International Journal of Ceramic Engineering & Science最新文献

Silicon carbide foams with an average pore diameter of 650 nm and an inter-pore ligament thickness of 150 nm have been synthesized using spherical polymethylmethacrylate (PMMA) particle templating of a β-SiC nanoparticle-loaded polycarbosilane (PCS) preceramic polymer and the effect of crystallization temperature upon their microstructure and mechanical properties investigated. Differential scanning calorimetry and thermogravimetric analysis were used to investigate both the kinetics of PMMA decomposition and the influence of β-SiC nanoparticles upon the mechanisms of PCS cure, pyrolysis, and partial crystallization. As the crystallization temperature was systematically increased, the inter-pore ligament structure coarsened and nanopores developed within the ligaments between the β-SiC nanoparticles. The foam's Young's modulus and compressive strength at first increased with crystallization temperature, reaching a maximum after processing at 1300˚C. However, further increases in temperature resulted in a rapid fall in both foam modulus and compressive strength. To gain insight into the fundamental processes responsible for the overall (macroscale) mechanical properties, models for open/closed cell foams were inverted and used in conjunction with the measured foam density, Young's modulus, and compressive strength to estimate the mechanical properties of the inter-pore ligaments. This procedure indicated that changes to the ligament properties were responsible for the observed dependence of the foam mechanical properties upon crystallization temperature.

As part of Roman Space Telescope component development, the slow crack growth (SCG) parameters of a glass were measured using constant stress rate testing of ASTM C1161 beams. Failures occurred on the faces, bevels and sides of the test specimens thereby providing an opportunity to examine the effects of failure location on SCG parameter estimates. Censoring of the data by location did not have a statistically significant effect on the slow crack growth parameter estimates. Linear and nonlinear fits were also made to various strength estimators. Nonlinear fits gave slightly lower estimates of the parameters. The main influence on parameter estimates was a low strength, infrequent flaw population. Exponential model parameters were estimated via swarm optimization.

Sustainability is becoming an increasingly important factor in the development of new building materials. In terms of the sustainability of concrete components, the biggest challenge is the high energy consumption and associated greenhouse gas emissions in the production of Portland cement. A common strategy used by the construction industry to improve sustainability is to use residuals to develop lower-emission geopolymer concretes that eliminate high-emission cement-based concretes. Because construction and demolition waste, at 3 trillion tons per year worldwide, also represents an environmental risk, this work will investigate the suitability of geopolymers based on real construction waste. In the course of the investigations, the manufactured geopolymer samples are examined for the material parameters relevant to building materials, namely compressive strength, flexural strength, raw density, total porosity, and thermal conductivity. The setting behavior and the forming structures are investigated by infrared spectroscopy, X-ray diffraction analysis and scanning electron microscopy. The present study is intended to contribute to the development of a suitable recycling strategy for the material recycling of construction waste in novel geopolymer material.

Both unwanted and induced crystallization can impact bioactivity, physical and mechanical properties of bioactive glasses (BGs). Uncontrolled crystallization has negative consequences, rendering BGs unreliable. However, by manipulating the type, size, shape, and quantity of crystals in BGs, plenty of opportunities arise for controlling, for example, mechanical properties and degradability, leading to unique applications and improved performance. Understanding crystallization is a key step in developing bioactive glasses and glass-ceramics (BGCs), and both fundamental and experimental research can aid in the design of BGCs for processing and biological function. In this perspective, we discuss the sources of crystallization and how controlled crystallization facilitates the functionalization of bioactive scaffolds, hybrids, coatings, composites, cements, and fibers.

Pure ZnO particles, doped and co-doped with Cu²⁺ and Mg²⁺ ions, were obtained by the simple sonochemical method. The wurtzite hexagonal structure was confirmed by X-ray diffraction (XRD) patterns. The images obtained by field emission scanning electron microscopy (FE-SEM) showed irregular and more agglomerated particles with the increase of Cu²⁺ and Mg²⁺ ions concentration in the ZnO lattice, with the average diameter of particles in the range of 57.23–170.77 nm. The photocatalytic activity was investigated by decolorizing the methylene blue (MB) dye under ultraviolet C (UVC) light irradiation which indicates that 1% Mg-doped ZnO particles have better the photocatalytic activity than the other samples, and presented the highest kinetic constant value. The co-doped samples showed a reduced global surface area which did not favor the good photocatalytic performance. The sacrificial agents showed that OH• radicals are the main species involved in the photocatalytic activity of this system and defects generated in the ZnO lattice promoted photoluminescent emission in the red and green regions.

In this work, vitreous material was produced, using ash from burning wood in a boiler, to obtain a glass-ceramic with the gehlenite phase. The glass obtained by melt-quenching at 1450°C was characterized by differential scanning calorimetry and other techniques to determine the glass transition and crystallization temperatures, and crystallization kinetics were investigated using the Kissinger model. Tablets prepared with glass powder were treated at 970, 990, 1074, and 1120°C for 1 h, to obtain the glass-ceramic material. The phase identified by X-ray diffraction was gehlenite, with two crystalline structures coexisting in the sample. According to the kinetics study, the phase with a tetragonal structure had a lower crystallization activation energy, and therefore, it may have been the first phase to be formed in the material. Scanning electron microscopy images revealed crystalline regions within the glassy matrix with a lamellar microstructure, with no geometrically defined morphology and no morphological or microstructural distinction, suggesting that both gehlenite phases coexist without apparent distinctions in the glass-ceramic. The best results for water absorption, apparent porosity, and apparent density were for the glass-ceramic sample sintered at 990°C, whose values were respectively 0.1, 0.29, and 2.89 g/cm³.

Previous studies have shown that selective laser flash sintering (SLFS) can be initiated in dielectrics that exhibit ionic or electronic conduction at high temperature. These materials required high laser powers to reach the temperatures where electrical conduction is sufficient to initiate SLFS. In this study, SLFS in lanthanum chromite (LC), an intrinsic electronic conductor with high conductivity, and lanthanum strontium chromite (LSC), which is doped to further increase electronic conductivity, were investigated with a focus on understanding the initiation mechanisms. Results show that the initiation of SLFS in LC and LSC occurs when electronic charge carriers are activated and flow to the electrode where the current is measured. A combination of carriers produced at the electrode, temperature-activated intrinsic charge carriers, and extrinsic charge carriers present in LSC due to doping are responsible for the facile initiation of SLFS.

This study presented the successful deposition of layered double hydroxide (LDH) onto non-pretreated carbon cloth (CC) using lactate salts as raw materials. Specifically, under the hydrothermal condition using urea hydrolysis and lactate salts as the source of Mg and Al, MgAl-LDH was deposited onto the CC surface, which is typically treated with organic solvents and acids to enhance its hydrophilicity prior to LDH deposition. X-ray diffraction patterns, field-emission electron microscope images, and elemental analyses revealed the deposition and coating of hexagonal platy particles of a carbonate-type MgAl-LDH with pseudo hexagonal phase and Mg/Al molar ratio of 1 onto CC. This LDH coating was not achieved when using chlorides and nitrates, which commonly used Mg and Al sources. These results demonstrated the effectiveness of the proposed method for facile LDH deposition on hydrophobic surfaces.

This work aims to improve the early age characteristics and water resistance of volcanic ash-based phosphate geopolymer materials by modifying the chemistry of the binder with calcium hydroxide (CH). Phosphate geopolymer binders with Ca/P molar ratios ranging from 0.49 to 0.80 were prepared. Then the early and late age physical properties were then determined. The hardened binder was characterized by various analytical techniques involving XRD, TGA-DSC, and SEM-EDS. The results showed that the use of CH decreases the initial setting time from several hours to less than 5 min. At the same time, the 1 d compressive strength was increased from 0 to 15 MPa with the increase in the Ca/P molar ratio. Moreover, the slow dissolution rate of volcanic ash was responsible for the low strength at an early age but beneficial to improving the geopolymerisation with time. This favored the high strength of the control phosphate geopolymer, which reached 52.5 MPa at 56d and was higher than those with CH (28.5–45.2 MPa). However, the control phosphate geopolymer had poor water resistance, with strength retention ranging from 21%–57% compared to 76%–90% for phosphate geopolymer with CH. This is because of the leaching of the reactive phase underwater that inhibits further reaction progress. In addition, the modification of the binder chemistry with CH leads to the formation of new calcium phosphate phases that also contribute to enhancing water resistance.

A liquid-phase polymer-to-ceramic approach is reported for the synthesis of hafnium carbide (HfC)/hafnium oxide (HfO₂) composite particles from a commercial precursor. Typically, HfC ceramics have been obtained by sintering of fine powders, which usually results in large particle size and high porosity during densification. In this study a single-source liquid precursor was first cured at low temperature and then pyrolyzed at varying conditions to achieve HfC ceramics. The chemical structure of the liquid and cured precursors, and the resulting HfC ceramics was studied using various analytical techniques. The nuclear magnetic resonance and Fourier transform infrared spectroscopy indicated the presence of partially hydrated hafnium oxychloride (Hf–O–Cl·nH₂O) in the precursor. Scanning electron microscopy of the resulting HfC crystals showed a size distribution in the range of approx. 600–700 nm. The X-ray diffraction of the pyrolyzed samples confirmed the formation of crystalline HfC along with monoclinic-HfO₂ and free carbon phase. The formation of HfO₂ in the ceramics was significantly reduced by controlling the low-temperature curing temperature. Pyrolysis at various temperatures showed that HfC formation occurred even at 1000°C. These results show that the reported precursor could be promising for the direct synthesis of ultrahigh temperature HfC ceramics and for precursor infiltration pyrolysis of reinforced ceramic matrix composites.