共查询到20条相似文献,搜索用时 15 毫秒
1.
《Journal of the European Ceramic Society》2003,23(1):99-106
A thermodynamic estimation of the ZrO2–CeO2 and ZrO2–CeO1.5 systems, as well as the cubic phase in the CeO1.5–CeO2 system has been developed and the complex relation between the nonstoichiometry, y, in CezO2–y and the oxygen partial pressure at different temperatures is evaluated. The behavior of the nonstoichiometry phase Zr1–zCezO2–x is described based on the thermodynamic estimation in the ZrO2–CeO2, CeO1.5–CeO2 and ZrO2–CeO1.5 systems. Additionally, the interdependence among miscellaneous factors, which can be used to describe the change in oxidation states of cerium such as the oxygen partial pressure, the CeO1.5 fraction in CeO1.5–CeO2 in the quasi-ternary system, the nonstoichiometry y and the difference between the activity of CeO2 and CeO1.5 are predicted. The calculated results are found to be very useful to explain the influence of pressureless sintering at different O2 partial pressures on the mechanical properties of CeO2-stabilised ZrO2 ceramics 相似文献
2.
The ignition temperature of the Al–CuO thermite was measured using DTA at a scan rate of 50 °C min?1 in a nitrogen atmosphere. Thermite reactions are difficult to start as they require very high temperatures for ignition, e.g. for Al–CuO thermite comprising micron particles it is ca. 940 °C. It was found that the ignition temperature is significantly reduced when the binary Si–Bi2O3 system is added as sensitizer. Further improvement is achieved when the reagents are nano-sized powders. For the composition Al + CuO + Si + Bi2O3 (65.3:14.7:16:4 wt.%), with all components nano-sized, the observed ignition temperature is ca. 613 °C and a thermal runaway reaction is observed in the DTA. 相似文献
3.
《Journal of the European Ceramic Society》2002,22(13):2297-2303
The study of the SnO2–ZrO2 phase diagram in the 1230–1750 °C temperature range has shown the existence of an immiscibility gap, leading to two (Zr1−xSnx)O2 and (Sn1−yZry)O2 limited solid solutions. Four compositions were synthesised for each solid solution, leading to pure phases, which were characterised by room-temperature and high-temperature X-ray diffraction. The unit-cell parameters of tetragonal (Sn1−yZry)O2, monoclinic (Zr1−xSnx)O2 and tetragonal (Zr1−xSnx)O2 were determined and correlated with the content of the substituted atom. The monoclinic to tetragonal and reverse reactions for the (Zr1−xSnx)O2 series were also characterised (transition temperatures) when varying the tin mole fraction. 相似文献
4.
N. V. Borisova V. G. Konakov T. G. Kostyreva M. M. Shultz 《Glass Physics and Chemistry》2003,29(1):28-34
The structural role of copper ions in melts (glasses) of the Na2O–SiO2–Cu2O–CuO system is analyzed in the framework of the acid–base concept with due regard for the geometric (the radius ratio for Cu2(1)+ and O2– ions) and energy (the mean enthalpies of the Cu2(1)+–O bonds) factors. It is demonstrated that copper ions in the structure fulfill the function of modifier cations. In these melts, the Cu1+–Cu2+ redox equilibrium can be described without regard for the formation of [Cu2(1)+O4/2]2(3)– ionic complexes (which could be incorporated into the structure of silicon–oxygen anions) and [Cu2+O
b/k
]2 – b/k
polyhedra providing the interaction between Cu2+ ions and anions. The influence of the formation of these polyhedra on the redox equilibrium is considered within the formalism of chemical thermodynamics. The composition dependence of the oxygen ion exponent pO is measured by an electromotive force (emf) technique. The ratio between the numbers of copper atoms with different valences is determined by chemical analysis. The experimental data obtained are in agreement with the theoretical inferences. 相似文献
5.
Effect of Tungsten Oxide on the Crystallization Properties of Glasses of the B2O3–La2O3–Nb2O5 System
Glass Physics and Chemistry - The effect of tungsten oxide on the crystallization properties of glasses of the 37.5B2O3 22.5La2O3 (40 – x)Nb2O5 xWO3 (where x = 10, 15, 20, 30, 40 mol %)... 相似文献
6.
A sol–gel method was utilized to synthesize the gel with the composition of 58 mol% SiO2–38 mol% CaO–4 mol% P2O5. The thermal properties were studied using thermogravimetric and differential thermal analysis (TG/DTA). Then the gels were sintered at 700, 900, 1000 and 1200 °C. The structure features were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), in addition in vitro assays were carried out in simulated body fluid (SBF). The results revealed that at sintering temperature above 900 °C, crystallization occurred and glass-ceramics with pseudowollastonite and wollastonite were formed. Furthermore with the increase of sintering temperature, the amount of pseudowollastonite decreased while that of wollastonite increased. In vitro tests indicated that the crystallization did not inhibit the samples bioactivity. After soaking in SBF, the formation of apatite was confirmed on glass and glass-ceramics surface, and the bioactivity of the glass-ceramics was based on the formed pseudowollastonite and wollastonite. 相似文献
7.
L. F. Grigor'eva S. A. Petrov O. Yu. Sinel'shchikova V. V. Gusarov 《Glass Physics and Chemistry》2003,29(2):188-193
The mechanism of solid-phase interaction in the BaO–TiO2(ZrO2) and Cs2O–BaO–TiO2(ZrO2) systems is investigated. It is established that the formation of the Ba2Ti9O20 compound and Ba2Ti9O20-based solid solutions is a multistage process proceeding through the formation of intermediate phases. The solid-phase interaction in the BaO–TiO2(ZrO2) system occurs through the formation of the BaTi4O9 intermediate compound. The Ba2Ti9O20 single-phase product is formed only in the presence of ZrO2 (0.82 mol %) upon heat treatment at a temperature of 1250°C for 5 h. In the Cs2O–BaO–TiO2(ZrO2) system, the BaTi5O11 metastable intermediate phase is formed at the first stage of the solid-phase interaction. The Cs
x
Ba2 – x/2Ti9 – y
Zr
y
O20 single-phase solid solutions are prepared upon heat treatment at 1100°C for 1 h. It is demonstrated that, in the Ba2Ti9O20 structure, cesium can isomorphously substitute for barium with the formation of Cs
x
Ba2 – x/2Ti9 – y
Zr
y
O20 solid solutions (0 x 0.8, y = 0 and 0.09). 相似文献
8.
《Ceramics International》2019,45(16):20354-20361
In this work, the influence of modifications of SHS-process on the microstructure and performance characteristics of composite ceramics MoSi2-HfB2-MoB with two-level structure was studied. Partial texturing of MoSi2 grains in samples obtained by force SHS pressing technology was revealed. The effect of preliminary mechanical activation on the macrokinetic parameters of combustion and on the microstructure of the synthesized ceramics was studied. A significant grinding of the synthesized ceramics grain and an increasing of physical-mechanical properties are achieved by increasing the velocity and lowering the combustion temperature of the activated mixtures. The sample obtained by hot pressing of SHS powder from MA reaction mixture showed the most optimal combination of hardness (19.5 GPa), porosity (0.4%) and oxidation resistance (1.82∙10-6 mg/(cm2∙s)). 相似文献
9.
V. V. Golubkov O. S. Dymshits A. A. Zhilin A. V. Redin M. P. Shepilov 《Glass Physics and Chemistry》2001,27(6):504-511
The changes in the structure and phase composition of glasses in the K2O–Nb2O5–SiO2system upon their heat treatment in the temperature range 700–800°C are studied by the small-angle X-ray scattering (SAXS) technique and X-ray powder diffraction. It is demonstrated that the crystallization is the primary process giving rise to microinhomogeneities in glasses due to heat treatment. Nanocrystals of an unidentified niobium-containing phase precipitate in glasses with the formation of regions with a decreased content of potassium and niobium oxides. An increase in the duration of heat treatment at the studied temperatures results in an increase in the size of nanocrystals without change in their phase composition. This is accompanied by the disappearance of diffusion zones, which leads to a decrease in the SAXS intensity in the range of small scattering angles and, correspondingly, to a decrease in the light scattering intensity. 相似文献
10.
《Catalysis communications》2002,3(3):135-139
The interaction between silica and cobalt was studied on supported catalysts with low silica loading. Below a threshold cobalt level of 0.41 wt%, the catalysts were inactive for dehydrogenation of 2-propanol at 450 K. Inactivity was attributed to irreducibility of cobalt ions. Samples that were impregnated at a level below the threshold, dried, calcined, then reimpregnated below the threshold level, redried and recalcined such that the total cobalt content exceeded the threshold, were inactive. These results are not consistent with a model in which a portion of the cobalt interacts with specific silica sites, forming an irreducible species. Rather, they suggest that strongly interacting cobalt ions are incorporated into the silica surface. 相似文献
11.
《Journal of the European Ceramic Society》1999,19(6-7):893-896
The PTCR effect was investigated in the ferroelectric BaNb2O6 phase doped with TiO2. Composite ceramics formed after sintering in a reducing atmosphere and subsequent reoxidation show the PTCR effect at around 70 and 300°C, respectively. Both PTCR anomalies are associated with the formation of high resistivity grain boundaries after controlled oxidation of reduced constituent phases. 相似文献
12.
《Ceramics International》2020,46(6):7403-7412
The impact of various volume percentages of TiB2 additive (0, 10, 20, and 30) on the microstructure, relative density (RD), Vickers hardness, flexural strength, and thermal conductivity of as-sintered TiC-10 vol% SiCw-based composite samples were scrutinized. All four samples were sintered using the SPS method under the following circumstances; sintering temperature of 1900 °C, dwell time of 7 min, and external pressure of 40 MPa. The best relative density of 98.73% was achieved for the sample with no TiB2 additive, indicating the negative effect of TiB2 additive on the RD and formation of porosity. The microstructural observations and XRD results confirmed the chemical interaction of TiO2 and B2O3 oxide layers and SiCw and in-situ formation of the TiSi brittle phase and TiC. The most significant values of flexural strength (511 MPa) and hardness (27.67 GPa) were related to TiC-10 vol% SiCw and TiC-10 vol% SiCw-30 vol% TiB2 samples, respectively. On the contrary, the specimens with 30 vol% and 10 vol% TiB2 as additive presented the poorest qualities of flexural strength (234 MPa) and Vickers hardness (22.12 GPa). Finally, the influence of the TiB2 content on the thermal conductivity was evaluated, indicating the positive impact of this secondary phase on this characteristic, so with adding 30 vol% TiB2 to TiC-10 vol% SiCw, a thermal conductivity of 30.7 W/m.K was obtained. 相似文献
13.
Hannes Kannisto Hanna Härelind Ingelsten Magnus Skoglundh 《Topics in Catalysis》2009,52(13-20):1817-1820
The role of hydrogen in H2-assisted HC–SCR of NO x over Ag–Al2O3 is investigated by XPS and in situ DRIFT spectroscopy. Hydrogen does not reduce the surface silver species to metallic silver, however direct reduction of surface nitrates by hydrogen is observed. It is proposed that one important role of hydrogen is the removal of nitrates from the Ag–Al2O3 surface. 相似文献
14.
Christina Siakati Alexios P. Douvalis Panagiotis Ziogas Arne Peys Yiannis Pontikes 《Journal of the American Ceramic Society》2020,103(3):2173-2184
Aiming to reduce the carbon dioxide emissions associated with cement production, alternative binders such as inorganic polymers currently receive substantial attention and slags from the non-ferrous metallurgy are promising precursors. However, studies that correlate their chemistry and crystallinity with the newly formed binder remain limited. In this work, the effect of three different solidification methods on glass formation and reactivity of FeOx–SiO2 slags, as well as on the molecular structure of the resultant Fe-rich inorganic polymers, was investigated. The inorganic polymers were synthesized by mixing the slags (approximate molar ratio FeO/SiO2 = 1.6) with an alkali silicate solution (molar ratios SiO2/Na2O = 1.6 and H2O/Na2O = 25). Results demonstrated that higher cooling rates promoted higher glass formation and faster reaction kinetics when the slags were activated. 57Fe Mössbauer spectroscopy indicated that all the slags consisted predominantly of Fe2+ ions with a minor amount of Fe3+ ions, regardless of the variability in glass content. The binder phase of all inorganic polymers consisted of iron in both Fe2+ and Fe3+ states, after 28 days of curing. After pulverizing the inorganic polymer pastes and exposing the powder to air for 28 additional days, the Fe2+ state in the binder transformed to Fe3+. The compressive strength evolution of the three slags showed that the 2-day strength was higher for the samples with a higher amorphous fraction, while after 28 days, this influence was less pronounced. 相似文献
15.
16.
《Inorganic chemistry communications》2002,5(7):468-471
The effect of Ph–NH–CH2– group (Ph: phenyl) on the luminescence properties of silica xerogel by sol–gel method has been investigated. The absorption spectra, excitation spectra and emission spectra of Ph–NH–CH2– group embedded in the network of silica xerogel have a red shift with increasing the ratios of Ph–NH–CH2– group in the samples. The relative photoluminescence (PL) intensity of the hybrid silica xerogel sample decreases with increasing the ratios of Ph–NH–CH2– group. From the complex luminescent centers, the novel luminescence properties have been observed from the hybrid silica xerogel sample containing Ph–NH–CH2– group. 相似文献
17.
《Powder Technology》2001,114(1-3):106-111
The surface characteristics of ternary ceramic powders in the system TiO2–SiO2–Al2O3 prepared by a sol–gel technique were studied through nitrogen gas adsorption at liquid nitrogen temperature and application of the Brunauer–Emmett–Teller (BET) equation. The total surface area, total pore volume and pore radius of the powders were calculated through the construction of plots relating the amount of nitrogen gas adsorbed V1 and the thickness of the adsorbed layer t (V1−t plots). These results permitted the detection of the different types of pores present in the samples. In a first approximation, the V1−t plots seem to demonstrate the correctness of the results obtained for the total specific area of the investigated samples. The influence of thermal treatment (drying, calcination) on the surface characteristics of the investigated powders was assessed. 相似文献
18.
19.
《Ceramics International》2020,46(5):6136-6140
The present work deals with the detailed investigations on the radiation shielding features of TeO2–B2O3–Bi2O3–LiF–SrCl2 glass system. The recent software namely Phy-X/PSD has been used to report the change in the photons attenuation features of this glass system with increasing the content of TeO2 from 25 to 85 mol% between 347 keV and 2506 keV. The results show that replacing B2O3 with TeO2 causes the increase in the density of the glass from 3.66 to 5.91 g cm−3 which lead to increase the linear attenuation factor (μ). The μ has a direct relationship with energy and has a highly large value at 0.347 MeV (between 0.550 and 0.896 cm−1). The maximum effective atomic number occurs at 0.347 MeV and equals to 17.75, 19.78, 21.94, 24.24, 26.68, 29.29 and 32.07 for the TeBBiLS1- TeBBiLS7 samples. Thereafter, Zeff decreases quickly down to 0.826 MeV, and becomes almost constant between 1.173 and 1.333 MeV and very slightly increases at 2.506 MeV. The tenth value layer results imply that increasing the weight percentage of TeO2 in the glasses from 25 to 85 mol% can reduce the thickness needed to attenuate or block the photons. TeBBiLS1 has the maximum half value layer (HVL) and was found to be in the range of 3.034–4.823 cm and TeBBiLS7 sample has the lowest HVL. Also, the results revealed that as the density increased, the mean free path (MFP) gradually decreased, and the attenuation ability improves. 相似文献
20.
Yu. B. Petrov Yu. P. Udalov J. Slovak Yu. G. Morozov 《Glass Physics and Chemistry》2002,28(3):139-146
The ZrO2–FeO
x
melts prepared by induction melting in a cold crucible in air are investigated experimentally. It is found that the immiscibility region exists in the liquid phase. The theoretical fusibility curves (calculated according to the authors' DIATRIS 1.2 program) for the ZrO2–FeO–Fe2O3 system are compared with the experimental temperatures of the formation of the secondary phase, liquidus and solidus lines, and X-ray microprobe spectroscopic and X-ray powder diffraction data for quenched and slowly cooled samples. It is demonstrated that the immiscibility region in the liquid phase in an air atmosphere is observed in the temperature range 1870–2230°C and the concentration range 34–82 wt % ZrO2. 相似文献