DRIFTS/MS/Isotopic Labeling Study on the NO-Moderated Decomposition of a Silica-Supported Nickel Nitrate Catalyst Precursor

In the preparation of silica-supported nickel oxide from nickel nitrate impregnation and drying, the replacement of the traditional air calcination step by a thermal treatment in 1% NO/Ar prevents agglomeration, resulting in highly dispersed NiO. The mechanism by which NO prevents agglomeration was investigated by using combined in situ diffuse reflectance infrared fourier transform (DRIFT) spectroscopy and mass spectrometry (MS). After impregnation and drying, a supported nickel hydroxynitrate phase with composition Ni(3)(NO(3))(2)(OH)(4) had been formed. Comparison of the evolution of the decomposition gases during the thermal decomposition of Ni(3)(NO(3))(2)(OH)(4) in labeled and unlabeled NO and O(2) revealed that NO scavenges oxygen radicals, forming NO(2). The DRIFT spectra revealed that the surface speciation evolved differently in the presence of NO as compared with in O(2) or Ar. It is proposed that oxygen scavenging by NO depletes the Ni(3)(NO(3))(2)(OH)(4) phase of nitrate groups, creating nucleation sites for the formation of NiO, which leads to very small (similar to 4 nm) NiO particles and prevents agglomeration.

Microstructure, mechanical properties and fractography of heat-treated manganese steel

A Fe-8.46%Mn-0.24%Nb-0.038%C (wt.%) manganese steel was investigated. The steel has a 100% bcc structure after heat treatment at 850°C for 1.5 h, water quenching or air cooling. Martensite interlocked microstructure consisting of fine martensite plates/needles with different spatial orientations was found. Austenite forms, in small amounts, after a 600°C reheating treatment. Scanning electron microscopy images and energy dispersive spectrometry of the fracture surfaces revealed both ductile and brittle types of failure and precipitates. Deep quenching after the heat treatments does not change the phase composition or the hardness. NbC is formed in the steel, in high number densities. It plays a role in the impact fracture process, by acting as void nucleation sites, facilitating ductile fracture with dimples appearing on the fracture surface.

Melt Processing and Properties of Polyamide 6/Graphene Nanoplatelet Composites

Graphene, due to its outstanding properties, has become the topic of much research activity in recent years. Much of that work has been on a laboratory scale however, if we are to introduce graphene into real product applications it is necessary to examine how the material behaves under industrial processing conditions. In this paper the melt processing of polyamide 6/graphene nanoplatelet composites via twin screw extrusion is investigated and structure–property relationships are examined for mechanical and electrical properties. Graphene nanoplatelets (GNPs) with two aspect ratios (700 and 1000) were used in order to examine the influence of particle dimensions on composite properties. It was found that the introduction of GNPs had a nucleating effect on polyamide 6 (PA6) crystallization and substantially increased crystallinity by up to 120% for a 20% loading in PA6. A small increase in crystallinity was observed when extruder screw speed increased from 50 rpm to 200 rpm which could be attributed to better dispersion and more nucleation sites for crystallization. A maximum enhancement of 412% in Young's modulus was achieved at 20 wt% loading of GNPs. This is the highest reported enhancement in modulus achieved to date for a melt mixed thermoplastic/GNPs composite. A further result of importance here is that the modulus continued to increase as the loading of GNPs increased even at 20 wt% loading and results are in excellent agreement with theoretical predictions for modulus enhancement. Electrical percolation was achieved between 10–15 wt% loading for both aspect ratios of GNPs with an increase in conductivity of approximately 6 orders of magnitude compared to the unfilled PA6.

Fate of organo-mineral particles in streams: Microbial degradation by streamwater & biofilm assemblages

Inland waters are of global biogeochemical importance. They receive carbon inputs of ~ 4.8 Pg C/ y of which, 12 % is buried, 18 % transported to the oceans, and 70 % supports aquatic secondary production. However, the mechanisms that determine the fate of organic matter (OM) in these systems are poorly defined. One aspect of this is the formation of organo-mineral complexes in aquatic systems and their potential as a route for OM transport and burial vs. their use as carbon (C) and nitrogen (N) sources within aquatic systems. Organo-mineral particles form by sorption of dissolved OM to freshly eroded mineral surfaces and may contribute to ecosystem-scale particulate OM fluxes. We experimentally tested the availability of mineral-sorbed OM as a C & N source for streamwater microbial assemblages and streambed biofilms. Organo-mineral particles were constructed in vitro by sorption of ¹³C:¹⁵N-labelled amino acids to hydrated kaolin particles, and microbial degradation of these particles compared with equivalent doses of ¹³C:¹⁵N-labelled free amino acids. Experiments were conducted in 120 ml mesocosms over 7 days using biofilms and water sampled from the Oberer Seebach stream (Austria). Each incubation experienced a 16:8 light:dark regime, with metabolism monitored via changes in oxygen concentrations between photoperiods. The relative fate of the organo-mineral particles was quantified by tracing the mineralization of the ¹³C and ¹⁵N labels and their incorporation into microbial biomass. Here we present the initial results of ¹³C-label mineralization, incorporation and retention within dissolved organic carbon pool. The results indicate that 514 (± 219) μmol/ mmol of the ¹³:¹⁵N labeled free amino acids were mineralized over the 7-day incubations. By contrast, 186 (± 97) μmol/ mmol of the mineral-sorbed amino acids were mineralized over a similar period. Thus, organo-mineral complexation reduced amino acid mineralization by ~ 60 %, with no differences observed between the streamwater and biofilm assemblages. Throughout the incubations, biofilms were observed to leach dissolved organic carbon (DOC). However, within the streamwater assemblage the presence of both organo-mineral particles and kaolin particles was associated with significant DOC removal (-1.7 % and -7.5 % respectively). Consequently, the study demonstrates that mineral and organo-mineral particles can limit the availability of DOC in aquatic systems, providing nucleation sites for flocculation and fresh mineral surfaces, which facilitate OM-sorption. The formation of these organo-mineral particles subsequently restricts microbial OM degradation, potentially altering the transport and facilitating the burial of OM within streams.