Calcium polyphosphate fiber

The calcium polyphosphate fibers are very very slowly dissolved in water. Even in boiling 0.1N HC1 the fibers are resistant to degradation, but the fibers are not as resistant to boiling 0.1N NaOH solutions. See Figure 2. 

Chrysotile asbestos is decomposed at temperatures below 500°C. Calcium polyphosphate fibers do not melt at temperatures below 970°C, but the P-phase phosphate is converted to a-phase phosphate at 940°C. 

It is concluded that calcium polyphosphate fibers are viable candidates as safe replacements for asbestos in many of its applications, particularly in those applications where human exposure is considered hazardous. 

Z. Y. Sun and L. Zhao (2002). Feasibility of calcium polyphosphate fiber as scaffold materials for... 

Calcium polyphosphate fibers were grown from a water soluble melt. The raw materials used were lime (CaO) and phosphoric acid (HjPO ) to give... 

Calcium polyphosphate fibers were grown as dendritic spherulites. Sodium calcium polyphosphates were grown as simple crystals and then milled. 

Cross-linked potassium Kurrol s is prepared in exactly the same manner as the calcium polyphosphate fibers. The only difference is potassium is substituted for calcium in the preparation of potassium Kurrol s salt. There is strong reason to question whether or not the strange solution behavior of cross-linked potassium Kurrol s salt is a result of cross-linking in the crystalline phase or is a result of ultra long polyphosphate chains mixed with an independent ultraphosphate phase that contains the required cross-linking. All of the observations which led to the belief that the molecule-ions in the crystalline phase were cross-linked can be explained based upon the two phase model where the ultraphosphate phase is rather quickly degraded in aqueous solutions to form acidic groups. 

To obtain high tensile strengths of calcium polyphosphate fibers crystals it is necessary to grow polyphosphate molecule-ions as long as possible. When a phosphate group from a high temperature melt system moves to a high... 

Kasuga T, Hosono H., and Abe Y, "Bioceramics Composed of Calcium Polyphosphate Fibers," Phosphorus Sulfur, Silicon, 76, 247-50 (1993). 

Rates of solution were measured for calcium sodium polyphosphates and calcium polyphosphate fibers. Figure 3.6 is a typical example. Again these results are not strictly reliable because no two systems will yield results that are precisely the same. Variables range from temperature, particle size, rate of stirring, enzymes, impurities, amorous content, influence of grinding or milling, and age of samples studied, to mention but a few. It was not as important to know an exact rate of dissolution as it was to know that samples would indeed dissolve in a matter of... 

The measured values for phosphate fibers compare very favorably with other fiber systems of common use. It is interesting that sodium calcium polyphosphate fibers have a higher tensile strength than calcium polyphosphate fibers. Fiber diameter could account for this difference, or that anions of calcium polyphosphate are more linearly packed in the crystals. Kevlar is a fiber that has been extensively used in nonasbestos brakes for automobiles and it performs well. 

Cookbook examples of methods of preparing calcium polyphosphate fibers are given in patents granted for these compositions of matter. For those interested in growing their own crystals, Example 1 of United States Patent No. 4,360,625 of November 23, 1982 will be repeated here. 

In the author s attempts to find substances that would modify properties of calcium polyphosphate fibers, additions of magnesium oxide or magnesium phosphates seemed to have the most favorable influence, but results were erratic. It seemed that sometimes there were vast improvements and, at other times, no influence could be seen. Answers to this behavior may have been similar to Mr. Ngo s discovery that two crystallizations were required to prepared outstanding fibers of [NaMg(P03)3]rt. These melts were first crystallized, remelted, and then crystallized again to yield some of the more beautiful fibers made in this work. Unfortunately, the doping of calcium phosphate remains a mystery. This project was terminated before it was completely understood. 

The first preparations of calcium polyphosphate fibers were orchestrated following a preplanned approach that was altered as results demanded. Conversely, sodium calcium polyphosphate fibers were discovered. Rather than following a calculated scientific logic we were exploring. We were prospecting a phase diagram around calcium metaphosphate compositions. This discovery was blind luck and it was not obvious that these crystals contained fibers until they were milled for analyses. 

Table 6.1. The Physical Properties of Calcium Polyphosphate Fibers Compared to...

Two entirely different approaches to the growth of fibers were required for [Ca(P03)2]Ai and [NaCa(P03)3] fibers. Calcium polyphosphate fibers were grown as dendritic spherulites, while sodium calcium polyphosphates were grown as single crystals that were not fibrous in any respect until milled. Both crystals could be grown in a belt furnace discussed below, but only the [NaCa(P03)3] crystals could be grown in a calciner in which feed crystals were sprayed with feed liquor. With additional work it is possible that even the [Ca(P03)2]n could have been grown in this approach, but the decision had been made to commercialize [NaCa(P03)3] crystals rather than calcium polyphosphate crystals. Both approaches will be discussed in detail. 

One young chemist was heard to say, If I wanted to torture a person, I would strip him and lock him in a room of calcium polyphosphate fibers. His point was well taken and this problem has never been solved, but it probably could be solved in a relatively short period of time. It should be emphasized that only [Ca(P03)2]n fibers, and not [NaCa(P03)3] , were irritating. Not all batches of [Ca(P03)2]n fibers were irritating. This alone is evidence that this problem can be eliminated. It is merely a matter of knowing which variables must be controlled. Some work... 

As problems were identified, solutions would arise almost as if by magic. Nevertheless, it was obvious that calcium polyphosphate fiber could never be commercialized as a commodity product using this process. It still has some very interesting properties for specialties where price is not a major issue. Some medical uses could fall in this area. Abe s work in Japan has concentrated on this particular compound and some outstanding results have been obtained. 

Because profit potential from an asbestos replacement in the pipe market is huge, much effort was expended attempting to reinforce cement pipes with calcium polyphosphate fibers. It should be mentioned that cement pipe utilized the very poorest, cheapest, and shortest grades of the chrysotile market. It was inexpensive and was not much better than a waste stream of the industry. This made it difficult for a manufactured fiber to compete, irrespective of its safety. It is doubtful that phosphate fibers could be economically attractive even if they performed in cement pipe. 

Despite the poor showing of calcium polyphosphate fibers in reinforcing Portland Cement, calcium polyphosphate and sodium calcium polyphosphate fibers were tested in plastics. In these tests [Ca(P03)2]n fibers performed very well indeed. This was particularly true for epoxy resins. 

Sodium calcium polyphosphate fibers performed similarly to asbestos in phenol formaldehyde resins. It did not compare well to potassium titanate in polyester resins. [Ca(P03)2]n fibers, being developed by Abe in Japan, should perform much as potassium titanate, but without the hazards. 

---