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Some physical and technological features of the electroconsolidation process were considered to determine its place among numerous electrodischarge sintering methods. Principal advantages over the other nanopowder compaction methods were noted. The effect of sintering regimes on the formation of a microstructure, the specific features of inhibition under heating in the growth of grains, and the temperature of the graphite press mold and the rate of its heating on the physicomechanical properties of ceramic composites was studied. Some original data on the electroconsolidation process were reposted alongside with the physicochemical properties of nanocomposites synthesized by this method. The probable scheme of electrodischarge processes under high-ampere currents through the graphite press mold is presented. [ABSTRACT FROM AUTHOR]

Peculiarities of sintering of foamy ceramic filters based on submicron aluminum oxide powders with additions of titanium oxide and manganese dioxide nanopowders are considered. The processes of removal of polymeric and binder paraffin material during sintering have been studied. The physical and mechanical properties of the obtained porous permeable filters with a foamy structure were analyzed in details. At a sintering temperature in an air atmosphere of 1350 °C, sufficiently high physical and mechanical properties were obtained, which made it possible to use the developed filters as catalyst carriers for vehicle exhaust gases. Bench comparative tests have shown that ceramic filters with a foamed structure are promising catalysts for afterburning car exhaust gases instead of ceramic honeycomb blocks of catalyst carriers. The developed technology allows reducing the sintering temperature of porous foam ceramic filters to 1350 °C and replacing expensive high-temperature ceramic heaters with cheaper nickel-chromium ones. [ABSTRACT FROM AUTHOR]

High sintered density is desired for heavy-duty applications and there are different ways through which the sintered density can be improved. In the current study, nanopowder is blended to the conventionally used micrometre-sized water-atomised steel powder to evaluate its impact on sintering. Both the powder variants, without and with nanopowder, were subjected to thermogravimetry analysis, and uniaxially compacted to the same green density of 7.15 g/cc or 90% relative density and sintered at 1250°C in pure hydrogen. A comparative analysis was performed with respect to the microstructural evolution between the micro and micro/nano bimodal powder compacts. JMatPro and electron backscattered diffraction was used to understand the microstructural evolution. An attempt was made to understand the improved linear shrinkage in the micro/nano bimodal powder compact using a combination of microstructure analysis and chemical analysis. [ABSTRACT FROM AUTHOR]

Nanoimprint lithography is a highly productive process and has an advantage in its resolution of printed patterns. In this paper, inorganic materials are imprinted using mixtures of nanopowders and polymer binder as starting materials. In our previous work, line-and-space patterns with the smallest pitch of about 8 μ m were shown on sintered ceramic sheets using ceramic powders with the smallest particle size of about 100 nm. In this study, we prepare alumina powders with an average particle size of about 100 nm and five kinds of molds with line-and-space patterns with line widths from 10 μ m to 250 nm. The line-and-space patterns were observed on all sintered samples. Although the patterns were not clear on the finer patterns, this result is remarkable. Also, we discuss how the pattern was affected by mold size and particle size. [ABSTRACT FROM AUTHOR]

Zirconium diboride ceramics with and without carbon and boron carbide nanopowder additives were prepared by ball milling with ZrB 2 grinding media and pressureless sintering. Additions of up to 1 wt% nano-B 4 C and 0.5 wt% C were made to the ZrB 2 powder. The materials were then sintered between 1800 and 2300 °C for between 90 and 360 min in an Ar/10H 2 atmosphere. After sintering at 2200 °C for 90 min, densities ranged from 88.3 to 90.7% for the ZrB 2 with 0–1.0% nano-B 4 C addition. Carbon additions of 0.5 wt% and nano-B 4 C additions from 0 to 1.0 wt% resulted in densities ranging from 90.9 to 91.9% after sintering at 2100 °C for 90 min. Grain size ranged from 16.6 to 21.7 μm for ZrB 2 with nano-B 4 C content increasing from 0 to 1.0 wt%, sintered at 2200 °C. For the ZrB 2 with 0.5 wt% C, increasing the nano-B 4 C content from 0 to 1.0 wt% resulted in a decrease in grain size from 25.4 to 18.5 μm. The densities achieved in this study were lower than previous pressureless sintering studies of ZrB 2 that used WC-6Co grinding media, presumably due to the absence of WC and Co that can also act as sintering aids. [ABSTRACT FROM AUTHOR]

• Grains rearrangement and coalescence of Lu 2 O 3 nanoparticles are observed during early stage of densification during SPS. • Intermediate stage of densification during SPS of Lu 2 O 3 nanoparticles is related to Rachinger sliding (n=2) then Lifshitz sliding (n=1). • For intermediate stage of densification with n=1, an average activation energy of 565 kJ.mol-1 was obtained. • SPS thermomechanical cycle can be well adapted to manufacture highly transparent polycristalline ceramics of Ho:Lu 2 O 3. This work was focused on the determination of densification mechanisms during Spark Plasma Sintering (SPS) of Ho:Lu 2 O 3 nanopowders. Strong variation of the stress exponent n was evidenced during the sintering process. At low relative density (i.e. ρ < 66 %), n = 3 and powder particles rearrangement and coalescence take place because of high value of effective stress and low size of primary nanoparticles. Then, for ρ between 66 % and 85 %, the stress exponent decreases to n = 2 then n = 1. Such values were related to Rachinger then Lifshitz sliding mechanisms, the last one was associated with an average activation energy of 565 kJ.mol−1. At the final densification stage (ρ > 85 %), the stress exponent suddenly increases to 4 in accordance with a power-law creep. From these investigations, an optimized thermomechanical cycle was proposed to obtain highly transparent Ho:Lu 2 O 3 ceramics suitable for laser applications. [ABSTRACT FROM AUTHOR]

Though press and sinter powder metallurgy (PM) steel offers cost-effective solutions for structural applications, there is a constant drive for improvement in their density. Addition of nanopowder to the conventional micrometre-sized metal powder is explored to improve the sinter density. In this study, the effect of nanopowder addition in varying amounts has been studied. Carbonyl iron powder (<5 μm) and water atomized iron powder (<45 μm) were used as the base powder to which varying amounts of iron nanopowder (<100 nm) was added. Dilatometric sintering studies under pure hydrogen atmosphere were carried out to analyze the densification behavior. The results revealed that the bimodal powder mixture containing 25% nanopowder exhibited the highest green density for both carbonyl and ASC 300 compacts. Master sinter curve for compacts was developed based on the dilatometer data. The apparent activation energy for sintering decreased with an increase in nanopowder content. This is reflected in the values of work of sintering. [Display omitted] • Nanopowder/micropowder bimodal compacts were made using conventional press and sinter method. • 25 wt% nanopowder containing compact had the highest green density for both micropowder variants. • Degree of sintering increased with increasing nanopowder content. • Two-peak sintering behavior of bimodal powder was attributed to the nanopowder. • Master sintering curves were developed for bimodal powder compacts. [ABSTRACT FROM AUTHOR]

Demand for high‐density press and sinter components is increasing day by day. Of the different ways to improve the sinter density, the addition of nanopowder to the conventional micrometer‐sized metal powder is an effective solution. The present investigation is aimed at studying the surface chemistry of iron nanopowder coated with graphitic carbon, which is intended to be mixed with the conventional iron powder. For this purpose, iron nanopowder in the size range of 30 nm to submicron (less than 1 micron) was investigated using thermogravimetry at different temperatures: 400°C, 600°C, 800°C, 1000°C, and 1350°C. The X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and high‐resolution scanning electron microscopy (HR‐SEM) were used for characterizing the powder as well as samples sintered at different temperatures. The presence of iron, oxygen, carbon, chromium, and zinc were observed on the surface of the nanopowder. Iron was present in oxide state, although a small metallic iron peak at 707 eV was also observed in the XPS spectra obtained from the surface indicating the oxide scale to be maximum of about 5 nm in thickness. For the sample treated at 600°C, presence of manganese was observed on the surface. Thermogravimetry results showed a two‐step mass loss with a total mass loss of 4 wt.% when heated to 1350°C where the first step corresponds to the surface oxide reduction. [ABSTRACT FROM AUTHOR]

In the present research, a novel low-temperature sol-gel process was developed for the synthesis of the aluminum oxynitride (AlON) phase using aluminum tri-sec-butoxide, acetonitrile, chloroform, and hydrazinium hydroxide. This straightforward process involves the nitridation of the as-synthesized sols under ultra-high purity nitrogen to form the AlON nano-powders. The effect of various parameters such as pH in the range of 8–11, the solvent to alkoxide molar ratio (30–100), and acetonitrile to chloroform molar ratio (20–100%), and heat treatment temperature (900–1500 °C) and time (4–12 h) on the composition of the prepared powders were studied. The characterization of the powders by X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM) demonstrated that the pure phase of AlON (nano powder) was obtained in the sample having the pH value of 10, the molar ratio of solvent to alkoxide of 100, the molar ratio of acetonitrile to chloroform of 80%, which annealed at 1500 °C for 8 h at nitrogen atmosphere with the heating rate of 3 °C/min. Finally, transparent AlON ceramic was fabricated by the spark plasma sintering of as-synthesized AlON powder at 1600 °C for 30 min with a density of 3.64 gr/cm3 and about 54% IR in-line transmission. [ABSTRACT FROM AUTHOR]

The densification behavior of nanostructured MgF2 ceramics in the spark plasma sintering process is studied. Nitrate synthesis is employed to produce fine magnesium fluoride powder. The high-purity and fine MgF2 powder has 300–500 nm grains and shows high density (~99.8%) and transparency (~ 90%) in the infrared range for samples 2.5 mm thick. [ABSTRACT FROM AUTHOR]

Abstract The sintering temperature decreases theoretically with the grain size of the ceramic powders, but it is not always right for fine grain sized nanopowders due to the inevitable agglomerations, and thus pores are hard to eliminate thoroughly during sintering. To overcome this difficulty, a new approach is designed to sintering ceramics at low temperature from nanoparticles. In this scheme, excessive dopants, such as ZnO, are synthesized into the nanoparticles, and they would be liberated again on the surfaces of the grains at high temperature as sintering aids homogenously to promote densification. Here, we compared the ceramic sintering of ZnO-doped barium zirconate titanate (BaZr x Ti1-x O3, BZT) nanoparticles with BZT nanoparticles using ZnO as additive at 1150 °C. Both kinds of nanoparticles were directly synthesized by the same process at room temperature and yielded the same initial grain size of ~10 nm. The dense BZT ceramic with relative density of 99% was fabricated from the 2 mol% ZnO-doped nanoparticles. On the other hand, the porous BZT ceramic with density of 78% was obtained from nanoparticles with 2 mol% ZnO as additive. Therefore, our strategy to ceramic sintering at low temperature from nanoparticles was confirmed.

High sinter density is desired in powder metallurgy components as the requirement for performance is increasing day‐by‐day. One of the promising ways to achieve improved densification during sintering is through the addition of nanopowder to the conventional micrometer sized metal powder. It is well known that the surface chemistry of the powder has a decisive effect on sintering and consequently the properties of the components produced. Extensive research has hence been conducted to elucidate the surface chemistry and its influence on sintering for powder used in conventional powder metallurgy. Nanopowder, owing to high surface to volume ratio, can contribute to the activation of sintering at lower temperatures and enhance the sinter density. In this context, the surface chemistry of the nanopowder is also expected to exhibit substantial influence on sintering. The present investigation is aimed at establishing a methodology to study the surface chemistry and oxide thickness of nanopowder. For this purpose, iron nanopowder of 3 different size fractions: 35 to 45, 40 to 60, and 60 to 80 nm with core‐shell structure were studied. Different approaches were adopted to evaluate the shell thickness of the iron nanoparticles. The methodology was developed and tried on low alloy steel nanopowder to measure oxide thickness. X‐ray photoelectron spectroscopy, thermogravimetry, and high‐resolution scanning electron microscopy techniques were used to study the nanopowder. Results from different core‐shell models for iron nanopowder were found to be consistent except in the case where depth profiling was taken into account. The results were in agreement with the values obtained from thermogavimetry‐surface area correlation. [ABSTRACT FROM AUTHOR]

Relevance of the research is caused by the necessity of profound processing of raw mineral and perfection of technology of obtaining alumoxide ceramic. The main aim of the research is to develop the activation methods of ceramic sintering based on corundum Al2O3 by mechanic treatment of powders in a planetary mill, additions of Al, Al2O3 nanopowder and TiO2 submicrom powder in a mixture, application of spark plasma sintering method. The methods: sieve analysis of a large-scale powder dispersion using the analyzer A20, x-ray phase analysis of the studied samples, hydrostatic weighting for determining a conditional density of the sintered samples, measuring microhardness of the sintered samples using microhardness tester PMT-3, measuring HRA hardness by the Rockwell hardness tester. The results. Addition of Al2O3 nanopowder in GK-5 corundum contributed to increase of sintering ceramic density and microhardness. Such activation effect is explained by the increase of interparticle contact area, which is related to Al2O3 nanopowder addition. Sintering activation is caused by high structural activity and surface energy of Al2O3 nanopowder, which are determined by crystal structure deficiency and particle small size. The most significant rise in density was observed for ceramic, containing 5…20 wt. % of Al2O3 nanowpoder. Additional activation of Al2O3 nanopowder sintering when adding aluminum nanopowder: its porosity decreased, was proved by the experiment. Sintering activation by adding Al nonopowder is explained by aluminum oxidation and phase transformation (Hedvall effect). TiO2 nanopowder additive in Al2O3 powder had the maximum activation effect: the density of sintering ceramic, containing 1,5 wt. % TiO2, achieved 3,48 g/cm3.

After evaluating three alternative possibilities, the present study shows that seemingly minor amounts (at least as low as 0.06 wt%) of chlorine impurities are responsible for the poor sintering behavior observed in chloride-derived 3 mol% yttria stabilized zirconia (3Y-TZP) nanopowders. Models and quantitative estimates are used to explain the role of evolved HCl and ZrCl4 gases in such anomalous behaviors as reduced sintered densities for higher green densities, de-densification, improved sintering in nitrogen over oxygen, and formation of a dense shell microstructure. Two solutions to problematic residual chlorides are compared: 1) a thermal treatment composed of an extended hold at 1000°C to allow HCl gas removal before the onset of closed porosity, and 2) a chemical treatment performed by washing bisque-fired samples at room temperature using a concentrated ammonium hydroxide solution to remove chlorides. The thermal treatment was found to be superior.

The influence of air and nitrogen atmosphere during heating on TiO2 nano and micro sized powders as well as sintered polycrystalline specimens was analyzed. Sintering of TiO2 nano and micro powders in air atmosphere was monitored in a dilatometer. Non compacted nano and micro powders were analyzed separately in air and nitrogen atmospheres during heating using thermo gravimetric (TG) and differential thermal analysis (DTA). The anatase to rutile phase transition temperature interval is influenced by the powder particle size and atmosphere change. At lower temperatures for nano TiO2 powder a second order phase transition was detected by both thermal techniques. Polycrystalline specimens obtained by sintering from nano powders were reheated in the dilatometer in nitrogen and air atmosphere, and their shrinkage is found to be different. Powder particle size influence, as well as the air and nitrogen atmosphere influence was discussed. [Projekat Ministarstva nauke Republike Srbije, br. OI172057 i br. III45014]

(Ni,Co,Mn)O 4 (NMC) oxides were prepared by conventional sintering (CS) and spark plasma sintering (SPS) using micro and nanopowders. Small hoping polaron theory was used in order to investigate effect of processing routes on electrical properties of NMC oxides as negative temperature coefficient (NTC) thermistors. Also, X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques were utilized to analyze compositional and structural effects on the electrical properties of NMC compounds. Hopping conduction in NMC prepared by SPS and CS using nanopowder occurs via variable range hopping (VRH) mechanism, however conduction in NMC prepared by CS using micropowder follows nearest neighboring hopping (NNH) mode. Hopping distance and activation energy for the VRH mode were calculated using corresponding physical model. [ABSTRACT FROM AUTHOR]

Highly transparent YAG:Ce ceramics (transmission of 72–82% for 2-mm-thick samples in 550–900 nm wavelength range) were fabricated by solid-state reactive sintering using a mixture of Ce 2x Y 2-2x O 3 (x = 0.001, 0.01, 0.03, and 0.05) and Al 2 O 3 nanopowders synthesized by laser ablation with an additional round of pre-calcining before compaction. The synthesized YAG:Ce ceramic materials showed intense luminescence with a maximum at 525–545 nm. The measured absolute light yields of the synthesized YAG:Ce ceramics were 18–21 photon/MeV for 1–5 at.% Ce and 5 photon/MeV for 0.1 at.% Ce. The energy resolutions of the fabricated thin ceramic samples (2 mm) under 662 keV gamma ray were measured to be 10–15%. The decay curves of scintillations consisted of two components with the decay times depending on the Ce 3+ concentration. The sample doped with 5 at.% of Ce exhibited the main fast component with 26 ns decay time. The measured data was compared to that of YAG:Ce and well-known CsI:Tl single crystal scintillators. The influence of dopant concentration on the optical, luminescence and scintillation properties was discussed. [ABSTRACT FROM AUTHOR]

The started nanopowder is an α-alumina (α-AlO) marketed by Baikowski (Baikalox-BMA15, France), with 99.99% of purity and an average particle size of 150 nm. Samples were shaped by slip casting. Natural sintering was performed at different temperatures (1200, 1300, 1400, and 1500 °C) for 1 and 3 h. Furthermore, samples were sintered by 'Spark Plasma Sintering (SPS)' using the dry method. The sintering temperature was between 1150 and 1350 °C with 50 °C step, with 100 °C/min as heating rate and for 3 and 10 min. We have used two pressures (25 to 50 MPa). The bulk density of the sintered samples was determined. Young's modulus was measured by the dynamic method. The microstructure of natural sintered specimens and SPS result were observed by scanning electron microscopy. Depending on the conditions of development, different microstructures (fine and coarse) were obtained. [ABSTRACT FROM AUTHOR]

This study aims to develop an eco-friendly fabrication method for micro-structured parts with high aspect ratio. To achieve this purpose, nanopowder printing (nPP) process was adopted to the plastic mold with microstructures produced by electrospinning nanofiber imprinting (ES-NFI) method. A novel method named as ES-NFI sacrificial plastic mold nanopowder printing (ES-NFI/nPP) was proposed and demonstrated in this study. Micro plastic molds were prepared by ES-NFI method using Si forms that have various micro-structures including line and space (L/S) pattern, multi-pillars and holes. The effects of aspect ratio in microstructure on the shape transcription were investigated by changing Si forms from 1µm to 50µm wide for 10µm high. Also the composition of paste materials made from TiO2 nano-sized powder and PEG water-soluble binder was varied for the optimization. It was shown from the experimental results that the sintered part with microstructures of 50µm wide for 10µm high could be formed soundly, and it was also desirable to use the paste materials with lower content of binder polymer in keeping adequate viscosity. It was confirmed that ES-NFI/nPP method was a useful method for fabricating the micro-structured parts in the mass production.

The sintering temperature decreases theoretically with the grain size of the ceramic powders, but it is not always right for fine grain sized nanopowders due to the inevitable agglomerations, and thus pores are hard to eliminate thoroughly during sintering. To overcome this difficulty, a new approach is designed to sintering ceramics at low temperature from nanoparticles. In this scheme, excessive dopants, such as ZnO, are synthesized into the nanoparticles, and they would be liberated again on the surfaces of the grains at high temperature as sintering aids homogenously to promote densification. Here, we compared the ceramic sintering of ZnO-doped barium zirconate titanate (BaZrTiO, BZT) nanoparticles with BZT nanoparticles using ZnO as additive at 1150 °C. Both kinds of nanoparticles were directly synthesized by the same process at room temperature and yielded the same initial grain size of ~10 nm. The dense BZT ceramic with relative density of 99% was fabricated from the 2 mol% ZnO-doped nanoparticles. On the other hand, the porous BZT ceramic with density of 78% was obtained from nanoparticles with 2 mol% ZnO as additive. Therefore, our strategy to ceramic sintering at low temperature from nanoparticles was confirmed. [ABSTRACT FROM AUTHOR]

One of the significant advantages of nanopowder is activated sintering and better surface finish of the final components. However, because of its drawbacks like higher cost and low formability, the mixture of nano and micro powder emerged as an effective solution. In this research, effects of nanopowder in nano/micro bimodal feedstock were studied. Bimodal powder in feedstock was prepared with nano and micro sized powders. These powders were mixed with different nanopowder volume ratio from 0 to 50%. The effects of nanopowder vol.% on the critical solids loading was investigated with rheometer experiments. From debinding behavior, apparent debinding activation energy for each feedstock was determined. Sintering behavior of micro and bimodal feedstocks were analyzed by dilatometer and compared with die compacted specimen. Nanopowder effect on sintered density and hardness of the samples were verified as well. [ABSTRACT FROM AUTHOR]

The present investigation studied the recycling of zinc from brass ash which is a secondary product produced during the brass smelting process. A retiring cycle was devised to produce high-purity ZnO nanopowders. Recovery of > 90 wt% of the total zinc available was achieved after the calcination of brass ash at 700 °C and a multistage hydrometallurgical treatment at room temperature. ZnO powder produced by the developed method was analyzed by X-ray diffraction, transmission electron scanning microscopy, ICP-AES and BET analysis. The ZnO nanopowder obtained from the brass ash was well dispersed and the size of the individual particles was in the range of 30–50 nm. The purity of the powder was 99.83 wt%, and the surface area was about 30.5 m 2 /g. A relative density level of about 98.1% was reached with ZnO pellets sintered at 1300 °C. [ABSTRACT FROM AUTHOR]

The problem of physical and mathematical prediction of rational pressure during sparkplasma sintering of zirconia nanopowder is being considered. The physical aspects of this problem are defined, and it is presented an approach to the calculation of the pressure in the compression cycle at the stage of pre-production and experimental development. The calculation is based on the use of the Paschen law in relation to the considered model of spark plasma consolidate of nanopowders under pressure. The calculation result is compared with the practical experience of energy-saving high-speed spark-plasma sintering of the fine high-density ceramics from (Zr0.94Y0.06)O1.88 nanopowder. [ABSTRACT FROM AUTHOR]

In this work, transparent sub-mircon Gd 2 Zr 2 O 7 (GZO) ceramic was successfully sintered for the first time by spark plasma sintering (SPS) using nanocrystalline powders synthesized via a solvothermal assisted co-precipitation route. With the aids of fast heating and cooling rate and high pressure, the GZO transparent sample with an average grain size of about 205 nm was obtained at 1400 °C for 5 min. The maximum transmittance of about 70% was achieved at a wavelength of 2000 nm. [ABSTRACT FROM AUTHOR]

Thorium dioxide is a refractory ceramic material and is difficult to sinter to high density. Commercial powder starts to sinter in SPS under 70 MPa above 1000 °C and compaction is not finished at 1600 °C. In contrast, a 13 nm nanopowder synthesised via low temperature decomposition of thorium oxalate starts to sinter at ∼500 °C; the onset of sintering shifts to higher temperatures for powders with larger crystallites. The initial crystallite size solely affects the onset of sintering, whereas the final stage of sintering is independent of the initial crystallite size for the powders used in this study. Pellets with density well above 95% of the theoretical density were prepared using SPS at sintering temperature of 1600 °C, 70 MPa pressure and 10 min dwell time. [ABSTRACT FROM AUTHOR]

Neodymium or ytterbium-doped transparent yttrium oxide ceramics with different tetravalent sintering additives (ZrO 2 , HfO 2 , or CeO 2 ) were fabricated from nanopowders produced by laser ablation method. Phase composition and distribution of dopants in the synthesized nanopowders and ceramics were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) spectroscopy. The tetravalent additives led to a decrease in grain size and an improvement in transmittance at the lasing wavelengths. However, an excess of tetravalent ions led to the formation of dispersed scattering volumes. We observed particles with modulated composition for nanopowder of Nd:Y 2 O 3 doped by 10 mol% HfO 2 . The estimations based on Rayleigh light scattering showed that the maximum size of the dispersed scattering volume is below 20 nm. [ABSTRACT FROM AUTHOR]

Doped ZnO nanopowders (<25 nm) with production rate of 2–3 kg h −1 was synthesized by a single step solution feeding flame spray pyrolysis and were characterized by XRD, TEM, SAED, ICP-OES and BET surface area measurements. The powders were consolidated into greater than 98% dense pellets by two step conventional sintering. The sintered samples showed the formation of spinel, δ-Bi 2 O 3 , γ-Bi 2 O 3 and pyrochlore phases along with the matrix ZnO. The grain size and density of the pellets were varied by changing the sintering temperatures. The grain growth exponent “ n ” was found to be in the range 3.5–4.0 and the activation energy for grain growth was found to be 304 ± 10 kJ mol −1 indicating that the grain growth to be dominated by volume and surface diffusion mechanisms. Electrical properties of samples prepared at different sintering conditions were studied using two different techniques. Breakdown voltage of 14.38 kV cm −1 , coefficient of non-linearity of 171.69 and leakage current density of 1.10 μA cm −2 were obtained for pellets made under different sintering conditions. It was observed that pellets sintered at higher temperatures yielded lower impedance values. The high temperature (>175 °C) impedance data was fitted into two parallel RC circuits to calculate the electrical properties of the varistors. [ABSTRACT FROM AUTHOR]

Transparent Yb-doped Lu 2 O 3 ceramic samples were fabricated via conventional vacuum and spark plasma sintering. Nanoparticles synthesized by laser ablation method were used as starting material. The morphology and phase evolution of the nanopowder were studied by transmission electron microscopy, simultaneous thermal analysis and X-ray diffraction. The obtained nanoparticles exhibited the monoclinic phase and were fully converted into the main cubic phase after calcination at 1100 °C for 1 h. Conventional vacuum sintering of Yb:Lu 2 O 3 powder compact at 1780 °C for 20 h resulted in a fully-dense ceramics with an average grain size of 1.6 μm and optical transmittance of 79.3% at 1080 nm. Spark plasma sintering of the calcined Yb:Lu 2 O 3 nanoparticles at 1450 °C and 15 kN for 40 min led to a 0.2 μm-grained ceramics exhibiting an optical transmittance of 75.6% at 1080 nm. [ABSTRACT FROM AUTHOR]

One of the promising low cost and non-vacuum approaches for the fabrication of semiconductor CuInSe 2 and Cu(In,Ga)(S,Se) 2 thin film absorbers is the printing of precursor materials followed by a sintering/selenization process. The selenization process parameters such as temperature, duration, and selenium vapor pressure strongly influence the morphology and electronic properties of the absorber film. In this study, the effect of pre-annealing in an inert atmosphere and selenization on printed mechanically synthesized CuInSe 0.5 alloy nanopowder precursor films was investigated. 1–2 μm thick CuInSe 0.5 alloy nanopowder layers were deposited on a Mo-sputtered glass substrate by means of doctor blade coating of a nanopowder based precursor suspension. Pre-annealing was performed on a hot plate inside a nitrogen gas filled glove box. Selenization was performed in a home-made rapid thermal processing (RTP) furnace with two RTP heating zones for independent temperature control of the selenium source and the coated substrate. The temperature of the selenium source was fixed at 390–410 °C during the selenization to provide a constant supply of selenium vapor. A two-step process, i.e., a pre-annealing in nitrogen atmosphere at 400 °C for 30 min followed by selenization at 530 °C for 15 min was found to result in better densification and grain growth of the CuInSe 2 phase, compared to a single step selenization at 530 °C for 15 min. The solar cell fabricated by the two-step process had an efficiency of 5.4% and a fill factor of 52%, while the device fabricated by the single step selenization had an efficiency of 1.1% and a fill factor of 31%. [ABSTRACT FROM AUTHOR]

Production processes for fine powders of tungsten, tungsten carbide, and WC-Co and sintering methods for nanosized WC-Co hard metals are reviewed. The properties, structure, and applications of nanosized WC-Co hard metals described in the literature are analyzed. It is established that, regardless of the process, the mandatory requirements for the production of fine hard metals are: (i) purity of starting materials, (ii) precise compliance with the process procedure, and (iii) careful control at all production stages, which exclude unwanted phases and defects in the structure. [ABSTRACT FROM AUTHOR]

The processing, microstructure, and material properties of monolithic Si3N4 were investigated by using two amorphous Si3N4 nanopowders doped with (1) 6 wt% Y2O3 and (2) 6 wt% Y2O3 + 8 wt% Al2O3. The orthorhombic Si2N2O-based phase was found in the two as-sintered bulks. Carbothermal reduction treatment (CRT) was thus applied at 1400 °C for 10 h with 3 wt% and 6 wt% carbon black added to the precursor powders of the Si-Y-O-N and Si-Y-Al-O-N systems, respectively, resulting in an increased nitrogen-to-oxygen (N:O) ratio and elimination of Si2N2O within the sintered bulks. The possible mechanisms of nucleation and grain growth of Si3N4 are discussed during CRT and the sintering process. The best wear resistance was achieved in ultrafine Si3N4 doped with Y2O3, which has good hardness, indentation toughness and a protective tribo-film. [ABSTRACT FROM AUTHOR]

Nanosized ZnNb2O6 powders obtained by high energy ball milling (HEBM) and subsequent heat treatment were compacted and sintered into near full density ceramics using pressureless sintering. The prepared ceramic samples were characterized by field emission scanning electron microscopy, X-ray diffraction, and microwave dielectrical property measurements. All samples prepared at sintering temperatures ranging from 975 to 1100°C, exhibit a single columbite phase and their relative densities range from ~87% to ~99%. The variation trend of permittivity and Q×f value was in accordance with variation trend of relative density. Pure columbite ZnNb2O6 ceramic sintered at 1050°C for 5h exhibited good microwave dielectric properties with a permittivity about 23.6, Q×f value about 72,357GHz, and temperature coefficient of resonant frequency about -67.72ppm/°C. [ABSTRACT FROM AUTHOR]

The influence of air and nitrogen atmosphere during heating on TiO2 nano and micro sized powders as well as sintered polycrystalline specimens was analyzed. Sintering of TiO2 nano and micro powders in air atmosphere was monitored in a dilatometer. Non compacted nano and micro powders were analyzed separately in air and nitrogen atmospheres during heating using thermo gravimetric (TG) and differential thermal analysis (DTA). The anatase to rutile phase transition temperature interval is influenced by the powder particle size and atmosphere change. At lower temperatures for nano TiO2 powder a second order phase transition was detected by both thermal techniques. Polycrystalline specimens obtained by sintering from nano powders were reheated in the dilatometer in nitrogen and air atmosphere, and their shrinkage is found to be different. Powder particle size influence, as well as the air and nitrogen atmosphere influence was discussed. [ABSTRACT FROM AUTHOR]

This paper presents the results of investigations on the consolidation of nanometric magnesium–aluminum spinel powders through pressure filtration of their aqueous suspensions. A portion of the pressure-filtrated samples was subjected to cold isostatic pressing. To assess the effectiveness of the pressure filtration method, dry powders were uniaxially or isostically pressed under various pressures and the pore size distributions of all samples were compared. Samples were sintered in a dilatometer at temperatures up to 1550°C and isothermally sintered in air at 1600°C for 3h. The agglomeration state of the powders was investigated using methods such as XRD, TEM, BET and laser diffraction, and the resulting characteristics were used to explain differences in the consolidation and sintering behavior of the powders. It was shown that the pressure filtration method was capable of consolidating nanometric spinel powders suspensions, leading to green samples with a narrow pore size distribution whose density exceeds 99% when sintered at 1600°C. [ABSTRACT FROM AUTHOR]

Using tetrabutyl titanate, zirconium nitrate and barium octahydrate as the raw materials, BZT nanoparticles with a grain size of ~10nm were directly synthesized at room temperature. With low energy consumption and without any contamination produce, the synthesis process is green, environmental-friendly, convenient and efficient. The graingrowth of the as-prepared nanoparticles annealed at different temperatures was checked, and a rapid graingrowth starting at 600°C was observed. The sintering characteristics were also studied and it was found that an adapted sintering aid was very important for the sintering of the BZT nanoparticles at low temperature. Here, adding the useful active liquid of Bi2O3–Li2O as the sintering aid results in obtaining the dense BZT ceramics with the relative density of 96% even sintering at the temperature as low as 900°C for 2h. [ABSTRACT FROM AUTHOR]

Commercial TiN and AlN powders were high-energy ball milled for various durations and consolidated without a binder using the pulsed current activated sintering method (PCAS). The effects of milling on the sintering behavior, crystallite size and mechanical properties of the TiN–AlN composites were evaluated. A dense nanostructured TiN–AlN composite with a relative density of up to 99% could be readily obtained within 3min. The ball milling effectively refined the crystallite structure of the TiN and AlN powders and facilitated subsequent densification. The sintering-onset temperature was appreciably reduced by milling for 40h from 1200°C to 1000 °C. Accordingly, the relative density of the TiN–AlN composite increased as the milling time was increased. This clearly demonstrates that the quick densification of nanostructured TiN–AlN bulk materials to near the theoretical density could be obtained by the combination of PCAS and the preparatory high-energy ball milling process. [ABSTRACT FROM AUTHOR]

Abstract: Commercial TiN powders were high-energy ball milled for various durations and consolidated without a binder using the pulsed current activated sintering method (PCAS). The effect of milling on the sintering behavior, crystallite size and mechanical properties of TiN compacts were evaluated. A dense TiN compact with a relative density of up to 99% could be readily obtained within 4min. The ball milling effectively refined the crystallite structure of TiN powders and facilitated the subsequent densification. The sinter-onset temperature was reduced appreciably by the prior milling for 40h from 1200°C to 800°C. Accordingly, the relative density of TiN compact increased as the milling time increases. The microhardness of sintered TiN was linearly proportional to the density. It is clearly demonstrated that a quick densification of TiN bulk materials to near the theoretical density could be obtained by the combination of PCAS and the preparatory high-energy ball milling process. [Copyright &y& Elsevier]

To lower the calcining and sintering temperatures of 16 at% Y-doped BaZrO (BYZ), Gd-doped BaCeO (BGC) and Smdoped BaCeO (BSC), nanopowders of BaCO and either (i) yttria stabilized zirconia, (ii) GdO and CeO or (iii) SmO and CeO, were used as starting materials, respectively. BYZ powders were prepared by two mixing methods (i.e. ball milling and magnetic stirring), followed by calcination at 1050-1250 °C, while BSC and BGC powders were prepared by ball milling and calcined at 1050 °C. The results reveal that the ball milling and magnetic stirring methods yield similar results for BYZ powder preparation. By adding 1 wt% ZnO nanopowder, the average relative densities of BYZ pellets were increased from ∼70% to ∼96% at the sintering temperatures of 1300 °C. Thus, with the utilization of nanopowders and ZnO as a sintering aid, the calcining and sintering temperatures were lowered to 1050 °C and 1300 °C, respectively, while still attaining the relative bulk densities of both BYZ and BGC higher than 95.7%. However, since the relative bulk density of BSC reached only 93% even sintered at 1400 °C, ZnO was not an effective sintering aid for the BSC fabrication. [ABSTRACT FROM AUTHOR]

Abstract: YAG:Eu nanopowder was synthesized through a sol–gel method. A master sintering curve was used as a practical approach to analyze the sintering behavior of the synthesized powder. The effect of MgO doping on sintering of the synthesized nanopowders was evaluated. An amorphous nanopowder was synthesized and crystallized to YAG after heat-treatment via a solid-state reaction. MgO improved the sintering rate of the YAG nanopowders and suppressed grain boundary mobility. The activation energy for sintering decreased from 917 to 837kJ/mol by adding MgO to the nanopowders. The results of this study can be used to predict the densification of YAG:Eu nanopowder. [Copyright &y& Elsevier]

Abstract: A methodology is proposed to investigate in detail shrinkage kinetics under isothermal spark plasma sintering (SPS) conditions applied to ceramic nano powders such as Y2O3 stabilized ZrO2. To do so, mild SPS conditions were used (low temperatures and pressure, long dwell times). The extracted experimental activation energy has the value of 246±37kJmol−1 and the slope of the curves on the intense densification stage is around 0.33. Results are in agreement with densification by a grain-boundary diffusion mechanism as for conventional sintering and the contribution from the specific pressure-assisted mechanisms as for hot pressing is insignificant. This result suggests that exploration of mild SPS might prove rewarding in separation and control of the sintering mechanisms leading to production of specific ceramic with new or improved functionality. [Copyright &y& Elsevier]

Abstract: The fabrication possibility of a highly transparent ceramics with various approaches was investigated. A difference of these approaches consists in transformations of Nd:Y2O3 and Al2O3 nanopowders into Nd:YAG: at a vacuum sintering (1), in a powder compact at annealing in air before vacuum sintering (2) and at calcination of nanopowders in air before them compaction (3). It is shown that the best characteristics realized in Nd:YAG ceramics prepared according to the third approach. Thus in ceramics there are no secondary phases, concentration of pores was 62.8ppm and transmittance at the wavelength of λ =1.06μm−83.28%. On such sample of ceramics lasing with the slope efficiency of 19.1% and full optical efficiency of 13.5% was received. Besides, with the third approach the highly transparent samples of Nd:YAG ceramics with 46mm in diameter and 3mm in thickness with a transmittance of 80.1% were successfully fabricated. [Copyright &y& Elsevier]

When 25-nm α-AlO powder is injected into an aluminum nitrate solution of ≥0.5 wt %, the kinetics of formation of the stable α phase is significantly accelerated upon subsequent heating of the precursor. The total transformation into α-AlO occurs at temperatures varying from 800 to 930°C in accordance with the amount and the method of seed injection. The resulting powder consists of crystallites 50-60 nm in size. They form porous agglomerates 10-20 μm in size, and their size does not depend on the amount of injected seed. Milling under soft conditions breaks the agglomerates and makes it possible to obtain a nanopowder which sinters into a material of 95-99% density in the range of 1300-1400°C. [ABSTRACT FROM AUTHOR]