Preparation method of high purity alumina with high purity aluminum as raw material and purity test thereof

I. Production process of high purity aluminum

Ultra high purity aluminum has better conductivity, ductility, reflectance and corrosion resistance than primary aluminum, which is widely used in the electronics industry and aerospace fields. At present, only a few manufacturers in China can produce high purity aluminum of 99.999% (mass fraction).  

At present, the production technology of high purity aluminum mainly includes condensation method, three-layer hydroelectrolysis method and segregation method, among which the segregation method can be divided into fractional crystallization method, directional solidification method and zone melting method.

II. Ultra high purity alumina preparation by hydrolysis of high purity aluminum  

To prepare high-purity alumina by hydrolysis of high-purity aluminum, it is necessary to activate high-purity aluminum first. The activated aluminum can react violently with deionized water and crystallize into high-purity alumina. Studies show that the conversion rate can be as high as 96%.  What needs special attention here is that the activation treatment of high purity aluminum is one of the key technologies for the preparation of high purity aluminum oxide by hydrolysis.  

1. Hydrolysis mechanism of high purity aluminum

The reason why hydrolysis reaction can occur is that elemental aluminum itself has high chemical activity.  However, the non-equilibrium crystal or quasicrystalline phase is formed in the elemental aluminum by activation. This kind of non-equilibrium crystal or quasicrystalline phase has high free energy and is thermodynamically unstable, which is one of the internal reasons for the hydrolysis reaction.  

The activated high-purity aluminum is granular powder with high surface energy, which is also an important driving force for the hydrolysis reaction.  

2. Crystallization kinetics analysis

High purity aluminum hydrolysis preparation of high purity alumina process essence for the crystallization process, in the process of crystallization, the metastable phase of the six-party bayer as solute phase, it is because it makes the dissolution of reaction system, formed the supersaturated solution and the solution is supersaturated solution method must have the premise of crystallization process.  

The crystallization behavior is different in different periods of hydrolysis reaction.  At the initial stage of the reaction, the crystallization is mainly nucleated due to the intense reaction and high supersaturation of the reaction system.  With the decrease of the reaction intensity, the supersaturation of the reaction system also decreases correspondingly, and the crystal growth and agglomeration phenomenon begin to appear in the system.

III. Purity analysis of high purity alumina

At present, the impurities in high purity alumina are mainly analyzed by inductively coupled plasma mass spectrometry, high resolution inductively coupled plasma mass spectrometry, spectrophotometry and inductively coupled plasma atomic emission spectrometry.  

1. Inductively coupled plasma mass spectrometry  

Inductively coupled plasma mass spectrometry (ICP-MS) is to further analyze the concentration of elements or their isotopes by ionizing high-purity alumina samples with high-frequency plasma and then determining the ions produced by MASS spectrometry.

The advantages are low detection limit, and can analyze multiple elements at the same time, so it is one of the most widely used methods at present.  

2. High resolution inductively coupled plasma mass spectrometry (HICP-MS)

HICP-MS has ultra-high sensitivity, allowing multi-element quantitative analysis at the trace level, even without sample processing.  

3. Spectrophotometry spectrophotometry

Also known as absorbance spectrophotometry, is based on the selective absorption of light and the establishment of the analysis method.  In the impurity analysis of high purity alumina, Si and Fe can be measured by ultraviolet spectrophotometry.  

The advantages of spectrophotometry are: good selectivity, high sensitivity, stability and reproducibility.  

4. Inductively coupled plasma atomic emission spectrometry (ICP-AES)

ICP-AES is used to detect the spectral lines emitted by the middle and outer electrons in the atoms of different elements during the transition from excited state to ground state.  The advantages are: high sensitivity, low detection limit, good stability, fast analysis speed.