Synthesis and characterization of ceramic composite materials based on silicon-carbide and cordierite

Predmet ove doktorske disertacije je sinteza i karakterizacija kompozitnih keramičkih materijala na bazi silicijum-karbida i kordijerita. Silicijum-karbid, SiC, je kovalentno jedinjenje male gustine, velike tvrdoće, odlične termičke stabilnosti, dobre toplotne provodljivosti, dobre otpornosti prema termošoku. Ovakva svojstva omogućavaju njegovu brojnu primenu u raznim oblastima. Zbog kovalentne prirode veze, dobijanje guste SiC keramike je nemoguće bez dodatka aditiva. Dosadašnja ispitivanja su pokazala da se dodatkom smese oksida, kao aditiva, dobija gusta SiC keramika na temperaturama ispod 2100°C. Kordijerit, 2MgO 2Al2O3 5SiO2, poseduje odličnu termičku stabilnost, nizak koeficijent toplotnog širenja i dobru otpornost prema termošoku. U ovom radu kordijerit je dobijen iz dva izvora: iz spinela, MgAl2O4, i iz Mg-izmenjenog zeolita LTA a zatim je uz dodatak silicijum-karbida korišćen za sintezu kompozitnih materijala. Kompozitni materijali dobijeni su mehaničkim mešanjem SiC sa 30 i 50 mas.% kordijerita, dobijeno je četiri vrste kompozita. Posebna pažnja posvećena je proučavanju procesa sinterovanja u cilju dobijanja keramike sa poboljšanim fizičko-hemijskim svojstvima variranjem parametara sastav-temperaturapritisak. Praćen je uticaj sadržaja dodatog kordijerita na termostabilnost SiC/kordijeritnog kompozitnog materijala pošto poznavanje otpornosti vatrostalnih materijala prema termošoku određuje njihovu primenu. Dodatak grafita omogućio je formiranje pora tokom sinterovanja. Sadržaj dodatog grafita značajno utiče na poroznost i čvrstoću kompozitnog materijala pa je proučavan uticaj poroznosti na termostabilnost kompozitne keramike. U okviru istraživanja korišćene su nedestruktivnih metode karakterizacije: ultrazvučne metode za određivanje dinamičkog Jungovog modula elastičnosti i čvstoće tokom ispitivanja termošoka, kao i primena alata za analizu slike, Image Pro Plus program, radi određivanja stepena oštećenja uzoraka pre i u toku ispitivanja termostabilnosti. Uspostavljene su zavisnosti i predloženi modeli između izmerenih brzina prostiranja ultrazvučnih talasa, Jungovog modula elastičnosti, kao i stepena oštećenja uzoraka sa brojem ciklusa termošoka. Ustanovljeno je veoma dobro slaganje između rezultata predloženih modela posmatranih veličina sa brojem ciklusa termošoka. Ovakav pristup je doveo do razvoja modela za predviđanje smanjenja čvrstoće kompozitnih materijala usled termošoka na osnovu promena brzine prostiranja ultrazvučnih talasa kroz kompozitne materijale, kao i stepena oštećenja površine kompozitnih materijala. Takođe, ovaj pristup je iskorišćen radi razvijanja modela koji određuju kritični broj ciklusa, koje kompozitni materijali izdrže a da ne dođe do razaranja 50 % čeone površine usled izlaganja termošoku, na osnovu promena posmatranih parametara (brzina prostiranja ultrazvuka kroz materijal i stepen oštećenja površine)...The aims of this dissertation are synthesis and characterization of silicon-carbide and cordierite based ceramic composite materials. Silicon-carbide, SiC, is low density covalent compound with high hardness value, excellent thermal stability, high thermal conductivity and good thermal shock resistance. These properties of SiC allow numerous applications in different fields. Covalent bond of SiC precludes formation of high density SiC ceramics without additive. Previous investigations show that the combination of oxide mixture and SiC results in dense SiC ceramics at temperatures up to 2100°C. Cordierite, 2MgO 2Al2O3 5SiO2, has excellent thermal stability, low coefficient of thermal conductivity and good thermal shock resistance. In this dissertation cordierite was synthesized by using two sources: spinel, MgAl2O4, and Mg-exchanged zeolite LTA and then, the mechanical commixtures with SiC powder were prepared with the aim of obtaining four types of composite materials with 30 and 50 wt% of cordierite. Particular attention in this thesis was focused on sintering process. Processing parameters such are composition, temperature, and pressure were changed with the aim of synthesizing ceramics with good physical-chemical properties. Variation of cordierite content in composite materials was applied due to examine his impact on thermal stability of SiC-cordierite composite materials. Graphite, as pore former during sintering, was added to change porosity of SiC-cordierite composite materials. Since addition of graphite has strong influence on porosity and hardness, the influence of graphite additions, 10, 20, and 30 wt%, on thermal stability of SiC-cordierite composite materials was investigated. Nondestructive methods of characterization were applied: ultrasonic pulse velocity technique for determination of dynamic Young modulus of elasticity and strength during the thermal shock investigation as well as tools for image analyses Image pro Plus program for determination of degradation level before and during the thermal shock experiment. Correlations and models between measured ultrasonic velocity, Young modulus of elasticity and degree of degradation were established. Good agreement between the results of suggested models of analyzed parameters with number of thermal shock cycles were obtained. This approach leads to the models for prediction of strength degradation level of composite materials during the thermal shock based on changes of ultrasonic velocity through the composite materials and level of surface degradation. Based on this analysis, model for prediction of critical number of cycles, the number of cycles that composite materials exposed to thermal shock can withstand without surface degradation less than 50 %, was developed..

Phase evolution of Si3N4 with Mg-exchanged zeolite additive

This paper deals with the chemical reactions and phase evolution during pressureless sintering of Si3N4 with Mg-exchanged zeolite as sintering additive. The XRD data show that the first MgO-rich liquid forms at as low as 1250 °C, which as a consequence results in a significant reduction of sintering temperature. At 1300 °C the β−Si3N4 phase had disappeared indicating its dissolution into the liquid phase. At 1500 °C the secondary phase had been completely converted into a glassy phase, however, no phase transformation from α−Si3N4 to β−Si3N4 had taken place. Thus the composition of this material consists of α−Si3N4 embedded in magnesium silicon oxynitride glassy phase.Physical chemistry 2006 : 8th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-29 September 200

Synthesis of fibrous SiC from natural precursor

Fibrous magnesio-silicate (mountain leather asbestos) of Serbian origin was used as Si precursor for the synthesis of SiC by carbothermal-reduction process [1, 2]. As a reducing agent, sugar (saccharose) was used. Formation of SiC was confirmed by XRD analysis and optical microscopy images. Results showed that obtained SiC possess fibrous morphology. Due to the experimental procedure MgF2 is also formed, which is known as an excellent additive for sintering of non-oxide ceramics.Physical chemistry 2006 : 8th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-29 September 200

Properties of Durable Mullite Bodies Manufactured from Waste Clay-Diatomite

Durable mullite bodies have been fabricated using diatom frustules from diatomite powder as the Si source and Al-nitrate as the Al precursor, resulting in fibrous pore morphology. The hard mullite ceramics prepared by mold pressing without additives showed high compressive strength (up to 133 MPa when sintered at 1500 °C). The diatomite-nitrate samples were sintered at three temperatures (1300, 1400, and 1500 °C) for 2 hours. XRPD analysis of the sintered samples showed that the crystalline mineral phases mainly comprise mullite, cristobalite, and corundum. SEM results indicate the presence of rod-like mullite grains measuring 5 µm in length and 500 nm in diameter (aspect ratio 1:10). XRPD analysis of the samples sintered at 1300 °C demonstrated good thermo-mechanical stability and the formation of new hard phases (mullite, corundum, and cristobalite), making the analyzed diatomaceous earth suitable to produce various types of ceramic, construction, and thermal insulating materials.Volume: Ceramic Materials for Advanced Applicatio

Modifying Mesoporous SBA-15 by a Microencapsulation Method in the Matrix of Sodium Alginate

The present work represents hydrogel as a composite based on sodium alginate and mesoporous SBA-15. The hydrogel was obtained by modifying mesoporous SBA-15 by a microencapsulation method of the SBA-15 in the sodium alginate matrix. The solution of CaCl2 provided a gelation complex of sodium alginate/SBA-15 in a rigid gel-like structure. The sodium alginate/SBA-15 hydrogels beads of about 3 mm diameter were prepared. Composite material was characterized by using powder X- ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. This composite material may have potential application in removal of metal ions – pollutants from aqueous solutions.XVI International Conference on Fundamental and Applied Aspects of Physical Chemistry : Proceedings, Vol. 2, September 26-30, Belgrad

Synthesis of spherical SBA-15 silica particles without the use of additional cosurfactant

The synthesis of SBA-15 material with spherical particles is performed by the template method by using only a surfactant Pluronic P123 under acidic conditions. In the synthesis of SBA-15 with spherical particles, an HCl solution was used after specialised chemical treatment of clay purification. The dominant presence of the spheres with diameters up to around 2 μm was confirmed by the scanning electron microscopy(SEM) method. In contrast, the Energy-dispersive X-ray spectroscopy(EDS) confirmed that the spheres consisted only of SiO2 in composition. In addition to the methods mentioned above, X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy(FTIR) methods were used to characterise SBA- 15 materials. Application of HCl solution after chemical treatment of clay purification represents the application of technology in the synthesis of spherical SBA-15.IX Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 20-21, 2021; Belgrad

Mechanical Properties of Biomorphic Silicon Carbide Ceramics

Bioinorphous beta-SiC ceramics were produced from linden wood by impregnation with tetraethyl orthosilicate (TEOS), followed pyrolysis and high temperature treatment at 1580 degrees C. Six specimen groups included charcoal and five groups with different number of impregnation were analyzed. Flexural and compressional strength of charcoal and woodlike SiC ceramic were characterized using three-point and compression testing. Mechanical! properties increased slightly with number of impregnation cycles. Ultrasonic pulse velocity testing (UPVT) was used to determine dynamic young modulus of elasticity. Laser surface modification was studied by interaction with Nd:YAG laser, operating at 1064 or 532 nm wavelengthss and pulse duration of 150 PS

Young's Modulus Evaluation and Thermal Shock Behavior of a Porous SiC/cordierite Composite Material

Porous SiC/Cordierite Composite Material with graphite content (10%) was synthesized. Evaluation of Young modulus of elasticity and thermal shock behavior of these samples was presented. Thermal shock behavior was monitored using water quench test, and non destructive methods such are UPVT and image analysis were also used for accompaniment the level of destruction of the samples during water quench test. Based on the level of destruction graphical modeling of critical number of cycles was given. This approach was implemented on discussion of the influence of the graphite content on thermal stability behavior of the samples

Erosive wear resistance of silicon carbide-cordierite ceramics: influence of the cordierite content

A cordierite/SiC composite was created in situ with reactive sintering at 1250 degrees C and 1300 degrees C. The cordierite precursor was made from commercially available spinel, alumina and quartz and was mixed with the comercial SiC powder to obtain composite materials during the sintering. It was found that cordierite particles bind efficiently with the SiC powder during sintering and that reactive sintering is an effective way to produce ceramics at a relativly low temperature. The goal of this investigation was to check the possibilities of using the silicon carbide-cordierite composite as a material resistant to the erosive wear. The fluid dynamic system of the experimental methodology was used here to produce ultrasonic erosive wear. Two kinds of SiC/cordierite samples were investigated, KS 50 and KS 30, with different mass contents of cordierite (w = 50 % and w = 30 % of cordierite). The mass loss and the level of surface degradation were measured before and during the experiment. The level of surface degradation of the samples was monitored using the Image-Pro Plus program for the image analysis. It was found that after 150 min the mass loss was below 1.3 mg and the surface degradation was below 7 %. The obtained results indicated that both samples exhibited an excellent erosion resistance during the cavitation experiment

Nondestructive evaluation of surface degradation of silicon carbide-cordierite ceramics subjected to the erosive wear

Covalent bond in SiC ceramic request high temperature for its sintering. In order to put down sintering temperature of SiC ceramics we choose cordierite as phase between SiC particles. Reactive sintering is an effective way to produce ceramics at relatively low temperature. We have created in situ SiC/cordierite composite at 1250 degrees C. Cordierite precursor was made from commercially available spinel, alumina and quartz. The possibilities of using silicon carbide-cordierite material as resistant to the erosive wear was goal of this investigation. The fluid dynamic system of the experimental methodology was used here to produce ultrasonic erosive wear. Mass loss and level of degradation were measured before and during the experiment. Level of degradation of the samples was monitored using Image Pro Plus program for image analysis. Average erosion ring diameter as well as average erosion area were monitored during experiment. Obtained results pointed out that after 150 min sample exhibited excellent erosion resistance compared to metal and ceramic samples. (C) 2013 Elsevier Ltd. All rights reserved