Key Engineering Materials Vols. 368-372

Abstract: The thermal decomposition of ammonium aluminum carbonate hydroxide was studied under non-isothermal conditions in air. The decomposition kinetics were evaluated from data of TG-DTA by means of the Kissinger equation and the Coats-Redfern equation. The values of the activation energy E, the preexponential factor A and the algebraic expression of integral G(α) functions of the thermal decomposition were calculated. The ammonium aluminum carbonate hydroxide (AACH) was characterized by X-ray diffraction, differential thermal analysis and thermogravimetric and field emission scanning electron microscopy.

Abstract: Spark-Plasma Sintering (SPS) involves rapid heating of powder by electric current with simultaneous application of external pressure. Numerous experimental investigations point to the ability of SPS to render highly-dense powder products with the potential of grain size retention. The latter ability is of significance for the consolidation of nano-powder materials where the grain growth is one of the major problems. A model for spark-plasma sintering taking into consideration various mechanisms of material transport is developed. The results of modeling agree satisfactorily with the experimental data in terms of SPS shrinkage kinetics.

Abstract: Practical evolutions of pores in BaTiO3 ceramics during sintering are studied, including the preparation of practical BaTiO3 ceramics and observation of ceramic microstructure by SEM. The reduction of porosity and thus dense process results from the change of the free energy in the ceramic system, which is altered by the disappearing of the interface between solid and pore. The sintering process are monitored, including sintering neck growth, pore shape and size changing, grain growth and compact body contracting. Theoretical formulae during the sintering process are applied for the computer simulation. The experimental results of BaTiO3 ceramics are in good agreement with that of simulation.

Abstract: Master sintering curve (MSC), in which the sintered density is a unique function of the integral of a temperature function over time, is insensitive to the heating path. In this paper, the densification of rutile TiO2 was continuously recorded at heating rates of 2 °C/min and 5 °C/min, respectively, by dilatometer. The MSC for rutile TiO2 was constructed for pressureless sintering using constant heating rate date based on the combined-stage sintering model. The construction and application of the MSC were described in detail for different thermal histories. The MSC can be used to predict and control the densification, final density, and microstructure evolution during the whole sintering. The final density can be predicted for an arbitrary temperature–time path. A good consistence exists between the predicted and experimental densification curve, confirming that it is possible to accurately predict and control the sintering behavior of TiO2 from the initial to final stage of sintering using MSC.

Abstract: In this work, Fe and Si powders were used to fabricate 6.5% Si silicon steel. The mixing powder was rolled into strip and then treated at 900°C in Ar. Sn was added into the mixing powder to investigate the effect of Sn on the sintering. The density, composition, and structure were examined. The results show that Fe almost does not react with Si at 900°C. But with the addition of Sn, Fe reacts with Si to produce Fe3Si at 900°C. Increasing the amount of Sn accelerates this reaction. When the amount of Sn addition is excessive, there will leave many pores in the alloy because the reaction rate is too fast to shrink. The proper amount of Sn addition can decrease the sintering temperature and shorten the sintering time.

Abstract: The joining of sintered ZrO2 to Al2O3 ceramics was realized using Al2O3-ZrO2-SiC interlayer composites, which was designed according to the Al2O3-ZrO2-SiO2 ternary phase equilibrium diagram. Effects of oxidizing SiC on joining were analyzed. The microstructure and components of the joints were studied using XRD and SEM.

Abstract: A simplified method, using microwave molding, to prepared zirconia porous ceramics was proposed, which was involved in the use of albumen and zirconia in aqueous medium, consolidation conducted by microwave heating, and sintering finally at elevated temperature. Microstructure and properties of porous zirconia ceramics prepared by microwave molding were compared with those by traditional heating consolidating process.