Rational technical parameters were designed in the crystal growth process, which are: the axial temperature gradient of 0.8℃/mm in solid-liquid interface, the radial temperature gradient of 0.3℃/mm, the growth speed of 2~4mm/h, the rotate speed of 40~45 r/min .
Optimum conditions of the Czochralski-pulling procedure are that the pulling speed is 0. 5-4 mm/h, the rotation rate 10-18r/ min, the cooling speed 18 ℃/h and the axial temperature gradient in solid-liquid interface 0. 7-1 ℃/mm.
The best condition of Nd:NBW crystal for growth by Czochralski method is resulted in the following: 7-10 /cm for axial temperature gradient along the centre of solid-fluid interface, 0.2-0.5mm/h for growth rate, 1-4rpm for crystal rotation rate, 15 /h for crystal cooling rate.
The condition of the Cz-pulling procedure was described in details, which were: the pulling speed 1～2mm/h, the rotation rate 10～18r/min ,the cooling speed 18℃/h and the axial temperature gradient of in solid-liquid interface 0 7～1℃/mm.
The analysis results prove that the radial temperature difference or the axial temperature difference caused by the cooling water is higher than that caused by hot oil, therefore the key point of the design of preventing deformation of coke drum lies in how to control the thermal stress during cooling operation.
So the radial temperature difference or the axial temperature difference caused by the cooling water is more than each of the difference by the hot oil, so the key point to prevent the deformation is that how to control the thermal stress during cooling operation.
Optimal parameters for cyrstal growth are:temperature gradients in axial direction is 28—35℃/cm,rotation speed is 5—10r/min,and pulling rate of KLN crystal depend on composition ration of growth raw materials.
选用的轴向温度梯度为28 ～35 ℃／cm ，晶体的旋转速度为5 ～10r／min ； 晶体的生长速度与 K L N 的生长原料的成分有关。
A remaking scheme is put forward in this article to reduce the longitudinal heat stresses that frequently and alternately arise in the weld in large value, with reducing appropriately the binding rigid and the longitudinal temperature gradient of the structure,according to the results of measuring the stresses and the temperatures in the weld region and the analysis of them.
Using same boundary condition, the temperature gradient along the z direction is gradually increasing to a constant from the solid liquid interface to the top of crystal while the internal heat generative is considered.
The Marangoni number was estimated to range from 3000 to 14000, based on the measured axial temperature difference.
A method for calculating the falling rate of the melt level in a crucible during crystal growth by Czochralski technique is proposed. The actual growing rate of the crystal can be accurately calculated with the calculation results. The crystal growth history can be studied and the transient axial temperature gradient of the melt in the crucible can be estimated.
In this paper, factors affecting cracking of the large-sized BaF_2 single crystals in the growth process are examined. Allowable maximun axial temperature gradient, rate of cooling as well as the maximun resultant strain due to the thermal stress during the growth of the above crystals are also discussed.Perfect crystals of 100mm in diameter, free ef cracks were obtained by improving the temperature field and establishing the optimum growth process for Bridgman-Stock-barger method.