LOTO-eng gas-loading system for DAC cell  permit to load liquid gas. Only the type of DAC endowed with a membrane can be used during gas loading, the remote-control system allows sample pressure to increase while the DAC is still immersed in liquid gas. This technique allows DACs to be loaded with condensed gases such as nitrogen, argon, oxygen, etc. The advantage over gas loading is the higher initial density that determines a smaller volume reduction under compression.

The gas-loading system has been constructed to load diamond-anvil cells with various kinds of gases at room temperature. The gases either serve as hydrostatic pressure media or samples by themselves. The present high-pressure vessel can accommodate various types of diamond-anvil cells simply by changing the holder.

How it works?

The gas-loading apparatus you can see on the layout below. The DAC is placed inside the gas-loading chamber and its flange closed.  Fluxing of the gas-loading with pure argon gas will guarantee the presence of only argon in the chamber.  Is possible to use a vacuum pump to evacuate all the impurity inside.
Then the gas-loading may be placed inside the vessel which will also hold the liquid nitrogen.  Liquid nitrogen is then spilled in to this vessel, while pure argon gas is let into the DAC’s chamber at an optimum rate. The level of liquid argon collected in the vessel is monitored through the top glass viewing port of the gas-loading helped of a blue light. Once the desired level, surely over the diamond anvil is reached, the flow of liquid gas can be stopped a.  The DAC by remote control is then tightened so that liquid gas becomes trapped in the gasket hole between the diamond anvils.
The cell then be removed from the gas-loading and slowly brought back to room temperature.  A low temperature heat exchanger ensures a very efficient cooling and condensation of the argon gas.  A special microvalve made by LOTO allows to close the capillary and disconnect the DAC from the gas loading kepping pressure in the membrane.The valve is small so to fit together with the DAC in the gas or cryogenic loading chambers. For this last purpose the microvalve has been tested up to 200 bar at room and at liquid nitrogen temperature. In this way is possible to linked again the cell to the pressure device.

The torque screwdriver ensure tightening to a specified torque and permit to give the right force to the DAC cell.

The screwdriver allow the torque to be set to any value within a range, our needs ask from 0,2 Nm to 2 Nm.

All have a torque-limiting clutch that disengages once the preset torque has been reached.

Is very useful to use the key to generate pressure also for indenting the gasket.

The HP200 permit the fine calibration of force inside the DAC’s hydrostatic room and is exerted by a metallic membrane which is inflated with pressurised gas through the capillary. Typically the gas used is helium or nitrogen gas pressure is below 200 bar.

How it works?

The complete membrane DAC system is composed by the Membrane Control Box and the Membrane Diamond Anvil Cell (DAC). The membrane is connected through a stainless steel capillary to the connection. This device allows to regulate the gas pressure in the membrane of the DAC. It is composed by the gas bottle, a pressure regulator, two valves and a pressure meter. Opening the outlet valve serves for releasing pressure while closing the inlet valve allows to disconnect the pressure regulator from the hydraulic circuit of the membrane DAC.  In some cases it may be useful to leave the inlet valve open, so to increase pressure. Using the pressure regulator, or to maintain the pressure constant when a small leak is present in the hydraulic circuit or more generally when the pressure in the membrane would naturally decrease and on the contrary the user wants to keep it constant. This last case happens for example when the DAC is cooled and the user wants to maintain a constant pressure. Maintenance: no periodic maintenance is needed. Simply refill the gas bomb when necessary, with a maximum pressure of 200 bar (generally with Helium).

DACs can be loaded with gaseous, liquid or solid samples. The direct compression of a solid determines non-hydrostatic pressure even at low pressures. For this reason, is recommended that solid samples, placed inside the gasket’s hole, is immersed in a gas or a liquid before compression. You can use for a good hydrostaticity until 15-20 GP is oil. Immersion oils are available with low or very low autofluorescence. Autofluorescence is the natural fluorescence emission of the oil when exposed to light. Each immersion oil has a different level of background emission.

The thickness gauge is a necessary tool to measuring the thickness of the gasket after indenting. Measure the thickness after indenting is useful to calibrate the force necessary to obtain the desired thickness and to have the right space for the sample. The gasket, which acts as a seal in the phase of hydrostatic pressure imposed on the sample, is a thin sheet of about 200 microns which, placed between the diamonds, is indented, reducing the thickness, and then enable the next phase of drilling.

The gasket is a component of thin material used to make an hydrostatic room It is a metal foil, typically 200 microns thick, which provides great yield strength, a high friction coefficient on diamonds along with a certain degree of ductility.

The gasket, which acts as a seal in the phase of hydrostatic pressure imposed on the sample, is placed between the diamonds, indented, enabling the next phase of drilling. The gasket after drilling  is used to contain the sample.

A stereo zoom microscope to align diamonds is the best device in the DAC set, also useful while filling the sample room through the of gasket hole.

The alignment of diamond anvils is a highly delicate procedure, decisive in order to avoid the premature failure of diamonds under high pressure. Its use is aimed to position the diamond faces parallel to each other.

Digital professional stereo microscope with pillar stand has long working distance to enable users to perform. It has a 5 MP camera with reduction lens and USB 2.0 output for capturing or displaying images on a computer or projector.Moreover, the micrscope is equipped with a trinocular viewing head with a pair of 10x super-widefield eyepieces, with an adjustable interpupillary distance.

The mechanical stability of the diamond anvils’ alignment must be maintained under pressure during all operation phases, including load application. The alignment of the diamonds culet is central to the achievement of ultra-high pressures. Also the concentricity of flat diamond surface are fundamental to reach very high pressure.

The SM4 085 DAC is a modular diamond anvil cell. It allows a basic DAC module, generally operated by screws, to be driven by a membrane, by means of  an external kit.

The DAC cell, on request, can work at low temperature because it is designed to be inserted in a cryostat.

The external membrane kit transmits the force to the diamond anvils to generate the high pressure on the sample. This pressure can be finely tuned by remotely controlling the gas pressure in the membrane.

Using the basic cell with screws is possible to control the pressure by means of a torque wrench.

Diamond Anvil Cell technology is nowadays within the reach of even the smallest physics or chemistry laboratory. The simplicity of this device and its affordable price permit any interested scientist to perform measurements at pressures in the 100 GPa range and above. By combining the DAC with different investigation techniques, from the simplest ones, as microscope visual observation, through optical or Infrared spectroscopy, Raman spectroscopy, to synchrotron x-ray scattering, researchers all around the word continues to investigate the changes under pressure of virtually any material. LOTO-eng manufactures a variety of types of DAC, among which, for sure, the one suitable for your purpose. LOTO-eng specialists will help you to identify the most suitable DAC cell, accessories and loading technique to meet your needs, in accordance with your scientific goal and your budget.