Method of growing lithium-magnesium molybdate monocrystals
SUBSTANCE: invention relates to the technology of growing lithium-magnesium molybdate Li2Mg2(MoO4)3 crystals. The method involves melting lithium-magnesium molybdate in a molten solvent, crystallising while cooling the melt and cooling the grown crystals, wherein the solvent used is lithium molybdate Li2MoO4 with molar ratio of lithium-magnesium molybdate to lithium molybdate Li2MoO4 of 2:3, respectively; crystallisation is carried out on an inoculating crystal revolving at a rate of 35 rpm, oriented on the  direction, rate of drawing rate of the inoculating crystal of 1-3 mm/day while simultaneously cooling the melt at a rate of 0.2-5 degrees/day and then separating the grown crystals from the melt and cooling at a rate of 30 degrees/hour.
EFFECT: method enables to obtain optically homogeneous lithium-magnesium molybdate crystals which do not contain inclusions, blocks and cracks.
The invention relates to the field of chemical technology, namely the growing of single crystals, and the receipt of large optically homogeneous crystals of lithium-magnesium molybdate Li2Mg2(MoO4)3.
A method of obtaining fine particles of a lithium-magnesium molybdate Li2Mg2(MoO4)3by spontaneous crystallization (Sebastian L., Y. Piffard, A.K. Shukla, F. Taulelle, Gopalakrishnan, J. Synthesis, structure and lithium-ion conductivity of Li2-2xMg2+x(MoO4)3and Li3M(MoO4)3(MIII=Cr, Fe), Journal of Materials Chemistry (2003), 13, 1797-1802). The crystals obtained from the melt of a mixture of Li2CO3, MgO Moo3and NH4F, with Li2CO3and NH4F take a 10% excess (by weight). The reaction is carried out at 750 for 18 hours and then gradually cooled down to room temperature (cooling rate is not specified). Get small crystals (0.17×0.045×0.045 mm
Lithium-magnesium molybdate, Li2Mg2(MoO4)3that melts with decomposition at 1060°C and therefore can not be obtained in the form of bulk homogeneous crystals conventional Czochralski method. A method of obtaining crystals of lithium-magnesium molybdate Li2Mg2(MoO4)3by spontaneous crystallization from the melt of a mixture of Li2Mo2O7and Li2Mg2(MoO4)3taken in the rate of 2:1 (Vgentoo, Pavlecov, "Synthesis of crystals of double molybdates lithium with divalent metals of Mg, Ni, Co and Zn", J. of neorganic. chemistry. 22 (1977) 1713-1715), selected as a prototype. Spontaneous crystallization of Li2Mg2(MoO4)3conducted by lowering the temperature of the solution-melt with the speed of 3-5 deg/HR in the temperature range from 1000 to 930 degrees. The size of the crystals in a length of 5-7 mm
These methods get small crystals unsuitable for practical application.
The objective of the invention is to increase the size of the crystals of lithium-magnesium molybdate, preserving their optical quality.
This object is achieved in that in the method of growing crystals of lithium-magnesium molybdate from the solution in the melt comprising a molten lithium-magnesium molybdate in the melt solvent, crystallization during cooling of the melt and cooling the grown crystals in the solvent used molybdate lithium Li2MoO4when the molar ratio of lithium and magnesium molybdate and lithium molybdate Li2Moo4equal to 2:3, respectively, crystallization lead to rotating a seed crystal at a speed of 35 rpm, oriented in the direction , the rate of withdrawal of the seed from 1 to 3 mm/day while cooling the melt at a speed ranging from 0.2 to 5 deg/day, and will follow them Department of the grown crystals from the melt and cooled at a speed of 30 deg/hour thus, pulling of the seed are with automatic weight control.
Distinctive features of the proposed method are:
as the solvent used molybdate lithium Li2MoO4,
- the ratio of the lithium-magnesium molybdate and lithium molybdate Li2MoO4,
rotation of the seed and its orientation in the direction ,
- speed drawing a dose from 1 to 3 mm/day,
the cooling rate of the melt from 0.2 to 5 deg/day,
- rotation starters with a speed of 35 rpm,
- cooling crystals with a speed of 30 deg/h
the process is carried out by automatic weight control.
The use of such parameters cultivation allows you to get large optically homogeneous single crystals of lithium-magnesium molybdate Li2Mg2(MoO4)3.
The molar ratio of the components of Li2Mg2(MoO4)3and Li2MoO4equal to 2:3. The choice of this molar ratio of the components of the system caused by the optimal modes of operation of the equipment and energy consumption.
The choice of lithium molybdate due to the fact that when using this solvent are more homogeneous, with no inclusions crystals (best quality).
Optimal conditions for crystal growth: the rate of extraction of seed from 1 to 3 mm/day obul who go to those the pulling of the seed crystal when the crystal is grown at a faster speed than 3 mm/day, does not match the speed stable homogeneous crystal growth under these conditions. The decrease in the rate of withdrawal is less than 1 mm/day is impractical because it leads to an increase in process time. The rotation of the seed crystal at a given speed (35 rpm) promotes uniform growth, thus avoiding the occurrence of defects in the crystal that affect its optical properties.
Cooling the melt at a speed ranging from 0.2 to 5 deg/day due to the fact that the decrease of the cooling rate is less than 0.2 deg/day at the beginning of the process leads to the decrease of mass crystallization rate, reduction of the sizes of the grown crystal and increase the process time. Increasing the cooling rate is above 5 deg/day in the end leads to the formation of concentration overcooling and, as a consequence, the capture of the solvent, the formation of blocks and other defects.
The orientation of the seed crystal in the direction  provides under these conditions the formation of the most homogeneous crystals compared to other crystallographic orientations.
Automatic weight control allows you to monitor the growth process all over crystal growth. The grown crystals is then gradually cooled, th is would not happen shrinkage, and the rate of cooling depends on their size.
In a platinum crucible with a diameter of 70 mm and a height of 120 mm was placed a mixture of compounds of Li2Mg2(MoO4)3and Li2MoO4synthesized in a known manner by means (solid phase synthesis) of Li2CO3, MgO Moo3while Li2Mg2(MoO4)3- 130,15 g and Li2MoO4- 62,57 g, or in the ratio 2:3, which corresponds to the concentration of the solution-melt 40 mol.%. The mixture is melted at 1000°C in air in a resistive furnace installation for growing crystals. For homogenizing the solution-melt is stirred platinum stirrer, the temperature was then reduced until the point of equilibrium crystal with a solution-melt for a given concentration of Li2Mg2(MoO4)3(994°C) and to the surface of the melt down of a rotating (35 rpm) of the seed crystal which is oriented in the direction .
After establishing the temperature at which there is visible growth of the seed, carry out the pulling of the seed at a rate of 1-3 mm/day, at the same time lower the temperature of the solution-melt with an initial velocity of 0.2 to 5 deg/day.
In the growth process by increasing the mass of the crystal speed pulling smoothly reduced to 1 mm/day, and a cooling rate of 5 deg/day in accordance with the schedule solubility crystal is s Li 2Mg2(MoO4)3in the melt Li2MoO4.
30 days grow the single crystal of lithium-magnesium molybdate weighing 80 g dimensions: length (cone + cylinder) to 45 mm and diameter up to 25 mm optical quality.
At the end of the process of growing the single crystal is separated from the solution-melt and cooled to room temperature at a speed of 30 deg/hour.
The optical quality of the grown crystals was determined visually under a microscope. In a crystal with inclusions of other phases not identified blocks and other defects.
Thus, the proposed method allows to obtain optically homogeneous crystals of lithium-magnesium molybdate, Li2Mg2(MoO4)3not containing inclusions, blocks and cracks with dimensions 25×45 mm, sufficient to study the physical properties and practical use.
1. The method of growing crystals of lithium-magnesium molybdate from the solution in the melt comprising a molten lithium-magnesium molybdate in the melt solvent, crystallization during cooling of the melt and cooling the grown crystals, characterized in that the solvent used molybdate lithium Li2MoO4when the molar ratio of lithium and magnesium molybdate and lithium molybdate Li2MoO4equal to 2:3, respectively, lead to crystallization of rotations is muusa the seed to a speed of 35 rpm, oriented in the direction , the rate of withdrawal of the seed from 1 to 3 mm/day while cooling the melt at a speed ranging from 0.2 to 5 deg/day and the subsequent separation of the grown crystals from the melt and cooled at a speed of 30 deg/h
2. The method according to claim 1, characterized in that the pulling of the seed are with automatic weight control.
FIELD: electrical engineering.
SUBSTANCE: according to the method, charge stock containing a gallium source and flux components is heated and maintained at the specified temperature or, alternatively, heated and slowly cooled down from the specified temperature inside a container, with a temperature gradient maintained between the upper and the lower parts of the container under a nitrogen-containing gas pressure. The flux, by way of core components, contains cyanides or cyanamides or dicyanamides of alkaline and/or alkaline-earth metals and modifying additives enhancing gallium nitride solubility and/or increasing growth rate and/or enabling control of physical properties of crystals obtained.
EFFECT: reduced rate of corrosion of the latter, improved quality of monocrystals obtained.
16 cl, 2 tbl
SUBSTANCE: method involves dissolving the starting mixture, homogenisation thereof, placing a revolving single-crystal seed into the solution and growing a crystal, wherein the starting mixture contains 40 wt % beryllium aluminate with a chromium oxide additive in amount of 1-60 wt % of a solvent which consists of 95-98 wt % lead oxide and 2-5 wt % boron oxide, and the crystal is grown at temperature of 1250°C, axial temperature gradient of 2-20°C, drawing rate of up to 5 mm/day and rotational speed of up to 10 rpm.
EFFECT: obtaining bulk monocrystals of alexandrite of optical quality with low dislocation density.
SUBSTANCE: invention refers to process of production of mono crystals of high temperature superconductors (HTSC) of "123" type, required for experimental research of fundamental properties of HTSC, and also for manufacture of instruments and devices of superconducting electronics. A crucible with mixture of powders containing 1 weight share of preliminary synthesized high temperature superconducting material of "123" type and 5÷15 weight shares of eutectic mixture of barium oxide and copper oxide are heated in a furnace to temperature of mixture melting, and conditioned at this temperature during 20-50 hours in a uniform temperature field. Crystals are being grown during crucible containing mixture cooling at presence of horizontally directed temperature gradient. Crucible with mixture heating and conditioning is performed at temperature 1000±5°C. Directly before cooling the crucible with the said mixture is gradually set off during 10÷15 minutes into a furnace area with horizontal temperature gradient 9÷11 °C/cm, maintaining constant temperature 1000±5°C of a hot wall of the crucible. Further, growth of crystals is performed by cooling the crucible with mixture at rate 0.5÷2°C/hour in constant temperature gradient.
EFFECT: production of mono crystals of HTSC possessing mirror surfaces and dimensions in plane ab more 1 mm.
FIELD: crystal growing.
SUBSTANCE: invention relates to preparation of chrysoberyl monocrystals and its varieties, including alexandrite - chromium-containing variety, which can be used for manufacturing high-quality faceting material in jewelry industry and for manufacturing quantum electronics elements. Growing of bulk chrysoberyl monocrystals and its varieties comprises melting starting blend, homogenizing melt, adding rotating monocrystalline seed, and growing crystal at temperature below phase transfer temperature. Starting blend contains elevated stoichiometric amount of one of its components, namely beryllium oxide by 3-6% or aluminum oxide by 5-6%, with corresponding reduction of content of other constituent. Growing of crystal is conducted under temperature lowering regime at a rate of 0.5-4°C/h, including lowering temperature below eutectic temperature. Starting blend may contain B3+ or Si4+ cations in the form of corresponding oxides in amount of 0.3-0.5%.
EFFECT: enabled growing of defectless chrysoberyl monocrystals at high mass growth rate.
2 cl, 1 dwg, 2 ex
FIELD: chemical industry; methods of growing of volumetric monocrystals.
SUBSTANCE: the invention is dealt with methods of production of volumetric monocrystals and may be used at controlled solution-melt growing of crystals of substances, for example of composite oxides. The device contains a compound cylindrical king-pot system made out of a ceramic material and consisting of the crystallization and auxiliary king-pots linked through a funnel, internal surfaces of which are made with a platinum cover. The crystallization king-pot on its external surface has two ring-type coaxial ledges, the first of which is located on the lower end of its lateral surface, and the second ledge - on the outer diameter of the bottom part of the crystallization king-pot as its extension. The central part of the bottom of the crystallization king-pot is made in the form of the hollow pyramid with the internal surface representing a cone and with its external surface representing a hexahedral pyramid. The furnace system of the king-pot heating is made in the form of three mechanically separated tubular furnace(modules of a planar structure mounted spatially coaxial - sequentially one after another. Autonomous heating elements of tubular furnace modules planar structure are electrically connected each with its power unit and each is supplied with the working temperature sensor and the thermostat. Outputs of the thermostats are connected to the inputs of the unit of the temperature controllers, and outputs of the unit of the temperature controllers are connected to the control inputs of the corresponding power units. Each working temperature sensor is connected to its own thermostat. The unit of temperature controls consists of the similar controllers, the number of which corresponds to the number of the self-contained heaters of the furnace modules. The temperature sensors for control over the temperature of bottoms of the auxiliary and crystallization king-pots are connected to their own thermostats and meters of temperature, and outputs of the temperature controllers and meters of temperature are connected to the computer. The device allows to increase chemical and configuration homogeneity of grown monocrystals at simultaneous decrease of costs of realization of the production processes.
EFFECT: the invention ensures increased chemical and configurational homogeneity of the grown monocrystals at simultaneous decrease of costs of realization of the production processes.
3 cl, 6 dwg
FIELD: metallurgy; chemical-metallurgical production of metals.
SUBSTANCE: method implies evaporation of platinum solution, obtained melt of chloroplatinic acid is granulated in inert condensed gas applied as cryogenic medium.
EFFECT: production of chloroplatinic acid in the form of high grade crystalline hydrate with specified platinum content.
1tbl, 1 ex
SUBSTANCE: invention refers to growth from molten metal of non-alloyed crystals of sodium tungstate-bismuth NaBi(WO4)2 being perspective material for Cherenkov detectors. Growth of crystals is performed using Chokhralsky method in air atmosphere at drawing speed of 4-5 mm/hour and crystal growth speed of 15-19 min-1.
EFFECT: method allows obtaining crystals transparent in visible range beginning from wave length of 352 nm.
3 dwg, 4 ex
SUBSTANCE: optical medium for converting monochromatic laser radiation with wavelength 975±5 nm to the 1483-1654 nm band is a complex calcium tetragermanate of erbium and yttrium of formula ErxY2-xCaGe4O12, where 0.1<x<0.3. The method of making the said optical medium involves preparation of two initial mixtures of components containing the following in wt %, respectively: calcium carbonate - 11.11; erbium oxide - 42.45; germanium oxide - 46.43 and calcium carbonate - 13.45; yttrium oxide - 30.34; germanium oxide - 56.21. Separate mixing of components of each mixture is carried out in the presence of an alcohol, as well as heating to 700-900°C and maintaining that temperature for 8-10 hours. Repeated heating is carried out to 1050-1100°C, while maintaining that temperature for 100-150 hours and reburdening every 20 hours. Both initial mixtures are then mixed in ratio of 1:4.6-15.3 in the presence of an alcohol and heating to 1050-1100°C and maintaining that temperature for 40-50 hours and reburdening every 10 hours.
EFFECT: possibility of converting monochromatic radiation into a band with simultaneous amplification during operation of the laser in continuous pumping mode.
2 cl, 3 dwg, 2 ex
SUBSTANCE: invention relates to growing high-temperature inorganic monocrystals and can be used in quantum electronics and elementary-particle physics, in particular for neutrinoless double beta decay detectors. The said monocrystals are grown by pulling zinc molybdate crystals ZnMoO4 from molten initial charge in a melting pot for inoculation. The initial charge used is a mixture of oxides ZnO and MoO3, taken in stoichiometric ratio with excess MoO3 in amount of 1.0-7.0 wt %, and growth takes place at crystallisation volume rate of over 0.4 cm3/h. Using Czochralski growth method, pulling rate is 0.3-3.0 mm/h with axial temperature gradient at the crystallisation front of 80-100°/cm. Using Kyropoulos growth method, pulling rate does not exceed 0.5 mm/h while maintaining crystal diametre of 80-95 % of the diametre of the melting pot.
EFFECT: proposed method allows for obtaining large monocrystals (size of 1 cm3 or more), with optical properties suitable for use as scintillation detectors and optical elements.
3 cl, 2 ex, 2 dwg