Recent Progress in Chemically Bonded Phosphate Ceramics

Chemically bonded phosphate ceramics have made an excellent progress in the last 10 years and are poised to be one of the major inorganic room-temperature setting materials for nuclear, structural, dental, and prosthetic applications. They are also poised to be the first inorganic industrial coatings for fire and corrosion protection applications. In 2004 the author in his book, Chemically Bonded Phosphate Ceramics, presented general theory, compositions, methods of fabrication, and preliminary commercial products that appeared in the market ten years ago. This paper reviews that background and presents advances of last ten years with an emphasis on the recent applications in the nuclear field. 1. Evolution of Chemically Bonded Phosphate Ceramics Discovery of ceramics has been concurrent with evolution of human civilization. Early ceramic tools used for hunting and self-defense, thatched mud houses for shelter, and earthenware used for cooking were the first products of survival that all used some binding mechanism to put particles together in a desired shape. Rocks, minerals, and dirt were readily available and hence they became the raw materials. Fire was known in early stages of civilization and fired products could be made easily. In spite of these advances in production of ceramics, their scientific understanding had to wait for development of science of materials. Thus, ceramic science is only few hundred years old, which now explains how the binding mechanisms work. High temperature diffusion of atoms between the particles and fusion of particles or chemical bonding are the two basic binding processes. Products of the first process are traditionally known as ceramics while those produced by the second process are cements. High temperature treatment was used in fabricating almost all ceramics. Since granting of the first patent on Portland cement [1], however, significant efforts were invested in understanding the role of chemical bonding in production of cements. The ready acceptance of Portland cement as a building material indicates the importance of chemical bonding as an alternative to high temperature sintering. Simplicity of casting large shapes was a great technological advancement over high temperature ceramics. From scientific viewpoint, Portland cement consists of noncrystalline binding phases, while most ceramics are identified by their dominant crystalline structure with an exception of glass that is noncrystalline but produced at high temperature. Thus dominance of noncrystalline binding phases in cements as against the crystal