Method for producing silicon hydrides. Chemical properties of silane Silicon hydride 4

Thermal transformations Monosilane is the most stable of the silanes. It begins to noticeably decompose into silicon and hydrogen at a temperature of -380 C. Above 500 C, decomposition proceeds at a very high speed. The hydrogen produced by the reaction inhibits decomposition; but the reaction does not stop. SiH4 = SiH2 + H2 SiH2 = Si + H2 At temperatures of 300 C and above, silane partially transforms into disilane And trisilane .. Monosilane ignites in air even at -180 C. Pure silane can be mixed in a certain proportion with air or oxygen at a temperature of 523 K and atmospheric pressure without explosion, if these mixtures lie beyond the upper and lower flammability limits. Under other conditions, especially in the presence of higher silanes, spontaneous combustion or explosion occurs.

During the combustion of monosilane, depending on the amount of oxygen and temperature, SiO, Si02, and silicic acid derivatives are obtained. Interaction with water For the first time, the interaction of silane with water and aqueous solutions of acids and alkalis was studied in the works. Pure water in quartz vessels does not decompose silane, but the slightest traces of alkali (the alkali extracted from glass by water is sufficient) accelerates the decomposition. Hydrolysis proceeds very quickly and leads to the elimination of all hydrogen associated with silicon: SiH4 + 2H20 = Si02 + 4H2 SiH4 + 2NaOH + H20 = Na2Si03 + 4H2 Hydrolysis of silane is also catalyzed by acids, but not as vigorously as by alkalis. Traces of moisture in combination with sufficiently active surfaces (for example, silane storage cylinders) react with excess monosilane almost completely to form siloxanes and hydrogen according to the equation: 2SiH4+H20 = (H3Si)20+2H2 Interaction with halogens, halogen derivatives and some other substances.

Halogens react with silane very vigorously, explosively. At low temperatures the reaction can be carried out at a controlled rate. Hydrogen chloride at atmospheric pressure in the absence of catalysts does not react with silane even at elevated temperatures. In the presence of catalysts, such as aluminum chloride, the reaction proceeds smoothly even at room temperature and leads to the formation of chlorine-substituted silanes. SiH4 + HCl = SiH3Cl + H2

SiH4 + 2HC1 = SiH2Cl2 + H2, etc. Silane reacts with phosphine at temperatures above 400 C to form SiH3PH2 and small amounts of SiH2(PH2)2, PH(SiH3)2 and Si2P; similar derivatives have been obtained with arsine. Interaction with organic compounds.

Silane does not interact with saturated hydrocarbons up to 600 C. Olefins, for example ethylene, add to silane at 460-510 C and atmospheric pressure. The main reaction products are mono- and dialkylsilanes. At 100 C the reaction occurs only under pressure. Under normal conditions, the interaction is observed upon irradiation with ultraviolet light. As a result of the thermal reaction of acetylene with silane, some vinylsilane is formed, but the main product of the reaction is ethynyldivinylsilane. The photochemical reaction produces mainly vinyl silane.

Currently, dozens of methods for producing monosilane are described in the literature. Not all of them found industrial development. On industrial methods for producing silane include: 1. Decomposition of metal silicides. 2. Reduction of silicon halides with metal hydrides. 3. Catalytic disproportionation of trialkoxysilane. 4. Catalytic disproportionation of trichlorosilane. Decomposition of metal silicides To obtain silane by the decomposition reaction of metal silicides, the most suitable starting material is magnesium silicide. The reaction equation for this method of producing silane is as follows: Mg2Si + 4H20 = SiH4 + 2Mg(OH)2 The total yield of silanes for silicon contained in the silicide is 25-30%. Of these, according to 37% - Sibi; 30% - Si2H6; 15% - Si3H8 and 10% - Si io; the rest are liquid silanes Si5Hi2 and Si6H14, as well as solid silanes (SiHi, . When magnesium silicide reacts with ammonium bromide in liquid ammonia, the yield of silanes increases to 70-80% (SiH4 - 97.2% and Si2H6 - 2.8% ): Mg2Si + 4NH4Br = 2MgBr2 + SiH4 + 4NH3. In silane, the presence of more than 20 impurity substances is indicated, including homologues of silane to Si8Hi8, light hydrocarbons, ammonia, benzene, toluene, hydrogen chloride. This method is. convenient, since the reaction occurs at ordinary temperatures and atmospheric pressure and with almost quantitative yield, the resulting silane is not contaminated with higher silanes.

Silicon hydrides, the so-called silanes, form a homologous series, similar to a number of saturated aliphatic hydrocarbons, but characterized by the instability of polysilane chains -Si-Si-. Silane SiH4 is the most stable first representative of the entire homologous series; Only at red heat does it decompose into silicon and hydrogen. Disilane Si2H6 decomposes when heated above 3000 into silane and a solid polymer; hexasilane Si6H14, which is the highest known member of the homologous series, slowly decomposes even at normal temperatures. All silanes have a characteristic odor and are highly toxic.

The main scheme for their preparation is the interaction of Mg2Si with hydrochloric acid. By fractionating the resulting mixture, the corresponding hydrogen silicas can be obtained. There are other methods for producing silanes. For example, the reduction of halosilanes with lithium hydride or lithium aluminum hydride, as well as the reduction of halosilanes with hydrogen in the presence of AICl3

SiH 3 CI + H2->SiH4 + HCI. In contrast to the very inert hydrocarbons, silanes are extremely reactive compounds. An important property that distinguishes silanes from hydrocarbons is the ease of hydrolysis of the Si-H bond in the presence of alkaline catalysts. Hydrolysis occurs very quickly, and this process can be depicted as follows:

SiH4 + 2H2O→SiO2 + 4H2

SiH4 + 2NaOH + H2O → Na2SiO3 + 4H2.

During the catalytic action of alkali on higher silanes, the Si-Si bond breaks

Н3Si-SiН3 + 6H2О→3SiО2 + 10H2.

They react with free halogens in a similar way to hydrocarbons, sequentially exchanging one hydrogen atom after another for the halogen. With hydrogen halides in the presence of a catalyst (AICl3), a similar, but not analogous in hydrocarbon chemistry, reaction occurs, the exchange of hydrogen for a halogen

SiН4 + HCI→H2 + SiН3СI.

Trichlorosilane SiH3CI can be obtained by direct synthesis from Si and HCI at elevated temperatures.

Silanes do not react with concentrated sulfuric acid.

Compounds containing it are used to protect metal.

Monosilane- a binary inorganic compound of silicon and hydrogen with the formula SiH4, a colorless gas with an unpleasant odor, spontaneously ignites in air, reacts with water, toxic

Silicon dioxide– a colorless crystalline substance with high strength and hardness. Formula SiO2.

Properties:

• melting point 1713 – 1728 °C
• interacts with basic oxides and alkalis (when heated)
• belongs to the group of acid oxides
• soluble in hydrofluoric acid
• is a glass-forming oxide (prone to forming a supercooled melt - glass)
• dielectric (does not conduct electric current)
• does not react with water
• durable

Application:

• production of glass, concrete products, ceramics, siliceous refractories, silicon, rubber, etc.
• electronics, radio electronics, ultrasonic devices
• Amorphous non-porous silica is used in the food industry (E551), pharmaceutical and parapharmaceutical industries.
• fiber optic cables

Preparation of silicon dioxide

You will need:

• liquid glass (sodium silicate);
• acid (sulfuric, hydrochloric or nitric);
• water;
• soda.

Pour sodium silicate into a glass and add acid.

When acid is added, a precipitate of silicon dioxide immediately begins to form. Add acid until a sufficient amount of silicon dioxide is formed.

In another glass, dilute a 5% soda solution and place the resulting precipitate there. This way we will get rid of the remaining acid.
Afterwards, the silicon dioxide must be rinsed several times with clean water to get rid of any remaining soda.

After washing, filter the sediment through a paper filter.

Magnesium silicide– inorganic binary compound of magnesium and silicon. Formula Mg2Si.

Properties:

• thermally stable
• melting point 1102 °C
• molar mass 76.7 g/mol
• density 1.988 g/cm3
• hydrolyzed by water
• decompose in acids

Application:

• production of silane gas

Preparation of magnesium silicide

You will need:

• silicon dioxide;
• magnesium (proshkoobrazny).

Grind silicon dioxide in a mortar.

Mix 4 g of silicon dioxide and 6 g of magnesium. If you have black magnesium powder, you need to grind it in a mortar with silicon dioxide.

Pour the mixture into a test tube mounted on a stand and heat it with a gas burner.
Important! All components must be well dried before heating! If even a small amount of moisture is present in the mixture, selanium will begin to be released during the reaction, which will subsequently ignite.

Under the influence of high temperature, magnesium silicide (a dark-colored substance) begins to form in the test tube.

Separate the parts of the test tube from the powder.

Silan– pyrophoric gas. Formula SiH4.

Properties:

• molar mass 32.12 g/mol
• gaseous state
• colorless
• poisonous
• ignites on contact with air
• easy to oxidize
• stable in neutral and acidic environments
• dissolves in gasoline, standard
• density 0.001342 g/cm3
• melting point – 185 °C
• boiling point – 112 °C
• decomposition temperature 500 °C

Application:

• in organic synthesis reactions (production of valuable organosilicon polymers, etc.)
• microelectronics
• obtaining ultra-pure polysilicon
• relationship between organic matrix and inorganic filler in composite dental materials

The invention can be used in the chemical and electronic industries. Silicon hydride - monosilane is obtained by reacting magnesium silicide with mineral acids. The preparation of magnesium silicide is carried out by thermal interaction of a mixture containing 1 wt. part of dispersed particles of silicon oxide, up to 10 wt. parts of silicon and from 3.5 to 4 wt. parts of lump fragments of magnesium, with continuous stirring. The particle size of silicon oxide does not exceed 3 mm, and the ratio of the size of silicon oxide particles and the size of lump fragments of magnesium is 1: (10-20). The interaction of the reacting components during the mixing process is carried out in the temperature range of 550-680°C. The proposed invention makes it possible to expand the raw material base for the production of monosilane and reduce the cost of the product. 2 salary f-ly.

The invention relates to the production of silicon hydrides, including high-purity monosilane, intended for the formation of semiconductor and dielectric layers, the synthesis of organosilicon compounds, and the thermal deposition (dissociation) of polycrystalline silicon.

There is a known method for producing silicon hydrides (monosilane) by catalytic disproportionation of trichlorosilane (German Patent No. 331165, dated 10/13/83), the essence of which is the catalytic hydrogenation (at a temperature of 400-500°C) of dispersed silicon and silicon tetrachloride according to the reaction:

Si+2H 2 +3SiCl 4 =4SiHCl 4

and subsequent dissociation of this compound according to the reaction:

4SiHCl 4 =SiH 4 +3SiCl 4

A significant disadvantage of this method is the presence of toxic chlorine, which is involved in all reactions, which sharply limits (for environmental reasons) the industrial development of this method.

There is a known method for the chloride-free production of silicon hydrides (Pat. No. RU 2151099, dated June 20, 2000, C01B 33/04), the technical essence of which lies in the thermal (at t - 450-600 ° C) interaction of dispersed quartzite with magnesium in a stoichiometric ratio , in the presence of aluminum salts, in a flow of atomic hydrogen, in a glow discharge. However, complete reduction of silicon dioxide to pure silicon by the magnesium-thermal method, with a stoichiometric mass ratio of SiO 2 and Mg, is difficult due to the high reaction rate and significant heat release (~92 kcal/mol), at which the temperature in the reaction zone reaches values ​​above 3000°C , with evaporation of reaction products, leading to an uncontrollable explosion. The introduction of an inert additive - aluminum salt, intended to compensate for the heat of reaction, leads to a decrease in the likelihood of direct contact of magnesium particles with all quartzite particles, which causes a local deviation of the interacting reagents from stoichiometry, with the formation of magnesium silicide (Mg 2 Si), the heat of formation of which is ~19 kcal/mol. The formation of this compound results in some of the silicon dioxide remaining unreduced. Thus, complete magnesium-thermal reduction of silicon dioxide according to the conditions given in the known technical solution is very difficult.

There is a known method for producing silicon hydrides, used by the Japanese company Komatsu MFG CO LTD (“Monosilane in the technology of semiconductor materials.” Review information, series “Organoelement compounds and their application,” NIIETKHIM, Chemical Industry, 1983). The technical essence of this method is that in the first stage, magnesium silicide is formed through a reaction carried out at a temperature of 500-600°C in a neutral environment:

Si+2Mg=Mg 2 Si+19 kcal/mol

In the second stage, magnesium silicide reacts with mineral acids or salts, releasing gaseous silicon hydrides, for example, through an acid hydrolysis reaction:

Mg 2 Si + 2HCl = MgCl 2 (L) + SiH 4 (G)

or acedolysis of magnesium silicide:

Mg 2 Si (T) + 4NH 4 Cl (T) = 2 MgCl 2 (T) + SiH 4 (G) + 6NH 3 (G)

This method is the closest in technical essence and achieved effect to the claimed technical solution and is adopted as a prototype.

A significant disadvantage of the prototype is that to obtain silicon that meets the properties applicable to its use in electronic or semiconductor technology (99.9999% purity), raw materials are used in the form of silicon with a purity of 98-99%, i.e. containing impurities. This significantly reduces the raw material base, i.e. excludes the possibility of using compounds other than silicon, for example quartzite (SiO 2) or silicic acid (H 2 SiO 3).

The purpose of the proposed technical solution is to expand the raw material supply of the process by creating the possibility of participating in the reaction to produce magnesium silicide (Mg 2 Si), silicon dioxide (SiO 2), widespread in nature, silica or quartzite, as well as silicic acid (H 2 SiO 3).

This technical result is achieved by introducing into the reaction for the production of magnesium silicide from silicon-containing compounds, including SiO 2 and H 2 SiO 3 , an additive that is inert with respect to the interacting components and does not introduce additional chemical elements into the overall reaction. Such an additive to the reaction

SiO 2 +2Mg=2MgO+Si+92 kcal/mol

is dispersed silicon. The addition of silicon is necessary to dissipate the heat generated during this reaction, without introducing additional chemical elements that can introduce “contaminants” into the final product.

To reduce heat generation during the simultaneous interaction of particles of silicon oxide (silicic acid) with magnesium, the latter is introduced into the reaction in the form of lump fragments, which prevents a complete volumetric reaction leading to an explosion, because Only those silicon dioxide particles that are in contact with the magnesium fragment participate in the reduction. To carry out a complete, volumetric reaction, the mixture of particles must be stirred to renew contacts of magnesium lump fragments with new, previously unreacted particles of silicon oxides. Mixing can be carried out, for example, in rotating or oscillating reactors. The stirring process, like the entire reaction process as a whole, is carried out until the complete disappearance (“eating”) of lump fragments of magnesium.

The masses of the reacting components must correspond to the ratio:

Up to 10:(3.5÷4.0), because the heat capacity of silicon in the temperature range 0-1000°C is equal to 3.58 cal/mol×deg, then to fully compensate for the thermal energy of 92 kcal/mol released during the stoichiometric, magnesium-thermal reaction of silicon dioxide reduction, an additional addition of up to 20 moles of pure dispersed silicon or up to 10 parts by weight (the mass of one mole of SiO 2 is ~ twice as much as a mole of Si). The mass of added silicon particles is ballast and does not participate in the final reaction of producing silicon hydrides when the mixture reacts with mineral acids and salts. This silicon is a technological recycled raw material of the proposed method for producing silanes.

The addition of 3.5-4 parts of magnesium is justified by the fact that 1.5-2 parts of magnesium are necessary for the reduction of silicon from its dioxide according to the reaction:

SiO 2 +2Mg=2MgO+Si,

the addition of two more parts of magnesium is necessary for the formation of magnesium silicide from reduced silicon according to the reaction Si+2Mg=Mg 2 Si.

The maximum size of silicon dioxide particles is 3 mm and the ratio of the sizes of the latter with the sizes of lump fragments of magnesium:

was determined experimentally, for reasons of minimizing the heat released during the reduction reaction, to optimize the time of the magnesium-thermal reaction. The interaction of magnesium with silicon dioxide particles larger than 3 mm leads to a local mini-explosion. The size of lump fragments of magnesium less than ten times the size of silicon dioxide also leads to a mini-explosion due to the large surface of interparticle interaction and insignificant heat absorption for the formation of magnesium silicide. A more than twenty-fold increase in the size of lump fragments of magnesium relative to silicon dioxide particles leads to an unreasonable increase in the total reaction time.

The temperature range for the magnesium silicide synthesis reaction of 550-680°C is justified by the fact that an increase in the total mass of the reacting components compared to the stoichiometric ratio leads to the need to increase the heating intensity, as well as the creation of the possibility of changing the aggregate state of magnesium fragments before melting. This leads to a reduction in the cost of the process by reducing the price of magnesium raw materials. The market price of magnesium castings is 80-90 rubles/kg, the price of dispersed magnesium (including magnesium shavings) is 400-600 rubles. kg. In a given temperature range, lump magnesium melts (t melt = 620°C) due to external heating and heat release and is evenly distributed in the reaction zone.

The analysis of the state of the art showed that the claimed set of essential features set out in the claims is unknown. This allows us to conclude that it meets the “novelty” criterion. To check whether the claimed invention meets the “inventive step” criterion, an additional search for known technical solutions was carried out in order to identify features that coincide with the features of the claimed technical solution that are distinctive from the prototype. It has been established that the claimed technical solution does not follow explicitly from the prior art. Therefore, the claimed invention meets the “inventive step” criterion. The essence of the invention is illustrated by an example of the practical implementation of the method.

Example of practical implementation

The proposed technical solution was specifically implemented in the production of silicon hydrides by acid hydrolysis of a mixture of silicon and magnesium silicide in hydrochloric acid:

A mixture of silicon and magnesium silicide was previously obtained by calcining the following components in a hydrogen environment:

Si+SiO 2 +4Mg=2MgO+Mg 2 Si+Si

(in the previous reaction the reaction of dissolution of magnesium oxide formed during the magnesium-thermal reduction of silicon dioxide according to the reaction is not shown). The particle size of silicon and silicon dioxide did not exceed 1 mm, and the size of magnesium fragments did not exceed 2.5 mm. The reaction was carried out at a temperature of 650°C in a rotary kiln with a nichrome heater. The furnace rotation speed was 5 rpm. The reaction charge sample included the following components: silicon dioxide 2 kg, dispersed silicon 20 kg, lump magnesium 8 kg. Calcination time 2 hours. As a result of the reaction carried out with the specified parameters, a mixture of Mg 2 Si and Si was obtained with a component ratio of 1:4. No residual silicon dioxide was detected in the reaction (in the residue after acid hydrolysis). The specified example of implementation confirms the compliance of the claimed method with the condition “inventive step”

1. A method for producing silicon hydride - monosilane from magnesium silicide, obtained by thermal interaction of dispersed silicon with active magnesium in an inert environment, followed by interaction of this compound with mineral acids, characterized in that the production of magnesium silicide is carried out by thermal interaction of a mixture containing 1 wt. .h. dispersed particles of silicon oxide, up to 10 parts by weight. silicon and from 3.5 to 4 parts by weight. lump fragments of magnesium, with continuous stirring.

2. The method according to claim 1, characterized in that the size of the silicon oxide particles does not exceed 3 mm, and the ratio of the sizes of silicon oxide particles to the size of lump fragments of magnesium is 1: (10-20).

3. The method according to claim 1, characterized in that the interaction of the reacting components during the mixing process is carried out in the temperature range of 550-680°C.

Similar patents:

The invention relates to a method for producing monosilane of high purity and low cost, suitable for the formation of thin semiconductor and dielectric layers, as well as poly- and monocrystalline silicon of high purity for various purposes (electronics, solar energy).

The invention relates to methods for separating mixtures of volatile substances in chemical technology processes and can be used to separate mixtures of chlorosilanes, hydrides, fluorides, organic products and other products to isolate the target product.

The invention relates to a method for producing high-purity monosilane, suitable for the formation of thin-film semiconductor products, as well as high-purity poly- and monocrystalline silicon for various purposes (semiconductor technology, solar energy).

The invention relates to a technology for producing silane for the production of highly pure semiconductor silicon used in power electronics, as well as silicon wafers for the production of ultra-large integrated circuits and for the formation of various silicon-containing layers and film coatings in microelectronics.

Other names: silane, silicon hydrogen, silicon hydride.

Monosilane is an inorganic compound with the chemical formula SiH 4. A colorless, highly reactive gas that is flammable in air.

Physical properties

Chemical properties and methods of preparation

Methods of obtaining:

• Reaction between silicon(IV) chloride and lithium tetrahydridealuminate.

Chemical properties:

• Starts to decompose above 400°C.

Storage

The gas can be stored in containers with lubricated taps at room temperature without decomposition for several months. Silane is practically insoluble in vacuum lubricant. However, it should be noted that taps sealed with silicone grease are difficult to open after standing for a long time. Significant quantities of silane should be stored in special steel cylinders with a special valve; The material suitable for the manufacture of cylinders is 40Mn alloy - 4 steel.

List of used literature

1. Volkov, A.I., Zharsky, I.M. Big chemical reference book / A.I. Volkov, I.M. Zharsky. - Mn.: Modern School, 2005. - 608 with ISBN 985-6751-04-7.
2. Hoffman W., Rüdorf W., Haas A., Schenk P. W., Huber F., Schmeisser M., Baudler M., Becher H.-J., Dönges E., Schmidbaur H., Ehrlich P., Seifert H. I. . Guide to inorganic synthesis: In 6 volumes. T.3. Per. With. German/Ed. G. Brouwer. - M.: Mir, 1985. - 392 p., ill. [With. 715-717]

3.1. Physical and chemical properties

Silicon tetrafluoride was discovered by Scheele in 1771. It is a colorless gas with a pungent irritating odor. Relative molecular weight – 104.08. Molar volume – 22.41 l/mol. Boiling point (sublimation) - -95˚C, melting point - -90.2˚C. Density in air under normal conditions is 3.6272, mass of 1 liter of gas is 4.69g.

Silicon tetrafluoride is extremely temperature resistant. Under normal conditions, it hardly reacts with heavy metals, their oxides and glass if they are completely dry; at elevated temperatures it is more reactive, especially towards alkali, alkaline earth and rare earth metals. When dissolved in water, silicon tetrafluoride undergoes hydrolytic decomposition:

SiF 4 +2H 2 O→SiO 2 +4HF.

It smokes in moist air because it easily reacts with water, giving hydrofluorosilicic acid:

3SiF 4 +(x+2)H 2 O→2H 2 SiF 6 +SiO 2 *xH 2 O.

Forms fluorosilicate with sodium fluoride:

SiF 4 +2NaF→Na 2 SiF 6.

Many reactions of silicofluoride with organic substances are of great interest. It forms adducts with acetone and aromatic amines. Reaction with the Grignard reagent leads to the formation of triorganofluorosilanes, which are more stable than the corresponding chlorosilanes:

SiF 4 +3RMgX→R 3 SiF+3MgFX.

3.2. Preparation and use of silicon tetrafluoride

In the laboratory, silicofluoride can be obtained by the reaction:

2CaF 2 +SiO 2 +2H 2 SO 4 (k)→SiF 4 +2CaSO 4 +2H 2 O.

The reaction is carried out by heating and the resulting gas is of high purity.

Silicon tetrafluoride has limited use and is not produced on an industrial scale. However, it is found in waste gases from the production of phosphate fertilizers and is considered the most promising source of fluorine. By treating these waste gases with water, the SiF 4 contained in them can be captured in the form of H 2 SiF 6 or Na 2 SiF 6 . They are beginning to be used as a source of fluorine in the synthesis of cryolite and aluminum trifluoride.

4. Silane

4.1. Physical and chemical properties of silane

Monosilane SiH 4 is a colorless gas that, when diluted, has a weak characteristic odor reminiscent of the smell of antimony hydrogen; in large concentrations it smells very unpleasant. Its relative molecular weight is 32.12; boiling point - -111.2˚C; its melting point is -184.6˚C. The mass of 1 liter of gas under normal conditions is 1.4469g. Air density – 1.12. The density of liquid silane at boiling point is 0.557 g/cm 3 ; at the melting point – 0.675 g/cm3.

In air, silane ignites explosively. When heated to 300 - 400˚C, it decomposes at high speed.

4.1.1. Thermal transformations

Monosilane is the most stable of the silanes. The hydrogen produced during decomposition inhibits the process of further decomposition, but the reaction does not stop. The silicon film deposited on the surface during the decomposition of silane is a silver-colored metallic mirror, which at low temperatures has a pronounced crystalline structure, and at higher temperatures it is amorphous.

In the presence of 1% arsine, the rate of silane decomposition increases.

At 470˚C, silane is partially converted to disilane, apparently through the formation of SiH 3 radicals. In the presence of ethylene at 450 - 500˚C, along with Si 2 H 6, Si 3 H 8 is formed. SiD 4 decomposes more slowly than SiH 4 .

4.1.2. Oxidation

Monosilane ignites in air even at -180˚C. When monosilane is carefully oxidized with oxygen, highly diluted with nitrogen, at a temperature of -110˚C, a white, sometimes brown, flaky precipitate is obtained, consisting mainly of prosiloxane (H 2 SiO) x.

When silane is burned, depending on the amount of oxygen and temperature, SiO, Si and other products are obtained. Thermodynamic calculations show that the amount of SiO increases with increasing temperature. Increasing the pressure helps reduce the formation of SiO.

4.1.3. Interaction with water and alcohols

Pure water in quartz vessels does not decompose silane, but the slightest traces of alkali accelerate the decomposition. Hydrolysis proceeds very quickly and leads to the elimination of all hydrogen associated with silicon:

SiH 4 +2H 2 O→SiO 2 +4H 2; SiH 4 +2NaOH+H 2 O→Na 2 SiO 3 +4H 2.

The hydrolysis of silane is also catalyzed by acids, but not as vigorously as by alkalis.

Alcohols, in the presence of alkali metal ions, react with silane to form orthosilicic acid esters Si(OR) 4 , along with greater or lesser amounts of HSi(OR) 3 and H 2 Si(OR) 2 .

4.1.4. Interaction with halogens, halogen derivatives and ammonia

Halogens react with silane very vigorously, explosively. At low temperatures the reaction can be carried out at a controlled rate.

Hydrogen chloride at atmospheric pressure in the absence of catalysts does not react with silane even at elevated temperatures. In the presence of catalysts, for example, aluminum chloride, the reaction proceeds smoothly even at room temperature and leads to the formation of chlorine-substituted silanes:

SiH 4 +HCl→SiH 3 Cl+H 2; SiH 4 +2HCl→SiH 2 Cl 2 +2H 2;

SiH 4 +3HCl→SiHCl 3 +3H 2; SiH 4 +4HCl→SiCl 4 +4H 2.

Hydrogen bromide reacts with silane more easily than hydrogen chloride. Hydrogen iodide reacts even more easily with silane.

Monosilane does not react with ammonia at ordinary temperatures, but in the presence of an amide the following reaction occurs:

SiH 4 +4NH 3 →1/x x +4H 2.

4.1.5. Interaction with organic compounds

The following reaction occurs with sodium tetramethoxyborate:

SiH 4 +NaB(OCH 3) 4 →NaBH 4 +Si(OCH 3) 4.

Silane interacts with diethylmagnesium in ether while splitting the ether:

SiH 4 +Mg(C 2 H 5) 2 +(C 2 H 5) 2 O→HMgOC 2 H 5.

4.2. Preparation and use of silane

4.2.1. Decomposition of metal silicides

To obtain silane using this method, magnesium silicide is most suitable: Mg 2 Si+4H 2 O→SiH 4 +2Mg(OH) 2.

Simultaneously with monosilane, higher silanes are obtained. The yield and relative amount of individual silanes depend on the conditions of preparation of magnesium silicide, in particular, on the temperature and time of fusion of the components. The maximum yield (~38%) is achieved if powdered silicon is fused with magnesium at 650˚C.

4.2.2. Disproportionation reactions of trialkoxysilanes

In industrial production, the reaction of hydrogen chloride with silicon produces trichlorosilane, which with alcohol gives triethoxysilane:

SiHCl 3 +3C 2 H 5 OH→SiH(OC 2 H 5) 3 +3HCl.

Disproportionation of the latter

4SiH(OC 2 H 5) 3 →SiH 4 +3Si(OC 2 H 5) 4

occurs in the presence of a catalyst - sodium metal.

4.2.3. Reduction of silicon halides with metal hydrides

This method is convenient since the reaction occurs at normal temperatures and atmospheric pressure. The resulting silane is not contaminated with higher silanes.

Reduction with lithium aluminum hydride is usually carried out in ethyl ether by adding silicon chloride to an ether suspension of aluminum hydride while cooling (~0˚):

SiCl 4 +LiAlH 4 →SiH 4 +LiCl+AlCl 3. Yield ~99%.

Calcium hydride begins to react with silicon fluoride to form silane at a temperature of ~250˚C:

2CaH 2 +SiF 4 →SiH 4 +2CaF 2. Yield 80 - 90%.

To increase the reaction surface, calcium hydride is ground into powder. The hydride is then loaded into the reactor. The reactor is evacuated and purged with hydrogen. Silicon fluoride is introduced into the reactor to a given pressure. The effluent silane is collected in traps cooled with liquid nitrogen. The process is unlimited in time. At the end of the reaction, the silane is transferred from the traps to a receiving cylinder and weighed.

4.2.4. Application

High-purity monoisotopic silane is used to produce polycrystalline silicon and coat quartz crucibles with a layer of silicon dioxide in order to grow monoisotopic silicon single crystals from them using the Czochralski method.

High purity silane is one of the main strategic materials of a modern industrialized state.

II. Experimental part

1. Diagram and technical description of the installation

The installation diagram is shown in the figure. Cylindrical reactors 1 and 2, made of stainless steel, are mounted vertically and placed in a resistive electric furnace. The reactors operate alternately. Switching of reactors into the flow system is carried out by valves 19 – 22, connection with the vacuum line by valves 17,18. The upper ends of both reactors are placed in a sealed plexiglass box with a gateway and a device for purging with inert gas.

During the process, the reactor used is connected to a system for forming a flow of gaseous reagent I and a system for receiving the gaseous target product II. The process temperature in the reactor is set and maintained by a temperature control system III. Temperature control in the reactor is carried out by temperature measurement system IV.

The system for generating a flow of gaseous reagent I consists of two identical branches operating in parallel and forming flows of silicon tetrafluoride and hydrogen. Each branch consists of a cylinder with a substance 24, 28, a gas pressure stabilizer (GPS) 25, 29, a leak valve 26, 30 and a gas flow regulator (RGR) 27, 31, connected by stainless steel tubes. The pressure at the outlet of the LDH is measured by pressure and vacuum gauges 32, 33. Through valves 2, 4, each branch is independently connected to the forevacuum line. After leaving the RRG, the streams of hydrogen and silicon tetrafluoride are mixed, forming a gaseous reagent. The latter is fed into the reactor through a line built into the bottom flange of the reactor. The pressure of the gas mixture at the outlet of the RRG is determined using pressure and vacuum gauge 34.

A mixture of the gaseous target product with hydrogen flows out of the reactor through a line mounted in the upper flange and enters the gaseous target product receiving system II. The pressure at the outlet of the reactor is determined by pressure-vacuum gauge 35. The gaseous target product receiving system II consists of three metal traps 36, cooled with liquid nitrogen and two receiving cylinders 37. The traps are used to separate the gaseous target product from the hydrogen flow by condensation (“freezing”) of the latter . As can be seen from the figure, the system of communications and taps 11-16 allows for various ways of including traps in the flow. The hydrogen exhaust stream is discharged through the rheometer 38 into the exhaust ventilation. After the process is completed, the target product is transferred from the traps into receiving cylinders, which subsequently serve for storage and transportation of the target product.

The pressure in the receiving system during overload is controlled by pressure-vacuum gauge 39. Through valves 3 and 5, the receiving system is connected to the fore-vacuum line.

The reactor is heated and the process temperature is maintained by temperature control system III. It consists of two control thermocouples placed at the ends of each of the reactors, a temperature control unit 40 and an amplifier 41, the output of which is connected to the reactor heating furnace.

Temperature control inside the reactor is carried out by temperature measurement system IV. It consists of six measuring thermocouples,

located along the axis of the reactor in a tube inserted into the reactor coaxially, a signal converter 42 and a personal computer. The temperature change during the process at the locations of each of the six thermocouples is displayed on the computer monitor.

The foreline line allows different parts of the installation to be connected to it independently. The pressure in the forevacuum line is recorded by pressure and vacuum gauge 44, rotameter 45 makes it possible to record even insignificant flows of residual gases.

2. Methodology of work on the installation

Initial state. The reactor is cleared of solid-phase reaction products; it contains air diluted with an inert gas - nitrogen. The top flange of the reactor has been removed. The box is closed and purged with nitrogen evaporating from the Dewar flask. All taps on the installation are closed. The silicon tetrafluoride line of the flow formation system I and the gas-phase target product receiving system II are evacuated.

Before loading the solid-phase reagent, the reactor is purged with hydrogen. To do this, open the tap on the hydrogen cylinder and set the pressure on the reducer to 1 atm. hut (control using pressure-vacuum gauge “N 2” - 33), open valves “leak” -30, 7, 20 (19), set the required flow at 33-35 divisions on RRG 31.

Cans of calcium hydride are placed through a lock into the box. After filling the reactor with hydrogen (~15 minutes), calcium hydride powder is poured into the reactor. During the filling process, it is necessary to lightly tap the reactor to achieve a more uniform filling of the reactor volume with the reagent. The required filling level is controlled with a special meter.

After finishing loading calcium hydride into the reactor, remove the box cover, install and bolt the upper flange of the reactor and open valves 22(21), 23, 9, 8. After the end of purging of the solid-phase reagent, valves 9, 8 are closed and the reactor is filled with hydrogen to excess pressure ~ 0.3 atm. The pressure is controlled using a pressure and vacuum gauge “SiH 4 +H 2” 35.

2.2. Starting the installation

The startup of the installation begins with heating the reactor. To do this, turn on the temperature controller, increase the reference voltage - the “task” - manually, first smoothly, then discretely to the specified value. Then the pumping of the system for forming a flow of silicon tetrafluoride and the system for receiving the gas-phase target product are turned on. To do this, open taps 4, 3, 6, 16, 14, 12.

Next, hydrogen is released into the traps using a vacuum line. For this purpose, close valves 4, 1, open valves on the hydrogen cylinder 28, on the reducer 29 and 2. The hydrogen pressure is monitored using a pressure and vacuum gauge “SiH 4” 39. In this case, the traps are cooled with liquid nitrogen.

In the process of filling the traps with hydrogen, the pressure in the reactor is reduced to atmospheric pressure, passing excess hydrogen into the traps. To do this, open valve 11. The pressure in the reactor is controlled using a pressure and vacuum gauge “SiH 4 + H 2” 35. When atmospheric pressure in the reactor is reached, valve 11 is closed.

When the hydrogen pressure in the traps reaches atmospheric pressure, valves 6, 2 are closed, valves 30, 20(19), 11, 8 are opened and the hydrogen flow is released through the reactor into the exhaust ventilation.

When the initial temperatures are reached at the first and second thermocouples from the bottom of the reactor (~100-105 o C and ~115-120 o C, respectively), a flow of silicon tetrafluoride is formed. To do this, open the tap of the cylinder with silicon tetrafluoride, the pressure at the outlet of the LDH rises to 1 atm., control using the pressure and vacuum gauge “SiF 4” 32. Next, open the “Leak SiF 4” 26 and the tap of the cylinder with silicon tetrafluoride completely. The high pressure gauge on the LDH shows the pressure of silicon tetrafluoride in the cylinder. Crane for SDH

gradually set to a position corresponding to an excess pressure at the outlet of ~0.9 atm. according to the pressure and vacuum gauge “SiF 4” 32, which corresponds to the flow rate reading on the RRG ~23-25%. In this case, the hydrogen flow decreases to ~26-28%. The given parameters determine the technological operating mode of the installation.

2.3. Progress of the silane synthesis process

In normal mode, the process proceeds stationary. Monitoring the progress of the process and recording possible deviations is carried out using the following instruments.

1. Pressure and vacuum gauge “N 2” 33 – carrier gas pressure at the inlet to the RRG. Mode ~1 atm.

2. Pressure and vacuum gauge “SiF 4” 32 – pressure of silicon tetrafluoride at the outlet of the LDH. Mode – 0.9 atm. hut

3. High pressure gauge on the SDH - rough control of silicon tetrafluoride flow.

4. Pressure and vacuum gauge “SiF 4 +H 2” 34 – pressure at the inlet to the reactor. Mode – 0.1-0.2 atm. hut

5. Pressure and vacuum gauge “SiH 4 +H 2” - pressure at the inlet to the traps. Atmospheric pressure mode.

6. Outlet rheometer – slight overpressure.

The flow indicator on the RRG is the proportion of the flow from the maximum under experimental conditions. Mode – H 2: 27-29%; SiF 4: 23-25%.

During the process, it is possible that condensate of gaseous reagents may block the flow area of ​​the first trap along the flow. This is recorded by an increase in pressure at the inlet to the traps, determined by a pressure-vacuum gauge “SiH 4 +H” 2 35 and a decrease in flow, determined by a rheometer 38. To restore the normal mode of the process, open valve 13, directing the flow of gaseous reaction products into the second trap. In this case, taps 11 and 12 are left open so that the condensation process continues in the first trap. Similar actions are taken when closing the second trap by opening valve 15.

2.4. Completion of the silane synthesis process

To complete the process, shut off the flow of silicon tetrafluoride using the valve on cylinder 24, and open the LDH valve completely. Then the hydrogen flow is increased to 40%, and purging is carried out for approximately 20 minutes.

Next, the reactors are pumped out through traps. To do this, close taps 8, 30 and open tap 3 and slowly tap 6. The pumping speed is controlled using a rheometer - the ball should not rise above 70 divisions. The pumping depth and its completion are determined using pressure and vacuum gauges "SiH 4 +H 2" 35 and "SiF 4" 32. After pumping is completed, turn off the heating of the reactor, close the tap on the SDH 25, the SiF 4 leak 26 and the taps 21 (22). The reactor is filled with hydrogen to a slight excess pressure (0.1-0.15 atm. g). After this, close valves 20 (19), “leak H 2” 30, and the valve on the hydrogen cylinder. The traps are pumped out for some more time (~5 min), then valves 11, 12, 14, 16, 5, 23 are closed.

2.5. Reloading the gaseous target product from traps into a receiving cylinder

Receiving cylinders 37 are pre-cooled with liquid nitrogen. Traps 36 are unloaded one by one, starting with the third one - closest to the receiving cylinders 37. Each trap is unloaded through the outlet line; if the cross section of the trap is blocked by condensate, then unloading is carried out simultaneously through the input and output lines. The method of unloading the gaseous product is as follows.

Open the tap on the receiving cylinder 37. The trap is heated with a stream of warm air. Heating begins from the top of the trap, then the heating zone is slowly moved down. The reloading speed is controlled by the pressure on the pressure and vacuum gauge “SiH 4” 39. If unloading is also carried out along the input line, then the pressure is also controlled by the pressure and vacuum gauge “SiH 4 + H 2” 35. After unloading of this trap is completed, they begin to unload the previous one along the line, repeating similarly all methodological actions described above. At the end of the overload of the gaseous target product, the valve on the receiving cylinder 37 is closed, the traps are pumped out to the forevacuum through valve 3. After the pumping of the traps is completed, valves 3, 6, 16 are closed.

2.6. Unloading the solid-phase reaction product from the reactor

To unload the solid-phase reaction product, excess hydrogen pressure is released from the reactor, the box at the upper end of the reactor is opened, and the upper flange is removed. Then, three bolts are unscrewed from the lower flange, a pin is inserted into one of the mounting holes, and nuts are screwed onto both ends. Next, a receiving vessel (3 liter glass jar) is placed under the lower end of the reactor so that the flange fits into the neck of the vessel. The fourth bolt is unscrewed and the flange gently slides down. Removal of solid-phase product powder is intensified by tapping a metal object on the reactor. The remaining powder of the solid-phase product is removed with a brush. Upon completion of unloading, the lower flange is installed in place, the box is closed and placed for purging with nitrogen gas evaporating from the Dewar vessel.

III. Discussion of results

The results obtained are displayed on a personal computer monitor and represent a system of graphs with pronounced maximums. Each curve corresponds to a specific measuring thermocouple; the maximum of the curve indicates that the reaction front has passed the junction of this thermocouple.

As can be seen from the figure, as a result of the exothermic effect of the reaction, the temperature in the reaction zone rises to ~280˚C. The further task is to reduce the maximum temperature, since an increase in temperature can lead to decomposition of the resulting silane and a decrease in its yield.

The synthesis process is interrupted when the reaction front passes the zone of the sixth thermocouple, since continuation of the synthesis process can lead to unreacted silicon tetrafluoride leaking through the reactor.

IV. List of sources used

Myshlyaeva, L.V., Krasnoshchekov, V.V. Analytical chemistry of silicon. – M.: Nauka, 1972. – 210 p.

Bezrukov, V.V., Guryanov, M.A., Kovalev, I.D., Ovchinnikov, D.K. Determination of gas-forming impurities in high-purity silicon using a tandem laser mass reflectron // High-purity substances and materials. Preparation, analysis, application: Abstract. report XII conference, Nizhny Novgorod, May 31 - June 3, 2004 / Ed. ak. G.G. Ninth, corresponding member. M.F. Churbanova. – Nizhny Novgorod: Publisher Yu.A. Nikolaev, 2004. – 368 p.

Zhigach, A.F., Stasinevich, D.S. Chemistry of hydrides. – L.: Chemistry, Leningrad branch, 1969. – 676 pp., with drawings.

Ishikawa, N., Kobayashi, E. Fluorine. Chemistry and application / Transl. from Japanese M.V. Pospelova / Ed. A.V. Fokina. – M.: Mir, 1982. – 280 p.

Rapoport, F.M., Ilyinskaya, A.A. Laboratory methods for obtaining pure gases. – M.: Goskhimizdat, 1963. – 420 p.

Bulanov, A.D., Troshin, O.Yu., Balabanov, V.V., Moiseev, A.N. Synthesis and deep purification of monoisotopic silane // High-purity substances and materials. Preparation, analysis, application: Abstract. report XII conference, Nizhny Novgorod, May 31 - June 3, 2004 / Ed. ak. G.G. Ninth, corresponding member. M.F. Churbanova. – Nizhny Novgorod: Publisher Yu.A. Nikolaev, 2004. – 368 p.

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