7789-78-8 Usage
Alkaline earth metal
Calcium hydride is an alkaline earth metal hydride, although it is not stable than lithium hydride, but stable than other alkali metal borohydride. Chemical formula is CaH2. Molecular weight is 42.10. It is white monoclinic crystals or lumps. Industrial is gray. When exposed to moist air hydrogen will release, and calcium hydroxide will leave. The proportion of is 1.9. The decomposition tempreture is about 600℃. Melting point is 816℃ (hydrogen). When meet water, carboxylic acids, lower alcohols, it can decompose to generate hydrogen. The decomposition When tempreture get 600℃, it begins to decompose. At room temperature, it can not react with dry oxygen, nitrogen, chlorine, but can react at high temperatures. This reaction can generate CaO, Ca3N2, CaCl2, respectively. At room temperature, it can react with water and the product is calcium hydroxide and hydrogen.
Calcium hydride has a strong reduction, and can make the metal liberate from the metal oxides, metal chlorides, for example,
2CaH2 + MO2→ 2CaO+2H2 + M (metal).
Calcium hydride can be used for strong reducing agent commonly, as well as used to make hydrogen when work in the field.
Preparation: The calcium metal is charged in the wok, and it can react with hydrogen to generate calcium hydride when temperature get about 300℃ with electric or oil.
Ca + H2 → CaH2 + 214kJ·mol-1
Or in a stream of hydrogen, magnesium can reduce calcium oxide reduction to get calcium hydride, due to the separation of calcium oxide is difficult, high purity calcium hydride products can not obtain.
CaO + Mg + H2 → CaH2 + MgO
Purpose: When be heated to 600 ~1000 ℃, the oxide of zirconium, niobium, uranium and chromium can be reduced to prepare powder of these metals, so calcium hydride can be used in powder metallurgy. It can be insoluble in ether, can react with ethanol to produce hydrogen and ethanol calcium.
Hydrogen can be obtained by the reaction of water, one gram of the product in the water can release one liter of hydrogen, so it is often used as a portable source of hydrogen. In addition, calcium hydride is also used dehydration of organic compounds, hydrogenation, condensation agent; or as a drying agent, the drying effect is better than sodium, phosphorus pentoxide.
The above information is edited by the lookchem of Wang Xiaodong.
Toxicity
When meet moisture, water or acids, hydrogen can be released and can cause combustion, it can react with oxidants and metal oxides violent. Dust can cause strong stimulating effect for the eyes, nose, skin and respiratory system. The product of calcium hydroxide is strong corrosive when meet moisture.
Other reference lithium hydride.
Chemical Properties
It is colorless orthorhombic crystallization; gray goods, orthorhombic or powder. It is sensitive to moisture. The relative density is 1.90. Melting point is 816℃ (in hydrogen). It can decompose to Ca and H2 at 600℃. With water it can decompose and release hydrogen at the same time, it can also generate hydrogen and ethanol calcium when react with ethanol. The reduction of metal oxides is more strongly than sodium hydride or lithium hydride.
Uses
Different sources of media describe the Uses of 7789-78-8 differently. You can refer to the following data:
1. It can be used as reducing agent and a condensing agent in organic synthesis, and desiccant in producing hydrogen material.
2. Calcium hydride is used as an efficient drying agent for aprotic base-stable solvents like ethers and tertiary amines. It is a useful dehydrating agent in a synthesis of aldehyde enamines in high yield and purity.
3. Calcium hydride is a relatively mild desiccant. It is
safer than the more reactive agents such as sodium
metal. Calcium hydride is widely used as a desiccant
for basic solvents such as amines and pyridine in
organic syntheses. It is also used to pre-dry solvents
prior to the use of a more reactive desiccant. The
compound has, however, been widely used for decades
as a safe and convenient means to inflate weather
balloons. Likewise, it is regularly used in laboratories
to produce small quantities of highly pure hydrogen
for experiments.
4. To prepare rare metals by reduction of their oxides; as a drying agent for liquids and gases; to generate hydrogen: 1 g of calcium hydride in water liberates 1 liter of hydrogen at STP; in organic syntheses.
Production method
The purity of about 99.5% purified calcium is put into the iron plate, then put on the central quartz reaction tube, at both ends of the quartz reaction tubes are installed into the trachea and a tube with rubber stopper, the purification of hydrogen go through from the intake pipe, the trachea is contact with by mineral oil bubbler and fume hood. The reaction tubes is electric heating.
At beginning, raction air in the system is replaced by large purified hydrogen, then heated by an electric furnace. The reaction starts from about 200℃, further heated to 250~300℃, then a flow rate of 0.6 m 1/ min of hydrogen gas introduce into the reaction, the reaction needs about 2h to complete, the product of calcium hydride is porous white crystalline powder, the purity of calcium hydride is about 99%.
Ca + H2 → CaH2
Category
Explosive substances.
Explosive hazardous characteristics
When the reaction was heated with tetrahydrofuran, it can cause explosion; when mix with potassium chlorate, hypochlorite, bromate, perchlorate, it is heat sensitive, friction sensitive and explosive.
Storage Characteristics
Treasury need ventilation low temperature drying; shockproof, moistureproof, against high temperature.
Extinguishing agent
Foam, carbon dioxide, dry powder.
Description
Calcium hydride is a gray powder (white if pure,
which is rare). It reacts vigorously with water liberating
H2 gas. CaH2 is thus used as a drying agent,
i.e. a desiccant. It is prepared directly from the metal
or by reacting CaCO3 with hydrogen at elevated temperatures. The overall reaction is shown as
follows:
CaCO3＋heat＋H2→CaH2＋H2O＋CO2
CaH2 is a saline hydride, meaning that its structure is
salt-like. The alkali metals and the alkaline earth metals
all form saline hydrides. These species are insoluble in
all solvents with which they do not react because they
have extended structures. CaH2 crystallizes in the
PbCl2 structural pattern.
The reaction of CaH2 with water can be represented
as follows:
CaH2＋2H2O0Ca(OH)2＋2H2
The two hydrolysis products, H2, a gas, and Ca(OH)2,
an aqueous mixture of solid plus liquid (i.e. a slurry), are readily separated from the solvent by distillation, filtration, or decantation.
Physical properties
Grayish orthorhombic crystal or powder; stable at ambient temperature; density 1.70 g/cm3; melts at 816°C; reacts with water and alcohol.
Preparation
Calcium hydride may be prepared from its elements by direct combination of calcium and hydrogen at 300 to 400°C. It also can be made by heating calcium chloride with hydrogen in the presence of sodium metal:
CaCl2 + H2 + 2Na → CaH2 + NaCl
Alternatively, calcium hydride may be prepared by the reduction of calcium oxide with magnesium in the presence of hydrogen:
CaO + Mg + H2 → CaH2 + MgO.
Production Methods
Calcium hydride ignites in air on heating and can explode violently if mixed and rubbed with a strong oxidizing agent such as perchlorate or bromate. Contact with water produces hydrogen which can create a fire hazard in a confined space.
General Description
Grayish-colored lump or crystalline solid. Irritating to skin and eyes. Used to make other chemicals.
Air & Water Reactions
Ignites in air or reacts violently, sometimes explosively, with air of high humidity [Bretherick 1979 p. 107]. Reacts exothermically with water to generate flammable hydrogen gas and calcium hydroxide, a base. [Merck, 11th ed. 1989].
Reactivity Profile
When silver fluoride is ground with CALCIUM HYDRIDE the mass becomes incandescent [Mellor 3:389 1946-47]. Heating the hydride strongly with chlorine, bromine, or iodine leads to incandescence. Mixtures of the hydride with various bromates, i.e. barium bromate; chlorates, i.e. barium chlorate, and perchlorates, i.e. potassium perchlorate; explode on grinding, [Mellor, 1946, vol. 3, 651]. CaH2 reacts incandescently with AgF if subject to friction. (Mellor, 1941, Vol. 3, 389, 651).
Hazard
Evolves highly flammable hydrogen when
wet; solid product is slaked lime. Irritating to skin.
Flammability and Explosibility
Notclassified
Check Digit Verification of cas no
The CAS Registry Mumber 7789-78-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,7,8 and 9 respectively; the second part has 2 digits, 7 and 8 respectively.
Calculate Digit Verification of CAS Registry Number 7789-78:
(6*7)+(5*7)+(4*8)+(3*9)+(2*7)+(1*8)=158
158 % 10 = 8
So 7789-78-8 is a valid CAS Registry Number.
InChI:InChI=1/Ca.2H/rCaH2/h1H2
7789-78-8Relevant articles and documents
Structural Distortion in Perovskite Type KCaH3–xFx (0.54 ≤ x ≤ 3)
Kohlmann, Holger,Pflug, Christian
, p. 175 - 179 (2020)
Representatives of the solid solution series KCaH3–xFx were synthesized by solid state reactions from binary metal hydrides and fluorides. Crystal structures were analyzed by Rietveld refinement based on X-ray powder diffraction. The degree of substitution was determined by refinement of site occupancy factors as well as elemental analysis for hydrogen. Three sections of x in KCaH3–xFx can be distinguished. For x 3 and the solid solution starts only at x = 0.54. The tetragonal SrTiO3 type structure with partial ordering of hydrogen and fluorine atoms is found for 0.54 ≤ x ≤ 1.7. Both anion positions show mixed occupation with some preference of hydrogen atoms for 8h and fluorine atoms for 4a sites (I4/mcm, SrTiO3 type). For fluorine-rich compounds a solid solution with orthorhombic GdFeO3 type structure (Pnma) and a perfectly statistical distribution of hydrogen and fluorine atoms is found (1.8 ≤ x ≤ 3). Interatomic distances resulting from the structure refinements are in the range of typical K–H, K–F, Ca–H, and Ca–F distances for mainly ionic compounds.
Synthesis of high-purity calcium hydride
Bulanov,Troshin,Balabanov
, p. 875 - 877 (2004)
A procedure for synthesizing high-purity calcium hydride in high yield was suggested. The admixture composition of the resulting CaH2 was determined by laser mass spectrometry.
X-ray and neutron powder diffraction study of the order-disorder transition in Eu2IrH5 and the mixed crystal compounds Eu2-xAxIrH5 (A = Ca, Sr; x = 1.0, 1.5)
Kohlmann,Moyer Jr.,Hansen,Yvon
, p. 35 - 43 (2003)
The title compounds and their deuterides have been prepared by solid-state and solid-gas reactions from the elements and investigated by X-ray and neutron powder diffraction as a function of temperature. At room temperature they crystallize with an anion-deficient cubic K2PtCl6-type structure (space group Fm3m) in which five hydrogen (deuterium) atoms surround iridium randomly on six octahedral sites with average bond distances of Ir-D=169-171pm. At low temperature they undergo a tetragonal deformation (space group I4/mmm) to the partially ordered Sr2IrD5 (T=4.2K)-type structure in which four hydrogen (deuterium) atoms occupy planar sites with full occupancy (Ir-D=166-170pm) and two hydrogen (deuterium) atoms axial sites (Ir-D=174-181pm) with ～50% occupancy, i.e., the data are consistent with a mixture of square-pyramidal [IrD5]4- complexes pointing in two opposite directions. The transitions occur at ～240K (Eu0.5Ca1.5IrD5, Eu0.5Sr1.5IrD5), ～210K (EuSrIrD5), ～200K (EuCaIrD5, Eu2IrD5), and are presumably of first order.
Johnson, W. C.,Stubbs, M. F.,Sidwell, A. E.,Pechukas, A.
, p. 318 - 329 (1939)
Synthesis and characterization of a new ternary imide-Li 2Ca(NH)2
Wu, Guotao,Xiong, Zhitao,Liu, Tao,Liu, Yongfeng,Hu, Jianjiang,Chen, Ping,Feng, Yuanping,Wee, Andrew T. S.
, p. 517 - 521 (2007)
The ternary imide Li2Ca(NH)2 was successfully synthesized by dehydrogenating a mixture of LiNH2 and CaH2 at a molar ratio of 2:1 in a stream of purified argon at 300°C. A powder X-ray diffraction measurement revealed that Li2Ca(NH)2 was of the trigonal anti-La2O3 structure (space group P3m1) with lattice constants of a = 3.5664(3)A and c = 5.9540(8) A. Ca occupied the 1b site (0, 0, 1/2), Li occupied the 2d site (1/3, 2/3, 0.8841(22)), and N occupied the 2d site (1/3, 2/3, 0.2565(15)). Nuclear magnetic resonance and X-ray absorption fine structure analyses demonstrated that each Li ion was coordinated with four imide ions and each Ca ion was coordinated with six imide ions.
Synthesis and Photoluminescence Properties of Rare-Earth-Activated Sr3- xAxAlO4H (A = Ca, Ba; x = 0, 1): New Members of Aluminate Oxyhydrides
Fujii, Kotaro,Matsuishi, Satoru,Murakami, Taito,Wu, Tong,Yashima, Masatomo
, p. 15384 - 15393 (2020)
A series of aluminate-based oxyhydrides, Sr3-xAxAlO4H (A = Ca, Ba; x = 0, 1), has been synthesized by high-temperature reaction of oxide and hydride precursors under a H2 atmosphere. Their crystal structures determined via X-ray and neutron powder diffraction are isostructural with tetragonal Sr3AlO4F (space group I4/mcm), consisting of (Sr1-x/3Ax/3)2H layers and isolated AlO4 tetrahedra. Rietveld refinement based on the diffraction patterns and bond-valence-sum analysis show that Ba preferentially occupies the 10-coordinated Sr1 sites, while Ca strongly prefers to occupy the 8-coordinated Sr2 sites. Luminescence owing to the 4f-5d transition of Eu2+ or Ce3+ was observed from Eu- and Ce-doped samples, Sr3-x-yAxByAlO4H (A = Ca, Ba; B = Eu, Ce; x = 0, 1, y = 0.02), under excitation of near-ultraviolet light. Compared with its fluoride analogue, Sr3AlO4H:Ce3+ shows red shifts of both the excitation and emission bands, which is consistent with the reported hydride-based phosphors and can be explained by the covalency of the hydride ligands. The observed luminescence spectra can be decomposed into two sets of sub-bands corresponding to Ce3+ centers occupying Sr1 and Sr2 sites with distinctly different Stokes shifts (1.27 and 0.54 eV, respectively), as suggested by the results of constrained density functional theory (cDFT). The cDFT results also suggest that the large shift for Ce3+ at Sr1 is induced by large distortion of the coordinated structure with shortening of the H-Ce bond in the excited state. The current findings expand the class of oxyhydride materials and show the potential of hydride-based phosphors for optical applications.
Hydride and ammonia dispersion of metals
Fokin,Fokina,Tarasov
, p. 1536 - 1540 (2010)
Chemical (hydride and ammonia) dispergation of Group II-V metals induced by hydrogen and ammonia in the temperature range of 100-500°C at a pressure of 0.5-2.0 MPa was studied. The phase transitions in the M-H2 and M-NH3 systems were investigated and conditions for metal hydride and nitride formation as highly dispersed powders were identified. The characteristic features of metal dispergation under the action of hydrogen and ammonia and the degrees of dispersity of the obtained powders were compared.
Phase diagram study of CaBr2-CaHBr system
Vishnu Vardhan, Chilakapati Venkata,Ghosh, Sajal,Nagaraj, Subramaniam,Sridharan, Raghavachary,Gnanasekaran, Thiagarajan
, p. 127 - 131 (2013/06/04)
A study of binary, CaBr2-CaHBr system was carried out by differential thermal analysis (DTA), covering the composition range from 100 % CaBr2 to 100 % CaHBr between room temperature and 800 C. From DTA results, the contour of solidus
