Microwave heating, isothermal sintering, and mechanical properties of powder metallurgy titanium and titanium alloys

This article presents a detailed assessment of microwave (MW) heating, isothermal sintering, and the resulting tensile properties of commercially pure Ti (CP-Ti), Ti-6Al-4V, and Ti-10V-2Fe-3Al (wt pct), by comparison with those fabricated by conventional vacuum sintering. The potential of MW sintering for titanium fabrication is evaluated accordingly. Pure MW radiation is capable of heating titanium powder to ≥1573 K (1300 C), but the heating response is erratic and difficult to reproduce. In contrast, the use of SiC MW susceptors ensures rapid, consistent, and controllable MW heating of titanium powder. MW sintering can consolidate CP-Ti and Ti alloys compacted from -100 mesh hydride-dehydride (HDH) Ti powder to ~95.0 pct theoretical density (TD) at 1573 K (1300 C), but no accelerated isothermal sintering has been observed over conventional practice. Significant interstitial contamination occurred from the Al2O3-SiC insulation-susceptor package, despite the high vacuum used (≤4.0 × 10-3 Pa). This leads to erratic mechanical properties including poor tensile ductility. The use of Ti sponge as impurity (O, N, C, and Si) absorbers can effectively eliminate this problem and ensure good-to-excellent tensile properties for MW-sintered CP-Ti, Ti-10V-2Fe-3Al, and Ti-6Al-4V. The mechanisms behind various observations are discussed. The prime benefit of MW sintering of Ti powder is rapid heating. MW sintering of Ti powder is suitable for the fabrication of small titanium parts or titanium preforms for subsequent thermomechanical processing

11. Metropolitan Calcutta and Economic Action

The main concern of the Calcutta Metropolitan Development Authority since its formation in 1970 has been the development activity in the field of municipal infrastructure, embracing water supply, sewerage and drainage, public cleansing, slum improvement, roads and area development. It is appropriate lo view this large-scale development effort in infrastructure as an essential support to the economic revival and growth of the metropolis. However, equally relevant to the future of the metropoli..

Effects of titration parameters on the synthesis of molybdenum oxides based catalyst

Molybdenum oxides catalysts are extensively used in various selective oxidation reactions. In this work, controlled precipitation method was used to synthesise molybdenum oxides. The effects of various titration parameters on the precipitate growth rate and structure throughout catalyst synthesis were investigated. The titration parameters varied for this study were molybdates (ammonium heptamolybdate) concentration, precipitation agent (HNO3) concentration, precipitating agent rate of addition and temperature of synthesis. X-Ray diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM) were used to characterize the catalysts. This study highlights the significant effects of the titration parameters varied on the supersaturation of the solution therefore yielding precipitate with different morphology. It was observed that the temperature played the major role followed by molybdate concentration in the formation of the bulk catalyst. Supramolecular structure (Mo36O112) was observed at lower temperature (30ºC) and lower molybdate concentration (0.07 M, 0.10 M) while at higher temperature (50ºC) and higher molybdate concentration(0.14 M) hexagonal (h-MoO3) phase structure was formed. Fast rate of addition and high concentration of precipitating agent affected the solution equilibrium leading to unclear inflection point (supersaturation point) at the titration curve

Chemically Modified Multi-walled Carbon Nanotubes (MWCNTs) with Anchored Acidic Groups

Surface functionalization of multi-walled carbon nanotubes (MWCNTs) was carried out using a gas phase treatment in a Universal Temperature Program (UTP) reactor by flowing SO3 gas onto the CNTs while being heated at different temperatures. The functionalized nanotubes were characterized using X-ray Fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FT-IR) and Raman spectroscopy. The amount of oxyen and sulfur containing groups was determined by acid-base titration. The titration results were in good agreement with elemental analysis using x-ray fluorescence. FTIR analysis showed the presence of oxygen and sulfur containing groups, S=O, C-S, C=O and -COOH. Raman spectroscopy confirmed that oxygen and sulfur containing acidic groups covalently attached to the sidewall of the MWCNTs

In situ measurement of shrinkage and temperature profile in microwave- and conventionally-sintered hydroxyapatite bioceramic

The clear advantages of microwave (MW) sintering in terms of energy savings as well as superior mechanical properties have led to the popularity of this technique in recent years, especially in the bioceramics community. However to date, no study has established a systematic comparison between the sintering behavior of the most commonly used bioceramic, hydroxyapatite (HA), during MW and conventional sintering. Here, we utilize in situ dilatometry along with optical pyrometry to monitor the rate of shrinkage and temperature profile for various sintering conditions of HA. Temperature-dependent dielectric measurements indicate that microwave coupling occurs around 900 degrees C and the maximum linear shrinkage is reached, on average, 4 times faster in MW sintering. Finally we show that by tuning the MW power, one can effectively benefit from the non-linear increase in relative permittivity to exert control over the evolution of microstructures and hence achieve the desired combination of physical properties for personalized biomedical applications. (C) 2015 Elsevier B.V. All rights reserved

Microwave-assisted fabrication of titanium implants with controlled surface topography for rapid bone healing

Morphological surface modifications have been reported to enhance the performance of biomedical implants. However, current methods of introducing graded porosity involves postprocessing techniques that lead to formation of microcracks, delamination, loss of fatigue strength, and, overall, poor mechanical properties. To address these issues, we developed a microwave sintering procedure whereby pure titanium powder can be readily densified into implants with graded porosity in a single step. Using this approach, surface topography of implants can be closely controlled to have a distinctive combination of surface area, pore size, and surface roughness. In this study, the effect of various surface topographies on in vitro response of neonatal rat calvarial osteoblast in terms of attachment and proliferation is studied. Certain graded surfaces nearly double the chance of cell viability in early stages (similar to one month) and are therefore expected to improve the rate of healing. On the other hand, while the osteoblast morphology significantly differs in each sample at different periods, there is no straightforward correlation between early proliferation and quantitative surface parameters such as average roughness or surface area. This indicates that the nature of cell-surface interactions likely depends on other factors, including spatial parameters

The effect of moisture conditions on the constitution of two bioceramic-based root canal sealers

Background/purpose Intraradicular moisture is not standardized and alters the sealing properties and adhesion of root sealers. The aim of this work was to evaluate the effect of different moisture on the constitution of bioceramic sealers. Materials and methods The sealers were evaluated before mixing, and after setting using X-ray diffraction (XRD), Energy Dispersive Analysis (EDX) and Scanning Electron Microscope (SEM) techniques. Twenty four extracted teeth were prepared and assigned to four groups according to the moisture conditions: (1) dry: using ethanol as final irrigation, (2) normal: using paper points until the last one appeared dry, (3) moist: using a Luer adapter for 5 s followed by 1 paper point, and (4) wet: the canals remained totally flooded. The roots were filled with MTA Fillapex® and Endosequence® BC and kept in phosphate buffer solution at 37 °C for 10 days. Each root was sectioned transversally and longitudinally. The sealers harvested from longitudinal sections were analysed using XRD. Whilst the transverse sections were analysed using SEM/EDX. Results The XRD analysis showed MTA Fillapex composed of Bismuth trioxide, calcium silicate and tricalcium aluminate. The intensity of peaks in the wet condition was reduced. Endosequence BC contained mainly calcium silicate, calcium silicate hydrate, zirconia and calcium hydroxide. The wet condition showed a small increase in hydrated calcium silicate. The EDX analysis showed changes in the elemental concentrations with different moisture conditions. The surface morphology differed with different moisture conditions. Conclusion Tested sealers have different constitution that not affected by the degree of moisture. However, it changed their relative quantity

Tailoring the morphological features of hydrothermally synthesized mesoporous hydroxyapatite using polyphenols and phosphate sources

Hydroxyapatite (HA) is a well-known material for biomedical applications and its performance depends greatly on its morphological features. Therefore, preparation of mesoporous HA with high surface area and adsorption capacity is highly deserved. In this research, a hydrothermal approach to synthesize mesoporous HA without post-processing calcination step is presented. The possibility using different polyphenols to generate mesoporous HA as well as using different phosphate sources to tailor the morphological features of HA is investigated. The as-prepared mesoporous HA particles are characterized by XRD, FTIR, SEM, TEM, BET, and zeta potential. Besides, the impacts of HA morphological features on model drug Dox are also studied. It is expected the strong interaction between –OH of polyphenols and Ca2+ makes polyphenols molecules occupy the inner sites of growing HA particles. After the removal of polyphenols by hydrothermal treatment and ethanol extraction, the occupied sites are transformed into mesopores. The typical mesoporous HA generated in present work has a rod-like morphology with BET specific surface area of 106.6 m2/g and an average pore size of 14.4 nm

Somatic growth in single ventricle patients: A systematic review and meta-analysis

Aim To map somatic growth patterns throughout Fontan palliation and summarise evidence on its key modifiers. Methods Databases were searched for relevant articles published from January 2000 to December 2021. Height and weight z scores at each time point (birth, Glenn procedure, Fontan procedure and >5 years after Fontan completion) were pooled using a random effects meta-analysis. A random effects meta-regression model was fitted to model the trend in z scores over time. Results Nineteen studies fulfilled eligibility criteria, yielding a total of 2006 participants. The z scores for height and weight were markedly reduced from birth to the interstage period, but recovered by about 50% following the Glenn procedure. At >10 years after the Fontan procedure, the z scores for weight seemed to normalise despite persistent lower height, resulting in increased body mass index. The review revealed a number of modifiers of somatic growth, including aggressive nutritional management, timing of Glenn/Fontan, prompt resolution of complications and obesity prevention programmes in adolescence and adulthood. Conclusion This review mapped the somatic growth of single ventricle patients and summarised key modifiers that may be amendable to improvement. These data provide guidance on strategies to further optimise somatic growth in this population and may serve as a benchmark for clinical follow-up.Developmen