Synthesis of functional gradient BCP/ZrO2 bone substitutes using ZrO2 and BCP nanopowders

BCP/BCP-ZrO₂/ZrO₂ scaffold with a functionally gradient layered structure (FG BCP/ZrO₂) was fabricated by the polymeric sponge replica method and subsequent dipping process. To enhance the compressive strength and bioactive properties of monolithic ZrO₂ scaffold, ZrO₂ and BCP phases were selected as a main frame and surface layer, respectively. The formation of microcracks was significantly decreased by incorporating an intermediate layer consisting of BCP-ZrO₂ phase. The thicknesses of the monolithic ZrO₂, BCP-ZrO₂, and BCP layer were around 10-30 μm, 3-5 μm, and 2-3 μm, respectively. The FG BCP/ZrO₂ scaffold showed highly interconnected pores as well as good material properties, which were 68% porosity and 7.2 MPa of compressive strength. Average pore size of FG BCP/ZrO₂ scaffold was about 220 μm in diameter. From MTT assay and SEM observation of osteoblast-like MG-63 cells, FG BCP/ZrO₂ scaffold showed good cell viability and faster proliferation behavior.     

Large-scale and ultra-low thermal conductivity of ZrO2 fibrofelt/ZrO2-SiO2 aerogels composites for thermal insulation

The large-scale fibrous/aerogels composites are prepared by using zirconia fibrofelt (ZFF) as skeleton to give high strength and ZrO₂-SiO₂ aerogels (ZSA) as filler to give excellent thermal insulation through vacuum impregnation. The ZFF/ZSA with a low density of 0.302?g/cm³ and a high porosity (89%) exhibits large size of 180?mm in length, 180?mm in width and 25?mm in height which is larger than other fibrous aerogels. Meanwhile, the ZFF/ZSA exhibits high compressive strength of up to 0.17?MPa which is approximately six times higher than that of ZFF (0.028?MPa). The ZFF/ZSA shows a much lower thermal conductivity of 0.0341?W?m^?1 K^?1 at room temperature and 0.0460–0.096?m^?1 K^?1 during 500?°C and 1100?°C which are lower than that of conventional fibrous materials, indicating its excellent thermal insulation property in a wide temperature range, and the thermal insulation mechanism is analyzed. Thus, the large-scale, low density, high strength, and low thermal conductivity of ZFF/ZSA composites show enormous potential application in the fields of architecture, engineering pipes and aerospace for thermal insulation and protection.     

Preparation and characterization of ZrO2/PES hybrid ultrafiltration membrane with uniform ZrO2 nanoparticles

In current or next-generation reuse systems, the development of new classes of antifouling membranes is needed before viable membrane-based approaches for wastewater reclamation can be achieved. In this study, ZrO₂/PES hybrid ultrafiltration membranes with uniform ZrO₂ nanoparticles were prepared by combining an ion-exchange process with a traditional immersion precipitation process. Hydrous ZrO₂ sol was synthesized by addition of anion-exchange resin in N,N-dimethylformamide solvent containing zirconyl chloride. Homogeneous ZrO₂/PES casting solution was then obtained by dissolving PES polymer in the ZrO₂ sol. The existence and dispersion states of ZrO₂ nanoparticles in the resultant membrane matrix were examined by X-ray photoelectron spectrometer, thermogravimetric analysis, scanning electron microscope and transmission electron microscope. The results indicate that the ZrO₂ nanoparticles were well dispersed throughout the PES matrix and the diameter of the formed nanoparticles was about 5–10 nm. The hydrophilicity of the membranes was determined by measuring the contact angles. The antifouling property was determined by antifouling experiments and atomic force microscopy. The results confirm that the existence of ZrO₂ nanoparticles improves the hydrophilicity and reduces protein adsorption of membranes.     

Preparation and characterization of monoclinic rod-shaped ZrO2 whiskers via sulfate flux

Monoclinic rod-shaped ZrO₂ whiskers were prepared in liquid conditions using a sulfate flux with ZnSO₄ and Na₂SO₄ in an alumina crucible. TG-DSC, XRD, SEM, TEM, HRTEM, SAED and EDS were employed to characterize the structure, morphology and growth mechanism of the as-synthesized whiskers. The results demonstrated that both the heating temperature and holding time influence the formation of ZrO₂ whiskers. When the heating temperature and holding time were 900?°C and 30?min, the ZrO₂ whiskers were elongated along the [$0\overline{1}1$] direction, had an average length and diameter of 600?nm and 70?nm, and exhibited a well-crystallized, one-dimensional structure and smooth surface with no distinct defects. The growth of the whiskers was dominated by the liquid-solid (LS) growth mechanism, affording anisotropic growth through dissolution/recrystallization.     

Adsorption/desorption of NOx on MnO2/ZrO2 oxides prepared in reverse microemulsions

A series of MnO₂/ZrO₂ mixed oxides were prepared in reverse microemulsions for NOx adsorption and abatement. The results show that the amount of NOx adsorbed was increased with increasing MnO₂ content in various MnO₂/ZrO₂ samples. The maximum uptake value of NOx was 27.66 mg NOx/g adsorbent on the 40% Mn–Zr sample at 200 °C with NOx initial adsorption rate as 2.63 mg/(g adsorbent min). TPD results show that the complete desorption of NOx was easily obtained by heating the sample to 450 °C, and the temperature for the complete desorption can be further decreased to 210 °C by adding carbon monoxide into the argon desorption streams. Furthermore, water vapor was found to reduce NOx adsorption capacity because of its stronger competitive adsorption with NOx species. It is noteworthy that a small amount of sulfur dioxide could significantly increase the initial rate of NOx adsorption although it slightly decreased the NOx adsorption capacity.     

Toluene oxidation on Pd catalysts supported by CeO2–Y2O3 washcoated cordierite honeycomb

A novel CeO₂–Y₂O₃ (CY) washcoat on cordierite honeycomb was prepared by an impregnation method, which was used as a support to prepare a Pd catalyst. A model reaction of the complete combustion of toluene was conducted to evaluate the performance of the developed Pd/CY catalyst. The CY washcoat support and the Pd/CY catalyst were characterized by XRD, Raman spectroscopy, H₂-TPR and SEM techniques. The results show that compared with conventional washcoat the CY washcoat has better adhesion and higher vibration- and heat-resistance. The CY washcoat can anchor well Pd onto the cordierite honeycomb substrate. The formation of a CeO₂–Y₂O₃ solid solution and the steady present of PdO occur at high calcination temperatures, resulting in a better thermal stability. On a Pd/CY catalyst calcined at 500 °C, a 99% of toluene conversion was obtained at 210 °C, and it was stable for reaction time up to 30 h.     

流体流动型态对膜通量影响的实验和计算流体力学研究

This paper reports a study on the role of fluid flow pattern and dynamic pressure on the permeate flux through a micro filtration membrane in laboratory scale. For this purpose, a dead-end membrane cell equipped with a marine type impeller was used. The impeller was set to rotate in the clockwise and counter clockwise directions with the same angular velocities in order to illustrate the effect of rotation direction on permeate flux. Consequently, permeate fluxes were measured at various impeller rotational speeds. The computational fluid dynamics (CFD) pre-dicted dynamic pressure was related to the fluxes obtained in the experiments. Using the CFD modeling, it is proven that the change in dynamic pressure upon the membrane surface has direct effect on the permeate flux.     

A comparative study of water gas shift reaction over gold and platinum supported on ZrO2 and CeO2–ZrO2

In this study platinum- and gold-based catalysts supported on ZrO₂ and ceria–zirconia solid solution have been characterized by several techniques (TPR, XRD, BET, HRTEM) and tested in the water gas shift (WGS) reaction under feed conditions typical of an autothermal reformer outlet. Platinum and gold catalysts behave differently especially in the range of 423–513 K, with gold being superior than platinum. The possibility of modifying the redox and structural characteristics of zirconia with the insertion of ceria allowed us to conclude that the bulk redox properties of the support play a secondary role, while the key parameter for an active WGS catalyst is the nature of metal support interface. This, in turn, depends on the metal particle distribution and on the structural and morphological properties of support. It has been found that the synergism between precious metals and support can be designed with an appropriate choice of the parameters of synthesis and the characteristics of support.     

Influence of carbon on phase stability of tetragonal ZrO2

In the present work, nanocrystallite ZrO₂ was synthesized by calcining zirconium (IV) acetylacetonate. X-ray diffraction results show the existence of tetragonal phase even when the nanocrystallite size reached ~47 nm. The presence of amorphous carbon was identified by Raman analysis while the Zr–C bonding was confirmed by X-ray photoelectron spectroscopy analysis. Transmission electron microscopy showed no hard-agglomeration in the samples treated at high temperatures. These results indicated that carbon has influence on the phase stability of t-ZrO₂ in two aspects: the amorphous carbon creates a reducing atmosphere, meanwhile carbon atoms bonded with zirconium atoms act as a stabilizer.     

SO42-/ZrO2催化膜的制备及其酯化性能研究

制备了负载SO24-/ZrO2固体酸陶瓷膜,并对其用于油酸和甲醇酯化反应进行研究。通过测定不同反应温度、不同催化膜负载率和不同甲醇/油酸物质的量的比条件下油酸的转化率,线性回归得到了酯化反应动力学参数。研究结果表明,酯化反应为拟均相二级反应。在最佳反应条件下,反应活化能由49.1 kJ/mol降至34.6 kJ/mol,油酸酯化率达到95.84%。     

ZrO2 对堇青石多孔陶瓷性能和显微结构的影响

以高岭土、滑石和αAl2O3微粉为主要原料,按堇青石的理论组成配料后,外加10%的化学纯活性炭为造孔剂,同时分别外加0、0.25%、0.5%、0.75%和1.0%的分析纯ZrO2,经湿混、干燥、造粒、成型和1340℃保温5h烧成后,制成不同ZrO2含量的堇青石多孔陶瓷,并研究了ZrO2外加量对试样热膨胀系数、显气孔率、吸水率及烧成收缩率的影响,并用XRD和SEM分析了试样的物相组成和断面形貌。结果表明:与未加ZrO2的相比,外加0.25%ZrO2时,试样的热膨胀系数显著降低,但超过0.25%时,热膨胀系数随ZrO2外加量的增加而略有升高;随ZrO2外加量的增加,试样的显气孔率和吸水率逐渐增大,而烧成收缩率降低;与未加ZrO2的试样相比,外加1.0%ZrO的试样内扁平状气孔的数量较多,且气孔在试样内分布较均匀。     

Phase stability and thermo-physical properties of ZrO2-CeO2-TiO2 ceramics for thermal barrier coatings

The properties of ZrO₂ co-stabilized by CeO₂ and TiO₂ ceramic bulks were investigated for potential thermal barrier coating (TBC) applications. Results showed that the (Ce_0.15Ti_x)Zr_0.85-xO7 (x?=?0.05, 0.10, 0.15) compositions with single tetragonal phase were more stable than the traditional 8YSZ at 1573?K. These compositions also showed a large thermal expansion coefficient (TEC) and a high fracture toughness, which were comparable to those of YSZ. However, the phase stability, fracture toughness and sintering resistance of the CeO₂-TiO₂-ZrO₂ system showed a decline tendency with the increase of TiO₂ content. The TEC of the ceramic bulks decreased with increase of TiO₂ content as well because the crystal energy was enhanced with increasing substitution of Zr⁴⁺ by smaller Ti⁴⁺. The (Ce_0.15Ti_0.05)Zr_0.8O₂ had the best comprehensive properties among the (Ce_0.15Ti_x)Zr_0.85-xO₂ compositions as well as a low thermal conductivity. Therefore, it can be explored as a TBC candidate material for high-temperature applications.     

Effect of calcination treatment of zirconia on W/ZrO2 catalysts for transesterification

In this present study, the nanocrystalline ZrO₂ particles synthesized by the solvothermal method were calcined in reductive (H₂), inert (N₂) and oxidative (O₂ and air) atmospheres prior to impregnation with tungsten (W) in order to produce the W/ZrO₂ (WZ) catalysts. Based on the ESR measurement, it revealed that only the ZrO₂ samples calcined in H₂ and N₂ exhibited the F-center (single charged oxygen vacancy) at g = 2.003. None of Zr³⁺ defect was detected for all calcined ZrO₂ samples. After impregnation with tungsten, the WZ catalysts were also characterized. It was present as the polycrystal, which can be seen by the selected area electron distribution (SAED). However, the presence of Zr³⁺ defect was evident in all WZ catalysts, while the F-center was absent. The highest Zr³⁺ intensity detected in the WZ catalyst using ZrO₂ under H₂ calcination atmosphere can be attributed to the transformation of F-center to Zr³⁺ defect. It revealed that the WZ-H₂ catalyst exhibited the highest conversion under transesterification of triacetin and methanol among other WZ catalysts. This can be attributed to the high surface acidity, which was probably induced by large amounts of Zr³⁺ defect.     

Improvements on the mechanical properties and thermal shock behaviours of MgO-spinel composite refractories by ZrO2 incorporation

Microstructural features and improvements on the mechanical properties and thermal shock behaviours of MgO-spinel composite refractories with ZrO₂ addition were examined. ZrO₂ incorporation into MgO-spinel led to improvements around ∼1.5-fold ratios on mechanical properties, R_st values and thermal shock results. The basic parameters improving mechanical properties and thermal shock resistance of MgO-spinel-ZrO₂ composite refractories were determined as follows: (i) propagation of microcracks for a short distance by interlinking each other, (ii) stopping or deviation of microcracks when reaching pores or ZrO₂ particles, (iii) concurrent occurrence of mostly intergranular and some transgranular cracks on fracture surfaces, and with the addition of ZrO₂ (iv) the increase in bulk density, and (v) a significant decrease in MgO grain size. The improvements observed in thermo-mechanical properties confirmed that MgO-spinel-ZrO₂ refractories showed a low strength loss and high thermal shock damage resistance at high temperatures, leading to longer service lives for using industrial applications.     

Preparation and properties of transparent PMMA/ZrO2 nanocomposites using 2-hydroxyethyl methacrylate as a coupling agent

Transparent PMMA/ZrO₂ nanocomposites were prepared by in-situ bulk polymerization of methyl methacrylate (MMA)/ZrO₂ dispersions that were firstly synthesized using nonaqueous synthesized ZrO₂ nanocrystals and the function monomer, 2-hydroxyethyl methacrylate (HEMA), as the ligand. The dispersion behavior of ZrO₂ nanoparticles in MMA, structure, mechanical and thermal properties of the PMMA/ZrO₂ nanocomposites were investigated comprehensively. It was found that ZrO₂ nanoparticles were well dispersed in MMA with HEMA ligand, but the MMA/ZrO₂ dispersions easily destabilized in air as well as at elevated temperatures. The destabilization temperature of the dispersion is raised by increasing the molar ratio of HEMA/ZrO₂ to match the bulk polymerization temperature. The PMMA/ZrO₂ nanocomposites showed an interesting chemical structure (namely, highly cross-linked structure even at ZrO₂ content as low as 0.8 wt% and hydrogen bonding interaction between polymer matrix and ZrO₂ nanoparticles), with enhanced rigidity without loss of the toughness and improved thermal stability. The relationship between the structure and the properties of the PMMA/ZrO₂ nanocomposites based on the HEMA coupling agent was discussed.     

Effects of operating conditions on membrane charge property and nanofiltration

The effects of the operating pressure, cross flow velocity, feed concentration, and temperature on the streaming and Zeta potential of the membranes were studied. The permeate flux and the retention rate under different nanofiltration operating conditions were also investigated. The results show that the higher pressure, feed concentration, temperature, and lower cross flow velocity lead to the higher absolute value of streaming and Zeta potential. The permeate flux of the nanofiltration decreases with the feed concentration and increases with not only the pressure but also the cross flow velocity and temperature. The higher the pressure and the cross flow velocity, the higher the retention rate. The lower feed concentration and higher temperature leads to lower retention rate. The effects of the operating conditions on the permeate flux and the retention rate were explained by the variation of the membrane charge property.     

The synergistic combination of bis-silane and CeO2·ZrO2 nanoparticles on the electrochemical behaviour of galvanised steel in NaCl solutions

Bis-1,2-[triethoxysilylpropyl]tetrasulfide silane films containing CeO₂·ZrO₂ nanoparticles were deposited by dip-coating on galvanised steel substrates. The morphological features of the coated substrates were evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The anti-corrosion performance of the modified silane film applied on galvanised steel substrates was studied by electrochemical impedance spectroscopy (EIS). The ability of nanoparticles to mitigate localized corrosion activity at artificially induced defects was investigated via the scanning vibrating electrode technique (SVET) and by the scanning ion-selective electrode technique (SIET). The results showed that the addition of nanoparticles provides good corrosion protection of the galvanised steel substrates pre-treated with the modified silane solutions. The corrosion activity was reduced by more than one order of magnitude. Complementary d.c. experiments, using zinc electrodes exposed to NaCl solutions containing the nanoparticles were also performed in order to better understand the role of the nanoparticles. An ennoblement of the corrosion potential and polarisation of the anodic reactions could be detected.     

Nickel cuprate supported on cordierite as an active catalyst for CO oxidation by O2

The physicochemical, surface and catalytic properties of 10 and 20 wt% CuO, NiO or (CuO–NiO) supported on cordierite (commercial grade) calcined at 350–700 °C were investigated using XRD, EDX, nitrogen adsorption at −196 °C and CO oxidation by O₂ at 220–280 °C. The results obtained revealed that the employed cordierite preheated at 350–700 °C was well-crystallized magnesium aluminum silicate (Mg₂Al₄Si₅O₁₈). Loading of 20 wt% CuO or NiO on the cordierite surface followed by calcination at 350 °C led to dissolution of a limited amount of both CuO and NiO in the cordierite lattice. The portions of CuO and NiO dissolved increased upon increasing the calcination temperature. Treating a cordierite sample with 20 wt% (CuO–NiO) followed by heating at 350 °C led to solid–solid interaction between some of the oxides present yielding nickel cuprate. The formation of NiCuO₂ was stimulated by increasing the calcination temperature above 350 °C. However, raising the temperature up to ≥550 °C led to distortion of cuprate phase. The chemical affinity towards the formation of NiCuO₂ acted as a driving force for migration of some of copper and nickel oxides from the bulk of the solid towards their surface by heating at 500–700 °C. The S_BET of cordierite increased several times by treating with small amounts of NiO, CuO or their binary mixtures. The increase was, however, less pronounced upon treating the cordierite support with CuO–NiO. The catalytic activity of the cordierite increased progressively by increasing the amount of oxide(s) added. The mixed oxides system supported on cordierite and calcined at 450–700 °C exhibited the highest catalytic activity due to formation of the nickel cuprate phase. However, the catalytic activity of the mixed oxides system reached a maximum limit upon heating at 500 °C then decreased upon heating at temperature above this limit due to the deformation of the nickel cuprate phase.     

Large scale synthesis of non-transformable tetragonal Sc2O3, Y2O3 doped ZrO2 nanopowders via the citric acid based gel method to obtain plasma sprayed coating

Non-transformable tetragonal scandia, yttria doped zirconia (SYDZ) nanopowders were prepared in large scale by the citric acid (CA) based gel method. The effect of ethylene glycol monobutyl ether (EGM):CA ratios and pH on the structure, morphology and SYDZ particle size was investigated. The microstructure of SYDZ was characterized by XRD, Raman scattering, TG–DTA, SEM, TEM, and FTIR analyses. The SYDZ nanopowders, synthesized with 1Zr⁴⁺:4EGM:4CA mole ratio in acidic medium (pH ∼1) at 700 °C, had an average diameter of 15±2 nm. Finally, air plasma spray (APS) coatings were produced from nanostructured SYDZ agglomerated powders.     

Application of microfiltration and ultrafiltration processes to cork processing wastewaters and assessment of the membrane fouling

The filtration of wastewaters generated in the cork industrial process is investigated by using three membranes in tangential filtration laboratory equipment. The three membranes used were two microfiltration membranes with pores sizes of 0.65 and 0.1 μm (DUR-0.65 and DUR-0.1 membranes), and a ultrafiltration membrane with a molecular weight cut-off of 300 kDa (BIO-300K membrane). The water hydraulic permeability was determined for each membrane (values of 860, 248 and 769 L h⁻¹ m⁻² bar⁻¹ were found), and the influence on the permeate flux of the main operating variables, such as transmembrane pressure, feed flow rate, temperature and nature of the membranes, was established. The effectiveness of the different membranes and operating conditions was evaluated by determining the removal obtained for several parameters which measure the global pollutant content of the effluent: COD, absorbance at 254 nm, tannic content, color and ellagic acid, which is selected as a major model pollutant among the different organic compounds present in this wastewater. The values of the corresponding retention coefficients depended on the operating conditions, but in all cases were in the sequence: ellagic acid and color > absorbance at 254 nm > tannic content > COD. Globally, the higher removals were obtained for the BIO-300K membrane at 20 °C, with Q_F = 5.3 L h⁻¹ and TMP = 1.8 bar. Finally, the fouling of the membranes was assessed, and the corresponding mechanism for each membrane was established by fitting the experimental data to various filtration fouling models reported in the literature.