Papers by Author: Jin Hong Li

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Authors: Jin Hong Li, Xiu Wen Wu, Jing Yang
Abstract: In this work, we encapsulated the titanium oxide particles with a layer of Al2O3 by a sol-gel process and investigated the UV-shielding properties of the obtained Al2O3-TiO2 composites. In this method, Al(NO3)3 aqueous solution mixed with raw titanium oxide powder was hydrolyzed by adding NH3·H2O. The hydrated materials were calcined at 500°C and then the composite of Al2O3-TiO2 was prepared. Different techniques including ICP-AES, XRD, SEM-EDS, and TEM were used to characterize the raw TiO2 and encapsulated TiO2 particles. Chemical analysis showed that TiO2 mass content in the raw titanium oxide particles is 98.25%, and Al2O3 is just 0.75%. After modification, the percentage Al2O3 was increased to 4.48% due to the encapsulation of Al2O3. Trace elements analysis displayed that the concentration of the trace elements were much lower than their original content in the raw titanium oxide, which prove that proved that there was no impurities incorporated into in the sol-gel process. XRD analysis indicated that the modified titanium oxide powders are mainly in phase of rutile, ca. 99.1%, and the profiles exhibit no peaks of crystalline Al2O3 suggesting the layer of Al2O3 exists in amorphous phase. SEM image suggests that the size is in 80~600nm of the raw TiO2 granula and became rougher on the surface, the packing of the agglomerations got looser after modification with Al2O3. HRTEM image shows that the TiO2 particles was evenly coated with a packed layer ~8 nm in thickness. The UV-Vis absorbency experiments showed that the range of wavelength shielded was narrowed from 208-316 nm in the raw titanium oxide to 225-285 nm in the case of the Al2O3-TiO2. The average absorbency of UV was improved from 1.07 to 1.98 at the same content 1.0 μg/mL in the suspended solution. The results reflected that Al2O3 modification process improve the titanium oxide particles UV-shielding properties in selectivity and performance.
Authors: Jin Hong Li, Ling Xin Tong, Lei Hou, Jie Shen
Abstract: The effects of MgO and temperature on the properties and microstructure of mullite ceramics synthesized from high-aluminium coal fly ash and bauxite are investigated in this paper. The results show that when the batch containing 4 wt% MgO is heated from 1100 °C to 1500 °C, the bulk density and flexural strength increase obviously with the sintering temperature rising, mullite ceramics with flexural strength as high as 169 MPa can be obtained at 1500 °C with the addition of 2 wt% MgO. According to the XRD results, the corundum, cordierite and cristobalite phases disappear completely upon 1400 °C, it indicates that MgO addition may effectively promote sintering process. The results of SEM indicate that the prepared ceramics mainly exist in the shape of long parallelepipeds with the aspect ratio of about 7-10.
Authors: Jin Hong Li, Ling Xin Tong, Wen Cai Zhou
Abstract: A new type aluminous cement containing magnesium aluminate (MA) spinel was prepared from mixtures of limestone, magnesian and bauxite at different ratios by sintering process. The phase composition, microstructure and mechanical properties of aluminous cements containing magnesium aluminate spinel were investigated in this paper. According to the XRD results, the magnesium aluminate spinel (MA),calcium monoaluminate (CA) and calcium bialuminate (CA2) are the primary phases of the obtained aluminous cements with a small quantity of calcium silicoaluminate (C2AS) and remained alumina (Al2O3). The results of SEM indicate that the MA mainly exist in the shape of octahedron with the length of about 2-5 μm, and it is agglomerated with the tabular or flaky-shaped CA among the obtained aluminous cements. In addition, the compressive strength of castables containing obtained aluminous cements increase obviously with the content of CA rising or the curing time increasing.
Authors: Lei Hou, Jin Hong Li, Ling Xin Tong
Abstract: Potassium feldspar (KAlSi3O8) can be used to extract potassium to solve the shortage of water soluble potash resources in China, but it will produce large amount of calcium silicate slag. Resource recycling from calcium silicate slag can be realized by synthesising wall materials. In this research, calcium silicate slag based lightweight wall materials have been successfully prepared by calcium silicate hydrates (CSH), lime and fly ash through autoklave process. Furthermore, the wall materials are charactered by strength determination, X-ray diffraction (XRD) analysis, and Scanning electron microscopy (SEM) analysis. The results show that the compressive strength is mainly influenced by the lime/fly ash mass ratio (L/F), CSH content and water/solid ratio (W/S). The compressive strength of 21.1-23.9 MPa and density of 0.87-0.91 g/cm3 are achieved respectively with the L/F value of 0.82-1.00, CSH content of 70 % and W/S of 0.9. The main hydrate product of wall materials is 11Å tobermorite [Ca5(OH)2Si6O16•4H2O], which is partly formed from the phase transformation of CSH, and partly produced by the reaction among raw materials during the process of autoclaving. The tobermorite is easy formed at low L/F value and it has a contribution to the low density for its flake-like structure that make the materials porous.
Authors: Yi He Zhang, Jing Xing, Li Yu, Jin Hong Li
Abstract: The geopolymer has been prepared from fly ash, metakaolin and Quartz sand, by using the liquid sodium silicate as structural template and sodium hydroxide solution as activator. The effect of glass fiber on the properties of the geopolymer has been studied.
Authors: Jin Hong Li, Hong Wen Ma, Ying Cao
Abstract: In this work, β-sialon ceramics were prepared from high-aluminium fly ash via carbothermal reduction-nitridation (CRN) and the physicochemical properties of the materials such as bulk density, apparent porosity, water absorption and flexural strength were also discussed. The results showed that the percentage of β-sialon phase in the product decreases as the temperature increases from 1400°C and the weight of the sintered specimen experienced an increase during 1350°C~1450°C due to the nitridation reactions, and followed by a gradual decrease till 1550°C for the decomposition of β-sialon. It is indicated that the optimum sintering temperature to obtain the highest yield of β-sialon ~93% lies in 1400°C~1450°C. The SEM images revealed that the prepared β-sialon sintered at 1400°C were mainly in shape of elongated prisms, typically ~5μm in length and 0.5~1μm in width. As the temperature increased to 1500°C and above, β-sialon decomposed and the new phases of SiC and AlN were formed at 1550°C as confirmed by XRD.
Authors: Lin Xin Tong, Jin Hong Li, Jie Shen, Xiao Qian Jiang
Abstract: Mullite nanocomposites powders have been successfully synthesized from high-aluminium coal fly ash via hydrothermal crystallization process. The mullite nanocomposites powders are investigated and charactered by laser particle size analysis, BET surface area analysis, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) analysis, selected area electron diffraction (SAED) analysis and energy-dispersive X-ray (EDX) analysis. Moreover, the reaction mechanism is speculated according to MAS-NMR results. The experimental results show that mullite nanocomposites powders can be prepared at 80-90 °C for 3 h with NaOH concentration of 2-4 mol/L and L/S ratio (liquid/solid ratio in mass) of 10 mL/g. The powder size of D50 is about 1.88-3.27 mm. Mullite nanocomposites are mainly rod-like, acicular and fibroid in shape with an range of 30-80 nm in length and an range of 4.5-30 nm in diameter. MAS-NMR analysis indicates that the nano-size mullite grow around the central atom-Al, Si of [AlSi]O4 tetrahedral and the growth unit Al[OH]4- is existed in this process definitely.
Authors: Jin Hong Li, Hong Wen Ma, Ying Cao
Abstract: The xerogel of mullite precursor with high specific surface area (422m2•g-1) was successfully prepared from the sol of aluminium isopropanol (AIP) and tetraethyl orthosilicate (TEOS) tuned by supercritical CO2 and subsequent supercritical fluid extraction. Nanometer mullite was prepared by calcining the xerogel of the precursor, and the obtained mullite together with the xerogel precursor was characterized by SEM, XRD, N2-adsorption and IR. The results showed that the xerogel precursor exhibit a shape of amorphous structure, with size of no more than 100 nm, and no huge blocks was found, indicating that the supercritical CO2 plays an important role in controlling the process of hydrolyzation, sol-gel transition, in which supercritical CO2 may promote the mixture of Si and Al on atomic scale. SEM indicated that the obtained mullite were mainly 2-3 μm in length and lath in shape with aspect ratios of 6-10, and the laths were interlaced with each other to construct a relative dense mullite aggregation. The mineralogical phases tracing experiment showed that the mullitization process underwent from 1200 °C to 1400 °C as followed by the phase transition from -Al2O3 to -Al2O3, and to -Al2O3, and the temperature of complete phase transformation into mullite was 1400 °C.
Authors: Jin Hong Li, Hong Wen Ma, Hong Wei Zhao
Abstract: Sulphoaluminate-alite cement (SAAC) was successfully prepared from high alumina fly ash. XRD analysis indicated that the optimal mineralogical phase of cement clinker was obtained under condition of MG=1.05, MS =0.95 at 1300oC, and C4A3 S reached the strongest intensity and is 58.73% in the phase of calcined clinckers. SEM observation showed that C4A3 S are well developed into regular diamond/hexagon-shaped crystal with the size of 1~3.5 μm in the clinker. Hydrated clinker exhibited its new formed dominant phases in AFt, C-S-H and Afm. Pillar shaped AFt and sheet shaped AFm coexisted among the colloidal C-S-H substrate. It is demonstrated that the prepared cement shows a compressive strength of 27 MPa (1d), 36 MPa (3d), 49 MPa (28d), and flexural strength of 5.9 MPa (1d), 5.9 MPa (3d), 6.1 MPa (28d), indicated that the hydration product owned a good mechanical strength at early ages and increased steadily in the later stages.
Authors: Jin Hong Li, Hong Wen Ma, Ling Xin Tong, Xiao Qian Jiang
Abstract: This research presented the kinetics of mullite formation in fly ash-bauxite reactants couples. Experiment on isothermal conversion of fly ash-bauxite at 1100°C, 1300°C, 1500°C has been carried out. XRD was used to quantitatively measure the content of mullite specimens sintered at different temperatures and times. The kinetics curve of conversion ratio versus time has been drawn. The results obtained showed that the full transformation of fly ash-bauxite to mullite takes place between 1300 °C and 1500 °C. The activation energy of secondary mullite formation is deduced to be 151 kJ/mol in the range of 1100-1500°C. The growth morphology parameter, n, is about 1.14 and 0.45 at 1100°C and 1500°C, respectively, indicating that bulk nucleation is dominant in mullite crystallization followed by three-dimensional growth of mullite crystal controlled by diffusion, but at 1500 °C diffusion process dominates mullite formation process.
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