Papers by Author: Hong Wen Ma

Abstract: In this paper, wollastonite nanopowder were successfully synthesized by the surfactants modified-calcined method using calcium silicate residue of potassium feldspar after extraction of potassium and alumina. The effects of modifier and calcined temperature on the phase composition, morphology and microstructure were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the phase of samples with different modifier processing is wollastonite-2M, while CTAB as modifier can avoid preferred orientation growth. The obtained wollastonite powder is spherical in morphology and well dispersed with the particle size of approximately 150nm.

Abstract: A novel aminotriacetic acid (NTA) intercalated MgAl-LDHs have been successfully synthesized by anion exchange method with MgAl-NO₃-LDHs as precursor. The XRD pattern implies that NTA anions have replaced NO₃^- in the interlayer of LDHs. The FT-IR spectra also indicates that NTA anions have intercalated into layers’ space of LDHs, and the carboxyl groups of NTA have been converted into carboxyl anions after intercalation process. When comparing IR spectra of MgAl-NTA-LDHs and MgAl-CO₃-LDHs, higher and stronger absorption was observed in the range of 1428-1250 cm^-1, especially in the range of 1111-909 cm^-1.

Abstract: Novel nanobranched Ni/Fe-LDHs were successfully prepared by coprecipitation method without adhesive condition. The effects of different factors as pH and aging time on its morphology were discussed in detail. According to the results, the branches diameters of Ni/Fe-LDHs are among 50-100nm and the optimum experiment pH equals 10 and experiment time is 48 hours. Therefore, the nanobranched Ni/Fe-LDHs can be expected to be potential for designing and investigating novel materials.

Abstract: Nanosized pseudoboehmite particles were synthesized by the precipitation of sodium sulfate and ammonia in aqueous solution at 70°C. After calcinations, the pseudoboehmite could successfully transfer to γ-Al2O3 nanoparticles while retaining their previous morphology. The influence of the reaction conditions on formation of pseudoboehmite and γ-Al2O3 had been researched in detail. The X-ray diffraction analysis showed that nanosized crystalline pseudoboehmite was formed at pH 8-8.5 after ageing 2 hours. Utilization of surfactant(PEG1000) would produce finer nanoparticles with well-dispersion. With the ageing time or the surfactant amount increasing, the morphology of the resulting particles transformed from spherical to fibrous

Abstract: The structure and composition of carbon materials affect obviously the result of carbothermic reduction of magnesia. Coke, charcoal and graphite were used in reduction experiments under the same conditions. The reactivity ratio of magnesia and XRD pattern of residues were analyzed and compared. The reactivity ratio of magnesia by coke was similar to the one by charcoal. The amorphous carbon in coke graphitized partly in reduction experiments of 1673K. The results show that the effective composition in coke is the amorphous carbon. It also suggests that the temperature of reaction should be control less than 1700K to avoid the amorphous carbon’s graphitization.

Abstract: The morphology and particle size of boehmite play a decisive role on the application of alumina that derived from it. In this paper, we employed pseudoboehmite that produced from Al2 (SO4)3•18H2O and NH3•H2O at 70 °C, pH 7.5 as precursor to synthesize boehmite, and utilized different seeding when preparing pseudoboehmite and boehmite. To identify the influence of seeding on the microstructure of pseudoboehmite and boehmite, the products were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and BET. The results indicate that the pseudoboehmite seeding has a significant influence on the morphology and particle size of pseudoboehmite to which we should pay high attention. However, the boehmite seeding does not play the role of crystal nucleus as expected. The further intrinsic mechanism study is ongoing.

Abstract: The present paper focuses on the experimental investigation of the aluminothermic reduction of magnesia under vacuum condition with the fixed magnesia to aluminum molar ratio of 11:6. The influences of reaction temperature and time on the reduction ratio of magnesia were studied. The chemical composition, phase constitution and morphology of the condensed magnesium and the briquettes after thermal reduction were investigated by X-ray diffraction, scanning electron microscopy equipped with energy dispersive spectrometry. The reduction ratio of magnesia increases with the increase in the reaction temperature and time. The briquettes after thermal reduction at 1050°C-1150°C are mainly composed of the spinel, unreacted magnesia and aluminum. The briquette after 1 hrs thermal reduction at 1200°C contains corundum, magnesium aluminium oxide, trace amount of spinel, unreacted MgO and aluminium.

Abstract: Pure magnesium hydroxide (Mg(OH)2) nanoparticles were synthesized successfully from dolomite-talc ore via chemical precipitation. Carbonate minerals in dolomite-talc ore were dissolved with hydrochloric acid, and Fe2+ was oxidized to Fe3+, then Fe3+ and Al3+ were removed by adding ammonia to adjust pH to reach 6. Magnesium hydroxide (Mg(OH)2) nanoparticles with about 20nm thickness and lamella shape were obtained successfully when pH>10 in the presence of a nonionic surfactant polyethyleneglycol (PEG) with 3wt %, which reached by adding more ammonia. The XRD results show that the amorphous precipitate with 87% Fe2O3 generates at pH=6. However, CaMg2Cl6 (H2O)12 generates when pH = 7, then disappears with the increasing of pH. Mg(OH)2 appears at pH= 9 and pure Mg(OH)2 particle is obtained at pH > 10. Meanwhile, PEG plays an important role in the growth of Mg(OH)2 nanoparticles.

Abstract: Zeolite A was successfully synthesized via convenient hydrothermal process using potassium-extracted residue of potassium feldspar as a combined source for silica and alumina. Optimization studies on the molar ratios of Na2O/SiO2 and H2O/SiO2, and aging time have been conducted. The results were that pure zeolite A with high crystallinity could be synthesized when the reaction mixture with molar ratios of Na2O/SiO2 and H2O/SiO2 of 2.0 and of 85, respectively, were crystallized at 100°C for 3h. Aging was found to be not prerequisite for the formation of zeolite A in the system. The product was characterized by XRD, FTIR, SEM and calcium exchange capacity. Finally, a comparative study of the zeolite A formation from the potassium-extracted residue and other industrial waste or natural silicate minerals was also carried out.

Abstract: Using coal fly ash from one thermal power plant in Ningxia, China as the raw material, aluminum hydroxide powder was successfully extracted by pre-desilication , calcination, dissolution and carbonation precipitation processes. The research results indicated that the mullite, Quartz and glass phase in the coal fly ash could be changed into NaSiO3, NaAlO2 and Na2CaSiO4 after the coal fly ash was treated by desilication and calcination. The SiO2and Al2O3 components in the coal fly ash were mainly separated by dissolving the calcined sample using water. The dissolution rate of Al2O3 from the calcined sample is 91%. The aluminum hydroxide powder extracted from the coal fly ash is bayerite with the particle size of more than 50m. The extraction rate of the aluminum hydroxide from the coal fly ash can be up to 83%.