B Sarkar

Bio: B Sarkar is an academic researcher from Central Glass and Ceramic Research Institute. The author has contributed to research in topics: Isocenter & Zirconia Toughened Alumina. The author has an hindex of 7, co-authored 29 publications receiving 174 citations.

The structural transformation of anatase TiO2 by high-energy vibrational ball milling

Abstract: The structural transformation of anatase TiO2 by high-energy vibrational ball milling was studied in detail by different analytical methods of x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). This structural transformation involves both phase transition and nanoparticle formation, and no amorphization was observed. The crystallite size was found to decrease with milling time down to nanometer size ∼13 nm and approaching saturation, accompanied by phase transformation to metastable phases, i.e., TiO2(II), which is a high-pressure phase and TiO2(B), which was identified in ball-milled powder reported for the first time in this paper. These phases eventually started transforming to rutile by further milling.

Observation of a high pressure polymorph of titania by vibrational ball milling

Abstract: Central Glass & Ceramic Research Institute, Jadavpur, Calcutta-700 032, India The observation of a high pressure polymorph of titania, originating from an anatase phase, using high energy impact vibrational ball milling (HEIVBM) is reported here for the first time. The observed polymorph conforms to the reported high pressure modified phase of titania [orthorhombic, α-PbO2 (Pbcn) structure] developed by static high pressure and shock wave techniques. X-ray diffraction (XRD) and electron spin resonance (ESR) techniques are used to characterize the polymorph.

Toughness determination of zirconia toughened alumina ceramics from growth of indentation-induced cracks

Abstract: Short surface cracks were generated by Vickers indentation on the polished surface of alumina and different zirconia toughened alumina (ZTA) specimens, and their morphology was studied by serial sectioning. These cracks were grown in three-point bend tests under stepwise loading, and variation of toughness with crack extension was plotted to graphically separate the contributions from residual stress intensity and applied stress intensity factors. The plateau toughness determined from the intercept height of the crack extension plots exhibited an upward trend with zirconia content up to 15 vol % ZrO2 addition in the composition, which was proportional to the fraction of transformable tetragonal grains contributing to transformation toughening.

Ageing of zirconia-toughened alumina ceramics under different hydrothermal conditions

Abstract: Changes in the crystalline phases of ZrO2 in different zirconia-toughened alumina (ZTA) compositions were studied at lower temperature (150–250 °C) by exposing them in a stream of humid air for a period of 24 h. Fresh samples of these compositions were also aged in an autoclave with superheated water for 2.5 h in the same temperature range, and the degree of phase transformation was compared with data from the previous samples to establish the effect of pressure on this phenomenon. It was observed for all the ZTA compositions that phase transformation increased monotonically with ageing time, temperature and pressure, although for the compositions with a lower percentage (15 vol%) of zirconia (3 mol% Y2O3), ageing in an autoclave was more detrimental particularly at lower temperature. As the ageing temperature increased in the composition with 15 vol% ZrO2 (3 mol% Y2O3), the influence of ageing duration on phase transformation of ZrO2 increased and the effect for 24 h of exposure time was found to be even more catastrophic than that of autoclave pressure at 250 °C. On the other hand, for the ZTA compositions containing more than 15 vol% zirconia (3 mol% Y2O3), the damaging effect of ageing in the autoclave was greater and this difference increased with increase in temperature.

Development of Si-Mn Alloyed Spring Steels Suitable for Elastic Rail Clip (ERC) Application

Abstract: Spring steels are used for making leaf springs for automotives, elastic rail clips (ERC) for railways, and coil springs for various applications. No residual plastic deformation is permissible even under heavy static or cyclic loads and springs must return to its original state after removal of external loads. The present paper relates to Si-Mn alloyed rolled spring steel billets and a process for its production through twin hearth furnace (THF) – top poured (TP) ingot – blooming and billet mill route, suitable for making elastic rail clip (ERC). A selective alloy design and process control for successful commercial production of rolled spring steel billets free from surface defects and internal defects like, subcutaneous pin/blow holes, off corner cracks and central piping or looseness to make it suitable for making elastic rail clip (ERC) and leaf springs favoring wide industrial application is described in the paper.

Mechanical Alloying And Milling

Abstract: Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Adipose-derived adult stromal cells heal critical-size mouse calvarial defects.

Abstract: In adults and children over two years of age, large cranial defects do not reossify successfully, posing a substantial biomedical burden. The osteogenic potential of bone marrow stromal (BMS) cells has been documented. This study investigates the in vivo osteogenic capability of adipose-derived adult stromal (ADAS) cells, BMS cells, calvarial-derived osteoblasts and dura mater cells to heal critical-size mouse calvarial defects. Implanted, apatite-coated, PLGA scaffolds seeded with ADAS or BMS cells produced significant intramembranous bone formation by 2 weeks and areas of complete bony bridging by 12 weeks as shown by X-ray analysis, histology and live micromolecular imaging. The contribution of implanted cells to new bone formation was 84-99% by chromosomal detection. These data show that ADAS cells heal critical-size skeletal defects without genetic manipulation or the addition of exogenous growth factors.

Pseudocapacitive Lithium Storage in TiO2(B)

Abstract: Phase-pure TiO2(B) with microfibrous morphology was prepared via a newly developed method from amorphous TiO2. Cyclic voltammetry evidences that Li-insertion into TiO2(B) is governed by a pseudocapacitive faradaic process, whose rate is not limited by solid-state diffusion of Li+ in a broad interval of scan rates. This unusual behavior was discussed in terms of the crystal structure of the TiO2(B) host, having freely accessible parallel channels for Li+-transport perpendicular to the (010) face. The characteristic Li-insertion electrochemistry of TiO2(B) allows re-interpretation of several previous reports, which did not consider explicitly this relation or the presence of TiO2(B) in various TiO2 materials of different origin.

Effect of Silica Additive on the Anatase-to-Rutile Phase Transition

Abstract: The effect of SiO2 addition on the anatase-to-rutile phase transition was investigated by DTA, XRD, FTIR, and XPS. TiO2 xerogels containing SiO2 up to 20 mol% were prepared by mixing and hydrolyzing titanium tetraisopropoxide (TTIP) and tetraethylorthosilicate (TEOS) with HNO3 as a catalyst. With increased amounts of SiO2 in the xerogels, the following results were obtained: (1) the crystallization temperature of anatase increased from 415°C in pure TiO2 to 609°C in 20-mol%-SiO2-containing xerogel in the DTA curves; (2) the formation temperature of rutile, according to quantitative XRD analysis, increased with increased SiO2 content up to 5 mol% SiO2 but became constant at higher SiO2 contents; (3) the crystallinity of anatase became lower; and (4) the lattice parameter a of the anatase decreased slightly, but the parameter c decreased greatly up to 20 mol% SiO2. Although the added silicon atoms were considered from these results to be incorporated into the amorphous TiO2 and anatase structures, the 29Si MAS NMR spectra of the xerogels containing 10 mol% SiO2 showed only tetrahedral silicon, with no indication of silicon in octahedral coordination. When calcined at higher temperatures, the xerogel showed polymerization of the SiO4 tetrahedra in the NMR spectra and the Si–O–Si vibration in the FTIR spectra. The chemical composition of the xerogel surfaces, measured using XPS, showed increased SiO2 content with increased calcining temperature, indicating the expulsion of silicon from inside the particles to form an amorphous SiO2 surface layer. The formation of this amorphous SiO2 surface layer was considered to be important in retarding the anatase-to-rutile phase transition by suppressing diffusion between anatase particles in direct contact and limiting their ability to act as surface nucleation sites for rutile. These effects of silicon additions were similar to those observed in the γ-Al2O3- to-α-Al2O3 transition.