Names | |
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IUPAC name Caesium chloride | |
Other names Cesium chloride | |
Identifiers | |
3D model (JSmol) | |
ChemSpider | |
ECHA InfoCard | 100.028.728 |
EC Number |
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PubChem CID | |
UNII | |
CompTox Dashboard (EPA) | |
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Properties | |
CsCl | |
Molar mass | 168.36 g/mol |
Appearance | white solid hygroscopic |
Density | 3.988 g/cm3 [1] |
Melting point | 646 °C (1,195 °F; 919 K) [1] |
Boiling point | 1,297 °C (2,367 °F; 1,570 K) [1] |
1910 g/L (25 °C) [1] | |
Solubility | soluble in ethanol [1] |
Band gap | 8.35 eV (80 K) [2] |
-56.7·10−6 cm3/mol [3] | |
Refractive index (nD) | 1.712 (0.3 μm) 1.640 (0.59 μm) 1.631 (0.75 μm) 1.626 (1 μm) 1.616 (5 μm) 1.563 (20 μm) [4] |
Structure | |
CsCl, cP2 | |
Pm3m, No. 221 [5] | |
a = 0.4119 nm | |
Lattice volume (V) | 0.0699 nm3 |
Formula units (Z) | 1 |
Cubic (Cs+) Cubic (Cl−) | |
Hazards | |
GHS labelling: | |
Warning | |
H302, H341, H361, H373 | |
P201, P202, P260, P264, P270, P281, P301+P312, P308+P313, P314, P330, P405, P501 | |
Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 2600 mg/kg (oral, rat) [6] |
Related compounds | |
Other anions | Caesium fluoride Caesium bromide Caesium iodide Caesium astatide |
Other cations | Lithium chloride Sodium chloride Potassium chloride Rubidium chloride Francium chloride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Caesium chloride or cesium chloride is the inorganic compound with the formula Cs Cl. This colorless salt is an important source of caesium ions in a variety of niche applications. Its crystal structure forms a major structural type where each caesium ion is coordinated by 8 chloride ions. Caesium chloride dissolves in water. CsCl changes to NaCl structure on heating. Caesium chloride occurs naturally as impurities in carnallite (up to 0.002%), sylvite and kainite. Less than 20 tonnes of CsCl is produced annually worldwide, mostly from a caesium-bearing mineral pollucite. [7]
Caesium chloride is widely used in isopycnic centrifugation for separating various types of DNA. It is a reagent in analytical chemistry, where it is used to identify ions by the color and morphology of the precipitate. When enriched in radioisotopes, such as 137CsCl or 131CsCl, caesium chloride is used in nuclear medicine applications such as treatment of cancer and diagnosis of myocardial infarction. Another form of cancer treatment was studied using conventional non-radioactive CsCl. Whereas conventional caesium chloride has a rather low toxicity to humans and animals, the radioactive form easily contaminates the environment due to the high solubility of CsCl in water. Spread of 137CsCl powder from a 93-gram container in 1987 in Goiânia, Brazil, resulted in one of the worst-ever radiation spill accidents killing four and directly affecting 249 people.
The caesium chloride structure adopts a primitive cubic lattice with a two-atom basis, where both atoms have eightfold coordination. The chloride atoms lie upon the lattice points at the corners of the cube, while the caesium atoms lie in the holes in the center of the cubes; an alternative and exactly equivalent 'setting' has the caesium ions at the corners and the chloride ion in the center. This structure is shared with CsBr and CsI and many binary metallic alloys. In contrast, the other alkaline halides have the sodium chloride (rocksalt) structure. [8] When both ions are similar in size (Cs+ ionic radius 174 pm for this coordination number, Cl− 181 pm) the CsCl structure is adopted, when they are different (Na+ ionic radius 102 pm, Cl− 181 pm) the sodium chloride structure is adopted. Upon heating to above 445 °C, the normal caesium chloride structure (α-CsCl) converts to the β-CsCl form with the rocksalt structure (space group Fm3m). [5] The rocksalt structure is also observed at ambient conditions in nanometer-thin CsCl films grown on mica, LiF, KBr and NaCl substrates. [9]
Caesium chloride is colorless in the form of large crystals and white when powdered. It readily dissolves in water with the maximum solubility increasing from 1865 g/L at 20 °C to 2705 g/L at 100 °C. [10] The crystals are very hygroscopic and gradually disintegrate at ambient conditions. [11] Caesium chloride does not form hydrates. [12]
Т (°C) | 0 | 10 | 20 | 25 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 |
---|---|---|---|---|---|---|---|---|---|---|---|---|
S (wt%) | 61.83 | 63.48 | 64.96 | 65.64 | 66.29 | 67.50 | 68.60 | 69.61 | 70.54 | 71.40 | 72.21 | 72.96 |
In contrast to sodium chloride and potassium chloride, caesium chloride readily dissolves in concentrated hydrochloric acid. [14] [15] Caesium chloride has also a relatively high solubility in formic acid (1077 g/L at 18 °C) and hydrazine; medium solubility in methanol (31.7 g/L at 25 °C) and low solubility in ethanol (7.6 g/L at 25 °C), [12] [15] [16] sulfur dioxide (2.95 g/L at 25 °C), ammonia (3.8 g/L at 0 °C), acetone (0.004% at 18 °C), acetonitrile (0.083 g/L at 18 °C), [15] ethylacetate and other complex ethers, butanone, acetophenone, pyridine and chlorobenzene. [17]
Despite its wide band gap of about 8.35 eV at 80 K, [2] caesium chloride weakly conducts electricity, and the conductivity is not electronic but ionic. The conductivity has a value of the order 10−7 S/cm at 300 °C. It occurs through nearest-neighbor jumps of lattice vacancies, and the mobility is much higher for the Cl− than Cs+ vacancies. The conductivity increases with temperature up to about 450 °C, with an activation energy changing from 0.6 to 1.3 eV at about 260 °C. It then sharply drops by two orders of magnitude because of the phase transition from the α-CsCl to β-CsCl phase. The conductivity is also suppressed by application of pressure (about 10 times decrease at 0.4 GPa) which reduces the mobility of lattice vacancies. [18]
Concentration, wt% | Density, kg/L | Concentration, mol/L | refractive index (at 589 nm) | Freezing point depression, °C relative to water | Viscosity, 10−3 Pa·s |
---|---|---|---|---|---|
0.5 | – | 0.030 | 1.3334 | 0.10 | 1.000 |
1.0 | 1.0059 | 0.060 | 1.3337 | 0.20 | 0.997 |
2.0 | 1.0137 | 0.120 | 1.3345 | 0.40 | 0.992 |
3.0 | 0.182 | 1.3353 | 0.61 | 0.988 | |
4.0 | 1.0296 | 0.245 | 1.3361 | 0.81 | 0.984 |
5.0 | 0.308 | 1.3369 | 1.02 | 0.980 | |
6.0 | 1.0461 | 0.373 | 1.3377 | 1.22 | 0.977 |
7.0 | 0.438 | 1.3386 | 1.43 | 0.974 | |
8.0 | 1.0629 | 0.505 | 1.3394 | 1.64 | 0.971 |
9.0 | 0.573 | 1.3403 | 1.85 | 0.969 | |
10.0 | 1.0804 | 0.641 | 1.3412 | 2.06 | 0.966 |
12.0 | 1.0983 | 0.782 | 1.3430 | 2.51 | 0.961 |
14.0 | 1.1168 | 0.928 | 1.3448 | 2.97 | 0.955 |
16.0 | 1.1358 | 1.079 | 1.3468 | 3.46 | 0.950 |
18.0 | 1.1555 | 1.235 | 1.3487 | 3.96 | 0.945 |
20.0 | 1.1758 | 1.397 | 1.3507 | 4.49 | 0.939 |
22.0 | 1.1968 | 1.564 | 1.3528 | – | 0.934 |
24.0 | 1.2185 | 1.737 | 1.3550 | – | 0.930 |
26.0 | 1.917 | 1.3572 | – | 0.926 | |
28.0 | 2.103 | 1.3594 | – | 0.924 | |
30.0 | 1.2882 | 2.296 | 1.3617 | – | 0.922 |
32.0 | 2.497 | 1.3641 | – | 0.922 | |
34.0 | 2.705 | 1.3666 | – | 0.924 | |
36.0 | 2.921 | 1.3691 | – | 0.926 | |
38.0 | 3.146 | 1.3717 | – | 0.930 | |
40.0 | 1.4225 | 3.380 | 1.3744 | – | 0.934 |
42.0 | 3.624 | 1.3771 | – | 0.940 | |
44.0 | 3.877 | 1.3800 | – | 0.947 | |
46.0 | 4.142 | 1.3829 | – | 0.956 | |
48.0 | 4.418 | 1.3860 | – | 0.967 | |
50.0 | 1.5858 | 4.706 | 1.3892 | – | 0.981 |
60.0 | 1.7886 | 6.368 | 1.4076 | – | 1.120 |
64.0 | 7.163 | 1.4167 | – | 1.238 |
Caesium chloride completely dissociates upon dissolution in water, and the Cs+ cations are solvated in dilute solution. CsCl converts to caesium sulfate upon being heated in concentrated sulfuric acid or heated with caesium hydrogen sulfate at 550–700 °C: [21]
Caesium chloride forms a variety of double salts with other chlorides. Examples include 2CsCl·BaCl2, [22] 2CsCl·CuCl2, CsCl·2CuCl and CsCl·LiCl, [23] and with interhalogen compounds: [24]
Caesium chloride occurs naturally as an impurity in the halide minerals carnallite (KMgCl3·6H2O with up to 0.002% CsCl), [26] sylvite (KCl) and kainite (MgSO4·KCl·3H2O), [27] and in mineral waters. For example, the water of Bad Dürkheim spa, which was used in isolation of caesium, contained about 0.17 mg/L of CsCl. [28] None of these minerals are commercially important.
On industrial scale, CsCl is produced from the mineral pollucite, which is powdered and treated with hydrochloric acid at elevated temperature. The extract is treated with antimony chloride, iodine monochloride, or cerium(IV) chloride to give the poorly soluble double salt, e.g.: [29]
Treatment of the double salt with hydrogen sulfide gives CsCl: [29]
High-purity CsCl is also produced from recrystallized (and ) by thermal decomposition: [30]
Only about 20 tonnes of caesium compounds, with a major contribution from CsCl, were being produced annually around the 1970s [31] and 2000s worldwide. [32] Caesium chloride enriched with caesium-137 for radiation therapy applications is produced at a single facility Mayak in the Ural Region of Russia [33] and is sold internationally through a UK dealer. The salt is synthesized at 200 °C because of its hygroscopic nature and sealed in a thimble-shaped steel container which is then enclosed into another steel casing. The sealing is required to protect the salt from moisture. [34]
In the laboratory, CsCl can be obtained by treating caesium hydroxide, carbonate, caesium bicarbonate, or caesium sulfide with hydrochloric acid:
Caesium chloride is the main precursor to caesium metal by high-temperature reduction: [31]
A similar reaction – heating CsCl with calcium in vacuum in presence of phosphorus – was first reported in 1905 by the French chemist M. L. Hackspill [35] and is still used industrially. [31]
Caesium hydroxide is obtained by electrolysis of aqueous caesium chloride solution: [36]
Caesium chloride is widely used in centrifugation in a technique known as isopycnic centrifugation. Centripetal and diffusive forces establish a density gradient that allow separation of mixtures on the basis of their molecular density. This technique allows separation of DNA of different densities (e.g. DNA fragments with differing A-T or G-C content). [31] This application requires a solution with high density and yet relatively low viscosity, and CsCl suits it because of its high solubility in water, high density owing to the large mass of Cs, as well as low viscosity and high stability of CsCl solutions. [29]
Caesium chloride is rarely used in organic chemistry. It can act as a phase transfer catalyst reagent in selected reactions. One of these reactions is the synthesis of glutamic acid derivatives
where TBAB is tetrabutylammonium bromide (interphase catalyst) and CPME is a cyclopentyl methyl ether (solvent). [37]
Another reaction is substitution of tetranitromethane [38]
where DMF is dimethylformamide (solvent).
Caesium chloride is a reagent in traditional analytical chemistry used for detecting inorganic ions via the color and morphology of the precipitates. Quantitative concentration measurement of some of these ions, e.g. Mg2+, with inductively coupled plasma mass spectrometry, is used to evaluate the hardness of water. [39]
Ion | Accompanying reagents | Residue | Morphology | Detection limit (μg) |
---|---|---|---|---|
AsO33− | KI | Cs2[AsI5] or Cs3[AsI6] | Red hexagons | 0.01 |
Au3+ | AgCl, HCl | Cs2Ag[AuCl6] | Gray-black crosses, four and six-beamed stars | 0.01 |
Au3+ | NH4SCN | Cs[Au(SCN)4] | Orange-yellow needles | 0.4 |
Bi3+ | KI, HCl | Cs2[BiI5] or 2.5H2O | Red hexagons | 0.13 |
Cu2+ | (CH3COO)2Pb, CH3COOH, KNO2 | Cs2Pb[Cu(NO2)6] | Small black cubes | 0.01 |
In3+ | — | Cs3[InCl6] | Small octahedra | 0.02 |
[IrCl6]3− | — | Cs2[IrCl6] | Small dark-red octahedra | – |
Mg2+ | Na2HPO4 | CsMgPO4 or 6H2O | Small tetrahedra | – |
Pb2+ | KI | Cs[PbI3] | Yellow-green needles | 0.01 |
Pd2+ | NaBr | Cs2[PdBr4] | Dark-red needles and prisms | – |
[ReCl4]− | — | Cs[ReCl4] | Dark-red rhombs, bipyramids | 0.2 |
[ReCl6]2− | — | Cs2[ReCl6] | Small yellow-green octahedra | 0.5 |
ReO4− | — | CsReO4 | Tetragonal bipyramids | 0.13 |
Rh3+ | KNO2 | Cs3[Rh(NO2)6] | Yellow cubes | 0.1 |
Ru3+ | — | Cs3[RuCl6] | Pink needles | – |
[RuCl6]2− | — | Cs2[RuCl6] | Small dark-red crystals | 0.8 |
Sb3+ | — | Cs2[SbCl5]·nH2O | Hexagons | 0.16 |
Sb3+ | NaI | or | Red hexagons | 0.1 |
Sn4+ | — | Cs2[SnCl6] | Small octahedra | 0.2 |
TeO33− | HCl | Cs2[TeCl6] | Light yellow octahedra | 0.3 |
Tl3+ | NaI | Orange-red hexagons or rectangles | 0.06 |
It is also used for detection of the following ions:
Ion | Accompanying reagents | Detection | Detection limit (μg/mL) |
---|---|---|---|
Al3+ | K2SO4 | Colorless crystals form in neutral media after evaporation | 0.01 |
Ga3+ | KHSO4 | Colorless crystals form upon heating | 0.5 |
Cr3+ | KHSO4 | Pale-violet crystals precipitate in slightly acidic media | 0.06 |
The American Cancer Society states that "available scientific evidence does not support claims that non-radioactive cesium chloride supplements have any effect on tumors." [40] The Food and Drug Administration has warned about safety risks, including significant heart toxicity and death, associated with the use of cesium chloride in naturopathic medicine. [41] [42]
Caesium chloride composed of radioisotopes such as 137CsCl and 131CsCl, [43] is used in nuclear medicine, including treatment of cancer (brachytherapy) and diagnosis of myocardial infarction. [44] [45] In the production of radioactive sources, it is normal to choose a chemical form of the radioisotope which would not be readily dispersed in the environment in the event of an accident. For instance, radiothermal generators (RTGs) often use strontium titanate, which is insoluble in water. For teletherapy sources, however, the radioactive density (Ci in a given volume) needs to be very high, which is not possible with known insoluble caesium compounds. A thimble-shaped container of radioactive caesium chloride provides the active source.
Caesium chloride is used in the preparation of electrically conducting glasses [43] [46] and screens of cathode ray tubes. [31] In conjunction with rare gases CsCl is used in excimer lamps [47] [48] and excimer lasers. Other uses include activation of electrodes in welding; [49] manufacture of mineral water, beer [50] and drilling muds; [51] and high-temperature solders. [52] High-quality CsCl single crystals have a wide transparency range from UV to the infrared and therefore had been used for cuvettes, prisms and windows in optical spectrometers; [31] this use was discontinued with the development of less hygroscopic materials.
CsCl is a potent inhibitor of HCN channels, which carry the h-current in excitable cells such as neurons. [53] Therefore, it can be useful in electrophysiology experiments in neuroscience.
Caesium chloride has a low toxicity to humans and animals. [54] Its median lethal dose (LD50) in mice is 2300 mg per kilogram of body weight for oral administration and 910 mg/kg for intravenous injection. [55] The mild toxicity of CsCl is related to its ability to lower the concentration of potassium in the body and partly substitute it in biochemical processes. [56] When taken in large quantities, however, can cause a significant imbalance in potassium and lead to hypokalemia, arrythmia, and acute cardiac arrest. [57] However, caesium chloride powder can irritate the mucous membranes and cause asthma. [51]
Because of its high solubility in water, caesium chloride is highly mobile and can even diffuse through concrete. This is a drawback for its radioactive form which urges a search for less chemically mobile radioisotope materials. Commercial sources of radioactive caesium chloride are well sealed in a double steel enclosure. [34] However, in the Goiânia accident in Brazil, such a source containing about 93 grams of 137CsCl, was stolen from an abandoned hospital and forced open by two scavengers. The blue glow emitted in the dark by the radioactive caesium chloride attracted the thieves and their relatives who were unaware of the associated dangers and spread the powder. This resulted in one of the worst radiation spill accidents in which 4 people died within a month from the exposure, 20 showed signs of radiation sickness, 249 people were contaminated with radioactive caesium chloride, and about a thousand received a dose exceeding a yearly amount of background radiation. More than 110,000 people overwhelmed the local hospitals, and several city blocks had to be demolished in the cleanup operations. In the first days of the contamination, stomach disorders and nausea due to radiation sickness were experienced by several people, but only after several days one person associated the symptoms with the powder and brought a sample to the authorities. [58] [59]
The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Together with hydrogen they constitute group 1, which lies in the s-block of the periodic table. All alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in their having very similar characteristic properties. Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour. This family of elements is also known as the lithium family after its leading element.
Caesium is a chemical element; it has symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 °C, which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium has physical and chemical properties similar to those of rubidium and potassium. It is pyrophoric and reacts with water even at −116 °C (−177 °F). It is the least electronegative element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined mostly from pollucite. Caesium-137, a fission product, is extracted from waste produced by nuclear reactors. It has the largest atomic radius of all elements whose radii have been measured or calculated, at about 260 picometers.
Rubidium is a chemical element; it has symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have a density higher than water. On Earth, natural rubidium comprises two isotopes: 72% is a stable isotope 85Rb, and 28% is slightly radioactive 87Rb, with a half-life of 48.8 billion years—more than three times as long as the estimated age of the universe.
Solubility equilibrium is a type of dynamic equilibrium that exists when a chemical compound in the solid state is in chemical equilibrium with a solution of that compound. The solid may dissolve unchanged, with dissociation, or with chemical reaction with another constituent of the solution, such as acid or alkali. Each solubility equilibrium is characterized by a temperature-dependent solubility product which functions like an equilibrium constant. Solubility equilibria are important in pharmaceutical, environmental and many other scenarios.
The term chloride refers to a compound or molecule that contains either a chlorine ion, which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond. Many inorganic chlorides are salts. Many organic compounds are chlorides. The pronunciation of the word "chloride" is.
Potassium chloride is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a salt-like taste. Potassium chloride can be obtained from ancient dried lake deposits. KCl is used as a fertilizer, in medicine, in scientific applications, domestic water softeners, and in food processing, where it may be known as E number additive E508.
In crystallography, the cubiccrystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.
Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release of heat energy, and gamma rays. The two smaller nuclei are the fission products..
Silver chloride is an inorganic chemical compound with the chemical formula AgCl. This white crystalline solid is well known for its low solubility in water and its sensitivity to light. Upon illumination or heating, silver chloride converts to silver, which is signaled by grey to black or purplish coloration in some samples. AgCl occurs naturally as the mineral chlorargyrite.
Caesium fluoride is an inorganic compound with the formula CsF. A hygroscopic white salt, caesium fluoride is used in the synthesis of organic compounds as a source of the fluoride anion. The compound is noteworthy from the pedagogical perspective as caesium also has the highest electropositivity of all commonly available elements and fluorine has the highest electronegativity.
Caesium iodide or cesium iodide is the ionic compound of caesium and iodine. It is often used as the input phosphor of an X-ray image intensifier tube found in fluoroscopy equipment. Caesium iodide photocathodes are highly efficient at extreme ultraviolet wavelengths.
Caesium (55Cs) has 41 known isotopes, the atomic masses of these isotopes range from 112 to 152. Only one isotope, 133Cs, is stable. The longest-lived radioisotopes are 135Cs with a half-life of 1.33 million years, 137
Cs
with a half-life of 30.1671 years and 134Cs with a half-life of 2.0652 years. All other isotopes have half-lives less than 2 weeks, most under an hour.
Caesium perchlorate or cesium perchlorate (CsClO4), is a perchlorate of caesium. It forms white crystals, which are sparingly soluble in cold water and ethanol. It dissolves more easily in hot water.
Caesium-137, cesium-137 (US), or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclear weapons. Trace quantities also originate from spontaneous fission of uranium-238. It is among the most problematic of the short-to-medium-lifetime fission products. Caesium-137 has a relatively low boiling point of 671 °C (1,240 °F) and easily becomes volatile when released suddenly at high temperature, as in the case of the Chernobyl nuclear accident and with atomic explosions, and can travel very long distances in the air. After being deposited onto the soil as radioactive fallout, it moves and spreads easily in the environment because of the high water solubility of caesium's most common chemical compounds, which are salts. Caesium-137 was discovered by Glenn T. Seaborg and Margaret Melhase.
Rubidium chloride is the chemical compound with the formula RbCl. This alkali metal halide salt is composed of rubidium and chlorine, and finds diverse uses ranging from electrochemistry to molecular biology.
Caesium chromate or cesium chromate is an inorganic compound with the formula Cs2CrO4. It is a yellow crystalline solid that is the caesium salt of chromic acid, and it crystallises in the orthorhombic system.
Thallium(I) chloride, also known as thallous chloride, is a chemical compound with the formula TlCl. This colourless salt is an intermediate in the isolation of thallium from its ores. Typically, an acidic solution of thallium(I) sulfate is treated with hydrochloric acid to precipitate insoluble thallium(I) chloride. This solid crystallizes in the caesium chloride motif.
Thallium(I) iodide is a chemical compound with the formula . It is unusual in being one of the few water-insoluble metal iodides, along with , , , , and .
Caesium bromide or cesium bromide is an ionic compound of caesium and bromine with the chemical formula CsBr. It is a white or transparent solid with melting point at 636 °C that readily dissolves in water. Its bulk crystals have the cubic CsCl structure, but the structure changes to the rocksalt type in nanometer-thin film grown on mica, LiF, KBr or NaCl substrates.
Caesium hydride or cesium hydride is an inorganic compound of caesium and hydrogen with the chemical formula CsH. It is an alkali metal hydride. It was the first substance to be created by light-induced particle formation in metal vapor, and showed promise in early studies of an ion propulsion system using caesium. It is the most reactive stable alkaline metal hydride of all. It is a powerful superbase and reacts with water extremely vigorously.
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