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The purpose of this development program was to investigate a promising alternative technique for control of a squirrel cage induction motor for subsea propulsion or hydraulic power applications. The techniques uses microprocessor based generation of the pulse width modulation waveforms, which in turn permits use of a true integral volt-second pulse width control for the generation of low harmonic content sine waves from a 3 phase Graetz transistor power bridge.

Progress is reported on research conducted to improve the efficiency and life expectancy of thermionic energy converters for space applications. The program has been modified to the development of a cylindrical converter, the emitter of which is thermally bonded to but electrically insulated from a central heat-source tubing carrying liquid metal. Significant progress has been achieved in the various portions of the program. A particular geometry employing the Cross Current Converter principle was selected and the overall design has been determined. Two promising methods for the application of the emitter insulation are being evaluated. The effects of cesium on ceramics at the various temperatures of interest were observed and the results analyzed.

Two phosphate bonded matrix materials for a composite system were studied. Polymorphism of the aluminum phosphate was responsible for wide variance in physical properties of the matrix material. Composites formed of these matrix materials reinforced with E-glass fibers had strengths two and one- half times that of matrix alone. Studies were conducted of the effect of corrosion on the fibers by the phosphate material. Corrosion varied as method of processing with wet layup specimens being more corrosive and dry pressed specimens being least corrosive. Boron fibers were investigated as a possible reinforcement material. Boron fibers were more corrosive resistant than glass fibers, but also were more brittle, presenting a processing problem. Microscopic examination of the fibers revealed several interesting structural habits of these fibers. Strength properties of the composites were determined on an automatic stress-strain apparatus designed and built specifically for that purpose., Report on Nonmetallic and Composite Materials.

Research was continued on the development of a low-work-function collector for thermionic converters operating in the ''Ball-of-Fire'' mode of the low-voltage arc. Changes in work function will be determined by comparative measurement in actual operation of converters under identically controlled conditions. Three approaches will be investigated: (1) the development of a material or surface which, when partially coated with cesium, gives a low-work-function, (2) the development of a low-work-function surface which is kept free of cesium, and (3) the addition of gas additives which, in conjunction with cesium on the base material, produces a low-work-function.

Development continued of thermionic energy converters for space applications. Work continued on optimization of geometry and ceramic insulation between emitters and the heat source. This work will include the development of a thermionic generator module to develop 3.0 V of potential from a liquid metal heat source. A converter, Type A-1198B, achieved output power in excess of 40 w at specified conditions. A three converter unit was designed to investigate the processing assembly procedures and unwanted low voltage arcs before fabrication of 3-V generator begins.

The subject contract was initiated to optimize the design and to determine the performance characteristics of a heat pipe as an efficient means of transferring heat from a fossil fuel flame to thermionic energy converters. A theoretical analysis of the heat pipe was performed and experimental data is being accumulated to verify the theoretical conclusions. During the Final report period, progress was made on the following tasks: the redesign of the barrier eliminated cracking in the heat dam section; lead will not wet the alumina and therefore is not a satisfactory working fluid; and techniques were developed which produced uniform pore size in the wick structures. Permeation testing determined that of the combustion products of the fossil fuel flame, only small quantities of oxygen passed through the barrier. (Author)

The report covers a program to investigate components for flame fired thermionic energy conversion systems. The objective of the program is to demonstrate the feasibility of integrating a thermionic converter with a barrier layer and a heat pipe to obtain 1500 hour reliability of the assembly. A basic subassembly was designed to deliver 100 electrical watts from the thermal energy of a fossil fuel flame operating in an air environment. Twelve of these units would be used in the one kilowatt power module. Problems of heat transfer, permeation barrier integration, heat pipe processing and closure, and burner temperature uniformity were encountered and substantially reduced or eliminated. After the separate components were evaluated and determined to be satisfactory, a fossil fuel-heated converter was assembled which delivered 100 watts of power during testing. (Author), See also AD-629 762.