In this paper phase transformations were considered that occur in the process of calcination of aluminium hydroxide, and for qualitative phase analysis low-temperature X-ray analysis was used. Two samples were used, one of chemical purity obtained under laboratory conditions and the other obtained under industrial conditions in the alumina production plant at Kidric?evo, Yugoslavia.It was determined that for both samples in the process of calcination of aluminium hydroxide identical transformations appear, and the sequence of transformations present may be shown in the following way: 相似文献
Zircon ore carbothermal reduction with yttria addition has been carried out. The influences of heating temperature and yttria addition on the phase transformations of zirconia from zircon ore by carbothermal reduction have been investigated in detail. The phase transformations of zirconia from zircon ore by carbothermal reduction were monitored by X-ray diffraction. The microstructure and micro-area chemical analysis of the products were characterized by scanning electron microscopy and energy dispersive spectrometer. The chemical states of Zr 3d, Y 3d and O 1s presented in the products of zircon carbothermal reduction with 10 wt% yttria addition were investigated by X-ray photoelectron spectroscopy. The results showed that the optimized heating temperature of zircon carbothermal reduction with no addition was 1600 °C, and the main phase of the products consists of m-ZrO2, c-ZrO2, ZrC and β-SiC. Yttria addition could be introduced into zirconia lattice and caused it to form Y2O3 stabilized zirconia. Zirconia in the products would be turned into partially stabilized zirconia with yttria addition from 1 wt% to 5 wt% while it would exist in the form of fully stabilized zirconia with over 8 wt% yttria addition. 相似文献
Hydrophobized dextrin, randomly substituted by long alkyl chain (C16), forms stable hydrogel nanoparticles by self-assembling in water. Hydrophobic chains, distributed along the polymer backbone, promote the formation of hydrophobic microdomains within the nanoparticles. The influence of degree of substitution with hydrophobic chains (DSC16) on nanoparticles size, colloidal stability, density, aggregation number and nanoparticle weight was studied. Size distribution was also evaluated at different pH, urea concentration and ionic strength conditions. As shown by dynamic light scattering and transmission electron microscopy, the particles are spherical having a diameter of about 20 nm. The more substituted polymer forms more densely packed hydrophobic microdomains, such that the colloidal stability (in water and PBS buffer) of nanoparticles is increased. The knowledge of the aggregate building process and the characteristics of the nanoparticles are crucial for the design of drug delivery systems. 相似文献
Lump-size and powdered gypsum samples were calcined at 135, 150 and 180°C. The products were thoroughly investigated by differential thermal analysis and X-ray diffraction, and their chemically-combined water was determined thermogravimetrically. Results indicated that almost all the treated samples contained gypsum, hemihydrate and anhydrite in varying proportions. Gypsum and anhydrite increased, and the hemihydrate decreased as the heating temperature was increased and the grain size decreased. Such a variation in the phase constitution of the treated samples is discussed.The relative intensity of the main gypsum X-ray diffraction characteristic lines changes upon treatment. In the atmospheric calcination the relative intensities of the lines at 3.059, 2.867, 2.679, 2.59, 2.495, 2.45 and 2.40 Å show a pronounced decrease. Autoclaving, on the other hand, causes a detected decrease in the relative intensity of the line at 7.56 Å and an increase in the 4.27, 3.059, 2.59, 2.495 and 2.45 Å lines. These findings postulate that X-ray diffraction data could hardly be used for the quantitative assessment of the gypsum phase in the dehydration products of any calcined material. 相似文献
TiO2?CSiO2 mesoporous materials were synthesised by deposition of TiO2 nanoparticles prepared by the sol?Cgel method on to the internal pore surface of wormhole-like mesoporous silica. In this work we synthesised wormhole-like mesoporous silica of different surface area by changing the hydrothermal temperature (70, 100, or 130?°C). Subsequent to this, titania solution was deposited on to the inner surface of the pores and this was followed by calcination at different temperatures (400, 600, or 800?°C). The effect of different hydrothermal and calcination temperature on the photocatalytic properties was evaluated. The samples were characterized by N2-sorption, X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The effect of different hydrothermal and calcination temperatures on the photocatalytic properties was evaluated by measuring the degradation of methylene blue in aqueous solution under UV light irradiation (mercury lamp, 125?W). The results indicated that appropriate surface area and degree of crystallinity are two important factors for obtaining high photocatalytic efficiency. Samples prepared at a hydrothermal temperature of 100?°C and calcined at 800?°C had the best photocatalytic performance, because of the highest surface area and high crystallinity. 相似文献
Mesoporous yttria stabilized zirconia (YSZ) membranes can be used as supports for ultrathin dense ceramic or metallic membranes, and for ultrafiltration (UF) applications in harsh environments. This paper reports synthesis and characterization of sol-gel derived UF YSZ membranes. 0.25 M zirconia sol was prepared by hydrolysis and condensation of zirconium n-propoxide. A solution-sol mixing method was used to dope 8 mol% yttria in zirconia. Supported YSZ membranes were prepared by dip-coating the yttrium doped zirconia sol on the porous α-alumina substrate, followed by drying and calcining under controlled conditions. The membranes prepared in this study are of cubic fluorite phase. Helium permeation experiments show that the supported membranes are pin-hole (or crack) free. The 5 time dip-coated membrane determined by SEM micrograph is about 3.5 μm in thickness, with an average pore diameter of 3 nm. 相似文献
In this thesis, we will elaborate on the sol–gel process during the preparation of monolithic copper-based aerogel. The microstructure of the copper-based aerogel appears to be various due to the different amounts of raw materials, such as polyacrylic acid, propene oxide, deionized water (H2O) and copper(II) chloride (CuCl2) in the sol–gel process. The proper molar ratios between these reactants play a crucial factor in mediating the morphology of the aerogel. The aerogels are characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy and Brunauer–Emmett–Teller methods. The combined results indicate that the copper-based aerogel shows a typical three-dimensional porous structure with a large surface areas about 568 m2/g, and the skeleton structure of the aerogel is composed of a large number of primary particles with the size about a few nanometers. 相似文献
Taking advantage of the fact that TiO2 additions to 8YSZ cause not only the formation of a titania-doped YSZ solid solution but also a titania-doped YTZP solid solution, composite materials based on both solutions were prepared by solid state reaction. In particular, additions of 15 mol% of TiO2 give rise to composite materials constituted by 0.51 mol fraction titania-doped yttria tetragonal zirconia polycrystalline and 0.49 mol fraction titania-doped yttria stabilized zirconia (0.51TiYTZP/0.49TiYSZ). Furthermore, Y2(Ti1−yZry)2O7 pyrochlore is present as an impurity phase with y close to 1, according to FT-Raman results. Lower and higher additions of titania than that of 15 mol%, i.e., x=0, 5, 10, 20, 25 and 30 mol% were considered to study the evolution of 8YSZ phase as a function of the TiO2 content. Furthermore, zirconium titanate phase (ZrTiO4) is detected when the titania content is equal or higher than 20 mol% and this phase admits Y2O3 in solid solution according to FE-SEM-EDX.The 0.51TiYTZP/0.49TiYSZ duplex material was selected in this study to establish the mechanism of its electronic conduction under low oxygen partial pressures. In the pO2 range from 0.21 to 10−7.5 atm. the conductivity is predominantly ionic and constant over the range and its value is 0.01 S/cm. The ionic plus electronic conductivity is 0.02 S/cm at 1000 °C and 10−12.3 atm. Furthermore, the onset of electronic conductivity under reducing conditions exhibits a −1/4 pO2 dependence. Therefore, it is concluded that the n-type electronic conduction in the duplex material can be due to a small polaron-hopping between Ti3+ and Ti4+. 相似文献
Phosphoaluminate cement (PAC) clinker had good mechanical properties at early and long-term period. In comparison, the compressive strength of PAC clinker modified by BaO was more prominent. As primary mineral phase for PAC clinker, CA’s mineralogical structure and hydration characteristics were intimately related to the compressive strength of hardened cement paste. In this study, the effects of BaO content on the calcination, mineralogical structure and hydration characteristics of CA were investigated. Experimental results showed that the appropriate calcination temperature of CA was 1400 °C. No more than 11% (the substitution ratio of BaO for CaO) addition of BaO can promote the conversion of C12A7 to CA and increase the formation ratio of CA. Appropriate content of 7 mol% BaO could endow the hardened paste with excellent compressive strength. In CA mineral phase the high limit addition of BaO was 15 mol%. The addition of BaO decreased and even restrained the formation of C2AH8 and C3AH6 of CA hydration products and also improved the content of CAH10. The addition of BaO dramatically decreased the hydration velocity and cumulative heat of CA mineral.
Micro-crystalline PbWO4 was sonochemically produced using Pb(CH3COO)2 · 3H2O and Na2WO4 · 2H2O in aqueous solutions with and without anionic surfactant (sodium dodecyl sulphate or sodium lauryl sulphate). The product
morphologies were influenced by the pH values and the surfactant. Micro-crystalline PbWO4 composing of Pb, W and O, and W-O stretching vibration band of WO4 tetrahedrons were detected using XRD, SEM, EDX, TEM, SAED and FTIR. Photoluminescent intensities, caused by the electronic
transition from 1T2 to 1A1 states, shown to increase with the increase in the pH values of the solutions. 相似文献
Fe-SBA-15 materials with different Si/Fe ratios (Si/Fe = 90, 50, 10) have been synthesized by a microwave-hydrothermal (M-H) process and characterized by several spectroscopic techniques. Electrons spin resonance and Mössbauer spectroscopies, along with electron microscopy and X-ray diffraction, allowed differentiation of several iron species. These species correspond to hematite particles, very small “isolated” or oligomeric FeIII species possibly incorporated in the mesoporous silica wall, and FeIII oxide clusters either isolated or agglomerated, forming “rafts” at the surface of the silica and exhibiting ferromagnetic ordering. Due to their agglomeration, these clusters appear with a two-peak size distribution, with one peak corresponding to the isolated clusters formed in the mesopores and still embedded in them (ca. 2 nm diameter) and the other corresponding to the agglomerates spread on the surface of the mesoporous silica particles (ca. 9 nm). 相似文献
The electrical conductivity study of Sn–Sb mixed oxide powders is consistent with an enrichment in Sb (due to calcination) of the surface region where a solid solution of Sb in SnO2 and a Sb2O4 surface phase coexist.