University of Illinois

Other

US Government as Represented by the Secretary of the Army

University

Keanetech, LLC

Waltraud M Kriven

Sang-Jin Lee

Ghassan Al-Chaar

My Nguyen

Kaushik Sankar

Mehmet Ali G&uuml;lg&uuml;n

Dong Kyu Kim

Dong-Hau Kuo

A method of using a flowable binder for construction or repair comprises providing a binder mixture including an alkali metal silicate, fly ash, slag, and added water, where a total water-to-solids mass ratio of the binder mixture is in a range from about 0.2 to 0.5. The binder mixture is mixed together with inert particles to form a flowable mortar. The flowable mortar is distributed over a bed of coarse aggregate, and the mortar seeps into interstices of the coarse aggregate. Upon curing, a composite comprising reinforcement material embedded in a cured binder is formed.

Flowable slag-fly ash binders for construction or repair

Porous aluminosilicate geopolymers having a desired molar ratio of silicon dioxide to aluminum oxide are prepared by mixing an aluminosilicate powder in an alkaline silicate solution, placing into a sealed container, and then curing. The desired density and compressive strength of the geopolymer are achieved by varying the excess of alkaline silicate and by varying the curing temperature. The desired pore size distribution of the geopolymer is achieved by varying the curing conditions.

Porous geopolymers

In general, this invention relates to a ceramic composite exhibiting enhanced toughness and decreased brittleness, and to a process of preparing the ceramic composite. The ceramic composite comprises a first matrix that includes a first ceramic material, preferably selected from the group including alumina (AlO), mullite (3AlO.2SiO), yttrium aluminate garnet (YAG), yttria stabilized zirconia (YSZ), celsian (BaAlSiO) and nickel aluminate (NiAlO). The ceramic composite also includes a porous interphase region that includes a substantially non-sinterable material. The non-sinterable material can be selected to include, for example, alumina platelets. The platelets lie in random 3-D orientation and provide a debonding mechanism, which is independent of temperature in chemically compatible matrices. The non-sinterable material induces constrained sintering of a ceramic powder resulting in permanent porosity in the interphase region. For high temperature properties, addition of a sinterable ceramic powder to the non-sinterable material provides sufficiently weak debonding interphases. The ceramic composite can be provided in a variety of forms including a laminate, a fibrous monolith, and a fiber-reinforced ceramic matrix. In the laminated systems, intimate mixing of strong versus tough microstructures were tailored by alternating various matrix-to-interphase thickness ratios to provide the bimodal laminate.

High temperature tolerant ceramic composites having porous interphases

Described are preferred polymerized organic-inorganic processes for producing mixed metal oxide powders suitable for use in the ceramics and related industries. The preferred processes employ a non-chelating polymer such as polyvinyl alcohol or polyalkylene glycol as a carrier and can provide single-phase, mixed oxide powders in high yields at relatively low temperatures.

Processes for preparing mixed metal oxide powders

Generally, this invention provides a toughened ceramic composite and a method of enhancing the mechanical strength of ceramic matrix composites through use of a transformation weakened interphase material. The ceramic composite provided in this invention includes a ceramic matrix, a second material as a second phase, and a metastable interphase material. The metastable interphase material is positioned between the ceramic matrix and the second phase material. The ceramic composite can include reinforcing elements such as fibers, whisker-shapes, platelets and particulates or have laminated or fibrous monolithic geometries. The metastable interphase material is capable of undergoing a shear or stress induced zero volume or negative volume, martensitic phase transformation, which may or may not be accompanied by a crystallographic unit cell shape change. In one embodiment, the metastable interphase material includes &bgr;-cristobalite.

Toughening of ceramic composites by transformation weakening of interphases

The invention comprises a multilayer high-strength, high-toughness, flaw-tolerant oxide ceramic composite having a metal phosphate later, a first yttria stabilized zirconia layer, a yttria stabilized zirconia-alumina layer and a second yttria stabilized zirconia layer; and a method for producing the same. The metal phosphate are selected from the group consisting of monazites, xenotimes, calcium phosphate, aluminum phosphate, zirconium phosphate and substituted zirconnium phosphate wherein Zr.sup.4+ is partially replaced by divalent metal ions. The ceramic composition of the invention may be further strengthened by the incorporation of selected particulates, whiskers or fibers, or mixture of the same, into the yttria stabilized zirconia layers, the yttria stabilized zirconia-alumina layers and the metal phosphate layers. A multilayer ceramic of the invention comprising a YPO.sub.4 layer, a first yttria stabilized zirconia layer, a 30 vol % yttria stabilized zirconia-70 vol % alumina layer and a second yttria stabilized zirconia layer was found to have a 4-point flexural strength of 358, 392 MPa and an apparent work-of-fracture in the range of 8.2, 10 kJ/m.sup.2.

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Champaign, IL, United States of America

Waltraud M Kriven