CN101850995B - Process for preparing 5-20mm high-purity polycrystalline magnesium fluoride by liquid crystallization method - Google Patents

Abstract

The invention discloses a process for preparing 5-20mm high-purity polycrystalline magnesium fluoride by a liquid crystallization method, which comprises the following steps: adding magnesium carbonate (Mg2CO3) into hydrofluoric acid (HF) to generate hydrated magnesium fluoride crystallite by fluoridation; and allowing the hydrated magnesium fluoride crystallite to be subjected to single crystal growth, then putting in a polycrystal generator to be subjected to polycrystalline growth, and finally putting in a cylindrical three-zone-temperature sintering furnace to be sintered so as to obtain the high-purity polycrystalline magnesium fluoride after cooling. The process of the invention adopts single crystal and polycrystalline growth to replace the steps of washing, drying, mechanical compaction and granulation in the existing process, does not need to add shielding gas and naturally forms the high-purity polycrystalline magnesium fluoride with extremely lower crystal water content and magnesium oxide content, so the pollution is reduced, the cost is reduced, the purity of the product is up to 99.99 percent, the transmittance of crystals is high, the collapse points are few and the input-output ratio is high during membrane plating.

Description

The technique of preparing 5-20 mm high-purity polycrystalline magnesium fluoride by liquid crystallization

Technical field

The present invention relates to the preparation technology of magnesium fluoride, specifically, is a kind of technique of preparing 5-20 mm high-purity polycrystalline magnesium fluoride by liquid crystallization.

Background technology

Magnesium fluoride is to use optical filming material the earliest, modal, excellent property, yet, difference on the material inside organization structures that cause owing to preparation process is different is the most at last to technique for vacuum coating, Film Optics performance (such as refractive index n) with collapse to count etc. and produce a very large impact.The technical process of present industrial preparation higher degree magnesium fluoride is first hydrofluoric acid and magnesiumcarbonate to be carried out chemosynthesis, then with the step of resultant through washing, filtration, drying, Mechanical Crushing, granulation, again at shielding gas (NH ₄HF ₂) condition that exists bends down vacuum sintering, can obtain content after the cooling and reach 99% hydration magnesium fluoride (MgF ₂X H ₂O).But above-mentioned technique also exists a lot of shortcomings: 1. crystal water content is higher in the product, and the magnesium fluoride crystal formation is little, pore is many, has the phenomenons such as specific refractory power departs from after venting, splash and the film forming during plated film; 2. drying process is weightless large, causes product proportion little, and single furnace output is low; 3. the magnesium fluoride particle is mechanical compaction gained but not Nature creating, and pressing process has dust to produce to pollute the environment and human body, and need to add a small amount of binding agent during compacting, will be cracked into powdery when long-term storage or the moisture absorption, and product is unstable; 4. in the process of rough vacuum dehydration, added shielding gas NH ₄HF ₂, the latter has pollution to environment, has increased simultaneously production cost; 5. the content of magnesium oxide (MgO) is higher in the product, has affected purity and the quality of product, makes the transmitance of magnesium fluoride crystal low, easily splashes during plated film, and generation is collapsed a little many.

The novel magnesium fluoride preparation technology of magnesium oxide impurity and crystal water content has to be developed in reduction cost, minimizing pollution, the minimizing product.

Summary of the invention

The object of the invention is to provide a kind of technique of preparing 5-20 mm high-purity polycrystalline magnesium fluoride by liquid crystallization, and its magnesium fluoride particle is that self-assembling formation but not mechanical compaction get, and preparation process need not to add shielding gas, not only reduces pollution but also reduce cost; Magnesium oxide impurity and crystal water content are extremely low in the magnesium fluoride product that makes, and product purity is high, produce during plated film to collapse a little to lack; Low and the proportion of the specific surface area of product increases, and input-output ratio improves.

Concrete technical scheme of the present invention is:

A kind of technique of preparing 5-20 mm high-purity polycrystalline magnesium fluoride by liquid crystallization adopts magnesiumcarbonate (Mg ₂CO ₃) the mode in the hydrofluoric acid (HF) of joining fluoridizes and generate hydration magnesium fluoride crystallite, then make first hydration magnesium fluoride crystallite carry out single crystal growing, move into and carry out polycrystalline growth in the polycrystalline maker, move into sintering in the vertical barrel type three-temperature-zone sintering oven at last again, namely obtain content after the cooling and be 99.99% high-purity polycrystalline magnesium fluoride.Concrete processing step is as follows:

(1) be first that 40% hydrofluoric acid adds in the reactor with concentration, add again magnesiumcarbonate (wherein content of magnesia 〉=41%), add hydrofluoric acid and magnesiumcarbonate mass ratio be 1: 1, the uniform stirring (reaction equation: Mg that reacts fully ₂CO ₃+ HF → MgF ₂XH ₂O+CO ₂+ H ₂O), generate hydration magnesium fluoride crystallite behind the reaction terminating, mother liquor is the hydrofluoric acid solution of PH=3～4 after the reaction;

(2) the hydration magnesium fluoride crystallite that generates is incubated 24 hours under 100 ℃～105 ℃ temperature, to carry out liquid single crystal growth, the magnesium fluoride single crystal of generating center particle diameter D50 〉=22 μ m;

(3) mother liquor (mother liquor can reuse) of sucking-off clarification moves into the polycrystalline growth device with the magnesium fluoride single crystal, and polycrystalline growth was carried out in insulation in 20 hours under 140 ℃～150 ℃ temperature, and generating particle diameter is the magnesium fluoride polycrystal of 5～20mm;

(4) with the magnesium fluoride polycrystal in the quartzy sintering oven of three warm areas of vertical barrel type under 500 ℃～550 ℃ temperature atmosphere sintering 24 hours;

(5) cooling is 24 hours, namely gets the high-purity polycrystalline magnesium fluoride that particle diameter is 5～20mm, its purity 〉=99.99%, crystal water content≤0.005%, content of magnesia≤0.001%.

In the existing technique, behind hydrofluoric acid and magnesiumcarbonate generation hydration magnesium fluoride crystallite, adopted and first hydration magnesium fluoride crystallite washed, under 150 ℃ temperature, carried out again dry mode, the crystal water content high (being about 0.5%) of the hydration magnesium fluoride crystallite that generates, pore is many, crystal formation is little, specific surface area is large, dry after weightlessness many (about 11%).And technique of the present invention replaces the liquid single crystal process of growth of step (2) and the polycrystalline growth process of step (3), namely under 100 ℃～105 ℃ temperature, be incubated 24 hours first and carry out the liquid single crystal growth, then without cleaning, directly polycrystalline growth was carried out in insulation in 20 hours under 140 ℃～150 ℃ temperature, the crystal water content low (≤0.005%) of the hydration magnesium fluoride crystallite that therefore generates, crystal formation large (being tetragonal body polycrystalline state structure), specific surface area is little, and in weightlessness after the polycrystalline growth only below 7%, obviously be less than dry rear about 11% weightlessness in the existing technique, product proportion improves, and single furnace output also improves.

In the existing technique, needing after the drying that hydration magnesium fluoride crystallite elder generation machinery is broken for the powder of particle diameter below 100 μ m, add again a small amount of binding agent powder is cold-pressed into sheet (being granulation), but the process of Mechanical Crushing has dust and produces, not only contaminate environment but also cause loss, in a single day binding agent makes moist or because long-term storage lost efficacy, then can cause product again to be cracked into powder, poor stability simultaneously.And technique of the present invention is by the magnesium fluoride single crystal being moved into the polycrystalline growth device, insulation was carried out polycrystalline growth in 20 hours and is directly generated the magnesium fluoride polycrystal that particle diameter is 5～20mm under 140 ℃～150 ℃ temperature, be that particle is self-assembling formation, not only need not Mechanical Crushing but also needn't add binding agent, environmentally safe, product is lossless and good stability, has saved simultaneously artificial and other costs.

In the existing technique, for reducing magnesian generation, the rough vacuum sintering process after the granulation need to add the shielding gas NH that environment is had pollution ₄HF ₂Only pipe so, also have crystal water content high (about 0.5%) in the product, pore is many, specific surface area is large, the problem that oxidation-resistance is poor, still very easily generate magnesium oxide (about 0.5%), the phenomenons such as the crystal transmitance is low after venting when causing plated film, splash, the film forming, specific refractory power departs from, generation is collapsed a little many during plated film.And technique of the present invention need not to add shielding gas, has not only reduced cost but also non-environmental-pollution; The even internal structure that in monocrystalline and polycrystalline growth process, forms simultaneously, can farthest get rid of pore and remaining crystal water (≤0.005%) for the impact of coating process, on the other hand, because sintering condition is abundant, the content of magnesia extremely low (≤0.001%) that generates, not splash when therefore having plated film, the pre-molten time is short and film refractive index departs from the advantages such as little.

In sum, the technique of preparing 5-20 mm high-purity polycrystalline magnesium fluoride by liquid crystallization of the present invention has the following advantages: 1. adopt monocrystalline and polycrystalline growth process to replace and wash first dry again mode in the existing technique, greatly reduced the content of crystal water in the product; 2. by monocrystalline and the complete tetragonal body crystal formation of polycrystalline growth process Nature creating, the step that need not carry out Mechanical Crushing and granulation, so no dust pollution, product-free loss, must not add binding agent, in protection of the environment, reduced production cost; 3. sintering process need not add the shielding gas that environment is had pollution, has not only reduced cost but also protection of the environment; 4. sintering condition is abundant, generate magnesian may be extremely low.5～20mm high-purity polycrystalline magnesium fluoride of preparing with technique of the present invention has the following advantages: 1. crystal formation is Nature creating, and particle is large and internal structure is even, and remaining crystal water content is few, is difficult for during plated film splashing; 2. specific surface area is little, than great, and the total significant quantity of crystal in the stove in the time of can guaranteeing the crystal growth, single pass yield is high, is 2 times that existing technique is prepared magnesium fluoride output; 3. the crystal formation internal structure of Nature creating is uniform and stable, and anti-adsorption conditions is good, can long storage time, be difficult for oxidation and deliquescence; 4. crystal formation is large, and specific surface area is little, thus little with the surface in contact of air, can be in atmosphere direct sintering and magnesium oxide generates few; 5. purity high (〉=99.99%), impure few (remaining crystal water≤0.005%, magnesium oxide≤0.001%), the crystal transmitance is high, and what produce during plated film collapses a little less, and yield rate is high; 6. product particle is evenly distributed, and particle diameter can directly be supplied with the player whose turn comes next and use between 5～20mm, is widely used in the fields such as magnesium fluoride monocrystal material, Coating Materials, anti-fake material, sensitive materials, far-infrared material.

Embodiment

Below further describe the present invention by embodiment, as known by the technical knowledge, the present invention also can describe by other the scheme that does not break away from the technology of the present invention feature, thus all within the scope of the present invention or the change that is equal in the scope of the invention all be included in the invention.

Embodiment 1

The high-purity polycrystalline magnesium fluoride for preparing 5～20mm according to following technique:

(1) be first that 40% hydrofluoric acid adds in the reactor with concentration, add again magnesiumcarbonate (wherein content of magnesia 〉=41%), add hydrofluoric acid and magnesiumcarbonate mass ratio be 1: 1, the uniform stirring (reaction equation: Mg that reacts fully ₂CO ₃+ HF → MgF ₂XH ₂O+CO ₂+ H ₂O), generate hydration magnesium fluoride crystallite behind the reaction terminating, mother liquor is the hydrofluoric acid solution of PH=3～4 after the reaction;

(2) the hydration magnesium fluoride crystallite that generates is incubated 24 hours under 100 ℃～105 ℃ temperature, to carry out liquid single crystal growth, the magnesium fluoride single crystal of generating center particle diameter D50 〉=22 μ m;

(3) (mother liquor can reuse the mother liquor of sucking-off clarification, and the magnesium fluoride single crystal is moved into the polycrystalline growth device, and polycrystalline growth was carried out in insulation in 20 hours under 140 ℃～150 ℃ temperature, and generating particle diameter is the magnesium fluoride polycrystal of 5～20mm;

(4) with the magnesium fluoride polycrystal in the quartzy sintering oven of three warm areas of vertical barrel type under 500 ℃～550 ℃ temperature atmosphere sintering 24 hours;

(5) cooling is 24 hours, namely gets the high-purity polycrystalline magnesium fluoride that particle diameter is 5～20mm, its purity 〉=99.99%, crystal water content≤0.005%, content of magnesia≤0.001%.

Claims (1)

1. the technique of a preparing 5-20 mm high-purity polycrystalline magnesium fluoride by liquid crystallization is characterized in that, comprises the steps:

(1) be first that 40% hydrofluoric acid adds in the reactor with concentration, add again magnesiumcarbonate, content of magnesia 〉=41% wherein, add hydrofluoric acid and magnesiumcarbonate mass ratio be 1: 1, uniform stirring reacts fully, reaction equation: Mg ₂CO ₃+ HF → MgF ₂XH ₂O+CO ₂+ H ₂O generates hydration magnesium fluoride crystallite behind the reaction terminating, mother liquor is the hydrofluoric acid solution of pH=3～4 after the reaction;

(2) the hydration magnesium fluoride crystallite that generates is incubated 24 hours under 100 ℃～105 ℃ temperature, to carry out liquid single crystal growth, the magnesium fluoride single crystal of generating center particle diameter D50 〉=22 μ m;

(3) mother liquor of sucking-off clarification, described mother liquor can reuse, and the magnesium fluoride single crystal is moved into the polycrystalline growth device, and polycrystalline growth was carried out in insulation in 20 hours under 140 ℃～150 ℃ temperature, and generating particle diameter is the magnesium fluoride polycrystal of 5～20mm;

(4) with the magnesium fluoride polycrystal in the quartzy sintering oven of three warm areas of vertical barrel type under 500 ℃～550 ℃ temperature sintering 24 hours in the atmosphere;

(5) cooling is 24 hours, namely gets the high-purity polycrystalline magnesium fluoride that particle diameter is 5～20mm, its purity 〉=99.99%, crystal water content≤0.005%, content of magnesia≤0.001%.