$electron backscatter diffraction$

$electron backscatter diffraction$

#Electron backscatter diffraction free#

If any modifications of Al 2O 3 occurred at lower temperatures, their amounts were below the detection threshold of the performed XRD-experiments. X-ray diffraction (XRD) analyses of the microspheres mainly indicated the presence of YAG and trigonal α-Al 2O 3 which was only identified after subsequent thermal treatments at 1,300 ☌ or higher 13, 14, 15, 17, 18, 19, 20.

$electron backscatter diffraction$

The produced microspheres range from 10 to 40 µm in diameter 13, 14, 15, 16, 17, 19. Powders of various nominal compositions in the Y 2O 3–Al 2O 3-system have been prepared using a combination of the Pechini method 26 and flame synthesis to enhance the chemical homogeneity 18, 19, 20, 21. Secondary crystallization events between 996 and 1,020 ☌ were also observed in some glasses 20, 21. Only the eutectic composition 40 Y 2O 3–60 Al 2O 3 and the composition doped with CeO 2 led to XRD-amorphous microspheres, glass transition temperatures (T g) of 870–898 ☌ and primary crystallization temperatures (T x) of 899–936 ☌ could be measured from the produced spheres 13, 14, 15, 16, 17, 18, 19, 20, 21. Precursor powders in the wt% composition range (25–57) Y 2O 3–(43–75) Al 2O 3 have been processed using flame synthesis 13, 14, 15, 16, 17, 18, 19, 20, 21, CeO 2 has also been added to the composition 17. Utilizing the method of flame synthesis to produce glass microspheres provides the high cooling rates necessary for preventing crystallization during glass production 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 while simultaneously limiting the maximum crystallite size to the maximum diameter of the respective sphere. The nano-crystallization of a glass containing an excess amount of Al 2O 3 to allow glass formation has recently allowed the fabrication of transparent YAG-Al 2O 3-nano ceramics without the need of elevated pressures 12.

#Electron backscatter diffraction free#

Applying levitation melting and reducing the SiO 2-content to only 4 wt% enables to produce glasses free of crystals 11. Both effects are problematic with respect to the transparency of the resulting materials. in glasses also containing SiO 2 often does not lead to the sole formation of YAG 7, 8, 9 or shows a low nucleation rate 10. While YAG has been crystallized from multiple glasses, their crystallization e.g. An alternative approach of producing YAG is the controlled crystallization of glasses where the high melting temperature (T m) of YAG (calculated to be 2,213 ☌ 6) combined with its high tendency towards spontaneous crystallization during cooling make glass production difficult. While single crystals and transparent ceramics are usually used as the host matrix for the optically active dopants allowing various applications, these materials are costly and time consuming to fabricate. Applying very large undercooling temperatures has also been described to cause a density driven phase separation 5. Melts of the Y 2O 3–Al 2O 3 system show polymorphism 3, 4, 5 including the probable formation of two immiscible liquids after the melting of YAG which crystallized to form YAP and Al 2O 3 4, 5. A further phase has been indicated 2 but remains undescribed to the best of our knowledge. The third chemical composition described in the system is monoclinic Y 4Al 2O 9 (YAM) which shows a phase transition to a low-temperature modification of the same space group at 1,370 ☌ 1. solid state laser materials for many years. Highly crystalline materials in the Y 2O 3–Al 2O 3 system have been intensely studied because cubic Y 3Al 5O 12 (YAG) and orthorhombic YAlO 3 (YAP) have been of interest as e.g. via irregular flight paths through the flame, contaminants or irregular cooling rates. The multitude of differing microsphere types showing polygon and dendritic crystal growth as well as phase separation indicate that flame synthesis can lead to a wide variety of parameters during microsphere production, e.g. Energy dispersive X-ray spectrometry results obtained from these microspheres show that their chemical composition can deviate from the nominal composition of the precursor powder. All three phases in the binary Y 2O 3–Al 2O 3-phase diagram (Y 3Al 5O 12, YAlO 3 and Y 4Al 2O 9) and α-alumina are located by EBSD. They are presented without regard for their relative occurrence some are extremely rare but illustrate the possibilities of flame synthesis in the analyzed system. 16 different types of crystallized bodies are cataloged for future reference. Growth models are formulated for individual microspheres crystallized during flame synthesis as well as after an additional heat treatment step. The crystallization of glass microspheres in the Y 2O 3–Al 2O 3-system produced from precursor powders of four different nominal compositions via flame synthesis is analyzed in detail by electron microscopy with a focus on electron backscatter diffraction (EBSD).

$electron backscatter diffraction$