Synthesis and characterization of nano-hydroxyapatite added with magnesium obtained by wet chemical precipitation

Biogenic hydroxyapatites from mammalian bones naturally contain traces of ions, like Mg, which play a vital role in the bone remodeling process. In this way, synthetic hydroxyapatites should include this kind of mineral. In this work, hydroxyapatite added with Mg was synthesized by wet precipitation using (NH₄)H₂PO₄, Ca(NO₃)₂.4H₂O, and Mg(NO₃)₂.6H₂O (0, 0.032, 0.061, and 0.123 ​M). Inductively coupled plasma and X-ray diffraction evidenced the Mg inclusion in the hydroxyapatite lattice in the same levels reported for natural hydroxyapatites. The calcination at 600 ​°C was performed to remove the reaction by-products, but it also gave rise to physicochemical changes as the coalescence and crystals recrystallization. It produced, in turn, an improvement in the crystalline quality, according to Raman analysis. Despite those physicochemical changes, all the samples remained nanometric according to scanning electron microscopy imaging.     

Identification of thermal effects involved in DSC experiment on Al-Cu-Mg-Ag alloys with high Cu:Mg ratio

Precipitation reactions in the differential scanning calorimetry (DSC) of an Al-Cu-Mg-Ag alloy were identified by analyzing the results from hardness test, electrical conductivity test, and transmission electron microscope (TEM) examination. It is discovered that thermal effects can be identified through selected area electron diffraction and bright-field images. The reaction peaks around 171, 231, and 276℃ can be attributed to a structural rearrangement of coherent zones, to the precipitation of Ω phases, and to the precipitation of Ω and θ' and possible combination with the transition of θ'→θ, respectively. In addition, the hardness and electrical conductivity of the alloy change proportionately with the progression of reactions during the heating process. This phenomenon can be attributed to the evolution of the microstructure.     

Significantly enhanced hydrogen desorption properties of Mg(AlH4)2 nanoparticles synthesized using solvent free strategy

Mg(AlH_4)_2 nanoparticles with a particle size less than 10 nm have been successfully synthesized by mechanochemical method using LiAlH_4 and MgCl_2 as raw materials together with Li Cl buffering additive. In comparison to Mg(AlH_4)_2 microparticles, Mg(AlH_4)_2 nanoparticles exhibit a faster hydrogen desorption kinetics and lower desorption temperature. The hydrogen desorption temperatures of the first and second dehydrogenation steps are 80 and 220 °C for the Mg(AlH_4)_2 nanoparticles, which are about 65 and 60 °C, respectively, lower than those of Mg(AlH_4)_2 microparticles. The decomposition activation energy is reduced from 135 k J/mol for Mg(AlH_4)_2 microparticles to 105.3 k J/mol for Mg(AlH_4)_2 nanoparticles. It is proposed that the shortened diffusion distance and enhanced diffusivity of Mg(AlH_4)_2/MgH_2 nanoparticles provide an energy destabilization for lowering the dehydrogenation temperature, and thus being the key factor for promoting the hydrogen desorption kinetics. More importantly, it is demonstrated that the dehydrided nano MgH_2 hydride with a particle size below 10 nm can be formed after rehydrogenation process, resulting in the good cycling hydrogen desorption performance of nano MgH_2.     

Preparation, characterization and thermal behavior of silver behenate nanocrystals

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Texture of the nano-crystalline AlN thin films and the growth conditions in DC magnetron sputtering

DC reactive magnetron sputtering technique has been used for the preparation of Al N thin fi lms. The deposition temperature and the fl ow ratio of N2/Ar were varied and subsequent dependency of the fi lms crystallites orientation/texture has been addressed. In general, deposited fi lms were found hexagonal polycrystalline with a(002) preferred orientation. The X-ray diffraction(XRD) data revealed that the fi lm crystallinity improves,with the increase of substrate temperature from 300 ℃to 500℃. The dropped in full width half maximum(FWHM) of the XRD rocking curve value further con fi rmed it. However, increasing substrate temperature above 500 ℃or reducing the nitrogen condition(from 60 to 30% in the environment) induced the growth of crystallites with(102) and(103) orientations. The rise of rocking curve FWHM for the corresponding conditions depicted that the fi lms texture quality deteriorated. A further con fi rmation of the variation in fi lm texture/orentation with the growth conditions has been obtained from the variation in FWHM values of a dominant E1(TO) mode in the Fourier transform infrared(FTIR) spectra and the E2(high) mode in Raman spectra. We have correlated the columnar structure in AFM surface analyses with the(002) or c-axis orientation as well. Spectroscopic ellipsometry of the samples have shown a higher refractive index at 500 ℃growth temperature.     

Synthesis of CdS nanowires on Cd foil and their photoluminescence properties

Cadmium sulfide(CdS) nanowires were synthesized on Cd foil via a simple solvothermal reaction at 180 ℃ using thiosemicarbazide as the sulfide source and ethylenediamine as the solvent.The CdS nanowires are hexagonal-phase single crystals with an average diameter of 50 nm and length of several microns.The as-prepared CdS nanowires show an absorption peak of around 483 nm in the absorption spectrum.The CdS nanowires exhibit bright photoluminescence(PL) with two distinct emission bands at 503 nm and 697 nm,which shows that the as-prepared CdS nanowires are high-quality nanocrystals.     

Synthesis of nano onion-like fullerenes by using Fe/Al2O3 as catalyst by chemical vapor deposition

Nano-carbon materials were synthesized by the catalytic decomposition of acetylene at 400℃ by using Fe/Al₂O₃ as catalyst. The product was refluxed in 36% concentrated HCl at 60℃ for 48 h in order to remove the catalyst support. The samples were examined by scanning and high resolution transmission electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The results show that nano onion-like fullerenes encapsulating a Fe₃C core were obtained. These had a structure of stacked graphitic fragments, with diameters ranging from 15―50 nm. When the product was further heat- treated at 1100℃ for 2 h, nano onion-like fullerenes with a clear concentric graphitic layer structure were obtained. The growth mechanism of nano onion-like fullerenes encapsulating metal cores is suggested to follow a vapor-solid growth model.     

A study on the double melting behavior of poly（trimethylene terephthalate）

Double melting behavior of poly（trimethylene terephthalate） （PTT） was studied in detail by means of differential scanning calorimetry （DSC） and optical microscopy. The results indicate that the low-temperature melting peak of PTT at ca. 218℃ for the samples crystallized isothermally at 203℃ is associated with the melting of crystals produced by secondary crystallization, while the high-temperature melting peak of it at about 227℃ is related to the melting of the crystals produced by primary crystallization. The results further demonstrate that the PTT crystals growing non-isothermally during cooling process are thermodynamically unstable and can undergo structure reorganization during the DSC heating scan. The reorganized crystals melt at temperature higher than the crystals produced by secondary crystallization at 203℃. Consequently, for the non-fully crystallized samples, the crystals grown during cooling also exhibit contribution to the high-temperature melting peak.     

Hot deformation behaviors of WE71 alloy under plain strain compression at elevated temperature

Hot deformation behaviors of WE71 (Mg–7Y-1Nd-0.5Zr) alloy was investigated by plain strain compression tests conducted at temperatures ranging from 350 °C to 500 °C and strain rates varying from 0.01 s^-1 to 10 s^-1. Results show that the hot deformation of WE71 was accompanied by the precipitation of rich Zr phase with granular shape and block-shaped phase rich in element Y. When deformed at low temperature and high strain rate, the softening behavior of the alloy was synergically determined by shear bands propagation, adiabatic heating, twinning formation and dynamic recrystallization (DRX). For the conditions of high temperature and high strain rate, DRX was the major softening mechanism while the formation and annihilation of extension twinning resulted in a special flow curve characteristic at the strain of around 0.3. According to the microstructural observations, it can be concluded that the irregular flow curves of WE71 alloy during plain strain compression process are mainly ascribed to shear bands propagation, adiabatic heating, twinning formation and DRX.     

超临界流体干燥法制备医用纳米羟基磷灰石

应用超临界流体干燥法制备医用纳米羟基磷灰石.以 Ca(NO3)2·4H2O和(NH4)2HPO4 为原料,采用超临界流体干燥法(SCFD)制备了纳米羟基磷灰石,并用 XRD,TEM,FTIR等手段进行了表征.超临界干燥法制备的羟基磷灰石具有结晶性好、分散性好、尺寸分布均匀,呈针状结晶,长度为 100~200 nm,宽度 10~15 nm.用溶胶凝胶结合超临界流体干燥法可以制备出颗粒大小均匀、分散性好的纳米羟基磷灰石.     

Influence of modulation period for β-Cu2+xSe/SiC nano-multilayer films on their thermoelectric properties

In this study, β-Cu_2+xSe/SiC nano-multilayer films with different modulation period were successfully deposited on SiO₂/Si substrates by sputtering alternately using Cu–Se and SiC targets. The deposited films were observed on both surface and cross-section, and the thermoelectric properties were studied. The results show that both carrier concentration and mobility at room temperature decreased with the reducing modulation period for the nano-multilayer films. The conductivity slightly decreased and Seebeck coefficient greatly increased with the reducing modulation period. As a result of competition, the power factor of the nano multilayer films increased with the reducing modulation period because the positive effect of the Seebeck coefficient exceeded the negative effect of the conductivity. In the case of β-Cu_2+xSe/SiC nano multilayer film with the smallest modulation periods (210 ?nm), the power factor reached 0.39 ?mWm^?1K^?2 and 0.59 ?mWm^?1K^?2 at room temperature and 325 ?°C, respectively. The enhanced power factor for nano multilayer films is attributed to the scattering process at the β-Cu_2+xSe/SiC layer interface, which reduces the carrier concentration and the mobility. It is concluded that the thermoelectric properties of β-Cu_2+xSe films can be effectively improved by designing nano multilayer structure.     

Carbothermal synthesis of Si3N4 powders using a combustion synthesis precursor

Si₃N₄ powders were synthesized by a carbothermal reduction method using a SiO₂ + C combustion synthesis precursor derived from a mixed solution consisting of silicic acid (Si source), polyacrylamide (additive), nitric acid (oxidizer), urea (fuel), and glucose (C source). Scanning electron microscopy (SEM) micrographs showed that the obtained precursor exhibited a uniform mixture of SiO₂ + C composed of porous blocky particles up to ～20 μm. The precursor was subsequently calcined under nitrogen at 1200–1550°C for 2 h. X-ray diffraction (XRD) analysis revealed that the initial reduction reaction started at about 1300°C, and the complete transition of SiO₂ into Si₃N₄ was found at 1550°C. The Si₃N₄ powders, synthesized at 1550°C, exhibit a mixture phase of α- and β-Si₃N₄ and consist of mainly agglomerates of fine particles of 100–300 nm, needle-like crystals and whiskers with a diameter of about 100 nm and a length up to several micrometers, and a minor amount of irregular-shaped growths.     

升温速率对砂浆渗透性及微观结构的影响

为了研究升温速率对砂浆渗透性以及微观结构的影响,现以3种升温速率（5℃/min、10℃/min、15℃/min）加热砂浆至500℃。通过新的实验技术允许在围压下用气体同时测量砂浆的渗透率和孔隙率,并采用核磁共振（NMR）和扫描电镜（SEM）技术,观察损伤后试样的T2谱图分布、孔径分布和裂缝演变情况。结果表明：在500℃下,随着升温速率的增大,砂浆气体渗透率与孔隙率逐渐增大。在加卸载围压的过程中,与孔隙率相比砂浆的气体渗透率对围压更敏感。不同升温速率作用后的砂浆T2谱图均出现2个波峰,主波峰的分布占据了3个数量级。随着升温速率增大,砂浆的孔径分布向右移动,孔径增大。高温作用后,砂浆致密结构变得多孔疏松,升温速率越快,其内部裂缝宽度越大。     

<Emphasis Type="Italic">In situ</Emphasis> measurement of PM<Subscript>1</Subscript> organic aerosol in Beijing winter using a high-resolution aerosol mass spectrometer

Organic aerosol (OA) is a crucial component of atmospheric fine particles. To achieve a better understanding of the chemical characteristics and sources of OA in Beijing, the size-resolved chemical composition of submicron aerosols were measured in-situ using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer in the winter of 2010, with a high time resolution of 5 min. During this study, the mean OA mass concentration was 20.9±25.3 μg/m3, varying between 1.9 and 284.6 μg/m3. Elemental analysis showed that the average H/C, O/C and N/C (molar ratio) were 1.70, 0.17, and 0.005, respectively, corresponding to an OM/OC ratio (mass ratio of organic matter to organic carbon) of 1.37. The average mass-based size distributions of OA present a promi- nent accumulation mode peaking at approximately 450 nm. The prominent presence of ultrafine particles (Dva < 100 nm) was mainly from the fresh emissions of combustion sources. A Positive Matrix Factorisation (PMF) analysis of the organic mass spectral dataset differentiated the OA into three components, including hydrocarbon-like (HOA), cooking-related (COA), and oxygenated (OOA) organic aerosols, which, on average, accounted for 26.9%, 49.7% and 23.4%, respectively, of the total organic mass. The HOA and COA likely corresponded to primary organic aerosol (POA) associated with combustion-related and cooking emissions, respectively, and the OOA components corresponded to aged secondary organic aerosol (SOA).     

Low temperature spark plasma sintering of TC4/HA composites

Ti6Al4V/hydroxyapatite composites(TC4/HA) have been prepared by high energy ball milling and low temperature spark plasma sintering at 600 °C, 550 °C, 500 °C and 450 °C, respectively. The sintering temperature of the composites was sharply decreased as the result of the activation and sur fi cial modi fi cation effects induced from high energy ball milling. The decomposition and reaction of hydroxyapatite was successfully avoided, which offers the composites superior biocompatibility. The hydroxyapatite in the composites was distributed in gap uniformly, and formed an ideal network structure. The lowest hardness, compressive strength and Young's modulus of the composites satisfy the requirements of human bone.     

Effect of long-term aging treatment on the tensile strength and ductility of GH 605 superalloy

Aging treatment is an effective way to optimize the mechanical properties of Co-based superalloys. In this study, commercial GH 605 superalloy was subjected to aging treatment at 650 ?°C in a wide time range up to 1000 ?h. The effects of aging time on the tensile characteristics, microstructure evolution and mechanical properties were systematically investigated at room temperature (RT) and 900 ?°C. The results showed that the volume fractions of M₆C and M₂₃C₆ carbide increased with the aging time. After long-term aging treatment, the yield strength (YS) at RT was enhanced from 490.3 ?MPa to 805.9 ?MPa, while the alloy still had high tensile ductility (above 20%). Microscopic observations by transmission electron microscopy (TEM) indicated that the strengthening mechanism was related to carbide precipitation inside the grains and the change in the dislocation slipping mode. Moreover, long-term aging treatment can increase the elongation from 24.1% to 47.3% at 900 ?°C accompanied by a slight increase of YS from 299.3 ?MPa to 313.9 ?MPa. Based on detailed microstructure analysis the strengthening mechanism can be attributed to the refined grains as well as carbide precipitation inside the grains and around the grain boundaries.     

Synthesis of glass ceramics from kaolin and dolomite mixture

Cordierite-and anorthite-based binary glass ceramics of the CaO-MgO-Al₂O₃-SiO₂ (CMAS) system were synthesized by mixing local and abundant raw minerals (kaolin and doloma by mass ratio of 82/18). A kinetics study reveals that the activation energy of crystallization (Ea) calculated by the methods of Kissinger and Marotta are 438 kJ·mol-1 and 459 kJ·mol-1, respectively. The Avrami parameter (n) is estimated to be approximately equal to 1, corresponding to the surface crystallization mechanism. X-ray diffraction (XRD) analysis shows that the anorthite and cordierite crystals are precipitated from the parent glass as major phases. Anorthite crystals first form at 850℃, whereas the μ-cordierite phase appears after heat treatment at 950℃. Thereafter, the cordierite allotropically transforms to α-cordierite at 1000℃. Complete densification is achieved at 950℃; however, the density slightly decreases at higher temperatures, reaching a stable value of 2.63 kg·m-3 between 1000℃ and 1100℃. The highest Vickers hardness of 6 GPa is also obtained at 950℃. However, a substantial decrease in hardness is recorded at 1000℃; at higher sintering temperatures, it slightly increases with increasing temperature as the α-cordierite crystallizes.     

Effect of Zr and Ti on isothermal oxidation behavior of Nb–Si based alloys

The isothermal oxidation behavior of 56Nb-16Si-(20-x)Ti–3Cr–3Al-2Hf-xZr (x ?= ?0, 2, 5, 10 ?at. %) alloys was investigated at 800 ?°C and 1250 ?°C, respectively. The results show that increasing the Zr content evidently increased the oxidation rates at 800 ?°C, accompanied by the obvious occurrence of pesting oxidation. The alloys showed alike linear oxidation kinetics at 1250 ?°C. With the increase of Zr content, the adherence and integrity of oxide scales were improved, but the overall oxidation resistance was slightly deteriorated. The observed oxidation behavior may be attributed to the composition variation of Zr and Ti in the alloys. The oxidation mechanism associated with the composition variation is discussed in this study.     

Highly mechanical and high-temperature properties of Cu–Cu joints using citrate-coated nanosized Ag paste in air

Today, a growing number of third-generation semiconductor-based power devices are used in products that can continuously operate at high temperatures for extended periods of time. Hence, traditional tin-lead and lead-free solders are no longer suitable for modern electronic packaging. A common method is to apply Ag paste for bare Cu–Cu joints under an inert or reductive atmosphere. In this study, the citrate-coated nanosized Ag paste was utilized to generate robust bare Cu–Cu joints under atmospheric conditions. The average size of citrate-coated Ag particles was approximately 4.76 ?nm after being cleaned by deionized water and acetone. The effects of process parameters, such as cleaning, joining temperature, holding time, and joining pressure, on the mechanical properties of the bare Cu–Cu joints were thoroughly investigated. Increasing washing and joining temperatures resulted in a shear strength increase of up to 28.2 ?MPa ?at a joining temperature of 260 ?°C after seven washes. In addition, a holding time of 30 ?min and a joining pressure of 1 ?MPa were selected as optimal process conditions for the application of citrate-coated nanosized Ag paste onto bare Cu–Cu joints. The newly developed Cu–Cu joints showed excellent thermal stability at 150 ?°C using the citrate-coated nanosized Ag paste. After long-term aging, the joints exhibited stability at 250 ?°C for 144 ?h, indicating a good high-temperature reliability for three-dimensional integrated circuits (3D ICs) fabricated under atmospheric conditions.     

Mangosteen peel-derived activated carbon for supercapacitors

This work reports the effects of activation temperatures on the porous development and electrochemical performance of activated carbons. Herein, activated carbons were prepared from the biowaste of mangosteen peel by using KOH activation at temperatures of 400, 600, and 800 ?°C. The results demonstrate that the specific surface area increases with increasing the activation temperatures in which the well-developed porous structure after KOH activation at 800 ?°C provides the highest specific surface area of 1039 ?m² ?g^?1. At 600 ?°C, the activated carbon delivers the highest specific capacitance value of 182 ?F ?g^?1 ?at a current density of 0.5 ?A ?g^?1 in 3 ?M KOH aqueous electrolyte. This is correlated well with its high micropore fractions (99%). Moreover, it was found that the activation temperature changes the major contribution of oxygen-containing functional group on surface of activated carbon, which is beneficial for the enhancement of the specific capacitance value of activated carbon at the temperature of 600 ?°C. This work suggests that the activation temperature is a key to optimizing the electrochemical performance of activated carbons. Overall, our activated carbons can be considered as a strong candidate for use as electrode materials in supercapacitors.