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Mechanical Alloying for Making Thermoelectric Compounds

Constituents are ball-milled into a powder, which is then hot pressed. An economical room-temperature mechanical alloying process has been shown to be an effective means of making a homogeneous powder that can be hot-pressed to synthesize a thermoelectric material having reproducible chemical composition. The thermoelectric materials to which the technique has thus far been applied with success include rare-earth chalcogenides [La3–xTe4 (0 < x < 0.33) and La3–xYbyTe4 (0 < x < 1, 0 < y < 1)] and Zintl compounds (including Yb14MnSb11 and Yb14BiSb11). The synthesis of a given material consists of the room-temperature thermomechanical- alloying process followed by a hot-pressing process. Relative to synthesis of nominally the same material by a traditional process that includes hot melting, this synthesis is simpler and yields a material having superior thermoelectric properties.

Posted in: Manufacturing & Prototyping, Briefs, TSP

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Fluorine-Based DRIE of Fused Silica

A suitable choice of process parameters enables etching of vertical side walls. A process of deep reactive-ion etching (DRIE) using a fluorine-based gas mixture enhanced by induction-coupled plasma (ICP) has been demonstrated to be effective in forming high-aspect-ratio three-dimensional patterns in fused silica. The patterns are defined in part by an etch mask in the form of a thick, highquality aluminum film. The process was developed to satisfy a need to fabricate high-aspect-ratio fused-silica resonators for vibratory microgyroscopes, and could be used to satisfy similar requirements for fabricating other fused-silica components.

Posted in: Manufacturing & Prototyping, Briefs

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Process for High-Rate Fabrication of Alumina Nanotemplates

Approximately regular hexagonal arrays of holes are formed in an anodizing process. An anodizing process, at an early stage of development at the time of reporting the information for this article, has shown promise as a means of fabricating alumina nanotemplates integrated with silicon wafers. Alumina nanotemplates are basically layers of alumina, typically several microns thick, in which are formed approximately regular hexagonal arrays of holes having typical diameters of the order of 10 to 100 nm. Interest in alumina nanotemplates has grown in recent years because they have been found to be useful as templates in the fabrication of nanoscale magnetic, electronic, optoelectronic, and other devices. The present anodizing process is attractive for the fabrication of alumina nanotemplates integrated with silicon wafers in two respects: (1) the process involves self-ordering of the holes; that is, the holes as formed by the process are spontaneously arranged in approximately regular hexagonal arrays; and (2) the rates of growth (that is, elongation) of the holes are high enough to make the process compatible with other processes used in the mass production of integrated circuits.

Posted in: Manufacturing & Prototyping, Briefs, TSP

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Separation and Sealing of a Sample Container Using Brazing

This process is an alternative to a prior explosive welding process. A special double-wall container and a process for utilizing the container are being developed to enable (1) acquisition of a sample of material in a “dirty” environment that may include a biological and/or chemical hazard; (2) sealing a lid onto the inner part of the container to hermetically enclose the sample; (3) separating the resulting hermetic container from the dirty environment; and (4) bringing that hermetic container, without any biological or chemical contamination of its outer surface, into a clean environment. The process is denoted “S3B” (separation, seaming, and sealing using brazing) because sealing of the sample into the hermetic container, separating the container from the dirty environment, and bringing the container with a clean outer surface into the clean environment are all accomplished simultaneously with a brazing operation. This container and process were conceived as a superior alternative to the double-wall container and process described in “Explosion Welding for Hermetic Containerization” (NPO-20868), NASA Tech Briefs, Vol. 27, No. 8 (August 2003), page 46. As in the previously reported case, the present container and process were originally intended to be used to return samples from Mars to Earth, but could also be used on Earth to store and transport material samples acquired in environments that contain biological and/or chemical hazards.

Posted in: Manufacturing & Prototyping, Briefs, TSP

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Diamond Smoothing Tools

Machined surfaces could be made much smoother. Diamond smoothing tools have been proposed for use in conjunction with diamond cutting tools that are used in many finish-machining operations. Diamond machining (including finishing) is often used, for example, in fabrication of precise metal mirrors.

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Fabrication of Buried Nanochannels From Nanowire Patterns

Sacrificial nanowires are buried, then etched away to form buried channels. A method of fabricating channels having widths of tens of nanometers in silicon substrates and burying the channels under overlying layers of dielectric materials has been demonstrated. With further refinement, the method might be useful for fabricating nanochannels for manipulation and analysis of large biomolecules at single-molecule resolution. Unlike in prior methods, burying the channels does not involve bonding of flat wafers to the silicon substrates to cover exposed channels in the substrates. Instead, the formation and burying of the channels are accomplished in a more sophisticated process that is less vulnerable to defects in the substrates and less likely to result in clogging of, or leakage from, the channels.

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Passivating Stainless Steel Parts

Procedures for commonly used stainless steels can use citric or nitric acid solutions. Maximizing the natural corrosion resistance of parts and components machined from stainless steels. It can make the difference between satisfactory performance and premature failure. Incorrectly performed, passivation can actually induce corrosion.

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