High Gravity Field Research Articles

Controlling Nucleation and Fabricating Nanoparticulate Formulation of Sorafenib Using a High-Gravity Rotating Packed Bed

Nucleation is the initial step of the crystallization process and is the significant step to prepare nanometer-sized crystalline materials. In this work, we systematically investigated the nucleation kinetics of poorly water-soluble drug sorafenib when precipitated by liquid antisolvent precipitation in high-gravity rotating packed bed. We found that high-gravity field tremendously promoted the nucleation rate, and the nucleation rate was increased by 2–3 orders of magnitude over that in the stirred tank reactor. Moreover, polymer excipients have a significant impact on nucleation; especially, poly(vinylpyrrolidone) (PVP) could increase the nucleation rate by 3 orders of magnitude over that without excipient. Finally, stable amorphous sorafenib nanoparticulate formulation with a particle size of 80 nm was obtained by controlling nucleation in RPB. Compared to the coarse drug, the nanoparticulate formulation performed faster drug release and had much better cytotoxicity. In vivo pharmacokinetics of the nan...

High Performance Clocks and Gravity Field Determination

Time measured by an ideal clock crucially depends on the gravitational potential and velocity of the clock according to general relativity. Technological advances in manufacturing high-precision atomic clocks have rapidly improved their accuracy and stability over the last decade that approached the level of 10$^{-18}$. Based on a fully relativistic description of the background gravitational physics, we discuss the impact of those highly-precise clocks on the realization of reference frames and time scales used in geodesy. We discuss the current definitions of basic geodetic concepts and come to the conclusion that the advances in clocks and other metrological technologies will soon require the re-definition of time scales or, at least, clarification to ensure their continuity and consistent use in practice. The relative frequency shift between two clocks is directly related to the difference in the values of the gravity potential at the points of clock's localization. According to general relativity the relative accuracy of clocks in 10$^{-18}$ is equivalent to measuring the gravitational red shift effect between two clocks with the height difference amounting to 1 cm. We show how clock measurements can provide geopotential numbers for the realization of gravity-field-related height systems and can resolve discrepancies in classically-determined height systems as well as between national height systems. Another application of clocks is the direct use of observed potential differences for the improved recovery of regional gravity field solutions. Finally, clock measurements for space-borne gravimetry are analyzed along with closely-related deficiencies of this method like an extra-ordinary knowledge of the spacecraft velocity, etc. For all these applications besides the near-future prospects, we also discuss the challenges that are related to using those novel clock data in geodesy.

A novel electro-catalytic degradation method of phenol wastewater with Ti/IrO2-Ta2O5 anodes in high-gravity fields.

In the electro-catalytic degradation process of phenol wastewater, bubbles and mass transfer limitation will result in the decrease in wastewater degradation efficiency, a long electrolysis time and a high energy consumption. Self-made Ti/IrO2-Ta2O5 anodes and a high-gravity electro-catalytic reactor were used to improve them. The Ti/IrO2-Ta2O5 anode was prepared with a thermal decomposition method and characterized by scanning electron microscopy (SEM). Under optimum conditions, the removal efficiencies of phenol, total organic carbon (TOC) and chemical oxygen demand (COD) respectively reached 94.77%, 50.96% and 41.2% after 2 h electrolysis in the high-gravity field, which were respectively 10.93%, 16.72% and 24.84% higher than those in the normal gravity field. For about the same removal efficiencies, the electrolysis time and energy consumed in the high-gravity field were 33.3% and 15.4% lower than those consumed in the normal gravity field, respectively. The degradation pathway of phenol detected by high performance liquid chromatography (HPLC) was unchanged in the high-gravity field, but the degradation rate of phenol increased. The Ti/IrO2-Ta2O5 anode provided good stability because the removal efficiencies of phenol and TOC decreased slightly and the surface morphology of the coating was almost unchanged when it had been used in electrolysis for 11 months, about 1,200 h, in the high-gravity field. Results indicated that the phenol wastewater degradation efficiency was improved, the time was shortened, and the energy consumption was reduced in the high-gravity field.

Preparation of Two-Dimensional Molybdenum Disulfide Nanosheets by High-Gravity Technology

In this paper, a high-gravity technology was described to prepare two-dimensional molybdenum disulfide nanosheets from bulk materials. This high-gravity field, producing by a rotating packed bed, provides shear force and collision force to exfoliate layered bulk molybdenum disulfide into nanosheets. The effects of rotational speed, surfactant concentration, exfoliation time, packing volume fraction, and exfoliation time on the concentration were systematically studied. The results showed that the concentration of the as-prepared suspension could be easily controlled. The concentration is 0.37 mg/mL under optimum conditions. Moreover, the dispersion of two-dimensional molybdenum disulfide nanosheets could be stabile for a long time. The lateral size of as-produced molybdenum disulfide nanosheets ranged from 50 to 800 nm, and the mean lateral size was 380 nm. Almost 84% of nanosheets were less than five layers. We also demonstrated that high-gravity technology also can be applied to tungsten disulfide. This...

High-efficiency mixing process in secondary rotating stream

Primary rotating flow (PRF) and secondary rotating stream (SRS) are two basic rotating flow patterns. We compared their mixing performances via the iodine transfer process from CCl4 to water. When the mixing power consumptions of the SRS mixer and PRF blender were approximated, the maximum value of KαSRS exceeded 71.7s−1. Kα‾SRS was higher than Kα‾PRF 3 orders of magnitude, but the total energy consumption of the SRS mixer was lower than that of the PRF blender 2 orders of magnitude. It was also found that Kα‾SRS increased sharply with the decrease of τ, which is consistent with the typical characteristics of Higee technology. Furthermore, computational fluid dynamics (CFD) was applied to simulate the pressure and flow field distributions of SRS. Based on the analysis of the velocity distribution mappings, it is concluded that SRS spontaneously generates intensive convection and vigorous shear stress under the reversing high-gravity field. The curve of KαSRS versus semi-circle channels is composed of a peak line and a wave line. In theory, we systematically illustrated the reasons for the high efficiency of SRS from four perspectives: time mixing, thermodynamics, momentum and mass transfers, opposite energy flows. Having many advantages and potentials, SRS will be widely explored and applied in chemical engineering field.

Comparison of Satellite Altimetric Gravity and Ship-borne Gravity - Offshore Western Australia

Since 2010 several new satellite altimetry missions have commenced delivering altimetry-derived gravity data with a global offshore coverage and with a quality in many regions nearing that of ship-borne gravity observations. This is resulting in greatly improved global offshore high resolution gravity fields. The DTU13 and Sandwell and Smith’s v23.1 grids of altimetric gravity anomalies from offshore Western Australia are compared with ship-track gravity anomalies computed from the Geoscience Australia marine gravity database. The standard deviation of the difference between the ship-borne gravity data and the satellite altimetric gravity data is 3.1mGal for the DTU13 data and 3.3 mGal for Sandwell and Smith’s v23.1 grid. In water depths less than 20m we observed significant differences between ship-borne gravity and altimetric gravity. Over the sampled wavelengths, the DTU13 altimetric gravity data appears to have the best resemblance to the reference marine gravity data, exhibiting the overall least difference amplitude over most wavelengths.

Polymer micelles as building blocks for layer-by-layer assembly of multilayers under a high-gravity field

Construction of layer-by-layer (LbL) self-assembled multilayers is fundamental to various research fields. But most conventional processes for LbL are time consuming, which restricts its further applications. There has been a general demand for shortening the construction time without affecting the multilayer structures. High-gravity (HG) technique is a well-established chemical engineering process which can strongly intensify mass and heat transfer. In this study, we introduced the HG technique into construction of multilayers through LbL self-assembly concerned with polymer micelles as building blocks. By using a model system of poly(diallyldimethyl ammonium chloride) (PDDA)/polystyrene-poly(acrylic acid) (PS-PAA) polymer micelle multilayers, the LbL process was examined under both conventional dipping conditions and a HG field. Ultraviolet–visible spectra and atomic force microscopy results showed that the time for LbL under a HG field has been shortened 6 times compared with dipping assembly while the resultant multilayers achieved comparable quality as those prepared under conventional dipping LbL.

Crystal Growth and Fracture Behavior of Solidified TiC-TiB<sub>2</sub> Prepared by Combustion Synthesis in High-Gravity Field

Based on the technology of combustion synthesis in high-gravity field, the TiC-TiB2 ceramics with refined microstructures have been fabricated by adjusting the technological parameter and proportioning of raw starting powders. The effects of particle size of raw powders on crystal growth and mechanical properties were studied in this paper. It found that the propagation rate and the combustion temperature can be improved by decreasing the grain size of raw powders, as well as the heat exchange and mass diffusion were enhanced too, so that the microstructure homogenization, densification and mechanical properties of the TiC-TiB2 ceramics were improved accordingly. The highest density, relative density, Vickers hardness and fracture toughness of TiC-TiB2 composites measured 4.07 g/cm3, 87.5%, 22.5 ± 1.2 GPa and 9.5 ± 0.8 MPa·m0.5, respectively, since that the fine B4C powder with particle size < 3.5 µm and the fine Ti powder with particle size < 38 µm were chosed as raw starting powders. The fracture behaviour of TiC-TiB2 composites was dominated by the strong coupled toughening mechanisms of crack deflection and crack-bridging, and the high fracture toughness of the TiC-TiB2 ceramics benefits mainly from the achievement of micro-nanocrystalline microstructure in the full-density solidified ceramic.

Microstructure, Densification and Mechanical Properties of TiB<sub>2</sub>-TiC-NiAl Ceramic-Based Composite

By adjusting mass fraction of Ni-Al composite additive in Ti-B4C primary system, a series of TiB2-based ceramic composites were prepared by combustion synthesis in high gravity field. Because the adiabatic temperature of the whole reaction system maintained a constant in the presence of mass fraction of Ni-Al additive smaller than 18.55%, increasing mass fraction of Ni-Al additive to be 15% brought about the improved homogeneity in refined microstructure of the enhanced-densification TiB2-based composite, so flexural strength and fracture toughness of the ceramic composite increased simultaneously due to the enhanced self-toughening mechanisms contributed by a number of fine TiB2 platelets.

Reaction Fusion and Spatial Span-Scale Microstructure Evolution of TiB<sub>2</sub>-Based Ceramic and Metal Achieved by High Gravity Field

The plates of 1Cr18Ni9Ti stainless steel were selected as metal substrates, and CrO3+Al thermites were introduced into B4C+Ti primary system for enhancing adiabatic temperature of reaction system. By improved processing route, i.e. respectively preparing, ball-milling and compacting B4C+Ti blends and CrO3+Al thermites and subsequently filling them one by one into the crucibles, TiB2ceramic to 1Cr18Ni9Ti graded composites were prepared by reaction joining in high-gravity field. it was found that refined TiB2 platelets were embedded in or around the irregular TiC grains, and Fe-Cr-Ni metallic phases were distributed between TiC and TiB2 phases, and Al2O3 inclusions disappeared completely at the intermediate between TiB2ceramic and 1Cr18Ni9Ti, the thickness of which reached 1.05 mm. The 3D net ceramic-metal composite microstructure (3DNCMCM) existed at the intermediate. The Vickers hardness distribution of the intermediate appeared the parabolic gradient composite feature, and the shear strength of the intermediate reached 325±15 MPa because of the increasing thickness of intermediate, at which 3D net ceramic-metal composite microstructure (3DNCMCM) existed.

Reaction Fusion and 3D-Network Span-Scale Graded Microstructure Evolution in Laminated Composite of TiB2-Based Ceramic and 42CrMo Steel

Based on liquid fusion and atomic interdiffusion of TiB2-based ceramic and 42CrMo steel, the ceramic-metal laminated composites with interfacial 3D-network span-scale graded microstructures were achieved by combustion synthesis in high gravity field. The presence of respective atomic concentration gradient of Ti, B, C, Fe and the others between the ceramic and the steel reasoned for continuously-graded interfacial microstructure in which the TiB2 and TiC phases transform sub-micrometer, micro-nanometer grains from the micrometer ones. The Fe-based liquid flow from the ceramic to the steel substrate resulted in the 3D-network distribution of Fe-based alloy phases from the ceramic to the steel substrate. Hence, interfacial shear fracture presented the mixed mode consisting of intercrystalline fracture along fine TiB2 platelets and ductile fracture in Fe-based alloy phases, presenting interfacial shear strength 415 ± 25 MPa of the laminated composite.

Ceramic-Metal Functionally Gradient Multilayer Composite Fabricated by Combustion Synthesis in High-Gravity Field

By taking combustion synthesis in high-gravity field to achieve fusion bonding of TiB2-based ceramic, Ti-6Al-4V alloy, the mid-ceramic and 42CrMo steel simultaneously, the ceramic-metal FG multilayer composites with the continuously-graded interfacial microstructures were successfully fabricated. XRD, FESEM and EDS results showed the formation of continuously-graded interfacial microstructures among TiB2-based ceramic, Ti-6Al-4V alloy, the mid-ceramic and 42CrMo steel resulted from thermal explosion reaction caused by high gravity field, liquid fusion of the ceramic, Ti-6Al-4V alloy, the mid-ceramic and 42CrMo steel, so hard-by-soft distribution in the hardness of FG multilayer composite was presented, and the interfacial shear strength of TiB2-based ceramic and Ti-6Al-4V alloy, and the mid-ceramic and 42CrMo steel measured 198 ± 25 MPa and 130 ± 15 MPa, respectively.

Spatial Span-Scale Microstructure Evolution and Ballistic Performance of Laminated Functionally Graded Composites of TiB<sub>2</sub>-Based Ceramic and Ti-6Al-4V Alloy

By inducing thermal explosion in high-gravity field to prepare the laminated composite of TiB2-based ceramic and Ti-6Al-4V alloy, spatial span-scale continuously-graded microstructure was achieved in interfacial region between the ceramic and Ti alloy, and the formation of the interfacial microstructure resulted from full-liquid ceramic-metal fusion, atomic interdiffusion and subsequent peritectic reaction of TiB2 primary phases with Ti liquid of graded concentration. By using 14.5 mm AP to conduct DOP test to evaluate ballistic performance of the laminated composite, it was considered that comparing to TiB2-based ceramic, the presence of spatial span-scale continuously-graded microstructure between the ceramic and Ti alloy brought about the enhanced ballistic performance of the laminated composite by 133.0%.

Direct fabrication of highly-dense Cu2ZnSnSe4 bulk materials by combustion synthesis for enhanced thermoelectric properties

Thermoelectric materials are attractive for solar thermal energy conversion and waste heat recovery. The preparation of bulk thermoelectric materials usually involves multi-step processes with considerable time and energy consumption. Here we report an alternative way called combustion synthesis to realize one-step and fast fabrication of bulk Cu2ZnSnSe4 thermoelectric materials. The combustion synthesis was carried out in 2MPa Ar gas atmosphere or in a high-gravity field in order to reduce the porosity in samples and complete simultaneous densification during synthesis. Nearly full-dense Cu2ZnSnSe4 samples with a porosity of <1% were prepared, showing thermoelectric properties similar to those of Cu2ZnSnSe4 materials prepared by other methods. The ZT of the Cu2ZnSnSe4 samples was clearly improved by partial substitution of Sn with In, and reached 0.59 at 773K for the composition of Cu2ZnSn0.9In0.1Se4. Compared with the conventional melt growth and powder sintering methods, combustion synthesis offers a fast, one-step, and furnace-free way for directly producing bulk Cu2ZnSnSe4 samples, which may open up new possibilities for synthesis and applications of Cu2ZnSnSe4-based thermoelectric materials.

Combustion Synthesis of TiB2-TiC/42CrMo4 Composites with Gradient Joint Prepared in Different High-Gravity Fields

The novel TiB2-TiC/42CrMo4-laminated composite materials were successfully fabricated by combustion synthesis in different high-gravity fields. This ceramic/metal composite material possesses continuously graded composition, and multilevel gradient microstructure, which is composed of TiB2-TiC ceramic substrate, ceramic-based intermediate layer, metal-based intermediate layer, and 42CrMo4 substrate. The ceramic-based intermediate layer is the main gradient transition region in the joint which shows that the TiB2 and TiC grains decrease gradually in size and volume fraction from the ceramic substrate to metal substrate. The experiment reveals that the increased high-gravity field not only leads to the higher combustion temperature and the remarkable thermal explosion mode, but also attributes to the enhanced interdiffusion and convection between the molten steel surface and liquid TiB2-based ceramic. So, the reliable fusion bonding of TiB2-TiC/42CrMo4 composite materials is achieved. Moreover, the phase separation and forced filling effect of high-gravity field is the key to improve the densification and bond performance of the joint. The ceramic/metal joint in the continuous gradient composition and microstructure represents not only the transitional change of Vickers hardness, but also the high shear bond strength of 420 ± 25 MPa.

Investigating Zigzag Film Growth Behaviors in Layer-by-Layer Self-Assembly of Small Molecules through a High-Gravity Technique.

The zigzag film growth behavior in the layer-by-layer (LbL) assembly method is a ubiquitous phenomenon for which the growth mechanism was rarely investigated, especially for small molecules. To interpret the zigzag increasing manner, we hypothesized that the desorption kinetics of small molecules was dominant for the film growth behavior and demonstrated this hypotheis by introducing the high-gravity technique into the LbL assembly of a typical polyelectrolyte/small molecule system of polyethylenimine (PEI) and meso-tetra(4-carboxyphenyl)porphine (Por). The results showed that the high-gravity technique remarkably accelerated the desorption process of Por; the high-gravity LbL assembly provides a good platform to reveal the desorption kinetics of Por, which is tedious to study in conventional situation. We found that as much as 50 min is required for Por molecules to reach desorption equilibrium from the substrate to the bulk PEI solution for the conventional dipping method; however, the process could be accelerated and require only 100 s if a high-gravity field is used. Nonequilibrated desorption at 10 min for normal dipping and at 30 s for high-gravity-field-assisted assembly both exhibited a zigzag film growth, but after reaching desorption equilibrium at 100 s under a high-gravity field, film growth began to cycle between assembly and complete disassembly instead of LbL assembly. For the first time we have proven that the high-gravity technique can also accelerate the desorption process and demonstrated the desorption-dependent mechanism of small molecules for zigzag film growth behaviors.

Fusion bonding and microstructure formation in TiB2-based ceramic/metal composite materials fabricated by combustion synthesis under high gravity

The novel ceramic/metal composite materials were successfully fabricated by combustion synthesis in high gravity field. In this paper, the Ti-B4C was selected as the main combustion reaction system to obtain TiB2-TiC ceramic substrate, and the 1Cr18Ni9Ti stainless steel was selected as the metal substrate. It was found that the TiB2-TiC/1Cr18Ni9Ti composite materials exhibited continuously graded composition and hybrid microstructure. The TiC1−x carbides and TiB2 platelets decreased gradually in size and volume fraction from the ceramic to stainless steel. Due to the rapid action of thermal explosion as well as the dissolution of the molten stainless steel into TiB2-TiC liquid, the diffusion-controlled concentration gradient from the ceramic liquid to the alloy liquid was observed. Finally, as a result of the rapid sequent solidification of the ceramic liquid and the melt alloy surface, the laminated composite materials were achieved in multilevel, scale-span hybrid microstructure.

Adjusting the Ion Permeability of Polyelectrolyte Multilayers through Layer-by-Layer Assembly under a High Gravity Field.

The layer-by-layer (LbL) assembled multilayer has been widely used as good barrier film or capsule due to the advantages of its flexible tailoring of film permeability and compactness. Although many specific systems have been proposed for film design, developing a versatile strategy to control film compactness remains a challenge. We introduced the simple mechanical energy of a high gravity field to the LbL assembly process to tailor the multilayer permeability through adjusting film compactness. By taking poly(diallyldimethylammonium chloride) (PDDA) and poly{1-4[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl sodium salt} (PAzo) as a model system, we investigated the LbL assembly process under a high gravity field. The results showed that the high gravity field introduced effectively accelerated the multilayer deposition process by 20-fold compared with conventional dipping assembly; the adsorption rate was positively dependent on the rotating speed of the high gravity equipment and the concentration of the building block solutions. More interestingly, the film compactness of the PDDA/PAzo multilayer prepared under the high gravity field increased remarkably with the growing rotational speed of the high gravity equipment, as demonstrated through comparisons of surface morphology, cyclic voltammetry curves, and photoisomerization kinetics of PDDA/PAzo multilayers fabricated through the conventional dipping method and through LbL assembly under a high gravity field, respectively. In this way, we have introduced a simple and versatile external form of mechanical energy into the LbL assembling process to improve film compactness, which should be useful for further applications in controlled ion permeability, anticorrosion, and drug loading.

Preparation of Fe3O4/MnOOH core–shell nanoparticles by a high-frequency impinging stream reactor

Well-defined Fe3O4/MnOOH nanoparticles with 61.1emu·g−1 in magnetization intensity and 90.53m2·g−1 in surface area have been synthesized by a new-style of high-frequency impinging stream (HFIS) reactor. In this reactor, two streams first collided together to form nano Fe3O4 suspension, which subsequently flew through an S-shaped main channel to generate high-frequency reversing high-gravity fields. At the same time, 24 thin liquid sheets impinged into the main channel at the frequencies higher than 100Hz to create nano Fe3O4/MnOOH colloids. The obtained powders were characterized by transmission electron microscopy/energy dispersive spectrometer (TEM/EDS), X-ray diffraction (XRD), Brunner–Emmet–Teller (BET) and vibrating sample magnetometer (VSM). Experimental results indicated that low coating ratio prolonged the induction period of heterogeneous nucleation. The high-frequency impingements of 24 thin liquid sheets greatly accelerated the macro-mixing and the initial dispersion. The high-frequency reversing high-gravity fields promoted the meso- and micro-mixing. As a result, nano Fe3O4 cores were fleetly and uniformly covered by MnOOH precursor. As a continuously operated and static high-gravity reactor, the high-frequency impinging stream (HFIS) reactor is being developed to the large-scaled and low-cost production of various nanocomposites.

Introducing a high gravity field to enhance infiltration of small molecules into polyelectrolyte multilayers.

Loading functional small molecules into nano-thin films is fundamental to various research fields such as membrane separation, molecular imprinting, interfacial reaction, drug delivery etc. Currently, a general demand for enhancing the loading rate without affecting the film structures exists in most infiltration phenomena. To handle this issue, we have introduced a process intensification method of a high gravity technique, which is a versatile energy form of mechanical field well-established in industry, into the investigations on diffusion/infiltration at the molecular level. By taking a polyelectrolyte multilayer as a model thin film and a photo-reactive molecule, 4,4'-diazostilbene-2,2'-disulfonic acid disodium salt (DAS), as a model small functional molecule, we have demonstrated remarkably accelerated adsorption/infiltration of DAS into a poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) multilayer by as high as 20-fold; meanwhile, both the film property of the multilayer and photoresponsive-crosslinking function of DAS were not disturbed. Furthermore, the infiltration of DAS and the surface morphology of the multilayer could be tuned based on their high dependence on the intensity of the high gravity field regarding different rotating speeds. The mechanism of the accelerated adsorption/infiltration under the high gravity field was interpreted by the increased turbulence of the diffusing layer with the thinned laminar boundary layer and the stepwise delivery of the local concentration gradient from the solution to the interior of the multilayer. The introduction of mechanical field provides a simple and versatile strategy to address the paradox of the contradictory loading amount and loading rate, and thus to promote applications of various membrane processes.