Rafael Mello Trommer

The addition of nanostructured hydroxyapatite to an experimental adhesive resin

OBJECTIVES Was produced nanostructured hydroxyapatite (HAnano) and evaluated the influence of its incorporation in an adhesive resin. METHODS HAnano was produced by a flame-based process and was characterized by scanning electron microscopy. The surface area, particle size, micro-Raman and cytotoxicity were evaluated. The organic phase was formulated by mixing 50 wt.% Bis-GMA, 25 wt.% TEGDMA, and 25 wt.% HEMA. HAnano was added at seven different concentrations: 0; 0.5; 1; 2; 5; 10 and 20 wt.%. Adhesive resins with hydroxyapatite incorporation were evaluated for their radiopacity, degree of conversion, flexural strength, softening in solvent and microshear bond strength. The data were analyzed by one-way ANOVA and Tukeys post hoc test (α=0.05), except for softening in solvent (paired t-test) and cytotoxicity (two-way ANOVA and Bonferroni). RESULTS HAnano presented 15.096 m(2)/g of specific surface area and a mean size of 26.7 nm. The radiopacity values were not different from those of 1-mm aluminium. The degree of conversion ranged from 52.2 to 63.8%. The incorporation of HAnano did not influence the flexural strength, which ranged from 123.3 to 143.4MPa. The percentage of reduction of the microhardness after immersion in the solvent became lower as the HAnano concentration increased. The addition of 2% nanostructured hydroxyapatite resulted in a higher value of microshear bond strength than the control group (p<0.05). CONCLUSIONS The incorporation of 2% of nanostructured hydroxyapatite into an adhesive resin presented the best results. CLINICAL SIGNIFICANCE The incorporation of nanostructured hydroxyapatite increases the adhesive properties and may be a promising filler for adhesive resin.

Nanostructured hydroxyapatite as filler for methacrylate-based root canal sealers.

AIM   To evaluate the effect of different concentrations of nanostructured hydroxyapatite on the radiopacity, flow and film thickness of an experimental root canal sealer. METHODOLOGY   An experimental dual-cured root canal sealer was produced with a methacrylate-based co-monomer blend. Nanostructured hydroxyapatite/calcium tungstate solutions (ratios 10:90, 20:80, 30:70 and 40:60) were added to produce the sealer. Radiopacity was evaluated using a digital system and an aluminium step wedge (n=5). Flow and thickness tests were conducted in accordance with ISO 6876 (n=3). The data were analysed using one-way anova and Tukeys test (α=0.05). RESULTS   All groups had levels of radiopacity in accordance with ISO 6876. The flow of the experimental sealers was not significantly different (P=0.204). All groups had a film thickness in accordance with ISO 6876 and with no statistical difference (P = 0.654). CONCLUSION The addition of up to 40% HA(nano) to root canal sealers did not alter their radiopacity and film thickness.

Heat Transfer in Steelmaking Ladle

The heat transfer in a steelmaking ladle was studied. The evaluation of heat transfer of the steel was performed by measuring steel temperature in points including all refining steel process. In the ladle, the temperatures in the refractories and the shell were also measured. To evaluate the thermal profile between the hot and cold faces of the ladle in the slag line position, an experiment which shows the importance of thermal contact resistance was carried out. Higher heat losses in the tapping and the vacuum were verified. The temperature measurements of the ladle indicate distinct thermal profiles in each stage of steel refining. Moreover, as each stage of the process depends on the previous one, the complexity of the ladle thermal control is incremental. So a complete model of heat losses in the ladle is complex.

Alternative technique to obtain hydroxyapatite coatings)

This work proposes the flame assisted chemical vapor deposition as an alternative technique to obtain crystalline hydroxyapatite coatings on AISI 316L stainless steel substrates. This is a novel technique that shows enormous potential for oxides deposition, mainly due to the low cost of equipment and precursors. In this work calcium acetate and ammonium phosphate, diluted in ethanol, were employed as precursor salts. A precursor solution with Ca/P molar ratio of 1.66, equivalent to biological hydroxyapatite, was used. The evaluated deposition parameters were: substrate temperature (500 and 550 oC), precursor solution flux (4, 8 and 12 mL/min) and deposition time (5, 10 and 20 min). The coatings obtained were porous, and thickness varying between 66 and 757 µm as a function of deposition parameters. Analysis with X ray diffraction identified crystalline coatings, with the presence of a major phase hydroxyapatite, and traces of tricalcium phosphate (β-TCP). Carbonates were identified by infrared spectroscopy, as well as phosphate and hydroxyl that are characteristic groups of hydroxyapatite

Materials for Bio-Applications

The recent advances in nanomaterials have brought potential applications in several fields of medicine and health care, such as diagnosis, treatment of diseases, tissue engineering, etc. This chapter introduces the main nanomaterials used in bio-applications as well as potential materials for future applications in biomedicine. Magnetic nanoparticles such as iron oxide are considered as one of the most promising nanomaterials. Hydroxyapatite is the main bioceramic used in orthopedics and dentistry, due to its chemical similarity to the inorganic fraction of the human bone. Carbon nanotubes present great potential for bio-applications such as biomaterials, drug delivery and tissue engineering. Metals like silver nanoparticles are potential antimicrobial agent, mainly because of their large surface area. Nanomaterials are being widely used and studied in bio-applications because of their novel and unique physicochemical properties, compared to bulk materials. Their unique properties, however, can present an unpredictable impact on human health. Therefore, the toxicology of nanomaterials has attracted much attention worldwide.

Evaluation of Flame-Sprayed Alumina Powders Produced Using Different Ethanol/Water Ratios in the Starting Solutions

Alumina powders were synthesized using a cost-effective process that used a Bunsen–Meker flame as the source of energy for the chemical reactions. With the aim of evaluating the influence of solvents on the morphology of powders, three starting solutions with different ethanol/water volume ratios were prepared. Ethanol/water ratios of 50:50; 20:80, and 1:100 were studied. X-ray diffraction analyses showed amorphous powders in the as-synthesized condition. After calcination at 1150°C, the powders became crystalline, and a major crystalline phase, α-alumina, was identified in all the powders. Using scanning electron microscopy, the typical morphology of the flame-sprayed powders, composed of aggregated spherical and unshaped particles, was observed. The specific surface area of the as-synthesized powder was greater than that of the calcined powder, with a maximum value of 36.75 m2/g, which corresponded to the powder obtained with the starting solution prepared only with water. Thermogravimetric analyses showed that the powder produced from a precursor solution composed only of water also had the highest loss (34.72%). Transmission electronic microscopy was used to observe the nanostructures of alumina powders. A maximum crystallite size of 24.6 nm, corresponding to the starting solution prepared only with water, was obtained.

Future Trends in Flame Spray Process

This chapter introduces the main future trends associated with the use and development of the flame spray (FS) technology. The FS process has been considered by many researchers as a novel and powerful method for the production of nanoparticles and nanostructured particles. However, if we consider that its principles and fundamentals are not fully understood, and considering that only few commodities (black carbon, titania, and silica for example) are commercially available up to now, there is a great demand for the development of the FS process. Today, there are several areas where FS process can be developed, which justify the strong efforts made by many scientists. In addition, we must consider that the increasing use and interest in the FS process makes it a promising technique for the production of a wide range of commodities, especially if we take in mind that most of the products obtained with FS are in the nanosize scale. Another important point concerning the future of the FS comprises the synthesis of unconventional oxides and can be also considered as a great development done for the improvement of this method. It is clear to many scientists that a deep understanding of the particle formation mechanisms in the flame is an important step in the development of the FS process. The better understanding of what happens in the flame basically comprises the acquisition of experimental data, leading to a further modeling and simulation of particle formation mechanisms and their kinetics in flames. The use of the principles of this technology but aiming the production of thin films and coatings is another point and has emerged as an important area inside this technology. These are just two short examples of the potential areas inside the FS technology. This chapter intends to present to reader the main future trends concerning the use of a flame to obtain ceramic products, as well as the development and improvement of new devices to be used as flame, powder collector, and atomization are discussed. Another important point of this chapter is the perspective of the production of nanoparticles aiming its application in several industrial concerns as biomaterials, electronics, catalysis, etc.

A Brief Overview on Flame Spray Synthesis

The technology involving the flame spraying of a precursor solution is based on the formation of small particles from the gas or vapor phase in a flame. Flame spray (FS) is regarded as a consolidated industrial technique, as discussed in the previous chapter. However, the principles and fundamentals of the particles synthesis in the flame are not completely understood. One of the main reasons for the absence of a complete description of FS synthesis is the fact that chemical reactions and particle formation occurs in a short time and high temperature during the process. The basic principle of FS technique is the formation of vapor or aerosol of the precursor compounds, which reacts in the high temperature of the flame leading to the formation of a ceramic compound. There are two basic types of process based on the formation of an aerosol and further spraying in a flame. The former is the conversion to a particle from the vapor phase, due to the presence of a flame, and named vapor synthesis in a flame. The second process comprises the conversion of a droplet to a particle, also assisted by a flame, and named FS pyrolysis.

Ceramic Products Produced by FS

The nanomaterials era has enormously contributed to the development of new materials, and the flame spray (FS) method has arrived as a potential technique for its development. One of the great features of the FS method is the wide range of ceramic commodities produced by this technique, as well the wide range of morphologies available for these nanomaterials. Consequently, several types of application for them are possible. In addition, more and more laboratories and companies around the world have been developed and upgraded different FS apparatus. Recent ceramic materials, which years ago were not imagined to be produced by the FS process, are nowadays obtained in a simple step process. Because the FS is a versatile technique, it allows the production of single and mixed oxides, since black carbon to more complex oxides as hydroxyapatite (HA) and spinels. Thus, this chapter presents numerous examples of ceramic nanomaterials produced in different equipments, either commercial or academic, as well their morphology and main applications. One example is black carbon, which is the first material produced by the FS technique and has a large industrial production rate, and even today, is widely used in different industries and products. Recent nanomaterials, such as Ca10(PO4)6(OH)2, ZnO, TiO2, Al2O3, Y2O3, GeO2, MgO-Al2O3, CoMo/Al2O3, and SnO2, are also describe in this chapter.

History of Flame Spray (FS) Technique

The flame spray (FS) technique has been practiced in a non-intentional way since the prehistoric age, according to paintings observed in the walls of caves in China. At that time, its principles were not understood, but people had the knowledge to produce the pigments used in the paint by the FS process. The first contemporary reactors for nanoparticles flame synthesis started in the 1940s, by the production of fumed silica. Only in 1971, G.D. Ulrich pioneered the first principles of the FS method. Since this day, several laboratories and companies have developed different apparatus and alternative methods, aiming to obtain materials with improved properties. This is the main driving force for the evolution of the FS process during the last decades, where more materials and equipments are reported in literature.