Thermal analyses applied to ceramic nanopowders: from synthesis to sintering

The free sintering of ceramic powders into fully dense nanostructured materials is still a challenging process, even more complex when nanostructured transition alumina is used as starting powder. In this paper, biphasic (Alumina–YAG) and triphasic (Alumina–YAG–ZrO₂) composite powders were produced by doping the same nanocrystalline transition alumina with inorganic precursors of the second-phases, which were subsequently yielded under controlled thermal treatments. The added dopants significantly increased both the θ- to α-phase transformation and the sintering temperatures, making even more difficult the retention of the starting nanometric grain size into the final dense materials. Thermal analyses (such as TG–DTA and dilatometry) are here used to support most of the ceramic processing steps involved in a successful elaboration of the desired ultra-fine structures. In fact, the thermal pre-treatments of the doped powders were set up on the ground of the DTA–TG curves whereas the dilatometric analyses were exploited to design optimised sintering cycles, through which the green bodies were successfully consolidated into fully dense materials, characterised by highly homogeneous and tailored micro/nanostructures.     

Silicon Oxycarbide Glasses Derived from Polymer Precursors

This paper describes a new predictive model to estimate compositions of ceramic materials from the structure of the preceramic polymer. The polymers are prepared by sol-gel methods and have M and T silicone functionality. The ceramic predictive model works well for highly branched silsesquioxanes, which are some of the most common ceramic precursors. This report describes the control of ceramic SiOC compositions which in turn make the materials useful as: (1) matrices for ceramic matrix composites and; (2) anodes for rechargeable lithium ion batteries.     

Composite ceramic monoliths with poly(ester acrylate) and poly(ester acrylate)-poly(<Emphasis Type="Italic">N</Emphasis>-vinylcaprolactam) coatings

Polymerization of a series of oligo(ester acrylates) on the surface of ceramic monoliths was studied with the aim to prepare composite monolithic sorbents, highly porous permeable ceramic materials with polymeric coatings. A chelating organoceramic sorbent was prepared by copolymerization of an oligoester with N-vinylcaprolactam on a ceramic support.     

Hydrophobization of Porous Ceramic Materials Based on Quartz Fibers with Solutions of Tetrafluoroethylene Telomers

Russian Journal of Applied Chemistry - Hydrophobization of highly porous heat-shielding ceramic materials based on quartz fibers was studied. Radiation-synthesized tetrafluoroethylene telomers...     

Characterization of Vacuum Brazed Joints for Superconducting Cavities

Brazing is a process to join metallic and non-metallic materials, without any melting or plastic state of the base metals. The poor wettability of ceramic may be improved by the use of alloys containing an element capable of changing the chemistry of the ceramic surface (active braze). In this paper we propose the substitution of the Electron Beam welding with Vacuum Brazing in order to join the resonator components, Nb, Cu OFHC, and Al₂O₃, with stainless steel flanges, in superconducting resonant cavities. Several combinations of brazed joints have been tested. The characterization of the joints has been performed with SEM-EDS and MICROPIXE. All the joints fulfil the requirements.     

Lithographic applications of highly metallized polyferrocenylsilanes

Organometallic polymers are excellent candidates for the introduction of metals into nanostructures using lithographic techniques due to their inherently high and uniform metal loadings and processibility. Soluble, high molecular weight polyferrocenylsilanes possess unique physical properties and function as excellent ceramic precusors. Recent advances in the use of lithographic techniques with a highly metallized PFS resist to form new nanopatterned materials will be presented.     

Development of carbon coatings for cordierite foams: an alternative to cordierite honeycombs

Cordierite foams were prepared by replication of polyurethane foams and were coated with three types of carbon xerogels. The dip coating and synthesis conditions were optimized, and the coated foams were characterized exhaustively. The composition of the starting solution, coat loading, and carbonization temperature are the most important parameters determining both textural and mechanical properties. Carbon xerogel coatings obtained from aqueous solutions of resorcinol (R) and formaldehyde (F) are macro-, meso-, and microporous but present the greatest shrinkage, which causes a loss of adhesion between ceramic foams and carbon coatings. The coatings from polyfurfuryl alcohol (PFA) and RF-poly(vinyl butyral) (Butvar) resin are highly microporous and present very good adhesion even after carbonization. In all cases, coatings induce the improvement of the mechanical properties, which is related to the fact that the coating fills the defects present in the cordierite foams, thereby affecting both the rigidity and the way cracks propagate through the coated samples. These materials, due to the synergetic role of the highly porous coatings and the tortuous channels of the ceramic foams, are suitable materials for adsorption or catalytic treatments of fluids.     

Thermochemical transformations of polycarbosilane precursors into a ceramic matrix

The possibility of preparing polymeric ceramic-forming precursors from polycarbosilane and oligosilazane was examined. Oligosilazane as a component of polycarbosilane formulations acts as a curing agent, ensuring curing at 150–300°C in the absence of oxygen and modifier. Pyrolysis of the cross-linked copolymer in argon yields an inorganic matrix whose yield is 1.3 times higher than that of pyrolyzates of the starting components. The major phase of the ceramic products obtained, according to the results of X-ray diffraction and chemical analyses, is X-ray amorphous silicon carbide. The ceramic obtained is highly resistant to thermal oxidation (up to 1400°C). The composition of the ceramic and the heat resistance and service characteristics of ceramic-matrix composite materials prepared on its basis using the “polymer technology” can be controlled by varying the ratio of the initial oligomers.     

固相萃取–气相色谱–串联质谱法测定塑料食品包装材料中3种抗氧化剂的残留量

建立了气相色谱–串联质谱法测定塑料食品包装材料中抗氧化剂二丁基羟基甲苯(BHT)、丁基羟基茴香醚(BHA)和特丁基对苯二酚(TBHQ)残留量的分析方法。样品采用环己烷–乙酸乙酯混合溶剂超声萃取,经固相萃取法富集和净化,采用气相色谱–串联质谱在多反应监测模式下进行测定。结果表明,3种抗氧化剂质量浓度在0.05~20 mg/L范围内线性关系良好,线性相关系数大于0.999;BHT,BHA,TBHQ的检出限分别为0.005,0.01,0.03mg/kg;平均添加回收率为88.7%~104.0%;测定结果的相对标准偏差小于5.5%(n=6)。该方法操作简便,灵敏度高,重复性好,可用于塑料食品包装材料中抗氧化剂BHT,BHA,TBHQ残留量的测定。     

On the importance of using scandium to normalize geochemical data preceding multivariate analyses applied to archaeometric pottery studies

This work enhances the importance on determining regional geochemical background by normalizing chemical data of archaeological ceramics, using one element as grain-size and mineralogical proxy, prior to any further statistical approach. It is well established that more relevant information can be derived from the concentration of any element when it is compared with some reference element. The main question is which element should be chosen to normalize concentration. A discussion on this issue is presented here.A case study is presented, which includes the geochemical tracing of Roman kilns productions, differentiating between and within two sedimentary basins pottery assembly, belonging to several Roman ceramic production centres identified in the Tagus and Sado basins of Portugal. Due to the homogeneity of the used raw materials (estuarine sediments), the distinction and establishment of signatures for each production center become difficult.A multivariate statistical approach after normalization of the chemical contents to a conservative element (Sc) is presented, well differentiating the three production centers and allowing the establishment of provenance for amphorae.     

Sol–gel synthesis of porous titania fibers by electro-spinning for water purification

In this study, porous ceramic fibers were prepared by the sol–gel-assisted electro-spinning process using colloidal dispersion of complex fluids for the application of phtotocatalysts. First, polystyrene nanospheres were synthesized by dispersion polymerization as sacrificial templates for porous fibers. Then, the mixture of polyvinylpyrrolidone and the ceramic precursor with the polymeric nanospheres was prepared as the spinning solution and self-organized by electro-spinning, followed by calcination of the electrospun composite fibers. The morphologies of the porous fibers could be controlled according to the size of the templates and the amount of the ceramic precursor. The nano-structure of the pores in the fibrous materials could also be adjusted as open or closed cavities with various potential applications. As a demonstrative application, the macroporous titania fibers could be utilized as photocatalysts for the removal of organic dyes dissolved in water. A better photocatalytic activity of the macroporous fibers with 700-nm pore diameter was observed compared to the result of nonporous titania fibers due to the increased porosity. Collectively, the macroporous ceramic fibers were found to be efficient functional materials to prepare the unique nano-structured materials other than simple nonporous fibers.     

Catalysts developed from waste plastics: a versatile system for biomass conversion

The end-of-life treatment for post-consumer plastic waste constitutes one of modern society’s greatest problems, whereby highly unsustainable landfilling and incineration are the two main disposal routes. At present, the chemical upcycling of plastic waste is largely limited to its pyrolytic conversion into hydrocarbon fuels or nanomaterials. Herein, we demonstrate the upcycling of high-volume plastic waste by turning them into catalysts for biomass valorization. Many existing studies synthesize organocatalysts from a bottom-up approach using specialized monomers. Yet, transforming widely available waste polymers into functionalized materials for catalysis remains relatively unexplored. In this study, homogeneous and cross-linked heterogeneous catalysts derived from waste polystyrene food containers are shown to convert readily available saccharide precursors from biomass into 5-hydroxymethylfurfural (5-HMF), a key biorefinery platform chemical, under short reaction times and mild conditions. In addition, the heterogeneous catalyst can be reused multiple times with little loss of yield between repeated runs. Other than 5-HMF, doping the reaction with water or halide salts also allowed the formation of valuable products such as formic acid and diformylfuran. Our work expands on existing upcycling options for post-consumer plastic waste by giving them a new lease of life as value-added catalysts.     

Thermal analysis and X-ray diffraction of untreated coffee’s husk ash reject and its potential use in ceramics

The agro and industrial activities are actually responsible for the production of large amounts of solid wastes in Brazil. The use of industrial wastes as alternative raw materials into ceramic products has been widely developed. The typical materials used in the ceramic formulations present a large diversification of chemical compositions, what allow the incorporation of different types of waste materials in the ceramic mixture. Brazil produces a massive amount of coffee and the lack of adequate landfill areas available to dispose the coffee’s husk ash reject material are causing an ambiental problem for the agro-industry. This work describes research carried out on the thermal characterization and X-ray diffraction of coffee’s husk ash reject and its possible use in the ceramic industry.     

Classical ceramic colors through colloidal and from alkoxides gels

Classical ceramic pigments are manufactured through the traditional method of firing a mixture of oxides previously mechanical homogeneized in a mill. From industrial overview sol-gel applied in ceramic pigments manufacture is more expensive than ceramic method because the high price of raw materials. However in some classical pigments it would be economically interesting to use a sol-gel route because raw materials in ceramic route are as well expensive and gel route give the pigment at lower firing temperature and soaking time. In this paper a discussion for several pigments is presented.     

Depollution of some radioactive residual waters on ceramic materials

The present paper deals with the study of retaining of⁵⁵⁺⁵⁹Fe³⁺ and¹¹⁵Cd²⁺ ions from residual waters, on ceramic materials. At the same time, the leaching of⁵⁵⁺⁵⁹Fe³⁺ ions previously retained on these ceramic materials in contact with a hydrochloric acid solution as corrosive agent, has been studied.     

Porous carbon and carbon composite hollow spheres

In this communication, we propose a template approach toward synthesis of carbon hollow spheres by direct carbonization of highly crosslinked sulfonated polystyrene gel hollow spheres (sPS). The sulfonic acid group can facilitate carbonization. Moreover, the acid group can also induce a favorable growth of other materials within the sPS gel-forming carbon-based composite shell such as bi-continuous C/SiO₂ and their derivative ceramic SiC. Release of small molecules during polymers decomposition results porous shell.     

Determination of trace amounts of heavy metals in arctic ice core samples using inductively coupled plasma mass spectrometry

Trace amounts of heavy metals in the ice cores from Canadian Arctic were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). A custom made plastic device and ceramic knives were used to remove the contamination on the ice core surface. Ice cores could be broken into small sections (2-3 cm thick) after decontamination with the plastic device and ceramic knives. High-resolution depth profiles of various elements, i.e. As, Cd, Co, Cu, Ni, Pb, Zn and U, were thus attained. Concentrations in 518 ice core samples range from 0.1 (U) to 673.3 (Zn) pg g(-1).     

Diffusion studies in non-oxide ceramics: analytical aspects of the use of ion implanted stable tracers and SIMS

The physical and chemical properties of complex non-oxide ceramic materials require advanced methods of diffusivity determination. In this study, we present a method based on the high-dose ion implantation of stable tracers in combination with secondary ion mass spectroscopy for depth profiling. The analytical basics, advantages and problems of the method are discussed for two examples of complex materials, the Si-B-C-N precursor ceramics and the Ti-based transition metal diborides. We demonstrate that is possible to measure the temperature dependence of diffusivities, especially for ceramic systems with low diffusivities, for systems that contain elements for which no suitable radioactive tracers exist for extended measurements.     

The influence of substrate surface roughness on microstrip transmission line loss using conventional analyses and length‐scale fractal analysis

Two components of conductor topography can impact conductor loss for signals in the GHz frequency range: conductor–ceramic interface roughness and conductor edge angle. This study is an experimental investigation of the influence of these conductor topographies on conductor loss in microstrip circuits produced by thick‐film technology. The aluminum nitride ceramic substrates have different surface roughnesses due to different surface finish processes. The substrate surfaces were characterized using conventional and length‐scale fractal analysis. The conductor–ceramic interface was measured with a contact profilometer. The conductor edge angle and conductor edge profile were measured optically. It was found that there is a direct correlation between conductor loss and conductor edge angle, whereas there is an inverse correlation between loss and substrate roughness or relative length of the conductor–ceramic interface. This is the opposite result to the conventional expectation of surface roughness effects on conductor loss. There is also a negative correlation between conductor edge angle and surface roughness or relative length. The loss behavior can be explained by the interaction of the conductor paste with the surfaces during processing. The paste tends to spread more on the smoother surfaces, and thus creates an elongated edge of diminishing cross‐section and a small edge angle. This leads to greater conductor loss. Copyright © 2009 John Wiley & Sons, Ltd.     

高发射率陶瓷材料研究进展

高发射率陶瓷材料是当前最热门的功能材料之一。将它应用于工业炉中不仅能够使炉内热量分布均匀还能提高加热速度,从而提高工业炉的加热效率并达到低碳节能的目的。 高发射率陶瓷材料优势突出,包括红外发射率较高、化学性质稳定且热稳定性佳等。本文从红外辐射机理出发,综述了近年来应用较多的几种高发射率陶瓷材料体系的研究进展。主要介绍了掺杂改性高发射率陶瓷材料的思路与工艺,进一步阐述了高发射率陶瓷材料应用于工业领域的研究现状,并对此类材料目前的缺陷与未来的发展方向作出了建议与展望。