Quantifying nematic order in evaporation-driven self-assembly of Halloysite nanotubes: Nematic islands and critical aspect ratio

Halloysite nanotubes (HNTs) are naturally occurring clay minerals found in Earth's crust that typically exist in the form of high aspect-ratio nanometers-long rods. Here, we investigate the evaporation-driven self-assembly process of HNTs and show that a highly polydisperse collection of HNTs self-sort into a spatially inhomogeneous structure, displaying a systematic variation in the resulting nematic order. Through detailed quantification using nematic order parameter $S$ and nematic correlation functions, we show the existence of well-defined isotropic-nematic transitions in the emerging structures. We also show that the onset of these transitions gives rise to the formation of nematic islands - phase coexisting ordered nematic domains surrounded by isotropic phase - which grow in size with $S$. Detailed image analysis indicates a strong correlation between local $S$ and the local aspect ratio, $L/D$, with nematic order possible only for rods with $L/D \ge 6.5 \pm 1$. Finally, we conclude that observed phenomena directly result from aspect ratio-based sorting in our system. Altogether, our results provide a unique method of tuning the local microscopic structure in self-assembled HNTs using $L/D$ as an external parameter.Comment: 9 pages, 4 figure

Mid-crustal contact metamorphism around the Chimakurthy mafic-ultramafic complex, Eastern Ghats Belt, India

Pelitic rocks were thermally metamorphosed at the contact of the Chimakurthy mafic-ultramafic igneous complex, Eastern Ghats Belt, India. The rocks show progressive change in mineralogy from biotite-sillimanite-quartz-garnet-K-feldspar (association I, 150 m from the intrusive contact) to garnet-spinel-cordierite-K-feldspar-sillimanite (association II, 20-30m from the intrusive contact) to cordierite-K-feldspar-(cordierite-orthopyroxene-K-feldspar symplectite after osumilite)-spinel-FeTiAl oxides with/without garnet (associations III and IV, 5m from the intrusive contact), and finally to spinel-orthopyroxene-cordierite-K-feldspar (association V, xenoliths). Oxide mineral clots in associations III and IV resemble emery-type rocks. Initial mineral reactions involved biotite-dehydration melting with partial segregation of the melt. Down-temperature mineral reactions were largely diffusion controlled and preservation of symplectitic and coronitic textures in microdomains is common. Interpretation of reaction textures in relevant petrogenetic grids for the sytems KFMASH and FMAS and combined with geothermobarometry suggest that the pelitic rocks were thermally metamorphosed at c. 6 kbar pressure along a heating-cooling trajectory within the temperature interval between c. 750°C and c. 1000°C

Phase Evolution and Microstructural Studies in CaZrTi<SUB>2</SUB>O<SUB>7</SUB>-Nd<SUB>2</SUB>Ti<SUB>2</SUB>O<SUB>7</SUB>System

A series of compositions with general stoichiometry Ca<SUB>1−x</SUB>Zr<SUB>1−x</SUB>Nd<SUB>2x</SUB>Ti<SUB>2</SUB>O<SUB>7</SUB> has been prepared by high-temperature solid-state reaction of component oxides and characterized by powder X-ray diffraction and electron probe for microanalyses (EPMA). The phase fields in CaZrTi<SUB>2</SUB>O<SUB>7</SUB>–Nd<SUB>2</SUB>Ti<SUB>2</SUB>O<SUB>7</SUB> system and distribution of ions in different phases have been determined. Four different phase fields, namely monoclinic zirconolite, cubic perovskite, cubic pyrochlore, and monoclinic Nd<SUB>2</SUB>Ti<SUB>2</SUB>O<SUB>7</SUB> structure types are observed in this system. The 4M-polytype of zirconolite structure is stabilized by substitution of Nd<SUP>3+</SUP> ion. The addition of Nd<SUP>3+</SUP> ions form a cubic perovskite structure-type phase and thus observed in all the compositions with 0.05 ≤ x ≤ 0.80. Cubic pyrochlore structure-type phase is observed as a coexisting phase in the nominal composition with 0.20 ≤ x ≤ 0.90. Only a subtle amounts of Ca<SUP>2+</SUP> and Zr<SUP>4+</SUP> are incorporated into the perovskite-type Nd<SUB>2</SUB>Ti<SUB>2</SUB>O<SUB>7</SUB> structure. EPMA analyses on different coexisting phases revealed that the pyrochlore and perovskite phases have Nd<SUP>3+</SUP>-rich compositions

Assessment of a Novel Chemical Analysis Technique to Investigate Cesium in Glass by Developing Cesium Bismuth Iodide

The present work aims at qualitative investigation of cesium content present in a glass. A glass comprising (wt%) Cs2O(30)-SiO2(35)-Na2O(7)-SnO2(4)-Z nO(24) was prepared in a conventional heating furnace. A novel method was developed adopting gravimetric analysis of cesium content in the glass samples using Dragendorff's reagent, leading to formation of Cs3Bi2I9 crystal (salt). Experimental methods were examined to purify the salt. Qualitative analysis was performed on Cs3Bi2I9 crystal with FESEM-EDX and XRD. Up to & SIM;93% pure Cs3Bi2I9 could be synthesized. Quantitative studies were performed with standard cesium solution prepared with Cs2CO3 with varying compositions of cesium within 1000 to 3000 ppm. Weight of salt produced was concluded to be strongly related to the cesium content present in the glass solution

Development of graded Ni-YSZ composite coating on Alloy 690 by Pulsed Laser Deposition technique to reduce hazardous metallic nuclear waste inventory

Alloy 690 based 'nuclear waste vitrification furnace' components degrade prematurely due to molten glass-alloy interactions at high temperatures and thereby increase the volume of metallic nuclear waste. In order to reduce the waste inventory, compositionally graded Ni-YSZ (Y<SUB>2</SUB>O<SUB>3</SUB> stabilized ZrO<SUB>2</SUB>) composite coating has been developed on Alloy 690 using Pulsed Laser Deposition technique. Five different thin-films starting with Ni80YSZ20 (Ni 80 wt% + YSZ 20 wt%), through Ni60YSZ40 (Ni 60 wt% + YSZ 40 wt%), Ni40YSZ60 (Ni 40 wt% + YSZ 60 wt%), Ni20YSZ80 (Ni 20 wt% + YSZ 80 wt%) and Ni0YSZ100 (Ni 0 wt% + YSZ 100 wt%), were deposited successively on Alloy 690 coupons. Detailed analyses of the thin-films identify them as homogeneous, uniform, pore free and crystalline in nature. A comparative study of coated and uncoated Alloy 690 coupons, exposed to sodium borosilicate melt at 1000 °C for 1-6 h suggests that the graded composite coating could substantially reduced the chemical interactions between Alloy 690 and borosilicate melt

Role of sulfate in structural modifications of sodium barium borosilicate glasses developed for nuclear waste immobilization

A sodium barium borosilicate glass matrix with a higher solubility of sulfate has been developed recently at Bhabha Atomic Research Centre for vitrification of sulfate bearing high-level nuclear waste. We report here the studies carried out to understand the influence of sulfate ion on the three-dimensional borosilicate network. Experiments were carried out with sodium barium borosilicate base glass samples loaded with varying amounts of SO<SUB>4</SUB><SUP>2-</SUP> (0–5 mol%). Phase separation studies on the samples revealed that as much as 3 mol% of SO<SUB>4</SUB><SUP>2-</SUP> can be loaded within the base glass without any phase separation, however, beyond this limit BaSO<SUB>4</SUB> (barite) crystallizes within the matrix. Thermal analyses of the samples indicated a shift in glass transition temperature from 534° (0 mol% SO<SUB>4</SUB><SUP>2-</SUP>) to 495°C (3 mol% SO<SUB>4</SUB><SUP>2-</SUP>) and it remained more or less unaltered afterwards even with high SO<SUB>4</SUB><SUP>2-</SUP> loading. A similar observation of structure stabilization was obtained from <SUP>29</SUP>Si MAS–NMR studies also, which showed that with 2 mol% of SO<SUB>4</SUB><SUP>2-</SUP> loading, the Q<SUP>2</SUP>:Q<SUP>3</SUP> ratio changed from 59:41 (for samples with 0 mol% SO<SUB>4</SUB><SUP>2-</SUP> loading) to 62:38 and it remained almost the same afterwards even with higher SO<SUB>4</SUB><SUP>2-</SUP> loading. 11B MAS NMR patterns of the glass samples, however, remained unchanged with SO<SUB>4</SUB><SUP>2-</SUP> loading ([BO<SUB>4</SUB>]:[BO<SUB>3</SUB>]=38:62). Based on <SUP>29</SUP>Si and 11B MAS NMR studies, the authors propose two different ways of interaction of SO<SUB>4</SUB><SUP>2-</SUP> ions with the borosilicate network: (i) the network modifying action of SO<SUB>4</SUB><SUP>2-</SUP> ions with -Si–O–Si- linkages, at low SO<SUB>4</SUB><SUP>2-</SUP> ion concentration (&#60;2 mol%) and (ii) the preferential interaction of SO<SUB>4</SUB><SUP>2-</SUP> with the Ba<SUP>2+</SUP> ions at high SO<SUB>4</SUB><SUP>2-</SUP> concentration (>2 mol%)

Metallurgical characterizations of Fe-Cr-Ni-Zr base alloys developed for geological disposal of radioactive hulls

Alloy melting route is currently being considered for radioactive hulls immobilization. Towards this, wide range of alloys, belonging to Zirconium-Iron binary and Zirconium-Stainless steel pseudo-binary systems have been prepared through vacuum arc melting route. Detail microstructural characterization and quantitative phase analyses of these alloys along with interaction study between Zirconium and Stainless steel coupons at elevated temperatures identify Zr(Fe,Cr)<SUB>2</SUB>, Zr(Fe,Cr), Zr<SUB>2</SUB>(Fe,Cr), Zr<SUB>3</SUB>(Fe,Ni), Zr<SUB>3</SUB>(Fe,Cr), Zr<SUB>3</SUB>(Fe,Cr,Ni), β -Zr and a-Zr as the most commonly occurring phases within the system for Zirconium rich bulk compositions. Nano-indentation studies found Zr(Fe,Cr)<SUB>2</SUB> and Zr(Fe,Cr) as extremely hard, Zr<SUB>3</SUB>(Fe,Ni) as moderately ductile and β-Zr, Zr<SUB>2</SUB>(Fe,Cr) as most ductile ones among the phases present. Steam oxidation studies of the alloys, based on weight gain/loss procedure and microstructural characterization of the mixed oxide layers, suggest that each of the alloys responded to the corrosive environment differently. Fe<SUB>2</SUB>O<SUB>3</SUB>, NiFe<SUB>2</SUB>O<SUB>4</SUB>, NiO, monoclinic ZrO<SUB>2</SUB> and tetragonal ZrO<SUB>2</SUB> are found to be most common constituents of the oxide layers developed on the alloys. Integrating the microstructural, mechanical and corrosion properties, ZrFeCrNi3 (Zr: 84.00, Fe: 11.20, Cr: 3.20, Ni: 1.60, in wt.%) is identified as the acceptable base alloy for disposal of radioactive hulls