Degradation of Nextel™ 610‐based oxide‐oxide ceramic composites by aluminum oxychloride decomposition products

Nextel? 610 alumina fibers and alumina‐YAG (yttrium‐aluminum garnet) matrices were used to make oxide‐oxide ceramic matrix composites (CMCs) with and without monazite (LaPO₄) fiber‐matrix interfaces. Twelve sequential aluminum oxychloride (AlOCl) infiltrations with 1 hour heat treatments at 1100°C and a final 1 hour heat treatment at 1200°C were used for matrix densification. This matrix processing sequence severely degraded CMC mechanical properties. CMC tensile strengths and interlaminar tensile (ILT) strengths were less than 10 MPa and 1 MPa, respectively. Axial fracture of Nextel? 610 fibers was observed after ILT testing, highlighting the extreme degradation of fiber strength. Extensive characterization was done to attempt to determine the responsible degradation mechanisms. Changes in Nextel? 610 fiber microstructure after CMC processing were characterized by optical microscopy, SEM, and extensively by TEM. In AlOCl degraded fibers, grain boundaries near the fiber surface were wetted with a glass that contained Y₂O₃/SiO₂ or Y₂O₃/La₂O₃/P₂O₅/SiO₂, and near‐surface pores were partially filled with Al₂O₃. This glass must also contain some Al₂O₃ and initially some chlorine. AlOCl decomposition products were predicted using the FactSage^® Thermochemical code, and were characterized by mass spectrometry. Effects of AlOCl precursors on monazite coated and uncoated Nextel? 610 fibers tow and filament strength were evaluated. A mechanism for the severe degradation of the oxide‐oxide CMCs and Nextel? 610 fibers that involves subcritical crack growth promoted by release of chlorine containing species during breakdown of intergranular glasses in an anhydrous environment is proposed.     

Precipitation Coating of Rare-Earth Orthophosphates on Woven Ceramic Fibers—Effect of Rare-Earth Cation on Coating Morphology and Coated Fiber Strength

Monazite (La, Ce, Nd, and GdPO₄) and xenotime (Tb, Dy, and YPO₄) coatings were deposited on woven Nextel^™ 610 and 720 fibers by heterogeneous precipitation from a rare-earth citrate/phosphoric acid precursor. Coating phases and microstructure were characterized by SEM and TEM, and coated fiber strength was measured after heat treatment at 1200°C for 2 h. Coated fiber strength increased with decreasing ionic radius of the rare-earth cation in the monazite and xenotime coatings, and correlates with the high-temperature weight loss and the densification rate of the coatings. Dense coatings with trapped porosity and high weight loss at a high temperature degrade fiber strength the most. The degradation is consistent with stress corrosion driven by thermal residual stress from coating precursor decomposition products trapped in the coating at a high temperature.     

Roles of Social Pain and Defense Mechanisms in Response to Social Exclusion: Reply to Panksepp (2005) and Corr (2005).

In comments on G. MacDonald and M. R. Leary (2005), J. Panksepp (2005) (see record 2005-01973-005) argued for more emphasis on social pain mechanisms, whereas P. J. Corr (2005) (see record 2005-01973-006) argued for more emphasis on physical defense mechanisms. In response to the former, the authors clarify their positions on the topics of anger, the usefulness of rat models, the role of analgesic mechanisms, and basic motivational processes. In response to the latter, the authors clarify their positions on the topics of the relation of social exclusion to fear, the value of the pain affect construct, and the nature of the social pain experience. The authors conclude that consideration of the roles of both social pain and defense mechanisms is essential to best understand human response to social exclusion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Age and sex differences in reaction time in adulthood: Results from the United Kingdom Health and Lifestyle Survey": Correction.

Reports an error in "Age and sex differences in reaction time in adulthood: Results from the United Kingdom Health and Lifestyle Survey" by Geoff Der and Ian J. Deary (Psychology and Aging, 2006[Mar], Vol 21[1], 62-73). In the article, the link to supplemental material is incorrect. The correct supplemental link follows. Supplemental materials are available online at http://dx.doi.org/10.1037/0882-7974.21.1.62.supp. (The following abstract of the original article appeared in record 2006-03906-007.) Reaction times (RTs) slow and become more variable with age. Research samples are typically small, biased, and of restricted age range. Consequently, little is known about the precise pattern of change, whereas evidence for sex differences is equivocal. The authors reanalyzed data for 7,130 adult participants in the United Kingdom Health and Lifestyle Survey, originally reported by F. A. Huppert (1987). The authors modeled the age differences in simple and 4-choice reaction time means and variabilities and tested for sex differences. Simple RT shows little slowing until around 50, whereas choice RT slows throughout the adult age range. The aging of choice RT variability is a function of its mean and the error rate. There are significant sex differences, most notably for choice RT variability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)