Segmentation effect on inhomogeneity of [110]-single crystal deformation

This work presents a detailed analysis of segmentation process in FCC single crystals with compression axis [110] and side faces( ̅110) and (001) considering effect of octahedral shear crystal-geometry and basic stress concentrators. Sequence of meso-band systems formation on side faces is determined. Macro-segmentation patterns are specified, that are common to the FCC single crystals under investigation. It is proved that rectangular shape of highly compressed crystals, elongated in direction of operating planes, is conditioned by orientation symmetry of compression axis, single crystal side faces and shears directions, which are characteristic for the given orientation. The specified patterns are characteristic only for the samples with initial height-to-width ratio equal to 2. When varying sample height relative to the initial one, segmentation patterns will also vary due to crystal geometry variations

Controlled ultraviolet (UV) photoinitiated fabrication of monolithic porous layer open tubular (monoPLOT) capillary columns for chromatographic applications

An automated column fabrication technique that is based on a ultraviolet (UV) light-emitting diode (LED) array oven, and provides precisely controlled "in-capillary" ultraviolet (UV) initiated polymerization at 365 nm, is presented for the production of open tubular monolithic porous polymer layer capillary (monoPLOT) columns of varying length, inner diameter (ID), and porous layer thickness. The developed approach allows the preparation of columns of varying length, because of an automated capillary delivery approach, with precisely controlled and uniform layer thickness and monolith morphology, from controlled UV power and exposure time. The relationships between direct exposure times, intensity, and layer thickness were determined, as were the effects of capillary delivery rate (indirect exposure rate), and multiple exposures on the layer thickness and axial distribution. Layer thickness measurements were taken by scanning electron microscopy (SEM), with the longitudinal homogeneity of the stationary phase confirmed using scanning capacitively coupled contactless conductivity detection (sC(4)D). The new automated UV polymerization technique presented in this work allows the fabrication of monoPLOT columns with a very high column-to-column production reproducibility, displaying a longitudinal phase thickness variation within ±0.8% RSD (relative standard deviation)

Hydrophobicity of polymer based anion-exchange columns for ion chromatography

The regularities of the retention of alkanoic and alkanesulfonic acids homologues were investigated for the set of 36 anion-exchange columns produced by various manufacturers. The role of hydrophobic and electrostatic interactions in the retention and separation of organic anions was studied. The methylene selectivity increments α(CH2) were measured for the studied columns with 10 mM sodium hydroxide eluent. The influence of matrix, surface area, polar group structure, ion-exchange capacity, the density of charged functional groups on the surface and other characteristics of anion-exchangers on resin hydrophobicity was considered.A unified approach for the measurements of hydrophobic properties of anion-exchange resins is proposed and the ratio of chloride retention factor (kCl) to α(CH2) was introduced as mixed-mode factor. The synergetic effect of electrostatic and hydrophobic interactions was observed

Preparation and properties of porous graphitic carbon monoliths embedded with nanodiamonds and other temperature-induced nano carbons

Porous graphitised carbon monoliths embedded with nanodiamonds (CMND) are presented in this work. Nanodiamond (ND) (sp3 carbon) has a variety of favourable properties including an interesting and tuneable surface chemistry, mechanical and thermal stability and conductivity. CMND was prepared using a hard templating method. Bare 5 μm silica particles and nanodiamonds (5-15 nm diameter) were added to the co-polymerisation mixture containing a resorcinol/iron(III) complex. Polymerisation of this mixture was followed by carbonisation at either 900 or 1250 °C under N2. Removal of the silica template and catalyst was achieved by hydrofluoric acid etching. A blank carbon monolith (CM blank) was also prepared using bare silica templates for comparative purposes. BET surface area measurements showed CMND to have a higher specific surface area than CM blank (400 m2/g and 349 m2/g respectively, with carbonisation at 900 °C). HRTEM and FESEM characterisation of CMND revealed a variety of interesting carbon nanostructures to be present in the monolith following carbonisation at 1250 °C. Apparent onion-like carbon (OLC), carbon nano-rods up to several μm in length and graphene sheets were observed. OLC clusters can be produced by a temperature-induced transformation of ND. The temperature of carbonisation was critical in the formation of these carbon nano-structures, as were the localised heating effects resulting from the thermal conductivity of ND. Carbon nano-structures have high surface areas and a high sorption capacity making them suitable for a variety of prospective applications. Porous graphitic carbons are also receiving significant research interest due to their high surface areas and bimodal pore structure which make them ideal for use in a variety of applications including energy storage, as electrode materials or as adsorbents in solid phase extraction

Segmentation effect on inhomogeneity of [110]-single crystal deformation

This work presents a detailed analysis of segmentation process in FCC single crystals with compression axis [110] and side faces( ̅110) and (001) considering effect of octahedral shear crystal-geometry and basic stress concentrators. Sequence of meso-band systems formation on side faces is determined. Macro-segmentation patterns are specified, that are common to the FCC single crystals under investigation. It is proved that rectangular shape of highly compressed crystals, elongated in direction of operating planes, is conditioned by orientation symmetry of compression axis, single crystal side faces and shears directions, which are characteristic for the given orientation. The specified patterns are characteristic only for the samples with initial height-to-width ratio equal to 2. When varying sample height relative to the initial one, segmentation patterns will also vary due to crystal geometry variations

Porous graphitized carbon monolith as an electrode material for probing direct bioelectrochemistry and selective detection of hydrogen peroxide

For the first time, graphitized carbon particles with a high surface area have been prepared and evaluated as a new material for probing direct electrochemistry of hemoglobin (Hb). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging revealed that the carbon monolithic skeleton was constructed by a series of mesopores with irregular shapes and an average pore diameter of 5.6 nm. With a surface area of 239.6 m2/g, carbon particles exhibited three major Raman peaks as commonly observed for carbon nanotubes and other carbon materials, i.e., the sp3 and sp2 carbon phases coexisted in the sample. A glassy carbon electrode modified with carbon monoliths and didodecyldimethylammonium bromide exhibited direct electron transfer between Hb molecules and the underlying electrode with a transfer rate constant of 6.87 s\u20131. The enzyme electrode displayed a pair of quasi-reversible reduction\u2013oxidation peaks at 120.128 and 120.180 V, reflecting the well-known feature of the heme [Fe3+/Fe2+] redox couple: a surface-controlled electrochemical process with one electron transfer. This reagentless biosensing approach was capable of detecting H2O2, a simple molecule but plays an important role in analytical and biological chemistry, as low as 0.1 \u3bcM with linearity of 0.1\u201360 \u3bcM and a response time of <0.8 s, comparing favorably with other carbon based electrodes (5 s).Peer reviewed: YesNRC publication: Ye