Electromagnetic radiation emitted during friction process

A series of studies of electromagnetic radiation (EMR) emitted during fracture of materials, enabled us to obtain a relationship between the width of a fracture and the wavelength of the emitted EMR. Applying this relation to friction we could check one of its suggested mechanisms, namely the Bowden-Tabor model, which states that during a friction process, asperities on the two contacting surfaces are welded together (at a microscopic level) and fractured. A uniaxial tension machine was used, whereby two half cylinders of chalk (CaCO3) bound together, were moved one against the other, generating friction. Calculations based on EMR observations showed that the average width of the fractured asperities was 26.3 m, while mechanical profilograph measurements of the average width of the total number of long asperilies before and after the experiment, yielded values of 15.6 and 18.4 m, respectively, implying that 25% of long asperities were fractured during a single friction process.     

Dual approach to multiple authorship in the study of collaboration/scientific output relationship

This paper presents an empirical study of the relations between scientific output and collaboration performed on two scales: (1) an individual scale, for members of a study model, and (2) a group scale, for three samples varying in the level of productivity. The rank approach was applied in the preparation of the study model resulting in the selection of a set of the most prolific authors. In the course of that process, multiple authorship problem was solved by a dual approach, consisting of normal count and modified straight count procedures. As shown by the analysis of collaborative patterns, either on individual or on group scales, scientific output is highly dependent on the frequency of collaboration among the same authors. Expressed as the collaboration measure, it might serve as an indicator in comparative analyses of scientific productivity in a given field of science.     

Fabrication of β- and β′′-Al2O3 tubes by pressureless powder packing forming and salt infiltration

A new forming method, pressureless powder packing (PLPP), was studied to fabricate the - and -Al2O3 tubes. Alkali sources were infiltrated into the pores of -Al2O3 tube preforms that had been prepared by the PLPP forming method. The composition for the synthesis of -Al2O3 phase was Na2O · 0. 138Li2 · 4.4Al2O3. The -Al2O3 fraction of calcined and sintered bodies was increased with the increase of calcination temperature, and phase formation was largely affected by the type of starting -Al2O3. Large particle size and narrow size distribution of fused -Al2O3 resulted in uniform green microstructure that enhanced the homogeneity of alkali salts after infiltration, which was very important for the -Al2O3 formation. Sintered microstructure was uniform in all specimens but further development was required for density improvement.     

Normal-State Gap, Supercarrier Mass Anisotropy and Isotope Effects in La2?xSrxCuO4

Magnetization measurements have been performed on the oxygen-isotopeexchanged samples (¹⁶O and ¹⁸O) of the one-layer cuprate superconductorsLa_2–x Sr _x CuO₄ (0.06x0.20). We find that there is an oxygen-isotopeeffect on the effective supercarrier mass m**, which is huge for x=0.06,and reduced to a smaller value for x=0.15. We also find that there coexistsmall (bi)polarons and free carriers for x0.09, but only small (bi)polaronsare present for x0.09. The normal-state gap is related to the bipolaronbinding energy which is inversely proportional to x for 0.05x0.15. Theobserved isotope effects, supercarrier mass anisotropy, normal-state gap,and mid-infrared spectra for x0.09 can be quantitatively explained by the small(bi)polaron theory of superconductivity proposed by Alexandrov, Kabanov, andMott (AKM).     

Microstructural and dimensional stabilities of a potential γ/γ′-α(Mo) directionally solidified eutectic superalloy under cyclic thermal exposure to 1000° C

A potential heat-resistant ductile eutectic composite,/-, in the Ni-Al-Mo ternary system has been thermally cycled in the temperature range 200 to 1000° C for up to 1000 cycles in an attempt to examine dimensional as well as microstructural stability of the composite under thermal fatigue conditions. The composite examined has two types of initial microstructure; in one, blocky -Ni₃Al encircles individual-Mo fibres (as-grown condition) whereas in the other, is in the form of fine cuboidal particles uniformly distributed in an Ni-rich fcc matrix (heat-treated condition). Dilatometric measurements upon temperature cycling show that the composite is stable against thermal ratchetting irrespective of initial microstructural conditions. However, the cycling induces microstructural change, which is characterized by segmentation of-Mo fibres or formation of a detrimental brittle phase identified as an intermetallic-NiMo that consumes-Mo fibres whether the fibres are encircled by or not. Post-cycling tensile tests at room temperature show that the fibre damage in the former has no fatal effect on tensile strength and ductility. A beneficial effect of the-encircling configuration is discussed on the basis of the recognition of a peritecto-eutectoid reaction:++ that has been disregarded.     

The effect of Ag additions on the microstructure of aluminium–lithium alloys

Minor quantities of Ag have been added to Al–Li–Cu–Mg–Zr alloys. Their microstructure has been studied by means of optical metallography, transmission electron microscopy and X-ray diffraction. In the high Li, low Cu:Mg ratio alloys the main phases found were , , S and T1, while fewer T2 and Al7Cu2Fe precipitates were also observed. The addition of up to 0.5 wt% Ag diminishes the and T1 precipitates size. This is attributed to a small increase of Li solubility in the matrix. In the low Li, high Cu:Mg ratio alloy the addition of 0.2 wt% Ag resulted in the precipitation of phase simultaneously with , , S and T1 phases. Due to the low Li concentration an unusual growth of the / precipitates at the expense of the precipitates was also observed. © 1998 Kluwer Academic Publishers     

The frequencies of occurrence of scientific papers with authors of each initial letter and their variation with nationality

This paper introduces alphabet spectra which are the 26 frequencies of occurrence of scientific papers in a given sample with at least one author of each initial, A, B,...Z. The sum of these frequencies exceeds unity because of multiple authorships. Formulae are given relating this sum to the mean number of authors per paper in the sample. The method is applied to show the increase in this number over the last 15 years in different fields of science and for different countries. The alphabet spectra vary greatly depending on the nationality of the scientists concerned and can be compared to frequency absorption spectra for chemical elements or molecules. The spectra can be used to determine the national composition of a country's scientific authors and how this has changed with time.     

Microstructural refinement of β-sintered and Ti-6Al-4V porous-coated by temporary alloying with hydrogen

A series of thermochemical treatments, in which hydrogen was used as a temporary alloying element to refine the lamellar microstructure of -sintered and porous-coated Ti-6Al-4V was formulated. Each step of the treatment sequence (hydrogenation, eutectoid decomposition and dehydrogenation) was studied separately, on uncoated specimens and then on porous-coated specimens. The resultant microstructures can have -grain sizes less than 1 m, aspect ratios near unity and discontinuous grain boundary (GB), microstructural attributes which increase the fatigue strength. Microstructural refinement occurs because hydrogen-alloying reduces the (+) transition temperature and enables a eutectoid decomposition reaction to occur. The optimal hydrogenation temperature is 850 °C, because hydrogen concentrations of 0.71 to 0.85 wt% are in-diffused and -transformation is achieved. These weight percentages are in the optimal range for efficient eutectoid decomposition kinetics, -transformation obviates the need for a separate -transformation treatment step. A separate eutectoid decomposition treatment step may be used, or eutectoid decomposition may be combined with dehydrogenation. The finest eutectoid microstructures are obtained if hydrogen concentrations are in the range 0.5 to 0.8 wt%. The criteria for dehydrogenation are efficient removal of hydrogen, with minimal grain growth and absence of GB. These criteria are best met by using dehydrogenation temperatures <700 °C. Altering the sintering temperature or adding a porous coating does not affect the parameters of the hydrogen-alloying treatment steps.     

Stress-induced phase transformations in a hot-deformed two-phase (α2+γ) TiAl alloy

Stress-induced 2, 2 and 9R phase transformations in a hot-deformed Ti–45 at% Al–10 at% Nb alloy have been investigated using high-resolution transmission electron microscopy. The 2 phase transformation is an interface-related process. The interfacial superdislocations emitted from the misoriented semicoherent 2– interface react with each other or with the moving dislocations in the phase, resulting in the formation of the 2 phase. The nucleation of the 2 phase transformation takes place either at the 2– interfaces or at the stacking faults on the basal plane of 2 phase, and the growth of plate is accomplished by the moving of a/61 0 1 0 Shockley partials on alternate basal plane (0 0 0 1)2. The 9R structure was usually found to form at incoherent twin or pseudotwin boundaries. During deformation the interfacial Shockley partial dislocations of these incoherent twin and pseudotwin boundaries may glide on (1 1 1) planes into the matrix, resulting in the formation of 9R structure. The interfaces (including 2– and – interfaces) as well as the crystallographic orientation relationship between the as-received or stress-induced 2, and 9R phase have been analysed. The mechanisms for the stress-induced 2, 2 and 9R phase transformations were also discussed. © 1998 Chapman & Hall     

Phase relationship between β′- and O′-sialon at 1623 K

-sialon whiskers and co-products of synthesis, such as -sialon powders and O-sialon powders, were annealed at 1623 K for 8 h in a closed graphite reaction tube under 1 atm nitrogen. Phase stabilities, Si/Al ratios, and crystallographic features were investigated. The O-sialon phase, which formed in the early stage of synthesis when oxygen partial pressure was relatively high, became less stable in the present annealing condition and decomposed. The majority of released aluminium and possibly oxygen from the decomposed O-powder was incorporated into -sialon whiskers with little change in its lattice parameters, when the -sialon whiskers were included in annealing. The aluminium contents were always lower in the -whiskers than in the powders even after increasing its aluminium content during 8 h annealing. The lattice parameters of both -whiskers and powders increased with increasing aluminium content and became closer after annealing. The lattice parameters of -whiskers remained the same before and after annealing despite the increased aluminium content, while the lattice parameters of -powders decreased despite its aluminium content remaining unchanged. The lattice parameters of O-sialon increased with increasing aluminium content, and the increase in thea direction is the largest when compared with other parameters.     

Investigation of the backscatter coefficient of Β radiations from an aluminum backing in a 2π geometry

Conclusions It follows from the investigation of backscatter of radiations (at maximum energies of 10–290 fJ, i.e., of 0.155–1.711 MeV) from an aluminum backing with a 2 geometry that for weightless samples the intensity of the saturation backscatter is virtually independent of the -radiation energy, whereas for weightable samples it increases with a rising energy of particles.The coefficients thus obtained for -radiators with a finite active-layer thickness, which include the effects of self-scatter and self-absorption of output radiation over an angle of 2, can be used for approximate computation of the activity of radiators with a known active-layer thickness from the measured external output of -particles (and vice versa).     

A high-temperature solid-state potentiometric sensor for nitrogen based on ceramic LaAl12O18N

The nitrogen-sensing properties of LaAl12O18N are described for the first time. Positive e.m.f. measurements at high temperature across the cells -Nb (N), -Nb2N, -Al2O3, LaAl12O18NLaAl11O18 (or LaAl12O18N)LaAl12O18N, -Al2O3, -Nb2N, -Nb4N3, were in agreement with PN2(-Nb2N, -Nb4N3)>PN2(-Nb(N), -Nb2N) for the idealized stoichiometric cell reaction -Nb4N3+2-Nb(N)3-Nb2N, thus demonstrating the nitrogen-sensing property of these cells. The e.m.f. for a variety of cells with electrodes containing -V2N, -Nb2N, -Ta2N and Ti2N, were consistent with the predicted equilibrium nitrogen partial pressures.     

Thermodynamic investigations of liquid Bi-Na and Sn-Na alloys by coulometric titration using β″-alumina

The following double galvanic cell was assembled and the thermodynamic properties of liquid Bi-Na and Sn-Na alloys, and the ion selectivity of -alumina during coulometric titration, were investigated. Mo, Na(I)¦-alumina¦M-Na(I), Mo [I] M-Na(I)¦-alumina¦Au + Au₂Na, Mo [II] (M = Bi or Sn) where M-Na(1) and Au + Au₂Na were used as the common electrode and reference electrode, respectively. Sodium was coulometrically titrated through the -alumina electrolyte of cell I both ways, and the EMFs were measured. It was found that no ion-exchange reaction occurs between the liquid alloys and the -alumina, and only Na was transferred in the -alumina during coulometric titrations. The thermodynamic properties of liquid Sn-Na and Bi-Na alloys were found to be in agreement with the literature.     

Anisotropy in the hardness and friction of calcium fluoride crystals

Anisotropy in the Knoop indentation hardness and the friction of diamond cones on calcium fluoride crystals has been investigated at experimental temperatures from 20 to 300° C. It is shown that the directions of minimum and maximum indentation hardness, on the (001) plane, are 110 and 100 respectively whilst the 1¯10 are harder than the 11¯2 directions on the (111) plane. Also, the sliding friction in the (001) plane is greatest in the 110 directions and least in the 100 and, on the (111) cleavage plane, [¯1¯12] sliding leads to higher friction than [11¯2]. The nature of anisotropy, for both hardness and friction measurements, does not change over the experimental temperature range covered in this work. Observations on the resultant deformation are made and these anisotropic properties are explained in terms of the effective resolved shear stresses developed on the {100} 011 primary slip systems at all experimental temperatures.     

The Interplay of Electronic and Nuclear Magnetism in PtFe x at Milli-, Micro-, and Nanokelvin Temperatures

We have measured ac susceptibility, nuclear magnetic resonance, and nuclear heat capacity of two PtFe _x samples with concentrations of magnetic impurities x = 11 ppm and 41 ppm at magnetic fields (0 ± 0.05) mTB248 mT. The susceptibility data have been measured at temperatures of 0.3 KT100 mK, no hint for nuclear magnetic ordering could be detected to a temperature of 0.3 K. The nuclear heat capacity data taken at 1.4 KT10 mK show enhanced values which scale with x at low polarization. This effect is described by a model assuming an internal magnetic field caused by the impurities. No indication for nuclear magnetic ordering could be detected to 1.4 K. The nuclear magnetic resonance experiments have been performed on these samples at 0.8 KT0.5 mK and 2.5 mTB22.8 mT as well as on three other samples with x = 5, 10, 31 ppm in a different setup at 40 KT0.5 mK and at 5.4 mTB200 mT. Spin-lattice and effective spin-spin relaxation times ₁and ₂ ^* of ¹⁹⁵ Pt strongly depend on x and on the external magnetic field. No temperature dependence of ₁and ₂ ^* could be detected and the NMR data, too, give no hint for nuclear magnetic ordering to 0.8 K.     

Influence of stabilizers on Na-β′′-Al2O3 phase formation in Li2O(MgO)-Na2O-Al2O3 ternary systems

The influences of stabilizers on - and -Al2O3 phase formations in Li2O(MgO)-Na2O-Al2O3 systems were investigated. When stabilized with 4MgCO3Mg(OH)25H2O, most of the -Al2O3 phase formed below 1200°C and further - to -Al2O3 transformation with an increase of temperature was not observed. On the other hand, when stabilized with Li2CO3,-Al2O3 formation occurred by two steps. First, -Al2O3 was partly formed below 1200°C, and, second, noticeable transformation from -Al2O3 to -Al2O3 occurred at higher temperature ranges. It was shown that transient eutectic liquid in the Li2O-Na2O-Al2O3 system promoted the - to -Al2O3 transformation at higher temperatures. Uniform distribution of both Mg2+ and Li+ stabilizing ions enhanced -Al2O3 formation at low temperatures. In the Li-stabilized systems, however, homogeneous distribution of Li+ ions hindered both the formation of transient eutectic liquid and the second - to -Al2O3 phase transformation at high temperatures.     

Mathematical simulation of the process of combustion of slightly gaseous porous compositions

A one-dimensional model of combustion of slightly gaseous porous compositions is considered. Using this model an analysis of the dependence of the combustion characteristics on the basic parameters such as the mass ratio of the gas-free and volatile components in the starting composition, initial porosity, position of the gas liberation source relative to the reaction front of the gas-free component, and degree of sample hermetic sealing is performed for different exothermicity and endothermicity levels of the chemical processes taking place.Deceased.Institute of Structural Macrokinetics of the Russian Academy of Sciences, Chernogolovka. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 4, pp. 461–465, October, 1993.     

The Ni3Al-Ni3Cr-Ni3Ru section of the Ni-Cr-Al-Ru system

An investigation is reported of the 75 at% nickel section of the Ni-Cr-Al-Ru system at 1523 and 1273 K. Constitutional data obtained by electron probe microanalysis, X-ray diffraction and microscopical examination are presented as partial isothermal sections. At 1523 K, the major part of the section consists of phase, while the aluminium-rich region contains a and+ region; the extent of the solid solution of chromium and ruthenium in totals ~ 4 at%. The ruthenium-rich corner of the section shows a two-phase region consisting of + ruthenium-rich solid solution. At 1273 K the,+ and + ruthenium regions increase in extent. The/ mismatch values in the equilibrated alloys studied lie in the range ~ –0.08 to –0.39%. Constitutional features of as-cast alloys are also reported.     

TEM study of metastable β-phase decomposition in rapidly solidified Ti-6Al-4V alloy

A new rationale is presented for various decomposition products obtained from the metastable -phase found in Ti-6A1-4V alloy produced by hot isostatic pressing comminuted melt-spun fibres and cooled to room temperature by furnace cooling. This alloy has an -matrix with about 8 vol% retained -phase, which is supersaturated with -stabilizers to such an extent that the martensitic transformation has been suppressed. The metastable -phase decomposes by different modes during continuous cooling, depending on the actual composition of individual -grains. Less enrichment of vanadium and iron favours the direct formation of the equilibrium -phase from the -matrix, while greater enrichment of vanadium and iron leads to a spinodal decomposition of the metastable -phase, resulting in a + two-phase structure. During further continuous cooling, the -phase which is lean in -stabilizers will transform into isothermal -phase. In addition, an unknown phase has also been observed in the -phase, which is typified by the appearance of 1/2{112} reflections in the SAD patterns.     

Multi-length scale modeling of CVD of diamond Part II A combined atomic-scale/grain-scale analysis

Chemical vapor deposition of polycrystalline diamond films is studied by combining an atomic-scale kinetic Monte Carlo model with two one three-dimensional and one two-dimensional grain-scale models. The atomic-scale model is used to determine the growth rates of 111- and 100-oriented surface facets, the surface morphology of the facets and the extent of incorporation of the crystal defects. Using the atomic-scale modeling predicted growth rates for the 111- and 100-oriented facets, grain-scale modelling is carried out to determine the evolution of grain structure, surface morphology and crystallographic texture in the polycrystalline diamond films. It is found that depending on the relative growth rates of the 111- and 100-oriented facets, which can be controlled by selecting the CVD processing conditions, one can obtain either 110-textured films with a relatively smooth faceted surface or 100-textured films with a highly pronounced deep facets. In both cases, however, the film surface is composed entirely of the 111 facets. This findings are found to be fully consistent with the available experimental results.