## 1 Introduction  
As an important strategic rare metal, Re is widely used in the metallurgy, chemical, alloy manufacturing and aerospace industries [1, 2]. At present, the preparation technologies for Re include plasma methods, electrolysis methods, vapor deposition methods, and the hydrogen reduction of ammonium perrhenate [3,4]. Rhenium powders have the advantages of excellent phase parameters and uniform particle size distribution when prepared by electrolysis, vapor deposition, and plasma methods. [PERSON] et al. [5] produced micro/nano rhenium powders by applying the plasma method. [PERSON] et al. [6] carried out the plasma spray spheroidization of rhenium powders produced by traditional processes and obtained spherical rhenium powders with microscopic morphologies. [PERSON] et al. [7] used a mixed solution of rhenic acid and sodium sulfate as electrolytes to produce spherical rhenium powders by electrolysis. [PERSON] et al. [8] produced spherical ultrafine rhenium powders with a small particle size by using the vapor deposition method. However, due to the complex equipment and the difficulties in process scale up, none of the above preparation processes have achieved large-scale production. The preparation of Re by the hydrogen reduction of ammonium perrhenate is the only industrial production process and has the advantages of straightforward operation, low production cost, and uncomplicated equipment [9]. However, there are still some problems to be solved with this preparation method. The rhenium powders are produced with an uneven particle size distribution and poor powder phase parameters. These powders cause difficulties during subsequent application and processing and cannot meet the high requirements for powders that are used for modern powder metallurgy fabrication methods [10]. These issues are mainly caused by the low efficiency of the mass transfer and heat transfer during the reduction process of ammonium perrhenate. Some scholars have made progress with the reduction control of metal powders. For instance, [PERSON] et al. [11] improved the particle uniformity of molybdenum powder by controlling heat release. [PERSON] et al. [12] studied the growth of molybdenum powder when the particle size was controlled by adding NaCl. [PERSON] et al. [13] prepared nanometer tungsten powder by applying a ball milling pretreatment of WO\({}_{3}\). All of the above studies aimed to improve the phase parameters and uniformity of the powder by improving its mass transfer and heat transfer efficiency by relying on the pretreatment of the reducing substances. Therefore, previous studies have shown that optimizing the phase parameters of ammonium perrhenate can affect the phase parameters of reduction products. Ammonium perrhenate is purified by recrystallization in industrial contexts [14]. The static cooling recrystallization process produces ammonium perrhenate with a large particle size, uneven particle size distribution, and serious particle agglomeration. [PERSON] et al. [15] prepared Ni(OH)\({}_{2}\) with uniform particle size distribution by airlift-loop and stirred reactors. [PERSON] [16] changed the size of the crystals by optimizing the structure of the stirred reactor. In conclusion, previous studies have provided references for improving the process of preparing rhenium powders by using the hydrogen reduction of ammonium perrhenate. The aim of the present study was to enhance the mass and heat transfer efficiency of ammonium perrhenate during the reduction process by relying on a homogeneous recrystallization reduction pretreatment to improve the uniformity and specific surface of the ammonium perrhenate. The influence of stirring paddle types and stirring intensities on the phase parameters during the recrystallization of ammonium rehenate is systematically explored, and the growth mechanism during ammonium perrhenate recrystallization is revealed.