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.

scholarly journals New triple molybdate and tungstate Na5Rb7Sc2(XO4)9 (X = Mo, W)

2021 ◽  
Vol 8 (4) ◽  
pp. 20218412
Author(s):  
Tatyana S. Spiridonova ◽  
Aleksandra A. Savina ◽  
Evgeniy V. Kovtunets ◽  
Elena G. Khaikina
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Rietveld Method ◽  
Ceramic Technology ◽  
Chemical Transformations ◽  
X Ray Diffraction ◽  
X Ray ◽  
Triple Molybdate ◽  
High Thermal Expansion ◽  
New Compounds

New compounds of the composition Na5Rb7Sc2(XO4)9 (X = Mo, W) were obtained via the ceramic technology. The sequences of chemical transformations occurring during the formation of these compounds were established, and their primary characterization was performed. Both Na5Rb7Sc2(XO4)9 (X = Mo, W) were found to melt incongruently at 857 K (X = Mo) and 889 K (X = W). They are isostructural to Ag5Rb7Sc2(XO4)9 (X = Mo, W), Na5Cs7Ln2(MoO4)9 (Ln = Tm, Yb, Lu) and crystallize in the trigonal crystal system (sp. gr. R32). The crystal structures were refined with the Rietveld method using the powder X-ray diffraction data. The thermal expansion of Na5Rb7Sc2(WO4)9 was studied by high-temperature powder X-ray diffraction; it was shown that this triple tungstate belongs to high thermal expansion materials.

scholarly journals Synthesis, Structure and Thermophysical Properties of Phosphates MNi0.5Zr1.5(PO4)3 (M = Mg, Ca, Sr)

2010 ◽  
Vol 12 (3,4) ◽  
pp. 241 ◽  
Author(s):  
M.V. Sukhanov ◽  
I.A. Schelokov ◽  
V.I. Pet'kov ◽  
E.R. Gobechiya ◽  
Yu.K. Kabalov ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Heat Capacity ◽  
Thermal Expansion ◽  
High Temperature ◽  
Single Phase ◽  
Rietveld Method ◽  
Type Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Expansion Behavior

<p>New phosphates MNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3</sub> (M = Mg, Ca, Sr) were prepared by the precipitating method.<strong><em> </em></strong>Phosphates were characterized using X-ray powder diffraction, IR-spectroscopy and electron microprobe analyses. The crystal structure of phosphates was refined by the Rietveld method. Phosphates CaNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3</sub> and SrNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3</sub> are shown to have been crystallized in the NaZr<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>-type structure and the phosphate MgNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3 </sub>was obtained as a single-phase with Sc<sub>2</sub>(WO<sub>4</sub>)<sub>3</sub>-type structure. Heat capacity of phosphate CaNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3</sub> was measured in the range 7 – 650 K and increased monotonically over the entire temperature range studied. Thermal expansion of phosphate CaNi<sub>0.5</sub>Zr<sub>1.5</sub>(PO<sub>4</sub>)<sub>3</sub> was studied in the interval 295-1073 K by the high temperature X-ray diffraction. This phosphate is similar to the best low-expansion ceramics, such as zircon, cordierite and silica glass in thermal expansion behavior.</p>

X-ray structure and microstructure determination of the mixed sesquioxides (Eu1−xYbx)2O3prepared by a sol–gel process

2003 ◽  
Vol 36 (6) ◽  
pp. 1411-1416 ◽  
Author(s):  
Z. K. Heiba ◽  
Y. Akin ◽  
W. Sigmund ◽  
Y. S. Hascicek
Keyword(s):  
Crystallite Size ◽  
Rietveld Method ◽  
Sol Gel ◽  
Average Crystallite Size ◽  
X Ray Diffraction ◽  
X Ray ◽  
Profile Fitting ◽  
Cationic Distribution ◽  
Sol Gel Process ◽  
Multiple Orders

Polycrystalline samples of (Eu1−xYbx)2O3(x= 0.0, 0.1, 0.2, 0.5, 0.8, 0.9 and 1.0) were synthesized by a sol–gel process. X-ray diffraction data were collected and the crystal structures were refined by the Rietveld method. All samples are found to have the same crystal system and formed solid solutions over the whole range ofx. The lattice parameters are found to vary linearly with the compositionx. The cationic distribution over the two non-equivalent sites 8band 24dof the space group Ia{\bar 3} is found to be random in the range 0.0 <x≤ 0.5 and preferential in the range 0.5 <x≤ 1.0. Replacing Eu3+and Yb3+by each other introduces slight changes in the atomic coordinates. Crystallite size and microstrain analysis are performed on single and multiple orders for each sample using profile fitting and the Warren–Averbach method. The obtained values of microstrain are correlated with the distribution of the rare earth (RE) ions over the two cationic sites of the structure. The average crystallite size ranges from 35 to 96 nm and the mean-square strain from 0.052 to 0.225 × 10−2.

scholarly journals Determination of the crystallite size and crystal structure of magnesium powder by x-ray diffraction

2020 ◽  
Vol 20 (3) ◽  
pp. 61-65
Author(s):  
ISMAIL ISMAIL ◽  
RESI MULIANI ◽  
ZULFALINA ZULFALINA ◽  
SITI HAJAR SHEIKH MD FADZULLAH
Keyword(s):  
Crystal Structure ◽  
Crystallite Size ◽  
Rietveld Method ◽  
Average Crystallite Size ◽  
Powder Sample ◽  
X Ray Diffraction ◽  
Magnesium Powder ◽  
X Ray ◽  
Lattice Constants ◽  
Packed Structure

Magnesium powder has become an important material in the development of science and technology such as alloy and hydrogen storage. In this work, the chemical composition, crystallite size, and crystal structure of the magnesium powder sample have been studied by using x-ray fluorescent and x-ray diffraction. The x-ray diffraction data of the magnesium powder sample was analyzed by using the Rietveld method to obtain the crystal structure. Our results show that the purity of our magnesium powder sample is 93.1%. Our sample has good crystallinity with the average crystallite size of 31 nm. The crystal structure is found to be a hexagonal closed-packed structure with the lattice constants of 3.2100 Å (a and b-axis) and 5.2107 Å (c-axis). Our result revealed that the lattice constant in the c-axis of magnesium powder is influenced by impurity. This finding suggests that the impurity can affect the crystal structure of a material in general.

Applications of X-ray Diffraction Crystallite Size/Strain Analysis to Seismosaurus Dinosaur Bone

1990 ◽  
Vol 34 ◽  
pp. 473-482 ◽  
Author(s):  
Steve J. Chipera ◽  
David L. Bish
Keyword(s):  
New Mexico ◽  
Crystallite Size ◽  
Profile Analysis ◽  
Rietveld Method ◽  
Strain Analysis ◽  
Morrison Formation ◽  
X Ray Diffraction ◽  
X Ray ◽  
A Minor ◽  
20 Nm

AbstractRecently, the remains of a giant Cretaceous Sauropod (~150 My old) were discovered in the Morrison Formation west of Albuquerque, New Mexico. This dinosaur, tentatively named Seismosaurus, was found in an exceptional state of preservation. Although it has been known since the 180Q's that fossilized bone is often composed of the mineral apatite, very few studies have been conducted to characterize farther the fossilized material. In an effort to gain insight into the state of preservation and Hie processes occurring in the bone since deposition, apatite in bone from Seismosaurus was compared with that from a contemporary elk from the Jemez Mountains, New Mexico, and with well-crystallized mineral apatite using X-ray powder diffraction and profile analysis techniques. Crystallite size/strain analyses were conducted using the Scherrer equation, the Warren-Averbaca and single-line methods, and the Rietveld method using the program GSAS. Heating the contemporary elk bone produced a decrease in the full-width-at-half-maximum (FWHM) of the reflections in the diffraction pattern. This decrease in FWHM is due to a decrease in microstrain along with a minor increase in crystallite size. Results from crystallite size/strain analysis show that both Seismosaurus and contemporary elk bone crystallites are elongate parallel to the c-axis. However, Seismosaurus bone crystallites are larger (-20-65 nm) with less strain than the contemporary elk bone crystallites (-8-20 nm), suggesting that if elk bone is an appropriate analog, then Seismosaurus bone must have undergone recrystallization.

XRD Studies on Transformation of Dolomite under CO2 and N2 Atmosphere

2020 ◽  
Vol 1010 ◽  
pp. 355-360
Author(s):  
Siti Sarahah Sulhadi ◽  
Maratun Najiha Abu Tahari ◽  
Salma Samidin ◽  
Wan Nor Roslam Wan Isahak ◽  
Muhammad Rahimi Yusop ◽  
...  
Keyword(s):  
High Temperature ◽  
Crystallite Size ◽  
Fluidized Bed ◽  
Chemical Reactions ◽  
Fluidized Bed Reactor ◽  
The Other ◽  
X Ray Diffraction ◽  
X Ray ◽  
Xrd Studies ◽  
Significant Chemical

In this study, dolomite was heated under CO2 and N2 gases using fluidized bed reactor from 85 °C to 835 °C. Dolomite under N2 atmosphere did not show any significant changes on its crystallite size, suggesting there is no significant chemical reaction. On the other hand, dolomite under CO2 atmosphere shows no significant changes on its crystallite size until it reaches high temperature (> 800 °C) where MgO started to be observed in X- ray diffraction. This shows that few chemical reactions started to happen in this reaction condition.

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.

Nonlinear thermal expansion in Li2NiMn3O8

2008 ◽  
Vol 23 (3) ◽  
pp. 224-227
Author(s):  
Lingmin Zeng ◽  
Yeqing Chen ◽  
Wei He ◽  
Liangqin Nong
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Room Temperature ◽  
Linear Thermal Expansion ◽  
Lithium Ion ◽  
Entire Temperature Range ◽  
X Ray Diffraction ◽  
Spinel Type ◽  
X Ray ◽  
Temperature Range

A lattice thermal expansion study on Li2NiMn3O8, a high-voltage cathode material for lithium-ion batteries, was carried out by high-temperature X-ray diffraction from room temperature to 973 K. Rietveld refinement of a high-quality room-temperature diffraction pattern confirmed that Li2NiMn3O8 has the cubic Al2MgO4 spinel type of crystal structure. The analysis of the high-temperature X-ray diffraction patterns showed that the Li2NiMn3O8 structure remained stable and no phase transition was detected over the temperature range from 298 to 973 K. As expected, the value of lattice parameter a or unit cell volume V increases with increasing temperature. The increase in a or V is linear only in the low-temperature region and nonlinear over the entire temperature range from 298 to 973 K. Least-squares analysis of the data for a or V showed the thermal expansion of a or V for Li2NiMn3O8 can best be fitted by a 3-degree polynomial function of temperature. The linear thermal expansion coefficients for a and V averaged over the entire temperature range from 298 to 973 K were also calculated, and αTa=1.10×10−5 K−1; αTV=3.29×10−5 K−1.

Structure and Thermo-Chemical Stability of Sr-Fe-Co-O Mixed Metal Oxides

2012 ◽  
Vol 549 ◽  
pp. 193-197
Author(s):  
Xiang Hong Huang ◽  
Jun Qiao ◽  
Qian Feng Zhang
Keyword(s):  
High Temperature ◽  
Metal Oxides ◽  
Chemical Stability ◽  
Elevated Temperatures ◽  
Mixed Metal Oxides ◽  
X Ray Diffraction ◽  
Crystalline Phases ◽  
X Ray ◽  
Mixed Metal ◽  
Two Samples

SrFexCo0.5Oδ(x=0.5, 0.75, 1.0, 1.25) mixed metal oxides were synthesized by the citrate method. The structure and thermo-chemical stability of the obtained SrFexCo0.5Oδpowders were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results show that the SrFexCo0.5Oδpowders are composed of perovskite-type cubic structure at both room temperature and high temperature. The crystalline phases of the SrFexCo0.5Oδpowders are dependent on the content of Fe and SrFe0.5Co0.5O3, SrFe0.19Co081O2.78are the main crystalline phases. The powders have good thermo-chemical stability at elevated temperatures in helium, which is confirmed by an in-situ high-temperature X-ray diffraction. The SEM images show that the product of the SrFexCo0.5Oδ(x=0.5, 1.0) is composed of single grain, while other two samples consist of layer structures and some open porosities.

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