Combustion synthesis of porous ceramic β- Si3N4 -based composites with the use of ferroalloys

A method for manufacturing silicon nitride-based composites with a desired porosity using a self-propagating high-temperature synthesis has been developed. The effects of the composition of starting specimens, pressure and diameter on the combustion parameters of pre-structured specimens based on ferro-silicoaluminum with addition of aqueous-alkali solution were studied. The phase composition of composites was determined. The obtained composites showed porosities of 25.11%–55.08% with a predominance of open pores of average size in the range of 21–305 μm.     

Characterization of smectite after acid activation with microwave irradiation

The effect of acid activation under microwave (MW) irradiation on the textural and structural properties of a smectite from Maghnia (Algeria) was investigated.Sample aliquots were treated with 2 M hydrochloric acid for various times under variable irradiation power. The influence of activation parameters (MW power and time duration) on the textural and structural properties of the activated samples (crystallinity, specific surface area, pore volume, pore diameter, porosity, pore size distribution and morphology) have been studied.The prepared materials were characterized by X-ray diffraction, Differential Thermal and Thermo Gravimetric Analysis (DTA and TGA), Scanning Electron Microscopy (SEM) and nitrogen adsorption/desorption to obtain information about their structure and surface texture.The treated samples consisted of microporous and mesoporous structures. The specific surface area, pore diameter and pore volume of an adsorbent prepared by the microwave-heating method were 165.80 m²/g, 50 nm and 0.1919 cm³/g, respectively. The pore volumes of mesopores and micropores were 163.90 · 10^− 3 and 28.89 · 10^− 3 cm³/g, respectively. Furthermore, small pores were created in the prepared materials with microwave irradiation.     

Characterisation of porous glasses prepared from Cathode Ray Tube (CRT)

Display tubes such as those used in TV receivers and computer monitors have an evacuated glass envelope, which consists mainly of a screen (front component) and a funnel (back component hidden inside the TV set or monitor). These two components have different compositions: the screen is composed of lead-free glass with strontium and barium oxides, whereas the funnel is composed of glass with lead oxides. In order to comply with future government measures, a method is required for the recycling or re-utilisation of CRT (Cathode Ray Tube) glasses in end-of-life electronic goods. One open-loop recycling method is to create foam glasses from CRTs using a reducing agent. The results for the chemical compositions of these glasses and their physical properties showed that foam glasses can be prepared from glasses from various CRT glassmakers. In this paper, we use several methods to determine the structures of these foam glasses. We use helium pycnometry, Hg porosimetry, specific surface area measurements and scanning electron microscopy as direct methods for determining foam glass structure. These methods provide information about the morphologies and reactivities of these porous materials. Densities, porosities and pore size distributions were measured, which enable us to suggest some potential applications for the fabricated foam glasses.     

Synthesis and characterization of composites based on polyaniline and styrene–divinylbenzene copolymer using benzoyl peroxide as oxidant agent

This work presents a method to prepare composites based on polyaniline (Pani) and styrene–divinylbenzene copolymers (SD) by in situ polymerization of aniline using benzoyl peroxide as oxidant agent. The composites were obtained from copolymers with two degrees of porosities which have higher and lower surface areas. Emeraldine Pani was prepared using hydrochloric acid as dopant. One cycle or four cycles of aniline polymerization were performed. The copolymers and their respective composites characterizations were performed by infrared spectroscopy, thermogravimetric analysis, physical nitrogen adsorption–desorption measurements, morphology analysis, elemental analysis and determination of Brönsted acid sites. The Pani was distributed overall porous SD copolymer producing composites with high surface area. Then, they were evaluated as catalysts for esterification reaction of a fat acid. It was found that that composites prepared with four cycles of in situ polymerization presented best catalytic activity than one cycle composites.     

Effect of fabric structure on the permeability and regeneration ability of porous SiCf/SiC composite prepared by CVI

In this paper, porous SiC_f/SiC composites are prepared by chemical vapor infiltration of SiC matrix on stitched fibrous preforms with different fabrics laminate structure. The microstructure of the fibrous preforms before and after infiltration of SiC matrix and the permeability and the regeneration efficiency of the porous SiC_f/SiC composites with different laminate structure have been determined. Experimental results show that the porous SiC_f/SiC composites with twill fabrics laminate structure exhibits a higher permeability with a higher volume porosity and mean pore diameter. In comparing the regeneration ability of two types laminate structure filter medium, as expected, the twill fabrics laminate structure exhibits a better regeneration efficiency than the plain fabrics laminate structure due to its higher air permeability.     

勃氏法测定水泥的比表面积

介绍了按照GB/T 8074-208《水泥比表面积测定方法勃氏法》测定水泥比表面积的方法,并对怒江州某水泥厂生产的水泥进行检测。通过对试验方法和检测结果的精密度、准确度进行分析讨论,以达到更好地应用在实际检测工作中的目的。     

Freeze-cast composite scaffolds prepared from sol-gel derived 58S bioactive glass and polycaprolactone

This work deals with the preparation of freeze-cast scaffolds using sol-gel derived 58S bioactive glass and a hypoeutectic naphthalene-camphor mixture as the starting powder and freezing vehicle, respectively. After the freeze-casting step, samples were air sintered at 1250?°C for 2?h, which led to the crystallization of 58S. The obtained scaffolds were subsequently infiltrated with poly(ε-caprolactone) (PCL), a biodegradable polymer with potential application for bone tissue repair. The prepared materials were examined by helium pycnometry, laser granulometry, scanning electron microscopy (SEM), Archimedes tests, X-ray microtomography (micro-CT), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption, X-ray diffraction (XRD), and uniaxial compression tests. Samples cytotoxicity was evaluated by (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium reduction (MTT) and LIVE/DEAD assays. Their biocompatibility was also examined after soaking in a simulated body fluid (SBF) solution at 37?°C for up to 14 days. It was observed that the infiltration of PCL into the 58S scaffolds greatly increased their mechanical stability. Moreover, it was shown that these composites displayed a high cell viability (above 70%), which reveals that they did not interfere in the production of osteoblast cells. A hydroxyapatite coating was observed on the samples surface upon soaking in SBF, reinforcing that they are biocompatible materials. As far as we know, this is the first time that freeze-cast scaffolds were obtained using sol-gel derived 58S particles and a naphthalene-camphor mixture. Besides, as the infiltration of PCL into freeze-cast bioactive glass scaffolds improved their mechanical stability without impairing their bioactivity, this is a promising approach to prepare samples for load-bearing applications in bone tissue engineering.     

Characterisation of thermal barrier coatings and ultra high temperature composites deposited in a low pressure plasma reactor

A low pressure plasma process working at 600-800 Pa was used to deposit from aqueous solution ZrO₂-4 mol% Y₂O₃ (Yttria partially stabilized Zirconia-YpSZ) layers and stacks of Ta₂O₅/YpSZ layers for use as thermal barrier coatings (TBC). The observation of the cross section revealed a high porosity. The thermal diffusivity of the layers (1 × 10⁻⁷ m² s⁻¹) was measured by a laser flash technique and compared with values obtained on air plasma sprayed material (3 × 10⁻⁷ m² s⁻¹). The plasma reactor were also used to deposit ZrB₂-ZrO₂-SiC layers used as Ultra High Temperature Composite (UHTC) from aqueous solutions of zirconyl and Boron nitrates containing suspensions of SiC. Layers up to 100 μm thick were obtained on SiC substrates. XRD was used to study the crystallinity of the layer. The presence of ZrB₂ and SiC phases was confirmed after the deposition. XRD analysis showed that heat treatment at 1073 K under oxidizing conditions led to the loss of ZrB₂ and the appearance of ZrO₂ phases. To understand the behaviour of the layers to interaction with atomic oxygen (combustion for TBC and spacecraft re-entry phase for UHTC), we have measured the atomic oxygen recombination coefficient to determine the number of adsorption sites on the surface of the coatings. This was accomplished by using a low pressure plasma reactor coupled with optical spectroscopic measurements as a diagnostic technique.     

环氧树脂多孔复合材料的制备及性能

以环氧树脂为基体、蓖麻油酸(RA)或二聚蓖麻油酸(DRA)改性的四乙烯五胺(TEPA)(RATEPA/DRATEPA)作为固化剂、水为致孔剂、釉粉为无机填料,通过树脂-水-填料悬浮乳液复合体系聚合法,在室温下合成了环氧树脂多孔材料,采用SEM、压汞仪、电子万能试验机、TGA对多孔材料的形貌、孔径分布、孔隙率、机械性能及热性能进行了表征和测试。结果表明:随着水相质量分数和填料粒径的增大,多孔材料的孔径和孔隙率增大,压缩强度减小;随着固化剂分子量的增大,多孔材料的孔径和孔隙率减小,压缩强度增大。当填料粒径为40μm,固化剂为RATEPA,m(水相)∶m(树脂相)=2∶1时,多孔材料的综合性能最佳,其最可几孔径为3.449μm,孔隙率为21.8%,压缩强度为26.89 MPa。TGA和DTG测试结果表明:环氧树脂多孔材料的热稳定良好,具有耐高温性能,可以在高温条件下应用。     

Elaboration and characterization of porous granules based on waste glass

The evolutions of the world today and the population increase have resulted in pollution and human wastes, which contaminate the environment and adversely affect the human's quality of life.All forms of food and drink packages, made of paper, plastic foam, aluminum and glass, are designed for the consumers' convenience. After being used, these packages are discarded as garbage and have today become a social problem.It is in this context that our work for obtaining a building material (foam glass granules) that is much lighter is registered with the properties of heat insulation and acoustic improved based on cullet in order to recycle it and for improving the present laws about the waste products in closed circuit (finished products → waste products → finished products).Investigations have shown that grinding waste glass to particle size less than 0.1 mm and adding 1% of Ca CO₃ content provide the production of material with the following properties: particle density of 0.5 g/cm³, strength of 17.50 MPa and water adsorption of 95%, with the temperature for foaming ranges determined at 850 °C. The microstructures are homogenous, with pore sizes of up to 2 mm. The foam glass is counted among the new glass products meeting certain requirements on comfort, in particular in the building industry (thermal and acoustic insulation). The product obtained presents excellent thermal (λ = 0,031 W/m°C) and acoustic (R = 15 dB) properties.     

不同泊松比复合材料的层板断裂韧性和裂纹尖端应力场

比较了两组具有不同平面泊松比的玻璃纤维／环氧树脂复合材料层板的断裂韧性和缺口断裂强度，发现低泊松比复合材料层板具有较高的断裂韧性和缺口断裂强度；用复变函数一变分方法计算了它们的裂纹尖端应力场；研究了主应力方向与纤维夹角的关系；结果表明：低泊松比材料独特的裂纹尖端应力场有利于提高缺口断裂强度。     

Crack propagation and residual stress in laminated Si3N4/BN composite structures

The level of residual stress and crack propagation in a new generation of laminates, based on silicon nitride (Si₃N₄) layer and a mixture of boron nitride (BN) and alumina (Al₂O₃) interlayer, was presented. The structure consists of alternated concentric rings of Si₃N₄ separated by the weak BN interlayer possessing no planes of easy crack propagation and fracture resistance much larger than that of any classical planar laminates. The results on direction of crack propagation and residual stress in relation to inter-layer composition, the number of layers, and their thickness are investigated and reported. The effect of residual stress on crack propagation was studied by using Vicksrs intentation. The highest compressive residual stress of ∼170 MPa was found in samples with five layers possessing an average layer thickness of ∼310 × 10⁻⁶ m.