Production and characterization of Al2O3-Cu composite materials

Enrique Rocha-Rangel,José G. Miranda-Hernández,Socorro Moreno-Guerrero,Ana B. Soto-Guzmán 한양대학교 세라믹연구소 2006 Journal of Ceramic Processing Research Vol.7 No.4

Using an intense powder mixture of Al2O3 with different copper contents (1, 5, 10, 20 or 30 mass %) several Al2O3-Cu composite materials were fabricated. The microstructure of the composites was observed by optical and scanning electron microscopy. The observations show a microstructure formed by an Al2O3 ceramic matrix with fine Cu metallic networks. Due to the liquid sintering mechanism, the relative density reached by the samples was higher than 95%, this together with the fine and homogeneous microstructure present in the samples let us obtain composite materials with good values of toughness, hardness, elastic modulus and electrical properties. The incorporation of a ductile metal inside a hard ceramic matrix increments its toughness. The probable toughening mechanism is crack bridging due to the presence of a homogeneous ductile metal networks in the material’s microstructure. The values of density, hardness, elastic modulus and electrical resistance of the composites are directly dependent on the copper content in the matrix, because with an increase in copper content the density of the composites is larger, whereas, the hardness, elastic modulus and electrical resistance are reduced. Using an intense powder mixture of Al2O3 with different copper contents (1, 5, 10, 20 or 30 mass %) several Al2O3-Cu composite materials were fabricated. The microstructure of the composites was observed by optical and scanning electron microscopy. The observations show a microstructure formed by an Al2O3 ceramic matrix with fine Cu metallic networks. Due to the liquid sintering mechanism, the relative density reached by the samples was higher than 95%, this together with the fine and homogeneous microstructure present in the samples let us obtain composite materials with good values of toughness, hardness, elastic modulus and electrical properties. The incorporation of a ductile metal inside a hard ceramic matrix increments its toughness. The probable toughening mechanism is crack bridging due to the presence of a homogeneous ductile metal networks in the material’s microstructure. The values of density, hardness, elastic modulus and electrical resistance of the composites are directly dependent on the copper content in the matrix, because with an increase in copper content the density of the composites is larger, whereas, the hardness, elastic modulus and electrical resistance are reduced.

Dielectric properties of strontium titanate synthesized by means of solid state reactions activated mechanically

Enrique Rocha-Rangel,Juan López-Hernández,José A. Rodríguez-García,Eddie N. Armendáriz-Mireles,Carlos A. Calles-Arriaga,W. J. Pech-Rodríguez,José A. Castillo-Robles 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.8

In this work, strontium titanate samples were prepared starting from SrCO3 and TiO2 powders mixture. Raw materials wereactivated mechanically in a planetary mill and then calcined at different temperatures (900 to 1300 oC). Powders after grindingwere analyzed by differential thermal analysis in order to follow the carbonate decomposition. On the other hand, samplesresulting from heat treatment were characterized by XRD, SEM and electrical measurements. XRD analysis determines thatSrTiO3 synthetized presents the cubic structure of perovskite. Complete reaction for SrTiO3 compound formation occurs at1200 oC. SEM observations indicate the presence of a microstructure with very small gran size and consequently a largenumber of grain boundaries. Electrical measurements suggest the formation of a material with high insulating capacity. Withthis evidence, it can be concluded that solid state reactions activated mechanically, proved to be an effective way to fabricatestrontium titanate compound with very fine microstructure and high insulating behavior.

Synthesis of Al₂O₃/Ti₃Al composites by in-situ displacement reactions

Enrique Rocha-Rangel 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.1

The employment of aluminothermic reactions of displacement as an alternative for the production of Al₂O₃/Ti₃Al composite materials has been investigated. Compacted samples from an intensely ground mixture of powders of TiO₂+Al₂O₃ +Al were sintered at 1500ºC during 1 hour by hot pressing in an argon atmosphere. The TiO₂ is used as predecessor to generate in-situ Al₂O₃ via its reduction by means of metallic Al. Al reacts also in a simultaneous way with the reduced titanium to form an intermetallic alloy of the type TixAly. The Al₂O₃ employed in the precursor materials is used as a way for the dissipation of the heat build-up during the aluminothermic reduction of the TiO₂. The results of the characterizations indicate that Al₂O₃- based composite materials were obtained with reinforcement particles of TixAly. The microstructure of these materials is dense, fine and homogeneous. The preliminary characterization of the microstructure and its composition features subsequent to the cycle of in-situ processing are presented here. The employment of aluminothermic reactions of displacement as an alternative for the production of Al₂O₃/Ti₃Al composite materials has been investigated. Compacted samples from an intensely ground mixture of powders of TiO₂+Al₂O₃ +Al were sintered at 1500ºC during 1 hour by hot pressing in an argon atmosphere. The TiO₂ is used as predecessor to generate in-situ Al₂O₃ via its reduction by means of metallic Al. Al reacts also in a simultaneous way with the reduced titanium to form an intermetallic alloy of the type TixAly. The Al₂O₃ employed in the precursor materials is used as a way for the dissipation of the heat build-up during the aluminothermic reduction of the TiO₂. The results of the characterizations indicate that Al₂O₃- based composite materials were obtained with reinforcement particles of TixAly. The microstructure of these materials is dense, fine and homogeneous. The preliminary characterization of the microstructure and its composition features subsequent to the cycle of in-situ processing are presented here.

Studying the wetting of carbon-coated alumina substrates by different aluminum alloys

Enrique Rocha Rangel,M. Socorro Moreno Guerrero,xico) 한양대학교 세라믹연구소 2006 Journal of Ceramic Processing Research Vol.7 No.1

The wetting of alumina ceramics was studied as a function of time and temperature by the sessile drop method using vacuum pressures of 10−5 Pa. Contact angles as small as 38 degrees were obtained for the combination carbon coated alumina and an Al-2.5 at.% La alloy, in a time of 4500s and at a temperature of 1300 oC. On the other hand, for the single system aluminaaluminum the final contact angle was of 82 degrees after 7200 seconds at the same temperature. Considering the free formation energy of different oxides and carbides that can be formed between elements used in the present experiments are favorable thermodynamically and considering the observation of undercutting of the substrate and ridge formation at the leading edge of the liquid aluminum in all samples it can be concluded that wetting is enhanced thanks to different chemical reactions that occur at the ceramic-metal interface.

Fracture toughness enhancement for metal-reinforced alumina

Enrique Rocha-Rangel,Elizabeth Refugio-García,José G. Miranda-Hernández,Eduardo Terrés-Rojas 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.6

With the idea to determine ways of tailoring alumina (Al2O3) in order that one or more toughening mechanisms are activated in service, investigations about the production of Al2O3-based composites with different reinforcement metals and intermetallics have been carried out. The synthesis of composites materials has been made by means of both; liquid and solid pressureless sintering of an intensive mechanical mixture of powders. With the use of some metals in the chemical formulations, significant improvements in ceramic toughness have been reported. From the fracture toughness measurements and microstructural observations, it can be concluded that the toughening mechanism in Al2O3/metal reinforced composites is due to crack bridging and crack deflection. With the idea to determine ways of tailoring alumina (Al2O3) in order that one or more toughening mechanisms are activated in service, investigations about the production of Al2O3-based composites with different reinforcement metals and intermetallics have been carried out. The synthesis of composites materials has been made by means of both; liquid and solid pressureless sintering of an intensive mechanical mixture of powders. With the use of some metals in the chemical formulations, significant improvements in ceramic toughness have been reported. From the fracture toughness measurements and microstructural observations, it can be concluded that the toughening mechanism in Al2O3/metal reinforced composites is due to crack bridging and crack deflection.

Fabrication of ZnO electroceramics by reaction bonding

Enrique Rocha-Rangel,Octavio Martínez-Urgell,Carlos Gómez-Yánez 한양대학교 세라믹연구소 2006 Journal of Ceramic Processing Research Vol.7 No.3

ZnO ceramics doped with small amounts of Bi2O3, CoO, MnO, Sb2O3 and Cr2O3 offer a great potential as electroceramic materials to be used as protectors to prevent electric surges. In the present communication, the reaction bonded alumina oxide (RBAO) technique is adapted for the production of ZnO-based ceramics by the reaction bonding zinc oxide (RBZnO) process with the idea of achieving the advantages of the RBAO process. Because Zn oxidation occurs between 330 °C and 468 °C, slow heating rates before the Zn melting point (419 °C) is very important in order to obtain the desired ceramic. The need for a fine microstructure of the matrix with many grain boundaries is discussed. ZnO ceramics doped with small amounts of Bi2O3, CoO, MnO, Sb2O3 and Cr2O3 offer a great potential as electroceramic materials to be used as protectors to prevent electric surges. In the present communication, the reaction bonded alumina oxide (RBAO) technique is adapted for the production of ZnO-based ceramics by the reaction bonding zinc oxide (RBZnO) process with the idea of achieving the advantages of the RBAO process. Because Zn oxidation occurs between 330 °C and 468 °C, slow heating rates before the Zn melting point (419 °C) is very important in order to obtain the desired ceramic. The need for a fine microstructure of the matrix with many grain boundaries is discussed.

Effects of the variations in milling time and sintering temperature on the production of mullite-ZrO2 composites

Enrique Rocha Rangel,Heberto Balmori Ram?rez 한양대학교 세라믹연구소 2004 Journal of Ceramic Processing Research Vol.5 No.1

Based on reactive sintering technology, mullite-ZrO2 composites were fabricated. A powder mixture of 64% wt ZrSiO4, 18.5% wt Al and 17.5% wt Al2O3 was attrition milled for different times (0.5, 3, 6, 12 and 24 h). Precursor powder was cold isostatic pressed at 400 MPa and heat-treated in air at 1450, 1500, 1550 and 1580캜 for 2 h. During firing Al oxidizes to Al2O3 completely, and ZrSiO4 dissociation allows the production of mullite with finly dispersed ZrO2. XRD analysis shows that increases in the milling time and sintering temperature favors densification and mullitization. The influence of both milling time and sintering temperature upon the phases evolution, microstructural development and final mechanical properties, as well as the processing details are discussed in this study.

Preparation of Water-Soluble Chitosan and Aloe vera Mucilage and Their Use for Assembly of Polyelectrolyte Complexes

( Adriana M. Rangel-rodriguez ),( J. Adriana Sañudo-barajas ),( Nagamani Balagurusamy ),( Louise Wicker ),( Rosabel Velez-de-la-rocha ),( Juan Carlos Contreras-esquivel ) 한국키틴키토산학회 2018 한국키틴키토산학회지 Vol.23 No.2

In this work, the preparation and characterization of water-soluble polysaccharides from chitosan and Aloe vera was studied. The water-soluble polysaccharides were used to study polyelectrolyte complexes. The reaction time effect for chitosan hydrolysis by endo-chitosanase was studied at 40ºC and pH 5.00 to produce water soluble chitosan (WSCh). The physico-chemical characteristics of chitosan hydrolysates, water-soluble A. vera polysaccharides and polyelectrolyte complexes were determined. After 3 h of chitosan processing, a viscosity reduction of 90%, while only 2.3% of reducing sugars were released. A WSCh was recover by ultrafiltration (1 kDa) from chitosan hydrolysate after 12 h and was spray-dried with a yield of 9.7%. Cold-water extraction of A. vera mucilage from pulp gives a crude polysaccharide yield of 0.81 g/kg (wet basis) based on whole leaf weight. The water isolated mucilage is composed of a mixture of protein and mannan rich-polysaccharide. The results show WSCh’s association capacity with A. vera mucilage by electrostatic interaction.

Physical Properties of the Sr4Al6O12SO4 Ceramic Compound

J.A. Rodríguez-García,E. Rocha-Rangel,J. López Hernández,C.A. Hernández Bocanegra,A.L. Leal Cruz,J.M. Almanza Robles,J. Torres Torres 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.11

The Sr4Al6O12SO4 ceramic compound was synthesized by a solid state reaction starting from stoichiometric mixtures of 3 : 3 : 1 molar ratio of reactive grade of SrCO3, Al2O3 and SrSO4, respectively. Cylindrical samples were confirmed by uniaxial pressing at 100 MPa and were heat treated at 1400 oC during 4 hrs. Subsequently, the samples were ground and re-conformed in cylindrical shape samples by uniaxial pressing at 300 MPa. The new samples were heat treated at 1400 oC during 24 hrs. This process was done in order to increase density of the samples. The Sr4Al6O12SO4 ceramic compound was characterized by the study of its physical properties such as: density, micro-hardness, thermal expansion and stability, enthalpy of formation, magnetic properties and electrical conductivity. Experimental results show that the maximum density obtained for the Sr4Al6O12SO4 ceramic compound was 2.913 grcm−3, with thermal expansion coefficient of 10.12E−06(oC−1); it also presents an enthalpy of 2.3 KJmol-1 and an excellent thermal stability at elevated temperatures in different atmospheres. In addition, the Sr4Al6O12SO4 ceramic compound is neither electrically conductive nor magnetic.

Production, microstructural comparison and mechanical behavior of reinforced alumina composites containing zirconia, silicon carbide, nickel and titanium

Mario Romero-Romo,Enrique Pastorino-Chassale,Enrique Rocha-Rangel 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.3

Using a mix of Al2O3 powders to which other reinforcing materials such as: ZrO2, SiC, Ni and Ti were added up to 10 wt%,and the combination of conventional techniques known as milling-pressing-sintering, several composite samples were fabricated. The microstructures of the composites reinforced with (Ni or Ti) examined in the scanning electron microscope showed a slight metallic network formed between the alumina grains. The action of several mechanisms such as crack bridging, crack deflection and microcracking seems to be the cause of the improvement in the fracture toughness of the composites with respect to that of monolithic alumina. The experimental values of elastic modulus and hardness of the composites diminished, although, on the other hand, the compressive and flexural fracture strengths were increased when alumina was reinforced with the materials studied here.