Recycling of rare earths: a critical review

Many reactive metals are difficult to prepare in pure form without complicated and expensive procedures Although titanium has many desirable properties (it is light, strong and corrosion-resistant), its use has been restricted because of its high processing cost In the current pyrometallurgical process--the Kroll process--the titanium minerals rutile and ilmenite are carbochlorinated to remove oxygen, iron and other impurities, producing a TiCl4 vapour This is then reduced to titanium metal by magnesium metal; the by-product MgCl2 is removed by vacuum distillation The prediction that this process would be replaced by an electrochemical route has not been fulfilled; attempts involving the electro-deposition of titanium from ionic solutions have been hampered by difficulties in eliminating the redox cycling of multivalent titanium ions and in handling very reactive dendritic products Here we report an electrochemical method for the direct reduction of solid TiO2, in which the oxygen is ionized, dissolved in a molten salt and discharged at the anode, leaving pure titanium at the cathode The simplicity and rapidity of this process compared to conventional routes should result in reduced production costs and the approach should be applicable to a wide range of metal oxides

Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride

Review on fluoride-releasing restorative materials--fluoride release and uptake characteristics, antibacterial activity and influence on caries formation.

Machining difficult-to-machine materials such as alloys used in aerospace, nuclear and medical industries are usually accompanied with low productivity, poor surface quality and short tool life. Despite the broad use of the term difficult-to-machine or hard-to-cut materials, the area of these types of materials and their properties are not clear yet. On the other hand, using cutting fluids is a common technique for improving machinability and has been acknowledged since early 20th. However, the environmental and health hazards associated with the use of conventional cutting fluids together with developing governmental regulations have resulted in increasing machining costs. The aim of this paper is to review and identify the materials known as difficult-to-machine and their properties. In addition, different cutting fluids are reviewed and major health and environmental concerns about their usage in material cutting industries are defined. Finally, advances in reducing and/or eliminating the use of conventional cutting fluids are reviewed and discussed.

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Environmentally conscious machining of difficult-to-machine materials with regard to cutting fluids

https://www.unitau.br/files/arquivos/category_126/Braga_et_al_2005_1455555240.pdf

Factors involved in the development of polymerization shrinkage stress in resin-composites: a systematic review.

Mechanical properties and microstructures of cast Ti-Cu alloys.

Electrochemical characterization of cast titanium alloys.

In vitro corrosion resistance of titanium made using different fabrication methods.

In casting titanium using a two-compartment casting machine, Hero et al. (1993) reported that the pressure difference between the melting chamber and the mold chamber affected the soundness of the castings. This study tested the hypothesis that differences in pressure produce castings with various amounts of porosity and different mechanical properties values. Plastic dumbbell-shaped patterns were invested with an alumina-based, phosphate-bonded investment material. Both chambers of the casting machine were evacuated to 6 x 10-2 torr; the argon pressure difference was then adjusted to either 50, 150, 300, or 450 torr. The porosity of the cast specimens was determined by x-ray radiography and quantitative image analysis. Tensile strength and elongation were measured by means of a universal testing machine at a strain rate of 1.7 x 10-4/s. The fractured surfaces were examined by SEM. Changes in Vickers hardness with depth from the cast surface were measured on polished cross-sections of the specimens. Raisi...

Effect of Pressure Difference on the Quality of Titanium Casting

Statement Of Problem. Poor chemical bonding of a denture base resin to cast titanium frameworks often introduces adhesive failure and increases microleakage. Purpose. This study examined the shear bond strengths of a denture base resin to cast pure titanium, Ti-6Al-4V, and a cobalt-chromium alloy using various adhesive primers. Material And Methods. Disks (6.0 mm diameter, 2.5 mm thick) were cast of the 3 alloys. The disk surfaces were grit-blasted with 50 μm alumina and treated with 5 different metal primers (Metal Primer II [MP]; Cesead Opaque primer [OP]; Meta Base [MB]; experimental primer [EP]; Siloc bonding system [SI]). A denture base resin (Palapress Vario) was then applied on the disks with hole-punched sticky tape (bonding area of 5.0 mm) and a Teflon (PTFE, New Age Industries Inc, Willow Grove, Pa.) ring (6.0 mm diameter × 2.0 mm thick). Specimens without primer were also prepared as controls. All specimens were immersed in 37°C water and thermocycled up to 2000 cycles. Shear bond strength values were determined at a crosshead speed of 0.5 mm/min. Data were statistically analyzed using 3-way ANOVA, followed by 1-way ANOVA and the Scheffe multiple range test. Results. Primers significantly ( P Conclusion. The application of 5 primers significantly improved the shear bond strengths of a denture base resin to cast CP titanium, Ti-6Al-4V, and Co-Cr alloy. OP and MP primers exhibited greater bond strength and durability than did MB and SI. (J Prosthet Dent 2000;83:50-7.)

Toru Okabe

Papers

Mechanical properties and microstructures of cast Ti-Cu alloys.

Electrochemical characterization of cast titanium alloys.

In vitro corrosion resistance of titanium made using different fabrication methods.

Effect of Pressure Difference on the Quality of Titanium Casting

Shear bond strengths of polymethyl methacrylate to cast titanium and cobalt-chromium frameworks using five metal primers.