Increasing the number of uses of the refractories in the slide gates of large steel-teeming ladles

Conclusions A method of enrichment of brucite by washing and sorting of it was developed. An experimental lot of composite slide gate plates for two teemings from the 300-ton steel teeming ladles of Magnitogorsk Metallurgical Combine was prepared from enriched fused brucite at Magnesite Combine. The physicochemical indices of the plates were 97.9 wt.% magnesium oxide with a nonequiaxiality of the periclase crystals of 1.94, 0.3% silica, 0.2% iron oxide, compressive strength 110 N/mm², and open porosity 12%. Under conditions of repeated openings and closings the plates made it possible to provide 100% quality teeming of the first heat and to direct 60% of the slide gates to repeated teeming, which was done with 32%. For a final experimental verification it would be desirable to prepare a larger experimental production lot of refractories using the method developed with specific repeated use.Translated from Ogneupory, No. 2, pp. 47–51, February, 1988.     

Surface wear structures and mechanisms in zirconia-based ceramics

Correlations between the scale of surface structures formed upon high-velocity friction and the wear intensity have been studied for Y-TZP ceramics with various values of the average grain size. An increase in the sliding velocity from 4 to 11 m/s in the ceramics-steel friction couple leads to a decrease in the wear rate (caused by a change in the mechanism of wear from high-temperature adhesive wear to that in the regime of friction with boundary quasi-liquid lubricant film formation) and is accompanied by a decrease in the scale of the crack network formed on the friction surface.     

Temperature dependence of the optical absorption spectra of InP/ZnS quantum dots

The optical-absorption spectra of InP/ZnS (core/shell) quantum dots have been studied in a broad temperature range of T = 6.5–296 K. Using the second-order derivative spectrophotometry technique, the energies of optical transitions at room temperature were found to be E ₁ = 2.60 ± 0.02 eV (for the first peak of excitonic absorption in the InP core) and E ₂ = 4.70 ± 0.02 eV (for processes in the ZnS shell). The experimental curve of E ₁(T) has been approximated for the first time in the framework of a linear model and in terms of the Fan’s formula. It is established that the temperature dependence of E ₁ is determined by the interaction of excitons and longitudinal acoustic phonons with hω = 15 meV.     

Interaction of hydrogen with the intermetallic compound Nd<Subscript>2</Subscript>Fe<Subscript>17</Subscript> studied by calorimetry

Interaction of hydrogen with the intermetallic compound Nd₂Fe₁₇ has been studied for the first time by calorimetry using a differential heat conduction calorimeter coupled to a Sieverts apparatus. Hydrogen absorption and desorption reactions were run at 200°C, and two types of data were obtained: p–C–T and ΔH–C–T (where p is the equilibrium hydrogen pressure, C = H/Nd₂Fe₁₇, ΔH is the reaction enthalpy, and T is the measurement temperature). The p–C–T curves obtained for the hydrogen absorption and desorption processes have no plateau or two-phase region, in contrast to what is characteristic of the formation of a hydride phase. At the same time, the ΔH(C) curves have a few portions where the enthalpy of reaction between hydrogen and the intermetallic compound remains constant: 0 < C < 2.0, with ΔH _abs =–85.05 ± 0.65 kJ/mol H ₂; 2.0 < C < 2.7, with ΔH _abs =–80.64 ± 1.00 kJ/mol H₂; and 1.9 < C < 2.7, with ΔH _des = 76.48 ± 0.85 kJ/mol H₂. The data obtained in this study suggest that positions 9e and 18g in the intermetallic compound are occupied by hydrogen in a particular order.     

Intensifying the firing of dolomite in rotary kilns

Conclusions The East Institute of Refractories has developed an effective method of using oxygen for burning the fuel in rotary kilns used for calcining refractory raw materials. The essence of the method consists in feeding oxygen and gas into the combustion chamber in the form of separate jets flowing from the nozzles at sonic and supersonic velocities and aimed at the material being fired.The proposed method is being introduced on rotary kilns for firing dolomite at the Chelyabinsk Factory, as a result of which there has been a big boost in the furnace output, a fall in the specific fuel consumption and dust removal, and also improvements in the quality of the fired powder. The method may be recommended for rotary kilns for firing magnesite and other forms of raw material.Translated from Ogneupory, No. 7, pp. 9–11, July, 1980.