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1.
Using coal fly ash slurry samples supplemented with different amounts of Al2O3, we fabricated mullite-based porous ceramics via a dipping-polymer-replica approach, which is a popular method suitable for industrial application. The microstructure, phase composition, and compressive strength of the sintered samples were investigated. Mullite was identified in all of the prepared materials by X-ray diffraction analysis. The microstructure and compressive strength were strongly influenced by the content of Al2O3. As the Al/Si mole ratio in the starting materials was increased from 0.84 to 2.40, the amount of amorphous phases in the sintered microstructure decreased and the compressive strength of the sintered samples increased. A further increase in the Al2O3 content resulted in a decrease in the compressive strength of the sintered samples. The mullite-based porous ceramic with an Al/Si molar ratio of 2.40 exhibited the highest compressive strength and the greatest shrinkage among the investigated samples prepared using coal fly ash as the main starting material.  相似文献   

2.
In recent years, circulating fluidized bed combustion fly ash (CFA) is used as a raw material for geopolymer synthesis. Hydrogen peroxide was employed as a foaming agent to prepare CFA-based foam geopolymer. The particle distribution, mineral composition, and chemical composition of CFA were examined firstly. Geopolymerization products were characterized by mechanical testing, scanning elec- tron microscopy (SEM), X-ray diffraction (XRD), and X-ray fluorescence (XRF). The CFA-based foam geopolymer was successfully fabri- cated with different contents of hydrogen peroxide and exhibited uncompleted alkali reaction and reasonable strength with relative low atomic ratios of Si/Al and Si/Na. Type-C CFA in this research could be recycled as an akernative source material for geopolymer production.  相似文献   

3.
To control the reverse-transformation austenite structure through manipulation of the micro/nanometer grain structure, the influences of cold deformation and annealing parameters on the microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. The samples were first cold-rolled, and then samples deformed to different extents were annealed at different temperatures. The microstructure evolutions were analyzed by optical microscopy, scanning electron microscopy (SEM), magnetic measurements, and X-ray diffraction (XRD); the mechanical properties are also determined by tensile tests. The results showed that the fraction of stain-induced martensite was approximately 72% in the 90% cold-rolled steel. The micro/nanometric microstructure was obtained after reversion annealing at 820-870℃ for 60 s. Nearly 100% reversed austenite was obtained in samples annealed at 850℃, where grains with a diameter ≤ 500 nm accounted for 30% and those with a diameter >0.5 μm accounted for 70%. The micro/nanometer-grain steel exhibited not only a high strength level (approximately 959 MPa) but also a desirable elongation of approximately 45%.  相似文献   

4.
Fe5O7(OH)·4H2O ferrihydrite is a low-crystal- linity antiferromagnetic material, γ-Fe2O3 (maghemite) magnetic nanoparticles were prepared from a ferrihydrite precursor, by chemically induced transformation in FeCl2/ NaOH solution. The magnetization, morphology, crystal structure and chemical composition of the products were determined by vibrating sample magnetometry, transmission electron microscopy, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy (XPS). Ferrihydrite underwent aggregation growth and transformed into α-FeO(OH) (goethite) particles, which subsequently transformed into γ-Fe2O3 nanoparticles, that became coated with NaCI. The γ-Fe2O3 particles had a flake-like morphology, when prepared from 0.01 mol/L FeCl2 and a FeCl2:NaOH molar ratio of 0.4. The γ-Fe2O3 particles were more spherical, when prepared from a FeCl2:NaOH molar ratio of 0.6. The Fe content of the flake-like particles was lower than that of the spherical particles. Their magnetizations were similar, and the coercivity of the flake-like particles was larger. The differences in morphology and magnetization were attributed to the surface effect, and the difference in coercivity to the shape effect.  相似文献   

5.
Co3O4-Ce O2 nanoparticles with increasing Co/Ce atomic ratio were prepared by wet impregnation and characterized by means of X-ray photoelectron. Co3O4 is prevalent in the samples with lower cobalt content, whereas Co3O4 is the main presence at high Co/Ce atomic ratios.Ce O2 is slightly reduced: Ce(III) is evident at the interface supported/ supporting oxide.X-ray diffraction and scanning electron microscopy allowed us to obtain interesting information concerning particle dimensions and growing morphology. New acidic/basic sites are evident on the surface of the nanocomposites; this is particularly evident in the samples with lower cobalt content.  相似文献   

6.
In this study, commercial V2O5-WO3/TiO2 catalysts were deactivated by loading with alkali metals (K and Na). These catalysts were then regenerated by washing with either deionized water or 0.5 mol/L H2SO4 (through the ultrasonic-assisted method). The samples used in this research were characterized by NH3-temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Results showed that Na2O and KaO doping can poison the V2O5-WO3/TiO2 catalyst and that the poisoning effect of Na2O was stronger than that of KaO. However, the Na2O-loaded sample was easier to regenerate than the KaO-loaded sample. The surfaces of catalysts can be sulfated by washing with dilute sulfuric acid because strong acid sites adhere to the catalyst surface. SO42- could also promote catalyst activity. As indicated by the NH3-TPD findings, the deposition of Na2Oand K2O could also reduce the amount of desorbed ammonia and destabilize the acid sites, especially strong chemisorption sites. XPS results revealed that catalysts were deactivated by the decrease in the concentration of chemisorbed oxy- gen [the Oα(Oα + Oβ) ratio]. In the Na2O-doped catalyst, much chemisorbed oxygen was lost (from 28.8 % to 10.6 %). However, the decrease in the Oα(Oα + Oβ) ratio was less significant in the K20-doped catalyst (from 28.8 % to 23.5 %). Nonetheless, the binding energies of Ols broadened with respect to both high and low energy. Inparticular, the binding energy of chemisorbed oxygen increased from 531.5 to 531.8 eV.  相似文献   

7.
Copper matrix composites consisting of chromium (Cr) or ferrochrome (Cr-Fe) as strengthening elements and molybdenum disulfide as a lubricant had been sintered in nitrogen and hydrogen atmosphere, respectively. Their morphology and energy-dispersive X-ray spectrometry (EDS) analysis showed that serious interaction occurred between MoS2 and Cr (or Cr-Fe) particles when the samples were sintered in hydrogen atmosphere. Chromium sulfide compound (CrxSy) was formed as a reaction product, which decreased the density and strength of the composites remarkably. This interaction was inhibited when the samples were sintered in nitrogen atmosphere; thus, the mechanical properties of the composites were improved.  相似文献   

8.
To enable the utilization of low-grade and high-sulfur bauxite, the suspension calcination was used to remove the sulfur and the activate silica minerals, and the calcinated bauxite was subjected to a desilication process in Na OH solution under atmospheric pressure. The desulfurization and desilication properties and mineralogical evolution were studied by X-ray diffraction, thermogravimetry–differential thermal analysis, scanning electron microscopy, and FactSage methods. The results demonstrate that the suspension calcination method is efficient for sulfur removal: 84.21% of S was removed after calcination at 1000°C for 2 min. During the calcination process, diaspore and pyrite were transferred to α-Al2O3, magnetite, and hematite. The phase transformation of pyrite follows the order FeS2 → Fe3O4 → Fe2O3, and the iron oxides and silica were converted into iron silicate. In the alkali-soluble desilication process, the optimum condition was an alkali solution concentration of 110 g/L, a reaction time of 20 min, and a reaction temperature of 95°C. The corresponding desilication ratio and alumina loss ratio were 44.9% and 2.4%, respectively, and the alumina-to-silica mass ratio of the concentrate was 7.9. The Al2O3·2SiO2, SiO2, and Al2O3 formed during the calcination process could react with Na OH solution, and their activity decreased in the order of Al2O3·2 SiO2, SiO2, and Al2O3.  相似文献   

9.
Ti-6Al-4V/Al7050 joints were fabricated by a method of insert molding and corresponding interfacial microstructure and mechanical properties were investigated. The interfacial thickness was sensitive to holding temperature during the first stage, and a good metallurgical bonding interface with a thickness of about 90 μm can be obtained at 750°C. X-ray diffraction, transmission electron microscopy, and thermodynamic analyses showed that the interface mainly contained intermetallic compound TiAl_3 and Al matrix. The joints featured good mechanical properties, i.e., shear strength of 154 MPa, tensile strength of 215 MPa, and compressive strength of 283 MPa, which are superior to those of joints fabricated by other methods. Coherent boundaries between Al/TiAl_3 and TiAl_3/Ti were confirmed to contribute to outstanding interfacial mechanical properties and also explained constant fracture occurrence in the Al matrix. Follow-up studies should focus on improving mechanical properties of the Al matrix by deformation and heat treatment.  相似文献   

10.
A mechanical activation process was introduced as a facile method for producing nickel oxide nanopowders. The precursor compound Ni(OH)2-NiCO3-4H2O was synthesized by chemical precipitation. The precursor was milled with NaCl diluent. A high-energy ball milling process led to decomposition of the precursor and subsequent dispersal in NaCl media. Nickel oxide nanocrystalline powders were produced by subsequent heat treatment and water washing. Milling rotation speed, milling time, ball-to-powder ratio (BPR), and nickel chlo-ride-to-precursor ratio were introduced as influential parameters on the wavelength of maximum absorption (λmax). The effects of these pa-rameters were investigated by the Taguchi method. The optimum conditions for this study were a milling rotation speed of 150 r/min, a mill-ing time of 20 h, a BPR of 15/1, and a NaCl-to-powder weight ratio (NPR) of 6/1. In these conditions,λmax was predicted to be 292 nm. The structural properties of the samples were determined by field emission scanning electron microscopy, X-ray diffraction, and energy dispersive spectrometry.  相似文献   

11.
Kaolin geopolymers were produced by the alkali-activation of kaolin with an activator solution (a mixture of NaOH and sodium silicate solutions). The NaOH solution was prepared at a concentration of 6–14 mol/L and was mixed with the sodium silicate solution at a Na2SiO3/NaOH mass ratio of 0.24 to prepare an activator solution. The kaolin-to-activator solution mass ratio used was 0.80. This paper aimed to analyze the effect of NaOH concentration on the compressive strength of kaolin geopolymers at 80°C for 1, 2, and 3 d. Kaolin geopolymers were stable in water, and strength results showed that the kaolin binder had adequate compressive strength with 12 mol/L of NaOH concentration. When the NaOH concentration increased, the SiO2/Na2O decreased. The increased Na2O content enhanced the dissolution of kaolin as shown in X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. However, excess in this content was not beneficial for the strength development of kaolin geopolymers. In addition, there was the formation of more geopolymeric gel in 12 mol/L samples. The XRD pattern of the samples showed a higher amorphous content and a more geopolymer bonding existed as proved by FTIR analysis.  相似文献   

12.
The recovery of iron from the screw classifier overflow slimes by direct flotation was studied. The relative effectiveness of sodium silicates with different silica-to-soda mole ratios as depressants for silica and silicate bearing minerals was investigated. Silica-to-soda mole ratio and silicate dosage were found to have significant effect on the separation efficiency. The results show that an increase of Fe content in the concentrate is observed with concomitant reduction in SiO2 and Al2O3 levels when a particular type of sodium silicate at a proper dosage is used. The concentrate of 58.89wt% Fe, 4.68wt% SiO2, and 5.28wt% Al2O3 with the weight recovery of 38.74% and the metal recovery of 41.13% can be obtained from the iron ore slimes with 54.44wt% Fe, 6.72wt% SiO2, and 6.80wt% Al2O3, when Na2SiO3 with a silica-to-soda mole ratio of 2.19 is used as a depressant at a feed rate of 0.2 kg/t.  相似文献   

13.
The effect of Na+ ion concentration on the crystalline phase composition and morphology of xonotlite crystals prepared in a CaO-SiO2-H2O system via hydrothermal synthesis was analyzed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicate that Na+ ion concentration has a significant impact on the composition and morphology of crystalline phases in the products under the initial conditions of a molar ratio of CaO/SiO2 of 1.0 and a reactant concentration of 0.05 mol·L?1 at 225°C for 15 h. The main crystalline phase in the products has a phase transition from xonotlite to pectolite, and the morphology changes from fibrous to broomlike shape with the Na+ ion concentration increasing. Therefore, the content of Na2O in the raw material should be less than 5wt% for preparing pure xonotlite crystals via hydrothermal synthesis in a CaO-SiO2-H2O system.  相似文献   

14.
以煅烧α-Al2O3粉、氧化铁为原料,采用MgO为添加剂,控制配料的Al2O3/Fe2O3的摩尔比为1、3、5,MgO引入量质量百分数分别为2%、4%、6%,成型压强为100 MPa,烧结温度为1500℃、1550℃、1600℃,保温3小时可获得Al2O3-Fe2O3复合材料,对烧后试样了烧结与抗热震性能研究。结果表明:控制Al2O3-Fe2O3复合材料试样AF34-2的Al2O3/Fe2O3摩尔比为3,MgO引入量为4%,烧成温度为1550℃保温3小时的工艺条件,可以制备出较高致密度、常温抗折强度及抗热震性能的Al2O3-Fe2O3复合材料。该复合材料试样AF34-2的SEM显微结构照片显示出材料晶粒间结合紧密,形成具有直接结合的镶嵌结构。  相似文献   

15.
研究了合金中Al含量的增加对铸态FeNiMnCr0.75Alxx=0.25,0.5,0.75,原子分数)高熵合金晶体结构及力学性能的影响。采用X射线衍射仪(XRD)和透射电子显微镜(TEM)对合金的微观结构及形貌进行分析,采用维氏硬度计和MTS万能试验机测试合金的硬度和室温压缩性能。试验结果表明,铸态下,FeNiMnCr0.75Alx高熵合金均由bcc和fcc两种晶体结构的相构成。随着Al含量的增加,合金中bcc结构的相的相对含量逐渐增加,导致硬度和压缩屈服强度也随之升高,应变量降低;且Al含量的增加最终也促使合金中无序bcc结构的相逐渐转变为Ni:(Mn+Al)=1:1(原子分数比)型有序bcc结构的相。  相似文献   

16.
采用乙二醇为溶剂,成功合成了耦合系统Cu2O/Bi2MoO6,分别采用X射线衍射(XRD)、拉曼光谱(Raman)、X射线光电子能谱分析(XPS)和透射电子显微镜(TEM)进行表征.样品的光催化活性通过在可见光下降解结晶紫来获得.结果表明,当Cu与Mo摩尔比为0.08,Cu2 O/Bi2MoO6展示出最高的光催化性能,仅在100 min结晶紫的降解率达到95.6%.同时,研究了耦合系统中Cu2O的量对其光催化活性的影响,并提出了合理的反应机制.  相似文献   

17.
Sm3+-activated Ca2SiO4 red phosphors were prepared by the conventional high-temperature solid-state reaction method, and the effects of sodium (Na+) and samarium (Sm3+) ions doping concentrations on their crystal structure and luminescent properties were investigated by X-ray diffraction (XRD) and fluorescent spectrofluorometer. XRD patterns demonstrate that a well-crystalline structure forms in the phosphors when they are treated by calcination at 1200°C for 4 h, and the excitation spectra exhibit good absorption in the range between 350 and 420 nm. Under the irradiation of 405 nm near-ultraviolet (NUV) light, the spectra of the phosphors show a main emission peak at 601 nm attributed to the 4G5/2??6H7/2 transition of Sm3+ ions, and its intensity is greatly influenced by the concentrations of Sm3+ and Na2CO3. When the concentrations of Sm3+ ions and Na2CO3 are 2mol% and 6mol%, respectively, the optimal emission intensity can be obtained. From strong absorption in the near ultraviolet zone, the Na0.06Sm0.02Ca1.92SiO4 phosphor is a promising red-emitting phosphor for white light emitting diodes (W-LEDs).  相似文献   

18.
SiO_2纳米颗粒稳定的泡沫体系驱油性能研究   总被引:1,自引:1,他引:0  
利用Warning Blender方法测定SiO2+SDS泡沫体系的泡沫性能,确定SiO2纳米颗粒的最佳使用浓度,并研究不同温度和矿化度对泡沫性能的影响。利用岩心驱替实验装置对比SDS和SiO2+SDS两种不同泡沫体系对岩心的封堵、调剖和驱油性能。利用微观可视化玻璃刻蚀模型,对比水驱、SDS泡沫体系以及SiO2+SDS泡沫体系对盲端油的驱替效果。室内实验结果表明,SiO2+SDS泡沫体系比单一SDS泡沫体系具有更强的稳定性,能够明显提高泡沫的封堵、调剖及驱油能力,增加盲端油的驱替效果。  相似文献   

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