Sintering in Snow and the Possible Role of Soluble Impurities

雪中​​烧结以及可溶性杂质的可能作用

• 批准号: 0537327
• 负责人: Jeff Dozier
• 金额: --
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Continuing grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-04-01 至 2010-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0537327&HistoricalAwards=false
• 关键词: Sintering; Snow; Possible; Role; Soluble

Four decades of snowpack sintering theory are at odds with observations and with theory for other materials. Vapor diffusion from ice grains to necks, controlled by surface radii of curvature, has long been considered the dominant sintering mechanism in dry snow. However, the detailed geometry of bonds and the shrinkage of snow during sintering are inconsistent with vapor diffusion and suggest combined grain boundary and surface diffusion as the dominant mechanisms. Snow contains minute quantities of soluble impurities, and scanning electron microscopy confirms their concentration on pore surfaces and at the boundaries separating bonded snow grains. Activated sintering of metals employs small quantities of dopants to reduce the powder melting temperature, activation energy and grain boundary energy, thereby increasing the rate and strength of sintering. Is sintering in snow a similar activated sintering process? Contrasting sintering theories lead to predictions about geometry that offer clear tests for identifying relevant processes under different conditions. For both pure and impure ice, we may distinguish between operative mechanisms and identify the controlling processes with a decisive set of sintering experiments across a wide range of temperatures, densities, particle sizes and geometries. Scanning electron microscopy will produce time-series observations of the sintering process from the compacted snow level down to the micrometer scale for snow crystals gathered in the field as well as those grown and allowed to sinter in the laboratory. Atomic force microscopy will carry the topographic component of the investigation down to molecular scale. Optical and electron scattering properties of ice allow us to track grain orientation, grain boundary geometry and migration, and pore evolution from initial adhesion through final stage sintering. Additional laboratory measurements will characterize changes in mechanical, bulk and microstructural properties due to sintering. This work has implications beyond sintering theory, from understanding snowpack stability and avalanche hazard during winter deposition to identifying factors affecting solute concentrations in the spring runoff.

四十年的积雪烧结理论与观察结果和其他材料的理论不一致。由表面曲率半径控制的从冰粒到颈部的蒸气扩散长期以来被认为是干雪中的主要烧结机制。然而，结合的详细几何形状和烧结过程中雪的收缩与蒸气扩散不一致，表明晶界和表面扩散相结合是主要机制。雪含有微量的可溶性杂质，扫描电子显微镜证实它们集中在孔隙表面和分隔粘合雪粒的边界处。金属的活化烧结采用少量的掺杂剂来降低粉末熔化温度、活化能和晶界能，从而提高烧结速率和强度。雪中​​烧结是否是类似的活化烧结过程？对比烧结理论导致了对几何形状的预测，为识别不同条件下的相关过程提供了清晰的测试。对于纯冰和不纯冰，我们可以通过一系列在各种温度、密度、颗粒尺寸和几何形状下进行的决定性的烧结实验来区分操作机制并确定控制过程。扫描电子显微镜将对现场收集的雪晶以及在实验室中生长和烧结的雪晶从压实的雪层到微米级的烧结过程进行时间序列观察。原子力显微镜将把研究的地形部分进行到分子尺度。冰的光学和电子散射特性使我们能够跟踪晶粒取向、晶界几何形状和迁移，以及从初始粘附到最后阶段烧结的孔隙演化。 额外的实验室测量将表征由于烧结而导致的机械、体积和微观结构特性的变化。这项工作的意义超出了烧结理论，从了解冬季沉积期间的积雪稳定性和雪崩危险，到确定影响春季径流中溶质浓度的因素。