Synthesis of fine-crystalline tourmaline in hydrothermal solutions

Abstract

In recent years, the synthesis of new nano and fine crystalline materials for production of ceramics, textures, filters, molecular sieves has stimulated increased interest in science and technology world wide [1]. The synthesis of fine crystalline tourmaline is of practical interest for production of piezoelectric ceramics and textures, since it is characterized by valuable piezo and pyroelectric properties.Tourmaline is a complex boron bearing silicate with a general crystal chemical formula XY 3 Z 6 Si 6 O 18 (BO 3 ) 3 V 3 W, where X = Na + , Ca 2+ , K + , vacancy; Y = Fe 2+ , Fe 3+ , Mg 2+ , Li + , Al 3+ , Co 2+ , Ni 2+ ; Z = Al 3+ , Fe 3+ , Cr 3+ ; V = HO -, O 2-; W = HO -, O 2-, F -[1]. In the first part of the last century, tourmaline was applied in various radio and acoustoelectronic instruments (for hydrolocators of submarines, mea surements of pressures during powerful explosions, etc.). The interest in this mineral decreased in the course of time, because of the appearance of industrial technologies of growth of quartz monocrystals, which are currently applied in piezotechnology, acoustoelec tronics, optics, and other spheres of science and tech nology. However, the main advantages of tourmaline are the higher values of piezoelectric constants and the frequency coefficient in comparison with quartz. Due to the high mechanical strength, tourmaline may be used for production of piezo and pyroelectric ele ments for high accuracy and high sensitivity instru ments. In spite of its wide abundance in nature, defectless tourmaline crystals applicable for produc tion of such instruments are rare. Moreover, the com position of the natural tourmaline crystal is very heter ogeneous due to the complex structure stimulating abundant iso and heterovalent isomorphism.The recent studies of tourmaline synthesis [2-5] are of scientific and practical interest in the field of investigation of the structural and crystal chemical peculiarities of the tourmaline group minerals. In the 1960s-1980s I.E. Voskresenskaya [6] worked out the methodology of monocrystal growth for Co , Ni , Fe , Cr , Mn , and Mg bearing tourmalines using highly concentrated hydrate solutions of chlorides of appro priate metals at 750°C and 200 MPa. Later [7-9], we performed synthesis at significantly lower parameters (500°C and 100 MPa) and demonstrated the possibil ity of tourmaline monocrystal growth on seeds in boric, boric-fluoride, boric-chloride, and boricchloride-fluoride hydrothermal solutions. The maxi mal growth rate (up to 0.05 mm/day) was registered for Co bearing tourmaline with the growth on seed not exceeding 2 mm. As a whole, it was shown that the growth of monocrystal tourmaline on a seed was char acterized by low rates and controlled by the high P-T parameters of the process and high concentration of solutions. In this relation, the synthesis of fine crystal line tourmaline for production of ceramics contributes to solving the problem of creation of new piezoelectric materials.The methodology of synthesis of fine crystalline material ...

Crystal Growth and Complex Characterization of Novel Gallium- and Germanium-Rich Tourmalines: Refinement of the Crystal Structure, Cation Distribution, and Raman and Mössbauer Spectroscopy

“…The single crystals were grown in Ni–Cr alloy high-pressure autoclaves using boric, boron alkaline, and boron fluoride solutions as the solvent (Table ). The solution compositions in which tourmaline crystals crystallize were determined from our previous works. ,− The seeds from natural elbaite with the idealized formula Na­(Li,Al) 3 Al 6 Si 6 O 18 (BO 3 ) 3 (OH) 4 were cut perpendicular to the c- axis [(0001) orientation] and at an angle of 45° to the c -axis (several runs). We applied two growth schemes (Figure ).…”