SPEX SamplePrep Mixer/Mills are a variant of the ball mill or jar mill, which grinds samples by placing them in a container along with one or more grinding elements, and imparting motion to the container. The containers are usually cylindrical; the grinding elements are most often balls but may be rods, cylinders, or other shapes. Generally the containers and grinding elements are made from the same material. As the container is rolled, swung, vibrated, or shaken, the inertia of the grinding elements causes them to move independently, into each other and against the container wall, grinding the sample. Variations of the “ball mill” range from laboratory mills with a sample capacity of a gram or less to large industrial mills with a throughput of tons per minute.

SPEX SamplePrep Mixer/Mills can be described as laboratory scale, high-energy ball mills (also known as high-energy shaker mills). They are designed to pulverize a sample rapidly while mixing it homogeneously—an approach long known to be effective in preparing samples for emission spectroscopy and XRF spectrometry. SPEX SamplePrep Mixer/Mills are also widely used for blending powders and making emulsions. Due to its high-energy action the SPEX SamplePrep 8000M Mixer/Mill in particular has recently become indispensable in the search for superconducting alloys. Since this often involves long-term continuous operation of the mill, our warranty is limited and special maintenance is advised. Contact one of our Application Specialists for details.

The shaking action of a SPEX SamplePrep Mixer/Mill is both complex and forceful. As the vial is swung back and forth in a shallow arc, its ends are displaced laterally in a “figure-8”; this distributes the grinding-ball impact over wide areas of the caps. In typical ball mills there are many grinding elements which travel only a short distance before impact; in SPEX SamplePrep Mixer/Mill vials there are one or two balls which travel the length of the vial at high velocity. Because SPEX SamplePrep Mixer/Mill clamp movement is extremely rapid, the balls develop high G-forces; this not only grinds brittle samples efficiently but can be used to bond metal compounds in a process called mechanical alloying.

A distinct advantage of the SPEX SamplePrep Mixer/Mill design is the large selection of vial materials: hardened steel, stainless steel, tungsten carbide, alumina ceramic, zirconia ceramic, silicon nitride, agate, and plastic. Not only do these different media offer a wide range of grinding and blending performance, but they reduce contamination problems by allowing the analyst to avoid materials whose presence in the ground sample is objectionable.

Which SPEX SamplePrep Mixer/Mill is best for your application can best be determined through three criteria: the weight/volume of the sample to be ground, the number of samples per day, and the preferred container material. The smaller of the SPEX SamplePrep Mixer/Mills, the 5100, has the capacity for running three 1/2 in. x 1 in. vials or two 3/4 in. x 2 in. vials; the weight of typical samples for this mill is around 0.5g for the smaller vials and 1g for the larger ones. The larger SPEX SamplePrep Mixer/Mills, the 8000M and 8000D, typically grind samples in the 10g range; both use the same vials but the SPEX SamplePrep 8000D has twice the output of the SPEX SamplePrep 8000M Mixer/Mill. For assistance in choosing the SPEX SamplePrep Mixer/Mill and grinding or blending containers which would be best for your application, please call SPEX SamplePrep Sample Preparation at 1-800-522-7739 or 732-549-7144.

5100 Mixer/Mill A Highly Effective Impact Grinder and Blender for Smaller Samples

As with the larger SPEX SamplePrep 8000M Mixer/Mill, the high grinding and mixing efficiency of the SPEX SamplePrep 5100 Mixer/Mill is a result of its three-dimensional action. A one-inch component of motion along the axis of the vial is complemented by two motions at right angles to the vial axis: a 3/16 in. horizontal movement and a 1/4 in. vertical oscillation. The resulting action is consistent with the general shape and size of the vials. That is, at every stroke there is an impact at the end of the vial—over 100 per second—to crush the material rapidly and reproducibly. The 5100 Mixer/Mill offers many advantages over other small mixers:

• Continuously adjustable jaws accept vials from 1 in. to 21/2 in. long and up to 3/4 in. in diameter without adapters.
• Simultaneous accommodation of two 3/4 in. diameter or three 1/2 in. diameter sample vials, thus permitting greater productivity.
• Vials available in plastic, steel, agate, and tungsten carbide.
• Motion along three axes affords more vigorous grinding action than any instrument its size.
• Rugged construction ensures a long life of heavy work.
• Housing protects entire mechanism and vials.
• Resettable electric timer ensures reproducible running times.

8000 Series Mixer/Mills

The SPEX SamplePrep 8000-series Mixer/Mills are efficient, compact laboratory mills capable of pulverizing one or two samples in the 10-gram range. Functionally described as shaker mills or high-energy ball mills, these Mixer/Mills shake one or two containers back and forth several thousand times a minute. Multi-purpose mills, they are capable of rapidly reducing hard, brittle samples to analytical fineness, blending powders, making emulsions, and performing mechanical
alloying. There are two versions: the classic 8000M Mixer/Mill, with one clamp, and the 8000D Mixer/Mill with two clamps.

In each clamp, the vial, which contains a sample and one or more balls, is shaken in a complex motion which combines back-and-forth swings with short lateral movements, each end of the vial describing a figure-8. The length of that swing is the same as the internal length of the vial, about two inches. With each swing the balls impact against one end of the vial, simultaneously milling the sample to a powder and blending it. Because of the amplitude and velocity of the clamp’s swing, each ball develops fairly high G-forces, enough to pulverize the toughest rocks, slags and ceramics.

The single-clamp 8000M Mixer/Mill, known simply as “the Spex Mill” to thousands of its users, has served spectroscopists and analytical chemists for over forty years. The clamp mechanism has changed little since the earliest versions, simply because it has proven extremely durable. Many of the earliest 8000 Mixer/Mills are still in service. Now the wind-up timer has been replaced by an electronic 100 minute timer and the mill’s safety features have been improved.

The dual-clamp 8000D Mixer/Mill combines two clamps on
one shaft with an electronic 100-minute timer. As the two clamps
move in balance, vibration is reduced and component life extended.
Two fans also keep the clamps and motor cool during operation. 

APPLICATIONS

8000-series Mixer/Mills have been used for pulverizing rocks, minerals, sand, cement, slag, ceramics, catalyst supports, and hundreds of other brittle, often hard samples. Early on, the 8000 was used to grind samples, then blend them with graphite for arc/spark spectroscopy; now similar samples are ground, then blended with binder before being pressed into sample discs for XRF. The vigorous motion of the clamp is also excellent for making emulsions, such as paints, inks and pharmaceuticals. 8000M Mixer/Mills have also achieved notoriety for their ability to mechanically alloy small quantities of superconductor materials.

VIALS

8000-series grinding vials are 21/4 inches wide and up to 3 inches long. They have an internal volume of 50-60 ml, with a grinding capacity of about 10 ml and a blending capacity of 25 ml. They are available in tool steel, hardened steel, tungsten carbide, alumina ceramic, zirconia ceramic, silicon nitride, agate, and methacrylate.We recommend that vials for the 8000D Mixer/Mill be purchased and used in pairs, to maintain the balanced motion of the clamps. If only one sample needs to be ground, the second similar vial should be clamped in place without sample or ball.

CONTROLS

The electronic timer of the 8000 series Mixer/Mill displays the programmed running time in minutes and seconds; while the mill is operating, the timer also counts down the amount of time left in the run. Push-button controls include start, stop and pause functions as well as timed programming. The timer is factory-set for a maximum of 100 minutes but this may be extended to 1000 minutes for special applications such as mechanical alloying. Prolonged continuous operation of Mixer/Mills requires special maintenance. Failure to conduct preventative maintenance will void the warranty. Contact one of our Application Specialists for details.

SAFETY FEATURES

Both 8000-series Mixer/Mills are equipped with safety interlocks so that they cannot be operated with the lid open. Each clamp has a lock nut to prevent it from loosening while the mill is running. The motors are also equipped with a thermal overload protector.