The effect of sintering conditions on the properties of WC–10wt%Co PIM compacts

The powder injection molding (PIM) process has an advantage of near net shaping of homogeneous micro structure and density at the complicate form. This study was investigated for microstructure and mechanical properties of WC–10%Co insert tool alloy fabricated by PIM process. The WC–10%Co feedstock mixed with wax binder was fabricated by two blade mixer. After WC–10%Co feedstocks were injection molded, debinding process was carried by two-steps methods with solvent extraction and thermal debinding. The binder was eliminated with normal hexane for 12 h at 50 °C by solvent extraction, and subsequently thermal debinding was examined for 1 h at the temperature 900 °C. After debinding process, the specimens were sintered at vacuum or N₂/H₂ mixed gas atmosphere at 1380 °C. The microstructure and phase were observed by FE-SEM. In the case of sintered at 1380 °C in vacuum atmosphere, the hardness was 1600 Hv, and the relative density of WC–10%Co was 92.5%. The density of WC–10%Co sintered at 1380 °C in mixed gas atmosphere was 87.5% and the hardness was lower than 1400 Hv. Residual carbon contents of sintered at vacuum and mixed gas atmosphere were 5.4 wt%.     

Preparation of Hot Water-Resistant Silica Thin Films from Polysilazane Solution at Room Temperature

Perhydropolysilazane (PHPS) films were deposited on single-crystal Si substrates by spin-coating using a xylene solution of PHPS, and then suspended over 1 mol L^?1 ammonia water at room temperature. The PHPS-to-silica conversion occurring on the exposure to the ammonia water vapor was studied by infrared absorption spectroscopy. Si--H and N--H infrared absorption peaks decreased and Si--O--Si bands increased, showing PHPS-to-silica conversion; the conversion was almost completed in 6 h. The exposed films were soaked in 80°C water for 24 h, and the reduction in thickness on soaking was evaluated. The PHPS-derived films suspended over the ammonia water for 6 h exhibited only 2% reduction in thickness on soaking in 80°C water. Alkoxide-derived silica gel films dried in the ambient atmosphere or suspended over the ammonia water, on the other hand, exhibited significant reduction in thickness on soaking in 80°C water.     

Fourier Transform Infrared Spectroscopy and Solid Phase Extraction Applied to the Determination of Oil and Grease in Water Matrices

 The solid phase extraction as a solvent-free method for the analysis of oil and grease in waters was studied. The use of a PTFE surface as a solid phase allows the retention of the volatile fraction of oil and grease, and further analysis of carbon–hydrogen bonds using infrared spectroscopy can be done on the surface. Various oils and grease samples were tested: n-hexadecane, n-tetradecane, n-nonadecane, n-docosane, isooctane, diesel oil and gasoline. Temperatures from 25° to 90 °C and a range of heating times were checked for extraction. Precision tests showed relative standard deviation values of around 10% in several samples of the same concentration. Calibration lines of n-hexadecane showed high correlation coefficients from 0.9 to 30 mg/l. Recoveries for the various oils using different calibration lines showed values from 90 to 110%. The method described here is fast and clean, and allows reproducible measurements of oil and grease in water that do not require the use of a solvent. Received March 1, 2001; accepted August 15, 2001; published online July 15, 2002     

Investigation of IrO2/SnO2 thin film evolution by thermoanalytical and spectroscopic methods

The formation mechanism of thermally prepared IrO₂/SnO₂ thin films has been investigated under in situ conditions by thermogravimetry combined with mass spectrometry (TG-MS) and infrared emission spectroscopy (IRES). Mixtures of varying composition of the precursor salts (SnCl₂·2H₂O dissolved in ethanol and IrCl₃·3H₂O dissolved in isopropanol) were prepared onto titanium metal supports. Then the solvent was evaporated and the gel-like films were heated in an atmosphere containing 20% O₂ and 80% Ar to 600°C. The thermogravimetric curves showed that the evolution of the oxide phases take place in several decomposition stages and the final mixed oxide film is formed between 490 and 550°C, depending on the noble metal content. Mass spectrometric ion intensity curves revealed that below 200°C crystallization water, residual solvent, and hydrogen-chloride (formed as a result of an intramolecular hydrolysis) are liberated. The decomposition of surface species (surface carbonates, carbonyls and carboxylates) formed via the interaction of the residual solvent with the precursor salts takes place up to 450°C as evidenced by emission Fourier transform infrared spectrometry. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of oxygen atmosphere on the photoluminescence properties of sol–gel derived ZrO2 thin films

Homogeneous and transparent ZrO₂ thin films were prepared by sol?Cgel dip coating method. The prepared ZrO₂ thin films were annealed in air and O₂ atmosphere at 500, 700 and 900?°C for 1, 5 and 10?h. X-Ray diffraction (XRD) pattern showed the formation of tetragonal phase with a change of stress in the films. Scanning electron microscope (SEM) revealed the nucleation and particle growth on the films. An average transmittance of >80?% (in UV?CVis region) was observed for all samples. The refractive index and direct energy band gap were found to vary as functions of annealing atmosphere, temperature and time. Photoluminescence (PL) revealed an intense emission peak at 379?nm weak emission peaks at 294, 586 and 754?nm. An enhancement of PL intensity was observed in films annealed in O₂ atmosphere. This is due to reconstruction of zirconium nanocrystals interfaces, which help passivate the non-radiative defects. At 900?°C, oxygen atoms react with Zr easily at the interface and destroy the interface states acting as emission centres and quench the PL intensity of the film. The enhancement of the luminescence properties of ZrO₂ by the passivation of non radiative defects presents in the films make it suitable for gas sensors development, tuneable lasers and compact disc (CD) read-heads.     

Effect of magnesium nitrate vaporization on gas temperature in the graphite furnace

The vaporization of magnesium nitrate was observed in longitudinally-heated graphite atomizers, using pyrocoated and Ta-lined tubes and filter furnace, Ar or He as purge gas and 10–200-μg samples. A charge coupled device (CCD) spectrometer and atomic absorption spectrometer were employed to follow the evolution of absorption spectra (200–400 nm), light scattering and emission. Molecular bands of NO and NO₂ were observed below 1000°C. Magnesium atomic absorption at 285.2 nm appeared at approximately 1500°C in all types of furnaces. The intensity and shape of Mg atomization peak indicated a faster vapor release in pyrocoated than in Ta-lined tubes. Light scattering occurred only in the pyrocoated tube with Ar purge gas. At 1500–1800°C it was observed together with Mg absorption using either gas-flow or gas-stop mode. At 2200–2400°C the scattering was persistent with gas-stop mode. Light scattering at low temperature showed maximum intensity near the center of the tube axis. Magnesium emission at 382.9, 383.2 and 383.8 nm was observed simultaneously with Mg absorption only in the pyrocoated tube, using Ar or He purge gas. The emission lines were identified as Mg ³P°–³D triplet having 3.24 eV excitation energy. The emitting species were distributed close to the furnace wall. The emitting layer was thinner in He than in Ar. The experimental data show that a radial thermal gradient occurs in the cross section of the pyrocoated tube contemporaneously to the vaporization of MgO. This behavior is attributed to the reaction of the sample vapor with the graphite on the tube wall. The estimated variation of temperature within the cross section of the tube reaches more than 300–400°C for 10 μg of magnesium nitrate sampled. The increase of gas temperature above the sample originates a corresponding increase of the vaporization rate. Fast vaporization and thermal gradient together cause the spatial condensation of sample vapor that induces the light scattering.     

Molecular-Level Reinforced Adhesion Between Rubber and PTFE Film Treated by Atmospheric Plasma Polymerization

Extremely strong reinforced adhesion between a polytetrafluoroethylene (PTFE) film and butyl rubber is achieved using an atmospheric pressure plasma graft polymerization, involving argon and acrylic acid vapor. The treated PTFE film is then placed over a raw butyl rubber plate and hot-pressed under 157 N/cm² for 40 min at 150 °C or for 10 min at 180 °C. This procedure results in molecular-level or chemical adhesion between the butyl rubber and the PTFE film. The 180° peeling test results show that a high peeling strength of 3.9 N, per 1 mm sample width, is achieved. Adherend failure of the rubber sheet occurs when the peeling is enforced. From X-ray photoelectron spectroscopy analysis of the treated films, chemical bonds with fluorine atoms are absent from the surface. From scanning electron microscopy analysis, a transparent hydrophilic poly(acrylic acid) layer composed of nanoscale spherical particles is formed. This PTFE-rubber composite material is suitable for high-quality, prefilled medical syringe gaskets.     

Chemiluminescence spectral analysis of styrene-butadiene and acrylonitrile-butadiene rubbers using a multichannel Fourier-transform chemiluminescence spectrometer

The chemiluminescence spectra of styrene-butadiene and acrylonitrile-butadiene rubbers isothermally heated in the range between room temperature and 200 °C were measured with a multichannel Fourier-transform chemiluminescence spectrometer. The observed spectra were analyzed by a least-squares fit using a Gaussian function to determine the peak intensity and the peak wavelength of emission bands. It was found that the peak wavelength of acrylonitrile-butadiene rubbers was slightly longer than that of styrene-butadiene rubbers due to the influence of the nitrile groups. The peak intensity of chemiluminescence from styrene-butadiene rubbers decreased with the styrene content, while that from hydrogenated acrylonitrile-butadiene rubbers increased with the iodine value. From these experimental results, it is concluded that the content of double bonds in the butadiene units in rubbers is measurable by chemiluminescence spectral analysis.     

Dissociation vapor pressure of sodium acetate trihydrate

The water vapor pressure over solid and liquid sodium acetate trihydrate was measured tensimetrically between about 10 and 80°C. Second law enthalpies and entropies of water vaporization were derived from the data. The results are interpreted on the basis of an existing phase diagram.     

Chemiluminescence upon isomerization of dimethyldioxirane in the gas phase and on a sorbent surface

Chemiluminescence (CL) was found upon the isomerization of dimethyldioxirane in the gas phase under argon atmosphere. The intensity of CL increases as temperature increases and decreases with time at constant temperature. If Silipor is placed in a cell containing the dimethyldioxirane vapor in argon, the intensity of CL sharply increases (more than 10 times) and then decreases following the exponential law. In all cases tripletly excited methyl acetate is the emitter of chemiluminescence.[/ p]Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2582–2583, October 1996.     

Use of volatile organic solvents in headspace liquid‐phase microextraction by direct cooling of the organic drop using a simple cooling capsule

A low‐cost and simple cooling‐assisted headspace liquid‐phase microextraction device for the extraction and determination of 2,6,6‐trimethyl‐1,3 cyclohexadiene‐1‐carboxaldehyde (safranal) in Saffron samples, using volatile organic solvents, was fabricated and evaluated. The main part of the cooling‐assisted headspace liquid‐phase microextraction system was a cooling capsule, with a Teflon microcup to hold the extracting organic solvent, which is able to directly cool down the extraction phase while the sample matrix is simultaneously heated. Different experimental factors such as type of organic extraction solvent, sample temperature, extraction solvent temperature, and extraction time were optimized. The optimal conditions were obtained as: extraction solvent, methanol (10 μL); extraction temperature, 60°C; extraction solvent temperature, 0°C; and extraction time, 20 min. Good linearity of the calibration curve (R² = 0.995) was obtained in the concentration range of 0.01–50.0 μg/mL. The limit of detection was 0.001 μg/mL. The relative standard deviation for 1.0 μg/mL of safranal was 10.7% (n = 6). The proposed cooling‐assisted headspace liquid‐phase microextraction device was coupled (off‐line) to high‐performance liquid chromatography and used for the determination of safranal in Saffron samples. Reasonable agreement was observed between the results of the cooling‐assisted headspace liquid‐phase microextraction high‐performance liquid chromatography method and those obtained by a validated ultrasound‐assisted solvent extraction procedure.     

Chemiluminescence of hydrocarbon polymers

The thermal oxidation of some hydrecarbon polymers differing by their degree of branching was studied simultaneously by chemiluminescence and infrared spectrophotometry. In the case of isotactic polypropylene, measurements were made at various temperatures ranging from 140 to 180°C. The other polymers—ethylene–propylene copolymer, low and high density polyethylene—were studied only at 160°C. In all cases, the induction times of chemiluminescence coincide with those of carbonyl growth. The previously proposed mechanisms of light emission are not consistent with the kinetic data or with the structure effects on luminescence, which seems directly related with the presence of tertiary hydrogens. A hypothetical mechanism based on the β scission of tertiary alkoxyls is proposed.     

Silymarin extraction from milk thistle using hot water

Hot water is attracting attention as an extraction solvent in the recovery of compounds from plant material as the search for milder and “greener” solvents intensifies. The use of hot water as an extraction solvent for milk thistle at temperatures above 100°C was explored. The maximum extraction yield of each of the silymarin compounds and taxifolin did not increase with temperature, most likely because significant compound degradation occurred. However, the time required for the yields of the compounds to reach their maxima was reduced from 200 to 55 min when the extraction temperature was increased from 100 to 140°C. Severe degradation of unprotected (plant matrix not present) silymarin compounds was observed and first-order degradation kinetics were obtained at 140°C.     

Three-Phase Solvent Bar Microextraction Combined with HPLC for Extraction and Determination of Plasma Protein Binding of Bisoprolol

A three-phase solvent bar microextraction (TPSBME) technique combined with high performance liquid chromatography (HPLC)?Cfluorescence detection was evaluated for the quantitative determination of plasma protein binding of bisoprolol. Bisoprolol was extracted from a 5.6-mL basified plasma sample (donor phase) into the organic solvent (n-octanol) impregnated in the pores of a hollow fiber and then extracted into an acidic solution (acceptor phase) inside the lumen of the hollow fiber. Metoprolol was used as the internal standard. Several parameters influencing the efficiency of the method were investigated and optimized including organic solvent (n-butanol, n-octanol, dibutyl phthalate, dihexyl ether), stirring rate (100?C1,000 rpm), extraction time (5?C35 min), extraction temperature (15?C45 °C), concentration of the donor phase (0.1?C2 M NaOH) and the acceptor phase (0.5?C5 M formic acid), salt concentration (2.5?C10%, w/v). Under the optimal condition, extraction recoveries from plasma samples were above 61.4% for bisoprolol. The calibration curves were obtained in the range of 10?C100 ng mL^?1 with reasonable linearity (r > 0.994). The method was successfully applied to determine the plasma protein binding rate of bisoprolol.     

Photo-induced chemiluminescence from fibrous polymers and proteins

A commercial thermal chemiluminescence (TCL) instrument was modified to allow in situ sample irradiation at wavelengths in the range 320-700 nm under a controlled atmosphere at constant temperature. Weak photo-induced chemiluminescence (PICL) emission was observed from commercial poly(ethylene terephthalate), polyacrylonitrile, and polyamide 6 fabrics, cotton fabric and from the fibrous proteins wool and feather keratin, silk fibroin and bovine skin collagen (Type 1) after exposure to UVA (320-400 nm) or visible light in nitrogen, followed by a change of the atmosphere to oxygen. Collagen emits PICL of similar intensity to keratin, which demonstrates that tryptophan is not essential for PICL emission from proteins. In all cases the decay of PICL with time is complex and does not follow simple first- or second-order kinetics. The effects of experimental variables, including wavelength of radiation and exposure time, sample temperature and fabric pH on the PICL intensity and decay profile are reported for wool keratin.     

Polytetrafluoroethylene Sputtered PES Membranes for Membrane Distillation: Influence of RF Magnetron Sputtering Conditions

Thin films of fluorocarbon were deposited on polyethersulfone membranes via argon plasma sputtering of a poly(tetrafluoroethylene) (PTFE) target in an RF magnetron plasma reactor. The obtained deposited ultrathin coatings had nanoscale roughnesses and high degrees of fluorination. The intensity of fluorine atom in plasma environment during fluorocarbon deposition was investigated. Depending on the deposition conditions comprising working gas pressure, applied RF power, and distance between the target and the substrate, polymeric films with different chemical compositions and/or morphologies were obtained. The morphologies of the films were analyzed by means of SEM, XPS, and AFM. The results suggested that the sputtered film deposited at a higher pressure and longer target–substrate distance and moderate RF power had a surface composition and chemical structure closer to those of the PTFE film. The treated hydrophobic PES membranes with water contact angles as high as 115° were applied for the first time in an air gap membrane distillation setup for removal of benzene as a volatile organic compound from water. The results showed that the plasma-treated membranes have a comparable or superior performance to that of commercial PTFE used in membrane distillation with similar permeate flux and separation factor after 20 h long term performance.     

Polyol-induced partitioning of essential oils in water/acetonitrile solvent mixtures

Polyol-induced extraction (PIE) is applied to the extraction of essential oils, using glycerol as a mass separating agent. In 1:1 acetonitrile (ACN)/water solvent mixtures, two immiscible phases can be generated. PIE as an alternative extraction technique was assessed by the extraction of the main flavor and fragrance compounds that comprise six essential oils. In the extraction of eugenol (4-allyl-2-methoxyphenol) from clove buds, the partition coefficients were determined and the % recovery and thermodynamic data in the temperature range of ?20 to 20°C were calculated. The main components present in each essential oil extract were identified through gas chromatography/mass spectrometry (GC/MS) and the compositional profile was compared to traditional extraction techniques. The optimized extraction conditions (?10°C, 1:1 ACN/water (v/v), 20% glycerol) for eugenol at ?10°C give a partition coefficient (K_PC) of 87 and an extraction efficiency of 97% in the acetonitrile-rich phase. The eugenol migration to the organic phase is a spontaneous process (ΔG°?=??9.3?kJ/mol) and an endothermic process (ΔH°?=?9.2?kJ/mol) with entropy being the driving force behind the reaction (ΔS°?=?70?J/K, TΔS°?=?18.4?kJ). The technique was applied to five other essential oils (cinnamon bark, caraway seed, spearmint leaf, peppermint leaf, and anise seed oils) with similar results.     

Ethylenebisdithiocarbamate fungicides

DTA curves were run for the ethylenebisdithiocarbamate fungicides maneb, mancozeb and zineb in a nitrogen atmosphere. Zineb produces a curve quite different from the others, with weak endothermic peaks at 166°C, 252°C and 293°C. Maneb and mancozeb have a relatively strong endothermic peak at 185–190°C corresponding to carbon disulphide evolution and a weaker endothemic peak at 290°C corresponding to hydrogen sulphide evolution. Maneb samples and some mancozeb samples also had a minor endothermic peak at 235°C, but this peak was lost after solvent extraction, which proved that it was due to an impurity or impurities. Elemental sulphur was found in the extract and on mixing sulphur with mancozeb, the peak at 235°C made its appearance. There is no distinguishing feature between the DTA curves for maneb and mancozeb. The shapes of the curves are, within experimental limits, indistinguishable, which means that the temperatures and energies of decomposition are the same. The chemist is left with the question whether differences in structure between maneb and mancozeb should lead to different DTA curves.     

Sonochemiluminescence of aromatic hydrocarbons

Multibubble sonoluminescence of water and a series of aromatic hydrocarbons, viz., benzene, toluene, ethylbenzene, and m-xylene (at 25 °C), and a naphthalene melt (at 110–120 °C) was studied. An analysis of the influence of oxygen and argon on the sonoluminescence intensity and the luminescence spectra of these liquid compounds, as well as the effect of additives of ionol, ethanol, and 9,10-dibromoanthracene on m-xylene sonoluminescence, showed that a considerable contribution to the sonoluminescence of aromatic hydrocarbons is made by chemiluminescence reactions associated with their oxidation. This sonochemiluminescence is observed in both the gas phase of cavitation bubbles and the bulk solution where luminescence is retained for a long time after ultrasonication switching-off (the initial intensity of the residual chemiluminescence is up to 10% of the luminescence intensity during sonolysis). As for thermoinitiated oxidation, the afterglow of m-xylene contains the radical and molecular components.     

Wavelength dependence in photochemical vapor deposition of aluminum film using dimethylaluminum hydride

In photochemical vapor deposition of aluminum film on silicon using dimethylaluminum hydride, (CH₃)₂AlH, a surface reaction dominated below a (CH₃)₂AlH pressure of 0.3 m Torr at 200°C, which was induced only with the 160 nm band emitted from a deuterium lamp. A gas-phase reaction occurred above 0.3 mTorr at 200°C, which could be induced by both 160 nm and 240 nm emission bands from the lamp. To distinguish between surface ad gas-phase reactions, a thickness profile was used. At 240°C the surface reaction could be induced even by the 240 nm band, while the deposits formed under illumination of the two bands were thinner than those obtained with only the 240 nm band, indicating occurrence of vacuum ultraviolet (VUV)-enhanced desorption. The mechanism responsible for the observed wavelength dependence in unclear. The electrical resistivity of the films deposited at 200°C was 4.5 μΩ cm, which did not change with wavelength.