S. Aich

Magnetic behavior of Sm-Co-based permanent magnets during order/disorder phase transformations

The structural transformation from the metastable disordered TbCu7-type SmCo7 structure to the equilibrium ordered Th2Zn17-type Sm2Co17 structure was revealed by x-ray diffraction analysis using Reitveld refinement. The magnetic properties depended strongly on the stage of the transformation, as the coercivity strongly depended on the annealing temperature. The as-solidified alloy in the TbCu7-type structure had a coercivity of 4 kOe, which increased to greater than 9 kOe. The coercivity decreased to around 5 kOe as the transformation neared completion upon annealing at higher temperatures. The magnetization processes were also strongly influenced by the structural state. Initially it was totally controlled by nucleation followed by the domain wall pinning-controlled magnetization process.

Magnetic reversal in three-dimensional exchange-spring permanent magnets

In this paper, we investigate the magnetization reversal in single-phase RE2Fe14B and two-phase α-Fe∕RE2Fe14B with varying nanoscale grain structures and intergranular exchange interactions produced via controlled segregation during crystallization. We show that the loss of coercivity arises because domain-wall processes dominate the magnetic reversal as the exchange interactions increase. Micromagnetic modeling corroborates a transition to strongly cooperative magnetic reversal as the exchange interactions increase. The magnetic reversal is controlled by the growth of interaction domains via discrete domain-wall motion, and the coercivity is intrinsically limited by the presence of interaction domains. To alleviate this problem, we have built an additional length scale into the structure that is below the interaction domain size but above the limit for intergranular exchange interactions to be significant. These “single-interaction domain” structures retain nucleation-type magnetic reversal and high coer...

Highly coercive rapidly solidified Sm-Co alloys

Highly coercive (Hc up to 37kOe at 300K), high remanent permanent magnets have been achieved by rapid solidification of binary Sm–Co alloys and Sm–Co alloys modified with Nb and C. Rapidly solidified SmCox alloys with x ranging from 5 to 11.5 formed predominantly a solid solution TbCu7-type SmCo7 phase, although hcp Co was observed for x>7.3. A coercivity value of 10kOe was observed for x<6.1, even though the microstructural scale was on the order of 1μm. The coercivity decreased significantly with the presence of the hcp Co phase, which formed initially as ∼80nm grains and, at higher x, as primary dendrites. Additions of 3at.% Nb or 3 and 5at.% C profoundly affected the coercivity values. Transmission electron microscopy (TEM) investigations revealed the origin of the improved coercivity. The addition of Nb resulted in a significant reduction in microstructural scale. The SmCo7 grain size decreased systematically with Nb content, reaching 150–200nm at 3at.% Nb. The addition of C also significantly enhanc...

On the microstructure and interfacial properties of sputtered nickel thin film on Si (1 0 0)

Ni films of thickness ranging from 150 to 250 nm were deposited by DC magnetron sputtering on to Si (100) substrates maintained at room temperature and followed by post-annealing at 300 and 500 °C for 30 min. Other set of Ni films were deposited on to Si (1 0 0) substrates held at annealing temperature of 300 and 500 °C for 30 min. Microstructural investigation by field emission scanning electron microscope (FE-SEM) and atomic force microscope (AFM) revealed columnar morphology with voided boundaries for films deposited at room temperature and was retained after post-deposition annealing at higher temperatures. Nickel silicide formation with isosceles triangle diffusion front was confirmed by cross-sectional high-resolution transmission electron microscopy (X-HRTEM) for post-annealed Ni films. Thin film deposited at high substrate temperatures having near-equiaxed structure found to be the best route to fabricate thin films without silicide formation.

Microstructures and magnetic properties of rapidly solidified Ni54Fe27−2xGa19+2x ferromagnetic Heusler alloys

Rapidly solidified Ni54Fe27−2xGa19+2x (x=0, 1, 2, 3, and 4) ferromagnetic shape memory alloys were made by melt-spinning with variation of Fe and Ga contents to report on the martensitic phase transformation, microstructures, and magnetic properties. Rapid solidification produced pure L21 phase by preventing the formation of γ-phase. To study the effect of heat treatment on the phase transitions, microstructures, and the magnetic properties, the melt-spun ribbons were partly heat treated at different temperatures of 800, 900, 1000, 1100, and 1200 K with holding times of 5, 10, and 15 min followed by either water quenching or air cooling. The microstructures of the as-spun ribbons as revealed by electron microscopy studies exhibited a gradual transition from cellular to dendritic structure with increasing Ga concentration and with the presence of some internal martensitic twin bands at higher Ga content. The ribbons exhibited very low coercivity with high saturation magnetization, as high as ∼87 emu/g (dec...

Synthesis of Mixed-Phase TiO2 Powders in Salt Matrix and Their Photocatalytic Activity

Three mixed-phase TiO2 powders, containing ∼80 volume % anatase and ∼20 volume % rutile, were prepared from amorphous titanium hydroxide and three different salt matrices—pure sodium chloride, pure Na2CO3, and pure disodium hydrogen phosphate (DSP). Amorphous titanium hydroxide and salt mixtures were heat treated at 875°C in a rapid thermal annealing system for different times, according to the time–temperature phase transformation graphs. Time-dependent UV degradation of aqueous solutions of methylene blue dye (15 ppm) in the presence of mixed-phase powders was used to monitor the activity of the catalysts. Microstructural study of the powders by scanning electron microscope and transmission electron microscope combined with phase analysis by XRD and optical absorbance by UV-absorption spectroscopy indicated that the higher photocatalytic activity of the powder obtained from pure DSP salt could be explained by its smaller rutile particle size and anatase–rutile interparticle bonding.

Substrate bias voltage and deposition temperature dependence on properties of rf-magnetron sputtered titanium films on silicon (100)

Thin films or a coating of any sort prior to its application into real world has to be studied for the dependence of process variables on their structural and functional properties. One such study based on the influence of substrate conditions viz. substrate-bias voltage and substrate temperature on the structural and morphological properties, could be of great interest as far as Ti thin films are concerned. From X-ray texture pole figure and electron microscopy analysis, it was found that substrate bias voltage strongly influence preferential orientation and morphology of Ti films grown on Si (100) substrate. Deposition at higher substrate temperature causes the film to react with Si forming silicides at the film/Si substrate interface. Ti film undergoes a microstructural transition from hexagonal plate-like to round-shaped grains as the substrate temperature was raised from 300 to 50 ∘C during film deposition.

Synthesis of nanoscale oxide scaffold on Nitinol surface using hydrothermal treatment

Abstract Nanostructured scaffolds were synthesized on the surface of equiatomic NiTi alloy (Nitinol) via hydrothermal treatment at 120 ± 1°C and 250 kPa using alkali (NaOH) solution of different strength. The scaffolds were found to be composed of intermingled nanopetals with varying morphology and phase content depending on the treatment time and alkali concentration. Single or mixed Ni3Ti3O, NiTiO3, H2Ti3O7 and TiO2 (anatase and rutile) phases were observed in the scaffold by X-ray diffraction study. Standard hemolysis testing showed significant biocompatibility improvement of the scaffolds grown in low strength alkali. Measurement of Ni release in the simulated body fluid (SBF) revealed that Ni release can be decreased from ∼60 μg L− 1 for the mechanically polished bare NiTi surface to ∼2·7 μg L− 1 for the scaffolded surface (scaffolds grown in low strength alkali).

Solar Energy Conversion Chemical Aspects, Gertz Likhtenshtein

The solar energy flux that is striking the earth surface is about a few thousand times the current usage of the primary energy by human beings. The renewable energy from solar power is increasingly becoming a practical alternative to fossil fuels. There are several well-known books published on solar energy=solar technology and its applications in human need, such as Photoelectrochemical Materials and Energy Conversion Processes (WileyVCH, 2010), Thermodynamics of Solar Energy Conversion (Wiley-VCH, 2008), Physics of Solar Cells – From Basic Principles to Advanced Concepts (Wiley-VCH, 2009), Applied and Industrial Photochemistry (Wiley-VCH, 2012), to name a few. Among them, this book, Solar Energy Conversion-–Chemical Aspects (Wiley-VCH, 2012) provides a unique pedagogical scaffold for undergraduate as well as graduate level students, which is an overview of all the principal aspects related to the structure, photochemical systems, and physicochemical mechanisms of solar cells and light energy conversion that underlies the modern solar cell=solar energy technology. The author, Professor Gertz I. Likhtenshtein, a renowned bright academician with a strong academic background, an internationally renowned scientist=researcher (recipient of several national and international awards), an experienced author (author of nine scientific books and 380 papers), and a Professor of Chemistry at Ben-Gurion University of Negev, Israel (emeritus since 2003), was able to father successfully such a well-organized and well-accomplished resourceful pedagogical text book. With a total of 273 pages, this book is well documented with 152 figures (including 9 colored figures), 1 table, 54 chemical reactions=analytical expressions, and a total of 1,017 references. This book comprises seven chapters. In Chapter 1, while addressing electron transfer theories, useful for electron transfer between a dye-semiconductor system, the author carefully picked up useful older as well as relatively new charge transfer models; from basic two state charge transfer between donor and acceptor to complicated long range electron transfer in multielectron processes are discussed stepwise. Chapter 2 talks about photochemical and photophysical mechanisms and kinetics involved in the process of biological conversion of photon energy to chemical energy which can be observed in any natural photosynthesis. Discussion about the photosynthesis bacteria is very interesting and insightful. The photochemistry of light energy conversion in donor-acceptor pair solution and in templates has been explained in Chapter 3. Reaction pathways and mechanisms for different organic and metalorganic systems are explained here in detail. Chapter 4 discusses the carrier transfer from dye to semiconductors. Relevant discussions of several complex organic dyes are explained systematically. Chapter 5 concentrates on the technical aspects of standard Gertzel cell which addresses important theoretical aspects of structure and physiochemical mechanisms of dye sensitized solar cells (DSSCs). The most recent developments of the DSSCs, mostly based on manipulation of the device design, such as solar cells based on optical fibers, tandem solar cells, solid state DSSCs are discussed in Chapter 6. Chapter 7 reviews on the recent progress in the field of photocatalytic reduction and oxidation of water. The author discusses thermodynamics and mechanisms of reductionoxidation in the presence of several organic and inorganic materials, unimolecular to very complex structure. Solar Energy Conversion-–Chemical Aspects is an interesting and appealing book, mainly based on review of a large amount of world class research works, both theoretical and experimental. Generally, each of the chapters are very well written and organized. Scientific thought processes, ideas, and explanations are nicely executed. However, a few drawbacks observed throughout the book can be listed as follows: (1) references are only up to 1,017: some good research references should be included in the future edition; (2) the author seems more interested in inorganic semiconductor-based DSSCs, which is covered in three chapters; discussions on photovoltaic cells based on organic acceptor-donors are relatively scattered and disorganized; and (3) some schemes (chemical and analytical expressions) for several photophysical and photochemical processes mentioned on pages 69, 106, 107, and 157 should be marked=numbered as scheme numbers. Despite these details, this is a good book based on the fundamentals of solar energy conversion, emphasizing photochemical and physicochemical aspects. Overall, this book is not only very informative and comprehensive for students and faculties related to biochemistry, biophysics, molecular biology, photovoltaic, and renewable energy, but also a valuable resource for a scientist and=or or an industrialist for new and novel challenges.

A Review of: “Introduction to Materials Chemistry, H. R. Allcock”

The field of materials science and technology encompasses the spectrum of materials: metals, ceramics, polymers, semiconductors, composites, and special materials used in advanced technology. We are always using materials, everywhere in our daily life, and the important applications of the materials have been extended even in the sophisticated research area in the field of modern science and technology. The subject of chemistry also has a big and highly remarkable impact in every aspect of life related to materials’ world. “Materials Chemistry” is a special branch of chemistry that involves four important aspects of materials science: fabrication, structure determination, characterization, and applications of different materials. Materials chemistry has a strong link with basic sciences (physical science and life science) and many existing and newly emerging technologies. This book provides a comprehensive resource for the fundamentals of materials science from a chemistry perspective, for both theoretical and experimental aspects. There are several well-known books published on introductory materials science as well as on several aspects of materials, such as “Materials Science and Engineering: An Introduction” (Wiley, 1985), “Introduction to the Thermodynamics of Materials” (Taylor & Francis, 2002), “Introduction to Solid State Physics” (Wiley Eastern Ltd., 1990), to name a few. Among them, this book, “Introduction to Materials Chemistry” (Wiley, 2008) provides a unique pedagogical scaffold for undergraduate as well as graduate level students, which is an overview of chemistry that underlies the modern materials science and technology. Being a renowned, bright academician with a strong academic background and a successful scientist/researcher in material science and chemistry, the author, Dr. Harry R. Allcock, an Evan Pugh Professor of Chemistry at Pennsylvania State University, was able to father successfully such a well-organized and well-accomplished resourceful pedagogical text book. With a total of 432 pages, this book is well documented with 210 figures (including 10 colored figures at the middle of the book), 24 tables, 145 chemical reactions, 2 mathematical equations, and 51 chemical structures. This book comprises three main parts, Parts I–III, which result in a total of seventeen chapters in the whole book. The first part is subdivided in four chapters and provides an overview of the elementary chemistry which is the scaffold of modern materials science. Chapter 1 describes the basic definition of materials chemistry and how this particular field of science contributes to the other important fields of modern technology society by serving as an engine to produce new and novel compounds. Chapter 2 describes the fundamentals of materials chemistry, the reasons for variations in structures and properties in different materials—various types of chemical bonds, bond angles, and effects of size, shape, and packing arrangements of the molecular units on solid state structures. Chapter 3 summarizes about the basic routes of several materials syntheses and the related reaction chemistry with 76 important chemical reactions. The fourth chapter is devoted to describe the novel materials characterization techniques (spectroscopy, thermal analysis, x-ray diffraction, and electron microscopy) to get information related to the structures and properties of different types of materials, starting from the interior of a bulk material to the surface of the material or thin-films, and for the solution-based analysis. The second part is involved with the core chemistry of materials science, how the chemistry is getting involved with the science of a wide range of materials commonly used, such as metals, polymers, ceramics, composites, and different types of alloys. This part is subdivided in five chapters. Chapter 1 describes the small molecules in solids, importance, and packing arrangement of different shaped small-molecules in solid state structures. Chapter 2 informs about the light-weight, easy to fabricate, corrosion-resistant, and inexpensive polymers, one of the most important areas of materials science. This chapter deals with the fabrication and structure-property correlation of different types of polymers, possibility of designing new, better quality polymers, and characteristics of some specific polymers. Chapter 3 deals with the technology of glasses and ceramics: oxide ceramics (silica, silicates, aluminosilicates and related minerals, chrysotile and other forms of asbestos) and glasses (silicate glasses, Pyrex glasses, phosphate glasses, borate glasses) produced directly from mineralogical materials, oxide ceramics obtained from small-molecule materials (inorganic and organometallic precursors—converted from minerals), and nonoxide ceramics (carbon fiber, different types of borides, and nitrides). Chapter 4 discusses metal, the most common elements in the periodic table. This chapter deals with some specific metals (most widely used in modern technology) and their alloys; extraction of those metals from their ores and their state of corrosion, color of the metals, solid state structures and related properties (electrical, thermal, mechanical, and magnetic)