Plasma nitriding of austenitic stainless steel in N2 and N2-H2 dc pulsed discharge

AISI 302/304 austenitic stainless steels have been nitrided in N₂ and N₂-H₂ glow discharge plasmas powered by a high frequency dc pulsed power supply. In a pure nitrogen plasma, no increase in surface hardness from the initial value has been observed. In a N₂-H₂ gas admixture, a 3-4 times increase in hardness has been found, which confirms the necessity of hydrogen gas as a powerful reagent. Grazing incidence X-ray diffraction (GIXRD) shows the presence of three phases of nitride (Fe₃N, Fe₄N and CrN) along with iron oxide (Fe₂O₃). It is found in a N₂ plasma at a sample temperature of 540 °C that at 200 kHz, maximum peak intensity of iron oxide/nitride decreases. In N₂-H₂ plasma treated sample the nitride peak intensity increased in comparison to the intensity in sample nitrided in N₂ plasma. Optical emission spectroscopy (OES) has been used to investigate the active species present during nitriding in the near-cathode region. Emission bands of neutral and ionic molecular species and ionic atomic species of nitrogen have been detected in a nitrogen plasma. In a N₂-H₂ gas admixture, the H_α and H_β lines of Balmer series in addition have been observed. At 20% H₂ addition in nitrogen plasma, a few vibrational state intensities of N₂ and N₂⁺ are observed to be optimized.     

Effect of glycidyl methacrylate on the physical properties of wood–polymer composites

Chemical modification of pinewood was carried out by impregnating the wood with styrene as the impregnating monomer and in combination with a crosslinking monomer glycidyl methacrylate (GMA). Polymerization was carried out by catalyst heat treatment. Dimensional stability in terms of antiswell efficiency was determined and improved on treatment with polymer. Water uptake percentage was also improved for styrene‐GMA treated wood samples over styrene treated or untreated wood samples. Mechanical properties such as bending strength measured in terms of modulus of elasticity and modulus of rupture of polymer‐treated samples showed an improvement over untreated ones. Treatment also resulted an improvement in compressive strengths. Thermal properties of the wood samples were evaluated by thermogravimetric analyzer and differential scanning calorimeter. Biodegradability of the treated and untreated wood samples was determined and improvement was obtained on treatment. As a whole, styrene‐GMA treated wood samples showed more improvement over untreated or styrene‐treated samples. POLYM. COMPOS., 28:1–5, 2007. © 2007 Society of Plastics Engineers     

Experimental investigations on high temperature transition of asphalt

Asphalt exhibits Newtonian, non-Newtonian and viscoelastic behavior as the temperature is varied. This investigation reports the temperature at which asphalt exhibits non-Newtonian to Newtonian transition. Air blown, blended asphalt and petroleum pitch were tested at different aging conditions. The temperature at which the material exhibited shear rate independent viscosity was taken as the transition temperature. The transition temperature varied with processing method and aging conditions. It was seen that blended asphalt exhibited greater increase in apparent viscosity during aging when compared to air blown asphalt, whereas air blown asphalt showed greater shift in transition temperature for the same aging conditions.     

Spectral and laser studies on energy transfer binary dye-doped polymer laser rods

The energy transfer mechanism of two different dyes, C450 as donor and C535 as acceptor incorporated into polymeric matrices, is investigated. The absorption and fluorescence characteristics of C450 and C535 dye-doped polymer modified with ethanol are studied. The results are compared with their respective liquid mixtures. The spectral parameters of C450 and C535 in polymer and the corresponding monomer compositions are obtained. We study the variation of gain for different acceptor concentrations whilst keeping the donor concentration fixed. The gain of acceptor with donor increased and then decreased as the acceptor concentration was increased. Both solid and liquid media showed similar trends. We also study the photobleaching of the dye-doped polymer rod under nitrogen laser excitation.     

Acid-base equilibria of sulfonephthalein dyes in aqueous polymer-surfactant media

The acid-base equilibria of three anionic sulfonephthalein dyes, viz., bromothymol blue (BTB), thymol blue (TB), and cresol red (CR), were studied spectroscopically in aqueous media containing the water-soluble noninonic polymers polyvinyl alcohol (PVA) and polyethylene glycol (PEG) in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). A partition equilibrium method was used to determine the equilibrium constant of partition of the dyes between the micellar pseudo phase and aqueous phase in the presence of PVA and PEG. The critical aggregation concentrations (CAC) of the surfactants in buffered aqueous systems containing the neutral polymers were also determined. The CAC of the polymer-surfactant systems were found to be lower than the critical micelle concentration of such systems in the absence of polymer, in otherwise identical conditions. The pH-dependent association constants, K _ass, of the sulfonephthalein dyes with the SDS-PVA system increased with the increase in molecular weight of the polymer. The interactions of the dyes with the buffered aqueous SDS-PVA and SDS-PEG systems were found to be endothermic and entropy oriented. In the polymer domain, the head group region of the micelles was more exposed at lower concentrations of the polymer, but under excess polymer concentration they were increasingly shielded, which impaired their electrostatic interaction with the dyes.     

Effects of polymer molecular weight,concentration, and role of polyethylene glycol as additive on polyacrylonitrile homopolymer membranes

Polyacrylonitrile (PAN), is an important base polymer to cast porous membranes. In this work, a detailed study of the effects of molecular weight of PAN homopolymer and its concentration on the cast membrane has been undertaken. The effects of molecular weight of additive polyethylene glycol (PEG) and its concentration have also been investigated. The membranes are cast using dimethyl formamide as solvent using phase inversion technique. They are characterized in terms of porosity, water permeability, molecular weight cut off, average pore diameter, contact angle, and tensile strength at breaking point. Fourier transform infrared spectroscopy and scanning electron microscopy are used to characterize the chemical and morphological changes of the membrane surface. Further studies have been considered to evaluate the antifouling property of various membranes using filtration of bovine serum albumin solution. Membrane modified by PEG 400 membrane shows an improved separation performance and antifouling characteristics. POLYM. ENG. SCI., 54:2375–2391, 2014. © 2013 Society of Plastics Engineers     

XRD and FT-IR investigations of sub-bituminous Assam coals

Two coal samples collected from Makum coal field, Assam, India were studied by XRD and FT-IR techniques. The X-ray diffractogram shows the existence of some crystalline carbons in Assam coals as proven by the appearance of peaks. The radial distribution functional (RDF) method was applied for the determination of structural aspects of the coals. The study indicates that the coals are lignite in type and there is no evidence of graphite-like structures. The maximum in the G(r) plots of function of radial distribution of atoms (FRDA) relates to different distances between carbon atoms of aliphatic chains. The first significant maximum relates to the C-C bond (type C-CH=CH-C), the second maximum relates to the distance between carbon atoms of aliphatic chains that are located across one carbon atom. The curve intensity profiles obtained from FRDA show quite regular molecular packets for this coal. The coals were found to be lignite in nature. FT-IR study shows the presence of aliphatic carbon, C=O and C-O stretching associated with -OH and -NH stretching vibrations. Kaolinite and quartz were also found to be major minerals in Assam coals by FTIR spectroscopy. The difference in intensities of carbonyl groups of the coal samples is likely to relate with the rank.     

Novel analytical reagent for the application of cloud-point preconcentration and flame atomic absorption spectrometric determination of nickel in natural water samples

Cloud-point extraction was applied as a preconcentration of nickel after formation of complex with newly synthesized N-quino[8,7-b]azin-5-yl-2,3,5,6,8,9,11,12octahydrobenzo[b][1,4,7,10,13]pentaoxacyclopentadecin-15-yl-methanimine, and later determined by flame atomic absorption spectrometry (FAAS) using octyl phenoxy polyethoxy ethanol (Triton X-114) as surfactant. Nickel was complexed with N-quino[8,7-b]azin-5-yl-2,3,5,6,8,9,11,12octahydrobenzo[b][1,4,7,10,13]pentaoxacyclopentadecin-15-yl-methanimine in an aqueous phase and was kept for 15 min in a thermo-stated bath at 40 degrees C. Separation of the two phases was accomplished by centrifugation for 15 min at 4000 rpm. The chemical variables affecting the cloud-point extraction were evaluated, optimized and successfully applied to the nickel determination in various water samples. Under the optimized conditions, the preconcentration system of 100 ml sample permitted an enhancement factor of 50-fold. The detailed study of various interferences made the method more selective. The detection limits obtained under optimal condition was 0.042 ngml(-1). The extraction efficiency was investigated at different nickel concentrations (20-80 ngml(-1)) and good recoveries (99.05-99.93%) were obtained using present method. The proposed method has been applied successfully for the determination of nickel in various water samples and compared with reported method in terms of Student's t-test and variance ratio f-test which indicate the significance of present method over reported and spectrophotometric methods at 95% confidence level.     

Comparison of predicted vehicular pollution concentration with air quality standards for different time periods

Air pollution is caused by variety of sources such as industries, vehicles, cremation, bakeries, and open burning. These sources have variation in emission with different time scales. Industry and bakeries have variation in emission with day or week, rest of the sources like vehicles and domestic sector have variation with time in a day. In fact, vehicles have a large variation in emission with time period of the day. The average concentration of 24 h is much less than hourly concentration of peak time when there is heavy vehicular emissions. The hourly concentration of off-peak time or lean time is very low due to low emission for that period. The air quality standards of India are prescribed for 24-h average concentration with which the predicted average concentration from models is compared. However, the peak time concentration may be much higher than the standard. In the peak time, outdoor concentration is more and since a large proportion of the population is out the exposure is also very high and can cause severe health effect. In this paper, vehicular pollution modeling has been carried out using AERMOD with simulated meteorology by Weather Research and Forecasting model. NO_x and PM concentrations were 3.6 and 1.45 times higher in peak time than off-peak and evening peak, respectively. Lean time has higher concentration for both NO_x and PM than off-peak and evening peak. It shows the misleading concept of comparing average predicted concentration of 24 h with standards for vehicles.