Reactive sintering is an environmentally-friendly processing for porous ceramics. If zero volume-shrinkage in the reactive sintering is realized, the reactive sintering will be more widely applied. Here, we report a new reactive sintering technique to realize near-zero volume-shrinkage (NZVS) in the MgO-TiO2 system. Porous MgTi2O5 pellets have been reactively sintered from LiF-doped hydromagnesite/TiO2 mixed powders with changing TiO2 anatase/rutile compositions. By using the anatase and rutile mixtures as TiO2 source, volume-shrinkage during the sintering was well-controlled. In particular, the NZVS is realized for the sintering temperatures at 1000-1100°C. To clarify the mechanism of the NZVS phenomenon, MgTi2O5 particle formation behavior from the identical starting powders without pelletizing was investigated in detail. From the microstructural observation for MgTi2O5 powders, TiO2 rutile prevented the crystal growth of MgTi2O5 particles.

Pseudobrookite-type oxide-based ceramics, such as Al 2 TiO 5 and MgTi 2 O 5 , have recently been studied as porous ceramic membranes. Here, the effect of LiF doping on the morphology of MgTi 2 O 5 particles is presented in detail. Water purification filters were produced using porous MgTi 2 O 5 , with different particle morphologies. MgCO 3 (basic) and TiO 2 powders with various LiF contents were wet-ball milled, dried, and then, calcined in air at 1100 • C to obtain the MgTi 2 O 5 powders. The powder compacts were sintered at 1000-1200 • C to produce the MgTi 2 O 5 disk filters. The 0.5 wt.% LiF-doped MgTi 2 O 5 disk filter, with elongated grains, showed well-balanced performance removing boehmite particles with diameter of 0.7 m. Non-doped MgTi 2 O 5 disk filter with equiaxed grains was suitable for precise filtration.

Volume-shrinkage of a sample in reactive sintering generally tends to be larger than that in conventional sintering. New techniques to suppress the volume shrinkage are eagerly needed for actual manufacturing. Recently, we have reported that reactively sintered porous MgTi2O5 from hydromagnesite and TiO2 rutile showed less volume shrinkage than that from hydromagnesite and TiO2 anatase. The result demonstrated that the compositional control of starting polymorphs can be a potential technique to optimize the volume shrinkage. In this paper, in order to evolve the reactive sintering technique, volume-changes during reactive sintering were dynamically monitored by thermomechanical analysis (TMA). The dimensional change behavior measured by TMA was linked up with the reaction behavior clarified by high-temperature X-ray diffraction (HT-XRD). In dilatometry curves, transient volume expansions were observed and they were well-explained by the formation and crystal growth of intermediate MgTiO3 and objective MgTi2O5 particles.

Well-controlled fine MgTi 2 O 5 powders, with pseudobrookite-type structure, are desired toward various industrial applications, however, commercial powders are hardly available to date. In this study, we focused the processing and characterization of well-controlled MgTi 2 O 5 powders with/without LiF additive. MgCO 3 (basic) and TiO 2 anatase powders with/without 0.5 wt. % LiF additive were calcined in air at 1100 °C for 2 h to obtain the MgTi 2 O 5 powders. SEM observation revealed that the non-doped MgTi 2 O 5 powder consisted of equiaxed particles with the diameter of 0.5-1.5 m, whereas, the LiF-doped MgTi 2 O 5 powder consisted of elongated particles with the length of ~ 5-10 m and the diameter of ~1.0-1.5 m. The smooth surface of elongated MgTi 2 O 5 particles demonstrates the effect of LiF doping as a flux, i.e., liquid phase formation during the reaction.

Well-controlled fine MgTi2O5 powders, with pseudobrookite-type structure, are desired toward various industrial applications, however, commercial powders are hardly available to date. In this study, we focused the processing and characterization of well-controlled MgTi2O5 powders with/without LiF additive. MgCO3 (basic) and TiO2 anatase powders with/without 0.5 wt. % LiF additive were calcined in air at 1100 °C for 2 h to obtain the MgTi2O5 powders. SEM observation revealed that the non-doped MgTi2O5 powder consisted of equiaxed particles with the diameter of 0.5-1.5 μm, whereas, the LiF-doped MgTi2O5 powder consisted of elongated particles with the length of ~ 5-10 μm and the diameter of ~1.0-1.5 μm. The smooth surface of elongated MgTi2O5 particles demonstrates the effect of LiF doping as a flux, i.e., liquid phase formation during the reaction.