Min Sintering Time Research Articles

Thermoluminescent composites of sintered synthetic-topaz/in situ corundum for dosimetry by a novel reversible process

Topaz (Al2F1·44(OH)0·56SiO4)/corundum (Al2O3) composites were prepared by a facile and novel reversible process from the sintering of synthetic topaz and AlF3 powders, with corundum formed in situ into the topaz matrix. The corundum formation reaction occurs in the temperature range 875–975 °C, from 40 min sintering time, obtaining the topaz- Al2F1·44(OH)0·56SiO4/corundum- Al2O3 composites. Although sintering temperature and time increment lead to higher corundum formation in the topaz matrix (78.4 wt % Al2O3 at 975 °C for 60 min), longer residence times give place to corundum percentage decrease due to topaz reconversion. The composites' microstructure is characterized by a rectangular bar with stacked pyramidal ends and polycrystals of hexagonal plates for topaz and corundum, respectively. For the topaz/corundum composites, the maximum density was 3.05 g/cm3 (17 % porosity) for specimens sintered at 925 °C for 20 min. The glow curves of the topaz/in situ corundum composite sintered at 975 °C and 0 min dwell time show thermoluminescent peaks between 180 and 250 °C, useful for dosimetric applications. The most helpful peak (at 221 °C) in the topaz/corundum composite's glow curves determined by computational deconvolution is sharp and exhibits the highest thermoluminescent response. Dose-response analysis of the composite (sintered at 975 °C for 0 min) with the best thermoluminescent response revealed two ranges of linear behavior, the first from 2 to 200 mGy, with an adjustment of 99.9 % and the second in the range 5–300 Gy (99.8 % fitting). The thermoluminescent response improvement of the topaz/corundum composites is attributed to the corundum formed in situ during sintering. Fading rate studies of the composite with the best sintering treatment revealed a signal decrease of 4 % after 15 days, which remained constant for up to 30 days, and 8 % after 60 days. The kinetic parameters, kinetics order (b), activation energy (E), and frequency factor (s) determined using the glow peak shape method showed second-order kinetics. The topaz/corundum composite with the best TL response (975 °C, 0 min) presents an effective atomic number (Zeff) of 11.74. The detection of lower doses (mGy) and the linear response at higher doses (Gy) of beta 90Sr, together with the other thermoluminescent properties, suggest that the topaz/corundum composites sintered at 975° for 0 min dwell time may find application in radiotherapy, geological dating, and environmental dosimetry.

Influence of sintering condition on tribological properties of (Hf-Ta-Zr-Nb-Ti)C carbides

The wear behavior of high-entropy (Hf-Ta-Zr-Nb-Ti)C ceramics (HECs) was investigated using the ball-on-flat linear reciprocating method/dry sliding in the air. The experimental materials were prepared by ball milling and spark plasma sintering at 2100 °C and 5, 10, or 20 min sintering time. The HECs achieved relative density from 99.5% to 99.9%, with homogeneous chemical composition and grain sizes of HEC from 8 μm to 11 μm. The sintering times showed no significant influence on the wear characteristics of the investigated specimens. However, very promising mechanical and tribological properties of HEC were obtained. The materials had Young's modulus from 452 GPa to 482 GPa, Vickers' hardness from 20.9 GPa to 22.0 GPa, and Indentation fracture resistance of ∼2.8 MPa·m1/2 - 2.9 MPa·m1/2. The measured values of specific wear rate varied from 1.18 × 10−6 mm3/N·m to 3.23 × 10−6 mm3/N·m and coefficient of friction under different loads were very similar, between 0.29 and 0.32. The dominant wear mechanisms in all cases were mild abrasion with limited oxidation-driven tribochemical reaction.

Preparation of Micro-Electrolytic Iron-Carbon Filler for Sewage by Recycling Metallurgical Dust

In this paper, a new iron-carbon micro-electrolytic filler for wastewater treatment was prepared using the blast furnace dust. The effects of preparation conditions on the performance of the filler during the wastewater treatment were investigated. The optimal preparation conditions of the filler were obtained, which provided an experimental theoretical basis for the use of metallurgical dust sludge in the preparation of micro-electrolytic fillers. From the results of treating methyl orange-simulated wastewater with fillers of different preparation conditions, it could be obtained that the improvement of the filler processing performance requires a suitable iron to carbon ratio, sintering time, and sintering temperature. The optimum preparation conditions were a 1:2 iron-carbon ratio, 30 min sintering time, and 1100 °C sintering temperature. The effect of treatment conditions on the performance of the iron-carbon micro-electrolytic filler was also investigated. The results showed that increasing the filler addition, increasing the treatment temperature, and decreasing the initial pH could effectively improve the treatment efficiency of the filler for methyl orange-simulated wastewater. More than 99% of the methyl orange could be removed in the wastewater under the conditions of 5 g of filler, 40 °C, and pH = 3.

Effect of sintering time on the structural and magnetocaloric properties of Mn-Fe-P-Si-Ge-B alloys prepared by spark plasma sintering

Spark plasma sintering (SPS) has some advantages for preparing multifunctional materials, such as fast heating rate, short sintering time, and high compactness of products. In this work, we reported the effect of sintering time on the structural and magnetocaloric properties of Mn1.15Fe0.85P0.65Si0.13Ge0.2B0.02 prepared by SPS. The crystalline structure, microstructure and composition were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). The results indicated that all the alloys crystallized in the hexagonal structure with a space group of P6 − 2m. A secondary phase of (Mn,Fe)3(Si,Ge) was not found in SEM but in TEM measurement. Transition temperature and isothermal entropy change were determined from thermal magnetization data measured in different constant magnetic fields. The results showed that the alloys undergo first-order phase transitions at transition temperatures between 248.8 K and 281.9 K. The maximum isothermal entropy change was found in the alloy sintered for 15 min, being 15.6 J ⋅ kg−1 ⋅ K−1 for a magnetic field change of 3 T. It indicated that no less than 15 min sintering time was required to prepare the alloy with good homogeneousness and large magnetocaloric effect. Consequently, SPS is an effective method for synthesizing the Fe2P-type alloys and the resultant alloys are promising magnetocaloric materials for magnetic refrigeration near room temperature.

Synthesis and characterization of CuxO/Bi2O3 oxides for removal of HCHO under visible light irradiation.

CuxO/Bi2O3 oxides grown on nickel foam were synthesized via an electrodeposition method to degrade indoor HCHO under visible light irradiation and fully characterized by XRD, SEM, FT-IR, and UV-Vis technologies. The characterization results showed that the CuxO/Bi2O3 oxides were successfully loaded on nickel foam and the visible light response spectrum was expanded to 740 nm. Plackett-Burman design combined with central composite design has been used to optimize factors that affect HCHO removal performance. The results demonstrated that bismuth nitrate content, polyethylene glycol 600 content, sintering time, and lactic acid concentration were the four most important factors affecting the HCHO removal performance over CuxO/Bi2O3 sample. The optimum CuxO/Bi2O3 sample could degrade 88.796% of HCHO in 300 min at the conditions of 4.28 mol/L lactic acid, 4.86% polyethylene glycol 600, 194.03 min sintering time, and 45.83 g bismuth nitrate, and the HCHO removal rate remained 82.3% after five cycles. A plausible mechanism for the degradation of HCHO under visible light irradiation was proposed. This work provides a feasible solution for removing indoor formaldehyde in the field of photocatalysis.

Microstructure and properties of the Nd2Fe14Bp/Al–Co composites fabricated via microwave sintering

This study aimed to fabricate a new type of aluminum matrix composite exhibiting high strength, good magnetic property, and toughness to solve the issues on current magnetic materials, such as brittleness and high density. In this paper, the Nd2Fe14Bp/Al–Co composites with different cobalt (Co) contents (wt.%) are fabricated via microwave sintering. The effects of the Co content on the composite microstructures and properties are studied. The results indicate that at a 580 °C sintering temperature, 30 min sintering time, and 30 °C/min heating rate, with an increase in the Co content (0 → 1%→2.5%→5%→7.5%→10%), the compactness initially increases and then decreases and reaches the maximum of 94.5% for the 5%Co sample together with a smaller grain size. The composites mainly consist of Nd2Fe14B with various sizes, Co particles, and the Nd2(Fe,Co)14B phase. The interfacial deformation resistance of the 5%Co sample tested via nanoindention is 22.8% higher than that of the Co-free sample, which can facilitate in the interfacial strengthening. The microhardness, yield strength, and tensile strength of the 5%Co samples are 107.4 HV, 210.84 MPa, and 139.8 MPa, respectively. The remanence Br, coercive force Hcj, and maximum magnetic energy product (BH)max of the 5%Co sample are 0.37 T, 0.65 T, and 45.12 kJ/m3, respectively, which are 48.6%, 29.2%, and 63.9% higher than those of the Co-free sample. The significant increase in the magnetic properties is mainly attributed to the interactive coupling between the Co particle soft magnetic phase and Nd2Fe14B hard magnetic phase.

Sinter bonding of AISI 4340 and WC-Co using Ni interlayer by inserted powder injection molding

An inserted powder injection molding (IPIM) method has been developed to overcome the size limitation (<10 mm) in the part production with powder injection molding process. In this method, the part called insert is placed into the mould and the feedstock is injected onto it and then the part is sintered. With this method it is possible to produce parts from different materials by using inserts. In this study, bonding of WC-Co feedstock and AISI 4340 insert during the sintering process was investigated by IPIM method using Ni interlayer. In EDS analyses, the most diffused element was determined as W depending on the concentration difference. When the intermediate zone was examined, it was observed that the Ni interlayer was infiltrated along 10 mm towards the WC-Co side. Meanwhile, on the AISI 4340 insert side, a diffusion zone which is 35 μm wide was determined. As the shear strength of the intermediate zone is increased, Ni interlayer thickness and sintering time is increased. The highest shear strength came out to be 266.5 MPa in the 240 min sintering time by using 100 μm Ni interlayer.

Effect of induction hardening of Fe-C-Ni-Cu-Mo-B metal matrix composites by powder metallurgy for gear production

Purpose: In this study, mechanical behavior of iron base (Fe-0.8 C-2.0 Cu-1.5 Ni-X Mo-YB (%wt.), x=0.6, 1.2 and 1.8; Y=0.2, 0.6 and 1.0) metal matrix composite (MMC) by powdermetallurgy was investigated for gear production. Effect of Mo and B elements on surfacehardness, density and microstructure of the composite samples.Design/methodology/approach: MMC has produced by warm compaction methodfollowed by free sintering in controlled Ar gas atmosphere. Green composite has producedunder 650 MPa pressure at 160ºC temperature. The green products have been sinteredat temperature of 1150ºC and 60 min sintering time. Hardness test have been conductedbefore and after induction hardening. The microstructure of the samples have beenexamined before and after induction hardening under optical microscopy.Findings: The results have showed that the highest surface hardness has been obtainedX=1.8 and Y=1.0 composition. Addition of Mo and B elements does not affect on the densityof the sample.Research limitations/implications: The ability of induction hardening to compositematerial has been investigated.Originality/value: The studies were carried out in experimental composition with warmcompacting method.

Viewpoint on fast creation of dense MgB2 phase in wires made by internal Mg diffusion process

Md Shahriar Al Hossain, University of Wollongong, shares his views on a letter by P KovaAcA○ and colleagues on fast creation of dense MgB phase in wires made by internal Mg diffusion process. According to him, In situ and ex situ powder metallurgical processes are currently used for the industrial fabrication of mono- and multi-filamentary MgB wires. The mass density in the MgB filaments of the wires after the final heat treatment is quite low with respect to the theoretical density. The typical effective superconductor area in the wire is only about 10%. Cold high pressure densification (CHPD) has been suggested as an alternative to enhance filament mass density. The authors showed that 8 min sintering time is sufficient for the formation of a uniform MgB2 phase 90 μm in thickness and without cracks, which is nearly identical to samples produced under the same sintering temperature conditions but longer sintering time of 3?5 h that were previously reported by the NIMS group. This finding is important for economical industrial production, but a question still remains as to how the round wires with a hollow filament will perform in magnet design and application, where enhancement of the filling factor, reduction of filament size, and mechanical and electrical stability and reliability are key factors.

Effect of MnO2 doping and temperature treatment on optical energy band gap properties in Zn-Bi-Ti-O varistor ceramics

In this study, the optical band-gap energy (Eg) was investigated with respect to MnO2 and sintering temperatures on ZnO based varistor ceramics. Eg of the ceramic (99-x) mol% ZnO + 0.5 mol% Bi2O3 + 0.5 mol% TiO2 + × MnO2 where × = 0, 0.2, 0.4, 0.6 and 0.8 mol%, were determined using UV-Vis spectrophotometer. The samples was prepared through solid-state route and sintered at the sintering temperature from 1110, 1140 and 1170 °C for 45 and 90 min in open air. At no doping of MnO2, the values of Eg are 2.991 ± 0.001, 2.989 ± 0.001 eV for 45 and 90 min sintering time; respectively. Eg was decreased to 2.192 ± 0.001 eV at 1140 °C at 45 min sintering time. Similar result of Eg was observed at longer heat treatment. Further addition of dopant causing the Eg decreases rapidly to 2.099 and 2.106 ± 0.001 eV at 45 and 90 min sintering time; respectively. XRD analysis indicates that there is hexagonal ZnO and secondary phases, Zn2MnO4, Bi4Ti3O12 and Zn2Ti3O8. The relative density of the sintered ceramics decreased or remain constant with the increase of MnO2 concentration for 45 min sintering time, however, further prolong sintering time; the relative density decreases form 90.25 to 88.35%. This indicates the pores are increasing with the increase of heat treatment. The variation of sintering temperatures to the optical band gap energy of based ZnO varistor doped with MnO2 due to the formation of interface states.

Development of a single-phase Ca-α-SiAlON ceramic from nanosized precursors using spark plasma sintering

Nitrogen-rich Ca-α-SiAlON ceramics were synthesized using nanosized precursors via spark plasma sintering process for various holding times (10, 20, 30min) at relatively low temperatures of 1500°C and 1600°C. The effects of the experimental conditions, namely sintering time and temperature, on the densification and mechanical properties of the processed α-SiAlON were investigated. All of the conditions yielded nearly completely densified ceramics. A remarkable combination of hardness and toughness was obtained for the samples at either sintering temperature; and these values were greatest after 30min sintering time, with Vickers hardness values of 21.6GPa and 20.5GPa and fracture toughness values of 7.3MPa√m and 9.7MPa√m for sintering temperatures of 1500°C and 1600°C, respectively. The differences in the mechanical properties of these samples were related to differences in the phases formed during the sintering process.

EFFECT OF MNO2 DOPING ON NONLINEAR COEFFICEINT OF ZN-BI-TI-O VARISTOR CERAMICS

The work aims the improvement of nonlinear coefficient ( ) can achieve by the addition of MnO2. The investigation regarding to the variation of MnO2 doping on ZnO-Bi2O3-TiO2 system is discussed. The crystalline phases were identified by an XRD (PANalytical (Philips) X’Pert Pro PW3040/60) with CuK radiation and the data were analyzed by using X’Pert High Score software. The density of varistor ceramics was measured by the geometrical method. The current-voltage characteristics of the varistor ceramics were evaluated. The average grain size ( ) was determined by lineal intercept method. The of ZnO doped with 0.5 mol% of Bi2O3, 0.5 mol% of TiO2 and x mol% of MnO2 was calculated from data analysis of current-voltage characteristics obtained through a Source Measure Unit (Keithley 236). The calculation of is done by using Origin Pro8.0 software which at low concentration at 1170 oC has the value 10.36 and 9.21 at 45 and 90 min sintering time, respectively, and then decreases to 5.63 and 5.27 at 0.8 mol% MnO2 concentrations. The addition of MnO2 dopant in Zn-Bi-Ti oxide ceramics sintered at 45 minutes cause the value of to increase up to 0.4 mol% and decrease after further addition.

Effect of Co&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; Doping on Nonlinear Coefficient in Zn-Bi-Ti-O Varistor Ceramics

In the ZnO based varistor, the improvement of nonlinear coefficient (α) and prevention of evaporation of Bi2O3 during heat treatments can be achieved by the addition of MnO2 or Co3O4. In this conjunction, it is proper to see the effect of these additives at different low mol percentage and sintering conditions to nonlinear coefficient improvement of the varistor ceramics. In this paper, the investigation regarding to the α variation of Co3O4 doping on ZnO-Bi2O3-TiO2 system is discussed. Here, the crystalline phases were identified by an XRD (PANalytical (Philips) XPert Pro PW3040/60) with CuKα radiation and the data were analyzed by using XPert High Score software. The density of varistor ceramics was measured by the geometrical method. The current-voltage characteristics of the varistor ceramics were evaluated. The average grain size (d) was determined by lineal intercept method. The α of ZnO doped with 0.5 mol% of Bi2O3, 0.5 mol% of TiO2 and x mol% of Co3O4 was calculated from data analysis of current-voltage characteristics obtained through a Source Measure Unit (Keithley 236). The calculation of α is done by using Origin Pro8.0 software. The value of α at low concentration at 1170 °C has the value 5.36 and 3 at 45 and 90 min sintering time, respectively, and then decreases to 4.99 and 2.98 at 0.8 mol% Co3O4 concentrations. When the amount of dopant is increased then the value of α increase up to 0.4 mol% and then the value are slightly dropped after further addition. The addition of Co3O4 dopant in Zn-Bi-Ti oxide ceramics sintered at 45 minutes cause the value of α to increase up to 0.4 mol% and decrease after further addition.

Wettability of TiN by Liquid Iron and Steel

The wettability of liquid iron and steel in contact with TiN substrates was studied. Initially, Spark Plasma Sintering (SPS) was used to prepare the samples using different operational conditions. It was found that a relative density of 96% and surface roughness values smaller than 250 nm could be obtained by using the following settings: a 1 873 K temperature, a 89.2 MPa pressure and a 5 min sintering time. Thereafter, the wettability of the liquid iron and steel in contact with the TiN substrates was measured based on video recordings, at the moment when the metals started to melt. The results show that the contact angle value for a TiN/pure Fe system (130 to 87.9 degrees for 900 s) is larger than the value for a TiN/steel system (110 to 50 degrees for 981 s). Therefore, it is concluded that TiN has good resistance to the corrosion of the liquid iron and steel. In the liquid iron case, its wetting behaviour occurs mainly due to the oxygen increase in liquid iron after a full melting. However, in the liquid steel case the contact angle decreases sharply due to both the effects of an oxygen increase in liquid steel and a precipitation of Ti(N,C,O) at the interface.

Microstructure and Mechanical Properties of Vacuum Hot Pressed P/M Short Steel Fiber Reinforced Aluminum Matrix Composites

Commercial purity aluminum powder of irregular shape and ligamental morphology having average particle size of 75 µm was blended with medium carbon steel short fibers having average diameter of 100 µm and maximum length up to 1000 µm. The green compacts of pure aluminum and reinforced compositions were hot-pressed in 10−3 torr vacuum, at 723 K, 773 K, and 823 K for 5, 10, and 15 min durations under 50 MPa axial stress on Gleeble 3800 simulator. Microstructures of the sintered composites have been studied by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The sintered compacts were characterized for densification behavior, hardness, and growth of FexAly reaction interface. Positive densification parameter was achieved for up to 10 wt.% reinforcement fraction. The maximum hardness of 51 Hv was achieved for 10 wt.% at 823 K for 15 min sintering time. The reaction interface was analysed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The reaction interface was found to be composed of Fe3Al, FeAl2, Fe2Al, Fe3Al, Fe4Al, Fe2Al5, and FeAl intermetallics. Growth of the reaction interface was diffusion-controlled which followed a nearly parabolic law with a rate constant of 1.41 × 10−12 m2 s−1 at 823 K.

Synthesis and investigation of blue and green emissions of ZnS ceramics

ZnS ceramics were successfully synthesized by the solid-state reaction method under different conditions. The structural transformation of ZnS ceramics from zinc-blende to hexagonal wurtzite was observed with the help of X-ray diffraction (XRD). The hexagonal wurtzite ZnS ceramics with much better quality were obtained at a sintering temperature of 1100°C and for 100min sintering time, meanwhile the relative density reaches 94%. Room temperature photoluminescence measurements with 325nm excitation showed four emission bands, that is, the near band edge (NBE) emission band at ∼342nm, the emission band of ∼407nm from the sulfur vacancies, the emission peak at 488nm which was explained as the radioactive transition from the conduction band to the energy level of zinc vacancies, and the green emission band at 525nm which was attributed to the recombination of electrons from the energy level of sulfur vacancies with the holes from the line or surface defects. The observed green PL emission of the wurtzite-type ZnS ceramics could provide an interesting application in the development of novel luminescent devices.

Rapid dye-sensitized solar cell working electrode preparation using far infrared rapid thermal annealing

TiO2 nanopowder sintering during dye-sensitized solar cell working electrode preparation usually takes hours and is the rate-limiting step to rapid production of dye-sensitized solar cells. Here, we show that by far infrared rapid thermal annealing (RTA) method, TiO2 working electrode sintering time reduces from hours to minutes. 5min binders/solvents removal time at 250°C plus 10min sintering time at 500°C in a RTA system gives a cell with the efficiency of 4.37%. Although the rapid removal of binders/solvents causes the TiO2 film structure collapsing and gives a more compact working electrode structure, the far infrared RTA method directly radiates TiO2 layer giving binders/solvents removal and sintering within minutes and is ideal for rapid DSSC fabrication.

Influence of Hot Pressing Sintering Temperature and Time on Microstructure and Mechanical Properties of TiB&lt;sub&gt;2&lt;/sub&gt;/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Tool Materials

In this paper, a TiB2/Al2O3composite was hot-pressed. The effect of hot pressing parameters on the TiB2/Al2O3composite microstructure and mechanical properties was investigated. The flexural strength and fracture toughness were measured by three point bending testing and direct indentation method, respectively. Experimental results show that the flexural strength decreases consistently with an increase in the sintering time, however, the fracture toughness increases consistently with an increase in the sintering time and sintering temperature. The maximum of the flexural strength is 1072 MPa at 1530 sintering temperature and 60 min sintering time. The microstructures were revealed by means of SEM. The results show that the TiB2grain size and density increases with the increasing temperature and time during hot pressing sintering, which benefits the fracture toughness and flexural strength.

Influence of hot pressing sintering temperature and time on microstructure and mechanical properties of TiB2/TiN tool material

In this paper, a TiB2/TiN composite was produced by the hot pressing sintering method. The effect of hot pressing parameters on the TiB2/TiN composite microstructure and mechanical properties was investigated. The results show that the fracture toughness and flexural strength of the composite increase firstly and then decrease with an increase of the sintering temperature. The flexural strength of the composite increases firstly and then decreases with an increase of the sintering time, while the fracture toughness increases consistently with an increase of the sintering time. The microstructure was revealed by the means of SEM and TEM. The results show that the TiB2 grain size and density increase with an increase of the sintering temperature and time. There are irregular shape grains at 1530 °C sintering temperature for 90 min sintering time. New phase of MoNi is found in the composite. Ni element increases in the vicinity around TiN particles with the increasing temperature. In the sample prepared at 1620 °C temperature, many dislocations can be found.

Application of Direct Current and Temperature Stresses of Low-Voltage ZnO Based Varistor Ceramics

Problem statement: The stresses to humidity, DC and AC bias, multiple impulse voltages and high temperatures are known to affect the varistor performance and it is also interesting to know the effect of both DC bias and temperature stresses at the same time. Approach: Here, the simultaneous DC and temperature stresses degradation was investigated to see the changes of nonlinear coefficient (α) in Zn-Bi-Ti oxide low-voltage varistor ceramics sintered at various sintering temperatures (1140-1260°C) and two sintering duration times of 45 and 90 min. The current-voltage characteristics of the varistor ceramics were evaluated. Results: The α of ceramic was observed to be decreased with increasing sintering temperature. After loaded with DC and temperature stresses of 0.75V1mA/80°C/12 h, the α of ceramics for 90 min sintering time decreases with sintering temperature, however that sintered for 45 min sintering time increase with sintering time. Conclusion: The application of DC and temperature stresses in Zn-Bi-Ti oxide ceramics sintered at very long time cause the α to decrease as evidence from higher leakage current.