Key Engineering Materials Vols. 368-372

Abstract: Wear-resistant ceramics were prepared successfully with Tangshan Ironstone-tailings. The effects of additives and sintering temperature on their mechanical property were studied. The erosive wear performance of ceramics was evaluated in liquid-solid flow. The erosive wear mechanism was also analyzed. The results showed that the wear-resistant ceramic prepared at 1200°C using 50wt% Tangshan Ironstone-tailings 10wt%, mild-clay and 40wt% high aluminum fly ash as the starting materials had high strength and good erosive wear resistance. The erosive wear mechanisms were washout particles’ micro-cutting and liquid washing.

Abstract: Aluminium titanate was synthesized using waste aluminium sludge and chemical pure TiO2 powder as raw materials. Effect of different compositions on crystal structure and contents of target product was discussed. XRD results showed that four crystal phases, aluminium titanate, perovskite, rutile and aluminum oxide, are formed in the sintered samples. The content of aluminium titanate increases first and then decreases with the decrease of the content of waste aluminum sludge. When the content of the sludge is 65.52wt%, the content of aluminium titanate reaches the maximum of 86.1wt%.

Abstract: Activated carbon was employed as the adsorption carrier for the metal ions in HCl solution of red mud, a solid waste produced in alumina industry. To improve the adsorption capacity to valuable metal ions, the activated carbon was modified by chemicals including HNO3, H2O2, H2SO4, H3PO4, NH3, Na2CO3, and tri-butyl phosphate (TBP). It was found that the modifications contributed the high adsorption capacity to almost all metal ions we focused on. In the case of TBP, remarkably higher adsorption capacity and selectivity of Sc3+ was observed. The correlation between the surface areas, IR spectra of those chemically modified activated carbons and adsorption was schemed.

Abstract: The calcined carbide slag was used to prepare xonotlite by replacing quicklime as the calcareous materials. Effects of calcination temperature on the mineral composition of the carbide slag, lime activity and synthesized xonotlite were studied. The results indicated that carbide slag after proper calcination can be used to prepare xonotlite. Calcination temperature has no effect on the synthesized xonotlite, but has a great impact on lime activity and morphology of secondary particles of xonotlite.

Abstract: A series of sorbents for SO2 in flue gas were prepared from hydrated lime and blast furnace slag using a factorial experiment design. It is found that the reaction between hydrated lime and blast furnace slag is fast. The reactivities of the as-prepared sorbents are higher than those of hydrated lime alone due to the formation of calcium silicate hydrates, and hence the utilization of hydrated lime as well as the Ca in the blast furnace slag is improved. Furthermore, the effects of preparation variables on the reactivity of the sorbents are also discussed.

Abstract: Behaviors of CO2 and pulsed YAG laser melting of ZrSiO4 have been investigated using infrared (IR) spectroscopy. The laser-melted ZrSiO4 decomposed into binary oxides (ZrO2 and SiO2), while other phases or complex ZrSiO4 tetrahedron networks are also observed. The local structures and the phases of the quenched melts depend strongly on the quenching rate and melting conditions. Monoclinic ZrO2 are found to be the main ZrO2 phase in the samples treated by CO2 laser, although tetragonal ZrO2 was found near boundaries between the untreated and melted regions. High concentrations of tetragonal ZrO2 were detected in the samples treated by pulsed YAG lasers. Observations indicate that the formation of tetragonal ZrO2 is related to relatively high quench rates. Micro-IR data from areas near the boundaries between the quenched melts and untreated zircon show systematic variations of local structures and compositions. A small region with relatively low density between the untreated and melted boundaries was observed, which consists of tetragonal ZrO2 or glassy ZrO2, and SiO2. Broad vibrational bands occur in the wave number region where the characteristic frequencies of zircon are located. This observation could indicate the possible existence of small amounts of glassy ZrSiO4 in the melt state of zircon, although zircon tends to decompose above the melting point.

Abstract: Lanthanum-modified bismuth titanate, Bi3.25La0.75Ti3O12 (BLT), powders were prepared from polymerized precursors using citric acid as a chelating agent and ethylene glycol as an esterification agent. The effect of calcination temperature on the microstructure and morphology of powders were studied. It was shown that the pure and normally stoichiometric phase of BLT powders could be obtained at relative low temperature from 550o to 700oC even if the bismuth content is not excess in the starting precursors while the secondary phase could be detected at both lower and higher calcination temperatures. The shape of the BLT grains is also strongly influenced by the calcination temperature.

Abstract: The research investigated the mass loss in SiC crystal growth process by analyzing the effects of the content of Si appending in sources material, growth temperature, growth time and atmosphere pressure. The results indicate that mass loss of total system material (source material + crucible + crystal) and crucible augments with increasing of content of Si in sources material, growth temperature and growth time, but crystal mass gain increases. With increasing of atmosphere pressure, mass loss of system material decreases, crucible mass loss increases, crystal mass gain decreases. Si inclusions in crystal multiply with the increasing of the content of Si in source material.

Abstract: Bulk silicon carbide (SiC) single crystal was fabricated by attaching abrasive SiC powder directly to graphite electrode. The substrate temperature was important to SiC crystal growth. When the temperature of substrate varied from 2300K to 2600K, with substrate temperature increase, the size of finally obtained SiC single crystal increased. At 2600K, the maximum size of SiC crystal, 2cm in diameter, was obtained. The effect of temperature to SiC single crystal growth rate and the growth kinetics were discussed. The phase composition and surface morphology was studied by XRD and SEM respectively.

Abstract: SiAlON family matrix materials have been fabricated from nonmetallic mine. The process of Carbothermal Reduction and Nitridation (CRN) is selected on the basis of raw rocks containing various Si/Al ratios. Thermodynamic analysis of Si-Al-O-N system at different sintering temperatures indicates once the temperature is above 1673 K, a series of chemical reactions occur in sequence, SiO2, SiO, Si2N2O, SiO2+Al2O3, mullite, X-SiAlON, O′-SiAlON, β-SiAlON, SiAlON- polytypiods and Si3N4+AlN. Moreover, most of the reactions are exothermal and are promoted by further heating. The adding or in-situ formed SiC can reduce mullite and Al2O3 to produce O′- or β-SiAlON, and its reaction is surprisingly endothermic and is inhibited when further heated. Also, atmosphere is essential to affect the sintering process. Either raising N2 partial pressures or reducing CO partial pressures can accelerate CRN progress. Correspondingly, phase content and microstructure of the product converted from nonmetallic ore are in detail investigated via X-ray diffraction (XRD) and scanning electron microscopy (SEM).