Refractory Properties Research Articles

Mechanical Characterization and Microstructural Analysis of Hybrid Composites (LM5/ZrO2/Gr)

Hybrid composites recently developed as highly effective, high-strength structural materials that are increasingly used. Aluminum matrix hybrid composites strengthened with ceramic particulates are commonly used in marine, aerospace, and defense applications because of their exceptional properties. Zirconia-reinforced composites are favored because these composites display high refractory properties, excellent abrasion resistance, and chemical resistance compared to composites of other reinforcements.For applications where lightweight and superior performance is paramount, such as parts for spacecraft, fighter aircraft, and racecars, graphite compositesare the material of choice. In this research work, an effort was made to combine the properties of zirconia and graphite by producing a unique metal matrix composite of LM5 aluminum alloy reinforced with 6% zirconium dioxide (zirconia), using the stir casting process by changing the percentage of the weight of graphite to 2%, 3%, and 4%. The test specimens were prepared and evaluated in compliance with ASTM standards to study micro- and macrohardness, and impact, tensile, and compressive strength. Microstructural studies of composites performed through optical microscopy and SEM expose the unvarying dispersal of particulates of ZrO2/graphite in the aluminum matrix. The hardness, impact, and compressive strength are enhanced due to the addition of reinforcement.

Trace Co coupled and tourmaline doped g-C3N4 for visible-light synergistic persulfate system for degradation of perfluorooctanoic acid

Removal of perfluorinated compounds (PFCs) from the environment is a major challenge due to their refractory, persistent and bioaccumulative properties. In this study, trace Co coupled via Co–P coordination and tourmaline (TM) doped g-C3N4 was fabricated (marked as Co/TM/g-C3N4) and used as the catalyst for activating peroxymonosulfate (PMS) to remove emerging PFOA under visible light irradiation. Several affecting parameters were systematically investigated, inlcuding Co/TM/g-C3N4 dosage, PMS concentration, initial pH, as well as coexisting Cl−, HCO3−, H2PO4−, NO3− and humic acid. Under the conditions of 0.5 g/L Co/TM/g-C3N4, 2.5 g/L PMS and pH 3.0, the developed synergistic system had the ability for 81.11% removal of PFOA within 4 h, 67.64% removal after the fourth run, and also could be effectively applied in actual water bodies. During the degradation process, π-π*, N–CN and graphite N played the vital role, with the final defluorination rate of 31.12% at 4 h. Free radical quenching and quantitative analysis, as well as electron paramagnetic resonance was used to verify the free radical and non-free radical pathways for PFOA removal, with the findings that SO4•− (2.61 μM at 1 h), •OH (0.067 μM at 4 h), O2•−, h+, and O12 were involved with possible time-dependent. By liquid chromatography-mass spectrometry analysis, the short-chain intermediates of C3–C7 were proposed and identified. From this study, trace Co coupled and TM doped g-C3N4 demonstrated higher catalytic potential to activate PMS for visible-light synergistic PFOA removal, with the expectation of achieving a cleaner water environment for human beings.

REFRACTORY PROPERTIES OF CONCRETE USING SINGLE MICRON FLY ASH AND GROUND GRANULATED BLAST FURNACE SLAG FINE POWDER

In Japan, high strength concrete over 100 N/mm2 is generally used for high-rise buildings. In order to achieve a high strength of 100 N/mm2 or more, silica fume is used as an admixture. However, concrete using silica fume, when a fire occurs, concrete explodes, and the fire resistance performance deteriorates. Therefore, fibers such as polypropylene is used to improve fire resistance. But, since silica fume and fiber are expensive in Japan, there is a problem that the cost of concrete becomes high. Therefore, the authors examined the possibility of giving high strength and fire resistance to concrete by adding fly ash or blast furnace slag those are ground to the single micron region. In this study, fly ash and blast furnace slag with different particle sizes of 50% cumulative volume passage diameter of about 1 ~ 3 μm were used. In the experiment, fresh properties, compressive strength, and fire resistance of concrete were evaluated comparing to those of concrete using silica fume. As a result, for single micron fly ash, the larger the particle size is used, the better the fire resistance. Concrete using blast furnace slag showed no explosion at all levels. From the above, it was found that high strength concrete with refractory properties can be realized by using single micron fly ash and blast furnace slag fine powder.

Preparation of high strength and low thermal conductivity mullite refractories based on reconstruction of fly ash

The preparation of refractories with both low thermal conductivity and high strength are continuously pursued in industrial furnaces. In this work, mullite refractories with low thermal conductivity and high strength were developed using fly ash as main raw material, and the influence of the quantity of fly ash and sintering temperature on the structure and properties of mullite refractories were investigated. The results show that mullite refractories with low thermal conductivity and high strength could be prepared by using fly ash in large proportion; the thermal conductivity of the samples decreased with the addition of the fly ash and increased with the increase of sintering temperature; the cold compressive strength and modulus of rupture of samples all are enhanced with the increase of sintering temperature, which is attributed to the formation of more elongated mullite by the reconstruction of fly ash at high temperature. For the mullite refractory using 65.04 wt% fly ash treated at 1600°C, the thermal conductivity was .732W/(m·k) at 1000°C, and the cold compressive strength and modulus of rupture could reach 143.5 ± 5.7 MPa and 47.0 ± 4.1 MPa respectively. It can be considered to use as a prospective work lining in industrial furnaces to meet energy saving requirements.

Investigative Study of Effects of Gallus domesticus guano, Cucumeropsis mannii shell and Elaeis guineensis shell Additives on the Refractory Properties of Isiagu Clay

This research investigated the effects of chicken dropping, melon shell and palm kernel additives on the refractory properties of Isiagu Clay. The raw materials were collected locally, processed and analysed using Scanning Electron Microscope/Energy Dispersive X-ray (SEM/EDX). The additives were added to the raw clay in the ratio of 2.5,5.0,7.5 and 10 wt% and fired at 900oC and 1100oC, respectively. The refractory properties measured were; linear shrinkage, apparent porosity and bulk density. The result of the SEM/EDX analyses showed that the clay is a fireclay since it contains 61.68% Al2O3 and 34.97% SiO2 while chicken dropping, melon shell, and palm kernel shell contained 37.41% SiO2, 84.62% P2O5, and 48.31% Nb2O5, respectively. Chicken dropping was responsible for strength, melon for toughness and palm kernel shell for conductivity. SEM/EDX morphological results showed that the clay sample contains tiny to coarse particles. The bulk density measurement confirmed the strength and toughness of melon shell, the only additive which met the international standard for refractory application. XRD analysis results showed the presence of two crystalline phases at 21.4o and 22.4o namely, quartz and calcite in the additives used which are both responsible for strength in the refractory brick. Sudden variation in properties was observed for chicken droppings due to the presence of a reasonable amount of P2O5. From the study, melon shell and palm kernel shell are suitable for refractory brick production and further studies are recommended for chicken dropping. ANOVA results confirmed that for melon shell and apparent porosity only temperature was significant.

REFRACTORY PROPERTIES OF CONCRETE USING SINGLE MICRON FLY ASH AND GROUND GRANULATED BLAST FURNACE SLAG FINE POWDER

In Japan, high strength concrete over 100 N/mm2 is generally used for high-rise buildings. In order to achieve a high strength of 100 N/mm2 or more, silica fume is used as an admixture. However, concrete using silica fume, when a fire occurs, concrete explodes, and the fire resistance performance deteriorates. Therefore, fibers such as polypropylene is used to improve fire resistance. But, since silica fume and fiber are expensive in Japan, there is a problem that the cost of concrete becomes high. Therefore, the authors examined the possibility of giving high strength and fire resistance to concrete by adding fly ash or blast furnace slag those are ground to the single micron region. In this study, fly ash and blast furnace slag with different particle sizes of 50% cumulative volume passage diameter of about 1 ~ 3 μm were used. In the experiment, fresh properties, compressive strength, and fire resistance of concrete were evaluated comparing to those of concrete using silica fume. As a result, for single micron fly ash, the larger the particle size is used, the better the fire resistance. Concrete using blast furnace slag showed no explosion at all levels. From the above, it was found that high strength concrete with refractory properties can be realized by using single micron fly ash and blast furnace slag fine powder.

Fly ash-based geopolymers with refractoriness properties

Fly ash-based geopolymers with refractoriness properties

Electrophysiological differences of deep sedation with dexmedetomidine versus propofol

Abstract Funding Acknowledgements Type of funding sources: None. Background Dexmedetomidine and propofol are commonly used drugs for deep sedation during cardiovascular interventions. Patients undergoing these interventions often have impaired sinus node function or atrioventricular (AV) conduction disease. Anesthetics used for deep sedation may further compromise sinus node function and AV nodal conduction, and thereby interfere with the intervention. Purpose To compare the electrophysiological effects of dexmedetomidine and propofol on the function of the sinus node and AV conduction. Methods We randomized patients undergoing first atrial fibrilation ablation 1:1 to deep sedation by dexmedetomidine (DEX group) versus propofol (PRO group), according to a standardized protocol. At the end of the ablation procedure with the patients still deeply sedated and hemodynamically stable, we conducted a standard electrophysiological study and assessed sinus node function, properties of AV conduction and atrial refractoriness. Results Of 160 patients (65±11 years old; 32% female) included into the study, 80 patients were randomized to the DEX and PRO group each. Procedure duration (128±59 minutes) and sedation depth, as assessed by the "Modified Observer’s Assessment of Alertness/Sedation" score (median 3; interquartile range 2, 3), was not different among groups. DEX group patients received a mean of 231±111 mcg of dexmedetomidine and PRO group patients a mean of 657±356 mg of propofol. The table shows the results of the electrophysiological study. DEX group patients had lower sinus rate and longer unadjusted sinus node recovery time (SNRT) at pacing cycle lengths of 600, 500 and 400 ms. However, both corrected (SNRT-RR) and normalized (SNRT/RR) SNRT did not differ among groups. Compared to PRO group patients, AV nodal conduction was slower in DEX group patients as evidenced by longer PR and AH intervals, and a higher Wenckebach cycle length and AV node effective refractory period (ERP) was observed. Conduction properties in the His-Purkinje system were not different among groups, as QRS width and HV interval were similar. An arrhythmia, mainly atrial fibrillation, was induced in 33 patients (21%) during the electrophysiological study, without differences among groups. Conclusions Sinus rate and AV conduction are slower during deep sedation with dexmedetomidine compared to propofol. These differences in electrophysiological effects need to be taken into account when using these anesthetics during cardiovascular interventions.

Short- and long-latency components of the eCAP reveal different refractory properties

BackgroundThe refractory recovery function (RRF) measures the electrically evoked compound action potential (eCAP) in response to a second pulse (probe) after masking by a first pulse (masker). This RRF is usually used to assess the refractory properties of the electrically stimulated auditory nerve (AN) by recording the eCAP amplitude as a function of the masker probe interval. Instead of assessing eCAP amplitudes only, recorded waveforms can also be described as a combination of a short-latency component (S-eCAP) and a long-latency component (L-eCAP). It has been suggested that these two components originate from two different AN fiber populations with differing refractory properties. The main objective of this study was to explore whether the refractory characteristics revealed by S-eCAP, L-eCAP, and the raw eCAP (R-eCAP) differ from each other. For clinical relevance, we compared these refractory properties between children and adults and examined whether they are related to cochlear implant (CI) outcomes. DesignIn this retrospective study, the raw RRF (R-RRF) was obtained from 121 Hi-Focus Mid-Scala or 1 J cochlear implant (Advanced Bionics, Valencia, CA) recipients. Each R-eCAP of the R-RRF was split into an S-eCAP and an L-eCAP using deconvolution to produce two new RRFs: S-RRF and L-RRF. The refractory properties were characterized by fitting an exponential decay function with three parameters: the absolute refractory period (T); the saturation level (A); and the speed of recovery from nerve refractoriness (τ), i.e., a measure of the relative refractory period. We compared the parameters of the R-RRF (RT, RA, Rτ) with those obtained from the S-RRF (ST, SA, Sτ) and L-RRF (LT, LA, Lτ) and investigated whether these parameters differed between children and adults. In addition, we examined the associations between these parameters and speech perception in adults with CI. Linear mixed modeling was used for the analyses. ResultsWe found that TR was significantly longer than ST and LT, and ST was significantly longer than LT. RA was significantly larger than SA and LA, and SA was significantly larger than LA. Also, Sτ was significantly longer in comparison to Rτ and Lτ, but no significant difference was found between Rτ and Lτ. Children presented a significantly larger SA and LA and a shorter RT in comparison to adults. Shorter Sτ was significantly associated with better speech perception in adult CI recipients, but other parameters were not. ConclusionWe demonstrated that the two components of the eCAP have different refractory properties and that these also differ from those of the R-eCAP. In comparison with the R-eCAP, the refractory properties derived from the S-eCAP and L-eCAP can reveal additional clinical implications in terms of the refractory difference between children and adults as well as speech performance after implantation. Thus, it is worthwhile considering the two components of the eCAP in the future when assessing the clinical value of the auditory refractory properties.

Image-processing-based automatic crack detection and classification for refractory evaluation

Crack generation and propagation in refractories is inevitable during their service life, which ultimately contributes to their failure. Accordingly, this study proposes a method that includes a watershed algorithm and classification criterion to quantitatively evaluate the fracture behavior in refractories. Additionally, to demonstrate the stability and reliability of the algorithm, its crack analysis results were compared with those of manual methods for alumina-magnesia ramming materials and corundum castables. The results indicated that the algorithm was capable of automatically identifying, extracting, and classifying cracks. Additionally, the type of crack propagation and its length and width were analyzed to determine the performance and properties of refractories. The proposed method was highly effective and accurate for the automated evaluation of material fracture behavior.

White Spot Lesions: A Serious but Often Ignored Complication of Orthodontic Treatment

Objective: The objective of this narrative review is to present an overview of the prevalence, clinical manifestation, diagnosis, and latest advances on white spot lesions. Background: White spot lesions have been defined as the earliest stage of demineralization on enamel surfaces that are easily discernible to the human eye. Methods: Relevant articles on white spot lesions were searched and reviewed from March 1975 till May 2021 in Pubmed, Scopus, Google Scholar, and ScienceDirect and were included in this review. Results: Even though the orthodontic field has seen several advances over the last few years, this is one complication that persists. White spot lesions are very commonly seen after completion of fixed orthodontic therapy when brackets are debonded. Previously conducted research has shown that there is a high prevalence rate of white spot lesions, which ranges from 50 to 90%. On intra-oral examination, a white spot can be seen as a matte-textured, opaque white lesion. Since the demineralization process takes place below the enamel surface, the outer layer only demonstrates pores that affect the natural light refractory properties of a tooth. This is what leads to the characteristic appearance of these lesions. One of the goals of modern dentistry is to treat non-cavitated lesions by promoting remineralization without the involvement of any invasive procedures. Conclusion: Fixed orthodontic therapy is usually a lengthy process and requires active cooperation between the orthodontist and the patient. However, it is the responsibility of the treating orthodontist to examine the tooth surfaces at each appointment to diagnose a developing white spot lesion as early as possible. With recent advances in diagnostic techniques, it has become much easier to identify these initial lesions and prevent their progression to cavitated lesions.

Thermo-mechanical finite element analysis of a fused cast AZS block applied to a glass melting furnace during the heating step

There is a great motivation to understand the best-operating practices for glass melting furnaces to improve their quality, increase the process energy efficiency and extend the working life of the refractory. Electrofused AZS (Alumina-Zirconia-Silica) refractories are used for furnace linings due to their good corrosion resistance and mechanical properties at high temperatures. Operating conditions can influence their performance, limiting the service life of the furnace. Computer simulations have proven to be useful for analyses wherein testing is difficult and involves certain risks for experiments and validations. Therefore, this work investigates the thermal and mechanical behavior of AZS blocks with a metal electrode support, which present cracks along the furnace heating-up. The simulations were carried out using the finite element method (FEM) to determine the AZS block temperature and maximum principal stress fields during furnace heating. Considering the refractory properties with the temperature, the results showed that the maximum principal stress reaches the modulus of rupture of AZS, after 42 h when the block hot face temperature is 145 °C. Analyses of the effects of a cooling system, heating curve and alternative hole designs to support the electrodes are also shown. In the case of cooling, there are no positive effects from the refractory behavior point of view, reaching the maximum allowable stress value after 40 h for the best scenario. Regarding the heating curves, the thermal and mechanical profiles and the location at it reaches the maximum principal stress were equivalent to that of the reference. Finally, changing the hole geometry showed that the crack initiation time was slightly longer than the reference, 43 and 44 h for the conical and single diameter holes, respectively. The critical region was observed closer to the hot face for the conical case, which can be interesting for further analysis to consider some post-cracking effects.

Optical Properties and Optimization of LaB6 Thin Films for Photothermal Applications

AbstractThe growth of highly crystalline LaB6 films with an excellent optical response and low loss is reported, which will be useful for high‐performance photothermal device applications when combined with their inherent refractory properties. Optimum growth parameters for realizing uniaxial and coherent LaB6 thin films, exhibiting an excellent plasmonic response for near‐ to mid‐infrared device applications, are established. Numerical electromagnetic simulations of the epitaxial LaB6 nanostructures revealed that the electromagnetic field at the LaB6 surface can be as high as that of the Au nanostructures. Furthermore, the LaB6 nanostructures show resonance in the visible (red) to mid‐infrared region comparable to those of Au with the added advantage of improved temperature stability that can withstand harsh photothermal device operations.

Effects of firing temperature and Al additive on the microstructures and properties of SiC-CA6 composite refractories

SiC-CA6 composite refractories were successfully prepared by using SiC aggregates, sintered CA6 powders, Al powders and calcined α-Al2O3 as the raw materials. The effects of the firing temperature and Al additive on the physical and mechanical properties, phase evolution and microstructures were studied. The Al additive can significantly affect the properties of the SiC-CA6 composite refractories. With the addition of metallic Al, whiskers with interlocking structures could form in the SiC-CA6 composite refractories during the firing process, which improved the properties of the materials. The SiC-CA6 composites fired at 1450 °C with Al additive had good comprehensive properties with low porosity (14.7%), high strength (15.78 MPa for CMOR and 13.98 MPa for HMOR) and high elastic modulus (54.21 GPa). Compared with the samples without the Al additive, the samples with the Al additive had a lower porosity, and higher density and strength at all firing temperatures. For the samples without Al addition, the decomposition of the phenolic resin could form residual carbon remaining in the samples, which could decrease the oxidation of the SiC in the materials and inhibit the sintering of the samples. With increasing firing temperature, the residual carbon decreased and gradually transformed from a flaky morphology to an amorphous morphology.

Hematite Nanoparticles Addition to Serpentine/Pyroxenes By-Products of Magnesite Mining Enrichment Process for the Production of Refractories

The present study focuses on the refractory upgrade and reuse of the mining wastes/by-products of the magnesite mine “Grecian Magnesite SA” (Chalkidiki, N. Greece), by the addition of hematite (α-Fe2O3) nanomaterial. These by-products were also examined after the application of thermal pre-treatment, i.e., treated at 850 °C for 30 min, prior to sintering. Different thermal treatments and times were applied, aiming to induce the formation of forsterite and attempting to examine the respective effects on the refractory properties of up-cycled products. The results indicate that hematite addition of 5 wt.% can improve the major refractory parameters of products, whereas the applied thermal pre-treatment was not found to be particularly beneficial. Nevertheless, the optimum results were realized after thermal treatment at 1300 °C for 120 min heating time, also revealing that the initial mineralogical content of the examined mineral wastes is a key factor for the subsequent upgrade ranking of the final product.

Effect of CaCO3 addition on the performance of lightweight Al2O3‐MgAl2O4 refractories with gradient density

AbstractIn this study, to improve the comprehensive performance of lightweight Al2O3‐MgAl2O4 refractories with gradient density, CaCO3 was added in the matrix to develop platelet structures by adding different amounts (1, 2, 3, and 4 wt%). The effect of CaCO3 addition on the phase composition, microstructure, and properties of lightweight refractories was investigated. The results showed that CaO·6Al2O3 and Ca2Mg2Al28O46 formed. Meanwhile, platelet structure is distributed at the junction between aggregate and matrix. With the increase of CaCO3 content, although there were no apparent changes in apparent porosity and bulk density, both the compressive strength and refractoriness under load improved significantly. Furthermore, the results of three‐point bending tests showed thermal shock resistance was improved in terms of the value of residual strength ratio from 14.2% to 22.5% for specimens before and after 4 wt% CaCO3 addition. The findings showed that the introduction of CaCO3 is feasible and effective for performance improvements of lightweight refractories.

Effect of selected organic additives on the properties of magnesia-chromite refractories

An attempt was made to adjust the kind of organic additives to the components of the mass for the magnesia-chromite products. This was done using Sanderson’s concept of electronegativity and molar electronegativity. Four organic additives were selected and their influence on the properties of the refractories was studied by performing a total factorial experiment 24. The basic properties of the refractories are presented in the form of seven response functions, six of which are described by statistically verified equations. The most favourable options were selected on the basis of six criteria that characterise the materials. The introduction of organic additives as slip agents into the mass, resulted in an improvement in practically all properties of the magnesia-chromite materials after firing. The purposefulness of the additive composition was demonstrated.

Influence of powder characteristics on the sintering behaviour of reactive alumina powders

Fine reactive alumina powders have a significant impact on the properties of refractories at high temperatures. Except for the hydration of cement and in situ reactions, the performance of castables is also correlated with the sintering of reactive alumina. The characteristics of fine alumina powders produced by various manufacturers are quite different. This work aims to investigate the comprehensive influence of powder characteristics on the sintering behaviour of reactive alumina powders. Three types of commercial reactive alumina powders were selected for experiments. The linear shrinkage, bulk density, apparent porosity and microstructure of alumina compacts calcined at different temperatures were analysed. It was demonstrated that large specific surface area and higher SiO2 content had a positive effect on the densification of alumina compacts. The calculation based on the hypothetical composition of alumina grain boundary indicated that SiO2 mainly participated in the formation of liquid. Therefore, more liquid was generated at the grain boundary of alumina grains containing higher SiO2 content, which resulted in better sinterability of reactive alumina powders.

Effect of selected organic additives on the properties of magnesia-chromite refractories

The addition of carbon nanomaterials influences the variety of properties, of cementitious composites. Despite the multiple researches in the topic of properties of the hardened cement materials the influence of the Mutiwall Carbon Nanotubes [MWCNT] on rheological parameters of the cement mortars is not sufficiently described. Research shows that rheological properties of cement mortars with the MWCNTs, determined with the use of Viscometer NT, proved to be strongly dependent on the sonication time and amount of MWCNT, added. Increase of sonication time of MWCNT suspension with surfactant and decrease of amount of MWCNT caused increment in fluidity while yield stress parameter and plastic viscosity parameter decreased.

Ceramic foam filters for filtration refining of ferrous metals

Literature review of refractories used for the production of ceramic foam filters is carried out, on the basis of which ceramic foam filters are made from combination of three different compositions of refractory suspensions, the physical and mechanical properties of the obtained filters are studied. It is found that filters with the composition 85 % Al2O3 + 15 % ТiO2 and 85 % Al2O3 + 15 % ZrO2•SiO2 have higher strength properties in comparison with other samples.