Search

Polycrystalline mullite fibers and novel zirconia-toughened mullite (ZTM) fibers with average diameters between 9.7 and 10.3 μm containing 3, 7 and 15 wt.-% tetragonal ZrO2 (ZTM3, ZTM7, ZTM15) in the final ceramic were prepared via dry spinning followed by continuous calcination and sintering in air. A shift in the formation of transient alumina phases and tetragonal ZrO2 to higher temperatures with increasing amounts of ZrO2 was observed. Concomitantly, the mullite formation temperature was lowered to 1229 °C for ZTM15 fibers. X-ray diffraction revealed formation of the desired tetragonal crystal structure of ZrO2 directly from the amorphous precursor. Room temperature Weibull strengths of 1320, 1390 and 1740 MPa and Weibull moduli of 9.5, 7.1 and 9.0 were determined for mullite, ZTM3 and ZTM15 fibers, respectively. Average Young’s moduli ranged from 190 to 220 GPa. SEM images revealed crack-free fiber surfaces and compact microstructures independent of the amount of ZrO2.

The surface of a commercial PAN-based carbon fiber (CF) was modified to optimize fiber–matrix adhesion (FMA) in a CF-reinforced polymer (CFRP) preform used for the manufacture of CF-reinforced silicon carbide (C/C-SiC) composites. For these purposes, CFs were thermally desized and then electrochemically oxidized. The surface of the fibers was investigated by atomic-force microscopy. The CFs’ chemical composition, specific surface acidity and wettability were investigated by different analytical methods. CFRPs based on electrochemically oxidized and untreated CFs were subsequently carbonized and transformed into C/C-SiC via liquid silicon infiltration (LSI). The microstructure of the composites was investigated by scanning electron microscopy (SEM). Single-fiber push-out tests were used to characterize FMA and revealed the highest interfacial fracture toughness for the CFRP based on electrochemically oxidized CFs. The surface treatment also showed positive effects after siliconization, e.g., a lower conversion rate of the CFs and improved mechanical properties.

Polycrystalline zirconia toughened alumina (ZTA) fibers were prepared from aqueous solutions of aluminum hydroxide chloride 2.5-hydrate and zirconium oxychloride octahydrate. Fiber processing was accomplished via dry spinning. Poly(vinylpyrrolidone) (PVP) was used as spinning aid. Polycrystalline ZTA fibers were obtained by calcination of the green fibers followed by sintering at defined temperatures in air. Ceramic fibers were 10 μm in diameter and had an average tensile strength of 1010 (±363) MPa with peak values reaching 1535 MPa. Differential scanning calorimetry/thermogravimetric analysis coupled with mass spectrometry (DSC/TGA-MS) showed an exothermic peak at 1156 °C assigned to the crystallization of α-Al 2 O 3 and tetragonal ZrO 2 and an overall ceramic yield of 41.7% at 1400 °C. X-ray diffraction (XRD) analysis showed that tetragonal ZrO 2 can be obtained at 1350 °C directly from the amorphous precursor whereas pure-phase α-Al 2 O 3 is formed stepwise via transition alumina phases.

The novel fiber CeraFib75 with a composition near to pure mullite was analyzed with respect to its potential for high-temperature applications. This mullite fiber free of glass phase was aimed to overcome the strength of commercial oxide fibers at high-temperatures. Tensile tests at room and high temperatures ranging from 900 to 1400 °C and creep tests were performed. Nextel™720, another crystalline mullite-alumina fiber, was tested as a reference. Microstructure and crystal phase analysis of the new fiber revealed mullite grains with traces of γ- and α-alumina in-between; it contains occasionally defects causing a reduced strength at room-temperature. Remarkably, at temperatures beyond 1200 °C, CeraFib75 presented a higher tensile strength than Nextel™720. During tensile tests at 1400 °C, an extended region of inelastic deformation was observed for CeraFib fibers only, which was related to a grain boundary sliding mechanism. Creep rates were of the same order of magnitude for both fibers.

Polycrystalline calcium phosphate ((Cl/OH)Ap = Ca5(PO4)3(OH/Cl); TCP = Ca3(PO4)2) fibres were prepared from aqueous solutions of calcium chloride and phosphoric acid using poly(ethylene oxide) (PEO) as spinning aid. Generation of nonwoven materials was accomplished via rotary jet spinning. Polycrystalline (Cl/OH)Ap fibres 10–25 μm in diameter were obtained with 37% ceramic yield by pyrolysis of the green fibres followed by sintering at 1150 °C in air. X-ray diffraction (XRD) analysis provided evidence for apatite formation starting at 650 °C while (Cl/OH)Ap ceramic fibres were obtained at 1100 °C via transformation through intermediate dicalcium dichloride hydrogen phosphate (Ca2Cl2(HPO4)) and calcium pyrophosphate (Ca2P2O7) phases. A glass-forming Al-based additive was applied to enhance the mechanical properties of the Cl/OH)Ap ceramic fibres and indeed resulted in the formation of (Cl/OH)Ap/Al2O3 fibres with improved mechanical stability. Finally, TCP, (Cl/OH)Ap and (Cl/OH)Ap/Al2O3 fibres were subjected to seeding with mesenchymal stem cells. Negligible cytotoxicity is observed.

Polycrystalline yttrium aluminum garnet (YAG, Y 3 Al 5 O 12 ) fibers were prepared from aqueous solutions of aluminum chlorohydrate and yttrium chloride. Fiber processing was accomplished via dry spinning. Poly(vinylpyrrolidone) (PVP) was used as spinning aid. Polycrystalline YAG fibers were obtained by pyrolysis of the green fibers followed by sintering at defined temperatures in air. Ceramic fibers were 9–16 μm in diameter. Differential scanning calorimetry/thermogravimetric analysis coupled with mass spectrometry (DSC/TGA-MS) showed an exothermic peak at 920 °C assigned to the crystallization of YAG and an overall ceramic yield of 38% at 1400 °C. X-ray diffraction (XRD) analysis showed that phase-pure YAG can be obtained at 1600 °C after intermediate formation of Y 2 O 3 and monoclinic yttrium aluminum oxide (YAM, Y 4 Al 2 O 9 ) phases.

Newmaterialsandprocessingroutesprovideopportunitiesfortheproductionofadvancedhighperformancestructuresfor different applications. Ceramic matrix composites(CMCs)areoneofthesepromisingmaterials.Bycombiningdifferent ceramic matrix materials with special suitablefibers, new properties can be created and tailored forinteresting technical fields. The demand for lightweight,high modulus, and high-temperature-resistant materialsforaerospaceandotherhightemperatureapplicationsgaverise to the development of CMCs. These materials exhibitmost of the positive properties of monolithic ceramics,however, are less brittle. The further optimization of thesematerials is closely connected to the development of highperformance ceramic fibers, which should be producedby cost-efficient processes.

Grain growth kinetics of mullite in laboratory-produced and commercial (3M-Nextel 720) alumino silicate fibers was analyzed in the temperature range between 1500° and 1700°C. The lab fibers consist of mullite plus traces of α-alumina, while the phase content of the commercial Nextel 720 fibers is about 60 wt% mullite plus 40 wt%α-alumina. The temperature-induced grain coarsening of mullite follows the empirical law D1/n−D01/n=kt. Two different temperature regimes can be distinguished with respect to the grain growth exponents: above 1600°C the growth exponent is ≈1/3, while below 1600°C the growth exponent of ≈1/12 is exceptionally low. Laboratory-produced and commercial fibers show almost identical mullite grain growth kinetics.

The article contains sections titled: 1. Introduction 2. Properties and Raw Materials 2.1. Physical Properties 2.2. Chemical Properties 2.3. Resources, Raw Materials 3. Production 3.1. Boron Monofilament 3.2. Silicon Carbide Fibers 3.3. High Alumina Fibers 3.4. Zirconia Fibers 4. Uses 5. Economic Aspects 6. Toxicology and Occupational Health

The article contains sections titled: 1. General Description of Inorganic Fibers 2. Crystalline Structure and Mechanical Properties 3. Testing Methods for Inorganic Fibers 4. Inorganic Fibers for Thermal Insulation 5. Inorganic Fibers for Reinforcement Purposes 5.1. Principles of Fiber Reinforcement 5.2. Commercial Continuous Inorganic Fibers 5.3. Surface Chemistry, Surface Treatment, and Surface Properties 5.4. High-Temperature Behavior of Inorganic Fibers

Aqueous spinning dopes for dry spinning of alumina green fibers were prepared by using basic aluminium chloride Al2(OH)5Cl · 2.5 H2O and SiO2 sol as inorganic components and poly(vinyl alcohol) (PVA) as polymeric organic component. Certain rheological properties of the mixtures are essential to achieve good spinnability at high spinning speeds. The rheology of the dope is influenced by the molecular weight and the degree of hydrolysis of the PVA, as well as by the composition and the concentration of the mixture. For mixtures without SiO2 best results were obtained at a PVA: Al2O3 mass ratio of 18:82 and an Oxide content of about 27 wt.-%. The PVA used has an average molecular weight of 70000 and a degree of hydrolysis of 89%. The dopes were spun to continuous green fibers at speeds up to 500 m/min. The structure and the ageing behaviour of concentrated solutions of basic aluminium chloride has been intensively studied. Wasrige Spinnmassen fur das Trockenspinnen von Aluminiumoxid-Grunfasern wurden hergestellt. Dabei wurden basisches Aluminiumchlorid Al2(OH)5Cl · 2,5 H2O und SiO2-Sol als anorganische Komponenten und Polyvinylalkohol (PVA) als polymere organische Komponente eingesetzt. Bestimmte rheologische Eigenschaften der Mischungen sind essentiell, um eine gute Spinnbarkeit bei hohen Spinngeschwindigkeiten zu erhalten. Die Rheologie der Spinnmassen wird zum einen vom Molekulargewicht und dem Verseifungsgrad des PVA beeinflust und zum anderen von der Zusammensetzung und der Konzentration der Mischung. Fur Mischungen ohne SiO2 wurden die besten Ergebnisse bei einem PVA:Al2O3, Massenverhaltnis von 18:82 und einem Oxidgehalt von ungefahr 27 Gew.-% erzielt. Der verwendete PVA hat ein mittleres Molekulargewicht von 70000 und einen Verseifungsgrad von 89%. Die Spinnmassen wurden mit Spinngeschwindigkeiten von bis zu 500 m/min zu kontinuierlichen Grunfasern versponnen. Die Struktur und das Alterungsverhalten von konzentrierten Losungen von basischem Aluminiumchlorid wurden ausfuhrlich untersucht.

PET and PA 66 fabrics were dyed with different disperse dyes under regular conditions. The dyed fabrics were irradiated with 180 kV electron radiation. It was observed that increasing radiation doses led to increasing total color differences dE if compared to the unirradiated materials. These color differences are mainly caused by two types of reactions. First by the reversible formation of dye radicals, which can be reoxidized (in air) to the original dye molecules, and second by the irreversible reaction of dye molecules with the fiber polymer. The latter reaction causes a permanent change of the color of the fabric, which can be kept low with the proper irradiation conditions. The decision whether or not this change can be tolerated depends on the further use of the textile. PET- und PA 66-Textilien wurden unter normalen Bedingungen mit verschiedenen Dispersionsfarbstoffen gefarbt. Die gefarbten Textilien wurden mit 180 kV Elektronenstrahlung bestrahlt. Es wurde beobachtet, das, verglichen mit den unbestrahlten Materialien, zunehmende Strahlungsdosen zu einer Zunahme des Gesamtfarbabstandes dE fuhrten. Diese Farbunterschiede werden hauptsachlich von zwei Reaktionen verursacht: Erstens von der reversiblen Bildung von Farbstoffradikalen, die (an Luft) wieder zu den Ausgangsfarbstoffen reoxidiert werden konnen und zweitens durch die irreversible Reaktion von Farbstoffmolekulen mit dem Faserpolymeren. Die zweite Reaktion ruft eine permanente Farbanderung des Textils hervor, die bei entsprechenden Bestrahlungsbedingungen klein gehalten werden kann. Die Entscheidung, ob diese Veranderung toleriert werden kann, hangt von der weiteren Verwendung des Textils ab.

New materials and processing routes provide opportunities for the production of advanced high performance structures for different applications. Ceramic matrix composites ( CMCs ) are one of these promising materials. By combining different ceramic matrix materials with special suitable fi bers, new properties can be created and tailored for interesting technical fi elds. This chapter gives an overview on fi ber types, which can be used as fi brous components in CMCs [1 – 5] . The production of these fi bers, as well as their structure and properties, will be discussed.

Ceramic composites can be considered as a new class of materials, which will be shortly introduced in the market. Because of their very good thermal and mechanical resistance and low specific weight ceramics fiber are an alternative for conventional materials in a lot of applications in the area of plant and mechanical engineering as well as construction of vehicles. The first developments of ceramic matrix composites were e conducted in the field of aerospace applications, but meanwhile other applications of light weight construction are under development. The paper gives a short overview about the fiber types currently available and about manufacturing techniques of faser preforms.

Es wird ein Verfahren zut gaschromatographischen Bestimmung von chlorierten Insecticiden neben PCB in Milch und Butter beschrieben. Aus Milch wurde der Fettanteil nach Zugabe von Natriumoxalat und Athanol mit Diathylater und Petrolather extrahiert. Die Reinigung der Extrakte erfolgte nach einer Modifikation der Methode von Hadorn u. Zurcher mit Propylencarbonat als selektivem Losungsmittel.