HAFNIUM химические свойства, назначение, производство
Химические свойства
Hafnium is a refractory metal which occurs in
nature in zirconium minerals.
Физические свойства
Hafnium is a ductile metal that looks and feels much like stainless steel, but it is significantlyheavier than steel. When freshly cut, metallic hafnium has a bright silvery shine. Whenthe fresh surface is exposed to air, it rapidly forms a protective oxidized coating on its surface.Therefore, once oxidized, hafnium resists corrosion, as do most transition metals, whenexposed to the air. Chemically and physically, hafnium is very similar to zirconium, whichis located just above it in group 4 on the periodic table. In fact, they are so similar that it isalmost impossible to secure a pure sample of either one without a small percentage of theother. Each will contain a small amount of the other metal after final refining.
Hafnium’s melting point is 2,227°C, its boiling point varies from about 2,500°C to5,000°C depending on its purity, and its density is 13.29 g/cm3. The compound hafniumnitride (HfN) has the highest melting point (over 3,300°C) of any two-element compound.
Изотопы
There are 44 known isotopes for hafnium. Five are stable and one of the unstableisotopes has such a long half-life (Hf-174 with a 2.0×10+15 years) that it is includedas contributing 0.16% to the amount of hafnium found in the Earth’s crust. The percentagecontributions of the 5 stable isotopes to the element’s natural existence on Earth areas follows: Hf-176 = 5.26%, Hf-177 = 18.60%, Hf-178 = 27.28%, Hf-179 = 13.62%,and Hf-180 = 35.08%.
Происхождение имени
Named after Hafnia, the Latin name for the city of Copenhagen, Denmark.
Вхождение
Hafnium is the 47th most abundant element on Earth. Thus, it is more abundant thaneither gold or silver. Because hafnium and zirconium are always found together in nature, bothmetals are refined and produced by the Kroll process. Pure samples of either hafnium or zirconiumare almost impossible to separate by the Kroll or other refining processes. Baddeleyite(ZrO2), a zirconium ore, and zircon (ZrSiO4) are treated with chlorine along with a carboncatalyst that produces a mixture of zirconium and hafnium tetrachlorides. These are reducedby using sodium or magnesium, resulting in the production of both metals. The molten metalsare separated by the process known as fractionation, which depends on their different meltingpoints and densities. As the mixture of the two metals cools during the fractionation process,the denser solidified hafnium sinks to the bottom of the vessel while the less dense zirconium(with a higher melting point than hafnium) floats on top.
Характеристики
As the first element in the third series of the transition elements, hafnium’s atomic number(72Hf ) follows the lanthanide series of rare-earths. The lanthanide series is separated out ofthe normal position of sequenced atomic numbers and is placed below the third series on theperiodic table (57La to 71Li). This rearrangement of the table allowed the positioning of elementsof the third series within groups more related to similar chemical and physical characteristics—for example, the triads of Ti, Zr, and Hf; V, Nb, and Ta; and Cu, Ag, and Au.
Использование
Hafnium has a great affinity for absorbing slow neutrons. This attribute, along with itsstrength and resistance to corrosion, makes it superior to cadmium, which is also used formaking control rods for nuclear reactors. This use is of particular importance for the type ofnuclear reactors used aboard submarines. By moving the control rods in and out of a nuclearreactor, the fission chain reaction can be controlled as the neutrons are absorbed in the metalof the rods. The drawback to hafnium control rods is their expense: it costs approximately onemillion dollars for several dozen rods for use in a single nuclear reactor.
In vacuum tubes and other applications that must have gases removed, hafnium is used asa “getter” to absorb any trace oxygen or nitrogen in the tube, thus extending the life of thevacuum tube. Hafnium’s qualities also make it ideal for filaments in light bulbs and, whenmixed with rare-earth metals, as a “sparking” misch metal. Hafnium is also used to a lesserextent as an alloying agent for several other metals, including iron, titanium, and niobium.
Определение
hafnium: Symbol Hf. A silvery lustrousmetallic transition element;a.n. 72; r.a.m. 178.49; r.d. 13.3; m.p.2227±20°C; b.p. 4602°C. The elementis found with zirconium and is extractedby formation of the chlorideand reduction by the Kroll process. Itis used in tungsten alloys in filamentsand electrodes and as a neutron absorber.The metal forms a passiveoxide layer in air. Most of its compoundsare hafnium(IV) complexes;less stable hafnium(III) complexesalso exist. The element was first reportedby Urbain in 1911, and its existencewas finally established by Dirk Coster (1889–1950) and Georgede Hevesey (1885–1966) in 1923.
Общее описание
HAFNIUM, is a grayish metallic colored powder. Dust from dry powder may be ignited by static electricity. The dry powder reacts with moisture to produce hydrogen, a flammable gas. The heat from this reaction may be sufficient to ignite the hydrogen. HAFNIUM does not appreciably react with large quantities of water.
Реакции воздуха и воды
Highly flammable. The dry powder reacts with moisture to produce hydrogen, a flammable gas. The heat from this reaction may be sufficient to ignite the hydrogen. HAFNIUM does not appreciably react with large quantities of water.
Профиль реактивности
Metals, such as HAFNIUM METAL(reactivity similar to zirconium), are reducing agents and tend to react with oxidizing agents. Their reactivity is strongly influenced by their state of subdivision: in bulk they often resist chemical combination; in powdered form they may react very rapidly. Thus, as a bulk metal HAFNIUM is somewhat unreactive, but finely divided material may be pyrophoric. The metal reacts exothermically with compounds having active hydrogen atoms (such as acids and water) to form flammable hydrogen gas and caustic products. The reactions are less vigorous than the similar reactions of alkali metals, but the released heat can still ignite the released hydrogen. Materials in this group may react with azo/diazo compounds to form explosive products. These metals and the products of their corrosion by air and water can catalyze polymerization reactions in several classes of organic compounds; these polymerizations sometimes proceed rapidly or even explosively. Some metals in this group form explosive products with halogenated hydrocarbons.
Опасность
Although the metal hafnium is not harmful, its powder and dust are both toxic if inhaledand explosive even when wet.
Угроза здоровью
Fire will produce irritating, corrosive and/or toxic gases. Inhalation of decomposition products may cause severe injury or death. Contact with substance may cause severe burns to skin and eyes. Runoff from fire control may cause pollution.
Пожароопасность
Flammable/combustible material. May ignite on contact with moist air or moisture. May burn rapidly with flare-burning effect. Some react vigorously or explosively on contact with water. Some may decompose explosively when heated or involved in a fire. May re-ignite after fire is extinguished. Runoff may create fire or explosion hazard. Containers may explode when heated.
Промышленное использование
Pure hafnium is a lustrous, silvery metal that is not so ductile nor so easily worked as zirconium; nevertheless, hafnium can be hot- and cold-rolled on the same equipment and with similar techniques as those used for zirconium. All zirconium chemicals and alloys may contain some hafnium, and hafnium metal usually contains about 2% zirconium.The metal has a closepacked hexagonal structure. The electric conductivity is about 6% that of copper. It has excellent resistance to a wide range of corrosive environments.
Because of the startling similarity in their chemical properties, zirconium and hafnium always occur together in nature. In their respective ability to absorb neutrons, however, they differ greatly, and this difference has led to their use in surprisingly different ways in nuclear reactors. Zirconium, with a low neutron-absorption cross section (0.18 barn), is highly desirable as a structural material in water-cooled nuclear reactor cores. Hafnium, on the other hand, because of its high neutron-absorption cross section (105 barns), can be used as a neutron-absorbing control material in the same nuclear reactor cores. Thus, the two elements, which occur together so intimately in nature that they are very difficult to separate, are used as individual and important but contrasting components in the cores of nuclear reactors.
Возможный контакт
Hafnium metal has been used as a
control rod material in nuclear reactors. Thus, those
engaged in fabrication and machining of such rods may be
exposed.
Перевозки
UN1326 Hafnium powder, wetted with not
<,25% water (a visible excess of water must be present)
(1) mechanically produced, particle size<53 μm; (2)
chemically produced, particle size<840 μm, Hazard Class:
4.1; Labels: 4.1-Flammable solid. UN2545 Hafnium pow der, dry, Hazard Class: 4.1; Labels: 4.1-Flammable solid.
UN1346 Hafnium powder, wetted with not less than 25%
water (a visible excess of water must be present)
(1) mechanically produced, particle size less than 53 μm;
(2) chemically produced, particle size less than 840 μm,
Hazard Class: 4.1; Labels: 4.1-Flammable solid.
Несовместимости
Fine powder or dust may form explosive
mixture in air. The powder is highly flammable and a strong
reducing agent. The powder or dust reacts with moisture
forming flammable hydrogen gas; may spontaneously ignite
on contact with moist air; and at higher temperatures, with
nitrogen, phosphorous, oxygen, halogens, and sulfur; contact
with hot nitric acid; heat, shock, friction, strong oxidizers;
or ignition sources may cause explosions.
Утилизация отходов
Recovery. Consider recycling,
otherwise, this chemical must be disposed of in compliance
with existing federal and local regulations.
HAFNIUM препаратная продукция и сырье
сырьё
препарат