Abstract: A method of forming a light weight, closed-back mirror. The mirror is formed as a monolithic construction by the use of chemical vapor deposition techniques. A first deposition forms sheets of the material, which are machined to the proper size to form reinforcing ribs. A sacrificial mandrel is formed with grooves to receive the ribs in their assembled positions. The upper surface of the mandrel is in proximity to the rear edges of the ribs to form a substantially continuous surface. The mandrel and ribs are then subjected to a chemical vapor deposition process which forms a first coating upon the outer face of the mandrel, forming a back plate and side wall. The mandrel is then turned over, and the base is removed by machining to expose the front edges of the ribs. This process leaves islands of mandrel material between the ribs to form a substantially continuous surface. The mandrel and ribs are then subjected to a chemical vapor deposition process.

Abstract: The surface of a zinc selenide substrate is ground to curve in the opposite direction from that which occurs due to the bimetallic effect when zinc sulfide is deposited on a flat substrate by the chemical vapor deposition process. The bowing of the interface that occurs upon cooling of the hot laminate when the surface of the substrate is flat before deposition is compensated for by the pre-figured bowing. A distortion free window for the transmission of infra-red radiation is provided by this invention.

Abstract: A semiconductor protection tube is a ceramic tube with a layer of silicon carbide covering at least a portion of the tube adjacent an open front end of the tube and extending forward of the open end to form a hollow, closed-end tip. The protection tube is formed by providing the ceramic tube, inserting a mandrel through the tube to extend forward of the front end, and depositing silicon carbide by chemical vapor deposition over at least a front portion of the ceramic tube and over the forward-extending portion of the mandrel. Subsequent removal of the mandrel completes the production of the protection tube.

Abstract: A semiconductor protection tube is a ceramic tube with a layer of silicon carbide covering at least a portion of the tube adjacent an open front end of the tube and extending forward of the open end to form a hollow, closed-end tip. The protection tube is formed by providing the ceramic tube, inserting a mandrel through the tube to extend forward of the front end, and depositing silicon carbide by chemical vapor deposition over at least a front portion of the ceramic tube and over the forward-extending portion of the mandrel. Subsequent removal of the mandrel completes the production of the protection tube.

Abstract: .beta.-silicon carbide which is optically transmitting in the visible and infrared regions is produced by chemical vapor deposition. Deposition conditions are temperatures within a 1400.degree.-1500.degree. C. range, pressure 50 torr or less, H.sub.2 /methyltrichlorosilane molar ratios of 4-30 and a deposition rate of 1 .mu.m or less.

Abstract: .beta.-silicon carbide which is optically transmitting in the visible and infrared regions is produced by chemical vapor deposition. Deposition conditions are temperatures within a 1400.degree.-1500.degree. C. range, pressure 50 torr or less, H.sub.2 /methyltrichlorosilane molar ratios of 4-30 and a deposition rate of 1 .mu.m or less.

Abstract: The surface of a zinc selenide substrate is ground to curve in the opposite direction from that which occurs due to the bimetallic effect when zinc sulfide is deposited on a flat substrate by the chemical vapor deposition process. The bowing of the interface that occurs upon cooling of the hot laminate when the surface of the substrate is flat before deposition is compensated for by the pre-figured bowing. A distortion free window for the transmission of infra-red radiation is provided by this invention.

Abstract: The surface of a zinc selenide substrate is ground to curve in the opposite direction from that which occurs due to the bimetallic effect when zinc sulfide is deposited on a flat substrate by the chemical vapor deposition process. The bowing of the interface that occurs upon cooling of the hot laminate when the surface of the substrate is flat before deposition is compensated for by the pre-figured bowing. A distortion free window for the transmission of infra-red radiation is provided by this invention.

Abstract: A process is disclosed for fabricating lightweight honeycomb type structures out of material such as silicon carbide (SiC) and silicon (S). The lightweight structure consists of a core to define the shape and size of the structure. The core is coated with an appropriate deposit such as SiC or Si to give the lightweight structure strength and stiffness and for bonding the lightweight structure to another surface. The core is fabricated from extremely thin ribs of appropriately stiff and strong material such as graphite. First, a graphite core consisting of an outer hexagonal cell with six inner triangular cells is constructed from the graphite ribs. The graphite core may be placed on the back-up side of a SiC faceplate and then coated with SiC to produce a monolithic structure without the use of any bonding agent. Cores and methods for the fabrication thereof in which the six inner triangular cells are further divided into a plurality of cells are also disclosed.

Abstract: Periodic pulsing of the gaseous reactant flows during chemical vapor deposition of gradient index optical material markedly improves the refractive index homogeneity of the deposit with the frequency of the pulsing being variable over a wide range but the number and size of the inhomogeneities, or nodules, being significantly reduced at higher pulsing frequencies.

Abstract: A process to fabricate lightweigth ceramic mirrors, and in particular, silicon/silicon carbide mirrors, involves three chemical vapor deposition steps: one to produce the mirror faceplate, the second to form the lightweight backstructure which is deposited integral to the faceplate, and the third and final step which results in the deposition of a layer of optical grade material, for example, silicon, onto the front surface of the faceplate. The mirror figure and finish are fabricated into this latter material.

Abstract: A process is disclosed by which the finish and figure of polished preshaped structures (such as mirrors) can be replicated directly by chemical vapor deposition, with only minor polishing of the replica being required to obtain a final product, and with the original substrate being reusable for further replication. Relevant conditions under which the process can be carried out are given. Featured in the process is a pretreatment step prior to the deposition of a layer of silicon carbide to form the replica, which pretreatment step involves the formation on the polished substrate of an oxide layer and a carbon layer of high finish and uniform thickness. The carbon layer allows easy separation of the substrate and replica which otherwise would be bound together.

Abstract: A fluid dynamic method and apparatus effects the isolation of a predetermined deposition area in a hot-walled chemical vapor deposition chamber and limits the deposition to that area. The disclosed technique reduces stress and cracking in materials produced by chemical vapor deposition, prevents backside growth, and has particular utility in the fabrication by the chemical vapor deposition process of large, lightweight mirrors.

Abstract: Backside growth on substrates in a vapor deposition system has been a problem resulting in cracking of the material deposited on the substrate, making replication in a vapor deposition system difficult to achieve, and requiring post deposition machining to separate the substrate-deposit from the deposition fixture. A solution to the problem is the following: the substrate is mounted on a plurality of graphite pillars, with the pillars being bonded to the substrate as near the periphery thereof as possible. A hollow body open on one side but closed on the other, and fabricated from GRAFOIL with graphite cement used as a bonding agent, is mounted on the pillars with the open end facing the substrate. The open end of the body is pressed against the substrate and sealed with a bonding agent. This completely covers the backside of the substrate and thus prevents any vapor deposition thereon.

Abstract: A spar for use in a helicopter is produced by a three step process including first a low temperature low pressure step, second a high pressure high temperature step for a short time and third a low pressure (atmospheric) medium temperature step for a relatively long time.