اکسید لانتان

از ویکی‌پدیا، دانشنامهٔ آزاد
پرش به ناوبری پرش به جستجو
فارسیEnglish
Lanthanum(III) oxide
Lanthanum(III) oxide
شناساگرها
شماره ثبت سی‌ای‌اس 1312-81-8 ✔Y
پاب‌کم 150906
کم‌اسپایدر 2529886 ✔Y, 133008 ✔Y
شمارهٔ آرتی‌ئی‌سی‌اس OE5330000
خصوصیات
فرمول مولکولی La2O3
جرم مولی 325.809 g/mol
شکل ظاهری White powder hygroscopic
چگالی 6.51 g/cm3 solid
دمای ذوب 2315 °C (2588 K)
دمای جوش
‎4200 °C (4500 K)
انحلال‌پذیری در آب Insoluble
نوار ممنوعه 4.3 eV
ساختار
ساختار بلوری Hexagonal hP5
گروه فضایی P-3m1 No. 164
خطرات
کدهای ایمنی R36/37
شماره‌های نگهداری S26, S۲۲, S37/39
خطرات اصلی Irritant
لوزی آتش
Flammability (red): no hazard codeHealth code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentineReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calciumNFPA 704 four-colored diamond
1
1
نقطه اشتعال Non-flammable
ترکیبات مرتبط
دیگر کاتیون‌ها اسکاندیوم اکسید
اکسید ایتریم(III)
Actinium(III) oxide
ترکیبات مرتبط Lanthanum aluminium oxide
LaSrCoO4
به استثنای جایی که اشاره شده‌است در غیر این صورت، داده‌ها برای مواد به وضعیت استانداردشان داده شده‌اند (در 25 °C (۷۷ °F)، ۱۰۰ kPa)
 ✔Y (بررسی) (چیست: ✔Y/N؟)
Infobox references

اکسید لانتان (به انگلیسی: Lanthanum oxide) ماده ایست که در اثر اکسید شدن فلز لانتان بدست می آید و با فرمول شیمیایی La۲O۳ یک ترکیب شیمیایی با شناسه پاب‌کم ۱۵۰۹۰۶ است. که جرم مولی آن 325.809 g/mol می‌باشد. شکل ظاهری این ترکیب، پودر سفید است.

جستارهای وابسته[ویرایش]

منابع[ویرایش]

  • «IUPAC GOLD BOOK». دریافت‌شده در ۱۸ مارس ۲۰۱۲.


Lanthanum(III) oxide
Lanthanum(III) oxide
La2O3structure.jpg
Names
IUPAC name
Lanthanum(III) oxide
Other names
Lanthanum sesquioxide
Lanthana
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.013.819
EC Number
  • 215-200-5
RTECS number
  • OE5330000
UNII
Properties
La2O3
Molar mass 325.809 g/mol
Appearance White powder, hygroscopic
Density 6.51 g/cm3, solid
Melting point 2,315 °C (4,199 °F; 2,588 K)
Boiling point 4,200 °C (7,590 °F; 4,470 K)
Insoluble
Band gap 4.3 eV
−78.0·10−6 cm3/mol
Structure
Hexagonal, hP5
P-3m1, No. 164
Hazards
Main hazards Irritant
Safety data sheet External SDS
GHS pictograms GHS07: Harmful[1]
GHS Signal word Warning[1]
H315, H319, H335[1]
P261, P280, P301+310, P304+340, P305+351+338, P405, P501[1]
NFPA 704 (fire diamond)
Flammability (red): no hazard codeHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity (yellow): no hazard codeSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acidNFPA 704 four-colored diamond
1
Flash point Non-flammable
Related compounds
Other anions
Lanthanum(III) chloride
Other cations
Cerium(III) oxide
Scandium(III) oxide
Yttrium(III) oxide
Actinium(III) oxide
Related compounds
Lanthanum aluminium oxide,
LaSrCoO4
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is ☑Y☒N ?)
Infobox references

Lanthanum oxide, also known as lanthana, chemical formula La2O3, is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock for certain catalysts, among other uses.

Properties

La2O3 powder

Lanthanum oxide is an odorless, white solid that is insoluble in water, but soluble in dilute acid. Depending on the pH of the compound, different crystal structures can be obtained.[citation needed] La2O3 is hygroscopic; under atmosphere, it absorbs moisture over time and converts to lanthanum hydroxide. Lanthanum oxide has p-type semiconducting properties and a band gap of approximately 5.8 eV..[2] Its average room temperature resistivity is 10 kΩ·cm, which decreases with an increase in temperature. La2O3 has the lowest lattice energy of the rare earth oxides, with very high dielectric constant, ε = 27.

Structure

At low temperatures, La2O3 has an A-M2O3 hexagonal crystal structure. The La3+ metal atoms are surrounded by a 7 coordinate group of O2−atoms, the oxygen ions are in an octahedral shape around the metal atom and there is one oxygen ion above one of the octahedral faces.[3] On the other hand, at high temperatures lanthanum oxide converts to a C-M2O3 cubic crystal structure. The La3+ ion is surrounded by six O2− ions in a hexagonal configuration.[4]

Elements obtained from Lanthana

Several elements were discovered as a consequence of lengthy analysis and decomposition of the ore Gadolinite. As the ore was progressively analysed, the residue was first given the label ceria and then lanthana and then subsequently yttria, erbia, and terbia. In order of date discovered, the list of elements includes Cerium 58, Lanthanum 57, Erbium 68, Terbium 65, Yttrium 39, Ytterbium 70, Holmium 67, Thulium 69, Scandium 21, Praseodymium 59, Neodymium 60 and Dysprosium 66. Several of these new elements were either discovered or isolated by Carl Gustaf Mosander in the 1830s and 1840s.

Synthesis

Lanthanum oxide can be crystallized in several polymorphs.

To produce hexagonal La2O3, a 0.1 M solution of LaCl3 is sprayed onto a preheated substrate, usually made of metal chalcogenides.[5] The process can be viewed as occurring in two steps – hydrolysis followed by dehydration:

2 LaCl3 + 3 H2O → La(OH)3 + 3 HCl
2 La(OH)3 → La2O3 + 3 H2O

An alternative route to obtaining hexagonal La2O3 involves precipitation of nominal La(OH)3 from aqueous solution using a combination of 2.5% NH3 and the surfactant sodium dodecyl sulfate followed by heating and stirring for 24 hours at 80 °C:

2 LaCl3+ 3 H2O + 3 NH3 → La(OH)3 + 3 NH4Cl
LaCl3·3H2O → La2O3

Other routes include:

2 La2S3 + 3 CO2 → 2 La2O3 + 3 CS2
2 La2(SO4)3 + heat → 2 La2O3 + 6 SO3

Reactions

Lanthanum oxide is used as an additive to develop certain ferroelectric materials, such as La-doped Bi4Ti3O12 (BLT). Lanthanum oxide is used in optical materials; often the optical glasses are doped with La2O3 to improve the glass' refractive index, chemical durability, and mechanical strength.

3 B2O3 + La2O3 → 2 La(BO2)3

When this 1:3 reaction is mixed into a glass composite, the high molecular weight of the lanthanum causes an increase of the homogeneous mixture of the melt which leads to a lower melting point.[6] The addition of the La2O3 to the glass melt leads to a higher glass transition temperature from 658 °C to 679 °C. The addition also leads to a higher density, microhardness, and refractive index of the glass.

Uses and applications

La2O3 is used to make optical glasses, to which this oxide confers increased density, refractive index, and hardness. Together with oxides of tungsten, tantalum, and thorium, La2O3 improves the resistance of the glass to attack by alkali. La2O3 is an ingredient for the manufacture of piezoelectric and thermoelectric materials. Automobile exhaust-gas converters contain La2O3.[7] La2O3 is also used in X-ray imaging intensifying screens, phosphors as well as dielectric and conductive ceramics. Gives off bright glow.

La2O3 has been examined for the oxidative coupling of methane.[8]

La2O3 films can be deposited by many different methods, including chemical vapor disposition, atomic layer deposition, thermal oxidation, sputtering, and spray pyrolysis. Depositions of these films occur in a temperature range of 250–450 °C. Polycrystalline films are formed at 350 °C.[5]

La2O3 tungsten electrodes are replacing thoriated tungsten electrodes in Gas tungsten arc welding (TIG) due to safety concerns with thorium's radioactivity.

References

  1. ^ a b c d "Lanthanum Oxide". American Elements. Retrieved October 26, 2018.
  2. ^ Shang, G.; Peacock, P. W.; Robertson, J. (2004). "Stability and band offsets of nitrogenated high-dielectric-constant gate oxides". Applied Physics Letters. 84 (1): 106–108. Bibcode:2004ApPhL..84..106S. doi:10.1063/1.1638896.
  3. ^ Wells, A.F. (1984). Structural Inorganic Chemistry. Oxford: Clarendon Press. p. 546.
  4. ^ Wyckoff, R. W.G. (1963). Crystal Structures: Inorganic Compounds RXn, RnMX2, RnMX3. New York: Interscience Publishers.
  5. ^ a b Kale, S.S.; Jadhav, K.R.; Patil, P.S.; Gujar, T.P.; Lokhande, C.D. (2005). "Characterizations of spray-deposited lanthanum oxide (La2O3) thin films". Materials Letters. 59 (24–25): 3007–3009. doi:10.1016/j.matlet.2005.02.091.
  6. ^ Vinogradova, N. N.; Dmitruk, L. N.; Petrova, O. B. (2004). "Glass Transition and Crystallization of Glasses Based on Rare-Earth Borates". Glass Physics and Chemistry. 30: 1–5. doi:10.1023/B:GPAC.0000016391.83527.44.
  7. ^ Cao, J; Ji, H; Liu, J; Zheng, M; Chang, X; Ma, X; Zhang, A; Xu, Q (2005). "Controllable syntheses of hexagonal and lamellar mesostructured lanthanum oxide". Materials Letters. 59 (4): 408–411. doi:10.1016/j.matlet.2004.09.034.
  8. ^ O.V. Manoilova; et al. (2004). "Surface Acidity and Basicity of La2O3, LaOCl, and LaCl3 Characterized by IR Spectroscopy, TPD, and DFT Calculations". J. Phys. Chem. B. 108 (40): 15770–15781. doi:10.1021/jp040311m.