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It has been reported that the presence of a smear layer on dentinal substrates can compromise bonding. Typically, smear layers are removed by acidic agents that selectively extract calcium salts from dentin surfaces to leave a collagen-rich substrate. Acid-conditioned dentin (i.e., demineralized) is then primed and an adhesive agent applied. In the present study, we removed smear layers by "polishing" dentin specimens with a hydroxyapatite paste and ultrasonication. Bonding procedures were carried out by means of an aqueous solution of 20% 2-methacryloyloxyethyl phenyl phosphoric acid (phenyl-P) and 30% 2-hydroxyethyl methacrylate, referred to as 2OP-30H, a "self-etching primer". The 20P-30H solution was applied to "intact" dentin (i.e., non-demineralized) for either 30 or 60 s. Control samples received no application (O s) of the self-etching primer. Mean tensile bond strengths (10 MPa) were similar in both the 30-second- and 60-second-primed groups. The widths of formed hybrid layers varied from 0.3 +/- 0.2 micron at O s application (control) to 2.1 +/- 0.3 micron for the 30-second group and 4.1 +/- 0.2 micron for the 60-second group. SEM and TEM observations revealed that the 20P-30H self-etching primer created diffusion channels into "intact" calcium-rich dentin which permitted monomer to infiltrate dentin substrates. Hybrid layers identified under microscopic examination demonstrated resistance to both HCI and NaOCI treatments, suggesting that the hybrid layer was not defective, and that bonding was stable.
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PMID:Bonding to intact dentin. 895 25

Monochlorobenzene (MCB), dichlorobenzenes (DCBs), and 1,2,4-trichlorobenzene (124TCB) dechlorination experiments in water were carried out with freshly synthesized Pd/Fe particles. The pre- and postreacted Pd/Fe samples were characterized by applying various analytical techniques (XRD, SEM, TEM, and XPS). Chlorinated benzenes could be completely reduced by the Pd/Fe to benzene and the reaction followed the pseudo-first-order kinetics. The reaction rates followed the order TCB < DCBs < MCB, while among the DCBs the order was 1,4-dichlorobenzene >1,3-dichlorobenzene > or = 1,2-dichlorobenzene. Insignificant reactions were observed with the unpalladized iron, suggesting that Pd was the only reactive site in the Pd/Fe particles. The aged Pd/Fe particles exhibited significant decrease in its dechlorination reactivity. The loss of Pd/Fe reactivity could be due to Pd dislodgment from the aged Pd/Fe particles and Pd islets encapsulation by the iron oxides film developed over aging period. Reactivity of the aged Pd/Fe could be only partially restored after HCI treatment, while regeneration with the NaBH4 reduction method could not restore its activity, although zerovalent state of the iron was reinstated.
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PMID:Catalytic reduction of chlorobenzenes with Pd/Fe nanoparticles: reactive sites, catalyst stability, particle aging, and regeneration. 1804 36

A comparison of different purification procedures for single walled carbon nanotubes (SWCNTs) synthesized by laser-vapourization has been presented. The methods involved gas-phase oxidation by calcination, liquid-phase oxidation by H2O2, hydrothermal treatment and acid refluxing in HCI. Sample purity is documented with Raman spectroscopy, Transmission electron microscopy, Scanning electron microscopy and thermogravimetric analysis. Multi-spot analyses were done to check the homogeneity of the purified samples. Different purification processes produced SWCNT material with purity in the range of 48-78%. Raman and TEM results suggested that prolonged calcination results in selective etching of larger diameter nanotubes. SEM and TGA analyses showed increase in density of SWCNTs with better oxidation resistance after purification.
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PMID:Purification of laser synthesized SWCNTs by different methods: a comparative study. 1919 41