Physical, Optical, and Spectroscopic Studies on MgO-BaO-B2O3 Glasses

The mixed alkaline effect in double alkaline borate glasses MgO-BaO-B2O3 containing small proportions of copper oxide (CuO) has been studied. The glass samples are characterized by optical absorption, electron paramagnetic resonance (EPR), and Fourier transform infrared spectroscopy (FTIR). A red shift in optical absorption peaks with increasing MgO (decreasing BaO) concentration has been observed. The values of “g” tensor and hyperfine “A” tensor have shown inflections with glass composition. The number of spins (N) and paramagnetic susceptibility (χ) also exhibited mixed alkaline effect. The broadening of glass network with increase in MgO concentration is found from the FTIR spectra. Interestingly both density and molar volume have shown decreasing trend with glass composition. The optical band gaps exhibited a nonlinear compositional dependence. As expected, the glass samples possessed higher values of optical basicity (Λ), molar electronic polarizability (αm), and Urbach energy (ΔE).

Recent Progress in Chemically Bonded Phosphate Ceramics

Chemically bonded phosphate ceramics have made an excellent progress in the last 10 years and are poised to be one of the major inorganic room-temperature setting materials for nuclear, structural, dental, and prosthetic applications. They are also poised to be the first inorganic industrial coatings for fire and corrosion protection applications. In 2004 the author in his book, Chemically Bonded Phosphate Ceramics, presented general theory, compositions, methods of fabrication, and preliminary commercial products that appeared in the market ten years ago. This paper reviews that background and presents advances of last ten years with an emphasis on the recent applications in the nuclear field.

Low Temperature Synthesis of α-Alumina with a Seeding Technique

This paper reports a method for producing α-Al2O3 at low temperature, which uses a seeding technique. White precipitate of aluminum hydroxide, which was prepared with a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution, was peptized by using acetic acid at room temperature and then transformed to a transparent alumina sol. To the alumina sol α-Al2O3 particles were added as a seed, and then the sol containing α-Al2O3 particles was transformed to an α-Al2O3-seeded alumina gel by drying the sol at room temperature. The nonseeded alumina gel was amorphous or fine crystallites even after being annealed at 600°C and was crystallized to γ-Al2O3 at 700°C. The α-Al2O3 seeding promoted crystallization of alumina gel to α-Al2O3. The promotion of crystallization was made remarkable with a decrease in α-Al2O3 particle size and an increase in α-Al2O3 particle content in weight for the final seeded alumina gel. With an α-Al2O3 particle size of 150 nm and an α-Al2O3 particle content of 5%, the seeded alumina gel was partially crystallized to α-Al2O3 by annealing at a temperature as low as 700°C and mostly at 900°C.

Preparation, Physicochemical Characterization, and Bioactivity Evaluation of Strontium-Containing Glass Ionomer Cement

Background. Glass ionomer cements are one of the most important restorative materials in dentistry. One of the disadvantages of glass ionomer cements is their undesirable mechanical properties and bioactivity. Aim. The aim of this work was preparation and characterization of strontium-containing glass ionomer cement and evaluation of its bioactivity in the simulated body fluid. Materials and Methods. The ceramic component of glass ionomer cement was made by melting method. Scanning electron microscope (SEM) was used to study the size and the shape of glass particles. In order to determine the phase combination in the produced material, X-ray diffraction (XRD) analysis was carried out. The chemical composition of the glass was evaluated by X-ray florescence (XRF), and the surface area of the particles was determined using BET method. In order to investigate the biological properties of the glass, samples were immersed in simulated body fluid (SBF). Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) were used to recognize and confirm the apatite layer on the composite surface. Results and Conclusions. The result of X-ray diffraction (XRD) analysis confirmed the glassy structure of the produced ionomer cements. The result of XRF confirmed the presence of Sr in the chemical composition. Fourier transform infrared spectroscopy test and electron microscope confirmed the formation of apatite layer on the surface of material. The final result of this research was gaining glass ionomer cement containing Sr with improved bioactivity.

Experimental Investigation on Flowability and Compaction Behavior of Spray Granulated Submicron Alumina Granules

Aqueous slurry with various solid loadings (up to 40 wt%) of alumina powder (D50 = 300 nm) with suitable rheological properties were spray dried into granules. Solid loading and feed rate of the slurry are found to have a prominent effect on the shape and size distribution of granules. Powder flow measurements exhibited a cohesive index of 28.45 signifying an extremely cohesive flow due to high surface area and irregular morphology. Finer sizes though it offers high geometrical surface area it leads to more surface contacts and hence, high interparticle friction. Spherical morphology achieved through optimum spray drying parameters significantly reduced the cohesive index to 6.45 indicating free flow behavior. Compaction studies of the spray-dried granules and corresponding plot of relative density versus compaction pressure revealed an agglomerate strength of 500 MPa followed by a plateau-like behavior reaching a maximum in the relative density of 59%-60% of the theoretical values.

Evaluation of DLC, WC/C, and TiN Coatings on Martensitic Stainless Steel and Yttria-Stabilized Tetragonal Zirconia Polycrystal Substrates for Reusable Surgical Scalpels

DLC, WC/C, and TiN coated SF 100 martensitic stainless steel and Yttria-Stabilized Tetragonal Zirconia Polycrystal (Y-TZP) surgical scalpels were tested, characterized, and comparatively evaluated with regard to chemical leach, micromorphology, and mechanical properties in order to evaluate their suitability as reusable surgical scalpels. Vickers microhardness (HV), Scratch Hardness Number (), and sharpening by grinding and cutting capabilities of all the coated scalpels were deemed appropriate for reusable surgical scalpels. However, coated Y-TZP scalpels demonstrated higher Vickers microhardness than martensitic stainless steel scalpels coated with the same coatings, except DLC coating on Y-TZP substrate that presented less adhesion than the other coatings. Uncoated and coated martensitic stainless steel scalpels presented corrosion and chemical leach when soaked for a defined period of time in a simulant physiological saline solution, while uncoated and coated Y-TZP scalpels did not present these drawbacks. Therefore, DLC, WC/C, and TiN coated SF 100 martensitic stainless steel surgical scalpels are unsuitable as reusable surgical scalpels, limiting their application to disposable scalpels only, as the uncoated ones, despite their higher microhardness and expected longer cutting capability duration. Based on these experimental results, WC/C and TiN coated Y-TZP scalpels can be proposed as candidates for reusable surgical scalpel applications.

Electrical Conduction in (Na0.5Bi0.5)1−xBaxTiO3 (0≤x≤1) Ceramic by Complex Impedance/Modulus Spectroscopy

The present work describes the piezoelectric, impedance, and conductivity studies of (Na0.5Bi0.5)1−xBaxTiO3; (1-x)BNT-xBT (0≤x≤1) ceramics. The ceramics were prepared by conventional ceramic fabrication technique. X-ray diffraction data confirmed the formation of a pure compound in all the compositions. Williamson-Hall plot yielded the apparent crystallite sizes ~26–52 nm, and SEM micrograph showed grain sizes ranging between 1.8–3.5 μm for the material samples. Values of longitudinal piezoelectric charge coefficients of the samples poled under a dc electric field of about 2.5 kV/mm at 80°C/15 min indicated that their piezoelectric properties near the MPB are rather sensitive to the phase composition and reach preferred values at x=0.08, where the relative content of the tetragonal phase is significantly higher than that of the monoclinic phase. Complex impedance/modulus spectroscopic analyses indicated the presence of grain-boundary effect along with the bulk contribution and also confirmed the presence of non-Debye type of multiple relaxations in the materials. The temperature dependent electrical conductivity data suggest the negative temperature coefficient of resistance behaviour. The activation energy studies allow insight into the nature of the conduction mechanisms occurring in the materials system which are explained on the basis of hopping model of charge carriers.

DSC and DC Conductivity of Bi2O3 · LiF · B2O3 Glasses

Fluoroborate glasses with Bi2O3 content and having compositions xBi2O3 · (40-x)LiF · 60B2O3 (x = 0, 5, 10, 15, and 20) are prepared using melt-quench technique. DSC characterization is carried out to observe glass transition temperature. Two such temperatures are observed for each of the reported samples. DC conductivity of the reported samples is studied with the variation in temperature from 313 K to 413 K by dividing this range into three regions, namely, low-, intermediate-, and high-temperature regions. DC conductivity responses for these temperature regions are explained using different conductivity models.

A Study of Parameters Affecting Wear Resistance of Alumina and Yttria Stabilized Zirconia Composite Coatings on Al-6061 Substrate

In this investigation, a composite coating of alumina and yttria stabilized zirconia in equal proportion was developed on Al-6061 substrate using Atmospheric Plasma Spraying technique. Two commercially available powders of chemical composition Al 25Fe7Cr5Ni and Al2O330(Ni 20Al) were used as bond coats. The coating samples were subjected to abrasive wear test as per ASTM G99. From the results it was found that wear rate and coefficient of friction depend on various parameters such as microstructure, surface roughness, porosity, coating thickness, and hardness. It was also found that the mechanism of wear is mainly due to abrasion and once the bond coat is exposed to the disc, it loses material by adhesion. As the coating systems possess α-Al2O3 and ZrO2, they can be used for wear and heat resistant applications such as cylinder liner of internal combustion engines.

Preparation and Catalytic Properties of Iron-Cerium Phosphates with Sodium Dodecyl Sulfate

Iron phosphate was prepared from iron nitrate and phosphoric acid with sodium dodecyl sulfate at various stirring hours. The chemical composition of the obtained samples was estimated from ICP and XRD measurements. Particle shape and size distribution were observed by SEM images and laser diffraction/scattering methods. Further, the catalytic activity was studied with the decomposition of the complex between formaldehyde, ammonium acetate, and acetylacetone. The peaks of FePO4 were observed in XRD patterns of samples prepared in Fe/Ce = 10/0 and then heated at 600°C. Other samples were amorphous in XRD patterns. Iron-cerium phosphates had high catalytic activity for the decomposition of the complex.