pp 359-360 October 2002 Alloys and Steels
In this study, austenite–martensite phase transformations which are formed by cooling effect in Fe–30% Ni–0.2% Mn alloy are investigated with Mössbauer spectroscopy and scanning electron microscopy. The single peak of the paramagnetic phase and the six peaks of the ferromagnetic phase of Fe–30% Ni–0.2% Mn alloy were observed in the Mössbauer spectrum. The internal magnetic field strength of ferromagnetic martensite phase was determined as 33.8 𝑇 and the isomer shift values were determined as – 0.11 mm.sec–1 and – 0.06 mm.sec–1, respectively, for the austenite and martensite phases. In this alloy, athermal transformation was observed. The results obtained are in agreement with literature.
pp 361-366 October 2002 Alloys and Steels
Microstructure, precipitates and fracture morphology in the coarse grained heat-affected zone (CGHAZ) of a new high-purity 0Cr18Mo2Ti ferritic stainless steel were studied by means of optical metallography, SEM, TEM, X-ray diffractometer, etc. Experimental results indicated that grain coarsening resulted in brittle fracture in the CGHAZ of 0Cr18Mo2Ti steel. The reduction of impact toughness in the CGHAZ due to change of cooling rate can be attributed to the increase of nitrides (TiN, Cr2N, etc). These nitrides in the CGHAZ promote initiation and propagation of brittle cracks. The precipitated Cr2N nitrides in the grain boundaries decrease impact toughness in the CGHAZ of 0Cr18Mo2Ti steel by promoting crack initiation. In practical applications, the welding heat input (𝐸) should be as low as possible to prevent toughness reduction in the CGHAZ.
pp 367-370 October 2002 Alloys and Steels
The chemical composition of the second phase precipitation in the vacuum diffusion-bonded zone of Fe3Al intermetallic compound and Q235 carbon steel was analysed by means of electron probe microanalyser (EPMA). The relative content of the second phase precipitation and grain size was evaluated through a micro-image analyser. The percentage of Fe and Al content in the diffusion zone was measured by EPMA. The results indicated that the relative content of the second phase precipitation rich in carbon and chromium at the Fe3Al/Q235 interface was much higher. With the transition from Fe3Al intermetallic compound to Q235 carbon steel across Fe3Al/Q235 interface, the grain diameter decreased from 250 𝜇m to 112 𝜇m, Al atom content decreased from 27% to 15%, while Fe atom content increased from 76% to 96%.
pp 371-373 October 2002 Alloys and Steels
The influence of heavy metal oxides on the chloride induced corrosion of steel reinforcement in concrete was studied. Significant inhibition and stimulation of chloride induced corrosion have been observed. Basicity and acidity of the relevant metal ions, and their ability to form complexes are considered as the main factors of the observed effects.
pp 375-379 October 2002 Alloys and Steels
The rate of corrosion of reinforcement being an electrochemical process, undoubtedly is dependent even on the level of the ambient temperature. Therefore, the ambient temperature seems to be an important factor of the corrosion rate and the durability of the reinforced concrete structures in aggressive environment.
The present data on the influence and significance of the ambient temperature in the process of corrosion of reinforcement of the reinforced structures are surprisingly limited and poor. It seems that it is supposed to be a simple increase of corrosion rate when the ambient temperature is increased.
The lack of information was a motivation for the present study. It was aimed at the experimental research of the influence of the increase of the ambient temperature on the rate of chloride induced corrosion of steel reinforcement. The results obtained show that the influence of the studied factor is more complex showing an acceleration effect till a temperature of 40°C diversified by the inhibition effects with further increase of the ambient temperature.
pp 381-385 October 2002 Composites
A synthetic porous ceramic composite material consisting of the mullite, cordierite and cristobalite phases is produced from a mixture of paper pulp waste and clay by reaction sintering at 1400°C. Physicomechanical properties such as bulk density, porosity, cold crushing strength and cold modulus of rupture have been studied. The presence of mullite, cordierite, cristobalite and quartz as major phases and montellecite, tatanite, forsterite and anorthite as minor phases have been confirmed by X-ray diffraction pattern. SEM studies revealed the presence of well developed needle shaped mullite and quartz crystals. The paper also discusses the possible uses of this type of porous composite material.
pp 387-390 October 2002 Composites
Four compositions of nitride bonded SiC were fabricated with varying particle size of SiC of ∼ 9.67, ∼ 13.79, ∼ 60 𝜇 and their mixture with Si of ∼ 4.83 𝜇 particle size. The green density and hence the open porosity of the shapes were varied between 1.83 to 2.09 g/cc and 33.3 to 26.8 vol.%, respectively. The effect of these parameters on room temperature and high temperature strength of the composite up to 1300°C in ambient condition were studied. The high temperature flexural strength of the composite of all compositions increased at 1200 and 1300°C because of oxidation of Si3N4 phase and blunting crack front. Formation of Si3N4 whisker was also observed. The strength of the mixture composition was maximum.
pp 391-398 October 2002 Thin Films
Equilibrium concentrations of various condensed and gaseous phases have been thermodynamically calculated, using the free energy minimization criterion, for the metalorganic chemical vapour deposition (MOCVD) of copper films using bis(2,2,6,6-tetramethyl-3,5-heptadionato)copper(II) as the precursor material. From among the many chemical species that may possibly result from the CVD process, only those expected on the basis of mass spectrometric analysis and chemical reasoning to be present at equilibrium, under different CVD conditions, are used in the thermodynamic calculations. The study predicts the deposition of pure, carbon-free copper in the inert atmosphere of argon as well as in the reactive hydrogen atmosphere, over a wide range of substrate temperatures and total reactor pressures. Thin films of copper, grown on SiO2/Si(100) substrates from this metalorganic precursor by low pressure CVD have been characterized by XRD and AES. The experimentally determined composition of CVD-grown copper films is in reasonable agreement with that predicted by thermodynamic analysis.
pp 399-402 October 2002 Thin Films
A design, development and validation work of plasma based ‘activated reactive evaporation (ARE) system’ is implemented for the deposition of the silicon films in presence of nitrogen plasma on substrate maintained at room temperature. This plasma based deposition system involves evaporation of pure silicon by e-beam gun in presence of nitrogen plasma, excited by inductively coupled RF source (13.56 MHz). The activated silicon reacts with the ionized nitrogen and the films get deposited on silicon substrate. Different physical and process related parameters are changed. The grown films are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and ellipsometry. The results indicate that the film contains silicon nitride and a phase of silicon oxy nitride deposited even at room temperature. This shows the feasibility of using the ARE technique for the deposition of silicon films in nitrogen plasma.
pp 403-406 October 2002 Thin Films
Studies on the surface micromorphology and surface conductivity in thin polymer films of poly vinyl alcohol (PVA) and poly ethylene oxide (PEO) in both as-grown and ion-implanted polymer films have been carried out to reveal certain specific features of the ordered state in these materials. Optical microscopic investigations revealed the existence and enhanced formation in number of spherulites and dendrites in ionimplanted films relative to the as-grown films. The number and rate of formation of spherulites indicated an increase in the degree of crystallinity in these films. Measurements of surface conductivity of as-grown and ion-implanted polymer films, employing four-point probe method, indicated a decrease in electrical conductivity on ion-implantation. Photomicrographic analysis of the PVA and PEO thin film surfaces, has enabled to propose a temperature–stress induced mechanism of crystallization in conjunction with the surface conductivity measurements. The decrease in surface conductivity on ion-implantation in both PVA and PEO thin films, is attributed to a decrease in mobility of macromolecular charged species due to an increase in degree of crystallinity as has been observed by optical microscopy.
pp 407-411 October 2002 Thin Films
The electrical properties of silver selenide thin films prepared by reactive evaporation have been studied. Samples show a polymorphic phase transition at a temperature of 403 ± 2 K. Hall effect study shows that it has a mobility of 2000 cm2V–1s–1 and carrier concentration of 1018 cm–3 at room temperature. The carriers are of 𝑛-type. X-ray diffraction study indicates that the as-prepared films are polycrystalline in nature. The lattice parameters were found to be 𝑎 = 4.353 Å, 𝑏 = 6.929 Å and 𝑐 = 7.805 Å.
pp 413-417 October 2002 Sol--gel Materials
Crystal behaviours such as crystallization temperature (amorphous to tetragonal (𝑡) zirconia), tendency of phase transformation (tetragonal to monoclinic (𝑚) zirconia) and lattice strain were studied with mechanical property e.g. tensile strength of sol–gel derived ZrO2–2 mol% RE2O3 (RE = La, Pr, Nd, Sm, Gd and Dy) spun fibres. Rare earth cations of varying sizes played a significant role in changing the above mentioned properties of ZrO2–2 mol% RE2O3 fibres. It was found that with decreasing the ionic size difference between the zirconium and RE ions, crystallization temperature (amorphous $\rightarrow \ t$-ZrO2) decreased, the probability of phase transformation ($t \rightarrow m$) decreased, lattice strain which is related to lattice distortion decreased and tensile strength increased.
pp 419-429 October 2002 Sol--gel Materials
This study investigates quantitatively and qualitatively the sol–gel derived bioactive glass–ceramic system (BGS)-apatite–wollastonite (AW) type granules in the size range of 0.5–1 mm, as an effective graft material for bone augmentation and restoration. Scanning electron micrographs (SEM) of the sintered granules revealed the rough material surface with micropores in the range 10–30 𝜇m. X-ray diffraction (XRD) pattern of the granules revealed the presence of crystalline phases of the hydroxyapatite and wollastonite, and the functional groups of the silicate and phosphates were identified by Fourier transform infrared spectroscopy (FT-IR). The in vitro cell culture studies with L929 mouse fibroblast cell line showed very few cells adhered on the BGS disc after 24 h. This could be due to the highly reactive surface of the disc concomitant with the crystallization but not due to the cytotoxicity of the material, since the cellular viability (MTT assay) with the material was 80%. Cytotoxicity and cytocompatibility studies proved that the material was non-toxic and biocompatible. After 12 weeks of implantation of the BGS granules in the tibia bone of New Zealand white rabbits, the granules were found to be well osteointegrated, as observed in the radiographs. Angiogram with barium sulphate and Indian ink after 12 weeks showed the presence of microcapillaries in the vicinity of the implant site implicating high vascularity. Gross observation of the implant site did not show any inflammation or necrosis. SEM of the implanted site after 24 weeks revealed good osteointegration of the material with the newly formed bone and host bone. New bone was also observed within the material, which was degrading. Histological evaluation of the bone healing with the BGS granules in the tibial defect at all time intervals was without inflammation or fibrous tissue encapsulation. After 2 weeks the new bone was observed as a trabeculae network around the granules, and by 6 weeks the defect was completely closed with immature woven bone. By 12 weeks mature woven bone was observed, and new immature woven bone was seen within the cracks of the granules. After 24 weeks the defect was completely healed with lamellar bone and the size of the granules decreased. Histomorphometrically the area percentage of new bone formed was 67.77% after 12 weeks and 63.37% after 24 weeks. Less bone formation after 24 weeks was due to an increased implant surface area contributed by the material degradation and active bone remodeling. The osteostimulative and osteoconductive potential of the BGS granules was established by tetracycline labelling of the mineralizing areas by 2 and 6 weeks. This sol–gel derived BGS granules proved to be bioactive and resorbable which in turn encouraged active bone formation.
pp 431-434 October 2002 Glasses
A.c. conductivity, dielectric constant and loss, and variation with temperature (302–373 K) for four different compositions of V2O5–B2O3 glasses were reported at 9.586 GHz microwave frequency. The quality factor (𝑄) and attenuation factor (𝛼) being the important parameters in the microwave range of applications were also studied. The change in the dielectric constant and loss was observed with composition of V2O5. The maximum loss was found to be at 15V2O5 mol%. The peak was observed in loss with temperature.
pp 435-441 October 2002 Instrumentation
A simple and fairly inexpensive total reflection X-ray fluorescence (TXRF) spectrometer has been designed, constructed and realized. The spectrometer is capable of ultra-trace multielement analysis as well as performs surface characterization of thin films. The TXRF setup comprises of an X-ray generator, a slitcollimator arrangement, a monochromator/cutoff-stage, a sample reflector stage and an X-ray detection system. The glancing angle of incidence on the two reflectors is implemented using a sine-bar mechanism that enables precise angle adjustments. An energy dispersive detector and a GM counter are employed for measuring respectively the fluorescence intensities and the direct X-ray beam intensity. A Cu-target X-ray generator with its line focus window is used as an excitation source. The spectrometer is quite portable with its compact design and use of a peltier cooled solid state detector for energy dispersive detection. Alignment and characterization of the TXRF system has been performed and the minimum detection limits for various elements have been determined to be in the range of 100 pg to 5 ng even at low X-ray generator powers of 30 kV, 5 mA. The capability of the TXRF system developed for thin film characterization is also demonstrated.
pp 443-447 October 2002 Building Materials
Fly ash (FA) poses serious problems to the industries. Integrated steel plants generate huge quantity of FA from their captive power plants and other furnaces. This ash is generally disposed off in the ash ponds along with other sludges and residues of steel making operations. This changes the constitution of FA and makes the brick manufacturing difficult. This paper has attempted to devise the ways for the use of this mixed ash for manufacturing mixed ash clay bricks successfully. The bricks thus made are superior in structural and aesthetic qualities and portents huge saving in the manufacturing costs with better consumer response.
Volume 42 | Issue 3