Refractory Ceramics Based on Local Materials

A technology for producing ShA and ShB refractories uses high-melting clays from the Rostov Region and high-alumina technogenic waste. The effect of the chamotte-to-clay ratio, the granulometric composition, and the additive introduction method on the properties of products is investigated.__________Translated from Steklo i Keramika, No. 1, pp. 15 – 16, January, 2005.     

FE3 EPR investigation of PLZT 1/65/35 and 8/65/35

X-band EPR spectra of PLZT 1/65/35 and PLZT 8/65/35 doped with 1% FE³⁺ were recorded at temperature range -175°C to 200°C. Three types of paramagnetic centers were found. Two of them are in strong axial and rhombic crystal field due to neighboring oxygen and lead vacancies. The other center has symmetry determined by polarization and oxygen octahedra tilt. EPR spectra of PLZT 8/65/35 are in agreement with its glassy behavior.     

Monitoring of electric discharge machining by means of acoustic emission

Electric discharge machining is accompanied by acoustic-emission signals, which may be used monitoring, diagnostics, and control of the process. Experiments show that the acoustic signals permit assessment of the efficiency of the current pulses supplied and optimal technological adjustment.     

Problems in the Development of Efficient Biotechnology for the Synthesis of Valuable Components from Microalgae Biomass

Theoretical Foundations of Chemical Engineering - In recent decades, active research has been under way to find alternative sources of renewable raw materials for the production of valuable...     

A method for determining the charge state of chromium in Cr-doped Bi<Subscript>12</Subscript>SiO<Subscript>20</Subscript> and Bi<Subscript>12</Subscript>TiO<Subscript>20</Subscript> materials

A chemical method for determination of the charge state of chromium in B₂O₃-based materials (Bi₁₂SiO₂₀ and Bi₁₂TiO₂₀ single crystals) in a wide Cr concentration range (1 × 10^–5 – 2 × 10^–2 wt.%)is proposed. The method is based on a color reaction between Cr⁶⁺ and diphenylcarbazide in an acid medium.Translated from Novye Ogneupory, No. 8, pp. 61 – 63, August, 2004.     

Peculiarities of phase formation in Al2O3-CeO2 nanopowders

The results of the investigations on the influence of CeO₂ adding on the transformation of the metastable Al₂O₃ forms obtained by thermal treatment of xerogels are presented. It is established that in the presence of CeO₂ the process of the formation of a stable phase of α-Al₂O₃ (corundum) takes place in a wider temperature range and is accomplished at a higher temperature (1300°C). It is suggested that the revealed mismatches on the diffractograms between the intensity values of the main analytical peaks of the corundum and its content in the samples are associated with the effect of screening caused by the differences in the mass coefficients of absorption of (μ) CeO₂ and Al₂O₃.     

Complex surface modification of carbide tool by Nb + Hf + Ti alloying followed by hardfacing (Ti + Al)N

The surface of the WC/Co carbide tool was modified by an electron beam with the magnetron sputtering of Nb + Hf + Ti alloy to obtain a gradient interlayer before hardfacing with (Ti + Al)N. The results of investigations of the composite using a scanning electron microscope equipped with a device for X-ray energy dispersion spectroscopy are given. The results of the comparative mechanical tests show reduced wear rate.     

Magnetic-field-induced superconductivity?

It is shown that a giant negative magnetoresistance effect in doped manganites can be explained using a model developed earlier to explain high-temperature superconductivity, based on allowance for the covalence of the transition metal-oxygen bond. This effect is caused by delocalization of π-electrons along asymmetric π-orbitals belonging to chains of covalently coupled Mn and O ions. Unlike high-temperature superconductors, in manganites this delocalization is induced by a magnetic field which ferromagnetically orients unpaired π-electrons and thereby lifts the restriction against their collective motion along the π-orbital when the manganese ions are ferromagnetically ordered. Pis’ma Zh. Tekh. Fiz. 25, 1–3 (July 12, 1999)