Estimation of activation parameters for diffusion‐controlled crystallization of barium tungstate from sodium tungstate melts by differential thermal analysis

Abstract

The proximity (dJ between a diffusing species and its host crystal necessary for a successful diffusion for diffusion-controlled crystallization of barium tungstate from sodium tungstate melts in platinum crucibles was estimated. These distances increased with increased cooling rates ( RT) and crystallization temperatures (To). Energy ( R ) , enthalpy (AH,), entropy (AS,) and free-energy (AGra) of activation and the pre-exponential fe.ctor (k,) were evaluated using an ordinary Arrhenius equation k,, = k, e-EIRT, where k D , waa the diffusion rate-constant. These parameters were virtually unaffected by the changes in To and RT.

Photoluminescent behavior of BaWO4 powders processed in microwave-hydrothermal

“…In the last years, the literature has reported the formation of barium tungstate (BaWO 4 ) by different techniques, such as: solid-state reaction [1,2], Czochralski [3][4][5], high temperature flux crystallization [6], hydrothermal-electrochemical [7], polymeric precursor [8,9] and molten salt [10]. However, these methods generally need of high reaction temperatures, long reaction time and sophisticated equipments.…”

The effect of an anionic starburst dendrimer on the crystallization of BaWO4 under hydrothermal reaction conditions

“…The traditional preparation methods of BaWO 4 are flux method [12], solidstate reaction [13,14], and hydrothermal-electrochemical method [15], but most of these methods need high reaction temperature, long-reaction time, or complicated equipment, which limit the application of this important material.…”

Structure Evolution of Highly Crystallized BaWO4 Film Prepared by an Electrochemical Method at Room Temperature

“…It produces the blue luminescence 1 needed for applications in the electrooptical industry. It is also effective for compensating the positive values of the temperature coefficient of resonant frequency (t f ) of microwave ceramics such as BaTi 4 O 9 , (Pb 0.7 Ca 0.3 )ZrO 3 , and (Na 0.5 La 0.5 )TiO 3 to nearly zero t f because of its negative t f (−33 ppm/°C). 2 The various applications of the material have generated many scientific investigations aimed at preparation 3,4 and characterization.…”

“…It is also effective for compensating the positive values of the temperature coefficient of resonant frequency (t f ) of microwave ceramics such as BaTi 4 O 9 , (Pb 0.7 Ca 0.3 )ZrO 3 , and (Na 0.5 La 0.5 )TiO 3 to nearly zero t f because of its negative t f (−33 ppm/°C). 2 The various applications of the material have generated many scientific investigations aimed at preparation 3,4 and characterization. 1,[5][6][7][8] Methods such as the flux method, 3 and traditional solid-state reaction, 1,4 have been used to prepare single crystals and powders of BaWO 4 .…”