Abstract: An erosion-resistant, chemically vapor-deposited zinc sulfide window and method of making the same are disclosed. The method includes the step of immersing a chemically vapor-deposited or a hot isostatic pressed, chemically vapor-deposited zinc sulfide body into a liquid comprising gallium, the liquid having a temperature of about 600.degree. C. to about 1000.degree. C., for at least about thirty minutes to form a gallium-doped body. The gallium-doped, chemically vapor-deposited zinc sulfide body according to the invention is one capable of transmitting light having a wavelength in the range of about 300 nanometers to about 15,000 nanometers. Furthermore, the gallium-doped, chemically vapor-deposited zinc sulfide window according to the invention is capable of transmitting light, having a wavelength in the range of about 380 nanometers to about 700 nanometers have been exposed to rain erosion for 20 minutes at 470 miles per hour with a 90.degree.

Abstract: Methods of fabricating a porous ceramic composite having voltage-variable dielectric properties. The composite is made as follows. A polycrystalline ferroelectric powder, which is a ferroelectric perovskite such as barium strontium titanate, for example, is provided. The powder, a binder and a filler are then mixed in water to form a slurry. The powder-binder-filler slurry is then dried. The dried powder-binder-filler slurry is granulated. The granulated powder-binder-filler is pressed into a die. The binder and filler are then burned out to form a fragile porous ash-like structure. The porous structure is then sintered to form porous ceramic parts. The porous ceramic parts are then machined tiles. The machined porous tiles may then be tested for microwave properties. Fabrication methods for producing porous ferroelectric ceramic-polymer composite tiles or subaperture blanks and continuous transverse stub electronically scanned antenna plates or subapertures are also disclosed.

Abstract: Single crystal sapphire is conventionally employed for mid-wave IR windows and domes exposed to high aerodynamic heating environments. Single crystal sapphire, however, suffers a loss of compressive strength in the c-axis of 95% on heating from ambient to 800.degree. C. This loss of compressive strength on heating results in poor thermal shock resistance. Poor thermal shock resistance jeopardizes the reliability of the windows and domes. The process of the present invention strengthens sapphire and improves its resistance to thermal shock by introducing magnesium (Mg) ions into the crystal lattice of sapphire to form a solid solution. The solid solution increases the strength of the sapphire. Additionally, a larger increase in strength results from converting the Mg into second phase precipitates comprising magnesium aluminate spinel.

Abstract: Bonding of expanded polymeric parts together to produce lost foam molds suitable for casting metallic details is accomplished by applying a non-aqueous, adhesive-free coating comprising a polar, highly dielectric component contained in a liquid vehicle to the interfacing surface of at least one of the parts to be joined. The interfacing surfaces of the parts to be joined are held in contact while the assembly is irradiated with high frequency electromagnetic energy. This energy enables the coating to dielectrically heat the mated expanded polymeric parts until a bond is effected by melting the polymeric parts and inducing expansion of the parts into one another.

Abstract: Low cost broadband infrared windows are fabricated using a near net shape process which greatly reduces the cost of machining and grinding window materials. The fabrication of zinc sulfide (ZnS) IR windows uses ceramic powder processing to avoid the expensive prior art chemical vapor deposition method. Further, the invention involves a means of hardening and strengthening ZnS as part of the powder process, with IR transmission performance comparable to undoped CVD-prepared ZnS. The compositional modification used in the practice of the invention involves the introduction of gallium sulfide (Ga.sub.2 S.sub.3) as a second phase which acts to toughen and harden the ZnS. The process of the present invention achieves a hardening effect without degrading the IR transmission properties also by means of controlling the polycrystalline microstructure grains to a very small size. At the same time, porosity, which strongly degrades IR transmission, is minimized by full densification.

Abstract: Low cost broadband infrared windows are fabricated using a near net shape process which greatly reduces the cost of machining and grinding window materials. The fabrication of zinc sulfide (ZnS) IR windows uses ceramic powder processing to avoid the expensive prior art chemical vapor deposition method. Further, the invention involves a means of hardening and strengthening ZnS as part of the powder process, with IR transmission performance comparable to undoped CVD-prepared ZnS. The compositional modification used in the practice of the invention involves the introduction of gallium sulfide (Ga.sub.2 S.sub.3) as a second phase which acts to toughen and harden the ZnS. The process of the present invention achieves a hardening effect without degrading the IR transmission properties also by means of controlling the polycrystalline microstructure grains to a very small size. At the same time, porosity, which strongly degrades IR transmission, is minimized by full densification.

Abstract: A microwave-absorbing material composed of blends of polar icosahedral molecular units with a variety of host matrices, or with polymers with the units covalently bonded in a pendant manner to the polymer chain. Both blends and polymers must impart a high degree of orientational mobility to the units so that they can absorb microwave radiation. These materials employ orientationally mobile, polar icosahedral molecular units as the source of dielectric loss at microwave frequencies. Examples of these units are the polar carboranes (ortho- and meta-carborane), polar carboranes with electronegative and/or electropositive substitutes, and polar "buckminsterfullerenes.

Abstract: Ferroelectric composites are prepared by sol-gel derived procedures. The present invention utilizes the sol-gel process (1) to form a gel in a mold of the desired size and shape, (2) to dry the gel using a supercritical fluid extraction, (3) to sinter the dried gel to a crystalline ceramic, and finally (4) to impregnate the pores with a low loss polymer. The aerogel composition may be a barium titanate-based composition such as barium strontium titanate (BST). Making a ferroelectric aerogel composite provides a unique and novel means of fully exploiting the voltage- and/or frequency-tunable properties of certain compositions by maximizing their desirable properties and minimizing their undesirable characteristics such as loss at operational frequencies.

Abstract: An inhomogeneous broadband absorber of electromagnetic energy constructed from an aerogel-lossy dielectric composite, where the concentration of the lossy dielectric increase across its thickness such that the composite's dielectric properties vary from those of the aerogel to those of the lossy dielectric. Materials useful for serving as the lossy dielectric include polar molecules, polar icosahedral molecules, polyaniline electron-conducting polymers, and polyprrole electron-conducting polymers. Another inhomogeneous layer absorber is constructed from an aerogel that is intrinsically a lossy dielectric. The variation in dielectric properties is achieved by increasing the density of the aerogel across the thickness of the material. Aerogel materials for such an absorber include organic aerogels which have been pyrolized in an inert atmosphere to give vitreous carbon aerogels. Methods for fabricating these absorbers are described.

Abstract: A microwave-absorbing material composed of blends of polar icosahedral molecular units with a variety of host matrices, or with polymers with the units covalently bonded in a pendant manner to the polymer chain. Both blends and polymers must impart a high degree of orientational mobility to the units so that they can absorb microwave radiation. These materials employ orientationally mobile, polar icosahedral molecular units as the source of dielectric loss at microwave frequencies. Examples of these units are the polar carboranes (ortho- and meta-carborane), polar carboranes with electronegative and/or electropositive substitutes, and polar "buckminsterfullerenes.