Rotating disk electrode method and apparatus for multi-elemental determination of concentration of particles in used oil

• US 5,408,306 A
• Filed: 02/16/1994
• Issued: 04/18/1995
• Est. Priority Date: 05/01/1992
• Status: Expired due to Fees

• Current Assignee: Spectro Incorporated (Spectro Scientific, Inc.)
• Original Assignee: Spectro Incorporated (Spectro Scientific, Inc.)
• Inventors: Anderson, Daniel P.
• Primary Examiner(s): Housel, James C.
• Assistant Examiner(s): Le, Long V.
• Application Number:
  US08/197,360
• Time in Patent Office: 426 Days
• Field of Search: 356/36, 356/313, 422/101, 436/177
• US Class Current: 356/36
• CPC Class Codes: G01N 21/67 using electric arcs or discharges
• CPC Class Codes: G01N 33/2858 metal particles
• CPC Class Codes: G01N 33/2888 Lubricating oil characteristics, e.g. deterioration lubricating properties G01N33/30
• CPC Class Codes: Y10T 436/25375 Liberation or purification of sample or separation of material from a sample [e.g., filtering, centrifuging, etc.]

Abstract

Spectrometric analysis for determining the elemental concentration of various wear metals, contaminants and additives present in a fluid sample for condition monitoring and preventive maintenance. RDE spectroscopy method and apparatus includes use of rotrode disk as a filter which captures large particles of the surface of the disk, which particles are then subjected to RDE spectroscopy for evaluation. In one method, the rotrode with the captured large-particle filtrate is subjected to a solvent wash, and the washed sample is then submitted to RDE spectroscopy to obtain a highly accurate multi-elemental determination of concentration of large particles. In another method, conventional RDE spectroscopy is used to characterize the small particles in a used oil sample, and this is combined with the obtained large particle data for highly accurate multi-elemental determination of concentration of wear debris, contaminants and additives in the fluid sample.

Claims

1. A filtration apparatus for use in a spectrographic system, said apparatus comprising:

a housing, said housing defining a vacuum port and means for capturing a bottom surface of a porous electrode disk having a central annulus, said capturing means including a port fluidly coupled with said annulus for hermetically capturing said disk;

a device for drawing a particle-bearing fluid sample through an exposed circumference portion of the disk and depositing filtering particles thereon;

said means for capturing further including a first device for capture of a first portion of the disk, and a second device for capture of a second portion of the disk, said first and second portions, cooperatively defining said exposed circumferential portion of said disk; and

said drawing device further including a vacuum source for application of a vacuum to said disk for drawing said particle-bearing fluid sample through said exposed circumferential portion for separating particles from said fluid sample and leaving a filtrate on said exposed circumferential portion, said fluid being substantially removed from said exposed circumferential portion.

2. Apparatus of claim 1 wherein said first device includes a cap for capture of said first portion of said disk, and wherein said second device includes a cup for capture of said second portion of said disk, wherein particles in said fluid sample are captured as said filtrate when said fluid is drawn through said disk by said vacuum source.

3. Apparatus of claim 2 wherein the cap and cup each comprises a disk capture portion defining a rim.

4. Apparatus of claim 3 wherein the cup comprises a cylinder formed on a hollow shaft, the cylinder having an inwardly tapered top surface forming a reservoir, the base of the reservoir terminating in said hollow shaft, adjacent to said cup rim and wherein the cap comprises a cylinder having a recessed portion adjacent to said cap rim.

5. Apparatus of claim 4 further comprising a plurality of said caps and cups, and further comprising a stand having a plurality of receivers coupled to said vacuum source, the receivers for receipt of a respective one of said plurality of said cups, in a configuration wherein a vacuum supplied by said vacuum source to one of said cups mounted in respective one of said receivers will draw fluid through a respective disk captured between a respective cap and a respective cup for filtering the fluid.

6. In a rotating disk spectrographic system using a spectrometer apparatus having a rod electrode, a rotating shaft for rotation of an annular rotrode disk thereon, the rotrode disk for carrying particles loaded on its circumference, the disk disposed for mounting on the end of the shaft with a gap between the rod and disk, the rod and shaft for coupling to respective sides of a discharge circuit for generating a spark in said gap, the improvement comprising

a filtration means, said filtration means defining a vacuum port and a device for capturing a bottom surface of the annular porous rotrode disk having a central annulus, the device including a port fluidly coupled with said central annulus for hermetically capturing said disk;

a device for drawing a particle-bearing fluid sample through an exposed circumference portion of said disk and depositing filtered particles thereon; and

means for rotating the disk and carrying the deposited particles through the spark in the gap for generation of a plasma for spectroscopic analysis.

7. The apparatus of claim 6 wherein said filtration means further comprises

a first device for capture of a first portion of the disk, and

a second device for capture of a second portion of the disk, the first and second portions defining the exposed circumferential portion of the captured disk, and

a vacuum source for application of a vacuum to the captured disk for drawing the particle-bearing fluid sample through said exposed circumferential portion of the captured disk circumference and leaving thereon deposited particles, and

said apparatus further comprising means for loading a preloaded disk on said shaft and for generation of said spark between said disk circumference portion and said electrode.

8. Apparatus of claim 7 wherein the first device includes a cap for capture of said first portion of the disk, and wherein the second device includes a cup for capture of said second portion of the disk, wherein particles in the sample fluid are captured on the disk circumference portion as the fluid is drawn through the disk.

9. Apparatus of claim 8 wherein the cap and cup each comprises a disk capture portion defining a rim.

10. Apparatus of claim 9 wherein the cup comprises a cylinder formed on a hollow shaft, the cylinder having an inwardly tapered top surface forming a reservoir, the base of the reservoir terminating in said hollow shaft adjacent to said cup rim.

11. Apparatus of claim 9 further comprising a plurality of said caps and cups, and further comprising a stand having a plurality of receivers coupled to said vacuum source, the receivers for receipt of a respective one of said plurality of said cups, in a configuration so that a vacuum supplied by said vacuum source to one of said cups mounted in respective one of said receivers will draw fluid through a respective disk captured between a respective cap and a respective cup for filtering the fluid.

12. A method of loading particles of at least a minimal size on a porous annular rotrode disk for RDE spectrometric analysis of a sample, comprising the steps of

selecting a porous rotrode disk having a central annulus,

placing the disk between a cap and an annular cup, a first interface of the cap and the disk forming a first seal, a second interface of the cup and the disk forming a second seal, the cap and the cup cooperating with the disk to define an exposed disk circumference between these interfaces,

submitting the exposed disk circumference to a fluid sample and applying a vacuum from said annular cup to said central annulus of said disk and

flowing the fluid sample through the exposed disk circumference toward the central annulus of said disk by applying said vacuum and capturing particles from the fluid sample on the exposed disk circumference, the minimal particle size collected on the exposed disk circumference being determined by the porosity of the disk.

13. The method of claim 12 further comprising the steps of

providing a plurality of porous annular rotrode disks, a plurality of caps and cups,

capturing each disk between a respective one of said plurality of caps and cups and forming a seal at each respective cap/disk interface and cup/disk interface, and respectively defining an exposed disk circumference between these interfaces on each said disk,

submitting each exposed disk circumference to a fluid sample,and

flowing a respective portion of the fluid sample through each exposed disk circumference toward the respective disk interior by applying a vacuum to the respective disk interior and capturing particles from the fluid sample on the respective exposed disk circumference.