Preparation of Samples by Back-loading Technique This presentation gives a description of the preparation of powder samples in PW1811 sample holders according to the backloading technique. The preparation of samples for analysis is of critical importance if accurate and fast results are to be obtained, and the procedures detailed in this section should be careful followed. Additionally, the introduction of errors, such as contamination, material loss, alteration of composition, especially of the sample surface, and change of lattice type, during the course of sample preparation, and afterwards, should be avoided. Contamination of the sample can be caused by dust, material from a previous sample which remained in the sample preparation equipment, or by material from the sample preparation equipment resulting from abrasion. Material loss is attributed to non-quantitative transfer in concentration determining operations (dilution, binder addition), loss of a small fraction of particle size as dust, and material remaining in the sample preparation equipment. Alteration of composition is attributed to losses of material particles which are of different composition to the average composition. For example, magnetic particles, fine dust, and volatile substances. Also, physical or chemical alteration; that is, by decomposition during preparation, such as oxidation, loss of combined water or carbon dioxide by overheating and pick-up of water or carbon dioxide from the air, or by the addition of materials of different composition such as by contamination. Change of lattice type; that is, transition to another phase, is attributed to pressure, temperature, or a combination of the two. The sample surface is only measured up to a depth of 1 or 2 mm in some cases, but in most cases only a hundred microns or even less. Typical examples of errors which can occur here are non-representativeness (sample surface has different composition than the average composition) caused by segregation, adhering particles or extracted particles, smearing and bad particle statistics, non-uniformity (sample surface is not equal for all samples) such as non-flat samples (concave or convex), or differences in surface roughness. Most of the errors can be avoided if samples are prepared carefully with cleaned equipment in a clean room. Once samples have been prepared they must be stored in a dust-free environment such as desiccators sometimes under vacuum or filled with moisture absorbers like Silica gel. If samples are difficult to handle, use pincers or gloves. Samples for X-ray analysis should be, in effect, infinitely thick, depending on the energy of the X-ray line and the matrix of the samples. Usually a 2 to 3 mm thickness seems to be sufficient. Once the sample has been prepared, care should be taken that it fits into the holder properly. To achieve a sufficient sample strength during sample preparation, the sample must be ground very fine, achieving an average grain size of 5 mm, with a maximum grain size of 25 mm. If both hard and soft materials are present together, the required size reduction of particles might be achieved by pressing the sample instead of grinding. This may prevent the softer material being ground by the harder one.

PW1770/10 Sample Preparation Kit The PW1770/10 Powder Sample Preparation Kit is designed for powder samples in the PW18xx sample holder series. It consists of a sample preparation table onto which the sample holder ring (PW1811/16 or PW1811) is clamped, a powder press block, a dusting brush and a Stanley knife blade.

Sample Preparation: Backloading Technique (1) Sample Holder Ring clamped onto the Preparation Table To prepare a powder sample in a PW1811 sample holder, proceed as follows: 1: Clamp the sample holder ring (PW1811/16 or PW1811/27) securely to the preparation table.

Sample Preparation: Backloading Technique (2) The Powder is spread in the Sample Holder Ring 2: Spread the powder in the holder ring, so that the powder is heaped up into a conical shape inside the holder ring.

Sample Preparation: Backloading Technique (3) The Powder is pressed with a Powder Press Block 3: Press the powder down firmly in the holder ring using the powder press block. Ensure that a firm and even pressure is applied by hand to the press block.

Sample Preparation: Backloading Technique (4) After pressing a Surplus of Powder is left 4: During pressing, some powder flows out of the holder ring. Use a knife blade to scrape the powder back into the holder ring and press down again using the powder press block.

Sample Preparation: Backloading Technique (5) Removal of the Powder Surplus with a Knife Blade 5: Remove all surplus powder above the rim of the holder using the knife blade.

Sample Preparation: Backloading Technique (6) Powder Surplus removed 6: Clean off all remaining surplus powder from the holder using the dusting brush.

Sample Preparation: Backloading Technique (7) Bottom Plate clamped onto the Holder Ring 7: Place the bottom plate (PW1811/00) onto the holder ring, and clamp it into position.

Sample Preparation: Backloading Technique (8) The Sample ready for use 8: Remove the complete sample holder from the preparation table by turning the sample preparation table upside down and pressing the spring loaded knob. A smooth, flat sample surface, flush with the sample holder ring surface is shown. NOTE: When the sample holders are used in X’Pert PRO systems, the reference plane of the holder must always be kept clean. Any spilled powder must be removed before loading the sample. The reference plane is the outer rim of the holder, where it is in contact with the three ball bearings in the ball bearings in the measuring position. The sample is now ready for use.

The Sample Gripper 9: When the sample holder, complete with the sample, is ready to be placed in the Sample Spinner (PW3064), use is made of the sample gripper. Place the sample on the table in front of the jaws of the sample gripper.

Loading the Sample into the Sample Gripper 10: Hold the sample gripper in one hand and carefully slide the sample holder into position in the sample gripper.

Loading the Sample into the Sample Spinner 11: The sample can then be loaded into the sample spinner. Place the sample spinner table in the loading position by pulling down the lever at the side of the sample spinner. Bring the sample in position above the table. Pull up the lever, so that the sample is fixed in the measuring position of the sample spinner. Then carefully pull back the sample gripper. The sample is now loaded into the sample spinner and ready for X-ray diffraction measurements.

Capillary mounted on Zero-Background Holder Glass capillaries can be attached with a little bit of modeling wax at the tips onto a silicon wafer (PW1817/32), which gives a very low background intensity. The silicon wafer can then be mounted in the PW1813/32 sample holder. This method is an alternative to using the capillary spinner in the transmission geometry.

Powder spread on Zero-Background Holder Small amounts of powder can also be attached to a silicon wafer with a drop of alcohol or a smear of petroleum jelly (vaseline). NOTE: Silicon supports must be cleaned carefully before use, preferably using an ultrasonic bath.