Synthesis and Characterization of Carbon-Stabilized Magnesium Nanoparticles

Magnesium nanopowder has attracted many interests in the recent years, which has a very difficult and costly synthesis process because of its high activity. In this work, magnesium nanoparticles stabilized with amorphous carbon (Mg–C nanoparticles) were synthesized by submerged arc discharge technique in kerosene. The arc discharge was generated between two electrodes of magnesium at the arc current of 1 A and arc voltage of 50 V. Mg–C nanoparticles were characterized by various techniques. Dynamic light scattering result indicated that size of magnesium nanoparticles is about 35 nm. X-ray diffraction showed that the produced sample consisted of hexagonal magnesium and amorphous carbon and there was no presence of magnesium oxides in the pattern. Field emission scanning electron microscopy and transmission electron microscopy results illustrated that the sample has morphology of agglomerated nanospheres. Energy dispersive X-ray spectroscopy demonstrated formation of 57 percent magnesium and 43 percent carbon. Differential scanning calorimetry analysis showed that the amorphous carbon increased ignition temperature of nanoparticles by 180 °C compared to pure magnesium micron-sized powder. Therefore, Mg–C nanoparticles can have many applications in different fields similar to magnesium nanopowders. However, by producing Mg–C nanoparticles, there is no need for vacuum chamber or inert gases during production and after that, since amorphous carbon protects magnesium nanoparticles from oxidation.     

Combined effect of zeolite and boric acid on thermal behavior of epoxy composites

The particles of natural zeolite in combination with boric acid were incorporated into the epoxy resin ED-20 in order to improve the thermal stability of epoxy polymer. Epoxy resin was cured using polyethylenepolyamine. Characterization of the epoxy composites was carried out by using Fourier transform infrared spectrometry, thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) under flow of air and argon. The thermal behavior of the zeolite/boric acid-based epoxy composites (total percentage 15 mass%) were compared with that of 15 mass% boric acid-based epoxy system and the neat epoxy resin. TG and DSC results revealed that the combination of 5 mass% zeolite and 10 mass% boric acid significantly increased the mid-point temperature and residue, and decreased the maximum decomposition rate of the epoxy composites at the heating.     

Ti-Zr催化剂对NaH/Al复合物可逆储氢特性的影响

采用机械球磨(NaH/Al+Ti)和(NaH/Al+Ti-Zr)复合物的方法加氢制备了NaAlH4配位氢化物, 系统研究了Ti、Ti-Zr催化剂以及不同加氢条件对其可逆储氢行为的影响. 结果表明, 对于NaH/Al体系的吸放氢性能, 共掺金属Ti粉/Zr粉的催化作用比单独掺金属Ti粉的催化作用要好. 随着加氢温度从85 ℃上升到140 ℃, 体系的吸氢容量先增后减, 并在120 ℃时达到最大值; 同时, 发现共掺Ti-Zr催化剂的复合物具有最佳的储氢性能, 在120和85 ℃时的吸氢量分别为4.61%和3.52%(w), 比仅掺Ti 催化剂的复合物分别高出0.40%和0.70%(w)的吸氢量. 随着加氢压力的增大, (NaH/Al+Ti-Zr)复合物的吸氢性能随之提高. XRD和DSC分析结果表明, NaAlH4体系的放氢过程明显发生两步分解反应, 共掺Ti-Zr催化剂的复合物储氢性能优于单独掺Ti 催化剂的原因是, 共掺催化剂能有效改善NaAlH4体系吸放氢反应的动力学性能,并降低体系的放氢温度.     

氢化燃烧法合成La1.5Ni0.5Mg17的工艺优化

采用正交实验设计方法安排实验，运用L9(3^4)优化氢化燃烧法合成La1.5Ni0.5Mg17的工艺，考察了施压制饼时间、合成保温时间、合成起始氢气压力、保温温度4个因素对储氢材料的储放氢容量和速率的影响，通过直观分析和方差分析得出优化的工艺为：保温温度903K，制饼施压时间40min，合成起始氢气压力为1MPa，合成保温时间1800min。此条件下合成储氢材料La1.5M0.5Mg17在573K的储放氢容量分别为：5．40和5．15％H(质量分数)；储放氢速率分别为：0．734和0.681％H／min。用XRD分析了材料吸氢和脱氢后的物相结构发现：用Ni适量取代La2Mg17中的La没有导致结构变化，存在的LaNi5，LaH3和La改善了材料的吸放氢速率。     

镨、钕氢化物催化剂对NaH/Al复合物吸放氢性能的影响

采用NaH和Al为合成原料,镨、钕氢化物为催化剂,通过机械球磨(NaH/Al+6%(摩尔分数)RE-H)(RE=Pr,Nd)复合物的方法并加氢合成NaAlH4络合氢化物,系统研究了催化剂对其吸放氢性能的影响。结果表明,加入PrH2.92和NdH2.27能明显改善NaH/Al复合物的吸放氢动力学性能,有效降低NaAlH4的脱氢温度。(NaH/Al+6%PrH2.92)和(NaH/Al+6%NdH2.27)复合物的120℃吸氢容量分别为3.57%和3.61%(质量分数),170℃放氢容量分别为2.57%和2.95%;且两者均具有较好的吸放氢循环稳定性,但吸(放)氢后样品中均存在少量Na3AlH6相,表明样品的吸(放)氢反应进行得并不彻底,使得其实际吸放氢容量低于理论可逆储氢容量。研究表明,PrH2.92和NdH2.27在球磨、吸/放氢过程中始终稳态存在,起着催化储氢作用;(NaH/Al+6%PrH2.92)复合物的放氢活化能稍低于(NaH/Al+6%NdH2.27)复合物。     

Effect of the TiC content on microstructure and thermal properties of Cu–TiC composites prepared by powder metallurgy

Copper matrix with an individual addition of TiC particles was prepared by means of powder metallurgy and hot pressing process, and the effect of TiC addition on microstructure, thermal properties, and electrical conductivity of Cu–TiC composites was investigated. The TiC quantity was changed as 1, 3, 5, 10, and 15 Cu (in mass%), and Cu–TiC powder mixtures were hot-pressed for 4 min at 700 °C under an applied pressure of 50 MPa. Microstructure studies revealed that TiC particles were distributed uniformly in the Cu matrix. Thermal Analysis result showed that there were two exothermic peaks and with rising TiC rate, oxidation amount of Cu composite decreased. With the increasing addition of TiC, hardness of composites changed between 58.6 HV_0.1 and 87.8 HV_0.1. The highest electrical conductivity for Cu–TiC composites was obtained in the Cu-1 mass% TiC composite, with approximately 81.2 % IACS.     

Hydrogen sorption characteristics of magnesium-based composites with addition of Mg<Subscript>2</Subscript>Ni<Subscript>0.7</Subscript>Co<Subscript>0.3</Subscript> and graphite

Magnesium-based composites of 75 wt% Mg — (10, 15, 20) wt% Mg2Ni0.7Co0.3 — (15, 10, 5) wt% C mechanically activated for 30 min under argon in a planetary mill, were obtained. Their absorption-desorption characteristics were investigated under a pressure P = 1 MPa and temperatures of 623, 573, 473, 423 and 373 K. Desorption was carried out at 623 K and 573 K and a pressure of 0.15 MPa. All the three composites showed improved hydriding kinetics as compared to pure magnesium. However, the desorption temperature was somewhat higher than needed for practical application.      

The non-isothermal kinetics of mullite formation in boehmite–zircon mixtures

In this work, we studied the kinetics of mullite formation in different composites under non-isothermal conditions using DTA. Different composites based of mullite, alumina, zircon and zirconia were prepared by reaction sintering of boehmite (as alumina source) and zircon. Several mixtures were used while varying the percentage of the boehmite from 30 to 70 mass% with a step of 10. Five compositions marked as B30, B40, B50, B60 and B70 corresponding to boehmite–zircon ratios (mass%) of 30/70, 40/60, 50/50, 60/40 and 70/30 were fabricated and studied. The DTA conducted at heating rates of 10, 20 and 30 K min^?1 showed an endothermic peak in all composites at about 1,603 K associated with mullite formation. The activation energies measured from non-isothermal treatments for five compositions (30, 40, 50, 60 and 70 mass% of boehmite) were 1,029, 1,085, 1,262, 1,508 and 1,321 kJ mol^?1, respectively. The n values (Avrami parameter) for all compositions are larger than 2.5, the mullite crystallization of these composites is followed by three-dimensional growth.     

LaMg8.40Ni2.34合金的相结构和储氢性能

利用真空感应熔炼和退火方法制备了LaMg_8.40Ni_2.34合金. 采用X射线衍射(XRD)分析、扫描电镜(SEM)和压力-组成-温度(PCT)测试仪测试了合金的相组成、微观形貌和储氢性能. LaMg_8.40Ni_2.34合金由La₂Mg₁₇、LaMg₂Ni和Mg₂Ni组成,且在第一次吸放氢循环中就可以完全活化. 在558 K下的可逆储氢量为3.01%(质量分数), 合金的PCT曲线表现出双吸氢平台, 分别对应着形成的MgH₂和Mg₂NiH₄. 但是放氢曲线却只有一个平台出现, 这是由MgH2和Mg2NiH4之间的协同脱氢作用产生的. LaMg_8.40Ni_2.34合金在吸放氢时的活化能分别为(52.4±0.4)和(59.2±0.1) kJ·mol^-1, 均低于Mg₂Ni合金. 与纯Mg和Mg₂Ni合金相比, LaMg_8.40Ni_2.34合金具有良好的活化性能、较高的储氢性能和优良的动力学性能.     

Carbon nanofibers reinforced soy polyol-based polyurethane nanocomposites

Vapor-grown carbon nanofiber (CNF)-modified soy polyol-based polyurethane (PU) nanocomposites with different hydroxyl value of polyols (OH) were synthesized. The glass transition, thermal stability, mechanical properties, and morphology of the PU nanocomposites were characterized through differential scanning calorimetry, thermogravimetry, universal test machine, and scanning electron microscopy. The addition of CNFs increased the glass transition temperature as well as significantly improved tensile strength and Young’s modulus of PU nanocomposites. Meanwhile, thermal and mechanical properties of PU composites were influenced by the different hydroxyl value of polyols due to those different structures. In particular, in the case of 2 mass% CNF addition in PU derived from soy polyol with the OH number of 164 mg KOH g^?1, 20.8 °C improvement in the glass transition temperature, 115 % increment in tensile strength, and nearly eightfold increase in Young’s modulus were obtained.     

纳米镁储氢材料吸放氢动力学性能的研究进展

综述近十年来国内外有关纳米镁储氢材料吸放氢动力学的研究现状和发展趋势.众多研究表明,应用高能球磨法制备纳米镁复合储氢材料,并以过渡金属氧化物为催化剂,或者用ABx型储氢合金与镁复合,都能显著改善镁的吸放氢动力学性能.     

Monitoring thermal,structural properties,methotrexate release and biological activity from biocompatible spray-dried microparticles

Boron phosphates (BPs) with different acidities were prepared by regulating the calcination temperatures for the reaction products of boric acid and phosphoric acid. The crystal structure, morphology, surface acidity, and thermal stability were characterized by X-ray diffraction, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), chemical absorbed apparatus, and thermogravimetric analysis (TG). The effects of BPs on the combustion behavior and catalyzing the carbonization of bisphenol-A epoxy resin (EP) were investigated by the limiting oxygen index (LOI) and cone calorimetry test. Upon loading 5 mass% BP prepared at 300 °C, the LOI value of the EP/BP composites increased to 29.6%, and moreover, the peak heat release rate and average specific extinction area decreased by 43 and 25%, respectively. A possible catalyzing carbonization mechanism was explored by TG coupled with Fourier transform infrared spectroscopy (TG–FTIR), TG, FTIR, SEM, Raman spectroscopy (Raman), and XPS. The results demonstrated that BP catalyzed EP to degrade at relatively low temperature, and the yield, compactness, and graphitization degree of the char residue were obviously enhanced with an increase in the ratio of Brønsted and Lewis acid sites (B/L value) and the total surface acid sites on the BP surface. Therefore, the catalyzing carbonization flame retardancy of the EP/BP composites can be improved through regulating the surface acidity of BP.     

Thermal analysis study on the grain refinement of Al–15Zn–2.5Mg–2.5Cu alloy

Computer-aided cooling curve analysis is a reliable method to characterize the solidification behavior of an alloy. In this study, the effect of Al–5Ti–1B grain refiner on the solidification path, microstructure and macrostructure of a new Al–Zn–Mg–Cu super high-strength aluminum alloy containing high amounts of zinc was investigated using thermal analysis technique. The grain size measurement showed that Al–5Ti–1B reduces the grain size from 1402 to 405 μm. Solidification parameters in the liquidus region were in a good accordance with microstructural results. The addition of 1 mass% of Al–5Ti–1B grain refiner decreased ΔT _N from 9.1 to 7.7 °C. It also diminished recalescence undercooling from 1.42 to 0.32 °C. The grain refinement also altered dendritic structure of the alloy from a coarse, elongated and non-uniform to a rosette and more uniform shape. Moreover, the grain refiner resulted in a more uniform distribution of eutectic structure between dendrite arms. Furthermore, the grain refinement enhanced fraction of solid at dendrite coherency point from 21 % for unrefined alloy to 25 % for the alloy containing 1 mass% Al–5Ti–1B. In the same trend, the addition of 1 mass% Al–5Ti–1B reduced the amounts of porosity from 2.3 to 1.8 %.     

Fabrication and characterization of gamma-irradiated recycled (thermoplastic/elastomer) matrix filled with feldspar composites

A composite of waste polyethylene, recycled waste rubber powder and reactive compatibilizing agent maleic anhydride, 60/40/2 mass%, was loaded with increasing contents, up to 20 mass%, of the reinforcing filler, feldspar [K (Al SiO₃O₈)]. The composites were gamma-irradiated at various doses up to 150 kGy. Selected physical, mechanical, and thermal parameters were investigated as functions of radiation dose and filler content. Gamma irradiation led to a significant improvement in the properties for all composites irradiated with 150 kGy. Similarly, the increase in feldspar content provided substantial improvement in properties as a result of development in the interfacial adhesion between the filler particles and composite components. The results were confirmed by examining the fracture surfaces using scanning electron microscopic techniques.     

Effects of Zr addition on solidification characteristics of Al–Zn–Mg–Cu alloy using thermal analysis

The effect of Zr as a grain refiner on the solidification behavior, micro- and macrostructure of a new Al–Zn–Mg–Cu aluminum super-high strength alloy containing high Zn content was studied. The addition of 2 mass% Zr reduced the grain size from 1500 to 190 μm. Moreover, the dendritic structure of the alloy altered from a coarse, elongated and non-uniform morphology to a rosette-like shape and more uniform one. The parameters of liquidus region of cooling curve obtained from thermal analysis were in a good correlation with grain size results. The maximum of first derivative in the liquidus region was introduced beside recalescence undercooling which could predict the grain refinement level even after disappearing of recalescence in the cooling curve. Furthermore, the addition of 1 mass% Zr enhanced fraction of solid in dendrite coherency point from 21 to 31% and lessened the amounts of porosity from 2.3 to 1.4%.     

MgH_2+20%(w)MgTiO_3复合材料的吸/放氢性能(英文)

为了降低MgH2的吸放氢温度,提高其吸放氢动力学性能,本文通过球磨方法制备了MgH2+20%(w)MgTiO3复合储氢材料,并研究了其储氢性能.X射线衍射(XRD)结果表明,MgTiO3在与MgH2球磨过程中生成Mg2TiO4和TiO2,并且Mg2TiO4和TiO2在体系的吸放氢过程中保持稳定,能够对MgH2的吸放氢过程产生催化作用.程序升温脱附和吸/放氢动力学测试结果表明,添加MgTiO3后MgH2的初始放氢温度从389°C降至249°C.150°C下的吸氢量从0.977%(w)提高到2.902%(w),350°C下的放氢量从2.319%(w)提高到3.653%(w).同时,MgH2放氢反应的活化能从116kJ·mol-1降至95.7kJ·mol-1.与MgH2相比,MgH2+20%(w)MgTiO3复合材料的热力学与动力学性能均有显著提高,这主要是由于球磨和放氢过程中原位生成的TiO2和Mg2TiO4具有良好的催化活性.     

Activated carbon aerogels with high bimodal porosity for lithium/sulfur batteries

Activated carbon aerogels (ACAs) with high bimodal porosity were obtained for lithium/sulfur batteries by potassium hydroxide (KOH) activation. Then sulfur–activated carbon aerogels (S–ACAs) composites were synthesized by chemical deposition strategy. The S–ACAs composites were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy, and N₂ adsorption/desorption measurements. It is found that the activated carbon aerogels treated by KOH activation presents a porous structure, and sulfur is embedded into the pores of the ACAs network-like matrix after a chemical deposition process. The Li/S–ACAs (with 69.1 wt% active material) composite cathode exhibits discharge capacities of 1,493 mAh g^?1 in the first cycle and 528 mAh g^?1 after 100 cycles at a higher rate of C/5 (335 mA g^?1). The S–ACAs composite cathode exhibits better electrochemical reversibility, higher active material utilization, and less severe polysulfide shuttle than S–CAs composite cathode because of high bimodal porosity structure of the ACAs matrix.     

New poly(ether-imide)/MWCNT nanocomposite

New polyimide (PI) nanocomposites containing two different amounts of MWCNT (PI/MWCNT) were prepared via in situ polymerization technique. Transmission electron microscopy showed that MWCNT was exfoliated in the polymer matrix, resulting in well-dispersed morphologies at 1 and 3 mass% MWCNT contents. The effects of multiwalled carbon nanotubes (MWCNT) on the thermal and flammability properties of new PI derived from 1,3-bis[4,4′-aminophenoxy]propane and biphenyl dianhydride were investigated by thermogravimetric analysis (TG) in nitrogen and air atmosphere, differential scanning calorimetry, and microscale combustion calorimeter (MCC). The PI/MWCNT nanocomposites were electrically conductive with maximum conductivity obtained at 3 mass% MWCNT, which is favorable for many potential applications. TG results showed that the addition of MWCNT resulted in a substantial increase of the thermal stability and char yields of the nanocomposites compared to those of the neat PI. Flame retardancy of the nanocomposites was significantly improved in the presence of MWCNT.     

Effects of nano-limestone on hydration properties of tricalcium silicate

In this research, the influences of nano-limestone (NC) on tricalcium silicate (C₃S) hydration, including early hydration rate, setting time, Ca(OH)₂ content, quantification of C–S–H, micrographs of hydration products and compressive strength, were investigated by different methods. Calorimetry results show that the first and second exothermic peak of C₃S with 1 mass% NC is ~29 and ~5% higher than that of control sample and the second peak appears 32 min in advance. Besides, the total hydration heat of C₃S with 1 mass% NC increases by 10.08% compared to control sample at 72 h. The initial and final setting time of C₃S with 1 mass% NC shortens by 23 and 17 min, respectively. In addition, thermal analysis results show that adding NC leads to higher Ca(OH)₂ and C–S–H content at all ages (1, 3 and 28 days). All of the above results imply that the hydration progress of C₃S is accelerated by NC. Correspondingly, the compressive strength of C₃S with 1 mass% NC increases by 9.88% at 28 days. Besides, EDS results reveal that the Ca/Si ratio of C–S–H gel decreases after NC modification. However, excessive content NC (4 mass%) reduces the acceleration effect of NC on C₃S hydration and finally leads to relative low content of Ca(OH)₂ and C–S–H compared with C₃S sample containing 1 mass% NC.     

Effect of nitrile butadiene rubber/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/YSZ fillers for PMMA denture base on the thermal and mechanical properties

This study is to investigate the effect of nitrile butadiene rubber (NBR as impact modifier) together with Al₂O₃/YSZ (toughening) as filler loading in PMMA denture base on the thermal and mechanical properties. PMMA matrix without fillers was mixed between PMMA powder and 0.5 mass% of BPO, and it is used as the control group. The liquid components consist of 90% of methyl methacrylate (MMA) and 10% as the cross-linking agent of ethylene glycol dimethacrylate. The denture base composites were fabricated by incorporating PMMA powder and BPO and fixed at 7.5 mass% NBR particles and filler loading (1, 3, 5, 7 and 10 mass%) of Al₂O₃/YSZ mixture filler by (1:1 ratio) as the powder components. The ceramic fillers were treated with silane (γ-MPS) and the powder/liquid ratio (P/L) according to dental laboratory practice. The TGA data obtained show that the PMMA composites have better thermal stability compared to unreinforced PMMA, while DSC curves show slightly similar Tg values. DSC results also indicated the presence of unreacted monomer content for both reinforced and unreinforced PMMA composites. The fracture toughness, Vickers hardness and flexural modulus values were statistically increased compared to the unreinforced PMMA matrix (P?<?0.05).