Central yielding, as well as peripheral slip, was observed in curved epitaxial silicon slices produced in the laboratory. The central plastic deformation is the result of compressive stresses set up by the entrapment of a hot central region within a colder annular zone. A stress analysis was performed which explains the occurrence and relative intensities of slip in the two regions by reference to the distortion energy densities throughout the slice. A model of the centrally localized plastic deformation in {HI} slices was presented in which the (110) slip vectors inclined to the {HI} surface are activated and produce relief of the central compressive stresses by vertical movements of pyramidal sections of the crystal.[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP: 131.94.

Guar gum (GG), along with its derivatives [e.g., hydroxypropyl guar (HPG)], is an important thickening agent in the hydraulic fracturing fluid system. However, as the oil reservoir gets deeper, GG is unable to tolerate the elevated temperature. In this study, the thermal stability of GG and HPG can be increased up to 95% and 80%, respectively, when phosphates are used as thermal stabilizer. The thermal stability is highest when the usage of phosphate is 1.84 mmol L −1 KH 2 PO 4 for GG and 2.27 mmol L −1 K 2 HPO 4 for HPG and the pH is 6.25-6.90 for GG and 6.25-8.75 for HPG. Furthermore, the heated GG with phosphate treatment demonstrates excellent crosslinking ability, which suggests that phosphate can be a good alternative for current thermal stabilizers and has potential application in the high-temperature formation oil or gas production.

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