Mechanical properties and microstructure of oil-well cement stone enhanced with submicron SiC whiskers

In order to improve the intrinsically brittle nature of the oil-well cement stone, a new type of submicron-fibrous whisker, referred to as the silicon carbide whisker (SiC whisker) was added into cement paste. The cement-based composites were prepared with the various amounts of submicron SiC whiskers. The composites were analyzed via scanning electron microscopy (SEM), mechanical testing, X-ray diffraction (XRD), infrared spectrum analysis (FTIR), and thermal stability analysis in order to understand the enhanced effect that the submicron SiC whiskers had on the applied properties and mechanisms of oil-well cement stone. The compressive strength, the tensile strength, and the flexural strength of the sample with 1% of additional submicron SiC whiskers increased by 9%, 104%, and 26%. The ultimate strain was more than 5%, which increased 194%. The elasticity modulus was 4648.4MPa, which decreased 31.1% after 28 curing days. These improved the mechanical properties of the cement-based composites primarily because of the microscopic mechanism of reinforcement via the submicron SiC whisker, including the bridging effect, the crack deflection, and the pull-out effect.

• HIGHLIGHTS

• A submicron SiC whisker was used to enhance the oil-well cement

• The submicron SiC whisker could significantly increase the mechanical behaviors of the oil-well cement

• The reinforcing mechanism that the submicron SiC whisker had on the oil-well cement was discussed in detail.

• The influence that the submicron SiC whisker had on the integrity of the cement sheaths were evaluated

     

Effects of SiC whisker addition on mechanical,thermal, and permeability properties of porous silica-bonded SiC ceramics

The effects of SiC whisker addition into nano-SiC powder-carbon black template mixture on flexural strength, thermal conductivity, and specific flow rate of porous silica-bonded SiC ceramics were investigated. The flexural strength of 1200°C-sintered porous silica-bonded SiC ceramics increased from 9.5 MPa to 12.8 MPa with the addition of 33 wt% SiC whisker because the SiC whiskers acted as a reinforcement in porous silica-bonded SiC ceramics. The thermal conductivity of 1200°C-sintered porous silica-bonded SiC ceramics monotonically increased from 0.360 Wm^–1K^–1 to 1.415 Wm^–1K^–1 as the SiC whisker content increased from 0 to 100 wt% because of the easy heat conduction path provided by SiC whiskers with a high aspect ratio. The specific flow rate of 1200°C-sintered porous SiC ceramics increased by two orders of magnitude as the SiC whisker content increased from 0 to 100 wt%. These results were primarily attributed to an increase in pore size from 125 nm to 565 nm and secondarily an increase in porosity from 49.9% to 63.6%. In summary, the addition of 33 wt% SiC whisker increased the flexural strength, thermal conductivity, and specific flow rate of porous silica-bonded SiC ceramics by 35%, 133%, and 266%, respectively.     

Effect of tungsten carbide,silicon carbide and graphite particulates on the mechanical and microstructural characteristics of AA 5052 hybrid composites

Reinforced aluminium metal matrix composite materials are being used extensively in diverse fields that include aerospace and automobile. In this investigation, we introduce two distinct and novel types of aluminium hybrid composites and characterize their mechanical properties and microstructure. The first type was fabricated by reinforcing aluminium alloy (AA 5052) with tungsten carbide (WC) and graphite particulates and the second type was fabricated by reinforcing AA 5052 with silicon carbide (SiC) and graphite particulates. The composite material was processed through the melt-stir casting method and characterized by analyzing their densities, micro hardness, Charpy impact strength, tensile strength and peak elongation. Melt-stir casting method was chosen due to its cost effectiveness and productivity. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) studies were conducted to analyze thorough mixing of the reinforcements in the aluminium matrix metal. It was found that addition of tungsten carbide and graphite particulates with AA 5052 resulted in an increase in micro hardness and Charpy impact strength by 10.3% and 34.2% respectively, which are found to be better when compared to that of adding SiC and graphite particulates with AA 5052. Moreover, tensile tests revealed that there was a drop in tensile strength for the Al/SiC/graphite composites, while the peak elongation increases for both composites. On the other hand, while adding WC and graphite particulates the tensile strength of the composite improved by 15.12%. Also, the SEM fractographs taken for Al/SiC/graphite composite samples, subjected to Charpy impact and tensile tests revealed the presence of particle fractures and cracks and confirmed the possibility of plastic deformation. The results showed the Al/WC/graphite composites to be the superior among the two fabricated composites in terms of mechanical properties and therefore have good potential for structural applications.     

反应烧结碳化硅陶瓷的制备及烧结机理

用溶胶-凝胶法合成的无机／有机杂化材料结合SiC+C混合粉料制成了反应烧结碳化硅陶瓷素坯,并对由这种素坯制成的碳化硅陶瓷进行了物相鉴定和显微结构观察;借助Si-C相图对反应烧结碳化硅的烧结机理进行了研究,分析表明其主要烧结机理为溶解-再沉淀型。     

Microstructure and mechanical properties of silicon carbide processed by Spark Plasma Sintering (SPS)

The unique combination of SiC properties opens the ways for a wide range of SiC-based industrial applications. Dense silicon carbide bodies (3.18±0.01 g/cm³) were obtained by an SPS treatment at 2050 °C for 10 min using a heating rate of 400 °C/min, under an applied pressure of 69 MPa. The microstructure consists of fine, equiaxed grains with an average grain size of 1.29±0.65 μm. TEM analysis showed the presence of nano-size particles at the grain boundaries and at the triple-junctions, formed mainly from the impurities present in the starting silicon carbide powder. The HRTEM examination revealed high angle and clean grain boundaries. The measured static mechanical properties (H_V=32 GPa, E=440 GPa, σ_b=490 MPa and K_C 6.8 MPa m^0.5) and the Hugoniot Elastic Limit (HEL=18 GPa) are higher than those of hot-pressed silicon carbide samples.     

Synthesis and characterization of submicron silicon carbide powders with silicon and phenolic resin

A novel three-step process is used to fabricate submicron silicon carbide powders in this paper. The commercially available silicon powders and phenolic resin are used as raw materials. In the first step, precursor powders are produced by coating each silicon powder with phenolic resin shell. Then, precursor powders are converted into carbonized powders by decomposing the phenolic resin shell. The submicron silicon carbide powders are formed in the reaction of silicon with carbon during the third step of thermal treatment. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and thermogravimetric (TG) analyses are employed to characterize the microstructure, phase composition and free carbon content. It is found that the sintered powders consist of β-SiC with less than 0.2 wt.% of free carbon. The particle size of the obtained silicon carbide powders varies from 0.1 to 0.4 μm and the mean particle size is 0.2 μm. The silicon carbide formation mechanism of this method is based on the liquid-solid reaction between liquid silicon and carbon derived from phenolic resin. The heat generated during the reaction leads to great thermal stress in silicon carbide shell, which plays an important role in its fragmenting into submicron powders.     

Electrical,thermal, and mechanical properties of porous silicon carbide ceramics with a boron carbide additive

The effects of the boron carbide (B₄C) content and sintering atmosphere on the electrical, thermal, and mechanical properties of porous silicon carbide (SiC) ceramics were investigated in the porosity range of 58.3%–70.3%. The electrical resistivities of the nitrogen-sintered porous SiC ceramics (∼10^–1 Ω·cm) were two orders of magnitude lower than those of argon-sintered porous SiC ceramics (∼10¹ Ω·cm). Both the thermal conductivities (3.3–19.8 W·m^–1·K^–1) and flexural strengths (8.1–32.9 MPa) of the argon- and nitrogen-sintered porous SiC ceramics increased as the B₄C content increased, owing to the decreased porosity and increased necking area between SiC grains. The electrical resistivity of the porous SiC ceramics was primarily controlled by the sintering atmosphere owing to the N-doping from the nitrogen atmosphere, and secondarily by the B₄C content, owing to the B-doping from the B₄C. In contrast, the thermal conductivity and flexural strength were dependent on both the porosity and necking area, as influenced by both the sintering atmosphere and B₄C content. These results suggest that it is possible to decouple the electrical resistivity from the thermal conductivity by judicious selection of the B₄C content and sintering atmosphere.     

Influence of potassium titanate whisker on the mechanical properties and microstructure of calcium aluminate cement for in situ combustion

This study investigated potassium titanate whisker-reinforced calcium aluminate cement (CAC)-based composites, and evaluated the influence of the quantity (0–5% of the weight of the binder) of potassium titanate whiskers on the mechanical properties of hardened cement mortar. X-ray diffraction analysis and Scanning electron microscopy (SEM) were employed to determine the phase compositions and micro-morphology of the cement composites, respectively. Experimental results indicated that the addition of potassium titanate whisker exhibits significant potential to improve the tensile strength and toughness of cement mortars. The compressive and tensile strengths of samples cured at 50 °C were increased by 46.90 and 74.10%, and the tensile strength samples under high-temperature treatment increased by 113.67%, with the addition of 4% potassium titanate whisker. Typical cement slurry properties, such as basic rheology, free water, and fluid loss could maintain stability when added with 0–5% dosages of potassium titanate whiskers. SEM analysis indicated that the whisker could increase the toughness of oil cement, which contributed to whisker pullout and whisker-cement coalition pullout in the cement matrix.     

Synthesis of microcrystalline brownmillerite Ca2(Al,Fe)2O5 and its influence of mechanical properties to the class G oil-well cement

This study investigated the use of calcium oxide (CaO), aluminum oxide (Al₂O₃) and ferric oxide (Fe₂O₃) as raw materials for the production of brownmillerite Ca₂(Al,Fe)₂O₅, after firing at 1330, 1350 and 1370 °C. Lithofacies analysis, SEM/EDS and XRD were used to analyze the phase transition and microstructure of the clinkers during the firing process, and the contents of free calcium oxide (f-CaO) in the clinkers were determined by chemical titration. The results showed that the optimum temperature for the preparation of brownmillerite was 1370 °C (within the selected temperature range). By firing and quenching, microcrystalline brownmillerite (MB) was obtained (crystallinity index was 0.7). Compared with the compressive strength of class G oil-well cement matrix (M0) without MB, the compressive strength of specimens (M4) with 4 wt% MB addition increased by 67, 12, 20 and 33% (after curing for 1, 3, 7 and 14 d, respectively). meanwhile, the elastic modulus of M4 (after curing for 7 d) was reduced by 24% relative to that of M0, indicating that the mechanical properties of M4 were better than that of M0. To investigate the effect of microcrystalline brownmillerite on the strength and toughness of the class G oil-well cement matrix, triaxial testing was used in this study, and the toughening mechanisms were established.     

Influence of silicon carbide as a mineralizer on mechanical and thermal properties of silica-based ceramic cores

Ceramic cores have been designed with compounds based on fused silica due to its excellent thermal stability and chemical inertness against molten metals. To endure the high temperatures present during investment casting, mineralizers have been widely used to enhance the flexural strength and shrinkage of ceramic cores. In this study, we demonstrated a silica-based ceramic core with silicon carbide as a mineralizer for improving the mechanical and thermal properties. The SiC in the silica-based ceramic cores can enhance the mechanical properties (i.e., flexural strength and linear shrinkage) by playing a role as a seed for the crystallization of fused silica to cristobalite. The SiC also improves the thermal conductivity due to its higher value compared with fused silica. The results suggest that using the optimal amount of silicon carbide in silica-based ceramic cores can provide excellent mechanical properties of flexural strength and linear shrinkage and improved thermal conductivity.     

Study on the erosion mechanism of acid coal slag interactions with silicon carbide materials in the simulated atmosphere of a coal gasifier

In this paper, the dynamic erosion of silicon carbide interaction with acid coal slag was studied in an improved rotary drum furnace under the simulated conditions of a slagging gasifier at temperature of 1500 °C. Microstructures of corroded samples were observed by SEM, and the erosion mechanism was investigated by thermodynamic simulation based on SEM analysis. This revealed that SiC reacted with FeO to form a Si-Fe-C alloy on the sample surface, and the active oxidation of SiC was conducted in the experimental atmosphere. Furthermore, SiO₂(s), SiO(g), CO(g), and CO₂(g) were formed. Finally, SiO₂ dissolved in the molten slag, and SiO(g), CO(g), and CO₂(g) spread continuously. The pore structures on were altered by the oxidation reaction, which facilitated slag penetration into the samples through the pores to form a thin reaction layer.     

Polyamide 6 composites reinforced with silicon nitride whiskers: Synthesis,interface interaction,and mechanical properties

In this study, polyamide 6 (PA6)/silicon nitride whisker (SNW) composites were fabricated via in situ hydrolytic ring‐opening polymerization of ε‐caprolactam. By this novel method, SNWs can be dispersed uniformly in PA6 matrix. The interface interaction between SNW and PA6 was investigated, and the reinforcing efficiency of SNW on PA6 was evaluated. It was revealed by Fourier transform infrared spectroscopy that a large amount of polar groups, such as ? SiOH, ? NH, and ? NH₂, were present on the SNWs, by which hydrogen bonding and covalent bonding can be formed at interface. Mechanical test showed that at a loading of 5.0 wt % SNW, the tensile strength, tensile modulus, flexural strength, flexural modulus, and impact strength of PA6/SNW composite were 37.9, 80.5, 60.3, 73.9, and 64% higher than those of neat PA6, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The influence of grain geometry and wear conditions on the material removal mechanism in silicon carbide grinding with single grain

High efficiency and precision grinding of brittle materials is challenging due to material physical and chemical properties. To understand the effect of grain geometry and wear conditions on the material removal mechanism in brittle material precision grinding, a single diamond grain grinding experiment was conducted on Silicon Carbide (SiC). The cutting edge radius and deflection angle were measured by confocal scanning. Under six different cutting edge radius and three maximum undeformed chip thickness, grinding force and ground surface were measured. Diamond grain wear was investigated by observing the grain morphology, wear rate, grinding force, and ground surface change over accumulative material removal volume. The result showed the existence of a critical cutting edge radius for improving SiC ground surface quality.. Normal grinding force increased with the cutting edge radius increase. Tangential grinding force increased with the cutting edge radius increase and reached the peak value at the critical cutting edge radius. Flank wear was the major wear mode in precision SiC grinding. The grain wear was associated with the grinding force and ground surface.     

Comparison of two different carbon nanotubes-based hybrid multiscale composites with respect to mechanical and electrical properties

Pristine and carboxylic acid functionalised carbon nanotubes (CNTs-P and CNTs-COOH) hybrid composites based on ultrasonically processed nanocomposite epoxy matrix have been prepared. The thermodynamic interactions between CNTs and epoxy components are evaluated through solution experiment. The measurements of mechanical properties and volume electrical resistivity are performed to characterise the structure-property interplay of CNTs hybrid composites. A 0.3?wt-% CNTs-COOH loading significantly enhances the glass transition temperatures (Tg) of the resultant hybrid composites. The re-agglomeration of CNTs-P has been ascribed to the thermodynamic and kinetic factors, which determine the morphological characteristics of CNTs within the overall composites. CNTs-P network enables a continuous conductive path to be present in the composites at lower CNTs-P concentration. An analysis of the effects of the functionalisation of CNTs on the structure and properties of their hybrid composites has been carried out.     

掺入纳米SiO_2对水泥净浆流动性和力学性能的影响

掺入纳米SiO2,采用2种掺入方法和不同掺量,讨论了对水泥净浆的流动度和强度等性能的影响,得出最佳掺量和掺入方法。进一步探究掺入不同粒径的纳米SiO2对水泥净浆性能的影响规律。实验得出,采用将纳米SiO2与水泥先干混再拌合方法更利于拌合分散均匀,掺量越大流动度降低程度越大,而粒径越小流动度明显降低;纳米SiO2掺量的强度影响临界值为1.5%;各个粒径对早、中期强度均有明显增强,30nm的效果最明显。     

A novel gel-cast SiC with potential application in turbine hot section: Investigation of the rheological behavior and mechanical properties

Using a gel-cast technique, SiC bodies were fabricated and their mechanical properties were thoroughly studied. The main goal of this study is improvement of SiC green body features by the adjustment of slurry composition or processing parameters. The influences of gel-casting parameters such as the monomer acrylamide (AM) content, tetramethyl ammonium hydroxide (TMAH) content as a dispersant, the ratio of the monomer to crosslinking agent AM/MBAM content and the ammonium persulfate (APS) as an initiator on the properties of the samples were investigated. Based on the viscosity measurement and sedimentation tests, TMAH exhibited great electro-sterically stability at the pH of 10–11. After the gel-cast process, the relative density of sintered body can be enhanced to 93% and its flexural strength can reach 293 MPa at the optimized gel-casting process that has an AM content 15%, a TMAH content of 0.4 wt%, an AM:MBAM ratio of 17.5:1, an APS 10% and a solid content of 50 vol%, comparable to the best results reported in the other works for SiC bodies.     

矿物掺合料对磷酸镁水泥性能影响及机理研究现状

磷酸镁水泥(MPC),具有快硬、早强等优点,应用于道路抢修、重金属固化等领域,但其存在凝结时间过快、耐久性差等缺陷.通过矿物掺合料对MPC进行改性,延缓其凝结时间、改善其耐久性的同时,实现了工业废渣的循环再利用.本工作综述了粉煤灰、矿渣、偏高岭土、硅灰等矿物掺合料对MPC流动度、凝结时间、力学性能、耐久性的影响,并对矿...     

Preparation,mechanical properties,and toughening mechanisms of SiCw/SiCp-reinforced zirconia-toughened alumina ceramics

Zirconia-toughened alumina (ZTA) ceramics with high mechanical properties were sintered by hot-pressing method using SiC particles (SiCp) and SiC whiskers (SiCw) as the reinforcing agents simultaneously. The influences of sintering temperature, SiCp, and SiCw contents on the microstructure and mechanical properties of ZTA ceramics were investigated. It was found that both SiCp and SiCw could contribute to grain refinement significantly and promote the mechanical properties of the ceramics. However, the excess addition of SiCp or SiCw led to the formation of pores with large sizes and degraded the mechanical properties instead. When 13 wt% SiCp was introduced, the maximum flexural strength of 1180.0 MPa and fracture toughness of 15.9 MPa·m^1/2 were obtained, whereas the maximum flexural strength of 1314.0 MPa and fracture toughness of 14.7 MPa·m^1/2 were achieved at 20 wt% SiCw. Interestingly, the simultaneous addition of SiCp and SiCw could further improve the mechanical properties, and the highest flexural strength of 1334.0 MPa and fracture toughness of 16.0 MPa·m^1/2 were achieved at a SiCw/SiCp ratio of 16/4. The reinforcement mechanisms in the ceramics mainly included the phase transformation toughening of ZrO₂, the crack deflection and bridging of SiCp and SiCw, and the pull-out of SiCw.     

反式聚异戊二烯/纳米碳化硅形状记忆复合材料的制备与性能

以反式聚异戊二烯（TPI）为基质,研究了纳米碳化硅用量对碳化硅/TPI形状记忆复合材料硫化特性、物理机械性能、热性能及形状记忆性能的影响。结果表明,随着碳化硅用量的增加,复合材料的焦烧时间和正硫化时间都逐渐缩短;拉伸强度呈现先增大后减小的趋势,硬度逐渐增大;结晶度逐渐降低,从纯TPI的16.5%下降至碳化硅用量20份（质量,下同）时的13.9%;碳化硅用量为10份时复合材料的单向形状记忆性能最好,而其双向形状记忆行为在应力为250 kPa时的形状回复率达到了最大值79.1%。     

Effects of pressure on densification behaviour,microstructures and mechanical properties of boron carbide ceramics fabricated by hot pressing

Effects of pressure, from ordinary (30 MPa) to high pressure (110 MPa), on densification behaviour, microstructures and mechanical properties of boron carbide ceramics sintered by hot pressing are investigated. With increasing pressure, the relative density sharply increases within 30–75 MPa, slowly increases within 75–100 MPa and finally stagnates. For samples within 75–100 MPa, densification begins at approximately 1000 °C, and the dominant densification process ends before the soaking stage. High relative densities of 98.49% and 99.76% are achieved. For samples within 30–50 MPa, densification begins at approximately 1500 °C, and the soaking stage (initial 20 min) is still important for the dominant densification process. The final relative densities are only 87.90% and 92.32%. The above-mentioned differences are derived from contributions of pressure, and the dominant densification mechanism under high pressure is plastic deformation. The average grain size of the samples slightly increases with increasing soaking time. The grain size under higher pressure is larger than that under lower pressure at corresponding periods because grains grow easily with reduced pores. Vickers hardness and fracture toughness increase as grain size decreases in fully dense samples. However, when the samples do not achieve full density, relative density becomes more influential than grain size in hardness and toughness. A soaking time of 30 min is enough for samples under 100 MPa. Prolonging the soaking time has deleterious effects on mechanical properties. The relative density, grain size, hardness and fracture toughness of the samples under 100 MPa for 30 min are 99.73%, 1.96 µm, 37.85 GPa and 3.94 MPa m^1/2, respectively.