Permanent hardness

Polymers are characteri2ed as thermosetting and thermoplastic with respect to the methods by which they are joined. Thermosetting polymers are permanently hard and do not soften upon the apphcation of heat they are joined by mechanical fasteners and adhesives. Several methods have been devised to join thermoplastic polymers, as weU as thermoplastic composite materials, which soften upon heating. 

Phenol—formaldehyde (PF) was the first of the synthetic adhesives developed. By combining phenol with formaldehyde, which has exceptional cross-linking abiHties with many chemicals and materials, and a small amount of sodium hydroxide, a resin was obtained. The first resins soHdified as they cooled, and it was discovered that if it was ground to a powder with a small amount of additional formaldehyde and the appHcation of more heat, the mixture would Hquify and then convert to a permanently hard material. Upon combination of the powdered resin mixture with a filler material such as wood flour, the result then being placed in a mold and pressed under heat and pressure, a hard, durable, black plastic material was found to result. For many years these resulting products were called BakeHte, the trade name of the inventor. BakeHte products are still produced today, but this use accounts for only a small portion of the PF resins used. 

Table 10. Properties of Permanent (Hard) Magnet Materials ...

The salts that cause permanent hardness are calcium sulfate, CaS04, calcium chloride, CaCl2, magnesium sulfate, MgS04, and magnesium chloride, MgCP. These are known as nonalkaline or noncarbonate hardness salts and cannot be removed by boiling they must be removed by chemical treatment. 

If the water is permanently hard due to MgS04, and lime is added, the precipitates calcium sulfate, CaS04, and magnesium hydroxide, Mg(OH)4, result, which are removed by sedimentation. 

Permanent hardness can also be due to the presence of CaS04, in which case the addition of soda (sodium carbonate), NaiC03, produces sodium sulfate, Na2S04, and calcium carbonate, CaCO, this precipitate once again is removed by sedimentation. 

The base exchange process removes both the temporary and permanent hardness salts from the water by allowing the water to flow through resin beads containing sodium zeolite, Na2Z. 

When the permanent hardness salt CaS04 passes through the bed, calcium zeolite (CaZ) and sodium sulfate (Na2S04 ) are formed, which are then flushed away. 

Many analyses quote total hardness. Some give temporary hardness (or carbonate hardness) and permanent hardness (or non-carbonate hardness), usually in consistent units so that the values can be added together to give the total hardness. The total hardness is actually the quantity of calcium (Ca) - - magnesium (Mg) in the water. If the total is not given directly, the values given for these two constituents must be added, after conversion to mg/1 as CaC03 if necessary. 

After the temporary hardness has been removed, any calcium and magnesium which remains is still capable of forming a scum with soap, and can also react to form boiler scale. This is called the permanent hardness. 

Most natural waters contain more hardness than bicarbonate. Only a few sources in the UK, usually from wells in sandstone strata, contain more alkalinity than hardness. In most cases the temporary hardness greatly exceeds the permanent hardness. This is especially tme of the hard alkaline waters, which come from chalk and limestone measures. 

This three-stage process is used for waters of high alkalinity and hardness. It actually removes most of the temporary hardness and so reduces the TDS of the water. However, in the process it increases the proportion of silica in the remainder. Any residual temporary hardness and the permanent hardness are softened in a conventional softener. 

The permanent hardness of a sample of water may be determined as follows. Place 250 mL of the sample of water in a 600 mL beaker and boil gently for 20-30 minutes. Cool and filter it directly into a 250mL graduated flask do not wash the filter paper,... 

Calculate the temporary hardness of the water by subtracting the permanent hardness from the total hardness. 

Permanent hardness or noncarbonate hardness is that portion of the total hardness that cannot be removed by heating water (e.g., chloride or sulfate hardness) and is the difference between total hardness and total alkalinity. 

The lime-soda softening process reduces the temporary hardness (icarbonate hardness) content of the RW, and often some of the permanent hardness (noncarbonate hardness) and some silica is also removed. 

Primarily the sum of Ca and Mg salts in water, although it may include other metal salts such as Al, Mn, Sr, and Zn. Temporary hardness (carbonate hardness) is that portion of the total hardness that can combine with C03 or HC03. The balance is non-carbonate or permanent hardness and is caused by Ca or Mg nitrates/sul-fates/chlorides, etc. Permanent hardness is equivalent to the excess of hardness over alkalinity. 

Temporary hard water contains divalent cations, such as Ca2+, Mg2+, and Fe2+ and the bicarbonate anion, HC03 . Heating produces, H20(1), C02 (g), and a carbonate precipitate. Permanent hard water does not form a precipitate upon heating the ions it contains, such as S042 are thermally stable. 

Installation type Temporary, often mobile setup Permanent, hard-wired and integrated... 

Percent by Mass proportion of the mass of each element in a compound expressed as a percent or proportion of solute mass as total mass of solution Perfect Gas see Ideal Gas Period a horizontal row in the periodic table Permanent Hardness condition of water when magnesium and calcium are combined with chlorides and sulfates rather than carbonates, cannot be removed by heating Petrochemical chemicals derived from oil or natural gas... 

Boiling does not remove magnesium salts, nor CaCOs at its own solubility level, nor noncarbonate calcium (i.e., Ca2+ that is counterbalanced by Cl- or another anion of which the Ca2+ salt is freely soluble). The hardness that remains after boiling is called permanent hardness. Permanent hardness plus temporary hardness is called the total hardness. 

How would the calculations be changed if 20 mg kg-1 CaCOs equivalent of the permanent hardness were actually due to noncarbonate calcium hardness ... 

What is meant by water hardness Explain the difference between temporary and permanent hardness. 

Temporary hardness, due to Ca(HC03)2, is lost by heating. Permanent hardness is derived from other salts, such as CaSO , and is not affected... 

The term hardness refers to the presence of calcium and magnesium salts. Temporary hardness is due to the presence of the bicarbonates of calcium and magnesium and permanent hardness to calcium and magnesium chlorides, sulphates and nitrates. Total hardness, as might be expected, is the sum of temporary and permanent hardness. Measurement is expressed as the equivalent concentration of calcium carbonate in milligrams pier litre or parts per million (m/v) and is also termed degree of hardness . Approximate classifications are... 

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