SU1659535A1 - Method for obtaining monocrystals of lead molybdate - Google Patents

Abstract

The present invention relates to a method for producing lead molybdate single crystals and allows to increase the size and improve the quality of single crystals. The raw material obtained by precipitating aqueous solutions of ammonium paramolybdate and lead acetic acid, taken in a stoichiometric ratio, is heated in a crucible at a speed of 100-150 ° C / h until melting, stand for 20-24 hours, then the single crystal is drawn at a speed of 0.25-2.00 mm / h on a seed rotating at a speed of 12-24 rpm, in the presence of a temperature gradient of 0.5-3.0 S / cm and a single crystal is cooled at a speed of 10-30 & S / h The stretching is carried out with a constant automatic weight control. To obtain active laser elements, 3-4 wt.% Neodymium oxide is added to the starting material. Single crystals are obtained with a diameter of up to 70 mm. 2 hp f-s

Description

This invention relates to the field of inorganic materials science and concerns the growth of lead molybdate single crystals.

The aim of the invention is to increase the size and improve the quality of single crystals.

Example 1. In a platinum crucible with a diameter of 100 mm and a height of 160 mm is placed a mixture of lead molybdate in the amount of 3700 g, synthesized by precipitation from aqueous solutions of ammonium paramolybdate and acetic acid lead. The crucible is installed in a three-zone crucible furnace on a ceramic stand connected with an autocompensation balance (mass sensor). A crucible is fitted on top of a tight-fitting platinum lid with a nozzle with a diameter of 26 mm and a height of 50 mm and mechanical balancing is performed. The mixture is heated to the melting point of 1060 ° C for 7 hours at a rate of 150 ° C / h. After holding the melt for 20 hours, a single-crystal, 001-oriented seed is lowered to the surface of the melt through the nozzle of the lid, and a temperature gradient of 0.5 ° C / cm is simultaneously set on top of the melt and in the volume of the melt. The balance of the seed with the melt set by the signal of the mass sensor. The process of growing single crystals is carried out automatically after starting the stretching of the seed, the initial drawing speed of 1 mm / h, the speed of rotation of the seed is constant 12.0 rpm. One time resr

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They include a block that forms the program of the process: the weight rate of crystallization at the site of growth to a constant cross section (cocus) and the speed at a constant cross section. The initial crystallization rate is 0.5 g / h. The crystallization rate at a constant cross section is 32 g / h. The error signal between the desired and the actual weight of the crystal is supplied to the control of the thermostats of the crucible furnace. As the cross section of the crystal increases, the draw rate decreases and at a constant cross section it is 9 mm / day (0.3-0.4 mm / h). For 12 hours, a lead molybdate crystal is grown in sizes: a conical part 50 cm, a cylindrical part 65 cm, diameter 70 cm

Upon reaching the specified size, disconnect the mass sensor feedback to the temperature controllers, stop 1 program and quickly raise the crystal manually until it melts. After soaking in the furnace for 8-10 hours, the furnace together with the crystal is cooled to room temperature at a rate of 20 degrees / hour. The weight of the grown crystal is 2000 g, the weight loss of the melt due to evaporation is about 1 g. The crystal has a weak yellow color, optically homogeneous, without blocks and macroscopic inclusions.

Example 2. A platinum crucible with a diameter of 70 mm and a height of 130 mm is deposited on a charge of lead molybdate obtained by precipitation from aqueous solutions of ammonium paramolybdate and lead acetic acid. The weight of the charge is 1500 g, the crucible is placed in an oven, and is closed with a lid with a nozzle with a diameter of 18 mm and a height of 55 mm. Heat at a rate of 100 ° C / h to the melting temperature and homogenize the melt for 24 hours. A seed of square section (5 x 5 mm2) 20 mm long is used, orientation perpendicular to the face 112. Lowering the seed is carried out slowly (1-2 hours) to avoid thermal shock. Before starting the drawing process, 2-3 mm seeds are melted to remove the damaged part. A single crystal is started to be pulled out (seed rotation speed of 12 rpm) at a speed of 0.25 mm / h. Spread with a temperature reset of 0.5 ° C / cm to a diameter of 25 mm and remove the discharge gradually after 40 mm of stretching. At the end of the experiment, the crystal is abruptly separated from the melt and cooled at a rate of 30 ° / h. The crystal has a weak yellow color, optically homogeneous, without blocks and macro-inclusions. At the bottom of the crystal has a diameter of 35 mm with a length of 70 mm, weight 791 g.

Example 3. The precipitate prepared by the precipitation method is heated at a rate of

150 ° / h. The process was accompanied by the smell of vinegar. The melt is kept for 24 hours at a temperature of 15 ° C above the melting point (1080 ° C). Then the temperature in

reduced to almost equilibrium, and seeding is carried out on an oriented seed. After seeding with a rotating seed, the stretching mechanism is turned on and single-crystal growth begins.

The drawing rate was 2 mm / h with a seed rotation of 24 rpm and with a temperature gradient in the melt of 3 ° / cm in the crystallizer. At the end of the process, the crystal is abruptly detached from the melt and cooled with

speed of 10 ° / h to room temperature.

The result is a single crystal of a slightly yellowish color, weighing 660 g, with a diameter of 30-40 mm and a length of 75 mm.

PRI me R 4. The mixture in the amount of 1070 g

loaded into the crucible, activate neodymium. For this purpose, 122 g of NdaOa are added to the initial charge. The mixture is heated to the melting temperature at a rate of 120 ° / h and

incubated for homogenization for 24 hours. Then, a single-crystal oriented seed is gently lowered to the surface of the melt through the nozzle. The balance of the seed and the melt is determined by the signal

mass sensor. The process of growing a single crystal, activated with neodymium, is carried out automatically after starting the stretching of the seed. Initial drawing speed of 1.5 mm / h, speed

rotation of the seed 12.5 rpm At the same time include a block that forms the program of the process. The draw rate decreases as the crystal cross section increases and at a constant cross section it is 0.4 mm / h.

Upon reaching the specified size, disable the mass sensor feedback to the thermostats and manually raise the crystal abruptly until detachment.

crystal temperatures are cooled at a rate of 10 degrees / h. Weight of grown crystal is 2200 g. Dimensions of lead molybdate crystal doped with neodymium: conical part 50 cm, cylindrical part 66 mm,

diameter is 70 mm.

The optical quality of the lead molybdate crystal is enhanced with neodymium alloying.

Example 5. 282 g of NdaOa was added to the starting mixture. Further, the process is carried out under the same conditions as the growth of a single crystal in Example 4.

The weight of the grown crystal is 2200 g, the quality of the crystal is visually optical

transparent, its optical quality is better than without neodymium additives.

Thus, the use of the method of growing single crystals of lead molybdate makes it possible to obtain large crystals (weighing up to 2 kg and more).

In addition, lead molybadate crystals obtained by this method are transparent and optically homogeneous, without cracks or damage. Adding neodymium oxide to the charge improves the quality of the crystals, as their optical transparency improves visually. The crystals are used to make elements for acousto-optic applications. Large single crystals allow either to increase the number of standard acousto-optic elements manufactured from a single crystal, or to make nonstandardly large acousto-optical elements of 40x40x30 mm in size.

Claims (3)

1. A method of producing lead molybdate single crystals, comprising starting material by precipitating aqueous solutions of ammonium paramolybdate and acetic acid lead, taken in a stoichiometric ratio, heating and melting it in the crucible and the pulling of the single crystal on the rotating seed in the presence of a temperature gradient and cooling of the single crystal, characterized in that, in order to increase the size and improve the quality single crystals, the starting material is heated at a rate of 100-150 ° C / h and held for 20-24 h, stretching is carried out at a speed of 0.25-2.0 mm / h, the seed is rotated at a speed of 12-24 rpm, the gradient is set value of 0.5-3.0 ° C / cm, and cooling lead at a speed of 10-30 ° C / h. 2. A method according to claim 1, characterized in that the stretching is carried out with automatic weight control. 3. The method according to claim 1, characterized in that, in order to obtain laser active elements, 3-4% by weight of neodymium oxide are added to the starting material.