#################################################### # Waltraud M. Kriven # requesting 6 days, at minimum=6 days # beamline 33BM, In situ Studies of Thermal Expansion of Doped Mullite Ceramics to 1800°C # instrument 33BM-C fourc #################################################### # top:/home/www/beamtime-requests/req00522.txt # UNICAT Member Beam Time Request #522 # created Sun Dec 07 15:35:01 CST 2003 #################################################### beamline: 33BM collaboration: Yes contact: kriven@uiuc.edu days: 6 description: We propose to continue our study on the the influence of metal ions doping on the thermal expansion of 3:2 mullite lattice, with studies conducted in-situ at high temperatures (~ 1800 degree Celsius) using a thermal image furnace. Powder x-ray diffraction patterns from powder samples will be acquired while the samples are subjected to high temperatures in specially designed sample holders in the thermal image furnace. Mullite is a strong candidate material for advanced structural applications at high temperature, because it has good chemical stability, high creep resistance, good high temperature strength, and is resistant to many corrosive environments. In addition, Mullite has a low coefficient of thermal expansion, and is a good thermal and electrical insulator even at very high temperatures (up to ~1800 degree Celsius). The most common applications of mullite are in high temperature structural components, infrared transparent windows, substrate for microelectronic package, high temperature protective coating. Mullite structure consists of chains of edge-sharing AlO6 octahedra parallel to c-axis and (Si, Al)O4 tetrahedra. The connection between the octahedral and tetrahedral chains creates wide channels along the c-axis. As mullite has a highly stable open structure, it can accommodate several ions in structure as solid solution. In this study, the 3:2 mullite structure is doped with Ga (0-10 mole %), Ti (1-4 mole %), and Cr (0-10 mole %) in order to modify the thermal expansion behavior of mullite. The equilibrium composition 3:2 was chosen because its structure depends on initial composition and efficiency of mixing, thus allowing for better observation of the doping effects. As larger diameter ions replace smaller ones, the lattice expands and a change in the thermal expansion coefficient is also expected. The theoretical calculations by other researchers have predicted that the Ga3+ ion should substitute for Al3+ in octahedral positions causing relatively high linear expansion along b axis, low expansion along c and very low expansion along a axis due to bond stretching in octahedral cell (Jahn - Teller distortion). In case of Ti-doped mullite, it has been suggested that Ti4+ ion goes into octahedral (AlO6) sites, and is accompanied with replacement of Si4+ ion by Al3+ ion for charge compensation. Cr3+ on the other hand, has been reported to occupy the octahedral site of Al3+. The design and synthesis of controlled metal ion doping of mullite (3Al2O3:2SiO2) using, either organic steric entrapment method or the sol-gel method has been optimized in this study, and preliminary experiments on the thermal expansion of mullite, have already been completed. However, essential information on lattice expansion behavior of transition metal-ion doped mullite is still missing. During the beamtime awarded to this project in Nov-Dec'03, we have completed the study on the Ga doped mullite systems, and the analysis is underway. The proposed experiments promise to conduct in-situ study of the high temperature thermal expansion behavior of mullite doped with Ti (1-4 mole %) and Cr (0-10 mole %). equipment_required: Huber 4 circle diffractometer experiment: In situ Studies of Thermal Expansion of Doped Mullite Ceramics to 1800°C foreign_nationals: Waltaud M. Kriven (Australian) Pankaj Sarin (Indian) Kerstin Jurkschat (German) hazards: The in situ experiment uses a four lamp quadrupole furnace to heat up a ceramic sample in air up to ~1800°C. The instrument is a small, 6 inch diameter apparatus which is water cooler, using a water chiller unit. No hazards have been experienced with this apparatus. instrument: 33BM-C fourc instrument_other: minimumdays: 6 name: Waltraud M. Kriven nonmembers: unacceptable_dates: Not before Feb 29th if possible April 18-22 z34ID_change_undulator: no z34ID_details: #REMOTE_HOST: mach-208.mse.uiuc.edu #REMOTE_ADDR: 128.174.228.208 #CONTENT_LENGTH: 4109 #HTTP_REFERER: http://www.uni.aps.anl.gov/unireq.htm #HTTP_USER_AGENT: Mozilla/4.0 (compatible; MSIE 5.16; Mac_PowerPC)