Nasser Y. Mostafa

Bio: Nasser Y. Mostafa is an academic researcher from Suez Canal University. The author has contributed to research in topics: Lattice constant & Crystallite. The author has an hindex of 26, co-authored 79 publications receiving 2024 citations. Previous affiliations of Nasser Y. Mostafa include Pennsylvania State University & Taif University.

Characterization, thermal stability and sintering of hydroxyapatite powders prepared by different routes

Abstract: Hydroxyapatite (HAP) powder precursors have been used as starting material for biomedical applications, such as synthetic bone graft materials and scaffold for hard tissue engineering. Considering the numerous applications of hydroxyapatite, three different routes for HAP powders preparations was investigated. Two powders were prepared by chemical precipitation reactions at 100 °C and one by mechanochemical reaction. The powders were characterized using chemical analysis, surface area measurements, laser diffraction, X-ray diffraction (XRD) and SEM. The Ca/P ratios were varied from 1.67 to 1.58. The chemical composition, the crystallinity and the agglomeration characters depend on the preparation route. The effect of powder characteristics on the sinterability was investigated. Although, the thermal stability and hence the start of sintering dependents on the Ca/P ratio, the final sintering density and hence the mechanical properties depends on the agglomeration characteristics and the particle size distribution. Hydroxyapatite powder prepared by mechanochemical route have nano-sized crystallites with a uniform smaller agglomerated particle size distribution and have a butter sinterability.

Heat of hydration of high reactive pozzolans in blended cements: Isothermal conduction calorimetry

Abstract: A study was carried out comparing silica fume (SF) and dealuminated kaolin (DK) as pozzolanic materials in blended cements. Ten, 20 or 30 wt% of SF or DK were substituted for Portland cement. The kinetics of hydration up to 45 h were studied using isothermal conduction calorimetry. Blends containing pozzolanic materials usually have decreased heats of hydration compared to pure cement during the period of C3S hydration, i.e. during the main hydration peak. Depending on the chemical composition and the activity of the pozzolan, the reaction taking place with the lime typically contributes to the heat output after the main hydration peak. The pozzolanic activity of DK is the principal factor and heat evolution increases with respect to pure PC mortar, during the first 15 h. The presence of hydrated silica (silanol groups) in DK increases the pozzolanic activity especially before and during induction period. The acidic silanol sites are capable of a fast acid–base reaction with the alkalis and with any Ca(OH)2 present in cement during the induction period.

Influence of air-cooled slag on physicochemical properties of autoclaved aerated concrete

Abstract: Lime and sand in autoclaved aerated concrete (AAC) were replaced by air-cooled slag (AS). The compressive strength and the type and nature of the hydration products were studied for samples autoclaved at 8 bar for different periods of times: 2, 6, 12 and 24 h. The hydration reactions were monitored by determining free-lime contents and combined water. The types of the hydration products were investigated using XRD and SEM/EDX. Slag substitutions for sand and lime up to 50% enhance the compressive strength, especially at short curing times (2 and 6 h). The optimum strength is obtained by 50% AS substitution for low-lime mixes (10% CaO) and 30% AS substitution for high-lime mixes (25% CaO). In high-lime mixes containing up to 30% AS, the initially formed fibrous calcium-rich CSH was changed to needle-like and lath-like 1.1 nm tobermorite. In low-lime mixes with AS-substitution, tobermorite appears at 2 h processing time with grass-like silica-rich CSH around quartz particles.

Hydrothermal synthesis and characterization of aluminium and sulfate substituted 1.1 nm tobermorites

Abstract: Substitutions of sulfate and aluminum ions in calcium silicate hydrate (tobermorite) were investigated at 175 °C under saturated steam pressure. Structure and morphology of different tobermorite samples were investigated using XRD, FTIR and SEM. A sample of pure xonotlite was prepared to assist in FTIR band assignment of different tobermorites. Al 3+ decreases the degree of crystallinity at short curing time and increases crystallinity at longer curing times, with a sort of stabilization of small crystals. Al 3+ changes the morphology of tobermorite from platy-shape to lath-shape. Sulfate ion increases imperfection of tobermorite crystal structure and the morphology of tobermorite change magnificently to leafy shape. The FTIR spectra of all 1.1 nm tobermorite samples are nearly similar. All tobermorite samples have a significant concentration of Q 3 Si sites, which indicates cross-linking of the chains. Sulfate substitution for silicate in tobermorite structure is associated with the appearance of the bands at 1610 and 631 cm −1 which indicates the incorporation of CaO–H group in tobermorite structure. This indicated the charge compensation mechanism; SiO 4 4− is substituted by SO 4 2− and 2OH − .

Effect of preparation conditions on physicochemical, surface and catalytic properties of cobalt ferrite prepared by coprecipitation

Abstract: Cobalt ferrite nanoparticles were prepared via thermal treatment of cobalt–iron mixed hydroxides at 400–600 °C. The mixed hydroxides were coprecipitated from their nitrates solutions using NaOH as precipitating agent. The effects of pH and temperature of coprecipitation and calcination temperature on the physicochemical, surface and catalytic properties of the prepared ferrites were studied. The prepared systems were characterized using TG, DTG, DTA, chemical analysis, atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), energy dispersive X-ray (EDX) as well as surface and texture properties based on nitrogen adsorption–desorption isotherms. The prepared cobalt ferrites were found to be mesoporous materials that have crystallite size ranges between 8 and 45 nm. The surface and catalytic properties of the produced ferrite phase were strongly dependent on coprecipitation conditions of the mixed hydroxides and on their calcination temperature.

Synthesis methods for nanosized hydroxyapatite with diverse structures.

Abstract: Hydroxyapatite (HAp) is the major mineral constituent of vertebrate bones and teeth. It has been well documented that HAp nanoparticles can significantly increase the biocompatibility and bioactivity of man-made biomaterials. Over the past decade, HAp nanoparticles have therefore increasingly been in demand, and extensive efforts have been devoted to develop many synthetic routes, involving both scientifically and economically new features. Several investigations have also been made to determine how critical properties of HAp can be effectively controlled by varying the processing parameters. With such a wide variety of methods for the preparation of HAp nanoparticles, choosing a specific procedure to synthesize a well-defined powder can be laborious; accordingly, in the present review, we have summarized all the available information on the preparation methodologies of HAp, and highlighted the inherent advantages and disadvantages involved in each method. This article is focused on nanosized HAp, although recent articles on microsized particles, especially those assembled from nanoparticles and/or nanocrystals, have also been reviewed for comparison. We have also provided several scientific figures and discussed a number of critical issues and challenges which require further research and development.

Bioceramics of calcium orthophosphates

Abstract: A strong interest in use of ceramics for biomedical applications appeared in the late 1960's. Used initially as alternatives to metals in order to increase a biocompatibility of implants, bioceramics have become a diverse class of biomaterials, presently including three basic types: relatively bioinert ceramics, bioactive (or surface reactive) and bioresorbable ones. Furthermore, any type of bioceramics could be porous to provide tissue ingrowth. This review is devoted to bioceramics prepared from calcium orthophosphates, which belong to the categories of bioresorbable and bioactive compounds. During the past 30-40 years, there have been a number of major advances in this field. Namely, after the initial work on development of bioceramics that was tolerated in the physiological environment, emphasis was shifted towards the use of bioceramics that interacted with bones by forming a direct chemical bond. By the structural and compositional control, it became possible to choose whether the bioceramics of calcium orthophosphates was biologically stable once incorporated within the skeletal structure or whether it was resorbed over time. At the turn of the millennium, a new concept of calcium orthophosphate bioceramics, which is able to regenerate bone tissues, has been developed. Current biomedical applications of calcium orthophosphate bioceramics include replacements for hips, knees, teeth, tendons and ligaments, as well as repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jawbone, spinal fusion and bone fillers after tumor surgery. Potential future applications of calcium orthophosphate bioceramics will include drug-delivery systems, as well as they will become effective carriers of growth factors, bioactive peptides and/or various types of cells for tissue engineering purposes.

A review: The comparison between alkali-activated slag (Si + Ca) and metakaolin (Si + Al) cements

Abstract: There are two main models of alkali-activated cements, one is the case of the activation of slag (Si + Ca) and the other is activation of metakaolin (Si + Al). This paper reviews current knowledge about the comparison between alkali-activated slag (Si + Ca) and metakaolin (Si + Al) cements, including the general properties of slag and metakaolin, hydration products reaction mechanisms, and the role of Ca and Al.

Quantum Confined Stark Effect in Single CdSe Nanocrystallite Quantum Dots

Abstract: The quantum-confined Stark effect in single cadmium selenide (CdSe) nanocrystallite quantum dots was studied. The electric field dependence of the single-dot spectrum is characterized by a highly polarizable excited state (∼10 5 cubic angstroms, compared to typical molecular values of order 10 to 100 cubic angstroms), in the presence of randomly oriented local electric fields that change over time. These local fields result in spontaneous spectral diffusion and contribute to ensemble inhomogeneous broadening. Stark shifts of the lowest excited state more than two orders of magnitude larger than the linewidth were observed, suggesting the potential use of these dots in electro-optic modulation devices.