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51.
This paper describes a kinetic method to predict the z-average molecular mean square radius of gyration of tree-like polymers formed by irreversible reactions, assuming Gaussian chains. It is based on the population balance equations for the two-sided molecular distributions of pendant chains associated with every chemically distinguishable kind of bonds. An automated method for the solution of those equations is valid both before as well as after gelation for complex kinetic schemes. Examples of its use are presented with polycondensation systems leading to hyperbranched polymers, the anionic polymerization of mono- and divinyl monomers and a radical polymerization with terminal branching and transfer to polymer. 相似文献
52.
High surface area Mn-based porous oxides (MANPO) containing additives like Ce, Sr and La were found to be very active and selective materials under 0.67% CH4/0.2% NO/5% O2 lean-deNO
x
conditions in the 200–300°C low-temperature range. These materials perform also impressively in the presence of 4% H2O in the feed stream, where a N2 selectivity of 98% and an excellent stability over 24 h on stream have been observed. The MANPO materials can be considered serious competitors of noble metals for low-temperature lean-deNO
x
applications. 相似文献
53.
G. L. Chen C. Guyon Z. X. Zhang B. Da Silva P. Da Costa S. Ognier D. Bonn M. Tatoulian 《Microfluidics and nanofluidics》2014,16(1-2):141-148
In this paper, tricobalt tetraoxide (Co3O4) catalyst was coated on the polydimethylsiloxane microchannel by the plasma-enhanced metal-organic chemical vapor deposition technology. The obtained Co3O4 film was characterized by SEM, XRD, XPS, and TEM, and the results show that the as-deposited Co3O4 film was initially composed of many cauliflowers-shaped microclusters. Also, the microcauliflower was transformed from an amorphous phase to a crystal phase when the Co3O4 film was treated by Ar and O2 plasma for more than 20 min, and the crystal lattice line occurred on the surface of nano-sized-Co3O4 particles. Meanwhile, the interface of Co3O4 particles with diameter between 3 and 12 nm became obvious and some nano-catkin structures were also formed on the Co3O4 film. The ratio of Co3+/Co2+ in the spinel-type Co3O4 was nearly 2, and the nano-particles predominantly expose their {311}, {111}, and {220} planes. These morphologies and structure characteristics were found to be ideal for increasing the catalytic activity efficiency of Co3O4 for CO oxidation, and the catalytic stability of Co3O4 coated on the organic microreactor lasted nearly 85 h for trace CO oxidation at room temperature. 相似文献
54.
Luis Carlos Ferreira Jr.Marcos A.S. Costa Pedro Ivo C. GuimarãesLuiz Claudio de Santa Maria 《Polymer》2002,43(14):3857-3862
Styrene polymerization was carried out with Ni(acac)2/MAO and Ni(acac)2/SiO2/MAO. The influence of reaction parameters (Al/Ni mole ratio, catalyst concentration, temperature and time polymerization) on styrene polymerization was evaluated. It was observed that both catalytic systems were affected by reaction parameters and that the heterogeneous catalyst presented higher activity than the homogeneous one. Polystyrenes with different molecular weight, stereoregularity and polydispersity were obtained. These results suggest that different active catalyst species could have been present. In addition, two types of methylaluminoxane (MAO) with different molecular weights were also evaluated as cocatalyst. As a result, the catalyst activity and stereospecificity were strongly affected by the MAO type. 相似文献
55.
A laboratory‐sized two‐roll mill was used to incorporate rice husk ash into natural rubber (NR). A conventional vulcanization system was used for curing and cure studies were carried out on a Monsanto rheometer. Physical testing of the NR vulcanizates involved determining tensile and tear resistances and hardness. Swelling behavior of NR compounds and scanning electron microscopy were used to investigate the interaction between rice husk ash and natural rubber. Also, dynamical mechanical thermal analysis was used to assess filler–rubber interactions in terms of storage modulus (E′) and loss tangent (tan δ). For comparison purposes, two commercial fillers, precipitated silica (Zeosil‐175) and carbon black (N774), were also used. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2331–2346, 2002 相似文献
56.
An optimization strategy has been applied to describe the chemical composition at the furnace bottom in the Kraft recovery boiler of a pulp production process. The concentrations of each involved chemical species were calculated through an optimization approach, minimizing the Gibbs free energy of the system. Various systems were proposed and tested, assuming different chemical species and phases number. Because serious initialization problems were found at this stage for some of the proposed systems, an optimization heuristic method (PSO) was used for the first approach to the problem. Once the appropriate phases number and chemical species in the system were determined, the initialization problems disappeared and the use of a deterministic optimization method (SQP) became viable. The proposed approach has shown to be satisfactory to reproduce industrial data and also data reported in the open scientific literature. 相似文献
57.
M. I. Viseu C. A. Nieto de Castro S. M. B. Costa 《International Journal of Thermophysics》1991,12(2):323-331
Diffusion coefficients of the electron acceptor dye tetrazolium blue were measured by the Taylor dispersion method, with an accuracy better than 4%, in two solvents: (i) a homogeneous one-aqueous phosphate buffer, 0.1 M, pH=7.0 (medium I); and (ii) a heterogeneous one-nonionic micelles of Triton X-100, 2.0 mM (where M stands for mol·dm–3), in the same aqueous phosphate buffer (medium II). The values obtained were D
12
I
=3.64×10–10m2·s–1 and D
12
II
=3.01×10–10m2·s–1·D
12
II
has the meaning of a macroscopird or average diffusion coefficient, in which the partition coefficient of tetrazolium blue between micelles and water, as well as the diffusion coefficients of this dye and of the micelles in the aqueous phase, are involved. 相似文献
58.
Jonathan Tenrio Vinhal Raquel Húngaro Costa Jorge Luís Coleti Denise C. R. Espinosa 《加拿大化工杂志》2021,99(1):166-177
The volume of tailings produced by the extractive industry has been increasing due to the processing of the low‐grade ore. This issue can cause environmental accidents and require significant investment to control the disposal of tailings. Therefore, this study aims to recover iron from zinc mine tailings by wet magnetic separation followed by the carbothermal reduction of self‐reducing briquettes. Two magnetic separation routes were investigated to concentrate iron. Zinc mine tailings were processed by route I, in a rougher stage followed by a scavenger stage; and route II, in a rougher stage followed by a cleaner stage. The carbothermal reductions were performed using self‐reducing briquettes composed of Fe concentrate from the route with high Fe content and charcoal. The products were analyzed by scanning electron microscopy with energy dispersive spectroscopy (SEM‐EDS), x‐ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP‐OES), and volumetric chemical analysis. Magnetic separation route II provided the highest‐grade Fe concentrate, 52% Fe, while route I provided 33% Fe. In the carbothermal reductions, a metallization degree of 98% in the Fe concentrate briquette, 97% in the briquette with a 10% replacement of its raw material by Fe concentrate, and 99% in the hematite briquette was reached. The replacement of raw material by Fe concentrate showed no significant change in Fe recovery. Considering the whole process, magnetic separation and carbothermal reduction, the recovery of Fe from the zinc mine tailings was 67%. Therefore, the process route suggested in this study will not only reduce tailings disposal and consequently the risk of environmental accidents, but it will also provide profitable raw material for the steel industry. 相似文献
59.
Ingrid R. Marques Camila Silveira Monique J. L. Leite Artur M. Piacentini Cristiano Binder Marta E. R. Dotto Alan Ambrosi Marco Di Luccio Cristiane da Costa 《应用聚合物科学杂志》2021,138(24):50558
The modification of the surface characteristics after treatment with plasma in polymeric materials, such as the aging phenomenon, calls the attention of research in the area of nonthermal plasma technology. In this work, a direct treatment with dielectric-barrier discharge plasma was used on the surfaces of ultrafiltration membranes. The measurements of the contact angle with water, attenuated total reflectance accessory, zeta potential, atomic force microscopy and scanning electron microscopy-MEV were performed on the surfaces to verify changes after plasma treatment and to understand the occurrence and timing of the plasma aging effect. In the analysis of the membrane performance, hydraulic permeation and protein retention tests were performed. The results showed an improvement in wettability and hydrophilic properties in the post-treated membranes. The study of reversibility/aging of the post-plasma surface is important for research that deals with the modification of polymeric membranes. Changes in surface morphology, topography and wettability of the membranes were observed up to seven days after treatment, with a tendency to return to the initial characteristics of the membranes. 相似文献
60.
Anna Raffaela de Matos Costa Juliana Cysneiros Lima Raquel dos Santos Lhaira Souza Barreto Mariana Alves Henrique Laura Hecker de Carvalho Yêda Medeiros Bastos de Almeida 《应用聚合物科学杂志》2021,138(36):50916
This work deals with the rheological, morphological, and thermal properties of composites having poly(ethylene terephthalate) (PET), polyamide-6 (PA6), and their blends as matrices, and rice husk ash (RHA) as a filler. The study determines the effect of composition on the change in viscosity and rate of degradation during processing in a torque rheometer. Our data indicates that thermal stability and degradation during processing depend on matrix composition and filler concentration. SEM micrographs show both partial adhesion of the filler to the matrices and filler pullout. Optical microscopy shows particle agglomeration and that agglomerate size increased with filler content. FTIR investigates the shifting of absorption bands of PET/PA6 composite after the addition of RHA and attributes the selective dispersion of RHA to the formation of hydrogen bonds. Our data supports the idea that filler employed here is an option to develop polymer composites with improved properties. 相似文献