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1.
On the Constitution of ‘KPbO2’ Transparent, orangered single crystals of K2Pb2O4 have been obtained by heating mixtures of K2O2 and PbO (K:Pb = 1:1) [Ag-cylinders, 560°C, 40 d, after cooling (15°C/h)]. The space group is P1 , a = 1295.94(9), b = 753.35(7), c = 697.12(8) pm, α = 118.00(1)°, β = 106.15(1)°, γ = 93.44(1)°, Z = 4, dx = 6.573 und dpyk = 6.54 g · cm3. The structure is characterized by rutilanalogous chains of edge-connected [PbO6] octahedra along [001] according to [PbO4/2O2/1] = PbO4. On both sides of such a chain there are respectively three O2?, which belong to two octahedra, alternating capped with Pb2+ or not capped, corresponding to [PbO4]Pb2[PbO4]□2… = Pb2O4. Those capped chains are held together by K(1)…K(4), each of them with C.N. 6. The order of the chains corresponds to the motive of a closest packing. The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated and discussed. 相似文献
2.
To investigate the nm-size dependence of structural and thermal properties for AgI, the formation of composites between AgI
and porous silica with controlled pore diameters of 10, 15, 30, and 50 nm was examined. The introduction of AgI within the
micropores of the porous silica was performed successfully by a salt-bridge precipitation method with using AgNO3 and KI aqueous solutions. The AgI formed within the micropores was identified to be β/γ-AgI, independent of the pore size
of 10-50 nm, by powder X-ray diffractometry. In differential scanning calorimetry, the composites showed thermal anomaly at
around 150°C on heating due to the phase transition from β/γ -AgI to α -AgI as in the case of bulk crystalline AgI (T
trs=147°C). However, the transition temperature from α-AgI to β/γ -AgI on cooling decreased remarkably with the decrease of the
pore size from 50 to 10 nm. The result indicates the possibility for AgI particles with diameter less than 10 nm to exist
as α -AgI even below 100°C.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
J. G. P. Binner G. Dimitrakis D. M. Price M. Reading B. Vaidhyanathan 《Journal of Thermal Analysis and Calorimetry》2006,84(2):409-412
The nature
of the β to α phase transition in silver iodide was investigated
by conventional and modulated temperature DSC and dielectric property measurements.
On cooling, the high temperature phase remained stable 2.5°C below its
normal transition temperature even at a very slow cooling rate 0.2°C h–1.
Dielectric property measurements under conventional and microwave heating
suggested an anomalous effect of the latter on the β to α phase
transition in this material. 相似文献
4.
The formation ofβ-phase Bi2Mo2O9 catalyst from a precursor precipitate has been studied using thein situ combined XRD/QuEXAFS technique and DSC during calcination. Accordingly the precursor was observed to undergo a number of
changes in both the molybdenum (VI) coordination and long-range ordering during this heating. Initially the two other forms
of bismuth molybdate (α-andγ-phases) were observed to form from the poorly crystalline precursor at about 230°C, however, theβ-phase eventually crystallised after prolonged heating at 560°C.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
5.
Yttrium
orthoborate crystallizes in the vaterite-type structure and has two polymorphous
forms, viz. a low- und a high temperature one. DTA measurements of YBO3
confirmed a reversible phase transition with a large thermal hysteresis. The
phase transition has been accurately characterized by the application of different
heating and cooling rates (β). Consequently, the extrapolation of the
experimental data to zero β yields the transition points at 986.9°C
for the heating up and at 596.5°C for the cooling down cycle. These values
correspond to samples just after treatment at 1350°C. For samples with
a different ‘thermal history’ other phase transition temperatures
are observed, (e.g. after having performed several heating and cooling cycles).
The linear relationship between the associated DTA signal ΔT=T
onset–T
offset and the square root
of the heating rate β was confirmed, but the relation between T
onset and square root of β
is not found here.
From the empirical data a good linear fitting
between T
onset and
ln(β+1) can be derived.
From the kinetic analysis (Kissinger
method) of the phase transformation of YBO3 an apparent
activation energy of about 1386 kJ mol–1
for heating and of about 568 kJ mol–1 for
cooling can be determined 相似文献
6.
K. De Buysser I. Van Driessche J. Schaubroeck S. Hoste 《Journal of Sol-Gel Science and Technology》2008,46(2):133-136
A novel sol–gel synthetic route using water-soluble precursor salts is presented as a synthetic path for a high-purity negative
thermal expansion material, ZrW2O8. This synthetic route involves a sol–gel method with the use of EDTA as complexing agent. The aqueous solution is transformed
into a ceramic material after a two-step heat treatment: gelation at 60 °C and reactive sintering at 1,180 °C. The decomposition
of the gel is monitored with infrared spectroscopy and TGA. The high-temperature heat treatment results in ZrW2O8 with its characteristic negative thermal expansion behaviour α[75–130 °C]: −9.8 ± 1.6 μm/m °C and α[175–300 °C]: −1.2 ± 0.2 μm/m °C. 相似文献
7.
Sergey V. Ushakov Divya Nag Alexandra Navrotsky 《Journal of Thermal Analysis and Calorimetry》2011,104(1):351-356
The severe heating of soil during wildfires and prescribed burns may result in adverse effects on soil fertility due to organic
matter loss. No rapid and reliable procedure exists to evaluate soil organic matter (SOM) losses due to heating. Enthalpy
of SOM combustion correlates with organic matter content. Quartz is a ubiquitous mineral in soils and has a remarkably constant
composition and reversible α–β phase transition at 575 °C. We suggest that SOM content in heated and unheated soils can be
compared using the ratio of SOM combustion enthalpy on heating to the β–α quartz transition enthalpy measured on cooling of
the same sample. This eliminates the need to dry and weigh the samples, making possible field applications of the proposed
method. The feasibility of using the (ΔH
comb SOM)/(ΔH
β–α Qz) ratio was established with experiments on soil samples heated in the laboratory and the method was then used for evaluation
of SOM loss on two pile burn sites at UC Berkeley’s Blodgett Forest Research Station in Georgetown, California. 相似文献
8.
Research of thermal decomposition kinetic characteristic of emulsion explosive base containing Fe and Mn elements 总被引:1,自引:0,他引:1
X. H. Wang X. J. Li H. H. Yan Y. D. Qu G. L. Sun X. H. Xie Y. J. Zhang 《Journal of Thermal Analysis and Calorimetry》2008,91(2):545-550
The kinetic characteristic of thermal decomposition of the Emulsion Explosive Base Containing Fe and Mn elements (EEBCFM)
which was used to prepare nano-MnFe2O4 particles via detonation method was investigated by means of non-isothermal DSC and TG methods at various heating rates of
2.5, 5 and 7.5°C min−1respectively under the atmosphere of dynamic air from room temperature to 400°C.
The results indicated that the EEBCFM was sensitive to temperature, especially to heating rate and could decompose at the
temperature up to 60°C. The maximum speed of decomposition (dα/dT)m at the heating rate of 5 and 7.5°C min−1 was more than 10 times of that at 2.5°C min−1 and nearly 10 times of that of the second-category coal mine permitted commercial emulsion explosive (SCPCEE). The plenty
of metal ions could seriously reduce the thermal stability of emulsion explosive, and the decomposition reaction in the conversion
degree range of 0.0∼0.6 was most probably controlled by nucleation and growth mechanism and the mechanism function could be
described with Avrami-Erofeev equation with n=2. When the fractional extent of reaction α>0.6, the combustion of oil phase primarily controlled the decomposition reaction. 相似文献
9.
Seto Y. Umemoto K. Arii T. Masuda Y. 《Journal of Thermal Analysis and Calorimetry》2004,76(1):165-177
New solid complex of nitrilotriacetic acid and bismuth trichloride was synthesized by a solid phase reaction of nitrilotriacetic
acid and bismuth trichloride at room temperature. The composition of the sample is BiCl3[N(CH2COOH)3]2.5. The crystal structure of the complex belongs to triclinic system with the lattice parameters: α=0.7849 nm, β=0.9821 nm,
χ=2.0021 nm, α=96.50°, β=98.76° and γ=90.49°. The far-infrared spectra show the bonding between the Bi ion and N atom of nitrilotriacetic
acid. The thermal analysis also demonstrates the complex formation between the bismuth ion and nitrilotriacetic acid. The
gaseous pyrolysis product and the final residue in the thermal decomposition process are determined to check the thermal decomposition
reaction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
N. T. Silva N. F. Nascimento L. S. Cividanes C. A. Bertran G. P. Thim 《Journal of Sol-Gel Science and Technology》2008,47(2):140-147
Diphasic cordierite gels were prepared from colloidal silica, aluminum and magnesium nitrates and citric acid. The mechanism
of xerogel decomposition was studied by infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). The thermal
decomposition of the xerogel forms a solid mixture of MgO, Al2O3 and SiO2 at around 250 °C. Cordierite crystallization was studied by X-ray diffraction (XRD) and differential thermal analysis (DTA).
Xerogels were initially thermally treated, and this sample crystallized to μ-cordierite at 850 °C, at 900 °C α-cordierite
crystallizes and at 1150 °C α-cordierite is the major phase and μ-cordierite is totally consumed. The apparent activation
energy for cordierite crystallization process was determined based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory, Ligero
methods and the Arrhenius law for dependence of activation energy with temperature. The apparent activation energy was (466.8 ± 34.3) kJ/mol,
the exponent of Avrami was (1.9 ± 0.2) and the frequency factor was (1.55 × 1020) s−1. The Avrami value indicates a nucleation controlled process, which can be a consequence of the high xerogel homogeneity,
a consequence of the early and simultaneous formation of the MgO, Al2O3 and SiO2 mixture. 相似文献
11.
K. Chrissafis K. M. Paraskevopoulos C. Manolikas 《Journal of Thermal Analysis and Calorimetry》2006,84(1):195-199
The
thermal effect accompanying the transition of Cu2–xSe
into a superionic conduction state was studied by non-isothermal measurements,
at different heating and cooling rates (β=1, 2.5, 5, 10 and 20°C
min–1). During heating the peak temperature
(Tp) remains almost
stable for all values of β, (136.8±0.4°C for Cu2Se
and 133.0±0.3°C for Cu1.99Se). A gradual
shift of the initiation of the transformation towards lower temperatures is
observed, as the heating rate increases. During cooling there is a significant
shift in the position of the peak maximum (Tp)
towards lower temperatures with the increase of the cooling rate. A small
hysteresis is observed, which increases with the increase of the cooling rate, β.
The mean value of transformation enthalpy was found to be 30.3±0.8
J g–1 for Cu2Se and
28.9±0.9 J g–1 for Cu1.99Se.
The transformation can be described kinetically by the model f(ǯ)=(1–ǯ)n(1+kcatX), with activation energy E=175 kJ mol–1,
exponent value n equal to 0.2, logA=20 and log(kcat)=
0.5. 相似文献
12.
A. H. Qureshi M. Arshad S. K. Durrani H. Waqas 《Journal of Thermal Analysis and Calorimetry》2008,94(1):175-180
Sol-gel process was employed to synthesize the Pb-BSCCO system having general composition Bi2−xPbxSr2Ca2Cu3O10−δ, where x=0.2, 0.4 and 0.8. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), dilatometry and vibrating sample
magnetometer (VSM) were employed to study the materials produced at different stages. Two-stage heating firstly at 300 and
then 800°C was adopted in order to avoid the burning of the materials and formation of carbonates. The carbonate formation
was avoided by heating the materials firstly at 300°C for 2 h and without intermediate cooling moved to the furnace having
temperature 800°C and hold for 2 h. The sintering behaviour of samples was studied by dilatometry and the results revealed
that the sample having x=0.4 was stabled up to a temperature of 700°C while samples having x=0.2 and 0.8 to a temperature of 625°C. The maximum shrinkage was observed at 850°C in all the samples. On the basis of dilatometry
results, the samples were sintered at 845°C for 60 h to observe the superconducting phases. The highest volume fraction of
high superconducting phase (2223) was noticed in the sample containing x=0.4 having onset T
c=110 K. 相似文献
13.
A. G. Magdalena A. T. Adorno T. M. Carvalho R. A. G. Silva 《Journal of Thermal Analysis and Calorimetry》2011,106(2):339-342
In the Cu–Al system, due to the sluggishness of the β ↔ (α + γ1) eutectoid reaction, the β phase can be retained metastably. During quenching, metastable β alloys undergo a martensitic
transformation to a β′ phase at Al low content. The ordering reaction β ↔ β1 precedes the martensitic transformation. The influence of Ag additions on the reactions containing the β phase in the Cu–11mass%Al
alloy was studied using differential scanning calorimetry and in situ X-ray diffractometry. The results indicated that, on
cooling, two reactions are occurring in the same temperature range, the β → (α + γ1) decomposition reaction and the β → β1 reaction, with different reaction mechanisms (diffusive for the former and ordering for the latter) and, consequently, with
different reaction rates. For lower cooling rates, the dominant is the decomposition reaction and for higher cooling rates
the ordering reaction prevails. On heating, the (α + γ1) → β reverse eutectoid reaction occurs with a resulting β phase saturated with α. The increase of Ag concentration retards
the β → (α + γ1) decomposition reaction and the β → β1 ordering reaction, which occurs in the same temperature range, becomes the predominant process. 相似文献
14.
Calcium plumbate Ca2PbO4 was prepared by sol–gel methods (Pechini complex route with two varieties and water soluble polymer method) and by solid
state reaction. The sol–gel prepared samples contained calcium plumbate as the only one phase as early as after 2 h annealing
at 800 °C. Phase composition was detected by XRD measurement and by Raman spectroscopy. The next annealing at 800 °C for 24 h
induced weak Pb losses displayed by present CaO (according to phase equilibrium) and confirmed by XRF measurement. The Pb
losses were smaller for the sol–gel prepared samples probably due to earlier formation of Ca2PbO4. Microstructure and grain size were also established. Sol–gel prepared samples had regularly distributed grains with a small
distribution interval with median value in order of 1 μm. Differences in microstructure of solid state and sol–gel samples
are presented on SEM micrographs. 相似文献
15.
Žaneta Dohnalová Petra Šulcová Miroslav Trojan 《Journal of Thermal Analysis and Calorimetry》2010,101(3):973-978
The main aim of this work was to synthesize the magnesium orthostannate doped by terbium cations and tested whether these
materials can be used for colouring of the different materials, e.g. organic binder and ceramic glazes. Initial composition
of pigments was counted according the general formula 2MgO(1 − x)SnO2–xTbO2, where values of x varied from 0.1 to 0.5 in 0.1 steps. The simultaneous TG/DTA measurements of mixture containing tin oxide, magnesium carbonate
hydroxide and terbium oxide showed that the formation of a new compound started at temperature 1,029 °C, but single-phase
system was not prepared. Granulometric compositions of samples that were prepared by calcining at temperatures 1,300–1,400 °C
are characterized by values of median (d
50) in range 4–8 μm. The calcining temperature 1,500 °C caused the increase of the particle sizes at around 12 μm. The composition
of sample 2MgO–1.5SnO2–0.5TbO2 and heating temperature 1,500 °C are the most suitable conditions for preparation of colourfully interesting pigment that
can be recommended also for colouring of ceramic glazes. Especially, for colouring of decorative lead containing glaze G 07091
containing 5 wt% of PbO and 8 wt% of Al2O3. 相似文献
16.
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
17.
N. Pistofidis G. Vourlias D. Chaliampalias E. Pavlidou K. Chrissafis G. Stergioudis E. K. Polychroniadis D. Tsipas 《Journal of Thermal Analysis and Calorimetry》2006,84(1):191-194
Zn
pack coating formation takes place in three steps as differential scanning
calorimetry shows. The initial step (at 193.9°C) is endothermic and involves
the transformation of α-NH4Cl to β-NH4Cl
and the NH4Cl decomposition to NH3
and HCl. During the second step (at 248.6°C), which is exothermic, Zn2+
salts are formed and most probably ZnCl2. Finally at
264.1°C (endothermic reaction) it seems that ZnCl2 is decomposed to form
Zn that is deposited on the ferrous substrate. The as-cast Zn diffuses in
the iron substrate forming the gamma and delta phase of the Fe–Zn phase
diagram. Al2O3 is not involved
in the above-mentioned mechanism and acts only as filler. 相似文献
18.
R. Igreja C.J. Dias J.N. Marat-Mendes 《Journal of Sol-Gel Science and Technology》1997,8(1-3):721-723
Powders of (Pb0.8Ca0.2)(Ti0.99Mn0.01)O3 have been prepared by sol-gel processing. A tetragonal phase is formed after heat treatment at as low as 800°C. The tetragonality
was found to be 1.053±0.005 and Curie temperature 315°C. Composite films with 0–3 connectivity were prepared from 800°C heat
treated powders and P(VDF-TrFE) by the solvent casting technique. Composites poled at 20 MV/m, exhibited a pyroelectric coefficient
of 17.4 μC/m2K and a pyroelectric figure of merit (FOMp=p/ε) of 0.51 μC/m2K. 相似文献
19.
Single-step sol–gel deposition was attempted for realizing submicron thick, (001) oriented Pb(Zr0.53Ti0.47)O3 (PZT) thin films, using an alkoxide solution containing polyvinylpyrrolidone (PVP). A solution of molar composition, Pb(NO3)2:Zr(OC3H7
n)4:Ti(OC3H7
i)4:PVP:H2O:CH3COCH2COCH3:CH3OC2H4OH:C3H7
nOH = 1.1:0.53:0.47:0.5:5:0.5:22:0.98, was prepared as a coating solution. Gel films were prepared on Pt(111)/TiO2/SiO2/Si(100) substrates by spin-coating, and calcined at 350 °C and annealed at 650 °C either in an electric furnace or in a near-infrared
(IR) furnace. When calcined in the near-IR furnace, the films became (001) oriented on annealing. When calcined in the electric
furnace, on the other hand, the films became randomly oriented on annealing. These observations indicate that the heating
the gel films from the substrate side in the calcination step at 350 °C induces crystallographic orientation in the annealing
step at 650 °C. The effects of the heating methods on the thermal decomposition of the gel films, and the microstructure and
dielectric properties of the fired films were studied. Finally 0.4 μm thick, (001) oriented PZT films could be successfully
prepared by non-repetitive, single-step deposition. The oriented film thus obtained had the remnant polarization 2P
r of 39 μC/cm2 and the dielectric constant ε′ of 960 ± 169. 相似文献
20.
M. Fujiwara T. Okano T. -H. Nakashima A. A. Nakamura G. Sugihara 《Colloid and polymer science》1997,275(5):474-479
For a sodium salt of α-sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, critical micellization
concentration (CMC), solubility and degree of counterion binding (β) were determined by means of electrocon-ductivity measurements
at different temperatures (at every 5 °C) ranging from 15 to 50 °C. The phase diagram of 14SFNa in pure water was constructed
from the CMC- and solubility-temperature data, in which the Krafft temperature (critical solution temperature) was found around
0 °C. The changes in the Gibbs energy, ΔG
0
m, enthalpy, ΔH
0
m, and entropy, ΔS
0
m, upon micelle formation as a function of temperature were evaluated taking βvalues into calculation.
Received: 28 August 1996 Accepted: 5 November 1996 相似文献