Using the Shatterbox

Use of the Shatterbox

Introduction

The shatterbox is made of tungsten carbide, and on that account is both very heavy and very fragile even though its interior surfaces are quite hard. (An alumina shatterbox differs only in that it is not quite as heavy.) The shatterbox is an extremely expensive piece of equipment, and its loss would shut the sample preparation lab down indefinitely until a replacement could be financed, purchased, and delivered. Don't be a Murgatroyd J. Muddleup -- follow the instructions given here exactly, and handle this piece of equipment with extreme care!!

Because the internal parts are both heavy and very smooth, they can be difficult to handle. DO NOT drop the shatterbox, any part of it, or strike the parts against one another: They will chip, and the shatterbox will be destroyed. DO NOT attempt to use the shatterbox unless you thoroughly understand how to use it safely and competently, and are prepared to put that knowledge into practice. Also, ON NO ACCOUNT should samples be introduced into either shatterbox which have not been previously crushed to less than 1/4 inch (6 mm) in longest dimension. Particle sizes larger than this will chip the shatterbox, destroying it. Large flakes can commonly be broken in the fingers, while more massive particles can be reduced in a Plattner mortar and pestle. YOU SHOULD UNDERSTAND that it is a great deal more injurious to run too little sample than too much: Never use less than 15 to 20 ml of sample (not including voids!), or the mill will be chipped and (as usual) destroyed. If you are using the tungsten carbide grinding vial for the Spex Mixer Mill, use between 3 and 10 ml of sample to avoid damage.

The instructions which follow assume that the tungsten carbide shatterbox is to be used, but there is no practical difference between it and the one made of alumina except that the run times are longer in the latter case. Where the tungsten carbide shatterbox uses run times of 10 to 20 seconds or so, the alumina shatterbox uses run times of approximately 5 to 7 minutes and you will therefore want to scale durations given below accordingly.

Note also that the building compressed-air system may have a great deal of water in it from time to time, especially during the summer months when the relative humidity is very high. (We're talking king-sized squirtgun here, so be careful or you'll get soaked with oily red water.) Because this water will contaminate the shatterbox and the residue is difficult to remove, it is always best to use compressed air from the water trap located on the wall immediately to the left of the water-lubricated rock saw. The water trap will intercept essentially all liquid water in the system, and though it cannot remove vapor, this turns out not to be a problem. Turn on both air shut-off valves and then open the bleed petcocks on both traps to drain any water they may contain, before you begin work and after you finish. Always leave the valve leading to the blue filter mechanism closed when you are done; the valve to the lower reservoir should remain open at all times. As always, use your head as well as the equipment and do not let the air hose rest against moving machinery, most particularly the shatterbox: When the hose is worn through the braid, it is ruined and the lab will be down until a replacement can be purchased and installed. It should be obvious, but for some reason commonly isn't, that this applies to power cords as well.

Procedure

1. Begin by connecting the lab timer (capable of measuring durations accurately in seconds) to the shaker and by using the air blast to clean the recess in the shaker that receives the shatterbox. Both the shaker top and the outer shell of the shatterbox are aluminum, and with use there develops a quantity of aluminum powder in the recess which can adhere to the outside of the shatterbox, ultimately to be dislodged into the sample when it is collected after a run. The recess should be blown clean every five or six samples.

2. Clean the interior of the shatterbox, and its parts, with an air blast, and then methanol and a Kimwipe. DO NOT, under any circumstances, clean the shatterbox with water, soap and water, or any hard object such as a spatula. If water is used for cleanup there is an intermediate liner of steel which will rust, both contaminating and eventually weakening the shatterbox. Hard instruments will themselves contaminate the shatterbox by leaving their streak on the inside, and they present a serious risk of chipping. If there is sample caked onto the inner parts of the box which cannot be removed with methanol and a Kimwipe, clean it by running a small handful of filter sand (obtained from the lab operator) for 10 seconds. See items 4, 5 and 6 below for instructions with regard to loading the shatterbox and securing it in the shaker. Running for a longer time than 10 seconds when cleaning is of no advantage because the sand becomes too fine to abrade the caked-on powder; if one run is not enough, repeat the treatment until the shatterbox is clean. Discard the spent charge of sand and clean the shatterbox with the air blast after each such treatment; methanol and a Kimwipe are not required until you are again ready to pulverize your rocks. Whether it is necessary to clean with sand or not, finish the preparation process by running a 5-dram vial full of twice-crushed blank (see items 4, 5 and 6) to "get the box dirty with your own rocks." Discard the powder and clean thoroughly, first with the air blast and then with methanol and a Kimwipe, before proceeding to the next step.

3. Thoroughly clean the sample splitter and a 5-dram sample vial with the air blast, and clean a spatula with methanol and a Kimwipe. Assemble a quantity of plain white sheets of paper, 8 1/2 by 11 inches, to use when unloading your sample from the shatterbox. You will need an indelible marker to write sample numbers on the sides of the vials.

4. If there is more than two-thirds of a 5-dram vial full of twice-crushed sample, then place the entire sample into the hopper of the sample splitter, and distribute it evenly with the spatula. Open the gate and split the sample into the aluminum containers provided. Use the spatula to chase any flakes which may hang up in the splitter, and GENTLY blow any lingering powder down into the containers with the air blast. Repeat this procedure until you have split a portion of the sample which fills the vial one-half to two-thirds full. Use the vial to load the sample into the shatterbox, taking care to see that it is evenly distributed in the annular spaces on either side of the ring. (Note that the alumina shatterbox does not have a ring.) Sweep any lingering chips of sample down into the box with your fingers and lay the top in place.

5. Put the closed shatterbox in its recess in the top of the shaker; lay the strongback across the top of it, taking care that the socket engages the boss on the top of the box; and tighten the strongback down with the handwheel. Use two hands and make certain that you get the handwheel tight! One group of students failed to observe this precaution and the box got away from them. It hit the wall on the other side of the room on the fly, and was destroyed. Fortunately, though the room was crowded with people, no-one was injured as a result of this rather spectacular and expensive mistake.

6. Make sure that the operating switch of the timer is in the "off" position, and set the timer for 10 to 15 seconds. The actual length of time used will vary depending on the hardness and the degree of alteration of your sample (harder = longer, altered = shorter), but a setting in this range will do to start. Flip the operating switch "on;" wait until the timer shuts the shaker off; and then flip the operating switch "off" again. Watch the assembly as it operates, and shut the shaker down if there is any indication that the handwheel is coming loose.

7. Release the shatterbox from the shaker and take it back to the bench. Use the air blast to blow any aluminum powder or chromium flakes from the outside of the box, and then open the lid. Use a clean Kimwipe to brush the sample clinging to the inside of the lid onto an 8 1/2 by 11 sheet of paper, and then lay the lid aside upside down.

8. Take hold of the puck in the center of the shatterbox, and move it gently from side to side. If the sample feels gritty as the puck moves over it, then it is not ground sufficiently fine. If the puck moves smoothly, then all is well; proceed to item 9. If the sample needs more grinding time, then put what you have removed of it back in the box, replace the lid, and put the box back in the shaker. DO NOT run the sample for another 10 or 15 seconds! You will run the risk of overgrinding, especially with altered samples. Run it for 5 seconds, and then check it again. Repeat this procedure as is necessary until the sample is ground sufficiently fine. Add all of the 5-second repeats to the original grinding time to get the total amount of time your samples require, and use this for similar rocks in subsequent runs. It is vital that the sample be properly pulverized: If it is not, your trace element analyses -- if conducted using briquetted pellets -- will be much less reliable, and your sample will damage the (very expensive -- it's a rule) equipment used to make the pellets. Also, there may be difficulty getting your powders to dissolve in the flux of the fusion methods.

9. When your sample is properly ground, fold a sheet of the 8 1/2 by 11 paper into a trough without creasing it, and use it to collect the powder. Crumple a dry Kimwipe and use it as a brush to sweep the powder off of the shatterbox parts, and out of the box, onto the paper trough. Be thorough. Be careful in transferring the powder from the paper trough into the 5-dram vial because the powder can clump and come down all in a heap. If this happens, and you have a spill, you will have to pulverize another aliquot of your sample, but folding the paper gently into a trough greatly reduces this tendency. After you have stoppered the vial, mark the sample name on the sides, NOT the top alone, in at least two places. Tops can get inadvertently swapped between vials, with potentially disastrous results if they alone carry the sample identification.

10. Thoroughly clean the shatterbox, the sample splitter, and spatula as outlined above, and proceed with the next sample. It may be that if your sample is altered, or you have drastically overground it, it will cake onto the inside of the shatterbox. If this is the case, clean the box with sand as described in item 2 and then follow with a blank charge. It may be possible to reduce the grinding time and reduce the caking, but do not reduce the time to the point that the puck feels gritty when you move it over the sample. It is not unusual for altered rocks, of all stripes, to have quartz or some other very hard mineral in them, and you must pulverize these materials along with the others. You may just have to live with a caking problem, and go to the trouble of cleaning the shatterbox with sand after each run.

11. When you are finished for the day, or have finished all your samples, ALWAYS clean the shatterbox for the next user and lock it away. Return any borrowed implements, including the timer, sample splitter, cart, and shatterbox key, to the lab operator.