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1.
The electrochemical behaviour of copper in neutral buffered and non-buffered synthetic seawater and in pure chloride solutions has been studied by cyclic voltammetry, weight loss measurements, open circuit potential and scanning electron microscopy (SEM). Values of the repassivation potentials of Cu in non-buffered and buffered synthetic seawater, at 50 mV s–1, were 0.12 and 0.46 V vs. SCE, respectively. The sharpness, heights and location of the different peaks as well as their charges were shown to be influenced by the composition of the solution, buffering conditions, deoxygenation, polarization potential and time. High chloride concentrations lead to higher oxidation charges. The anodic and the cathodic charges were shown to increase as the chloride concentration increases. The open circuit potential transients of copper in non-deoxygenated, non-buffered synthetic seawater indicate pitting from the beginning of the exposure, while in buffered solutions the pitting appeared only after a quite long exposure period, i.e. after 40 days. Corrosion rates of Cu samples after 3 months of immersion were higher in solutions of pure chloride (0.5 M) than in synthetic seawater. After six months the differences were even more noticeable. SEM images have showed a somewhat higher density of pits on copper samples immersed in the chloride solution (0.5 M), in comparison with those in synthetic seawater. 相似文献
2.
The compost isolate,Aspergillus fumigatus, produces the exoglucanase, endoglucanase, and Β-glucosidase enzymes required for the breakdown of crystalline cellulose.
Cellulose breakdown and extracellular enzyme levels in liquid culture can be affected by low pH values attained during fungal
growth. During growth ofA. fumigatus on modified Czapeck-Dox medium containing 1% (w/v) Avicel, it was found that Β-glucosidase activity was lost and endoglucanase
activity, reduced, when pH values fell below 3.
The effect of buffering (0.2M phosphate, pH 6.15) was examined and compared with the unbuffered medium. Beta-glucosidase activity could be detected throughout
the incubation period in the buffered medium and endoglucanase activity was approximately tenfold greater. Exoglucanase activity
also showed an increase in the buffered system.
Concentrations of phosphate buffer ranging from 0.05 to 0.8M were incorporated into the medium and optimum cellulose breakdown and extracellular enzyme production occurred between 0.1
and 0.2M.
Reports suggest that increasing substrate concentration does not improve upon the levels of extracellular cellulase produced
because of enzyme inactivation resulting from rapid decreases in pH. Using the buffered medium described previously,A. fumigatus was grown on concentrations of Avicel ranging from 0.5 to 10% (w/v). Cellulose breakdown and extracellular enzyme production
was compared with that achieved by a similar nonbuffered system.
Endoglucanase and Β-glucosidase activity increased with time and with substrate concentration up to 5% (w/v) in the buffered
medium. Beta-glucosidase was negligible at all concentrations of Avicel in the unbuffered medium and endoglucanase activity
decreased with increasing substrate concentration with maximum levels approximately eightfold lower than in the buffered system.
Extracellular exoglucanase activity was lower in the buffered medium and only increased to levels comparable with those achieved
by the unbuffered medium towards the end of the incubation period. In the unbuffered system, exoglucanase activity decreased
with increasing substrate concentration, but no such effect was observed in the buffered medium. Negligible growth occurred
in both media at 10% (w/v) substrate.
The percentage weight loss recorded in the Czapeck-Dox medium also decreased with increasing substrate concentration, while
in the buffered medium, over 95% weight loss was recorded in up to 5% (w/v) Avicel.
It appeared that cellulose breakdown was more rapid in the buffered medium and a time-course carried out to determine the
rate of cellulolysis showed 97% cellulose breakdown after 12 d, corresponding to a plateau and a subsequent decrease in extracellular
cellulase levels. 相似文献
3.
G. D'Andrea V. Mucciante F. Fantauzzi 《Journal of Thermal Analysis and Calorimetry》2001,65(3):737-743
At 298.15 K, the solubilization of hen ovotransferrin at buffered pH 7.8 (0.08 M Tris⋅HCl buffer, containing 0.1 M CaCl2) and the solubilization of α-chymotrypsin (from bovine pancreas) at non-buffered pH 3.0 (0.001 M HCl) both resulted in large
exothermic reactions, being the apparent ΔHs –2485 in the first case and –780.1 kJ mol–1 in the second case, respectively. By contrast, the complete hydrolysis of ovotransferrin (pH 7.8) achieved by using a-chymotrypsin
(pH 3.0) gave an endothermic reaction with ΔH=+31.84 kJ mol–1.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
A. N. Kharlanov L. N. Ikryannikova V. V. Lunin A. Yu. Stakheev 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(7):1117-1123
The physicochemical properties of the surface of the Y0.1Ce
x
Zr1−x
O2−δ, La0.1Ce
x
Zr1−x
O2−δ (x=0.1–0.7), and Y0.1Pr0.3Zr0.6O2−δ. complex oxide systems were studied using IR and X-ray photoelectron spectroscopies. An appreciable enrichment of the surface
of the solids in rare-earth-metal cations (cerium or praseodymium) during the synthesis was revealed. While cations are uniformly
spread over the surface of cerium-zirconium solid solutions, the Y0.1Pr0.3Zr0.6O2−δ surface is covered by the clusters or even a phase of praseodymia. Reductive treatment in hydrogen with subsequent reoxidation
results in the segregation of cerium ions on the Y0.1Ce0.3Zr0.6O2−δ surface at a temperature as low as 770 K.
Original Russian Text ? A.N. Kharlanov, L.N. Ikryannikova, V.V. Lunin, A. Yu. Stakheev, 2007, published in Zhurnal Fizicheskoi
Khimii, 2007, Vol. 81, No. 7, pp. 1271–1277. 相似文献
5.
Zanaty Rady Komy 《Mikrochimica acta》2000,135(1-2):35-43
A highly sensitive, selective, and rapid differential pulse anodic stripping voltammetric method at HMDE is described for
the determination of trace concentrations of Mn2+. The determination of Mn2+ in non-buffered chloride solution is seriously disturbed by the presence of Ni2+, Co2+, Cr3+, Zn2+ and Cu2+ due to intermetallic compound formation. The procedure is based on the addition of low amounts of cyanide as a masking agent.
The interference of < 20 μgL−1 of Ni2+, Co2+ and Cr3+ and < 75 μgL−1 of Cu2+ and Zn2+ can thus be avoided, as the formed cyanide complexes prevent intermetallic compound formation during the short accumulation
period. Thus, the addition of cyanide greatly improves the DPASV determination of manganese in non-buffered medium. A comparison
between the determination of Mn2+ in the presence of a mixed cyanide/non-buffered chloride and in the ammoniacal buffer solution shows that the peak current
of manganese in the presence of cyanide is four times higher with the same peak potential. The proposed method is shown to
be applicable for the Mn2+ determination in both ground and tap water. A good agreement is obtained between the results by DPASV and AAS.
Received May 14, 1999. Revision May 25, 2000. 相似文献
6.
Andrei Blasko Alana Leahy-Dios William O. Nelson Steven A. Austin Robert B. Killion Gary C. Visor Ian J. Massey 《Monatshefte für Chemie / Chemical Monthly》2001,132(7):789-798
Summary. The kinetic and thermodynamic solubilities of Roche (Ro) pharmaceutical compounds were determined by HPLC, titrimetry, and UV/Vis spectroscopy in aqueous buffers and in non-buffered
systems. For kinetic solubility, a turbidimetric method that allows the rapid determination of solubilities using small amounts
of compounds (5–50 mg) was used. Two types of precipitation were observed during the kinetic solubility determinations: i) a disperse precipitation where the solution became foggy with very small particles uniformly distributed in the solution,
and ii) discrete precipitation characterized by formation of crystals that rapidly sediment. The thermodynamic solubility was determined
by shake flask and titrimetrically using a pH-STAT. The pH-STAT titrimetric method for the pH-thermodynamic solubility profile determination eliminates the buffer species and represents a new way to approach the solubility
characterization of pharmaceutical compounds. The strengths of the turbidimetric method for determining the kinetic solubility
are its rapidity, minimal compound requirements, and suitability for high throughput screening. The limitations are that the
maximum solubility is limited to less than 100 mg · cm−3, and the precipitation of trace impurities cannot be distinguished from precipitation of the analyte. The pH-STAT titrimetric approach for the thermodynamic solubility has a lower throughput and is suitable for the characterization
of the lead candidate. It is not limited in its solubility range and provides a common basis for the comparison of the solubility
values at different pH values in contrast to traditional buffered systems.
Received August 21, 2000. Accepted (revised) February 5, 2001 相似文献
7.
Paula Loureiro Paulo Thais Adriana Colman-Novaes Laynara Dayene Soares Obregão Marc Árpád Boncz 《Applied biochemistry and biotechnology》2013,169(8):2457-2466
Cassava wastewater (cww) contains high concentrations of easily acidifying compounds, requiring a buffered system to allow a stable operation during anaerobic digestion (AD). The possibility to include a preliminary one-step fungi treatment aimed at raising the pH and buffering the cww prior to AD was studied. Preliminary tests were performed with a naturally grown fungal mixed culture, under aerated (AE), non-aerated (NAE) and initially oxygen-deprived (IOD) conditions. The cww was pre-treated by the NAE condition, until reaching a soluble chemical oxygen demand (COD) of 10 g?L?1 and pH 6.4 (batch A) and pH 5.7 (batch B). The fungal mixed culture showed ability to biodegrade the cww with initial pH of 4.4 and 14,500 mg?COD?L-1, raising the pH over 8.5, with only 13 % of COD remaining within 27 days for both AE and NAE condition. The fungal pre-treated-cww (FPTcww) was subjected to anaerobic digestion under different buffered (CaCO3 and NaHCO3) and non-buffered conditions. The FPTcww with initial pH at 6.4 provided stability during the anaerobic biodegradability tests, showing the possibility of system operation without buffer addition, with final pH around 7. The application of a fungal pre-treatment can be a promising strategy to permit the anaerobic digestion of carbohydrate-rich wastewaters. 相似文献
8.
Conductometric and calorimetric titrations of Extremely Diluted Solutions (EDS) were performed by adding HCl or NaOH solutions.
The aim of this study is to obtain further confirmation of the hypothesized presence, in the EDS, of molecular aggregates
of water molecules. The measurements on the EDS evidenced some relevant differences compared to those on solutions with just
water as solvent. The conductivity and the pH caused by adding the titrant, namely NaOH or HCl, were markedly different to
those of the control solutions. We suppose that the preparation procedure of the EDS could produce non-equilibrium changes
in the supramolecular structure of water. The experimental results were interpreted by considering the interactions that can
take place between the OH− or H3O+ and the hypothesized molecular aggregates of water molecules i.e. dissipative structures. A comparison was made about the
nature of the driving force that leads to the formation of the complexes between the two ions deriving from probes and the
molecular aggregates of water molecules (dissipative structures). In this study, we have determined the thermodynamic parameters
of association between molecular aggregates of water molecules (dissipative structures) in the EDS and OH− or H3O+ probe ions. The experimental results were interpreted by considering a favorable interaction between the H3O+ and OH− ions and the dissipative structures, due, probably, to steric hindrance and chemical affinity with the aggregates. 相似文献
9.
D. Cui A. Puranen J. Devoy A. Scheidegger O. X. Leupin P. Wersin R. Gens K. Spahiu 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(2):349-354
To understand the fate of 79Se in a repository-like environment, the interactions between iron canister surface with dissolved selenite (SeO3
2−) and selenate (SeO4
2−) in anaerobic solutions have been investigated. Se(IV) immobilization on iron surface was observed to be about 100 times
faster than that of Se(VI) at same conditions. An iron surface coated with a FeCO3 layer corrosion product is more reactive than a polished iron to immobilize Se(IV) and Se(VI). The reacted iron surfaces
were analysed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Raman
spectrometry and micro-X-ray Absorption Spectroscopy (XAS). The result show that Se(IV) and Se(VI) were reduced and precipitated.
The dominating phase was found to be FeSe2. 相似文献
10.
Raman spectroscopy at 25 °C was performed to analyze speciation in quenched solutions after experiments on sodium tungstates
and sodium tungstate bronze dissolution at t=500 °C, p=1000 bar. The experiments were conducted under different oxidation-reduction conditions in sodium chloride solution media.
The spectra of the quenched solutions were different from those of the reference solutions of 0.02 mol⋅kg−1 W(VI) (H2O) in the pH range 2.3–7.2. Thermodynamic models were established and the fields of predominance of different isopolytungstate
species at 25–50 °C were determined. The experimental results of tungstate dissolution demonstrates that reduced tungstate
solutions may contain a significant amount of tungsten species with valence states lower than W(VI). 相似文献
11.
F. Soares Afonso M. M. M. Neto M. H. Mendonça G. Pimenta L. Proença I. T. E. Fonseca 《Journal of Solid State Electrochemistry》2009,13(11):1757-1765
The corrosion of copper in a typical Portuguese soil was studied. The original soil was characterised, and modifications were
produced by adding chloride, and HClO4 solutions, or by increasing its relative humidity. The aggressiveness degree of the various soil samples was determined.
Copper coupons exposed for 3 months in the original and in the modified soil samples were analysed. The average corrosion
rates determined from gravimetric data were in good correlation with the soil aggressiveness. The morphology of the corroded
copper surfaces, with and without corrosion products, was analysed by visual observation, optical microscopy and scanning
electron microscopy. Energy dispersive spectroscopy was used for the semi-quantitative analysis of the corrosion products
and X-ray diffraction spectroscopy to identify the crystalline products. Cuprite has been identified on the copper samples
corresponding to the interfaces Cu|S6 and Cu|S8, plus paratacamite on the copper coupon exposed to the soil with higher concentration
of chloride (S6). Polarisation curves of copper samples in neutral solutions made by adding different amounts of chloride
ions to the soil washing water, under deaereated conditions, were recorded and analysed. The passivity breakdown potential
has shown, as expected, a displacement to the cathodic direction as the Cl− ion concentration increases. 相似文献
12.
A. L. Stroyuk V. M. Dzhagan S. Ya. Kuchmii M. Ya. Valakh D. R. T. Zahn C. von Borczyskowski 《Theoretical and Experimental Chemistry》2007,43(5):297-305
The luminescent characteristics of CdxZn1−xS nanoparticles were studied. It was shown that the emission is due to the recombination of holes in the valence band with
electrons captured by two sorts of traps, of which the traps with lower energy were ascribed to the surface states of the
CdxZn1−xS nanoparticles. It was established that the CdxZn1−xS nanoparticles have more pronounced ability than CdS nanoparticles to accumulate excess negative charge under the conditions
of pulsed irradiation. It was shown that the consumption of the photogenerated electrons in nanosecond and microsecond time
scales involves the participation of one and the same electron traps. It was established that the rate of interaction of the
electrons captured by the surface traps with oxygen increases with decrease in the size of the nanoparticles.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 275–281, September–October, 2007. 相似文献
13.
Lachezar Radev Maria Helena V. Fernandes Isabel Miranda Salvado Daniela Kovacheva 《Central European Journal of Chemistry》2009,7(4):721-730
In this work we present our experimental results on synthesis, structure evolution and in vitro bioactivity assessment of new gelatin/silicocarnotite hybrid materials. The hybrids were obtained by diluting gelatin (G)
and silicocarnotite (S) ceramic powder with G:S ratios of 75:25 and 25:75 wt.% in hot (40°C) water. The hybrids were characterized
using XRD, FTIR, SEM/EDS and XPS. FTIR depicts that the “red shift” of amide I and COO− could be attributed to the fact that the gelatin prefers to chelate Ca2+ from S. The growth of calcium phosphates on the surface of the hybrids synthesized and then immersed in 1.5 SBF for 3 days
was studied by using of FTIR, XRD and SEM/EDS. According to FTIR results, after an immersion of 3 days, A and B-type CO3HA can be observed on the surface. XRD results indicate the presence of hydroxyapatite with well defined crystallinity. SEM/EDS
of the precipitated layers show the presence of CO3HA and amorphous calcium phosphate on the surface of samples with different G/S content when immersed in 1.5 SBF. XPS of the
G/S hybrid with 25:75 wt.% proved the presence of Ca-deficient hydroxyapatite after an in vitro test for 3 days. 相似文献
14.
Summary The separation of inorganic anions (NO3
−, NO2
−, Cl−, Br−, I−, SO4
2−, S2O3
2−) by ion-interaction chromatography mediated with a specific dye has been investigated. Chromatography was performed on a
LiChrospher RP-18 colum dynamically coated with crystal violet, using acetonitrile-water buffered with phthalate as the mobile
phase. The presence of the dye in the eluent enabled indirect spectrophotometric detection of the analytes, which have no
significant UV absorption. Retention data were collected for the different anions by varying the composition of the mobile
phase according to a full factorial experimental design. A theoretical model for the retention of singly- and doubly-charged
analytes, on the basis of the two main processes of ion-exchange and ion-pair formation, has been proposed and validated with
the experimental data. 相似文献
15.
Imre Miklós Szilágyi István Sajó Péter Király Gábor Tárkányi Attila L. Tóth András Szabó Katalin Varga-Josepovits János Madarász György Pokol 《Journal of Thermal Analysis and Calorimetry》2009,98(3):707-716
This article discusses the formation and structure of ammonium tungsten bronzes, (NH4)
x
WO3−y
. As analytical tools, TG/DTA-MS, XRD, SEM, Raman, XPS, and 1H-MAS NMR were used. The well-known α-hexagonal ammonium tungsten bronze (α-HATB, ICDD 42-0452) was thermally reduced and
around 550 °C a hexagonal ammonium tungsten bronze formed, whose structure was similar to α-HATB, but the hexagonal channels
were almost completely empty; thus, this phase was called reduced hexagonal (h-) WO3. In contrast with earlier considerations, it was found that the oxidation state of W atoms influenced at least as much the
cell parameters of α-HATB and h-WO3, as the packing of the hexagonal channels. Between 600 and 650 °C reduced h-WO3 transformed into another ammonium tungsten bronze, whose structure was disputed in the literature. It was found that the
structure of this phase—called β-HATB, (NH4)0.001WO2.79—was hexagonal. 相似文献
16.
Yevgeny M. Paransky Alexander I. Berner Irena Y. Gotman Elazar Y. Gutmanas 《Mikrochimica acta》2000,134(3-4):171-177
The combination of energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD) techniques in scanning
electron microscope was employed to characterize the reacted interface between Ti matrix and AlN particles. Due to the high
localization of EDS and EBSD, representative measurements of chemical composition and reliable determination of the crystal
structure were possible for each phase in the reaction zone with complex morphology. The TiN1−x (cubic, NaCl type), Ti3AlN (cubic, perovskite type) and Ti-rich Ti3 Al (hexagonal, Ni3Sn type) phases were identified in the reaction zone after annealing at 1100 °C. EDS+EBSD combination is an efficient tool
for phase analysis at the interface in reactive multicomponent systems.
Received August 21, 1999. Revision November 21, 1999. 相似文献
17.
Chen-Zhong Yao Hui-Xuan Ma Xi-Sheng Zhang Li-Xin Meng Li-Ping Zhao Ling Tai Yu-Chun Wang Qiao-Juan Gong Ye-Xiang Tong 《Journal of Solid State Electrochemistry》2011,15(6):1193-1199
Magnetic dendrites of Co
x
Pb1−x
were fabricated through potentiostatic electrochemical deposition on Cu substrates in boric acid solution at room temperature.
The as-deposited dendrites were determined by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron
microscopy (TEM), electrodeposition (ED), and energy dispersive X-ray spectroscopy (EDS). SEM results indicate that the Co
x
Pb1−x
dendrites are highly symmetrical in structures. The diameters of the branches are about 50 ~ 200 nm, and the backbones are
continuous with lengths up to about 10 μm. XRD patterns show that the as-deposited dendrites are solid solutions. The annealing
treatment can result in the recrystallization of these metastable alloys into two separate phases. TEM, ED, and EDS results
also reveal that the backbones and the branches of the dendrites are composed of different amounts of cobalt. Magnetic measurements
confirm that the as-deposited Co
x
Pb1−x
dendrites have a softly ferromagnetic behavior, and a small coercive force (about 80 Oe). Also the saturation magnetizations
of the Co
x
Pb1−x
dendrites decrease rapidly with the temperature increasing. 相似文献
18.
Tanţa Spătaru Maria Marcu Loredana Preda Petre Osiceanu Jose Maria Calderon Moreno Nicolae Spătaru 《Journal of Solid State Electrochemistry》2011,15(6):1149-1157
Polytyramine (PTy) is shown to be a possible alternative to other conducting polymers as a support material for fuel cell
electrocatalysts such as platinum. In this work, a Pt–PTy composite was prepared via potentiodynamic deposition of polytyramine
on graphite substrate, followed by the electrochemical deposition of Pt nanoparticles. The material obtained by this straightforward
method exhibited, for platinum loadings as low as ca. 0.12 mg cm−2, a specific electrochemically active surface area of the electrocatalyst of ca. 54 m2 g−1, together with a good electrocatalytic activity for methanol oxidation in acidic media, thus ensuring better efficiency of
Pt utilization. The system Pt–PTy appears to be worthy of development for methanol fuel cell applications also because the
results suggested that, when deposited as small particles in a PTy matrix, platinum is less sensitive to fouling during CH3OH oxidation. 相似文献
19.
M. R. Baklanov A. A. Karpushin K. P. Moginikov A. N. Sorokin 《Journal of Structural Chemistry》1996,37(1):11-17
We used the AM1 quantum chemical and cluster models to study the mechanism of formation of a SiF2-like layer and dissociation of the Si−Si bond during the interaction of atomic fluorine with the (111) surface of silicon.
It is shown that the negatively charged (Si3−Si−F2)− complex with the five-coordinated centered silicon atom plays an important part in these processes. The above complex participates
in the interaction of atomic fluorine with silicon to form a SiF2-like layer and break the subsurface Si−Si bonds without penetration of fluorine atoms into the subsurface silicon layers.
Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 14–21, January–February, 1996.
Translated by I. Izvekova 相似文献
20.
Kolosova AY Shim WB Yang ZY Eremin SA Chung DH 《Analytical and bioanalytical chemistry》2006,384(1):286-294
A direct competitive enzyme-linked immunosorbent assay (ELISA) based on a monoclonal antibody has been developed and optimized
for detection of aflatoxin B1 (AFB1), and an ELISA kit has been designed. This immunoassay was highly specific, sensitive, rapid, simple, and suitable for aflatoxin
monitoring. AFB1 concentrations determinable by ELISA ranged from 0.1 to 10 μg L−1. The IC50 value was 0.62 μg L−1. Recovery from spiked rice samples averaged between 94 and 113%. The effect of different reagents on the stability of HRP–AFB1 conjugate solution was studied. The performance of a stabilized enzyme tracer in ELISA was determined and compared with that
of a freshly prepared control solution of HRP–AFB1 conjugate. The results showed that stabilizing media containing 0.02% BSA, 0.1% Kathon CG, and 0.05 mol L−1 calcium chloride in 0.05 mol L−1 Tris-HCl buffer (pH 7.2) maintained the activity of HRP–AFB1 at a dilution of 1:1000 for a period of at least 12 months at room temperature whereas the reference conjugate solution without
the additives lost its activity within a few days. Several additives were tested for their stabilizing effect on a monoclonal
antibody (MAb) immobilized on the surface of polystyrene microtitre plates. It was shown that immobilized MAb, treated with
post-coating solutions containing PVA, BSA, and combinations of these substances with trehalose, retained its activity for
at least 4 months at 4°C, whereas the untreated MAb-coated plate lost its activity within 2 days. 相似文献