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Industrial laboratory. Diagnostics of materials

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Vol 84, No 6 (2018)
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SUBSTANCES ANALYSIS

5-10 586
Abstract

A technique for analysis of surfacing materials (cast cobalt-based carbide alloys) using by ICP-AES in combination with microwave autoclave sample preparation is developed. Composition of the acid mixture, temperature and time parameters of the sample preparation under microwave heating in an autoclave are specified, thus ensuring complete quantitative transfer of the sample into a convenient analytical form without losses of volatile components for the subsequent ICP-AES analysis. Analytic lines of the elements free from spectral interference were chosen to determine all the rated components in the casting materials from cast carbide alloys. Study of surfacing materials was carried out using alloys Pr-B3K-PrH-U10Kh63B5, Pr-B3K-P-PrN-U20Kh57B10 and TsN-2-E-190K62X29B5C2, containing the alloying elements (% wt.): Co (up to 65); Cr (28.0 – 32.0); W (4.0 – 11.0); Si (1.0 to 3.0); C (1.0 – 2.0); Ni (0.1 – 2.0); Mn (0.3 – 0.6) and Fe (up to 2.0). The correctness of determining rated element was confirmed in analysis of standard samples using sample weight variation. The developed technique was tested on industrial prototypes of surfacing materials made of cobalt-based cast carbide alloys of tested grades. The method is rapid (11-fold reduction in the time of analysis) and reagent-saving (by 12.5 times) procedure compared to single-element methods by 11 times and reduction of the volume of applied reagents. Combination of the multielement ICP-AES method with microwave sample preparation provides an increase in the accuracy of Si, Cr, Mn, Fe, Ni, and W determination in surfacing materials of cast carbide alloys within a range of rated concentrations.

11-17 1044
Abstract

A method for separation of ethylene glycol (EG) and alkali metal salts in aqueous solutions is developed using solid-phase extraction on carbon nanotubes (CNT) and dialysis with a domestic mosaic membrane AK-45. Both methods enable effective separation of the components of EG + NaCl (KCl) aqueous solution which is necessary for gas chromatographic determination of EG in the mixtures. Hydrophobic-hydrophilic interactions in the EG – water – CNT system provide efficient sorption of EG and almost zero sorption of potassium chloride by CNT. Coefficients of EG and KCl separation on Dealtom carbon nanotubes range within 7 – 15 (for 0.001 ≤ C0 EG ≤ 0.1, 0.001 ≤ C0 KCl ≤ 0.1 mol/liter), EG extraction rate is 86 – 94% for single extraction. CNT practically do not absorb potassium chloride. High and low permeability of mosaic membranes for metal salts EG, respectively, is a basis for separation of EG and alkali metal salts by dialysis. During a 4-hour dialysis, 96% and 87% of NaCl (C0 = 0.001 mol/dm3 and C0 = 0.01 mol/dm3, respectively), are transferred as NaCl through the AK-45 membrane (86% and 82% for KCl). At the same time an amount of less than 3% EG (C0 = 0 mol/dm3) is transferred during dialysis through AK-45 membrane. Mosaic membrane AK-45 appeared to be the most effective one regarding the transfer of alkali metal salts from low-mineralized aqueous solutions, unlike traditional ion-exchange membranes in the absebce of such transfer due to the Donnan phenomenon. Coefficients of alkali metal chloride and EG separation by dialysis with an AK-45 membrane range within 13 – 38, which indicates to their rather efficient separation.

18-22 724
Abstract

Analytical control of the technological process of linear alpha-olefins (LAO) production using a zirconium carboxylate based catalyst according to α-SABLIN technology calls for determination of the residual zirconium in the solvent when washing equipment, in the reaction products and wastewater, the purity of which is strictly regulated. Features of photocolorimetric determination of zirconium impurities with different complexing agents are considered and sensitivity of the determination with iron, aluminum, nickel and chromium present is estimated by comparing the values of the «sensitivity index» (by E. Sendel) and «specific absorption» (by Z. Marchenko). The reaction of complex formation with arsenazo III in 9 – 10 M HCl is used for determination of zirconium in the LAO production related products. The resulting colored complex exhibits the maximum light absorption at a wavelength of 670 nm. The measured content ranges from 0.100 to 100 mg/kg, 103-fold amounts of Ni2+, Fe3+, Al3+ and 400-fold amounts of Cr3+ do not interfere with the determination. The method of additives is used to eliminate the interfering effect of the acidity of the medium. It is shown that the developed technique provides a satisfactory level of the reproducibility and correctness of the results for analytical control of LAO production.

MATERIALS MECHANICS: STRENGTH, DURABILITY, SAFETY

44-51 1061
Abstract

The nature and character of the destruction of the high-loaded airscrew shaft of the gas turbine engine made of steel 40KhN2MA are studied using the methods of scanning electron and optical microscopy and X-ray spectral microanalysis. We determined the chemical composition, microstructure and character of destruction of the flange part of the shaft. It is shown that chemical composition of the shaft material meets the requirements of the regulatory documents and defects of metallurgical origin are absent both in the metal of the shaft and in the fatigue fractures. All the identified cracks have been formed during operation, and developed according to the fatigue mechanism. Zones of fretting-wear and fretting-corrosion damage to the surface in the stud holes are the foci of the fatigue crack birth in the airscrew shaft. The cause of formation and development of the fatigue cracks in the shaft flange is a high level of contact stresses in the flange body, attribute to a poor quality of the interface of the splined joint due to significant fretting corrosion damage to the splines and vibration damages. A set of recommendations and measures aimed at elimination of the adverse factors is elaborated. To exclude the formation and development of fatigue cracks in the splined flange upon operation, we recommend to: optimize the tightening torque of the splined joint; introduce quality control of the interface between contact surfaces of the splined joint when replacing the airscrews; address the issue of dynamic balancing of the airscrews upon their production and repair.

52-58 612
Abstract

The effect of allotropic carbon modification content, graphene (G), in the range of 0.5 – 2.0 wt.% on tribological, strength and structural characteristics of Al2O3/G nanocomposite processed by 10-min plasma spark sintering (pressure 50 MPa, temperature 1550 °C) of nanopowder mixture previously subjected to ultrasonic dispersion in organic solvent is studied. The results of tests for friction and wear without lubricant on a tribometer under a load of 20 N at room temperature and roundabout motion of a ruby ball penetrator on a disk are presented along with data on kinetic indentation with determination of the nanohardness and elastic module and observations of the fracture surface structure and friction track using a scanning microscope. Methods of the transmission electron microscopy of thin foils in dark and bright fields and Raman spectroscopy, respectively, were used to determine the microstructure in the bulk of a nanocomposite and prove the graphene thermal stability during plasma spark sintering. It is shown that introduction of graphene contributes to the increase of micro- and nanohardness, elastic modulus, wear resistance by two or three orders of magnitude and a slight decrease in the coefficient of friction. Increase in graphene content to 2 wt.% changes the wear mechanism from brittle breakage to viscous shear due to strengthening in coupling of matrix grains and presnrce of agglomerates. Lack of degradation and retention of graphene thermal stability are proved. The morphology of graphene particles indicates to their preferential arrangement inside the corundum grains and more rarely — on the grain boundaries.

59-62 1079
Abstract

Processing of metals by pressure suggests using of various measuring devices. We developed and manufactured a device for measuring angular deformations upon elastic and plastic torsion of circular specimens. The design is based on the operation principle of the planetary mechanism without a movable solar central wheel. Design of the device is based on the Boyarshinov concept added with a round protractor with a graduated scale from 0 to 360° and rotating needle placed on the axis to indicate the angular displacement. The use of the planetary gear significantly improves the accuracy of measuring the angles of rotation of the cross sections of the sample relative to each other at a distance of the calculated length. To low the weight of the device, the main parts were made of aluminum alloy D16Т. Rated diameters of the central wheel and satellite are D1 = 220 mm, D3 = 20 mm, respectively; the linkage module m = 1 mm; the number of teeth on the wheel and satellite is 220 and 20, respectively. Laboratory tests of the device were carried out on a KM-50 torsional machine using a cylindrical sample with a diameter of 15 mm and a working length of 120 mm made of steel 40Kh. The results provided determination of the elastic shear modulus with a deviation of ~2.5% of the reference value. Experimental data were used to plot the torsion diagram and then to get shear diagram τ = τ(γ) according to P. Ludwik’s formula. This diagram was transformed into the hardening curve σ = σ(e) using von Mises theory of the plasticity. The obtained mechanical characteristics allowed us to draw a conclusion on the essential accuracy of measuring angular displacements using the developed device. Thus, the developed and easy to use device can be recommended as testing equipment for determination of the mechanical characteristics of materials under conditions of shear deformations.

COMPLIANCE VERIFICATION. LABORATORY ACCREDITATION

63-70 846
Abstract

The issue of assuring the traceability of the results of water determination in solid and liquid substances and materials is discussed. The stages of development and improvement, as well as composition of the State primary measurement standard of mass fraction and mass (molar) concentration of water in liquid and solid substances and materials (GET 173) are considered. The problems of the limited applicability of GET 173 in case of separation of water with different binding energies and impossibility of conducting qualitative analysis of non-water volatile compounds during heating of substances and materials are revealed. The results regarding upgrading of GET 173 due to incorporation of additional reference installation which implements the methods of thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and mass-spectrometry (MS) are presented. The composition and operating principle of the new reference unit are described. An algorithm for estimating the uncertainty of reproducing a unit mass fraction of water using this reference facility is presented and sources of the uncertainty are identified. The results of the experiment on determination of the lower limit of the reproduction range for a unit water mass fraction are presented. We also present the results of comparisons regarding determination of the water mass fraction in crystalline hydrates obtained using the improved State primary standard and high-precision installations of the metrological and leading sectorial research institutes of the European countries. The results of developing a certified reference material of water mass fraction in sodium molybdate dihydrate (Na2MoO4 · 2H2O CRM UNIIM 10911–2017 intended for metrological support of measurement instruments and measurement procedures based on thermo-gravimetric method are presented. Additional possibilities which result from the introduction of a new reference installation into the state primary standard of GET 173 are disclosed: identification and the quantification of non-water volatile components, adjustment of drying regimes both in laboratory and process conditions, determination of water content as one of the main impurities in estimating mass fraction of the main component of high-purity substances.

70-76 749
Abstract
A brief review on using the Bayesian concept of the likelihood ratio (LR) in forensic activities is presented. It is proved that the use of the likelihood ratio provides assessing the measure of uncertainty regarding the truth or falsity of the assumption of expertise when taking into account a priori chances and new information appearing in the course of expert research. A possible simulation experiment is presented as an example to calculate a set of the likelihood ratio values from the validation database for forensic examination of sound recordings. Different approaches of using the likelihood ratio in assessing the trueness of the judicial evidence are considered. The concept of the likelihood ratio has been adopted as the standard procedure for different types of examinations used in the laboratory practice, including that of the European network of forensic institutes (ENFSI).

STRUCTURE AND PROPERTIES INVESTIGATION

23-33 661
Abstract

A set of new approaches and techniques of non-destructive testing is described and implemented within a unified computer analysis of the patterns of multi-scale dynamic thermography. Depending on the size of the inspected area, nature, location, orientation and size of the defects, various energy sources were used for probe dynamic heating of the controlled article: air flow, focused laser beam, and point contact. The non-stationary thermal picture of the monitored area was recorded with a high resolution thermal imaging device and then analyzed using original model approaches and developed software. A set of discussed approaches allows detecting and quantitative characterizing of the defects of various types, size (from fractions to tens of millimeters) and orientation, including cracks, coating delamination or degradation, welding and glue seams defects, deposits, etc., both at the outer and inner surfaces of tubes, tanks, and reactors, etc. The developed methods provides determination of the thermophysical characteristics of the material, i.e., the thermal diffusivity coefficient with an accuracy better than ±3%.

34-37 708
Abstract

The atomic structure of substances can be studied using X-ray diffraction methods. X-ray diffractometers contains X-ray source and goniometer with a detector of scattered radiation. A sample holder (a cuvette) with the material under study is placed in the center of the goniometer. The diffraction spectrum which represents the structure of the sample under study is recorded upon angular scanning of the sample and detector. Study of crystalline powders, amorphous substances, nanocrystalline and partially crystalline objects is often based on the Bragg-Brentano scheme (θ – 2θ-scanning) with divergent X-ray beams irradiating the entire sample surface. Scattered radiation from the cuvette can also enter the detector and affect the recorded diffraction spectrum. The aforementioned distortion is rather weak for polycrystalline samples due to strong intensity of crystalline reflections. However, when studying amorphous substances, nanocrystalline and partially crystalline objects, contribution of the scattered radiation can be compared with the radiation from the sample and thus interfere with an unambiguous determination of the sample structure. The results of using standard cuvettes for X-ray diffractometers D500, D5000 (Siemens), D8 ADVANCE (Bruker) and DRON are analyzed with a special attention paid to distortion of X-ray spectra attributed to the use of cuvettes made of plastic or amorphous quartz when studying amorphous, nanocrystalline and partially crystalline samples. Special cuvettes, being a kind of optical shutters for background scattering, which do not distort the diffraction spectra of the objects under study are developed: single crystal plates of a special orientation with cylindrical cavities for the samples. The advantages of a single-crystal silicon cuvette compared to plastic cuvette usually supplied for D500 diffractometer are estimated when studying an amorphous sample.

38-43 788
Abstract

A comparative study of structural features of the blade castings having a single-crystal structure and made of heat-resistant carbon-free and carbon-containing high-temperature nickel alloys upon directional crystallization with 001 crystallographic orientation is carried out. The results of the effect of directional crystallization modes on the formation of the structure and defects of castings of working blades made of carbon-containing and carbon-free high-temperature nickel alloys are presented. Changes in the degree of pickling of the near-surface layer of casting are presented as a function of pickling conditions. The microstructure of the near-surface zone of castings made of ZhS32 heat-resistant alloy is studied after different modes of their technological processing. It is shown that blade castings with a single-crystal structure made of heat-resistant carbon-free superalloys have a tendency to formation of the block structure and appearance of surface recrystallized grains. Recommendations on the use of methods of nondestructive X-ray control of blades made of carbon-frees alloys and precautions regarding birth of microporosity on the shelf and in the blade lock are specified.



ISSN 1028-6861 (Print)
ISSN 2588-0187 (Online)