A machinable carbon aerogel composite with a low thermal conductivity and
enhanced mechanical properties
Changshou Yea, Rubing Zhanga, Zhimin Ana and Baolin Wangb
aSchool of Civil Engineering, Beijing Jiaotong University, Beijing, People’s Republic of China; bGraduate School at Shenzhen, Harbin Institute of Technology, Harbin, People’s Republic of China
ABSTRACT
Carbon aerogels are prepared via the sol–gel polymerisation of resorcinol with formaldehyde, followed by supercritical drying and carbonisation. The fabricated carbon aerogels have low densities in the range 0.028–0.196 g cm −3, ultra-low thermal conductivities in the range 0.0259–0.0707 W (m K) −1 and high specific surface areas (>520 m2 g −1 ). The carbon aerogel
composites are reinforced with short carbon fibres by adding the carbon fibres to the resorcinol–formaldehyde solution to reduce their brittle nature and improve their machinability. The compressive strength of the composites containing 2 wt-% carbon fibres
is 1.75 MPa, which is 56% higher than that of pure carbon aerogel. Both fracture toughness and compressive strength of these composites are improved. These composites also have good machinability, with the ability to maintain their shape after being machined with traditional steel tools. Furthermore, the composites with nanoporous structure exhibit ultralow thermal conductivity up to 1400°C.
KEYWORD S
Carbon aerogel; supercritical drying; thermal properties; toughness
Enhanced mechanical properties of carbon fi bre/lithium aluminosilicate
composites modifi ed by SiB6 addition
Long Xiaa, Chi Wanga, Dongdong Fenga, Ke Wangb, Haibo Hanb, Tao Zhanga and Guangwu Wena
aSchool of Materials Science and Engineering, Harbin Institute of Technology, Weihai, People’s Republic of China; bShanghai Institute of Spacecraft Equipment, Shanghai, People’s Republic of China
ABSTRACT
Carbon fibre-reinforced lithium aluminosilicate matrix composites (Cf/LAS) with different SiB6 contents were prepared by the hot pressing method to assess their mechanical properties and oxidation resistance. Composite that was incorporated with 2 wt-% SiB6 exhibited the highest flexural strength of 500 ± 22.3 MPa. Weight loss and residual strength of Cf/LAS modified by SiB6 were analysed. The results indicated that the addition of SiB6 had a remarkable effect on improving the oxidation resistance for Cf/LAS. To establish a direct relationship among interfacial microstructure, mechanical and oxidation behaviour of the studied composites, their connection was examined and discussed.
KEYWORD S
Carbon fibres; ceramics matrix composites; fracture mechanics/toughness; oxidation resistance
Study of the electrophoretic deposition copper– carbon nanotubes composite
coatings in deep eutectic solvent using a Taguchi experimental design
approach
W. J. Pech-Rodríguez a, E. Rocha-Rangela, Carlos Adrian Calles-Arriaga a, G. Vargas-Gutiérrezb and
F. J. Rodríguez-Varelab
aIngeniería Mecatrónica, Universidad Politécnica de Victoria, Ciudad Victoria, Tamaulipas, México; bSustentabilidad de los Recursos Naturales y Energía, Cinvestav Unidad Saltillo, Ramos Arizpe, Coahuila, México
ABSTRACT
The present work discusses the electrophoretic deposition (EPD) of copper–carbon nanotubes (Cu–CNTs) composite coatings in a Deep Eutectic Solvent (DES) media, using a non-symmetric deposition process. A Taguchi experimental design is implemented in order to assess the effect of the different parameters on the microstructural characteristics of the coatings. The analysis of
the design of experiments (DOE) is performed with the signal to noise (S/N) ratio and the analysis of variance. The results clearly reveal that the time of deposition is the most influential parameter on crystallite size, whereas the asymmetric factor has the highest effect on the preferential deposition of Cu or C and thus on the chemical composition. It is therefore concluded that by changing some of the parameters, EPD can be implemented to develop nanostructured composite coating having a desired crystallite size and morphology.
KEYWORD S
Electrophoretic deposition; deep eutectic solvent; copper–carbon
Synthesis of hierarchically porous mullite ceramics with improved thermal
insulation via foam-gelcasting combined with pore former addition
Shengtao Gea, Liangxu Lina, Haijun Zhang a, Yubao Bia, Yangfan Zhenga, Junyi Lia, Xiangong Denga and
Shaowei Zhangb
aThe State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan, People’s Republic of China; bCollege of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
ABSTRACT
To further improve the thermal insulation performance of porous mullite ceramics used in important industrial sectors, a combined foam-gelcasting and pore-former addition approach was investigated in this work, by which hierarchical porous mullite ceramics with excellent properties, in particular, thermal insulation property, were prepared. Both mesopores (2–50 nm) and macropores (117.8–202.7 μm) were formed in porous mullite ceramics resultant from 2 h firing at 1300°C with various amounts of submicron-sized CaCO3 pore former. The former mainly arose from the decomposition of CaCO3, and the latter from the foamgelcasting process. The porous samples prepared with CaCO3 addition had low linear shrinkage of 2.35–4.83%, high porosity of 72.98–79.07% and high compressive strength of 5.52–14.82 MPa. Most importantly, they also exhibited a very low thermal-conductivity, e.g. 0.114 W m −1 K−1 at 200°C, which was much lower than in the cases of their counterparts prepared via the conventional foam-gelcasting route.
KEYWORD S
Porous mullite ceramics; foam-gelcasting; hierarchical pore structure; thermal conductivity
The infl uence of spinel and magnesia powder bed on mechanical properties of
alumina sintered under air and nitrogen atmosphere
Monika Michálková, Martin Michálek, Gurdial Blugan and Jakob Kuebler
Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for High Performance Ceramics, Dübendorf, Switzerland
ABSTRACT
The aim of the present work was changing the surface properties of alumina ceramic via sintering of samples in spinel MgAl2O4 and magnesia MgO powder bed. During sintering nitrogen and air atmosphere were used; and the reference material was sintered at the same conditions but in an alumina powder bed. All samples were sintered to a density higher than 99.2% of theoretical density of alumina. In order to examine samples SEM, EDX and XRD (Xray diffraction from 18 to 70 °2Theta) analysis were performed together with B3B flexural strength measurement. Results revealed that by sintering of alumina samples in a spinel
powder bed pore-free surfaces were prepared, which had a favourable effect on B3B flexural strength. This was ascribed to the high solubility of Al3+ in spinel at sintering temperatures, which increases the sintering driving force. A further positive effect on B3B flexural strength was observed when samples were sintered in nitrogen instead of air.
KEYWORD S
Alumina; sintering; solid state diffusion; microstructure; flexural strength
β -Tricalcium phosphate silica aerogel as an alternative bioactive ceramic for the
potential use in dentistry
Viktória Hegedű sa**, Farkas Kerényi b, Róbert Bodac, Dóra Horváthc, István Lázár d, Enikő Tóth-Győria,
Balázs Dezsőe* and Csaba Hegedusb*
aDepartment of Pediatric Dentistry and Orthodontics, University of Debrecen, Faculty of Dentistry, Debrecen, Hungary; bDepartment of Biomaterials and Prosthetic Dentistry, University of Debrecen, Faculty of Dentistry, Debrecen, Hungary; cDepartment of Oral and Maxillofacial Surgery, University of Debrecen, Faculty of Dentistry, Debrecen, Hungary; dDepartment of Inorganic and Analytic Chemistry, University of Debrecen, Faculty of Science, Debrecen, Hungary; eDepartment of Oral Pathology and Microbiology, University of Debrecen, Faculty of Dentistry, Debrecen, Hungary
ABSTRACT
In this study, a mesoporous silica aerogel with β-tricalcium phosphate (β-TCP-AE) was manufactured. The effect of β-TCP-AE on gene expressions (BMP2, BMP7, Runx2 and OSX) of SAOS-2 cells was tested. For the in vivo evaluation, the ‘calvaria critical-size defect’ model was used: following 1 and 3 months of the artificial surgical bone defects filled with β-TCPAE, histopathological analyses were performed. Gene expression studies demonstrated a mild osteoblastic differentiation of the SAOS-2 cells triggered after seven days of β-TCP-AE treatment. Digital histology of rat’s calvarial bone defects reconstructed with β-TCP-AE showed that after 1 month, calcifications and early ossifications developed with the presence of capillary-rich fibrous inflammation and remnants of exogenous compounds which nearly disappeared by the third month, and replaced with multiple newly formed bone islets mediated by osteoblasts. Based on our results, this bioceramic compound appears to have
favourable properties for the use as a scaffold in the reconstructive medical practice.
KEYWORD S
β-tricalcium phosphate; bioactive ceramic; silica aerogel; scaffold; SAOS-2; ossification; bone defect; osteoblast; histo-morphology
Wear performance of self-glazed zirconia crowns with different amount of
occlusal adjustment after 6 months of clinical use
Andi Shia*, Zhe Wua*, Jiangyong Huanga*, Qian Lianga*, Qianqian Lia*, Lvhua Guoa* and Zhijian Shenb**
aKey Laboratory of Oral Medicine, Stomatology Hospital of Guangzhou Medical University, Guangzhou, Guangdong, People’s Republic of China; bDepartment of Materials and Environmental Chemistry Arrhenius Laboratory, Stockholm University, Stockholm, Sweden
ABSTRACT
The amount of enamel wear on the antagonist occlusal surfaces caused by self-glazed zirconia crowns was compared with that caused by contralateral natural teeth. Thirteen self-glazed zirconia crowns were placed in situ. The impressions of self-glazed zirconia crowns, their antagonists and the control teeth were taken and scanned at baseline and 6-month followup. The patients were divided into two groups, the self-glazed crowns in one group were subjected to a large amount of grinding with well polishing (LaP group, n = 7), while the other group required a little amount of grinding with well polishing (LiP group, n = 6).
Statistics were analysed by two-sided paired Student’s t-tests to a significance level of p < .05. The results revealed that the maximum and mean enamel wear significantly different between the antagonists of self-glazed crowns and the control teeth (p < .05). Increased amount of enamel wear was found in LaP group (p < .05). The self-glazed zirconia crowns caused more enamel wear of antagonists than natural teeth after 6 months. Occlusal adjustment and polishing were considered as possible confounders which affected wear behaviour.
KEYWORD S
Self-glazed zirconia; enamel wear; polishing; grinding
