Structural studies of nanodiamond by high-energy X-ray diffraction

The atomic scale structure of explosive diamond nanoparticles has been studied using high-energy X-ray diffraction. The diffraction data have been converted to the real space representation in the form of the radial distribution function. Spherical and truncated octahedron nanodiamond clusters containing from 729 to 1182 atoms have been computer generated and then relaxed using the molecular dynamics method with the reactive empirical bond order potential for carbon-carbon interaction and the Lennard–Jones potential with parameters for inter-layer interactions. Validity of such constructed models has been verified by comparison of the simulations and the experimental data in both real and reciprocal space. The obtained results show that the structure of the investigated diamond nanoparticles cannot be satisfactorily described in terms of the model based on the perfect diamond lattice. The core-shell model with an average size of 22.5–23.4 Å, consisting of the diamond core and the graphite-like shell, accounts very well for the experimental data.     

Measuring strain distributions in amorphous materials.

A number of properties of amorphous materials including fatigue, fracture and component performance are governed by the magnitude of strain fields around inhomogeneities such as inclusions, voids and cracks. At present, localized strain information is only available from surface probes such as optical or electron microscopy. This is unfortunate because surface and bulk characteristics in general differ. Hence, to a large extent, the assessment of strain distributions relies on untested models. Here we present a universal diffraction method for characterizing bulk stress and strain fields in amorphous materials and demonstrate its efficacy by work on a material of current interest in materials engineering: a bulk metallic glass. The macroscopic response is shown to be less stiff than the atomic next-neighbour bonds because of structural rearrangements at the scale of 4-10 A. The method is also applicable to composites comprising an amorphous matrix and crystalline inclusions.     

Integrated control and user interfaces for a space

Many of a building’s systems, including heating, cooling, lighting and ventilation, work separately with each other as ‘isolated islands’. While separate systems do not typically work optimally in terms of total performance, integrated control has the potential to improve energy efficiency, occupant comfort and satisfaction and cost efficiency. Preceding studies also have stressed the needs for individual control and usability in order to achieve occupant satisfaction. First, this paper provides a solution concept for integrated control for a space and describes various inputs and outputs of integrated control. As an example, an optimisation strategy for discontinuous use of buildings is presented. The optimisation strategy was first simulated and then implemented in a real building. Second, modular user interfaces for adjusting environmental conditions are provided in the paper. The user interfaces modules are based on user research and usability testing to avoid the usability problems that have been identified in many studies regarding user control of indoor environments. The modules can be utilised in different user interface configurations for different types of spaces in a building.     

Roughened glass slides and a spectrophotometer for the detection of the wavelength-dependent refractive index of transparent liquids

We describe a method to determine the wavelength-dependent refractive index of liquids by measurement of light transmittance with a spectrophotometer. The method is based on using roughened glass slides with different a priori known refractive indices and immersing the slides into the transparent liquid with unknown refractive index. Using the dispersion data on the glass material it is possible to find the index match between the liquid and the glass slide, and hence the refractive index of the liquid.     

Detection of copper in water using on-line plasma-excited atomic absorption spectroscopy (AAS)

A measurement method and apparatus was developed to measure continuously toxic metal compounds in industrial water samples. The method was demonstrated by using copper as a sample metal. Water was injected into the sample line and subsequently into a nitrogen plasma jet, in which the samples comprising the metal compound dissolved in water were decomposed. The transmitted monochromatic light was detected and the absorbance caused by copper atoms was measured. The absorbance and metal concentration were used to calculate sensitivity and detection limits for the studied metal. The sensitivity, limit of detection, and quantification for copper were 0.45 ± 0.02, 0.25 ± 0.01, and 0.85 ± 0.04 ppm, respectively.     

Active wear and failure mechanisms of TiN-Coated high speed steel and tin-coated cemented carbide tools when machining powder metallurgically made stainless steels

In this study, active wear and failure mechanisms of both TiN-coated high speed steel and TiN-coated cemented carbide tools when machining stainless steels made by powder metallurgy in low and high cutting speed ranges, respectively, have been investigated. Abrasive wear mechanisms, fatigue-induced failure, and adhesive and diffusion wear mechanisms mainly affected the tool life of TiN-coated high speed steel tools at cutting speeds below 35 m/min, between 35 and 45 m/min, and over 45 m/min, respectively. Additionally, fatigue-induced failure was active at cutting speeds over 45 m/min in the low cutting speed range when machining powder metallurgically made duplex stainless steel 2205 and austenitic stainless steel 316L. In the high cutting speed range, from 100 to 250 m/min, fatigue-induced failure together with diffusion wear mechanism, affected the tool life of TiN-coated cemented carbide tools when machining both 316L and 2205 stainless steels. It was noticed that the tool life of TiN-coated high speed steel tools used in the low cutting speed range when machining 2205 steel was longer than that when machining 316L steel, whereas the tool life of TiN-coated cemented carbide tools used in the high cutting speed range when machining 316L steel was longer than that when machining 2205 steel. formerly with the Laboratory of Engineering Materials, Helsinki University of Technology     

Structural studies of oriented carbon nanotubes in alumina channels using high energy X-ray diffraction

Structural studies of multi-wall carbon nanotubes prepared by template pyrolytic carbon deposition from thermal decomposition of propylene at 800 °C inside channels of an alumina membrane have been performed using X-ray diffraction. The two-dimensional diffraction pattern of the deposited carbon nanotubes, recorded directly within the alumina template using an image plate detector, exhibits two dark arcs corresponding to the (0 0 2) graphitic reflection. The anisotropic scattering distribution indicates alignment of the nanotubes. The diffracted intensity was measured for the powdered samples after removing the alumina membrane using a point detector. A maximum scattering vector of K_max = 20 Å⁻¹ yielded the radial distribution function, providing evidence that the investigated nanotubes form a distorted hexagonal network that implies the presence of five-membered rings.     

Electric-field-induced phase-change behavior in (Bi0.5Na0.5)TiO3–BaTiO3–(K0.5Na0.5)NbO3: A combinatorial investigation

The electric-field-induced strain behavior in (1 ? x ? y)(Bi_0.5Na_0.5)TiO₃–xBaTiO₃–y(K_0.5Na_0.5)NbO₃ electroceramics has been studied using a combinatorial technique. A stoichiometrically graded sample was produced to contain compositions across the ternary phase diagram between the two end-member components of 0.93(Bi_0.5Na_0.5)TiO₃–0.07BaTiO₃ and 0.86(Bi_0.5Na_0.5)TiO₃–0.14(K_0.5Na_0.5)NbO₃. Both composition and structural information were measured simultaneously during the application of electric fields using secondary X-ray fluorescence and high-energy X-ray microdiffraction, respectively. An initial electric-field-induced distortion from the pseudo-cubic structure is seen across all compositions, while those with a greater concentration of BaTiO₃ also undergo an electric-field-induced phase transformation. The microstructural contribution to the macroscopic strain within the 0.93(Bi_0.5Na_0.5)TiO₃–0.07BaTiO₃ end member is quantified at a field strength of 5.5 kV mm^?1; 0.08% and 0.11% of the measured macroscopic strain of 0.4% is contributed by the induced ferroelastic domain texture and the volumetric strain associated with the electric-field-induced phase transformation, respectively.     

Microstructure of pyrocarbons from pair distribution function analysis using neutron diffraction

We present a microstructural investigation of two different pyrocarbons (PyCs), belonging respectively to the rough laminar (RL) and smooth laminar (SL) families. The structure of the materials is analyzed in terms of their pair distribution functions (PDFs) as determined from neutron diffraction experiments. The data are correlated with polarized light optical microscopy, high resolution transmission electron microscopy, Raman microspectrometry, X-ray diffraction, He pycnometry, elastic recoil detection analysis and secondary ion mass spectrometry. Results show that the two materials may be clearly distinguished using the PDF data above a 15 Å distance. The PDF of the more ordered carbon (the RL PyC) is also compared to data obtained from an image-guided atomistic reconstruction, showing excellent agreement.     

Integrated waste management in a small programme

The Finnish nuclear waste management programme consists of handling, intermediate storage and final disposal of the spent fuel and operating waste as well as decommissioning of nuclear power plants and disposal of waste from dismantling. There are two final repositories for low- and intermediate-level operating waste, one of which is in operation at Olkiluoto and the other will be commissioned at Loviisa in 1997. A new company, Posiva, takes care of the necessary research, and later, will oversee construction and operation of the disposal facility for spent fuel. The next main target of the programme for spent fuel disposal is selection of a site in the year 2000. Construction of the final disposal facility should start during the 2010s and operation begin around 2020.