Poly mineral composite is being explored as an alternate material to the conventional polymer composite matrix.
The matrix is based on poly mineral resin, which is an alumino-silicate binder. Although these binders are processed at temperatures below 150°C (typically 80°C to 120°C, with techniques commonly used for thermoset organic resins), polymerized poly mineral resins can resist temperatures up to 1200°C (long-term exposure). Poly mineral resins therefore allow the production of ceramic-like materials and high temperature composites by using simple, low temperature processes.
Composites are made at room temperature or thermoset in a simple autoclave. A concrete type material is produced, which after four hours has higher strength and durability than the best currently-used concrete. The advantages of geo polymer composites over organic composites and other materials are: they are easy to make, as they handle easily and do not require high heat; they have a higher heat tolerance than organic composites (carbon reinforced geopolymer composites showed that they will not burn at all, no matter how many times ignition might be attempted); and mechanical properties are similar to those of organic composites. In addition, geo polymers resist all organic solvents, and are only affected by strong hydrochloric acid.
The matrix is based on a poly(silicate) (Si-O-Al-O) structure whose atomic ratio of Si:Al determines the properties and application fields. A low ratio (1, 2, 3) results in a rigid three-dimensional network. A ratio above 15 results in a more polymeric material. A ratio of 1:1 can be used for bricks, ceramics and fire protection applications. A 2:1 ratio is suitable for cements and concretes. Fiberglass composites and tooling for titanium processing are based on a 3:1 ratio. These composites can be used between 200° and 1000°C.
High performance fiber composites are based on a two-dimensional crosslinking network with a ratio between 20:1 and 35:1. The working temperature and curing process is dependent on the type of fiber: for E glass it is room temperature for both; for carbon it is <400°C and room temperature up to 180°C, respectively, for steel it is <750°C and 80 to 180°C, respectively; and for SiC it is 1000°C and 80-1800°C, respectively.
Research at Rutgers University at New Brunswick, NJ, USA has studied various fiber compositions including high modulus C, SiC, steel, micofibers, rovings, fabrics, hybrids (glass mat carbon fabric). By combining a matrix hybrid organic with a geo polymer, a high strength and high temperature resistance material is obtained that is nontoxic. The composite consists of a core made from a glass mat carbon fabric impregnated with vinyl ester, which is coated with a skin of reinforced geo polymer. These C/poly silicate composites have a tensile strength comparable to higher cost composites. Challenges remain regarding achieving uniform nanometer-sized particle dispersion, extending pot life, reducing shrinkage and increasing strain capacity. |