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Synthesis And Characterization Of Novel Rare Earth Phosphates And Rietveld Structural Analysis Of Rare Earth OrthoboratesSeyyidoglu, Semih 01 October 2010 (has links) (PDF)
This thesis covers the synthesis and the characterization of sodium lanthanide oxide
phosphates, rare earth added strontium pyrophosphates and the Rietveld structural
analysis of rare earth orthoborates. Solid state and microwave-assisted synthesis
method was employed for the synthesis of desired materials. The formation of the
produced phases was confirmed by X-ray Diffraction (XRD), Infrared FT-IR,
Raman, Scanning Electron Microscopy (SEM) methods. By using Rietveld
Refinement method, structural analysis of rare earth orthoborates were done and
three dimensional crystal structures were found.
In the first part of the thesis, some new sodium lanthanide oxide phosphates were
synthesized by solid state reaction method from Ln2O3 (where Ln= La, Nd, Sm, Gd,
Dy, Ho, Er, Yb), Na2CO3, NH4H2PO4 at 1100 oC. Na2LaOPO4, Na2NdOPO4, and
Na2SmOPO4 produced with the space group is Pmm2. With the help of the same
procedure new orthorhombic Na2DyOPO4, Na2HoOPO4, Na2ErOPO4, and
Na2YbOPO4 were synthesized for the first time in the literature at 1100 oC with the
same space group Pmm2.
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In the second part of the thesis, Sr2P2O7 - ZrP2O7 solid solution was obtained by the
solid state reaction and they were characterized for the first time in literature and
subjected to thermoluminescence measurements showing Sr2P2O7 has glow curve
around 100 oC. Then CuO and some rare earth oxides (Y2O3, La2O3, CeO2, Pr6O11,
Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3)
0.5-15% (by weight) were added to pure Sr2P2O7. After structural determinations by
XRD, thermoluminescence studies showed two glow peaks of Pr, Ho, and Nd along
with Cu-added samples, one of them is always at around 90 oC and the other TLthermoluminescence-
peak around 180, 275, and 285 oC, respectively. This study
showed that rare earth added Sr2P2O7 materials can be promising material for
dosimetric applications.
In the third part of this work, time saving microwave-assisted synthesis method was
applied to produce pure LnBO3 (Ln=La, Nd, Dy, Ho) by using urea and sucrose as a
microwave active organic additive. For LaBO3 and NdBO3, space group found as
Pnma and for DyBO3 and HoBO3 powders crystallized in hexagonal unit cell with
P-6c2 space group. All microwave-assisted products have particle sizes lower than 1 micrometer.
In the final part of this study, pure LnBO3 (Ln=Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er,
Tm, Yb, Lu) powder samples were produced by using solid state reactions of Ln2O3
and H3BO3 (ratio=1:2) heated at 900 oC for 10 hours and 1000 oC for 5 hours. The
crystallographic studies conducted with rietveld structural refinement and unit cell
parameters, background functions, profile parameters, zero shift, atomic positions,
and unisotropic thermal parameters were refined. LaBO3 and NdBO3 were solved
based on Pnma orthorhombic structure while the crystal structure of YBO3, DyBO3
and HoBO3 were monoclinic C2/c. SmBO3 showed triclinic P-1 structure.
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Investigating The Extrusion Of Alumina Silicate Pastes For Synthesis Of Monolith Zeolite AOzcan, Aysenur 01 August 2005 (has links) (PDF)
Zeolites are highly porous materials that are most commonly used in granular or beaded forms. In general, zeolite granules, beads or monoliths are manufactured by using an inorganic binder which helps to cement zeolite crystals together. However, this inorganic binder decreases the purity of the zeolite structures and accessibility to the zeolite pores. A new and relatively easy method was offered for the production of binderless zeolite A tubes and bars from amorphous alumina silicate extrudates in this study. Amorphous alumina silicate powder, which is obtained by filtering the homogenous hydrogel with a composition of 2.5Na2O:1Al2O3:1.7SiO2:150H2O, is mixed with an organic binder (HEC-Hydroxyethyl Cellulose) to obtain the paste. The paste is then extruded through a die of a home-made extruder into bars and tubes. These extrudates were dried at room temperature for 24 hours, then calcined at 600oC for 2
hours and finally synthesized at 80oC for 72 hours in hydrothermal conditions to convert amorphous alumina silicate to zeolite.
The most appropriate amorphous alumina silicate powder (A) / 4wt% HEC solution (H) ratio to prepare paste, hence to prepare bars and tubes was found as 0.82. The crystallinity of bars and tubes was 91% and 97%, respectively, and zeolite A was the only crystalline material. The bars and tubes were composed of highly intergrown zeolite A crystals with high porosity. Porosity of the bars is approximately 39% and porosity of the tubes is 29%, with a narrow pore size distribution. Bars have macropores of 2 & / #956 / m, while the macropores of the tubes are 3-4 & / #956 / m. The BET surface area of the bars was 411 m2/g and of tubes was 439 m2/g, which are comparable with the commercial zeolite A beads. Bars had a crushing strength of 0.42 MPa, which is sufficiently high to handle.
In conclusion, zeolite A bars and tubes, with their high purity, macroporous structure and high mechanical strength, can be used in adsorption and ion exchange processes. The developed synthesis method can be scaled up to prepare honeycomb monoliths that provide higher surface are per unit volume with an appropriate extruder die.
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