Search

In this study, porous halloysite nanotube ceramics were prepared by the foam-gelcasting method using sodium carboxymethyl cellulose (CMC) as a foam stabilising agent, Isobam 104 as a dispersant and triethanolamine lauryl sulphate (TLS) as a foaming agent, respectively. Then, the effects of firing temperature on the phase composition, microstructure, and pore size distribution of porous halloysite nanotube ceramics were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunner-Emmet-Teller (BET), thermogravimetry (TG) and differential scanning calorimetry (DSC). The results showed that the prepared porous ceramics contained both mesopores (10–50 nm) and macropores (100–300 μm). As the firing temperature rose, the linear shrinkage and compressive strength of samples increased, while the porosity decreased. When the porosity was as high as 75.7%, the samples still remained the compressive strength of 1.1 MPa, and had the lowest thermal conductivity, reaching 0.194 W/(m·K) (at a testing temperature of 100 °C).

In this study, the relationship between the decomposition process and properties of zircon ceramic was analysed. The decomposition process of zircon was investigated by kinetics model, thermodynamics and experimental phenomena. The Coats-Redfern and Kissinger models were used as basic kinetics models, and thermodynamics, thermogravimetry (TG) and differential scanning calorimetry (DSC) were used to characterize the decomposition process and calculate the kinetics parameters. The microstructure, pores characteristics, densification and physical properties were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Archimedes’ principle. The results showed that the decomposition process of zircon could be divided into two stages, with the first and the second stages controlled by the phase boundary reaction and diffusion control reaction, respectively. The decomposition rate of the first decomposition stage was slow and the mechanism function was g(x) = 1-(1-α)1/3 while the decomposition rate of the second stage was fast and the mechanism function was g(x)=(1–2/3α)-(1-α)2/3. The large decomposition amount of zircon increased the amount of liquid phase, which would reduce the densification of zircon.

Aluminium nitride high-temperature co-fired ceramic (AlN HTCC) substrate is a preferred electronic packaging material. It displays a low thermal expansion coefficient, low dielectric constant, low dielectric loss, and high thermal conductivity at a high frequency. It can also prefabricate the circuit inside. Considering the need to increase the specific surface area of AlN HTCC substrates and thereby enhance the heat dissipation performance, a rapid fabrication method involving chemically assisted laser ablation is proposed to machine microstructures on AlN HTCC substrates. The influence of power, atmosphere, and other factors on the ablation quality of AlN HTCC substrates was explored on this basis. The main component of the ablation products was Al in an Ar atmosphere. However, the modification layers in N2 and O2 atmospheres were composed of multiple components including Al, AlN, and Al2O3. The accuracy of the top and bottom widths of the microgrooves in the Ar atmosphere was higher than those for the N2 and O2 atmospheres. However, the variation of atmosphere had a negligible effect on the ablation depth. When the laser-energy density was 100 J/mm2 and the scanning distance was 10 μm, the ablation depth increased linearly from 150 μm to 350 μm as the laser power increased from 8 W to 20 W. The deviation in laser-energy density was established to predict the surface roughness and optimise the laser parameters. It was observed that the surface roughness increased with an increase in the deviation in laser-energy density. The surface roughness could be reduced by two–three times from that obtained by laser ablation with optimisation.

In this paper, eight zircon granules were prepared by granulation method, using zircon powders as raw material, α-Al2O3 and γ-Al2O3 as additives and sodium carboxymethyl cellulose (CMC) as binder, respectively. Then, the influence of α-Al2O3 and γ-Al2O3 addition on phase composition, lattice parameters, microstructure and physical characterization were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results reveal that Al2O3 could influence the Al2O3–ZrSiO4 system by reacting with SiO2 and dissolving into the zircon crystal lattice. The changing of the crystal lattice and the formation of mullite were the main influence factor. The zircon aggregate with 3.0 wt% γ-Al2O3 rendered an optimal apparent porosity of 25.2 %, a high cylinder compressive strength retention rate of 55.1 %, a relatively homogeneous pore size distribution and a smaller changing in lattice parameters.

The deformation shrinkage of a poly(lactide-co-glycolide) (PLGA) fibrous material seriously affects its biomedical application. To demonstrate the underlying shrinking mechanism and to find a method to prevent the shrinkage of an electrospun PLGA membrane, we investigated the shrinking behavior of PLGA electrospun membranes under various test conditions and discussed the underlying shrinking mechanism. The results indicated that the shrinkage of the electrospun PLGA membrane was mainly regulated by the glass transition of its polymer fiber; the temperature and liquid environment were found to be the two main factors leading to the shrinkage of the electrospun PLGA membrane through affecting its glass transition. Then a heat stretching (HS) technique was proposed by us to stabilize the electrospun PLGA membrane. After HS treatment, the glass transition temperature (Tg) of the electrospun PLGA membrane could increase from 48.38 °C to 54.55 °C. Our results indicated that the HS-treated membranes could maintain a high area percentage of 90.89 ± 2.27% and 84.78 ± 3.36% after immersion respectively in PBS and blood at 37 °C for 2 hours. Further experiments confirmed that the HS technique could also stabilize the dimensional structure of the electrospun PDLLA membrane in PBS and blood at 37 °C. This study provides an effective strategy for preventing the shrinkage of electrospun polyester biomaterials in a physiological environment that may benefit both the material structural stability and the in vivo biological performance.

In this study, five mullite-corundum gas-permeable refractories reinforced by SiC whiskers were prepared with spherical porous mullite-corundum aggregates. The influence of the silicon powder content on the microstructure, phase composition, mechanical and gas-permeability properties were investigated through XRD, SEM and EDS. It was found that the silicon powder content strongly affected the mechanical and gas-permeability properties by changing the formation and distribution of mullite and SiC whiskers. SiC whiskers were formed both in the matrix and inside the pores of the aggregates. As the silicon powder content increased, the amount of SiC whiskers in the pores of the aggregates as well as at the aggregate/matrix interface increased, meanwhile more mullite was also formed at the interface. However, when the silicon powder content was larger than 9 wt%, much less mullite was observed at the interface, reducing the bonding between particles in the matrices. The formation of SiC whiskers and mullite at the interface improved the mechanical properties at a small expense of air permeability. The optimized refractory contained 6 wt% silicon powder which combined the highest cold and hot flexural strength (17.0 MPa and 10.2 MPa, respectively), as well as the best strain at fracture and a homogeneous gas permeability.

In this study, four zircon granules are prepared by using granulation method and using TiO2 and sodium carboxymethyl cellulose (CMC) as a sintering additive and binder, respectively. Then, the effects of TiO2 addition on phase composition, pore size distribution and sintering process are analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results reveal that only a small portion of zircon is decomposed into ZrO2 and SiO2 after sintered at 1250 °C, however, the zircon granules consist of zircon, ZrTiO4 and mullite after sintering at 1550 °C. In general, the addition of TiO2 accelerated the sintering process, promoted the migration rate of grains and transformed the apparent pores into closed pores, resulting in decreased pore size and enhanced compressive strength. The zircon granule, with 2.0 wt% TiO2, rendered an optimal apparent porosity of 24.0%, a high closed porosity of 8.35%, a high cylinder compressive strength retention rate of 44.9% and a relatively homogeneous pore size distribution after sintering at 1550 °C.

Mullite-corundum foamed ceramics were prepared by direct-foaming method using white clay and industrial alumina as raw materials, and calcium aluminate cement (CAC) as the binder. Effects of the calcium aluminate cement content on the phase compositions, microstructures and properties of the foamed ceramics were investigated through X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), etc. The results showed that with increasing the calcium aluminate cement content from 0 wt% to 8 wt%, the viscosities of the initial slurries decreased, the porosities of the samples improved, the thermal conductivities decreased, and the compressive strengths increased first and then decreased. The optimized sample with 4.0 wt% CAC content had a high porosity of 80.8%, a low bulk density of 0.56 g/cm3 and a low thermal conductivity of 0.232 W/(m·K) (800 °C). On the foundation of research results, the Gong equation (GE model) and a modified GE model were used to predict the thermal conductivity at 200 °C and 800 °C of the mullite-corundum foamed ceramics with different pore characteristics and phase compositions, respectively.

SKD11 is widely used in manufacturing die. With the development of industrial level, the size of the die is further reduced, and the difficult processing problem of high aspect ratio (HAR) micro-structures is exposed. Micro-milling is a suitable method for machining HAR micro-structures; however, the inevitable generation of burrs deteriorates the machined surface. Previous studies have mostly focused on the burr formation process of shallow grooves but have ignored HAR grooves. This paper investigated the burr formation mechanism in HAR (2:1) grooves on harden steel (SKD11). Due to the fact that the burr formation process was difficult to be observed in the actual micro-milling process, a finite element model was established. A corresponding experimental research was conducted, which revealed a good consistency between simulation and experimental results. Moreover, a new burr type was formed on the sidewall of the HAR groove, which was transformed from top burrs and was named as side burr. The results demonstrated that the chip flow on the rake face of the micro-mill was hindered by the sidewall, which caused chip crumbling, chip accumulation, and surface scraping, seriously affecting the burr formation mechanism. This paper revealed the burr formation mechanism for HAR grooves on SKD11, which provides basic data for manufacturing die with complex structure and small size.

The development of multi-functional strontium (Sr) and simvastatin (SIM) loaded biomaterials to promote angiogenesis and osteogenesis is a promising therapeutic strategy. In order to overcome the complex synthesis process, low drug loading and burst release of drug-loaded biomaterials, in this study, we developed a microwave-assisted hydrothermal one-step approach to prepare Sr- and SIM-loaded hydroxyapatite microspheres for achieving long-term sustained-release of Sr and SIM. The developed one-step preparation method can maintain the chemical structure of simvastatin, and the drug loading rate of simvastatin can reach more than 30 wt%. The prepared double-loaded hydroxyapatite microspheres could sustainable release Sr and SIM for more than 35 days. The prepared hydroxyapatite microspheres containing Sr and SIM have a good application prospect in promoting bone formation. This simple and feasible one-step method can also provide reference for the preparation of other drug-loading microspheres.

Scaffold degradation regulation has become the key aspects in promoting bone regeneration and reconstruction. In the study, a novel stepwise-degraded PLGA/PCL/HA:Yb/Ho/Zn (PPHZ) scaffold was designed to compare with the fast-degradable PLGA/HA:Yb/Ho/Zn (PLHZ) scaffold to investigate the effects of scaffold degradation regulation on osteogenesis and to trace the scaffold degradation process. Micro-CT reconstruction, confocal fluorescence imaging, and histological sections were used for the analyses of the harvested animal samples, which demonstrated that the degradation regulated stepwise-degraded PPHZ scaffold maintaining higher mechanical strength and longer scaffold integrity is more advantageous for in vivo osteogenesis than the fast-degradable PLHZ scaffold. Meanwhile, the multifunctional HZ particles would help the anti-infection and tracking the distribution during scaffold degradation. The PPHZ scaffold may benefit future repair of anti-infective bone defects and in vivo multimodal tracking.

ICCD was one of the main instruments in the experimental system of Laser-induced breakdown spectroscopy (LIBS). It was used to realize photoelectric conversion. Gain was the key parameter of ICCD, and the gain had a great influence on the acquisition of spectra. In this paper, the effect of ICCD gain on the intensity and Signal-to-Background Ratio (SBR) of the laser-induced alloy steel spectra has been investigated. Furthermore, the influence of ICCD gain on the detection sensitivity and detection of limit (LOD) of the trace elements (Mn, Cr)in alloy steel has also been studied. It is found that when the ICCD gain varies from 0 to 4000, both the spectral intensity and background increase with the gain, and the SBR of the spectra first shows a rapid growth trend with the increase of the gain. Then the curve of the SBR with the gain has a tendency of saturation. The internal standard method is used to quantitatively analyze the trace elements (Mn, Cr) in the alloy steel. The results have shown that the ICCD gain affects the detection sensitivity of the elements. With the increase of the gain, the LOD of the two elements is decreasing gradually. When the gain is greater than 2000, the LOD is stable at a certain value. Considering the results of spectral signal and quantitative analysis of the trace elements, the optimal ICCD gain can be set to 2000. The results of this paper will help to further optimize the parameters of the experimental system and improve the analysis performance of LIBS.

The well dispersed and porous PMo12-rGO nanocomposite was synthesized via a chemical reduction method by the facile and economical reducing agent of thiourea. By optimizing the amount of reducing agent of thiourea, PMo12 was reduced to heteropoly blue, and then reacted with GO to assemble PMo12 clusters onto the rGO by the strong interaction between rGO and PMo12. The SEM, HTEM, FT-IR, UV–vis, XPS and Raman were performed to verify the structure of the PMo12-rGO nanocomposite. The as-prepared PMo12-rGO nanocomposite exhibits high stability and excellent electrocatalytic activity towards the reduction of nitrite and hydrogen peroxide compared with individual PMo12 catalysts, which could be mostly attributed to the synergistic effects of rGO and PMo12. The method is facile, economical and suitable for mass production and common POMs, which opens a new way to fabricate a wide range of hybrid materials using different type of polyoxometalates, and such as-prepared materials have potential applications in catalysis, electrochemisty and related fields.

In this paper, CaO granules were prepared, using the slaked lime as the raw material as well as ZrO2, TiO2, and V2O5 as additives, respectively. The influence of different additives on the sintering properties, microstructure and hydration resistance of CaO granules was investigated. The results indicated that the introduction of additives could obviously promote the densification and the hydration resistance of the specimens. Especially, the sintering mechanisms of the specimens with different additives were studied. For the specimens with ZrO2 and TiO2 as additives, the in-situ formed CaZrO3 and Ca3Ti2O7 between grain boundaries promoted the densification to enhance the properties of the granules. However, the adding of V2O5 generated a coating on the surfaces of CaO granules which contributed to the best hydration resistance.