A FLOW LAW FOR DISLOCATION CREEP OF QUARTZ AGGREGATES DETERMINED WITH THE MOLTEN-SALT CELL
A FLOW LAW FOR DISLOCATION CREEP OF QUARTZ AGGREGATES DETERMINED WITH THE MOLTEN-SALT CELL
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DOI：
10.1016/0040-1951(95)00011-b
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发表时间：
1995-07-30
期刊：
影响因子：
2.9
通讯作者：
TULLIS, J
中科院分区：
文献类型：
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作者：
GLEASON, GC;TULLIS, J
我们使用熔盐池对一种天然石英岩的流变学进行了实验研究，该石英岩的水含量接近0.15wt.%。同轴变形实验是在恒定的活塞位移速率下进行的，在低应变时近似于恒定应变率。我们的天然石英岩在熔盐池中测量的强度大约是在固体介质中相同条件下测量的强度的一半，因为与固体封闭介质不同，熔融盐不会增加样品的强度；它减少了移动活塞上的摩擦，并允许清楚地识别‘命中点’。我们将实验条件限制为位错蠕变所需的条件，并仅使用攀移调节位错蠕变过程中测得的稳态流动应力来计算流动规律参数。确定了两个流动定律，一个是含有少量熔体(1-2%)的样品，另一个是不含熔体的样品。在这两种情况下，幂函数应力指数n均为4.0+/-0.9，大于以往报道的固体介质中石英集合体的位错蠕变流动定律。有熔体样品的活化能Q为137+/-34kJ摩尔(-1)，无熔体样品的活化能Q为223+/-56kJ摩尔(-1)，在先前测定的含0.1wt%水的石英团聚体的范围内。未熔体样品的指前项A为1.1×10(-4+/-2)Mpa(-n)S(-1)，熔体样品为1.8X10((-8+/-2))Mpa(-n)S(-1)。在熔盐池中测得的较低强度表明，以前在固体介质中实验确定的石英压力计关系式是不正确的。将无熔体集料的流动定律外推到自然应变率，可以预测出比大多数以前的石英流动定律更高的强度。然而，准确的外推需要确定流动应力与f(H2O)和/或a(H+)的关系。
We have used the molten salt cell to conduct an experimental study on the theology of a natural quartzite containing similar to 0.15 wt. % water. Co-axial deformation experiments were conducted at constant piston displacement rates, approximating constant strain rates at low strain. The strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because, unlike solid confining media, molten salt does not contribute to the strength of the sample; it reduces the friction on the moving piston, and it allows clear identification of the 'hit' point. We have limited the experimental conditions to those required for dislocation creep, and have used only steady-state flow stresses measured during climb-accommodated dislocation creep to calculate the flow law parameters. Two flow laws were determined, one for samples containing minor amounts of melt (1-2%) and one for melt-free samples. In both cases, the power law stress exponent, n, is 4.0 +/- 0.9, which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media. The activation energy, Q, is 137 +/- 34 kJ mol(-1) for samples with melt and 223 +/- 56 kJ mol(-1) for those without, within the range of previously determined values for quartz aggregates containing similar to 0.1 wt. % water. The pre-exponential term, A, is 1.1 X 10((-4+/-2)) Mpa(-n)s(-1) for samples without melt and 1.8 X 10((-8+/-2)) MPa(-n)s(-1) for those with melt. The lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct. Extrapolation of the flow law for melt-free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws. However, accurate extrapolation requires determining the dependence of flow stress on f(H2O) and/or a(H+).