Crystallinity and specific gravity

Crystallinity and specific gravity of PFA parts decrease when the cooling rate of the molten polymer... 

PTFE exists in multiple forms that are influenced by temp>erature, pressure, and thermal history. In turn, these forms significantly influence the physical, electrical, and processing properties of the polymer. Particularly, the percent crystallinity and specific gravity have been found to relate to a large number of properties, and since these parameters are influenced by processing history, it is very important to specify precise sample preparation conditions. In equations below, % C = percent crystallinity, and p = density. 

TTie crystallinity and specific gravity of PFA parts decrease when the cooling rate of the molten polymer is increased. The lowest crystallinity obtained by quenching molten PFA in ice was 48% (specific gravity 2.123). 

Crystallinity and specific gravity of PFA parts decrease when the cooling rate of the molten poljmier is increased. The lowest crystallinity obtained by quenching molten PFA in ice was 48% (specific gravity 2.123). PFA exhibits one first order transition at -5°C in contrast to two temperatures for PTFE at 19 and 30°C. It has three second order transitions at -100, -30 and... 

Citric acid, anhydrous, crystallizes from hot aqueous solutions as colorless translucent crystals or white crystalline powder. Its crystal form is monoclinic holohedra. Citric acid is dehquescent in moist air. Some physical properties are given in Table 1 (1 3). The solubiUty of citric acid in water and some organic solvents is given in Table 2. The pH and specific gravity of aqueous solutions of citric acid are shown in Table 3. 

Whilst completely atactic material would be amorphous, commercial materials have a small measure of crystallinity. This is often assessed in terms of insolubility in n-heptane which is usually of the order of 5-10%. Viseosity average moleeular weights are in the range 20 000-80 000 and specific gravities are about 0.86 g/cm. ... 

Atomic weight 28.06. Three kinds are produced amorphous, crystalline and graphite-type. The crystalline form has a cone, black gray metallic lustre and specific gravity of 2.4/ the graphite-type form is black and has a specific gravity of 2.7. All of them have the same crystal structure. Silicon melts at 1420°C and boils at 2335 C. Insoluble in water. The amount of heat generated at oxidation is 7300 kcal per 1 kg of silicon, which is equal to 0.9 times the amount per 1 kg of carbon. 

Prepared 3BejC.BOgC by heating a mixture of BeO and B in a carbon crucible in the electric furnace. Crystalline with specific gravity of 2.4. 

Crystalline form, specific gravity and refractive index of HIPRESICA are listed in Table 8-1. The specific gravity of HIPRESICA Type N3N is 1.8, which is smaller than that of sihca glass. It is assumed that the microscopic voids and hydroxyl groups remain in the particle. Also the refractive index of 1.35 for HIPRESICA is smaller... 

The melting point of commercial Teflon PEA is 305°C, ie, between those of PTEE and EEP. Second-order transitions are at —100, —30, and 90°C, as determined by a torsion pendulum (21). The crystallinity of the virgin resin is 65—75%. Specific gravity and crystallinity increase as the cooling rate is reduced. An ice-quenched sample with 48% crystallinity has a specific gravity of 2.123, whereas the press-cooled sample has a crystallinity of 58% and a specific gravity of 2.157. 

Nitrates. Iron(II) nitrate hexahydrate [14013-86-6], Fe(N03)2 6H20, is a green crystalline material prepared by dissolving iron in cold nitric acid that has a specific gravity of less than 1.034 g/cm. Use of denser, more concentrated acid leads to oxidation to iron(III). An alternative method of preparation is the reaction of iron(II) sulfate and barium or lead nitrate. The compound is very soluble in water. Crystallisation at temperatures below — 12°C affords an nonahydrate. Iron(II) nitrate is a useful reagent for the synthesis of other iron-containing compounds and is used as a catalyst for reduction reactions. 

Aluminum iodide [7884-23-8] AIL, is a crystalline soHd with a melting poiat of 191°C. The presence of free iodine ia the anhydrous form causes the platelets to be yellow or brown. The specific gravity of this soHd is 3.98 at 25°C. Aluminum iodide hexahydrate [10090-53-6] AIL -6H20, and aluminum iodide pentadecahydrate [65016-30-0], AIL -15H20, are precipitated from aqueous solution. They may be prepared by the reaction of hydroiodic acid [10034-85-2], HI, with aluminum or aluminum hydroxide. 

Strontium Acetate. Strontium acetate [543-94-2] Sr(CH2C02)2, is a white crystalline salt with a specific gravity of 2.1, and it is soluble to the... 

Strontium carbonate is a colorless or white crystalline soHd having a rhombic stmcture below 926°C and a hexagonal stmcture above this temperature. It has a specific gravity of 3.70, a melting point of 1497°C at 6 MPa (60 atm), and it decomposes to the oxide on heating at 1340°C. It is insoluble in water but reacts with acids, and is soluble in solutions of ammonium salts. 

Physical Properties. Anhydrous sodium sulfite [7757-83-7] Na2S02, is an odorless, crystalline soHd and most commercial grades other than by-product materials are colorless or off-white (331—334). It melts only with decomposition. The specific gravity of the pure soHd is 2.633 (15.4°C). Sodium sulfite is quite soluble in water. It has a maximum solubiHty of 28 g/100 g sol at 33.4°C at higher and lower temperatures, it is less soluble in water. Below this temperature, the heptahydrate crystallizes above this temperature, the anhydrous salt crystallizes. Sodium sulfite is soluble in glycerol but insoluble in alcohol, acetone, and most other organic solvents. 

Stannous Sulfate. Stannous sulfate (tin(Il) sulfate), mol wt 214.75, SnSO, is a white crystalline powder which decomposes above 360°C. Because of internal redox reactions and a residue of acid moisture, the commercial product tends to discolor and degrade at ca 60°C. It is soluble in concentrated sulfuric acid and in water (330 g/L at 25°C). The solubihty in sulfuric acid solutions decreases as the concentration of free sulfuric acid increases. Stannous sulfate can be prepared from the reaction of excess sulfuric acid (specific gravity 1.53) and granulated tin for several days at 100°C until the reaction has ceased. Stannous sulfate is extracted with water and the aqueous solution evaporates in vacuo. Methanol is used to remove excess acid. It is also prepared by reaction of stannous oxide and sulfuric acid and by the direct electrolysis of high grade tin metal in sulfuric acid solutions of moderate strength in cells with anion-exchange membranes (36). 

The PVC crystaUites are smaU, average 0.7 nm (3 monomer units), in the PVC chain direction, and are packed lateraUy to a somewhat greater extent (4.1 nm) (21,33). A model of the crystaUite is shown in Figure 6. The crystalline stmcture of PVC is found to be an orthorhombic system, made of syndiotactic stmctures, having two monomer units per unit cell and 1.44—1.53 specific gravity (34—37). 

Cesium Halides. Cesium bromide, [7787-69-1], CsBr, mol wt 212.82, theoretical cesium content 62.45%, is a colorless crystalline soUd, having a melting point of 636°C, a specific gravity of 4433 kg/m, and a solubUity of 1.23 kg/L of water at 25°C. It is usuaUy prepared by neutrali2ing the carbonate or hydroxide with HBr, but it is also the primary product of the Dow process (25) for poUucite processing. 

Cesium hydroxide monohydrate [35103-79-8] CsOH H2O, mol wt 167.93, theoretical cesium content 79.14 wt %, is a colorless, hygroscopic, crystalline powder, having a melting point of 205—208°C and a specific gravity of 3500 kg/m. It is highly soluble, 8.6 kg/L of water at 15°C similar to the anhydrous hydroxide, it is an extremely strong base. 

Choline Chloride. This compound [67-48-17 is a crystalline dehquescent salt, usually with a slight odor of trimethyl amine (6). It is very soluble in water, freely soluble in alcohol, slightly soluble in acetone and chloroform, and practically insoluble in ether, benzene, and ligroin. Its aqueous solutions ate neutral to litmus and are stable (4). The specific gravity of these solutions is a straight-line function between pure water and the value of 1.10 for the 80% solution, which represents the approximate limit of solubiUty. Choline chloride absorbs moisture from the atmosphere at relative humidities greater than 20% at 25.5°C. 

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