Previous articles mentioned the discovery of erbium oxide by scientist Mosander, leading not only to the separation of ytterbium (Yb) but also holmium (Ho) and thulium (Tm). Now, let’s dive into the rare earth element “holmium”!
Table of Contents
Introduction
Holmium (Ho) has 35 isotopes, with naturally occurring 165Ho being the most stable. The remaining isotopes are artificially synthesized and radioactive, with the most stable being 163Ho. Holmium is generally found in gadolinite but mainly sourced from monazite ore, where it constitutes just 0.05%, making its production yield quite low.
Initially, in 1878, Swiss scientists J. L. Soret and M. Delafontaine observed holmium’s spectral characteristics, though they couldn’t confirm it at the time. The following year, Swiss chemist P. T. Cleve isolated holmium from erbium oxide and named the rare earth oxide after Stockholm, his hometown, using the Latin name “Holmia.”
Holmium can be extracted from monazite using ion exchange technology, though separating it from other rare earths remains challenging. To obtain pure holmium metal, its anhydrous chloride or fluoride must be reduced with metallic calcium.
Holmium (Ho)
Atomic number: 67
Atomic weight: 164.930 u
Atomic structure: Its outermost electron structure is 4f11 6s2.
Physical/chemical properties: It is a bright silver-white metallic luster, soft and ductile metal, and is in a solid state under normal temperature and pressure. It reacts slowly with water and is soluble in dilute acid.
Holmium is relatively stable and corrosion-resistant in dry air. However, it forms a light-yellow oxide in humid, high-temperature conditions, which easily fades.
The oxide color changes under different lighting: it appears yellow-brown under natural light and red under tricolor lighting.
Main Application Areas of Holmium
- Due to having the highest magnetic moment, holmium is used to produce the strongest artificial magnetic fields, in manufacturing high-intensity rare-earth magnets, and as an additive in new magnetic alloys. Small amounts of holmium can be added to magnetostrictive alloys, like Terfenol-D, to reduce the external field required to reach magnetic saturation.
- Holmium has no significant role in the human body, but holmium salts can aid metabolism. While humans typically use about 1 mg of holmium per year, ingestion, inhalation, or injection of large amounts of holmium salts can cause severe health issues.
- Holmium can regulate nuclear reactors, as it serves as a control rod material that absorbs neutrons produced by nuclear fission.
- Due to the long half-life of its radioactive isomer 166m1Ho, holmium can be used for calibrating gamma-ray spectrometers.
- Optical Fiber Applications: Holmium is used in the optical fiber field to produce fiber lasers, fiber amplifiers, fiber sensors, and other optical communication devices.
- Colorant for Zirconia and Glass: Holmium serves as a yellow or red colorant for cubic zirconia and glass. It is also used as a calibration standard for monochromators and spectrophotometers and in the production of metal halide lamps.
- Laser Material Dopant: Holmium is used as a dopant in yttrium iron garnet (YIG) laser materials and in microwave devices, particularly in holmium-doped yttrium iron garnet (Ho
) and yttrium lithium fluoride (YLF) solid-state lasers. Ho is also applied in optical isolators and microwave equipment, including YIG spheres. - Medical and Dental Equipment: Holmium is widely found in various medical and dental devices. As an additive in yttrium aluminum garnet, it forms holmium-doped yttrium aluminum garnet (Ho:YAG Laser), used in medical lasers for treating glaucoma, bladder tumors, ureteral tumors, and for minimally invasive laser surgeries in ENT and oral surgery. It’s also used in procedures like percutaneous laser lumbar disc decompression (PLLD) and percutaneous laser disc decompression (PLDD). Its applications include cutting, excising, coagulating, vaporizing, and soft tissue hemostasis, suitable for open surgery, laparoscopy, and endoscopic applications such as percutaneous nephrolithotomy for kidney stones.
During research on this rare earth element, it was found that holmium lasers have numerous applications.
The principle involves hemoglobin and water molecules in tissue absorbing the energy of holmium laser pulses, which are converted from electrical energy to high-energy pulses. This rapidly reaches the boiling point, causing tissue vaporization and shattering stones into a fine powder, which can then be naturally expelled or used to cut tissue.
The laser’s high temperature leaves a thin coagulation layer on the cauterized tissue surface, achieving hemostasis.
Holmium laser is mainly used in routine renal stone surgery (RIRS) or urological procedures for prostate enlargement, urinary tract stones, etc., via endoscopic lithotripsy. It can simultaneously treat coexisting soft tissue diseases, such as urethral strictures, ureteral stenosis, and polyps. Additionally, excised soft tissue can serve as specimens for further analysis and diagnosis.
The Quanta Litho Holmiumsurgical laser system, combined with flexible ureterorenoscopy/fiberoptic systems, enables new-generation holmium laser lithotripsy with minimal bleeding, reduced surgery time, low risk, fast recovery, fewer complications, and reduced post-operative pain, offering an optimal solution for high-risk traditional surgeries and becoming a valuable aid in prostate treatment for men.
