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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ti4O7 by Materials Project

Ti4O7 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are four inequivalent Ti+3.50+ sites. In the first Ti+3.50+ site, Ti+3.50+ is bonded to six O2- atoms to form a mixture of distorted face, edge, and corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 43–55°. There are a spread of Ti–O bond distances ranging from 1.88–2.18 Å. In the second Ti+3.50+ site, Ti+3.50+ is bonded to six O2- atoms to form a mixture of distorted face, edge, and corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 44–55°. There are a spread of Ti–O bond distances ranging from 1.87–2.18 Å. In the third Ti+3.50+ site, Ti+3.50+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 44–60°. There are a spread of Ti–O bond distances ranging from 1.94–2.08 Å. In the fourth Ti+3.50+ site, Ti+3.50+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 43–60°. There are a spread of Ti–O bond distances ranging from 1.95–2.12 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to three Ti+3.50+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to three Ti+3.50+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to three Ti+3.50+ atoms. In the fourth O2- site, O2- is bonded to four Ti+3.50+ atoms to form distorted edge-sharing OTi4 trigonal pyramids. In the fifth O2- site, O2- is bonded to four Ti+3.50+ atoms to form a mixture of distorted edge and corner-sharing OTi4 trigonal pyramids. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Ti+3.50+ atoms. In the seventh O2- site, O2- is bonded to four Ti+3.50+ atoms to form a mixture of distorted edge and corner-sharing OTi4 trigonal pyramids.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Electrochemical incineration of wastes

The novel technology of waste removal in space vehicles by electrochemical methods is presented to convert wastes into chemicals that can be eventually recycled. The important consideration for waste oxidation is to select a right kind of electrode (anode) material that should be stable under anodic conditions and also a poor electrocatalyst for oxygen and chlorine evolution. On the basis of long term electrolysis experiments on seven different electrodes and on the basis of total organic carbon reduced, two best electrodes were identified. The effect of redox ions on the electrolyte was studied. Though most of the experiments were done in mixtures of urine and waste, the experiments with redox couples involved 2.5 M sulfuric acid in order to avoid the precipitation of redox ions by urea. Two methods for long term electrolysis of waste were investigated: (1) the oxidation on Pt and lead dioxide electrodes using the galvanostatic methods; and (2) potentiostatic method on other electrodes. The advantage of the first method is the faster rate of oxidation. The chlorine evolution in the second method is ten times less then in the first. The accomplished research has shown that urine/feces mixtures can be oxidized to carbon dioxide and water, but current densities are low and must be improved. The perovskite and Ti4O7 coated with RuO2 are the best electrode materials found. Recent experiment with the redox agent improves the current density, however, sulphuric acid is required to keep the redox agent in solution to enhance oxidation effectively. It is desirable to reduce the use of acid and/or find substitutes.

Bhardwaj, R. C.↗
NASA NTRS1992

Innovative techniques for the production of energetic radicals for lunar processing including cold plasma processing of local planetary ores

Hydrogen reduction of ilmenite has been studied by a number of investigators as a potential means for recovery of oxygen from lunar soil. Interest in this process has always rested with the simplicity of the flow diagram and the utilization of established technology. Effective utilization of hydrogen in the reduction process at temperatures of 1200 C and below has always been disappointing and, as such, has led other investigators to focus attention on other systems. Effective utilization of hydrogen in the reduction of ilmenite can be significantly enhanced in the presence of a non-equilibrium hydrogen plasma. Ilmenite at solid specimen temperatures of 600 C to 970 C were reacted in a hydrogen plasma. Those experiments revealed that hydrogen utilization can be significantly enhanced. At a specimen temperature of 850 C the fraction of H2 reacted was 24 percent compared to the 7 percent theoretical limit calculated with thermodynamic theory for the same temperature. An added advantage for a hydrogen plasma involves further reduction of TiO2. Reduction of the iron oxide in ilmenite yields TiO2 and metallic iron as by products. Titanium forms a number of oxides including TiO, Ti2O3, Ti3O5 and the Magneli oxides (Ti4O7 to Ti50O99). In conventional processing of ilmenite with hydrogen it is possible to reduce TiO2 to Ti7O13 within approximately an hour, but with poor utilization of hydrogen on the order of one mole of H2 per thousand. In the cold or non-equilibrium plasma TiO2 can be rapidly reduced to Ti2O3 with hydrogen utilization exceeding 10 percent. Based on design considerations of the plasma reactor greater utilization of the hydrogen in the reduction of TiO2 is possible.

Bullard, D.↗
NASA NTRS1994

Space-based bacterial production of hydrogen

This paper deals with the electrochemical production of hydrogen by depolarizing the oxygen evolution reaction using human feces and urine, which contains 30-40% bacteria and yeast. The electroactivity of graphite, tungsten carbide, perovskite and RuO2-coated Ebonex (Ti4O7) as anode materials are compared. The scale-up of the process in a laboratory-scale three-dimensional packed bed cell is discussed.

NASA Discipline Life Support Systems↗
DOE OSTI2024

Atomically Dispersed Ru-doped Ti 4 O 7 Electrocatalysts for Chlorine Evolution Reaction with a Universal Activity

Chlorine has been supplied by the chlor-alkali process that deploys dimensionally stable anodes (DSAs) for the electrochemical chlorine evolution reaction (ClER). The paramount bottlenecks have been ascribed to an intensive usage of precious elements and inevitable competition with the oxygen evolution reaction. Herein, a unique case of Ru 2+ -O 4 active motifs anchored on Magnéli Ti 4 O 7 (Ru-Ti 4 O 7 ) via a straightforward wet impregnation and mild annealing is reported. The Ru-Ti 4 O 7 performs radically active ClER with minimal deployment of Ru (0.13 wt%), both in 5 m NaCl (pH 2.3) and 0.1 $\tiny{M}$ NaCl (pH 6.5) electrolytes. Scanning electrochemical microscopy demonstrates superior ClER selectivity on Ru-Ti 4 O 7 compared to the DSA. Operando X-ray absorption spectroscopy and density functional theory calculations reveal a universally active ClER (over a wide range of pH and [Cl - ]), through a direct adsorption of Cl - on Ru 2+ -O 4 sites as the most plausible pathway, together with stabilized ClO* at low [Cl - ] and high pH.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗