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This study investigated the activation energy and kinetic characteristics of silicon nitride (Si3N4) composite ceramics produced using different preparation methods. The effects of the linear shrinkage, expansion ratio, and heating rate on the sintering process were analysed in detail. The obtained results reveal that the finer particle size produced using the urea homogeneous precipitation method obviously enhanced the densification rate and reduced the atomic diffusion distance. Moreover, the densification sintering process was carried out efficiently, and the largest densification rate was achieved in advance. According to the Arrhenius curve, the activation energy of the Si3N4 composite ceramics calculated using the urea homogeneous precipitation method (310.94 kJ/mol) was lower than that achieved using the mechanical ball-milling method (365.11 kJ/mol). Additionally, the flexural strength and hardness of the Si3N4 composite ceramic prepared using the urea homogeneous precipitation method were 740 ± 42 MPa and 16.20 ± 30 GPa, respectively, which is attributed to this composite ceramic's higher diffusion rate and small grain size.

In this study, the forms of occurrence of impurity elements in silicon carbide (SiC) with different particle sizes were systematically investigated using a combination of X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometry (ICP-OES), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The experimental results showed that in SiC powders prepared using the Acheson process, the contents of O, free-Si, free-C, and Fe impurities are high, and those of other trace impurity elements follow the order: Ti > Al > Ni > V. Moreover, O impurities mainly cover the SiC particle surface in the form of amorphous SiO2. Fe impurities exist around SiC particles as Fe2O3, FexSiy, FexSiyTiz, and FexAlySiz phases. Impurity elements are often introduced during the smelting of SiC and/or during milling or subsequent storage.

In this work, hierarchically porous SiC ceramics were prepared via the foaming method. Porous ceramics with tunable, uniform, and bimodal pore structures were successfully fabricated in a facile way. The formation mechanisms of the 1st and 2nd modal macropores are the H2O2 foaming process and SiC particle overlap, respectively. The effect of pore-foaming agent amount, foaming temperature, and surfactant was investigated. According to the results, with increasing H2O2 amount, the porosity, pore size, and interconnectivity of the 1st modal pores increased, whereas bulk density and strength decreased. The porosity increased while the strength decreased as the foaming temperature increased. Surfactants increased pore interconnectivity and porosity. When the foaming temperature was 85 °C, and the addition of H2O2 was 5 wt.%, the porosity, bulk density, flexural strength, and compressive strength were 56.32%, 2.8301 g/cm3, 11.94 MPa, and 24.32 MPa, respectively. Moreover, SiC porous ceramics exhibited excellent corrosion resistance to acids and alkalis.

Silicon nitride (Si3N4) ceramics with Al2O3, MgO and Y2O3 as sintering additives were fabricated via hot-pressing sintering and gas pressure sintering, respectively, focusing on the texture and fracture toughness. The hardness and fracture toughness on the plane perpendicular and parallel to the hot-pressing direction were different in the hot-pressing sintered samples, and similar values were obtained in the gas pressure sintering. The orientation distribution function (ODF) analyses via X-ray diffraction measurements revealed the presence of 11 2 ¯ 0 〈 0001 〉 type texture in the hot-pressing sintered samples. This suggested that the 0001 planes of most rod-shaped β-Si3N4 grains were oriented in the hot-pressing direction or their c-axes were oriented towards the radial directions of the sintered cylinder-shaped samples. The presence of such a β-Si3N4 grain texture led to the anisotropy in fracture toughness, with its values changing from 9.3–11.3 MPa m1/2 with increasing indentation angles on the plane parallel to the hot-pressing direction.

In this study, a hierarchical macroporous–mesoporous structure B4C/C preform was prepared via gel-casting, using which the pore structure, as well as the B4C slurry stability, could be adjusted by using B4C powders with varying multimodal particle size distributions. The coarse, medium, and fine particle distributions of the B4C powders, and their effects on mechanical properties of the RBBC composites obtained by liquid Si infiltration were investigated. The results showed that the lowest B4C slurry viscosity and the densest B4C/C preform were obtained at a 6:1:3 ratio of coarse, medium, and fine particles. The Vickers hardness, fracture toughness, and flexural strength of the RBBC composites reached 21 ± 3 GPa, 4.09 ± 0.17 MPa m1/2, and 299 ± 17 MPa, respectively. Furthermore, the lowest residual Si content was 7.22 vol%, and fine residual Si phases had a toughening effect owing to their internal compressive stress.

A novel multiphase composite coating composed of Hf0.8Ti0·2B2 solid solution, SiC and Si was prepared by a joint procedure of slurry method and silicon reactive infiltration (SRI). The oxidation and ablation experiments were conducted to investigate oxidation and ablation resistance of the Hf0.8Ti0·2B2–SiC–Si coated graphite samples, respectively. The results revealed that the coated sample was oxidized at 1823 K for 108 h with a mass gain of 1.49%, which was ascribed to the high viscosity oxide layer improved by HfSiO4 and TiO2 in conjunction with dense structure of the coating, thereby presenting excellent high temperature stability. Furthermore, after 90 s ablation at 3273 K under a heat flux of 5.62 MW/m2, the composite coating was not peeled off, which had mass ablation rate (MAR) and linear ablation rate (LAR) of 3.1 mg/s and 1.5 μm/s, respectively. The refractory oxide layer comprising oxides of Hf and Ti on the surface acted as an oxygen barrier, which can weaken the mechanical erosion force of oxyacetylene flame, finally protecting the inner coating and graphite matrix from further consumption.

A novel and facile one-pot method, named high-temperature high-energy mechanical force (HTHEMF), was successfully used to synthesize the Fe2P/LiFePO4/C composites. In this method, the combination of the high-energy mechanical force with the high-temperature not only simplified the synthesis process, but also reduced the temperature and time of the calcinations process. The temperature and time were 600°C and 10 h, respectively. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and electrochemical performance tests were employed to analyze the properties of the samples. The results suggested that Fe2P phase has a favorable effect on improving the electrochemical performance of the LiFePO4 material, such as high-rate capacity, low polarization phenomena and stable cycling performance. The composites delivered higher discharge capacities at different discharge rates, and it provided the first discharge capacities of 155 mA h g–1 about 7.6% more than which of the LiFePO4/C composites at 0.1 C. It indicated that the one-pot HTHEMF method is promising approaches to obtain the Fe2P/LiFePO4/C composites with good properties.

In the current work, SiC powders with various levels of oxygen content were obtained by two ways: acid leaching and heat treatment; and these SiC powders were densified by a pressureless sintering technique with boron carbide and carbon additives. The techniques of X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, transmission electron microscope, and mechanical testing were combined to examine the effects of oxygen impurities on the densification process of SiC ceramics. The experimental analyses indicated that high oxygen content is detrimental to the final sintering and mechanical properties of SiC ceramics. As the oxygen content increases from 0.55 to 2.10 wt%, the relative density and the hardness both decrease: the relative density drops from 98.53% to 70.55% (a 28% decrease), and the hardness drops from 27.1 ± 0.7 GPa to 6.7 ± 1.1 GPa (a 75% decrease). Furthermore, oxygen impurities can accelerate the abnormal growth and coarsening of SiC grains during sintering. In order to impede abnormal grain growth and achieve high densities of SiC ceramics, it is proposed that the oxygen content of the powders should be limited to less than 1.30 wt%.

TiO2 nanobelts (NBs) have received much attention due to their chemical stability, nontoxicity, special one-dimension morphology and also have found many applications. However, extensively employed hydrothermal processes are time-consuming. In this work, a microwave-assisted hydrothermal (MAH) method is for the first time reported for the rapid fabrication of TiO2 NBs. TiO2 NBs with widths of 25–200 nm and lengths up to tens micrometers can be successfully fabricated by adjusting the concentration of NaOH solution, reaction time and reaction temperatures. By MAH method, the reaction time can be greatly shortened to 4 h under microwave irradiation compared to 1–3 days reported in literature. Bi-crystalline structures with monoclinic TiO2(B) and tetragonal anatase can be tuned by simply adjusting thermal treatment temperatures. The evolution of different crystalline structures from starting H2Ti3O7 to crystalline TiO2 phases with increasing calcination temperatures was analyzed by different techniques. The photocatalytic activity results reveal that bi-crystalline structures with TiO2(B)/anatase phases (optimal B:A ratio of 66:34) are advantageous to enhance the photocatalytic performance of TiO2 NBs in photo-decomposing Rhodamine B molecules in water under UV irradiation.

A new type of pore structure of B4C/C preform was fabricated by a resorcinol-formaldehyde (RF) hydrogel gel-casting system. Pore structure controllability of the B4C/C preform was achieved by adjusting the content of the catalyst Na2CO3. Increasing the content of Na2CO3 could achieve accurate control of the B4C/C preform from a single macroporous or mesoporous structure to a hierarchical macroporous-mesoporous structure. The reaction bonded boron carbide (RBBC) composites were prepared by the infiltration of B4C/C preforms of different pore structures with liquid silicon. The residual silicon content and mechanical properties of the RBBC composites were studied. The residual silicon content was controlled by the modification of the open porosity and pore structure of the B4C/C preforms, and the lowest residual silicon content was 33 vol%. Sample S300, which was prepared through liquid silicon infiltration of a B4C/C preform with a single mesoporous structure (with the optimum aperture size of 49 nm), had the best mechanical properties, including a flexural strength and fracture toughness of 419 ± 17 MPa and 4.12 ± 0.12 MPa·m1/2, respectively.

SiC ceramics are important high-temperature structural materials with excellent chemical and physical properties. However, the different impurities are usually introduced into the raw materials in the preparation of SiC powders, especially Fe2O3 impurity. The current work aims to investigate the effect of Fe2O3 contents (0–0.8 wt%) on the sintering behaviour and mechanical properties of SiC ceramics. Fe2O3-containing SiC ceramics were prepared by pressureless sintering using carbon and boron carbide as sintering additives. The X-ray diffraction, inductively coupled plasma-atomic emission spectrometry, scanning electron microscope, and mechanical testing were used to understand the effect of Fe2O3 on a few key properties of sintered samples. The results indicated that the hardness (from 24.4 ± 1.0 GPa to 27.2 ± 1.3 GPa) and flexural strength (from 360 ± 38 MPa to 394 ± 18 MPa) can be increased by 10% upon a gentle introduction of only 0.02 wt% of Fe2O3, due to the formation of fine gains and homogenous microstructures. However, the further increase of Fe2O3 contents above 0.4 wt% is found to be detrimental to sintering of SiC ceramics. It is suggested that excessive Fe2O3 reacts with C leading to the formation of more volatile species (CO, Fe), and increasing the porosity of SiC matrix, which hampers the densification process and is harmful to mechanical properties of sintered SiC.

In order to protect graphite from oxidation and ablation, novel double layer HfB2-SiC-Si/SiC-Si coatings were designed and fabricated by a joint process of slurry method and gaseous silicon infiltration on graphite substrates. X-ray diffraction analysis and scanning electron microscopy were used to study the phase composition and microstructure of the as-fabricated coatings. The tests of oxidation and oxyacetylene flame were conducted to assess the oxidation and ablation resistance ability of the HfB2-SiC-Si/SiC-Si coatings. Results indicated that the coated samples can endure 752 h and 1200 h of oxidation at 900 °C and 1500 °C with weight gains of 0.099% and 0.26%, respectively, whereas the coated sample had a weight gain of 0.34% after 230 h of oxidation at 1600 °C. The compact double layer structure of coating resulted in the attractive anti-oxidation property at low temperature (900 °C), while the good oxidation and exfoliation resistance at high temperatures (1500–1600 °C) were ascribed to the formed compound silicate oxide layer comprising SiO2 and HfSiO4 on the coating surface. Meanwhile, the fabricated coating exhibited good ablation resistance property, after ablation for 90 s with a heat flux of 2.38 MW/m2, the mass and linear ablation rates of the coated sample were 0.36 mg/s and −0.31 μm/s, respectively. The formed compound oxides containing HfO2 and SiO2 on the surface acted as a thermal barrier that prevented the further consumption of coated sample.

A monolayer TaB2-SiC-Si protective coating was fabricated by impregnation and in-situ reaction method on the surface of graphite to prevent graphite materials from oxidation and ablation, and the microstructure, oxidative and ablative protection properties of the coating were investigated. Experimental results revealed that the coating could protect graphite from oxidation at 1020 °C and 1550 °C for more than 321 h and 168 h, respectively, and from ablation for 120 s with a heat flux of 2.38 MW/m2. The good oxidative protection performance was ascribed to the low oxygen diffusivity of the coating and oxide film formed on the coating surface, which effectively inhibited oxygen diffusion to the graphite substrate. Under oxyacetylene flame, a Ta2O5 layer was gradually formed on the coating surface and acted as a protective layer, which weakened the erosion of flame to the inner coating. The increase of ablative time promoted the fierce evaporation of gaseous Si and oxide phases, such as B2O3(g), SiO2(g), CO(g) and CO2(g), which resulted in the damage to the TaB2-SiC-Si coating, leading to the reduction of anti-ablation property of the coating.

This work demonstrates that using sodium silicate as precursor, hierarchical mesoporous silica (HMS) microspheres with ordered mesochannels and large intra-particulate mesopores can be prepared by partitioned cooperative self-assembly process based on a P123 templated system. The influence of various experimental parameters on mesostructures and particle morphology was investigated, including the ethanol, addition combinations, interval times, synthesis temperatures and hydrothermal treatment temperatures. Importantly, the crucial role of ethanol in shaping the particle morphology and hierarchical mesostructures was identified. The resultant micro-sized HMS microspheres reveal clew-like feature: the ‘yarns’ comprise bundles of ordered mesochannels (1st mode mesopores, ca. 10–15 nm in sizes), while the 2nd mode intra-particulate pores (ca. 20–45 nm in sizes) exist between the intertwined ‘yarns’. For example, a representative HMS microsphere prepared under optimized conditions (6-6 h-4Et5@36H140) shows two modes of mesopores, 12.3 nm and 27.7 nm for the 1st and 2nd mode mesopores, respectively. The spherical particle size is around 1.5 μm. Both the regularity of the 1st mode mesostructure templated by the P123 and well-defined 2nd mode mesostructures can be secured when the hydrothermal treatment (HTT) temperature is controlled at 140 °C, while higher HTT temperature at 160 °C disintegrates the 1st mode mesostructures and thus destroy the meso-orderings. In the release performance tests of indomethacin (IMC) in simulated intestinal fluid (SIF), HMS microspheres with high 2nd mode mesoporosity show higher drug release rate than that with low 2nd mode mesoporosity, while two of them both show higher drug release rate than conventional SBA-15 fibers. This work, as we believe, also represents a new strategy to regulate drug releasing performance by simply tuning the hierarchical mesostructures of HMS and can allow flexible design of IMC/meso-silica formulations.

A convenient one-pot method, called high-temperature high-energy mechanical force (HTHEMF), was successfully developed for the preparation of LiFePO4/C composites. Upon the combination of high-temperature with high-energy mechanical force, the whole synthesis process of this method is very simple and only involves two steps, the precursor preparation and the calcination step. The results of XRD, SEM, BET and electrochemical performance tests indicated that after calcination at 600 °C for 9 h, the LiFePO4/C composites have the best properties. The discharge capacity of the composites was 150.3mA h g-1 at 0.1 C. After 30 cycles test, the reversible capacity was 147 mA h g-1 and the retention ratio to the initial capacity was 97.8%. The results indicated that LiFePO4/C composites with good properties can be obtained by one-pot HTHEMF method.

To improve the oxidation resistance of Si-SiC coating, single-phase ultra-high temperature boride (ZrB 2 or TaB 2 ) modified Si-SiC coating was designed and established on graphite substrates by combination of dipping and reactive infiltration process. ZrB 2 or TaB 2 phase was introduced in Si-SiC coating by directly mixing raw materials and phenol formaldehyde resin in the slurry, and then the ZrB 2 -SiC-Si and TaB 2 -SiC-Si coatings were fabricated on the graphite samples by dipping-curing, pyrolysis, and siliconizing. The crystalline phases and microstructure of the as-obtained multiphase coatings were investigated by X-ray diffraction analysis and scanning electron microscopy. The interrupted oxidation tests from room-temperature to 1500 °C were conducted to assess the anti-oxidation property of the prepared coatings. After 1200 h of oxidation at 1500 °C in air (30 times thermal cycles), the mass losses of the graphite substrates coated with ZrB 2 -SiC-Si and TaB 2 -SiC-Si coatings were 0.086% and 0.537%, respectively, and the high-temperature stability of the modified coatings was greatly improved compared to the Si-SiC coating. The excellent anti-oxidation performances of the compound coatings were attributed to the compact structure of the coatings and the formation of compound oxide layers covering on the surfaces. The compound Zr-Si-O and Ta-Si-O films possessed low oxygen diffusion rate and appropriate viscosity, which can provide appreciable oxidation protection for the internal coatings, thus obtaining the excellent oxidation and spallation resistance property.

In order to improve the survivability of in-orbit spacecraft against the hypervelocity impact (HVI) of space debris, the lightweight B4C/Al composite is fabricated by the pressureless presintering and Al infiltration in vacuum and applied as the bumper of Whipple shield configuration. The HVI tests ranging from 3 km/s to 6.5 km/s are carried out to assess the shield performance of B4C/Al bumper. The fitting line of the ballistic limit for the B4C/Al bumper is obtained, and its critical projectile size can be improved by about 20% in comparison to the conventional Al alloy Whipple shield configuration. Based on the damage features of bumper and rear wall, the B4C ceramic phase of B4C/Al composite is the key reason to break the projectile into smaller fragments or liquid droplets of debris cloud. The Al plastic phase with three-dimensional network enhances the toughness of B4C/Al composite bumper, which plays an important role in avoiding structural failure caused by shock waves. Hence, the impact kinetic energy of debris cloud is obviously dispersed, and the subsequent impact damages on real wall are alleviated accordingly. The primary investigation provided theoretical and technical instructions for the design and application of B4C/Al composite in MMOD shield configuration. Keywords: B4C/Al composites, MMOD, Hypervelocity impact, Damage behavior, Shield performance

A monolayer MoSi 2 –CrSi 2 –SiC–Si multiphase coating was designed and prepared by slurry impregnation combined with reactive infiltration of gaseous silicon onto a graphite substrate. The phase composition and microstructure of the as-prepared coating were studied by X-ray diffraction analysis and scanning electron microscopy. Oxidation and oxyacetylene flame tests were performed to evaluate the anti-oxidation and anti-ablation performance of the MoSi 2 -CrSi 2 -SiC-Si coating. Results showed that the as-prepared coating can withstand long–duration oxidation at low temperature (900 °C) for 1320 h and at high temperature (1600 °C) for 1190 h with mass gains of 0.06% and 1.24%, respectively. The compact structure of the coating, which had a thickness of approximately 600 µm, resulted in the excellent anti-oxidation behavior at 900 °C, whereas the excellent oxidation resistance at 1600 °C is attributed to the formation of an oxide layer with slow oxygen diffusivity on the coating surface and the presence of dispersed MoSi 2 and CrSi 2 in the coating. Further, the as-prepared coating displayed good ablation resistance, after ablation for 60 s, the mass and linear ablation rates of the coated sample were 0.31 mg/s and 0.33 µm/s, respectively. Under an oxyacetylene flame, active oxidation of silicon carbide and severe evaporation of oxides, for instance, gaseous silica, molybdenum oxide, and chromium trioxide, were the main causes of damage to the MoSi 2 –CrSi 2 –SiC–Si coating.

A novel monolayer Hf0.5Ta0.5B2-SiC-Si coating with defect-free structure for protecting graphite materials was prepared by dipping-pyrolysis combined with reactive infiltration of gaseous silicon. The phase synthesis, microstructure, oxidation and ablation resistance properties of the prepared Hf0.5Ta0.5B2-SiC-Si coating were studied. Results demonstrated that the as-prepared coating exhibited excellent low and high temperature oxidation resistance, after isothermal oxidation at 900 °C and 1500 °C for 1320 h and 2080 h, respectively, the mass gains were 0.14% and 1.74%, respectively. The excellent anti-oxidation performance at 900 °C was ascribed to the defect-free structure of coating, while the formed compound Hf-Ta-Si-O glassy oxide layer on the coating surface was responsible for the excellent oxidation resistance at 1500 °C. Moreover, the Hf0.5Ta0.5B2-SiC-Si coating had good ablation resistance, after ablation for 60 s, the mass and linear ablation rates of the coated sample were 1.05 mg/s and −10.2 μm/s, respectively. The ablation behaviors of the coated sample mainly included thermal-physical and thermal-chemical erosion along with thermos-mechanical denudation.

A dense structure and well-bonded Si-SiC coating was fabricated by impregnation-pyrolysis combined with gaseous silicon infiltration to protect graphite materials from oxidation and ablation. The phase synthesis, microstructure, anti-oxidation and anti-ablation properties of the obtained Si-SiC coating were studied. Results indicated that the Si-SiC coating was defect-free, and SiC particles were surrounded by residual silicon. The prepared coating can withstand 300 h, 468 h, 223 h and 223 h of isothermal static oxidation at 800 °C, 1000 °C, 1300 °C and 1500 °C, respectively, which was considered to be the dense structure of coating and glassy SiO2 film formed on the coating surface. The coated sample presented good ablation resistance performance, after ablation for 90 s, the mass and linear ablation rates of Si-SiC coated sample were 0.13 mg/s and 0.02 µm/s, respectively. Thermal physical and chemical erosion along with thermos-mechanical denudation of the Si-SiC coating are responsible for the ablation behaviors of the Si-SiC coating.

A new-designed mullite-SiC-Si coating with dense structure for protecting graphite materials was prepared by dipping-pyrolysis combined with reactive infiltration. The phase synthesis, microstructure and anti-oxidation property of the fabricated mullite-SiC-Si coating were studied. Results demonstrated that the as-prepared coating exhibited excellent low and high temperature oxidation resistance, after isothermal oxidation at 900 °C and 1600 °C for 752 h and 550 h, respectively, the mass gains were 0.1% and 0.99%, respectively. The excellent anti-oxidation performance was ascribed to the dense structure of coating and the formed glassy oxide layer on the coating surface. The oxidation process of mullite-SiC-Si coating was controlled by the diffusion of oxygen, and the as-prepared coating after oxidation was composed of oxide layer and dense mullite-SiC-Si layer. In contrast to SiC-Si coating, the high temperature stability of mullite-SiC-Si coating was greatly improved.

Silicon nitride composite ceramics with excellent mechanical properties were prepared by hot pressing. The effects of temperature on the sintering process, β-Si3N4 phase transformation ratio (β%) and mechanical properties were investigated. By calculating the diffraction intensity (I), the β-Si3N4 phase transformation ratios of the three samples considered in this study were 57.2% (pre-sintered samples, PSN), 63.5% (urea homogeneous precipitation method, USN) and 66.6% (mechanical milling method, MSN) at 1550 °C, respectively. These results showed that the Si3N4 composites coated by using Y-Al precursor (USN) have a lower ratio of the phase transformation from α to β. Meanwhile, from the analysis of SEM images of the etched surface, the grain sizes were 0.47 µm (PSN), 0.39 µm (USN), and 0.43 µm (MSN) at 1650 °C, respectively. Compared to the other samples, the USN sample offered superior sintering behaviour and mechanical properties. The optimal flexural strength, hardness and fracture toughness of the Si3N4 composites coated by using the Y-Al precursor were 911 ± 69 MPa, 16.23 ± 0.24 GPa and 4.9 ± 0.35 MPa/m2 at 1650 °C, respectively.

Based on the simplest TEOS/P123/HCl(aq.) templating system, it is demonstrated in this work that different SBA-15 platelets can be controllably prepared via the partitioned cooperative self-assembly (PCSA) process without using any additives or complicated procedures. Experimental results show that the reduced amounts of TEOS added in the 2nd additions in the PCSA process play a determining role in transforming the SBA-15 platelet morphologies from the plane ones to a unique kind of UFO-shaped ones. The obtained SBA-15 platelets, plane or UFO-shaped ones, are composed of plugged mesochannels aligned in a 2D hexagonal symmetry, with neighboring channels connected by large tunnel holes (intrawall pores). Different platelet morphologies and their evolution were found to be dependent on partitioning conditions (2nd TEOS addition and interval time). A competitive process involving the aggregation of SBA-15 primary particles dictates the formation of SBA-15 particles with different morphologies, meanwhile the UFO-shaped SBA-15 platelets (U-SBA-15P) can be deemed as intermediate ones between rod-like particles and plane platelets. Moreover, upon the release of indometacin (IMC) in simulating intestinal fluid, UFO-shaped SBA-15 platelets show faster drug release performance compared with their plane counterparts or conventional SBA-15 fibers. The larger the protruded areas in UFO-shaped platelets, the higher the release rate will be. This work, as we believe, presents a new strategy to regulate drug releasing performance by simply tuning particle morphologies of SBA-15 platelets and can allow rational design of IMC/meso-silica formulations.

To protect graphite materials from oxidation, a dense (ZrTa)B2–SiC–Si coating was for the first time prepared on graphite substrate by slurry dipping and vapour silicon infiltration process. (ZrTa)...

A novel kind of dense MoSi 2 -SiC-Si coating was prepared on the surface of graphite substrate by slurry dipping and vapor silicon infiltration process. Mo-SiC-C precoating was fabricated via slurry dipping method, and then MoSi 2 -SiC-Si coating with dense structure consisting of Si, MoSi 2 and SiC was obtained by vapor silicon infiltration process. The isothermal oxidation tests at temperatures from 800 to 1600 °C and TGA test from room temperature to 1500 °C were used to evaluate the oxidation resistance ability of the MoSi 2 -SiC-Si coating. The experimental results indicate that the prepared coating has good oxidation protection ability at a wide temperature range from room temperature to 1600 °C. Meanwhile, the oxidation of the coated samples is a weight gain process at temperatures from 800 to 1500 °C due to the formed SiO 2 layer on the surface of coating. After oxidation for 220 h at 1600 °C, the weight loss of the coated sample was only 0.96%, which is considered to be the excessive consumption of the outer coating and the appearance of defects in the coating. Two layers can be observed in the coating after oxidation, namely, SiO 2 layer and MoSi 2 -SiC-Si layer.

In order to protect graphite materials from oxidation, a dense single layer ZrB2-MoSi2-SiC-Si coating was for the first time prepared on the surface of graphite substrate by slurry dipping and vapor silicon infiltration process. The phase compositions and microstructure of the prepared coating were analyzed by XRD and SEM. The isothermal thermal cycle oxidation tests were conducted at 1600 °C in air. The results showed that the prepared coating exhibited excellent oxidation protection ability, after oxidation for 150 h, the weight loss was only 0.21%, which was considered to be the depletion of the outer coating and the appearance of defects in the coating. The excellent protection ability was attributed to the dense structure of the coating and the formation of thick oxide layer with immiscible ZrO2 on the outer surface of coating. Two layers could be observed in the coating after oxidation, namely, glassy oxide layer and ZrB2-MoSi2-SiC-Si layer. After thermal shock between 1200 °C and room temperature for 100 cycles, the weight gain was 0.11%. The good thermal shock resistance could be ascribed to the gradient thermal expansion coefficients of different components in the coating and the C/SiC interface layer between the substrate and coating.

In this work, it is demonstrated that hierarchical mesoporous silica monoliths (HMSMs) with trimodal porosities can be facilely prepared using P123 as structure-directing agent and tetraethoxysilane as precursor. In such HMSMs, classic co-continuous macrostructures with interconnected macropores and smooth isotropic skeletons can be obtained in a tunable way, depending on the synthesis variables, including the amounts of P123 and 1,3,5-trimethylbenzene and acid concentrations. Skeletons feature randomly oriented SBA-15-type primary particles with 2D hexagonally ordered mesochannels largely accessible from bimodal macropores. Co-continuous macropore size of a typical HMSM (P1.2) is 19.6 μm, intra-skeleton macropore of 1.9 μm and mesopore size of 9.9 nm. The BET surface area by N2 sorption and total pore volume by Archimedes principle reach 590 m2 g-1 and 3.56 cm3 g-1, respectively. Based on systematic study on the relationship between synthetic compositions and porous structures, the ternary diagram and formation mechanism of these HMSMs were analyzed.

In this study, Si 3 N 4 ceramic composites were fabricated by using ball-milling, titration preparation and urea preparation methods, respectively. The effect of different preparation methods on microstructure and mechanical properties of the Si 3 N 4 ceramic composites was investigated. Obviously, the Si 3 N 4 ceramic composite prepared by the urea preparation method (U-SN sample) showed better sintering behavior and higher mechanical properties than that prepared by the other two methods. Compared with the Si 3 N 4 ceramic composite by the titration preparation method (T-SN sample), we could avoid the complex titration process or uncontrollable pH value during the preparation process of the U-SN sample. Meanwhile, the coated Y-Al precursor layer in thickness of nanometers was more homogeneous than that prepared by the traditional titration method. B-SN represented the Si 3 N 4 ceramic composite prepared by the ball-milling method. These samples were all sintered from room temperature to 1750 °C via hot-pressing sintering. The U-SN specimen showed the optimal flexural strength and fracture toughness of being 817 MPa and 6.90 MPa/m 2 , respectively, which could be attributed to its smallest grain size (0.46 µm) among these three samples.

In this paper, a simple precipitation method has been developed for the preparation of yttrium aluminum garnet (YAG) precursor coated Si3N4 powders (YAG@Si3N4) without resorting to either titration or uncontrollable pH value. Yttrium aluminum garnet (Y3Al5O12) precursor was prepared via urea homogeneous preparation technology by using urea as precipitant. This method solved a problem that Y3+ and Al3+ exhibited different precipitation in the conventional method. The pH value would be maintained at 7.9 during the reaction process. This phenomenon could be explained that the heated urea could be decomposed continuously to keep the pH value stable. After sintering, the composition and microstructure of samples were analyzed by X-ray diffraction (XRD analysis), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These results indicated that the microstructure of the precursor exhibited a core-shell structure, and the thickness of the shell was ranging from 37 to 66 nm. Moreover, the flexural strength was up to 817 ± 46 MPa via hot pressing at 1750 °C. The Si3N4 matrix by utilizing urea homogeneous co-precipitation coating might be a potential adding sintering aids method for reinforcing ceramic densification.

A novel kind of 3D interconnected porous carbon-bonded B4C preform with flexural strength of about 20MPa is fabricated by gel-casting method. As the control, the B4C/C preforms via molding-produced method are fabricated. The B4C/C preforms own the same carbon content and almost the same porosity with different molding method. Compared with the conventional compression molding-produced B4C/C preform, the 3D-interconnected porous carbon-bonded boron carbide preforms afford three-fold advantages in the fabrication of reaction-bonded boron carbide (RBBC) composite via the liquid silicon infiltration (LSI) process, including induced formation of continuous SiC-bonded boron carbide skeleton structure, a reduction in the size of residual silicon, and prevented the coarsening of ceramic grains as well. As a result, the RBBC composite fabricated by gel-casting appears as a more refined structure resulting in enhanced mechanical properties: the Vickers hardness, flexural strength, and fracture toughness of I-GC composites fabricated from 3D-interconnected porous carbon/B4C preforms are 19.4 ± 1.3 GPa, 389 ± 17 MPa, and 4.37 ± 0.1 MPa·m1/2, respectively, which are statistically higher than those of RBBC fabricated by the conventional compression molding-produced B4C/C preform.

The resorcinol-formaldehyde (RF) gel-casting system is employed for the first time to fabricate a hierarchical porous B4C/C preform, which was subsequently used for the fabrication of reaction bonded boron carbide (RBBC) composites via a liquid silicon infiltration process. The effect of the carbon content and carbon structures of this perform on the microstructures and mechanical properties of B4C/C preform and the resultant RBBC composites is reported. The B4C/C preform (16 wt% carbon) exhibit a strength of 34±1 MPa. The obtained RBBC composites shown uniform microstructure is consisted of SiC particles bonded boron carbide scaffold and an interpenetrating residual silicon phase. The Vickers hardness, flexural strength and fracture toughness of the RBBC composites (16 wt% carbon) are 24 GPa, 452 MPa and 4.32 MPa m1/2, respectively.

This work reports the controllable preparation of a unique kind of hierarchically mesoporous silica (HMS) fibers with bimodal porosities based on a simple TEOS/P123/HCl(aq.) templating system via the partitioned cooperative self-assembly (PCSA) process. Experimental results show that the formation of hierarchical mesostructures, especially the 2nd mode porous structure, depends on the interval time pertaining to the PCSA process. Synthetic conditions, including the interval time, temperature and stirring, are all found to be important in the evolution of fiber particle morphology. Moreover, such HMS fibers can be used as building units to prepare mesoporous silica monoliths with hierarchical trimodal pore systems via a simple gel-casting method, with additional (the 3rd modal) macropores originating from the packing of micron-sized HMS fibers. Such materials might further expand the application of both HMS fibers and HMS monoliths in various fields.

In order to avoid fluorine loss and contamination, and recover the fluorine resource in bastnaesite, a new process of decomposing bastnaesite with aluminum hydroxide followed by sulfuric acid leaching was proposed. The calcination mechanism was discussed by TG-DSC and XRD analyses. Fluorine could be taken up by Al2O3, and the discharge of fluorine was prevented. Leaching from calcined ore was achieved with dilute sulfuric acid, and the parameters affecting the leaching rates of fluorine and rare earths (REs) were investigated. It shows that the leaching rates of F, Ce and total RE of 92.71%, 98.92% and 98.61% could be obtained under the conditions of n(Al)/n(F) 1/2, calcination temperature 500 °C, calcination time 1 h, sulfuric acid concentration 3 mol L−1, leaching temperature 90 °C and leaching time 1 h. Fluorine could be separated from REs after extraction, and was recovered as Na3AlF6 with the recovery rates of fluoride and aluminum greater than 96%. XRD and SEM analyses indicated that the monoclinic phase cryolite was obtained.

Bilayer B4C based composites, B4C/Si-B4C, consisting of B4C and B4C/Si two-layer, were obtained using hot pressing method. Effect of Si content on microstructure and mechanical properties of the B4C based layered composites was investigated. The B4C/Si-B4C samples showed good interfacial bonding with different Si additions (x = 4, 8, 12 and 16 wt.%) in the B4C/Si layer. Secondary phases SiC and/or TiB2 dispersed randomly in B4C matrices for both layers of the composite by SEM observation. Vickers hardness data for both layers were in a range from 33.1 to 35.2 GPa. Flexural strength and fracture toughness both first increased and then slightly decreased as Si content increased from 4 to 16 wt.%. The fracture toughness of the B4C/Si-B4C composite was significantly improved compared with that of pure B4C material.

This work was aimed to study the mechanical properties and microstructure evolution of SiC ceramics prepared from the purified powders. SiC ceramics were fabricated by solid-phase pressureless sintering using SiC powders (UN-SiC) with a small amount of impurities. The results showed that impurities are detrimental to the mechanical properties of SiC ceramics, the flexural strength, fracture toughness and hardness of the sample UN-S are too low after sintering to 2000 °C, which are only 240.9 ± 1.5 MPa, 4.2 ± 0.5 MPa/m2, and 22.7 ± 1.4 GPa, respectively. Moreover, the presence of impurities retards the phase transformation (6H–4H) of SiC during sintering. To remove impurities in the UN-SiC powders and improve the mechanical properties of the sintered samples, the UN-SiC powders were purified by two methods: HF pickling with mechanical stirring, and HF pickling with ultrasonic-assisted. After ultrasound-assisted pickling, it is suggested that the purity of the powders and the mechanical properties of the obtained samples are significantly improved: the flexural strength increases from 240.9 ± 1.5 to 298.3 ± 39.5 MPa (a 24% increase), the fracture toughness increases from 4.2 ± 0.5 to 5.1 ± 0.2 MPa/m2 (a 21% increase), and the hardness increases from 22.7 ± 1.4 to 26.0 ± 0.8 GPa (a 15% increase). The excellent mechanical properties can be related to the high relative density and fine grain size of the sintered samples.

This work investigates the coarsening of boron carbide grains during the infiltration of porous boron carbide preforms by molten silicon with respect to fabrication of reaction-bonded boron carbide ceramics. Experimental results reveal that the shape of boron carbide grains evolve from the irregular shape to faceted shape due to dissolution-precipitation during infiltration. For infiltration temperatures below 1750 °C, the boron carbide grains are irregular and exhibit an unimodal size distribution, which can be ascribed to the normal grain growth. The growth of the irregular grains follow a cubic law of diffusion control. In contrast, for infiltration temperatures above 1750 °C, the boron carbide grains become faceted and exhibit a bimodal size distribution, indicative of the typical abnormal grain growth. The abnormal growth of faceted grains is proposed to be controlled by coalescence-enhanced two-dimensional nucleation.

In this work, hierarchically mesoporous silica (HMS) microspheres with ordered mesochannels and ultra-large intra-particulate pores are for the first time prepared via a ternary nonionic surfactant templating system (TEOS/P123/HCl(aq.)). Several crucial experimental parameters pertaining to the employed partitioned cooperative self-assembly process and their roles in shaping the mesostructures and morphology were investigated. It was found that relatively low synthesis temperatures, optimal at 36 °C, lead to much improved meso-ordering in the 1st mode mesostructures, while partitioned addition combinations of silica precursor ( e.g. , 6/4 combination) at such temperatures show to play an important role in inducing spherical particle morphology. By simply increasing the hydrothermal treatment (HTT) temperature up to 140 °C, enhanced porosity together with ultra-large intra-particulate pores can be obtained without compromising meso-orderings, depending mainly on the HTT induced mesostructural transformation process. Higher HTT temperature causes the fragmentation in the 1st mode mesostructures and disappearance of meso-orderings. The resultant micro-sized HMS spheres reveal certain clew-like features: the ‘yarns’ comprise bundles of ordered mesochannels (1st mode mesopores, ca. 8–12 nm), while the 2nd mode intra-particulate pores ( ca. 33–128 nm in sizes) exist between the intertwined ‘yarns’. Such HMS microspheres with tunable porous structures might find some interesting applications in chromatographic separations and controlled delivery, etc.

Amino-functionalized mesoporous materials based different mesoporous silica were prepared for the recovery of Mo(VI) from Re(VII)-containing solutions. The adsorption materials were characterized by SEM, HRTEM, TGA, XRD, N2 adsorption–desorption isotherms and Elemental analysis. The optimum type (SS5-1h-5.5@95) of mesoporous silica was determined by anchoring of mesoporous silica substrate with 3-aminopropyltriethoxysilane (APTES) via conventional methods and partitioned cooperative self-assembly process (PCSA process). Adsorption experimental data showed that the SS5-1h-5.5@95-APTES had a high affinity for Mo(VI) from Re(VII), and the maximum adsorption capacity was evaluated as 194.32 mg g− 1 in case of pH 1. Moreover, adsorption behavior, adsorption isotherm, adsorption kinetics and thermodynamics of Mo(VI) on the SS5-1h-5.5@95-APTES were studied, and adsorption mechanism was confirmed by FT-IR, Raman spectra and XPS analysis. The excellent affinity and selectivity make the SS5-1h-5.5@95-APTES become a potential material for recovery Mo(VI) from Re(VII) solution.

This work demonstrated that mesoporous TiO2 (meso-TiO2) with controllable mesoporous and crystalline structures can be facilely prepared by using poly (ethylene glycol) (PEG) as structure-directing (SD) agent and peroxotitanic acid (PTA) as precursor. Meso-TiO2 with high specific surface area (157 m2∙g-1), pore volume (0.45 cm3∙g-1) and large mesopore size of 13.9 nm can be obtained after calcination at 450°C. Such meso-TiO2 also shows relatively high thermal stability. BET surface area still reaches 114 m2∙g-1 after calcination at 550°C. In the synthesis and calcination process, PEG that plays multiple and important roles in delivering thermally stable and tunable mesoporous and crystalline structures shows to be a suitable low-cost SD agent for the controllable preparation of nanocrystalline meso-TiO2. The photocatalytic activity tests show that both high surface area and bi-crystallinity of obtained meso-TiO2 are important in enhancing the performance in photo-decomposing Rhodamine B in water.

In this work, a facile and controllable multi-templating approach based on a solo nonionic surfactant P123 and peroxotitanic acid (PTA) was reported for the preparation of bimodal meso-mesoporous titania (BMM-TiO 2 ) with high surface area (150–243 m 2 g −1 ), high pore volume (0.3–0.6 cm 3 g −1 ), large mesopore sizes spanning from 8 to 16 nm (BJH pore size), and high & tunable crystallinity (Anatase or Anatase + Rutile). The BMM-TiO 2 was shown to be a homogeneous ‘mixture’ of two series of wormhole mesostructures with two modes of mesopore sizes that depend on both the contents of P123 and synthetic conditions. The formation of BMM structures was proposed to arise from both the formation of differentiated micellar structures of P123 (dual soft-templating) and their subsequent different mesostructural shrinkages driven by prolonged drying process ( i.e. , 100 °C for 12 h) in the presence of PTA. The low-temperature crystallization behaviours of PTA, unusual hard-templating effect of P123 and its carbon derivatives (3rd fold templating), large mesopores relative to the surrounding TiO 2 crystals are all believed to be responsible for the high thermal stability of the obtained BMM-TiO 2 . To our knowledge, it is for the first time reported that P123 plays such multiple templating roles (three folds in this work) in the preparation of meso-TiO 2 , not to mention that P123 was also confirmed to be a prerequisite for the formation bi-crystalline BMM-TiO 2 . In the photodegradation test of Rhodamine B in water by UV irradiation, other than the high surface area and synergistic effect between anatase and rutile phases, the BMM structures were also found to be advantageous to enhance the photocatalytic properties of mesoporous TiO 2 .