RU1649859C - Method of thermal treating of leucosapphire articles - Google Patents

Abstract

The invention relates to the processing of single crystals of leucosapphire and products from them, can be used at the enterprises of the Ministry of Chemical Industry, the Ministry of Electron Industry and allows to increase the resistance of the products to UV radiation. Heat treatment is carried out in the presence of graphite 9 heating the product up to 1800-2000 ° C in an atmosphere of natural gas at a pressure of 7-10-4-2-105 Pa. Then hold for a while (012T-19.6), m, where Ј is the thickness radiation-hardenable layer of a leucosapphire product, mm After isothermal exposure, reduce the temperature in the furnace and remove the products from it. “The main indicators of the increase in radiation resistance after annealing are the relative change in the mass of the annealed crystal (& amp) and the intensity of induced absorption ( & D) last e-irradiation of the crystal for one hour with lamp light. The annealed crystals have & t 0, 0051,, 016-0.030. 1 table 00 s

Description

The invention relates to the processing of single crystals of leucosapphire and products from them and can be used in enterprises of the Ministry of Chemical Industry, Ministry of Electronics, Ministry of Instrument Engineering, Ministry of Fertilizers

The aim of the invention is to increase the resistance of products to UL radiation

The method includes the following sequence of operations: heating products from leucosapphire in the presence of graphite to 1800-2000 ° C in a natural gas environment at a pressure of 7 10-4-2 10 Pa, isothermal holding at this temperature for a time Ј, cooling of the product, room temperature temperature

(the cooling rate depends on the characteristics of the annealing furnace, but should not exceed 000 deg / h in order to avoid cracking of crystals due to thermoelastic stresses)

To exclude contact interaction, the annealed articles and graphite are spatially separated. The depth of diffusion propagation of reduction processes in the crystal volume is equal to the thickness of the radiation-hardened layer of the annealed crystal and is determined by the ratio

(1)

X I7,

:ABOUT

$

With

; SL

Yu

where D3 is the effective coefficient

diaphusia of the front with tg srdoyaznoy recovery

reactions „

For articles made of leucosapphire, the dependence of VEЈr on the annealing temperature in the range of 1800–2000 C was experimentally established;

D

9q

1SG6. (0, b) (cm2 / s) 1 1 (GB (0, 6) -3.6-10 (cm2 / h),

(2)

From equations (l) and (2), the final expression is obtained for determining the duration of isothermal exposure during annealing of leucosapphire in a carbon atmosphere at 1800-2000 ° С

(h)

2-D

4

Ј2 (SM2)

„()

(3)

In practice, o is measured in mm. Therefore, before calculating the time Ј to fulfill the dimensional conditions, the measured value in mm is converted to cm

o (mm) / 0.1 $ (cm) o Then the formula (2) takes the form

fr (4) J9il: Jl.lЈЈl

ICH 2B ЈрТcm2 / h7

where Ј in mm „

Taking into account the value of D) e, p, we obtain

(H) .llSfdUJcMfl ...-. (H)

2-10- (0.0121-19.6). 3.6-103 (SM2 / H) 0.012T-19.6

where Ј is the thickness of the radiation hardened layer of leucosapphire products,

The choice of the temperature range from crystal annealing in accordance with the proposed method is determined by the efficiency of diffusion processes in leucosapphire. It has been established that leucosapphire recovery process is quite effective at temperatures above 1750 ° C, however, reductive annealing under pre-conditions (Tm 2050 ° C) is not justified due to the high probability of emergency melt of annealed products

Annealing in the atmosphere of natural gas, which mainly consists of methane (CH4), corresponds to annealing in a hydrocarbon medium and exhibits a combined reducing effect with respect to single crystals. When annealing by the proposed method, in addition to saturating the crystal with hydrogen atoms in the crystal, the content of anionic vacancies whose concentration is determined by the annealing temperature

The presence of anionic vacancies, firstly, eliminates the presence of neutral oxygen atoms in the crystalline matrix, and secondly, additionally reduces or compensates for the positive charge of impurity transition metal ions, thereby completely eliminating the causes of induced optical absorption (HFl) with UL radiation 0 A characteristic feature of high

5 0 g

0

5

0

5

The temperature (Totzh 1750 ° С) annealing of leucosapphire () in the presence of graphite is an intense thermochemical etching of the surface of the annealed crystal. This process is caused by chemical transport reactions in the gas phase, and its intensity substantially depends on the pressure of the annealing medium. It has been experimentally established that for the temperature range 1800-2000 ° С deterioration of the surface quality of products as a result of thermochemical etching does not occur at a natural gas pressure in the annealed space of more than 7-104 Pa0 an increase in the pressure of the annealing medium of more than 2-103 Pa is not advisable, since it is not accompanied by an additional positive effect, however, it leads to a structural complication of the annealing chamber due to special requirements for equipment operating at elevated pressures x0

EXAMPLE PO Polished sapphire wafers (windows for defectors) (diameter 25 mm, height 50 mm) are placed in an open molybdenum container and loaded into a furnace with a graphite heater. The furnace’s working space is evacuated to a pressure and then filled with natural gas to a pressure of 7-104 Pa. The furnace is heated at a speed of 700 deg / h to temperature T. During the temperature rise, the pressure in the furnace increases and, when banner B is reached, it is stabilized by venting excess gas in the atmosphere. The duration of isothermal exposure is determined from the above ratio. For example, at an annealing temperature of 1900 ° C

about . LA L T, 25 W

0.0121-19.5 3.2

- 2.5 (h).

After isothermal exposure, the temperature in the furnace is reduced at a speed of 700 deg / h and after the furnace has completely cooled down, the products are removed from the furnace

To control the effectiveness of increasing radiation resistance, a relative change in the mass of the annealed crystal is recorded.

Ј- (t- - lO / t

t

 "

where t - is the mass of the crystal after annealing;

mft is the mass of the crystal before annealing, as well as the intensity of the induced absorption (& D) after UV irradiation of the crystal for one hour with a PRK-4 lamp.

Heat treatment modes and the results are presented in the table on

After comparing the annealing results, the main indicators are il) and о о. As can be seen from the table, the optimal modes are those described in examples 2-, 7, 80. Reducing the annealing temperature to 1750 ° C (example 1) or reducing the duration of isothermal exposure ( example 10) corresponds to insufficient radio5

0

hardening annealed product. The use of the duration of isothermal exposure longer than the proposed e (example 11) is ineffective and is accompanied by an increase in the change in the mass of the annealed crystal (Јт). A decrease in the annealing pressure to 2–10 Pa (example 6) leads to the broaching of defects on the surface of the annealed products, and the increase in pressure is higher 2-10s (example 9) is inefficient, as it is accompanied by an increase in the intensity of induced absorption (compare with examples 2-1, 7, 8)

Thus, the modes limited by the limits specified in the proposed method (examples 2-1, 7, 8), provide the optical resistance of leucosapphire to UV radiation is higher than that of the prototype method, on average, than

Claims (1)

The claims 5 The method of heat treatment of products from leucosapphire, including their heating, isothermal exposure in a gaseous medium and cooling, is distinguished by the fact that, in order to increase the resistance of the products to UV radiation, the heating is carried out in the presence of graphite to 1800-2000 ° C in the atmosphere natural gas 0 at a pressure of 7-10 5 2-105 Pa, and exposure is carried out over time Ј -1, U2 / (0.012T - 19.6) (h), where O is the thickness of the radiation-hardening - 0 layer of the product on leucosapphire, mm about Crystal melted 8 Continuation of the table