Молибден (VI) оксид

Химические свойства

Molybdenum trioxide is an odorless, white crystalline powder that turns yellow when heated.

Molybdenum trioxide is perhaps the most important compound of molybdenum. Pure molybdenum trioxide is used in chemical and catalyst manufacture. The technical product is added to steel as an alloying agent. Molybdenum trioxide also serves as a catalyst in the petroleum industry and as a component of ceramics, enamels and pigments.

Физические свойства

Soft white powder; orthorhombic crystals; turns yellow on heating; density 4.69 g/cm³ at 21°C; melts at 795°C without decomposition to a dark yellow liquid; vapor pressure 20 torr at 851°C and 200 torr at 1,014°C; boils at 1,155°C; sparingly soluble in cold water (1.066 g/L at 18°C) and moderately soluble in hot water (20.55 g/L at 70°C); dissolves in acids and alkalies.

Использование

Molybdenum trioxide (MnO3) is a compound used to make enamels adhere to metals.

Подготовка

Molybdenum(VI) oxide is obtained by igniting molybdenum or its compounds in air:
2Mo + 3O2 → 2MoO3
2MoS2 + 7O2 → 2MoO3 + 4SO2
MoS2 + 4O2 → MoO3 + SO2 + SO3
Roasting the sulfide is carried out in a multiple-hearth roaster under controlled temperature and airflow. The product mixture is sublimed to obtain high purity oxide.
Purified molybdenum(VI) oxide also is made by prolonged heating of ammonium molybdate in air:
(NH4)2Mo2O7 → 2MoO3 + 2NH3 + H2O
An alternative method involves repeatedly evaporating a mixture of ammonium molybdate and nitric acid. Ammonium nitrate so formed is separated from the product molybdenum(VI) oxide by extraction with water:
(NH4)2Mo2O7 + 2HNO3 → 2MoO3 + 2NH4NO3 + H2O

Общее описание

Colorless to white or yellow odorless solid. Sinks in water.

Реакции воздуха и воды

Insoluble in water.

Профиль реактивности

Molybdenum trioxide reacts violently with chlorine trifluoride, lithium, potassium and sodium. Readily combines with acids and bases to form a series of polymeric compounds. Incompatible with interhalogens and metals. A violent detonation occurs when heated with molten magnesium.

Опасность

Toxic material.

Угроза здоровью

Compound is relatively nontoxic. Dust irritates eyes.

Пожароопасность

Flash point data for Molybdenum trioxide are not available, but Molybdenum trioxide is probably non-flammable.

Профиль безопасности

Poison by ingestion, subcutaneous, and intraperitoneal routes. Human systemic effects by inhalation: pulmonary fibrosis and cough. Questionable carcinogen with experimental neoplastigenic data. A powerful irritant. Explodes on contact with molten magnesium. Violent reaction with interhalogens (e.g., bromine pentafluoride, chlorine trifluoride). Incandescent reaction with hot sodium, potassium, or lithium. When heated to decomposition it emits toxic fumes of Mo.

Возможный контакт

Molybdenum trioxide is used in agriculture; manufacture of metallic molybdenum, ceramic glazes; enamels, pigments, and in analytical chemistry.

Перевозки

UN2811 Toxic solids, organic, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous materials, Technical Name Required.

Методы очистки

Crystallise it from water (1g/50mL) between 70o and 0o. The solubility in H2O is 0.1% at 18o, and 2% at 70o. It is a white powder which turns yellow reversibly on heating. It sublimes readily at 1155o/760mm. [Hein & Herzog Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol II p 1412 1965.]

Несовместимости

Explodes on contact with molten magnesium. Violent reaction with strong oxidizers, such as chlorine trifluoride; bromine pentafluoride. Not compatible with strong acids; active metals (sodium, potassium, lithium).