Chemically induced fracturing in alkali feldspar
Chemically induced fracturing in alkali feldspar
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DOI：
10.1007/s00269-013-0617-1
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发表时间：
2014-01-01
影响因子：
1.4
通讯作者：
Abart, R.
中科院分区：
文献类型：
--
作者：
Scheidl, K. S.;Schaeffer, A. -K.;Abart, R.
实验研究了NaCl-KCl盐熔体交换Na+-K+阳离子过程中碱长石的破裂。由于碱长石的晶格参数对组分有明显的依赖性，任何由阳离子交换引起的组分梯度都会引起相干应力。如果应力超过临界水平，就会发生压裂。对（010）和（001）表面抛光的富钾宝石级碱长石进行了实验。当长石的钠含量超过10摩尔%时，形成了一个平行裂缝系统，裂缝间距规则。裂缝有一个一般的（洞）取向，不对应于任何长石解理。裂缝的方向与最大拉应力方向相当垂直。启动压裂所需的临界应力约为325 MPa。根据特征裂纹间距与相干应力之间的系统关系，估计I型裂纹扩展的临界应力强度因子K （Ic）为2.30 ~ 2.72 MPa m(1/2) （73 ~ 86 MPa mm(1/2)）。纵向弹性刚度的各向异性在裂纹平面上表现为最大值，而在裂纹法线方向上表现为最小值，这是由于纵向弹性刚度的各向异性造成的。
Fracturing in alkali feldspar during Na+-K+ cation exchange with a NaCl-KCl salt melt was studied experimentally. Due to a marked composition dependence of the lattice parameters of alkali feldspar, any composition gradient arising from cation exchange causes coherency stress. If this stress exceeds a critical level fracturing occurs. Experiments were performed on potassium-rich gem-quality alkali feldspars with polished (010) and (001) surfaces. When the feldspar was shifted toward more sodium-rich compositions over more than about 10 mole %, a system of parallel cracks with regular crack spacing formed. The cracks have a general (h0l) orientation and do not correspond to any of the feldspar cleavages. The cracks are rather oriented (sub)-perpendicular to the direction of maximum tensile stress. The critical stress needed to initiate fracturing is about 325 MPa. The critical stress intensity factor for the propagation of mode I cracks, K (Ic), is estimated as 2.30-2.72 MPa m(1/2) (73-86 MPa mm(1/2)) from a systematic relation between characteristic crack spacing and coherency stress. An orientation mismatch of 18A degrees between the crack normal and the direction of maximum tensile stress is ascribed to the anisotropy of the longitudinal elastic stiffness which has pronounced maxima in the crack plane and a minimum in the direction of the crack normal.