Minimum Sintering Research Articles

Study of the Phase Composition, Structure and Mechanical Properties of Synthetic Composites Produced by High-Temperature Vacuum Sintering of SHS-Fabricated CrNi-TiN Powders

This work studies the phase composition, structure and mechanical properties of composite materials obtained by high-temperature vacuum sintering of SHS-fabricated CrNi–TiN powders synthesized in semi-industrial-scale production conditions. It was found that changes in the synthesis conditions have no effect on the phase composition and structure of the final products. Additionally, a small increase in the average size of ceramic TiN particles was observed. Compacted rectangular samples were obtained by high-temperature vacuum sintering of fine-ground CrNi–TiN SHS products. A minimum sintering temperature was found at which specimens with a density of 95% of the theoretical one could be obtained. The structure of sintered composites inherits the metal-matrix structure of a part of SHS products. It was shown that CrNi–TiN composite materials are superior to NiTi–TiB2 composites in terms of hardness as well as binding strength for three-point bending at temperatures up to 550 °C.

Surface and Wear Investigation on Microwave Sintered Nitinol Composite

The present research of the article is used to describe the microwave sintering of nitinol composite and its surface topography analysis by atomic microscopy (AFM). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) technique is used to analyze the characterization and alloying composition of the composite. Silicon carbide is the reinforcing particle between nickel and titanium. Wear test is conducted to investigate the worn surface morphology of the sintered specimen. The synthesized composite has exceptional material properties such as ultimate tensile strength of 1020MPa, 16% of elongation to fracture, 7.51 g/cc of density and hardness of 310 HV. Low wear rate of 0.01 mg/m is perceived at minimum load and minimum sintering time. Surface roughness is varied from 22.87 to 54.05nm at different sintering time. Maximum roughness height of 327.6 nm is observed in the surface profile of the composite.

Removal of Ag remanence and improvement in structural attributes of silicon nanowires array via sintering

Metal-assisted chemical etching (MACE) is popular due to the large-area fabrication of silicon nanowires (SiNWs) exhibiting a high aspect ratio at a low cost. The remanence of metal, i.e., silver nanoparticles (AgNPs) used in the MACE, deteriorates the device (especially solar cell) performance by acting as a defect center. The superhydrophobic behavior of nanowires (NWs) array prohibits any liquid-based solution (i.e., thorough cleaning with HNO3 solution) from removing the AgNPs. Thermal treatment of NWs is an alternative approach to reduce the Ag remanence. Sintering temperature variation is chosen between the melting temperature of bulk-Ag (962 °C) and bulk-Si (1412 °C) to reduce the Ag particles and improve the crystallinity of the NWs. The melting point of NWs decreases due to surface melting that restricts the sintering temperature to 1200 °C. The minimum sintering temperature is set to 1000 °C to eradicate the Ag remanence. The SEM–EDS analysis is carried out to quantify the reduction in Ag remanence in the sintered NWs array. The XRD analysis is performed to study the oxides (SiO and Ag2O) formed in the NWs array due to the trace oxygen level in the furnace. The TG-DSC characterization is carried out to know the critical sintering temperature at which remanence of AgNPs removes without forming any oxides. The Raman analysis is studied to determine the crystallinity, strain, and size of Si nanocrystals (SiNCs) formed on the NWs surface due to sidewalls etching. An optimized polynomial equation is derived to find the SiNCs size for various sintering temperatures.

Effects of Soda-Lime-Silica Glass and Borax Decahydrate as Alternative Fluxing Agents on the Stoneware Physico-Mechanical Properties

Stoneware especially tableware is manufactured by mixing the clay, quartz and flux such as feldspar. Thus, the aim of this work is to investigate the possibility of two alternative fluxing agents namely; soda-lime-silica glass (SLS), and borax decahydrate (BD) on characterization, and physico-mechanical properties of stoneware to demonstrate its suitability for tableware production. SLS and BD are incorporated into stoneware at the dosage of 5 %, and 10 % by weight, respectively. The sample was performed by uniaxial pressing (40 MPa) sintered at 1000, 1050, 1100, and 1150°C (2 hours soaking time) to establish minimum sintering temperature. Bulk density, water absorption, and modulus of rupture (MOR) were measured for each sample. Characterization of XRF, XRD, and SEM was carried out and discussed. Results indicated SLS, BD showed higher physico-mechanical properties and vitrified at 1050-1100°C, lower than normal temperature applied for stoneware (1150°C). Consequently, it was determined that the usage of SLS and BD as fluxing agent in stoneware is possible.

Sintering behavior and dielectric properties of ultra-low temperature glass/ceramic composites

Na2O-K2O-SiO2-B2O3-Al2O3-P2O5 (NKAP) glasses with low melting temperatures were obtained by melting. NKAP glass/ceramic composite ULTCC (ultralow temperature co-fired ceramic) materials were prepared at sintering temperature (<700 °C) by mixing traditional ceramic materials (alumina, quartz and zirconia) and low melting NKAP glasses. Quartz and monolithic zirconia can form stable composites with low melting NKAP glasses. Thus, we prepared ULTCC composite materials containing high amounts of quartz and zirconia. However, alumina and NKAP glasses partially reacted during sintering. Sintering temperature of NKAP glass/ceramic ULTCC composite was lower than 680 °C with the minimum sintering temperature of ˜ 550 °C. All samples containing NKAP glass/quartz ULTCC composites demonstrated excellent dielectric permittivity (equal to 6.51 with loss ˜8 × 10−3) and mechanical bending strength equal to 82 MPa. Our results can be used for fabrication of multilayer ULTCC packaging structures with tailored physical properties.

Effect of sintering temperature on surface morphology and electrical properties of samarium-doped ceria carbonate for solid oxide fuel cells

The effects of sintering temperature on the surface morphology, roughness, and electrical properties of samarium-doped ceria (SDC)–carbonate (SDCC) composite electrolyte were examined. SDCC composite pellets were fabricated and sintered at various temperatures ranging from 500°C to 650°C. Brunauer–Emmett–Teller technique and atomic force microscopy were used to investigate the surface area and surface roughness of the composite materials, respectively. Conductivity measurements using impedance spectroscopy were conducted from 350°C to 550°C. The specific surface area of the pure SDC powder decreased from 8.85m2/g to 4.24m2/g after the carbonate phase was incorporated into the SDC phase with increasing particle size. The composite pellet sintering temperature affected the continuity between the two phases [SDC and (Li/Na) carbonate], roughness, mean particle size, and conductivity of the composite electrolyte. A fully dense SDCC composite electrolyte pellet sintered at 550°C exhibited a maximum ionic conductivity of 0.077S/cm at 550°C. In addition, 550°C was the minimum sintering temperature to achieve good wetting between the two phases, moderate particle size, low surface roughness, and high ionic conductivity.

Effect of Starch Addition on Microstructure and Strength of Ball Clay Membrane

The use of starch as pore-forming agent is one of the frequently used methods to produce porous ceramics membrane with controlled microstructure (porosity and pore size) because corn starch are cheap, non- toxic and environmental friendly. A membrane with the mixture 0–35 wt% of corn starch and ball clay were prepared by compaction process and sintered at 1200°C. Thermal analysis has been done to identify the minimum sintering temperature for ball clay. The sintered membranes show the range value of shrinkage is 4.5–22.76 % and apparent porosity of 9.14–31.83 % depending on the starch content. The pore structures were analyzed by FESEM. The strength of sintered samples was tested by 3-point bending test. The flexural strength reduced from 21–7 MPa. These clay membrane are promising porous ceramic structure for water filtration applications due to their excellent combination physical and mechanical properties.

Fabrication of circular shaped ceramic membrane using mixed clays by uniaxial compaction method for the treatment of oily wastewater

Circular shaped ceramic membrane was fabricated using inexpensive mixed clays by uniaxial compaction method and subsequently fired at 900°C. TGA analysis demonstrates that the minimum sintering temperature required to fabricate the membrane is above 800°C. A volume median diameter d(0.5) of the raw material mixture is found to be 2.78 µm. XRD analysis verifies that the membrane undergoes phase transformation during sintering. SEM images reveal that the membrane does not have any micro crack. The porosity, average pore diameter and pure water permeability of the membrane is found to be 34%, 0.464 µm and 7.82 × 10−7 m/s kPa, respectively. The flexural strength of the membrane is estimated to be 10 MPa that elucidates the good mechanical stability. The chemical stability of membrane is also found to be good. The performance of the membrane was evaluated by treating with synthetic oily wastewater. The rejection value is found to be varying from 60 to 96% and the maximum rejection of 96% with good permeates flux is observed for higher oil concentration of 200 mg/L at pressure of 69 kPa.

Effects of Li2CO3 and Sm2O3 additives on low-temperature sintering and piezoelectric properties of PZN-PZT ceramics

To assist the development of applications for multilayer piezoelectric devices, the low-temperature sintering piezoelectric ceramics of 0.3Pb(Zn 1/3 Nb 2/3 )O 3 -0.7Pb(Zr 0.49 Ti 0.51 )O 3 with Li 2 CO 3 and Sm 2 O 3 additives were fabricated by a conventional solid-state reaction, and their structural and piezoelectric properties were studied. With the addition of Li 2 CO 3 , the minimum sintering temperature of 0.3Pb(Zn 1/3 Nb 2/3 )O 3 -0.7Pb(Zr 0.49 Ti 0.51 )O 3 piezoelectric ceramics was reduced from 1125 °C to 950 °C through the formation of a liquid phase and its piezoelectric properties showed almost no degradation. When the sintering temperature was below 950 °C, however, the piezoelectric properties degraded obviously. The additional Sm 2 O 3 resulted in a significant improvement in the piezoelectric properties of 0.3Pb(Zn 1/3 Nb 2/3 )O 3 -0.7Pb(Zr 0.49 Ti 0.51 )O 3 ceramic with added Li 2 CO 3 . When sintered at 900 °C, the optimized properties of the 0.3Pb(Zn 1/3 Nb 2/3 )O 3 -0.7Pb(Zr 0.49 Ti 0.51 )O 3 piezoelectric ceramic with 0.3 wt% Li 2 CO 3 and 0.3 wt% Sm 2 O 3 were obtained as d 33 = 483 pC/N, k 31 = 0.376, Q m = 73, ɛ r = 2524, tan δ = 0.0178.

Mechanical behaviour of pressed and sintered CP Ti and Ti–6Al–7Nb alloy obtained from master alloy addition powder

The Ti–6Al–7Nb alloy was obtained using the blending elemental approach with a master alloy and elemental titanium powders. Both the elemental titanium and the Ti–6Al–7Nb powders were characterised using X-ray diffraction, differential thermal analysis and dilatometry. The powders were processed using the conventional powder metallurgy route that includes uniaxial pressing and sintering. The trend of the relative density with the sintering temperature and the microstructural evolution of the materials sintered at different temperatures were analysed using scanning electron microscopy and X-ray diffraction. A minimum sintering temperature of 1200°C has to be used to ensure the homogenisation of the alloying elements and to obtain a pore structure composed of spherical pores. The sintered samples achieve relative density values that are typical for powder metallurgy titanium and no intermetallic phases were detected. Mechanical properties comparable to those specified for wrought Ti–6Al–7Nb medical devices are normally obtained. Therefore, the produced materials are promising candidates for load bearing applications as implant materials.

Synthesis of garnet structured Li7+x La3Y x Zr2-x O12 (x = 0–0.4) by modified sol–gel method

Preparation of lithium garnet Li7La3Zr2O12 (LLZ) in cubic phase by solid state method requires high temperature sintering around 1,200 °C for 36 h in Al2O3 crucible with intermittent grinding. Synthesis of LLZ in cubic phase at lower temperatures by wet chemical methods was reported earlier, however that decompose at high temperature around 850 °C. In this work we report the systematic studies on synthesis of garnet structured electrolytes by modified sol–gel method by the simultaneous substitution of Li+ and Y3+ for Zr4+ according to the formulae Li7+xLa3YxZr2-xO12 (x = 0, 0.1, 0.2, 0.3 and 0.4). The present investigation revealed that the cubic garnet phase is obtained at much lower temperature for Li7La3Zr2O12 and the simultaneous increase of both Li+ and Y3+ in Li7+xLa3YxZr2-xO12 requires slightly higher sintering temperatures for the formation of cubic garnet phase. SEM micrographs of the Li7+xLa3YxZr2-xO12 (x = 0, 0.1, 0.2, 0.3 and 0.4) annealed at minimum sintering temperature required for the formation of cubic garnet phase revealed the increase in grain size and relatively dense structure with increase of x in Li7+xLa3YxZr2-xO12.

Sticking behavior caused by sintering in gas fluidisation reduction of haematite

The sticking of haematite and iron powder during the fluidisation process was investigated using a visual fluidised bed reactor. The results showed that the amount of iron needed to stick decreased with increasing fluidisation temperature. Owing to no iron whisker formation in the experiments, the sticking phenomenon was discussed in the special case where iron morphology was dense or porous, and much attention should be paid to the effect of sintering of iron–iron contact on sticking, especially, surface nano-/microstructures of fresh iron that caused an increase in particle cohesiveness and sticking tendency. It was assumed that haematite covered with iron transformed into cohesive particles that self-agglomerated above minimum sintering temperature. Owing to the interface reaction induced, the sticking temperature of haematite was always lower than that of iron powder in the same size ranges. On the basis of sintering with surface diffusion mechanism, the tendency of sticking was enhanced by reduction reaction through reinforcing mass transfer on particle surface. Therefore, when iron whiskers were suppressed, sticking phenomenon was viewed as the agglomeration fluidisation among cohesive particles under sintering action.

Influence of sintering on deposit formation during pool boiling of calcium sulphate solutions

The objective of this work is to determine the influence of sintering effects on crystalline deposits formed during pool boiling of CaSO 4 solutions. Fouling experiments have been performed with plain tubes where the surface temperature of the heating element was varied to investigate its effect on boiling and crystallisation. Samples of the deposit layers were removed at the end of each fouling run for subsequent analysis using the scanning electron microscope. It was found that sintering of the fouling layer occurs if the temperature of the fouling layer is above a minimum sintering temperature, and that the fouling resistance reaches an asymptotic value if sintering takes place. Operating heat exchangers under pool boiling at a temperature above the minimum sintering temperature of the fouling layer accelerates the asymptotic behaviour and leads to a thinner and more compact deposit, compared to non-sintering conditions where the fouling layer thickness and thermal resistance continuously increase. Crystallisation fouling during pool boiling mainly occurs at sites where the steam bubbles grow, i.e. large pores in the deposit known as steam chimneys. However, as sintering takes place, the size and the number of pores are reduced, leading to reduced number and size of bubbles, and consequently to a declining fouling rate. For pool boiling heat transfer, the sintering-related change in fouling layer from a porous structure to a fully sintered structure is the main cause for the asymptotic behaviour.

Stabilisation of Cr(VI) in stainless steel plant dust through sintering using silica-rich clay

Stainless steel plant dust is considered a hazardous waste due to the fact that it contains significant levels of Cr(VI) and other heavy metals such as lead and zinc. It should therefore be treated before being stockpiled or land filled. Solidification/stabilisation processes are effective techniques for the immobilisation of heavy metals. This paper consequently describes an investigation into the stabilisation of Cr(VI) in stainless steel plant dust with silica-rich clay in a sintering process. The results indicate that Cr(VI) in the stainless steel dust can be stabilised in a 50 mass% dust:50 mass% clay mixture at an optimum sintering temperature of 1100 °C, and minimum sintering time of 5 h. Chromium emission during the sintering process was found to be low, and within environmental limits.

Promotion of Au(en)2Cl3-Derived Au/Fumed SiO2 by Treatment with KMnO4

A new method for the removal of organic ligands used in the synthesis of nanoparticle catalysts via solution-phase chemical oxidation and subsequent pretreatment at moderate temperatures was developed. This synthesis protocol is advantageous for the preparation of highly dispersed gold catalysts with minimum sintering. Highly active Au/SiO2-based catalysts were prepared by treating Au(en)2Cl3-derived Au/fumed SiO2 in strongly oxidative KMnO4 solutions. The low-temperature activity in CO oxidation increased dramatically following the KMnO4 treatment and subsequent thermal activation (including treatment in O2−He at 300–600 °C). The influences of the pH values of KMnO4 solutions and temperatures of activation in O2−He prior to the reaction testing were investigated, and relevant characterization using XRD, TEM, TG/DTG, SEM, EDX, and ICP-OES was conducted. The catalyst stability in CO oxidation was studied as a function of reaction time on stream. The origin of the promotional effect was discussed.

Two-stage sintering of nano-sized yttria stabilized zirconia process by powder injection moulding

Abstract Powder injection moulding (PIM) is capable of mass producing intricately shaped components. In recent years, this technology has been adopted in the electronic, computer, chemical and medical industries. The 3 mol% yttria stabilized zirconia (Y-TZP) is well recognised for its high fracture toughness. PIM of nano-sized Y-TZP hence offer attractive potential applications. Grain growth however is a major problem for nano-sized powder. Initial researches proposed that high green density and minimum sintering temperature are beneficial in controlling the grain growth of nano-sized powder. In view of the constraint of low green density of PIM samples, grain growth control will be even challenging. Two-stage sintering (2SS) is reported to be able to refine the microstructure and enhance the material properties. This method simply modifies the sintering route by firing the sample at high temperature follow by rapidly cooling down and dwelling at lower temperature. The objective of this work is to monitor the effect of 2SS on the nano-sized Y-TZP process by PIM. Dimensional changes, weight loss, density, hardness as well as microstructure are study after the sintering and compare to the conventional isothermal sintering. The process condition at 1350 °C follow by 900 °C is found to be able to achieve comparable hardness as isothermal sintering at 1500 °C. With a finer microstructure, 2SS can potentially improve the grain size dependant material properties of nano-Y-TZP in the near future.

Low-temperature sintering method for NiCuZn ferrite and effect of Mn addition on electromagnetic properties

Low temperature sintering NiCuZn ferrite was employed at most cases due to its co-firability with Ag (below 960 °C). The NiCuZn ferrite sintered body with high-strength and high-frequency magnetic properties was fabricated. Firstly, NiCuZn ferrite powder was synthesized under CO 2 atmosphere at 500 °C from the mixed doxalate synthesized by liquid phase precipitation method. Then a small amount of boric acid (H 3BO 3) was added to the powder, and the NiCuZn ferrite powder compact was prepared with Newton press and CIP methods. Finally, NiCuZn ferrite sintered body was fabricated by sintering at 900 °C under CO 2 atmosphere. The minimum sintering temperature (800 °C) was determined by the study of high temperature shrinkage. By this method, NiCuZn ferrite sintered body with 0.5% (mass fraction) boric acid was obtained, which has the bending strength of 340 MPa. The effect of various Mn addition on electromagnetic properties were studied.

AGGLOMERATION BEHAVIOR IN A BUBBLING FLUIDIZED BED AT HIGH TEMPERATURE

Minimum fluidization velocity and agglomeration behavior were investigated at high temperature in an 80 × 30 mm two-dimensional quartz fluidized bed and in an 82 mm i.d. circular fluidized bed. Bed materials tested were two sizes of glass beads as well as three sizes of fluidized bed combustor (FBC) ash. The minimum fluidization velocity decreased with increasing bed temperature, whereas the minimum sintering fluidization velocity increased with the bed temperature. The sintering of glass beads belongs to visco plastic sintering, the first type. FBC ash agglomerate has higher amounts of SiO2, Al2O3, Na2O, K2O, and SiO2 than in the original ash, indicating that low melting eutectics were formed and that the liquid phase in a silicate system was formed. The agglomeration of FBC ash belongs to the second type, an excessive quantity of liquid being formed by melting or chemical reaction.

Deactivated sintering by particle coating: the significance of static and dynamic surface phenomena

The suppression of bonding of micron-sized host particles due to the application of heat at temperatures below their melting point (deactivated sintering) when coated with submicron guest particles is theoretically predicted and confirmed by experiments. It was possible to preserve individual particles of polymethylmethacrylate (PMMA) at 150°C, about 45°C above the minimum sintering temperature (MST) of the uncoated particles, and individual glass beads at 750°C, about 175°C above the minimum sintering temperature of the uncoated glass beads, by applying a surface coating of silicon carbide.A dense monolayer of submicron particles coated onto the surfaces of much larger host particles prevents contact of their surfaces (host–host contact) and suppress the dilation of their mobile surfaces. At the temperature at which the host particle material starts to flow, the coated particles behave as solid colloid particles sitting on the surface of a liquid. If the adhesion energy at the interface between the host and guest particles is not small in comparison to the cohesion energy, i.e., when the contact angle is not very large, the decrease in bonding energy due to the coating is small and sintering deactivation is weak. If the contact angle is very large, i.e., the work of adhesion is very small compared to the work of cohesion, the decrease in bonding energy is large resulting in appreciable sintering deactivation. This deactivation is only temporary, however, because of the forced intrusion of the host fluid into the pores of the coating layer (CL). This process is similar to the intrusion of mercury, which occurs in mercury porosimetry. Models for the intrusion dynamics are developed for both a dense coating monolayer and polylayers with account for different pore size distributions.

Phase interaction and oxygen transport in La 0.8Sr 0.2Fe 0.8Co 0.2O 3–(La 0.9Sr 0.1) 0.98Ga 0.8Mg 0.2O 3 composites

Composite ceramics made of two perovskite-type compounds, (La 0.9Sr 0.1) 0.98Ga 0.8Mg 0.2O 3− δ (LSGM) and La 0.8Sr 0.2Fe 0.8Co 0.2O 3− δ (LSFC) mixed in the ratio 60:40 wt.%, possess relatively high oxygen permeability limited by both bulk ionic conduction and surface exchange at 700−950 °C. Sintering at elevated temperatures (1320–1410 °C) necessary to obtain dense materials leads to fast interdiffusion of the components, forming almost single perovskite phase ceramics with local inhomogeneities. This phase interaction decreases the oxygen ionic transport in the composites, where the level of ionic conductivity is intermediate between those of LSGM and LSFC. The scanning electron microscopy (SEM) suggests a presence of Ga-enriched domains, probably having a high ionic conductivity. The size and concentration of these domains can be increased by decreasing sintering temperature or using preliminary coarsened LSGM powders. The maximum oxygen permeability is thus observed for the composite prepared under minimum sintering conditions sufficient to obtain gas-tight ceramics, including the use of LSGM, preliminary passivated at 1150 °C, and sintered at 1320 °C. The activation energy values for total conductivity, which is predominantly p-type electronic and slightly decreases due to component interaction, vary in the narrow range from 24.0 to 26.2 kJ/mol at 25–575 °C. The average thermal expansion coefficients (TECs) of LSGM-LSFC composites, calculated from dilatometric data in air, are (12.4–13.5)×10 −6 K −1 at 100–650 °C and (17.8–19.8)×10 −6 K −1 at 650–1000 °C.