Separate Grains Research Articles

Разработка органолептической методики контроля степени измельчения лабораторных проб золотосодержащих руд

The sample preparation of gold-bearing ores for the analysis is an important part of the gold fields’ chemical approbation. One of the operations in sample preparation is a control of the size of sample particles. Traditional sieve method to control the particle size is labor intensive and has low rapidity. In addition, the modern equipment for the particle-size analysis is of high cost. In order to implement a cheap, simple and express method to control the particle size of gold-bearing ores in production laboratories this paper presents an algorithm to control the crushing ratio of laboratory samples of gold-bearing ores. Using this new method, it is first necessary to carefully mix a sample and to spread it on a smooth surface of the table to form a layer of 5-7 mm thick, and then divide it into approximately equal squares. After this, an operator rubs the sample material with a finger at the control points, immersing the finger in the material until the contact with the polymeric film is made. If at the same time between the film and the finger there will be a sample particle with the size of 0.08-0.1 mm, the operator will have a steady I type tactile sensation (the sensation of the fine sand). If at the same time between the film and the finger there will be a sample particle with the size of more than 0.1 mm and less than 0.2 mm, the operator will feel a steady II type tactile sensation (the sensation of the separate grains). This procedure allows controlling the quality of the sample preparation. To control the crushing ratio of gold-bearing ores used in the routine analysis it is enough to use 9 control points. The developed algorithm of the organoleptic method to control the crushing quality was checked on a large group of samples, and its results agreed nicely with the results received using the classical sieve method. Using the organoleptic method, the quickness of control increases and the labor input of control decreases in comparison to the sieve method. Key words: organoleptic method, crushing ratio of laboratory samples, control of powder size, gold-bearing ores DOI: http://dx.doi.org/10.15826/analitika.2016.20.4.004 О . А . Belavina 1 , V. А . Shvetsov 1 , V.V. Pakhomova 2 , D.V. Shun'kin 1 Kamchatka State Technical University, ul. Kliuchevskaia, 35, Petropavlovsk-Kamchatskii, 683003, Russian Federation JSC «Kamchatgeology», Russian Federation, ul. Mishennaia, 106, Petropavlovsk-Kamchatskii, 683016, Russian Federation

Photometric Analysis of Chips after Grinding Different Steel

The characteristic feature of the grinding process is that the removal of the metal envelope is carried out with the help of separate abrasive grains. The result of this is the formation of a great number of chips. The analysis of these chips after grinding is of great interest first of all from the point of view of the study of the cutting mechanics while grinding, the formation of the chip surface and the exposure of geometric features of the zone of plastic deformation.The article presents a fundamental approach to the in-depth physical study of the grinding process with modern devices. An absolutely new approach to the physics of interconnection of a cutter and a blank is described, which also considers, apart from the traditional chip formation, the micrometallurgical processes, which result in coagulated microstructures. The results of the research can be used in mathematical models of grinding process which describe the mechanics of interconnection of the abrasive and work material.

Electrical conductivity peculiarities of SrTiO3ZrO2–ceramic system

Ceramic (1−x)SrTiO3–xZrO2 samples with x=0, 0.2, 0.4, 0.6, 0.8 and 1.0 were synthesized using solid-state processing techniques. Coexistence of the cubic Pm3¯m phase and the tetragonal P42/nmc phase was found for the compositions with x=0.2, 0.4, 0.6 and 0.8 through the use of XRD analysis and SEM experiments. These phases are in separate grains of the material. An examination of the electrical properties of all the compositions showed unusual behaviors of the temperature and compositional dependencies of the specific electrical conductivity for the composition with x=0.2.

Episodic carbonate precipitation in the CM chondrite ALH 84049: An ion microprobe analysis of O and C isotopes

We have determined the O and C isotope compositions of dolomite grains and the C isotope compositions of calcite grains in the highly altered CM1 chondrite, ALH 84049, using Secondary Ion Mass Spectrometry (SIMS). Chemically-zoned dolomite constitutes 0.8 volume percent (vol%) of the sample and calcite 0.9vol%. Thirteen separate dolomite grains have δ13C values that range from 37 to 60 (±2) ‰, δ18O values from 25 to 32 (±3) ‰, and δ17O values from 10 to 16 (±3) ‰ (VSMOW). Intragrain δ13C values in dolomite vary up to 10‰. The δ13C values of three calcite grains are distinct from those of dolomite and range from 10 to 13 (±2) ‰ (PDB). Calcite and dolomite appear to record different precipitation episodes. Carbon isotope values of both dolomite and calcite in this single sample encompass much of the reported range for CM chondrites; our results imply that bulk carbonate C and O isotope analyses may oversimplify the history of carbonate precipitation. Multiple generations of carbonates with variable isotope compositions exist in ALH 84049 and, perhaps, in many CM chondrites. This work shows that one should exercise caution when using a clumped isotope approach to determine the original temperature and the isotopic compositions of water for CM chondrite carbonates. Less altered CM meteorites with more-homogeneous C isotope compositions, however, may be suitable for bulk-carbonate analyses, but detailed carbonate petrologic and isotopic characterization of individual samples is advised.

Magnetic Properties and Microstructure of FePt(MoC, C) Granular Films

High magnetocrystalline anisotropy (Ku) material was required for future heat assisted magnetic recording media. The ordered L1 0 FePt film can be prepared to have high [001] texture which shows high perpendicular magnetic anisotropy. Epitaxial growth of FePt films on MoC/CrRu/glass have been proved to promote chemical ordering and texturing. Dual-segregants such as transition metal-oxide with carbon have been used to obtain FePt granular structure and columnar grains. In this study, the magnetic properties and microstructure of FePt(MoC, C) films were discussed and the segregant materials were MoC and C. The Mo 40 C 60 was co-sputtered with FePt and the carbon was diffused from the MoC intermediate layer. The MoC phase is formed at equal atomic ratio or higher C concentration. The Mo 50 C 50 film with equal atomic ratio has been studied previously [1] and chemical composition of Mo 40 C 60 film was discussed in this study. When the atomic concentration of C is above 50%, the MoC and C phases are co-existed. The excess C was used as one of the segregant to diffuse up to separate FePt grains from intermediate layer.

Structurization and phase formation in the course of preparing nanocomposite TiN–Ni ion-plasma vacuum–arc coatings and their thermal stability

Structure and phase formation in the course of fabricating composite ion–plasma vacuum-arc nanocrystalline TiN–Ni coatings are investigated in a broad range of nickel concentrations (from 0 to 26 at %). It is established that the introduction of Ni into the coating composition refines the nitride phase crystallites. The arithmetic mean size of TiN grains decreases from 100–120 to 15–18 nm upon varying the Ni concentration from 0 to 12 at % and normal particle-size distribution. The further increase in the Ni content is accompanied by the transition to the polymodal particle distribution with an increase in their arithmetic mean diameter to 27 nm for the third mode. Nickel in coatings at a concentration of 12–13 at % Ni is in the X-ray amorphous state. As the concentration increases above 13 at %, the TiNi intermetallic compound is formed in the composition of coatings. This phenomenon in turn causes the appearance of porosity in the structure of the deposited layer. The blocking role of nickel simultaneously weakens with the formation of the intermetallic compound, which manifests itself in the growth of separate TiN grains to 30–35 nm. The TiN–Ni coatings are characterized by the thermal stability of the structure and composition upon heating to 800°C.

Shock melting of K-feldspar and interlacing with cataclastically deformed plagioclase in granitic rocks at Toqqusap Nunaa, southern West Greenland: Implications for the genesis of the Maniitsoq structure

Folded sheets of Mesoarchaean, leucocratic plagioclase-K-feldspar-mesoperthite-bearing granitic rocks in the Toqqusap Nunaa area of the Maniitsoq structure, West Greenland, are characterised by their very fine grain sizes and microstructures without normal igneous or planar/linear tectonic fabrics. Quartz forms equidimensional and branching, ductilely deformed aggregates and bifurcating panels with protrusions, constrictions and chains of ball-shaped grains with healed, radiating intergranular fractures. Plagioclase (An10–20) was cataclastically deformed and comminuted, whereas K-feldspar and mesoperthite are devoid of cataclastic microstructures. K-feldspar forms dispersed, highly irregular grains with numerous cusps and saddles, indicating almost ubiquitous direct (shock) melting of this mineral. It is commonly located along former fractures in plagioclase, resulting in an ‘interlaced’ feldspar microstructure with contact shapes indicating subsequent melting of plagioclase directly adjacent to K-feldspar. Mesoperthite forms separate, rounded, and irregular grains with protrusions and cusped margins indicating crystallisation from melts. Some mesoperthite grains are texturally and compositionally heterogeneous and contain internal lenses of K-feldspar and/or plagioclase. Other mesoperthite grains comprise coarsened, ‘unzipped’ areas, presumably due to localised, fluid-controlled dissolution–reprecipitation processes. The ternary feldspar precursor of the mesoperthite is interpreted as having crystallised from variably effectively mixed K-feldspar shock melts and plagioclase contact melts.Direct melting of K-feldspar, but no whole-rock melting, requires shock metamorphism with a short-lived temperature excursion to above the melting temperature of K-feldspar (~1300°C). The presence of three different feldspar species and absence of chemical zonation, magmatic mantling, or metamorphic coronas furthermore hinders interpretations solely by means of endogenic magmatic or ultrametamorphic processes. The feldspar microstructures with direct K-feldspar melts in the leucocratic orthogneisses of the Toqqusap Nunaa area thus confirm that the recently discovered Maniitsoq structure represents the deep-crustal remnants of a giant Mesoarchaean meteorite impact.

Influence of columnar grain microstructure on thermal shock resistance of laser re-melted ZrO2-7 wt.% Y2O3 coatings and their failure mechanism

In this study, influence of columnar grain morphology on thermal shock resistance of laser re-melted ZrO2-7wt.% Y2O3 thermal barrier coatings (TBCs) has been researched. The influence of variation in columnar grain microstructures on the fatigue mechanism of laser re-melted coatings in thermal shock experiments has been investigated. The thermal shock experiments have confirmed the positive effect of small grain size on thermal fatigue life. This is thought to have resulted from an increase in the number of grain boundaries that restrict the grain motion during deformation. Further, “void effect” could be responsible for promoting peeling of the laser re-melted coatings when spallation is less than 10% because it can cause a relatively large tensile stress between the columnar grains and the underlying splats. However, it is found to have negligible effect on the shedding of LRCs shed when the spallation percentage is 20% or more because the remaining LRCs are relatively homogeneous having less or no voids. The presence of separate columns and large intergranular clearance may have allowed better compliance of stress through free-movement of the individual columnar grains. There are many more restrictions on stress relaxation. An additional moving resistance is found to be present at the undulate intergranular interfaces for the irregular gear-like columnar grains with small inter-crystalline space and large intergranular contact area. The one-piece structure with pseudo-columnar grains was found to improve the thermal cycle lifetime slightly. It is believed to be due to its relatively lower strain tolerance as well as lower fracture toughness as compared to that of the structure with separate columnar grains.

Aerodynamic properties of lentil seeds

Abstract Aerodynamic properties of solid materials have long been used to convey and separate seeds and grains during post-harvest operations. The objective of this study was evaluation of the aerodynamic properties of green and red lentil seeds as a function of moisture content from 10 to 25% (w.b.). The results showed that as the moisture content increased from 10 to 25%, the terminal velocity of seeds increased, following a linear relationship, from 6.90 to 9.14 and from 6.37 to 7.67 m s−1 for green and red lentil seeds, respectively. Seeds of the green variety had terminal velocities with a mean value of 7.89 m s−1, while the red variety had a mean value of 7.02 m s−1, for moisture content from 10 to 25%. The Reynolds number increased linearly from 2 310.90 to 3 269.23 and from 1 215.02 to 1 535.09 for green and red lentil seeds, respectively, with the increase of seeds moisture content from 10 to 25%. While, drag coefficient decreased from 0.69 to 0.40 and from 0.84 to 0.69 for green and red lentil seeds, respectively, with the increase of moisture content. Mathematical relationships were developed to relate the change in seeds moisture content with the values of aerodynamic properties obtained. The analysis of variance showed that the effect of moisture content on all aerodynamic properties of lentil beans was significant at the 1% probability level.

Possible melting produced chondrule destruction in NWA 6604 CK4 chondrite

AbstractIn analyzing a thin section of the NWA 6604 CK4 meteorite, only altered chondrules and various components that are probably left behind the destruction of former chondrules can be observed. We suggest that melting, grain size decrease, resorption of the original chondrules, and crystallization of opaque minerals were the main processes that destroyed the chondrules. Four different events could be identified as having occurred during this alteration. First, opaques crystallized along former fractures producing chains of separated grains. Later, opaques and Ca‐rich minerals crystallized together in veins and large melt pockets; this was the strongest recrystallization phase involving the largest volume of melt. This occurred along different fractures than the first phase above. During the third phase, only Ca‐rich plagioclase crystallized along thin veins, and in a fourth phase, fractures formed again, partly along those formed during the second phases but without substantial mineral infill. Two simple possible case models should be considered for this meteorite: alteration by purely impact‐driven processes or mainly by melt‐driven processes. Although for CK4 chondrites, the shock‐produced alteration driven by impact is the more accepted and widespread approach, melting is also compatible with the observed textural characteristics of chondrule destruction. During melting, recrystallization took place producing iron‐rich minerals earlier and Ca‐Si‐rich ones later. The penetration of melts into veins contributed in the chondrule destruction. The stress directions also changed during these alterations, and minerals that formed later filled differently oriented fractures than the earlier ones. From our observations, we favor a view where heat‐driven melting and recrystallization produced the destruction and uniform mineralogy in the sample.

Formation of hydroxylapatite on CVD deposited titania layers

AbstractBioactive coatings on medical implants can be prepared from titanium dioxide due to its ability to induce the formation of hydroxylapatite (HA) from physiological solutions. In this study TiO2 layers were formed by chemical vapor deposition at different substrate temperatures in order to controllably change their structure from amorphous to consisting of preferentially oriented anatase crystallites. To evaluate the influence of phase composition and surface morphology of the deposited layers on their ability to form HA titania samples were immersed in Dulbecco's phosphate‐buffered saline (DPBS). The obtained results showed that structure of TiO2 layers determines the structure of HA formed on their surface. Polycrystalline titania layers with random orientation of anatase crystallites are the most favorable for intensive nucleation and formation of continuous HA coatings in DPBS solution. The textured TiO2 layers with smooth surface enhanced formation of HA deposits which consisted of sparsely distributed large separate grains. On the basis of the experimental results it was proposed that formation of hydroxylapatite nuclei on the surface of titania layers occurs by a mechanism of epitaxial growth. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fine grained microstructure crystallographic feature and its effect on mechanical behavior in Ni–Cr–W superalloy

The microstructure, texture and microsegregation in conventional and fine grained ingots of Ni–Cr–W superalloy were experimentally charactered by metallography, field emission scanning electron microscope equipped with an Electron Backscatter Diffraction and electron probe microanalysis, respectively. Distribution of misorientation angles results indicates that the proportion of low-angle grain boundaries and high-angle grain boundaries is about 15% and 85%, respectively, demonstrating that the particles are genuinely separate grains with mostly high-angle boundaries. Further, inverse pole figure results supply evidence for elucidating the mechanism of grain refinement due to a high effective nucleation rate which is attributed to extremely uniform temperature and composition fields in the bulk liquid at early stages of solidification. Element segregation at the grain boundary of equiaxed fine grain microstructure is smaller than that of the conventional dendrite grain microstructure. The effect of different morphologies of microstructure on yield strength was investigated. The effect of different average grain sizes on micro-hardness and yield strength was also analyzed. Relationship between yield strength and the grain size of this alloy followed the Hall–Petch relationship: σs=700+422d−1/2.

Time dependent driving forces and the kinetics of tricalcium silicate hydration

Simulations of tricalcium silicate (C3S) hydration using a kinetic cellular automaton program, HydratiCA, indicate that the net rate depends both on C3S dissolution and on hydration product growth. Neither process can be considered the sole rate-controlling step because the solution remains significantly undersaturated with respect to C3S yet significantly supersaturated with respect to calcium silicate hydrate (C–S–H). The reaction rate peak is attributed to increasing coverage of C3S by C–S–H, which reduces both the dissolution rate and the supersaturation of C–S–H. This supersaturation dependence is included in a generalized boundary nucleation and growth model to describe the kinetics without requiring significant impingement of products on separate cement grains. The latter point explains the observation that paste hydration rates are insensitive to water/cement ratio. The simulations indicate that the product layer on C3S remains permeable; no transition to diffusion control is indicated, even long after the rate peak.

A criterion for cracking during solidification

Cracking during solidification is a serious defect in castings and welds. When solidification shrinkage and thermal contraction of the semisolid and its surrounding solid are obstructed, tensile deformation can be induced in the semisolid to cause cracking along grain boundaries that are not fed with sufficient liquid. A criterion for cracking was derived, focusing on events occurring at the grain boundary including separation of grains from each other, lateral growth of grains toward each other, and liquid feeding between grains. An index for the susceptibility of an alloy to cracking during solidification was also proposed, that is, |dT/d(fS1/2)| near (fS)1/2=1, where T is temperature and fS the fraction solid in the semisolid. The index affects: (a) the lateral growth rate of two neighboring grains toward each other to bond together to resist cracking, and (b) the length of the grain-boundary liquid channel through which feeding has to occur to resist cracking. The index was verified with experimental data in casting and welding of Al alloys.

A luminescence imaging system for the routine measurement of single-grain OSL dose distributions

In optically stimulated luminescence (OSL) dating and other retrospective dosimetry studies there is considerable demand for the ability to measure luminescence from individual dosimeters in the size range 50–500 μm diameter, either as separate grains or as part of a matrix. This work tests the potential of an electron multiplying charge-coupled device (EMCCD), providing extremely low level light detection. We characterize the performance of the device by discussing reproducibility and evaluating uncertainties in OSL signals. Finally we derive a typical single grain natural dose distribution with associated uncertainties.

Grain Bending at Deformation of the Steel and Arrangement of Internal Stresses

Arrangement of Internal Stresses in Deformed Austenitic Steel is Studied. the Internal Stresses are Determined Using Parameters of Bending Extinction Contours Observing on Electron Microscope Images of the Steel. at the Deformation Degree ε = 14% the Average Internal Stress Values inside Separate Grains with Complex Bending is much Greater than <σ> in a Grain with Simple Bending. the Difference of <σ> at the Deformation Degree ε = 25% in Grains with Simple and Complex Bending is Small. this is Explained by Considerable Relaxation of the Internal Stresses in the Deformed Steel Caused by Appearance at ε > 20% of a Great Number of Microtwin Packages

Evaluation and modeling of aerodynamic properties of mung bean seeds

Abstract Aerodynamic properties of solid materials have long been used to convey and separate seeds and grains during post harvest operations. The objective of this study was the evaluation of the aerodynamic properties of mung bean seeds as a function of moisture content and two grades referred to above and below a cut point of 4.8 mm in length. The results showed that as the moisture content increased from 7.8 to 25% (w.b.), the terminal velocity of seeds increased following a polynomial relationship, from 7.28 to 8.79 and 6.02 to 7.12 m s-1, for grades A and B, respectively. Seeds at grade A had terminal velocities with a mean value of 8.05 m s-1, while at grade B had a mean value of 6.46 m s-1. The Reynolds number of both grades increased linearly with the increase of seeds moisture content, while the drag coefficient decreased with the increase of moisture content. Mathematical relationships were developed to relate the change in seeds moisture content with the obtained values of aerodynamic properties. The analysis of variance showed that moisture content had a significant effect, at 1% probability level, on all the aerodynamics properties of mung beans.

Acoustic Emission Response of 316LN Welded Joint during Intergranular Corrosion

The acoustic emission (AE) response of 316LN welded joint during intergranular corrosion (IGC) was investigated in this study. The boiling nitric acid method was chosen to provide the IGC environment and AE signals were detected by Macro-SAMOS AE testing system. The metallographic structures and AE results were studied and analyzed in detail. The results show that the IGC process of 316LN welded joint can generate many AE signals and the AE activity is high. The AE amplitude is below 35dB and mainly ranges from 25dB to 34dB. Two types of AE signals are obtained and both the frequency peaks are 50 kHz. It is believed that grain boundary corrosion, ferrite corrosion and separation of grains are the possible AE sources.

Numerical estimation of carbonate rock properties using multiscale images

ABSTRACTCharacterizing the pore space of rock samples using three‐dimensional (3D) X‐ray computed tomography images is a crucial step in digital rock physics. Indeed, the quality of the pore network extracted has a high impact on the prediction of rock properties such as porosity, permeability and elastic moduli. In carbonate rocks, it is usually very difficult to find a single image resolution which fully captures the sample pore network because of the heterogeneities existing at different scales. Hence, to overcome this limitation a multiscale analysis of the pore space may be needed. In this paper, we present a method to estimate porosity and elastic properties of clean carbonate (without clay content) samples from 3D X‐ray microtomography images at multiple resolutions. We perform a three‐phase segmentation to separate grains, pores and unresolved porous phase using 19 μm resolution images of each core plug. Then, we use images with higher resolution (between 0.3 and 2 μm) of microplugs extracted from the core plug samples. These subsets of images are assumed to be representative of the unresolved phase. We estimate the porosity and elastic properties of each sample by extrapolating the microplug properties to the whole unresolved phase. In addition, we compute the absolute permeability using the lattice Boltzmann method on the microplug images due to the low resolution of the core plug images.In order to validate the results of the numerical simulations, we compare our results with available laboratory measurements at the core plug scale. Porosity average simulations for the eight samples agree within 13%. Permeability numerical predictions provide realistic values in the range of experimental data but with a higher relative error. Finally, elastic moduli show the highest disagreements, with simulation error values exceeding 150% for three samples.

Selective formation of hydroxyapatite layers on titanium dioxide

Influence exerted by the structure of layers of titanium dioxide produced by chemical vapor deposition on its ability to form hydroxyapatite in Dulbecco’s phosphate-salt buffer solution was studied. The results obtained demonstrated that the surface phase composition of TiO2 determines the morphology of the mineral layer formed on its surface. The polycrystalline titanium dioxide with random orientation of anatase crystallites is the most favorable for intense nucleation and formation of homogeneous hydroxyapatite layers composed of densely packed grains with diameter of 3.0 ± 0.5 μm in Dulbecco’s solution. Textured TiO2 layers with smooth surface also resulted in that hydroxyapatite was formed. In this case, it was composed of separate coarse grains 8.0 ± 2.0 μm in size. It is the most probable that the nucleation of this mineral on the surface of titanium dioxide layers occurs by the epitaxial growth mechanism.