Surface‐enhanced Raman scattering study of monolayers formed from mixtures of 4–mercaptobenzoic acid and various aromatic mercapto‐derivative bases

Monolayers formed from aromatic compounds have many potential applications, for example in construction of bioelectronic elements having high efficiency of electron transfer. In this paper, the composition of monolayers formed on silver surfaces from mixtures of 4‐mercaptobenzoic acid (MBA) and four model (stable and easily available) aromatic thiols with strong base properties: 4,6‐diamino‐2‐mercaptopyrimidine (APY), 1H‐1,2,4‐triazole‐3‐thiol (HTR), 4‐methyl‐4H‐1,2,4‐triazole‐3‐thiol (MTR) and 3‐amino‐1,2,4‐triazole‐5‐thiol (ATR), were determined from surface‐enhanced Raman scattering (SERS) measurements. Our investigations showed that among studied aromatic bases, APY is the most promising candidate for the formation of mixed monolayers with MBA. In the whole pH range studied (2–12.5), mixed MBA + APY monolayers with similar surface concentration of both components are formed during the adsorption from the 0.5 mM MBA + 0.5 mM APY aqueous solution. Desorption of MBA and APY from the mixed monolayer is, however, significantly different. During immersion in water, surface concentration of APY decreases significantly faster than MBA (a significant part of the adsorbed MBA molecules is present on the silver surface even after 2 h of soaking in water). Presence of chlorides, bovine serum albumin or laccase in the surrounding solution does not observably influence the structure of MBA + APY monolayers. The properties of monolayers formed from MBA and substituted triazoles were found to be significantly different than those of MBA + APY monolayers. Copyright © 2009 John Wiley & Sons, Ltd.     

Weak ferromagnetism in BiFeO3 doped with titanium

The Bi_1−xA_xFe_1−xTi_xO₃ (A—Ca, Sr, Pb, Ba) and BiFe_1−xTi_xO_3+δ systems have been studied using X-ray, neutron powder diffraction and magnetization measurements in a magnetic field up to 14 T. It was found that all Bi_1−xA_xFe_1−xTi_xO₃ solid solutions are rhombohedral up to x=0.3. In the case of BiFe_1−xTi_xO_3+δ the rhombohedral distortion preserved up to x=0.11. A homogeneous weakly ferromagnetic state was found for Bi_1−xCa_xFe_1−xTi_xO₃ (0.15≤x≤0.25) and BiFe_1−xTi_xO_3+δ (0.06≤x≤0.11), probably due to magnetoelectric interactions, whereas Bi_1−xA_xFe_1−xTi_xO₃ (A—Sr, Pb, Ba) compounds above doping level x>0.1 seem to be collinear antiferromagnets.     

Spontaneous ignition of ultra-fine magnesium powder without an original oxide coat at room temperature in O2/N2 mixture streams

To examine the pyrophoric characteristics of Mg powder, we generated ultra-fine Mg particles (average particle diameter: about 0.3 μm) without an original oxide coat in an Ar stream. The ignition of the powder was measured by using the impinging O₂/N₂ mixture streams over a wide range of the experimental parameters: pressure, oxygen concentration and velocity of the streams. The Mg powder was found to ignite even at room temperature. The spontaneous ignition temperatures in the range of 278  324 K were insensitive to all the experimental parameters. The ignition delay time had a tendency to decrease with increasing experimental parameters.The ignition process of the Mg powder was found to be controlled by the surface reaction rate without an oxide coat. We proposed a new ignition hypothesis considering a critical oxide thickness on the Mg powder particles at the transition temperature from protective to non-protective nature: that is, the ignition of the Mg powder occurs when the powder temperature rises above the transition temperature before surface reactions form a protective oxide coat with the critical thickness on the individual particle surfaces. According to this hypothesis, an ignition model of Mg powder cluster was developed, and the relation between the spontaneous critical ignition temperature and the ultra-fine powder size, depending on the critical thickness of the protective oxide coat, was clarified. The critical oxide thickness was estimated.     

微波水热法制备铋铕共掺杂氧化钇磷光粉

用微波水热法制备化学计量比为(Y_0.94-x,Eu_0.06, Bi_x)₂O₃(x=0, 0.01~0.06 )的铋铕共掺杂氧化钇磷光粉。用XRD、SEM、EDS、荧光光谱及HRTEM等进行表征。结果表明:该系统由于铋的加入使(211)晶面的生长受到抑制;在激发波长346 nm时,由于铋的掺入使发光增强;随铋掺杂量的增加,其发光先增强后减弱,并在x=0.03时有最大值;因此该系统可作为320~375 nm的近紫外(如白光LED及高压汞灯)激发用磷光粉。该系统在激发波长为254 nm时,铋的加入使发光强度减弱;因此该系统不适合用于低压汞灯。     

硫代铝酸钡(BaAl_2S_4:Eu)靶材制备工艺研究

为制备薄膜无机电致发光显示器件中的硫代铝酸钡(BaAl2S4:Eu)蓝色发光层薄膜,采用粉末烧结的方法,经过对BaS,Al2S3,等原材料的粉碎、研磨、高温烧结,以及热压等过程,制备出用于溅射镀制BaAl2S4:Eu蓝色发光层薄膜的靶材样品。对制备的BaAl2S4:Eu发光层薄膜进行的光致发光分析表明,在300nm紫外光激发下,薄膜能够发射出峰值位于470nm处的蓝光。对发光层薄膜的XPS分析结果表明,发光层薄膜中含氧量较高,随着溅射功率的提高,薄膜中铝元素有显著增加;而随着淀积压强的增大,硫元素则显著减少。     

用傅立叶变换红外光谱法研究核辐照对三七粉成分的影响

本文采用红外光谱法对经不同剂量核辐照的三七粉进行了对比研究, 比较了它们红外光谱的异同。三七粉的红外光谱主要由淀粉吸收带及碳水化合物的吸收带组成, 低辐照剂量(低于15 kGy)处理的三七粉组成成分的化学结构及含量几乎未发生变化; 较高辐照剂量(高于18 kGy)处理的三七粉组成成分中少数成分的化学结构及含量可能已经发生了变化。表明采用适当核辐照剂量杀灭三七粉中污染微生物和各种寄生虫卵是可取的。辐照剂量高于15 kGy后, 糖类(主要是多糖、庶糖)增加, 增加的糖可能是淀粉转化而来的。     

苯亚磺酸钠在聚乙烯醇为粘合剂的光敏热成像材料中的化学增感

以水溶性聚乙烯醇(PVA)为粘合剂,以异位法制备的颗粒尺寸为100nm的AgBr乳剂作光敏元,考察了苯亚磺酸钠(SBS)的用量、增感时间和增感温度对光敏热成像(PTG)材料照相性能的影响.实验结果表明:分别增感硬脂酸银(AgSt)、AgBr或者两者混合物,PTG材料均可取得明显的增感效果;灰雾随着苯亚磺酸钠用量增加而增加;增感温度以及增感时间不同,PTG材料的感光度不同.     

纳米金属氧化物粉体爆轰合成

对含能前驱体如硝酸盐和控制炸药装药的情况下爆轰反应生成纳米金属氧化物进行了探索研究。采用透射电子显微镜表征了爆轰产物。氧化物爆轰产物中的碳微粒即爆轰灰在某种意义上反映了晶型生长机制。通过爆轰合成技术产生的氧化物肯定了纳米粉体爆轰合成技术的有效性。介绍了纳米氧化铝的制备,测试了氧化铝的微观结构和分布状态。结果表明:通过硝酸盐炸药的爆轰产生了纳米尺度的金属氧化物,球形氧化铝粒径主要分布于20~50 nm之间。该方面研究工作的开展也将促进在细微观尺度上的工业炸药设计和爆轰理论的发展。     

一种普适型国产银盐感光胶的全息特性实验研究

实验研究了一种普适型国产HR_1型卤化银乳胶的主要全息特性;论述了其曝光量对衍射效率的影响;比较了两种化学后处理方法对衍射效率和信噪比的影响。实验结果表明,HR_1型卤化银乳胶是一种适合于记录透射和反射型合成全息图的记录介质,可以获得较高的衍射效率和信噪比。     

富氧条件下Ag/Al2O3和Cu/Al2O3组合催化剂催化C3H6选择性还原Nox的性能

 在全自动催化剂活性评价装置上,考察了富氧条件下Ag/Al2O3和Cu/Al2O3两种催化剂上催化丙烯还原NOx的活性. 在实验温度范围(200～650 ℃)内,Ag/Al2O3具有 优异的催化丙烯选择性还原NOx的活性,但同时有大量副产物CO形成. Cu/Al2O3选择性催化丙烯还原NOx的活性不高,却能有效促进CO的氧化. 在无水条件,Ag/Al2O3-Cu/Al2O3组合体系具有与Ag/Al2O3相似的脱除NOx活性,同时使CO在300 ℃以后几乎完全转化. 在10%水蒸气存在的情况下,Ag/Al2O3-Cu/Al2O3组合催化剂脱除NOx的活性下降,但水蒸气对CO转化率的影响不大.