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Applied Chemistry and Physics
Published in Robert A. Burke, Applied Chemistry and Physics, 2020
Definition of solid. Matter in the solid state maintains a fixed volume and shape. Solids can be transformed into liquids by melting, and liquids can be transformed into solids by freezing. Solids can also change directly into gases through the process of sublimation. Solids are the easiest state of matter to deal with. Unless there is wind or rain, the material will not likely go anywhere beyond the location where it was spilled (Figure 3.14). Tarps can be used to cover the solid to protect it from the wind. Sublimation is a process whereby a solid turns into a gas without entering the liquid phase. One example of sublimation is dry ice. Dry ice turns directly into a gas without becoming a liquid. Snow and ice under certain conditions can turn directly into water vapor (gas) without first becoming a liquid. Camphor and moth balls are also examples of materials that sublime.
Properties of Pure Substances
Published in Kavati Venkateswarlu, Engineering Thermodynamics, 2020
The temperature at which any two phases of a pure substance coexist in equilibrium depends on the pressure for solid–liquid, solid–vapor, and liquid–vapor equilibrium states. For most of the substances, there is a pressure below which solid and vapor phases coexist in equilibrium and the substance cannot exist as a liquid below this pressure. For each substance, there is a fixed relation between pressure and temperature for solid–vapor saturation states. The phase transformation from a solid to vapor is called sublimation and the solid–vapor saturation line on the p-T diagram (discussed later) is called the sublimation line. The well-known example of sublimation is the phase transformation of solid carbon dioxide (dry ice) to a gas instead of a liquid.
Lexicon
Published in Samuel C. Sugarman, HVAC Fundamentals, 2020
sublimation: (Chemistry) The transition of a substance (e.g., carbon dioxide, CO2) from the solid phase (state) to the gas (vapor) phase without passing through an intermediate liquid phase. At normal pressures most chemical compounds and elements possess three different states (solid, liquid, gas) at different temperatures. Therefore, the normal transition from solid state to gas state requires an intermediate liquid state.
Inert particles as process aid in spray-freeze drying
Published in Drying Technology, 2020
Fan Zhang, Xiaoyu Ma, Xiusheng Wu, Qing Xu, Wei Tian, Zhanyong Li
The influences of three different freeze-drying methods (FD, SFD, SFD-IP) on drying time are first discussed in this section. Then, the effect of inert particle size on drying time in spray freeze-drying is analyzed. Figure 4 shows the variation of pressure in the drying chamber with time in different experimental schemes. The pressure decreased rapidly (not shown in this figure for clarity) and recovered with the acceleration of sublimation process. At about 20 min, the pressure of SFD reached the maximum value and then began to decline. The sublimation of ice affects the pressure change in the vacuum chamber. Before the pressure drops to 4.4 Pa, the moisture in milk is not completely removed, and the vapor pressure keeps the drying chamber under a certain pressure. With the decrease of moisture content, the pressure gradually decreases. The decrease of pressure and the increase of temperature are beneficial to the process of sublimation. The pressure in FD drops more slowly than in SFD, resulting in longer drying time. Figure 5 shows the experimental results of drying time under different drying conditions (Table 1).
Curvatures of smectic liquid crystals and their applications
Published in Journal of Information Display, 2018
Thermal phase transitions of thermotropic soft matters show various kinds of structures as a function of temperature. Among them, the isotropic liquid to LC phase transition is the most common in LC materials and is known as a clearing point because it does not fully become “solid”. Sublimation is commonly known as a phase transition between the solid to gas phases without passing through the liquid phase, as observed in dry ice (carbon dioxide) at room temperature. More generally, when temperature falls below 0°C in the early morning, gaseous water molecules in air kinetically deposit onto the substrate as observed in frost on plants, in which water vapor-deposition sublimates to frost (Figure 5(a)). Another example is that slightly separated ice cubes in humid conditions are merged together by sublimation/condensation of nearby water vapor (Figure 5(b)). Such sublimation/condensation on each surface can be considered as sintering processes, where the term sintering can be broadly defined as a process of compacting, forming, and shaping a solid mass of materials by heat or pressure without melting. For example, sintering occurs naturally in the deposition of minerals [83,84], and geyser cones are occasionally formed as a result of such depositions of incrusted minerals (such as amorphous silica or opaline) near hot springs or petrifying springs, referred to as a “siliceous sinter” (Figure 5(c)). However, this kind of morphogenesis is not controllable, making it difficult to obtain desired patterns at the micron or nanometer scale during the sintering process.