Self-propagating high-temperature synthesis of high porosity foam materials in microgravity

Ceramic and metalloceramic foam materials are important construction, building, and thermal insulation materials for space stations of the 21st century. Delivery of these materials from Earth to space using rockets is not profitable due to the low density of these materials. Production of foam materials in space using traditional methods requires large energy consumption. Using SHS in space solves this problem

A Macrokinetic Study of the High-Temperature Solid-Phase Titanium-Carbon Reaction

An experimental method, electro thermal explosion (ETE), is used to measure the macro kinetic parameters of the high-temperature titanium/carbon reaction. Different stages of the reaction have been identified, but the focus of this study is on the reaction between solid titanium and solid carbon, i.e., prior to the melting of titanium. The reaction has high activation energy, and an electric current is used to heat the cylindrically shaped sample to a specified temperature. The current is shut off at a temperature below the melting point of titanium; any further temperature rise is only due to reaction. The output of the ETE equipment is temperature time data that can be processed to recover the kinetic parameters. The activation energy and preexponential factor of the reaction rate constant are calculated and comprise 214 kJ mol-1 and (6.2 ( 1.5) _ 107 s-1, respectively. An important aspect of solid-phase reactions is the contact area between reactants. The contact area between titanium and carbon particles is calculated, and the reaction constant is corrected for this effect

Measuring pressure in the source region for geysers, Geyser Valley,

Liquid water and steam that erupt at geysers are provided from deeper reservoirs, whose location, geometry and pressure are in general poorly known. Here we report measurements at two geysers from a field experiment in Geyser Valley, Kamchatka, designed to measure pressure in the reservoir providing water to the geysers. Water level in the geyser conduit was controlled, and the recharge to the geyser conduit was measured by monitoring the discharge needed to maintain the controlled water level. Recharge is not constant, but depends on water level in the geyser. From the relationship between water level in the conduit and recharge to the conduit, we can estimate the hydraulic head in the reservoir that supplies water to the geyser. Hydraulic head in the two studied reservoirs is within a couple of meters of the elevation of the geyser vents and the adjacent rivers. Pressures in the reservoirs are low enough that the reservoirs should not be prone to hydrothermal explosions, and explain why flooding of geysers in Geyser Valley terminated their eruptions

Production of Advanced Materials by Methods of Self-Propagating High-Temperature Synthesis

XIX, 156 p. 106 illus.online resource

Production of advanced materials by methods of self-propagating high-temperature synthesis

This translation from the original Russian book outlines the production of a variety of materials by methods of self-propagating high-temperature synthesis (SHS). The types of materials discussed include: hard, refractory, corrosion and wear-resistant materials, as well as other advanced and speciality materials. The authors address the issue of optimal parameters for SHS reactions occurring during processes involving a preliminary metallothermic reduction stage, and they calculate this using thermodynamic approaches. In order to confirm the effectiveness of this approach, the authors describe experiments focussing on the synthesis of elemental crysalline boron, boron carbides and nitrides. Other parts of this brief include theoretical and experimental results on single-stage production of hard alloys on the basis of titanium and zirconium borides, as well as macrokinetics of degassing and compaciton of SHS-products.This brief is suitable for academics, as well as those working in industrial manufacturing companies producing hard alloys and composites for making metal-working machinery or drilling equipment

Geyser preplay and eruption in a laboratory model with a bubble trap

We present visual observations and temperature measurements from a laboratory model of a geyser. Our model incorporates a bubble trap, a zone in which vapor can accumulate in the geyser's subsurface plumbing, in a vertical conduit connected to a basal chamber. Analogous features have been identified at several natural geysers. We observe three types of eruptions: 1) rising bubbles eject a small volume of liquid in a weak spout (small eruption); 2) boiling occurs in the conduit above the bubble trap (medium eruption); and 3) boiling occurs in the conduit and chamber (large eruption). In the last two cases, boiling in the conduit causes a rapid hydrostatic pressure drop that allows for the rise and eruption of liquid water in a vigorous spout. Boiling initiates at depth rather than propagating downward from the surface. In a single eruption cycle, multiple small eruptions precede every medium and large eruption. At least one eruption cycle that culminates in a medium eruption (i.e., a quiescent period followed by a series of small eruptions leading up to a medium eruption) precedes every eruption cycle that culminates in a large eruption. We find that the transfer of fluid with high enthalpy to the upper conduit during small and medium eruptions is necessary to heat the upper conduit and prepare the system for the full boiling required for a large eruption. The placement of the bubble trap midway up the conduit allows for more efficient heating of the upper conduit. Our model provides insight into the influence of conduit geometry on eruption style and the importance of heat transfer by smaller events in preparing the geyser system for eruption