Studies Of The Solution Properties And The Precipitation Process Of Polyaluminocarbosilane

The polymer-derived technology has been widely used to prepare various advanced ceramic materials because it offers many advantages such as easy to shaping, low processing temperature and tailorable ceramic compositions. The preceramic polymer can be shaped by means of either melting or solution. The shaping with polymer solution can be carried out at room temperature without inert gases. It is necessary to study the properties of preceramic polymer solution because it has wide applicationsIn this paper, polyaluminocarbosilane (PACS), precursor of SiC(Al) ceramic fiber, was considered as the starting point of the study. Basic thermodynamics parameters of PACS solution were determined to investigate the solubility of PACS in various solvents. The phase separation behavior of PACS / solvent / precipitant systems can be elucidated by ternary phase diagrams constructed by cloud point titration. Instead of using the conventional precipitation method (adding precipitant into solution, or Prec-Solu), PACS was precipitated by means of dropping PACS solution into precipitant (Solu-Prec). With the later method, PACS precipited in the form of fine dispersed white particles with small size. The molecular weight among these particles is relatively uniform. In the process of precipitation for PACS in THF solution, linear macromolecules precipitate at the beginning, followed by branched molecules and then low molecular weight species.Basic studies and technological investigations of the precipitation behavior of PACS solution indicate that the purification of PACS by precipitation is an effective method. Comparing with the conventional PACS purified by distillation (Dis-PACS), the PACS purified by precipitation (Pre-PACS) is composed of less low molecular weight species, that leads to a higher ceramic yield. This is an advantage to prepare SiC ceramic materials with higher properties.The rheological property of Pre-PACS was investigated with comparison of Dis-PACS. For both samples with similar melting temperature, the apparent viscosity of Pre-PACS is higher than that of Dis-PACS at any specific temperature because of the differences of the molecular weight and the distribution. Therefore, the spinning temperature of Pre-PACS should be higher than conventional Dis-PACS. Si-C-Al-O fiber with excellent properties can be prepared by melting spinning, air curing and pyrolysis with Pre-PACS.