The new mineral zvÄstovite-(Fe), ideally Ag.sub.6 (Ag.sub.4 Fe.sub.2 )As.sub.4 S.sub.13, has been found in the small abandoned Ulatayskoe Ag-Cu-Co occurrence, Ovyurskiy District, Tuva Republic, ...eastern Siberia, Russia. It occurs as anhedral grains, up to 1 x 0.4 mm in size but usually much smaller, closely intergrown with native silver, in Mg-bearing siderite-quartz gangue. Other associated minerals include acanthite, cobaltite, As-rich members of the tetrahedrite group (kenoargentotennantite-(Fe), tennantite-(Zn), zvÄstovite-(Zn)), gersdorffite, jalpaite, krutovite, löllingite, pearceite, safflorite, skutterudite, Br-bearing chlorargyrite, malachite, and muscovite. ZvÄstovite-(Fe) is iron black and opaque and has a black streak and metallic lustre. It is brittle and has a conchoidal fracture. No cleavage or parting is observed. The Vickers micro-indentation hardness (Vickers hardness number, VHN; 25 g load) is 169 kg mm.sup.-2 (range of 149-187 kg mm.sup.-2, n=4), corresponding to a Mohs hardness of 3-3.5. The calculated density is 4.979 g cm.sup.-3 . In reflected light, zvÄstovite-(Fe) is light grey with a greenish tint and isotropic. Internal reflections are ubiquitous and deep red in colour. The reflectance values for wavelengths recommended by the Commission on Ore Mineralogy of the International Mineralogical Association are (R, %): 32.5 (470 nm), 31.1 (546 nm), 30.1 (589 nm), and 28.8 (650 nm). The chemical composition (wt %, electron microprobe data, mean of eight spot analyses) is as follows: Cu 1.81, Ag 56.02, Fe 4.60, Zn 0.01, As 13.85, Sb 2.63, S 21.50, total 100.42. The empirical formula, calculated on the basis of 16 atoms per formula unit, is Ag.sub.9.93 Cu.sub.0.54 Fe.sub.1.58 As.sub.3.54 Sb.sub.0.41 S.sub.12.83 . ZvÄstovite-(Fe) is cubic and has a space group of I4-3m, with a=10.8601(3), V=1280.86(11) Ã.sup.3, and Z=2. The strongest lines of the X-ray powder diffraction pattern (d, Ã (I, %) hkl) are 7.68 (11) 110, 3.136 (100) 222, 2.717 (12) 400, 1.984 (8) 521, 1.921 (23) 440, and 1.638 (11) 622. The crystal structure of zvÄstovite-(Fe) was refined to R.sub.1 =0.0551 for 400 unique reflections with F.sub.o >4Ï (F.sub.o). The possible ordering of the split M(2) sites is discussed. The new mineral is the Fe isotype of zvÄstovite-(Zn). Both these minerals form the zvÄstovite series within the tetrahedrite group.
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This report describes the results of comparison COOMET.M.H-S3. The comparison measurements between the five participants NSC "IM" (pilot laboratory), PTB, CMI, BelGIM, KazInSt were started ...in December 2014 and ended in December 2016. In the RMO SC, one set of hardness reference blocks was used consisting of 6 (six) blocks of the Superficial-Rockwell scales and hardness levels 90-94 HR15N, 40-50 HR30N, 76-84 HR30N, 43-54 HR45N, 47-53 HR30TW, 70-82 HR30TW. Agreement between the results of the participants is good.
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The overview of ISO 185: 2020 Grey Cast Irons-Classification, the main contents of standard revision and typical applications were introduced.The main contents of the standard were described in ...detail, including the scope, material brand, tensile strength of cast sample, tensile strength of body sample, hardness, metallographic structure, sample preparation and retests.
Based on the first-principles method, the effects of pressure and temperature on the physical properties of Nbsub.2Bsub.3 and Tasub.2Bsub.3 were discussed. The approximate linear increase in B, G, ...and E with pressure was observed for Nbsub.2Bsub.3 and Tasub.2Bsub.3 with a minor difference for bulk modulus and similar values for shear and Young’s modulus. Nbsub.2Bsub.3 shows higher Vickers hardness and similar fracture toughness as compared with Tasub.2Bsub.3. An abnormal phenomenon of the simultaneous increase in hardness and B/G (σ) with the increased pressure was observed. The strong anisotropies of bulk, Young’s, and shear modulus were observed, and the differences of anisotropy between Nbsub.2Bsub.3 and Tasub.2Bsub.3 increased with pressure. At low temperatures, the α of Nbsub.2Bsub.3 is smaller than that of Tasub.2Bsub.3, but is larger than that of Tasub.2Bsub.3 at high temperatures. The Θ of Nbsub.2Bsub.3 are larger than those of Tasub.2Bsub.3 under the same conditions. The combination of relatively high Vickers hardness and fracture toughness is determined by the metallic bond and covalent bond. With the increased pressure, Nbsub.2Bsub.3 possesses the greater strength of B–B bonds than Tasub.2Bsub.3, which leads to its high hardness and Debye temperature.
Rare earth elements have been widely utilized in material manufacturing to enhance properties in various ways. In order to obtain the WC-10Co4Cr coating with uniform distribution of rare earths, ...CeOsub.2-modified powder was prepared by mixing 1 wt.% nano-sized CeOsub.2 during the initial ball-milling of the powder fabrication process. Bare and CeOsub.2-modified WC-10Co4Cr coatings were deposited via high velocity oxygen fuel spraying to investigate the impact of CeOsub.2 modification on the coating's microstructure, mechanical properties and abrasive wear performance. The results show that the addition of CeOsub.2 increased the interface energy, inhibiting the formation of the Cosub.3Wsub.3C phase during the powder sintering process, as well as the Wsub.2C phase and CoCr alloy during the high-velocity oxy-fuel (HVOF) process. This led to a significantly decreased porosity and higher concentration of undissolved Cr-rich areas. The microhardness and fracture toughness of the CeOsub.2-modified coating were 1230 HVsub.0.3 and 5.77 MPamsup.1/2, respectively. The abrasive wear resistance of the CeOsub.2-modified coating was only 70.9% of that of the unmodified coating. Due to the weak cohesive strength between WC and Cr, Cr-rich areas were preferentially removed, resulting in an increased wear rate in the CeOsub.2-modified coating.
Hardness is one of the critical physical characteristics of minerals and rocks, which indicates the resistance of the rock to penetration, scratch, or permanent deformation. As a basic concept, rock ...hardness has a significant role in rock mechanics and geological engineering and is an appropriate diagnostic tool for the classification of minerals and rocks. The main purpose of this study is to guide rock engineers to measure the rock hardness faster, easier, and more accurately using Leeb’s dynamic hardness test. Accordingly, this paper presents a new rock hardness classification system based on the Leeb dynamic and portable hardness testing method. It is a well-known method for its fast and straightforward procedure testing equipment. A set of 33 different rock types were collected and tested during this study. Next, in-depth microscopic mineralogical studies were performed to determine the precise Mohs hardness value. The Mohs hardness was considered the leading hardness benchmark during the experimental studies, and the Leeb hardness was adopted to classify based on this hardness. A series of laboratory studies and statistical analysis was performed to predict the Shore and Vickers hardness using Leeb hardness. Finally, based on the comparative studies, it is recommended to classify the rocks considering the Leeb hardness method in six different categories: extremely soft (1–250), soft (250–450), moderately soft (450–750), moderately hard (750–850), hard (850–920), and extremely hard (920–1000). The provided classification could be useful in a vast range of rock engineering applications, especially for feasibility studies of rock engineering projects and engineering geology.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A ZrBsub.2–copper–graphite composite was produced through powder metallurgy and was tested as a new electric brush material. The aim of this paper was to study the effect of ZrBsub.2 addition on the ...composite’s properties. Besides its physical properties such as density and resistivity, its mechanical properties, such as hardness, bending strength and wear resistance, were studied. A scanning electron microscope (SEM) was used to study the morphology of the wear surface, and a configured energy-dispersive spectrometer (EDS) was used to research the chemical composition of the samples. The results showed that, with the addition of ZrBsub.2, the composite’s properties such as density, resistivity, hardness, and bending strength improved significantly. Compared with samples without ZrBsub.2, samples with the addition of 4% ZrBsub.2 achieved a hardness of 87.5 HRA, which was improved by 45.8%, and a bending strength of 53.1 MPa, which was increased by nearly 50.0%. Composites with 1% content of ZrBsub.2 showed the best wear resistance under non-conductive friction; however, under conductive friction, composites with 4% content of ZrBsub.2 showed better wear resistance.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Abstract
Reference materials for the Rockwell, Brinell and Vickers hardness scales are fundamental for the Brazilian industrial sector. Mechanical property Hardness is the most common mechanical test ...used for quality control of raw materials in finished products as well as in research and development of new products and materials. A description of the main findings of two studies and the revalidation of the last on the demand of hardness reference blocks in Brazil is presented. This paper shows national demand of hardness reference blocks could be supplied on a large scale by Inmetro´s Force Laboratory.
![ZrB[sub.2]–Copper–Graphite ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1996-1944/small "ZrB[sub.2]–Copper–Graphite Composite for Electric Brushes: Positive Effect of ZrB[sub.2] Addition on Composite Properties")
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