Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1998-07-22
2001-01-09
Lin, Kuang Y. (Department: 1722)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S332000
Reexamination Certificate
active
06170556
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to equipment and the relative process for the preparation of electric conducting composite samples starting from powders, (this term also comprising lyophilized organic compounds), in the form of matrices or as a carrier by impregnation, adsorption or dispersion of liquids or by impregnation or adsorption of gases, which may or may not be insulating and of an organic or inorganic origin, to be subjected to instrumental chemical analysis with techniques for the direct analysis of solid conductors.
2. Description of Prior Art
Various advanced instrumental techniques and/of of consolidated use, such as, for example, AAS, GFAAS, ICP-OES, ICP-MS, LC-ICP-MS, voltammetry, etc. can be used for the chemical characterization of organic and inorganic materials and in particular for the quantitative determination of element traces: in all cases there is dissolution of the sample and dilution in water.
Some alternative anlaytical techniques, capable of reaching detecting limits (LoD) for many elements of less than 1 ppb, such as SIMS, SSMS, GDMS, allow direct analysis of the sample without preliminary chemical attack and subsequent dilution.
An application limit of the latter pair of techniques is due to the necessity for the material under examination to be a (semi)conductor. In the contrary case, the matrix must be manipulated so as to obtain a sample for analysis which is conducting; for this purpose it is possible:
to mix it with ligand metals (Ti, Cu, Ga, Ag and Ta are those most commonly used) or with graphite,
to couple it to a secondary cathode, exploiting the partial redeposition effects of the vaporized metal coming from the cathode on the insulating sample,
to subject it to infiltration, according to the preparative procedure described in “An innovative sample preparation procedure for trace and ultratrace analysis on non-conducting powders by direct current glow discharge mass spectrometry”, (Battagliarin M., Sentimenti E., Scattolin R.—Spectrochimica Acta, Vol. 50B, Nr. 1, pages 13-25, 1995).
The equipment described in the article cited above essentially consists of a high pressure container which houses a mould containing the powder and metal to be melted and compressed.
The process using this equipment essentially comprises the following steps:
introduction of the powder to be analyzed into a tube in PTFE of the equipment;
insertion of a rod of low-melting metal ligand into the tube;
vapor and gas evacuation and subsequent heating to melt the ligand;
pressurization for the infiltration of the powder;
cooling and extraction of the sample for analysis.
As an alternative to the above methods, sources can be used with discharge in alternating radio-frequency current (rf GDMS); the results so far obtained however, even if promising, are only partial and cannot be transferred to a commercial level.
For minimum quantities of material however, the infiltration system as a supporting means of the material of the sample is extremely useful if not indispensable.
Both the introduction of a conducting ligand and resort to a secondary cathode have a series of drawbacks which limit the instrumental performances.
The main disadvantages relating to each preparative method are summarized below:
it is essential to apply very high pressures, on an average not less than 10-15 tonn/cm
2
, with considerable stress of the moulds and relative contamination of the sample on the part of the material forming the mould itself;
it is necessary to eliminate these surface contaminations by means of a vigorous chemical attack and a prolonged sputter etching;
it is necessary to carefully clean the mould to minimize any possible residual effects;
the ligands which are most suitable for the purpose and commercially available at reasonable prices, except for gallium and graphite, do not easily reach the desired degree of purity;
a significant dilution of the sample is introduced with a decrease in the LoD;
it is particularly difficult to obtain a satisfactory homogenization of the mixture resulting in a deterioration in the repeatability of the measurements;
it is necessary to find the correct weight ratio ligand/matrix to have good mechanical resistance of the sample;
traces of water adsorbed on the powder granules can significantly lower the sputtering yield and slow down the vaporization rate.
For coupling with a secondary cathode:
it is essential to pellet the material to be analyzed by pressing with suitable moulds;
residual effects are easily generated in the material in the mould, which must be eliminated with suitable chemical attacks;
with this geometry the sputtering yield and detecting limits are lower than those obtained from rods;
the selection of the material forming the cathode, the dimensions of the central hole (focal spot) of the cathode/mask, the presputtering and discharge conditions are extremely critical; consequently the set-up of an analysis protocol is rather complex;
it is extremely important to have a mask made of material with a very high purity;
optimum operating parameters vary considerably from matrix to matrix.
For infiltration in PTFE mould:
equipment is used which already exists (designed for the preparation of composite materials with a metallic matrix [MMCs], for mechanical components by infiltration with molten aluminum and its alloys) which is greatly overdimensioned and cannot be easily installed in a sample preparation area of group
100
(for example, glove box);
the design does not allow efficient control of the process development and it is therefore necessary to excessively prolong the residence times of the charge in the chamber to obtain complete melting of the ligand before applying the necessary pressure for infiltration;
the material used for the mould (PTFE) is easily deformed and can tolerate only a few operating cycles; the main components must be frequently substituted;
the seal (O-ring in Viton) does not ensure perfect insulation between the pressurized environment and the base of the charge;
the molten ligand cannot be adequately confined once compressed; this results in poor reproducibility of the end-dimensions of the sample for analysis and a consumption of ligand of more than 25-30% with respect to the useful quantity;
the molten ligand may come into contact with the seal;
the degree of vacuum which can be reached is relatively low (1-10 mbars), as is also the rate at which the gases adsorbed on the matrix are removed.
SUMMARY OF THE INVENTION
We have found new equipment for infiltration in mould which enables most of the disadvantages arising from both the equipment and processes of the known art described above to be overcome, also minimizing the necessity of material for the preparation of the samples and of characterizing matrices available in an extremely reduced quantity.
The equipment and relative process of the present invention can be used for both the qualitative and quantitative determination of minor elements and traces in mass spectrometry with glow discharge in direct current (direct current Glow Discharge Mass Spectrometry, or dc GDMS) and also, without any particular adaptations, with other similar instrumental techniques (SIMS, SSMS, ICP-MS laser ablation, ICP-OES spark ablation, GD-OES).
The equipment for the preparation of electric conducting composite samples by infiltration in mould, of the present invention, is characterized in that it essentially comprises:
a pressurization/infiltration chamber having at least one opening to connect it by means of appropriate pipes with a vacuum line and a pressure line and devices for sealing both under vacuum and under pressure;
a sample-holder, inside said chamber, made of a material with a high thermal conductivity with one or more seats, preferably vertically positioned, in each of which a mould is housed consisting of:
a chemically inert and thermally stable tube made of a non-porous material;
a plug, situated at one end of the tube, at the lower end in the case of a vertical seat, of a material wh
Battagliarin Marino
Meregalli Letizia
Sentimenti Emilio
Enirisorse S.p.A.
Lin Kuang Y.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Equipment and process for the preparation of electric... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Equipment and process for the preparation of electric..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Equipment and process for the preparation of electric... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2461231