The atomic pair distribution function (PDF) method was used to study the structure of cesium aluminosilicate geopolymer (CsThe geopolymer was prepared by reacting metakaolin with cesium silicate solution followed by curing at 50 °C for 24 h in a sealed container. Heating of Cs-geopolymer above 1000 °C resulted in formation of crystalline pollucite (CsAlSi 2 O 6 ). PDF refinement of the pollucite phase formed displayed an excellent fit over the 10-30 Å range when compared with a cubic pollucite model. A poorer fit was attained from 1-10 Å due to an additional amorphous phase present in the heated geopolymer. On the basis of PDF analysis, unheated Cs-geopolymer displayed structural ordering similar to pollucite up to a length scale of ∼9 Å, despite some differences. Our results suggest that hydrated Cs + ions were an integral part of the Cs-geopolymer structure and that most of the water present was not associated with Al-OH or Si-OH bonds.

The atomic structure of geopolymers is often described as amorphous with a local structure that is equivalent to that of crystalline zeolites. However, this structural relationship has never been quantified beyond a first-nearest-neighbor bonding environment. In this study, the short to medium range ($1 nm) structural order of metakaolin-based KAlSi 2 O 6 $5.5H 2 O geopolymer was quantified and compared to zeolitic tetragonal leucite (KAlSi 2 O 6 ) using the X-ray atomic pair distribution function technique. Unheated KAlSi 2 O 6 $5.5H 2 O was found to be structurally similar to leucite out to a length of $8 A ˚, but had increased medium range disorder over the 4.5 A ˚< r < 8 A ˚range. On heating to >300 C, changes in the short to medium range structure were observed due to dehydration and removal of chemically bound water. Crystallization of leucite occurred in samples heated beyond 1050 C. Refinements of a leucite model against the PDF data for geopolymer heated to 1100 C for 24 h yielded a good fit.

The thermal expansion of a low symmetry crystal can be much more interesting than the lattice parameter expansion would suggest. Here, the complete thermal expansion tensors for monoclinic and tetragonal phases of ZrO 2 and HfO 2 have been measured in air, by high-resolution, high-temperature X-ray diffraction. These results reveal the highly anisotropic nature of thermal expansion in the monoclinic phase as well as a cooperative movement of ions and the existence of a zero thermal expansion plane.

W e present the results of an experiment comparing two popular methods for encoding probability distributions of continuous variables in decision analysis: eliciting values of a variable, X, through comparisons with a fixed probability wheel and eliciting the percentiles of the cumulative distribution, F X , through comparisons with fixed values of the variable. We show slight but consistent superiority for the fixed variable method along several dimensions such as monotonicity, accuracy, and precision of the estimated fractiles. The fixed variable elicitation method was also slightly faster and preferred by most participants. We discuss the reasons for its superiority and conclude with several recommendations for the practice of probability assessment.