Effect of a MgO–CaO–ZrO2-based refractory on the cleanliness of a K4169 Ni-based superalloy

Laboratory experiments were carried out to study the effect of a MgO–CaO–ZrO₂-based refractory (MCZ refractory) on the cleanliness of a K4169 Ni-based superalloy. The chemical composition and characteristics of the refractory, alloy, and inclusions were analysed by X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS). Characterisation results indicated that the CaZrO₃ phase was stable, the amount of the spinel phase increased whereas that of the MgO phase decreased, and Ca₂Al₂SiO₇ and Ca₂SiO₄ transformed into Ca₃Ti₈Al₁₂O₃₇ and CaSiO₃, respectively, in the refractory during the melting of the Ni-based superalloy. In addition, a new phase of Mg₈Cr₁₆O₃₂ was simultaneously formed. The MCZ refractory penetrated the liquid alloy and reacted with it, which increased the Mg and Ca contents of the alloy. The erosion depth of the refractory in the alloy was more than 20 μm after melting for 100 min. Inclusions composed of MgO–Al₂O₃-Ti_xO_y wrapped with TiN were observed in the alloy after melting in the MCZ refractory. The inclusions were large, numerous, and distributed inhomogeneously in the alloy near the side and bottom of the refractory. The chemical reactions among the refractory, liquid alloy, and inclusions were analysed, and FactSage software was used to investigate these interactions. The effect of the dissolution of the MCZ refractory on the composition and transformation of the liquid alloy and inclusion was estimated. The thermodynamic results agreed well with the experimental results.     

Effects of WC particles on microstructure and mechanical properties of 316L steel obtained by laser melting deposition

Stainless steel has many excellent characteristics such as high strength, weldability, corrosion resistance, easy processing and surface gloss. It has been widely applied in many industrial and architectural decoration aspects such as aerospace, chemical, and automotive. However, 316L material manufactured by Laser melting deposition has poor wear resistance and tensile strength. In this paper, WC particles are used as a strengthening phase to make up for these deficiencies of 316L. In order to comprehensively evaluate the effect of WC particles on the mechanical properties of 316L formed by laser melting deposition, 316L samples with different proportions of WC particles and different fabricating directions were prepared. The microstructure of samples was observed, and the phase composition, Vickers hardness, friction and wear properties, tensile properties were analyzed. The mechanism of the influence of WC particles on the structure and the mechanism of friction, wear and tensile fracture were studied. The results show that most of the WC particles are evenly distributed in the coating. The microhardness and wear resistance of the 316L/WC composite coating have been significantly improved with the increase in the proportion of WC. The tensile strength and elongation are the best when the WC mass fraction is 6%.     

Influence of pyrolysis and melt infiltration temperatures on the mechanical properties of SiCf/SiC composites

In order to improve the degree of matrix densification of SiC_f/SiC composites based on liquid silicon infiltration (LSI) process, the microstructure and mechanical properties of composites according to various pyrolysis temperatures and melt infiltration temperatures were investigated.Comparing the microstructures of SiC_f/C carbon preform by a one-step pyrolysis process at 600 °C and two-step pyrolysis process at 600 and 1600 °C, the width of the crack and microcrack formation between the fibers and matrix in the fiber bundle increased during the two-step pyrolysis process. For each pyrolysis process, the density, porosity, and flexural strength of the SiC_f/SiC composites manufactured by the LSI process at 1450–1550 °C were measured to evaluate the degree of matrix densification and mechanical properties. As a result, the SiC_f/SiC composite that was fabricated by the two-step pyrolysis process and LSI process showed an 18% increase in density, 16%p decrease in porosity, and 150% increase in flexural strength on average compared to the composite fabricated by the one-step pyrolysis process.In addition, among the SiC_f/SiC specimens fabricated by the LSI process after the same two-step pyrolysis process, the specimen that underwent the LSI process at 1500 °C showed 30% higher flexural strength on average than those at 1450 or 1550 °C. Furthermore, under the same pyrolysis temperature, the mechanical strength of SiC_f/SiC specimens in which the LSI process was performed at 1500 °C was higher than that of the 1550 °C although both porosity and density were almost similar. This is because the mechanical properties of the Tyranno-S grade SiC fibers degraded rapidly with increasing LSI process temperature.     

Influence of solution composition on sprayed ZnO nanorods properties and formation process: Thermoanalytical study of the precursors

ZnO is an important inorganic material for numerous applications. Different physical and chemical methods have been applied to deposit ZnO. Spray pyrolysis method being simple, rapid and low-cost is amongst the many options and has been chosen for this study. Fabrication of ZnO nanorods crystals by chemical spray pyrolysis was performed using an acidic solution of ZnCl₂1 or a basic ammonia-containing solution of ZnCl₂2. All layers were studied using X-ray diffractometry and Scanning Electron Microscopy. The formation of ZnO nanorods from 2 appeared at 450?°C, whereas spraying acidic solution 1 yielded ZnO nanorods like morphology at 550?°C.Thermal decomposition of precursors for ZnO layers prepared by de-watering of acidic aqueous solution of ZnCl₂ with pH =?3 (1) and basic solution of ZnCl₂ and NH₄OH with pH =?10 (2) was monitored by simultaneous thermogravimetric and differential thermal analysis (TG/DTA) in air coupled online with evolved gas analyses by Fourier transformed infrared spectroscopy (FTIR).The precursor (1) is ZnCl₂ *nH₂O; the precursor (2) is a mixture of (NH₄)₃(ZnCl₄)Cl, Zn(NH₃)₂Cl₂, NH₄Cl(NH₃)₃ and Zn(OH)₂ phases. The thermal decomposition of (1) and (2) in the temperature range of 30–700?°C consists of two steps with total mass losses of 86.2% and 93.8%, respectively. The main evolved gases from (1) are H₂O and HCl, whereas the main evolved gases from (2) are H₂O, NO_x and NH₃. Degradation of (1) and (2) is completed by 670 and 620?°C, respectively. The final decomposition product of (1) and (2) at 700?°C is ZnO.This study shows that the use of basic solutions enables to decrease the temperature of ZnO formation and the deposition temperature of ZnO nanorods layers.     

Influence of gypsum additive on the gyrolite formation process

The influence of gypsum additive on the gyrolite formation process and a sequence of intermediary compounds formation in the CaO-SiO₂·nH₂O-H₂O system was examined and explained. The synthesis has been carried out in unstirred suspensions. The molar ratios of primary mixtures were CaO/SiO₂ = 0.66. The amount of sulphate ions to be added to a raw mixture was 1-10%. The duration of isothermal curing at 200 °C was 4, 8, 16 and 72 h.It was determined that the quantity of sulphur which penetrates into the crystalline structure of gyrolite depends not only on the synthesis conditions but also on the composition of initial mixture. A larger amount of sulphate ions stimulate the formation not only of gyrolite, but also of CaSO₄. Gypsum additive has no influence on the re-crystallization temperature of C-S-H(I), Z-phase and gyrolite into wollastonite. The composition of initial mixtures is recommended to calculate according to molar ratios. In other cases, upon increasing the amount of sulphate ions, the basicity of the mixture decreases and gyrolite forms more difficult.     

Phase and porosity changes in a calcium aluminate cement and alumina system under hydrothermal conditions

When refractory castables are dried, hydrothermal conditions may result inside the bodies if the H₂O cannot escape from the material. Under such high-pressure conditions, problems such as explosive spalling can arise. As different curing temperatures during the hydration of calcium aluminate cement (CAC)-bound castables lead to the formation of different hydrate phases, different microstructures can develop in the hardened material. This study presents the changes in porosity and in the mineralogical composition of a refractory castable model system under hydrothermal conditions depending on the curing temperature (5, 23 and 40 °C).Quantitative X-ray diffraction (QXRD) measurements show that different hydrate phases are formed during curing, while C₃AH₆ and boehmite are formed in the same quantities after hydrothermal treatment in an autoclave at ～11 bar/180 °C. Although the mineralogical composition after autoclaving is not different, the three samples differ in their microstructure. Mercury intrusion porosimetry measurements reveal that although the total porosity after autoclaving is the same, the 40 °C samples have a higher proportion of large pores. SEM images also show that the appearance of C₃AH₆ in the 40 °C autoclaved samples varies, which originates from the starting phase composition and microstructure after curing.     

Surface modification of SiC to improve joint strength via a Corona plasma treatment

The high mechanical and chemical properties of SiC make it difficult to texture and modify its surface using such conventional methods as mechanical machining and wet etching. Among possible alternative strategies, Atmospheric Pressure Plasmas (APPs) could be used, cutting cost and time, but much still has to be understood about their feasibility for the surface treatment of ceramic materials.In this work, the effectiveness of a commercial corona discharge system in modifying the surface of SiC has been evaluated, focusing on its positive effect on the joint strength of adhesively bonded plasma-treated SiC.The objective of the study has been to observe the surface changes, in terms of chemical composition and texture, that take place as a result of exposure to corona plasma and to compare the obtained results with previous studies on laser and low-pressure plasma textured SiC samples. These very first results, derived from characterization and mechanical testing, suggest that this approach could be a promising alternative.     

Influence of different bonding and fluxing agents on the sintering behavior and dielectric properties of steatite ceramic materials

The focus of the study was on providing insights into interconnections between sintering and development of the crystalline microstructure, and consequently variations in dielectric behavior of four steatites fabricated from a low-cost raw material, i.e. talc. The changes, induced by the alternations of the binders (bentonite, kaolin clay) and fluxing agents (BaCO₃, feldspar), were monitored in the temperature range 1000° to 1250 °C in which complete densification and re-crystallization of the investigated structures were accomplished. The critical points in the synthesis of steatite materials were assessed by instrumental analyses. Crystallinity changes and mineral phase transition during sintering were monitored by X-ray diffraction technique. Microstructural visualization of the samples and the spatial arrangements of individual chemical elements were achieved via scanning electron microscopy accompanied with EDS mapping. The thermal stability was observed on the green mixtures using differential thermal and thermo gravimetric analyses. Electrical measurements recorded variations of the dielectric constant (ε_r) and loss tangent (tan δ) as a function of the sintering temperature. The investigation highlighted critical design points, as well as the optimal combinations of the raw materials for production of the steatite ceramics for advanced electrical engineering applications.     

Effect of the fabrication process on the microstructural evolution of carbon fibers and flexural property on C/SiC composites by the NITE method

Nano-infiltration and transient eutectic phase (NITE) SiC matrix composites are designed for application in aerospace propulsion systems, particularly in fasteners and thrusters. A variety of carbon fibers with different properties have been selected as reinforcements for SiC matrix composites. Carbon fibers are known to be stable at high temperatures; however, the effects of high applied pressure at high temperatures on the fiber microstructure evolution and mechanical properties are not well-known. As a scoping study for fabricating NITE C/SiC composites, the behaviors of various carbon fibers in SiC composites. Pitch-based fibers, namely, GRANOX XN-05 and YS-90A, and a polyacrylonitrile-based fiber, namely, TORAYCA T-300B, were selected for matrix reinforcement. The 3-point bending test results indicated pseudo-ductile behaviors in the cases of YS-90A and T-300B fiber reinforcements. Fracture resistance evaluation based on the single-notch bending test indicated that the YS-90A fiber reinforced composite afforded the highest fracture resistance among the three C/SiC composites. The microstructure evolution on YS-90A and T-300B fibers was limited to near the fiber surface. Therefore, YS-90A and T-300B carbon fibers are potential candidates for reinforcement in NITE C/SiC composites.     

Sintering of anorthite ceramic body based on interstratified illite-smectite clay

The effects of the different properties of plastic raw materials for whitewares based on different clay minerals (kaolinite vs interstratified illite/smectite [I/S]) on the sintering process (according to vacuum water absorption) was studied for anorthite porcelain body creation after firing in the range of 950–1500 °C to achieve optimal sintering temperature. The mineralogical composition of the fired bodies was observed from the firing temperature of 950 °C to the sintering temperature. Calcium carbonate decreases the sintering temperature and creates a new mineralogical phase in the fired body – anorthite – which decreases the linear thermal expansion coefficient and increases the strength (modulus of rupture) of the sintered bodies. All the described effects take place at lower firing temperatures when the I/S plastic raw material is compared with kaolin.     

Influence of the C/S and C/A ratios of hydration products on the chloride ion binding capacity of lime-SF and lime-MK mixtures

The mechanisms of chloride ion binding in cementitious systems when supplementary cementing materials are present are not completely understood, although it is believed to relate to the alumina content of the mixture. This relationship is investigated through the use of lime-silica fume and lime-metakaolin mixtures. It was found that while the alumina content does have an important influence, the chloride binding capacity was also controlled by the calcium-to-alumina and calcium-to-silica ratios. At a high C/A ratio, the formation of monocarboaluminate is favoured, which has a high ability to form Friedel's salt, and does so at low chloride concentrations (less than 0.1 M). With a low C/A ratio, the formation of stratlingite is favoured, with little formation of monocarboaluminate. If alumina is not present, chloride is bound by the C-S-H phase. The binding capacity of the C-S-H was found to depend on its calcium-to-silica ratio, C-S-H with a higher C/S having a greater binding capacity.     

An estimate of quartz content and particle size in porcelain tiles from young's modulus measurements

The influence of quartz particle size, weight content and firing temperature on the Young's modulus of porcelain tiles was studied. To simulate a porcelain tile microstructure, an albite glass matrix with added crystalline quartz particles was developed. Average particle size of quartz (3.4 and 31 µm) and volume content (18.5 and 37.6 vol%) were varied. An acoustic impulse excitation technique was used to measure the elastic modulus from room temperature up to 700 °C. Results showed that quartz has a major influence on the elastic modulus of porcelain tiles. At temperatures below 573 °C, a hysteresis area between the Young's modulus curves during heating and cooling was closely related to quartz particle size. Between 573 and 700 °C, the variation of the Young's modulus was related to the quartz volume fraction. By using those correlations, a prediction of quartz content and quartz particle size in commercial porcelain materials can be carried out from Young´s modulus data.     

Effects of calcination condition on expansion property of MgO-type expansive agent used in cement-based materials

Previous research indicated that the expansion property of MgO-type expansive agent (MEA) depended strongly on the calcining conditions, i.e. kiln temperature and residence time. However, the intrinsic effect of calcination condition on the expansion property of MEA has not been clearly demonstrated. In the present work, the effects of calcination condition on the microstructure, hydration activity, and expansion property of MEA have been investigated, and their correlations are also studied. Results indicate that the microstructure of MEA is the intrinsic factor that controlling its expansion property, which is influenced by the calcination condition. MEA produced under higher temperature and longer residence time has less interior pores, larger crystal size of MgO, and smaller specific surface area, thus resulting in lower hydration activity and slower expansion at early age, but larger “ultimate” expansion at late age. While, a new expansion model of MEA is proposed to explain these results.     

Concrete cover cracking with reinforcement corrosion of RC beam during chloride-induced corrosion process

This paper deals with the evolution of the corrosion pattern based on two beams corroded by 14 years (beam B1CL1) and 23 years (beam B2CL1) of conservation in a chloride environment. The experimental results indicate that, at the cracking initiation stage and the first stage of cracking propagation, localized corrosion due to chloride ingress is the predominant corrosion pattern and pitting corrosion is the main factor that influences the cracking process. As corrosion cracking increases, general corrosion develops rapidly and gradually becomes predominant in the second stage of cracking propagation. A comparison between existing models and experimental results illustrates that, although Vidal et al.'s model can better predict the reinforcement corrosion of beam B1CL1 under localized corrosion, it cannot predict the corrosion of beam B2CL1 under general corrosion. Also, Rodriguez's model, derived from the general corrosion due to electrically accelerated corrosion experiments, cannot match natural chloride corrosion irrespective of whether corrosion is localized or general. Thus, for natural general corrosion in the second stage of cracking propagation, a new model based on the parameter of average steel cross-section loss is put forward to predict steel corrosion from corrosion cracking.     

Application of [001]-textured (K,Na)(Nb,Sb)O3-CaZrO3 thick films to piezoelectric energy harvesters

A (K, Na)NbO₃ (KNN)-based lead-free piezoceramic for a piezoelectric energy harvester (PEH) should exhibit a large k_ij, Q_m, d_ij, and a small ε^T₃₃ to generate a large power output. Texturing was used to enhance the piezoelectricity of KNN-related piezoceramics. In particular, the k_ij and d_ij values of the KNN-based piezoceramics were considerably improved after texturing along the [001] direction, with a small change in the ε^T₃₃/ε₀ value, indicating that the [001]-textured KNN-based thick films are good candidates for use in PEHs. The 0.97(K_0.5Na_0.5)(Nb_0.93Sb_0.07)O₃-0.03CaZrO₃ [KN(N_0.93S_0.07)-CZ] thick film was textured along the [001] direction, and this thick film exhibited a large k_p (0.57) and d₃₃ × g₃₃ (25.7 pm²/N), which is the largest d₃₃ × g₃₃ of the KNN-based piezoceramics reported to date. A cantilever PEH fabricated using the textured KN(N_0.93S_0.07)-CZ thick film exhibited a power density of 21.4 μW/mm³ at the resonance frequency. This is the highest power density observed for PEHs fabricated using lead-free piezoceramics. The PEH also exhibited a power density of 0.023 μW/mm³ at the off-resonance frequency. Therefore, the textured KN(N_0.93S_0.07)–CZ thick film is a good candidate for use in PEHs.     

Influence of ionic liquid on the photoelectrochemical properties of ZnO particles

ZnO particles synthesized by the microwave-assisted hydrothermal method were sensitized with different amounts of ionic liquid (IL) 1.3-dimethylimidazolium iodide (MMI.I). The structure of the modified and unmodified ZnO particles were characterized by X-ray diffraction, Raman spectroscopy, field emission gun-scanning electron microscopy (FEG-SEM), ultraviolet-visible (UV–vis) absorption spectroscopy, photoluminescence (PL), and photoelectrochemical measurements. While the sensitization of ZnO particles by the ionic liquid does not change the ZnO phase, it reduces the particle size and converts shallow defects to deep defects. These changes cause the photocurrent density of the ZnO/IL films to increase significantly from 0.05?mA?cm^?2 for pure ZnO to 0.52 and 1.24?mA?cm^?2 for the ZnO films containing 20% and 35% by mass of the IL, respectively, at 1.08?V vs. Ag/AgCl. This about 24-fold increase in the photocurrent density of the ZnO/IL35 sample may indicate that the MMI.I IL may be acting as a dye, since it is constituted by an organic part, MMI⁺. This good performance presented by this sample indicates that this is a promising material for photoanode in solar cells.     

Evolution of strength, microstructure and mineralogical composition of a CKD–GGBFS binder

Characterization of a nontraditional binding material containing cement kiln dust (CKD) and ground granulated blast furnace slag (GGBFS) is discussed in this paper. Significant compressive strength was obtained for a CKD–GGBFS blend with 70% CKD and 30% GGBFS at a water-to-binder ratio of 0.40 after 2 days of curing at elevated temperature. Similar strength was also obtained for the samples subjected to normal moisture curing over a period of 28 days. The compressive strength increased with additional moist curing in both the cases. The microstructural and the mineralogical examinations show that the strength development was mainly due to the formation of calcium silicate hydrate (C-S-H). In addition to normal C-S-H, aluminum and magnesium incorporated C-S-H phases were also present in the CKD–GGBFS blends. The formation of ettringite appears to be a contributing factor in early age strength development of CKD–GGBFS binder.     

Pyrophosphate ions inhibit calcium phosphate cement reaction and enable storage of premixed pastes with a controlled activation by orthophosphate addition

The standard preparation routine of a calcium phosphate cement includes mixing a solid and a liquid component (reactive cement powder and mixing liquid) in an open bowl at the operating theatre. This poses the risk of preparation-related deviations of the resulting properties when the cements are mixed by different persons. Hence, facilitating this mixing procedure is highly desirable. It can be achieved by application of premixed cement pastes: The mixing liquid and a stable suspension of the cement powder are assembled and mixed in a special syringe, minimizing the impact of these preparation-related effects.In this study, a suspension of reactive α-tricalcium phosphate powder in water was stabilized by sodium pyrophosphate decahydrate (PP). Controlled activation of these premixed pastes was then accomplished by adding a concentrated Na₂HPO₄/NaH₂PO₄ (Na₂/Na) solution. Systematic assessment of the activation mechanism, including the effect of the PP concentration and the amount of Na₂/Na added, was performed by isothermal calorimetry, quantitative in-situ X-ray diffraction, rheological characterization and automated Gillmore needle measurements at 37 °C.Premixed pastes with addition of at least 0.05 wt% PP were successfully stabilized for up to 2 weeks at 25 °C, and even 4 weeks at 4 °C. This pre-storage had no significant impact on the setting performance of the pastes. Increasing the PP concentration at constant Na₂/Na amount systematically retarded the setting reaction, while an elevated quantity of Na₂/Na addition at constant PP concentration resulted in an acceleration.Based on these results, a composition stabilized with 0.05 wt% PP and activated with 20.8 vol% Na₂/Na related to the amount of liquid in the premixed pastes appears ideal with respect to the desired setting performance.     

Effects of mechanical-activation and TiO2 addition on the behavior of two-step sintered steatite ceramics

Steatite, as ceramic with composition predominantly resting on magnesium silicate, was produced from economic resources – talc, aluminosilicate clays, and either BaCO₃ or feldspar as flux. Titanium dioxide was a doping agent. Four steatite mixtures were mechanically activated in a planetary ball mill for 30, 45 or 60?min, prior to the thermal treatment. Two-step sintering with initial phase set at 1350?°C and holding period conducted at 1250?°C was applied to initiate diffusion and prevent grain growth. Thereby, a high density ceramic material with low-porous submicron structure was acquired. The effects of TiO₂ addition on densification, microstructure, and dielectric characteristics of steatites were monitored. The thermal stability of green mixtures was tested by differential thermal and thermogravimetric analyses. Changes in crystallinity and mineral phase composition were observed by the X-ray diffraction technique. Microstructural visualization with spatial arrangements of individual chemical elements on surface of the sintered ceramics was acquired by scanning electron microscopy accompanied with EDS mapping. In order to test the possibility of employment of the obtained steatites in insulation materials, electrical measurements were conducted by recording variations of the dielectric constant and loss tangent as a function of alternations in the mix-design and the mechanical activation period.     

A two dimensional infrared correlation spectroscopic study on the structure changes of PVDF during the melting process

Two-dimensional infrared (2D IR) correlation spectroscopy was applied to study the conformation change during poly(vinylidene fluoride) (PVDF) melting process. The absorption spectral changes are observed with increasing temperature. These observed changes in IR spectra might be attributed to three kinds of PVDF components: α-PVDF, β-PVDF, and amorphous component. 2D IR correlation analysis indicates that during melting process three kinds of PVDF component change asynchronously: above all, the amorphous component relaxes its molecule chains, and then the β-PVDF transfers to amorphous component, finally the α-PVDF transfers to amorphous component.