Although many solid samples are already in microcrystalline state, they are usually coarse powder particles or large aggregates, and more solid samples are coarse particles with recognizable crystal structure or shape, so it is generally necessary to process them into appropriate fine powder in experiments. Because most solid particles are fragile, the most commonly used methods are grinding and sieving. Only when the sample is extremely fine powder, and there is no graininess by hand, can it be considered that the granularity meets the requirements. Grinding continuously in mortar or ball mill until

The preparation method of sample powder can also be designed according to the physical and chemical properties of the sample For example, NaCl powder can be prepared by precipitating NaCl from a saturated solution of NaCl with alcohol, and the diffraction analysis effect of the obtained sample is excellent.

The properties of some samples will affect the diffraction pattern, so pay attention to it when working. For example, some soft crystalline substances will cause certain damage to the lattice after long-term grinding, which will lead to the broadening of the diffraction peak. At this time, annealing can be used; Some samples are unstable in the air and prone to physical and chemical changes (such as deliquescence, weathering, oxidation, volatilization, etc. ), so special sample preparation equipment and necessary protective and preventive measures are needed; For some anisotropic grains, the method of mixing isotropic substances can also be used for internal standard.

2. Manufacturing skills of powder diffractometer specimens

Powder diffractometer requires the sample to have a very flat plane, which often requires that the orientation of grains in the plane is completely disordered and there is no preferred orientation (sometimes it is required to make oriented samples in clay analysis). Common methods of making qualified diffractometer specimens.

Usually very fine sample powder (manual non-graininess), if it has no obvious anisotropy and is stable in the air, can be made into test pieces by "tabletting method". Firstly, the sample preparation rack attached to the diffractometer is fixed on a smooth glass sheet (such as mirror glass, microscope slide, etc.). Glue it with adhesive tape, then spread the sample powder into the window of the sample preparation rack as evenly as possible (preferably with a fine screen-360 mesh screen), then chop it gently with the blade of a small scraper to spread the powder evenly in the window, then press it gently with a small scraper, and finally use a safety blade (or the fracture of the glass slide). This method requires a large amount of sample powder, about 0.4cm3.

The smear method requires the least sample size. Sprinkle the powder on the microscope slide with the size of about 25×35× 1mm3 (the sprinkling position should be equivalent to the window position of the sample preparation frame), then add enough acetone or alcohol (if the sample is insoluble in it) to make the powder become a thin slurry and spread it evenly. The amount of powder only needs to be the thickness of a single particle layer. After acetone evaporates, the powder will adhere to the glass.

The above two methods are simple and commonly used, but it is still difficult to avoid a certain degree of preferred orientation of grains in the sample plane.

A special method for preparing samples with almost no preferred orientation;

Spray method. Sift the powder into a glass beaker. When the bottom of the cup is covered with a thin layer of powder, spray the plastic into fog beads and drop them on the powder. In this way, the plastic fog beads will gather the powder particles into fine particles. After drying, these fine particles are swept out of the beaker, and particles smaller than 1 15 mesh are separated for making test pieces. The preparation of the specimen is similar to the above smear method. The fine powder particles obtained by spraying method can also be made into test pieces by conventional tabletting method. Or directly spray the sample powder on the inclined glass slide coated with adhesive, and the obtained specimen can also greatly overcome the preferred orientation, and the disorder degree of powder orientation is much better than that of conventional smear method. Plastic method. Mix the sample powder with soluble hard plastic, dissolve it with appropriate solvent, dry it, and then grind it into powder. The obtained powder can be made into test pieces by conventional tabletting method or smearing method.

Please refer to C.S.Huthison, 1974 "Laboratory Manual of Petrography Technology" P226 for the method of making clay samples without preferred orientation, in which four methods with good reproducibility are introduced. I. Bajeva and D. Jenkins' filter pressing method (clay minerals, 1978, 13, 127) is very effective and time-saving. It usually takes only five minutes to prepare a sample, but a special filter is needed. The above method can also be used to manufacture other specimens with strong preferred orientation.