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# Waltraud M. Kriven <w-kriven@uiuc.edu>
# requesting 7 days, at minimum=3 days
# beamline 33BM, "In situ, high temperature phase transformation studies in lanthanide niobates and titanates"
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# top:/home/www/beamtime-requests/req00393.txt
# UNICAT Member Beam Time Request  #393
# created Mon Mar 17 16:47:04 CST 2003
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beamline:
	33BM

collaboration:
	Yes

collaborator+Paul:
	on

contact:
	w-kriven@uiuc.edu

days:
	7

description:
	Toughening mechanisms in ceramics include: transformation  (e.g., with zirconia, where the volume change is positive) and transformation weakening causing debonding of interphases (e.g., cristobalite, enstatite, where the volume change is negative). It is proposed to study potentially new martensitic phase transformations in yttrium niobate and  dysprosium titanate, as examples of model systems for academic understanding as well as potentially technologically useful ceramics for aerospace applications at 1600 degrees C. Theoretical predictions of the relationships between parent and product phases quantify the magnitude of macroscopic shape changes and describe the nature and relative amounts of lattice invariant shears of slip and/or twinning.  These will then be compared with experimental observations made as a function of temperature, using synchrotron radiation.  This basic crystallographic data will guide the design and processing of high temperature, transformation toughened ceramic composites. Preliminary work in a previous thesis study by Lay Foong Siah indicates that the high temperature cubic phase (discovered in our experiments) occurs in yttrium niobate above 1800 degrees, but more precise information is needed, before this material can be applied as a high temperature, transformation toughener in an oxide system. The nature of the sequence of four phase transfomations in dysprosium titanate is not known, since there are a choice of three space group symmetries for each of the HT cubic, hexagonal, orthorhombic and RT cubic phases present. 
	       This work is important because it does basic research to find new phase transformations in oxide ceramics particularly at elevated temperatures. The crystallographic data measured by state of the art Rietveld technques from data collected in situ at high temperatures in air, will guide the design and fabrication of tough, strong ceramic matrix composites.  It will also guide the development of large force actuators and shape memory behavior in ceramics.

equipment+required:
	Water chiller

experiment:
	In situ, high temperature phase transformation studies in lanthanide niobates and titanates

foreign+nationals:
	Prof. W.M. Kriven (Australian)
	Dr. Pankaj Sarin (indian)
	Dr. Kerstin Jurkschat (German)

hazards:
	The experiment uses a small, watercooled, four-lamp furnace capable of 2000%B0C temperatures.  There are no apparent hazards other than those normally associated with using high energy radiation.  the samples are small sintered rods of dimensions 400 microns by 2.54 cms which are mounted with high temperature alumina cement in the furnace, and through which the synchrotron rays penetrate. All of the ceramic powder samples are non-toxic.

minimumdays:
	3

name:
	Waltraud M. Kriven

new+request:
	on

nonmembers:
	Dr. Jason Hodges at IPNL

unacceptable+dates:
	None


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