Unmixing of Phosphorus-Bearing Melts on Earth and Mars

研究了磷对硅酸盐熔体粘度异常影响的结构原因。已发现磷的添加增加过碱性组合物熔体的粘度。进一步添加P2 O 5导致熔体粘度降低。尽管在以前的研究表明，这些含磷熔体是未混合的，无论是拉曼光谱，也没有NMR光谱证明这一点。初步的量热测量的玻璃化转变温度的一些目前的P2 O 5轴承过碱性Na 2 O-Al 2 O3-SiO2熔体已显示有2个玻璃化转变温度，表明有2个未混合的玻璃存在于样品中，尽管玻璃是无色和透明的。通过扫描电子显微镜对宏观结构的进一步研究表明，玻璃样品确实未混合。在高温（文献数据）和低温（本数据）下观察到的粘度增加表明，该熔体在高达1446 ℃时未混合。鉴于这些意见，可能的不混合的P2 O 5轴承熔体将在这里使用量热法，粘度，拉曼，和SEM技术进行研究。所研究的一系列成分范围从简单的Na 2 O-Al 2 O3-SiO2和CaO-Al 2 O3-SiO2到更复杂的火星成分（古谢夫陨石坑中的香槟岩）。这些熔体的不混合不仅对粘度，而且对不同成分的共存共混岩浆的结晶过程也有影响。磷在熔体中一般被归类为助熔剂。其它助熔剂是B、F和H2O。硼也被认为会导致熔体不混合。此外，由于向具有CaO和Na 2 O的熔体中添加硼将导致过碱度增加，反应BO 4 = BO 3 +NBO随着CaO/Na 2 O的增加而向右移动，因此熔体中B2 O3的存在预计会影响含P2 O 5熔体的不混合。一旦含P2 O 5熔体的不混合问题得到解决，该项目将扩展到含P2 O 5熔体与添加的B2 O3，F和H2O的不混合。

The structural reasons for the anomalous effect of phosphorus on silicate melt viscosity will be investigated. The addition of phosphorus has been found to increase the viscosity of peralkaline composition melts. Further addition of P2O5 results in a decrease in melt viscosity. Despite indications in previous studies that these phosphorus-bearing melts are unmixed, neither Raman spectroscopy, nor NMR spectroscopy has proven this. Preliminary calorimetric measurements of the glass transition temperature of some of the present P2O5-bearing peralkaline Na2O-Al2O3-SiO2 melts has shown there to be 2 glass transition temperatures, indicating that there are 2 unmixed glasses present in the sample, despite the glass being colourless and transparent. Further investigation of the macroscopic structure via scanning electron microscopy reveals that indeed the glass sample has unmixed. The increase in viscosity observed at both high (literature data) and low (present data) temperature indicates that this melt is unmixed up to 1446 °C. In view of these observations, the possible unmixing of P2O5-bearing melts will be investigated here using calorimetry, viscosity, Raman, and SEM techniques. The array of compositions investigated range from the simple Na2O-Al2O3-SiO2 and CaO-Al2O3-SiO2 to more complex Martian compositions (the Champagne rock in the Gusev Crater). The unmixing of these melts has implications not only for viscosity but also for crystallisation processes in co-existing co-mixed magmas of different composition. Phosphorus is in general classed as a fluxing agent in melts. Other fluxing agents are B, F and H2O. Boron is also known to cause melts to unmix. Further, as the addition of boron to the melt with both CaO and Na2O will result in an increase in peralkalinity with the reaction BO4=BO3+NBO shifting to the right with increasing CaO/Na2O, the presence of B2O3 in the melt is expected to affect the unmixing of the P2O5-bearing melts. Once the question of the unmixing of P2O5-bearing melts has been addressed, the project will extend to the unmixing of P2O5-bearing melts with added B2O3, F and H2O.