Short Induction Period Research Articles

The Role of Poly(N-vinyl-2-pyrrollidone) in Ag ∕ Pd Nanoparticles Formation and Its Application to Electroless Deposition

Poly(-vinyl-2-pyrrollidone) (PVP) has been widely used as a stabilizer to synthesize various kinds of nanoparticles. However, the effect of PVP and its role in the formation process of nanoparticles are not well understood. In our PVP-protected nanoparticles system, ions have higher priority to be reduced in the formation process of nanoparticles. The presence of PVP hinders both and ions. However, the steric obstacle effect of PVP is more pronounced for ions and thus ions are more difficult to diffuse through the polymeric barrier in the particle growth stage. Accordingly, ions deposit onto the preformed nuclei later than ions rendering the palladium-rich surface structure of nanoparticles. Moreover, the steric barrier of PVP is less effective with increasing molecular weight, possibly owing to the decreasing molecular numbers. The feasibility of nanoparticles as activators for electroless copper deposition was also carried out. The crystalline structure of electroless Cu film was not affected by the manner of activation. Furthermore, the nanoparticles had the shortest induction period and thus exhibited the highest activity, which demonstrated their potential to be novel activators for electroless deposition.

Biomimetic deposition process of an apatite coating on NiTi shape memory alloy

Biomimetic deposition process of an apatite coating on NiTi shape memory alloy (SMA) after it was pretreated with 30% H2O2 solution and subsequently 1 M NaOH solution was studied using a simulated body fluid (SBF) soaking test. Biomimetic nucleation of apatite on the chemically pretreated NiTi SMA has a short induction period down to 6 h. With longer soaking time, more apatite appeared on the NiTi substrate but our control experiments did not reveal any apatite formation on the chemically polished NiTi SMA. After immersion in SBF for 48 h, the chemically pretreated NiTi SMA was fully covered with a dense hydroxyapatite coating. The biomimetic deposition of the apatite coating was attributed to the catalytic effect of abundant Ti–OH groups and Na2TiO3 on the surface of the chemically pretreated NiTi SMA.

Analysis of Heat Transfer Fouling by Dry‐Grind Maize Thin Stillage Using an Annular Fouling Apparatus

ABSTRACTIn dry‐grind processing to produce ethanol from corn, unfermented solids are removed from ethanol by distillation and dried to produce distillers dried grains with solubles (DDGS), an animal food. Fouling of thin stillage evaporators has been identified as an important energy consumption issue in dry‐grind facilities. Using an annular fouling apparatus, four batches of thin stillage were analyzed to determine repeatability of fouling rate and induction period measurements. Dry solids, protein and ash concentrations, and pH were correlated to fouling rate and induction period to determine how variation in thin stillage from the same dry‐grind facility affects these fouling parameters. Effects of increasing Reynolds number (Re) in the laminar region on fouling rate, induction period, and fouling deposit protein and ash concentrations were also determined. Repeatability of fouling rate measurements was similar to other studies (CV < 7.0%) but repeatability of induction period measurements was high relative to other studies (CV < 88.7%). Fouling rate increased with increasing dry solids concentration. Thin stillage at Re = 440 had shorter induction periods and greater fouling rates than at Re = 880. Fouling deposits collected from Re = 440 tests had similar protein concentrations and lower ash concentrations compared with deposits from Re = 880 tests.

Oxyhalogen−Sulfur Chemistry: Kinetics and Mechanism of Oxidation of N-Acetylthiourea by Chlorite and Chlorine Dioxide

The oxidation reactions of N-acetylthiourea (ACTU) by chlorite and chlorine dioxide were studied in slightly acidic media. The ACTU-ClO(2)(-) reaction has a complex dependence on acid with acid catalysis in pH > 2 followed by acid retardation in higher acid conditions. In excess chlorite conditions the reaction is characterized by a very short induction period followed by a sudden and rapid formation of chlorine dioxide and sulfate. In some ratios of oxidant to reductant mixtures, oligo-oscillatory formation of chlorine dioxide is observed. The stoichiometry of the reaction is 2:1, with a complete desulfurization of the ACTU thiocarbamide to produce the corresponding urea product: 2ClO(2)(-) + CH(3)CONH(NH(2))C=S + H(2)O --> CH(3)CONH(NH(2))C=O + SO(4)(2-) + 2Cl(-) + 2H(+) (A). The reaction of chlorine dioxide and ACTU is extremely rapid and autocatalytic. The stoichiometry of this reaction is 8ClO(2)(aq) + 5CH(3)CONH(NH(2))C=S + 9H(2)O --> 5CH(3)CONH(NH(2))C=O + 5SO(4)(2-) + 8Cl(-) + 18H(+) (B). The ACTU-ClO(2)(-) reaction shows a much stronger HOCl autocatalysis than that which has been observed with other oxychlorine-thiocarbamide reactions. The reaction of chlorine dioxide with ACTU involves the initial formation of an adduct which hydrolyses to eliminate an unstable oxychlorine intermediate HClO(2)(-) which then combines with another ClO(2) molecule to produce and accumulate ClO(2)(-). The oxidation of ACTU involves the successive oxidation of the sulfur center through the sulfenic and sulfinic acids. Oxidation of the sulfinic acid by chlorine dioxide proceeds directly to sulfate bypassing the sulfonic acid. Sulfonic acids are inert to further oxidation and are only oxidized to sulfate via an initial hydrolysis reaction to yield bisulfite, which is then rapidly oxidized. Chlorine dioxide production after the induction period is due to the reaction of the intermediate HOCl species with ClO(2)(-). Oligo-oscillatory behavior arises from the fact that reactions that form ClO(2) are comparable in magnitude to those that consume ClO(2), and hence the assertion of each set of reactions is based on availability of reagents that fuel them. A computer simulation study involving 30 elementary and composite reactions gave a good fit to the induction period observed in the formation of chlorine dioxide and in the autocatalytic consumption of ACTU in its oxidation by ClO(2).

Cardiac Risks of Breast-cancer Radiotherapy: A Contemporary View

For some time, there has been compelling evidence both from randomised-controlled trials and from observational studies, that some of the breast-cancer radiotherapy regimens used in the past have led to increased risk of mortality from heart disease. There is also some evidence that the more recent regimens used in the USA are associated with lower risks than previous ones, but it is not clear whether current regimens are free from cardiac risk, especially in the light of recent evidence from the survivors of the bombings of Hiroshima and Nagasaki, in whom a clear relationship was observed between the risk of mortality from heart disease and radiation dose for doses in the range 0–4 Gy. Mortality from radiation-induced heart disease usually occurs at least a decade after irradiation. Symptomatic heart disease might have a much shorter induction period, but little information about it is available at present. Subclinical vascular abnormalities have been observed within months of irradiation, via myocardial perfusion imaging studies, but little is known about the relationship between these and later overt heart disease. At present, few data relate heart dose and other specific characteristics of breast radiotherapy to cardiac outcome. Further information on these topics is needed to enable estimation of the cardiac risk, that is likely to arise from radiotherapy regimens in current use and from those being considered for future use. Such knowledge would facilitate radiotherapy treatment planning and enable a reduction in cardiac risk while maintaining the known benefit in terms of breast cancer mortality.

Synthesis of Hydrophilic and Hydrophobic Pd Nanoparticles with in situ Generated Reducing Agent and Their Application as Activator for Electroless Copper and Nickel Depositions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Methylmethacrylate polymerization photoinitiated by 1‐(bromoacetyl)pyrene

AbstractThe photopolymerization of methylmethacrylate induced by pyrene, 1‐acetylpyrene (AP), and 1‐(bromoacetyl)pyrene (BP) has been investigated. Under all conditions employed, pyrene was completely ineffective. Introduction of a carbonyl and a bromo group in pyrene enhanced the polymerization efficiencies. Efficiency of AP as photoinitiator was very low; however, BP was proved to be a good photoinitiator. The polymerization with BP follows first‐order kinetics with respect to monomer conversion, with a shorter induction period as compared with that of AP. The value of the initiator exponent (0.5) and the linear dependence of reciprocal average degree of polymerization on the square root of the initiator concentration suggest radical polymerization with bimolecular termination. IR and NMR spectra showed the atactic nature of polymethylmethacrylate. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 920–926, 2006

A Chain Catalytic Reaction Involving Pd Cluster as Chain Carrier

α−Alkyl- and α,α′-dialkyl-substituted benzylic alcohols PhCR′R′′OH (R′=H, Me, Et, Bu; R′′=H, Me) are transformed to the corresponding dilbenzylic ethers and water in acid-free neat substrate media shortly after the addition of the palladium(I) cluster [Pd4(CO)4(OAc)4] (1). During the catalytic reaction occurring under anaerobic conditions, cluster 1 is gradually decomposed to form Pd black, whereas neither original cluster 1 nor Pd black is responsible for the observed reaction. The true reaction catalyst is generated from cluster 1 after a short induction period. On the basis of the reaction kinetics and the HREM, X-ray diffraction, DTA-TG, and elemental analysis data, the catalytic dehydration is suggested to occur through a nonradical chain mechanism involving an unstable intermediate Pd cluster as the chain carrier.

Compound clathrate hydrate on Titan's surface

Large‐scale multicomponent (compound) clathrate hydrate formation is stable relative to water ice on the surface of Titan. Compound clathrate hydrates are nonstoichiometric crystal of guest molecules trapped inside cages of varying sizes formed by latticeworks of water molecules. They have shorter induction periods and faster reaction rates than pure clathrate hydrates. Compound hydrate is a likely sink for many chemicals occurring on Titan's surface, including ethane, xenon, and other preferred clathrate formers. Water, whose availability is the main control to hydrate formation on Titan, moderates hydrate formation given its relatively small abundance compared to the other hydrate‐forming components.

Synthesis of Hydrophilic and Hydrophobic Pd Nanoparticles with In Situ Generated Reducing Agent and Their Application as Activator for Electroless Copper and Nickel Depositions

A novel method to selectively prepare hydrophilic or hydrophobic Pd nanoclusters simply by regulating reflux time has been developed. By this method, uniform Pd nanoclusters, well-dispersed in aqueous or organic solvents, can be obtained. Both and can be used successfully as activators for electroless metal deposition. The surface modifications of the hydrophilic and hydrophobic Pd nanoparticles both display a short induction period for catalyzing electroless nickel (EN) bath due to protection-agent inhibited adsorption of the reducing agent of a neutral EN bath. In an alkaline electroless copper (EC) bath, easily catalyzes in the bath and has a faster deposition rate compared with because the surfactant, sodium dodecyl sulfate (SDS), could be repulsive and desorbed by . Finally, the electroless copper deposition rate was found to increase if SDS concentration was decreased.

In Situ Ellipsometry Analysis on Formation Process of Al2O3-Ta2O5 Films in Ion Beam Sputter Deposition

thin films are known as highly corrosion-resistant materials for coatings. Here the formation process of films was analyzed by in situ ellipsometry during deposition by ion beam sputtering. Composite targets composed of and plates were used for sputter deposition. During deposition, the formation process of thin films was monitored by a single-wavelength rotating analyzer ellipsometer attached to the sputtering system. The composition, the chemical binding states of constituent elements, and the depth profile of the elements of the films were analyzed by inductively coupled plasma-atomic emission spectroscopy, X-ray photoelectron spectroscopy (XPS), and auger-electron spectroscopy (AES), respectively. Ellipsometric analysis showed that the thickness of the film increased linearly with time after short induction periods. The refractive index of the films increases with increasing tantalum cationic fraction. The extinction coefficient of the films was larger than those of single and films. The XPS analysis showed that the preferential deposition of the component occurred in the induction period and the codeposition of and in the linear growth stage. The AES analysis showed that the content of constituent elements was homogeneous from the top to the bottom of the films in the linear growth stage.

S-Oxygenation of Thiocarbamides II: Oxidation of Trimethylthiourea by Chlorite and Chlorine Dioxide

The kinetics of the oxidation of a substituted thiourea, trimethylthiourea (TMTU), by chlorite have been studied in slightly acidic media. The reaction is much faster than the comparable oxidation of the unsubstituted thiourea by chlorite. The stoichiometry of the reaction was experimentally deduced to be 2ClO2- + Me2N(NHMe)C=S + H2O --> 2Cl- + Me2N(NHMe)C=O + SO4(2-) + 2H+. In excess chlorite conditions, chlorine dioxide is formed after a short induction period. The oxidation of TMTU occurs in two phases. It starts initially with S-oxygenation of the sulfur center to yield the sulfinic acid, which then reacts in the second phase predominantly through an initial hydrolysis to produce trimethylurea and the sulfoxylate anion. The sulfoxylate anion is a highly reducing species which is rapidly oxidized to sulfate. The sulfinic and sulfonic acids of TMTU exists in the form of zwitterionic species that are stable in acidic environments and rapidly decompose in basic environments. The rate of oxidation of the sulfonic acid is determined by its rate of hydrolysis, which is inhibited by acid. The direct reaction of chlorine dioxide and TMTU is autocatalytic and also inhibited by acid. It commences with the initial formation of an adduct of the radical chlorine dioxide species with the electron-rich sulfur center of the thiocarbamide followed by reaction of the adduct with another chlorine dioxide molecule and subsequent hydrolysis to yield chlorite and a sulfenic acid. The bimolecular rate constant for the reaction of chlorine dioxide and TMTU was experimentally determined as 16 +/- 3.0 M(-1) s(-1) at pH 1.00.

Study on the combustion behavior of methane over Ce–Zr-modified Pd/Al 2O 3 catalysts

The effects of ceria and zirconium additions to alumina-supported palladium catalysts on methane combustion behavior have been investigated. A series of Ce–Zr-modified Al 2O 3 supports and their supported Pd catalysts are prepared using impregnation method and then characterized by BET, XRD, LR, TEM, XPS techniques. The results show that the addition of Ce–Zr improves the thermal stability of alumina. The thermal stability of alumina increases with increasing the loading of Zr. The methane oxidation activity and thermal stability is found to be dependent on the Ce:Zr ratio over the Pd/Ce x Zr 1− x /Al 2O 3 catalysts. The Pd/Ce 0.2Zr 0.8/Al 2O 3 exhibits the highest activity and thermal stability for methane oxidation. The temperatures for the 90% methane conversion are 448 and 455 °C for the Pd/Ce 0.2Zr 0.8/Al 2O 3 catalysts calcined at 500 and 1100 °C, respectively. TEM results show that the particle size of Pd is not the key factor influencing the activity of Pd/Ce 0.2Zr 0.8/Al 2O 3 catalyst. An induction period is present during methane combustion reaction for the Pd/Al 2O 3 and Pd/Ce x Zr 1− x /Al 2O 3 catalysts (calcined at 1100 °C), but the lengths of induction period are obviously different and the Pd/Ce 0.2Zr 0.8/Al 2O 3 catalyst exhibits the shortest induction period. XPS results show that comparing to Pd/Al 2O 3 catalyst the addition of Ce–Zr stabilizes Pd in a high oxidation state and enhances the reoxidation of metallic Pd to the active PdO under reaction conditions. Therefore the Pd/Ce x Zr 1− x /Al 2O 3 catalysts compared to Pd/Al 2O 3 catalysts have higher thermal stability and shorter induction period.

Oxyhalogen−Sulfur Chemistry: Kinetics and Mechanism of Oxidation of Guanylthiourea by Acidified Bromate

This article reports on the kinetics and mechanism of oxidation of the biologically active molecule guanylthiourea (GTU) by acidic bromate. This was a follow-up of a previous study in which mild oxidizing agents acidic iodate and molecular iodine oxidized GTU to a ring-cyclized product: 3,5-diamino-1,2,4-thiadiazole. In contrast, acidic bromate and molecular bromine, as stronger oxidizing agents, were able to oxidize GTU all the way to a complete desulfurization to yield guanylurea. No N-bromination was observed on any of the amino groups on guanylurea. The stoichiometry of the reaction was deduced to be 4BrO3- + 3H2N(NH)CNH(CS)NH2 + 3H2O → 4Br- + 3H2N(NH)CNH(CO)NH2 + 3SO42- + 6H+. In excess bromate conditions in which the ratio of oxidant to reductant R = [BrO3-]0/[GTU]0 > 1.6, the stoichiometry of the reaction was 8BrO3- + 5H2N(NH)CNH(CS)NH2 + H2O → 4Br2(aq) + 5H2N(NH)CNH(CO)NH2 + 5SO42- + 2H+. The direct reaction of aqueous bromine with GTU was extremely fast with an estimated lower limit bimolecular rate constant of 7.5 ± 1.2 × 104 M-1 s-1. This rapid reaction with bromine produced reaction dynamics which involved bromine formation after a short induction period which was determined by the time it took for the complete oxidation of GTU and its oxidation intermediates. The mechanism of the reaction involved the initial formation of the ring-cyclized 3,5-diamino-1,2,4-thiadiazole which was later successively oxidized through the sulfoxide and sulfone, followed by the opening of the ring to yield sulfate and guanylurea. All the observed global reaction dynamics were satisfactorily modeled by a simple mechanism involving 14 elementary reactions.

PALM OIL CRYSTALLIZATION: EFFECTS OF COOLING TIME AND OIL CONTENT

ABSTRACT Isothermal crystallization behavior of fluid shortening formulation from blends of palm oil and palm olein was investigated. The oil blends filled in nuclear magnetic resonance (NMR) tubes to a height of 2.5 cm were melted at 70C for 30 min crystallization time. A set of 11 tubes for each temperature was placed at selected crystallizing time and the solid fat content (SFC) measured in a Bruker pulse NMR spectrometer. Crystal distribution of the same blend was observed under polarized microscope at the same time interval. A correlation was developed between SFC and crystal distribution. The crystallization curves demonstrated two distinct steps corresponding to two crystallization stages as a result of the occurrence of mixed crystallization. Crystallization was selective to the high melting triacylglycerols (TAG) at all temperatures as shown by shorter induction periods in blends with more than 41.8% palmitic acid. High melting TAG crystallized first and acted as nuclei for recrystallization of the low melting TAG. However, the low melting TAG at the same time could also solubilize the formed crystals. The average SFC as a function of time was 50% lower than the SFC profile. Slow crystallization temperature was able to promote large crystal formation that influences SFC of palm‐based shortenings. Blends of 40–60% palm oil showed promising formulations of stable fluid palm‐based shortening.

Characterization by Chemiluminescence of Unstabilized and HALS-Stabilized LDPE Films Exposed to Natural Weathering Conditions

ABSTRACT Photostability of low-density polyethylene (LDPE) films under natural weathering conditions was investigated in the absence and the presence of various structures of hindered amine light stabilizers (HALS) by chemiluminescence (CL) and Fourier transform infrared (FTIR) spectroscopy. The stabilizers studied were Sanduvor PR 31 (as grafted HALS) and Uvasil 299 and Tinuvin 123 (as non-grafted HALS). The HALS were added separately to LDPE at the same concentration, namely 0.3% (w/w). It was found that the weathered stabilized samples exhibited a relative long period during which the CL signal slowly increased, while for unstabilized samples, CL increased after a short induction period. This behavior could be explained by reduction in the rate of hydroperoxide decomposition caused by nitroxyl radicals. However, the very high increase in stability observed in the case of Sanduvor PR 31 sample could be assigned to the grafting effect of the HALS on the polymer chain. At longer exposure times, the oxidation induction time decreased slowly as a result of stabilizer consumption in the photooxidative process. These changes in CL parameters were found to correlate with carbonyl index determined by FTIR spectroscopy.

Emulsifier-free ultrasonic emulsion copolymerization of styrene with acrylic acid in water

A copolymer of styrene with acrylic acid (Poly(St–co–AA)) was directly synthesized by random emulsion copolymerization under ultrasonic irradiation without any volatile organic solvent (VOC) and emulsifier being used. Only water was used as solvent. The copolymer has been characterized by FT-IR spectra and H-NMR; its characteristic viscosity has been used to measure its average molecular weight. Our results show that high monomer conversion and short induction period were achieved. The effects of ultrasonic power and time on the average molecular weight and monomer conversion are discussed. The self-assembly behavior of the copolymer into regular pattern structures was imaged by atomic force microscopy (AFM).

The activity of Pt/SiO2 catalysts obtained by the sol-gel method in the hydrosilylation of 1-alkynes

Heterogeneous platinum catalysts (Pt/SiO2) obtained by the sol-gel process at pH 3 and 9 have been used in the hydrosilylation reaction of 1-alkynes using various silanes. Once the catalysts were activated they were used in the hydrosilylation of 1-alkynes after a short induction period. The product distribution was quite similar in either case but important differences in catalytic activity and turnover reactions were observed. The catalyst obtained in the basic medium after each reaction lost its catalytic activity, so further activation was needed. To understand this behavior, the catalysts were characterized by 29Si CPMAS NMR, FT IR, and BET surface area measurements. The 29Si CPMAS NMR studies showed the presence of terminal and bridged hydroxyl groups in the Pt/SiO2 catalyst at pH = 9. Similar results were observed by FT IR analysis because of the catalysts' synthetic conditions.Key words: hydrosilylation, sol-gel, Pt/SiO2, supported-metal catalysts, phenylacetylene, diphenylacetylene, 29Si NMR CP-MAS.

A study of the polymer flocculation reaction in a linear pipe with a focused beam reflectance measurement probe

A linear pipe reactor (LPR) system was used to study the flocculation of mineral suspensions with commercial flocculants under a variety of operating conditions. Incorporation of a Lasentec focused beam reflectance measurement (FBRM) probe into the system provided real-time, in situ characterisation of the aggregate dimensions during the flocculation process. At constant flow rate, variation of the distance between the flocculant addition point and detection by the FBRM probe enabled control of the reaction time for flocculation. Once flocculant is mixed with the slurry, the size of the aggregates at a given point downstream in the LPR is determined by the relative rates of the competing processes of aggregate formation and rupture. These processes depend upon, amongst others, upon the mixing conditions, flocculant dosage and solids concentration of the slurry. The mixing intensity present within the LPR is determined by the pipe diameter and the slurry flow rate. Both a calcite slurry and a slimes fraction from a sand-processing operation were studied to assess their flocculation performance under different operating conditions (flow rate, flocculant dosage). Following a short induction period, aggregate size increased rapidly to a peak, with the rate of change indicative of the net aggregation kinetics. Rupture processes then dominated with aggregate size decreasing at a slower rate. The flow rate and hence the shear conditions had a marked effect on the aggregate structure. The effective (net) aggregation rate increased as shear increased, but the ultimate aggregate size decreased reflecting the fragility of large aggregates. For both systems, increasing the flocculant dosage increased the maximum aggregate size, but the effective aggregation rate only increased for the sand slimes, while reaching a constant rate for the calcite system. It is proposed that this reflects the degree to which the particle surface is effectively covered by the adsorbed flocculant.

Reconstructing the Incidence of Human Immunodeficiency Virus (HIV) in Hong Kong by Using Data From HIV Positive Tests and Diagnoses of Acquired Immune Deficiency Syndrome

Summary The human immunodeficiency virus–acquired immune deficiency syndrome (HIV–AIDS) epidemic in Hong Kong has been under surveillance in the form of voluntary reporting since 1984. However, there has been little discussion or research on the reconstruction of the HIV incidence curve. This paper is the first to use a modified back-projection method to estimate the incidence of HIV in Hong Kong on the basis of the number of positive HIV tests only. The model proposed has several advantages over the original back-projection method based on AIDS data only. First, not all HIV-infected individuals will develop AIDS by the time of analysis, but some of them may undertake an HIV test; therefore, the HIV data set contains more information than the AIDS data set. Second, the HIV diagnosis curve usually has a smoother pattern than the AIDS diagnosis curve, as it is not affected by redefinition of AIDS. Third, the time to positive HIV diagnosis is unlikely to be affected by treatment effects, as it is unlikely that an individual receives medication before the diagnosis of HIV. Fourth, the induction period from HIV infection to the first HIV positive test is usually shorter than the incubation period which is from HIV infection to diagnosis of AIDS. With a shorter induction period, more information becomes available for estimating the HIV incidence curve. Finally, this method requires the number of positive HIV diagnoses only, which is readily available from HIV–AIDS surveillance systems in many countries. It is estimated that, in Hong Kong, the cumulative number of HIV infections during the period 1979–2000 is about 2600, whereas an estimate based only on AIDS data seems to give an underestimate.