Growth and scintillation properties of gadolinium and yttrium orthovanadate crystals

Aiming to explore the possibility of using the undoped rare-earth orthovanadates as scintillation materials, we developed the procedure for growth of gadolinium (GdVO₄) and yttrium (YVO₄) orthovanadate single crystals by Czochralski method, and determined the optimal conditions of their after-growth annealing. Optical, luminescent, and scintillation properties of YVO₄ and GdVO₄ were discussed versus known literature data. Scintillation characteristics of GdVO₄ were determined for the first time.     

Effect of adding mineral additives to alkali-activated natural pozzolan paste

Natural pozzolans are raw materials from geological deposits with a range of chemical compositions that when combined with suitable alkali activators can be converted to geopolymer cement for concrete production. In this paper the concept of adding mineral additives to enhance the properties of geopolymer cement is introduced. Taftan andesite, a natural Iranian pozzolan, was used to study the effect of adding mineral additives such as kaolinite, lime and other calcined pozzolans on the compressive strength of geopolymer cement under both normal and autoclave curing. Scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) was used to determine the composition of the gel phase in both alkali-activated Taftan pozzolan with and without mineral additions. The work has shown that deficiencies in SiO₂, Al₂O₃ and CaO content in the raw natural pozzolan can be compensated for by adding mineral additives for enhanced properties.     

A New Method to Obtain C60 and Higher Fullerenes

Abstract

In this paper we describe a new experimental method to produce fullerenes with substantial yield, based on the simple vaporisation of graphite rods in a low-frequency plasma jet. The proposed method is sustained by our earlier work on differently configured carbon structures produced by condensing carbon from vapor phase. Our goal is to provide a better-controlled, straightforward and low-cost method for generating large quantities of fullerene-containing carbon soot. A key feature of the vaporisation apparatus is that it is a combination between arc discharge and plasma jet dissociation. The vaporisation of the carbon rod is not driven by ohmic heating but rather by a discharge between the end of graphite rod and the cathode of the plasma-jet system. There are several attractive features of this procedure. First, variations in the parameters of plasma jet may be used to control systematically the size distribution of fullerene clusters. Secondly, this could be used for solid studies of larger fullerenes clusters since large clusters are only produced in low yield by the arc-discharge method. Also, we believe that there is great potential to investigate systematic doping of fullerene cluster using this technique since dopants can be easly introduced into the plasma jet prior to thermal dissociation.     

High-energy methods of creating a mesocomposite material with inclusions containing nanocrystalline particles

A thermally stable high-strength mesocomposite containing nano-sized particles of titanium diboride (TiB₂) is obtained by combining methods of self-propagating high-temperature synthesis and quasi-dynamic high-velocity pressing. The use of self-propagating high-temperature synthesis ensured obtaining a hardening component of the mesocomposite — nanocomposite with a TiB₂ particle size of ≈ 100 nm. The quasidynamic method of obtaining a material characterized by high deformations determines self-organization of the mesocomposite microstructure with an unchanged size of the hardening TiB₂ particles in the inclusion structure. Mechanical properties of the mesocomposite are substantially better than the properties of the composite matrix.     

The (Cr) + (NbC) quasibinary eutectic in the Cr - Nb - C system

An experimental investigation of the Cr - Nb - C alloys has shown that in the (Cr) + (NbC) two-phase region there are the fold with maximal solidus temperature and the saddle point (Cr_79.5Nb_12.2C_8.3) on the liquidus surface, relating to L_c ⇔ (Cr) + (NbC) invariant equilibrium at ≥1640°C. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 48–54, May–June, 2000.     

Photoluminescence of localized exitons in coherently strained ZnS-ZnSe/GaAs(001) quantum wells

The low-temperature photoluminescence (PL) of ZnS-ZnSe heterostructures grown in the form of single quantum wells (QW) by the non-conventional technology of photo-assisted vapor phase epitaxy has been investigated. It is shown that the inhomogeneity of the quantum wells can be explained in terms of a model based on disordering of the heterointerfaces. It is found that the mobility edge which separates the localized states from the delocalized states is 6 meV below the heavy-exciton ground state in the quantum wells with a nominal width L _z=11 Å.     

Influence of arsenic on the corrosion resistance of low-carbon low-alloy steel. Part 1

Literature data regarding the influence of arsenic on the corrosion resistance of low-carbon low-alloy steel are analyzed. A mechanism explaining this influence in air and in sea water is proposed.