Dielectric Measurements of PAN Precursor and Stabilized Fibers

Given that the carbon fiber production is an energy intensive process, new approaches are investigated. One option might be dielectric heating, but in order to design an efficient applicator, the knowledge of the temperature dependent dielectric properties is a requirement. In this paper the focus is on the dielectric measurements of the Polyacrylonitrile (PAN) precursor fibers and stabilized fibers. A measurement system was developed that is capable to monitor in-situ changes of the dielectric properties during the stabilization process of the PAN fiber. First results show that the losses of the PAN fiber are strongly varying with the temperature. Additionally, the change in the dielectric properties due to the chemical transformation during the stabilization process can be tracked. The strong temperature dependency is decreasing with a higher degree of stabilization

Dielectric monitoring of the pan fiber stabilization process

The production of carbon fibers based on Polyacrylonitrile (PAN) precursor fibers is a very energy intensive process. In order to increase the energy efficiency, microwave plasma processes and, alternatively, dielectric heating with microwaves are in the focus. In this latter case, the knowledge of the dielectric properties over temperature is the key in the design of an appropriate microwave heating system. A measurement system was developed that is capable to monitor in-situ the change of the dielectric properties during the stabilization process of the PAN fiber. First results show that the loss tangent of the PAN fiber is strongly varying with temperature. Additionally, the dielectric properties are changing during the stabilization process due to the chemical transformation

Reaction Kinetics and Process Model of the Polyacrylonitrile Fibers Stabilization Process Based on Dielectric Measurements

Microwave-based dielectric heating is a suitable method for energy- and time-efficient processes. Considering the energy required in the production of carbon fibers, it is evident that microwave-based dielectric heating during the different phases of the production needs to be considered too. Nevertheless, the dielectric properties of the processed material needs to be known for the design of an appropriate microwave applicator. When looking at the first stage in the production, the stabilization stage of the PAN fiber, the important data about the dielectric properties is very limited in literature. For this reason, first in-situ temperature-dependent measurements of the dielectric properties during the stabilization stage are presented. The impact of raising temperatures and chemical reactions on the dielectric properties of the heated PAN fiber is discussed. Secondly, the steps taken to set up the reaction kinetics from the dielectric loss point of view are given. This enables determination of the reaction degree as a function of the measured dielectric loss for the first time. The established correlation opens the potential for the application to processes such as an in-situ quality determination. The strong temperature impact on the process is shown, and reaction kinetics are analyzed accordingly. In a final third step, a heat transfer model is presented. It utilizes the evaluated reaction kinetics data and microwave heating, creating a first modelling approach for monitoring and controlling the desired fiber temperature, leading towards an online process

Untersuchung zur Resistenz der Rassen Merinolandschaf und Rhönschaf gegenüber Haemonchus contortus unter besonderer Berücksichtigung von Kreuzungseffekten

Gegenstand der Untersuchung war es zu prüfen, ob eine Steigerung der Parasitenresistenz mittels Kreuzungszucht gegenüber den Rassen Merinolandschaf und Rhönschaf möglich ist. Dafür standen in zwei Versuchsjahren zu den Proben vier und acht Wochen nach der Infektion Lämmer der Elternrassen Merinolandschaf (Ml) (n = 48 bzw. 49) und Rhönschaf (Rh) (n = 70) sowie die reziproken Kreuzungslämmer dieser Rassen (Rh x Ml n = 176 bzw. 175 und Ml x Rh n = 159) zur Verfügung. Die Tiere wurden nach dem Absetzen mit 5000 Haemonchus contortus-Larven infiziert und vier bzw. acht Wochen p.i. auf die Indikatoren der Parasitenresistenz Eizahl pro Gramm Kot (EpG) und Hämatokrit untersucht. Weiterhin wurden die visuellen Indikatoren FAMACHA©-Score und Dag Score aufgenommen um deren Eignung als praxistaugliche Indikatoren der Parasitenresistenz zu prüfen. Es konnten keine einheitlichen Ergebnisse hinsichtlich der Beziehung zwischen Dag Score und der Haemonchus contortus-Infektion gewonnen werden. Die Erfassung des Scores erwies sich als nicht geeignet zur Identifikation einer niedrigen bzw. hohen Eiausscheidung durch Haemonchus contortus. Unter den gegebenen Infektionsbedingungen ist der Score nicht für die praktische Schafhaltung als Indikator zu empfehlen. Durch die Ermittlung der Konzentration der Schilddrüsenhormone ergaben sich nicht vorhandene bzw. gering positive Korrelationen zwischen den Merkmalen T4 und T3 mit LogEpG und der Gesamtanzahl Würmer, so dass kein Rückschluss hinsichtlich einer Beeinträchtigung des Gesamtstoffwechsels durch Parasiteninfektion zu gelassen werden konnte.The primary aim of the study was to proof if there is a possibility to increase the resistance for parasites in crossbreeding the pure breed lines Merinoland sheep and Rhoen sheep. A crossbreeding program was conducted with animals of the breeds Merinoland sheep (Ml) (n = 48 adv. 49) and Rhoen sheep (n = 70) as well as the reciprocal counterparts (Rh x Ml n = 176 adv. 175 and Ml x Rh n = 159). Each animal was orally infected after weaning with 5000 infective-stage larvae (L3) of the nematode Haemonchus contortus. Faecal egg counts (FEC) and haematocrit values of all the lambs were collected four and eight weeks post infectionem. FAMACHA©-Score and dag score were given at the same time to proof their ability as practicable indicators for parasite resistance. There were no consistent results concerning the relationship between dag score and an infection with Haemonchus contortus. Taking the dag scores was unsuitable for detecting high or low resistant lambs. Under these circumstances of artificial infection the dag score is not recommendable as a suitable indicator for sheep farming. The concentration of the thyroid hormones show any or weak relationships between LogEpG and the number of worms. It was not possible to make any conclusions in respect of interference of the metabolism caused by parasite challenge

Combination of Scattering Matrix Code and Process Model to Optimize a Microwave Applicator Suitable for the Stabilization of PAN Fibers

Carbon fiber production is an energy intensive process requiring new approaches for energy efficient heating. One possible option might be the dielectric heating. A basic requirement to design an efficient applicator is the knowledge of the variation of dielectric properties during processing. The experience shows strongly increasing dielectric loss of a Polyacrylonitrile (PAN) fiber with increasing temperatures while it decreases during the chemical transformation in the stabilization stage. For the applicator design an electrical field that counteracts the variation of the dielectric loss is a suitable choice. In this presentation the focus is on the combination of the generalized scattering matrix (GSM) code with a process model. It shall allow for the optimization of the geometry of a cylindrical resonator usable during the stabilization stage of the PAN fiber. The scattering matrix code is utilized to calculate the field profile of a cylindrical resonator with step-wise changing diameter that acts as applicator. The number of steps can be varied, depending on the ability of production and spacial requirements

A large ameloblastic fibro-odontoma of the right mandible

The ameloblastic fibro-odontoma is a rare mixed odontogenic tumor. It occurs predominantly in children and young adults with no sex predilection and locates most often in the posterior segment of the mandible. A painless swelling is the most common clinical sign. Radiologically, ameloblastic fibro-odontoma shows a circumscribed radiolucency, which contains radio-opaque foci of various sizes and shapes. Histological examination reveals a fibrous soft tissue, islands of odontogenic epithelium and a disordered mixture of dental tissues. The tumor produces enamel or enamel matrix, dentin and cementum. The treatment of ameloblastic fibro-odontomas usually consists of enucleation or surgical curettage, which is possible due to their benign biological behaviour

Path-designed 3D printing for topological optimized continuous carbon fibre reinforced composite structures

In current 3D printing technologies, it remains a great challenge to print continuous carbon fibre reinforced composites with complex shapes and high mechanical performances. The main reason lies in the limitation of printing path design, which cannot guarantee to print carbon fibres along load transmission paths of composite parts. Here we address this issue by proposing an ingenious path-designed 3D (PD-3D) printing approach that considers the load transmission path and anisotropic property of the continuous carbon fibre reinforced filament. Complex structures of carbon fibre reinforced composites, with enhanced lightweight, were demonstrated. Such structures of carbon fibres paving along load transmission paths, greatly reduce stress concentration and achieve a quasi-isotropic performance. By comparing printed specimens with drilled holes and semicircles, the PD-3D printed specimens with holes and semicircles are 67.5% and 62.4% higher in tensile and flexural strength, respectively. And the strength to weight ratio of the tensile and flexural specimens also increase by 55.1% and 35.2%, compared with the drilled ones