pH effect on the morphology of ZnO nanostructures grown with aqueous chemical growth

ZnO nanostructures were grown for various pH values on Corning 7059 by aqueous chemical growth (ACG) using an equimolar aqueous solution of Zn(NO₃)₂·6H₂O (zinc nitrate hexahydrate) and C₆H₁₂N₄ (HMTA; hexamethylenetetramine). It was indicated that the increasing of the pH of the solution significantly leads to a modification of the ZnO morphology from rod-like to prism-like and flower-like structures.     

Growth of fibrous hydroxyapatite in the gel system

Hydroxyapatite (HAP) was prepared in the agar gel system, where Ca²⁺ ions were incorporated in the gel and PO ₄ ^3– solution was layered over the gel. When the concentration of Ca²⁺ was lower than 1.0 M and the initial solution Ca/P molar ratio was lower than about unity, fibrous HAP several centimetres to several tens of centimetres in length was grown upwards in the PO ₄ ^3– solution from the gel phase, while at the larger Ca²⁺ concentration and initial Ca/P molar ratio CaHPO₄ · 2H₂O (DCPD) in the form of gelatinous precipitate, particulate precipitates or needle-like crystals were preferred to HAP. The fibrous HAP was calcium deficient and composed of small elongated hollow ovals linked in a zigzag row. This was considered to be formed in the following manner. First, Ca²⁺ ions supplied through pores in the gel reacted with PO ₄ ^3– ions to form a small spherulite at the pore exit, then the spherulite was bloated and elongated by the osmotic pressure or capillary force until a part of the oval was broken for Ca²⁺ ions to be gushed out into the PO ₄ ^3– solution. The above two processes were repeated to form elongated hollow ovals linked to the preceding ones.     

Fibrous growth of strontium substituted hydroxyapatite and its drug release

The effect of strontium on the crystallization of helical ribbon of hydroxyapatite (HAp) was investigated by single diffusion technique in silica gel matrix at 27 °C and physiological pH. Fibers of HAp were obtained on addition of strontium. The length of the HAp fibers, were found to decrease as the strontium substitution increases. The presence of strontium ion increased the crystallinity as well as crystallite size of HAp. The strontium substituted HAp (Sr-HAp) has similar stoichiometry to that of biological apatite. Sr-HAp was found to have increased surface area (35%) compared to control. Further, strontium substitution leads to an enhancement of in vitro bioactivity. The cumulative in-vitro amoxicillin drug release in phosphate buffer solution (PBS, pH 7.2) showed a prolonged release profile for Sr-HAp.     

Effect of cooling rate and polyvinyl alcohol on the morphology of porous hydroxyapatite ceramics

Hydroxyapatite (HAP) ceramics with unidirectional lamellar pores and ceramic walls were fabricated by the unidirectional freezing process and freeze drying method. The composition of HAP aqueous slurry and the cooling rate both affected the shape and size of pores. The size of lamellar pores in HAP ceramic was longer than that in HAP ceramic with polyvinyl alcohol (PVA) additive. When the PVA additive was added into the slurries, there were smaller dendrite structures on the ceramic walls frozen with higher cooling rate, while the lower cooling rate resulted in the smooth surfaces. However, there was no obvious distinction between the ceramics without additive fabricated with different cooling rates.     

Effects of pH and temperature on microstructure and morphology of hydroxyapatite/collagen composites synthesized in vitro

Hydroxyapatite/collagen composites (HAp/Col) were synthesized, in vitro, using the self-organization mechanism, by the co-precipitation of collagen, extracted from pork skin, and aqueous H₃PO₄ and Ca(OH)₂. The effects of pH and temperature, on the microstructure and morphology of HAp/Col composites, were extensively studied.It was shown that the yield of the composite is closely related to the pH value, during preparation. At high pH, the white precipitate of the composites was formed in a large quantity. In contrast, the yield was quite low, at low pH, owing to the dissolution of the composite precipitates. The electrophoretogram of the as-prepared composite shows that the α1(I) chain was dominant and that there was no protein residue in the supernatant of the reaction solution. Accordingly, it is reasonable to assume that the collagen molecules had completely reacted with hydroxyapatite.A closer look at the structural evolution of HAp/Col composites revealed that, at pH = 5, there was no sign of interfacial interaction between hydroxyapatite and collagen, during the first 36 h. In contrast, under alkaline conditions, the amount of α(I) chains was indeterminate, at the start of precipitation, while the concentration of β-chains decreased gradually. The chemical structure of HAp/Col, as determined by FTIR spectra, revealed that the bending vibration of phosphate contours can be attributed to the dissolution of HAp, at low pH. The crystalline of HAp was readily discerned, for all samples, as revealed by the XRD patterns. The morphology of the HAp/Col, prepared under neutral to alkaline conditions (7 ≤ pH ≤ 9), exhibited a compact, coral reef-like structure. In summary, HAp/Col composites can be synthesized, in vitro, under conditions native to animal physiology. The desirable conditions for synthesis are a higher pH (8 to 9) and a temperature of 40 °C.     

Controlled growth and investigations on the morphology and mechanical properties of hydroxyapatite/titania nanocomposite thin films

In this paper, the focus is on understanding the properties of nanocomposite hydroxyapatite (HAp)/titania (TiO₂) thin films with respect to TiO₂ concentration. HAp/TiO₂ nanostructured composite thin films with different TiO₂ concentrations were successfully fabricated by a simple sol–gel dip coating method. Highly stable HAp and TiO₂ sols were prepared prior to the formation of nanocomposite thin films. The coatings were performed under controlled dipping and heat treatment processes. Phase pure HAp and TiO₂ were well developed in the nanocomposite after the heat treatment and this was confirmed by XRD. The SEM and AFM analyses of HAp/TiO₂ nanocomposite coatings show the variation in the morphology as a consequence different TiO₂ concentration. This shows a reduction in the particle size to nanoscale due to the addition of TiO₂. The mechanical strength of the coating also increased upon the addition of TiO₂ as determined by nanoindentation. The composite thin films with 50 and 80 vol.% of TiO₂ show good mechanical strength when compared to other concentrations of TiO₂.     

温度梯度和生长速率对CdZnTe-VBM生长晶体的影响

计算模拟了半导体材料CdZnTe垂直布里奇曼法(CdZnTe-VBM)单晶体生长过程，分析了炉膛温度梯度和坩埚移动速率对结晶界面形态和晶体内组份偏析的影响。计算结果表明炉膛温度梯度和生长速率的变化明显影响固-液界面前沿对流场的形态和强度。界面凹陷深度随着炉膛温度梯度的增加和生长速率减小而减小。炉膛温度梯度的增加和生长速率的减小虽然均能有效的减小径向偏析，但却增加轴向偏析，减小轴向等浓度区的长度。     

Crystallographic orientation and temperature effects on the fatigue crack growth rate and resulting fracture surface morphology in PWA1484 single crystal superalloy

This research looked at the effect of crystallographic orientation and temperature on the fatigue crack growth rate and the resulting fracture surface morphology in PWA1484 single crystal superalloy. Two groups of single edge notch tension specimens, one group with controlled secondary orientations and one group with uncontrolled secondary orientation, were tested at temperatures from 649°C to 982°C at R‐ratios of 0.1 and 0.7. It was found that the effect of temperature on the crack growth rate becomes more pronounced as the crack driving force increases while the secondary orientation and R‐ratio effects on the crack growth rate increase with increasing temperature. Two types of crack surface morphology were seen during fractography. The first was a precipitate avoidance (γ′ avoidance) morphology that was rolling but still predominantly flat when observed on a larger scale. In <001> primary oriented specimens, this fracture mode tended to follow the precipitate/matrix faces (microscopically cubic) while macroscopically staying essentially normal to the applied loads. The second mode was a form of cleavage (γ′ shearing) and occurred predominantly on octahedral crystallographic planes.     

Effect of mechanical activation on the morphology and structure of hydroxyapatite

We have studied the effect of grinding in planetary mills on the phase composition, morphology, and water content of hydroxyapatite powder. The results indicate that milling for even relatively short times, which reduces the average particle size by a factor of 2, causes the monetite present in the unmilled powder to disappear and reduces the crystallite size of the hydroxyapatite. The fraction of nanoparticles in the powder is then 98% and remains constant during further milling. Milling for longer times leads to hydroxyapatite amorphization. For an average size of large particles R ≥ 1 μm, the surface area of the particles per unit volume, E (cm⁻¹), is determined only by R (E ∼ 1/R).     

Effect of the solution pH on the growth of spray-deposited CuInS2 thin films

The effect of solution pH on the growth of spray deposited CuInS₂ thin films has been investigated. Solutions with pH 1.5, 2.4, 3.5 and 4.5 are used to deposit the films on glass substrates held at 550 K. The films have been characterized using optical absorption, X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. At pH 1.5, no film formation is observed. Films deposited from 2.4 pH solution contain binary phase Cu_{2 S}. Near stoichiometric, single phase CuInS₂ films with chalcopyrite structure are formed when solution pH=3.5. Films deposited from 4.5 pH solution are also found to be single phase, near stoichiometric CuInS₂ and exhibited chalcopyrite structure. However, an additional optical absorption process is observed which is attributed to a sub-band gap absorption.     

The growth morphology of the Ni-rich Ni-Ta-Cr-Mn system

The solidification of an Ni-Ta-Cr-Mn alloy has been investigated for a range of cooling rates and the cellular-to-dendrite transition characterized. The growth directions of the primary and secondary dendrite branches are parallel to 〈100〉. Microsegregation produces a white core in the dendrite interior in some growth conditions.     

Effect of gas flow rate on surface morphology and crystal quality of ZnTe epilayers grown on GaAs substrates

The effect of gas flow rate on surface morphology and crystal quality of ZnTe layers grown on the (1 0 0) GaAs substrates by atmospheric pressure metalorganic vapor phase epitaxy with dimethylzinc and diethyltelluride as the source materials was investigated. The surface morphology of the ZnTe epilayers is significantly improved with increasing the total gas flow rate. X-ray rocking curve and photoluminescence measurements indicate that the total gas flow rate plays a vital role in the growth characteristics of the ZnTe epilayers, and the ZnTe epilayer with best crystal quality is obtained at the total gas flow rate around 300 standard cubic centimeters per minute (sccm) in this work.     

水热体系中不同的前驱物对羟基磷灰石微结构的影响

纳米羟基磷灰石由于具有良好的生物相容性和生物活性而应用广泛,形貌控制对其应用至关重要。本文以磷酸为磷源前驱物,利用XRD、SEM及EDS系统比较研究了水热体系中不同钙源前驱物对合成羟基磷灰石(HAP)晶体微结构及晶体生长的影响,同时利用配位体理论对其生长机理进行了初步探讨。研究结果表明,不同钙源前驱物在pH值=10,水热温度200℃、水热时间8h的条件下,均可以合成结晶度较好的纳米羟基磷灰石晶体,不同钙源前驱物对合成HAP产物的物相、分散性、结晶性及微结构有一定的影响,碳酸钙、氢氧化钙为钙源前驱物制备的HAP为类球状的纳米HAP,氯化钙、硝酸钙为钙源前驱物制备的HAP呈短棒状,但与以硝酸钙为钙源前驱物制备的HAP晶体的结晶度、规整度、均一性及晶体极性生长特性相比,氯化钙较差。EDS分析证实,不同的前驱物合成产物的HAP晶体不含有任何杂质,但HAP晶体的钙磷比略有差别,平均钙磷比约为1.75,合成的HAP属于富钙型的纳米羟基磷灰石。     

Effect of pH on the precipitation of hydroxyapatite on silica gels

Silica-HAp composites have been produced with particle size ranging from several nm to few μm, through control of the pH of the solution, which also controls morphology. A calcium ions reservoir has been made available as a Ca/EDTA soluble complex allowing the production of HAp at low temperature and short periods of time (hours). The presence of silica seems to promote the formation of HAp under these conditions. Electronic Publication     

催化剂结构与形态对碳纳米管生长的影响

采用溶胶-凝胶超临界流体干燥技术制备了含铁、钴的纳米SiO2复合气凝胶催化剂,用于碳纳米管和纳米碳包覆磁性纳米粒子的合成。利用N2物理吸附、XRD、TEM、HRTEM、EDS、SAED等手段对催化剂在不同温度下处理后晶型的转变、形态的变化进行了分析,并考察了催化剂对碳纳米管形貌、结构和碳增重率的变化。结果表明:随着处理温度从600℃升高到1000℃,催化剂比表面积从312.4m2 g降低到79.6m2 g,催化剂粒子从非晶态向晶态转变,粒径从5nm增大至60nm左右,碳的增重率从254.8%下降41.5%。采用低温处理的催化剂,碳产物中以碳纳米管为主,而采用较高温度处理后的催化剂,碳产物中则以碳包覆粒子为主,且随处理温度的升高碳包覆粒子的含量逐渐增加。     

羟基磷灰石的形态结晶控制

对化学沉淀法制备羟基磷灰石中的制备温度、pH值、分散剂浓度、反应物浓度以及搅拌速度等因素对羟基磷灰石生长形态和结晶的影响进行了系列研究。结果表明：上述因素分别对HA的生长形态和结晶状况有不同程度的影响．通过对工艺参数的合理选择可以得到具有不同结晶状况和形态的羟基磷灰石颗粒。