Elaboration and Characterization of Mullite Refractory Products from Moroccan Andalusite
Enrichment of schist mined in Morocco resulted in an extract essentially made of andalusite, quartz and muscovite, which was investigated with the aim to synthesize mullite refractory materials. X-ray diffraction analysis was used to assess phase transformations upon heating at different temperatures. Mullite formation starts as early as 1200℃ and seems almost total at 1450℃. This process correlates with a weak shrinkage (3.5% at 1450℃) and the formation of an important glass phase. Green compacts obtained by unidirectional pressing the extract powder were heated under air in the temperature range 1200℃ - 1600℃. Chemical and mechanical properties of these materials were investigated and correlated with their microstructure.
Mullite grown from fired andalusite grains: the role of impurities and of the high temperature liquid phase on the kinetics of mullitization and consequences on thermal shocks resistance
Mullitization and microstructure of mullite grown from fired andalusite grains has been studied in the literature. Mechanisms of mullite formation are well known: during heating, andalusite single crystal grains are transformed into a composite made of a 3:2 mullite single crystal with a capillary network filled with silica rich liquid. But very few works studied the influence of the impurities on the kinetics of mullitization. This paper shows that the presence of impurities (mainly iron and alkalis) in the andalusite increases the amount of the liquid phase and decreases the liquid viscosity. The mullitization kinetics depends on the andalusite grain size, the chemical composition, the origin of the andalusite deposit and the amount and the properties of the liquid phase. Because of the specific microstructure and the presence of the liquid phase, during thermal shocks in air, the mullitized andalusite crystals exhibit a behaviour typical of composite materials: microcracks are deflected by mullite/glass interfaces and stopped in glass zones. During a further heating, cracks generated by a thermal shock are healed.
A New Vacuum Pressure Infiltration CFRP Method and Preparation Experimental Study of Composite
In order to prepare a carbon-fiber-reinforced polymer composite (CFRP) with ideal microstructure and properties, a new vacuum pressure infiltration CFRP method is proposed based on an analysis of existing CFRP preparation process methods. Research on composite material preparation systems was carried out by using this new method principle. The system mainly includes a fiber pre-forming module, a vacuum heating infiltration module, a hot-press curing molding module, and a data acquisition control module. Under the conditions of natural curing at 0 MPa + 6 h + 25 °C, vacuum heating curing at –0.05 MPa + 30 min + 80 °C, and hot-press curing at 0.7 MPa + 5 min + 50 °C, a two-dimensional (2D) CFRP with excellent microstructure and properties was successfully prepared. Observing the microstructure of the prepared composite material, it can be found that the inside of the composite material was sufficiently and uniformly infiltrated, and common preparation defects such as holes and delamination were effectively controlled. Through the performance test, the bending strength of the material reached 790 MPa.