Thermal analysis of calcium sulfate dihydrate sources used to manufacture gypsum wallboard

Abstract

Gypsum wallboard has been used for over 100 years as a barrier to the spread of fire in residential and commercial structures. The gypsum molecule, CaSO 4 •2H 2 O, provides two crystalline waters that are released upon heating providing an endothermic effect. Manufacturers have recognized that the source of the gypsum ore is a factor that affects all aspects of its performance; thus, it is hypothesized that the impurities present in the gypsum ore are the causes of the performance differences. Differential Thermal Analysis/Thermogravimetric Analysis (DTA/TGA) and X-ray Diffraction (XRD) were used to compare and characterize samples of gypsum ore representing sources of natural, synthetic from a Flue Gas Desulfurization process (FGD) and blends thereof. The hemihydrate phase of representative natural, FGD, and reagent grade calcium sulfate were rehydrated with distilled water and evaluated by DTA/TGA. Analysis of the data shows distinct areas of similarity separated by the conversion to anhydrite ~250°C. Compositional reconstructions based on DTA/TGA and XRD data were compared and although, the results were comparable, the DTA/TGA suggests thermally active compounds that were not detected by XRD. Anhydrite, silica and halite were reported by XRD but were not thermally reactive in the temperature range evaluated by DTA/TGA (ambient to 1050°C). The presence of carbonate compounds (e.g., calcite and dolomite) were indicated by XRD and estimated from the thermal decomposition reaction ~700°C.

Measurement of heat flow through cast slabs of calcium sulfate dihydrate

“…Gypsum slabs were prepared with cast‐in‐place thermocouples from three different hemihydrates, which were selected from a natural source, a flue gas desulfurized (FGD) gypsum source, and a reagent grade source . Kaolin and borax were added to each of the hemihydrates using a designed experiment to facilitate analysis.…”

“…This design permitted the analysis of the main factors only, or analysis of the experiments in subset of 2 3 full factorials; kaolin:borax:natural‐FGD, kaolin:borax:natural‐reagent, and kaolin:borax:FGD‐reagent. Two sources of commercially prepared hemihydrate were selected to be representative of the two categories of commercially available sources (natural source and FGD source) and a reagent grade source. Distilled water (675 mL) was used to fluidize the mixture.…”

A novel method for purification of phosphogypsum

“…Natural gypsum is an important non-metallic mineral, which can be used in cement retarder, ceramics, gypsum plaster, gypsum wallboard, gypsum mortar and other building materials industry (Islam et al, 2017;Schug etal., 2017;Engbrecht et al, 2016;Rashad et al, 2017). A large amount of gypsum resources is needed every year, among which the building materials industry is the largest consumer of gypsum.…”

Effect of Cu2+ on the nucleation kinetics and crystallization of rod-shaped CaSO4·2H2O in aqueous solution

“…In nature, it is present as large-scale deposits of CaSO 4 $2H 2 O (DH), CaSO 4 -$0.5H 2 O (HH) and CaSO 4 (AH), [1][2][3][4] and is the source material for the preparation of high volumes of compounds including plaster and cement and for use in agricultural applications. [5][6][7] In particular, DH, as a crucial mineral, is widely used in industry for bone tissue regeneration, as a medical carrier and in 3Dprinting. [8][9][10][11] However, in addition to these highly protable applications, undesirable DH precipitation can also induce huge damage in industrial processes that depend on water handling systems such as waste water treatment, desalination plants and oil/gas production, where the accumulation of its precipitates can seriously impede ow and reduce production efficiency.…”