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1.
V-alloyed AlCrN hard coatings were deposited on silicon wafers (Si (100)) by reactive arc evaporation in a commercial coating system at 500 °C for 10 min, resulting in a coating thickness of ∼500 nm. The chemical composition of the stoichiometric coatings is constant at approximately Al0.70Cr0.05V0.25N regardless of the applied bias voltage during deposition. Coatings synthesized at a low bias of −40 V show a dual-phase structure (hexagonal close-packed and face-centered cubic (fcc)), whereas coatings deposited at a high bias of −150 V have a metastable single-phase structure (face-centered cubic). All samples were oxidized for 15 min under 20 mbar O2 atmosphere and at four different temperatures (550, 600, 650, and 700 °C). The oxidized coatings were subject to depth profiling and element mapping by a time of flight secondary ion mass spectrometry instrument, equipped with a Bi-cluster analysis gun and Cs+-sputter gun. The evaluation of the in-depth distribution of several elements and species points out distinctive differences in the oxidation behavior of the two different coatings, whereas element mapping shows the formation of islands made of oxidized vanadium and aluminum species as the top-most layer of the single-phase (fcc) coating at temperatures above 650 °C.  相似文献   

2.
Phases formed by the reduction of compounds of the type La0.5Sr0.5MO3 (M=Fe, Co) have been characterized by means of temperature programmed reduction, X-ray powder diffraction, 57Fe Mössbauer spectroscopy and Fe K-, Co K-, Sr K-, and La LIII-edge X-ray absorption spectroscopy. The results show that treatment of the material of composition La0.5Sr0.5FeO3 (which contains 50% Fe4+ and 50% Fe3+) at 650 °C in a flowing 90% hydrogen/10% nitrogen atmosphere results in the formation of an oxygen-deficient perovskite-related phase containing only trivalent iron. Further heating in the gaseous reducing environment at 1150 °C results in the formation of the Fe3+-containing phase SrLaFeO4, which has a K2NiF4-type structure, and metallic iron. The material of composition La0.5Sr0.5CoO3 is more susceptible to reduction than the compound La0.5Sr0.5FeO3 since, after heating at 520 °C in the hydrogen/nitrogen mixture, all the Co4+ and Co3+ are reduced to metallic cobalt with the concomitant formation of strontium- and lanthanum-oxides.  相似文献   

3.
A series of sulfated mixed oxides of alumina and zirconia having a relative composition of 5% and 10% of ZrO2 was prepared by means of sol-gel methods using zirconium propoxide or zirconium acetylacetone as precursor. The characterization of the physicochemical properties was carried out using 27Al NMR, XRD, N2 adsorption at 77 K, thermogravimetry, FTIR analysis of adsorbed pyridine, 27Al NMR-MAS and XPS. The catalytic properties were studied by means of isomerization of n-hexane at 250°C. Results obtained allowed to propose that the use of Zr(acac)4 as a zirconium precursor leads to a better retention of sulfate species which seems to form polymeric superficial sites. The symmetry of aluminium undergo an increase from tetrahedral to octahedral coordination and Zirconium atoms seems to be located in the second coordination sphere of Al. XRD analysis indicated an amorphous structure of obtained solids calcined at 650°C. The sulfated solids presented both Lewis and Brönsted acidic sites. Catalytic results showed that both activity and selectivity towards isomerization products were better using Zr (acac)4 as precursor. Furthermore, the increase of the Zr loading affected considerably the catalytic properties of sulfated zirconia supported by alumina.  相似文献   

4.
Sol-gel routes were used to prepare pure and 5 at% and 10 at% Ta- or Nb-dope TiO2 nano-sized powders. The thermal decomposition behaviour of the precursors was studied using simultaneous thermogravimetric and differential thermal analysis (TG/DTA). X-ray diffraction (XRD) analysis showed that the powders heated to 400°C were crystalline in the anatase TiO2 structure. The pure TiO2 powder heated to 850°C showed the rutile structure. The addition of Ta and Nb inhibited the anatase-to-rutile phase transformation up to 950–1050°C. Ta was soluble in the titania lattice up to the concentration of 10 at%, while the solubility of Nb was 5 at%. Thick films were fabricated with these powders by screen printing technology and then fired for 1 h at different temperatures in the 650–1050°C range. Scanning electron microscopy (SEM) observations showed that the anatase-to-rutile phase transformation induces a grain growth of about one order of magnitude for pure TiO2. The addition of Ta and Nb is effective to keep the TiO2 grain size at a nanometric level even at 950°C, though grain growth was observed with increasing temperature. The gas-sensitive electrical response of the thick films were tested in laboratory, in environments with CO in dry and wet air. Conductance measurements showed a good gas response only for the nanostructured titania-based films. For field tests, the prototype sensors were placed beside a conventional station for atmospheric pollutant monitoring. The electrical response of the thick films was compared with the results of the analytical instruments. The same trend was observed for both systems, demonstrating the use of gas sensors for this aim.  相似文献   

5.
The layered LiNi0.6Co0.4O2 powders were synthesized at low temperature by a sol-gel method using citric acid as a chelating agent. Submicron-sized particles of the precursor were obtained at temperature below 400°C and microcrystalline powders were grown by thermal treatment at 700°C for 4 h in air. The carboxylic-based acid acted such as a fuel, decomposed the homogeneous precipitate of metal complexes at low temperature, and yielded the free impurity LiNi0.6Co0.4O2 single-phase suitable for electrochemical application. The synthesized products have been characterized by structural (XRD, SEM), spectroscopic (FTIR, Raman) and thermal (DTA/TG) analyses. Raman and FTIR measurements provide information on the local environment of the cationic sublattice of LiNi0.6Co0.4O2 solid solution. Electrochemical performance of the synthesized products in rechargeable Li cells were evaluated by employing as cathodes in non-aqueous organic electrolyte mixture of 1M LiPF6 in EC + DMC. The electrochemical behaviour of synthesized LiNi0.6Co0.4O2 is discussed in relation with its synthesis procedure.  相似文献   

6.
Ag colloid-containing coatings on soda lime glass and fused silica are prepared via the sol-gel process. To incorporate Ag+-ions in the coatings homogeneously, they are stabilized by a functionalised silane (aminosilane) and then mixed with the basic sol prepared from 3-glycidoxypropyl trimethoxysilane (GPTS) and tetraethoxysilane (TEOS). Crack-free and transparent coatings with a thickness of 0.5 to 1.2 m, are obtained by heat treatment between 120°C and 600°C. The Ag-colloid formation was monitored by UV-VIS spectroscopy as a function of temperature. The investigations reveal that the substrate has a deciding influence on the Ag-colloid formation caused by alkali diffusion from the substrate into the coating. High resolution transmission electron microscopy (HRTEM) investigations prove that poly-crystalline AgxOy-nanoparticles are formed during thermal densification in the coatings and that this change is accompanied by a vanishing of the yellow colour of the coatings. A post-heat treatment in a reducing atmosphere (90% N2, 10% H2) turns back the yellow colour and single-crystalline Ag-colloids can be detected by HRTEM. A suitable choice of the temperature and time conditions allows the control of the colloid size during heat treatment in a reducing atmosphere. For comparison, ion-exchange experiments have been carried out which showed that a spontaneous Ag-colloid formation was achieved in the soda lime substrate at 400°C. Since Ag containing SiO2-coatings remained colourless after thermal treatment between 400°C and 600°C in air, on soda lime substrates, a remarkable diffusion of Ag+ into the substrate was excluded.  相似文献   

7.
Pure, 5 at%, and 10 at% Ta- or Nb-doped TiO2 nanosized powders were prepared by the sol-gel method. The powders heated to 400°C have the crystalline anatase structure. While the pure TiO2 powder heated to 850°C has the rutile structure, the addition of Ta and Nb inhibited the anatase-to-rutile phase transformation at this temperature. Ta was soluble in the titania lattice up to the concentration of 10 at%, while the solubility of Nb was 5 at%. Thick films were fabricated with these powders by screen printing technology and then fired at 650°C and 850°C for 1 h. SEM observations showed that the anatase-to-rutile phase transformation induces a grain growth of about one order of magnitude for pure TiO2. The addition of Ta and Nb is effective to keep the TiO2 grain size at the nanometric level even at 850°C. Conductance measurements showed that a good gas response is observed only for the nanostructured titania-based films. The CO response of these materials is only slightly affected by humidity.  相似文献   

8.
The spinel LiMn2O4 and layered oxides LiNi x Co1 – x O2 (x = 1; 0.75; 0) have been prepared by Complex Sol-gel Process (CSGP). The appropriate sol compositions were obtained from acetate aqueous solution of metals containing ascorbic acid by alkalizing it with aqueous ammonia. Gels were produced from the systems by evaporation of water and other volatilies at elevated temperatures. A very intense foaming was observed during the heating at the temperatures higher than 140°C. To avoid foaming in the course of the final thermal treatment, a very long (lasting several days) soaking step was found necessary. However pretreated materials exhibit self-ignition at temperature range 320–500°C dependent on socking conditions. The dependence of self-ignition temperature on carbon content in bed as well as on specific surface has not been proved. Final thermal transformation of gel to solid was studied by TG, DTA, XRD, and IR methods. It was observed that final compounds are formed faster from precursors which did not contain Ni (e.g. LiMn2O4 and LiCoO2), while Li carbonate is not formed in these systems. In contrast, in Li-Ni(Co)-O the formation of Li(or Ni)CO3 was always proved. In addition, during the thermal treatment Ni species are partially reduced even to metallic phase. This effect evidently restrains the formation of pure layered oxides phase. Electrochemical properties of carbonate free compounds are definitely better than of those containing CO3.  相似文献   

9.
In situ variable temperature XRD (VT-XRD) measurements on the transformation of nano-precursors to LaNiO phases are presented. Experimental results showed that LaNiO3 and La2NiO4 phases were formed at ca. 700 °C via the reaction of La2O3 and NiO (from the initial nano-precursors), where a relatively low temperature of 700 °C was found for the synthesis of La2NiO4. The formation of La3Ni2O7 at higher temperature (up to 1150 °C) appeared to proceed through a further reaction of La2NiO4 with unreacted NiO, whilst the formation of La4Ni3O10 (at 1075 °C) proceeded via a further decomposition of LaNiO3. Although phase pure La3Ni2O7 and La4Ni3O10 were not directly obtained under the processing conditions herein, the results of this study allow for a better understanding of formation pathways, particularly for the higher order La-Ni-O phases.  相似文献   

10.
The thermal decomposition of the only known antimony nitrate antimony(III) oxide hydroxide nitrate Sb4O4(OH)2(NO3)2, whose synthesis routes were reviewed and optimized was followed by TG-DTA under an argon flow, from room temperature up to 750°C. Chemical analysis (for hydrogen and nitrogen) performed on samples treated at different temperatures showed that an amorphous oxide hydroxide nitrate appeared first at 175°C, and decomposed into an amorphous oxide nitrate above 500°C. Above 700°C, Sb6O13 and traces of -Sb2O4 crystallized.Author to whom all correspondence should be addressed  相似文献   

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