A mixed solution of several substances, during the freezing process, some components are crystallized at the beginning, and the concentration of the remaining solution changes. When a certain temperature or temperature region is reached, the liquid and the components in the formed solid are exactly the same. The solution at this time is called a eutectic solution. The temperature or temperature interval is referred to as the eutectic or eutectic region of the solution, also known as the full cure temperature, which is the maximum temperature at which the product transitions from a liquid end to a solid state during cooling. The eutectic temperature is the highest temperature that should be reached during pre-freezing in the freeze-drying process. Generally, the pre-freezing process should be lower than the eutectic temperature of 10-20 °C. Cosolvent temperature When the solid mixed solution is heated and melted, when a certain temperature is reached, a liquid phase begins to appear in the solid. This temperature is called the co-melting point of the solution, or the melting temperature is started. It is the lowest temperature at which liquidity begins to appear in the solid state during product warming. The temperature of the material freezing layer must be lower than the co-melting point in one drying. The measurement of the eutectic point is measured by electric resistance measurement, thermal differential analysis, direct observation by a cryogenic microscope, and numerical formula calculation. During the freezing process of the solution, the drift rate of the ions gradually decreases with the decrease of the temperature, and the electric resistance increases. As long as the liquid exists, the current can flow. Once all the freezing, the charged ions cannot move, and the resistance will suddenly increase. According to this principle. , the eutectic point of the solution is measured. Collapse temperature: When the lyophilization, the ice crystals in the material disappear, and the space occupied by the ice crystals originally becomes a cavity, so the lyophilized layer has a porous honeycomb sponge structure. This structure is temperature dependent. When the solid matrix temperature of the honeycomb structure is high, its rigidity is lowered. When the temperature reaches a certain critical value, the rigidity of the solid matrix is ​​insufficient to maintain the honeycomb structure, the solid substrate wall of the cavity will collapse, and the original vapor diffusion channel is closed. This critical temperature is called the collapse temperature of the freeze-dried material. Or collapse temperature. Glass transition temperature: When the temperature is lowered, the liquid state changes to a solid state, and there are two different states - a crystalline state and an amorphous state. In amorphous solid materials, the arrangement of atoms, ions or molecules is random. Since inorganic substances that have been accustomed to crystallization of molten substances during cooling are called glasses, the other amorphous states are later referred to as glass states. Due to the stricter requirements in the lyophilization of pharmaceuticals, it is desirable that the drug be below the glass transition temperature during lyophilization. However, the glass transition temperature here does not refer to complete vitrification, because complete vitrification means that the entire sample forms a glassy state, and it is almost impossible to achieve a very high cooling rate for complete vitrification. The glass transition temperature of the lyophilization process refers to the glass transition temperature of the maximum frozen concentrate. Because the concentration of the remaining solution gradually increases with the precipitation of ice crystals during the freezing process, when a certain concentration is reached, the remaining water is no longer crystallized, and the solution reaches the maximum freeze-concentration state, and the corresponding temperature is called the maximum frozen concentrated liquid. Glass transition temperature Glass Premium Tempered,Heat Tempered Glass ,Exterior Oven Door Glass ,Microwave Oven Door Tempered Glass WCH Temper Glass Co., Ltd , https://www.temperglasswch.com
June 09, 2021