Seaweed‐derived κ‐carrageenan: Modified κ‐carrageenan as a recyclable green catalyst in the multicomponent synthesis of aminophosphonates and polyhydroquinolines

A seaweed‐derived biopolymer, κ‐carrageenan (KCAR), with a slight modification was assumed as an organosulfonic‐type Bronsted acid in the catalysis of polyhydroquinoline and α‐aminophosphonate syntheses through one‐pot multicomponent reaction procedures under aqueous conditions. In this investigation, KCAR was found to be an efficient, heterogeneous and homogeneous, recyclable, economical, and green catalyst. Moreover, biocompatibility, ease of separation, high chemoselectivity, and lower reaction time were other aspects of this catalyst. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43190.     

The effects of NbC nanoparticles synthesized by combustion method on the mechanical properties of Cu–NbC nanocomposite

In the first stage of this work, the master nanocomposite of niobium carbide (NbC)–Cu (ceramic-based nanocomposite) was synthesized by a mechanically induced magnesiothermic combustion in the Nb₂O₅/CuO/Mg/C system. Ignition time in this system was recorded to be ∼28 min of milling. In the second stage, appropriate amounts of NbC–Cu nanocomposite powder were mixed with pure copper powder to prepare Cu-based nanocomposite with 0, 5, 10, 15, and 20 volume fraction of NbC. The final metal matrix nanocomposite powder was sintered by spark plasma sintering method. The density of nanocomposite specimens decreased with increasing the percentage of NbC nanoparticles, while the microhardness of specimens increased with increasing nano-NbC content. Regarding the tensile test, the sample Cu–10 vol.% NbC nanocomposite with a strength of 372 MPa (∼63% higher than that of nonreinforced copper) was the best composition, and the nanocomposite strength decreased at higher NbC concentrations, mostly due to the agglomeration and nonhomogeneous distribution of reinforcing nanoparticles.     

Preparation of cerium oxide nanoparticles in Salvia Macrosiphon Boiss seeds extract and investigation of their photo-catalytic activities

Cerium oxide nanoparticles (CNPs) with desired particle size and spherical morphology were prepared from cerium nitrate in bio media of Salvia macrosiphon Boiss seeds extract, as a green synthesis route. Then they were characterized by XRD, UV–Vis and FTIR spectroscopies, FESEM and TGA. Band gap energy of the prepared powders was also determined which was found in the range of 2.5–3.5?eV. Determination of DLS and zeta potential were showed that CNPs had the small size and unique colloidal stability, respectively. Then the photo-catalytic activity of them was investigated by degradation of Rhodamine B (RhB) dye as a model of waste water pollutants, under UV-irradiation and optimum conditions were evaluated. Results showed that decreasing the particle size increased the rate of photo-catalytic reaction remarkably but ascending the band gap energy, in contrast. The photo-catalytic mechanism was also studied by using different scavengers.     

Kinetics of hydrochloric acid leaching of smithsonite

The dissolution kinetics of smithsonite ore in hydrochloric acid solution has been investigated. As such, the effects of particle size (−180 + 150, −250 + 180, −320 + 250, −450 + 320 μm), reaction temperature (25, 30, 35, 40, and 45°C), solid to liquid ratio (25, 50, 100, and 150 g/L) and hydrochloric acid concentration (0.25, 0.5, 1, and 1.5 M) on the dissolution rate of zinc were determined. The experimental data conformed well to the shrinking core model, and the dissolution rate was found to be controlled by surface chemical reaction. From the leaching kinetics analysis it can be demonstrated that hydrochloric acid can easily and readily dissolve zinc present in the smithsonite ore, without any filtration problems. The activation energy of the process was calculated as 59.58 kJ/mol. The order of the reaction with respect to HCl concentration, solid to liquid ratio, and particle size were found to be 0.70, −0.76 and −0.95, respectively. The optimum leaching conditions determined for the smithsonite concentrate in this work were found to be 1.5 M HCl, 45°C, −180 + 150 μm, and 25 g/L solid to liquid (S/L) ratio at 500 rpm, which correspond to more than 95% zinc extraction. The rate of the reaction based on shrinking core model can be expressed by a semi-empirical equation as:

Preparation and properties of one‐pack polybenzoxazine‐modified polyurethanes with improved thermal stability and electrical insulating properties

A novel method has been developed for the combination of polyurethanes and polybenzoxazines. For this purpose, firstly, p‐nitrophenol blocked polyurethanes (BPUs) were prepared via the reaction of poly(tetramethylene ether) glycol of various molecular weights, 2,4‐tolylene diisocyanate and p‐nitrophenol. The BPUs were then mixed with 2,2‐bis(3,4‐dihydro‐3‐phenyl‐2H‐1,3‐benzoxazine)propane (Ba) at various weight ratios. To prepare poly(urethane‐co‐benzoxazine) networks, the BPU/Ba mixtures were subjected to a heating programme derived from detailed differential scanning calorimetry and gel content measurements. Results showed about 30 to 40 °C reduction of polymerization temperature for complete curing of BPU/Ba mixtures in comparison to neat Ba. This phenomenon was related to catalytic action of librated p‐nitrophenol molecules. The thermal, mechanical, viscoelastic and electrical properties of prepared thermoset polymers were measured and correlated with their chemical structures. A significant improvement of thermal stability and dielectric strength in comparison to neat polyurethanes was found. Also, enhancement of tensile properties, ease of curing and ability to be transformed into thin films are fascinating features of these newly developed materials in comparison to neat polybenzoxazines. Therefore, these polymers have potential applicability as high‐performance materials in modern electrical industries. Copyright © 2010 Society of Chemical Industry     

Numerical simulation of cooling performance in microchannel heat sinks made of AlN ceramics

Microsystem Technologies - The problem of generating a high amount of heat in microelectronic equipment should be minimized properly. Allowing systems to run for long periods of time in high...     

Research trend prediction in computer science publications: a deep neural network approach

Scientometrics - Thousands of research papers are being published every day, and among all these research works, one of the fastest-growing fields is computer science (CS). Thus, learning which...     

Butyl chloride as promoter in ethylene polymerization by magnesium ethoxide‐supported catalyst

The effects of butyl chloride as a promoter in the ethylene polymerization were studied using a Mg(OEt)₂/TiCl₄/triethyl aluminum (TEA) Ziegler–Natta catalyst system, where Mg(OEt)₂, TiCl₄, TEA were used as support, catalyst, and activator, respectively. The influence of BC on the catalyst performance, polymerization rate, and polymer properties were investigated. This study strongly indicates that BC could act as a promoter with high performance in the ethylene polymerization. There was a remarkable increase in the catalyst yield and polymerization rate, in particularly, in the presence of hydrogen which was used for controlling the molecular weight. A reduction in the polymer molecular weight was observed in the presence of BC and hydrogen. The morphology of the polymers was evaluated through scanning electron microscopy and particle size distribution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40189.     

Fabrication of copper/aluminum composite tubes by spin-bonding process: experiments and modeling

The aim of this work is to produce two layered thin-walled Cu/Al composite tube by the spin-bonding process. The process is utilized to bond the aluminum tube into the copper one at thickness reductions of 20?C60% and process temperatures of 25°C, 130°C, and 230°C. The bond strength is measured by T-peeling test, and the bond interfaces are examined by metallography and scanning electron microscopy (SEM). The results show that after a threshold thickness reduction of about 30%, the bond strength increased with the amount of deformation. SEM fractography of the peel surfaces confirms that the copper oxide film is broken in a shear manner during deformation. Severe shear strains applied during spin-bonding process, in fact, make it appropriate for bonding the copper to aluminum. Based on the results, at higher temperatures the resulted bond strength is decreased. It is shown that formation of the brittle intermetallic layer on the interface at high temperatures leads to decrease in the bond strength. In addition to the experiments, a procedure is proposed by which it is possible to calculate the bonding length through the comparison of FEM simulations and the experiments. Based on these calculations and the bonding mechanism, a bond strength model is developed and verified by the experiments.