Crystal Rod Research Articles

Thermal stress and local crystallization parameters in single-crystal rods of Ni-Mn-Ga ferromagnetic shape memory alloys

Abstract Ni-Mn-Ga single crystal material shows a strong magnetic shape memory (MSM) effect with reversible strains of up to 12%. Single crystal rods of up to 40 mm diameter are produced in Bridgman type processes. For actuator applications small sticks are cut out of the rods. The magneto-mechanical performance of these sticks depends among other parameters on their alignment with the crystal lattice. Thus, each inhomogeneity of lattice orientation within the rod reduces the achievable yield. The lattice orientation within the single crystal rods usually differs slightly between bottom and top region, and it shows local scattering due to misorientations between the growing dendrites. In the present study the macroscopic thermal stresses induced during the crystallization process are simulated. It is found that these stresses do not affect the crystal orientation. However, they may lead to shape changes of the single crystal rod.

区熔法拉制硅单晶中多晶棒化刺工艺探讨

区熔法拉制硅单晶中多晶棒化刺工艺探讨

Porous niobia spheres with large surface area: alcothermal synthesis and controlling of their composition and phase transition behaviour.

Submicron-sized niobia (Nb2O5) porous spheres with a high specific surface area (300 m2 g−1) and nano concave–convex surfaces were synthesized via a rapid one-pot single-step alcothermal reaction. Prolonged reaction time or high reaction temperatures resulted in a morphology change of Nb2O5 from amorphous sphere to rod crystals with hexagonal crystal phase. A similar alcothermal reaction yielded TiO2–Nb2O5 composite porous spheres, whose Ti : Nb molar ratio was controlled by changing the precursor solution component ratios. A simple thermal treatment of amorphous TiO2–Nb2O5 porous spheres consisting of 1 : 2 (molar ratio) Ti : Nb at 600 °C for 2 h induced crystal phase transfer from amorphous to a monoclinic crystal phase of submicron-sized TiNb2O7 porous spheres with a specific surface area of 50 m2 g−1.

Tailoring structural features and functions of fullerene rod crystals by a ferrocene-modified fullerene derivative

Effective functional intercalation and facile structural manipulation of fullerene crystals could be achieved by ferrocene-modified fullerene based on the liquid–liquid interfacial precipitation process.

Blocking of dislocation propagation by faceted solid liquid interface during Ge crystal growth by the low thermal gradient Czochralski technique

• Study of initial stage of Ge crystal growth by Low Thermal Gradient Cz technique. • Ge crystal growth in 〈1 1 1〉 with faceted interface blocks dislocation propagation. • Ge crystal growth in 〈1 0 0〉 with rounded interface provides low dislocation density. The initial stage of germanium crystal growth by the low thermal gradient Czochralski technique of pulling from the melt (LTG CZ) has been studied in a series of experiments, in which the processes have been interrupted after pulling 6 mm in dia., 70–80 mm in length crystal rod and then up to 20 mm long a cone part. The axial gradients estimated from computer modelling were 2–2.5 K/cm. Crystals pulled in 〈1 1 1〉 direction with totally faceted interface were dislocation-free if facet formation was not disturbed. Crystals pulled along 〈1 0 0〉 under identical conditions, had rounded interface due to thermal roughens of (1 0 0) faces. In that case, the dislocation density was low, but not below ~10 2 cm −2 .

Effect of oxalic acid-leaching levels on structure, color and physico-chemical features of palygorskite

Palygorskite (Pal) was treated with organic acids to explore effects of acid-leaching levels on its structure, shape of rod crystals, color and physico-chemical features. The leaching behavior of octahedral cations of Pal was studied by evaluating the effect of organic acid types, concentration and reaction time. The results show that oxalic acid (OA) has the strongest ability to leach octahedral metal cations in selected organic acids. OA, having acidity, complexing ability and reduction ability, can be attached to the surface of Pal to promote the leaching reaction, and the position at which the reaction occurs is concentrated on the cylinder surface of the rod crystal. The occupied position of metal cations in the octahedral sheets is the key factor in controlling the leaching of Pal. Mg2+ ions at the edge of the octahedral sheet prefer to leach out, then gradually deepens into the interior octahedral sheet, and Fe3+ and Al3+ ions are leached in turn. When the metal cations are almost completely leached, it means that the octahedral sheets are almost eliminated, at this time, the stacked structure is maintained by the deformed tetrahedron. Compared to conventional inorganic acid leaching methods, organic acid leaching does not destroy the shape of the Pal nanorods. Finally, the one-dimensional amorphous silica nanorods with high SiO2 content of 91.68 wt%, decent rod length, large specific surface area (323 m2/g), high porosity and high whiteness (L* = 86.6, a* = 0.1, b* = 3.2) were obtained by leaching with 1 M OA solution for 120 h, indicating that the non-destructive dissolution of the Pal was achieved.

The hidden structure of human enamel

Enamel is the hardest and most resilient tissue in the human body. Enamel includes morphologically aligned, parallel, ∼50 nm wide, microns-long nanocrystals, bundled either into 5-μm-wide rods or their space-filling interrod. The orientation of enamel crystals, however, is poorly understood. Here we show that the crystalline c-axes are homogenously oriented in interrod crystals across most of the enamel layer thickness. Within each rod crystals are not co-oriented with one another or with the long axis of the rod, as previously assumed: the c-axes of adjacent nanocrystals are most frequently mis-oriented by 1°–30°, and this orientation within each rod gradually changes, with an overall angle spread that is never zero, but varies between 30°–90° within one rod. Molecular dynamics simulations demonstrate that the observed mis-orientations of adjacent crystals induce crack deflection. This toughening mechanism contributes to the unique resilience of enamel, which lasts a lifetime under extreme physical and chemical challenges.

Preparation and Characterization of Chromium Metal Organic Framework for Carbon Dioxide Adsorption

Air pollution is a widely discussed topic in both academic and industry sectors, especially in the developing countries. According to the risk assessment report from the Global Burden of Disease Study conducted in 2010, air pollution had caused 6.85 million deaths globally and out of 4.3 million from these numbers is attributed by the indoor air pollution. Government regulatory bodies in most of the countries impose strict regulatory on the CO2 limit in the indoor air condition. CO2 is captured by several methods such as solvent adsorption, physical adsorption, cryogenic fractionation and membrane system. Recently, metal organic frameworks (MOF) such as MIL-100(Cr) have been identified as attractive material for CO2 adsorption as it requires low energy consumption and relatively moderate production volume, if compared to the conventional gas adsorption techniques. These advantages have spurred much interest from industries and academics to speed up the commercial viability of the CO2adsorption by MOF. In this work, the effect of metal oxide loading on the CO2 absorption by chromium (III) chloride hexahydrate and trimesic acid were investigate. The fabricated MOF were characterized using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) to observe its surface morphology and composition. The SEM morphology suggested that Cr-TA-3 possesses highest surface area to volume ratio attributed to the formation of agglomerate of crystal rod structure. In this paper, CO2 gas adsorption was carried bythemogravimetricanalyzer (TGA). The gas adsorption result indicated Cr-TA-3 recorded the highest CO2 adsorption at 0.038 mmol/g. The results obtained from this study suggested that MOF fabricated by chromium (III) chloride hexahydrate and trimesic acid possesses the potential to be applied in CO2 absorption.

Solvent-mediated phase transformation of C60 crystals with well-defined hexagonal shape

CCl4-solvated C60 crystals with hexagonal shape were grown by the liquid-liquid interfacial precipitation method with CCl4 and toluene as poor and good solvents, respectively. Interestingly, the morphology of the hexagonal crystals with the growth liquid are drastically changed with drying in air. A lot of fine rod crystals appear over the original crystals with air-drying, whereas the hexagonal outline of the original crystals is kept even after the transformation. Such change in the morphology is explained by the solvent-mediated phase transformation due to the dissolution of the original crystals by toluene and then re-precipitation of the rod crystals.

CLAYEY SOIL TREATED BY CEMENT AND QUICKLIME BY MICROSTRUCTURE: A MINERALOGICAL ANALYSIS

Soft clayey soil was treated by a combination of cement (PC) and Quicklime (LQ) in order to modify and stability. This study shows an improvement of clay soil brought from Garma Ali site in the Al Basra governorate, Iraq. The PC was added in percentages of 0, 2, 4, 6, 8, and 10%, and LQ was added to 2 and 4%, of dry weight. Also, this research used Microstructure Analysis by Scanning Electron Microscope (SEM) testing and Mineralogical Analysis by X-Ray Diffraction (XRD) testing on the examination soil treated with mix between cement (PC) and Quicklime (LQ) for the purpose of knowing the reasons for the increase in the shear strength and decrease maximum dry density. Through the micrographs that result from the scanning electron microscoping and the curves of X-ray that demonstrate presentence, the formation of the hydration reaction product (CSH gel) shows tiny bristle (rod) crystals. The CSH gel and the tiny bristle (rod) crystals worked on coating and contact the particles together. The micrographs for soils treated with (2% LQ + 10% PC) show an increase in the amount hydrated gel (CSH) compared to the soil treated with 6% PC and 2% LQ and 8% PC and 4% LQ, but the number of bristle-like crystals decreases compared to soil treated by 8% PC and 4% LQ.

Formation of MgCO3·3H2O in the CO2 mineralization system using Mg(OH)2 as an intermediate at 20 °C

The formation of MgCO3·3H2O in the CO2 mineralization system was investigated using Mg(OH)2 as an intermediate at 20 °C. Liquid and solid analyses were done for qualitative and quantitative composition characterizations of the reacted samples. Results showed that the morphology of Mg(OH)2 had an obvious effect on the growth rate, size and morphology of MgCO3·3H2O. The formation of MgCO3·3H2O might be explained by the dissolution–recrystallization mechanism. Larger bundle-like MgCO3·3H2O which composed of middle-binding rod crystals was obtained from the plate-like Mg(OH)2. These findings could pave the way for controllable crystallization of MgCO3·3H2O in a CO2 mineralization system.

A modified formula of thermal focal length for lamp pumping Cr, Er:YSGG crystal with high performance 2.79 μm laser

We demonstrate the laser and thermal properties on the four Cr,Er:YSGG crystal rods with different diameters from 3 to 6 mm. A maximum pulse energy 1261 mJ operated at 5 Hz and 2.79 μm is obtained on the rod of 4 mm diameter, corresponding to electrical-to-optical efficiency of 1.53% and slope efficiency 1.82%, respectively. Combining with the electrical-to-optical efficiency and thermal distribution, the formula of the thermal focal length is modified further. The simulation results of the thermal focal length for four crystals with different diameters are in good consistence with the measurement values, suggesting the revised formula is accurate and effective to calculate the thermal focal length.

The characteristics of high-quality Yb:YAG single crystal fibers grown by a LHPG method and the effects of their discoloration.

Single crystal fibers (SCFs), especially ytterbium (Yb) doped crystal fibers, have great potential in the field of high-power lasers. Colorless Yb:YAG single crystal fibers were fabricated using a laser heated pedestal growth (LHPG) method with a diameter fluctuation of less than 2% and a length to diameter ratio greater than 320 : 1. An abnormal color issue exists with respect to Yb:YAG crystals. The origin of coloration was studied via density functional theory, single-crystal X-ray diffraction, XPS and Raman spectroscopy and it was confirmed that the cyan coloration of Yb:YAG crystals is due to oxygen vacancies. Yb:YAG SCFs prepared via the LHPG method could avoid this type of defect due to the large specific surface area and melt convection caused by surface tension. The fundamental properties of the cyan Yb:YAG crystal source rod and colorless Yb:YAG SCFs were systematically investigated. The colorless Yb:YAG SCFs have higher infrared transmittance and thermal conductivity. The distributions of Yb3+ along the radial and axial directions were also measured. Meanwhile we demonstrated the propagation loss and a fiber laser using the colorless Yb:YAG SCFs, obtaining a minimum loss coefficient of 0.008 dB cm−1 and a maximum continuous-wave (CW) output power of 3.62 W. The colorless Yb:YAG SCFs with good thermal conductivity, low propagation loss, wide transparency and uniform ion distribution show promise for acting as the host material in single-mode lasers.

3D defective graphenes with subnanometric porosity obtained by soft-templating following zeolite procedures.

By applying the well-known templating mechanism employed for the synthesis of mesoporous silicas to the structuration of sodium alginate, a novel defective 3D tubular graphene material (graphenolite) with hierarchical macro/meso/micro-porous structure, very high powder specific surface area (1820 m2 g−1) and regular micropore size (0.6 nm) has been obtained. The key feature of the process is the filmogenic property of alginate that is able to replicate the liquid crystal rods formed by the CTAC template in the aqueous phase. The 3D graphene exhibits 2.5 times higher capacitance using Li+ electrolyte compared to K+, indicating that Li+ can ingress to the ultramicropores which, in contrast, are not accessible to K+. Electrochemical impedance measurements also indicate much lower resistance for Li+ in comparison to K+ electrolyte, confirming the benefits of controlled microporosity of 3D graphene granting selective access to Li+, but not to K+. The present report opens the door for the synthesis of a wide range of 3D graphene materials that could be prepared following similar strategies to those employed for the preparation of zeolites and periodic mesoporous aluminosilicates.

Seed orientation and pulling rate effects on bubbles and strain distribution on a sapphire crystal grown by the micro-pulling down method

Undoped sapphire rod crystals along different crystallographic orientations (a [112̄0], m [101̄0], c [0001] and c [0001] shifted 30° off axis) were successfully grown by the micro-pulling down (μ-PD) method.

Compact 20 W femtosecond laser system based on fiber laser seeder, Yb:YAG rod amplifier and chirped volume Bragg grating compressor.

In this work we presented a compact femtosecond laser system based on Yb doped fiber seed laser and efficient Yb:YAG crystal rod power amplifier. Matched pair of chirped fiber Bragg grating stretcher and chirped volume Bragg grating compressor were used to obtain high fidelity - Strehl ratio 76%, pulses of 764 fs duration, 104 µJ energy at 200 kHz repetition rate at the output of the laser system.

Non-isothermal crystallization kinetics of waxy crude oil

The crystallization behavior of Shengli waxy crude oil from the sol state to gel state was studied by the microscopic observation and DSC curve. The study shows that as the cooling rate decreases, the number of wax grains becomes smaller, the area is larger and the morphology of wax crystals is more irregular. Moreover, under different cooling rates, wax crystals were homogeneous transient nucleation, but the growth mode of wax crystals was different. When the cooling rate is between 1–4 °C/min, Crystallization Peak 1 wax crystal grows according to the mixed crystal mode of one-dimensional rod crystal and two-dimensional discoid crystal; When the cooling rate is between 6–8 °C/min, Crystallization Peak 1 wax crystal grows according to the mixed crystal mode of two dimensional discoid crystal and three-dimensional spherical crystal; Crystallization Peak 2 wax crystal grows according to the mixed crystal mode of two dimensional discoid crystal and three-dimensional spherical crystal at different cooling rates. Crystallization activation energy of crystallization Peak 1 and Peak 2 are 556.91 kJ/mol and 299.62 kJ/mol, respectively.

High-throughput growth of SmxPr1-xFeO3 all-in-one single crystal rod with quasi-continuous composition distribution

SmxPr1-xFeO3 (x = 0, 0.4, 0.7, 0.9, 1.0) all-in-one single crystal rod with quasi-continuous composition distribution was successfully grown by a hetero-seed and hetero-feed optical floating zone technique in flowing air. The lattice mismatch between each adjacent composition is very small, leading to the high-quality continuous growth of SmxPr1-xFeO3 single crystal rod. X-ray back-reflection Laue photographs indicate that all single crystals at different positions along the growth direction have good crystallization quality and the same crystallographic axis. The composition change of the quasi-continuous single crystals along growth direction was analyzed by energy-dispersive X-ray spectroscopy (EDS), which shows that the composition varies continuously and smoothly near the different composition boundaries. At a distance relatively far away from the boundary, the composition remains constant. Finally, we measured the anisotropic magnetic properties of these single crystals when x = 0.7. Our study shows that the hetero-seed and hetero-feed optical floating zone technique has a great potential for high-throughput growth of crystalline materials, and could serve as an effective method to collect single crystal material properties in materials database research.

Observation of two-times self-focusing of femtosecond laser beam in ZnO crystal by two-photon luminescence

By “seeing” the green two-photon luminescence, two separate focusing points are observed on the propagation axis of a converging femtosecond laser beam in a ZnO single crystal rod. It is found that the self-focusing effect makes a significant contribution to the formation of the first focusing point, while the second focusing point is caused by self-refocusing. The position of the first focusing point is in good agreement with the value predicted by a model developed by Chin and his co-workers. These experimental findings could be the unprecedented evidence for the self-focusing and refocusing effect of the femtosecond laser filament propagation in nonlinear media.

A new design of optical add/drop filters and multi-channel filters based on hexagonal PhCRR for WDM systems

In this research, using photonic crystal dielectric rods with a triangular lattice constant, a photonic crystal ring resonator (PhCRR) has been designed in order to be used in optical add/drop filters (ADF).Query Using the proposed hexagonal PhCRR with four different dropping waveguides, new ADFs have been designed and simulated. At a central wavelength of 1550.5 nm, the four proposed ADFs have an average transmission coefficient, a bandwidth, and a quality factor of 100%, 1.2 nm and 1330, respectively. The results obtained from these structures indicate the high flexibility of the proposed PhCRR and ADFs and their applicability in optical communication systems. Using the ADFs, two multi-channel drop filters have been designed in order to be used as optical MUX/DeMUX with a channel spacing of 4 nm which are suitable for wavelength division multiplexing systems. In this study, the plane wave expansion and finite difference time domain methods are, respectively, used, to characterize the photonic band gap and to investigate the optical behavior of the structures.