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The use of CO in place of H2 for the reducing step did not appreciably increase solderability of interconnects. Cells were also made printing the pastes on top of ITO coatings. Some of these cells were the best electrically but the metallization was still not adhering. Sequential use of H2 and CO had no effect on adhesion (or lack of it).
Solar cells were produced using a Mo/Sn/TiH screen printed paste with a lead/borosilicate frit that are electrically comparable to control silver cells. The process is currently unsuccessful because the soldering of interconnects to these cells has proved difficult. Future work will investigate using CO instead of H2 as the reducing gas and putting an ITO coating on the cell prior to metallization.
This experiment is involved in determining bulk resistivity values for different past concentrations. Experiments were performed on silicon Cz and non-Cz wafers. To determine bulk resistivity more accurately, pastes were printed on ceramic substrates. Contact resistance was determined by measuring the voltage drop at constant current. Because of irregularity of grid profiles, accurate determination of cross sections of grid lines is difficult. The bulk resistivity is accurate when the resistivity of the metallization is much less than that of the layer beneath it. When the resistivity of the metal approaches that of the substrate, the actual resistivity will be larger than the measured value.
Method is based on measurements of electrical conductivity through layer of distilled water that has been deposited on metal surface. Conductivity is measured for 15-30 minute period, which is sufficient time to allow surface impurities to dissolve in water.
Various Mo/Sn screen printing pastes were scheduled for evaluation. Cells are first prefired in air and then fired in a H2 atmosphere. Preliminary results are encouraging.
Solar cells without AR coating achieved efficiencies of 10.5% with the Type A Mo/Sn/TiH paste. Curve shape, series resistance, and shunt resistance are all excellent and comparable to silver paste controls. Other pastes were not successful.
A process for the spray-application of a strongly adhesive, thick antifriction layer on titanium and titanium alloys is proposed. The titanium/titanium alloy component to be coated is first subjected to cleaning in a pickling bath with reducing additives and sand-blasting, then coated with an intermediate layer of nickel, after which the final layer is applied. The formation of TiNi at the interface ensures strong bonding of the antifriction layer.
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Processing of metallic melts in microgravity containerless experiments requires control of contaminants like oxygen and water vapor to below parts-per-billion (ppb) levels.
Manufacturing of structural metal parts directly from computer aided design (CAD) data has been investigated by numerous researchers over the past decade. Researchers at NASA Langley REsearch Center are developing a new solid freeform fabrication process, electron beam freeform fabrication (EBF), as a rapid metal deposition process that works efficiently with a variety of weldable alloys. The EBF process introduces metal wire feedstock into a molten pool that is created and sustained using a focused electron beam in a vacuum environment. Thus far, this technique has been demonstrated on aluminum and titanium alloys of interest for aerospace structural applications nickel and ferrous based alloys are also planned. Deposits resulting from 2219 aluminum demonstrations have exhibited a range of grain morphologies depending upon the deposition parameters. These materials ave exhibited excellent tensile properties comparable to typical handbook data for wrought plate product after post-processing heat treatments. The EBF process is capable of bulk metal deposition at deposition rated in excess of 2500 cubic centimeters per hour (150 cubic inches per our) or finer detail at lower deposition rates, depending upon the desired application. This process offers the potential for rapidly adding structural details to simpler cast or forged structures rather than the conventional approach of machining large volumes of chips to produce a monolithic metallic structure. Selective addition of metal onto simpler blanks of material can have a significant effect on lead time reduction and lower material and machining costs.
Current plans for practical missions leading to a sustained human presence on our Moon and Mars rely on utilizing their in situ resources. Initially, resource availability must be assessed followed by the development of economically acceptable and technically feasible extractive processes. In regard to metals processing and fabrication, the lower gravity level on the Moon (0.125 g) and Mars (0.369 g) will dramatically change the presently accepted hierarchy of materials in terms of specific properties, a factor which must be understood and exploited. Furthermore, significant changes are expected in the behavior of liquid metals during processing. In metal casting, for example, mold filling and associated solidification processes have to be reevaluated. Finally, microstructural development and therefore material properties, presently being documented through ongoing research in microgravity science and applications, needs to be understood and scaled to the reduced gravity environments. These and other issues are addressed in this paper.
Processing, testing and application of refractory metals to various high temperature environments
Process aids development of composites of metals that are immiscible in liquid plase. Aligned uniformly dispersed spheres or rods of bismuth in aluminum, lead in aluminum, bismuth in zinc, and other systems have been prepared. Dispersed and matrix metal are selected according to desired electrical or mechanical properties.
Process imparts dome shape to titanium sheets and is applicable to shaping other metals. Method is of interest to automobile and aircraft body manufacturers.
This paper reviews material properties of adhesion, friction and wear of single-crystal silicon carbide in contact with metals and alloys involved in a metal removal process such as grinding. The tribological properties in the metal removal processes are divided into properties which remove metal by adhesion between sliding surfaces, and metal removal by silicon carbide sliding against a metal, indenting it, and plowing a series of grooves or furrows. The paper also deals with fracture and deformation characteristics of the silicon carbide surface; the adhesion, friction and metal transfer to silicon carbide is related to the relative chemical activity of the metals. Atomic size and content of alloying elements play a dominant role in controlling adhesion and friction properties of alloys. The friction and abrasive wear decrease as the shear strength of the bulk metal increases.
Fabrication processes for producing refractory metal alloy wire
Material properties are considered as they relate to adhesion, friction, and wear of single crystal silicon carbide in contact with metals and alloys that are likely to be involved in a metal removal process such as grinding. Metal removal from adhesion between sliding surfaces in contact and metal removal as a result of the silicon carbide sliding against a metal, indenting into it, and plowing a series of grooves or furrows are discussed. Fracture and deformation characteristics of the silicon carbide surface are also covered. The adhesion, friction, and metal transfer to silicon carbide is related to the relative chemical activity of the metals. The more active the metal, the higher the adhesion and friction, and the greater the metal transfer to silicon carbide. Atomic size and content of alloying elements play a dominant role in controlling adhesion, friction, and abrasive wear properties of alloys. The friction and abrasive wear (metal removal) decrease linearly as the shear strength of the bulk metal increases. They decrease as the solute to solvent atomic radius ratio increases or decreases linearly from unity, and with an increase of solute content. The surface fracture of silicon carbide is due to cleavages of 0001, 10(-1)0, and/or 11(-2)0 planes.
Thermochemical processes which lead to the production of hydrogen and oxygen from water without the consumption of any other material have a number of advantages when compared to other processes such as water electrolysis. It is possible to operate a sequence of chemical steps with net work requirements equal to zero at temperatures well below the temperature required for water dissociation in a single step. Various types of procedures are discussed, giving attention to halide processes, reverse Deacon processes, iron oxide and carbon oxide processes, and metal and alkali metal processes. Economical questions are also considered.