Hardenability of austenite in a dual-phase steel

A low-carbon, low-alloy steel was intercritically heat treated and thermomechanically processed to study the martensitic hardenability of austenite present. Rolling of the two-phase (α+γ) microstructure elongated austenite particles and reduced their martensitic hardenability because the α/γ interface where new ferrite forms during cooling was increased by the particle elongation. The martensite particles obtained in rolled material were also elongated or fibered in the rolling direction. Therefore, the thermomechanical processing of a two-phase (α+γ) mixture has the detrimental effect of increasing the quenching power needed to yield a specific amount of martensite.     

Crosslinking of polyamides using dianhydrides,diacid chloride and dialdehyde: a promising approach for water treatment

New crosslinked polyamides were successfully produced from the condensation of pre‐synthesized monomer, 5‐(2,2,2‐trifluoroacetamido)isophthaloylchloride (TFAIAC) and diamines at low temperature. These polyamides were used as promising metal‐chelating adsorbents due to the presence of O and N donor sites on the crosslinked polyamides. For this purpose, trifluoroacetic anhydride was used to protect the amino group of 5‐aminoisophthalic acid, thus generating 5‐(2,2,2‐trifluoroacetamido)isophthalic acid (TFAIA). TFAIA was converted into TFAIAC using oxalyl chloride, which was exploited as a suitable monomer for the synthesis of aromatic polyamides. Amino groups were then set free under basic conditions and the crosslinking was carried out through amino groups present on the polyamide chains with different dianhydrides, isophthaloyl chloride and 2,5‐thiophenedicarboxaldehyde. The synthesis of monomers and polymers was confirmed by Fourier transform infrared, ¹H and ¹³C NMR spectroscopy and molar masses of the polyamides were measured by gel permeation chromatography. The crosslinked macromolecules were found to possess enough chain alignment as depicted by their XRD patterns. The thermal stability of the crosslinked polyamides was increased as their decomposition temperatures were improved from 420 to 619 °C. Metal ion uptake was scrutinized through atomic absorption spectroscopy with 83%–85% adsorption capacity at optimized parameters, i.e. a contact time of 3 h at pH 6. The mechanism of adsorption was further investigated through the Freundlich and Langmuir adsorption isotherms. The results reveal that uptake of metal ions followed monolayer adsorption of cations owing to coordination to electronegative centers on the macromolecules, confirming the Langmuir adsorption model. © 2019 Society of Chemical Industry     

Synthesis and Antimicrobial Activity of p-tetranitrocalix[4]arene Derivative

The present study demonstrates the synthesis and antimicrobial activity of the p-tetranitrocalix[4]arene (3). The microbial activity was determined against a variety of microorganisms, i.e., Gram-positive and Gram-negative bacterial strains such as Staphylococcus aureus ATCC 10231, Streptococcus viridans ATCC 12392, Escherichia coli ATCC 8739, as well as some fungal species including Aspergillus niger ATCC 16404, Aspergillus flavus ATCC 90906, and Candida albicans ATCC 32333. Kirby-Bauer well agar diffusion method was employed for the determination of antimicrobial activity. All the microorganisms were applied to a selective agar medium (Mueller Hinton Agar) for growth. It was observed that compound 3 is considerably effective against selected microorganisms. The MIC values were also evaluated. Thus, from the results it could be deduced that compound 3 may be a valuable addition to the therapeutic index.     

Correction to: Power and Resource Allocation in Wireless Communication Network

Wireless Personal Communications - Relying on the fact that, cascaded $$\alpha$$ – $$\mu$$ distribution provide simplified and excellent fitting to the measurement data compared to the other...     

Thermal and mechanical properties of aramid-based titania hybrid composites

The sol–gel process has been used to prepare various types of aramid–titania hybrid materials. Specifically, a mixture of m- and p-phenylenediamines was reacted with terephthaloyl chloride to produce linear polyamide chains in a dimethylacetamide solvent. Various proportions of tetrapropylorthotitanate (TPOT) were added, and its subsequent hydrolysis–condensation in the polymer solution produced a titania (TiO₂) network in the aramid matrix. Thin films prepared from these materials were tested for their tensile strength, which was found to decrease with increasing proportions of titania. To remedy this through chemical bonding between the matrix and the inorganic network, a slight excess of terephthaloyl chloride or 1,3,5-benzenetricarbonyl chloride was added near the end of the polymerization reaction. These aramid chains were thus end-capped with single or double carbonyl chloride groups. This allowed the chains to be further modified, with aminophenyltrimethoxysilane end caps. Chemically bonding the titania network to the aramid chains was then achieved by in situ hydrolysis–condensation of TPOT along with that of aminophenyltrimethoxysilane. In this way, thin transparent and tough films could be obtained with up to 30 wt % titania. The values of the tensile strength in the case of bonded hybrid materials increased with the addition of titania, and the polyamide system with nonlinear end groupings showed larger increases than did those with the linear chains ends. The systems with linear and nonlinear aramid chain ends were able to withstand maximum tensile stresses of the order of 193 and 246 MPa, respectively. This is presumably due to the extensive bonding between the polymeric chain ends and the inorganic phases as compared to the unbonded system. The thermal decomposition temperature of these composites was found to be in the range of 500–600°C and the overall weight loss was found to be minimized in an inert atmosphere. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 297–302, 1998     

Properties of polyamide‐zirconia nanocomposites prepared from sol‐gel technique

Transparent nanocomposites were prepared by producing zirconia network in glassy polyamide matrix using sol‐gel technique. Different amounts of tetrapropyl zirconate (TPZ) were added in polymer solution using anhydrous dimethylformamide as solvent. TPZ was hydrolyzed and condensed in situ in the matrix for the generation of inorganic networks using diethylamine. Thin and transparent films containing different proportions of zirconia were obtained by evaporating the solvent. Mechanical, dynamic mechanical thermal and morphological analyses of these films were carried out. An increase in tensile modulus was observed with the films containing zirconia contents up to 15 wt%, but the elongation at rupture was found to decrease sharply on further addition of zirconia. Toughness of the hybrid materials decreased with increased amount of zirconia. Dynamic mechanical thermal analysis (DMTA) performed on the samples indicates an increase in the glass transition temperature; 102°C with pure polyamide to 132°C with polyamide containing 15 wt% zirconia contents. The storage modulus was also found to increase with increase in zirconia proportion in the matrix. The decrease in the storage modulus of the hybrids with rise in temperature was observed to be much smaller as compared with that of pure polymer. Thermal decomposition temperatures of the hybrids were found in the range of 450–500°C. The weights of the residues left at 700°C were nearly proportional to the zirconia contents in the original hybrids. The morphological studies suggest a uniform dispersion of zirconia domains in the matrix. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers