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Chemical Attack (chemical + attack)
Selected AbstractsKinetics of the thermal decomposition of bis(trifluoromethyl) peroxydicarbonate, CF3OC(O)OOC(O)OCF3INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2003Maximiliano A. Burgos Paci Thermal decomposition of bis(trifluoromethyl) peroxydicarbonate has been studied. The mechanism of decomposition is a simple bond fission, homogeneous first-order process when the reaction is carried out in the presence of inert gases such as N2 or CO. An activation energy of 28.5 kcal mol,1 was determined for the temperature range of 50,90°C. Decomposition is accelerated by nitric oxide because of a chemical attack on the peroxide forming substances different from those formed with N2 or CO. An interpretation on the influence of the substituents in different peroxides on the OO bond is given. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 15,19, 2003 [source] A study of the recycling and stability of flexographic photopolymer platesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Cristina C. Cordeiro Abstract Flexographic photopolymer plates have a wide range of commercial applications despite the fact that recycling of such materials is difficult. In consequence, there is a large bulk of leftover material around the world. In this research, the photopolymer plate waste products, identified as styrene-butadiene rubber (SBR)/polyester are blended into common polypropylene (PP) and ethylenevinylacetate (EVA) resins at different loading percentages. PP and EVA are used as the polymer matrix and the recovered styrene-butadiene rubber (SBR) material as the filler. Evaluation of the mechanical, spectroscopic, thermal and chemical properties, as well as morphology, is done by means of scanning electron microscopy (SEM). Mechanical results show that elongation strongly depends on the matrix polymer: the greater the amount of solid-sheet photopolymer (SSP), the smaller the elongation. No specific interactions were detected; however, thermal degradation and transitions were displaced, suggesting some miscibility. More homogeneity is seen for EVA blends, with no significant chemical attack detected. It is possible to reuse these recycled materials in blends with PP and EVA resins. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Chemical Agent Simulant Release from Clothing Following Vapor ExposureACADEMIC EMERGENCY MEDICINE, Issue 2 2010Robert J. Feldman MD ACADEMIC EMERGENCY MEDICINE 2010; 17:1,4 © 2010 by the Society for Academic Emergency Medicine Abstract Objectives:, Most ambulatory victims of a terrorist chemical attack will have exposure to vapor only. The study objective was to measure the duration of chemical vapor release from various types of clothing. Methods:, A chemical agent was simulated using methyl salicylate (MeS), which has similar physical properties to sulfur mustard and was the agent used in the U.S. Army's Man-In-Simulant Test (MIST). Vapor concentration was measured with a Smiths Detection Advanced Portable Detector (APD)-2000 unit. The clothing items were exposed to vapor for 1 hour in a sealed cabinet; vapor concentration was measured at the start and end of each exposure. Clothing was then removed and assessed every 5 minutes with the APD-2000, using a uniform sweep pattern, until readings remained 0. Results:, Concentration and duration of vapor release from clothing varied with clothing composition and construction. Lightweight cotton shirts and jeans had the least trapped vapor; down outerwear, the most. Vapor concentration near the clothing often increased for several minutes after the clothing was removed from the contaminated environment. Compression of thick outerwear released additional vapor. Mean times to reach 0 ranged from 7 minutes for jeans to 42 minutes for down jackets. Conclusions:, This simulation model of chemical vapor release demonstrates persistent presence of simulant vapor over time. This implies that chemical vapor may be released from the victims' clothing after they are evacuated from the site of exposure, resulting in additional exposure of victims and emergency responders. Insulated outerwear can release additional vapor when handled. If a patient has just moved to a vapor screening point, immediate assessment before additional vapor can be released from the clothing can lead to a false-negative assessment of contamination. [source] Corrosion of Ceramics in Aqueous Hydrofluoric AcidJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2000Kurt R. Mikeska A variety of commercially available ceramic-based oxides, carbides, nitrides, and borides were evaluated for chemical attack in an azeotropic aqueous hydrofluoric acid (HF) test protocol at 90°C. Weight change measurements and microstructure analysis showed that HF corrosion in polycrystalline ceramics generally occurred at grain boundaries by the dissolution of grain boundary phases although the bulk single crystal may inherently resist attack. Virtually all commercially prepared polycrystalline oxide ceramics (i.e., Al2O3, TiO2, ZrO2) and nonoxide ceramics (i.e., Si3N4, AlN, BN) were extensively corroded while polycrystalline pure carbides (i.e., SiC, TiC, B4C, WC) resisted corrosion. Equilibrium thermodynamic calculations show that these materials are soluble in HF; however, the kinetics of dissolution are slow enough in some cases to permit useful engineering lifetimes. [source] Isomeric Squaraine-Based [2]Pseudorotaxanes and [2]Rotaxanes: Synthesis, Optical Properties, and Their Tubular Structures in the Solid StateCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2010Min Xue Abstract On the basis of formation of [2]pseudorotaxane complexes between triptycene-derived tetralactam macrocycles 1,a and 1,b and squaraine dyes, construction of squaraine-based [2]rotaxanes through clipping reactions were studied in detail. As a result, when two symmetrical squaraines 2,d and 2,e were utilized as templates, two pairs of isomeric [2]rotaxanes 3,a,b and 4,a,b as diastereomers were obtained, owing to the two possible linking modes of triptycene derivatives. It was also found, interestingly, that when a nonsymmetrical dye 2,g was involved, there existed simultaneously three isomers of [2]rotaxanes in one reaction due to the different directions of the guest threading. The 1H,NMR and 2D NOESY NMR spectra were used to distinguish the isomers, and the yield of [2]rotaxane 5,a with the benzyl group in the wider rim of the host 1,a was found to be higher than that of another isomer 5,b with an opposite direction of the guest, which indicated the partial selection of the threading direction. The X-ray structures of 3,b and 4,a showed that, except for the standard hydrogen bonds between the amide protons of the hosts and the carbonyl oxygen atoms of the guests, multiple ,,,,, stacking and CH,,,, interactions between triptycene subunits and aromatic rings of the guests also participated in the complexation. Crystallographic studies also revealed that the [2]rotaxane molecules 3,b and 4,a further self-assembled into tubular structures in the solid state with the squaraine dyes inside the channels. In the case of 4,a, all the nonsymmetrical macrocyclic molecules pointed in one direction, which suggests the formation of oriented tubular structures. Moreover, it was also found that the squaraines encapsulated in the triptycene-derived macrocycles were protected from chemical attack, and subsequently have potential applications in imaging probes and other biomedical areas. [source] Shielding Nanowires and Nanotubes with Imogolite: A Route to NanocablesADVANCED MATERIALS, Issue 43 2009Agnieszka Kuc The use of an imogolite (aluminosilicate) sheath to protect a conducting core consisting of a carbon nanotube (CNT) or nanowire from mechanical and chemical attacks is proposed. The cross-sectional structure of such a nanocable is shown in the figure. The most stable CNT@ imogolite nanocable is calculated to have a tube,tube distance of 2.8,Å and an insertion energy of ca. 60,meV per carbon atom. [source] Subcritical crack growth behavior of Al2O3 -glass dental compositesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2003Qingshan Zhu Abstract The purpose of this study is to investigate the subcritical crack growth (SCG) behavior of alumina-glass dental composites. Alumina-glass composites were fabricated by infiltrating molten glass to porous alumina preforms. Rectangular bars of the composite were subject to dynamic loading in air, with stressing rates ranging from 0.01 MPa/s to 2 MPa/s. The SCG parameter n was determined to be 22.1 for the composite, which is substantially lower than those of high-purity dense alumina. Investigations showed that glass phases are responsible for the low n value as cracks propagate preferentially within glass phases or along the interface between glass phases and alumina phases, due to the fact that glasses are more vulnerable to chemical attacks by water molecules under stress corrosion conditions. The SCG behavior of the infiltration glass was also investigated and the SCG parameter n was determined to be 18.7. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 65B: 233,238, 2003 [source] Structural, Mechanical, and Reactivity Properties of Tricalcium Aluminate Using First-Principles CalculationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2009Hegoi Manzano Although tricalcium aluminate (C3A) is one of the most important components of Portland cement, neither its reactivity nor its elastic moduli tensor have been fully determined yet. This work aims to shed some insights on these questions by means of ab-initio simulations. First our simulations have reproduced the details of its crystalline structure. Second, we have computed the full elastic moduli tensor of C3A, where we found that our value for the Young modulus (E=138.7 GPa) is in agreement with the values obtained by nanoindentation measurements. Finally, we have identified which atoms and sites are more suitable to suffer chemical attacks. [source] | |||||||||||||