Microstructural properties,thermal insulation and thermal degradation behavior of boron-containing monolithic novolac xerogels

Enhancement of thermal stability-insulation performance of hyper porous materials is the premier issue to design of novel porous thermal protection systems. Boron-containing monolithic novolac xerogels (BCNXs) were synthesized using sol–gel networking of novolac resin with hexamethylenetetramine (HMTA) and boric acid at the solvent saturated vapor atmosphere (SSVA). The aim was to elucidate the effect of higher crosslinking density and thermal stable boron containing chemical bonds on the microstructure, thermal conductivity, and thermal oxidation stability of novolac xerogels. The results of FESEM and BET analysis showed that the microstructural characteristics of xerogels are significantly depend on the HMTA and boric acid concentration. The thermogravimetric results were analyzed using characteristic kinetic temperature (CKT)-characteristic kinetic temperature range (CKTR) approximations. The effect of micromorphology of xerogels on the thermal conductivity was investigated. The effective thermal conductivity of samples were in the range of 0.031–0.048 W/m K.     

A bio-inspired gelatin-based pH- and thermal-sensitive magnetic hydrogel for in vitro chemo/hyperthermia treatment of breast cancer cells

Gelatin (Gel)-based pH- and thermal-responsive magnetic hydrogels (MH-1 and MH-2) were designed and developed as novel drug delivery systems (DDSs) for cancer chemo/hyperthermia therapy. For this goal, Gel was functionalized with methacrylic anhydride (GelMA), and then copolymerized with (2-dimethylaminoethyl) methacrylate (DMAEMA) monomer in the presence of methacrylate-end capped magnetic nanoparticles (MNPs) as well as triethylene glycol dimethacrylate (TEGDMA; as crosslinker). Afterward, a thiol-end capped poly(N-isopropylacrylamide) (PNIPAAm-SH) was synthesized through an atom transfer radical polymerization technique, and then attached onto the hydrogel through “thiol-ene” click grafting. The preliminary performances of developed MHs for chemo/hyperthermia therapy of human breast cancer was investigated through the loading of doxorubicin hydrochloride (Dox) as an anticancer agent followed by cytotoxicity measurement of drug-loaded DDSs using MTT assay by both chemo- and chemo/hyperthermia-therapies. Owing to porous morphologies of the fabricated magnetic hydrogels according to scanning electron microscopy images and strong physicochemical interactions (e.g., hydrogen bonding) the drug loading capacities of the MH-1 and MH-2 were obtained as 72 ± 1.4 and 77 ± 1.8, respectively. The DDSs exhibited acceptable pH- and thermal-triggered drug release behaviors. The MTT assay results revealed that the combination of hyperthermia therapy and chemotherapy has synergic effect on the anticancer activities of the developed DDSs.     

Preparation and characterization of poly(vinyl alcohol)/gum tragacanth/cellulose nanocomposite film

The effects of gum tragacanth obtained from two species of Astragalus Gossypinus (GT-G) and A. Parrowianus (GT-P) at two levels of 10% and 30% combined with cellulose nanofibers (CNF; 5%) on the physico-mechanical and structural properties of polyvinyl alcohol (PVA) nanocomposite film were investigated in this study. The water solubility and water vapor permeability of the films decreased with increasing the content of both gums, especially in the film containing 30% GT-P. The highest values of the tensile strength (39.3 MPa) and elongation at break (445%) belonged to the treatment containing 10% GT-P (90/10P/0). The FTIR and DSC analyses confirmed good interactions between GT and PVA in the 90/10P/0 treatment. SEM images indicated the dense structure of this film as the optimum treatment. Although the presence of CNF in the films containing GT-G improved some properties, especially the Young modulus, it impaired all the functional properties of nanocomposite GT-P film.     

Solving singular control problems using uniform trigonometrization method

This study investigates the application of a recently developed construct, the uniform trigonometrization method (UTM), to the singular control problems in chemical engineering. The UTM involves minimal modifications to the original problem, thereby generating near-singular control solutions that can be used for conceptual design and serve as an alternate to direct techniques like nested and simultaneous approaches. Eight classical singular control problems with known analytical solutions and three complex singular control problems from chemical engineering domain are solved in this study. The results obtained using the UTM for these problems are found to match well with the literature and are of higher resolution as compared to the results obtained using a direct pseudospectral-based solver. The ability of the UTM to handle complex chemical engineering problems with both singular controls and state path constraints has also been demonstrated in this study.     

Pre-aging time dependence of microstructure and mechanical properties in nanostructured Al-2wt%Cu alloy

This work is focused on the effect of pre-aging time on the properties of Al-2wt%Cu alloy processed by accumulative roll bonding (ARB) process. Following aged at 190 °C for 10 or 30 min, the samples were deformed up to a strain of 4.8 by the ARB process. The microstructure evolution was investigated by transmission electron microscope and electron backscattering diffraction analyzes. The results showed that the Al₂Cu precipitates were formed with different sizes due to the different pre-aging times and the finer precipitates were more effective on the formation of high angle grain boundaries during the ARB process. The grain size of Aged-10 min and Aged-30 min specimens decreased to 400 nm and 420 nm, respectively, after 6 cycles of the ARB process. Also, the final texture after 6 cycles of the ARB process, shown in the {111} pole figure, were different depending on the starting microstructures. The mechanical properties of specimens were investigated by the Vickers microhardness measurements and the tensile tests. The results showed that the mechanical properties are affected by the starting microstructure. The mechanical properties of Aged-10 min specimen were different compared to Aged-30 min specimen due to the different size of the pre-existing precipitates. Although by continuing process, the precipitates were probably dissolved due to the heavy deformation.     

Study of inhibition effect of carboxylic salt derivative on corrosion of C1010 carbon steel in saline solution

In the present work, sodium 4-[(4-formylbenzylidene) amino] benzoiate (4) was synthesized and its structure was confirmed using spectroscopic techniques. Prepared compound was successfully applied as a corrosion inhibitor for C1010 carbon steel in 3.5% NaCl solution at 25°C. Different electrochemical measurements such as linear polarization resistance (LPR), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) were used to evaluate the suggested inhibitor (4). The results of different electrochemical measurements show that inhibition efficiencies obtained from EIS curves are in consistence with the results of potentiodynamic polarization and LPR measurements due to increase corrosion inhibition efficiency by increasing the concentration of organic inhibitor (4). Semi-empirical calculations with PM3 method were used to find relationship between molecular structure and inhibiting effect of suggested inhibitor (4).     

The Ablation and Oxidation Behaviors of SiC Coatings on Graphite Prepared by Slurry Sintering and Pack Cementation

SiC coatings were generated on graphite using slurry sintering (SS) and pack cementation (PC). The samples’ ablation features were assessed by an oxyacetylene torch. The rates of mass ablation of the PC–SiC and SS–SiC coatings were approximated 2.17?×?10^?3 and 9.52?×?10^?3 g s^?1, respectively, decreased by 84.1 and 29.6% compared to the uncoated samples. It was mainly attributed to the formation of a SiO₂ layer on the surface. The continuous SiO₂ molten film formed via the PC–SiC oxidation generates a sealing mechanism which can be an obstacle against the oxygen diffusion and hinder more ablation. This is while discontinuous SiO₂ film formed from the thin SS–SiC cannot protect the graphite effectively. The non-isothermal oxidation test shows that without the SiC coating, the sample weight is lost largely from 25 to 1500 °C, and its weight loss was 2.2% after the TGA. However, after coating, the samples possessed excellent oxidation protection and weight losses of SS–SiC and PC–SiC coatings are down to 1.3 and 0.6%, respectively. The more oxidation of the graphite substrate occurred due to the formation of macrocracks in the coating during the TGA and also the formation of holes on SiO₂ glass layer owing to release of CO or CO₂.     

Evaluation of the localized corrosion on Mg electrode surface by electrochemical noise technique

The symmetrical and asymmetrical electrodes made of Mg were studied in 0.1-M NaCl electrolyte adjusted at pH 12. The statistical and wavelet methods were employed for analyzing the electrochemical current noise (ECN) signals. The asymmetric configuration was used for electrochemical detection of filiform corrosion on Mg electrode. The real time scale of the dominant transients of the asymmetric electrodes was detected on the basis of the maximum peak in the SDPS plots. The SDPS values of the real time scale crystals of the ECN signals resulting from asymmetrical electrodes increased with the increase in immersion time due to the onset of filiform corrosion.     

辊速差对连铸连轧7075铝板显微组织、 织构及力学性能的影响

研究辊速差对连铸连轧7075铝板显微组织、织构及力学性能的影响.采用3种不同上辊/下辊转速比(ω/ω0,ω为上辊转速,ω0为下辊转速)1:1、1:1.2及1:1.4进行多次试验.结果显示,在最大辊速差条件下(ω/ω0=1:1.4),7075铝板在轧制方向的屈服强度和极限抗拉强度分别提高41.5％和21.9％.此外,当辊...