To analyze the effects of particle size on nano-crystalline materials, a method where the particle size can be adjusted is required. This study used SPEX SamplePrep’s 8000M Mixer/Mill® (Figure 1) equipped with zirconia and alumina vials to produce various nano-crystalline materials.
Ball milling is ideal for this application due to its ease of use and its ability to grind a wide variety of materials in relatively large quantities.
Figure 1. SPEX SamplePrep’s 8000M Mixer/Mill®
Li2O, LiNbO3, LiBO2, B2O3, TiO2 and Li2O:B2O3 mixtures were the media analyzed. The average particle size was identified by the grinding time and subsequently investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques.
The lithium containing materials were chosen due to their potential application as solid electrolytes. TiO2 is an interesting material because of its application as a photo catalyst.
Hygroscopic materials were handled by filling in the corundum grinding vial in an argon atmosphere and putting it into an airtight stainless steel container.
Grinding characteristics varied for each oxide, but a minimum particle size of approximately 20 nm was collected after grinding for 8 to 10 hours. XRD analysis and TEM data were used to determine the particle size.
The nano-crystalline materials analyzed are metastable, and particle growth was driven by heating as revealed by DSC. This information was considered during the sintering process to produce a solid, compact ceramic from the samples.
Earlier analysis by other groups revealed the particular suitability of the two-step sintering process with a lower temperature during the second step.
During the grinding process, TiO2, which was studied by two methods, exhibited partial phase transformation. Rutile consisting of additional impurities was reduced into smaller particles of pure Rutile (devoid of any impurities) when subjected to ball milling. Anatas that had the same impurities showed a higher fraction of these impurities after grinding. The use of TiO2 is extremely limited in high-energy ball milling experiments.
A heterogeneous material with a large number of different boundary layers is produced by mixing and subsequently pressing the ceramic components. It is possible to modify this network of different interfaces by changing the particle size.
Chemical changes caused by this chemical-mechanical procedure were identified during the analysis of a 50:50 mix of Li2O:B2O3. During the XRD analysis, the lines of the original compounds are identified after a short period of time, while new lines are observed after four hours. The newly formed product was found to be Li2B4O7, revealing that the end product of the reaction relies on the conditions on the boundary layers, but not on the composition of the mixture.
High-energy ball milling is an ideal method for particle size reduction and the analysis of subsequent chemical and physical changes. The characteristics of particle size reduction and following growth were similar with all oxides analyzed.
Some materials exhibited phase transformations, while other materials exhibited chemical reactions, which did not happen with the microcrystalline starting material.
This information has been sourced, reviewed and adapted from materials provided by SPEX SamplePrep.
For more information on this source, please visit SPEX SamplePrep.