Nanocrystalline Hydroxyapatite/Si Coating by Mechanical Alloying Technique

A novel approach for depositing hydroxyapatite (HA) films on titanium substrates by using mechanical alloying (MA) technique has been developed. However, it was shown that one-hour heat treatment at 800°C of such mechanically coated HA layer leads to partial transformation of desired HA phase to beta-tri-calcium phosphate (β-TCP) phase. It appears that the grain boundary and interface defects formed during MA promote this transformation. It was discovered that doping HA by silicon results in hindering this phase transformation process. The Si-doped HA does not show phase transition to β-TCP or decomposition after heat treatment even at 900°C

North-south asymmetry of geomagnetic and tropospheric events

The influences of the solar plasma on geomagnetic and atmospheric phenomena are considered. There are the north-south asymmetry in the reaction of the geomagnetic field, of the geopotential and of the pressure in the magnetically conjugate points relative to the direction of the interplanetary magnetic field. There are the synchronism between direction of the meridinal component of wind at the level of the tropopause and the direction of the interplanetary magnetic field. © 1974

Growth of 3C-SiC Films on Si (111) and Sapphire (0001) Substrates by MOCVD

Thick silicon carbide films were grown on sapphire (0001) and silicon (111) substrates using metal organic chemical vapor deposition (MOCVD). Diethylmethylsilane (DEMS) has been used as a single precursor, which contain Si and C atoms in the same molecule, without any carrier or bubbler gas. Atomic structure, surface composition and morphology have been investigated by XRD, AES, SEM and AFM analysis. SiC films of 5-7 micron thickness were grown at a rate of ~ 40 nm/min on sapphire (0001) and Si (111) substrates. The films grown at low temperature (850 ºC and 900 ºC) on both substrates show crystalline 3C-SiC in the (111) orientation. XRD results show that the orientation of the crystal structure does not depend of the substrate orientation AFM pictures of SiC films grown on sapphire (0001) exhibit more crystalline order as compared to films grown on the Si (111) substrates. AES of the grown films shows that in both cases the Si peak intensity is greater than that of carbon. This work shows promise for the development of alternative processes for developing low cost, large area substrates for application to IIInitrides LED and UV photodetector fabrication and also for gas detector application

Combination of the Sol-Gel and SHS-Technologies for Obtaining the Carbonauces Refractories

The present paper contains the results of the carbonaceous refractories SHS-synthesis carried out in the presence of nanodispersed silica added to the system by means of sol heterocoagulation. The SHSrefractory compositions have been optimized based on periclase-chromite and alumino-silicate mortars and their physical and technical properties have been determined. This material has been successfully used for lining of the induction melting furnace at one of the machinery plants

Mechanochemical Synthesis of Nanocrystalline Hydroxyapatite Coating

A novel approach for depositing of hydroxyapatite (HA) films on titanium substrates by using high energy ball milling (HEBM) has been developed. It was demonstrated that a heat treatment of the mechanically coated HA at 800 °C for one hour leads to partial transformation of HA phase to -TCP. It appears that the grain boundary and interface defects formed during MCS reduce this characteristic transformation temperature. Also, it was shown that Ti incorporation into the HA structure causes the lattice shrinkage and reduction of its grain size as compared to pure HA, but also promote the phase transformation of HA to TCP at high temperature. It is important that doping HA by silicon, while also significantly decrease crystallinity of deposited HA layer, results in hindering of the phase transformation process. The Si-doped HA does not show phase transition or decomposition after heat treatment even at 900 °C. The samples were investigated by X-ray diffraction, scanning electron microscope, Energy dispersive spectroscopy, Atomic force microscopy, Transmission electron microscopy, inductively coupled plasma (ICP) optical emission spectrometer, Vickers microhardness, Electron paramagnetic resonance

Van der Waals and Graphene-Like Layers of Silicon Nitride and Aluminum Nitride

A systematic study of kinetics and thermodynamics of Si (111) surface nitridation under ammonia exposure is presented. The appeared silicon nitride (8 × 8) structure is found to be a metastable phase. Experimental evidences of graphene-like nature of the silicon nitride (8 × 8) structure are presented. Interlayer spacings in the (SiN)2(AlN)4 structure on the Si (111) surface are found equal to 3.3 Å in SiN and 2.86 Å in AlN. These interlayer spacings correspond to weak van der Waals interaction between layers. In contrast to the widely accepted model of a surface structure (8 × 8) as monolayer of β-Si3N4 on Si (111) surface, we propose a new graphene-like Si3N4 (g-Si3N3 and/or g-Si3N4) model for the (8 × 8) structure. It is revealed that the deposition of Al atoms on top of a highly ordered (8 × 8) structure results in graphene-like AlN (g-AlN) layers formation. The g-AlN lattice constant of 3.08 Å is found in a good agreement with the ab initio calculations. A transformation of the g-AlN to the bulk-like wurtzite AlN is analyzed

Self-Propagating High Temperature Synthesis of Composition Materials using Mineral Raw Materials

The possibility of obtaining multicomponent refractory composition materials on the basis of quarts containing raw material by SHS method was studied. The use of a modifying carbon additive in the form of graphite power, carbonized rice husk, apricot stones and shungit was considered. It is shown that a complex use of preliminary mechanochemical activation (MA) and modification of the charge mixture with carbon containing additives contributes to formation of carbide and nitride phases in synthesis products

Formation of Hydroxyapatite Coating by Mechanical Alloying Method

Hydroxyapatite [Ca10(PO4)6(OH)2 − HA] material has been clinically applied in many areas of dentistry and orthopaedics. Presented work describes the effect of mechanical alloying treatment, as a non-conventional solid-state process, on the microstructure of hydroxylapatite powder and Ti-alloy substrate. The relationship between the crystallinity, crystallite size and strain of the HA with milling factors was investigated. Milled HA powders and Ti-substrate were characterized by X-Ray Diffraction (XRD) and/or scanning probe microscope (SPM) using atomic force microscopy (AFM). Increasing the ratio of the weight of the ball to the powder (Wb:Wp) ratio and milling time accelerates the broadening and intensity reduction of XRD peaks. There was no evidence that milling time up to 2 hrs or Wb:Wp can change chemical composition of the HA. Decomposition of HA phase or secondary phases such as α and/or β-tri-calcium phosphate (α, β − TCP), and calcium oxide (CaO) was not observed throughout the milling process. The average grain size and the internal strain are calculated from the XRD by Scherrer's formula and Hall–Williamson method. The Ti doped HA samples shows a notable broadening and intensity reduction comparing with HA powders before and after milling

Oil Spill Cleanup from Sea Water by Porous Sorbents

Sorbents were produced on the basis of rice husk, rubber crump and apricot stone by carbonization. They all possessed a high sorption capacity for oil and oil products. With the use of these sorbents an oil overflow was experimentally removed from the surface of the river Syrdarya (Kyzylorda). Results showed that the oil sorption capacities of carbonized rice husk, rubber crumb and apricot stone were 18, 14 and 7 g/g, respectively. The material obtained by carbonization of rice husk has very good buoyancy characteristics, high oil sorption capacity and high hydrophobicity. The effects of contact time, water temperature, amount and type of sorbents on the oil sorption capacity of the carbonized sorbents were further studied on the basis of microstructure and morphology using optical digital microscopy and scanning electron microscopy (SEM). The results of the SEM and optical microscopy studies strongly indicate that carbonization is a suitable method for improving the porous structure of the sorbents particles compared to the virgin samples. This research provides the basis for the development of a new environmental material with optimal characteristics, providing efficient sorption of oil and oil products from an aqueous medium