română DORINEL TĂLPEANU, LAURA ELENA GEAMBAZU, ALINA IULIA DUMITRU, FLORENTINA CLICINSCHI, VIOLETA TSAKIRIS, ANDREI CUCOȘ, VIRGIL MARINESCU
Abstract
The main objectives of this work are represented by both the development of hydroxyapatite (HAP) and the technique of casting it into plaster forms order to develop of ceramic structures with complex shapes for applications in neurosurgery. The tested models were made from ceramic powders based on HAP and, shaped by the casting technique in plaster molds. In order for the process of casting ceramic suspensions to be more efficient, specific techniques were performed such as: rheological curves of shear stress variation depending on the speed gradient and the dependence of the viscosity of the HAP suspensions on the speed gradient. Experimental models of cranial prostheses were developed in the form of a skull cap with an average thickness of ~3.5 mm, rods with a diameter of 5 mm, length of 50 mm. The samples were sintered at temperatures of 1275˚C and 1350˚C, for 2 hours. The variation of density and porosity with sintering temperature were determined by Archimedes method and the mechanical properties were investigated by bending and compression tests. The average values for the bending strength, for the two obtained models, are in the range of 32.64-36.68 MPa and for the compression strength they range from 44.54 to 50.10 MPa. Furthermore, the obtained samples were characterized by scanning electron microscopy (SEM) and the X-ray diffraction data for the HAP powder were confirmed by FT-IR spectra and thermogravimetric measurements. In order to establish the biocompatibile character, a first set of bacteriological and sterility determinations was performed. The novelty of this work consists in the fact that both the rheological characteristics have been optimized (ceramic suspensions with a solid phase content of min. 60%) as well as the technique of casting ceramic suspensions in plaster molds through ultrasonic and degassing processes/deaeration, obtaining shaped products with a raw density of min. 50% of roth.
Keywords
hydroxyapatite, biomaterials, casting in plaster forms, viscosity curves
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Year
2023
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Issue
53 (1)
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Pages
3-12
.FLORENTINA MARILENA CLICINSCHI, DORINEL TĂLPEANU, ALINA IULIA DUMITRU, VIOLETA TSAKIRIS, GABRIELA BEATRICE SBÂRCEA, DELIA PĂTROI, MARINESCU VIRGIL EMANUEL
Abstract
The aim of the work is to obtain through the spark plasma sintering (SPS) technique, ceramic composite materials based on Si3N4 and SiC, with different sintering additions (Al2O3 and Y2O3) with improved mechanical properties. The spark plasma sintering process was carried out in vacuum at a pressure of 50 MPa, at temperatures between 1600-1800°C and a maximum sintering time of 5 minutes. In order to put in evidence the structural and morphological behavior of the obtained composites at different sintering temperature that lead to their improved mechanical properties, they were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Physical-mechanical characteristics (apparent density, apparent porosity and Vickers hardness) were determined for all sintered samples. Structural analysis by X-ray diffraction, revealed the formation of two major phases α and β-Si3N4, with an increase of their crystallographic transformation from one phase to another (α→β) with the increasing of the sintering temperature. Si3N4 and SiC based ceramic composites sintered at 1800°C and with a 5wt.% Y2O3 content, showed a good correlation of physical-mechanical and structural characteristics, having a relative density of 93% of the theoretical density, Vickers hardness values of 18.39 GPa and bending strength of 336 MPa.
Keywords
Spark Plasma Sintering,Si3N4, SiC, ceramic composites, X-ray diffraction, scanning electron microscopy
OLURANTI ABIOLA , TEMITAYO OGEDENGBE, ADEKOLA OKE
Abstract
Ceramic is an engineering material that has endeared itself to many sectors especially the building services sector where it is used for floor tiles. Machining is a necessary finishing operation after casting and other forming operations. A very important machining operation performed on ceramic materials such as tiles is grinding to pave way for easy installation, aesthetics and safety. This work investigates the elemental and chemical composition of the raw materials used in the production of the ceramic tiles under investigation and study the effect of different grinding procedures on some mechanical properties of the ceramic tiles. The tiles were ground at two different grinding speeds and two different levels (continuous and intermittent at 2 seconds intervals). Breaking strength, flexural strength, hardness, and surface roughness before and after grinding were analyzed using the Signal-to-Noise (S/N) ratio. The result revealed that the elements and their respective oxides present in the raw materials were able to give strength, rigidity and support to the ceramic article. Also, grinding was found to affect the mechanical properties of the ceramic tile samples as the breaking strength and flexural strength reduces from 339.77 N for the control sample to as low as 273.30 N and 16.40 N/mm2 respectively.
Keywords
ceramic tiles, grinding, breaking strength, flexural strength, hardness
MIHAI-ALEXANDRU EFTIMIE, CARMEN-CRISTINA UDREA, MIHAELA-ALINA MELINESCU, ANA-VIOLETA FILIP
Abstract
Borosilicate glasses that possess UV transmission can be used in materials that facilitate the disinfection or inactivation of bacteria using UV light. Three compositions were elaborated in the low alkali domain of borosilicate glasses through the classical melt-quenching technique at temperatures up to 1680 °C. The analysis of the samples was performed using thermal expansion, hydrolytic stability, density, UV-Vis transmission, Raman spectroscopy, and X-ray diffraction. The hydrolytic stability of the analysed samples showed that they are chemically stable. From the thermal expansion it was observed that the processed samples had low expansion coefficients. Regarding the UV-Vis transmittance, glasses have acceptable transmittances in the ultraviolet region down to 260 nm. Raman spectroscopy was used to identify the glass network bonds and the presence of nonbridging oxygen ions in the processed glass samples by the presence of specific high-frequency peaks in the spectrum. XRD analysis also showed that the borosilicate glass samples did not crystallize.
Keywords
borosilicate glass, UV-Vis transmission, germicidal applications
MARISELVAM.P, VELMURUGAN.T, G.KARTHIKEYAN
Abstract
This paper focuses on the thermal properties of R-Glass/Epoxy laminate in response to temperature variations. The elastic properties and coefficient of thermal expansion in the material s principal direction were measured across the temperature range from room temperature to the cure temperature. These properties were then characterized as functions of temperature. Using the characterized properties and the principles of classical lamination theory, a method was proposed to predict the changes in the coefficient of thermal expansion for a general laminate subjected to temperature variations. The measured values of the coefficient of thermal expansion for laminates with varying angle plies were compared with the predicted values. The experimental results demonstrate that the proposed method accurately predicts the changes in the coefficient of thermal expansion for a general laminate under temperature variations. Additionally, an analytical formulation was proposed and validated to predict the changes in the coefficient of thermal expansion for R-Glass/Epoxy laminates subjected to temperature variations.
Keywords
R-Glass/Epoxy laminate, Thermal properties, Analytical model, Thermal expansion, Experimental
BRUNA MOREIRA, CARLOS JESUS, RAPHAELE MALHEIRO, AIRES CAMÕES
Abstract
Promoting the circular economy is one of the main tools to achieve carbon neutrality by 2050. The culture of using residues in cementitious materials, mainly in concrete, is already established, favouring circularity. Fly ash is commonly used in blended cement or concrete production as supplementary cementing material. However, waste glass is not as commonly used as a cement substitute. In this context, this research contributes to the knowledge about the use of waste glass as partial cement replacement, developing an experimental work. Glass bottles were transformed into glass powder using two different grinding processes. They were produced glass powders with different colours and fineness. These powders were used to produce mortars with 25% of glass powder replacing cement. Mortars containing fly ash were also produced. Their compressive strengths were evaluated over time. Results concluded that white, green, and brown glass powders are acceptable to be used as cement replacements. The results also identify glass powder as a potential substitute for fly ash.
Keywords
Glass powder; Fly ash; Cementitious materials; Circular economy; Low CO2