Effects of sintering temperature on microstructure,properties, and crushing behavior of ceramic proppants

Ceramic proppants with excellent performance were successfully prepared by second grade bauxite. The phase structure and the microstructure were investigated via X-Ray diffraction and scanning electron microscopy. The results suggested that bulk density and apparent density constantly increased, while the breakage ratio gradually decreased with the increasing in sintering temperature. When the sintering temperature reached to 1500°C, the breakage ratio obtained lowest value of 3.6% under 52 MPa closed pressure, which satisfied the requirement of Chinese Petroleum and Gas Industry standard. Furthermore, the mode of fracture for ceramic proppants was transformed from intergranular fracture into transgranular fracture and open pores had larger influence than closed pores for breakage ratio of ceramic proppants.     

Preparation of ultra-light ceramic foams from waste glass and fly ash

Ultra-light ceramic foams were successfully prepared by a green spheres technique, which used waste glass powder and fly ash as the main material. Besides, borax and SiC were introduced as fluxing agent and foaming agent, respectively. The effects of fly ash content, borax content and sintering temperature on the microstructures and properties of ceramic foams were systematically investigated. The optimum composition is 30?wt-% fly ash, 70?wt-% waste glass, 15?wt-% borax and 0.5?wt-% SiC. Ultra-light ceramic foams sintered at 680–780°C possess bulk density of 0.14–0.41?g?cm^?3, porosity of 82.9–94.1%, compressive strength of 0.91–6.37?MPa and thermal conductivity of 0.070–0.121?W?m^?1?K^?1, respectively. This method is convenient, low-cost and environment friendly, which makes it a promising way for recycling solid wastes.     

Reuse of mineral wool waste and recycled glass in ceramic foams

Novel ceramic foams have been prepared by high temperature sintering of waste mineral wool and waste glass using SiC as a foaming agent. The aim of the research was to understand the effects of composition and sintering conditions on the properties and microstructure and produce commercially exploitable ceramic foams. Optimum ceramic foams were formed from 40 wt% mineral wool waste and 2 wt% SiC, sintered at 1170 °C using a heating rate of 20 °C/min with a 20 min hold at peak temperature. The ceramic foams produced had a bulk density of 0.71 g/cm³ and a uniform pore size distribution. The research shows that ceramic foams can be formed from waste mineral wool and these can be used for thermal insulation with associated economic and environmental benefits.     

Densification behaviour and physico-mechanical properties of porcelains prepared using spark plasma sintering

Porcelain powder was consolidated using spark plasma sintering (SPS) at a constant heating rate of 100°C?min^?1 to peak temperatures ranging from 1000 to 1200°C and was observed to sinter at relatively low temperature ～920°C under the SPS conditions while conventional sintering requires ～1050°C. SPS produced densification rates about 10 times greater than conventional sintering. The dwelling step at the optimal peak temperature was negligible due to rapid flow of the molten glass assisted by applied pressure. SPSed samples exhibited denser microstructures, resulting in improved physico-mechanical properties compared with conventionally sintered samples such as apparent bulk density improved from 2.38 to 2.48?g?cm^?3, Vickers hardness improved from 3–5 to 6–7?GPa, and fracture toughness improved from 2–3 to 4–6?MPa?m^1/2.     

Effects of CaCO3 additive on properties and microstructure of corundum- And mullite-based ceramic proppants

Corundum-mullite ceramic proppants have been successfully synthesized using raw materials of natural bauxite and solid waste coal gangue, CaCO₃, as additive. The influences of calcium carbonate additive on phase composition, microstructure, and mechanical performances were systematically investigated. The results indicate that the addition of CaCO₃ promotes the formation of liquid phase at lower temperature during sintering process, which is beneficial to the densification of the samples and the reduction of sintering temperature. Moreover, the mullite grains become finer and finer with the content of CaCO₃ additive increasing, which improves the toughness and strength of the samples via a grain refinement strengthening mechanism. The ceramic proppants exhibit optimal performances with additive of 5 wt.% at 1350°C, and the breakage ratio under 52 MPa closed pressure is the lowest. Additionally, the sintering temperature is dropped by 150°C compared with the samples without adding calcium carbonate.     

Effect of calcium carbonate on the preparation of glass ceramic foams from water-quenched titanium-bearing blast furnace slag and waste glass

ABSTRACT

Glass ceramic foams were fabricated with powder sintering technology at a low temperature (900°C), using water-quenched titanium-bearing blast furnace slag (WTS) and waste glass as the primary raw materials. Additionally, calcium carbonate, sodium borate and sodium phosphate were chosen as sintering aids to form excellent performance products. The effects of calcium carbonate additions on foaming process, crystal content, morphology and properties of the prepared samples were systematically researched. The research indicates that increasing the calcium carbonate content made the foaming process harder and the pore size got more uniform. Consequently, the compressive strength and bulk density increased, while the porosity and water absorption decreased. The homogenous porous structures and optimal comprehensive properties were achieved with 5–7?wt-% CaCO₃ addition, including a bulk density of 0.79–0.82?g?cm^–3, porosity of 73.13–75.28%, water absorption of 3.29–3.75% and compressive strength of 13.13–13.85?MPa.     

Waste-bearing foamed ceramic from granite scrap and red mud

Using granite scrap and red mud as raw materials, SiC as foaming agent, powder sintering method was used to prepare closed-pore foamed ceramic. The effects of the ratio of red mud and granite scrap, foaming agent content, sintering temperature and holding time on the crystalline phase, pore structure, and performance of foamed ceramic were systematically studied. The results showed that, when the content of red mud was 10 wt%, together with 1.0 wt% SiC addition, the heating rate was 5°C/min, the foamed ceramic sintered at 1130°C for 30 min exhibited optimal properties, including bulk density of 483.11 kg/m³, porosity of 77.27%, compressive strength of 1.62 MPa and water absorption of .49%. Based on these properties, it possessed broad potential application prospects in the fields of sound and thermal insulation, lightweight construction materials. In this study, the utilization ratio of industrial solid waste was 100%, realized the comprehensive utilization of granite scrap and red mud, and provided a new idea to realize their low-cost utilization by preparing foamed ceramic with associated economic and environmental benefits.     

Preparation and properties of InGaZn4O7 ceramic by cold sintering

When the traditional method is used to prepare IGZO ceramic, it needs to be sintered under ultra-high temperatures and for a long time, and the preparation cost is high. To reduce the sintering temperature and energy consumption, a mixed-phase IGZO green compact with ultra-high density was first prepared using cold sintering process. Then, the IGZO ceramic with excellent properties was successfully prepared by the conventional sintering method at low sintering temperature. The effects of sintering temperature on the microstructure, density, and electrical properties of IGZO green compact and ceramic were studied. The densification process of ultrahigh density IGZO green compact was also discussed. The results show that the IGZO green compact with a relative density of over 96% can be obtained under cold sintering at 400 °C/475 MPa and assisted by the acetic acid solution. An IGZO ceramic with a relative density of 98.12% and resistivity of 4.87 × 10⁻³ Ω cm was obtained by sintering at 1100 °C for 5 h. This paper provides a reference for improving green compact density and preparing high-performance transparent oxide ceramics at low temperature.     

Sintering behaviour and characterisation of low-cost ceramic foams from coal gangue and waste quartz sand

New ceramic foams have been successfully synthesised with coal gangue and waste quartz sand, which supply a feasible way to recycle these hazardous solid wastes. An objective of this research was to investigate the sintering behaviour and effects of sintering conditions on the crystalline phase change, microstructure and main properties of final ceramic foams. Good correlations among porosity, thermal conductivity, water absorption, bulk density, mechanical properties were studied. Results indicated that increasing sintering temperature or time had similar effects on the physical–mechanical properties. Samples sintering at 1140°C for 1 hour exhibited the highest porosity (87.5%), lowest bulk density (0.39?×?10^?3?kg?m^?3), lowest thermal conductivity (0.085?W·(m?K)^?1), moderate water absorption (9.38%) and adequate flexible strength (2.4?MPa). Combined with excellent properties and low-cost characteristics, the new development for ceramic foams preparation will be widely used in building insulation materials for no-load bearing walls.     

Microstructure and properties of a graphene platelets toughened boron carbide composite ceramic by spark plasma sintering

A kind of B₄C/SiC composite ceramic toughened by graphene platelets and Al was fabricated by spark plasma sintering. The effects of graphene platelets and Al on densification, microstructure and mechanical properties were studied. The sintering temperature was decreased about 125–300?°C with the addition of 3–10?wt% Al. Al can also improve fracture toughness but decrease hardness. The B₄C/SiC composite ceramic with 3?wt%Al and 1.5?wt% graphene platelets sintered at 1825?°C for 5?min had the optimal performances. It was fully densified, and the Vickers hardness and fracture toughness were 30.09?±?0.39?GPa and 5.88?±?0.49?MPa?m^1/2, respectively. The fracture toughness was 25.6% higher than that of the composite without graphene platelets. The toughening mechanism of graphene platelets was also studied. Pulling-out of graphene platelets, crack deflection, bridging and branching contributed to the toughness enhancement of the B₄C-based ceramic.     

The effect of SPS parameters on the production of yttria transparent ceramic

In this work, the spark plasma sintering (SPS) of commercial yttria nanopowder is investigated. The SPS parameters such as sintering temperature, applied pressure, and dwell time are varied. Densification without grain growth occurring at occurred up to a sintering temperature of 1400°C and grain growth without further densification taking place at the higher temperature. The optimum sample was obtained at a temperature of 1400°C with a pressure of 70 MPa and dwelling time of 15 minutes. The highest relative density of 99.8% and the average grain size of 1.26 μm were obtained at 1400°C. The yttria ceramic annealed at 1200°C had the in-line transmission of 5%-70% and 70%-82% in the visible and infrared wavelength region, respectively. The measurements of hardness and fracture toughness characteristics of the transparent yttria ceramic showed 9.2 GPa and 2.24 MPa.m^1/2, respectively.     

Structural and chemical stability of multiwall carbon nanotubes in sintered ceramic nanocomposite

Abstract

Abstract

The structural and chemical stability of multiwall carbon nanotubes (MWNTs) in ceramic nanocomposites prepared by spark plasma sintering was studied. High resolution electron microscopy, X-ray diffraction and Raman spectroscopy were used to evaluate any degradation of the MWNTs. They were found to be well preserved in alumina after sintering up to 1900°C/100?MPa/3?min. In boron carbide, structural degradation of MWNTs started from ～1600°C when sintered for 20?min. Multiwall carbon nanotubes maintained their high aspect ratio and fibrous nature even after being sintered in boron carbide at 2000°C for 20?min. However, no Raman vibrations of MWNTs were observed for nanocomposites processed at temperatures <2000°C, which indicates that they were severely degraded. Structural preservation of MWNTs in ceramic nanocomposites depends on the ceramic matrix, sintering temperature and dwell time. Multiwall carbon nanotubes were not preserved for matrices that require high sintering temperatures (>1600°C) and longer processing times (>13?min).     

Field assisted sintering of ceramic constituted by alumina and yttria stabilized zirconia

We show that a two-phase 50 vol% 3YSZ-alumina ceramic flash-sinters at a furnace temperature of 1060 °C under an electrical field of 150 V cm⁻¹. In contrast undoped, single-phase alumina remains immune to field assisted sintering at fields up to 1000 V cm⁻¹, although single-phase 3YSZ flash sinters at 750 °C (furnace temperature). The mechanisms of field assisted sintering are divided into two regimes. At low fields the sintering rate increases gradually (FAST), while at high fields sintering occurs abruptly (FLASH). Interestingly, alumina/zirconia composites show a hybrid behavior such that early sintering occurs in FAST mode, which is then followed by flash-sintering. The specimens held in the flashed state, after they had sintered to near full density, show much higher rate of grain growth than in conventional experiments. These results are in contrast to earlier work where the rate of grain growth had been shown to be slower under weak electrical fields.     

Effect of microwave sintering on the properties of copper oxide doped Y-TZP ceramics

The effect of various amounts of copper oxide (CuO) up to 1?wt% on the densification behaviour and mechanical properties of 3?mol% yttria-tetragonal zirconia polycrystal (Y-TZP) were studied by using microwave (MW) sintering method. The MW sintering was performed at temperatures between 1100?°C and 1400?°C, with a heating rate of 30?°C/min. and holding time of 5?min. The beneficial effect of MW in enhancing densification was also compared for the undoped and 0.2?wt% CuO-doped Y-TZP when subjected to conventional sintering (CS) method. The results showed that significant enhancement in the relative density and Vickers hardness were observed for the undoped Y-TZP when MW-sintered between 1100?°C and 1250?°C. It was revealed that the 0.2?wt% CuO-doped Y-TZP and MW sintered at 1250–1300?°C could attain ≥?99.8% of theoretical density, Vickers hardness of about 14.4?GPa, fracture toughness of 7.8 MPam^1/2 and exhibited fine equiaxed tetragonal grain size of below 0.25?µm. In contrast, the addition of 1?wt% CuO was detrimental and the samples exhibited about 50% monoclinic phase upon sintering coupled with poor bulk density and mechanical properties. The study also revealed that the addition of 0.2?wt% CuO and subjected to conventional sintering produced similar densification as that obtained for microwave sintering, thus indicating that the dopant played a more significant role than the sintering method.     

Effect of technological parameters on densification of reaction bonded Si/SiC ceramics

Si/SiC composite ceramics was produced by reaction sintering method in process of molten silicon infiltration into porous C/SiC preform fabricated by powder injection molding followed by impregnation with phenolic resin and carbonization. To optimize the ceramics densification process, effect of slurry composition, debinding conditions and the key parameters of all technological stages on the Si/SiC composite characteristics was studied. At the stage of molding the value of solid loading 87.5% was achieved using bimodal SiC powder and paraffin-based binder. It was found that the optimal conditions of fast thermal debinding correspond to the heating rate of 10?°C/min in air. The porous C/SiC ceramic preform carbonized at 1200?°C contained 4% of pyrolytic carbon and ～25% of open pores. The bulk density of Si/SiC ceramics reached 3.04?g/cm³, silicon carbide content was 83–85?wt.% and residual porosity did not exceed 2%.     

Spark plasma sintering of transparent Y2O3 ceramic using hydrothermal synthesized nanopowders

Y₂O₃ nanopowders were synthesized by the hydrothermal treatment of Y(NO₃)₃·6H₂O and citric acid (CA) as Y⁺³ and the capping agent, respectively. The effect of different CA:Y⁺³ mol ratios, heat treatment time, and calcination temperature was investigated in order to determine their influence on the morphology, particle size and phase of Y₂O₃ nanopowders. The narrow size distribution of particles was obtained with CA:Y⁺³ mol ratio=1.6, heat treatment time of 6 h, and a calcination temperature at 900 °C for 90 min. Then, the synthesized Y₂O₃ nanopowder was consolidated by the spark plasma sintering technique at 1500 °C with a heating rate of 100 °C/min and held for 8 min before turning off the power. As a result, the ceramic prepared with 3 mm thickness got the highest transmission of 80% at 2.5–6 µm wavelength. The highest density and the grain size of yttria ceramic were 99.58% and 1–1.2 µm at 1500 °C, respectively.     

High-porosity mullite ceramic foams prepared by selective laser sintering using fly ash hollow spheres as raw materials

A novel method to prepare high-porosity mullite ceramic foams by selective laser sintering (SLS) using fly ash hollow spheres (FAHSs) as raw materials was reported. The complex-shaped FAHS green bodies and ceramic foams without delamination or cracks were prepared by SLS. The influence of sintering temperatures on linear shrinkage, phase composition, porosity and mechanical properties was investigated. With the increase of sintering temperature from 1250?°C to 1400?°C, the compressive strength of ceramic foams increased from 0.2?MPa to 6.7?MPa causing the fracture mechanism change from fracturing along FAHSs to across FAHSs, while the porosity of ceramic foams decreased from 88.7% to 79.9% which was higher than those of ceramic foams prepared by the conventional methods. The relatively high porosity of ceramic foams was resulted from the inner hollow structure of FAHSs, the interspaces between stacking FAHSs, and the gaps between FAHSs directly related to SLS. The results above indicated that the fabrication of high-porosity FAHS ceramic foams by SLS could achieve the advanced utilization of FAHS solid waste.     

Processing of porous glass ceramics from highly crystallisable industrial wastes

This study was carried out to gain understanding about the sintering behaviour of highly crystallisable industrial waste derived silicate mixtures under direct heating and rapid cooling conditions. The materials used in this study were plasma vitrified air pollution control waste and rejected pharmaceutical borosilicate glass. Powder compacts sintered under direct heating conditions were highly porous; compacts with particle size <?38?μm reached a maximum density of 2.74 g?cm^??3 at 850°C, whereas compacts with particles of size <?100?and <?250?μm reached maximum densities of 2.69 and 2.72 g?cm^??3 at 875 and 900°C respectively. Further increase in sintering temperature resulted in a rapid decrease in density of the glass ceramics. Image analysis results were used to link the sudden drop in density to the increase in volume of microsized pores formed in the samples during sintering. In particular, compacts made from <?38 μm particles sintered at 950°C resulted in 65 vol.-% porosity with a pore size of ～20?μm. Such materials can be used for sound and thermal insulation purposes.     

Integrated utilization of high alumina fly ash for synthesis of foam glass ceramic

Due to the numerous increase of the building energy consumption and huge volume of industrial wastes produced in China, the development of thermal insulation materials is quite needed. Herein, foam glass ceramic, a kind of thermal insulation materials, was fabricated by using solid wastes high alumina fly ash and waste glass as the main raw materials. First, in this study the proportion scheme of this research was designed by using Factsage 7.1 and the foaming agent was CaSO₄. Secondly, the decomposition of calcium sulfate and the influence of process parameters, namely the sintering temperature and the foaming agent additive amount, on the microstructure and mechanical properties of foam glass ceramic were investigated. The experimental results showed that when the proposed foam glass ceramic was sintered at between 1180 and 1220?°C, it exerted excellent macro and micro properties. The optimum parameters were 2% CaSO₄ addition and sintering temperature of 1200?°C, and the corresponding bulk density and compress strength values were 0.98?g/cm³ and 9.84?MPa, respectively. Overall these results indicated that the preparation of foam glass ceramic made up a promising strategy for recycling industrial waste into new kind of building insulation materials.     

Evolution of phase composition and microstructure of sodium potassium niobate –based ceramic during pressure-less spark plasma sintering and post-annealing

This study was designed to better understand the microstructural and phase evolution of lead-free sodium potassium niobate based piezoceramics with a nominal composition (K_0.5Na_0.5)_0.99Sr_0.005NbO₃ (KNNSr) during pressure-less spark plasma sintering followed by post-annealing in oxygen. The as-sintered samples were dark-coloured and electrically conductive as a result of partial reduction of Nb⁵⁺ to Nb⁴⁺ and formation of oxygen vacancies confirmed by X-ray photoelectron and Raman spectroscopy. The Rietveld refinement analysis showed that the as-sintered samples contained two perovskite phases with monoclinic Pm unit cell and slightly different unit-cell parameters. The microstructure with sub-micrometre-sized grains unambiguously confirmed that rapid heating and short dwell time hindered the grain growth. We found that post-annealing the samples at 950?°C in oxygen led to improvement in functional properties. The samples became white-coloured, the both perovskite unit cells decreased as a result of re-oxidation, while the microstructure remained essentially unchanged. The KNNSr sintered at nominal sintering temperature of 1300?°C for 3?min and post-annealed possessed a relative density of 88% and dielectric and piezoelectric properties similar to those of the conventionally sintered samples. Our findings contribute to the understanding of pressure-less spark plasma sintering of sodium potassium niobate-based materials and suggest that arrested grain growth and minimisation of alkali evaporation not necessarily lead to dense ceramic.