Calcium relative humidity

Because calcium chloride has a number of hydrates, the one that is in equiUbrium with a saturated solution is a function of the temperature. In this case, the sohd is dissolved as it absorbs water to form the saturated solution, and three phases are present soHd, saturated solution, and vapor. Systems having these three phases, or two soHds and a vapor phase, have a constant vapor pressure at a given temperature. Therefore, Class 2 drying agents can be used to maintain a constant relative humidity. 

Calcium cyanide Ca(CN)2 Reacts with air moisture to release HCN. If finely ground and the relative humidity of the air is >35%, this can occur fairly rapidly Releases HCN slowly on contact with water or CO2, or rapidly with acids Do not handle with bare hands Nonflammable white powder or crystals... 

With many electrolytes, AP is so large that the solid, when exposed to moist air, picks up water (deliquesces). This occurs with calcium chloride, whose saturated solution has a vapor pressure only 30% that of pure water. If dry CaCl2 is exposed to air in which the relative humidity is greater than 30%, it absorbs water and forms a saturated solution. Deliquescence continues until the vapor pressure of the solution becomes equal to that of the water in the air. 

White crystal, powder or flake highly hygroscopic the compound and its solutions absorb moisture from the air at various rates depending on calcium chloride concentrations, relative humidity and vapor pressure of water in the air, temperature, surface area of exposed material, and the rate of air circulation at 40% and 95% relative humidity and 25°C, one gram anhydrous calcium chloride may absorb about 1.4 g and 17 g water, respectively. (Shearer, W. L. 1978. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., vol. 4, pp. 432-6. New York Wiley Interscience) density 2.15, 2.24, 1.85, 1.83 and 1.71 g/cm for the anhydrous salt and its mono-, di-, tetra- and hexahy-drates, respectively anhydrous salts melts at 772°C, while the mono-, di-, tetra- and hexahydrates decompose at 260°, 175°, 45.5° and 30°C, respectively the anhydrous salt vaporizes at 1,935°C highly soluble in water, moderate to high solubility in alcohol. 

Results from studies using calcium carbonate showed that, relative to dry powder, the effect of conditioning at 55% relative humidity (at 20 °C) increased agglomerate strength threefold, which was attributed to the development of liquid-bridge forces [86]. 

Calcium and strontium salts of hyaluronic acid, at relative humidities of 66-92%, crystallize in a trigonal unit-cell, with a = b — 2.093 nm and c = 2.83 nm. On drying, the base-plane dimensions reduce to a = b = 1.832 nm, with c = 2.847 nm. Seven water molecules per disaccharide residue exist in the wet form, and two in the dry form. The adjacent chains are antiparallel, and the space group is P3212. The three disaccharide units in the 3(- 0.94) helix are nonequi-... 

C. Sulfamates prepared from weak bases form acidic solutions, whereas those prepared from strong bases produce neutral solutions. The pH of 5 wt % solution of ammonium sulfamate is 5.2. Crystals of ammonium sulfamate deliquesce at relative humidity of 70% and higher. Both ammonium sulfamate [7773-06-0] and potassium sulfamate [13823-30-2] hbemte ammonia at elevated temperatures and form the corresponding imidodisulfonate (12). Inorganic sulfamates are quite water-soluble, except for the basic mercury salt. Some relative solubilities of sulfamates at 25°C in 100 g of water are ammonium, 103 g sodium, 106 g magnesium, 119 g calcium, 67 g barium, 34.2 g zinc, 115 g and lead, 218 g. The properties of a number of sulfamates may be found in the literature (see Table 5). 

MCC, lactose, calcium phosphate dibasic, and mannitol were selected as common tableting diluents and were evaluated as received from their vendors. These materials are summarized in Table 2. Each material is available from several vendors with multiple grades. Three grades within each excipient were selected for their diverse range of physical and mechanical properties (3). These materials typically comprise 5% to 70% of a formulation. The samples were stored at environmentally controlled laboratory conditions of 20 2°C and 40% 10% relative humidity. 

The hygroscopicity of atorvastatin calcium, Form-I, was determined by exposing the samples to controlled relative humidity (RH) conditions (21-92% RH) at ambient temperature, and after 7 days the percent weight change was recorded. The substance was found to show less than 0.1%... 

Pantoprazole sodium was separately mixed in 1 1 ratios with sodium carbonate, mannitol, calcium stearate, colloidal anhydrous silica, povidone K90, crospovidone, and hydroxypropyl methylcellulose. The blends were stored at 40°C and 75% relative humidity, at 50°C and 75% relative humidity, and at 65°C for 30 days. No evidence for instability was noted, indicating that pantoprazole sodium is compatible with these common excipients. 

Calcium chloride is both hygroscopic and deliquescent. Thus, solid material will absorb moisture from the air or snow and ice until it dissolves, and the solution will continue to absorb moisture until an equilibrium is reached between the vapor pressure of the solution and that of the air. At 95 percent relative humidity, one pound of anhydrous calcium chloride will absorb 17.3 lb of water. The ability of calcium chloride to absorb moisture makes it useful in many construction, commercial, and industrial applications. Table 26.13 gives the market distribution of calcium chloride.47 U.S. demand for calcium chloride in 2000 was 1.3 million tons. 

Although these handsheets were stable toward dry aging at 90°C, they were unstable toward accelerated aging at 90°C and 50% relative humidity. However, they were more stable than aluminum-exchanged handsheets without calcium carbonate filler. 

Selenium and tellurium The elements are present as selenite and tellurite in dilute nitric acid solution. The mixture is spotted upon paper and dried thoroughly in the air. The solvent is dry n-butyl alcohol containing 4 per cent (v/v) of dry methanol. The atmosphere in the separation vessel is saturated with respect to the solvent vapour and the relative humidity is also maintained at 50 per cent by means of a saturated solution of calcium nitrate. The solvent is allowed to diffuse 8-10 cm down the strip (c. 2 hours). After evaporation of the solvent, the strip is sprayed with 0 5m tin(II) chloride in dilute hydrochloric acid. The tellurium is indicated by a black band (RF 0 1) and the selenium as an orange band (RF 0 5). It is possible to detect 1-5 pg of Se in the presence of 1 mg of Te by this method (see also Fig. VI.5g). 

A classic example of a solid—fluid ceramic powder synthesis reaction is that of calcination and dehydration of natural or synthetic raw materials. Calcination reactions are common for the production of many oxides from carbonates, hydrates, sulfates, nitrates, acetates, oxalates, citrates, and so forth. In general, the reactions produce an oxide and a volatile gaseous reaction product, such as CO2, SOg, or HgO. The most extensively studied reactions of this type are the decompositions of magnesium hydroxide, magnesium carbonate, and calcium carbonate. Depending on the particular conditions of time, temperature, ambient pressure of CO2, relative humidity, particle size, and so on, the process may be controlled by a surface reaction, gas diffusion to the reacting... 

From the CO2 partial pressure, we can determine the temperature at which the mineral becomes unstable when heated in air. For example, calcium carbonate becomes unstable above 810 K (MgCOs K, Mg(OH)2 T > 445 K, depending on relative humidity). At other partial pressures of CO2 different destabilization temperatures ire applicable. 

Insoluble solids, regardless of particle size, that have a relatively low interfacial tension and are readily wetted by water are called hydrophilic solids. These solids include clays (bentonite, kaolin, talc, magnesium aluminum silicate) bismuth salts, barium sulfate, carbonates, hydroxides, or oxides of calcium, magnesium, zinc, and aluminum and titanium dioxide. The hydro-philicity of a powder surface can be investigated with the help of moisture absorption studies in which the solid particles are exposed to varying relative humidities. Insoluble powders that absorb moisture below relative humidities of 70-80% at room temperature are said to be hydrophilic solids. 

Moisture content slightly hygroscopic. A well-defined crystalline hydrate is not formed although surface moisture may be picked up or contained within small pores in the crystal structure. At relative humidities between about 15% and 65%, the equilibrium moisture content at 25°C is about 2.0%. At relative humidities above about 75%, tribasic calcium phosphate may absorb small amounts of moisture. Particle size distribution Tribasic calcium phosphate powder typical particle diameter 5-10 pm 98% of particles <44 pm. 

Even when calcium hydrogen phosphate tablets with 2.5% crospovidone were stored for 3 months at 75% relative humidity, the rate of dissolution of the amaranth dye was increased rather than reduced [95]. Similar results were obtained with tiaramide tablets [405]. 

The conditions under which the free water is removed arc as important to proper drying as the physical and chemical properties of the sample. These two factors must be considered simultaneously when designing a drying procedure. Drying by controlling the temperature alone would not be reliable because of the effect the relative humidity (RH) has on the amount of water desorbed from the solid surface. However, drying under controlled conditions of temperature and relative humidity may be effective in free water removal only when a pure calcium sulfate is present. 

When a drying temperature is selected, the relative humidity should not be too low so as to initiate calcination, or too high so as to promote surface adsorption and capillary condensation. In addition the drying conditions of temperature and relative humidity must not affect the chemical equilibrium. However, since each calcium sulfate compound has its own stability region in the phase diagram, the drying conditions must be in a region where all the phases present in the sample remain stable. 

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