Development of ceramic bulk materials and coatings with near zero thermal expansion and polymer nanocomposites with controllable thermal expansion
Abstract
This project seeks a comprehensive understanding of the relationship between microstructure (e.g., mean grain size and porosity), thermal (coefficient of thermal expansion and thermal conductivity) and mechanical (YoungÕs modulus, modulus of rupture, Weibull modulus) properties of ceramic bulks of low positive CTE Al2W3O12 (CTE = 1.75 x 10-6 K-1) and near zero CTE ZrMgMo3ÂO12 (CTE = 1.00 x 10-7 K-1) phases. As a consequence, thermal shock resistance potential of this new class of thermomiotics and related phases will be evaluated for the first time. This project also aims to correlate all steps of Al2W3O12 nanopowder preparation, including drying and chemical surface treatment, functionalization of matrix and pre-processing and processing parameters of melt-compounding, in order to develop thermoplastic polymer with considerably reduced CTE without increase in weight or decrease in transparency. A thoroughly study of deagglomeration of Al2W3O12 and Y2W3O12 nanopowders was carried out, allowing the synthesis of highly deagglomerated nanopowders through adjustments during co-precipitation method and drying stage. Al2W3O12 nanopowder with the lowest agglomeration degree (d0.5=0.218 µm) was synthesized through co-precipitation by mixing reactants, using sodium tungstate as tungstate source, a pH=4 during synthesis and microwave drying. Y2W3O12 nanopowder that exhibited the lowest agglomeration (d0.5=0.570 µm) was also synthesized by co-precipitation by mixing reactants and freeze drying. Processing of a dense Al2W3O12 bulk was carried out achieving 92% of relative density after a uniaxial + isostatic pressing, followed by a three steps sintering process. This material presented an improvement in hardness when compared to conventionally sintered Al2W3O12 bulk. Chemical treatment of Al2W3O12 nanopowders with a silane coupling agent (Vinyltrimethoxysilane: VTMS) was performed to improve the compatibility between the filler (VTMS-g-Al2W3O12) and the polymer matrix. HDPE/Al2W3O12 and HDPE/VTMS-g-Al2W3O12 composites were fabricated by microcompounding. The assessment of thermal and mechanical properties of composites showed improvements on the following properties: - The highest reductions on thermal expansion coefficient (10-14 %) of composites were achieved using pristine Al2W3O12 as nanofiller and these reductions did not depend on the filler content. - Increases on Young Modulus of composites were reached using both nanofillers, and they were slightly higher for composites reinforced with chemical treated nanofillers. Increments around 21 % and 28% on this property were observed for a filler loading of 6 mass % of Al2W3O12 and VTMS-g-Al2W3O12, respectively. - All the composites presented an increase on yield stress (5 to 8 %) when compare with neat HDPE. The synthesis of a cubic zero thermal expansion material Zr0,4Sn0,6Mo2O8 was successfully performed by co-precipitation method and the dilatometry measurment of the bulk sample presented a CTE = -6.8 x 10-8 ¡C-1 in cooling.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 22, 2019
- Source ID
- W911NF1510081
Entities
People
- Bojan A Marinkovic
Organizations
- Army Contracting Command
- United States Army