Development of temperature-heating rate diagrams for the pyrolytic removal of binder used for powder injection moulding

A polypropylene-based binder system was used to injection mould test bars containing 65 vol% aluminium powder. Specimens, 3 and 6 mm thick, made from these bars were used for pyrolytic binder removal experiments in static air and nitrogen. The development of a carefully defined experimental procedure for the determination of the heating rate at which binder removal can be carried out at a given temperature without the creation of macro defects is fully described. The use of isothermal heat treatments during pyrolysis are also considered and results are presented as temperature-heating rate diagrams for each atmosphere and thickness investigated. These diagrams show a lower and an upper boundary. Defect formation occurs if the temperature-heating rate relationship lies between the boundaries. Near optimum binder removal schedules deduced from each diagram have been experimentally verified.     

The creep behaviour of isotropic polyethylene

Dead loading creep and constant strain rate yield experiments have been used to study the tensile creep behaviour of three grades of isotropic polyethylene. This has provided further evidence for the existence of two yield points in isotropic polyethylene. Two different models have been used to attempt to describe this behaviour. Although the results can be described by to both the two process model of Wilding and Ward and the co-operative jump model of Fotheringham and Cherry, it appears that the two process model provides a more convincing quantitative fit to the data. This revised version was published online in September 2006 with corrections to the Cover Date.     

Bulk changes in the microhardness of a solid WC-110G13 steel alloy exposed to a low-energy, high-current electron beam

Bulk changes in the microhardness of a solid WC-110G13 steel alloy are studied as a function of the energy density of a low-energy, high-current electron beam, the number of pulses, and the target thickness. It is established that the beam energy density has a threshold at which quasiperiodic changes in the microhardness occur in the bulk of the alloy. Pis’ma Zh. Tekh. Fiz. 25, 54–59 (October 26, 1999)     

Complex susceptibility analysis of magneto-fluids: Optical band gap and surface studies on the nanomagnetite-based particles

An aqueous stable magnetic fluid containing Fe₃O₄ nano-particles with a mean diameter of 4–7 nm, which is in the range of super-paramagnetism, is prepared. The particles are synthesized via co-precipitation method from ferrous and ferric solutions. X-ray diffraction, transmission electron microscopy, transformer method are used to study the physical properties of the magnetic fluids and powders. A method is given to analyze and resolve the real and imaginary parts of the measured complex susceptibility of magnetic fluids. The band gap parameters of the magneto-nanopowders such as the direct-, indirect-band gap energies, Fermi energy and Urbach energy are determined. A comparative study between the different techniques used to calculate the powder particle size is presented. Adsorption of nitrogen gas is used to identify and determine the particles mean diameter and to study their microstructure, the magnetic properties and surface porosity. The study showed that the total pore system of the magnetic nano-powders consists mainly of mesopores.     

Experimental results on radiative cooling of submicron carbon-black particles

The change in the temperature of the submicron carbon-black particles formed behind the reflected shock wave as a result of the pyrolysis of ethylene was investigated by the photoemission method. It has been established that the temperature of the carbon black substantially differs (by a value of the order of 400–600 K) from the temperature of the gas medium in which it is formed and grown. It is shown with the use of scanning electron microscopy that the average diameter of the carbon nanoclusters forming the carbon black comprises 55–30 nm at a pyrolysis temperatures of 2100–2800 K. The porosity of the primary nanoparticles is equal to 0.95–0.97.     

Sorption of CH<Subscript>3</Subscript><Superscript>131</Superscript>I from water vapor-air medium on porous inorganic sorbents containing triethylenediamine and <Emphasis Type="Italic">d</Emphasis> element nitrates

Sorption of CH₃ ¹³¹I from a water vapor-air medium on porous inorganic sorbents based on silica gel of KSKG grade and containing triethylenediamine (CH₂-CH₂)₃N₂ and d element nitrates was studied. The sorbents prepared by impregnation with (CH₂-CH₂)₃N₂ and Zn, Ni, and Cu nitrates from aqueous solution recover CH₃ ¹³¹I from a water vapor-air flow poorly (degree of recovery <10%). Calcination of the sorbents at temperatures exceeding 250°C does not noticeably affect their sorption power. Heating of the complex Ag(NO₃)(OH)·(CH₂-CH₂)₃N₂H to 160°C causes its exothermic decomposition with a large heat release and formation of metallic silver. Thermal decomposition of the complex of Cu²⁺ with (CH₂-CH₂)₃N₂, synthesized from an aqueous solution at the molar ratio Cu(NO₃)₂: (CH₂-CH₂)₃N₂ = 1: 2, occurs similarly.     

Microstructure of fracture of a laser–electric spark coating on titanium after abrasive wear

We present results of a study of the microstructure of a ZrB₂-containing combined laser–electric spark coating deposited on a titanium alloy and subjected to wear with a nonrigidly fastened abrasive performed by scanning electron microscopy in combination with an electron-probe microanalysis. It is established that the coating is characterized by a gradient microstructure over the thickness, and its subsurface layer is modified by Zr, O, Si, and C additives. We put forward the assumption that an increase in the hardness of the coating after abrasive treatment is due to its plastic deformation with the fragmentation of the structural elements and alloying with the indicated additives.     

Optical and electrical properties of polyamide acid and metal-polymer complex based on terbium

The basic optical and electrical properties of polyamide acid and its complex with Tb⁺² have been studied. The occurrence of room-temperature photoluminescence (PL) with an emission peak at 520 nm is established. The activation energy of conductivity at temperatures above 350 K is 2.1 eV. Polyamide acid is comparable in PL intensity with an electroluminescent polymer, poly(p-phenylvinylene).     

Scalable, Hybrid Optical-RF Wireless Communication System for Broadband and Multimedia Service to Fixed and Mobile Users

This paper describes a system concept for providing, flexible high capacity multimedia communication that compliments terrestrial cellular communication systems, by supporting end-to-end broadband information services. A key element of the proposed concept is the use of optical HAP-HAP and HAP-satellite links using single color (SONET protocol based) or upon multicolor DWDM technology. The effectiveness of optical communication links is enhanced through the use of advanced optical fine pointing and tracking technology. A concept for a hybrid, optical-RF, HAP based wireless communication is presented and key technologies, capabilities and limitations are described. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dry etching of GaN using chemically assisted Ion beam etching with HCI and H2/Cl2

The dry etching characteristics of GaN were investigated using chemically assisted ion beam etching (CAIBE) with HCI and H₂/Cl₂ gas. Etch rates using CAIBE/HC1 were investigated as a function of Ar ion beam energy and substrate temperature. These results were compared to CAIBE/C1₂. Etch rates were also investigated for CAIBE/H₂/Cl₂ for various ratios of H₂:C1₂. Highly anisotropic submicron lines are demonstrated using CAIBE/HC1. Auger electron spectroscopy was used to investigate surface stoichiometric changes of samples etched with CAIBE/HC1, CAIBE/H₂/Cl₂,, and CAIBE/C1₂. The diffusion of deuterium into GaN during etching was also investigated using secondary ion mass spectrometry.