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題名 | 碳烴磷灰石(CAP)在溶液中的亞穩定平衡溶解度(MES)行為=Metastable Equilibrium Solubility Behavior of Carbonated Apatites |
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作者 | 許哲; 王澤人; Hsu, Jer; Wang, Zeren; Fox,Jeffrey L.; Higuchi,William I.; |
期刊 | 界面科學會誌 |
出版日期 | 19970400 |
卷期 | 20:1 1997.04[民86.04] |
頁次 | 頁43-65 |
分類號 | 341.34 |
語文 | chi |
關鍵詞 | 碳烴磷灰石; 亞穩定平衡溶解度; CAP; MES; |
中文摘要 | 本文研究的目的在於驗證一個至今尚未被列入考慮的假設(Hypothesis),這假設認為碳烴磷灰石 (Carbonated Apatite,或簡稱為 CAP) 樣品在溶液中將呈現亞穩定平衡溶解度 (Metastable Equilibrium Solubility,或簡稱為 MES) 之現象。造成 MES 現象的原因可能為在溶液中 CAP 溶解的速率遠大於 CAP 結晶的速率,當然這比較是建立於晶體╱溶液之間大小相同但正負相反的化學能(Chemical Potential)之基礎上。在MES現象下所測得的CAP溶解度並不見得是真正熱力學平衡狀態 (Thermodynamic Equilibrium)下所得到的溶解度。除了本實驗室所合成的CAP外,本文也使用其他實驗室所合成的CAP以作比較。CAP 之MES及MES分佈的測定乃將CAP與一系列代表不同飽和狀態的溶液作平衡,各個溶液含有不同量的鈣離子及磷酸根離子;而且為了方便,溶液飽和程度則以溶液活度積K其數學式為(aCa)��(aPO��)��(aOH)��)來表示。實驗時溶液使用量對CAP量的極高比率使得平衡過程中溶液組成分可被當作不變;CAP經1、2、4、或8天的平衡後,溶液中之未溶物將回收以決定在不同飽和液中CAP溶解的量,以及溶解是否達到平穩;CAP剛開始溶解的非常的快,然後趨於平穩,通常在2-4天的平衡後,再進一步的溶解已不多了。所測到的溶解度分佈可表示成CAP的溶解分數對溶液的pK的關係,這關係和一常態分佈(Normal Distribution)的模式相當符合。另外,a) 未溶殘留物的IR檢測,及 b) 在較低飽和度溶液中平衡的未溶物將與較高飽和度溶液再平衡(Re-equilibration)這兩個實驗用來進一步驗證在溶解達到平穩是處於MES的現象或是處於一個因CAP溶解與新磷灰石結晶之間互補的�睆A(Steady State);這些實驗結果更有力的說明CAP在溶液中所呈現的MES行為。 |
英文摘要 | The purpose of this investigation was to examine the heretofore not considered hypothesis that carbonated apatite (CAP) preparations exhibit the phenomenon of metastable equilibrium solubility (MES). The MES phenomonon may arise when crystal dissolution rates are very much greater than crystal-growth/precipitation rates when compared at equal but opposite (in sign) chemical potential differences between a crystal phase and solution. Preliminary studies had suggested that CAP preparations may be expected to exhibit the MES phenomenon and yield apparent solubilities very far removed from true theremodynamic equilibrium solubility. CAP samples prepared in our laboratories as well as samples prepared elsewhere were studied in the following manner. MES ans MES distributions were determined by equilibrating under stirred conditions each of the CAP samples in a series of acetate buffers containing various levels of calcium and phosphate ions corresponding to various magnitrdes of the solution ion acitvity product. K=(aCa)��(aPO��)��(aOH)��. A large solution-to-solid ratio was used to ensure that changes in the solution K before and after equilibration would be negligible. In a typical set of experiments, the residues were recovered after 1,2,4, and 8 days, dried, and weighed to determine whether MES had been attained. Generally, dissolution proceeded rapidly and, after 2 to 4 days, further CAP dissolution could not be detected. The resulting apparent solubilities were plotted as fraction of CAP dissolved versus pK and, typically, a normal distribrtion function satisfactorily fitted the experimental data. In order to demonstrate that the results corresponded to a true MES and not a steady-state situation involving equal dissolution and precipitation rates, (a) IR spectra of the residues were obtained and (b) residues from lower K equilibrations were reequilibrated in buffers with higher K values. Both these procedures showed that the apparent CAP solubilities and solubility distributions were closely consistent with the MES phenomenon and not a steady-state condition. Importantly, it has been shown in a separate study in this laboratory that the MESs and MES distributions of the CAPs also govern the surface-controlled kinetics of CAP crystallite dissolution in acetate buffers. One infers from this that the CAP MESs determined in the present study govern dissolution of CAPs over, at least, a time scale range from seconds to 10�� seconds. Also, this appears to be the first time that the driving force for dissolution of apatite crystallites has been independently and directly quantified via "solubility" measurements. |
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