The Effect of Copper Bearing Particles Liberation on Copper Recovery from Smelter Slag by Flotation

The impact of the liberation of copper bearing particles on copper recovery in the flotation has been the subject of research in this paper. Tests have shown that grinding of material highly impacts the recovery rate in the flotation process. Results of flotation of smelter slag samples with different contents of grain size fraction ?74 µm: 50%, 60%, 70%, 80%, and 90%, have shown that by an increasing the content of the ?74 µm fraction in the feed, the recovery of copper was increasing as well. The highest recovery rate of copper was obtained with 90% of grain size fraction ?74 µm in the feed. The microscopic analysis of concentrates have shown that increased content of grain size fraction ?74 µm, was followed by increased contribution of liberated particles in the 0 to 70 µm fraction, while the contribution of middlings had been decreasing.     

Zrc ceramics incorporated with different-sized SiC particles

ABSTRACT

Three different SiC powders with average particle sizes of 0.45, 3.5 and 10?µm were used to prepare ZrC-20vol.-% SiC ceramics by hot pressing. The effects of SiC particle size on the densification, microstructure, mechanical properties and thermal properties of ZrC–SiC ceramics were studied. Ceramics prepared from SiC with finer particle sizes exert higher bending strength, hardness and lower thermal conductivity. The ZrC–SiC ceramics with a starting SiC particle size of 3.5?µm has relative high fracture toughness than others. Analysis indicates that SiC grain size and the grain boundaries control the thermal conductivity ZrC–SiC ceramics. Ceramics prepared from SiC with the particle size of 10?µm exhibits the highest thermal conductivity due to the larger grains and less grain boundaries.     

Grain size analysis and characterization by Raman spectroscopy of a homogeneous sintered MOX fuel

The grain size distribution of an U_0.89Pu_0.11O₂ MOX fuel, sintered from a freeze-granulated powder to 97% of the theoretical density at 1700 °C during 4 h, for an oxygen potential set to ? 387 kJ/mol, was investigated. The sintered microstructure is constituted by 8.5 vol% of clusters of small grains, having an average grain size around 1.5 µm, dispersed in a polycristalline matrix made of larger grains having an average grain size around 7–8 µm. Characterizations by Raman micro-spectroscopy showed that the Pu/(U+Pu) content was not the same depending on the type of grain. The large grains constituting the sintered polycrystalline matrix have a Pu/(U+Pu) content in the range 9.0–11.0 mol%, which is close to the overall target. The small grains agglutinated in the form of clusters are however clearly depleted in Pu.     

Numerical simulation analysis and experimental validation on wear/fracture mechanisms of polycrystalline cubic boron nitride superabrasives in high-speed grinding

In this study, a two-dimensional finite element model is proposed to investigate the wear/fracture mechanisms of polycrystalline cubic boron nitride (PCBN) superabrasives in high-speed grinding process. The special geometric microstructures of PCBN grains are constructed by using the classic Voronoi tessellation technique, and cohesive elements are embedded into the geometric model of PCBN grains as the potential crack propagation paths for simulating the wear/fracture behaviours of PCBN grains under grinding loads. The effects of uncut chip thickness per grain (a_gmax) on the stress distribution characteristics and wear/fracture behaviours of PCBN grains during grinding are discussed in detail. Results show that the wear behaviour of PCBN grains during grinding mainly occurs around the grain vertex region; however, the fracture behaviour, leading to the quick failure of PCBN grains, is prone to appear around the grain–filler bonding interface, which is usually on the opposite side of the in-feed direction. Moreover, to separate the PCBN grains from the macro-fracture during grinding, the uncut chip thickness per grain should be kept smaller than 1.0?µm to prevent the unfavourable fracture behaviour from appearing around the grain–filler bonding interface. Furthermore, the corresponding single-grain grinding trials are performed to validate the numerical simulation results by evaluating the wear/fracture morphologies of the PCBN superabrasives in the actual grinding operation.     

A novel approach toward microstructure evaluation of sintered ceramic materials through image processing techniques

In this paper, an image processing technique is introduced to measure the grain size and their distributions from the SEM image of copper oxide (CuO) and titanium dioxide (TiO₂) doped sintered alumina ceramics accurately. The noise present in SEM image is removed by applying low pass Gaussian filter followed by suppression of regional minima over a threshold. The clarity of individual grains and grain boundaries have been done by applying Watershed transform to this preprocessed SEM image. Morphological operations like dilation and erosion are used to make the grain-boundary edges clear and continuous. The individual grain size in µm scale is measured from the pixel length of the rectangular bounding box drawn around the segmented grain. The normal Gaussian type distribution of grain size is observed in both CuO- and TiO₂-doped grains in SEM image. The average grain size of CuO-doped alumina grains (2.24 µm) is very close to G₅₀ value (2.17 µm), but G₅₀ value of TiO₂-doped grains (8.59 µm) is slightly higher than its average grain size (7.96 µm). The proposed algorithm is compared with linear intercept method and the grain sizes obtained are very close to each other.     

Comparison of different alumina powders for the aqueous processing and pressureless sintering of Al2O3–SiC nanocomposites

Four different alumina powders, from European and Japanese sources having similar particle size (350–700 nm) were used for the fabrication of nanocomposites. They were compared in terms of green properties, sintering behaviour, microstructure and mechanical properties. The processing route used (attrition milling and freeze-drying) leads to a reduction in green density of the processed aluminas and composites compared to the as-received alumina. All powders had similar green properties except one, which contained a binder from the manufacturer. The presence of this binder led to the formation of hard agglomerates. In this case the pressing did not eliminate, totally, the inter-agglomerate pores, leading to an incomplete sintering. Calcining the powder to remove the binder resulted in similar pressing and sintering behaviour to the other powders and densities >99% were achieved at 1750 °C by pressureless sintering. All the composites exhibited similar microstructures (matrix grain size ∼3 μm) and elastic properties, hardness and fracture toughness. A finer matrix microstructure could be obtained with one of the European powders which achieved ∼99% density at 1700 °C. The presence of 5 vol.% SiC resulted in a mean grain size of ∼2 μm for the alumina matrix compared with 13.9 μm for a monolithic alumina prepared under identical conditions.     

Influence of Grain Size on the Grinding Response of Alumina

The effect of grain size on the grinding response, i. e., grinding forces, surface roughness, and grinding-induced subsurface damage, is investigated in a series of alumina ceramics with the average grain size ranging from 3 to 35 μm. The grinding forces are measured as a function of depth of cut in surface grinding. It is found that the grinding forces decrease as the grain size is increased from 3 to 9 μm. But at larger grain sizes, the grinding forces are independent of the grain size. Subsurface damage in grinding is observed using a bonded-interface sectioning technique. The subsurface damage is found to consist of intragrain twin/slip bands and intergranular microcracks. The density of grinding-induced subsurface microcracks increases with the grain size. In addition to using optical microscopy on the sections of the ground specimens, a nondestructive thermal wave measurement technique is used directly on the ground surfaces for the detection of grinding-induced subsurface microcracks. The grain size dependence of the microcrack density estimated from the thermal images is found to agree with the results obtained using the bonded-interface technique.     

DC and RF performance of surface channel MESFETs on H-terminated polycrystalline diamond

DC and RF performance of submicron gate-length metal–semiconductor field effect transistors (MESFETs) fabricated on hydrogen-terminated polycrystalline diamond is investigated in detail for different material electronic quality (grain size in the range 100–200 µm) and device geometry (drain-source channel length in the range 1–3 µm). DC characteristics appear almost independent of both properties, giving maximum drain-source current values in the range 120–140 mA/mm in MESFETs having same gate length (0.2 µm) and gate width (25 µm). The layer properties underneath the hydrogenated surface seem then to affect the DC behaviour to a lesser extent when the same hydrogenation procedure is used. At variance, the electronic quality of diamond layers employed for MESFETs realization largely affects the RF performance, resulting into a low oscillation frequency f_max for a MESFET realized by a self-aligned process (1 µm drain-source channel length) onto low quality diamond polycrystalline film. Such a performance improves to f_max = 35 GHz for devices realized onto large grain polycrystalline diamond, although fabricated without self-aligned gate procedure (3 µm drain-source channel length). These findings are discussed in terms of different roles played by surface hydrogenation, device geometry detail and electronic quality of the polycrystalline diamond substrate for MESFET realization.     

Continuous aluminum oxide-mullite-hafnium oxide composite ceramic fibers with high strength and thermal stability by melt-spinning from polymer precursor

Continuous aluminum oxide-mullite-hafnium oxide (AMH) composite ceramic fibers were obtained by melt-spinning and calcination from polymer precursor that synthesized by hydrolysis of the aluminum isopropoxide, dimethoxydimethylsilane and hafnium alkoxide. Due to the fine diameter of 8–9 µm, small grain size of less than 50 nm and the composite crystal texture, the highest tensile strength of AMH ceramic fibers was 2.01 GPa. And the AMH ceramic fibers presented good thermal stability. The tensile strength retention was 75.48% and 71.49% after heat treatment at 1100 °C and 1200 °C for 0.5 h respectively, and was 61.57% after heat treatment at 1100 °C for 5 h. And the grain size of AMH ceramic fibers after heat treatment was much smaller than that of commercial alumina fibers even when the heat treatment temperature was elevated to 1500 °C, benefited by the grain size inhibition of monoclinic-HfO₂ (m-HfO₂) grains distributed on the boundary of alumina and mullite grains.     

Intensive grinding of powders in an electro-magneto-mechanical mill

The paper presents the results of high-energy grinding in the electro-magneto-mechanical (EMM) mill. Ground powder is treated in a very specific and intensive way owing to several field forces operating simultaneously in the EMM mill. The grinding power in the centre of the mill's working chamber is in the order of 2 MW/m³, which is much more than in ordinary mills. Therefore, the grinding time is very short, i.e., several tens of seconds. The self-disintegrated Fe–Al–Si powders of 155 μm on average undergo size reduction to 8 μm after 120 s. Over 25% of the total weight get the size of less than 1.3 μm. Very hard materials, such as SiC and B₄C reduce their grain size over 30 times after 120 s of grinding in the EMM mill. The results of the grinding of Fe₂O₃ powder are even better. In ball mills, vibration and planetary mills, similar results can be achieved after a period several hundreds times longer. The treatment of Fe–Al–Si powder presented here is intended as the preparation procedure for sintering, plasma spraying or laser surface alloying.     

Recycling of silicone rubber waste: Effect of ground silicone rubber vulcanizate powder on the properties of silicone rubber

The silicone rubber vulcanizate powder (SVP) obtained from silicone rubber by mechanical grinding exists in a highly aggregated state. The particle size distribution of SVP is broad, ranging from 2 µm to 110 µm with an average particle size of 33 µm. X‐ray Photoelectron Spectroscopy (XPS) and Infrared (IR) Spectroscopy studies show that there is no chemical change on the rubber surface following mechanical grinding of the heat‐aged (200°C/10 days) silicone rubber vulcanizate. Addition of SVP in silicone rubber increases the Mooney viscosity, Mooney scorch time, shear viscosity and activation energy for viscous flow. Measurement of curing characteristics reveals that incorporation of SVP into the virgin silicone rubber causes an increase in minimum torque, but marginal decrease in maximum torque and rate constant of curing. However, the activation energy of curing shows an increasing trend with increasing loading of SVP. Expectedly, incorporation of SVP does not alter the glass‐rubber transition and cold crystallization temperatures of silicone rubber, as observed in the dynamic mechanical spectra. It is further observed that on incorporation of even a high loading of SVP (i.e., 60 phr), the tensile and tear strength of the silicone rubber are decreased by only about 20%, and modulus dropped by 15%, while the hardness, tension set and hysteresis loss undergo marginal changes and compression stress‐relaxation is not significantly changed. Atomic Force Microscopy studies reveal that incorporation of SVP into silicone rubber does not cause significant changes in the surface morphology.     

Preparation and study of the mechanical and optical properties of infrared transparent Y2O3–MgO composite ceramics

In this study, fine Y₂O₃–MgO composite nanopowders were synthesized via the sol–gel method. Dense Y₂O₃–MgO composite ceramics were fabricated by pre-sintering the green body in air at different temperatures for 1 h and then subjecting the sintered bodies to hot isostatic pressing at 1300°C for 1 h. The effects of pre-sintering temperature on the microstructural, mechanical, and optical properties of the resulting ceramics were studied. The average grain size of the ceramics was increased, whereas their hardness and fracture toughness were decreased with increasing pre-sintering temperature. A maximum fracture toughness of 1.42 MPa·m^1/2 and Vickers hardness of 10.4 GPa were obtained. The average flexural strength of the ceramics was 411 MPa at room temperature and reached 361 MPa at 600°C. A transmittance of 84% in the 3–5 µm region was obtained when the composite ceramics were sintered at 1400°C. Moreover, a transmittance of 76% in the 3–5 µm region was obtained at 500°C.     

Surface microstructural changes of spark plasma sintered zirconia after grinding and annealing

Spark plasma sintered zirconia (3Y-TZP) specimens have been produced of 140 nm 372 nm and 753 nm grain sizes by sintering at 1250 °C, 1450 °C and 1600 °C, respectively. The sintered zirconia specimens were grinded using a diamond grinding disc with an average diamond particle size of about 60 µm, under a pressure of 0.9 MPa. The influence of grinding and annealing on the grain size has been analysed. It was shown that thermal etching after a ruff grinding of specimens at 1100 °C for one hour induced an irregular surface layer of about a few hundred nanometres in thickness of recrystallized nano-grains, independently of the initial grain size. However, if the ground specimens were exposed to higher temperature, e.g. annealing at 1575 °C for one hour, the nano-grain layer was not observed. The resulted grain size was similar to that achieved by the same heat treatments on carefully polished specimens. Therefore, by appropriate grinding and thermal etching treatments, nanograined surface layer can be obtained which increases the resistance to low temperature degradation.     

The complex evaluation of functional properties of nearly dense BCZT ceramics and their dependence on the grain size

In this article, the effect of dwell time (2–48?h) during isothermal sintering at 1520?°C on the grain size, density and crystal structure of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ is demonstrated. All ceramics exhibited the phase transition from orthorhombic to mixed orthorhombic and tetragonal phases between 12 and 24?h dwell time. The piezoelectric, dielectric and ferroelectric properties of these ceramics show a strong correlation with grain size in the range of 16.5–44.5?µm. Nearly dense microstructure (93.1–94.3% t.d.) was maintained during entire dwell time range without sacrificing much of its functional properties. Increasing grain size caused a little decrease in d₃₃* piezoelectric constant from 480 pC/N to 460 pC/N while mechanical quality factor (Q_m) increased from 62 to 136. Diffusivity coefficient (γ) ranges between 1.46 and 1.55 which indicates a normal ferroelectric behavior.     

Characterization and Low-Temperature Sintering of Reactive Mn-Zn Ferrite Powder

Highly sinterable Mn-Zn ferrite powder consisting of sub-micrometer-size particles with structural distortion has been prepared by grinding a coprecipitated powder with a media agitation mill. Dense pure Mn-Zn ferrites (>98% of theoretical) with an average grain size of 1.9 μm can be fabricated by heating at 900°C in a stream of N₂. They show high permeability of 820 at 10 kHz through 1 MHz and an electric resistivity of 50 Ω cm at 1 kHz.     

Effect of average grain size and sintered relative density on the imaginary part – µ″ of the complex magnetic permeability of (Cu0.12Ni0.23Zn0.65)Fe2O4 system

The influence of the sintered microstructure on the electromagnetic properties of Cu-doped NiZn ferrites were investigated. Two of the main variables of the thermal cycle have been modified: the maximum sintering temperature and the dwell time at that temperature, or sintering time. The evolution of the imaginary part – µ″ of the complex magnetic permeability was studied as a function of relative density, grain size and amplitude of the grain size distribution of the sintered pieces. The results show that µ″ depends on the sintered microstructure and that there is a limiting value of the average grain size (~20–25 µm) from which the electromagnetic properties of these kinds of materials worsened significantly.     

Sintering and characterization of in situ formed porous cordierite ceramics with nano boehmite additions

In this study, we investigated the effect of sintering temperature and nano boehmite additions on the phase composition, densification, and mechanical properties of porous cordierite ceramics. Ceramic samples were sintered at temperatures ranging from 1200 to 1400°C. Carbon powder was used as a pore forming agent to improve the porosity of the ceramic structure. Nano boehmite and carbon additions significantly enhanced ceramic porosity and average pore size in sintered samples. The bulk density and apparent porosity of the sintered samples were found to be 0.96–1.53 g/cm³ and 42.3%–65.6%, respectively. Sintered samples had cold crushing strengths of 1.5–14.3 MPa. The microstructure obtained by scanning electron microscopy was used to measure average pore size in sintered samples and was found to be 41.93 µm for stoichiometric composition (SC), 67.72 µm for SC and nano boehmite, and 102.98 µm for SC, nano boehmite, and carbon. The microstructure of the sintered samples revealed that the crystallinity of the in situ formed phases increased with the increase in nano boehmite additions.     

Additive manufacturing of SiC-Sialon refractory with excellent properties by direct ink writing

Additive manufacturing of SiC-Sialon refractory with complex geometries was achieved using direct ink writing processes, followed by pressureless sintering under nitrogen. The effects of particle size of SiC powders, solid content of slurries and additives on the rheology, thixotropy and viscoelasticity of ceramic slurries were investigated. The optimal slurry with a high solid content was composed of 81 wt% SiC (3.5 µm+0.65 µm), Al₂O₃ and SiO₂ powders, 0.2 wt% dispersant, and 2.8 wt% binder. Furthermore, the accuracy of the structure of specimens was improved via adjustment of the printing parameters, including nozzle size, extrusion pressure, and layer height. The density and flexural strength of the printed SiC-Sialon refractory sintered at 1600 °C were 2.43 g/cm³ and 85 MPa, respectively. In addition, the printed SiC-Sialon crucible demonstrated excellent corrosion resistance to iron slag. Compared to the printed crucible bottom, the crucible side wall was minimally affected by molten slag.     

Preparation of vanadium‐modified phenolic resin/modified zirconia composites and its applied properties in cubic boron nitride (cBN) grinding wheels

In this work, novolac bisphenol‐F‐based vanadium–phenolic resin/modified zirconia (Bis‐VPF/m‐ZrO) composites were obtained successfully. In the preparation process, ammonium vanadate reacted with Bis‐PF resin to form Bis‐VPF resin with the V O chemical bonds. Simultaneously, zirconia (ZrO₂) was modified with N‐(2‐aminoethyl‐3‐aminopropyl)trimethoxysilane (AEAPTMS). Then, this modified zirconia (m‐ZrO) was fully mixed with Bis‐VPF to form Bis‐VPF/m‐ZrO composites. The thermal properties and mechanical strength of Bis‐VPF are higher than those of Bis‐PF. When the m‐ZrO was additionally incorporated into Bis‐VPF, the well‐dispersed and well‐adhered m‐ZrO can further promote all the above‐mentioned properties of the composites. Furthermore, Bis‐VPF/m‐ZrO was compared with Bis‐PF in the performance as a binder for cBN grinding wheels. The results of grinding experiments indicated that Bis‐VPF/m‐ZrO is a better binding resin than Bis‐PF, and so the grinding wheels made from the Bis‐VPF/m‐ZrO composites have better grinding effect and quality. POLYM. COMPOS., 37:3354–3364, 2016. © 2015 Society of Plastics Engineers     

Studies on RDX Particle Size in LOVA Gun Propellant Formulations

This paper presents the results of systematic studies carried out on the role of fine RDX in determining the burning rate and ballistics of LOVA gun propellants. Propellant formulations containing fine RDX particles with a size of 4.5, 6, 13 and 32 µm as energetic ingredient, cellulose acetate as inert binder, triacetin as inert plasticizer, nitrocellulose of lower percentage nitrogen content as energetic binder and carbamite as stabilizer were made. The evaluation of the propellant batches has been carried out by static firing using closed vessel technique. It indicates the linear relation between the burning rate of the propellant and the fine RDX particle size used in this formulation. The results of the present studies revealed that fine RDX of 4.5 to 6 µm size may be the most suitable for LOVA gun propellant to meet the desired burning rate for satisfactory ballistics.