Oxidization Degree Research Articles

Influence of Raw Material Size on the Microstructure of Graphene Oxide and Its Early Strengthening Properties of Cemen

With the purpose of exploring the influence of raw material size on the structure-performance of graphene oxide (GO) for cement reinforcement, this paper used natural flaked graphite with different particle sizes as raw material to prepare GO nanosheets by a method of enhanced Hummers, and then used scanning electron microscope (SEM) , X-ray diffraction (XRD) , Raman spectrum, infrared spectrum (IR) and other means to characterise the microstructure of GO products in detail, and then investigated the effects of raw material size and graphene oxide GO dosage on its early strengthening effect in cement. The experimental results showed that with the decrease of raw material particle size, the spacing between the layers of GO products is basically the same, while the oxidization degree is increased, and the oxygen-containing groups on the surface are increased. When the GO matt was used to prepare cement mortar with same GO extent, the mechanical strengths at an age of 3 days were found to initially increase and then decrease with the reduction of raw material particle size, and the GO products had the best effect on the improvement of early mechanical strength of cement when the raw material particle size was 13μm. On the other hand, GO matt being obtained from the raw material particles in a size of 13μm was employed to prepare cement mortar with different GO content, of which the 3d strength was found to increase apparently with the increasing GO content, and thus resulted in the increment of 8. 85% to the 3d compressive strength and 6. 34% to the 3d flexural strength for the mortar specimen obtained with a GO content of about 0. 05%, but the further increasing of the GO content is not proposed, which might gave rise of a relative low mechanical strength.

Chemically stable polypyrrole-modified liquid metal nanoparticles with the promising photothermal conversion capability

• PPy acts as a protected “armor” for elevated stability of EGaSn liquid metal. • Diverse synthetic strategy for structured EGaSn@PPy composite with regulated shape morphologies, size distribution, and oxidization degree. • The synergistic mechanism between EGaSn and PPy endows the composite a superior photothermal performance. • Failure analysis reveals that the higher stability of EGaSn@W-PPy results in better photothermal performance. The gallium-based eutectic alloy has gained particular attention in various fields due to its natural features of metallic fluids at room temperature. However, these alloy nanoparticles are extremely susceptible to be oxidized accompanied by de-alloying during the preparation, storage, and application. Here, with the assistance of the macromolecular stabilizer and dopant , sodium dodecylbenzene sulfonate (SDBS), we demonstrate a stable polypyrrole (PPy) layer acts as a protected “armor” on the surface of liquid metal (i.e., gallium-tin, EGaSn). SDBS enables the EGaSn to keep well dispersion and protects dispersed EGaSn from being durative oxidized before PPy coating. Furthermore, PPy greatly inhibits the oxidation of EGaSn owing to the strong interface interaction between the lone pair electrons around the N atoms of Py rings and the Ga 3+ orbit of EGaSn. Consequently, the fabricated EGaSn nanoparticles possess the features of smaller particle size, superior uniform distribution, and stronger antioxidant capacity. The prepared EGaSn@PPy composite exhibits superior stability even after storing in an aqueous solution for up to 100 days. As a proof-of-concept application, the EGaSn@PPy composite displays remarkable photothermal performance with an enhanced photothermal conversion efficiency. This work provides a novel surface engineering strategy to ameliorate liquid metal for photothermal therapy applications.

Microfluidic Oxidation of Graphite in Two Minutes with Capability of Real-Time Monitoring.

Graphite oxide and its exfoliated counterpart, graphene oxide, are important precursors for the large-scale production of graphene-based materials and many relevant applications. The current batch-style preparation of graphite oxide suffers from safety concern, long reaction time, and nonuniform product quality, due to the large volume of reactors and slow energy exchange. Reaction in microchannels can largely enhance the oxidization efficiency of graphite due to the enhanced mass transfer and extremely quick energy exchange, by which the controllable oxidization of graphite is achieved in ≈2 min. Comprehensive characterizations show that the graphene oxide obtained through the microfluidic strategy has features like those prepared in laboratory beakers and industrial reactors, yet with the higher oxidization degree and more epoxy groups. More importantly, the microfluidic preparation allows for on-line monitoring of the oxidization by Raman spectroscopy, ready for the dynamical control of reaction condition and product quality. The capability of continuous preparation is also demonstrated by showing the assembly of fibers and reduction of graphene oxide in microfluidic channels, and the applicability of graphene oxide prepared from the microfluidic strategy for thermally and electrically conductive films.

A comprehensive study on preparation of nanocellulose from bleached wood pulps by TEMPO-mediated oxidation

In this work, nanocellulose (NCs) was prepared from bleached wood pulps by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) - mediated oxidation method using sodium hypochlorite (NaClO) as oxidizer. By this method, both the chemical modification of the cellulose structure and the mechanical treatment played a very important role in obtaining NCs. Thus, the effects of pH values, oxidizer content on the oxidation degree of the cellulosic molecules and the effects of both the oxidation degree and the ultrasonic times during the mechanical disintegration of oxidized cellulose were investigated. The structure and properties of NCs were characterized by Fourier - transform infrared spectroscopy (FTIR), X- ray diffraction (XRD) analysis, phase - contrast microphotograph and scanning electron microscopy (SEM). The oxidization degree of cellulosic molecules was determined by the carboxylate content in the cellulosic molecules. The higher the carboxylate content, the higher was the oxidation degree. The results revealed that the optimal reaction conditions to get high carboxylate content and reaction yield were NaClO content of 10 mmol/g, pH of 10, and oxidation reaction time of 253 min. At these reaction conditions, the carboxylate content and reaction yield were 1.18 mmol/g and 87 %, respectively. With an ultrasonic treatment time up 60 min, NCs with 10–30 nm in widths and lengths of 40–60 nm were obtained. The crystalline degree of NCs was 65.2 % and it was nearly unchanged compared to that of pristine cellulose.

Study on the Oxygen Reduction Reaction Activity Induced By Quick Oxidation of Carbon Nanotube

1.IntroductionIn recent years, carbon nanotube (CNT)-based ORR electrocatalysts have attracted a lot of attention due to their appropriate physical and chemical properties. However, the pristine CNT is inert in ORR due to its electroneutrality of sp2 network. Creating topological defects in carbon materials is an efficient way to boost its electrochemical performance. Many techniques have been developed to break sp2 network on CNTs. Unzipping pristine CNTs by oxidants, such as KMnO4 [1], can form active defect sites. However, harsh oxidation process followed by a high temperature reduction of the carbon by removing the oxygen functional groups was generally required for preparing such kind of defective carbon materials. The active sites for this kind of defective carbon is considered to be the intrinsic defects of CNTs (edges or topological defects) It will be interesting if we can introduce intrinsic defects without intensive oxidation of CNTs with a well-controlled process, Aiming on direct forming the intrinsic defects to better understand the catalytic mechanism for the defective carbon nanotubes, In this work, The oxidation process to form defects in CNTs were precisely controlled by the rapid thermal annealing (RTA) strategy with CoOx as the oxidation catalyst to chemically drill defects on CNTs under relatively mild condition.2.Experimental MethodsCo(NO3)2 was deposited on the CNTs by ultrasound sonication and drying. The obtained powder was annealed at 300 °C under Ar atmosphere for 1h. To carefully control the oxidation condition, rapid thermal annealing (RTA) was used for oxidation the CNTs in several seconds by using IR-lamp heater. The ORR activity was evaluated by the cyclic voltammogram (CV) and the linear sweep voltammetry (LSV). The defective nature of DMWNT was studied by Raman.3.Results and DiscussionCobalt oxides can oxidize carbon at mild temperatures (250 °C) according to the TGA results [2]. First, 270°C and 30min was first selected as the oxidation condition. The Id/Ig ratio increased from 1.56 to 1.63, while no increase in the onset potential (0.5V) was observed after oxidation. This means that the CNTs became more defective but there is no impact on its electrochemical performance. The highly active site was not formed in the prolonged oxidation.To control oxidation extent of CNTs, RTA was employed to control the annealing process where temperature was raised up in 8~9 s. As a result, quick oxidized DMWNT showed improved onset potential of 0.68 V. The carbon defects in quick oxidized DMWNT with proper structure were expected to be beneficial for ORR activity by decreasing the overpotential.An obvious redox couple (C=O + 2H+ + 2e- ⇋C-OH) at ~0.6 V was showed in CV profiles of the DMWNT with prolonged oxidation but decreased significantly in quick oxidized DMWNT, confirming the presence of oxygen species on the surface. The small redox peak also indicated the slight oxidization degree in quick oxidation. The high ORR performance is benefit from these small defects and the resulted fewer OFGs around the carbon edges.Reference[1] L. Xue , Y. Li, X. Liu, Q. Liu, J. Shang, H. Duan, L. Dai, J. Shui, Nat. Commun., 9, 3819, (2018).[2] K.Waki, R. A. Wong, H. S. Oktaviano, T. Fujio, T. Nagai, K. Kimoto, K. Yamata, Energy Environ. Sci., 7, 1950 (2014). Figure 1

Stable and biocompatible fibrillar hydrogels based on the self-crosslinking between collagen and oxidized chondroitin sulfate

Stable and biocompatible collagen-based hydrogels based on natural extracellular matrix (ECM) with a homogeneous microstructure are ideal scaffolds for tissue engineering; however, lack of structural stability and mechanical property have hindered their application. In this work, Chondroitin Sulfate (CS) was periodate-oxidized to prepare dialdehyde ECM-derived biopolymer with the weight average molecular weight of 3.7 × 104 g/moL to construct the stable collagen-based fibrillar hydrogels. The results of Fourier Transform Infrared (FTIR) analysis and hydroxylamine hydrochloride titration assay confirmed the presence of aldehyde groups in oxidized CS (CSox) with an oxidization degree of 30.67%. Gelation time test and scanning electron microscopy (SEM) observation showed that gel formation and fibrillogenesis process were accelerated by adding CSox, and all hydrogels exhibited a tight fibrillar structure. With an increase in CSox concentration from 0.125 to 2.000 mg/mL, the crosslinking degree increased from 24.95% to 35.05% due to the formation of covalent bonds between the ε-amino groups of collagen and aldehyde of CSox. The mechanical strength of collagen/CSox hydrogels reached a maximum value of 11.79 KPa, which was more than triple that of pure collagen hydrogel (3.58 KPa) at 0.125 mg/mL CSox. The swelling ratio, enzymatic resistance, and thermal stability were also improved with the increasing concentration of CSox. When the CSox concentration reached 0.500 mg/mL, the collagen-based hydrogels exhibited the highest thermal denaturation temperature, which was approximately 7.5 °C higher than that of the pure collagen hydrogel. Moreover, the results of the CCK-8 assay and LIVE/DEAD staining demonstrated that all the collagen/CSox hydrogels accelerated cell proliferation and showed acceptable biocompatibility. This work broadens the avenue for the design of natural collagen-based hydrogels for tissue engineering.

Synthesis of composite of graphene and UO3 composite via one-step solution chemical reaction and its application to UO2-based accident tolerant fuel

In this paper, two kinds of composites constructed by UO3 nanoflakes (which is UO3·yNH3·xH2O, precisely) and different graphene oxide (GO) nanosheets (homemade GO, GO-h, and commercial GO, GO-c) were prepared via solution chemical reaction. The two kinds of GO share similar morphology and possess the same species of functional groups. Nevertheless, GO-h possesses higher oxidization degree and thus could adsorb more uranyl ions, and the corresponding composite shows a much more regular shape: UO3 nanoflakes and GO nanosheets cross each other, which would help overcome the disadvantage of graphene aggregation. As a result, homemade reduced graphene oxide (RGO-h) sheets inside the final UO2 pellets (named as UO2/GO-h) could construct a well-bulit thermally conductive network to enhance its thermal conductivity. However, similar RGO-c network cannot be observed in the UO2/GO-c pellest originated from GO-c. Therefore, only the thermal conductivity of UO2/GO-h pellet acquires a dramatic increase, 37.30% relative to UO2 pellet at 1200 °C, showing that UO2/GO-h possesses great potential for the development of novel UO2-based ATF fuels.

Mineralogical Prediction on the Flotation Behavior of Copper and Molybdenum Minerals from Blended Cu–Mo Ores in Seawater

The copper ore in Chilean copper porphyry deposits is often associated with molybdenum minerals. This copper–molybdenum (Cu–Mo) sulfide ore is generally mined from various locations in the mining site; thus, the mineral composition, oxidation degree, mineral particle size, and grade vary. Therefore, in the mining operation, it is common to blend the ores mined from various spots and then process them using flotation. In this study, the floatability of five types of Cu–Mo ores and the blending of these ores in seawater was investigated. The oxidation degree of these Cu–Mo ores was evaluated, and the correlation between flotation recovery and oxidation degree is presented. Furthermore, the flotation kinetics of each Cu–Mo ore were calculated based on a mineralogical analysis using mineral liberation analysis (MLA). A mineralogical prediction model was proposed to estimate the flotation behavior of blended Cu–Mo ore as a function of the flotation behavior of each Cu–Mo ore. The flotation results show that the recovery of copper and molybdenum decreased with the increasing copper oxidization degree. In addition, the recovery of blended ore can be predicted via the flotation rate equation, using the maximum recovery (Rmax) and flotation rate coefficient (k) determined from the flotation rate analysis of each ore before blending. It was found that Rmax and k of the respective minerals slightly decreased with increasing the degree of copper oxidation. Moreover, Rmax varied greatly depending on the mineral species. The total copper and molybdenum recovery were strongly affected by the degree of copper oxidation as the mineral fraction in the ore varied greatly depending upon the degree of oxidation.

Molecular Insight into the Adsorption Thermodynamics and Interfacial Behavior of GOs at the Liquid-Liquid Interface.

The adsorption of two-dimensional (2-D) graphene oxide (GO) nanosheets at liquid-liquid interfaces has broad technological implications from functional material preparations to oil-water emulsification. Molecular-level understanding of the adsorption thermodynamics and the interfacial behavior is of great significance. Here, the adsorption free energy of GO nanosheets at the water-cyclohexane system was simulated, in which the effect of oxygen-containing groups and deprotonation has been investigated. It was observed that the neutral GO (GO-COOH) has obvious interfacial activity with a reduction of interfacial tension, while the deprotonated GO (GO-COO-) shows a weak interface affinity. There exists an optimal oxidization degree that could cause the best interfacial stability, which is attributed to the balance of interfacial hydrophilic-hydrophobic interactions. The interaction arising from water is the main factor determining interfacial activity. The interfacial morphology and dynamics of GO nanosheets have also been simulated, in which an anisotropic 2-D translation and rotation along the interface were revealed. Our simulation results provide new insight into the adsorption mechanism and dynamics behavior of GO at the oil-water interface.

Cu@Pd/C with Controllable Pd Dispersion as a Highly Efficient Catalyst for Hydrogen Evolution from Ammonia Borane.

A series of Cu@Pd/C with different Pd contents was prepared using the galvanic reduction method to disperse Pd on the surface of Cu nanoparticles on Cu/C. The dispersion of Pd was regulated by the Cu(I) on the surface, which was introduced by pulse oxidation. The Cu2O did not react during the galvanic reduction process and restricted the Pd atoms to a specific area. The pulse oxidation method was demonstrated to be an effective process to control the oxidization degree of Cu on Cu/C and then to govern the dispersion of Pd. The catalysts were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscope (HRTEM), high angular annular dark field scanning TEM (HAADF-STEM), energy-dispersive spectroscopy (EDS) mapping, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), and inductively coupled plasma optical emission spectrometer (ICP-OES), which were used to catalyze the hydrogen evolution from ammonia borane. The Cu@Pd/C had much higher activity than the PdCu/C, which was prepared by the impregnation method. The TOF increased as the Cu2O in Cu/C used for the preparation of Cu@Pd/C increased, and the maximum TOF was 465 molH2 min−1 molPd−1 at 298 K on Cu@Pd0.5/C-640 (0.5 wt % of Pd, 640 mL of air was pulsed during the preparation of Cu/C-640). The activity could be maintained in five continuous processes, showing the strong stability of the catalysts.

Molecular interlayer intercalation of ethanol-water mixture towards GO laminated membranes

The practical functions of graphene oxide (GO) layered membranes in liquid phase separation are dependent on the interlayer solvation intercalation, however, it is very challenging to attain the qualitative information on the intercalation kinetics, inserted amount, and composition in the multilayer structures of GO membranes from experiment techniques. In this work, molecular dynamics simulations were conducted to investigate the competitive insertion/adsorption behavior of ethanol-water mixtures into the nanochannels of layered GO structures. Our simulations demonstrate that both water and ethanol can spontaneously intercalate into GO channels and there is no highly selective interlayer intercalation. Two insertion mechanisms have been revealed for GO nanochannels. In general, large ethanol is found to penetrate more significantly than small water. The underlying mechanism can be attributed to the enhanced surface affinity of GO pores with ethanol molecules. However, for smaller pores with high oxidization degree, the insertion of ethanol can be restricted due to pore sieving effect. The mixture concentrations, confined structures, and diffusion dynamics for ethanol-water mixtures confined within GO pores were analyzed. Our results provide new insight into the solvation intercalation of GO layered structures, which is beneficial to the separation application of GO laminated membranes.

Molecular dynamics simulation of water-ethanol separation through monolayer graphene oxide membranes: Significant role of O/C ratio and pore size

Molecular dynamics (MD) simulations were employed to investigate water-ethanol separation through monolayer graphene oxide (GO) membranes with different pore sizes and O/C ratios. The ultrahigh water flux and infinite water separation factors were achieved. The separation properties under 50/50 w/w water-ethanol mixtures reveal that higher O/C ratios favor water selectivity, and water flux is enhanced with O/C ratio and pore size. With the help of highest oxidization, water largely sorption amount governs permeation process. On the contrary, with low oxidization degree of GO membrane, water diffusion effect becomes dominant factor of permeation. We screen an optimal microstructure of GO membrane which equipped with an adequately sized pore (D = 2.4 Å) and a highest O/C ratio (R = 0.49). This optimal one D2.4Å_R0.49 achieves the highest water flux and fully ethanol rejection in the mimicked experimental system. This simulation study elucidates the role of O/C ratio and pore diameter in water-ethanol separation through porous GO membranes on the microscopic level and uncovers the governing effects for water permeation and also suggests a potential candidate as a water-ethanol separation membrane.

Heterogeneous oxidization of graphene nanosheets damages membrane

Graphene-based materials exhibit unique properties that have been sought to utilize for various potential applications. Many studies suggest that graphene-based materials can be cytotoxic, which may be attributed to destructive effects on cell membranes. However, there still are conflicting results regarding interactions between graphene-based materials and lipid membranes. Here, through cryo-electron microscopy (Cryo-EM) and dye-leakage experiments along with in silico methods, we found that graphene oxide nanosheets induce significant membrane damage, while the effect of pristine graphene is negligible. We revealed the importance of heterogeneous oxidization of graphene-based nanosheets in damaging vesicle membranes. Moreover, that not only the oxidization degree but also the oxidization loci and membrane tension play important roles in the cytotoxicity of the graphene-based nanosheets.

The surface characterization and passive behavior of Type 316L stainless steel in H2S-containing conditions

The protectiveness and characterization of passive films formed at various potentials in H2S-containing environments were studied using electrochemical measurements and surface analysis method. The corrosion resistance of 316L in H2S-containing environment decreases with the applied potential. The Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) results indicate that Ni participates in the film formation, which results in the corresponding enrichment in the passive film. The oxidization degree analysis indicates that metallic elements are present in the passive film. Sulfide ions are significantly favored in the passive film at higher potentials, which is responsible for the breakdown of passive film.

Molecular Dynamics Simulations of CO2/N2 Separation through Two-Dimensional Graphene Oxide Membranes

Graphene oxide (GO), as an ultrathin, high-flux, and energy-efficient separation membrane, has shown great potential for CO2 capture. In this study, using molecular dynamics simulations, the separation of CO2 and N2 through the interlayer gallery of GO membranes was studied. The preferential adsorption of CO2 in the GO channel derived from their strong interaction is responsible for the selectivity of CO2 over N2. Furthermore, the influences of interlayer spacing, oxidization degree, and channel length on the separation of CO2/N2 were investigated. Our studies unveil the underlying mechanism of CO2/N2 separation in the interlayer GO channel, and the results may be helpful in guiding rational design of GO membranes for gas separation.

Oxygen adsorption and diffusion on an Al(111) surface and subsurface: a theoretical study

The generalized gradient approximation of the density functional theory was used to investigate the adsorption and dissociation of the O2molecule on an Al(111) surface and the subsequent diffusion of an oxygen atom into the subsurface with different oxygen coverages. The total adsorption energies of oxygen atoms on the Al(111) surface increase as the number of adsorbed oxygen atoms increases, while the adsorption heats per oxygen atom decrease firstly and then increase. The adsorption heats for O2physisorption on the Al(111) surface would increase as the oxidization degree of Al(111) surface increased. As the oxidization degree of Al(111) surface increases, the adsorption heats for O2chemisorption decrease firstly and then increase, and the O2molecule would not dissociate when the oxidization degree was up to 1.0 monolayer. In general, the energy barriers for both the interlayer and intralayer diffusions of the oxygen atom on the Al(111) surface would become larger as the number of initial adsorbed oxygen atoms on the Al(111) surface increased due to an increasing repulsion force.

Core-shell Co@Co3O4 nanoparticle-embedded bamboo-like nitrogen-doped carbon nanotubes (BNCNTs) as a highly active electrocatalyst for the oxygen reduction reaction.

The current bottleneck for fuel cells and metal-air batteries lies in the sluggish oxygen reduction reaction (ORR) on the cathode side. Despite tremendous efforts, to develop a highly efficient ORR catalyst at low cost remains a great challenge. Herein, we have synthesized core-shell Co@Co3O4 nanoparticles embedded in the bamboo-like N-doped carbon tubes (BNCNTs) by a simple approach comprising thermal treatment of cobalt carbonate hydroxide and urea and oxidization. The ORR catalytic activities of the Co@Co3O4/BNCNT composites are closely dependent on the oxidization degree of the Co nanoparticles and the N content in the BNCNTs. When oxidized at 300 °C, the as-formed Co@Co3O4/BNCNTs-300 composite catalyst with an N/C molar ratio of ∼ 1.6% achieves the maximum ORR catalytic activity. The composite catalyst also exhibits a higher ORR catalytic activity than the Co3O4/carbon nanotube (CNT) catalyst. The tolerance for methanol molecules and the cycle stability performance of the composite catalyst are even superior to those of the highly efficient Pt/C catalyst. Such an excellent ORR catalytic activity can be ascribed to (1) the core-shell Co@Co3O4 nanoparticles embedded in BNCNTs, (2) the N-doping in BNCNTs, and (3) the synergetic effect of (1) and (2) on Co3O4 firmly attached to both Co nanoparticles and BNCNTs, resulting in accelerated electron transport and enhanced charge delocalization.

Simulation and analysis of cellular internalization pathways and membrane perturbation for graphene nanosheets

Clarifying the mechanisms of cellular interactions of graphene family nanomaterials is an urgent issue to the development of guidelines for safer biomedical applications and to the evaluation of health and environment impacts. By combining large-scale computer simulations, theoretical analysis, and experimental discussions, here we present a systematic study on the interactions of graphene nanosheets having various oxidization degrees with a model lipid bilayer membrane. In the mesoscopic simulations, we investigate the detailed translocation pathways of these materials across a 56 × 56 nm2 membrane patch which allows us to fully consider the role of membrane perturbation during this process. A phase diagram regarding the transmembrane translocation mechanisms of graphene nanosheets is thereby obtained in the space of oxidization degree and particle size. Then, we propose a theoretical approach to analyze the effects of various initial equilibrium states of graphene nanosheets with membrane on their following cellular uptake process. Finally, we demonstrate that the simulation and theoretical results reproduce some important experimental findings towards the mechanisms of cytotoxicity and antibacterial activity of graphene materials. These results not only provide new insight into the cellular internalization mechanism of graphene-based nanomaterials but also offer fundamental understanding on their physicochemical properties which can be precisely tailored for safer biomedical and environment applications.

A covalently crosslinked polysaccharide hydrogel for potential applications in drug delivery and tissue engineering

The development of non-cytotoxic hydrogels that can allow for the controlled release of molecules has important clinical and therapeutic applications. In this paper, we developed a series of in situ hydrogels by combining N,O-carboxymethyl chitosan and oxidized alginate without additional crosslinking agents. The rheological properties of these hydrogels as well as their gelling time, swelling ratio, and in vitro degradation behavior were investigated. We observed that although gelation was rapid at physiological temperature, it was even faster in the presence of higher oxidization degree of alginate. In vitro cytotoxicity study showed that the developed hydrogels were not cytotoxic after 24 h of culturing with NIH-3T3 cells. Additionally, bovine serum albumin was released from the hydrogels initially by diffusion at early stages followed by a degradation-dependent mechanism at later stages. In conclusion, the developed hydrogel might have potential application in the drug delivery system and tissue engineering.

Synthesis of Sphere GdN for Magnetic Refrigeration

Spherical GdN material with diameter of 0.85 ∼ 1.0 mm was synthesized by the hot isostatic pressing (HIP) method aiming at the application to the magnetic refrigeration for hydrogen liquefaction. Conditions of the HIP nitridation starting from metallic Gd spheres were investigated to obtain the spherical GdN materials free from unwanted deformation and/or cracks. We found that slower temperature rising rate, 10°C/h, around the melting point of Gd metal, 1300-1600°C, is favorable because it would allow the metallic Gd core to transform into nitride by reacting with nitrogen diffusing from the surface. We have successfully synthesized spherical GdN material of 300 g, which is enough to operate a test device for the magnetic refrigeration. Oxidization degree of this spherical GdN material was investigated by exposing it to air with some controlled humidity. It was found that only 2.5 % of the GdN was degraded after 56 hour exposition to air dried with silica gel.