首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
In the sodium-orthophosphate-based solid solutions in Na3 – 2x M x PO4 systems (M = Cd, Pb), the electroconduction is maximum near the upper concentration boundaries of the single-phase regions: x 0.4 for M = Cd and x 0.25 for M = Pb. The conductivity values at 300°C are 6.25 × 10–3 and 2.5 × 10–3 S/cm, respectively. The conduction of synthesized solid electrolytes has a co-cation nature. Their electric characteristics, inferior to those of the Na3PO4-based solid solutions obtained via heterovalent substitutions of another type, may be a manifestation of an effect similar to the polyalkali effect.  相似文献   

2.
Thermodynamic parameters, G°, H° and TS° are reported for the formation of proton amine–hexacyanoferrate(II) complexes, in aqueous solution, at 25°C. H° were determined by the temperature dependence of formation constants and/ or by direct calorimetry in aqueous solution, at T = 25°C. Enthalpy changes for the reaction HiAi+ + Hj Fe(CN) 6 j-4 = AFe (CN)6H i+j i+j-4 (where A = methylamine, ethylenediamine, and tetraethylenepentamine) are quite low and the main contribution to the stability of these complexes arises from the entropic term, as expected for electrostatic interactions. When j = 0, the formation entropy is linearly dependent on i according to the simple equation TS° = 13.4 i kJ-mol–1.  相似文献   

3.
The title metallocenium salts form crystalline 2:1 host:guest inclusion compounds with-cyclodextrin, [(5-C5H5)2M]PF6 · 2-CD · 8H2O (1, M = Fe;2, M = Co;3, M = Rh). The X-ray crystal structures of1 and3, and the lattice constants, crystal system and space group of2 have been determined. Crystal data: triclinic, space groupP1 (No. 1),Z = 1;1,a = 13.865 (2) Å,b = 13.839 (2) Å,c = 15.520 (2) Å, = 91.43 (2)°, = 85.81 (2)°, = 120.22 (2)°, andR F = 0.089 for 4257 observed MoK reflections [I > 3(I)];2,a = 13.810 (2) Å,b = 13.872 (2) Å,c = 15.560 (2) Å, = 93.99 (2)°, = 87.06 (2)°, = 120.04 (2)°;3,a = 13.756 (1) Å,b = 13.863 (1) Å,c = 15.561 (2) Å, =94.39 (1)°, = 86.92 (1)°, = 119.89 (1)°, andR F = 0.061 for 11142 observed MoK reflections [I > 3(I)]. In the crystals of1 and3, two -cyclodextrin molecules are arranged head-to-head to form a dimer by means of intermolecular hydrogen bonding across the secondary hydroxyl faces of adjacent -CD monomers. The dimers are stacked along the crystallographicc axis to form a channel-type structure. The metallocenium cation is encapsulated within the cavity of the dimer, while the PF 6 anion is located outside the cavity, being centered between the primary hydroxyl faces of adjacent dimers. Eight water molecules of hydration per asymmetric unit reside in the spaces between the -CD columns. In view of the almost identical crystal data for2 a similar structure can be assumed for the cobaltocenium adduct.  相似文献   

4.
The enthalpies of dilution of aqueous solutions of HCl, H3PO4, NaOH, NaH2PO4, Na2HPO4 and Na3PO4 in the molality range 0.1 to 1.0 mole-kg–1 have been determined at 30°C. The relative apparent molal enthalpies L of HCl, NaOH, NaH2PO4 and Na2HPO4 have been determined with the aid of an extended form of the Debye-Hückel limiting law. The relative apparent molal enthalpies for Na3PO4 solutions have been corrected for hydrolysis. A value of H H o =9525±150 cal-mole–1 was determined for the heat of hydrolysis of PO 4 –3 . This value gives H 3 o =3815±150 cal-mole–1 for the ionization of H2PO 4 , which is in good agreement with the value of H 3 o =3500±500 cal-mole–1 determined directly by Pitzer at 25°C. The relative apparent molal enthalpies for H3PO4 solutions have been corrected for ionization. A value of H 1 o =–1900±150 cal-mole–1 was obtained for the heat of ionization of H3PO4 to H++H2PO 4 . This value is in good agreement with the value of H 1 o =–2031 cal-mole–1 at 30°C determined by Harned and Owen from the temperature coefficient of the equilibrium constant and H 1 o =–1950±80 cal-mole–1 at 25°C determined from calorimetry by Pitzer.  相似文献   

5.
Usingn-hexadecyl acrylate, surface pressure-area (F-A) curves and equilibrium spreading pressuresF e were measured at various temperatures (5.7°–46°C) by the Langmuir balance (F-A) and the Wilhelmy-plate method (F e). At low temperatures (T<13 °C) condensed films and the liquid-condensed/solid condensed transition can be observed. At high temperatures (T>30 °C) liquid-expanded films occur. In the intermediate range the compression curves have two transition points. The transition pressureF 1 between liquid-expanded and condensed film has a marked temperature dependence. The transition enthalpiesH 1 decrease with increasing temperature and become zero at 29.2 °C. The second transition is related to a transition between the condensed films (F 2). The slight temperature dependence of this transition is accompanied by an increasing change of area as well as by increasing transition enthalpiesH 2.TheF e-T curve has two distinct breaks, at the melting pointT m and atT=30 °C. The break atT m is due to the melting process and the break atT=30 °C is caused by a phase transition between a liquid-expanded film and a condensed film.The phase diagram was constructed from the transition pressures. It can be demonstrated that the highest pressures of the thermodynamic stable film occurs atT m. At temperaturesT>T m equilibrium spreading pressure and equilibrium collapse pressure are identical whereas atT m supercompression of the monolayer occurs. The film in this state behaves like a supercooled liquid. Obviously, rupture and collapse of such a film lead to a thermodynamically metastable bulk phase.  相似文献   

6.
The macroradical decay in poly(methyl methacrylate) samples with different thermal histories was investigated in the temperature interval 20–100 °C using ESR spectroscopy and the second order kinetic model. The rate constants exhibit two different regimes with the transitions atT tr=68±1°C which are independent of thermal treatment. ForT<T tr andT>T tr the rate constants as well as the corresponding activation parameters are sensitive to history because of different physical microstructures. The compensation law, i.e., the linear relation between lnk o, eff andE eff, was analyzed in terms of the so-called compensation quantitiesk c andT c and a proximity betweenT c=T tr andT o=53±3 °C — Vogel temperature for -segmental dynamics was found. A comparison of kinetic and dynamic data suggests that the decay of terminal macroradicals in the low-temperature region is controlled by secondary relaxations and that the -mobility contributes to a more rapid decay at higher temperatures belowT g.  相似文献   

7.
The melting point, T f of water in a pore decreases as the surface area to pore volume ratio of the pore decreases. Analysis of water absorbed in the pores of silica gels using differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS) shows that the thickness of the bound, non-freezing water layer adjacent to the pore surface increases as its temperature increases, but that it is independent of the surface silanol concentration, [SisOH]. In contrast, the thickness decreases as the cylindrical pore radius r H decreases. Thus, the increase in the bound water thickness from 0.45 nm for gels with r H =1.2 nm to 1.2 nm for gels with r H =7.5 nm is due to the increase from –53°C to –7°C of the temperature (e.g., the melting point T f ) at which the bound water thickness was measured, and not due to the increase in t H or the decrease in [SisOH]. The T f of bulk water measured in a DSC was –0.3°C. The boiling point T v of bulk water measured in a DSC was 81.3°C. T v increased to 94°C in 7.5 nm pores and to 109°C K in 1.2 nm pores.  相似文献   

8.
Solid electrolytes K3 – 2x M x PO4 (M = Ca, Sr, Ba) are synthesized and the temperature and concentration dependences of their electroconductivity are studied. Adding calcium and strontium stabilizes the high-temperature -form of K3PO4 at room temperature, while barium-containing solid electrolytes undergo an eutectoid decomposition below 430°C. Maximum electroconductivity is exhibited by K3 – 2x Sr x PO4 (7.1 × 10–3 and 1.25 × 10–1 S cm–1 at 300 and 700°C).  相似文献   

9.
Solid solutions based on K3PO4 in systems K3 – 4x E" x PO4 (E" = Si, Ti, Ge, Zr, Sn, Hf, Ce) are synthesized. The crystal structure, thermal behavior, and electroconduction of the synthesized solutions is studied. The narrowest single-phase regions take place in the systems where E" = Si, Ge (x 0.025), and the widest, in the system with Zr (x 0.125, at 700°C). Introducing Ti or Sn additives (x 0.05) and minimum quantities of Zr, Hf, or Ce (x = 0.025) into potassium orthophosphate leads to stabilization of highly-conductive -modification of K3PO4 at room temperature. Maximum values of potassium-cation conduction in all the systems studied correspond to regions of single-phase solid solutions based on K3PO4. The maximum electroconductivity (0.005 S cm–1 at 300°C, 0.1 S cm–1 at 700°C) and the smallest activation energies (32–35 kJ mol–1) take place in the systems with Zr and Hf.  相似文献   

10.
The -crystalline form zirconium phosphate was investigated. For its lattice parameters was found:a=0.538 nm,b=0.664 nm,c=2.459 nm, =94.2° and basal spacing (d)=1.22 nm. It was determined by IR spectrophotometric method that the phosphate is present in groups of H2PO 4 and PO 4 3– of equal quantity. Two moles of crystalline water per formula unit were found where the moles are bound differently. The compound can be characterized by the following chemical formula: Zr(HPO4)(PO4)·2H2O.  相似文献   

11.
Structural changes at annealing temperatures (Tan) of 500–1,100°C were investigated for thin Ta films which were sputter-deposited onto pure Si substrates and onto thermally oxidized Si. In the as-deposited state, the Ta layers predominantly consist of metastable tetragonal -Ta, whereby the [001] texture is independent of the substrate material. At lower annealing temperatures, the microstructural evolution is essentially the same for both Ta films. Incorporation of O atoms causes an increase of the intrinsic compressive stress, and diffusion of C atoms into the Ta layer leads to the formation of Ta2C. Additionally, a partial transformation of the original -Ta phase into a second phase with tetragonal unit cell (denoted as -Ta) occurs. For the Ta/Si system, the formation of a Ta–Si intermixing layer is initiated at Tan=550°C, and nucleation of crystalline TaSi2 occurs at Tan=620°C. The formation of a second Ta silicide was not detected up to Tan=900°C. In the case of the Ta film deposited onto the SiO2 substrate, the metastable -Ta and the -Ta transform completely into the thermodynamically stable cubic -Ta at Tan=750°C. A marked reaction with the substrate indicated by the formation of Ta2O5 and Ta5Si3 occurs at Tan=1,000°C.  相似文献   

12.
The —T and d/dTT curves of the FeCuNbSiB amorphous alloy, which are the relationship between the total saturated magnetic moment per unit mass and temperature, are investigated by magnetic thermogravimetry analysis (TG(M)) technique. It is found that the crystallization process of the samples can be divided into five stages. The studies of samples annealed in temperature range of 480–610°C for 1h show that when the annealing temperature (Ta) is less than 540°C, the quantity of nanocrystalline -Fe(Si) phase increases evidently with Ta, and the Curie temperature (TC) of residual amorphous phase also increases linearly with Ta, i.e. TC=0.52Ta+91.7°C, with correlation coefficient =0.98. The variation of volume fraction of -Fe(Si) nanocrystalline phase or residual amorphous phase with Ta is measured by TG(M) technique.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

13.
FT-IR and X-ray techniques were used to get an insight into the structure of synthetic Salmonella lipid A membranes. While FT-IR was sensitively providing structure information at the molecular level from different parts of the molecule, X-ray scattering gave data on long-range order phenomena and on fatty acid chain packing pattern. The lipid A membranes exhibited lamellar structures throughout the temperature range of 4°C to 60°C and showed up to three temperature induced transitions. The main transitionT 3 at 47°C was assigned to anL L transition. The weak features atT 1 andT 2 localized between 15 and 40°C seemed to be connected to packing phenomena of lipid A aggregates within the distorted lattice.  相似文献   

14.
Sbai  K.  Atibi  A.  Charaf  A.  Radid  M.  Jouini  A. 《Journal of Thermal Analysis and Calorimetry》2002,69(2):627-645
We have studied the dehydration and the calcination under atmospheric pressure of cyclotriphosphate tetrahydrate of nickel and sodium, NiNa4(P3O9)2·6H2O, between 25 and 700°C by thermal analyses (TG, DTA) infrared spectrometry and X-ray diffraction. This study allows us the identification and the crystallographic characterization of a new phase, NiNa4(PO3)6, obtained between 350 and 450°C. NiNa4(PO3)6 crystallizes in the triclinic system, P–1, with the following unit cell parameters a=6.157(3) Å, b=6.820(6) Å, c=10.918(6) Å, =80.21(5)°, =97.80(9)°, =113.49(3)°, V=409.8 Å3, Z=1, M(19)=25 and F(19)=48 (0.0095; 42). The calcination of NiNa4(PO3)6, between 500 and 600°C, leads to a mixture of long-chain polyphosphates NiNa(PO3)3 and NaPO3. The kinetic characteristics of the dehydration of NiNa4(P3O9)2·6H2O were determined and discussed. The vibrational spectrum of the title compound, NiNa4(P3O9)2·6H2O, was interpreted in the domain of the stretching vibrations of the P3O9 rings, on the basis of its crystalline structure and in the light of the calculation of the normal IR frequencies of the P3O9 ring with D3h symmetry.
This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

15.
Densities and apparent molar volumes of aqueous 2-chloroethanol were determined at temperatures from 15.0 to 34.4°C using digital densimetry. The results of the volumetric measurements have been used to calculate the following thermodynamic quantites at 25°C: V 2 o = 55.05 ± 0.02 cm3-mol–1, (V 2 o/T)p = 0.01486 ± 0.00318 cm3-K–1-mol–1, and (2 V 2 o/T 2)p = 0.02972 ± 0.00318 cm3-K–2-mol–1. Partial molar volumes of transfer from water to 1 mol-dm–3 2-chloroethanol have also been determined for L-glycine, L-alanine, L-serine, L-glutamic acid, and L-aspartic acid at 35.0°C. The transfer results have been explained in terms of the nature of the interactions of the groups in the solute and solvent. Hydration numbers of L-glycine and L-alanine have also been calculated in aqueous 2-chloroethanol.  相似文献   

16.
Specific heat capacities and apparent molar heat capacities of aqueous nicotinamide have been determined from 25.0 to 55.0°C using microdifferential scanning calorimetry in the molality range of 0.07433 to 1.50124 mol-kg–1. Densities and apparent molar volumes have also been determined for aqueous nicotinamide from 10.30 to 34.98°C using a digital densimeter in the molality range 0.07804–2.02435 mol-kg–1. The results of these measurements have been used to calculate the following partial molar quantities and temperature derivatives for aqueous nicotinamide as a function of temperature: C p,2,m o, (C p,2,m o/T)p, (2Cp,2,m o/T 2)p, V 2,m o, ( V 2,m o/T)p, and (2 V 2,m 2/T 2)p. The results are discussed in terms of the changes in the packing of nicotinamide molecules in the crystal, interactions in the aqueous form, and its structure-promoting ability with rise in temperature.  相似文献   

17.
N-tris[Hydroxymethyl]-4-aminobutanesulfonic acid (TABS) has been investigated for the determination of the values of the second dissociation constant, pK 2, in water at 12 temperatures in the range 5–55°C, including 37°C. This zwitterionic compound is useful as a secondary pH standard in the range of pH (7–9) for physiological applications. The electromotive force (emf) measurements have been carried out using a hydrogen gas electrode and a silver–silver chloride electrode. The values of pK 2 are fitted as a function of temperature with the following results: pK 2 = 1671.305/T+14.8737–2.04383 ln T, where T is the thermodynamic temperature in Kelvins. The experimental values of pK 2 are 8.834 ± 0.0005 and 8.539 ± 0.0004 at 25 and 37°C, respectively. The related thermodynamic quantities, G°, H°, S°, and C p ° characterizing the dissociation process have been derived from the pK 2 and its temperature coefficients.  相似文献   

18.
Summary The kinetics of the anation reaction of [Co(NH3)5H2O]3+ by H3PO3/H2PO 3 , to give [CoH2PO3(NH3)5]2+, have been studied at 60, 70 and 80°C, in the acidity range [H+](M)=1.5 · 10–1 –2.0 · 10–3. Only H2PO3 is found to be reactive. The rate data is consistent with an Id mechanism. The mean value of outer sphere association of [Co(NH3)H2O]3+ with H2PO 3 is 1.5 M–1. Values of the interchange constants are: 1044ki(s–1)= 0.29, 1.47, 5.13, at 60, 70 and 80 °C respectively (H= 1.4 · 102KJmol–1, S=8.3 · 10 JK–1 mol–1). The first acidity constant of H3PO3 at I=1.0 has also been determined: 102Ka(M)=4.8, 5.2 and 5.5, at 25, 40 and 50 °C respectively.  相似文献   

19.
The two thermodynamic dissociation constants of glycine at 11 temperatures from 5 to 55°C in 50 mass % methanol-water mixed solvent have been determined from precise emf measurements with hydrogen-silver bromide electrodes in cells without liquid junction. The first acidic dissociation constant (K 1)for the process HG+H++G± is expressed as a function ofT(oK) by the equation pK 1 = 2043.5/T – 9.6504 + 0.019308T. At 25°C, pK 1is 2.961 in the mixed solvent, as compared with 2.350 in water, with H°=1497 cal-mole–1, G°=4038 cal-mole–1, S°=–8.52 cal-°K–1-mole–1, and C p o =–53 cal-°K–1-mole–1. The second acidic dissociation constant (K 2)for the process G±H++G over the temperature range studied is given by the equation pK 2 = 3627.1/T – 7.2371 + 0.015587T. At 25°C, pK 2is 9.578 in MeOH–H2O as compared with 9.780 in water, whereas H° is 10,257 cal-mole–1, G° is 13,063 cal-mole–1, S° is –9.41 cal-°K–1-mole–1, and C p o is –43 cal-°K–1-mole–1. The protonated glycine becomes weaker in 50 mass % methanol-water, whereas the second dissociation process becomes stronger despite the lower dielectric constant of the mixed solvent (=56.3 at 25°C).  相似文献   

20.
A 0.5 dm3 aqueous solution of 0.1 M FeCl3 dissolving 1 wt% poly(vinyl alcohol) (PVA) was treated hydrothermally in a stainless steel autoclave at various temperatures (T h=110–200 °C). Highly ordered red corpuscle-like hematite particles around 2 m in diameter were produced after aging the solution at T h=110 °C for 7 days, though large numbers of spherical PVA microgels around 2–4 m in diameter were produced together with the red corpuscle-like particles at T h120 °C. The number of red corpuscle-like hematite particles decreased but that of spherical PVA microgels increased with increasing T h, leading to the proposal that the method carried out in the present study will become a new synthetic method of polymer microgels. The ferric ions acted as a cross-linking agent to make PVA insoluble in water. The red corpuscle-like hematite particles produced at T h=110 °C had high specific surface areas and showed high mesoporosity. The mesoporosity appeared to be more pronounced after evacuating the particles above 300 °C. The diameter of the mesopores after evacuation above 300 °C ranged from 2 to 20 nm, with a maximum at around 5–6 nm. The H2O and N2 adsorption experiments revealed that there are no ultramicropores in the particles. The H2O and CCl4 adsorption experiments further disclosed that the surface hydrophobicity of the particles is low even though PVA molecules remain after evacuation of the particles at 100–400 °C. Furthermore, the micropores produced after evacuation of the particles at 400 °C exhibited a high size restriction effect, i.e., the micropores produced were accessible to H2O (diameter 0.253 nm) and N2 (diameter 0.318 nm) molecules but not to CCl4 (diameter 0.514 nm).  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号