Microchemical investigation of Greek and Roman silver and gold plated coins: coating techniques and corrosion mechanisms

Within the framework of a project financially supported by the European Commission (contract Nr. 509126, acronym PROMET) the metallurgical techniques used by Romans and Greeks for coating the copper core of coins with a thin or thick layer of gold or silver are studied by means of the combined use of scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS) and optical microscopy (OM) techniques.This approach is utilised to gain further insight into the micro-chemical structure of the external regions of the coins as well as into the bulk metallurgical features. The results indicate that several methods were used by the Greek and Roman craftsmen including the mechanical application of a thin malleable gold or silver foils to be welded via thermal treatment. The analytical approach is also used for investigating the corrosion products grown on the coins during the long-term burial and for identifying degradation mechanisms.PACS 68.55Jk; 68.35 Dv; 68.37Hk; 68.55 Nq; 81.05 Bx     

Combined use of SEM-EDS, OM and XRD for the characterization of corrosion products grown on silver roman coins

In the framework of the PROMET project (European Commission contract No. 509126) aimed to develop new analytical techniques and materials for monitoring and protecting metal artefacts and monuments from the Mediterranean region, the corrosion products grown on silver Roman coins during archaeological burial is studied by means of scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD) and optical microscopy (OM) techniques. PACS 68.55.Jk; 68.35.Dv; 68.37.Hk; 68.55.Nq; 81.05.Bx     

Combining wire and coaxial powder feeding in laser direct metal deposition for rapid prototyping

Powder and wire deposition have been used separately in many laser-cladding, rapid prototyping and other additive manufacturing applications. In this paper, a new approach is investigated by simultaneously feeding powder from a coaxial nozzle and wire from an off-axis nozzle into the deposition melt pool. Multilayer parts are built from 316L steel using a 1.5 kW diode laser and different configurations of the powder and wire nozzles are compared in terms of surface roughness, deposition rate, porosity and microstructure. The parts are analysed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and optical microscopy techniques. Results show that deposition efficiency increased and surface roughness decreased with the combined process; some porosity was present in samples produced by this method, but it was 20-30% less than in samples produced by powder alone. Wire injection angles into the melt pool in both horizontal and vertical planes were found to be significant for attaining high deposition efficiency and good surface quality. Reasons for the final sample characteristics and differences between the combined process and the separate powder and wire feeding techniques are discussed.     

Combined confocal and magnetic resonance microscopy

Confocal fluorescence optical microscopy and magnetic resonance microscopy are each used to study live cells in a minimally invasive way. Both techniques provide complementary information. Therefore, by examining cells simultaneously with both methodologies, more detailed information is obtained than is possible with each microscope individually. In this paper two configurations of a combined confocal and magnetic resonance microscope are described. The first configuration is capable of studying large single cells or three-dimensional cell agglomerates, whereas the second configuration is designed for the investigation of monolayers of mammalian cells. In both cases the sample compartment is part of a temperature regulated perfusion system. Images obtained with the combined system are shown forXenopus laevis oocytes, model JB6 tumor spheroids, and a single layer of Chinese hamster ovary cells. Finally, potential applications of the combined microscope are discussed.     

Application of hemisphere radiation shields with temperature-dependent emissivity for reducing heat transfer between two concentric hemispheres

The radiation network method has been applied to calculate the net radiation heat transfer between two concentric hemispheres separated by two hemispherical radiation shields with temperature-dependent surface emissivities. Three different materials are chosen for radiation shields: aluminum oxide, silicon carbide, and tungsten. The reduction in heat transfer with shields depends not only on the surface characteristics of the two shields, but also on the locations of the shields. Three illustrative examples are presented to illustrate the effects of temperature dependent emissivities and shield locations on the percentage heat transfer reduction. The analysis can be used to study other cases as warranted.     

超高速撞击Kevlar纤维布填充防护结构研究

 利用二级轻气炮,对Kevlar纤维布填充Whipple防护结构进行了超高速撞击实验研究。基于Nextel/Kevlar撞击极限曲线,分析了单层及双层Kevlar纤维布填充防护结构的防护性能以及填充材料、舱壁的损伤情况。实验表明,Kevlar纤维布填充Whipple防护结构在低速区具有优良的防护性能。分层布局可改善Kevlar纤维布填充Whipple防护结构在低速区的防护性能。在低速区,Kevlar纤维丝主要依靠大量的塑性变形及断裂吸收弹丸的动能;在高速区,Kevlar纤维丝存在高温熔化及碳化现象,使弹丸破碎或熔化为更小的碎片或熔球,从而减轻对舱壁的损伤。     

Exploring the environmental transmission electron microscope

The increasing interest and development in the field of in situ techniques have now reached a level where the idea of performing measurements under near realistic conditions has become feasible for transmission electron microscopy (TEM) while maintaining high spatial resolution. In this paper, some of the opportunities that the environmental TEM (ETEM) offers when combined with other in situ techniques will be explored, directly in the microscope, by combining electron-based and photon-based techniques and phenomena. In addition, application of adjacent setups using sophisticated transfer methods for transferring the specimen between specialized in situ equipment without compromising the concept of in situ measurements will be exploited. The opportunities and techniques are illustrated by studies of materials systems of Au/MgO and Cu(2)O in different gaseous environments.     

Nanoscale determination of surface orientation and electrostatic properties of ZnO thin films

Scanning force microscopy related techniques are applied to study surface nanoscale properties. We show that nanogoniometry can be combined with local electrostatic measurements – electrostatic force microscopy and Kelvin probe microscopy – to identify surface planes families and to study their local electrical properties. The scanning force microscopy techniques employed are analyzed and the correct way of acquiring and interpreting data is discussed in detail. The experiments performed on ZnO films grown along the nonpolar [112̄0] direction show that these films completely facet into {101̄1} and {101̄1̄} planes, which follow a well defined pattern of surface potential along the [0001] direction. This pattern is explained in terms of the different ionic termination – Zn or O ions – of the exposed facets. Finally, the presence of inversion domain boundaries is discussed. PACS 68.47.Gh; 73.30.+y; 68.37.-d; 73.63.-b     

制冷型红外光学系统温栏杂散辐射分析及消除方法

在致冷型红外光学系统中加入温栏会引入杂散辐射。杂散辐射包括温栏自身的辐射及对外部热光的反射。这两种辐射进入探测器后,会降低系统的信噪比和动态范围,影响成像质量。基于辐射及传热理论,提出温栏杂散辐射所引起噪声等效温差的计算模型,并研究了消除温栏杂散辐射的方法。用LIGHT TOOLS进行了光线追迹,对比分析了传统平面环状温栏和球面反射镜型温栏的杂散辐射,验证了理论推导的正确性和消除方法的可行性。结果表明,采用半径为30.3 mm的高反射率球型温栏代替原设计中的粗糙平面型温栏,控制其曲率半径和位置,可使由温栏引入的杂散辐射降低99%以上。     

Bronze roman mirrors: the secret of brightness

The surface microchemical structure of high tin leaded bronze Roman mirrors has been studied by means of scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD) and optical microscopy (OM) techniques. The results allowed understanding of the origin of their high chemical stability and silvery-lustrous appearance. Indeed, some areas of the selected Roman mirrors are still characterised by a highly reflective and silver coloured surface even though they have been buried in the soil for about 2000 years. The micro-chemical results obtained from these areas have revealed that the mirror surface was tin enriched via inverse-segregation phenomenon by tailoring the cooling parameters. Furthermore, the presence of tin could be likely enhanced via cycles of oxidation and selective copper corrosion processes, thus resulting in a tin surface enrichment as a semi-transparent amorphous-like tin oxide (SnO₂) film, as well as a copper depletion at the outer surfaces.     

TMSR白光中子源本底屏蔽设计

为了满足钍基熔盐堆对核数据的需求,中国科学院上海应用物理研究所自行设计并建造了紧凑型的15 MeV电子加速器驱动的白光中子源。电子直线加速器、中子产生靶以及探测器系统处于同一个实验大厅,中子/伽马射线本底较高,原有屏蔽并不能满足在低能区进行热中子物理实验测量的低中子本底需求。为了降低热中子本底,提高在热区的测量能力,需要对中子源进行局部屏蔽。根据调试运行经验以及模拟计算结果,分析了中子伽马射线本底的来源,利用MCNP5模拟计算了混凝土、铅、含硼聚乙烯对中子/伽马射线的屏蔽效果,优化设计了局部屏蔽方案。模拟计算结果显示,该屏蔽方案可将热中子本底降低三个量级,伽马本底降低两个量级。屏蔽后的实验测量结果表明,探测器处的有效热中子与本底热中子的比值达到约100:1,屏蔽效果显著,为后续在热中子能区顺利开展中子物理测量实验奠定了基础。     

Mössbauer effect and TEM in mineralogy

Mössbauer effect (ME) provides useful information on oxidation state, co-ordination number, co-ordination state, site occupancies, and magnetic properties of Fe-bearing phases. The information gained by ME together with the information provided by other conventional techniques is used to extract temperature, pressure, and kinetics of rockforming processes. Nevertheless, ME requires that the phases studied are homogeneous over an extremely large volume and that Fe is a major component of the system. Transmission electron microscopy (TEM), on the other hand, provides similar information over a very small volume for a system of any component. However, present TEM spectrometers do not provide sufficient resolution to detect the mixed oxidation state. A complete characterisation of phases in rocks requires, therefore, that conventional techniques be combined with TEM.     

Serial sectioning methods for 3D investigations in materials science

A variety of methods for the investigation and 3D representation of the inner structure of materials has been developed. In this paper, techniques based on slice and view using scanning microscopy for imaging are presented and compared. Three different methods of serial sectioning combined with either scanning electron or scanning ion microscopy or atomic force microscopy (AFM) were placed under scrutiny: serial block-face scanning electron microscopy, which facilitates an ultramicrotome built into the chamber of a variable pressure scanning electron microscope; three-dimensional (3D) AFM, which combines an (cryo-) ultramicrotome with an atomic force microscope, and 3D FIB, which delivers results by slicing with a focused ion beam. These three methods complement one another in many respects, e.g., in the type of materials that can be investigated, the resolution that can be obtained and the information that can be extracted from 3D reconstructions. A detailed review is given about preparation, the slice and view process itself, and the limitations of the methods and possible artifacts. Applications for each technique are also provided.     

The gamma-ray burst monitor on board the SAX satellite

Summary The anticoincidence lateral shields of the high-energy ((15÷200) keV) detector PDS aboard the SAX satellite will be used to detect celestial gamma-ray bursts. As a gamma-ray burst monitor (GRBM), the shields have a 5σ sensitivity in the (60÷600) keV nominal energy band about 10⁻⁶ erg/cm², and a capability of determining the burst location to an accuracy of a few tenths of degree to several degrees, depending on burst direction and strength. The GRBM will be mainly devoted to study the burst time profile with a time resolution down to 0.5 ms. Its expected performances are evaluated by means of Monte Carlo simulations. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Studying the characteristics of the photosensitive elements of photodetector matrices based on Si Pt: Si by means of induced potential and transmission electron microscopy

The prospects for the combined use of scanning and transmission electron microscopy in studying defects in the matrix elements of the infrared photodetectors are considered. It is shown that combining these techniques allows us to fully realize the potential of high-voltage transmission microscopy for detecting defects that impair matrix parameters.     

Melt-mediated coalescence of solution-deposited ZnO nanoparticles by excimer laser annealing for thin-film transistor fabrication

Nanoparticle solutions are considered promising for realizing low cost printable high performance flexible electronics. In this letter, excimer laser annealing (ELA) was employed to induce melting of solution-deposited ZnO nanoparticles and form electrically conductive porous films. The properties of the films were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, DC conductance, and photoluminescence measurements. Thin-film field-effect transistors have been fabricated by ELA without the use of conventional vacuum or any high temperature thermal annealing processes. The transistors show n-type accumulation mode behavior with mobility greater than 0.1 cm²/V s and current on/off ratios of more than 10⁴. Optimization and control of the laser processing parameters minimized thermal impact on the substrate. This technique can be beneficial in the fabrication of metal oxide based electronics on heat sensitive flexible plastic substrates using low-cost, large-area solution processing combined with direct printing techniques.     

Calculation of combined conduction-radiation heat transfer reduction using thick concentric spheres with temperature-dependent emissivity as radiation shields

In this study, the rate of conduction-radiation heat transfer between two thick concentric spheres is analytically investigated because of the ever-increasing importance of radiation shield applications. The heat transfer rate, the percentage of reduction in heat transfer, temperature and emissivity of surfaces are calculated when one and two thick radiation shields are placed between two thick spheres. The calculations show that the use of a radiation shield with a lower emissivity is better than two radiation shields with a higher emissivity to reduce the heat transfer rate. In addition, optimal combinations of radiation shields with different materials are proposed.     

Imaging the Hydrated Microbe‐Metal Interface Using Nanoscale Spectrum Imaging

PdAu nanocrystals are synthesised by Geobacter sulfurreducens, a dissimilatory metal‐reducing bacterium, and the resulting bimetallic nanocrystal‐decorated microbes are imaged using a range of advanced electron microscopy techniques. Specifically, the first example of elemental mapping of fully hydrated biological nanostructures using scanning transmission electron microscope (STEM) energy dispersive X‐ray (EDX) spectrum imaging within an environmental liquid‐cell is reported. These results are combined with cryo‐TEM and ex situ STEM imaging and EDX analysis with the aim of better understanding microbial synthesis of bimetallic nanoparticles. It is demonstrated that although Au and Pd are colocalized across the cells, the population of nanoparticles produced is bimodal, containing ultrasmall alloyed nanocrystals with diameters <3 nm and significantly larger core‐shell structures (>200 nm in diameter) which show higher Pd contents and exhibit a Pd enriched shell only a few nanometers thick. The application of high‐resolution imaging techniques described here offers the potential to visualize the microbe‐metal interface during the bioproduction of a range of functional materials by microbial “green” synthesis routes, and also key interfaces underpinning globally relevant environmental processes (e.g., metal cycling).     

Effect of intense energy fluxes on vacuum-tight rubber

Vacuum-tight rubber is widely used in various structures. Composite shields protecting space vehicles against micrometeorites include natural-rubber-like materials, which are similar to vacuum-tight rubber in properties. It is, therefore, of interest to study the behavior of vacuum-tight rubber subjected to an intense pulsed energy flux. From the response of this material to a high-energy action, one can construct a behavioral model for natural-rubber-like materials used in the protective shields. The behavior of vacuum-tight rubber exposed to a high-energy pulsed electron beam (with an energy density of up to 600 J/cm² and a half-width of 10⁻⁷ s) is investigated. The rate of material expansion toward the beam, as well as the velocities of propagation of strong and weak perturbations over the material, is measured. Spalls on the front and back surfaces of the sample are detected. The Grüneisen constant (a fundamental thermodynamic parameter that characterizes the pressure in a medium upon isochoric heating) is found.