عنوان

Role of additives in vapor phase synthesis of titania

شماره

TLpq304028255

زبان متن نوشتاري يا گفتاري و مانند آن

انگلیسی

عنوان اصلي

Role of additives in vapor phase synthesis of titania

نام عام مواد

[Thesis]

نام نخستين پديدآور

M. K. Akhtar

نام ساير پديدآوران

S. E. Pratsinis

نام ناشر، پخش کننده و غيره

University of Cincinnati

تاریخ نشرو بخش و غیره

1993

نام خاص و کميت اثر

364

جزئيات پايان نامه و نوع درجه آن

Ph.D.

کسي که مدرک را اعطا کرده

University of Cincinnati

امتياز متن

1993

متن يادداشت

The vapor phase synthesis of ceramic powders is attractive because it allows microengineering and control of submicron particle characteristics. This work focuses on the synthesis of nanophase titania from titanium tetrachloride (TiCl4) oxidation in a hot wall tubular flow aerosol reactor. First, an experimental study is conducted into the effects of temperature, TiCl4 concentration and residence time on the morphology and phase composition of pure titania particles. It is found that polyhedral faceted particles are formed and that their morphological features do not change within the range of operating conditions investigated. The particles are primarily anatase though the rutile weight fraction increases with increasing reactor temperature. The role of dopants (SiCl4, POCl3, BCl3) in controlling the morphology and phase composition of titania is studied. The addition of dopants, most notably silicon and phosphorus, drastically altered the morphology of titania particles from polyhedral to spherical, increased the extent of aggregation, increased the specific surface area, reduced the primary particle size and decreased the rutile content. The ionic radii of silicon, phosphorus and boron are much smaller than that of titanium (Ti = 0.68 A, Si = 0.40 A, p = 0.35 A, B = 0.23 A) and they form interstitial solid solution with titania. This interferes with the coordinated movement of Ti and O atoms and retards the rate of transformation to rutile. While titania synthesized in the absence of aluminum was about 90% anatase, the introduction of aluminum resulted in pure rutile at AlCl3/TiCl4 = 0.07. The effects of aluminum on titania phase composition and morphology are explained by the creation of oxygen vacancies in the titania crystallites and by the enhancement of the sintering rate of titania grains. The competition between hydrolysis and oxidation of TiCl4 during synthesis of titania resulted in rounded titania particles instead of the faceted ones observed in the absence of water; this effect was most pronounced at lower reactor temperatures. The phase composition of titania was sensitive to the temperature at the mixing point of the water and TiCl4 vapor streams. The use of ionic additives to control aggregation is investigated. Aqueous solutions of ionic additives are sprayed into the process stream and the effect of NaCl, KCl and CsCl (by themselves and when complexed with either AlCl3 or SiCl4) on titania particle characteristics is studied. Significant reduction in titania aggregate size is obtained with alkali halides only in the presence of either AlCl3 or SiCl4 at 1673 K though not at 1473 K. CsCl is the most effective in reducing aggregate size while NaCl is the least effective. These changes are explained on the basis of complex ion formation, particle charging and the subsequent retardation of coagulation.

موضوع مستند نشده

Applied sciences

موضوع مستند نشده

Chemical engineering

موضوع مستند نشده

Chemical engineering

موضوع مستند نشده

Materials science

مستند نام اشخاص تاييد نشده

M. K. Akhtar

مستند نام اشخاص تاييد نشده

S. E. Pratsinis

نام الکترونيکي

فرمت انتشار

p

نوع ماده

[Thesis]

کد کاربرگه

276903

سطح دسترسي

a

تكميل شده

Y