer-sized TiB2 particles by gas-phase combustion reactions of sodium vapor with TiCl4 and BCl3: a low-pressure, low-temperature burner and a high-temperature flow reactor. Both methods produce TiB2 particles that are less than 15 nm in diameter. The combustion by-product, NaCl, is efficiently removed from the TiB2 by water washing or vacuum sublimation. Material collected from the low-temperature burner and annealed at 1000 °C consists of loosely agglomerated particles 20 to 100 nm in size. Washed material from the high-temperature flow reactor consists of necked agglomerates of 3 to 15 nm particles. A thermodynamic analysis of the Ti/B/Cl/Na system indicates that near 100% yields of TiB2 are possible with appropriate reactant concentrations, pressures, and temperatures.

scholarly journals Vysokoteplotní fázové transformace kaolinitu v závislosti na krystalinitě

2020 ◽  
Vol 27 (1-2) ◽  
Author(s):  
Petr Štursa ◽  
Dalibor Všianský ◽  
Karel Lang ◽  
Lenka Nevřivová ◽  
Lukáš Tvrdík ◽  
...  
Keyword(s):  
High Temperature ◽  
Crystallite Size ◽  
Rietveld Method ◽  
Exothermic Effect ◽  
X Ray Diffraction ◽  
Spinel Type ◽  
X Ray ◽  
Heat Flow Curve ◽  
Two Samples ◽  
Low Crystallinity

Although kaolinite is one the most important industrial minerals, the processes of its transformation to mullite have not been completely explained so far. The study is focused on kaolinite crystallinity calculation and its effect on high-temperature phases transitions in the series kaolinite-mullite. Samples of purified natural kaolins from several sites were analysed using X-ray diffraction (XRD). Besides the determination of the complex mineral composition, kaolinite crystallite size was calculated from XRD data by the Rietveld method, Scherrer equation and using the Hinckley crystallinity index. Thermal analysis (DSC/TG) was used as the principal approach to examine endothermic and exothermic effects of kaolinite transformations. The course and maximum temperatures of the observed effects were correlated with the original crystallite size of kaolinite. Two samples with different kaolinite crystallinity were also analysed by high-temperature X-ray diffraction (ht-XRD) to study the formation of mullite. Scanning electron microscope (SEM) was used to visualize morphology of kaolinite.It was found out that the original crystallinity of kaolinite affects all three examined processes-kaolinite dehydroxylation, formation of crystalline phases from metakaolinite and development of mullite crystal structure. Dehydroxylation of samples with higher kaolinite crystallinity takes place at higher temperatures. Similar effect applies for the reaction(-s) at the temperature about 980 °C observed at heat flow curve where crystallization of spinel type phase and mullite with very low crystallinity occurs. Broadening of FWHM of the exothermic effect points to decreasing kaolinite crystallinity. Crystallization of mullite exhibits different dependence on kaolinite crystallinity than the previous processes. The results show that mullite with larger crystallite size develops faster from kaolinite of low crystallinity and vice versa.

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