Determination of Amorphous Phase in Quartz Powder by X-Ray Powder Diffractometry

Abstract

A powder diffraction method was applied to the quantitative analysis of amorphous silica in several quartz powders. Two calibration methods, i.e., direct analysis and the standard addition method were examined. Calibration mixtures were made by mixing a standard silica gel powder ground to under 5 μm particle size with a matrix quartz powder which was ground to 10 to 40 μm particle size and treated with NaOH solution to remove the amorphous phase caused by grinding. Intensity of the amorphous halo was measured at 23.0° 2θ, and the background intensity at 53.0° 2θ was subtracted. Linear calibration curves were obtained over the ranges of 0 to 50 wt% by direct analysis and 0 to 20 wt% by standard addition methods, respectively. The analytical results obtained by the two calibration methods were in good agreement with each other. The relative standard deviations for 4.3 wt% of amorphous silica were 4.6% by the direct analysis and 5.4% by the standard addition method. These methods were successfully applied to a correction of reference intensity ratios (RIR) for several quartz powders containing amorphous silica. After the correction for amorphous content, the relative standard deviations of the RIR values for quartz powders became smaller.

Calcium Phosphate Flocs and the Clarification of Sugar Cane Juice from Whole of Crop Harvesting

“…As was reported for SiO 2 , the variation in the size of the halo may be a representation of the variation of the interatomic distances between P−O−P structural units, which is related to the arrangement of the phosphorus molecules. 14 The addition of phosphate broadens the XRD halo relative to the control, indicating that the calcium phosphate phase is far less ordered (smaller particles, i.e., more amorphous) than that of the control. The increased amorphous nature of the calcium phosphate particles will increase the amount of impurities removed because of an increase in surface area.…”

The Deposition of Calcium Oxalate and Amorphous Silica Scale under Dynamic Conditions which Simulate sugar mill Evaporators

“…X-ray powder diffraction analysis was conducted on the Si02 and composite scales in order to identify the crystalline phases involved in the composite fouling. The XRD spectra of all the scales gave a smooth broad peak or "halo" with a 26 value of approximately 23' caused by the presence of amorphous silica [23]. However, ths peak appeared to be narrower for the composite scales compared to that of the pure Si02 scale.…”

Estimation of Purity of Chrysotile Asbestos by X-ray Diffractometry/Rietveld Refinement

“…Altree-Williams [28][29][30] and Nakamura 31 pointed out that, in pure quartz, the amorphous surface content of crystalline particles caused a variation in the crystallinity index of several quartz samples. The crystalline purity of six chrysotile powder samples was determined via powder X-ray diffractometry/Rietveld refinement.…”