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1.
Thermal behaviour of the glass series (100-x)[50ZnO-10B2O3-40P2O5]·xSb2O3 (x=0-42 mol%) and (100-y)[60ZnO-10B2O3-30P2O5]·ySb2O3 (y=0-28 mol%) was investigated by DSC and TMA. The addition of Sb2O3 results in a decrease of the glass transition temperature and crystallization temperature in both compositional series. All
glasses crystallize on heating in the temperature range of 522–632°C. Thermal expansion coefficient of the glasses monotonously
increases with increasing Sb2O3 content in both series and varies within the range of 6.6–11.7 ppm °C−1. From changes of thermal capacity within the glass transition region it was concluded that with increasing Sb2O3 content the ‘fragility’ of the studied glasses increases. 相似文献
2.
A novel surfactant peptide consisting of an arginine cation with laurate anion has been synthesized, purified and characterized.
The critical micellar concentration (cmc) of peptide in aqueous solutions has been determined using spectroscopic techniques
and is found to increase from 0.06 to 0.11 mM with increasing temperature (15–45 °C). Cmc is also determined in the presence
of salts like NaCl, KCl and sodium acetate and it is found that these electrolytes hinder aggregation with a significant increase
in the case of sodium acetate. The aggregation number of the surfactant peptide has been determined using fluorescence quenching
measurements and is observed to decrease from 14 to 6 with increasing temperature (15–45 °C). The standard free energy change
(ΔG
0
m) and standard enthalpy change (ΔH
0
m) of the peptide aggregate are found to be negative with a small positive value for standard entropy change (ΔS
0
m). The peptide aggregate seems to undergo phase transition above 50 °C as observed from UV–vis and fluorescence spectroscopy.
From pyrene binding studies, it is shown that the interior dielectric constant increases from 5.08 at 34 °C to 8.77 at 50 °C
and further decreases with increase in temperature indicating a phase change at 50 °C. Also, the ratio of excimer intensity
to monomer intensity, which is a measure of microviscosity of the aggregate, decreases with increase in temperature with a
change at 50 °C indicating a phase change.
Received: 14 February 1997 Accepted: 13 August 1997 相似文献
3.
It has been shown that the swelling of poly-N-isopropyl-acrylamide (poly-NIPAM) microgel particles can be controlled by the addition of alcohols, in addition to the previously
observed effect of temperature. The degree of swelling is also controlled by the amount of cross-linker within the microgel
particles. At 25 °C, poly-NIPAM microgel particles collapse upon the addition of MeOH, EtOH and 2-PrOH to a minimum size and then, reswell again
as the alcohol-rich region is approached. This trend was also observed for poly-NIPAM microgel particles dispersed in 2-PrOH/water
mixtures upon heating to 50 °C. The particles, dispersed in either water or alcohol/water mixtures were found to be stable to flocculation between 25 °C and 50 °C.
Received: 27 February 1997 Accepted: 5 August 1997 相似文献
4.
P. Bermejo-Barrera Antonio Moreda-Piñeiro Jorge Moreda-Piñeiro Adela Bermejo-Barrera 《Analytical and bioanalytical chemistry》1997,358(7-8):844-847
Rapid methods were developed for the direct determination of Ag, Al, Cd and Mn in cocaine and heroin by ETAAS using programmes
omitting the charring step . Sample pretreatment was simple: dissolution in ultrapure water or in 35.0% (v/v) HNO3 for heroin or cocaine, respectively. Optimum drying temperatures were 250 °C for Ag, Al and Mn, and 300 °C for Cd. The run
cycles were 35 and 37 s, for Ag and Al respectively, and 36 s for Cd and Mn. The best results were obtained with Pd, Mg(NO3)2 and (NH4)2HPO4, as chemical modifiers. The limits of detection were 8.6, 55.9, 2.2 and 12.4 μg kg-1 for Ag, Al, Cd and Mn, respectively.
Received: 14 November 1996/Revised: 14 January 1997/Accepted: 18 January 1997 相似文献
5.
Uniform particles of manganese compounds obtained by forced hydrolysis of manganese(II) acetate 总被引:1,自引:0,他引:1
M. Ocaña 《Colloid and polymer science》2000,278(5):443-449
Procedures for the preparation at low temperature (80 °C) of uniform colloids consisting of Mn3O4 nanoparticles (about 20 nm) or elongated α-MnOOH particles with length less than 2 μm and width 0.4 μm or less, based on
the forced hydrolysis of aqueous manganese(II) acetate solutions in the absence (Mn3O4) or the presence (α-MnOOH) of HCl are described. These solids are only produced under a very restrictive range of reagent
concentrations involving solutions of 0.2–0.4 mol dm−3 manganese(II) acetate for Mn3O4 and of 1.6–2 mol dm−3 Mn(II) and 0.2–0.3 mol dm−3 HCl for α-MnOOH. The role that the acetate anions play in the precipitation of these solids is analyzed. It seems that these
anions promote the oxidation of Mn(II) to Mn(III), which readily hydrolyze causing precipitation. The evolution of the characteristics
of the powders with temperature up to 900 °C is also reported. Thus, Mn3O4 particles transform to Mn2O3 upon calcination at 800 °C; this is accompained by a sintering process. The α-MnOOH sample also experiences several phase
transformations on heating. First, it is oxidized at low temperatures (250–450 °C) giving MnO2 (pyrolusite), which is further reduced to Mn2O3 at 800 °C. After this process the particles still retain their elongated shape.
Received: 19 October 1999 Accepted: 24 November 1999 相似文献
6.
Sol and Gel state properties of aqueous gelatin solutions of concentrations 4%, 6%, 8% and 10% (w/v) have been investigated
through dielectric relaxation studies done at various temperatures in the range T=20–60 °C carried out over a frequency range f=20 Hz–10 MHz and no relaxation of any nature was observed. The sharp transition observed at the gelation temperature T
gel provided an excellent matching with the same measured through differential scanning calorimetry (DSC). The capacitance (C
p) values above f=100 kHz became increasingly negative as the gel was melted to the sol state. However, in the gel state C
p was found to be almost independent of temperature for frequencies above 100 kHz. At frequencies lower than 10 kHz, C
p measured was ∼105 F, implying pronounced interfacial polarization either due to electro-chemical reaction or because of ions getting trapped
at some interface within the bulk.
Received: 10 February 1997 Accepted: 2 September 1997 相似文献
7.
Silvana V. Rodrigues Decio Nepomuceno Luci Viana Martins W. Baumann 《Fresenius' Journal of Analytical Chemistry》1998,360(1):58-61
The solubility of two related series of each three triazine compounds has been determined in supercritical CO2, at 40 °C and pressures between 80 and 220⋅105 Pa. A high pressure small volume cell with adjustable optical path and built-in circulation pump has been constructed to
be used with quartz windows in a Perkin Elmer UV-VIS spectral photometer. At 220 bar solubilities are between 0.3 and 25 g/L,
dependent on the specific triazine structure. The isothermal pressure dependence of the solubility could be modelled using
the pressure dependent dielectric constant of CO2 as the only variable.
Received: 30 October 1996/Revised: 3 April 1997/Accepted: 13 April 1997 相似文献
8.
S. Lokhande S. A. Parab 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(13):2346-2349
Determination of ion-exchange equilibrium constant (K) for Cl−/I− and Cl−/C2O42− system was studied at different temperatures from 25 to 45°C and by varying concentration of iodide and oxalate ion solution.
For both uni-univalent and uni-bivalent exchange systems, using 0.5 g of ion-exchange resin DUOLITE A-116 (in chloride form),
the value of K increases with rise in temperature i.e., from 13.0 at 25°C to 19.05 at 45°C for Cl−/I− system and 33.0 at 25°C to 63.0 at 45°C for Cl−/C2O42− system indicating the endothermic ion-exchange reaction. The difference in K values at the same temperature for the two was related to the ionic charge of exchangeable ions in the solution. 相似文献
9.
Wolfgang Preis Michael Holzinger Werner Sitte 《Monatshefte für Chemie / Chemical Monthly》2001,132(4):499-508
Summary. The van der Pauw method has been applied to conductivity relaxation experiments on YBa2Cu3O6+δ at 600°C in order to determine the chemical diffusion coefficient as a function of the oxygen partial pressure in the surrounding
atmosphere (100 > p
O
2/bar > 10−3). It is shown that the van der Pauw technique is suitable for monitoring the conductivity relaxation when the oxygen diffusion is perpendicular to the direct
current flowing through the sample in accordance with the van der Pauw geometry using thin tablets as samples. The oxygen partial pressure is changed stepwise (generally Δlogp
O
2 ≤ 0.5) by employing appropriate gas mixtures as well as an electrochemical oxygen pump device. An evaluation formula is given
for the determination of the chemical diffusion coefficient neglecting slow surface processes. In addition, the electronic
conductivity of YBa2Cu3O6+δ has been measured at 600°C as a function of oxygen partial pressure of the ambient atmosphere (100 > p
O
2/bar > 10−5) by means of the van der Pauw method applying the same experimental set-up. Typical values of the chemical diffusion coefficient are in the range of 10−6 cm2·s−1; the results of the conductivity measurements are interpreted in terms of an appropriate defect model.
Received May 30, 2000. Accepted June 8, 2000 相似文献
10.
S. Durón R. Rivera-Noriega M. A. Leyva P. Nkeng G. Poillerat O. Solorza-Feria 《Journal of Solid State Electrochemistry》2000,4(2):70-74
A ruthenium-sulfur carbonyl cluster electrocatalyst, Ru
x
S
y
(CO)
n
, was synthesized by pyrolysis of Ru3(CO)12 and elemental sulfur in a sealed ampoule at 300 °C. The pyrolyzed compound was characterized by DSC, FT-IR, XRD and SEM (EDX)
techniques. The electrocatalytic activity and kinetic parameters for the molecular oxygen reduction were determined by a rotating
ring-disk electrode (RRDE) in a 0.5 M H2SO4 solution at 25 °C. The cathodic polarization indicates two Tafel slopes: −0.124 ± 0.002 V dec−1 at low and −0.254 ± 0.003 V dec−1 at high overpotentials, and first-order kinetics with respect to O2 concentration. From the analysis of Levich plots and RRDE results, the oxygen reduction on Ru
x
S
y
(CO)
n
was determined to proceed mostly via a multielectron transfer path (4e−) to water formation ( >94%).
Received: 4 March 1999 / Accepted: 26 May 1999 相似文献
11.
Suwa K. Yamamoto K. Akashi M. Takano K. Tanaka N. Kunugi S. 《Colloid and polymer science》1998,276(6):529-533
We examined the effects of salt on the lower critical solution temperature (LCST) and lower critical solution pressure (LCSP)
of aqueous solutions of poly (N-vinylisobutyramide), polyNVIBA, and compared them with those on poly(N-isopropylacrylamide), polyNIPAAm. We found that the addition of salt (such as Na2SO4, NaCl, or KCl) decreased the LCST of aqueous polyNVIBA from 45 °C to below 20 °C, almost linearly with the salt concentrations
and dependent on the type of salt. We observed a similar concentration-dependent decrease in LCST for polyNIPAAm. When KI
or NaSCN was added to each aqueous polymer solution, some smaller increases in LCST were observed at relatively low salt concentrations;
higher concentrations of salt gave an almost linear decrease in LCST. As for LCSP, the addition of most types of salt lowered
the transition pressure, but the effects were much more dependent on the type and the valence of the salt (especially of anion)
in both polymers. Salt with divalent anion showed a larger decrease in LCSP, but those with mono valent anion showed a relatively
small decrease, even showed a slight increase at lower salt concentrations in the case of polyNVIBA. Salt with I- or SCN- showed evident increases in LCSP up to 1 M and was maintained higher than the control even at 2 M. We discuss the interactions
of the amide group in the side chains of polymers and water and their perturbation by ions.
Received: 13 November 1997 Accepted: 22 January 1998 相似文献
12.
Jie Cai Jia Guo Minglei Ji Wuli Yang Changchun Wang Shoukuan Fu 《Colloid and polymer science》2007,285(14):1607-1615
Fe3O4/SiO2/poly (N-isopropylacrylamide-co-N,N-dimethylaminoethyl methacrylate) [P(NIPAM-co-DMA)] multiresponsive composite microspheres with core–shell structure were synthesized by template precipitation polymerization.
First, the magnetite nanoparticles were coated with silica and then modified with 3-(trimethoxysilyl)-propyl methacrylate
(MPS). Subsequently, the Fe3O4/SiO2 particles grafted with MPS were used to seed the precipitation copolymerization of NIPAM and DMA. The composite microspheres
with core–shell structure were superparamagnetic, pH-sensitive, and thermoresponsive. The swelling ratio (D25 °C,
pH = 3/D50 °C,
pH = 9)3 coupling of pH and temperature increased up to 21.2, which was much higher than that without comonomer DMA. 相似文献
13.
Yoshihiro Kawakami Hiromasa Ikuta Masataka Wakihara 《Journal of Solid State Electrochemistry》1998,2(4):206-210
Perovskite-type compounds, Li
x
La(1−
x
)/3NbO3 and (Li0.25La0.25)1−
x
Sr0.5
x
NbO3 as lithium ionic conductors, were synthesized by a solid-state reaction. From powder X-ray diffraction, the solid solution
ranges of the two compounds were determined to be 0≤x≤0.25 and 0≤x≤0.125, respectively. In the Li
x
La(1−
x
)/3NbO3 system, the ionic conductivity of lithium at room temperature, σ25, exhibited a maximum value of 4.7 × 10−5 S · cm−1 at x = 0.10. However, because of the decrease in the lattice parameters with increasing Li concentration x˙, σ25 of the samples decreased with increasing x from 0.10 to 0.25. Also, in the (Li0.25La0.25)1−
x
Sr0.5
x
NbO3 system, the lattice parameter increased with the increase of Sr concentration and the σ25 achieved a maximum (7.3 × 10−5 S · cm−1 at 25 °C) at x = 0.125.
Received: 12 September 1997 / Accepted: 15 November 1997 相似文献
14.
Fu Qiang KeNing Sun NaiQing Zhang ShiRu Le XiaoDong Zhu JinHuo Piao 《Journal of Solid State Electrochemistry》2009,13(3):455-467
A-site-deficient perovskite cathode material La0.58Sr0.4Co0.2Fe0.8O3 − δ
(L58SCF) is coated on the yttria-stabilized zirconia electrolyte by screen-printing technique. Several key fabrication parameters
including selection of additives (binder and pore former), effect of coating thickness, sintering temperature and time on
the microstructure, and electrochemical performance of cathode are investigated by scanning electron microscopy and electrochemical
impedance spectroscopy. We study the microstructure and the electrochemical property of the cathode with different kinds of
additives. Results show that the cathode possesses fine microstructure, enough porosity, and ideal electrochemical property
when polyvinyl butyral serves as both binder and pore former in the cathode. The cathode with three screen-printing coats
(thickness 28 ± 7 μm, weight 6.07 ± 0.72 mg cm−2) sintering at 1,000 °C for 2 h shows lower polarization resistance of 0.183 Ω cm2 at 800 °C. Based on the optimized parameters, the polarization resistances of the L58SCF–Ce0.8Gd0.2O1.9 – δ
composite cathode display the R
p values of 0.067 Ω cm2 at 800 °C, 0.106 Ω cm2 at 750 °C, 0.225 Ω cm2 at 700 °C, and 0.550 Ω cm2 at 650 °C. 相似文献
15.
3]2+. Whereas the initial method is carried out in an aqueous solution, the improved one employs an aqueous micellar medium formed
by the cationic surfactant cetylpyridinium bromide (CPBR). The λmax in both methods is the same, i.e. 510 nm. The mean apparent
molar absorptivity (ɛ) and Sandell’s sensitivity (Ss) were calculated as ɛ=2.10×104 Lmol-1 cm-1 and Ss=8.37 ng cm-2 for the initial procedure, and ɛ=2.62×104 Lmol-1 cm-1 and Ss=6.72 ng cm-2 for the improved one. The regression line equation for the improved method was: A=1.487×10-1C −1.415×10-2 (r=0.9998). The accuracy and the precision of the improved method were investigated and the conclusions were satisfactory.
The results obtained for ASCA by both the described method and an official one, were statistically compared by means of the
Student’s t-test and by the variance ratio F-test; and no significant difference was observed.
Received: 15 January 1996/Revised: 7 March 1996/Accepted: 13 March 1996 相似文献
16.
C. Vanderdonckt M. Krumova F. J. Baltá Calleja H. G. Zachmann S. Fakirov 《Colloid and polymer science》1998,276(2):138-143
Poly(ethylene terephthalate) (PET) was annealed in vacuum at different temperatures (190–260 °C) for different times (10 min–24 h)
in order to examine the mechanical properties (microhardness) of PET samples with a wide range of molecular weights (10 000–120 000).
Short annealing times result in a twofold decrease in mol. wt. due to hydrolytic decomposition. However, long annealing times
give rise to a substantial molecular weight increase. It is found that microhardness (H) rises linearly with the degree of crystallinity obtained during up-grading of mol. wt. and its extrapolation leads to H-values of completely crystalline PET, H
PET
c=405 MPa for samples with conventional mol. wt. and of 426 MPa for samples with mol. wt. higher than 30 000. It is shown that
the increase of mol. wt. for each set of samples with a given range of degree of crystallinity also causes a slight increase
of H. The influence of mol. wt. upon hardness is discussed in the light of the changes in the physical structure (crystallinity,
crystal thickness) which is formed at given heat treatment conditions.
Received: 29 April 1997 Accepted: 23 September 1997 相似文献
17.
Christopher J. G. Plummer Rudolf Gensler Hans-Henning Kausch 《Colloid and polymer science》1997,275(11):1068-1077
Melt crystallized isotactic polypropylene thin films of thickness between 30 and 100 nm have been investigated by high-resolution
transmission electron microscopy at room temperature. The c-axis projection of the 2*31 helices and their packing in the lattice were clearly visible in flat-on lamellae of the α-phase following reconstruction
from the components of the image Fourier transform corresponding to the (1 1 0) and (0 4 0) lattice planes, and the image
power spectra also indicated contributions from (1 3 0) and (0 6 0) relfections, corresponding to a line resolution of about
0.35 nm. These results are discussed in terms of Bloch wave calculations based on the generally accepted structure for the
α-phase. Attempts to obtain lattice images of the β-phase in isotactic polypropylene and melt crystallized syndiotactic polypropylene
under similar operating conditions are also briefly discussed, although these provided relatively little structural information.
Received: 27 June 1997 Accepted: 15 August 1997 相似文献
18.
P. C. Schulz M. A. Morini M. E. Gschaider de Ferreira 《Colloid and polymer science》1998,276(3):232-238
The system dodecyltrimethylammonium hydroxide (DTAOH)–water was studied by surface tension, ion-selective electrodes and
evaporation in an electrobalance. Results confirmed earlier conclusions about a stepwise aggregation mechanism in DTAOH solutions.
The aggregation process started at a total concentration C
T=(2.51±0.10)×10-4 mol dm-3) which probably corresponds to the formation of dimers. At C
T= (1.300±0.041)×10-3 mol dm-3 there was a change in the surface and evaporation behavior, corresponding to the formation of small, fully ionized aggregates
which grew with increasing concentration. At C
T= (1.108±0.010)×10-2 mol dm-3 the formation of true micelles with hydroxide counterions in the Stern layer did not change significantly the evaporation
and adsorption behavior. This means that between this concentration and C
T=(3.02±0.28)× M28.8n10-2 mol dm-3, the changes in structure were gradual. At the latter concentration there was a sudden change in the monolayer state at the
air/water interface, with a strong surfactant desorption, and a major change in evaporation behavior. The changes are compatible
with the formation of few, large aggregates reducing the total concentration of kinetically independent solute units, which
in turn increased the activity of the solvent. This phenomenon is in agreement with literature information. The reduction
in the evaporation rate of water was mainly due to the reduction of the water activity, caused by colligative effects. The
reduction of the effective area available for evaporation had only a slight effect in water evaporation.
Received: 9 January 1997 Accepted: 19 October 1997 相似文献
19.
Boris Orel Marjeta Maček Jože Grdadolnik Anton Meden 《Journal of Solid State Electrochemistry》1998,2(4):221-236
Niobium oxide (Nb2O5) films and powders have been obtained via the sol-gel route from an NbCl5 precursor. XRD spectra revealed that films with pseudohexagonal (TT-phase) and orthorhombic (T-phase) structure were formed
at 500 °C and 800 °C, respectively, while at 300 °C films were amorphous. Infrared (IR) and Raman spectra of powders and
films of Nb2O5 in different polymorphic forms were detected, and vibrational band assignments were made. Electrochromic properties of amorphous
films and films with the TT-phase were established from in situ ultraviolet visible (UV-Vis) spectroelectrochemical measurements
and correlated with ex situ IR transmission spectra of charged films. Ex situ IR spectra revealed that charging of amorphous
films is accompanied by variations of the Nb-O stretching mode intensity, while, for films with the TT- and T-phase, splitting
of the Nb3-O stretching modes and the appearance of polaron absorption were noted with Li+ ion insertion. Ex situ X-ray diffraction (XRD) spectra of charged films with the TT-phase showed changes of the unit cell
dimensions with charging. The influence of the polaron absorption on the ex situ near-grazing incidence angle (NGIA) IR reflection-absorption
spectra of charged/discharged films is discussed in detail.
Received: 21 August 1997 / Accepted: 9 October 1997 相似文献
20.
Summary The cross-linkings of the surface polymer layer on mono disperse, poly(maleic anhydride-styrene)-modified silica particles
by the reaction with diisocyanate were studied. The extent of cross-linking was estimated by the weight decrease by immersing
the particles in the buffer solution of pH 2.0, 4.0 and 9.0 at a room temperature for 24 h. The reaction of the polymer-modified
silica with 1,6-diisocyanatohexane afforded relatively stable composite particles which lost less than 5 wt% of the polymer
in aqueous solution in the pH range 2.0–9.0. The diisocyanate was a preferable cross-linker to 2,4-diisocyanatotoluene in
terms of stability in acidic or basic aqueous solution. The flexibility of the cross-linker molecule possibly plays an important
role in the cross-linking reaction. The carboxyl and amino groups were formed by treating the cross-linked composite particles
with diluted HCl solution; 5–6 and 0.5–1.1 μmol g-1, respectively. The cross-linked composite particles exhibited the characteristic property of ζ-potential, −44 to −47 mV and
−102 to −107 mV in a neutral aqueous solution and ethanol, respectively.
Received: 26 May 1997 Accepted: 4 August 1997 相似文献