Whisker-Driven Templated Grain Growth Enables [001]-Oriented Interlocking Microstructures and Phase Manipulation in Alumina-Mullite Fibres
Description
Research Hypothesis Alumina–mullite fibres are critical toughening agents for high-temperature structural materials in oxygen-rich environments; however, their mechanical properties are inherently limited by equiaxed grain structures. In this study, using mullite whiskers as templates, a sol-based dry-spinning process was employed to synthesise alumina–mullite fibres with an oriented, rod-like interlocking structure via templated grain growth (TGG). We hypothesise that mullite whiskers can induce heterogeneous epitaxial growth in the fibre matrix during sintering, thereby promoting the formation of oriented rod-shaped grains and delaying the α-alumina phase transformation. This dataset characterises the phase composition, microstructure, and grain orientation of the synthesised fibres to elucidate the effects of whisker content on phase transformation and microstructural evolution. Data Content and Acquisition Methods This dataset comprises three categories of files derived from characterisation of the synthesised whiskers and alumina–mullite fibres: XRD Data: Raw files were collected using a D/max-3c diffractometer (Rigaku) at 40 kV and 100 mA with Cu Kα radiation. Analysed results include phase identification via HighScore Plus and quantitative phase ratios determined by RIR semiquantitative analysis. SEM Images: Microstructural images were acquired using an S-4800 field-emission SEM (Hitachi) at 15 kV, with EDS (Bruker) for elemental mapping. Grain diameter and porosity measurements derived from these images are included. TEM Images: Nanostructural characterisation was performed using a JEM-2100F field-emission TEM (JEOL). Images reveal fine-scale morphology, crystal structure, and defects or interfaces within the fibres. Key Findings and Data Interpretation Preliminary analysis confirms the target crystalline phases via XRD, with RIR analysis providing phase ratios correlated to processing parameters. SEM reveals fibre morphology and elemental composition, while TEM discloses grain boundaries, lattice fringes, and secondary phases or defects. Collectively, these data support the correlation between processing conditions, phase evolution, and microstructural development, and can be reused for comparative studies or validation of computational models.
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Steps to reproduce
1. Synthesis of mullite whisker templates: Following our previous work, rapidly heat a mixture of aluminium nanopowders, silica nanopowders and aluminium fluoride in an airtight alumina crucible at 1200°C. Grind and disperse the sintered whiskers for use as template particles. 2. Preparation of starting materials: Use acidic silica sol (SiO₂, 20 nm) as the silicon source, aluminium chlorohydrate (Al₂(OH)₅Cl·2H₂O, ACH) as the aluminium source, and polyvinyl alcohol (PVA, [C₂H₄O]n) as the spinning aid. 3.Sol preparation: Prepare a transparent sol by stirring a mixture of ACH and distilled water at room temperature. Sequentially introduce the acidic silica sol and mullite whiskers under continuous stirring for 3 h, yielding a composite sol with an effective Al₂O₃–SiO₂ weight ratio of 85:15 and whisker contents of 0, 1, 3 and 5 wt.%. Gradually incorporate a 5 wt.% PVA solution under magnetic stirring to achieve a final PVA content of 7 wt.%. Condense the sol at 60°C in a water bath and cool to room temperature until the optimal spinning viscosity is reached. 4. Dry-spinning: Process the spinnable sol using a laboratory-fabricated miniature dry-spinning apparatus. Collect the gel fibres on a bobbin winder, during which the mullite whiskers naturally achieve oriented alignment along the flow streamlines within the fibres. 5. Drying and sintering: Dry the as-spun gel fibres at 40°C for 2 h. Subsequently sinter in a muffle furnace at 950°C, 1100°C, 1250°C, 1400°C and 1550°C. During sintering, first gradually heat to 800°C at a rate below 1°C/min, followed by rapid heating at a rate exceeding 10°C/min to the final temperature, and hold for 20 min. 6. Characterisation: Collect XRD patterns using a D/max-3c diffractometer (Rigaku) with Cu Kα radiation (40 kV, 100 mA). Perform phase identification via HighScore Plus software and quantify phase ratios by RIR semiquantitative analysis. Observe microstructures using an S-4800 field-emission SEM (Hitachi) at 15 kV with EDS (Bruker) for elemental mapping, and examine nanostructures using a JEM-2100F field-emission TEM (JEOL). 7. Data analysis: Measure grain diameter and porosity from SEM images. Calculate the aspect ratio and orientation angle of rod-shaped grains from the acquired micrographs to evaluate the oriented interlocking structure.