P-5-01: Conditions for Stable Propagation of SHS Combustion Wave

The experiments have been carried out in an apparatus to investigate reduction/ agglomeration of an iron ore compact including the aluminum dross. Photographic observations of sequential propagation of the SHS-wave from an end of the compact, cross-sectional macrostructures and appearances of the synthesized specimens as well as temperature measurements and X-ray diffraction analysis have been conducted.

Appropriate preheating of the specimen, say around 800K, caused a self-sustaining propagation of the wave whereas excessive preheating was accompanied by down-flow percolation of melt which often caused explosive propagation. The reaction could be activated at a temperature exceeding the m.p of aluminum, suggesting the onset of the reaction is basically associated with the activation energy of the system. Proper selection of process parameters allowed stable propagation of the wave even when using aluminum dross whose aluminum content is only about 10%.
 
 

P-5-02: Possibility of Processing Zirconium Chips by Self-Propagating

Institute of Structurtal Macrokinetics and Materials Science,

Chernogolovka, Moscow, 142432 Russia
 
 

The feasibility of recycling Zr chips by SHS is investigated. In our experiments, we used Zr chips (Zr content above 97%) with a residue of cutting emulsion. Waste removing chips were up to 0.3 mm thick and up to 4 mm wide. The chips were found to burn well in air flow (yielding zirconium oxynitride) and still better in oxygen flow (yielding zirconia). For experiments under nitrogen pressure in a closed vessel, the chips were pelleted to a relative density of 0.2–0.5. Depending on nitrogen pressure and pellet density, the nitriding degree was found to attain a value of up to 8 wt %. After comminution and repeated nitriding, it may be made above 10 wt % (in zirconium nitride, the nitrogen content is 13.3 wt %). Combustion of Zr pellets stuffed with carbon black under nitrogen pressure yielded zirconium carbonitride while in compressed air, zirconium oxycarbonitride. The products are readily grindable. Combustion in air or oxygen flow yields powdered products. The best results were obtained for combustion in oxygen flow and for double nitriding in a closed vessel under nitrogen pressure. In these cases, the extent of conversion was above 90%. Apparently, this technique can be used for recycling Ti chips.
 
 
 
 

P-5-03: SHS-Ceramics as Effective Material for Radiation Protection

- neutron shielding in the body of liquid metallic, gas and other high temperature reactors,

- biological shielding components adjoining the body of above mentioned reactors.

SHS technology of boron nitride – boron, boron nitride – boron – oxide and boron nitride – titanium diboride – boron materials has been developed.

Trials of materials of boron nitride – boron and boron nitride – boron – oxide groups demonstrated radiation resistance of the materials at neutron fluence of no less than 1018 neutron/cm². Samples were treated with rays at temperatures of 100° C and 600° C. After the treatment the samples had the same color and shape . Maximal deviation from initial sizes was below 0.5%. Metallographic analysis of the samples showed that the material structure does not vary considerably during radioactive irradiation. The amount, size and surface morphology of pores are inalterable in the materials. Strength performance (s compression) measured at various temperatures (100° C and 600° C) has an increase of 35–40% at 600° C. Coefficient of thermal conductivity of the materials changes from 30 W/(mЧ K° ) at 100° C to 10 W/(mЧ K° ) at 600° C.

Thus, it is shown that neutron fluence of 1018 neutron/cm2 at working temperatures below 600° C does not significantly influence the performance of above mentioned SHS materials.
 
 

P-5-04: Modes of Gasless Combustion in a Cylindrical Sample.

P-5-05: Mechanical Activation Effect on Macrokinetic Characteristics

Moscow Steel and Alloys Institute (Technological University),

Leninsky prospect, 4, Moscow 117936, Russia, Fax/Phone: (095) 236-5298.
 
 

All growing requirements to materials used in various branches of industry, have stipulated the necessity of developing various types of composite materials, including titanium-based. Such composite materials should combine in themselves high heat- and electroconductivity, propensity to welding and other metal properties and, simultaneously, high heat resistance, chemical inertness and high hardness of non-metal substances. The known modes of deriving titanium borides, carbides and silicides have a series of shortages, such as high temperature, long duration and multystageness of processes, contamination by accessory reaction yields and impurities. Mechanical activation allows intensifying synthesis of chemical compounds and overcoming the above shortages. The influence of the preliminary mechanical activation on the temperature and thermal effect of interaction in ternary systems Ti-B-Si, Ti-B-C and Ti-C-Si is investigated with the purpose of consequent realization of the composite material synthesis in the conditions of self-propagating high-temperature synthesis (SHS). The correlation between the modification of a specific surface and thermal effect of a reaction at mechanical activation of components was determined. It is established, that mechanical activation at synthesis of composite materials in the conditions of the SHS-process ensures for all systems 400 - 600⁰ C drop of the starting temperature of initial components` interaction, a reduction of the synthesis time from several hours to several seconds. Heat evolution from the interaction of investigated mixture components was sufficient for a spontaneous reaction in the conditions of the self-propagating high-temperature synthesis (SHS-process).