Growing Large Beta-Type Ammonium Tetramolybdate Monocrystals
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Solution Overview
Problem
Current methods for preparing β-type ammonium tetramolybdate monocrystals are challenging, particularly in achieving large size crystals, due to the instability of α-type ammonium tetramolybdate and the difficulty in controlling the crystallization process, resulting in low yields and mixed crystal forms.
Innovation Solution
A method involving the preparation of an ammonium molybdate solution with specific pH and temperature adjustments, using β-type ammonium tetramolybdate crystal seeds, and controlled crystallization conditions to grow large size β-type ammonium tetramolybdate monocrystals, with pH adjusted to 5-7 and temperature maintained between 70-90°C, allowing for slow evaporation and cooling crystallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional acid precipitation method is used to prepare ammonium tetramolybdate, then the preparation rate is high and the process is simple, but the crystal structure becomes mixed (α-type and β-type) and the product quality deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling pH (adjusting to 5-7 using ammonia water or nitric acid) and temperature (maintaining 70-90°C) during crystallization. These parameter changes transform the crystallization process from uncontrolled rapid precipitation to controlled monocrystal growth, achieving both high preparation rate and uniform β-type crystal structure.
Solution Approach 2:
The patent uses preliminary action by preparing β-type ammonium tetramolybdate crystal seeds first, then using these seeds as nucleation sites for controlled crystallization. This preliminary preparation of seeds ensures that the crystallization process produces uniform β-type monocrystals rather than mixed crystal forms, while maintaining efficient preparation rate.
2Ease of manufacture
If α-type ammonium tetramolybdate is used as raw material, then the preparation process is straightforward, but the thermal stability is poor and intermediate compounds are generated during thermal evolution
Solution Approach 1:
The patent changes the crystallization parameters (pH 5-7, temperature 70-90°C, slow cooling rate) to produce β-type ammonium tetramolybdate monocrystals instead of α-type. The β-type crystals possess inherent thermal stability and do not generate intermediate compounds during thermal evolution, thus resolving the thermal stability issue while maintaining ease of manufacture through controlled crystallization.
3Productivity
If rapid crystallization is employed to increase production efficiency, then the output increases, but the crystal size remains small and the monocrystal quality is compromised
Solution Approach 1:
The patent prepares β-type crystal seeds in advance and uses them as nucleation sites. This preliminary action allows the crystallization process to proceed efficiently with controlled growth on existing seeds, producing large-sized monocrystals rather than numerous small crystals, thus maintaining both high productivity and large crystal size.
Solution Approach 2:
The patent employs periodic action through controlled cooling crystallization, where the solution is slowly cooled at a controlled rate after reaching saturation temperature. This periodic temperature change allows crystals to grow steadily in size while maintaining monocrystal quality, achieving both high production efficiency and large crystal dimensions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables the controlled growth of large size β-type ammonium tetramolybdate monocrystals up to a centimeter level, ensuring thermal stability and homogeneous crystal structure, improving the quality and processing performance of metal molybdenum products.
Implementation Method 1
the crystallization system stands still at room temperature, naturally cooling, and the β-type ammonium tetramolybdate crystal seed grows up as the large size β-type ammonium tetramolybdate monocrystal particle product
Implementation Method 2
allowing for slow evaporation and cooling crystallization
Data Source
AI summary
A method for preparing large size beta-type ammonium tetramolybdate monocrystal particle includes industrial ammonium molybdate, ammonia, de-ionized water are used to prepare ammonium molybdate solution with concentration of 0.2˜0.6 g/ml; pH is adjusted to 5˜7, temperature is adjusted to the first temperature of 70˜90° C. to obtain the first ammonium molybdate solution; beta-type ammonium tetramolybdate crystal seed is put into crystallization container, and the first ammonium molybdate solution is poured in the crystallization container, to form crystallization system; the crystallization system stands still at room temperature, naturally cooling, the beta-type ammonium tetramolybdate crystal seed grows into large size beta-type ammonium tetramolybdate monocrystal particle. A beta-type ammonium tetramolybdate crystal seed is obtained by constant-temperature crystallization at 70˜90° C. The obtained beta-type ammonium tetramolybdate crystal seed is put stewing in the first ammonium molybdate solution and is naturally cooling to produce large size beta-type ammonium tetramolybdate monocrystal particle forms.