α"-Fe16N2薄膜结构热稳定性的研究

α〃-Fe16N2的结构及其高饱和磁化强度是磁性材料研究中最有争议的问题.本文用对向靶反应溅射法制备了α〃-Fe16N2薄膜,用X射线衍射(XRD)、透射电子显微镜(TEM)和振动样品磁强计(VSM)对其结构、磁性以及结构的热稳定性进行了分析讨论.结果表明,随退火温度的升高,α〃-Fe16N2相逐渐分解为α-Fe和γ＇-Fe4N两相.     

α^〃—Fe16N2薄膜结构热稳定性的研究

α＾〃－Ｆｅ１６Ｎ２的结构及其高饱和磁化强度是磁性材料研究中最有争议的问题。本文用对向靶反应溅射法制备了α＾〃－Ｆｅ１６Ｎ２薄膜,用Ｘ射线衍射（ＦＸＲＤ）、透射电子显微镜（ＴＥＭ）和振动样品α＾〃－Ｆｅ１６Ｎ２相逐渐分解为α－Ｆｅ和γ＾′－Ｆｅ４Ｎ两相。     

α″- Fe_(16)N_2薄膜结构热稳定性的研究

α″- Fe16N2的结构及其高饱和磁化强度是磁性材料研究中最有争议的问题。本文用对向靶反应溅射法制备了α″- Fe16N2薄膜 ,用 X射线衍射 (XRD)、透射电子显微镜 (TEM)和振动样品磁强计 (VSM)对其结构、磁性以及结构的热稳定性进行了分析讨论。结果表明 ,随退火温度的升高 , α″- Fe16N2相逐渐分解为α- Fe和α′- Fe4N两相。     

α-Fe2O3 nano-platelets prepared by mechanochemical/thermal processing

A new method to prepare plate-shaped Fe₂O₃ nanoparticles was investigated and their magnetic properties were characterised. First, Fe₂O₃ nanoparticles of ~ 6 nm in diameter were synthesised by mechanochemical processing, involving the solid-state exchange reaction Fe₂(SO₄)₃ + 3 Na₂CO₃ → Fe₂(CO₃)₃ + 3 Na₂SO₄ → Fe₂O₃ + 3 Na₂SO₄ +  3 CO₂ (g) effected by high-energy ball milling and subsequent heat treatment at 400 °C. Next, nano-platelets were grown from the nanoparticles by further heat treatment in a salt matrix at 700 °C. Removal of the salt and by-product phases after heat treatment led to well-dispersed platy haematite particles of 20-200 nm in diameter with aspect ratio of 4-10. The hematite nano-platelets were weakly ferromagnetic with coercivity of ~ 160 Oe and remanent magnetisation of 0.2 emu/g.     

α-Fe2O3空心球的溶剂热合成与表征

以FeCl3.6H2O为原料,乙醇为溶剂,采用聚乙二醇(PEG-400)辅助的溶剂热法制备了大小均匀的α-Fe2O3空心微球,其直径约为900 nm,粒径分布均匀。产物经X射线衍射仪(XRD)、扫描电镜(SEM)和透射电镜(TEM)进行了表征。     

Room temperature NO2 gas sensor based on PPy/α-Fe2O3 hybrid nanocomposites

Polypyrrole–iron oxide (PPy/α-Fe₂O₃) hybrid nanocomposite sensor films were prepared by spin coating method on glass substrate and characterized for structural and morphological properties by means of X-ray diffraction (XRD), Fourier transform infra red (FTIR) spectroscopy and scanning electron microscopy (SEM), which proved the strong interaction between polypyrrole and α-Fe₂O₃ nanoparticles. The gas-sensing properties of the hybrid nanocomposites were studied and compared with those of PPy and α-Fe₂O₃. It was found that PPy/α-Fe₂O₃ hybrid nanocomposites can complement the drawbacks of pure PPy and α-Fe₂O₃ to some extent. It was revealed that PPy/α-Fe₂O₃ (50%) hybrid sensor operating at room temperature could detect NO₂ at low concentration (10 ppm) with very high selectivity (18% compared to C₂H₅OH) and high sensitivity (56%), with better stability (85%). The sensing mechanism of PPy/α-Fe₂O₃ materials to NO₂ was presumed to be the synergism of PPy and α-Fe₂O₃ or the effect of p–n heterojunctions.     

Magnetite/maghemite mixture prepared in benzyl alcohol for the preparation of α″-Fe16N2 with α-Fe

Fine powder of iron oxide has been required in the preparation of ferromagnetic α″-Fe₁₆N₂ powder in low temperature nitridation. Magnetite and maghemite mixture was obtained by the reaction of iron acetylacetonate Fe(acac)₃ in benzyl alcohol. It was reduced to α-Fe in hydrogen at 400 °C. Particle size of the α-Fe was 300 nm in the reduction of iron oxides obtained from 2 g of Fe(acac)₃. It decreased to 100 nm in the preparation using 8 g of Fe(acac)₃. After the successive nitridation under ammonia flow at 160 °C, the highest yield of α″-Fe₁₆N₂ in 66 wt.% was observed on the nitrided product from the latter α-Fe, because of the smallest α-Fe particle size after the reduction in the present study. The yield and reproducibility of α″-Fe₁₆N₂ formation in low temperature nitridation was improved using the iron oxide prepared in non-aqueous benzyl alcohol compared to the use of magnetite obtained from aqueous solution.     

聚苯胺改性纳米ZnO/α-Fe2O3降解亚甲基蓝的研究

以聚苯胺(PANI)为载体,采用共沉淀-水热反应和原位聚合法制备了PANI-ZnO/α-Fe2O3复合光催化剂,应用于模拟日光催化氧化印染废水的处理中。SEM、XRD测试结果表明,活性组分ZnO/α-Fe2O3在聚苯胺载体中以纳米颗粒形式稳定存在。与载体聚苯胺相比,复合光催化剂的吸附能力有所降低,但在模拟日光下催化效果显著。对于50 mL模拟印染废水(亚甲基蓝10 mg/L),投加20 mg PANI-ZnO/α-Fe2O3,辐照7 h脱色率可达90.03%。     

改善PEC用α-Fe2O3光阳极性能的策略

通过光电化学(PEC)电池将太阳能收集和储存为氢燃料,为未来的能源需求提供了一条清洁和可再生的途径。在多种常用材料中赤铁矿(α-Fe₂O₃)由于其来源丰富、价格低廉、优异的光稳定性等特点,近几十年来一直是研究热点。对PEC水分解用赤铁矿光阳极的最新进展进行了综述。首先,介绍了掺杂手段提高赤铁矿体相电导率。其次,介绍了负载助催化剂和沉积表面钝化层改善赤铁矿表面反应的有效途径。以及引入中间层促进界面传输3个方面进行了综述。展望了PEC水分解用赤铁矿光电极的发展前景和面临的主要挑战。     

非晶态Si3N4结晶及α-Si3N4晶种的调控结晶行为

采用液相界面反应法制备高α相的Si₃N₄粉体。以SiCl₄为硅源,液氨为氮源,甲苯为溶剂,通过液相界面法合成硅亚胺,硅亚胺在1 000℃分解为非晶态Si₃N₄粉体,在1 550℃晶化为α-Si₃N₄粉体。研究了非晶态Si₃N₄的晶化过程,并讨论了添加α-Si₃N₄晶种对非晶态Si₃N₄结晶过程的影响。结果表明:晶核从具有短枝状结构的非晶态Si₃N₄团聚体的表面和内部形成,进而生长成为α-Si₃N₄晶粒;添加α-Si₃N₄晶种,能够增加形核数量,加快了非晶态Si₃N₄向α-Si₃N₄的结晶转...     

柔顺剂的微观结构以及相稳定性研究

本文用光学显微镜、偏光显微镜以及粒径仪研究了有效成分为双氢化牛油基二甲基氯化铵的柔顺剂的微观结构。体系不是乳液结构,而是由DHTDMAC形成双分子层的囊泡结构,具有明显的液晶特征。电解质强度、配方成分及工艺参数等对囊泡的粒径分布有明显影响,从而影响成品黏度。     

First principles study of the structure and stability of carbynes

Possible structures for carbynes are investigated by a first principles study and their free energy as a function of temperature and pressure is examined. A possible model combining elements from previous models is proposed for carbyne structures. Simulations show that structures can be constructed which agree well with results previously proposed in characterization work. The free energy of carbynes is calculated within wide ranges of temperature and pressure (1000-4000 K and 0-18 GPa) for 12 different structures. Results indicate that it is higher than the free energy of graphite in the whole studied region. Therefore, it seems that carbon-only carbynes are meta-stable structures. Introducing additional elements to stabilize the carbyne structures is discussed. Our calculations confirm that a solid consisting of carbyne chains can be stabilized by 3 CH₃ end groups.     

Carbon fiber structure and stability studies

A study has been made of the thermal-oxidative stability of several commercially available carbon fibers. Significant differences in the weight loss behavior were observed in air aging studies run on the bare fibers at 600°F (589 K). The stability of high temperature laminates, such as those based on NR-150 polyimide precursor solutions, was found to be directly affected by the stability of the reinforcing carbon fibers. In studies carried out to determine the reasons for carbon fiber instability, residual sodium sulfate was found to be the principle destabilizing factor. A mechanism whereby the sodium sulfate promotes the oxidation of carbon in the presence of air is proposed.     

Influence of the chemical structure of PUR prepolymers on thermal stability

The thermal stability of adhesives for load-bearing construction has been one of their key parameters since engineered wood products were introduced in timber construction. In the case of one-component moisture-curing polyurethane (1C PUR) adhesives, knowledge about relationships between their chemical structure and the resulting bonding properties is limited, especially under high-temperature conditions. In this study the structure-property relationships of 1C PUR prepolymers were analyzed in the temperature range from 20 to 200 °C by means of mechanical and rheological tests. NCO-terminated urethane prepolymers were prepared from systematically varied MDI and polyether mixtures. The structural parameters investigated were the urea and urethane group content, cross-link density, ethylene oxide content and the adjustment of functionality via NCO or polyether component. Bonded wood joints were tested for their tensile shear strength and polymer films were analyzed by means of DMA and DSC. The results revealed a significant influence of hard segment content and cross-link density on the thermal stability of the prepolymers. Not all parameters that affect the film properties significantly influence bonding.     

去污泡沫稳定性研究

为提高去污泡沫稳定性,提升去污效率,借助泡沫扫描分析仪对以APG为发泡剂主要组分的去污泡沫的稳定性进行了研究。结果表明,随着碳链的增长,泡沫体积衰减变小,持液半衰期变长,结合泡沫形貌分析及二次废液处理问题,推荐C_(8-14)APG用于去污泡沫;通过添加黄原胶可显著增加去污泡沫稳定性,黄原胶的添加量不宜超过2 g/L。     

有机硅乳液稳定性的研究

以阳离子型乳液聚合为例，详细讨论了聚合反应因素及环境因素对环氧改性有机硅乳液稳定性的影响。结果表明：在聚合反应温度为65℃、催化剂的用量为总加料量的0．3％～0．5％、硅烷偶联剂的用量为D4质量的3％～5％、乳化剂用量为总加料量的10％、阳／非离子型乳化剂的质量比为1．5～1．8、D4与水的质量比为0．3～0．4条件下，制得的环氧改性有机硅乳液稳定性良好；采取急冷的方式中止聚合反应，并以醋酸中和至pH值为6～7，有利于环氧改性有机硅乳液稳定性的提高。     

去污泡沫稳定性研究

为提高去污泡沫稳定性,提升去污效率,借助泡沫扫描分析仪对以APG为发泡剂主要组分的去污泡沫的稳定性进行了研究。结果表明,随着碳链的增长,泡沫体积衰减变小,持液半衰期变长,结合泡沫形貌分析及二次废液处理问题,推荐C_(8-14)APG用于去污泡沫;通过添加黄原胶可显著增加去污泡沫稳定性,黄原胶的添加量不宜超过2 g/L。     

Solution structure and stability of tryptophan-containing nucleopeptide duplexes

Covalently linked peptide-oligonucleotide hybrids were used as models for studying tryptophan-DNA interactions. The structure and stability of several hybrids in which peptides and oligonucleotides are linked through a phosphodiester bond between the hydroxy group of a homoserine (Hse) side chain and the 3'-end of the oligonucleotide, have been studied by both NMR and CD spectroscopy and by restrained molecular dynamics methods. The three-dimensional solution structure of the complex between Ac-Lys-Trp-Lys-Hse(p3'dGCATCG)-Ala-OH (p=phosphate, Ac=acetyl) and its complementary strand 5'dCGTAGC has been determined from a set of 276 experimental NOE distances and 33 dihedral angle constraints. The oligonucleotide structure is a well-defined duplex that belongs to the B-form family of DNA structures. The covalently linked peptide adopts a folded structure in which the tryptophan side chain stacks against the 3'-terminal guanine moiety, which forms a cap at the end of the duplex. This stacking interaction, which resembles other tryptophan-nucleobase interactions observed in some protein-DNA complexes, is not observed in the single-stranded form of Ac-Lys-Trp-Lys-Hse(p3'dGCATCG)-Ala-OH, where the peptide chain is completely disordered. A comparison with the pure DNA duplex, d(5'GCTACG3')-(5'CGTAGC3'), indicates that the interaction between the peptide and the DNA contributes to the stability of the nucleopeptide duplex. The different contributions that stabilize this complex have been evaluated by studying other nucleopeptide compounds with related sequences.     

酶的寡聚结构与催化稳定性

酶的结构与催化稳定性是生物催化与转化过程中的研究热点之一。与单体酶相比,寡聚酶在进化过程中亚基之间的聚合使其在结构和功能上具有一定的优越性,然而寡聚酶独特的四级结构导致其在制备和应用中存在诸多问题,如制备效率低、催化位点利用率低、催化稳定性差等,其中亚基解离导致的催化稳定性问题在很大程度上限制了其工业化应用。目前,介质工程、多亚基固定化、亚基界面工程和融合蛋白策略被应用于寡聚酶的催化稳定性改造,而寡聚酶至单体酶的改造策略则试图从根本上解决寡聚酶的制备和应用问题,具有较好的应用前景。本文介绍了酶的寡聚结构演替所产生的新功能,总结了寡聚酶在制备和应用中存在的问题,重点阐述了提高寡聚酶制备效率和催化稳定性的策略。