Holmium(III) oxide, or holmium oxide is a
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
of a
rare-earth element
The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides ( yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silv ...
holmium
Holmium is a chemical element with the symbol Ho and atomic number 67. It is a rare-earth element and the eleventh member of the lanthanide series. It is a relatively soft, silvery, fairly corrosion-resistant and malleable metal. Like a lot of oth ...
and
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
with the
formula Ho
2O
3. Together with
dysprosium(III) oxide
Dysprosium oxide (Dy2O3) is a sesquioxide compound of the rare earth metal dysprosium. It is a pastel yellowish-greenish, slightly hygroscopic powder having specialized uses in ceramics, glass, phosphors, lasers, as a Faraday rotator
A Faraday ro ...
(Dy
2O
3), holmium oxide is one of the most powerfully
paramagnetic
Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...
substances known. The oxide, also called holmia, occurs as a component of the related erbium oxide
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
called
erbia
Erbium(III) oxide is the inorganic compound with the formula . It is a pink paramagnetic solid. It finds uses in various optical materials.
Structure
Erbium(III) oxide has a cubic structure resembling the bixbyite motif. The Er3+ centers are o ...
. Typically, the oxides of the trivalent
lanthanides coexist in nature, and separation of these components requires specialized methods. Holmium oxide is used in making specialty colored
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...
es. Glass containing holmium oxide and holmium oxide solutions have a series of sharp
optical absorption
In physics, absorption of electromagnetic radiation is how matter (typically electrons bound in atoms) takes up a photon's energy — and so transforms electromagnetic energy into internal energy of the absorber (for example, thermal energy). ...
peaks in the visible
spectral range
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from b ...
. They are therefore traditionally used as a convenient calibration standard for
optical spectrophotometers.
Properties
Appearance
Holmium oxide has some fairly dramatic color changes depending on the lighting conditions. In daylight, it is a tannish yellow color. Under trichromatic light, it is a fiery orange red, almost indistinguishable from the way erbium oxide looks under this same lighting. This is related to the sharp emission bands of the phosphors.
[ Holmium oxide has a wide ]band gap
In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference ( ...
of 5.3 eV[ and thus should appear colorless. The yellow color originates from abundant lattice defects (such as oxygen vacancies) and is related to internal transitions at the Ho3+ ions.]
Crystalline structure
Holmium oxide has a cubic, yet rather complex bixbyite
Bixbyite is a manganese iron oxide mineral with chemical formula: (Mn,Fe)2O3. The iron/manganese ratio is quite variable and many specimens have almost no iron. It is a metallic dark black with a Mohs hardness of 6.0 - 6.5. It is a somewhat rare ...
structure, with many atoms per unit cell and a large lattice constant of 1.06 nm. This structure is characteristic of oxides of heavy rare-earth elements, such as Tb2O3, Dy2O3, Er2O3, Tm2O3, Yb2O3 and Lu2O3. The thermal expansion coefficient of Ho2O3 is also relatively large at 7.4 ×10−6/°C.
Chemical
Treating holmium oxide with hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
or with ammonium chloride affords the corresponding holmium chloride:[
:Ho2O3 + 6 NH4Cl → 2 HoCl3 + 6 NH3 + 3 H2O
Holmium(III) oxide can also react with hydrogen sulfide to form holmium(III) sulfide at high temperatures.
]
History
Holmium (''Holmia'', Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
name for Stockholm) was discovered by Marc Delafontaine and Jacques-Louis Soret
Jacques-Louis Soret (30 June 1827 – 13 May 1890) was a Swiss chemist and spectroscopist. He studied both spectroscopy and electrolysis. He held the chairs of chemistry (1873-1887) and medical physics (1887-1890) at the University of Genev ...
in 1878 who noticed the aberrant spectrographic absorption bands of the then-unknown element (they called it "Element X"). Later in 1878, Per Teodor Cleve
Per Teodor Cleve (10 February 1840 – 18 June 1905) was a Swedish chemist, biologist, mineralogist and oceanographer. He is best known for his discovery of the chemical elements holmium and thulium.
Born in Stockholm in 1840, Cleve earned his B ...
independently discovered the element while he was working on erbia
Erbium(III) oxide is the inorganic compound with the formula . It is a pink paramagnetic solid. It finds uses in various optical materials.
Structure
Erbium(III) oxide has a cubic structure resembling the bixbyite motif. The Er3+ centers are o ...
earth ( erbium oxide).
Using the method developed by Carl Gustaf Mosander
Carl Gustaf Mosander (10 September 1797 – 15 October 1858) was a Swedish chemist. He discovered the rare earth elements lanthanum, erbium and terbium.
Early life and education
Born in Kalmar, Mosander attended school there until he moved ...
, Cleve first removed all of the known contaminants from erbia. The result of that effort was two new materials, one brown and one green. He named the brown substance holmia (after the Latin name for Cleve's home town, Stockholm) and the green one thulia. Holmia was later found to be the holmium oxide and thulia was thulium oxide
Thulium(III) oxide is a pale green solid compound, with the formula Tm2 O3. It was first isolated in 1879, from an impure sample of erbia, by Swedish chemist
A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval ...
.
Occurrence
Holmium oxide occurs in trace amounts in the minerals gadolinite, monazite
Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the ceriu ...
, and in other rare-earth mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
s. Holmium metal readily oxidizes in air; therefore presence of holmium in nature is synonymous with that of holmia. With the abundance of 1.4 mg/kg, holmium is the 56th most abundant element.[ The main mining areas are China, ]United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
, Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
, India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, Sri Lanka and Australia with reserves of holmium oxide estimated as 400,000 tonnes.[
]
Production
A typical extraction process of holmium oxide can be simplified as follows: the mineral mixtures are crushed and ground. Monazite, because of its magnetic properties can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of several rare earth elements. The acidic filtrates are partially neutralized with sodium hydroxide to pH 3-4. Thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
precipitates out of solution as hydroxide and is removed. After that, the solution is treated with ammonium oxalate
The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...
to convert rare earths in to their insoluble oxalate
Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl ...
s. The oxalates are converted to oxides by annealing. The oxides are dissolved in nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
that excludes one of the main components, cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 ...
, whose oxide is insoluble in HNO3.
The most efficient separation routine for holmium oxide from the rare-earths is ion exchange
Ion exchange is a reversible interchange of one kind of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, ...
. In this process, rare-earth ions are adsorbed onto suitable ion-exchange resin by exchange with hydrogen, ammonium or cupric ions present in the resin. The rare earth ions are then selectively washed out by suitable complexing agent, such as ammonium citrate or nitrilotriacetate.
Applications
Holmium oxide is one of the colorants used for cubic zirconia
Cubic zirconia (CZ) is the cubic crystalline form of zirconium dioxide (ZrO2). The synthesized material is hard and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirco ...
and glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...
, providing yellow or red coloring. Glass containing holmium oxide and holmium oxide solutions (usually in perchloric acid
Perchloric acid is a mineral acid with the formula H Cl O4. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid, nitric acid and hydrochloric acid. It is a powerful oxidizer when hot, but aqueous s ...
) have sharp optical absorption peaks in the spectral range 200-900 nm. They are therefore used as a calibration standard for optical spectrophotometers and are available commercially. As most other oxides of rare-earth elements, holmium oxide is used as a specialty catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
, phosphor and a laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fi ...
material. Holmium laser operates at wavelength of about 2.08 micrometres, either in pulsed or continuous regime. This laser is eye safe and is used in medicine, lidars, wind velocity measurements and atmosphere monitoring.
Health effects
Holmium(III) oxide is, compared to many other compounds, not very dangerous, although repeated overexposure can cause granuloma and hemoglobinemia
Hemoglobinemia (or haemoglobinaemia) is a medical condition in which there is an excess of hemoglobin in the blood plasma. This is an effect of intravascular hemolysis, in which hemoglobin separates from red blood cells, a form of anemia.
Hemogl ...
. It has low oral, dermal and inhalation toxicities and is non-irritating. The acute oral median lethal dose (LD50) is greater than 1 g per kilogram of body weight.
References
{{oxygen compounds
Holmium compounds
Sesquioxides