Separation of motor oils, oily wastes and hydrocarbons from contaminated water by sorption on chrome shavings

In this paper, the ability of chrome shavings to remove motor oils, oily wastes and hydrocarbons from water has been studied. To determine amount of hydrocarbons sorbed on tanned wastes, a FT-NIR methodology was used and a multivariate calibration based on partial least squares (PLS) was employed for data treatment. The light density, porous tanned waste granules float on the surface of water and remove hydrocarbons and oil films. Wastes fibers from tannery industry have high sorption capacity. These tanned solid wastes are capable of absorbing many times their weight in oil or hydrocarbons (6.5-7.6g of oil and 6.3g of hydrocarbons per gram of chrome shavings). The removal efficiency of the pollutants from water is complete. The sorption of pollutants is a quasi-instantaneous process.     

Waste with chrome in the Portland cement clinker production

Hazardous wastes, coming from industries are usually used in the Portland cement production in order to save energy, costs and/or stabilize toxic substances and heavy metals inside the clinker. This work focuses on the effect produced on the Portland cement clinker when it is obtained using tanned leather shavings whit chrome salts as part of the process. The raw materials were clinkered in laboratory with different percentages of shavings, which contained 2% of Cr(2)O(3). DTA-TG of the raw mixtures was performed to evaluate the thermal behavior changes that can take place during the clinkering process, analyzing the crystalline phases obtained by XRD. The milling behavior of clinkers was studied, analyzing also the refractoriness variation on those clinkers. The chrome retention was evaluated by leaching tests. The structural modification determined by the chrome presence in the silicate structure brought consequences in the hydration speed, mechanical resistance and pore distribution.     

Buffing dust as a filler of carboxylated butadiene-acrylonitrile rubber and butadiene-acrylonitrile rubber

Buffing dust from chrome tanned leather is one of the difficult tannery wastes to manage. It is also hazardous to both human health and the environment. The scientific literature rarely reports studies on dust management, especially on its utilization as a filler for elastomers. In this connection we have made an attempt to use this leather waste as a filler for rubbers such as XNBR and NBR. The addition of the buffing dust to rubber mixes brought improvement in mechanical properties, and increase in resistance to thermal ageing as well as in electric conductivity and crosslink density of vulcalizates.     

Electrophoretic deposition of alumina,yttria, yttrium aluminium garnet and lutetium aluminium garnet

The electrophoretic deposition (EPD) method has been adapted for the deposition of ceramic green bodies from aqueous nanodispersions of alumina, yttria, yttrium aluminium garnet and lutetium aluminium garnet. These materials have been selected, since they are promising candidates for optically transparent ceramics. Films as well as cylindrical bodies have been successfully prepared by application of pulsed direct current (pDC) EPD. To guarantee constant deposition yield during pDC, a variant with variable pulse widths and pulse heights has been developed. The obtained green bodies were studied by surface area analysis, scanning electron microscopy, optical transmittance measurements, determination of pycnometric density and sintering behaviour. The effect of colloid-chemical dispersion properties on green and sintered ceramics is discussed as well. The green ceramics received are nanoporous and dense, providing excellent properties for further processing under mild conditions to optical materials. For comparison, EPD-formed green bodies were either processed directly to ceramic bodies or after additional compacting by hot-pressing in a piston-cylinder apparatus.     

Sintered glass ceramic composites from vitrified municipal solid waste bottom ashes

A glass ceramic composite was obtained by sinter-crystallisation of vitrified municipal solid waste bottom ashes with the addition of various percentages of alumina waste. The sintering was investigated by differential dilatometry and the crystallisation of the glass particles by differential thermal analysis. The crystalline phases produced by the thermal treatment were identified by X-ray diffraction analysis. The sintering process was found to be affected by the alumina addition and inhibited by the beginning of the crystal-phase precipitation. Scanning electron microscopy was performed on the fractured sintered samples to observe the effect of the sintering. Young's modulus and the mechanical strength of the sintered glass ceramic and composites were determined at different heating rates. The application of high heating rate and the addition of alumina powder improved the mechanical properties. Compared to the sintered glass ceramic without additives, the bending strength and the Young's modulus obtained at 20 degrees C/min, increased by about 20% and 30%, respectively.     

Possible production of ceramic tiles from marine dredging spoils alone and mixed with other waste materials

Dredging spoils, due to their composition could be considered a new potential source for the production of monolithic ceramics. Nevertheless, abundance of coloured oxides in these materials preclude the possibility of obtaining white products, but not that of producing ceramics with a good mechanical behaviour. As goal of the present research we have produced and studied samples using not only dredging spoils alone, but also mixtures with other waste materials such as bottom ashes from an incinerator of municipal solid waste, incinerated seawage sludge from a municipal seawage treatment plant and steelworks slag. Blending of different components was done by attrition milling. Powders were pressed into specimens which were air sintered in a muffle furnace and their shrinkage on firing was determined. Water absorption, density, strength, hardness, fracture toughness, thermal expansion coefficient of the fired bodies were measured; XRD and SEM images were also examined. The fired samples were finally tested in acidic environment in order to evaluate their elution behaviour and consequently their environmental compatibility. It is observed that, although the shrinkage on firing is too high for the production of tiles, in all the compositions studied the sintering procedure leads to fine microstructures, good mechanical properties and to a limitation of the release of many of the most hazardous metals contained in the starting powders.     

Transparent Polycrystalline Alumina Ceramic with Sub‐Micrometre Microstructure by Means of Electrophoretic Deposition

The optical quality attainable in coarse‐grained polycrystalline alumina is severely limited by grain‐boundary scattering, which is inherent to non‐cubic materials. The optical properties of sub‐micrometre polycrystalline alumina are of growing interest triggered by the fact that a decrease in the grain sizes of the final sintered material yields an improvement in the optical quality while the scattering mechanism changes as the grain size becomes comparable with the wavelength of light. To achieve transparent alumina ceramics with a fine‐grained microstructure, however, porosity and other defects must be avoided. This necessitates the optimization of processing and sintering procedures. Electrophoretic deposition (EPD) is a colloidal process in which ceramic bodies are directly shaped from a stable suspension by application of an electric field. Electrophoretic deposition enables the formation of homogeneous, uniform green microstructures with high density, which can be sintered to transparency. It is a simple and precise technique to synthesize not only monoliths, but also composites with complex geometries [1]. Alumina green bodies were deposited from stabilized aqueous suspensions with and without doping. Green alumina compacts were evaluated based on their pore size distribution and density. Densification behaviour was characterized by dilatometric studies conducted at constant heating rate. Samples were sintered at different temperatures with subsequent post‐densification by hot isostatic pressing. Transparency was evaluated by means of spectroscopic measurements. The measured in‐line transmission of the samples at 645 nm was more than 50 % and that is 58 % of the value of sapphire. The influence of dopings on transparency was investigated. The mechanical properties of the samples were tested.     

Interactions between Ti and alumina-based ceramics

Reactive metal coatings have been frequently used on ceramic materials for various purposes. However, little work was done in the past to understand the interactions between coating and ceramic substrates and their effects on the mechanical properties of the ceramics. In this study, titanium coatings were applied to single-crystal (sapphire) and polycrystalline alumina to study the interface reactions. Also, the effect of the coating on the mechanical properties of the substrates was quantified in terms of modulus of rupture (MOR) in four-point bending strength. Reactions between the coating and the Al₂O₃-based substrates at 980°C caused the formation of a new phase, Ti₃Al[O], and a significant decrease (15%–65%) in the MOR strength of the ceramic materials. This study showed that in polycrystalline alumina, interactions between titanium and the glassy grain-boundary phase in the ceramic materials were responsible for reduction in the MOR strength, while the effect of thermal expansion mismatch between titanium and the ceramic substrate appeared to be dominant for singlecrystal alumina.     

Ceramic material processing by electrical discharge in electrolyte

New ceramic materials receive a great deal of attention as machine components, but they are hard to work. So a hybrid processing which combines electrical discharge processing with grinding is proposed. In this study, in order to examine the possibility of this hybrid processing, the electrical discharge processing on four kinds of ceramics was carried out with a needle electrode. The ceramic materials were alumina and three kinds of silicon nitride series to which are added alumina (ASN), magnesia (MSN), yttria and alumina (YASN). The results obtained showed that a pit can be formed on any ceramic and the pit depth apparently varies with the ceramic material. The removal rates of ASN, alumina, YASN and MSN become low in turn, and are independent of their mechanical properties. In the case of the silicon nitride series, the removal rates depended on their sintering additives, and the higher the applied voltage, the greater was the volume removed. High removal rate and low electrode loss are obtained when the needle electrode is negative. The ceramic materials are mainly removed by etching the grain boundary in a high-temperature electrolyte during the discharging process.     

三种机械密封材料的摩擦磨损性能研究

研究了3种核主泵用机械密封陶瓷材料(氮化硅、氧化铝和碳化硅)在室温干摩擦条件下及水润滑条件下分别与氮化硅陶瓷球对磨的摩擦磨损性能。研究结果表明,在与氮化硅球干摩擦的3种材料中氧化铝陶瓷具有最大的摩擦系数和最小的磨损质量,氮化硅具有最小的摩擦系数。在氮化硅陶瓷自配对摩擦副摩擦磨损试验中,水润滑条件下氮化硅摩擦系数及摩擦质量损失都有很大程度的减小,且摩擦系数随转速增加而减小。综合考虑力学性能和摩擦磨损性能,选择氮化硅陶瓷作为核主泵机械密封材料更合适。     

3D Printing of Ceramics with Controllable Green-Body Configuration Assisted by the Polyvinyl Alcohol-Based Physical Gels

Additive manufacturing of ceramics has received intense attention. In particular, 3D-printed ceramics with customized shapes are highly desirable in the chemical industry, aerospace, and biomedical engineering. Nevertheless, developing a simple and cost-effective process that shapes dense ceramics to complex geometries remains challenging because of the high hardness and low ductility of ceramic materials. Extrusion-based printing, such as direct ink writing (DIW), often requires supporting materials that pose additional difficulties during printing. Herein, a simple approach is developed to produce stretchable ceramic green bodies of zirconia and alumina for DIW. The ink is composed of polyvinyl alcohol (PVA) and an aqueous suspension of ceramic powders. Besides the colloidal network formed by the ceramic particles, PVA plays an important role in tuning the printability of the aqueous ink. Through a freeze-thaw process, PVA crystallizes to form physical networks. This strategy provides highly stretchable hydrogel green bodies that can be reprogrammed to complex geometries difficult for common DIW printing. The subsequent drying, debinding, and sintering processes produce ceramics with dense structures and fine mechanical properties. In short, this work demonstrates an efficient method for the DIW of ceramic parts that can be reprogrammed to complex geometries.     

On the comparison of the ballistic performance of 10% zirconia toughened alumina and 95% alumina ceramic target

Ballistic performance of different type of ceramic materials subjected to high velocity impact was investigated in many theoretical, experimental and numerical studies. In this study, a comparison of ballistic performance of 95% alumina ceramic and 10% zirconia toughened alumina (ZTA) ceramic tiles was analyzed theoretically and experimentally. Spherical cavity model based on the concepts of mechanics of compressible porous media of Galanov was used to analyze the relation of target resistance and static mechanical properties. Experimental studies were carried out on the ballistic performance of above two types of ceramic tiles based on the depth of penetration (DOP) method, when subjected to normal impact of tungsten long rod projectiles. Typical damaged targets were presented. The residual depth of penetration on after-effect target was measured in all experiments, and the ballistic efficiency factor of above two types ceramic plates were determined. Both theoretical and experimental results show that the improvement on ballistic resistance was clearly observed by increasing fracture toughness in ZTA ceramics.     

Using granite rejects to aid densification and improve mechanical properties of alumina bodies

The industrial use of waste materials in the ceramic industry has been widely investigated. This work describes the research carried out on the manufacturing of alumina bodies with granite reject additions. The reject was used as produced by a local industry that saws granite stones into blocks and slabs. This industrial process produces a significant amount of that reject, which is discarded in sedimentation lagoons, landfill areas or simply thrown in rivers, resulting in environmental pollution. Alumina and the granite reject were ball-mill mixed with 5 wt% manganese oxide and pressed under an uniaxial load of 20 MPa. Samples were subjected to thermal analysis (DTA, TG and dilatometry) and sintered in air at 1300 and 1350^∘C during 1 h in an electric furnace. Sintered specimens were characterized by X-ray diffraction, apparent density, open porosity and flexural strength. The results showed that the addition of granite reject and manganese oxide enables low temperature sintering and remarkably improves (~300%) the cold mechanical properties of the alumina body.     

Densification,mechanical and microstructure properties of β-spodumene—alumina composites

New systems consisting of ceramic composites have been recently developed to replace conventional alumina as a substrate for high performance large scale integrated packaging. Few investigations on the β-spodumene—alumina composites have been performed. Accordingly, the effect of β-spodumene content on the sintering behaviour and mechanical properties of the β-spodumene—alumina composites is the aim of the present study. Microstructural characteristics, thermal expansion and phase relations were also discussed. Fine β-spodumene and alumina powders of high purity were synthesized by aqueous sol-gel processing. The gels were dried and calcined and the resulting materials characterized by XRD. Various compositions of β-spodumene—alumina were prepared and conventional sintering studies were conducted at temperatures of 1400°–1600 °C with soaking periods of 1–4 h. The obtained results showed that densification was reduced with the increase of β-spodumene content. Mullite was detected in bodies containing 5% β-spodumene. There was no evidence of mullite presence with higher contents of β-spodumene. Increasing β-spodumene from 5 mass% up to 15 mass% increased the bodies bending strength by ≈43%, while the thermal expansion coefficient was slightly changed from 1.05 to 2.67×10⁻⁶/°C in the range of 20° to 1000 °C.     

Fracture toughness of the interface between Ni–Cr/ceramic,alumina/ceramic and zirconia/ceramic systems

Few studies have focused on the interface fracture performance of bi‐layered structures, which have an important role in dental restorations, using ceramic materials. The purpose of this study is to evaluate the fracture mechanics performance of the Ni–Cr/ceramic, alumina/ceramic and zirconia/ceramic interfaces by investigating the propagation of an interfacial crack under a wide range of mode mixities. The effect of the mechanical properties of the base materials and the interface, on the crack initiation and crack path, will also be studied. The finite element method (FEM) was used to calibrate the production of the experimental specimens, allowing to obtain the minimum dimensions and amounts of material needed to correctly characterize the fracture event. The specimens were tested until failure using a three‐point bending test machine. The interface fracture parameters were obtained using the FEM. For all specimens, the cracks propagated into the ceramic. The results suggest that, in Ni–Cr/ceramic, alumina/ceramic and zirconia/ceramic bi‐layered structures, the ceramic is weaker than the interface, which can be used to explain the clinical phenomenon that the ceramic chipping rate is larger than interface delamination rate. Consequently, a ceramic material with a larger fracture toughness is needed to decrease the failure rate of ceramic restorations.     

Reuse of incinerator bottom and fly ashes to obtain glassy materials

Bottom and fly ashes coming from the urban wastes incineration represent a by-product nowadays landfilled. By mixing different amount of these residues with others inert materials, such as glass cullet and feldspar waste, two vitrifiable mixtures are tailored. Glasses, obtained by means of vitrification process, are chemically stable with low leachability of contaminants and show comparable properties to those of commercial soda-lime glasses. Moreover, from the thermal and mechanical characterisation the tendency of these glasses to crystallise, for their transformation into glass-ceramic materials, has been evidenced.     

拟薄水铝石凝胶制备牙科托槽用ZTA陶瓷的研究

利用拟薄水铝石的凝胶作用,以浓HNO_3为引发剂,将Al_2O_3(1μm)粉末和含3%Y_2O_3的ZrO_2(200nm)粉末均匀填充在拟薄水铝石的溶胶双电层内,在一定温度和时间下胶凝固化并干燥成坯。将生坯通过不同的温度烧结后,制备出ZTA陶瓷正畸托槽材料。主要研究拟薄水铝石的胶体行为、不同固含量下生坯的性能以及ZrO_2对陶瓷晶粒结构和力学性能的影响。结果表明,经拟薄水铝石凝胶制备的陶瓷生坯具有一定抗弯强度(达4 MPa),可用于力学加工。在该制备方法中,ZrO_2可更好地发挥增韧作用,增加陶瓷烧结后致密度,提高陶瓷托槽材料的抗弯强度。     

Processing and characterization of porous alumina scaffolds

Bioceramic materials are used for the reconstruction or replacement of the damaged parts of the human body. In this study an improved procedure is described for producing ceramic scaffolds with controlled porosity. Bioinert alumina ceramic was used to make porous scaffolds by using indirect fused deposition modeling (FDM), a commercially available rapid prototyping (RP) technique. Porous alumina samples were coated with hydroxyapatite (HAp) to increase the biocompatibility of the scaffolds. Initial biological responses of the porous alumina scaffolds were assessed in vitro using rat pituitary tumor cells (PR1). Both porous alumina and HAp coated alumina ceramics provided favorable sites for cell attachments in a physiological solution at 37 °C, which suggests that these materials would promote good bonding while used as bone implants in vivo. Based on these preliminary studies, similar tests were performed with human osteosarcoma cells. Cell proliferation studies show that both the ceramic materials can potentially provide a non-toxic surface for bone bonding when implanted in vivo.     

Effect of additives on the microstructure and mechanical properties of commercial alumina ceramics

The effect of impurities or additives on the microstructure of some commercial alumina ceramic samples have been characterized by scanning electron microscope-energy dispersive x-ray spectrometer and the mechanical properties investigated. Both the hardness and the toughness have been found to increase as the SiO₂ content decreases, and the theoretical density is reached in these materials. Grain size and distribution seem to be important factors in the mechanical properties of alumina ceramics. If the additives are controlled carefully, finer grain size and distribution can be obtained, together with a high relative density in terms of pore distribution characteristics and consequently enhanced mechanical properties.     

水溶性高分子PVP对陶瓷凝胶注模成型坯体表面起皮的抑制作用与机理

在凝胶注模成型的丙烯酰胺单体溶液中加入适量的聚乙烯吡咯烷酮(ＰＶＰ),可有效地克服在空气气氛下单体聚合形成凝胶网络的氧阻聚问题,从而消除了坯体表面起皮现象,达到精确控制坯体尺寸的目的．本文研究了加入ＰＶＰ对Ａｌ_２Ｏ_３粉料的分散性、陶瓷浆料的静/动态流变特性、生坯的强度以及显微结构的影响;并通过红外光谱初步分析了ＰＶＰ消除陶瓷坯体表面起皮现象的作用机制,即利用ＰＶＰ增稠作用和ＰＶＰ分子间的氢键作用在表面处起到粘结粉体的作用．