Investigation of the morphological changes promoted by heating of Si–C–O ceramics derived from a phenyl-rich hybrid polymer. Effect of Ni in the polymeric precursor

This study focuses on the structural and morphological changes promoted by heating of silicon oxycarbide ceramics obtained from hybrid polymeric precursors based on poly(methylsiloxane) and divinylbenzene, with or without nickel acetate, by pyrolysis under Ar at different temperatures. The increase of the temperature from 950 to 1500 °C promoted the densification and crystallization of SiC and graphite nanodomains in the ceramic bulk with or without Ni, as identified by HRTEM. Moreover, the Ni-containing precursor led to the formation of ultra-long amorphous nanowires on the surface and voids in the ceramic body obtained at 1500 °C. These nanowires presented different sizes and morphologies, but similar compositions, basically composed by silicon and oxygen, with the presence of carbon at their external layers. The growth mechanism and the nature of the nanowires are also proposed. The addition of nickel acetate in the polymeric precursor induced the formation of nanowires with different morphologies in the Si–O–C system.     

Arsenical grafted membranes for immobilization of thioredoxin-like proteins

In this work, we describe the cografting of glycidyl methacrylate and dimethyl acrylamide onto a macroporous polysulfone polymer. Aminophenyl arsenical compounds were covalently attached to the copolymer through epoxy ring add-on reactions followed by a 2-mercaptoethanol activation. Thioredoxin and thioredoxin-fusion proteins were immobilized onto this surface and detected by specific antibody recognition. Preservation of native protein folding was confirmed by the detection of the enzymatic activity of an unstable fusion protein. Immobilized fusion protein onto the modified material maintains the enzymatic activity for a longer time, up to two weeks, against the free protein under the same storage conditions that remains active for 2 days.     

Polyurethane networks from formiated soy polyols: Synthesis and mechanical characterization

Polyurethanes can be prepared using polyols obtained from vegetable oils in natura, such as castor oil, or from functionalized vegetable oils, such as hydroxylated soybean oil. These polyurethanes have different valuable properties, determined by their chemical composition and cross-linking density. In this study, soy epoxy polyols with different OH contents were prepared through a one-step reaction using the method of in situ performic acid generation. Polyols with OH functionalities from 1.9 to 3.2 were reacted in bulk with different diisocyanates at a NCO/OH molar ratio of 0.8 and 60°C for 24 h. Mechanical properties of the polyurethanes were determined by dynamic mechanical thermal analysis, hardness (Shore A), and swelling measurements. Polymer networks with glass-transition temperatures (T _g ) from −13 to 48°C were obtained. We observed that the higher the OH functionality of the polyols, the higher the T _g and cross-linking density of the polyurethane network. The influence of diisocyanate structure (rigid or flexible chain), curing temperature, and curing reaction time on mechanical properties was also investigated.     

Preparation,alumina-pillaring and oxidation catalytic performances of synthetic Ni-saponite

Synthetic saponite containing Ni²⁺ as octahedral cations has been prepared by a simple hydrothermal procedure, and has been intercalated with Al₁₃-polycations. The catalytic performance of the pillared solids in the epoxidation of (Z)-cyclooctene and the oxidation of cyclohexanone in the presence of benzonitrile, Baeyer–Villiger reaction, using hydrogen peroxide (70%) as a clean oxidant have been studied. For comparison, Mg-saponite was synthesized under the same conditions and tested for the same reaction.     

Lipase-catalyzed synthesis of poly-l-lactide using supercritical carbon dioxide

The present work shows that the enzyme mediated ring-opening polymerization of l-lactide at 65 °C can be achieved using supercritical carbon dioxide. It is reported a biphasic media system where the supercritical phase coexists with a liquid organic phase, which is mainly composed of melted monomer, wherein the growing poly-l-lactide chains are soluble. The immobilized lipase B from Candida antartica was used as the biocatalyst. The results indicated that semi-crystalline polymers with a molecular weight (M_w) up to 12,900 g mol⁻¹ can be attained and that the monomer conversion is related to the biocatalyst concentration and its initial water activity (a_wi). Experiments carried out with denatured enzyme gave no monomer conversion which confirms that the enzymatic mechanism is only involved in our system.     

Ultrafine grinding of sugar cane bagasse ash for application as pozzolanic admixture in concrete

Sugar cane bagasse ash, a byproduct of sugar and alcohol production, is a potential pozzolanic material. However, its effective application in mortar and concrete requires first the controlled use of grinding and classification processes to allow it to achieve the fineness and homogeneity that are required to meet industry standards. The present paper investigates the role of mill type and grinding circuit configuration in grinding in laboratory- and pilot plant-scale on the particle size, specific surface area and pozzolanic activity of the produced ashes. It was observed that, although different size distributions were produced by the different mills and milling configurations, the pozzolanic activity of the ground ash was directly correlated to its fineness, characterized by its 80% passing size or Blaine specific surface area. From a low pozzolanic activity of less than 50% of the as-received ash, values above 100% could be reached after prolonged grinding times. Electric power requirements to reach the minimum pozzolanic activity were estimated to be in the order of 42 kWh/t in an industrial ball mill. Incorporation of an ultrafinely-ground ash in a high-performance concrete in partial replacement of Portland cement (10, 15 and 20% by mass) resulted in no measurable change in mechanical behavior, but improved rheology and resistance to penetration of chloride ions.     

Thermal polymerization of styrene in the presence of TEMPO

To investigate aspects of the contribution of (thermal) self-initiation in nitroxide-mediated radical polymerization (NMRP) of styrene, selective styrene polymerizations with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in the absence of initiator were carried out at 120 and 130 °C. The results of these experiments (including conversion data, molecular weight averages, polydispersity and molecular weight distribution information) were compared with regular thermal polymerization of styrene and NMRP of styrene in the presence of a bimolecular initiator (benzoyl peroxide; BPO). It was observed that although the thermal polymerization of styrene can be controlled to some extent in the presence of TEMPO to provide polystyrene with low polydispersity, the polymerization was never as controlled as that obtained by a BPO-initiated NMRP.     

Catalytic behavior of hybrid Co/SiO2-(medium-pore) zeolite catalysts during the one-stage conversion of syngas to gasoline

The catalytic properties of 10-MR (membered ring) zeolites (ZSM-5, MCM-22, IM-5, ITQ-2, all with a similar Si/Al ratio of ca. 15) in hybrid Co/SiO₂-zeolite catalysts for the direct conversion of syngas to mainly high-octane gasoline-range hydrocarbons has been studied under typical Fischer-Tropsch (FT) conditions: 250 °C, 2.0 MPa, and H₂/CO = 2. Special emphasis has been given to the deactivation behavior and the characterization of the amount and nature of the carbonaceous deposits formed by a combination of techniques (elemental analysis, TGA (thermogravimetric analyses), GC–MS, and DR (diffuse reflectance) UV–vis spectroscopy). The presence of the medium-pore zeolite increases the gasoline yield by about 20–50%, depending on the particular zeolite, and enhances the formation of branched products with respect to the base Co/SiO₂ catalyst, which is explained by the promotion of isomerization and cracking of long-chain (C₁₃₊) n-paraffins formed on the FT component. The initial zeolite activity is mostly determined by the surface acidity rather than by the total amount of Brønsted acid sites, pointing out to the existence of limitations for the diffusion of the long-chain n-paraffins through the 10-MR channels under FT conditions. Thus, ITQ-2 bearing the largest surface area presents the highest initial yield of branched gasoline-range products, followed by ZSM-5, IM-5, and MCM-22. All zeolites experience a loss of activity with TOS, particularly during the initial reaction stages. This deactivation is governed by the morphological and structural properties of the zeolite, which finally determine the amount and location of the coke species, and not by the acidity.     

The geology and mineralogy of a range of kaolins from the Santa Cruz and Chubut Provinces, Patagonia (Argentina)

In the Santa Cruz and Chubut provinces, Patagonia, Argentina, kaolin deposits were formed by “in situ” alteration of volcaniclastic rocks, such as the Bajo Grande, Chon Aike or Marifil Formations, or by erosion, transportation, and deposition of residual clays in small basins. This paper describes the genesis; geology; mineralogy; major, minor, and trace element geochemistry; grain size distribution; and specific surface area of natural and washed kaolins in an attempt to understand their behavior in the ceramic process. The sedimentary clays of the Baqueró Fm Lower Member, related to the Bajo Grande basement, are kaolinitic–smectitic, very fine-grained, and with a very high specific surface area. The clays related to the Chon Aike or Marifil Fms are kaolinitic, showing intermediate values of specific surface area and a coarser particle size distribution, associated with quite a fine-grained texture. The Baqueró Fm Upper Member received a considerable pyroclastic supply, fostering the development of a fine-grained clay in which kaolinite (± halloysite) with higher values of kaolinite crystal order prevailed. Primary kaolins – derived from weathering of pyroclastic sequences of Chon Aike and Marifil Fms – are coarse-grained, composed of kaolinite + quartz ± halloysite and exhibit a very low specific surface area. Alteration of mostly crystalline pyroclastics yielded ordered kaolinite and illite (+ halloysite) with a fine particle size distribution and intermediate values of specific surface area. Alteration of mainly vitreous pyroclastics produced halloysite (+ kaolinite) with a fine-grained texture and moderately high values of specific surface area. A supergene origin of primary kaolins is inferred on the basis of palaeoclimatic and geochemical evidence that corroborates stable isotopic data. The mineralogy, grain size, and textural characteristics of clays are controlled by parent rock composition (primary kaolins) or by provenance and proximity to source areas (sedimentary kaolins).     

The influence of mineralogical,chemical and physical properties on grindability of commercial clinkers with high MgO level

This research investigates various methods able to identify possible mineralogical, physical and chemical influences on the grindability of commercial clinkers with high MgO level. The aim of the study is to evaluate the hardness and elastic modulus of the clinker mineral phases and their fracture strength during the comminution processes, comparing samples from clinkers with low MgO level (0.5%) and clinkers with elevated MgO levels (> 5.0%). The study of the influence of mineralogical, chemical and physical properties was carried out using several analytical techniques, such as: optical microscopy, X-ray diffraction with Rietveld refinement (XRD) and X-ray fluorescence (XRF). These techniques were useful in qualifying the different clinker samples. The drop weight test (DWT) and the Bond ball mill grindability test were performed to characterize the mechanical properties of clinkers. Nanoindentation tests were also carried out. Results from the Bond ball mill grindability test were found to be related to the hardness of the mineral phase and to mineralogical characteristics, such as type and amount of inclusions in silicates, belite and alite crystals shape, or microcracked alites. In contrast, the results obtained by the DWT were associated to the macro characteristics of clinkers, such as porosity, as well as to the hardness and mineralogical characteristics of belite crystals in clusters. Hardness instrumented tests helped to determine the Vickers hardness and elastic modulus from the mineral phases in commercial clinkers and produced different values for the pure phases compared to previous publications.