Fine Crystallite Size Research Articles

Feasibility studies on newly identified LiCrP2O7 compound for lithium insertion behavior

A new category of lithium intercalating cathode candidates, namely LiCrP2O7, was synthesized at 800°C using a citric acid assisted modified (CAM) sol–gel method and examined for possible lithium insertion behavior. The formation of a phase pure and monoclinic LiCrP2O7 compound with finer crystallite size was confirmed from the X-ray diffraction patterns. The presence of nano-sized particles as observed from a transmittance electron microscope image of LiCrP2O7 and the presence of a preferred local cation environment, evidenced from Fourier transform infra-red and 7Li nuclear magnetic resonance studies, are the added advantages of the present study. Further, cyclic voltametry study performed on 2016 coin cells consisting of the synthesized LiCrP2O7 cathode revealed an excellent cycling reversibility and structural stability. Hence, CAM sol–gel synthesized LiCrP2O7 is found to possess desirable physical as well as electrochemical properties, leading one to consider the same as a possible lithium intercalating cathode material.

NO2-aided Soot Oxidation on LaMn0.7Ni0.3O3 Perovkite-type Catalyst

The LaMnO3-based perovskite-type mixed oxides were studied for both trapping of NOx and combustion of diesel soot. The LaMn0.7Ni0.3O3 (LMN3) perovskite shows high NOx adsorption capacity, quick adsorption rate and efficient adsorbed species. After the catalyst interacts with NO at low temperature around 325 °C, decomposition of the nitrates leads to the decrease of the maximum soot oxidation temperature to 430 °C. The fine crystallite size, increased surface area and readily reducibility at low temperature also favor the oxidation of soot over LMN3 under loose contact conditions.

CAM sol–gel synthesized LiMPO4 (M=Co, Ni) cathodes for rechargeable lithium batteries

The emerging category cathode candidates such as LiCoPO4 and LiNiPO4 were synthesized at 800 °C using Citric acid assisted modified sol–gel (CAM sol–gel) method and examined for possible lithium intercalation behavior. Compound formation temperature is confirmed from thermogravimetry and differential thermal analysis (TG/DTA). Powder X-ray diffraction (PXRD) pattern evidenced the absence of undesirable peaks and confirmed the formation of phase pure LiMPO4 (M=Co, Ni) compounds with an orthorhombic structure and finer crystallite size. Presence of nanosized particles as observed from TEM image of LiCoPO4 and the presence of preferred local cation environment as understood from FT–IR studies are the added advantages of CAM sol–gel synthesis. Further, Cyclic voltametry (CV) and Impedance spectroscopy (EIS) studies performed on the synthesized LiCoPO4 and LiNiPO4 cathodes revealed excellent reversibility and structural stability of CAM sol–gel synthesized cathodes, especially upon storage as well as during cycling.

Precipitation of Nanocrystalline CeO2 Using Triethanolamine

Synthesis of cerium oxide nanocrystallites via precipitation using triethanolamine is reported. The molecular water associated with the cerium nitrate precursor is exploited to generate hydroxyl ions with the help of triethanolamine, facilitating precipitation. The small crystallite diameter (3 nm) in the as prepared powder is believed to result from the limited amount of water present. Solvent type has no effect on the final crystallite size or structure; however, it plays an important role in the dispersion of the nanoparticles with dispersity of the particles increasing with increasing carbon chain length of the solvent alcohol used.

Microstructural and magnetic properties of nanostructured Fe and Fe 50Co 50 powders prepared by mechanical alloying

This work focuses on the preparation of nanocrystalline Fe and Fe 50Co 50 powders using high-energy milling. A body-centred cubic (bcc) nanocrystalline Fe 50Co 50 alloy is resulted after 8 h of the milling process with a lattice parameter close to a = 0.2862 nm and with an average grain size of about 12 nm. The coercivity increased from 72 to 102 Oe, by milling for 3 h, followed by a reduction of 47.95 Oe on milling for longer periods. This latter effect is attributed to the effect of the very fine crystallite size associated with prolonged milling. The saturation magnetization increased dramatically from 178 to 208 A m 2/kg due to the formation of Fe 50Co 50 alloy.

Characterisation of salt films on dissolving metal surfaces in artificial corrosion pits via in situ synchrotron X-ray diffraction

The salt films formed on metal surfaces dissolving inside artificial corrosion pits formed in 1 M HCl have been probed with synchrotron X-ray diffraction. NiCl 2 · 6H 2O is the main phase in the salt film on nickel, whereas salt films on both iron and 316 L stainless steel are predominantly FeCl 2 · 4H 2O. However, the salt film on iron has a very fine homogeneous crystallite size whereas that on stainless steel is much coarser. The potential-dependence of the film formed on iron has been determined.

Effect of sintering and melt casting methods on properties of a machinable fluor-phlogopite glass–ceramic

Abstract The effects of the melt casting and the sintering methods on the machinability and other characteristics of a SiO2–Al2O3–MgO–K2O–B2O3–F glass–ceramic composition were examined. The results show that the specimen prepared by the sintering method had better machinability and mechanical properties, due to a higher mica volume percent and finer crystallite size. It was found that the specimen had undergone surface crystallization; hence, it was concluded that preparation of the specimen by the sintering route would be less sensitive to heating conditions.

Influence of B site Substituents on Lanthanum Calcium Chromite Nanocrystalline Materials for a Solid‐Oxide Fuel Cell

Highly reactive and nanocrystalline powders of LaCrO3based compositions, having the general formula La0.9Ca0.1Cr1−xMxO3−δ (0≤x≤0.1, and M=Al, Co, or Mg), suitable for solid‐oxide fuel cell (SOFC) applications, have been synthesized using an auto‐combustion technique with ammonium dichromate as the chromium source. Owing to very fine crystallite size (ranging from 10 to 50 nm) and the high reactivity of the powders (surface area as high as 25 m2/g), the sintering temperature reduces drastically and a highly dense, uniform, and fine‐grained microstructure is obtained. A dramatic improvement in densification (nearly theoretical density) is observed for aluminum substitution, when sintered at as low a temperature as 1300°C. The microstructure shows a uniform distribution of grains having an average grain size of ∼0.5 μm. Depending on the substituent, the electrical conductivities of the sintered samples in air, at 1000°C, were found to be in the range of 10–45 S/cm, and are more than that of the values required for SOFC application. The thermal expansion coefficients, as obtained, are also comparable with the other SOFC cell components.

Mechanical and electrical properties of Cu–Ta nanocomposites prepared by high-energy ball milling

Cu–Ta bulk nanocomposites with varying amounts of Ta were produced by high-energy ball milling followed by compaction and sintering. The final crystallite size of Cu and Ta during the high-energy ball milling depends on the deformation behavior of the Cu–Ta composite rather than the melting point of the elements. The grain size of the nanocomposites after sintering is less than 100nm. The Cu–Ta nanocomposites showed a superior sintering behavior compared with the microcomposites. The hardness and compressive strength of the Cu–Ta nanocomposites are 3.6–3.8 and 3.6–5 times higher than that of the microcomposites, respectively. The electrical resistivity of the nanocomposites is slightly higher than that of the microcomposites. However, the normalized hardness to resistivity ratio of the nanocomposites is higher than that of the microcomposites, which signifies that it is the increase in hardness rather than in resistivity that is predominant. A major contribution to the strength of the nanocomposite comes from the nanocrystalline grain size of Cu, in accordance with the Hall–Petch relation.

Structural and magnetic properties of mechanically milled Y 1− xPr xCo 5 compounds [ x = 0, 0.1, 0.3, 0.5

Samples of composition Y 1− x Pr x Co 5 ( x = 0, 0.1, 0.3, 0.5) were arc melted in an argon atmosphere, mechanically milled for various times and heat treated at about 1073 K for short periods of time, in order to obtain nanocrystalline compounds. The X-ray diffraction patterns after the heat treatment indicated a single hexagonal 1:5 phase for each composition. The unit cell parameters varied with Pr content in the Y 1− x Pr x Co 5 series. The crystallite size determined from transmission electron micrographs was about 13 nm. The intrinsic coercivity increased with Pr content; a maximum coercivity of 1.17 MA/m and an enhanced relative remanence magnetization to maximum magnetization ratio σ r/ σ max = 0.71 were achieved after heat treatment for the composition Y 0.5Pr 0.5Co 5. The enhanced magnetic properties suggest strong intergranular exchange coupling in this composition, consistent with the very fine crystallite size.

Effect of process parameters on the production of nanocrystalline silicon carbide from water glass

Nanocrystalline silicon carbide was synthesized from the precursor prepared by spray drying slurry of water glass and carbon black. The effect of process parameters, such as reaction temperature, reaction time and carbon content, on phase evolution, crystallite size and specific surface of the resulting samples were characterized by XRD, SEM and BET. The results show the powder produced in this process has a very fine crystallite size and high specific area and the reaction can be completed at 1550 °C for 2 h when the C/Si ratio is 5 or larger. In addition, the powder is of high purity, because sodium oxide in the precursor can be eliminated by the escape of sodium at high temperature. It is a simple and cost-efficient method to synthesize nanocrystalline silicon carbide using cheap and abundant water glass as silicon source.

On the electrochemical behavior of LiM XFe 1 − XPO 4 [M = Cu, Sn; X = 0.02] anodes – An approach to enhance the anode performance of LiFePO 4 material

An attempt, for the first time, has been made to explore the possible electrochemical activity of partially substituted LiFePO 4 as negative electrode for lithium battery applications. In this regard, cationic substitution of Cu and Sn to the native LiFePO 4/C electroactive material has been made individually via. ball milling treatment. This simple procedure has resulted in the formation of metal substituted LiFePO 4 powders of phase pure nature and finer crystallite size (<1 μm) with better distribution of particles. Herein, 2% of metals such as Cu (transition) and Sn (non-transition) were chosen as dopants with a view to understand the effect of transition and non-transition metals upon LiFePO 4 individually. It is interesting to note that irrespective of the nature of the dopant metal, the simple route of cationic substitution via. ball milling endowed with improved conductivity of LiFePO 4, as evidenced by the augmented reversible specific capacity values of substituted LiFePO 4 anodes. In other words, the LiCu 0.02Fe 0.98PO 4/C anode delivered a reversible capacity of ∼380 mAh/g with an enhancement in the capacity retention behavior and excellent coulumbic efficiency value compared to that of LiFePO 4. In contrast, LiSn 0.02Fe 0.98PO 4/C anode displayed an appreciable reversible capacity of ∼400 mAh/g with a significant steady discharge profile. Results of Fourier Transform Infra Red (FTIR) spectroscopy and Cyclic Voltammetric studies of LiM X Fe 1 − X PO 4 (M = Cu, Sn)/C composites are also appended and correlated suitably.

Crystallite size refinement in elemental species under mechanical processing conditions

A systematic study of the crystallite size refinement process of elemental species under mechanical processing conditions has been carried out. Elemental powders were treated in a milling device at different intensities. The dependence of the rate of size reduction as well as of the final crystallite size attained on both impact energy and collision frequency was thus investigated. The final crystallite size shows only a weak dependence on the average impact energy. Conversely, the latter greatly affects the rate of crystallite size decrease. A threshold impact energy is also observed below which no significant structural refinement occurs. The threshold energy is found to scale with the shear modulus of the chemical species.

Thermodynamic properties and absorption–desorption kinetics of Mg 87Ni 10Al 3 alloy synthesised by reactive ball milling under H 2 atmosphere

In this work, the synthesis of Mg 87Ni 10Al 3 hydride by reactive ball milling under H 2 atmosphere is presented. Reactive milling under hydrogen induces the conversion of Mg into nanocrystalline MgH 2 (final crystallite sizes ∼ 8 nm). The percentage of the hydride increases with the milling time and after 20 h of mechanical treatment the reaction is complete. Only at longer milling time, when a high conversion degree of Mg into the hydride is reached, the reaction with Ni to form Mg 2NiH 4 is observed. Thermal analysis shows that, for the shorter milling time, the decomposition of the hydride starts at ∼ 200 ° C, but the stability of the hydride slightly increases with increasing milling time. Fast absorption–desorption kinetics is obtained at 300 ° C.

Spark-plasma sintering the 8-mol% yttria-stabilized zirconia electrolyte

The 8-mol% yttria-stabilized zirconia (YSZ) is a widely chosen electrolyte for solid oxide fuel cells (SOFC) and oxygen sensors because of its excellent hightemperature ionic conductivity [1–4]. The ionic conductivity and mechanical strength of the electrolyte are strongly related to the microstructure of the electrolyte [5]. Gibson et al. [6] investigated the relationship between YSZ sample density and its corresponding ionic conductivity. Tomonari Takeuchi et al. [7] reported that different sintering methods of the electrolyte could get distinct microstructure and induce variety of the ionic conductivity of the electrolyte. Spark plasma sintering (SPS) method enables the manufacture of dense materials in a short period at low sintering temperatures compared with current methods. SPS method is a manufacturing technology for materials, which utilizes the high energy of a high temperature plasma (discharge plasma) generated when pulseformed electric energy is applied to the space among fine particles [8]. SPS has been employed to study alloys [9], functionally gradient materials [10, 11] and several ceramics such as SiC [12], ZrO2 [13], Al2O3 [14], Zr2O/Al2O3 [15] and TiC/Al2O3 [16]. However, for SPS sintered ZrO2 ceramics, the past research was interesting mainly for its microstructural and mechanical properties, In this article, the electrical properties of the 8-mol% YSZ sintered by SPS was studied in comparison to conventional sintering. Commercial 8-mol% YSZ powder (TZ-8YS, Tosoh Corp., Tokyo, Japan) with an average particle size of ca. 0.1 μm was used as starting material. The YSZ powder was sintered to disks by SPS with Dr. Sinter LAB 515 System (Sumitomo Coal Mining, Kanagawa, Japan) or by conventional sintering in air. For SPS, the following sintering steps were taken: YSZ powder (∼2 g) was placed in a graphite die (15 mmφ), and the SPS system was evacuated to 5 Pa and uniaxial pressure of 28 Mpa was applied. During theses procedures, the sintering temperature was increased to 1350 ◦C at a rate of ca.160 ◦C min−1 and maintained at 1350 ◦C for 10 min. Then the sample was cooled to room temperature naturally (SPS pellet). The SPS pellet were annealed in air at 1000 ◦C for 2 hrs to remove carbon contamination. For conventional sintering (CS), the green pellet with a dimension of 15 mm in diameter and approximately 4 mm in thickness was formed by die compaction at similar uniaxial pressure of 140 MPa to ensure the comparable green density. The pellets were then sintered at 1450 ◦C for 4 hrs by electrical resistance furnace and cooled to room temperature naturally (CS pellet). The sintered densities of the samples were obtained using the conventional Archimedes technique and a digital micrometer measuring the exact diameters and thickness. The Jeol JSM-5900LV (Jeol Pte Ltd., Tokyo, Japan) scanning electron microscope (SEM) and X’Pert Pro MPD X-ray Diffraction System (Philips, Netherlands) were employed to study the microstructural characteristics of the sintered samples. The sintered electrolytes were coated with platinum paste on both sides as electrodes and fired at 1200 ◦C for 2 hrs. The ionic conductivity of the sintered samples was measured by AC impedance analyzer (HP4194A, USA). The measuring frequency range is from 100 Hz to 1 MHz with an applied voltage of 100 mV. Measurements were carried out between 300–850 ◦C at an increment 50 ◦C. The relative density of the SPS pellet and CS pellet are 99 and 97% respectively. The XRD patterns for the SPS pellet and CS pellet as shown in Fig. 1, indicated a cubic unit cell (Fm3m). Using the value of full width at half maximum (FWHM) of the peak (111). The calculated finer crystallite size of the SPS pellet is 154 nm and that of the CS pellet is more than 1 μm. Fig. 2 shows SEM micrographs of the surface of the SPS pellet and CS pellet, and shows that the average grain size of SPS is 0.8 μm and they are in close contact with each other. In contrast to the SPS pellet, the grain size of the CS pellet increased to more than 3 μm, as reported previously for dense 8YSZ ceramics sintered by conventional heating [17].

Electrical property of 8-mol% yttria-stabilized zirco-nia electrolyte by spark-plasma sintering

Spark-plasma sintering (SPS) process was used to sinter ZrO2 (8Y) powders, and a relative density of 99% has been reached at a low temperature (1350°C) and short dwelling time (10 min) compared to the conventional sintered identical samples (1450°C 4 h)(CS). By the X-ray diffraction (XRD) patterns, the microstructure of the SPS pellet and CS pellet are both indexed by the cubic unit cell (Fm3m). The finer crystallite size (D111) of the SPS pellet is 154 nm and D111 of the CS pellet is more than 1 μm. The AC impedance spectroscopy shows that the ionic conductivity of SPS pellet is different from that of CS pellet. The activation energy for the SPS ceramics, estimated from the slope in the range of 400–800°C, was 91 kJ mol−1, which is in good agreement with CS pellet (96 kJ mol−1), indicating that the conduction mechanism in SPS ceramics is similar to that in CS ceramics.

Enhanced magnetoresistance in Sr2FeMoO6 by combustion synthesis

A novel method of producing magnetoresistive oxides is described, which involves low temperature combustion synthesis from a mixture of nitrates and fuel, as applied to Sr2FeMoO6. The method yields ceramics with a fine crystallite size of 100–200 nm and a room temperature resistivity of 200 µΩ m. Low field magnetoresistance (6.5% in 0.1 T) is enhanced dramatically compared to samples prepared by conventional solid-state reaction due to the efficient intergrain tunnelling arising from the high density of grain boundaries. Magnetoresistance in low fields is essentially independent of temperature from 5–300 K, and it persists up to 350 K, providing the prospect of sensor applications in an extended temperature range.

Plastic forming and microstructural development of α-alumina ceramics from highly compacted green bodies using extrusion

Abstract High density (>99% TD) and microstructurally controlled α-alumina ceramics were produced from seeded nano-size boehmite (γ-AlOOH) sols with a very fine crystallite size (2–3 nm). A totally wet processing technique comprising vacuum filtering and pressure filtration (PF) was applied in order to increase the solids-loading of the sol and hence form an extrudable paste suitable for plastic forming using extrusion. High packing densities (>68% TD in the green state) are achieved by PF starting from the slurry state resulting in the formation of a consolidated paste which is further consolidated by extrusion. This combined processing technique was successfully applied, in an attempt to reduce the γ-Al2O3 formation temperature, and hence lower the θ- to α-Al2O3 transition temperature. The microstructure of dense α-Al2O3 bodies derived from seeded boehmite sol contains very fine (250 nm) alumina grains after sintering at 1200 °C for 2 h. Although the DTA evidence points to a θ- to α-Al2O3 transition temperature of 1208 °C for a seeded (with 30 nm TiO2) sample, X-ray analysis indicates that a seeded, pressure filtrated and extruded sample is transformed to α-Al2O3 phase after sintering at 1100 °C for 2 h.

Crystallite growth of nanocrystalline transition metals studied in situ by high temperature synchrotron X-ray diffraction

The thermal stability of nanocrystalline iron; Palladium and oxygen-doped nickel was investigated in situ by synchrotron X-ray diffraction. Synchrotron experiments allow the determination of crystallites up to the μm-range and the high flux of the synchrotron source enables in situ experiments with very high time resolution. For the normal crystallite growth of nanocrystalline iron we found two different growth regimes. At low temperatures (663 < T < 739) the activation energy of the growth rate constant is about 100 kJ/mol whereas 173 kJ/mol can be determined for higher temperatures (T > 739K). Our advanced X-ray technique allows also the detection of a bimodal crystallite size distribution. The crystallite growth of nanocrystalline palladium shows above 628 K an anomalous behaviour. Nanocrystalline nickel can be stabilized by the pulse-reverse electrodeposition technique due to co-deposition of oxygen in the grain boundaries. The effect of nickel oxide on the thermal stability of n-Nickel was studied using samples with oxygen contents between 956 and 6039 wt.-ppm. At 873 K samples with a low oxygen content grow immediately up to the μm-range; Samples with 2000 ppm oxygen can be stabilized at final crystallite sizes of about 100 nm whereas n-nickel with the highest oxygen concentration even after several hours exhibits a constant crystallite size of only 40 nm.

Mechanical alloying during cryomilling of a 5000 Al alloy/AlN powder: the effect of contamination

Elemental powders of 80 vol% 5000 Al alloy (3 wt% Mg) and 20 vol% AlN were milled either in liquid nitrogen or at room temperature under argon. The milling of the mixture involved changes in the chemical composition: Fe contamination, oxidation and in-situ nitridation. The effects of milling time and temperature on the contamination of the system were analysed. Oxidation and in-situ nitridation were characterized by a LECO analyser and thermal desorption measurements, whereas Mössbauer spectroscopy was used to study the mechanical alloying of the Al alloy. The results show that a metastable solid solution of Mg and Fe in Al is formed during cryomilling. The occurrence of mechanical alloying in spite of the very low milling temperature is interpreted as a consequence of the fine crystallite size of the Al matrix.