Search

Silicon carbide (SiC) samples have been joined by a pressureless slurry based method. The CaO–Al2O3 (CA) glass-ceramic joining material has been characterized in term of crystalline phases and thermal and mechanical properties. A torsion test based on miniaturized hourglass shaped specimens has been used as pure shear strength test method for joined ceramic samples. Torsion results are compared to those obtained by a single lap offset (SLO) test in compression on the same joined materials. Pure shear strength of 104 ± 25 MPa has been measured by torsion test, whereas single lap offset gave 36 ± 8 MPa.

The results of an experimental investigation on epoxy-joined silicon carbide tested in shear mode by four different configurations of torsion test are presented and compared to results obtained by asymmetric four-point bending and four different lap tests in compression. All samples have been joined by an epoxy adhesive (Araldite AV119) which is to be considered as a model brittle joining material chosen to obtain several joined samples in a reasonable time. Advantages and disadvantages of each configuration are discussed and compared to results previously obtained with epoxy-joined Carbon/Carbon composites and ceramics tested with the same methods.

The aim of this work was to develop a new joining/repairing material suitable to be easily applied at temperature not exceeding 300°C, in air atmosphere, on large surfaces of SiCf/SiC composites for aerospace applications. The joining/repairing material proposed here is based on a Carbon Fiber-reinforced commercial Adhesive (CFA) where silicon carbide particles were added. Mechanical strength of the joined SiC/SiC was tested before and after heat treatment at the maximum working temperature for these SiC/SiC. Flexural strengths higher than 200 MPa and 90 MPa, before and after heat treatment, respectively, were obtained by coupling mechanical and adhesive bonding techniques.

Silver nanocluster - silica composite coatings have been deposited by radio frequency (RF) cosputtering on silica substrates. Field Emission Scanning Electron Microscopy (FESEM) and X-ray diffraction spectra of the as deposited and heated samples (150°C - 600°C) revealed the presence of metal silver nanoclusters,their size depending on the heating treatment. The antibacterial activity of the as deposited and heated samples has been measured in accordance to National Committee for Clinical Laboratory Standards, (NCCLS) and it has been demonstrated on samples heated up to 450°C in contact mode and for samples heated at 600°C in a liquid environment. Their antibacterial activity was still present after gamma ray and ethylene oxide gas (EtO) sterilization of the samples. Silver leaching tests on the as deposited and heated samples has been measured by graphite furnace atomic absorption spectrometer (GF-AAS), revealing an amount ranging from 0,1 to 0,9 μg/mm2, over 28 days. Tape resistance (ASTM D3359-97) and scratch resistance tests have been done on each sample revealing a good adhesion of the coatings on silica

This work describes the design and development of a new glass-based coating, suitable to be applied as slurry on foam glass. The glass-based coating was doped with copper oxide for esthetic purposes and reinforced by glass fiber nets. Compression strength tests have been measured on coated and uncoated samples, measuring a slight decrease in the compression strength after coating. Microstructures of the coatings were investigated by X-ray diffraction and scanning electron microscopy analysis. The glass-coated Foamglas® resulted to be class A+ to citric, acetic, and sulfuric acids. Vickers micro-hardness of the coated foam glass is HV0.5=430± 34.

A torsion test on hour-glass-shaped samples with a full joined or a ring-shaped joined area was chosen to measure shear strength of glass–ceramic joined silicon carbide. Shear strength of about 100 MPa was measured for full joined SiC with fracture completely inside their joined area. Attempts to obtain this shear strength with a ring-shaped joined area failed due to mixed mode fractures. On the contrary, full joined and ring-shaped steel hour-glasses joined by a glass–ceramic gave the same shear strength, thus suggesting that this test measures shear strength of joined components only when their fracture is completely inside their joined area.

Carbon-fiber-reinforced carbon (CfC) composites have been joined by using different joining agents: metals (silicon, aluminum, and titanium), an intermetallic compound (magnesium silicide, Mg{sub 2}Si), and glasses (borosilicates and zinc borates). These joining agents have been chosen by considering their possible use in a thermonuclear fusion reactor, as suggested by their low-activation properties, reasonably high working temperature, industrial feasibility, and potential scale-up of the joined carbon-carbon structures using pressureless-processing techniques. Each joined structure (CfC composite-joining material-CfC composite) has been first morphologically characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffractometry. Then, single-lap shear tests have been performed on the most-promising joined structures, i.e., silicon- and aluminum-joined CfC-composite samples, which have shown an average shear strength of 22 and 10 MPa, respectively.

The vacuum plasma spray technique (VPS) has been successfully employed to coat Ti-6A1-4V substrates with bioactive glasses and Ti-particle/glass-ceramic matrix biocomposites. The composites were prepared by sintering, under an Ar flow, green bars of bioactive glass powders and 30% volume Ti particles. The bioactive glasses have the two following compositions: SCB (48.8SiO2−48.8CaO−2.4B2O3) and TSCB (46.6SiO2−48.7CaO−2.5B2O3−2.2TiO2) (mol%). The VPS bioactive coatings were characterized by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and mechanical tests (Vickers indentations and tensile and shear tests). Their bioactivity was tested by soaking the samples in a simulated body fluid (SBF) and by analyzing the growth of hydroxylapatite (HA) by SEM, EDS, and XRD. Leaching tests of Ca, Si, and P in SBF were made by inductively coupled plasma-atomic emission spectroscopy (ICP-AES, Perkin-Elmer 5000) to study the in vitro bioactivity of the samples versus time. Each coating was found to be bioactive and well bonded to the substrate; the composites showed better mechanical properties than the pure glass matrices and the hydroxylapatite coatings deposited by the same VPS technique.

Two different types of SiCf/SiC composites were successfully joined using a zinc borate glass as a joining agent. The characterization of the joined specimens included XRD, DSC, DTA, SEM-EDS, macroporosimetry, and shear testing measurements. For both composites, the interfaces were continuous and crack-free, and a reaction occurred between the liquid glass and the composite's surface. The large porosity of the chemical vapor deposited (CVI) composite allowed the glass to infiltrate the sandwich structure, the driving force being gaseous product pressurization and capillary surface forces.

This work describes the design and development of two new silica-based glass-ceramic coatings, suitable to be applied as slurries on a foam glass substrate. The coating process was optimized for both compositions, according to their sintering behavior. Scanning electron microscopy (SEM) observations and coefficient of thermal expansion (CTE) measurements revealed a good thermomechanical compatibility between the foam glass substrate and both coatings. The proposed coatings showed excellent chemical durability: no weight loss was observed after soaking in distilled water at 90°C for 16 days.

Glass matrix composites have been obtained by mixing and sintering “negative cost” materials coming from municipal solid waste incinerators (MSWIs) and from one aluminium foundry. The bottom ashes from two MSWIs were used to obtain the glass matrix and the solid wastes from an aluminium alloy industry were employed as a second phase. The bottom ashes were vitrified by heating at 1400°C without any additive. The vitrification process reduces the bottom ash initial volume by about 60%. The obtained glass has a Young modulus of 96 GPa and a Vickers hardness of 6 GPa. The composites were prepared in air by a low temperature pressure-less viscous phase sintering process (740–830°C) and were morphologically and mechanically characterised. The composites showed a bending strength up to 50 MPa at room temperature and could be proposed for applications in the field of tiles.

A protective coating for SiC fiber reinforced borosilicate glass-matrix composites based on zinc borosilicate (ZBS) glass-ceramic was developed. The coating was deposited on the composite surfaces by a simple and cost-effective method, based on slurry dipping followed by a densification and crystallisation stage carried out at optimised temperature and holding time. The coatings were shown to be able to withstand temperatures of up to 700 °C without softening and without exhibiting microcracking.